Air Suspension System Model and OptimizationDate Published: 2011-04-12Paper Number: 2011-01-0067 DOI: 10.4271/2011-01-0067 Citation:Moshchuk, N., Li, Y., and Opiteck, S., "Air Suspension System Model and Optimization," SAE Technical Paper 2011-01-0067, 2011, doi:10.4271/2011-01-0067.Author(s):

Nikolai Moshchuk - General Motors Company Yunjun Li - General Motors Company Steve Opiteck - General Motors Company

Abstract:

An air suspension system can consist of many different components. These components include an air compressor, air springs, pneumatic solenoid valves, height sensors, electronic control unit, air reservoir, air lines, pressure sensor, temperature sensor, etc. The system could be designed as a 2-corner rear air suspension or a 4-corner air suspension.

In this paper, the pneumatic models of air suspension systems are presented. The suspension system models are implemented in AmeSim. The suspension controls are implemented using Matlab/Simulink. The compressor was modeled using the standard AmeSim element with known mass flow rate as a function of pressure ratio. Air lines were modeled using a friction submodel of pneumatic pipe and control (isolation) valves are modeled using 2 position, 2 port pneumatic servo valves. The air spring is modeled as a single pneumatic chamber, single rod jack with spring assistance to account for spring nonlinearities. Vehicle dynamics equations are modeled using the AmeSim control library. Simulated scenarios include raising and lowering the test vehicle at different loading conditions. The test results were correlated in development vehicles equipped with either a 4-corner speed dependent air suspension or a 2- corner rear air suspension.

The air suspension system models can be used as design tools to assist in air suspension performance optimization, air compressor selection, solenoid valve sizing, etc. With these tools, engineers could design an air suspension system virtually. The system performance could be optimized before parts are built to reduce engineering development time and prototype hardware cost.

Pistonless Pump

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Definition

Rocket engines requires a tremendous amount of fuel high at high pressure .Often th pump costs more than the thrust chamber.One way to supply fuel is to use the expensive turbopump mentioned above,another way is to pressurize fuel tank. Pressurizing a large fuel tank requires a heavy , expensive tank. However suppose instead of pressurizing entire tank, the main tank is drained into a small pump chamber which is then pressurized. To achieve steady flow, the pump system consists of two pump chambers such that each one supplies fuel for ½ of each cycle. The pump is powered by pressurized gas which acts directly on fluid. For each half of the pump system, a chamber is filled from the main tank under low pressure and at a high flow rate, then the chamber is pressurized, and then the fluid is delivered to the engine at a moderate flow rate under high pressure. The chamber is then vented and cycle repeats.

The system is designed so that the inlet flow rate is higher than the outlet flow rate.This allows time for one chamber to be vented , refilled and pressurized while the other is being emptied.A bread board pump has been tested and it works great .A high version has been designed and built and is pumping at 20 gpm and 550psi.

Nearly all of the hardware in this pump consists of pressure vessels, so the weight is low.There are less than 10 moving parts , and no lubrication issues which might cause problems with other pumps. The design and constr. Of this pump is st, forward and no precision parts are required .This device has advantage over standard turbopumps in that the wt. is about the same, the unit,engg.and test costs are less and the chance for catastrophic failure is less.This pump has the advantage

over pressure fed designs in that the wt. of the complete rocket is much less, and the rocket is much safer because the tanks of rocket fuel do not need to be at high pressure.The pump could be started after being stored for an extended period with high reliability.It can be used to replace turbopumps for rocket booster opn. or it can be used to replace high pressure tanks for deep space propulsion.It can also be used for satellite orbit changes and station keeping.

Performance Validation:

A calculation of the weight of this type of pump shows that the power to weight ratio would be dominated by the pressure chamber and that it would be of the order of 8-12 hp per lb., for a 5 second cycle using a composite chamber. This performance is similar to state of the art gas-generator turbopump technology. (The F1 turbopump on the Saturn V put out 20 hp/lb) This pump could be run until dry, so it would achieve better residual propellant scavenging than a turbopump. This system would require a supply of gaseous or liquid Helium which would be heated by a heat exchanger mounted on the combustion chamber before it was used to pressurize the fuel, as in the Ariane rocket.. The volume of gas required would be equivalent to a standard pressure fed design, with a small additional amount to account for ullage in the pump chambers. The rocket engine itself could be a primarily ablative design, as in the NASA Fastrac, scorpious rocket or in recent rocket engine tests.

HYPERCARS

Definition

The Hypercar design concept combines an ultralight, ultra-aerodynamic autobody with a hybrid-electric drive system. This combination would allow dramatic improvements in fuel efficiency and emissions. Computer models predict that near-term hypercars of the same size and performance of today's typical 4–5 passenger family cars would get three times better fuel economy . In the long run, this factor could surpass five, even approaching ten. Emissions, depending on the power plant, or APU, would drop between one and three orders of magnitude, enough to qualify as an “equivalent” zero emission vehicles (EZEV).

In all, hypercars' fuel efficiency, low emissions, recyclability, and durability should make them very friendly to the environment. However, environmental friendliness is currently not a feature that consumers particularly look for when purchasing a car. Consumers value affordability, safety, durability, performance, and convenience much more. If a vehicle can not meet these consumer desires as well as be profitable for its manufacturer, it will not succeed in the marketplace. Simply put, market acceptance is paramount. As a result, hypercars principally strive to be more attractive than conventional cars to consumers, on consumers' own terms, and just as profitable to make.

Revolution concept car design

The Revolution fuel-cell concept vehicle was developed by Hypercar, Inc. in 2000 to demonstrate the technical feasibility and societal, consumer, and competitive benefits of holistic vehicle design focused on efficiency and lightweighting. It was designed to have breakthrough fuel economy and emissions, meet US and European Motor Vehicle Safety Standards, and meet a rigorous and complete set of product requirements for a sporty five-passenger SUV crossover vehicle market segment with

technologies that could be in volume production within five years (Figure 1).

The Revolution combines lightweight, aerodynamic, and electrically and thermally efficient design with a hybridized fuel-cell propulsion system to deliver the following combination of features with 857 kg kerb mass, 2.38m2 effective frontal area, 0.26CD, and 0.0078 r0:

Seats five adults in comfort, with a package similar to the Lexus RX-300 (6% shorter overall and 10% lower than a 2000 Ford Explorer but with slightly greater passenger space)

1.95-m3 cargo space with the rear seats folded flat 2.38 L/100km (99 miles per US gallon) equivalent, using a

direct-hydrogen fuel cell, and simulated for realistic US driving behaviour

530-km range on 3.4 kg of hydrogen stored in commercially available 345-bar tanks

Zero tailpipe emissions Accelerates 0±100 km/h in 8.3 seconds No body damage in impacts up to 10 km/h (crash

simulations are described below) All-wheel drive with digital traction and vehicle stability

control Ground clearance adjustable from 13 to 20 cm through a

semi-active suspension that adapts to load, speed, location of the vehicle's centre of gravity, and terrain

Body stiffness and torsional rigidity 50% or more higher than in premium sports sedans

Designed for a 300 000á-km service life; composite body not susceptible to rust or fatigue

Modular electronics and software architecture and customizable user interface

Potential for the sticker price to be competitive with the Lexus RX-300, Mercedes M320, and BMW X5 3.0, with significantly lower lifecycle cost.

Lightweight design

Every system within the Revolution is significantly lighter than conventional systems to achieve an overall mass saving of 52%. Techniques used to minimize mass, discussed below, include integration, parts consolidation, and appropriate application of new technology and lightweight materials. No single system or materials substitution could have achieved such overall mass savings without strong whole-car design integration. Many new engineering issues arise with such a lightweight yet large vehicle. While none are showstoppers, many required new solutions that were not obvious and demanded a return to engineering fundamentals.

A Detailed Report On Energy Crisis

An energy crisis is any great bottleneck (or price rise) in the supply of energy resources to an economy. It usually refers to the shortage of oil and additionally to electricity or other natural resources. An energy crisis may be referred to as an oil crisis, petroleum crisis, energy shortage, electricity shortage electricity crisis. While not entering a full crisis, political riots that occurred during the 2007 Burmese anti government protests were initially sparked by rising energy prices.Likewise the Russia- Ukraine gas dispute and the Russia-Belarus energy dispute have been mostly resolved before entering a prolonged crisis stage. Market failure is possible when monopoly manipulation of markets occurs. A crisis can develop due to industrial actions like union organized strikes and government embargoes. The cause may be ageing over-consumption, infrastructure and sometimes bottlenecks at oil refineries and port facilities restrict fuel supply. An emergency may emerge during unusually cold winters. emerging shortages Crisis that currently exist include;

• Oil price increases since 2003 - Cause: increasing demand from the U.S and China, the falling state of the U.S. dollar, and stagnation of production due to the U.S. occupation of Iraq. Iraq is #3 in the world (besides Saudi Arabia and Iran) for its oil reserves. However some observers have stated the global oil production peak occurred in December 2005. If this is correct it is also to blame.

• 2008 Central Asia energy crisis, caused by abnormally cold temperatures and low water levels in an area dependent on hydroelectric power

• South African electrical crisis Solution for Energy Crisis next time on the roads, don’t scoff at the speed-breakers. They could actually light up small villages

off the highway.

 

This project is about generation of electricity with the speed breakers. Generally when vehicle is in motion it produces various forms of energy like, due to friction between vehicle’s wheel and road i.e. Rough surface heat energy is produced, also when vehicle traveling at high speed strikes the wind then also heat energy is produced which is always lost in environment and of which we can’t make use it directly. we can say that all this energy that we can’t make use of is just the wastage of energy that is abundantly available around us. In this project we are just trying to make use of such energy in order to generate an electrical energy. This project will work on the principle of “potential energy to electrical energy conversion” potential energy can be thought of as energy stored within a physical system. This energy can be released or converted into other forms of energy, including kinetic energy. It is called potential energy because it has the potential to change the states of objects in the system when the energy is released if h is the height above an arbitrarily assigned reference point, then kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. Negative work of the same magnitude would be required to return the body to a state of rest from that velocity.

The kinetic energy can be calculated using the formula: in this project a

Mechanism to generate power by converting the potential energy generated by a vehicle

Going up on a speed breaker into kinetic energy. When the vehicle moves over the

Inclined plates, it gains height resulting in increase in potential energy, which is wasted in

A conventional rumble strip when the breaker come down, they crank a lever fitted to a

Ratchet-wheel type mechanism (a angular motion converter). This in turn rotates a geared

Shaft loaded with recoil springs. The output of this shaft is coupled to a dynamo to convert kinetic energy into electricity. A vehicle weighing 1,000 kg going up a height of 10 cm on such a rumble strip produces approximately 0.98 kilowatt power. So one such speed-breaker on a busy highway, where about 100 vehicles pass every minute, about one kilo watt of electricity can be produced every single minute. “a vehicle weighing 1,000 kg going up a height of 10 cm on such a rumble strip produces approximately 0.98 kilowatt power. So one such speed-breaker on a busy highway, where about 100 vehicles pass every minute, about one kilo watt of electricity can be produced every single minute. The figure will be huge at the end of the day,” he said. The assam power ministry is expected to back the iit pilot project. Das says a storage module like an inverter will have to be fitted to each such

Rumble strip to store this electricity. The cost of electricity generation and storage per mega watt from speed-breakers will be nearly rs 1 crore as opposed to about rs 8 crore in thermal or hydro power stations.

Next time on the roads, don't scoff at the speed-breakers. They could actually light up small villages off the highway.an amateur innovator in guwahati has developed a simple contraption that can generate power when a vehicle passes over a speed breaker. Kanak gogoi, a small time businessman, has developed a mechanism to generate power by converting the potential energy generated by a vehicle going up on a speed breaker

Into kinetic energy. The innovation has caught the eye of the indian institute of technology (iit), guwahati, which will fund a pilot project to generate electricity from speed-breakers.

The idea is basic physics. Gogoi has welded five-metre-long metal plates into the

Speed-breaker instead of the conventional bitumen-and-stone-chip rumble strip. The plates are movable and inclined with the help of a spring-loaded hydraulic system. The fulcrum-attached plates are pushed down when a vehicle moves over them and bounce back to original position as it passes. "when the vehicle moves over the inclined plates, it gains height resulting in increase in potential energy, which is wasted in a conventional rumble strip," gogoi says. "when the plates come down, they crank a lever fitted to a ratchet-wheel type mechanism. This in turn rotates a geared shaft loaded with recoil springs. The output of

This shaft is coupled to a dynamo to convert kinetic energy into electricity," he explains.

Iit guwahati has evaluated the machine and recommended it to the assam ministry of power for large scale funding. A k das, a professor at iit's design department says it is a 'very viable proposition' to harness thousands of mega watts of electricity untapped across the country every day.

"a vehicle weighing 1,000 kg going up a height of 10 cm on such a rumble strip produces approximately 0.98 kilowatt power. So one such speed-breaker on a busy highway, where about 100 vehicles pass every minute, about one kilo watt of electricity can be produced every single minute. The figure will be huge at the end of the day," he said.

The assam power ministry is expected to back the iit pilot project.

Das says a storage module like an inverter will have to be fitted to each such rumble strip to store this electricity. The cost of electricity generation and storage per mega watt.

BASIC PRINCIPLES:

·         Simple energy conversion from mechanical to electrical.

·         To generate electricity using the vehicle kinetic energy as input we can develope electricity from speed breakers

·         They are using 3 different mechanisms:

I. Roller mechanism

II. Rack- Pinion mechanism

III. Crank-shaft mechanism

1.1  ROLLER MECHANISM:

ake use of….OR directly we can say that

A roller blind mechanism for winding and unwinding a rollable blind, the mechanism comprising a support element, a drive sprocket which is rotatably mounted on the support element for transmitting rotational

movement to a blind supporting member, and a manually-movable elongate flexible drive element which includes a plurality of interlinked tooth-engaging elements, the drive sprocket including a plurality of flexible teeth engagable with the tooth-engaging elements of the flexible drive element. A roller blind mechanism as claimed in claim 1, wherein a radial extent of the teeth of the drive sprocket is equal to or greater than a maximum dimension of the tooth-engaging elements of the flexible drive element. A roller blind mechanism as claimed in claim 2, wherein the radial extent is equal

to or greater than twice the maximum dimension of the tooth-engaging elements of the

flexible drive element. A roller blind mechanism as claimed in claim 1, wherein the teeth of the drive sprocket flex in a circumferential direction of the sprocket.

1.2  RACK AND PINION MECHANISM:

Rack and pinion gears normally change rotary motion into linear motion, but sometimes we use them to change linear motion into rotary motion. They transform a rotary movement (that of the pinion) into a linear movement (that of the rack) or vice versa. We use them for sliding doors moved by an electric motor.The rack is attached to the door and the pinion is attached to the motor. The motor moves the pinion which moves the rack and the door moves.

1.3  CRANKSHAFT MECHANISM :

The crankshaft is a mechanism that transforms rotary movement into linear movement, or vice versa. For example, the motion of the pistons in the engine of a car is linear (they go up and down).But the motion of the wheels has to be rotary. So, engineers put a crankshaft between the engine and the transmission to the wheels. The pistons of the engine move the crankshaft and the movement becomes rotary. Then the rotary movement goes past the clutch and the gear box all the way to the wheels.

Out of all these arrengements the rack and pinion arrengement have a higher efficiency than others so we chose to make a hybrid mechanism of it

by using a hybrid technology to increase the development of power as compared to the conventional model.

HYBRID SYSTEMS: A hybrid system is usually consist of two or more energy sources used together to provide increased system efficiency as well as greeater balance in energy supply.

                                      LITERATURE REVIEW

2.1  ELECTRICITY GENERATION FROM SPEED BREAKER USING A HYBRID   MODEL:

In the present scenario power becomes major need for human life. Due to day-to-day increase in population and lessen of the conventional sources, it becomes necessary that we must depend on non-conventional sources for power generation. While moving, the vehicles posses some kinetic energy and it is being wasted. This kinetic energy can be utilized to produce power by using a special arrangement called “power hump”. The kinetic energy of moving vehicles can be converted into mechanical energy of the shaft through rack and pinion mechanism. This shaft is connected to the electric dynamo and it produces electrical energy proportional to traffic density. This generated power can be regulated by using zenor diode for continuous supply .all this mechanism can be housed under the dome like speed breaker, which is called hump. The generated power can be used for general purpose like streetlights, traffic signals. The electrical output can be improved by arranging these power humps in series this generated power can be amplified and stored by using different electric devices. The maintenance cost of hump is almost nullified. By adopting this arrangement, we can satisfy the future demands to some extent.

In the present scenario power becomes the major need for human life .the availability and its percapita consumptions is regarded as the index of national standard of living in the present day civilization. Energy is an important input in all the sectors of any countries economy. Energy crisis is due to two reasons, firstly the population of the world has been increased rapidly and secondly standard of living of human beings has increased. India is the country, which majorly suffers with lack of sufficient power generation. The capital energy consumption of u.s.a. Is about 8000 k.w.h., where as per india is only 150 k.w.h. U.s.a. With 7% of world population

consumes 32% of total power generation where as india as developing country with 20% of world population consumes only 1% of total energy consumed in the world. The availability of regular conventional fossil fuels will be the main sources for power generation, but there is a fear that they will get exhausted eventually by the next few decades. Therefore, we have to investigate some approximate, alternative, new sources for the power generation, which is not depleted by the very few years. Another major problem, which is becoming the exiting topic for today is the pollution. It suffers all the living organisms of all kinds as on the land, in aqua and in air. Power stations and automobiles are the major pollution producing places. Therefore, we have to investigate other types of renewable sources, which produce electricity without using any commercial fossil fuels, which is not producing any harmful products. There are already existing such systems using renewable energy such as solar wind), otec (ocean thermal energy conversions) etc…for power generation. The latest technology which is used to generate the power by such renewable energy can be extracted from speed breakers.

Whenever the vehicle is allowed to pass over the dome it gets pressed downwards then the springs are attached to the dome are compressed and the rack which is attached to the bottom of the dome moves downward in reciprocating motion. Since the rack has teeth connected to gears, there exists conversion of reciprocating motion of rack into rotary motion of gears but the two gears rotate in opposite direction. A flywheel is mounted on the shaft whose function is to regulate the fluctuation in the energy and to make the energy uniform. So that the shafts will rotate with certain r.p.m. These shafts are connected through a belt drive to the dynamos, which converts the mechanical energy into electrical energy. The conversion will be proportional to traffic density. Whenever an armature rotates between the magnetic fields of south and north poles, an e.m.f (electro motive force) is induced in it. So, for inducing the e.m.f armature coil has to rotate, for rotating this armature it is connected to a long shaft. By rotating same e.m.f, is induced, for this rotation potential energy of moving vehicles is utilized. The power is generated in both the directions; to convert this power into one way a special component is used called zenor diode for continuous supply. Also the pizo-electric material which is kept below the supporting springs of the speed breaker also generate a small amount of charge which can be utilized for the storage purpose so that more amount of energy can be developed from the same system. All this mechanism can be housed under the dome, like speed breaker, which is called hump. The electrical output

can be improved by arranging these power humps in series. This generated power can be amplified and stored by using different electrical devices.

2.2   ORIGIN OF THE PROPOSAL :

           

Before starting I have one question to you all who is really very happy with the current situation of the electricity in India? I suppose no one . so this is my step to improve the situation of electricity with a innovative and useful concept ie Generating Electricity from a Speed breaker First of all what is electricity means to us? Electricity is the form of energy. It is the flow of electrical Power . Electricity is a basic part of nature and it is one of our most widely used forms of energy. We get electricity, which is a secondary energy source, from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources. Many cities and towns were built alongside water falls that turned water wheels to perform work. Before electricity generation began slightly over 100 years ago, houses were lit with kerosene lamps, food was cooled in iceboxes, and rooms were warmed by wood-burning or coal-burning stoves. Direct current (DC) electricity had been used in arc lights for outdoor lighting. In the late-1800s, Nikola Tesla pioneered the generation, transmission, and use of alternating current (AC) electricity, which can be transmitted over much greater distances than direct current. Tesla's inventions used electricity to bring indoor lighting to our homes and to power industrial machines. How is electricity generated?

Electricity generation was first developed in the 1800's using Faradays dynamo generator. Almost 200 years later we are still using the same basic principles to generate electricity, only on a much larger scale. The rotor(rotating shaft) is directly connected to the prime mover and rotates as the prime mover turns. The rotor contains a magnet that, when turned, produces a moving or rotating magnetic field. The rotor is surrounded by a stationary casing called the stator, which contains the wound copper coils or windings. When the moving magnetic field passes by these windings, electricity is produced in them. By controlling the speed at which the rotor is turned, a steady flow of electricity is produced in the windings. These windings are connected to the electricity network via transmission lines.

Now I m throwing some light on the very new and innovative concept i.e. GENERATING ELECTRICITY FROM A SPEED BREAKER . Producing electricity from a speed breaker is a new concept that is under going

research. The number of vehicles on road is increasing rapidly and if we convert some of the potential energy of these vehicle into the rotational motion of shaft then we can produce considerable amount of electricity, this is the main concept of this project. In this project, a rack and pinion arrengement is fitted between the case anh the shaft of a generator when a vehicle passes over speed breaker it rotates the pinon. This movement of pinion which is connected to shaft of D.C. generator by the help of drive or a pulley which is there to provide 1:5 speed ratio . As the shaft of D.C. generator rotates, it produces electricity. This electricity is stored in a battery. Then the output of the battery is used to lighten the street lamps on the road. Now during daytime we don?t need electricity for lightening the street lamps so we are using a control switch which is manually operated .The control switch is connected by wire to the output of the battery.

The control switch has ON/OFF mechanism which allows the current to flow when

needed.

2.3  OBJECTIVES OF THE PROJECT :

The main objectives of this project are:

·         Tapping of potential energy of the vehicles - The potential energy during the running of the vehicles should be tapped so as to make the model work accordingly this can be done is very simple manner as in by making an arrangement of a shell type dome which is supported by the springs, this dome will go in downward direction whenever a vehicle step on it and the spring force will keep the dome into its initial position after a vehicle pass by the speed breaker.

·         Structural formation of a power generating unit – A power generating unit is to be designed which can develop sufficient amount of power with the arrangement most feasible with the model for an optimal power generation. The structure of the power generating unit includes the shaft and the rotor arrangement which is connected to the generator assembly also the piezo-electric material have some rectifier circuit to have a steady output of current.

·         Design and development of a hybrid power generation – A design it made to make a hybrid model to generate power through it using two energy resources and tapping maximum energy from the power generating unit by the use of alternative methods.

·         Reduce power and friction losses – By using alternative methods and hybrid model the power loss and frictional losses can be minimized up to a large extent and the maximum power can be generated with reduced losses in the energy.

·         Less corrosion and erosion – A model is to be made such that to reduce the corrosion in the components and less erosion or wearing rate of the components.

·         Easy maintenance – To develop a power generation system which has easy maintenance as well as improved quality of work can be obtained by the system.

·         To develop a system this is always in standby mode.

·         Development of a power generation system which is more economical than other methods.

 Technical Details

While moving, the vehicles possess some potential energy and it is being wasted. This potential energy can be utilized to produce power by using a special arrangement. It is an Electro-Mechanical unit. It utilizes both mechanical technologies and electrical techniques for the power generation and its storage. This is a dome like device likely to be speed breaker.

                                                           

Whenever the vehicle is allowed to pass over the dome it gets pressed downwards then the springs are attached to the dome are compressed and the rack which is attached to the bottom of the dome moves downward in reciprocating motion. Since the rack has teeth connected to gears, there

exists conversion of reciprocating motion of rack into rotary motion of gears but the two gears rotate in opposite direction. A flywheel is mounted on the shaft whose function is to regulate the fluctuation in the energy and to make the energy uniform. So that the shafts will rotate with certain R.P.M. these shafts are connected through a belt drive to the dynamos, which converts the mechanical energy into electrical energy. The conversion will be proportional to traffic density. Whenever an armature rotates between the magnetic fields of south and north poles, an E.M.F (electro motive force) is induced in it. So, for inducing the E.M.F armature coil has to rotate, for rotating this armature it is connected to a long shaft. By rotating same e.m.f, is induced, for this rotation kinetic energy of moving vehicles is utilized.

The power is generated in both the directions; to convert this power into one way a special component is used called zenor diode for continuous supply. All this mechanism can be housed under the dome, like speed breaker, which is called HUMP. The electrical output can be improved by arranging these speed breakers in series. This generated power can be amplified and stored by using different electrical devices.

The various machine elements used in the construction of power hump are:

·         RACK & PINION

·         SPUR GEAR

·         FLY WHEEL

·         BEARINGS

·         SHAFT

·         SPRINGS

·         ELECTRIC DYNAMO

·         PIEZO-ELECTRIC UNIT

The basic principle of working of above components is as follows:

3.1 RACK AND PINION:

Its primary function is to convert translatory motion into rotary motion in other words A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack"; rotational motion applied to the pinion causes the rack to move, thereby translating the rotational motion of the pinion into the linear motion of the rack. It must have higher strength, rigidity and resistance to shock load and less wear and tear.

The rack and pinion arrangement is commonly found in the steering mechanism of cars or other wheeled, steered vehicles. This arrangement provides a lesser mechanical advantage than other mechanisms such as recirculating ball, but much less backlash and greater feedback, or steering "feel". The use of a variable rack (still using a normal pinion) was invented by Arthur Ernest Bishop, so as to improve vehicle response and steering "feel" especially at high speeds, and that has been fitted to many new vehicles, after he created a specialised version of a net-shape warm press forging process to manufacture the racks to their final form, thus eliminating any subsequent need to machine the gear teeth. For every pair of conjugate involute profile, there is a basic rack. This basic rack is the profile of the conjugate gear of infinite pitch radius.

A generating rack is a rack outline used to indicate tooth details and dimensions for the design of a generating tool, such as a hob or a gear shaper cutter.

A ‘rack and pinion’ gears system looks quite unusual. However, it is still composed of two gears. The ‘pinion’ is the normal round gear and the ‘rack’ is straight or flat. The ‘rack’ has teeth cut in it and they mesh with the teeth of the pinion gear. The pinion rotates and moves the rack in a straight line - another way of describing this is to say ‘rotary motion’ changes to ‘linear motion’.

In this project this rack and pinion assembly is used to convert the downward motion of the rack into the rotator motion of the pinion gear.

3.2   SPUR GEAR :

It is a positive power transmission device with definite velocity ratio. In volute teeth profile is preferred for adjusting some linear misalignment. Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with the teeth projecting radially, and although they are not straight-sided in form, the edge of each tooth is straight and aligned parallel to the axis of rotation. These gears can be meshed together correctly only if they are fitted to parallel shafts.

The pinion is the smallest gear and the larger gear is called the gear wheel. A rack is a rectangular prism with gear teeth machined along one side- it is in effect a gear wheel with an infinite pitch circle diameter.   In practice the action of gears in transmitting motion is a cam action each pair of mating teeth acting as cams.  Gear design has evolved to such a level that throughout the motion of each contacting pair of teeth the velocity ratio of the gears is maintained fixed and the velocity ratio is still fixed as each subsequent pair of teeth come into contact.   When the teeth action is such that the driving tooth moving at constant angular velocity produces a proportional constant velocity of the driven tooth the action is termed a conjugate action.   The teeth shape universally selected for the gear teeth is the involute profile.

Spur gears are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions.Spur gears are used in many devices that you can see all over , like the electric screwdriver, dancing monster, oscillating sprinkler, windup alarm clock, washing machine and clothes dryer. But you won't find many in your car. This is because the spur gear can be really loud. Each time a gear tooth engages a tooth on the other gear, the teeth collide, and this impact makes a noise. It also increases the stress on the gear teeth

Spur Gear Design:The spur gear is is simplest type of gear manufactured and is generally used for transmission of rotary motion between parallel shafts.  The spur gear is the first choice option for gears except when high speeds, loads, and ratios direct towards other options.  Other gear types may also be preferred to provide more silent low-vibration operation.  A single spur gear is generally selected to have a ratio range of between 1:1 and 1:6 with a pitch line velocity up to 25 m/s.  The spur gear has an operating efficiency of 98-99%.  The pinion is made from a harder material than the wheel.  A gear pair should be selected to have the highest number of teeth consistent with a suitable safety margin in strength and wear.   The minimum number of teeth on a gear with a normal pressure angle of 20 degrees is 18.

Design Process

To select gears from a stock gear catalogue or do a first approximation for a gear design select the gear material and obtain a safe working stress e.g Yield stress / Factor of Safety. /Safe fatigue stress

Determine the input speed, output speed, ratio, torque to be transmitted

Select materials for the gears (pinion is more highly loaded than gear) Determine safe working stresses (uts /factor of safety or yield

stress/factor of safety or Fatigue strength / Factor of safety ) Determine Allowable endurance Stress Se

Select a module value and determine the resulting geometry of the gear

Use the lewis formula and the endurance formula to establish the resulting face width

If the gear proportions are reasonable then - proceed to more detailed evaluations

If the resulting face width is excessive - change the module or material or both and start again

The gear face width should be selected in the range 9-15 x module or for straight spur gears-up to 60% of the pinion diameter.Materials used for spur gears design: Mild steel is a poor material for gears as it has poor resistance to surface loading.   The carbon content for unhardened gears is generally 0.4 %( min) with 0.55 %( min) carbon for the pinions.  Dissimilar materials should be used for the meshing gears - this particularly applies to alloy steels.  Alloy steels have superior fatigue properties compared to carbon steels for comparable strengths.  For extremely high gear loading case hardened steels are used the surface hardening method employed should be such to provide sufficient case depth for the final grinding process used.

Contact Ratio for spur gear:

The gear design is such that when in mesh the rotating gears have more than one gear in contact and transferring the torque for some of the time. This property is called the contact ratio.  This is a ratio of the length of the line-of-action to the base pitch.   The higher the contact ratio the more the load is shared between teeth.  It is good practice to maintain a contact ratio of 1.2 or greater. Under no circumstances should the ratio drop below 1.1.

A contact ratio between 1 and 2 means that part of the time two pairs of teeth are in contact and during the remaining time one pair is in contact.   A ratio between 2 and 3 means 2 or 3 pairs of teeth are always in contact.   Such as high contact ratio generally is not obtained with external spur gears, but can be developed in the meshing of an internal and external spur gear pair or specially designed non-standard external spur gears.

For an optimal performance of the spur gear it should have low wear and tear, high shock-absorbing capacity.

3.3  FLYWHEEL:

The primary function of flywheel is to act as an energy accumulator. It reduces the fluctuations in speed. It absorbs the energy when demand is less and release the same when it is required.

A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed. Energy is transferred to a flywheel by applying torque to it, thereby causing its rotational speed, and hence its stored energy, to increase. Conversely, a flywheel releases stored energy by applying torque to a mechanical load, which results in decreased rotational speed.

Flywheels have three predominant uses:

They provide continuous energy when the energy source is not continuous. For example, flywheels are used in reciprocating engines because the energy source (torque from the engine) is not continuously available.

They deliver energy at rates beyond the ability of an energy source. This is achieved by collecting energy in the flywheel over time and then releasing the energy quickly, at rates that exceed the capabilities of the energy source.

They control the orientation of a mechanical system. In such applications, the angular momentum of a flywheel is purposely transferred to a load when energy is transferred to or from the flywheel.

Flywheels are typically made of steel and rotate on conventional bearings; these are generally limited to a revolution rate of a few thousand RPM. Some modern flywheels are made of carbon fiber materials and employ magnetic bearings, enabling them to revolve at speeds up to 60,000 RPM

Flywheels are often used to provide continuous energy in systems where the energy source is not continuous. In such cases, the flywheel stores energy when torque is applied by the energy source and it releases stored energy

when the energy source is not applying torque to it. For example, a flywheel is used to maintain constant angular velocity of the crankshaft in a reciprocating engine. In this case, the flywheel—which is mounted on the crankshaft—stores energy when torque is exerted on it by a firing piston, and it releases energy to its mechanical loads when no piston is exerting torque on it. Another example of this is friction motors, which use flywheel energy to power devices such as toy cars.A flywheel may also be used to supply unsustained pulses of energy at energy transfer rates that exceed the capabilities of its energy source, or when such pulses would disrupt the energy supply (e.g., public electric network). This is achieved by accumulating stored energy in the flywheel over a period of time, at a rate that is compatible with the energy source, and then releasing that energy at a much higher rate over a relatively short time. For example, flywheels are used in punching machines and riveting machines, where they store energy from the motor and release it during the punching or riveting operation.

The phenomenon of precession has to be considered when using flywheels in vehicles. A rotating flywheel responds to any momentum that tends to change the direction of its axis of rotation by a resulting precession rotation. A vehicle with a vertical-axis flywheel would experience a lateral momentum when passing the top of a hill or the bottom of a valley (roll momentum in response to a pitch change). Two counter-rotating flywheels may be needed to eliminate this effect. This effect is leveraged in momentum wheels, a type of flywheel employed in satellites in which the flywheel is used to orient the satellite's instruments without thruster rockets.

3.4  BEARINGS:A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle.

There are at least six common principles of operation of bearings:

plain bearing, also known by the specific styles: bushings, journal bearings, sleeve bearings, rifle bearings

rolling-element bearings such as ball bearings and roller bearings jewel bearings, in which the load is carried by rolling the axle slightly

off-center fluid bearings, in which the load is carried by a gas or liquid magnetic bearings, in which the load is carried by a magnetic field

flexure bearings, in which the motion is supported by a load element which bends.

Reducing friction in bearings is often important for efficiency, to reduce wear and to facilitate extended use at high speeds and to avoid overheating and premature failure of the bearing. Essentially, a bearing can reduce friction by virtue of its shape, by its material, or by introducing and containing a fluid between surfaces or by separating the surfaces with an electromagnetic field.

By shape, gains advantage usually by using spheres or rollers, or by forming flexure bearings.

By material exploits the nature of the bearing material used. (An example would be using plastics that have low surface friction.)

By fluid exploits the low viscosity of a layer of fluid, such as a lubricant or as a pressurized medium to keep the two solid parts from touching, or by reducing the normal force between them.

By fields exploits electromagnetic fields, such as magnetic fields, to keep solid parts from touching.

Combinations of these can even be employed within the same bearing. An example of this is where the cage is made of plastic, and it separates the rollers/balls, which reduce friction by their shape and finish.

ROLLING ELEMENT BEARINGS:

Rolling element bearing life is determined by load, temperature, maintenance, lubrication, material defects, contamination, handling, installation and other factors. These factors can all have a significant effect on bearing life. For example, the service life of bearings in one application was extended dramatically by changing how the bearings were stored before installation and use, as vibrations during storage caused lubricant failure even when the only load on the bearing was its own weight; the resulting damage is often false brinelling. Bearing life is statistical: several samples of a given bearing will often exhibit a bell curve of service life, with a few samples showing significantly better or worse life. Bearing life varies because microscopic structure and contamination vary greatly even where macroscopically they seem identical.

PLAIN BEARINGS:

For plain bearings some materials give much longer life than others. Some of the John Harrison clocks still operate after hundreds of years because of

the lignum vitae wood employed in their construction, whereas his metal clocks are seldom run due to potential wear.

FLEXURE BEARINGS:

Flexure bearings rely on elastic properties of material. Flexure bearings bend a piece of material repeatedly. Some materials fail after repeated bending, even at low loads, but careful material selection and bearing design can make flexure bearing life indefinite.

It is a machine element, which supports another machinery. It permits relative motion between the contacting surfaces while carrying the loads. They reduce the friction and transmit the motion effectively. These bearings are used in the shaft attached to the flywheel.

They are useful in friction less movement of the shaft.

3.5  SHAFTS:

A shaft is a rotating member usually of circular cross-section (solid or hollow), which is used to transmit power and rotational motion. Axles are non rotating member. Elements such as gears, pulleys (sheaves), flywheels clutches, and sprockets are mounted on the shaft and are used to transmit power from the driving device (motor or engine) through a machine. The rotational force (torque) is transmitted to these elements on the shaft by press fit, keys, dowel, pins and splines. The shaft rotates on rolling contact or bush bearings. Various types of retaining rings, thrust bearings, grooves and steps in the shaft are used to take up axial loads and locate the rotating elements.

It is a rotating element, which is used to transmit power from one place to another place. It supports the rotating elements like gears and flywheels. It must have high torsional rigidity and lateral rigidity.

3.6 SPRINGS:

A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication. Some non-ferrous metals are also used including phosphor bronze and titanium for parts requiring corrosion resistance and beryllium copper for springs carrying electrical current (because of its low electrical resistance).When a spring is compressed or stretched, the force it exerts is proportional to its change in length. The rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring. That is, it is the gradient of the force versus deflection curve. An extension or compression spring has units of force divided by distance, for example lbf/in or N/m. Torsion springs have units of force multiplied by distance divided by angle, such as N·m/rad or ft·lbf/degree. The inverse of spring rate is compliance, that is: if a spring has a rate of 10 N/mm, it has a compliance of 0.1 mm/N. The stiffness (or rate) of springs in parallel is additive, as is the compliance of springs in series.Depending on the design and required operating environment, any material can be used to construct a spring, so long as the material has the required combination of rigidity and elasticity: technically, a wooden bow is a form of spring.

SPRINGS CAN BE CLASSIFIED DEPENDING ON HOW THE LOAD FORCE IS APPLIED TO THEM:

Tension/Extension spring – the spring is designed to operate with a tension load, so the spring stretches as the load is applied to it.

Compression spring – is designed to operate with a compression load, so the spring gets shorter as the load is applied to it.

Torsion spring – unlike the above types in which the load is an axial force, the load applied to a torsion spring is a torque or twisting force, and the end of the spring rotates through an angle as the load is applied.

THEY CAN ALSO BE CLASSIFIED BASED ON THEIR SHAPE:

Coil spring – this type is made of a coil or helix of wire Flat spring – this type is made of a flat or conical shaped piece of

metal. Machined spring - this type of spring is manufactured by machining

bar stock with a lathe and/or milling operation rather than coiling wire. Since it is machined, the spring may incorporate features in addition to the elastic element. Machined springs can be made in the typical load cases of compression/extension, torsion, etc.

THE MOST COMMON TYPES OF SPRING ARE:

·         Cantilever spring – a spring which is fixed only at one end.

Coil spring or helical spring – a spring (made by winding a wire around a cylinder) and the conical spring – these are types of torsion spring, because the wire itself is twisted when the spring is compressed or stretched. These are in turn of two types:

o Compression springs are designed to become shorter when loaded. Their turns (loops) are not touching in the unloaded position, and they need no attachment points.

A volute spring is a compression spring in the form of a cone, designed so that under compression the coils are not forced against each other, thus permitting longer travel.

o Tension or extension springs are designed to become longer under load. Their turns (loops) are normally touching in the unloaded position, and they have a hook, eye or some other means of attachment at each end.

Hairspring or balance spring – a delicate spiral torsion spring used in watches, galvanometers, and places where electricity must be carried to partially-rotating devices such as steering wheels without hindering the rotation.

Leaf spring – a flat spring used in vehicle suspensions, electrical switches, and bows.

V-spring – used in antique firearm mechanisms such as the wheellock, flintlock and percussion cap locks.

It is defined as an elastic body whose function is to distort when loaded and to recover its original shape when the load is removed. It cushions, absorbs or controls energy either due to shocks or due to vibrations.

3.7   ELECTRIC DYNAMO/ ELECTRIC GENERATOR:

Electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge (usually carried by electrons) to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow (but does not create water). The source of mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed air or any other source of mechanical energy.The reverse conversion of electrical energy into mechanical energy is done by an electric motor, and motors and generators have many similarities. In fact many motors can be mechanically driven to generate electricity, and very frequently make acceptable generators.

Before the connection between magnetism and electricity was discovered, electrostatic generators were invented that used electrostatic principles. These generated very high voltages and low currents. They operated by using moving electrically charged belts, plates and disks to carry charge to a high potential electrode. The charge was generated using either of two mechanisms:

Electrostatic induction. The triboelectric effect, where the contact between two insulators

leaves them charged.

Because of their inefficiency and the difficulty of insulating machines producing very high voltages, electrostatic generators had low power ratings and were never used for generation of commercially significant quantities of electric power. The Wimshurst machine and Van de Graff generator are examples of these machines that have survived.Simple loop generator is having a single-turn rectangular copper coil rotating about its own axis in a magnetic field provided by either permanent magnet or electro magnets. In case of without commutator the two ends of the coil are joined to slip rings which are insulated from each other and from the central shaft. Two collecting brushes ( of carbon or copper) press against the slip rings. Their function is to collect the current induced in the coil. In this case the current waveform we obtain is alternating current ( you can see in fig). In case of with commutator the slip rings are replaced by split rings. In this case the current is unidirectional (observe in fig).

Generator working :In figure see the case when the coil is rotating in anticlock-wise direction without commutator. As the coil assumes successive positions in the field, the flux linked with it changes. Hence, an e.m.f is induced in it which is proportional to the rate of change of flux linkages (e=-N dΦ/dt). When the plane of the coil is at right angles to lines of flux then flux linked with the coil is maximum but rate of change of flux linkages is minimum.

It is so because in this position, the coil sides do not cut or shear the flux, rather they slide along them i.e they move parallel to them.Hence,there is no induced e.m.f in the coil.Generaly this no e.m.f is taken as the starting position i.e zero degrees position.The angle of rotation or time wil be measured from this position.

As the coil continues rotating further, the rate of change of flux linkages (and hence induced e.m.f in it) increases till the coil rotates 90° from its starting position. Here the coil plane is vertical (see in fig) i.e parallel to the lines of flux. As seen, the flux linked with the coil is minimum but rate of change of flux linkages is maximum. Hence, maximum e.m.f is induced in the coil when in this position.

In the next quarter revolution i.e. from 90° to 180°,the flux linked with the coil gradually increases but the rate of change of flux linkages decreases .  Hence, induced e.m.f decreases gradually till it becomes zero.

So,we find that in the first half revolution of the coil, no e.m.f is induced in it at 0°, maximum when the coil is at 90° position anno e.m.f when coil is at 180°.The direction of this induced e.m.f can be found by applying Fleming's Right hand rule.

In the next half revolution i.e. from 180° to 360°, the variations in the magnitude of e.m.f are similar to those in the first half revolution . Its value is maximum when coil is at 270° and minimum when the coil is at 360° position . But it will be found that the direction of induced current is reverse of the previous direction of flow.

Therefore, we find that the current which we obtain from such a simple generator reverses its direction after every half revolution. Such a current undergoing periodic reversals is known as alternating current . It should be noted that alternating current not only reverses its direction, it does not even keep its magnitude constant while flowing in any one direction.The two half- cycles may be called positive and negative half-cycles respectively.

Now see when the coil is rotating with commutator . In this case the slip rings are replaced by split rings. The split rings are made out of a conducting cylinder which is cut into two halves or segments insulated from each other by a thin sheet of mica or some other insulating material .As before, the coil ends are joined to these segments on which rest the carbon or copper brushes.

In case of split rings, the positions of the segments of split rings have also reversed when the current induced in the coil reverses i.e. when the current direction reverses the brushes also comes in contact with reverse segments as that of positive half-cycle. Hence, this current is unidirectional. It should be noted that the position of the brushes is so arranged that the changeover of segments from one brush to other takes place when the plane of the rotating coil is at right angles to the plane of the lines of flux. It is so because in that position, the induced e.m.f in the coil is zero. You can observe this in two cases by pausing the waveform.

Another important point is that now the current induced in the coil is alternating as before. It is only due to the rectifying action of the split-rings (also called commutator) that it becomes unidirectional in the external circuit.

Electro - Hydraulic Brake ( EHB )

Brake performance can be divided into two distinct classes:

 

1)      Base brake performance

2)      Controlled brake performance.

           A base brake event can be described as a normal or typical stop in which the driver maintains the vehicle in its intended direction at a controlled deceleration level that does not closely approach wheel lock.All other braking events where additional intervention may be necessary, such as wheel brake pressure control to prevent lock-up, application of a wheel brake to transfer torque across an open differential, or application of

an induced torque to one or two selected wheels to correct an under- or over steering condition, may be classified as controlled brake performance. Statistics from the field indicate the majority of braking events stem from base brake applications and as such can be classified as the single most important function. From this perspective, it can be of interest to compare modern-day Electro-Hydraulic Brake (EHB) hydraulic systems with a conventional vacuum-boosted brake apply system and note the various design options used to achieve performance and reliability objectives.

 

INTRODUCTION

The next brake concept. This system is a system which senses the driver's will of braking through the pedal simulator and controls the braking pressures to each wheels. The system is also a hydraulic Brake by Wire system.

Many of the vehicle sub-systems in today’s modern vehicles are being converted into “by-wire” type systems. This normally implies a function, which in the past was activated directly through a purely mechanical device, is now implemented through electro-mechanical means by way of signal transfer to and from an Electronic Control Unit. Optionally, the ECU may apply additional “intelligence” based upon input from other sensors outside of the driver’s influence. Electro-Hydraulic Brake is not a true “by-wire” system with the thought process that the physical wires do not extend all the way to the wheel brakes. However, in the true sense of the definition, any EHB vehicle may be braked with an electrical “joystick” completely independent of the traditional brake pedal. It just so happens that hydraulic fluid is used to transmit energy from the actuator to the wheel brakes.  This configuration offers the distinct advantage that the current production wheel brakes may be maintained while an integral, manually applied, hydraulic failsafe backup system may be directly incorporated in the EHB

system. The cost and complexity of this approach typically compares favorably to an Electro-Mechanical Brake (EMB) system, which requires significant investment in vehicle electrical failsafe architecture, with some needing a 42 volt power source. Therefore, EHB may be classified a “stepping stone” technology to full Electro-Mechanical Brakes.

HYDRAULIC DESIGN CONSIDERATIONS

FAILSAFE AND SYSTEM COMPLEXITIESAnalogous to a vacuum boosted system in base brake mode, EHB supplies a braking force proportional to driver input, which reduces braking effort. The boost characteristics also contribute to the pedal “feel” of the vehicle. If the boost source fails, the system resorts to manual brakes where brake input energy is supplied in full by the driver. As would be expected, the pedal forces vs. vehicle deceleration characteristics are significantly affected.

This is shown by the input pedal force vs. Brake line pressure output in Figure 1 of a typical vacuum boosted vehicle. 

Looking at a comparison using the failsafe pedal force input limit of 500 N, the difference between the resulting    brake line pressure is 2.5 MPa unboosted vs. 8.5 MPa    boosted. This correlates to an approximately proportional difference in vehicle deceleration. In this example there approximately correlates to 0.3 g’s decel. Unboosted, and 0.9 g’s boosted. With EHB systems, there is room to improve this performance, but only at the expense of pedal travel, which becomes a hydraulic lever    arm of sorts. For example, to achieve a higher decel   from 0.3 g to 0.5 g in failed system, the pedal travel may    have to increase from 50 - 75 mm to perhaps 150 mm, which is about the practical limit for brake pedal travel.    Thus, due to the consequences of boost failure, careful    attention must be paid to component system design irrespective    of the type of mechanism employed.   

A comparison     between the conventional vacuum boosted system     and an EHB system is shown in Figure 

The conventional system utilizes a largely mechanical link all the way from the brake pedal through the vacuum booster and into the master cylinder piston. Proportional     assist is provided by an air valve acting in conjunction with the booster diaphragm to utilize the stored vacuum    energy. The piston and seal trap brake fluid and transmit    the hydraulic energy to the wheel brake.   

Compare this to the basic layout of the typical EHB system.     First, the driver’s input is normally interpreted by up     to three different devices: a brake switch, a travel sensor, and a pressure sensor while an emulator provides the normal pedal “feel”. To prevent unwanted brake applications, two of the three inputs must be detected to     initiate base brake pressure. The backup master cylinder     is subsequently locked out of the main wheel circuit     using isolation solenoid valves, so all wheel brake pressure     must come from a high-pressure accumulator     source. This stored energy is created by pressurizing brake fluid from the reservoir with an electro-hydraulic pump into a suitable pre-charged vessel. The accumulator pressure is regulated by a separate pressure sensor     or other device. The “by-wire” characteristics now come     into play as the driver’s braking intent signals are sent to the ECU. Here an algorithm translates the dynamically changing voltage input signals into the corresponding     solenoid valve driver output current waveforms.

As the apply and release valves open and close, a pressure sensor at each wheel continuously “closes the loop” by   feeding back information to the ECU so the next series of current commands can be given to the solenoid   valves to assure fast and accurate pressure response.     

It is obvious the EHB system is significantly more complex in nature. To address this concern, numerous steps   have been taken to eliminate the possibility of boost failure   due to electronic or mechanical faults. In the ECU design, component redundancy is used throughout. This       includes multiple wire feeds, multiple processors and internal circuit isolation for critical valve drivers. The extra components and the resulting software to control them, does add a small level of additional complexity in itself. Thermal robustness must also carefully be designed       into the unit, as duty cycles for valves and motors will be higher than in add-on type system. Thus, careful attention must be given to heat sinking, materials, circuit designs, and component selection. Special consideration       must be given to the ECU cover heat transfer properties, which could include the addition of cooling fins. On the mechanical side there is redundancy in valves and wheel brake sensors in that the vehicle may still be braked with two or three boosted channels. In regards to the E-H pump and accumulator, backup components   are not typically considered practical from a size, mass, and cost viewpoint. However, these few components are extremely robust in nature and thoroughly tested to       exceed durability requirements.      

The second area used to evaluate potential failure concerns   is through the study of past warranty data of similar systems. The system chosen for comparison was an early ABS system integrated into a hydraulic booster. The data was collected from two different North American passenger vehicles built in the early 1990’s at a 12-month PPM level. Both vehicles utilized a central hydraulics unit that in turn supplied power to the hydraulic brake booster and ABS block. The data in Table 1 represents an approximation of warranty comparison based upon an averaging of returns from both vehicle lines. Note any vehicles requiring a vacuum pump (such as diesel) would also have to take those failures into consideration for the baseline calculation.

  

Although the total failure frequency is higher, many of the failures may illuminate the fault light on the dashboard, but would not affect the base brakes. For example, there is sufficient redundancy in sensors and in hydraulic valve block components that the vehicle would still maintain boosted braking on the unaffected wheels. As previously noted, multiple feed wires and grounds are being employed which could therefore negate many of the concerns related to wiring harness defects. In similar         fashion, many of the ECU failures would also not result in loss of the base brake boost function. Thus, when adding the E-H pump and some smaller percentage of wiring and ECU failures, the total combination that would affect base brake performance could be expected to be         closely the same or even less than the conventional system. This type of comparison using ten-year-old data is only a guideline since modern technology and manufacturing methods continue to make both electronic and mechanical components more reliable. 

  

BASE NON-ISOLATED HYDRAULIC CIRCUITDESIGN

Designing for base brake systems poses a challenge to be able to utilize the same hydraulic components to  meet two extreme braking conditions. One is a panic mode situation, where an extreme amount of hydraulic          energy needs to be transmitted through the brake system in a very short amount of time in order to apply the wheel brakes as quickly as possible. Current specifications    typically call for reaching pressures at the wheel          brakes of approximately 8 MPa in 120 milliseconds or  less. For a typical midsize vehicle, this translates into average power requirements of 1,200          watts with flow rates in excess of 40 cm3/s at each wheel brake.

The second challenge is to be able to modulate pressures in a very stiff system when the brakes are applied. Pressure resolution of approximately 30 kPa is required. The problem of control becomes apparent. Very small quantities of brake fluid must be sufficiently modulated to give a good base brake pedal feel. To meet the requirements the selected control valves must  be designed to have very good response time characteristics          (i.e. < 10 millisecond) with relatively unrestricted flow paths. The basic means to achieve wheel brake modulation comes from using two normally closed proportional control valves per wheel brake. The apply valve regulates flow from the high pressure central accumulator to the           wheel brake, while the release valve regulates flow from the wheel brake back to reservoir, which is maintained at  atmospheric pressure. A typical single wheel schematic is shown in Figure 3.   

For failsafe operation, it becomes necessary to include  an isolation valve between the pedal feel emulator -master cylinder (PFE-MC) assembly and wheel brake. Its functions include blocking the driver’s manual output pressure during a boosted apply as well as providing a vent path back to reservoir when the brakes are not activated. Additionally, a balance valve is placed between wheel brakes on each axle to prevent momentary pressure imbalance during panic-type base brake applies.           This design is especially well suited for front/rear (T-T) type of systems since the master cylinder circuits are also allocated to each axle. In this design the accumulator  circuit leads directly into the master cylinder and           wheel brake circuits through the apply valve as is shown  by the arrows on the graph.

Most EHB’s utilize brake fluid stored in a central, gas pressurized            accumulator. Typical sizes for a North American midsize vehicle may range from 200 to 300 cm3. A typical accumulator pressure operating range may be 16 MPa (pump turn on) to 18 MPa (pump turn off). The gas most commonly used is nitrogen due to its relatively low cost and relative inertness. The nitrogen gas is kept separated from the brake fluid by either an elastomeric or metallic membrane or diaphragm. Most            elastomeric membranes have a single, curved shape which folds back upon itself as the device fills with brake fluid. The all-metallic type of membrane is usually in the shape of a bellows with a number of folds (much like an accordion) and relies on thin plate bending with large            deformations and low stress levels to accomplish the task of displacing brake fluid. Due to the small size of the nitrogen molecules, permeation is also a factor to consider, particularly with elastomeric types of diaphragms. The nitrogen gas will typically find its way through most elastomeric materials, and enter the molecular “pores” within the spaces of the pressurized brake fluid volume

until all of the voids are filled. At that time, equilibrium is re-established and finally permeation diminishes.

High temperatures may also accelerate this phenomenon. With the latest multi-layer proprietary materials being developed, certain accumulator

manufacturers are claiming improvements in permeation reduction of five to six times. Thus, estimated useful life is now in the range of 10 – 15 years.

Failure Mode Considerations – Non-isolated Circuit

Returning to considerations for the high pressure accumulator. This device stores significant amounts of energy, typically as much as 1,700 watt-seconds. This has the advantage of being able to supply numerous (i.e. 5 –15) reserve stops should the electro-hydraulic pump fail. It was previously noted the pressurized nitrogen gas was separated from the brake fluid by one of two types of diaphragms. Even though the latest versions of both these devices have become extremely reliable through years of development, it might not yet be possible to classify either of these types of units as a true zero defect type of device since manufacturing quality must always be considered. Therefore, the consequence of diaphragm failure must be investigated. A test was devised utilizing a non-isolated wheel brake circuit of the type shown in Figure 3. A carefully constructed accumulator with a small hole punctured in the diaphragm was installed in a vehicle. The brakes were subsequently applied and released at discreet intervals to study any change in operating characteristics. The graph in Figure 4 below shows the status of the measured brake pedal force and travel parameters after 100 powered base brake applies, where functionality was shown to be normal. (The unit was fully checked every 50 strokes.)

The pedal feel emulator-master cylinder in this test had a lockout feature. The bottom curve represents the system in normal powered mode showing the simulated pedal travel. The top curves shows brake performance in failsafe mode. At stroke number 114 of the brake pedal, the diagnostics of the ECU detected a “pressure out-of-bounds” failure indicating base brake output pressure was no longer able to follow the driver’s brake pedal input commands. The system immediately reverted to the hydraulic failsafe backup mode.

Figure 5 is a plot of the brake system performance just one stroke after the failure occurrence. In this case, in the failed system backup mode, the PFE-MC assembly achieved the full travel of 120 mm with an input force of only

45 N. This is the approximate force required to displace the master cylinder springs to full travel with no hydraulic load present and indicates there is minimal pressure output to the wheel brakes.

Attempts were made to find where the nitrogen gas might have migrated to in the system. The circuit was first partially re-bled just between the master cylinder and isolation valve inside the hydraulic control unit (refer again to Figure 3). The results are shown in Figure 6.

The brake pedal force reached approximately 37% of its previous full-travel pedal force value prior to failure. This indicates a significant percentage of the nitrogen also

made its way into the HCU-to-wheel brake circuit. As a final step the system was then bled between the HCU and wheel brakes. The results of the re-bleed are shown in Figure 7. Note this curve is nearly identical to that shown in Figure 4 indicating all of the escaped nitrogen gas had been removed from the brake circuits. The test was subsequently repeated with similar results. The gas expulsion could not be anticipated with the diagnostic methods utilized at the time.

These test results verify the severity level of nitrogen discharge due to a defective accumulator diaphragm. The total amount of gas which migrated into the wheel brake and master cylinder circuits was not measured but was at least equivalent to the aster cylinder volume. One technique to assure some level of braking can still be maintained with this type of failure is to allow the pump to run in a continuous mode to eventually compress the discharged gas and subsequently build wheel pressure. The effectiveness of this solution will be determined by pump flow rate and the quantity of gas discharged. For a pump with a nominal flow rate of 8 cm3/s any substantial quantity could result in relatively slow braking response times. If the gas permeates the master cylinder circuit, there could be limited or no force feedback from the pedal feel emulator, which would result in abnormal pedal feel.

 One method to maintain a non-isolated circuit is to employ accumulator travel sensing. This is accomplished by incorporating a suitable sensor to track the displacement of the accumulator membrane and works especially well with the metal bellows type of unit. In addition to the travel associated with the normal filling and release of fluid, the metal bellows also has an elastic memory. Thus a defect in the bellows, which allows brake fluid to begin to fill the accumulator can be immediately detected and shut down

boosted braking to prevent the possibility of gas expulsion. It is also necessary to know temperature information with this approach to be able to account for pressure variations due to temperature changes. Since the open flow path to the wheel and master cylinder circuits are still present, the sensing method must be robust.

ISOLATED HYDRAULIC CIRCUIT DESIGNAn alternative approach is to utilize an isolated base brake circuit. A typical single-wheel circuit is shown in Figure 8.

There are some distinct differences between the isolated and non-isolated concepts. The first, and most obvious is the addition of an isolation piston assembly between the pump circuit and each wheel brake circuit which will positively stop nitrogen from entering the wheel brake circuit. The arrows in the graph highlight the restricted

flow path. For design simplification, cost reduction, and improved durability, a single seal design is shown although a dual seal, vented design may also be substituted.The other change is that the proportional release valve is normally open. This provides an open flow path back to reservoir, which is independent of the wheel brake circuit. Any escaping nitrogen from the accumulator will have an unrestricted path back to reservoir in failsafe mode. Also note that the balance valve is placed in the pump circuit and may now be a normally open valve for either the T-T or X type of hydraulic circuits.

         Another indirect benefit with this approach is the amount of nitrogen gas, which can be permanently trapped, is limited to the drilled holes in the HCU housing, the clearance volume behind the isolation piston, and the volumes around the proportional control valves. Therefore, running the pump to boost brake output in the event of accumulator diaphragm failure is likely to be more effective.

As isolation piston previously mentioned included only a single seal. Although this solution raises the question of introducing a latent (i.e. undetectable) failure, there are

means, both in plant and algorithmically, of detection. The many benefits of using a single seal include occupation of less space, fewer holes to drill, and fewer components, all of which translate to saving cost. In addition, seal stress loading is reduced by maintaining the seal in near pressure equilibrium. This has the added benefit of reducing wear and reducing

frictional forces with the bore. The seal force values shown in Figure 9 were derived from prior generic seal testing.

To be able to detect a missing or defective seal, a suitable algorithm must be employed. State-of-the art assembly plant air testing can detect functionality of a seal

in a bore. However, even though this is assured as a new product, it does not assure seal functionality over the ten to fifteen year design life. A leak test procedure, which can be performed on the vehicle, however, may be implemented. The procedure is outlined in detail in Figure 10.

One other step required in assuring a failsafe approach to an EHB design which utilizes isolated wheel circuits, is understanding the volume relationships between the

three variable displacement devices: wheel brake, isolation piston, and master cylinder. The typical wheel cylinder and master cylinder may be simply represented as a piston inside a bore as shown in Figure 11.

By knowing the exact volumetric relationships between wheel brake, isolation piston, and master cylinder, a system can be designed that will assure failed system performance. For example, in the lower half of the diagram above, the piston and cylinder assemblies each graphically represent the volumetric comparisons between the three aforementioned devices. First, consider the brake circuit between the HCU and master cylinder. Note the compliance this circuit may be accurately assessed from knowing the travel position of the master cylinder piston. This is true even when pedal feel emulator displacement is considered, since that is also a fixed pressure-to volume relationship and is known from the component geometry. To further test for system effectiveness, the isolation piston may be applied to a target pressure by appropriate activation of the apply valve. If the wheel brake circuit is not able to achieve the requested pressure, then system compliance is excessive, and appropriate

warning can be issued. If, on the other hand, the target pressure is achieved at the wheel brake, the system is functioning properly. The isolation piston may also be utilized as a means to purge the master cylinder circuit as referred to in step no. 2 of Figure 10.

One additional factor for EHB failsafe braking must also be considered which can best be defined as “base brake system compliance allowances”. These are the factors

that can contribute to a soft or spongy brake pedal such as from brake pad warpage or distortion from aging or abuse. These allowances should be recognized and included in initial component sizing. In summary, careful employment of isolation pistons, with accompanying diagnostics can be an effective solution for accumulator isolation.

2-WHEEL VS. 4-WHEEL FAILSAFE MODE

Yet another area of failsafe performance which requires consideration is 2-wheel vs. 4-wheel manual operation. Past hydraulically boosted, backup systems in the field

have largely been configured with 2-wheel backup. However, utilizing a four-wheel failsafe approach offers more design flexibility, and potential stopping distance

reduction on certain classes of vehicles.

The first step is to evaluate suspension and vehicle dynamics. In some vehicles, such as those with front wheel drive and a higher center of gravity, there may be insufficient normal force on the rear wheels during a moderate braking stop in the range of 0.4 to 0.6 g’s that use of rear wheel brakes is not very efficient. However,

there are some classes of vehicles, particularly rear wheel- drive cars and trucks, as well as some of the larger front-wheel-drive cars, where there may be sufficient wheel-to-road braking torque available. For those vehicles use of all four wheels for emergency braking could be considered.

The next step is to measure is front vs. rear wheel brake relative efficiency. The variable in question is defined as:

WHEEL BRAKE RELATIVE EFFICIENCY

Rel.Efficiency = OUTPUT TORQUE T (p)

INPUT ENERGY = P * V (p)

In this instance, the input hydraulic energy is the brake line pressure capable of being generated by the driver times the displacement used to achieve that pressure. Thus, from an energy viewpoint, it is better to utilize

the wheel brakes on a vehicle that have the highest specific torque output at the lowest displacement. Some rear wheel brakes (disc or drum) tend to have similar specific torques to the front brakes, yet require less fluid displacement. By taking instantaneous wheel brake torque, pressure, and displacement readings, the measure of wheel brake relative efficiency can be plotted, as shown in Figure 12.

In the example given, it will be more efficient to utilize front and rear brakes together to minimize stopping distances, provided vehicle dynamic conditions are met. Delphi utilizes a in-house computer program to estimate stopping distances. This tool takes into account all of the variables mentioned and combines them with a vehicle suspension model, which captures such factors as weight transfer, to calculate decel and stopping distance.

Actual vehicle data is taken to be able to input wheel brake specific torque. Additional information about the base brake system is then fed into the model to calculate a parameter called apply system gain. This variable is defined as the pedal ratio divided by master cylinder bore area.

A 3-dimensional plot of apply system gain is shown in Figure 13. The larger the gain, the larger the mechanical advantage in transferring energy from the driver’s foot to the wheel brake, and the larger the pressure which can be applied for a given input force. The tradeoff is pedal travel. It is also increased in proportion to mechanical gain, which ultimately limits the amount of gain for the entire system. An output plot for a typical midsize vehicle is shown in Figure 14. In this single graph, the failsafe performance of the selected system may be analyzed for deceleration and pedal travel at both LLVW and GVW conditions.

When evaluating the question of 2-wheel vs. 4-wheel braking, this program was used to evaluate deceleration capabilities of the same vehicle but with either one or both axles active in braking. The estimates for a specific North American light duty truck are shown in Table 2.

In this particular case, there was a 32% increase in estimated vehicle deceleration at LLVW and a 37% increase in estimated vehicle deceleration at GVW. It may also be observed higher apply system mechanical gains are required for 2-wheel brakes while trying to achieve equivalent vehicle braking forces. This can create some practical problems. Pedal ratios can become very large which dictate specially designed pedals to maintain a minimum master cylinder push rod arc length, or conversely, master

cylinder bores become very small (i.e. less than ø 19.0) with long travel requirements.

As previously noted, not all classes of vehicles necessarily show significant improvement in moving from 2-wheel to 4-wheel backup braking mode. However, designing for only 2-wheel failsafe may exclude optimization on some types of  vehicles that can benefit from 4-wheel braking. The range of improvement from the limited numbers of vehicles, which have thus far been analyzed, has run from a few percent to over 30%. In each case, cost vs. performance trade-off should be evaluated when selecting the final design since additional hydraulic components may be required for 4-wheel backup.

PEDAL FEEL EMULATOR LOCKOUTThe graph in Figure 16 shows a typical, customer requested force-displacement curve required for the emulator.

Figure 17 shows a typical hardware arrangement to meet the pedal feel requirements. This unit consists of a master cylinder with emulator piston and spring assembly. As the driver’s foot applies the brake pedal, an input push rod displaces the primary master cylinder piston, while at the same time the isolation valves in the HCU are commanded to close. This blocks both primary and secondary master cylinder outlet ports. The secondary piston becomes locked in place due to the trapped fluid. The fluid contained by the primary piston is displaced into the drill path, which leads to the emulator assembly. As pressure continues to build, the spring begins to deform under the load from the hydraulic pressure acting on the surface of the piston. This causes additional displacement that allows the brake pedal to move in proportion to the force exerted by the driver. The force vs. travel characteristics can be “tuned” to customer directives. If the vehicle is required to stop in failed system, the isolation valves remain open so that fluid is permitted to flow to both the wheel brakes and the emulator.

Since emulator piston deflection occurs at relatively low pressures, the compliance of the wheel brakes and emulator are additive, which results in additional pedal travel. Thus the driver’s total available input energy for failsafe braking is reduced by the additional emulator displacement which does not contribute to vehicle braking.

One solution is to incorporate a solenoid valve lockout device in-between the emulator and master cylinder. Whenever a failure is detected, the ECU would causethe valve to close to prevent the unwanted displacement. A second, more cost-effective approach to consider is to incorporate a seal bypass arrangement in the main bore as shown in Figure 18. In normal boosted operation, as previously noted, the primary and secondary outlets are both blocked by the isolation valves. Since the secondary piston is held rigidly in the bore, the fluid from the primary piston is permitted to flow around the by-pass lip seal as shown in Figure 19 and into the drilled path for the emulator.

As before, in failsafe braking, the isolation valves open and both primary and secondary piston circuits are now directly connected to the wheel brakes. As the secondary piston can now move forward, the lip seal re-enters the main bore and keeps the higher pressure primary circuit from losing any additional fluid to the emulator. It should be noted, however, with any types of lockout mechanism that they are ineffective should there be an “in-stop” failure. Once the PFE displacement is utilized, that amount of pedal travel is lost until the subsequent stop. Thus, worst case conditions must always be considered in the final design process assuming no lockout present.

CONCLUSIONSimilar to the days of early ABS introduction, multiple EHB hydraulic design configurations have emerged. From the mid 80’s through the latter part of the 1990’s

numerous ABS configurations ranging from hydraulically boosted open systems, to four valve flow control designs, to modulators based upon ball screws and electric motors came to market before the 8-valve, closed recirculation system became the de facto standard. As with any new technology, there are concerns and tradeoffs to be dealt with. In the case of the electro-hydraulic brake they center around increased electrical and mechanical complexity, failsafe braking performance, accumulator safety, and 2-wheel versus 4-wheel backup modes. Each of these concerns has been answered by prudent designs and incorporation of new component technologies. The configuration adopted in Delphi’s EHB development  has included use of four-wheel failsafe with individual isolation pistons and utilization of mechanical pedal feel lockout. This particular design allows system flexibility, inherent accumulator precharge isolation, and the ability to tune for optimum failed system stopping performance for all vehicle classes.

 Ultimately, no matter which final configuration is selected for a specific vehicle platform, it will have to undergo the rigors of full brake system validation. A carefully de-signed and implemented EHB system holds the promise of enabling the new brake-by-wire features while still reliably performing the everyday task of stopping the vehicle.

Seminar Report On CONTACT LESS ENERGY TRANSFER

 In this paper a new topology for contactless energy transfer is proposed and tested that can transfer energy to a moving actuator using inductive coupling. The proposed topology provides long-stroke contactless energy transfer capability in a plane and a short-stroke movement of a few millimeters perpendicular to the plane. In addition, it is to lerant to small rotations. The experimental setup consists of a platform with one secondary coil, which is attached to a linear actuator and a 3-phase brushless electromotor. Underneath the platform is an array of primary coils that are each connected to a half-bridge square wave power supply. The energy transfer to the electromotor is measured while the platform is moved over the array of primary coils by the linear actuator. The secondary coil moves with a stroke of 18cm at speeds over 1m/s, while up to 33W power is transferred with 90% efficiency.

INTRODUCTION

            Most high-precision machines are positioning stages with Multiple

degrees of freedom(DOF), which often consist of cascaded long-and short-

stroke linear actuators that are supported by mechanical or air bearings.

Usually, the long stroke actuator has micrometer accuracy, while the

Submicron accuracy is achieved by the short-stroke actuator. To build a

high-precision machine, as much disturbances as possible should be

eliminated. Common sources of disturbances are vibrations, Coulomb and

viscous friction in bearings, crosstalk of multiple cascaded actuators and

cable slabs.

          A possibility to increase throughput, while maintaining accuracy is to

use parallel processing, i.e. movement and positioning in parallel within

section, calibration, assembling, scanning, etc. To meet the design

requirements of high accuracy while improving performance, a new design

approach is necessary, especially if vacuum operation is considered, which

will be required for the next generation no lithography machines. A lot of

disturbance sources can be eliminated by integrating the cascaded long-and

short-stroke actuator into one actuator system. Since most long-stroke

movements are in a plane, this can be done by a contactless planar actuator.

         The topology proposed and tested in this paper provides long-stroke

contact less energy transfer (CET) in a plane with only small changes in

power transfer capability.

ACTUATOR

Actuator is a mechanical device used for moving or controlling a mechanism

or system. It converts electrical signals into motion.

Here we are using a linear actuator; it converts electrical signals into linear

motion i.e. the movement is linear in manner along a plane.

  

CET    TOPOLOGY

The design of the primary and secondary coil is optimized to get a coupling

that is as constant as possible for a sufficiently large area. This area should

be large enough to allow the secondary coil to move from one primary coil to

the next one without a large reduction in coupling. If this can be achieved,

the power can be transferred by one primary coil that is closest to the

secondary coil. When the secondary coil moves out of range the first primary

coil is turned off and the next one will be energized. To ensure a smooth

energy transfer to the moving load, the position dependence of the coupling

should be minimized, while keeping the coupling high enough to get a high-

efficiency energy transfer.

                A lot of systems use 2D spiral coils for the primary and secondary

coil, since the spiral coil geometry allows relatively high coupling (upto60%)

and some tolerance form is alignment of the coils. However, to allow the

secondary coil to move from one primary coil to the next, the tolerance for

misalignments should be increased. In the proposed system this is done by

using a 3D geometry for the primary coil. This results in a fairly constant B-

field around the primary coil, which accommodates good coupling in a large

area. Further more, since the system is supposed to transfer power to a load

moving in a plane, it is convenient to use a shape that is symmetrical in 2D

for both the primary coil and the secondary coil:

a square for instance. The geometry of the primary and the secondary coils

are optimized with FEM using Maxwell 3D10 Optimetrics. The resulting

geometry of the coils is shown in Fig.1 and 2 and the dimensions are listed

in Table 1

            The drawing in Fig.3 shows one secondary coil above nine primary

coils. The black square shows the area in which the center of the secondary

coil can move while maintaining good coupling with the middle primary coil.

The secondary coil is situated in the bottom-left corner of the area of

interaction with the middle primary coil. The coupling between the primary

coil and the secondary coil within that area is calculated with Maxwell 3D

10Optimetrics and measured. The results are shown in Fig.4, which show

that the FEM predictions are very close to the measured values. The

coupling K is fairly constant within most of the area, only on the outer edges

it drops fast. However, the ripple defined by Eq.1 is 25%, which is quite

small considering the large displacement of the secondary coil:

              Ripple = max (k) - min (k) ·100% (1)

                                     max (k)

Although this system is designed with square shaped coils, it is also possible

to design a system with similar characteristics using rectangular coils.

STEADY-STATE ELECTRIC CIRCUIT ANALYSIS

                     Since the system will be used in a maglev application based on

repulsive forces between coils and permanent magnets, the use of iron or

ferrites is prohibited. In addition, the use of cores will limit the stroke of the

system. Therefore, a coreless or air core inductive coupling is used to

transfer the energy. To keep the efficiency of an air core inductive coupling

high a resonant capacitor is used for both the primary and the secondary

coil. Moreover, due to the position dependent coupling, a series resonant

capacitor is used for both coils to ensure that the resonant frequency of the

circuit does not depend on the coupling. The electric circuit of the CET

system is shown in Fig.5, where V 1 is the RMS voltage of the power supply,

I 1 is the RMS current supplied by the power supply, I 2 the RMS current

induced in the secondary circuit. C 1and C 2 are the series resonant

capacitors in the primary and secondary circuit, R 1 is the resistance of the

primary coil, R2 is the resistance of the secondary coil. L 1 and L 2 are the

self inductance of the primary and secondary coil, respectively. k is the

inductive coupling factor between the primary and secondary coil, and R L is

the resistance of the load. The load R L represents the rectifier and

additional power electronics.

          Simplified versions of the circuit are shown in Fig.6a and b, where Z R

is the reflected load of the secondary circuit on the primary circuit and Z 1is

the load seen by the power supply.

  

EXPERIMENTAL SETUP

An experimental setup was built to test the CET design, which consists of an

array of three stationary primary coils that are fixed in a row on top of a

ceramic structure. The ceramic structure is used to allow heat from the coils

to be conducted to the iron base frame and at the same time to prevent eddy

current losses in the iron base frame. The primary coils are made of litz

wire. Each bundle of litz wire consists of 60 strands of 71 µm and the

strands are wrapped together with a layer of cotton. The strand size has

been chosen after examining the AC losses. The turns of the coil are fixed by

glue that has been applied during the winding process. Approximately 120

turn fitted in the cross-section, resulting in a 0.3 filling factor.

Each primary coil is connected in series with a resonance capacitor. Each

resonant circuit is driven by a separate half-bridge power supply that

applies a square wave voltage of 191 kHz over the resonant circuit. The

schematic of the half-bridge power supply is shown in Fig. 7. An overview of

the primary coils and the corresponding series capacitors is shown in Table

II. The secondary coil is fixed onto a ceramic plate that is bolted to the

mover of a linear actuator. Again ceramic material is used for heat

conduction and the minimization of eddy current losses. The linear actuator

can move the secondary coil over the three primary coils. The position of the

secondary coil with respect to the array of primary coils is measured by the

encoder of the linear actuator. A picture of the experimental setup is shown

in Fig. 8.

                      The secondary coil is connected in series with a resonant

capacitor. The circuit is then connected to a full-bridge diode rectifier to

generate a DC output. The DC output of the rectifier is connected to the

load, which is an electromotor of

a CD drive running at 12 VDC as shown in Fig. 9.

                       All subsystems are connected to a ds1103 dSpace system

running the control program at 8 kHz. This way the DC bus voltage of the

primary coil power supplies is controlled as well as which of the primary coil

power supplies is enabled. The position of the linear actuator is controlled

using a PID controller running on the dSpace system. Depending on the

position of the linear actuator the dSpace system enables the primary coil

that is completely overlapped by the secondary coil.

                       The primary coil activation is controlled by a multi-port

switch. The multi-port switch has four active coil states; state1 enables the

power supply of the first primary coil, state 2 and 3 enable the power supply

of the second and third primary coil, respectively. State 4 disables all power

supplies and this state is used for switching from one power supply to the

next. When the secondary coil moves out of range of primary coil 1 (active

coil state 1), the active supply is switched off (active coil state 4) and one

sample time later the second supply is switched on (active coil state 2). For

one sample time none of the power supplies is active (active coil state 4),

which is necessary to allow the triac in the power supply that is switched off

(see Fig. 7) to block the circuit after the current in the resonant circuit is

damped. There is no other control mechanism in the power electronics, and

the system operates without any measurement on the secondary site, except

for the position of the secondary coil

RESULTS

                   An electromotor of a CD drive that runs on 12 VDC is connected

to the rectifier. The voltage and current from the DC bus supply as well as

the voltage and current to the CD drive are measured and shown in Fig. 10

and 11. The secondary coil is moving over all three primary coils following a

sinusoidal position reference, which represents a total displacement of 18

cm (i.e. the amplitude of the sine wave is 9 cm). The frequency of the

sinusoidal position reference is 2 Hz, so in one second the secondary coil

makes two cycles (one cycle implies moving from primary coil 1 over

primary coil 2 to primary coil 3 and back). The cycle is clearly visible from

the Active Coil plot in Fig. 10 and 11, which represents the state of the

active coil multi-port switch. The secondary coil reaches a maximum speed

of 1.1 m/s over the second primary coil. Due to this speed the secondary coil

is in range of the second primary coil for only 60 ms.

                   By calculating the RMS values of the voltages and currents

the power from the DC bus supply Pin as well as the power to the CD drive

load Pout and the efficiency η according to Eq. 14 can be calculated. This

calculation includes losses in the power electronics. The values are listed in

Table III.

                    In Fig. 12, the transient behavior is shown when the secondary

coil is moving from primary coil 1 to primary coil 2. It is clearly visible that

all power supplies are switched off when the active coil state has value 4.

There is also some delay between the active coil state switch and the

response from the power electronics, which is caused by a slow rising edge

of the enable signal and by delay in the power electronics. In Fig. 10 and 11

the switching is also visible in the current waveforms, since no current is

drawn from the DC bus supply and no current is available for the

electromotor of the CD drive.

                   The ripples visible in the voltage and current waveforms

from the DC bus power supply and to the CD drive are related to the

changing coupling. However, since the CD drive does not represent a purely

resistive load, the ripple is somewhat smoothed by the inductance of the

load. This effect is more visible when a purely resistive load will be

connected to the system. In addition, the CD drive does not need much

power to operate and a resistive load can be operated at higher power

levels. Therefore, a 50 Ω resistive load is used at a higher power level. The

same trajectory is used for the secondary coil. The measured voltage and

current waveforms of the DC bus supply and the load are shown in Fig. 13

and 14 respectively. The RMS values of voltage, current and power as well

as the efficiency are shown in Table IV.

                       The variation in coupling is now clearly visible in the current

and voltage waveforms of the load. This suggests that the power transfer

can be further smoothed by measuring the coupling and changing the

voltage of the DC bus supply accordingly. The results are very similar to the

results of the CD drive. Higher power levels have not been tested using the

linear actuator, since the capacitors in the resonant circuit cannot operate

above 800 V. Operating at higher power requires new capacitors which have

not been realized yet. It is expected that power transfer up to 300 W is

feasible.

CONTACTLESS ENERGY TRANSFER

   A Better Solution for a Mobile World

Talk to any plant engineer or production system designer and you’ll find that

electrical wiring is the bane of their existence. From installing the wires, to

rewiring as production lines need to be changed, to repairing damage

caused by careless workers, electrical wires represent an ongoing cost and

risk for downtime in manufacturing plants. Until recently, the miles of

electrical wiring that snake around any manufacturing facility, hanging

down from ceilings and extending across corridors between equipment, have

been viewed as a necessary aspect of industrial automation. But today

industry is moving toward a wireless world. Like consumers with their cell

phones, laptops and PDA’s, industrial companies want wireless technologies

that improve versatility, reduce costs and maintain connectivity. One of the

latest developments to draw interest among engineering personnel is

contactless energy transfer for powering and controlling motors. While

wireless communication is now common in factories, wirelessly transferring

16kW of electricity through the air to power equipment is a relatively new

phenomenon in the United States.                                         

             In a typical automated manufacturing environment, where carts full

of parts must be moved between the different stages of a production

process, a contactless system transfers electrical energy inductively from an

insulated conductor in a fixed installation to one or more mobile loads.

Electromagnetic coupling is realized via an air gap, so it is not subject to

wear and costly maintenance. Contactless energy transfer reduces costs in

several ways: It eliminates festooning or overhanging utilities. The

underground wiring is compact and poses no trip hazards. There is no

carriage to run out on the shop floor. There are also no pits to be dug to

drop in trailing utilities.

                      In addition to lower costs, a mobile system using contactless

energy transfer provides greater versatility: The contactless system enables

more flexible track layout with curves and switches, simple segmentation of

tracks, which makes it easy to extend a track or change travel directions,

and higher speeds.

APPLICATIONS

         Contactless energy transfer is ideal for applications where:

• The mobile equipment has to cover long distances

• A variable, extendable track layout is required

• High speeds have to be achieved

• The energy transfer has to be maintenance free

•Additional environmental contaminants are not permitted in sensitive areas

• The operation takes place in wet and humid areas

       Maintenance and ambient conditions are important factors in

constructing systems for material handling and transportation applications,

such as automotive assembly, storage and retrieval logistics and sorting.

Typical applications that could benefit from

Contactless energy transfer includes:

• Overhead trolleys

• Conveyor trolleys

• Guided floor conveyors

• Push-skid conveyors

• Storage and retrieval units

• Pallet transportation systems

• Baggage handling

• Panel gantries

• Elevator equipment

• Amusement park rides

• Battery charging stations

             By replacing a drag-chain system in a conveyor trolley that

transports and sorts pallets, for example, contactless energy transfer

enables pallets to transverse over longer distances. Complicated holders for

drag chains are eliminated, as is downtime for repairing cable breaks and

battery charging. Repairs for wear from bending or torsion are also

eliminated. The wear-free power supply in a contactless system has many

advantages in designing and maintaining push-skid conveyors used in

automotive assembly, for example, or in storage and retrieval units in a

high-bay warehouse. Because there is no conductor rail, there is no danger

of introducing contaminants from system leakages and no components that

are difficult to reach for maintenance. Problems with fitting the platforms

into conveyor belts are also eliminated, since there’s no need for high

mechanical tolerances between the line cable and pick-up.

           Perhaps the biggest advantage of a system based on   contactless

energy transfer is higher system availability because the system is

essentially maintenance free. In a manufacturing environment where change

is a constant and speed is an imperative, the versatility, flexibility and

reliability of contactless energy transfer systems can reduce the wear-and-

tear on plant engineers as well as equipment.

  

CONCLUSION

                    A new topology for contact less energy transfer (CET) to a

moving load has been proposed, built and tested. The CET topology allows

for a long-stroke movement in a plane and a short-stroke movement of a few

millimeters perpendicular to the plane. In addition, it is tolerant to small

rotations. The power electronics consist of a half-bridge square wave power

supply for each primary coil and series resonant capacitor and a full-bridge

diode rectifier at the load.

                     Power transfer up to 33 W with resistive load of 50 Ω has been

demonstrated The CET system was used to power a 3-phase brushless

electromotor of a CD drive and showed stable power transfer of 3.44 W. The

power was transferred at approximately 90 % efficiency, while the

secondary coil was moving with speeds up to 1.1 m/s over the primary coils