A Seminar Report On

“Independent Wheel Vehicle suspension”

By

Pathan Yunuskhan Sherkhan

Exam. No. B2210851

Under Guidance Of

Mr. N. D. Gaikwad

Department Of Mech. Engg.A. I. S. S. M. S. C. O. E.

Pune-1

2003-2004

Acknowledgement

All said and done. It’s Simple. Since the idea of this project we got help from many people in both direct and indirect manner and in numerous ways. Through this acknowledgement, I am trying to express my gratitude to all the people who were part of the successful completion of this report. People who gave an unending support right from the choice of the subject to the completion of the seminar.

In particular, I wish to thank Prof. N. D. Gaikwad our project guide for his valuable support and guidance which inspired me very much and due to which I was able to complete this seminar in the stipulated time period. I would also like to thank Prof. Phadkule our H.O.D who always inspired and build in my confidence.

Special thanks and heartfelt appreciation to all my friends and colleagues who always remained a constant source of help, information and inspiration.

Seminar Approval Sheet

This is to certify that the seminar entitled“INDEPENDENT WHEEL VEHICLE SUSPENSION”

Submitted by,

Pathan Yunuskhan Sherkhan

Exam. No. – B2210851

Of A. I. S. S. M. S. C. O. E. Pune-1.

The partial fulfillment for the award of degree of B. E. (Mechanical Engg.) is approved..

Mr. N. D. Gaikwad Mr. V. N. Phadkule

(Seminar Guide) (Head Of Department)

Mechanical Engg. Dept.

A.I.S.S.M.S’s.

C.O.E. Pune 1

(Examiner)

CONTENTS

1. Introduction.

2. Degree of freedom of wheel suspension .

3. Elements of wheel suspension .

4. Independent suspension layouts .

5. Independent front wheel suspension .

6. Independent rear wheel suspension .

7. Conclusion .

8. References .

Independent Wheel Vehicle Suspension

Introduction:-

The suspension system connecting a vehicle body to wheels and its tyre allows the wheel

to move in an essentially vertical direction in response to good surface irregularities, a spring

element temporarily stores and releases energy thus insulating the vehicle body form

acceleration peaks. A shock absorber ‘damper’ insures that oscillation induced by road

unevenness or aerodynamic forces (or by accelerating breaking) which would impair ride

comfort and road holding die away quickly.

Conventional system provides greater simplicity. They contain systems like rigid axle

suspension. They are most widely used in heavy carriers. Suspension is directly using leaf

spring hence they have less complexity. In this system both wheels of the vehicle are

suspended in combination as directly axle is suspended. Simplicity is the only advantage,

they do not provide effective suspension.

With development of technology a new concept called independent wheel suspension has

emerged. In this system both the wheels are suspended independently as every wheel has it’s

independent suspension system. This provides suspension for actual road conditions. This

system is very complex but have advantages like low weight, plenty of scope for achieving

favorable elasto-kinematics effects, no coupling of masses, no suspension parts that run right

across the vehicle. Hence now a days in most of the passenger cars this system is used and

preferred over conventional system, providing the real smooth drive.

Degrees Of Freedom Of Wheel Suspension

A fast road vehicle should have a mainly vertically directed motion at each, wheel, one

‘degree of freedom’, in order to respond to road surface irregularities. A degree of freedom is

the displacement of a spatial components or body following a defined and reproducible

function Fig. 1 shows that this degree of freedom not only can be realized by an exactly

vertical travel alone (a) but also can consist of combination over vertical and lateral

displacement and a rotation (camber change, b), where all the parameters o movements are at

any moments strictly interdependent (so called ‘constrained motion’).

If two wheels are mounted together on one wheel carrier, as on a rigid beam axle (d), this

carrier needs two degrees of freedom to give each wheel one degree of freedom, permitting

the axle both parallel travel and rolling motion in relation to the vehicle body. A rigid axle

suspension is therefore a mechanism with two degrees of freedom.

If all wheels are always to be able to contract the road surface, not more than three of

them may be fixed to one carrier, while not more than two wheel planes are not more two

wheel axes may be aligned.

Elements Of Wheel Suspension

1. The Wheel Carrier

Every wheel is attached to the suspension by a wheel bearing normally of the rolling

element (ball or roller) type. The part of the suspension on which this bearing is mounted is

called the wheel carrier. In the independent suspension of Fig. 1(b), of the swing- axle type,

the swing axle itself represents the wheel carrier, which is immediately connected to the

vehicle body by a single joint.

The suspension of Fig.1(c) is, on the other hand, a kinematic mechanism—a four—

joint system, consisting of the wheel carrier as its ‘coupler’ and two links which guide the

wheel carrier in non-linear motion. The rigid axle of Fig.1(d) is simply a wheel carrier with

two wheels.

2. Joint of Wheel Suspension

The smallest construction element of a mechanism is a joint. Joints serve either for a

immediate connection of the coupler of the mechanism (here the wheel carrier) to the ‘fixed

part’ of the mechanism (here the vehicle body) or to the connect the two indirectly by means

of links.

In space, there are six degrees of freedom, namely three translations and three

rotationals. One joint may provide six degrees of freedom.

The ball joint Fig.2 (a) allow the free relative motion of both joint halves (the ball and

the socket) about three independent axes of rotation and thus offer three (rotational) degrees

of freedom. In that case a rubber joint as shown in Fig.2 (b) can be employed with the

advantages of good resistance against transient overload, freedom from maintenance, better

noise isolation and low cost.

The true turning joint, Fig.2 (c) caters for pure rotation (f=1), while the turning—and—

sliding joint, Fig.2 (d) allows both rotation about an axis and independent translation along

the same axes (f=2). Fig.3 (left), while the most common application of the turning—and—

sliding joint is the piston in the telescopic damper of a suspension strut (Fig.3 right).

3. Suspension Links

These links provide the indirect connection of a wheel carrier to the vehicle body, the

most important types being illustrated in Fig.4. The simple example rod link Fig.4 (a), with a

ball joint at each end (or with equivalent rubber joints as in Fig.2 (b))

The combination of a turning joint and a ball joint leads to the triangular link or ‘A-

arm’ Fig.4 (b).

Two turning joints, possible with skew axes, form a trapezoidal link Fig.4 (c). Each

joint has on degree of freedom, so the trapezoidal link reduce the degree of freedom of

mechanism by four.

4. The Kinematic Chain

Except for the case where a wheel suspension system is based on an immediate

connection of the wheel carrier and the vehicle body by a joint suspension forms a kinematic

chain, consisting of one or several wheel carriers, links and on “fixed part” Fig. 5 shows

schematically such a kinematic chain, where the most important types of joints links are

utilized.

The only wheel carrier K is the coupler of the spatial suspension mechanism, and the

vehicle body S is the fixed part.

F=6(k+1)r (6fi) or

F=6(k+lg)r+fi

Where,

k=number of wheel carriers, l=number of links

g=number of joints, r=number of individual rotations of links

fi=degree of freedom of joint i.

The suspension show the valued k=1, l=3, g=6. Four ball joints, the turning joint and the

sliding joint bring in

fi=43+1+2=15.

The rod link and turning/sliding links can rotate individually (r=2). Thus the degree of

freedom of the suspension becomes;

F=6(1+36) 2+(43+1+2)=1,

as necessary for independent wheel suspension.

Independent Suspension Layouts

The simple way to give a wheel carrier one degree of freedom with respect to the

vehicle body is to connect the two by joint. However, the only joint with one degree of

freedom is the tuning joint, trailing arm suspension Fig. 6(a), semi-trailing arm suspension (b)

or swing axle suspension (c).

A tuning and sliding joints provide two degrees of freedom and is therefore not on its

own sufficient to form an independent suspension. The surplus degree of freedom can be

cancelled by a rod link, Fig.7 and the layout hence becomes an example of rare but still

encountered vertical telescopic suspension for front wheels.

If the wheel carrier and the vehicle body are immediately connected by a ball joint which

introduces three degree of freedom, the suspension needs two additional rod links to reduce

the overall degree of freedom to F=1 Fig.8. The “double-wishbone” version Fig.8(a), has

quit often been employed, while there has been only one instance of the semi-trailing link

version Fig.8(b).

The suspension layout shown in Fig.8 clearly represents a transition stage from a direct

to an indirect connection of wheel carrier and vehicle body. As all points of the wheel carrier

travel on surface of spheres centered on the ball joints at the vehicle body these suspension

can be described as “spherical” mechanisms.

The simplest chain mechanism results from the combination of a trapezoidal link and a

rod link, Fig.8. The axis of the two turning joints of the trapezoidal link need not be parallel

nor lie in a common plane.

A triangular link can be regarded as a combination of two rods, as already mentioned. By

building up two triangular links from four rods, the suspension changes into the well known

“wishbone” types with its numerous variations.

Independent Wheel Suspension

Fig. 9 shows schematically an independent wheel suspension system. Component 1 is

the wheel with tyre, 2 is the wheel carrier which accommodates the wheel bearing and

determines the attitude of the wheel in relation to the vehicle body. The wheel carrier also

usually incorporates the static part of the braking system—e.g. the brake caliper and

sometimes a reduction gear.

The wheel carrier 2 is the coupler of the three dimensional wheel suspension linkage.

Component 3 is a “wishbone link” or “arm” and component 4 is a transverse link. Both

connected to the vehicle body and to wheel barrier by flexible joints. A tension link 5

triangulates the transverse link 4 to the vehicle body by a joint that is very compliant for good

noise isolation. Another link of the suspension is the track rod 6, the inboard end of which is

moved by a steering gearbox 7. A spring 8 and a damper 9 complete the system. The source

of driving torque (e.g. the final –drive unit), not shown in the sketch is assumed to be

mounted on the vehicle body and a drive shaft 10 with universal joints transmits the torque to

the wheel.

Independent Front Wheel Suspension

DOUBLE WISHBONE SUSPENSION OF MERCEDES BENZ

Fig.10 shows a (planer) of double wishbone. It can be seen above the crankpin and beside

its lower end. The wishbone are not directly connected to the vehicle body but through a sub

frame attached to the body by rubber mountings, for better noise insulation and ride comfort.

Due to their simple and space saving design and the wide separation of the joint position on

the vehicle body (and consequently, the low reaction forces), strut and damper, strut suspension

are widely used today for front wheels, they hold their ground on all classes of passenger cars

and even light trucks. Handicap of strut suspensions – namely the transverse forces acting on

the piston and the piston rod causing increase friction and wear- has been overcome by the

invention of a spring layout that compensates for those transverse forces, at least in the case of

vertical wheel loads, and by measures for minimizing friction, strut suspension therefore are no

longer inferior to other types in respect of the response properties of the springing.

Strut suspension are mechanism where a triangular links has been replaced by a turning –and

sliding link, i.e. the piston road of the damper the latter has therefore become a suspension link

and so carried being moments under the external loading. Already the offset of the wheel load

force vector from that exerts a bending moments on the piston rod.

If the suspension links and the track-rod lie approximately in a common plane, which is true

form may of the strut system, the spatial attitude of the force FK at the strut mounting, resulting

form the wheel- load force Fz can easily be imated, Fig.11(a) the line of action of FK must run

through the intersection point of the wheel-load force Fz in the plane under consideration.

The force Fk has a transverse component FQ that causes reaction force F1and F2 at the

piston rod guidance and at the piston itself. Fig.11(b).These forces result in friction and wear

and also impair the response of the spring.

On steerable strut suspensions, the upper and lower spring abutments are usually fixed to

the piston rod and the damper tube respectively, and the spring swivels together with the strut

under steering action. Total compensation of the transverse force at the piston rod then

requires that the venture line of the spring coincides with the line of action of the force Fk

Fig.11(c). This leads to a considerable inclination of the spring axis, and to lateral deflection

of its end with wheel bump and rebound. A helpful comprise is shown in Fig.11(d); the

spring axis is inclined by a significantly smaller angle and is displaced relative to the strut

mounting in order to intersect with the external force Fk in the working plane of the piston rod

guidance. This allows equilibrium to be established between the force Fk, spring force F and

the (considerable reduced) guidance force F1. The piston force F2 is zero, so the portion of

the rod that has plunged into the damper is free of bending moment and the piston rod slides

in its guidance without elastic jamming.

DAMPER STRUT FRONT SUSPENSION

In a damper- strut suspension, the spring usually acts on the transverse link and loads

the wheel carrier via its supporting ball-joint in Fig.12. The supporting ball-joint should be as

near to the wheel center plane as possible to minimize the moment generated by the wheel

load, and hence the transverse force at the piston rod. This optimum positioning follows

almost automatically if the scrub radius is desired to be very small or even negative the “King

pin axis” is the line between the supporting ball-joint and the struts upper mounting.

The anti-roll bar is connected to the transverse arm of the suspension links via short

shackles and serves only for springing purposes.

Independent Rear Wheel Suspension

FIVE LINK SUSPENSION

(DAIMLER BENZ)

Two lower and two upper transverse links, mutually inclined in plan view, carry the

longitudinal and lateral forces and a “track link” Sp at roughly axle height determines the

steering or toe-in angles it may have been positioned deliberately in the neutral axis of the

elastic chamber.

If Sp is the envisaged as the “track-rod” of a steerable suspension, the four transverse

link would generate a “virtual” king pin axis (i) during a steering event. In plan view, the

lower links intersect outside their outer joints, while the upper ones cross each other inboard

of their outer joints. The virtual king pin (i) runs approximately through these intersections or

crossing points – see the upper drawing in Fig.13. So a deliberate choice of the “king pin

inclination angle” is possible –so important for the proper attunement of the elastic steering

angles under traction and braking forces. This design demonstrates one again the did variety

of kinematics harmonization possible with multi-link suspensions.

The five—link principle allows the elasto-kinematic attunement to be optimized for all

important cases of external loading. However, as the braking torque is reacted by links in two

planes on above the other, there is a limit to the suspension’s longitudinal compliance in

terms of the wind—up effect. On the other hand, an elastically mounted sub frame is usually

provided for better noise insulation and easier assembly so its rubber mountings take over a

significant share of the longitudinal compliance.

SPATIAL MECHANISM REAR SUSPENSION

(FORD ‘FOCUS’ REAR SUSPENSION)

With three transverse links and one longitudinal arm, the suspension in Fig.14 looks

similar to the spherical double wishbone layout, but actually belongs in the spatial category.

Suitable positioning of the joints of the transverse links and the latter’s angular inclination

in the plant view enables the achievement of the desired kinematic properties and elasto

kinematic effects under braking, traction and cornering forces.

Because the three transverse links cancel three degrees of freedom, the longitudinal arm

has unlike the rigid one in to be replaced by flexible vertical leaf or ‘Sword’ which

corresponds to a triangular link.

In side view the wheel carrier swivels approximately about the front joint of the

longitudinal arm. For this reason, the vertical displacement of the front lower transverse

links outer joint with wheel travel is smaller than that of the corresponding joint in the rear

link. To avoid toe – out with wheel travel, the transverse components of the circular paths of

both joints must be equal. This requires a front transverse link considerably shorter than the

rear one.

Although the suspension as already mentioned, is not a spherical but a spatial

mechanism. It’s kinematic properties in side view are similar to those of suspension.

CONCLUSION

This system is very complex but have advantages like,

Low weight.

Plenty of scope for achieving favourable elasto-kinematics effects.

No coupling of masses.

No suspension parts that run right across the vehicle.

Hence now a days in most of the passenger cars, this system is used and preferred over

conventional system, providing the real smooth drive.

References

“Road Vehicle Suspensions”

Wolfgang Matschinsky

“Race Car Vehicle Dynamics”

William F. Milliken

Douglas L. Milliken

“Theory Of Machines”

R. S. Khurmi

J. K. Gupta

Website:-

www.howstuffworks.com