Steering System2

7/29/2019 Steering System2

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TEERING SYSTEM

It is the system which provides direction

hange in the performance of an automobile. This system

onverts rotary movement of the steering wheel into

ngular move men t o f the f ron t whe e l s . I t

m u l t i p l i e s d r i v e r s e f f o r t b y m e c h a n i c a l

d v an t ag e , enabling him to turn the wheels easily.

teering system requirements and functions:For proper and smooth operation and

erformance of the system, the steering system of anyvehicl

hould fulfill the following requirements:1.It should

multiply the turning effort applied on the steering

wheel by the driver .2 . I t s ho ul d b e to a ce r t ai n

x t e n t i r r e v e r s i b l e . I n o t h e r w o r d s , t h e sh o c k sf t h e ro a d surface encountered by the wheels should not

ransmitted to the drivers hands.3.The mechanism shoul

ave self rightening effect i.e., when the driver

eleases thesteering wheel after negotiating the turn

he wheel should try to achieve straightahead

osition.Functions of the steering system are as follows:a)It

elps in swinging the wheels to the left or right. b)It

elps in turning the vehicle at the will of the driver.c ) I tr o v i d e s d i r e c t i o n a l s t a b i l i t y . d)It helps in controlling


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wear and tear of ty res.e ) I t he lp s in ac h i ev in g th e se l f -

i g h t e n i n g e f f e c t . f)I t converts the rotary movement of th

teering wheel into an angular turn of the front wheels.g)It

m u l t i p l i e s t h e e f f o r t o f t h e d r i v e r b y l e v e r a g e i nr d e r t o m a k e i t f a i r l y easy to turn the wheels.h ) I t a b s o r b

m a j o r p a r t o f t h e r o a d s h o c k s t h e r e b y p r e v e n t i n g

h e m t o g e t transmitted to the hands of the driver.The complete

eering system which performs the above functions, can be divided i

wo portions, namely, steering gear provided at the end of the steerin

olumn and the linkage between the steering gear and the wheels.Typf steering system:Steering system is of the following types(a) Fifth

wheel steering system,(b) Side pivot steering system.fth wheel steering system

t is single pivot steering system inwhich the front axle along with

hewheels, moves to right or left . The m o v e m e n t t o t h e

w h o l e a x l e a n d w h e e l a s s e m b l y i s a f f e c t e d b

m e a n s o f a s t e e r i n g a n d a w h e e l w h i c h i s p l a c ee t w e e n c h a s s i s f r a m e a n d a x l e . T h e f i f t h w h e e

c t s a s a t u r n t a b l e . T h e a x l e

s s e m b l y i s c o n n e c t e d w i t h t h e f r a m e b y

m e a n s o f a p i n w h i c h serves as a pivot around

which the a x l e a s s e m b l y m o v e s . T h e f i f t h

w h e e l c o n t a i n s a r i n ge a r mounted at its rim and is moved by


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m e a n s o f a s t e e r i n g . M o v e m e n t o f t h e s t e e r i n g w h e

e n d s t h e f r o n t a x l e a n d w h e e l assembly to move away.

ide pivot steering mechanism

There are two types of steering gear mechanisms:1. Davis steering g

mechanism2. Ackermann steering gear mechanismThe main

ifference between the two steering gear mechanisms is th

he Davis steeringhas sliding pairs, whereas the Ackermann steeri

as only turning pairs. The sliding pair has more friction than the

urning pair; therefore the Davis steering gear will wear

ute a r l i e r a n d b e c o m e i n a c c u r a t e a f t e r c e r t a i n t i m e

h e A c k e r m a n n s t e e r i n g g e a r i s n o t m a t h e m a t i c a l l y

c c u r a t e e x c e p t i n t h r e e p o s i t i o n s , c o n t r a r y t o t h ea v i s s t e e r i n g g e a r which is mathematically correct in all

ositions. However, the Ackermann steering gear is preferred to the

avis steering gear.avis Steering Gear


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The Davis gear mechanism consists of a cross link KL sliding parall

o another link ABand is connected to the stub axles of the tw

ront wheels by means of two similar bellcrank levers ACK

nd DBK pivoted at A and B respectively. The cross link Klides inslides in the bearing and carries pins at its end K

nd L. The sl ide blocks are pivoted onthese pins and move wi

he turning of bell crank levers as the steering wheel is When thevehi

running straight, the gear said to in its mid-position. The short arm

AK and BLare inclined an angle 90+ to thei r s tub axles AC

nd BD. The correct steering dependsupon a suitab1e selectionross-arm angle , and is given bytan = b / 2lWhere b=AB=distanc

etween the pivots of front axles.l=wheel base.The range of b / l is 0

o 0.5 hence angle lies between 11.3 and 14.1

ckermann Steering Gear

he Ackermann steering gear mechanism consists of a cross link KL

onnected to the shortaxles AC and BD of the two front wheels throuhe short arms AK and BL, forming bellcrank levers CAK and D

espectively. When the vehicle is running straight, the

rosslink KL is parallel to AB, the short arm AK and BL

oth make angle to the horizontalaxis of chassis. In orde

o satisfy the fundamental equation for correct steering, th

nksAK and KL are suitably proportioned and angle is suitablyelected.For correct steeringcot cot = b / l2


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he angles and are shown in the Figure. The value of b

is between 0.4 and 0.5,generally 0.455. the value of cot cot

orresponds to the positions when the steering iscorrect. In fact

here are three values of angle which give correct steerinf the vehicle:first while it is turning to right, second while it is

urning to left and third while it is runningstraight.undamental condition for true rolling and correct steering angle

he perfect steering is achieved when all the four wheel

re rolling perfectly under allconditions of running. While

aking turns, the condition ofperfect rolling is satisfied if theaxes ohe front wheels when produced meet the rear wheel axis ane point. Then this point is the instantaneous centre of the vehic

is seen that the inside wheel is required toturn though a greater ang

han the outer wheel. The larger the steering angle, the smaller is the

urning circle. There is, however, a maximum to which we

an go as regards thes t ee r i ng an g l e . I t ha s be en fo un d

h a t s t e e r i n g a n g l e ( o f t h e i n n e r w h e e l ) c a n h a v em a x i m u m v a l u e o f a b o u t 4 4

T h e e x t r e m e p o s i t i o n s o n e i t h e r s i d e a r e c a l l e d

l o c k positions. The diameter of the smallest circle whic

he outer front wheel of the car can3


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r a v e r s e a n d o b t a i n e d w h e n t h e w h e e l s a r c a t t h e i r

x t r e m e p o s i t i o n s i s k n o w n a s t h e turning circle.Referring


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ig, for correct steering,Equation represents the basic condition for th

eering mechanism for perfect rolling of allwheels.omponents of Steering system:Steering wheel

teering is effected by the steering wheel. The steering wheels ofommercial vehicles havea metal armature comprised of a screw

machined hub with metal spokes and rim. The hub,spokes and rim ar

ll fabricated into one piece by welding. The armature serves as the

oad bearing structure of the wheel. The armature is surrounded by a

moulded rubber or plasticmaterial. Rubber wheels are painted, and

lastic wheels utilize impregnated colours.The steering wheel is of laiameter. This helps to convert the available driver rim pullinto

maximum input torque. However, the size of the wheel is limited by

ollowing: (1)The comfort of the driver when using the

teering wheel. (2) The space available for thesteering in the

nterior of the cabin. (3) The ease of performing maneuvers requiring

morethan an eighth of a turn of the steering wheel.T h e d i a m e t e r

h e s t e e r i n g w h e e l l i e s b e t w e e n 4 2 a n d 4 5 c m t h ea s e o f m o t o r c a r s , whereas it is 50 to 55 cm in the case of

ommercial vehicles.The rim of the steering wheel is elliptica

n cross section with the finger indentations onthe

ndersurface. The section of the rim is so designed and

imensioned to provide thedriver a good grip both with and

without heavy gloves.T h e l o w e r p o r t i o n o f t h e s t e e r i n gw h e e l h u b f i t s i n t o t h e u p p e r f l a n g e o f t h e

t e e r i n g column. Within the steering column, the steering

haft exis ts and is free to rotate . On theinside diameter of the

eering wheel hub, female serrations are provided. On the upper end


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h e s t e e r i n g s h a f t m a t c h i n g m a l e s e r r a t i o n s a n d a

o c k i n g t a p e r a r e p r o v i d e d . T h e 4


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eering wheel is mated to the upper end of the steering shaft by mean

f the locking taper a n d t h e s e r r a t i o n s . T h e s t e e r i n g w h e

s h e l d o n t h e s t ee r i n g co l u m n an d f i x e d t o t h e steeri

haft by a nut. The nut mates with the male threads on the upper end

he steeringshaft.Modern steering wheels have spring spokes. These

pokes are generally so arranged to givean unrestricted view of thenstrument panel.Some cars have a telescoping steering whee

his wheel can be moved out of or into theveering column to

uit the drivers convenience.In some designs, the hub of the steering


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wheel also houses part of the turn signal, horn, andvehicle hazard

asher mechanism.teering column:

teering column positions the steering wheel in the drivers cabin inelation to the driversseat and pedal controls. The steering column is

made either as fixed or adjustable.In the fixed type, the location of th

eering wheel cannot be changed. The steering wheel position is

hen decided taking into account the range of seat position

nd driver size. Ont h e o t h e r h a n d , i f t h e s t e e r i n g

o l u m n i s m a d e a d j u s t a b l e , t h e n t h e s t e e r i n gw h e e l movement can take care of the optimum wheel to driver

elationship in all seat positions.The fixed steering column is attached

he cabin by brackets on the instrument panel andfirewall. In some

ases, a bracket on the toe board is used for structural integrity. The

xedsteering column is usually tubular in construction. It has a stamp

ange welded

on to theupper end.A bearing in the upper part

he steering column serves for centering the steeringhaft.The type of bearing, bush or ball bearing or roller bearing

rovided for the shaft affects thesteering effort. Usually no bearing is

laced in the lower end of the steering column, if thesteering shaft

as adequate support at the steering gear. However, when t

ower end of the steering shaft is terminated by a double

ardan or constant velocity joint, a bearing is provided at tower end of the steering column. This bearing becomes

ssential for the proper functioning of the joint.T h e a d j u s t a b

t e e r i n g c o l u m n c a n b e s u b d i v i d e d i n t o

d j u s t m e n t b y r o t a t i o n a n d adjustment by sliding. The


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ormer type is called tilt steering wheel column assembly whilethe la

ype is called collapsible steering column assembly.ilt steering wheel column assembly

n this unit, the steering wheel is pivoted about a p o i n t i n t h et e e r i n g c o l u m n . T h e w h e e l c a n now be moved in a circula

rc, forward and upor rearward and down. The tilting wheel permitst

river to change the steering wheel angle tot h e

o r i z o n t a l t o s u i t h i s b u i l d . H e c a n a l s o change

he posi tion of the steering wheel to thehorizontal during a lon

rive to suit his driving posture.The tilting and telescoping steeringolumn can be seen in figure.Al l the above devices, wherein th

osition of the steering wheel can be altered with respect tothe driv

ave locking mechanisms, which lock the steering wheel into the

osition selected.5


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y p e i s c l a i m e d t o g i v e a m o r e u n i f o r m collapse rate tha

he Japanese lantern type.teering shaft

he steering shaft assembly performs two important functions:1. Itansmits the drivers turning effort or torque from the

teering wheel to the steeringgear.2. I t absorbs the angular

nd/or length changes in the relationship between the

teeringw h e e l ( c h a s s i s m o u n t e d ) a n d s t e e r i n g g e a r

c a b m ou nt e d ) f o r t h e f o l lo w i ng o pe r a t i n g conditions:

o chassis movement during driving, length change for adjustableolumnsand cab on tilt cab models.On the non-adjustable colum

nstallations, the axial length displacement of the

teerings h a f t i s u s u a l l y a c h i e v e d t h r o u g h t h e u s e o f

i sp la c em en t ch ar ac te r i s t i c s o f a f l ex ib le coupling, pot

oint or splined section in the shaft with cardan or constant velocity

oint.

teering gearh e h e a r t o f t h e s t e e r i n g s y s t e m i s t h e s t e e r i n g g e a

h i s u n i t i s a l s o c a l l e d s t e e r i n g mechanism. This unit is

rdinarily fixed to the bottom of the steering column. This unit isloca

etween the steering shaft and the steerable stub axles which carry th

oad wheels.The input shaf t of the steering gear is operated b

he s teer ing shaft . The steering gear performs two functions:1 converts the rotary motion of the steering wheel into lin

motion of the steeringlinkage which moves the front wheels.2. It

ntroduces a leverage between the steering wheel and the

tub axles. This leveragere du ce s th e e f fo r t th a t ha s to


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p p l i e d b y t h e d r i v e r t o t h e s t e e r i n g w h e e l i n o r d e r

o overcome the frictional forces opposing the turning of the stub axl

nd the road wheels.In order to have the above leverage, the

teering wheel has to be turned through larger angles than thub axles. In the case of automotive vehicles, normally the road whe

redeflectable to about 500 on each side of the straight ahe

osition. The extreme wheel positions are called full lock positio

f the wheels. To effect this extent of turning of theroad wheels, the

eering wheel may have to be turned through from 4 to 9 or 10 times

hatangle. This rela tionship is called steer ing ratio. The terteering ratio is the ratio of the6

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