Braking systems & Lifting Devices.

FLUID MECHANICS

CASE STUDIES RELEVANT TO THE ENGINEERING STUDIES STAGE 6 SYLLABUSBOARD OF STUDIES NSW • Note to teachers.

• – Case Studies relate to two separate modules found in the current Engineering Studies syllabus. One engineering application module (3) – Braking systems, can be found on the preliminary course 30 hours indicative. The second can be found as a focus module (3) – Aeronautical engineering, found in the HSC course 30 hours indicative.

• Other parts of the syllabus can be linked to this digital teacher resource.

• Fluid mechanics :

The scientific study of static and dynamic actions of liquids and gasses in motion (fluid dynamics) and at rest (Hydrostatic). Fluid mechanics as a topic also investigates internal and external forces and how these forces affect the flow properties of fluids.

LIQUID AND GAS

• Liquid is a fluid that will spread out but remain in pools if poured onto a flat surface. Liquid poured into a container will fill the container in any shape starting from base.

• Gas will disperse in all directions if released. If forced into a container gas will fill the shape making contact with all surfaces.

SECTION ONE – BRAKING SYSTEMS.

• Syllabus outcomes: P2.1,P3.1,P4.1

• If all the systems of a vehicle were to be broken down and prioritised the braking system would have to be one the most important.

• Fluid Mechanics- are linked with basic hydraulics found in braking systems. Early mechanical braking systems such as levers and cables, were not only unreliable and unsafe, they also inadequate in providing equal braking pressure to the braking system.

BLAISE PASCALHydraulic systems work on the principle that confined fluid under pressure, will be transmitted undiminished and equally in all directions.

UNDER NORMAL CONDITIONS LIQUID CANNOT BE COMPRESSED.

Here we can see the weight putting force on the liquid; this force is acting in all directions thus increasing the pressure on all sides of the container. The pressure being the same at all points.

This image shows that liquid takes the shape of any container; the whole area is occupied filling it in between two weights.

Applying force to the left cylinder or weight demonstrates that the liquid is not compressible so its volume stays the same.

The effect is that the force gets transferred to the opposite cylinder.Where only the weight is free to move, due to the shape of the container. What we can also see is that both cylinders are equal thus the pressure exerted in each force is the same.

Pascals theory – mathematically

F1

A1 A2

F2

F1A1 =

F2A2

A similar or relevant principle can be explained by this man, Archimedes investigated density and buoyancy over 2000 years ago.

Archimedes Principle states that the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object.

Or………..The weight of the displaced liquid is equal to the weight of the floating object click on the link to watch a short clip.

THE USE OF HYDRAULIC PRINCIPLES IN PERSONAL AND PUBLIC TRANSPORT- BRAKING SYSTEMS• Syllabus outcomes: P1.1,P2.1,P3.1,P4.1,P4.2P4.3.

PASSENGER CAR

Here’s an example of a disc braking system, commonly found in passenger cars, motorcycles and light duty trucks.

Hydraulic drum brakes using Pascals principle.

MOTORCYCLE

Hydraulic disc brakes

An attempt to slow or stop the rotation of a wheel by friction, brake pads are used to clamp to a disc connected to the wheel.

DIFFERENCE BETWEEN HYDRAULIC AND AIR BRAKES IS THAT AIR CAN BE COMPRESSED.

From a scientific point of view liquid cannot be compressed.

INNOVATIONS IN BRAKING SYSTEMS. • Syllabus outcomes:P1.1,P2.1,P3.1,P3.3,P4.1,P4.2,P4.3

• One of the most common innovations in braking systems would have to be

ABS- Antilock Braking System.

In 1988 BMW introduced the first ABS system for a motorcycle. An electro-hydraulic brake servo and adaptive brake-power distribution system which was the first of its kind in the world.

How is the BMW Integral ABS innovative?

• The hand-brake lever and pedal-operated brake act simultaneously on both wheels

• To ensure optimum decaccellartion • When reaching the wheel lock limit,

the brake power is distributed and regulated electronically

• Two seperate brake servos relieve pressure build up on both wheels.

Motorcycle disc brakes :• Usually made from different materials such as stainless steel , to prevent rust• They are drilled and slotted to dissipate water from the road or rain• The drilled brake or slotted wholes also act as a heat sink under heavy braking • can be electronically controlled to include ABSBicycle disc breaks:• Range from simple cable systems to expensive six-piston hydraulic systems• Can be manufactured from aluminium and titanium for weight reduction and

durabilityLarge lightweight trucks, passenger rail cars, some aeroplanes• Replacing drum brakes• Less wear and maintenance • Commonly manufactured out of grey iron due to hardness, chemical

composition, tensile strength

WHY HYDRAULIC DISC BRAKES SUPERCEED DRUM BRAKES

SECTION TWO – LIFTING DEVICES

• Syllabus outcomes:P2.1,P4.3,H2.2,H4.1,

Lifting devices can range from simple to computer controlled machines that are part of our daily lives.

EXAMPLES OF COMMON LIFTING DEVICES.

If it’s too heavy or awkward to carry or move a lifting device either simple or complex will make it easier for you.

HOW THREE SIMPLE MACHINES WORK DIFFERENTLY TO COMPLETE THE SAME TASK• They all have a screw mechanism two of these designs are force magnifiers.

HYDRAULICS & PNEUMATICS & COMPRESSIBILITY

• Fluid volume can be reduced by an increase of pressure if we are working with a gas. Due to the molecules being close together or cohesive (attracted to each other) liquid cannot compress even if a lot of pressure is applied.

• Gases have molecules that are far apart thus allowing it to either compress under pressure or compress reducing the volume of the gas.

• Syllabus outcomes: H4.3,H6.1,

THE IMPACT OF LIFTING DEVICES THROUGH THE DEVELOPMENT OF A SAFER SYSTEM.

• Without hydraulic lifting devices that range from car jacks to construction cranes it can be said the effort it would take to move or lift objects heavier than humans would be near impossible.

• One innovation available that makes lifting a car safer and more convenient must be the Safe T Jack system.

The bottle jack system if not supported correctly in the recommended lift area may be unstable and dangerous.

The hydraulic floor jack may hold more weight than the bottle jack however is heavy and takes up a lot of floor space especially working on a small car or cramped area.

Features of the Safe T Jack• Available in 2 and 3 tonne capacities• A removable power/lifting unit leaving

the jack stand in place• Transfer between a hydraulic jack to a

mechanical stand • All components can be assembled to

produce a conventional jack stand.• Click on the link to learn more.

PNEUMATICS & HYDRAULICS IN AN AERONAUTICAL APPLICATION.

• Syllabus outcomes: H4.1,H4.3,H6.1,H3.2,H3.3

• So far we have understood that a hydraulic system uses the pressure of a liquid to preform a mechanical function.

• The hydraulic system can also be a force multiplier if one piston is smaller than the other despite travelling a longer distance a greater load can be lifted.

THE PNEUMATIC SYSTEM• Create more noise when at work in comparison to hydraulic systems that use oil.

• At first an effort is applied to a piston

• The piston compresses the air in a tank that is connected to a pipe or hose.

• The pipe or hose is fitted with a relief valve that allows the control of air to be turned off or on the pressure of the controlled air powers gears connected to fans

• Several tools are use available for work in several different applications,

ranging from dentists’ drills to jack hammers.

Compressed air is directed through the air inlet.The system moves the piston in the intended direction forcing it move in a reciprocating action.

BERNOULLI’S PRINCIPLE.

The use of hydraulics in the aero industry start from the actual production of the aircraft to the take off and landing .• Elevators• Ailerons• Rudders• Flaps• Electronic hydraulic controllers• computational fluid dynamics CFD

AN AERONAUTICAL INNOVATION• Wing tip devices known as SHARKLETS.

Aerodynamic improvements such as • 15% reduction in fuel consumption• Lower operating costs• Reductions in engine noise & emissions• Assists with the wing tip vortex creating safer flights for passengers and crew.