Abstract2 Final

7/27/2019 Abstract2 Final

1/94

1

CERTIFICATE

Certified that ROHIT KUMAR CHAUBEY (0912740088),

PRABHAKAR PATEL (0912740066), VIPIN SINGH (0912740116),

SANDHAYA TRIPATHI (0912740093), RAVI PRAKASH

(0912740084), RADHE SHYAM TIWARI (0912740073) has carried

out the Project work presented in this Project entitled

AUTOMOBILE ROTATABLE HEAD LIGHT SYSTEM for the

award of B.Tech(ME) from Gautam Buddh Technical University,

Lucknow under my supervision. The Project embodies results of

original work, and studies are carried out by the student himself/herself

and the contents of the Project do not form the basis for the award of

any other degree to the candidate or to anybody else from this or any

other Institution.

Col.V.K.Tomar

HOD (ME) Department

IIMT ENGINEERING COLLEGE,MEERUT

Date:


2/94

2

ACKNOWLEDGEMENT

We would like to express our gratitude and appreciation to all those who gave us thepossibility to complete this report. A special thanks to our final year project

coordinator, Mr. Hemant Kumar sir, whose help, stimulating suggestions and

encouragement, helped us to coordinate our project.

We would also like to acknowledge with much appreciation the crucial role

of the staff of Mechanical Laboratory, who gave the permission to use all required

machinery and the necessary material to complete the Differential Simulation Rig.

We would like to say thanks to our project guide Col.V.K.Tomar Sir whose have

given his full effort in guiding the team in achieving the goal as well as his

encouragement to maintain our progress in track. We would to appreciate the

guidance given by other supervisor as well as the panels especially in our project

presentation that has improved our presentation skills by their Consult and tips.

Last but not least, many thanks to GOD and our parents for their love and affection

during project report.

ROHIT KUMAR CHAUBEY

PRABHAKAR PATEL

VIPIN SINGH

SANDHAYA TRIPATHI

RAVI PRAKASH

RADHE SHYAM TIWARI


3/94

3

ABSTRACT

The number of vehicles on our roads is burgeoning day by day. This is turn forced

almost all this vehicle manufactures to think about the extra safety instruments and

electronic controls to attach with these products for giving the users a safety derived in

all road conditions through a mass flow traffic.Rotatable headlight in a four-wheeler

according to the steering movement is an approach to avoid accidents at severe road

turnings. In this dynamic era the high-speed vehicle need to adapt the mechanism to

have the increased visibility. When steering of any four-wheeler moves in any

direction, the wheel will also move in the same direction. It is alright in the daydriving. But it become risky in the hilly areas, in dark and foggy nights. Because

headlights will not take turn on the turning roads according to the steering. Then driver

has to drive by his own personal experience, by using clutch and brake more number of

times than that on the straight path. Thus, the mechanism of Rotatable headlight

enhances the safety view while driving on the road in such fast moving era.

In the project our main aim has been to provide smooth and safety ride in curved

roads especially in mountains in night.


4/94

4

TABLE OF CONTENT

S NO TITLE NAME PAGE NO.

i. Introduction 05ii. Working Operation 06

iii. Literature Review 07iv. Ackermann steering geometry 08v. About the mechanisms 12

vi. Part of steering mechanismtie rod steering arm King pin 17

vii. Recent Application 19viii. Production cars with active four

wheel steering 20

ix. Basic Steering components 23x. Major Components 35

xi. Rack and Pinion Steering 36xii. DC Motor 37

xiii. Gear 46xiv. Power Supply 75xv. LDR Circuit 79

xvi. Head Lamps 80xvii. Pulley Introduction 83

xviii. Links 87xix. Wheels 88xx. References 94


5/94

5

INTRODUCTION:

Rotatable headlight in a four-wheeler according to the steering movement is an

approach to avoid accidents at severe road turnings. In this dynamic era the high-speed

vehicle need to adapt the mechanism to have the increased visibility. When steering of

any four-wheeler moves in any direction, the wheel will also move in the samedirection. It is alright in the day driving. But it become risky in the hilly areas, in dark

and foggy nights. Because headlights will not take turn on the turning roads according

to the steering. Then driver has to drive by his own personal experience, by using

clutch and brake more number of times than that on the straight path. Thus, the

mechanism of Rotatable headlight enhances the safety view while driving on the road

in such fast moving era.

This Rotatable head light mechanism provides less time in use of clutch and

breaks that means saving of fuel. So less fuel consumption that in term increase theefficiency of engine. By using this mechanism visibility area of headlight can beincreases up to 55. So increase in safety in enhances.

This mechanism needs not to have any kinds of power supply any source.

This mechanism doesnt affect the quantity of the effort on the steering by the driver.

In case of turning, the mechanism definitely works but in straight path driving, the

mechanism doesnt work. No part of mechanism is in the contact in the straight path

driving thus there is very-very less wear and tear in this mechanism.

Despite of having mechanical components, there are no vibrations. Hence no noise

is produced that could be irritating. The cost of cylinders, pistons, fluid and links is not

so much high in comparison of a car. Hence, if one can afford the car, he woulddefinitely afford the car with this mechanism.


6/94

6

WORKING OPERATION

A link is fixed to the rack and pinion steering arrangement. The rack and pinion

steering is moving to one direction, automatically the head lamp is turn in that

direction.


7/94

7

Literature Review

STEERING ARM

Aims on the hub to which the steering is connected. They are usually angled inwards the

centre of the back and to get an Ackermann geometry or something close to it. The steering

arms are actually responsible for transmitting steering inputs to the front wheels and must be

capable of proving flex-free performance when under load.

STEERING AXIS

The line that intersects the upper and lower steering pivots on a steered wheel. On a

car with a strut suspension, the steering axis is defined by the line through the strut

mount on lop and the ball joint on the bottom.


8/94

8

Ackermann steering geometry

Ackermann steering geometry is a geometric arrangement of linkages in the steeringof a car or other vehicle designed to solve the problem of wheels on the inside and

outside of a turn needing to trace out circles of different radii.This engineering solution

is attributable to Langensperger in 1816, but was patented by arrangement in London,

in 1817, by Rudolph Ackermann, whose name stuck to it. The same idea was also

developed in France in the late 1870s, by Bollee and Jeantaud.

When a vehicle is steered, it follows a path which is part of the

circumference of its turning circle, which will have a centre point somewhere along a

line extending from the axis of the fixed axle. The steered wheels must be angled so

that they are both at 90 degrees to a line drawn from the circle centre through thecentre of the wheel. Since the wheel on the outside of the turn will trace a large circle

than the wheel on the inside, the wheels need to be set at different angles. The

Ackermann steering geometry arranges this automatically by moving the steering pivot

points inward so as to lie on a line drawn between the steering kingpins and the centre

of the rear axle. The steering pivot points are joined by a rigid bar, the tie rod, which

can also be part of the, for example, rack and pinion steering mechanism. This

arrangement ensures that at any angle of steering, the centre point of all of the circles

traced by all wheels will lie at a common point.Modern cars do not use pure

Ackermann steering, party because it ignores important dynamic and compliant effects,

but the principle is sound for low speed man oeuvres.


9/94

9


10/94

10


11/94

11

STEERING KUNUCKLE

The part on the hub that is attached to the steering system lie rod ends and ball joints.

STEERING RATIO

The reduction ratio of the steering gear, such as the rack to the pinion or worm to nut.

Variable ratio steering systems sometimes have higher ratio on lock than in the straights head

position; sometimes the other way round.

THE ROD

The tie is that part of the steering system that links or lays the steering system to the

steering knuckle on the wheel. Also a general term for any road acting in tension andcompression, tie rods is also called track rods.


12/94

12

About the Mechanisms:

The mechanism of Rotatable Headlights in four wheelers according to its steering

movement helps to reduce the problems which driver has to face.In this mechanism, theheadlights of four-wheeler are coupled with the tie rod so that it can also move as per the

displacement of tie rod. Because as steering moves, the steering road accepts the rotary

motion. In the steering gear box this rotary is converted in to linear motion of tie rod. With

the help of linear motion of tie rod, the links will also move which is already

fastened to the tie rod This link, however, transfers, it movements to the headlight in

the form of angular displacement. For the angular displacement of the headlight according to

steering movement, two mechanisms are suggested here, will be described later.

MECHANISM CONSTRUCTION:

In its simplest construction, it consists of two cylinders, two pistons, fluid, connectionpipes, two springs and two links for the headlight for one side.

One link is fastened to the tie rod to take its linear displacement and another link is

fastened to the headlight to give the angular displacement to the headlight. The reciprocating

motion of pistons inside the cylinders transfers the displacement from one link to second. The

pistons are moved by the pressure difference of the fluid, which is in the fluid carrying pipe.


13/94

13

Working:

The working of this mechanism can easily be understood by the following steps:

As, in the previous figure, the simple construction of coupled headlight withsteering is shown. According to this fig. the vehicle is moving in forward direction.

As the steering moves in the leftward direction, the wheel will also move in the

leftward direction.

As the wheels take the direction, the tie rod moves in rightward direction and due

to this movements the link I will also move in rightward direction.

As the link 1 moves, it pushes piston 1 inside cylinder. Thus the fluid is also pushed

inside the cylinder and fluid carrying pipe.

This fluid moves inside the pipe and makes the pressure difference in the cylinder 2,

which will now push the piston 2.

This piston 2 again pushes the link 2. This link gives the angular displacement to the

headlights of left side, which is hinged.From the step 1 to step 6, it is seen that headlight is turned in the desired direction

according to steering movement.


14/94

14

When steering comes again to its mean position, links will also regain their previous position.

Then the compressed springs will cause the headlights to regain their previous position.

The same procedure is followed when the steering is turned to right ward direction to

take right turn.


15/94

15

Advantages:

By applying the hydraulic mechanism, there are various advantages over the mechanism

based on the principle of electromagnetism. But there are several such kinds of advantage

that may affect our daily life. These types of advantages are as follows:

When having the Rotatable headlights, the no. of times uses the clutch & brake isreduced. This cause to save the fuel.

From the economic point of view this mechanism can be adapted easily because thefluid used in this mechanism can be adapted easily because the fluid used in this

mechanism is very cheap and need not to refill again and again.

Visibility area of the headlights of the car be increased up to about 55 degrees byapplying this mechanism.

This mechanism needs not to have any kind of power supply any source. Thismechanism doesnt affect the quantity of the effort on the steering by the driver.

In case of turning, the mechanism definitely works but in straignt path driving, themechanism doesnt work. No part of mechanism is in the contact in the straight pathdriving thus there is very-very less wear and tear in this mechanism.

Despite of having mechanical components, there are no vibrations. Hence no noise isproduced that could be irritating.

The cost of cylinders, pistons, fluid and links is not so much high in comparison of acar. Hence, if one can afford the car, he would definitely afford the car with this

mechanism.

EXPECTED RESULTS

With the help of this mechanism, the headlights of the car will also move as the steering moves

in either direction. From the safety point of view this mechanism also enhances the better economic

opinion by saving the fuel. In this phenomenon, the use of clutch & brake is reduced while taking the

turn. It may be that in spite of applying this mechanism the driving of four-wheeler on turning roads is

not as safe as on the straight path but in some cases this is more reliable economic and safe. On the

turning roads the visibility area of the headlights of the car will be increased by applying thismechanism. That is also very important for the racing cars and high-speed vehicles in the night.


16/94

16

APPLICATIONS:

Since this mechanism is not costly and it has advantages of fuel saving and safety

enhancement phenomena, it can used with vehicle which moves fast.Now a day it becomes need of fast moving vehicle. Here this mechanism will work

effectively.

Shortly its application can be view in two fields:

1. in fast moving car2. in sharp turning road

In sharp turning road especially in mountain valley, where there is very

sharp turning, this mechanism will play a significant role.

Steering is the term applied to the collection of components, linkages, etc. which will

allow for a vessel (ship, boat) or vehicle (car) to follow the desired course. An exception is

the case of rail transport by which rail tracks combined together with railroad switches

provide the steering function.


17/94

17

Part of steering mechanism: tie rod, steering arm, king pin.

Introduction

The most conventional steering arrangement is to turn the front wheels using a handoperated

steering wheel which is positioned in front of the driver, via the steering column, which may

contain universal joints to allow it to deviate somewhat from a straight line. Other

arrangements are sometimes found on different types of vehicles, for example, a tiller or

rearwheel steering. Tracked vehicles such as tanks usually employ differential steering

that is, the tracks are made to move at different speeds or even in opposite directions to bring

about a change of course.

Rack and pinion, recirculating ball, worm and sector

Rack and pinion animation

Rack and pinion unit mounted in the cockpit of an Ariel Atom sports car chassis. For most high

volume production, this is usually mounted on the other side of this panel

Many modern cars use rack and pinion steering mechanisms, where the steering wheel turns

the pinion gear; the pinion moves the rack, which is a sort of linear gear which meshes with

the pinion, from side to side. This motion applies steering torque to the kingpins of the

steered wheels via tie rods and a short lever arm called the steering arm.

The rack and pinion design has the advantages of a large degree of feedback and direct

steering "feel"; it also does not normally have any backlash, or slack. A disadvantage is that it

is not adjustable, so that when it does wear and develop lash, the only cure is replacement.


18/94

18

Older designs often use the recirculating ball mechanism, which is still found on trucks and

utility vehicles. This is a variation on the older worm and sector design; the steering column

turns a large screw (the "worm gear") which meshes with a sector of a gear, causing it to

rotate about its axis as the worm gear is turned; an arm attached to the axis of the sector

moves the pitman arm, which is connected to the steering linkage and thus steers the wheels.

The recirculating ball version of this apparatus reduces the considerable friction by placinglarge ball bearings between the teeth of the worm and those of the screw; at either end of the

apparatus the balls exit from between the two pieces into a channel internal to the box which

connects them with the other end of the apparatus, thus they are "recirculated".

The recirculating ball mechanism has the advantage of a much greater mechanical advantage,

so that it was found on larger, heavier vehicles while the rack and pinion was originally

limited to smaller and lighter ones; due to the almost universal adoption of power steering,

however, this is no longer an important advantage, leading to the increasing use of rack and

pinion on newer cars. The recirculating ball design also has a perceptible lash, or "dead spot"

on center, where a minute turn of the steering wheel in either direction does not move the

steering apparatus; this is easily adjustable via a screw on the end of the steering box toaccount for wear, but it cannot be entirely eliminated or the mechanism begins to wear very

rapidly. This design is still in use in trucks and other large vehicles, where rapidity of steering

and direct feel are less important than robustness, maintainability, and mechanical advantage.

The much smaller degree of feedback with this design can also sometimes be an advantage;

drivers of vehicles with rack and pinion steering can have their thumbs broken when a front

wheel hits a bump, causing the steering wheel to kick to one side suddenly (leading to driving

instructors telling students to keep their thumbs on the front of the steering wheel, rather than

wrapping around the inside of the rim). This effect is even stronger with a heavy vehicle like

a truck; recirculating ball steering prevents this degree of feedback, just as it prevents

desirable feedback under normal circumstances.

The steering linkage connecting the steering box and the wheels usually conforms to a

variation of Ackermann steering geometry, to account for the fact that in a turn, the inner

wheel is actually traveling a path of smaller radius than the outer wheel, so that the degree of

toe suitable for driving in a straight path is not suitable for turns.

The worm and sector was an older design, used for example in Willys and Chrysler vehicles,

and the Ford Falcon (1960's).

Power steering

As vehicles have become heavier and switched to front wheel drive, the effort to turn the

steering wheel manually has increased - often to the point where major physical exertion is

required. To alleviate this, auto makers have developed power steering systems. There are

two types of power steering systemshydraulic and electric/electronic. A hydraulic-electric

hybrid system is also possible.

A hydraulic power steering (HPS) uses hydraulic pressure supplied by an engine-driven

pump to assist the motion of turning the steering wheel. Electric power steering (EPS) is

more efficient than the hydraulic power steering, since the electric power steering motor only

needs to provide assistance when the steering wheel is turned, whereas the hydraulic pump

must run constantly. In EPS the assist level is easily tunable to the vehicle type, road speed,


19/94

19

and even driver preference. An added benefit is the elimination of environmental hazard

posed by leakage and disposal of hydraulic power steering fluid.

Speed Adjustable Steering

An outgrowth of power steering is speed adjustable steering, where the steering is heavily

assisted at low speed and lightly assisted at high speed. The auto makers perceive that

motorists might need to make large steering inputs while manoeuvering for parking, but not

while traveling at high speed. The first vehicle with this feature was the Citron SM with its

Diravi layout, although rather than altering the amount of assistance as in modern power

steering systems, it altered the pressure on a centring cam which made the steering wheel try

to "spring" back to the straight-ahead position. Modern speed-adjustable power steering

systems reduce the pressure fed to the ram as the speed increases, giving a more direct feel.

This feature is gradually becoming commonplace across all new vehicles.

Four-wheel steering

Four-wheel steering (or all wheel steering) is a system employed by some vehicles to

improve steering response, increase vehicle stability while maneuvering at high speed, or to

decrease turning radius at low speed.

In most active four-wheel steering systems, the rear wheels are steered by a computer and

actuators. The rear wheels generally cannot turn as far as the front wheels. Some systems,

including Delphi's Quadrasteer and the system in Honda's Prelude line, allow for the rear

wheels to be steered in the opposite direction as the front wheels during low speeds. This

allows the vehicle to turn in a significantly smaller radius sometimes critical for large

trucks or vehicles with trailers.

Many modern vehicles offer a form ofpassive rear steering to counteract normal vehicle

tendencies. For example, Subaru used a passive steering system to correct for the rear wheel's

tendency to toe-out. On many vehicles, when cornering, the rear wheels tend to steer slightly

to the outside of a turn, which can reduce stability. The passive steering system uses the

lateral forces generated in a turn (through suspension geometry) and the bushings to correct

this tendency and steer the wheels slightly to the inside of the corner. This improves the

stability of the car, through the turn. This effect is called compliance understeer and it, or its

opposite, is present on all suspensions. Typical methods of achieving compliance understeer

are to use a Watt's Link on a live rear axle, or the use of toe control bushings on a twist beam

suspension. On an independent rear suspension it is normally achieved by changing the rates

of the rubber bushings in the suspension. Some suspensions will always have compliance

oversteer due to geometry, such as Hotchkiss live axles or a semi trailing arm IRS.

Recent application

In an active 4ws system all four wheels turn at the same time when you steer. There can becontrols to switch off the rear steer and options to steer only the rear wheel independent of

the front wheels. At slow speeds (e.g. parking) the rear wheels turn opposite of the frontwheels, reducing the turning radius by up to twenty-five percent, while at higher speeds both


20/94

20

front and rear wheels turn alike (electronically controlled), so that the vehicle may change

position with less yaw, enhancing straight-line stability. The "Snaking effect" experienced

during motorway drives while towing a travel trailer is thus largely nullified. Four-wheel

steering found its most widespread use in monster trucks, where maneuverability in small

arenas is critical, and it is also popular in large farm vehicles and trucks.

General Motors offers Delphi's Quadrasteer in their consumer Silverado/Sierra and

Suburban/Yukon. However, only 16,500 vehicles have been sold with this system since its

introduction in 2002 through 2004. Due to this low demand, GM will not offer the

technology on the 2007 update to these vehicles.

Previously, Honda had four-wheel steering as an option in their 1987-2000 Prelude, and

Mazda also offered four-wheel steering on the 626 and MX6 in 1988. Neither system was

very popular, in that whatever improvement they brought to these already excellent-handling

vehicles was offset by an unavoidable decrease in sensitivity caused by the increased weight

and complexity.

A new "Active Drive" system is introduced on the 2008 version of the Renault Laguna line. It

was designed as one of several measures to increase security and stability. The Active Drive

should lower the effects of under steer and decrease the chances of spinning by diverting part

of the G-forces generated in a turn from the front to the rear tires. At low speeds the turning

circle can be tightened so parking and maneuvering is easier.

Production cars with active four wheel steering

Efini MS-9 (high and lowspeed)

GMC Sierra (2002) (high andlow speed)

Honda Prelude (high and lowspeed, fully mechanical from

1987 to 1991)

Honda Accord (1991) (highand low speed, mechanical)

Infiniti G35 Sedan (option onSport models) (2007-Present)

(high speed only?)

Infiniti G35 Coupe (option onSport models) (2006-Present)

(high speed only)[3]

Infiniti J30t (touring package)(1993-1994)

Infiniti M35 (option on Sportmodels) (2006-Present) (high

speed only?)

Infiniti M45 (option on Sportmodels) (2006-Present) (high

speed only?)

Infiniti Q45t (1989-1994) (highspeed only?)

Mitsubishi Galant/Sigma (high speed only) Mitsubishi GTO (also sold as the Mitsubishi3000GT and the Dodge Stealth) (high speed

only)

Nissan Cefiro (A31) (high speed only) Nissan 240SX/Silvia (option on SE models)

(high speed only)

Nissan 300ZX (all Twin-Turbo Z32 models)(high speed only)

Nissan Laurel (later versions) (high speedonly)

Nissan Fuga/Infiniti M (high speed only) Nissan Silvia (option on all S13 models) (high

speed only)

Nissan Skyline GTS, GTS-R, GTS-X (1986)(high speed only)

Nissan Skyline GT-R (high and low speed) Renault Laguna (only in GT version of 3rd

generation which was launched October 2007,

GT launched on April 2008)

Toyota Aristo (1997) (high and low speed?) Toyota Camry JDM 1991 Camry Prominent

2.0 L V6[citation needed]

Toyota Celica (option on 5th and 6thgeneration, 1990-1993 ST183 and 1994-1997


21/94

21

Mazda 626 (1988) (high andlow speed)

Mazda MX-6 (1989-1997)(high and low speed)

Mazda RX-7 (optional,computerized, high and lowspeed)

ST203) (Dual-mode, high and low speed)

Toyota Soarer (UZZ32)

Articulated steering

A front loader with articulated steering.

Articulated steering is a system by which a four-wheel drive vehicle is split into front and

rear halves which are connected by a vertical hinge. The front and rear halves are connected

with one or more hydraulic cylinders that change the angle between the halves, including the

front and rear axles and wheels, thus steering the vehicle. This system does not use steering

arms, king pins, tie rods, etc. as does four-wheel steering. If the vertical hinge is placed

equidistant between the two axles, it also eliminates the need for a central differential, as both

front and rear axles will follow the same path, and thus rotate at the same speed.

SuperSteer

SuperSteer is used by NewHolland to make tractors turning radius smaller. The SuperSteer

front axle articulates when the wheels turn. The inside wheel moves away from the frame,

while the outside wheel moves in front of the bumper/nose of the tractor, providing more tire

clearance and a greater turn angle. A picture of this turning action can be seen here.

Steer-By-Wire

The aim of steer-by-wire technology is to completely do away with as many mechanical

components (steering shaft, column, gear reduction mechanism, etc.) as possible. Completely

replacing conventional steering system with steer-by-wire holds several advantages, such as:

The absence of steering column simplifies the car interior design. The absence of steering shaft, column and gear reduction mechanism allows much

better space utilization in the engine compartment.

The steering mechanism can be designed and installed as a modular unit.


22/94

22

Without mechanical connection between the steering wheel and the road wheel, it isless likely that the impact of a frontal crash will force the steering wheel to intrude

into the driver's survival space.

Steering system characteristics can easily and infinitely be adjusted to optimize thesteering response and feel.

As of 2007 there are no production cars available that rely solely on steer-by-wire technology

due to safety and reliability concerns, but this technology has been demonstrated in numerous

concept cars.

Safety

For safety reasons all modern cars feature a collapsible steering column (energy absorbing

steering column) which will collapse in the event of a heavy frontal impact to avoid excessive

injuries to the driver. Non-collapsible steering columns very often impaled drivers in frontal

crashes. Audi has a retractable wheel system called procon-ten.Collapsible steering columns

were invented by Bela Barenyi.This safety feature first appeared on cars built by General

Motors after an extensive and very public lobbying campaign enacted by Ralph Nader.Ford

started to install collapsible steering columns in 1968.

Steering : essential to driving

Elsewhere on this site you can learn about all the other stuff that makes a car go and stop, so

this page is where you'll learn about how it goes around corners. More specifically, how the

various steering mechanisms work.

Like most things in a car, the concept of steering is simple - you turn the steering wheel, thefront wheels turn accordingly, and the car changes direction. How that happens though is not

quite so simple. Well - it used to be back in the days when cars were called horseless

carriages, but nowadays, not so much.

Basic steering components

99% of the world's car steering systems are made up of the same three or four components.

The steering wheel, which connects to the steering system, which connects to the track rod,

which connects to the tie rods, which connect to the steering arms. The steering system can

be one of several designs, which we'll go into further down the page, but all the designsessentially move the track rod left-to-right across the car. The tie rods connect to the ends of

the track rod with ball and socket joints, and then to the ends of the steering arms, also with

ball and socket joints. The purpose of the tie rods is to allow suspension movement as well as

an element of adjustability in the steering geometry. The tie rod lengths can normally be

changed to achieve these different geometries.


23/94

23

The Ackermann Angle : your wheels don't point the same direction.

In the simplest form of steering, both the front wheels always point in the same direction.

You turn the wheel, they both point the same way and around the corner you go. Except thatby doing this, you end up with tyres scrubbing, loss of grip and a vehicle that 'crabs' around

the corner. So why is this? Well, it's the same thing you need to take into consideration when

looking at transmissions. When a car goes around a corner, the outside wheels travel further

than the inside wheels. In the case of a transmission, it's why you need a differential (see the

Transmission Bible), but in the case of steering, it's why you need the front wheels to actually

point in different directions. This is the diagram from the Transmission Bible. You can see

the inside wheels travel around a circle with a smaller radius (r2) than the outside wheels (r1):


24/94

24

In order for that to happen without causing undue stress to the front wheels and tyres, they

must point at slightly different angles to the centreline of the car. The following diagram

shows the same thing only zoomed in to show the relative angles of the tyres to the car. It's

all to do with the geometry of circles:

This difference of angle is achieved with a relatively simple arrangement of steering

components to create a trapezoid geometry (a parallelogram with one of the parallel sides

shorter than the other). Once this is achieved, the wheels point at different angles as thesteering geometry is moved. Most vehicles now don't use 'pure' Ackermann steering

geometry because it doesn't take some of the dynamic and compliant effects of steering and

suspension into account, but some derivative of this is used in almost all steering systems:


25/94

25

Why 'Ackermann'?

This particular technology was first introduced in 1758 by Erasmus Darwin, father of Charles

Darwin, in a paper entitled "Erasmus Darwin's improved design for steering carriages--and

cars". It was never patented though until 1817 when Rudolph Ackermann patented it in

London, and that's the name that stuck.

Steering ratios

Every vehicle has a steering ratio inherent in the design. If it didn't you'd never be able to turn

the wheels. Steering ratio gives mechanical advantage to the driver, allowing you to turn thetyres with the weight of the whole car sitting on them, but more importantly, it means you

don't have to turn the steering wheel a ridiculous number of times to get the wheels to move.

Steering ratio is the ratio of the number of degrees turned at the steering wheel vs. the number

of degrees the front wheels are deflected. So for example, if you turn the steering wheel 20

and the front wheels only turn 1, that gives a steering ratio of 20:1. For most modern cars,

the steering ratio is between 12:1 and 20:1. This, coupled with the maximum angle of

deflection of the wheels gives the lock-to-lock turns for the steering wheel. For example, if a

car has a steering ratio of 18:1 and the front wheels have a maximum deflection of 25, then

at 25, the steering wheel has turned 25x18, which is 450. That's only to one side, so the

entire steering goes from -25 to plus 25 giving a lock-to-lock angle at the steering wheel of

900, or 2.5turns(900/360).This works the other way around too of course. If you know thelock-to-lock turns and the steering ratio, you can figure out the wheel deflection. For example


26/94

26

if a car is advertised as having a 16:1 steering ratio and 3 turns lock-to-lock, then the steering

wheel can turn 1.5x360 (540) each way. At a ratio of 16:1 that means the front wheels

deflect by 33.75 each way.

For racing cars, the steering ratio is normally much smaller than for passenger cars - ie. closer

to 1:1 - as the racing drivers need to get fuller deflection into the steering as quickly as

possible.

Turning circles

The turning circle of a car is the diameter of the circle described by the outside wheels when

turning on full lock. There is no hard and fast formula to calculate the turning circle but you

can get close by using this:

turning circle radius=(track/2)+(wheelbase/sin(average steer angle))

The numbers required to calculate the turning circle explain why a classic black London

taxi has a tiny 8m turning circle to allow it to do U-turns in the narrow London streets. In this

case, the wheelbase and track aren't radically different to any other car, but the average

steering angle is huge. For comparison, a typical passenger car turning circle is normally

between 11m and 13m with SUV turning circles going out as much as 15m to 17m.

Steering System designs : Pitman arm types

There really are only two basic categories of steering system today; those that have pitman

arms with a steering 'box' and those that don't. Older cars and some current trucks use pitman

arms, so for the sake of completeness, I've documented some common types. Newer cars andunibody light-duty trucks typically all use some derivative of rack and pinion steering.

Pitman arm mechanisms have a steering 'box' where the shaft from the steering wheel comes

in and a lever arm comes out - the pitman arm. This pitman arm is linked to the track rod or

centre link, which is supported by idler arms. The tie rods connect to the track rod. There are

a large number of variations of the actual mechanical linkage from direct-link where the

pitman arm is connected directly to the track rod, to compound linkages where it is connected

to one end of the steering system or the track rod via other rods. The example below shows a

compound link.


27/94

27

Most of the steering box mechanisms that drive the pitman arm have a 'dead spot' in thecentre of the steering where you can turn the steering wheel a slight amount before the front

wheels start to turn. This slack can normally be adjusted with a screw mechanism but it can't

ever be eliminated. The traditional advantage of these systems is that they give bigger

mechanical advantage and thus work well on heavier vehicles. With the advent of power

steering, that has become a moot point and the steering system design is now more to do with

mechanical design, price and weight. The following are the four basic types of steering boxused in pitman arm systems.

Worm and sector

In this type of steering box, the end of the shaft from the steering wheel has a worm gear

attached to it. It meshes directly with a sector gear (so called because it's a section of a full

gear wheel). When the steering wheel is turned, the shaft turns the worm gear, and the sector

gear pivots around its axis as its teeth are moved along the worm gear. The sector gear is

mounted on the cross shaft which passes through the steering box and out the bottom where it

is splined, and the the pitman arm is attached to the splines. When the sector gear turns, it

turns the cross shaft, which turns the pitman arm, giving the output motion that is fed into themechanical linkage on the track rod. The following diagram shows the active components

that are present inside the worm and sector steering box. The box itself is sealed and filled

with grease.


28/94

28

Worm and roller

The worm and roller steering box is similar in design to the worm and sector box. The

difference here is that instead of having a sector gear that meshes with the worm gear, there is

a roller instead. The roller is mounted on a roller bearing shaft and is held captive on the end

of the cross shaft. As the worm gear turns, the roller is forced to move along it but because it

is held captive on the cross shaft, it twists the cross shaft. Typically in these designs, theworm gear is actually an hourglass shape so that it is wider at the ends. Without the hourglass

shape, the roller might disengage from it at the extents of its travel.


29/94

29

Worm and nut or recirculating ball

This is by far the most common type of steering box for pitman arm systems. In a

recirculating ball steering box, the worm drive has many more turns on it with a finer pitch. A

box or nut is clamped over the worm drive that contains dozens of ball bearings. These loop

around the worm drive and then out into a recirculating channel within the nut where they arefed back into the worm drive again. Hence recirculating. As the steering wheel is turned, the

worm drive turns and forces the ball bearings to press against the channel inside the nut. This

forces the nut to move along the worm drive. The nut itself has a couple of gear teeth cast

into the outside of it and these mesh with the teeth on a sector gear which is attached to the

cross shaft just like in the worm and sector mechanism. This system has much less free play

or slack in it than the other designs, hence why it's used the most. The example below shows

a recirculating ball mechanism with the nut shown in cutaway so you can see the ball

bearings and the recirculation channel.

Cam and lever

Cam and lever steering boxes are very similar to worm and sector steering boxes. The worm

drive is known as a cam and has a much shallower pitch and the sector gear is replaced with

two studs that sit in the cam channels. As the worm gear is turned, the studs slide along the

cam channels which forces the cross shaft to rotate, turning the pitman arm. One of the design

features of this style is that it turns the cross shaft 90 to the normal so it exits through the

side of the steering box instead of the bottom. This can result in a very compact design when

necessary.


30/94

30

Steering System designs : Rack and pinion

This is by far the most common type of steering you'll find in any car today due to it's relativesimplicity and low cost. Rack and pinion systems give a much better feel for the driver, and

there isn't the slop or slack associated with steering box pitman arm type systems. The

downside is that unlike those systems, rack and pinion designs have no adjustability in them,

so once they wear beyond a certain mechanical tolerance, they need replacing completely.This is rare though.

In a rack and pinion system, the track rod is replaced with the steering rack which is a long,

toothed bar with the tie rods attached to each end. On the end of the steering shaft there is a

simple pinion gear that meshes with the rack. When you turn the steering wheel, the pinion

gear turns, and moves the rack from left to right. Changing the size of the pinion gear alters

the steering ratio. It really is that simple. The diagram below shows an example rack and

pinion system as well as a close-up cutaway of the steering rack itself.


31/94

31

Variable-ratio rack and pinion steering

This is a simple variation on the above design. All the components are the same, and it all

works the same except that the spacing of the teeth on the rack varies depending on how


32/94

32

close to the centre of the rack they are. In the middle, the teeth are spaced close together to

give slight steering for the first part of the turn - good for not oversteering at speed. As the

teeth get further away from the centre, they increase in spacing slightly so that the wheels

turn more for the same turn of the steering wheel towards full lock. Simple.

Vehicle dynamics and steering - how it can all go very wrong

Generally speaking, when you turn the steering wheel in your car, you typically expect it to

go where you're pointing it. At slow speed, this will almost always be the case but once you

get some momentum behind you, you are at the mercy of the chassis and suspension

designers. In racing, the aerodynamic wings, air splitters and undertrays help to maintain an

even balance of the vehicle in corners along with the position of the weight in the vehicle and

the supension setup. The two most common problems you'll run into are understeer and

oversteer.

Understeer

Understeer is so called because the car steers less than you want it to. Understeer can be

brought on by all manner of chassis, suspension and speed issues but essentially it means that

the car is losing grip on the front wheels. Typically it happens as you brake and the weight is

transferred to the front of the car. At this point the mechanical grip of the front tyres can

simply be overpowered and they start to lose grip (for example on a wet or greasy road

surface). The end result is that the car will start to take the corner very wide. In racing, that

normally involves going off the outside of the corner into a catch area or on to the grass. In

normal you-and-me driving, it means crashing at the outside of the corner. Getting out of

understeer can involve letting off the throttle in front-wheel-drive vehicles (to try to give the

tyres chance to grip) or getting on the throttle in rear-wheel-drive vehicles (to try to bring theback end around). It's a complex topic more suited to racing driving forums but suffice to say

that if you're trying to get out of understeer and you cock it up, you get.....


33/94

33

Oversteer

The bright ones amongst you will probably already have guessed that oversteer is the

opposite of understeer. With oversteer, the car goes where it's pointed far too efficiently and

you end up diving into the corner much more quickly than you had expected. Oversteer is

brought on by the car losing grip on the rear wheels as the weight is transferred off themunder braking, resulting in the rear kicking out in the corner. Without counter-steering (see

below) the end result in racing is that the car will spin and end up going off the inside of the

corner backwards. In normal you-and-me driving, it means spinning the car and ending up

pointing back the way you came.

Counter-steering

Counter-steering is what you need to do when you start to experience oversteer. If you get

into a situation where the back end of the car loses grip and starts to swing out, steering

opposite to the direction of the corner can often 'catch' the oversteer by directing the nose of

the car out of the corner. In drift racing and demonstration driving, it's how the drivers are

able to smoke the rear tyres and power-slide around a corner. They will use a combination of

throttle, weight transfer and handbrake to induce oversteer into a corner, then flick the

steering the opposite dirction, honk on the accelerator and try to hold a slide all the way

around the corner. It's also a widely-used technique in rally racing. Tiff Needell - a racing

driver who also works on some UK motoring programs - is an absolute master at counter-

steer power sliding.


34/94

34


35/94

35

MAJOR COMPONENTS

The Following main components of our projects are

1. Rack and pinion steering

2. DC motor

3. Gear

4. Power supply

5. LDR Circuit

6. Head Lamps

7. Pulley

8. Links

9. Wheels


36/94

36

Rack and pinion steering

In steering systems, the rotary motion of the steering wheel is converted into angularturning of the front wheels.

Steering is done by moving the axes of rotation of the front wheels with respect tothe chassis frame.


37/94

37

DC motor

Faradays used oersteds discovered, that electricity could be used to produce motion, to build

the world first electric motor in 1821. Ten years later, using the same logic in reverse, faradaywas interested in getting the motion produced by oersteds experiment to be continuous, rather

then just a rotatory shift in position. In his experiments, faraday thought in terms of magnetic

lines of force. He visualized how flux lines existing around a current carrying wire and a bar

magnet. He was then able to produce a device in which the different lines of force could

interact a produce continues rotation. The basic faradays motor uses a free-swinging wire that

circles around the end of a bar magnet. The bottom end of the wire is in a pool of mercury.

Which allows the wire to rotate while keeping a complete electric circuit.


38/94

38

BASIC MOTOR ACTION

Although Faraday's motor was ingenious. It could not be used to do any practical work. This

is because its drive shaft was enclosed and it could only produce an internal orbital motion. It

could not transfer its mechanical energy to the outside for deriving an external load. However

it did show how the magnetic fields of a conductor and a magnet could be made to interact to

produce continuous motion. Faradays motor orbited its wire rotor must pass through the

magnets lines of force.

When a current is passes through the wire ,circular lines of force are produced around the

wire. Those flux lines go in a direction described by the left-hand rule. The lines of force of

the magnet go from the N pole to the S pole You can see that on one side of the wire, the

magnetic lines of force are going in the opposite direction as a result the wire, s flux lines

oppose the magnets flux line since flux lines takes the path of least resistance, more lines

concentrate on the other side of the wire conductor, the lines are bent and are very closely


39/94

39

spaced. The lines tend to straighten and be wider spaced. Because of this the denser, curved

field pushes the wire in the opposite direction.The direction in which the wire is moved is determined by the right hand rule. If the current

in the wire went in the opposite direction. The direction of its flux lines would reverse, and the wire

would be pushed the other way.

Rules for motor action

The left hand rule shows the direction of the flux lines around a wire that is carrying current.

When the thumb points in the direction of the magnetic lines of force. The right hand rule for

motors shows the direction that a current carrying wire will be moved in a magnetic field.

When the forefinger is pointed in the direction of the magnetic field lines, and the centre

finger is pointed in the direction of the current in the wire the thumb will point in the

direction that the wire will be moved.


40/94

40

TORQUE AND ROTATORY MOTION

In the basic action you just studied the wire only moves in a straight line and stops moving

once out of the field even though the current is still on. A practical motor must develop a

basic twisting force called torque loop. We can see how torque is produced. If the loop is

connected to a battery. Current flows in one direction one side of the loop, and in the opposite

direction on the other. Therefore the concentric direction on the two sides.

If we mount the loop in a fixed magnetic field and supply the current the flux lines

of the field and both sides of the loop will interact, causing the loop to act like a lever with a

force pushing on its two sides in opposite directions. The combined forces result in turning

force, or torque because the loop is arranged to piot on its axis. In a motor the loop that

moves in the field is called an armature or rotor. The overall turning force on the armaturedepends upon several factors including field strength armature current strength and the

physical construction of the armature especially the distance from the loop sides to the axis

lines. Because of the lever action the force on the sides are further from the axis; thus large

armature will produce greater torques.


41/94

41

In the practical motor the torque determines the energy available for doing useful work. The

greater the torque the greater the energy. If a motor does not develop enough torque to pull its

load it stalls.

Producing Continuous Rotation

The armature turns when torque is produced and torque is produced as long as the fields of

the magnet and armature interact. When the loop reaches a position perpendicular to the field,

the interaction of the magnetic field stops. This position is known as the neutral plane. In the

neutral plane, no torque is produced and the rotation of the armature should stop; however

inertia tends to keep a moving object in the motion even after the prime moving force is

removed and thus the armature tends to rotate past the neutral plane. But when the armature

continues o the sides of the loop start to swing back in to the flux lines, and apply a force to

push the sides of the loop back and a torque is developed in the opposite direction. Instead of

a continuous rotation an oscillating motion is produced until the armature stops in the neutral

plane.


42/94

42


43/94

43

To get continuous rotation we must keep the armature turning in the same direction as it

passes through the neutral plane .We could do this by reversing either the direction of the

current flow through the armature at the instant the armature goes through the neutral pole.

Current reversals of this type are normally the job of circuit switching devices. Since theswitch would have to be synchronized with the armature, it is more logical to build it into the

armature then in to the field. The practical switching device, which can change the direction

of current flow through an armature to maintain continuous rotation, is called a commutator.

THE COMMUTATOR

For the single-loop armature, the commutator is simple. It is a conducting ring that is split

into two segment with each segment connected to an end of the armature loop. Power for the

armature from an external power source such as a battery is brought to the commutator

segments by means of brushes. The arrangement is almost identical to that for the basic dc

generator.

The logic behind the operation of the commutator is easy to see in the figures. You

can see in figure A that current flows into the side of the armature closest to the South Pole of

the field and out of the side closest to the North Pole. The interaction of the two fields

produces a torque in the direction indicated, and the armature rotates in that direction.

No torque is produced but the armature continues to rotate past the neutral plane due toinertia. Notice that at the neutral position the commutator disconnects from the brushes sides

of the loop reverse positions. But the switching action of the commutator keeps the direction

of current flow through the armature the same as it was in the figure. A. Current still flows

into the armature side that is now closest to the South Pole.

Since the magnets field direction remains the same throughout the interaction of

fields after commutation keeps the torque going in the original direction; thus the same

direction of rotation is maintained.

As you can see in figure D, Inertia again carries the armature past neutral to theposition shown in the fig. A while communication keeps the current flowing in the direction

that continues to maintain rotation. In this way, the commutator keeps switching the current

through the loop, so that the field it produces always interacts with the pole field to develop a

continuous torque in the same direction.


44/94

44


45/94

45


46/94

46

THE ELEMANTARY D-C MOTOR

At this point, you have been introduced to the four principal parts that make up the

elementary D.C motor. These parts are the same as those you met in your study of the basic

D.C generator .a magnetic field, a movable conductor, a commutator and brushes. In practice,

the magnetic field can be supplied by a permanent magnet or by an electromagnet. For mostdiscussions covering various motor operating principles, we will assume that a permanent

magnet is used at other times when it is important for you to understand that the field of the

motor is develop electrically, we will show that an electromagnet is used. In either case, the

magnetic field itself consists of magnetic flux lines that form a closed magnetic circuit. The

flux lines leave the north pole of the magnet, extend across the air gap between the poles of

the magnet, enter the South Pole and then travel through the magnet itself back to the north

pole. The movable conductor, usually a loop, called armature, therefore is in the magnetic

field.

When D.C motor is supplied to the armature through the brushes and commutator,

magnetic flux is also build up around the armature. It is this armature flux that interacts with

the magnetic field in which the armature is suspended to develop the torque that makes the

motor operate.


47/94

47

GEAR

Gears, toothed wheels or cogs are positive type drives which are used to transmit motion

between two shafts or a shaft and a component having linear motion, by meshing of two or

more gears. They have advantage over other drives like chains, belts etc. in case of precision

machines where a definite velocity ratio is of importance and also in case where the driverand the follower are in close proximity; the downside is that gears are more expensive to

manufacture and their operating cost is also relatively high.

Spur gears found on a piece of farm equipment.

Gears of differing size are often used in pairs for a mechanical advantage, allowing the torque

of the driving gear to produce a larger torque in the driven gear at lower speed, or a smaller

torque at higher speed. The larger gear is known as a wheel and the smaller as a pinion. This

is the principle of the automobile transmission, allowing selection between various

mechanical advantages.The ratio of the rotational speeds of two meshed gears is called the Gear ratio.A gearbox

is not an amplifier or a servomechanism. Conservation of energy requires that the amount of

power delivered by the output gear or shaft will never exceed the power applied to the input

gear, regardless of the gear ratio. Work equals the product of force and distance, therefore the

small gear is required to run a longer distance and in the process is able to exert a larger

twisting force or torque, than would have been the case if the gears were the same size. There

is actually some loss of output power due to friction.


48/94

48

SPUR GEARS

The most common type of gear wheel, spur gears, are flat and have teeth projecting

radially and in the plane of the wheel. The teeth of these "straight-cut gears" are cut so that

the leading edges are parallel to the line of the axis of rotation. These gears can only mesh

correctly if they are fitted to parallel axles.

HELICAL GEARS

Helical gears offer a refinement over spur gears. The teeth are cut at an angle,

allowing for more gradual, hence smoother meshing between gear wheels, eliminating the

whine characteristic ofstraight-cut gears. A disadvantage of helical gears is a resultant thrust

along the axis of the gear, which needs to be accommodated by appropriate thrust bearings,

and a greater degree of sliding friction between the meshing teeth, often addressed with

specific additives in the lubricant. Whereas spur gears are used for low speed applications

and those situations where noise control is not a problem, the use of helical gears is indicatedwhen the application involves high speeds, large power transmission, or where noise

abatement is important. The speed is considered to be high when the pitch line velocity (ie.

circumferential velocity) exceeds 5000 ft/min or the rotational speed of the pinion (ie. smaller

gear) exceeds 3600 rpm.

Helical gears from a Meccano construction set.

DOUBLE HELICAL GEARS

Double helical gears, invented by Andr Citron and also known as herringbonegears, overcome the problem of axial thrust presented by Single helical gears by having teeth

that are 'V' shaped. Each gear in a double helical gear can be thought of as two standard, but


49/94

49

mirror image, helical gears stacked. This cancels out the thrust since each half of the gear

thrusts in the opposite direction. They can be directly interchanged with spur gears without

any need for different bearings.

BEVEL GEARS

Where two axles cross at point and engage by means of a pair of conical gears, the

gears themselves are referred to as bevel gears. These gears enable a change in the axes of

rotation of the respective shafts, commonly 90. A set of four bevel gears in a square make a

differential gear, which can transmit power to two axles spinning at different speeds, such as

those on a cornering automobile.

Helical gears can also be designed to allow a ninety degree rotation of the axis of

rotation.

BEVEL GEAR IN FLOODGATE

WORM GEAR

If the axles are skewed, that is, non-parallel, then a worm gearcan be used. This is a

gear that resembles a screw, with parallel helical teeth, and mates with a normal spur gear.

The worm is always the driving gear. The worm gear can achieve a higher gear ratio than

spur gears of a comparable size. Designed properly, a built in safety feature can be obtained:

This gear style will self-lock if power is lost to the drive (worm). It doesn't work if the pinion

is powered.


50/94

50

A Worm Gear and Pinion from a Meccano construction set

SUN GEAR

The central gear of a Planetary gear

SECTOR GEAR

A sector gearis merely a segment of a spur gear, such as one half or one quarter of

the circumference, but still attached to the axle in the normal fashion. Such a gear will

operate normally as long as the gear with which it meshes does not drive off the edge of the

sector, for instance in a worm and sector automotive steering gear or its descendant the

recirculating ball. It is useful for saving space and weight when only limited movement is

necessary rather than the full 360 degrees of rotation.

RACK AND PINION

Torque can be converted to linear force by a rack and pinion. The pinion is a spur

gear, and meshes with a toothed bar or rod that can be thought of as a sector gear with an

infinitely large radius of curvature. Such a mechanism is used in automobiles to convert the

rotation of the steering wheel into the left-to-right motion of the tie rod(s).


51/94

51

CROWN GEAR

A crown gearor contrate gearis a special form of bevel gear which has teeth at right

angles to the plane of the wheel; it meshes with a straight cut spur gear or pinion on a right-angled axis to its own, or with an escapement such as found in mechanical clocks.

Simple gears suffer from backlash, which is the error in motion that occurs when gears

change direction, resulting from hard to eliminate manufacturing errors. When moving

forwards, the front face of the drive gear tooth pushes on the rear face of the driven gear.

When the drive gear changes direction, its rear face is now pushing on the front face of the

driven gear. Unless deliberately designed to eliminate it, there is slight 'slop' in any gearing

where briefly neither face of the driving gear is pushing the driven gear. This means that

input motion briefly causes no output motion. Assorted schemes exist to minimize or avoid

problems this creates.

A crown gear

SHIFTING OF GEARS

In some machines it is necessary to change the gear ratio to suit the task. There are

several ways of doing this. For example:

Manual transmission automatic gearbox derailleur gears which are actually sprockets in combination with a roller chain hub gears (also called epicyclic gearing or sun-and-planet gears) continuously variable transmission transmission (mechanics)


52/94

52

Friction and wear between two gears is highly dependent on the profile of the teeth.

The tooth form used for most applications is involute but there are other tooth forms such as

cycloidal (used in mechanical clocks) or rack (used in automobile steering).

GEAR MATERIALS

Numerous nonferrous alloys, cast irons, powder-metallurgy and even plastics are used

in the manufacture of gears. However steels are most commonly used because of their high

strength to weight ratio and low cost.

Worm gear

Worm and worm gear

A worm gear, or worm wheel or worm drive, is a type of gear that consists of a cylinder

with a spiral groove mounted on a shaft. It is used to greatly reduce rotational speed, or to

allow higher torque to be transmitted. The image shows a section of a gear box with a bronze

worm gear being driven by a worm. A worm gear is an example of a screw, one of the six

simple machines.

Explanation

A gearbox designed using a worm and worm-wheel will be considerably smaller than one

made from plain spur gears and has its drive axes at 90 to each other. With a single start

worm, for each 360 turn of the worm, the worm-gear advances only one tooth of the gear.

Therefore, regardless of the worm's size (sensible engineering limits notwithstanding), the

gear ratio is the "size of the worm gear - to - 1". Given a single start worm, a 20 tooth worm

gear will reduce the speed by the ratio of 20:1. With spur gears, a gear of 12 teeth (the

smallest size permissible, if designed to good engineering practices) would have to bematched with a 240 tooth gear to achieve the same ratio of 20:1. Therefore, if the diametrical


53/94

53

pitch (DP) of each gear was the same, then, in terms of the physical size of the 240 tooth gear

to that of the 20 tooth gear, the worm arrangement is considerably smaller in volume.

A double bass features worm gears as tuning mechanisms

Direction of transmission

Unlike ordinary gear trains, the direction of transmission (input shaft vs output shaft) is not

reversible, due to the greater friction involved between the worm and worm-wheel, when a

single start (one spiral) worm is used. This can be an advantage when it is desired toeliminate any possibility of the output driving the input. If a multistart worm (multiple

spirals) then the ratio reduces accordingly and the braking effectof a worm and worm-gear

may need to be discounted as the gear may be able to drive the worm.

Worm drives where the gear can not drive the worm are said to be self-locking. Whether a

worm and gear will be self-locking depends on a function of the lead angle, the pressure

angle, and the coefficient of friction; however it is approximately correct to say that a worm

and gear will be self-locking if the tangent of the lead angle is less than the coefficient of

friction.

Applications

Worm gears are a compact, efficient means of substantially decreasing speed and increasing

torque. Small electric motors are generally high speed and low torque, the addition of a worm

and worm-wheel increases the range of applications that it may be suitable for, especially

when the worm gears compactness is considered.

In the era of sailing ships the introduction of a worm gear drive to control the rudder was a

significant advance. Prior to its introduction, a rope drum drive was used to control the rudder

and rough seas could cause substantial force to be applied to the rudder, often requiring

several men to steer the vessel, with some drives having two large diameter wheels to allow

up to four crewmen to operate the rudder.


54/94


55/94

55

Worm Gears

Introduction

A worm gear is used when a large speed reduction ratio is required between crossed axis

shafts which do not intersect. A basic helical gear can be used but the power which can be

transmitted is low. A worm drive consists of a large diameter worm wheel with a worm

screw meshing with teeth on the periphery of the worm wheel. The worm is similar to a

screw and the worm wheel is similar to a section of a nut. As the worm is rotated the worm

wheel is caused to rotate due to the screw like action of the worm. The size of the worm gear

set is generally based on the centre distance between the worm and the worm wheel.

If the worm gears are machined basically as crossed helical gears the result is a highly stress

point contact gear. However normally the worm wheel is cut with a concave as opposed to a

straight width. This is called a single envelope worm gear set. If the worm is machined

with a concave profile to effectively wrap around the worm wheel the gear set is called adouble enveloping worm gear set and has the highest power capacity for the size. Single

enveloping gear sets require accurate alignment of the worm-wheel to ensure full line tooth

contact. Double enveloping gear sets require accurate alignment of both the worm and the

worm wheel to obtain maximum face contact.

The worm is shown with the worm above the worm wheel. The gear set can also be arranged

with the worm below the worm wheel. Other alignments are used less frequently.


56/94

56

Nomenclature

As can be seen in the above view a section through the axis of the worm and the centre of the gear

shows that , at this plane, the meshing teeth and thread section is similar to a spur gear and has the

same features

n = Normal pressure angle = 20o

as standard

= Worm lead angle = (180 / ) tan-1 (z 1 / q)(deg) ..Note: for n= 20o should be less than 25o

b a = Effective face width of worm wheel. About 2.m (q +1) (mm)b l = Length of worm wheel. About 14.m. (mm)

c = clearance c min = 0,2.m cos , c max = 0,25.m cos (mm)d 1 = Ref dia of worm (Pitch dia of worm (m)) = q.m (mm)

d a.1 = Tip diameter of worm = d 1 + 2.h a.1 (mm)

d 2 = Ref dia of worm wheel (Pitch dia of worm wheel) =( p x.z/ ) = 2.a - d 1 (mm)d a.2 = Tip dia worm wheel (mm)

h a.1 = Worm Thread addendum = m (mm)

h f.1 = Worm Thread dedendum , min = m.(2,2 cos - 1 ) , max = m.(2,25 cos - 1 )(mm)m = Axial module = p x / (mm)m n = Normal module = m cos (mm)M 1 = Worm torque (Nm)

M 2 = Worm wheel torque (Nm)

n 1 = Rotational speed of worm (revs /min)

n 2 = Rotational speed of worm wheel (revs /min)

p x = Axial pitch of of worm threads and circular pitch of wheel teeth ..the pitch between adjacent

threads = . m. (mm)

p n = Normal pitch of of worm threads and gear teeth (m)q = diameter factor selected from (6 6,5 7 7,5 8 8,5 9 10 11 12 13 14 17 20 )

p z = Lead of worm = p x. z 1 (mm).. Distance the thread advances in one rev'n of the worm. For a 2-

start worm the lead = 2 . p x

R g = Reduction Ratio

q = Worm diameter factor = d 1 / m - (Allows module to be applied to worm )

= coefficient of friction= EfficiencyVs = Worm-gear sliding velocity ( m/s) z 1 = Number of threads (starts) on worm

z 2 = Number of teeth on worm wheel


57/94

57

Worm gear design parameters

Worm gears provide a normal single reduction range of 5:1 to 75-1. The pitch line velocity is ideally

up to 30 m/s. The efficiency of a worm gear ranges from 98% for the lowest ratios to 20% for the

highest ratios. As the frictional heat generation is generally high the worm box is designed disperse

heat to the surroundings and lubrication is and essential requirement. Worm gears are quiet in

operation. Worm gears at the higher ratios are inherently self locking - the worm can drive the gear

but the gear cannot drive the worm. A worm gear can provide a 50:1 speed reduction but not a 1:50

speed increase....(In practice a worm should not be used a braking device for safety linked systems e.g

hoists. . Some material and operating conditions can result in a wormgear backsliding )

The worm gear action is a sliding action which results in significant frictional losses. The ideal

combination of gear materials is for a case hardened alloy steel worm (ground finished) with a

phosphor bronze gear. Other combinations are used for gears with comparatively light loads.

Specifications

BS721 Pt2 1983 Specification for worm gearingMetric units.

This standard is current (2004) and provides information on tooth form, dimensions of gearing,

tolerances for four classes of gears according to function and accuracy, calculation of load capacity

and information to be given on drawings.


58/94

58

Worm teeth Profile

The sketch below shows the normal (not axial) worm tooth profile as indicated in BS 721-2 for unit

module (m = 1mm) other module teeth are in proportion e.g. 2mm module teeth are 2 times larger

Materials used for gears

Material Notes Applications

Worm

Acetal / Nylon Low Cost, low dutyToys, domestic appliances,

instruments

Cast IronExcellent machinability, medium

friction.

Used infrequently in modern

machinery

Carbon Steel Low cost, reasonable strengthPower gears with medium

rating.

Hardened Steel High strength, good durabilityPower gears with high rating

for extended life

Worm wheel

Acetal /Nylon Low Cost, low dutyToys, domestic appliances,

instruments


59/94

59

Phos BronzeReasonable strength, low friction

and good compatibility with steel

Normal material for worm

gears with reasonable

efficiency

Cast Iron

Excellent machinability, medium

friction.

Used infrequently in modern

machinery

Design of a Worm Gear

The following notes relate to the principles in BS 721-2

Method associated with AGMA are shown below..

Initial sizing of worm gear.. (Mechanical)

1) Initial information generally Torque required (Nm), Input speed(rpm), Output speed (rpm).

2) Select Materials for worm and worm wheel.

3) Calculate Ratio (R g)

4) Estimate a = Center distance (mm)

5) Set z 1 = Nearest number to (7 + 2,4 SQRT (a) ) /R g

6) Set z 2 = Next number < R g . z 17) Using the value of estimated centre distance (a) and No of gear teeth ( z 2 )obtain a value

for q from the table below

8) d 1 = q.m (select) ..

9) d 2 = 2.a - d 1

10) Select a worm wheel face width b a (minimum =2*m*SQRT(q+1))

11) Calculate the permissible output torques for strength (M b_1 and wear M c_1 )

12) Apply the relevent duty factors to the allowable torque and the actual torque

13) Compare the actual values to the permissible values and repeat process if necessary

14) Determine the friction coefficient and calculate the efficiency.

15) Calculate the Power out and the power in and the input torque

6) Complete design of gearbox including design of shafts, lubrication, and casing ensuring

sufficient heat transfer area to remove waste heat.


60/94

60

Initial sizing of worm gear.. (Thermal)

Worm gears are often limited not by the strength of the teeth but by the heat generated by the

low efficiency. It is necessary therefore to determine the heat generated by the gears = (Input

power - Output power). The worm gearbox must have lubricant to remove the heat from the

teeth in contact and sufficient area on the external surfaces to distibute the generated heat to

the local environment. This requires completing an approximate heat transfer calculation. If

the heat lost to the environment is insufficient then the gears should be adjusted (more starts,

larger gears) or the box geometry should be adjusted, or the worm shaft could include a fan to

induced forced air flow heat loss.

Formulae

The reduction ratio of a worm gear ( R g )

R g = z 2 / z 1


61/94

61

eg a 30 tooth wheel meshing with a 2 start worm has a reduction of 15

Tangential force on worm ( F wt )= axial force on worm wheel

F wt = F ga = 2.M 1 / d 1

Axial force on worm ( F wa ) = Tangential force on gear

F wa = F gt = F wt.[ (cos n - tan ) / (cos n . tan + ) ]

Output torque ( M 2 ) = Tangential force on worm wheel * Worm wheel reference diameter /2

M 2 = F gt* d 2 / 2

Relationship between the Worm Tangential Force F wt and the Gear Tangential force F gt

F wt = F gt.[ (cos n . tan + ) / (cos n - tan ) ]Relationship between the output torque M 2and the input torque M 1

M 2 = ( M 1. d 2 / d 1 ).[ (cos n - tan ) / (cos n . tan + ) ]

Separating Force on worm-gearwheel ( F s )F s = F wt.[ (sin n ) / (cos n . sin span> + .cos ) ]

Efficiency of Worm Gear ( ) =[(cos n - .tan ) / (cos n + .cot )]

Sliding velocity ( V s )...(m/s)

V s (m/s ) = 0,00005236. d 1. n 1 sec = 0,00005235.m.n (z 1

2+ q

2)

1/2

Peripheral velocity of worm wheel ( V p) (m/s)

V p = 0,00005236,d 2. n 2

Friction Coefficient

Cast Iron and Phosphor Bronze .. Table x 1,15

Cast Iron and Cast Iron.. Table x 1,33

Quenched Steel and Aluminum Alloy..Table x 1,33Steel and Steel..Table x 2

Friction coefficients - For Case Hardened Steel Worm / Phos Bros Wheel

Sliding

Speed

Friction

Coefficient

Sliding

Speed

Friction

Coefficient

m/s m/s


62/94

62

0 0,145 1,5 0,038

0,001 0,12 2 0,033

0,01 0,11 5 0,023

0,05 0,09 8 0,02

0,1 0,08 10 0,018

0,2 0,07 15 0,017

0,5 0,055 20 0,016

1 0,044 30 0,016

Worm Design /Gear Wear / Strength Equations to BS721

Note: For designing worm gears to AGMA codes AGMA method of Designing Worm Gears

The information below relates to BS721 Pt2 1983 Specification for worm gearing Metric

units. BS721 provides average design values reflecting the experience of specialist gear

manufacturers. The methods have been refined by addition of various application and duty factors as

used. Generally wear is the critical factor..

Permissible Load for Strength

The permissible torque (M in Nm) on the gear teeth is obtained by use of the equation

M b = 0,0018 X b.2bm.2. m. l f.2. d 2.

( example 87,1 Nm = 0,0018 x 0,48 x 63 x 20 x 80 )

X b.2 = speed factor for bending (Worm wheel ).. See Below

bm.2 = Bending stress factor for Worm wheel.. See Table belowl f.2 = length of root of Worm Wheel tooth

d 2 = Reference diameter of worm wheel

m = axial module

= Lead angle


63/94

63

Permissible Torque for Wear

The permissible torque (M in Nm) on the gear teeth is obtained by use of the equation

M c = 0,00191 X c.2cm.2.Z. d 21,8

. m

( example 33,42 Nm = 0,00191 x 0,3234 x 6,7 x 1,5157 x 801,8

x 2 )

X c.2 = Speed factor for wear ( Worm wheel )

cm.2 = Surface stress factor for Worm wheelZ = Zone factor.

Length of root of worm wheel tooth

Radius of the root = R r= (d 1 /2 + h ha,1 (= m) + c(= 0,25.m.cos )R r= d 1 /2 + m(1 +0,25 cos)

l f.2 = 2.R r.sin-1

(2.R r / b a)

Note: angle from sin-1

(function) is in radians...

Speed Factor for Bending

This is a metric conversion from an imperial formula..

X b.2 = speed factor for bending = 0,521(V)-0,2

V= Pitch circle velocity =0,00005236*d 2.n 2 (m/s)

The table below is derived from a graph in BS 721. I cannot see how this works as a small worm has a

smaller diameter compared to a large worm and a lower speed which is not reflected in using the

RPM.

Table of speed factors for bending

RPM (n2) X b.2 RPM (n2) X b.2

1 0,62 600 0,3

10 0,56 1000 0,27

20 0,52 2000 0,23

60 0,44 4000 0,18


64/94

64

100 0,42 6000 0,16

200 0,37 8000 0,14

400 0,33 10000 0,13

Additional factorsThe formula for the acceptable torque for wear should be modified to allow additional factors which

affect the Allowable torque M c

M c2 = M c. Z L. Z M.Z R / K C

The torque on the worm wheel as calculated using the duty requirements (M e) must be less than the

acceptable torque M c2 for a duty of 27000 hours with uniform loading. For loading other than this

then M e should be modified as follows

M e2 = M e. K S* K H

Thus

uniform load < 27000 hours (10 years) M e M c2Other conditions M e2 M c2

Factors used in equations Lubrication (Z L)..

Z L = 1 if correct oil with anti-scoring additive else a lower value should be selected

Lubricant (Z M)..

Z L = 1 for Oil bath lubrication at V s < 10 m /s

Z L = 0,815 Oil bath lubrication at 10 m/s < V s < 14 m /s

Z L = 1 Forced circulation lubrication

Surface roughness (Z R ) ..

Z R = 1 if Worm Surface Texture < 3 m and Worm wheel < 12 melse use less than 1

Tooth contact factor (K C

This relates to the quality and rigidity of gears . Use 1 for first estimate

K C = 1 For grade A gears with > 40% height and > 50% width contact

= 1,3 - 1,4 For grade A gears with > 30% height and > 35% width contact

= 1,5-1,7 For grade A gears with > 20% height and > 20% width contact

Starting factor (K S) ..

K S =1 for < 2 Starts per hour


65/94

65

=1,07 for 2- 5 Starts per hour

=1,13 for 5-10 Starts per hour

=1,18 more than 10 Starts per hour

Time / Duty factor (K H) ..

K H for 27000 hours life (10 years) with uniform driver and driven loads

For other conditions see table below

Tables for use with BS 721 equations

Speed Factors

X c.2 = K V .K R

Note: This table is not based on the graph in BS 721-2 (figure 7) it is based on another more easy to

follow graph. At low values of sliding velocity and RPM it agrees closely with BS 721. At higher

speed velocities is gives a lower value (e.g at 20m/s -600 RPM the value from this table for X c.2 is

about 80% of the value in BS 721-2

Table of Worm Gear Speed Factors

Note -sliding speed = Vs and Rotating speed = n2 (Worm wheel)

Sliding speed K V Rotating Speed K R

m/s Rpm

0 1 0,5 0,98

0,1 0,75 1 0,96

0,2 0,68 2 0,92

0,5 0,6 10 0,8

1 0,55 20 0,73

2 0,5 50 0,63

5 0,42 100 0,55

10 0,34 200 0,46

20 0,24 500 0,35

30 0,16 600 0,33


66/94

66

Stress Factors

Table of Worm Gear Stress Factors

Other

metal

(Worm)

P.B. C.I.0,4%

C.Steel

0,55%

C.Steel

C.Steel

Case.

H'd

Metal

(Worm wheel)

Bending

(bm ) Wear ( cm )

MPa MPa

Phosphor Bronze

Centrifugal cast69 8,3 8,3 9,0 15,2

Phosphor Bronze

Sand Cast Chilled63 6,2 6,2 6,9 12,4

Phosphor Bronze

Sand Cast49 4,6 4,6 5,3 10,3

Grey Cast Iron 40 6,2 4,1 4,1 4,1 5,2

0,4% Carbon steel 138 10,7 6,9

Zone Factor (Z)

If b a < 2,3 (q +1)1/2

Then Z = (Basic Zone factor ) . b a /2 (q +1)1/2

If b a > 2,3 (q +1)1/2 Then Z = (Basic Zone factor ) .1,15

Table of Basic Zone Factors

Q

z1 6 6,5 7 7,5 8 8,5 9 9,5 10 11 12 13 14 17 20

1 1,045 1,048 1,052 1,065 1,084 1,107 1,128 1,137 1,143 1,16 1,202 1,26 1,318 1,402 1,508


67/94

67

2 0,991 1,028 1,055 1,099 1,144 1,183 1,214 1,223 1,231 1,25 1,28 1,32 1,36 1,447 1,575

3 0,822 0,89 0,989 1,109 1,209 1,26 1,305 1,333 1,35 1,365 1,393 1,422 1,442 1,532 1,674

4 0,826 0,83 0,981 1,098 1,204 1,701 1,38 1,428 1,46 1,49 1,515 1,545 1,57 1,666 1,798

5 0,947 0,991 1,05 1,122 1,216 1,315 1,417 1,49 1,55 1,61 1,632* 1,652 1,675 1,765 1,886

6 1,131 1,145 1,172 1,22 1,287 1,35 1,438 1,521 1,588 1,625 1,694 1,714 1,733 1,818 1,928

7 1,316 1,34 1,37 1,405 1,452 1,54 1,614 1,704 1,725 1,74 1,76 1,846 1,98

8 1,437 1,462 1,5 1,557 1,623 1,715 1,738 1,753 1,778 1,868 1,96

9 1573 1,604 1,648 1,72 1,743 1,767 1,79 1,88 1,97

10 1,68 1,728 1,748 1,773 1,798 1,888 1,98

11 1,732 1,753 1,777 1,802 1,892 1,987

12 1,76 1,78 1,806 1,895 1,992

13 1,784 1,806 1,898 1,998

14 1,811 1,9 2

Duty Factor

Duty - time Factor K H

Impact from Prime mover

Expected

life

hours

K H

Impact From Load

Uniform

Load

Medium

Impact

Strong

impact

Uniform Load

Motor Turbine Hydraulic

motor

1500 0,8 0,9 1

5000 0,9 1 1,25

27000 1 1,25 1,5


68/94

68

60000 1,25 1,5 1,75

Light impact

multi-cylinder engine

Documents

Abstract2 Final