Suspension (Repaired)

7/31/2019 Suspension (Repaired)

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2009

PRADEEP KUMAR MUNGAMURUGU

MSc Automotive Engineering 2009

3/20/2009

Vehicle Dynamics: Suspension system




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ABSTRACT

In order to provide the ideal driving conditions, responsive handling, passenger comfort and

stable vehicle dynamics are required in today‟s modern roads networks. The geometry of the

suspensions system does this by providing automatic compensation that minimizes deviations

caused by external forces.

This journal analyses the role of different types of suspension systems and looks at its

advantages and disadvantages. This is conducted by explaining the function and modeling

techniques of current suspension systems using the „quarter model‟. An explanation of the

methods to measure the suspension parameters such as roll center, camber, caster, instant center,

steering axis, etc is also included in this study. With the aid of a laboratory rig test consisting of

kinematic and compliance rigs, an experiment has been developed specifically for measuring

suspension parameters by applying loads to an existing vehicle suspension system.

This journal also describes the relation between the performances of the suspension system, the

tire and the full vehicle dynamics




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CONTENTS

1. Introduction

1.1 Role of suspension system

2. Types of suspension systems

3. Suspension calculations

4. Laboratory tests for suspension systems

5. Relationship between the suspension systems and vehicle dynamics.

6. Summary

7. Conclusion




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1. INTRODUCTION

1.1 ROLE OF SUSPENSION SYSTEM

The role of vehicle suspension system is to maximize the friction between the tires and the road

surface, to provide steering stability with good handling and to ensure the comfort of the

passenger. Designing of suspension and mounting the suspension points on frame are critical to

proper vehicle handling. For that it is very important to know the two designing factors Anti-

squat and Anti-dive. [6]

Anti-squat refers to the reaction of the body of a vehicle during acceleration. Anti-squat refers to

the degrees to which this normal force is neutralized.

Anti-dive, The force that causes the front of the vehicle to drop down while break.

So, it is important to design with accuracy to get proper vehicle handling.

The suspension system addresses mainly six basic needs for the vehicles having more than four

wheels [1]

Reduction of vertical wheel load variation.

Isolation of road inputs from the body.

Control of transmission of handling loads to body.

Control of wheel plane geometry due to compliance effect.

Control of wheel plane geometry due to Kinematics effect.

Comprehension of component load environment.

The above mentioned needs are very crucial and important for setting, investigating and verify

the design targets. And the Suspension design activities are listed as follows.

Wheel load

variation

Body

isolation

Handling

load

control

Compliance

wheel plane

control

Kinematic

wheel

planecontrol

Component

Loading

environment

Investigate Set targets Verify For Quantifying matter in these above 18 ways any stringent design process must required.




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2. TYPES OF SUSPENSION SYSTEMS

Basically they are two types of suspension systems, Dependent suspension and independent

suspension system.

2.1 DEPENDENT SUSPENSION [2]

Suspension with a solid connection between the left and

right wheels is called Dependent suspension. That

connection is nothing but the solid axle as shown in the

figure 1. Different types of linkage attaches to the solid

axes give the different types of Dependent suspension

system. Most commonly used suspensions with straight

line motion are watts suspension with pan hard arm,

Robert suspension, De Dion Suspension and solid axle

Fig 2.1 Solid axle with Hotchkiss[2] suspension with coil springs. And the graphical

representation of these suspensions is as shown in the figure 2.2

a)

Watt suspension b) Robert suspension

c) Solid axle suspension with coil spring d) De Dion suspension

Fig 2.2[2]




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2.1.1 ADVANTAGES OF DEPENDENT SUSPENSION [3]

1. Solid axle suspension is the best suspension in the off road usage. Because of the heavy

uneven surfaces in the road vehicle bounce very high. Using the solid axle suspension we

can eliminate the tucking as shown in the figure 2.3.

Fig 2.3

2. Dependent suspensions exaggerate their bending and twisting under different loads. So

under different load conditions it provides better ride.

3. It‟s not more expensive and geometry is very simple to construct.

2.1.2 DISADVANTAGES [2]

1. Uncomfortable for passenger vehicles and may also produce unwanted steering.

2. The unsprung mass problem is worse in front, and it is the main reason they are no longerused in street cars.

Dependent suspensions are good for heavy machinery like trucks and buses. This solid

axle suspension does not reduce the mass ratio very much.

2.2 INDEPENDENT SUSPENSION:

Independent suspension is to let a wheel to move up and down without affecting the opposite

wheel. They are many forms and designs of independent suspension. But the most commonly

used and the simplest designs are double wishbone suspension (Fig 2.4) and McPherson

suspension system (Fig 2.4).




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Fig: 2.4 [2]

And the graphical representation of the independent suspension systems are shown below

a) Double wish bone b) McPherson strut

c) Multi-link d) Swing arm




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e) Trailing arm f) Semi-trailing arm

Fig : 2.5 [2]

2.2.1 ADVANTAGES

1. Independent suspension usually lowers the roll centers, so that the body will roll before

the wheels break away from the road, which gives a warning to the driver.(3)

2. The engine and chassis structure can be lowered so that the centre of the car may also be

lowered and the engine may be brought forward to provide more room for the

passenger.(3)

3. Using a separate or independent suspension for each side of the car will reduced any

interaction between opposite roads-wheels, so there is less chance of vibrational

resonance causing wheel wobble(3).

4. All the driving forces, braking and lateral forces are sustained by the suspension linkage

alone (3).5. Suspension inputs to the body can be fed to inherently stiff areas and well spaced and

allows considerable design flexibility (4).

2.2.2 DISADVANTAGES:

1. Reduced cornering power, due to wheel cambering with roll (3).

2. There will be a slight change in wheel track if the wheel bounces and causes tyre scrub(3)

3. Suspension is more expansive and subjected to more wear because of is complicated

suspension and steering linkages and pivot joints (3).

4. Unbalanced-wheel-assembly effects will be transmitted to the steering-wheel more easily

and will be more pronounced (3).

2.2.3 VEHICLES USING INDEPENDENT SUSPENSION:

FRONT SUSPENSION:

Ford used Macpherson basic strut system with a forward-running tie and no anti-roll bar

in front suspension(4)

Multi-link front suspension for the 1990 Nissan 300ZX allows a much longer upper

wishbone to be used , offset to clear a low-mounted coil spring and damper unit(4)

Renault 25 with Double wishbone front suspension has the damper and spring above thetop wishbone to make room for the driver shaft to the front wheel (4).

Audi 100 front suspension the anti-roll locates the lower links according to the

description in the original Macpherson patent (4).

Volkswagen golf and Vauxhall Carlton front suspension is designed to provide a self-

stabilizing system through the inner wish bone bushes with featured wide-based lower

links and separate anti-roll bar system(4).




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REAR SUSPENSION:

Mercedes model W201 used multi-link system as a rear suspension and this type of

suspension is used as a benchmark during the International Association for vehiclesystem dynamics (IAVSD) exercise(1).

Mercedes Benz started the trend with rear suspension as double wishbone suspension

system in the year 1972 with S-Class (4).

Semi-trailing arms are used by the Ford sierra rear suspension with a trail angle of 18

degrees and Vauxhall Carlton with a less trail angle and incorporates self-stabilizing

articulation(4).

The Mazda 323 rear suspension used strut and link type system keeping the coil springs

on the top of the damper(4).

3. SUSPENSION CALCULATIONS WITH COMPUTER SIMULATION OF

SUSPENSION CHARACTERSITICS

MEASURED OUTPUTS

3.1 BUMP, REBOUND, WHEEL RECESSION AND HALF TRACK NOTES (5)

Suspension movements of the vehicle can be extract by motion of the suspension system at either

the wheel centre or wheel base. So, the displacements of the wheel centre are used to determine

the moments. If we visualize 3D view of a suspension system we can easily carried out thesuspension movements as shown in the Fig 3.1.

Bump movement is the independent variable and if we taken as a positive as the wheel moves

upwards in the positive z-axis relative to the vehicle body and it‟s vice versa is Rebound.

BM = DZ (WC, FG)

Wheel recession is the independent variable and taken as a positive as the wheel moves along the

x-axis relative to the vehicle body.

WR = DY (WC, FG)

Positive Half track change is the independent variable and if we taken as positive as the wheel

moves along the positive y-axis relative to the vehicle body and it‟s vice versa is Negative Half

track change

HTC = DX (WC, FG)




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a) Bump and HTC b) Wheel recession

Fig: 3.1 [1]

3.2 STEER AXIS (1)

McPherson strut system, Steer axis (Geometry steer axis) is defined as the passing through a

point located at the lower ball joint and a point located where the upper part of the strut ismounted to the vehicle body.(Fig 3.2)

Note: Steer axis is not necessarily parallel to the sliding axis of the upper part of the strut.

Fig: 3.2 Geometric and instant steer axis of a suspension system

For Multi-link system, the location of the steer axis (Instant steer axis) is not immediately evident

from the suspension geometry. In this case the steer axis should be the instant axis of rotation of

the wheel carrier parts. (Fig 3.2)

For all the suspension characteristics initial computation of the suspension system steer axis is

crucial.




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3.3 STEER or TOE ANGLE (δ)

The angle measured in the top elevation between the longitudinal axis of the vehicle and the line

of interaction of the wheel plane and road surface as shown in the fig 6.Steer angle is taken here

as positive if the front of the wheel toes towards the vehicle(1). As the suspension moves

between the bump/rebound small amount of change introduced due to suspension geometry andthat change is called steer change(5).

steer is also described as the comparison

of the horizontal lines through the both

wheels as shown in fig.3.3[6].total steer is

often expressed in angles .because of front

wheels are tied together through the tie

rod and centre link, steer angle(Total toe)

Fig:3.3 is always equally splits the between the

front wheel s when the vehicle moves forward(6).

When a front wheels leading edges are pointed toward each other, the wheel pair is said to have

Steer-in and the vice versa is steer- out.

Fig: 3.4[2]

Steer setting affect three major performances: Tire wear, straight line stability and corner entry

handling.

Steer-in increases the directional stability of the vehicle, where as steer-out increases the steering

response. Hence, steer-in setting makes the steering function lazy, while a steer-out makes the

vehicle unstable. When the driving torque is applied to the wheels, they pull themselves forward

and try to create steer-in. further when pushed down the road, a non-driven wheel or a braking

wheel will tend to steer-out. So street cars are generally set up with steer-in, while race cars are

often set up with toe-out.




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Calculation of steer angle (1)

Steer angle is calculated by using two markers located on the wheel spindle axis. Here, a

marker is used at the wheel centre (WC) and another on the spindle axis (SA), taken in

the figure to be out board of the wheel centre. The steer angle is converted from radians

to degrees by the factor (180/π).

δ= (180/π) ATAN (DX (WC, SA)/DY (SA, WC))

Fig: 3.5 [1]

3.4 CAMBER ANGLE (γ)

The angle measured in the front elevation between the wheel plane and the vertical. Taken as

positive if the top of the wheel leans outwards relative to the vehicle body or away from the

centre of mass as shown in Figure 3.6 [1].




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Fig: 3.6 [2]

The suspension should provide a slight camber angle in the direction of rotation to increase the

tire performance in the turn. As the body rolls in a turn, the suspension deflects vertically. The

wheel is connected to the chassis by suspension mechanism, which must rotate to allow for the

wheel deflection. Therefore, the wheel can be subjected to large camber changes as the

suspension move up and down. So, the more the wheel must deflect from the static position, the

more difficult it is to maintain an ideal camber angle.

Thus, the relatively large wheel travel and soft roll stiffness needed to provide a smooth ride in

passenger cars presents a difficult design challenge, while the small wheel travel and high roll

stiffness inherent in racing cars reduces the problem.

Calculation of camber

Camber angle is calculated by two markers located on the wheel spindle axis. Here a marker is

used at the wheel centre and another at the spindle axis, taken in the figure to be out board of the

wheel centre. The camber angle is converted from radians to degrees by factor (180/π).

γ = (180/π) ATAN (DZ (WC, SA)/DY (SA, WC))




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Fig: 3.7 [1]

What’s wrong if there is no camber compensation [5]

The outer wheel will be tucking. Poor contact patch between wheel and the ground surface

Camber thrust will not helping.

3.5 CASTER ANGLE (Ф)

Caster is the angle to which the steering pivot or king pin axis is tilted forward or rearward from

vertical, as viewed from side. If the steering axis is turned about the wheel positive y-axis then

the wheel have positive caster and vice versa is negative caster as shown in the figure 3.8(2)

.negative casters tends to straighten the wheel when the vehicle is travelling forward, and thus is

used to enhance straight-line stability(1).

Fig: 3.8 [2]




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Calculation of the caster (1)

Caster angle is calculated by measuring the

angle between the kingpin axis to the wheel

vertical and the angle is converted to the

radians to the degrees by factor (180/π).

Ф = (180/π) ATAN (DX (UB, LB)/DZ

(UB, LB))

Characteristics of caster in front axle (2)

Easy steering into the corner, low

steering out of the corner, low straight line

Fig: 3.9 [1] stability when zero caster provide. Low steering in the corner, easy steering out of the corner, more straight-line stability,

high tire print area during turn, good turn in response, good directional stability, good

steering feel.

When castered wheel rotates about the steering axis, the wheel gains camber. This

camber is generally favorable for cornering.

3.6 SUSPENSION TRAIL AND ITS CALCULATION

The force that causes the wheel to follow the steering axis is proportional to the distance between

the steering axis and the wheel-to-ground contact point, if the caster is small. this distance is

called suspension trail as shown in the figure 3.9 (2).For, calculating that suspension trail use the

following equation.

TR = DX(WB,LB) + DZ(LB,WB) * DX(UB,LB)/DZ(UB,LB)

Also, the distance between the centre of the wheel and the lower joint of the kingpin axis is

called the pneumatic trail. Due to stress distribution in tire contact path (5).Suspension trail

combines with the pneumatic trail and contributes to the suspension feel (1).

3.7 STEERING AXIS INCLINATION (θ) AND GROUND LEVEL OFFSET (GO)

Steer axis inclination, θ, is the angle measured in the front elevation between the steering axis

and the vertical and it is taken as positive when the top of the steering axis leans inwards (1). The

front road steering wheels pivot on either swivel-pins or kingpins depending upon the design of




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suspensions used. The axis of these king pins are laterally tilted so that steer axis inclination is

the lateral inward slope to body from the lower to the upper king pin joint to the vertical as

shown in the Figure 3.10. Thus a line drew through the king pin joints intersecting the ground

nearer to the centre of the tire contact patch than if there was no inclination of the pivot joints.

The much reduced ground level offset or scrub radius between the centre line of the wheel and

that of king pin at ground level has several benefits which are discussed as follows.

Fig: 3.10 [1]

It reduces the scrub radius between the centre of the tire contact patch and the pivot axis

at ground level. Thus it minimizes the scrub turning effort to turn the front wheels so that

the over steering will becomes considerably lighter.

The geometry of laterally inclining the king pin has the effect of lifting the front

suspension and body in proportion to the amount the steering wheels are turned.

It is desirable to have negative scrub radius to stabilize braking on a split negative friction

surfaces (5).

And the steer axis inclination and scrub radius is calculated by the equations given below (1)

θ = (180/π) (A TAN (DY (LB, UB)/DZ (UB, LB))

GO = DY (WB, LB)-DZ (LB, WB) * (DY (LB, UB)/DZ (UB, LB)

3.8 INSTANT CENTRE AND ROLL CENTRE [1]

The concept of instantaneous center and roll center is has been used extensively by vehicle

designers in order to relate suspension layout to vehicle handling performance, particularly when

consider under steer or over steer.

Instantaneous center and roll center for double wish bone suspension system and its

calculation




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Fig: 3.11 [1]

The roll center of the front and rear suspension is the instantaneous center of rotation of body

with respect to the ground (2). The roll center of a double wish bone suspension system can be

internal or external. An internal suspension roll center is towards the vehicle body. While anexternal suspension roll center goes away from the vehicle body.

And suspension roll center may be on, above or below the road surface, and it is directly

proportional to the vehicle roll center.

For, calculating the roll centers we have to set up the gradients GR1 and GR2 for the upper arms

and lower arms of the double wishbone suspension system.

Let the points be A, B, C and D as shown in the figure 3.11.

GR1 = (BZ-AZ)/ (BY-AY)

GR2 = (DZ-AZ)/ (DY-CY)

Where, AY, AZ, BY, BZ, CY, CZ, DY, DZ, are the y and z co-ordinates of the points A, B,C

and D.

Let the co-ordinates of instantaneous center ICY and ICZ are established from the two

simultaneous equations:

ICZ = AZ + GR1 (ICY-AY)

ICZ = CZ + GR2 (ICY-CY)

From the above two equations

AZ + (GR1*ICY) – (GR1*AY) = CZ + (GR2*ICY) – (GR2*CY)

(GR1 - GR2) ICY = (GR1*AY) – (GR2*CY) + CZ – AZ




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ICY = ((GR1*AY) – (GR2*CY) + CZ – AZ)/(GR1 – GR2)

ICZ = AZ + GR1(1CY-AY)

The gradient GR3 of the line joining the wheel base to the instant center can be expressed as

GR3 = (ICZ-WBZ)/(ICY-WBY)

Where WBZ and WBY are the y and z co-ordinates of the wheel base.

This allows roll center is located using:

RCY = 0.0

RCZ = WBZ + GR3 (RCY-WBY)

Roll centre height can be determined by

RCH = RCZ – RZ

Where RZ is the z co-ordinate of the road

Instantaneous and roll centre for McPherson strut suspension system and its calculation

Fig: 3.12 [1]

Projecting a line intersected along the transverse arm and perpendicular to the axis of strut is

Instantaneous center. And the line projected between the wheel base and instant center and the

point at which the line intersects the centre line of the vehicle is Roll center.

Calculating these centers is same as the procedure followed in double wish bone suspension

system




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4. TESTS FOR SUSPENSION SYSTEM

4.1 SUSPENSION REQUIREMENTS

4.1.1 KINEMATIC REQUIREMENTS OF A SUSPENSION SYSTEM [2]

A wheel co-ordinate system is attached to the centre of the wheel to express the motion of the

wheels, Let the co-ordinate system be W (ox, y, z). Taken the wheel as a rigid body, it has a six

degree of freedom with respect to the vehicle body where, three in translation and the remaining

in rotation, as shown in figure 10.

Fig: 4.1[2] Fig: 4.2[2]

The axes x, y and z indicates the directions of forward, lateral, and vertical translations and

rotaions. In this position shown in figure 10, the rotation about the x-axis is the camber angle,

about the y-axis is the spin and about the z-axis is the steer angle.

Lets taken a non-steerable wheel, for this non steerable wheel only two DOF is allowed. One is

translation in z-axis and the other rotation in the spin about y-axis. So, we need to take four

degree of freedom. If the wheel is steerable, then translation in z-axis, spin about y-axis and steer

rotation about z-axis are the three DOF allowed. So, we must take three DOF of a steerable

wheel.




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Fig: 4.3[1]

Kinematically, non-steerable and steerable wheels should be supported as shown in figure 10 and

11 respectively. Providing the required freedom, as well as eliminating the taken DOF, are the

kinematic requirements of the suspension system.

4.1.2 DYNAMIC REQUIREMENTS [2]

Wheels should be able to propel, steer, and stop the vehicle. So, the suspension system must

transmit the driving traction and deceleration braking forces between the vehicle body and the

ground. The suspension members must also resist the lateral forces acting on the vehicle. Hence,

the wheel suspension system must make the wheel rigid for the taken DOF. However, there must

be taken some compliance members to limit the untaken DOF. The most important compliant

members are spring and dampers to provide returning and resistance forces in the z- direction.

4.2 COMPLIANCE MATRIX APPROACH [1]

The suspension compliance approach relates progressive movements of the suspension

incremental forces applied at the wheel centers. This approach is well suited to an automated

computer MBS analysis particularly when the influence of compliance requires consideration

and this matrix is computed at each movement of the suspension through its range of travel.

Compliance matrix, [C] is defined as the derivation of the displacements with respect to the

forces.

[C] =

Taken the system in linear and compliance matrix is predicted the movements due to force

inputs.

{} = [C] {F}




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Expanding the equation leads to 12 X 12 matrix relating the motions of the left and right wheel

centers to unit forces and torque applied to the wheel centers. Matrix element Ci,j is the

Displacement of system degree of freedom i , due to the unit force at DOF j where the degree of

freedoms are the three displacements X, Y, and Z and the three rotations Ax, Ay and Az at

each wheel centers.

From, above equation we can clearly seen that the coefficients of the leading diagonal matrix [C]

directly relates the displacement or rotation to the associated forces or torque applied at the

degree of freedom.

4.3 LABORATORY TESTS FOR SUSPENSION SYSTEMS [7]

Laboratory test for suspension systems is very essential and crucial for a vehicle to know and

measure the suspension parameters by applying loads to an existing suspension system. And the

most commonly used laboratory tests are kinematic and compliance rig and shaker rig tests.

4.3.1 KINEMATIC AND COMPLIANCE RIG TEST

Kinematics has defined as study of motion without reference to the mass and force. where,

Compliance is defection resulting from the application of force. when this rig test applied to

vehicle suspension system, The suspension kinematics describes the controlled orientation of

load wheels by suspension links, based on assumptions of rigid parts and frictionless joints. K &

C rig has ability to apply the lateral and longitudinal forces at the tire contact patch. suspension

parameters such as toe and camber are measured at the wheel hub, while vertical, longitudinal

and lateral tire loads are measured at the tire contact patch.




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Fig: 4.4

K & C Rig cannot measure the theoretical points; the rig software calculates the instant centers

from the measured movements of the hub center. In addition the K & C rig is able to account for

any compliance effects by calculating force-based roll centers, used measured jacking forces

resulting from lateral forces. Force base anti dive and anti squat angles are calculated from the

application of longitudinal forces and he measurement of vertical loads on the tires. These are

close enough to kinematic parameters that they can be used to verify kinematic measurement.

4.3.2 KINEMATICS AND COMPLIANCE RIG TEST METHODOLOGY[7]

Basic steps used to determine the kinematics and compliance of a vehicle.

Kinematics are found by monitoring the wheel orientation and wheel center motion as the vehicle

chassis is moved in pure vertical motion(Bounce) or pure roll.

Compliance values are obtained by holding the chassis in a fixed position and applying ground

plane force through the tire contact patch to isolate the various types of compliance issues in the

vehicle, The force has to applied in a quasi-static manner.

Example

Lateral force is applied at the contact patches both in-phase between the left and right wheels

and out-of-phase. Aligning torque about the tire contact patch in the ground plane is applied in

similar fashion either in-phase or out-of-phase. Comparing these results of these pair tests

allows isolation of some variables. In this case the forces are applied with either the brakes or

transmission locked.




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The forces are usually applied independently between the front axle and rear wheels as clamped

chassis as affectively isolates the front and rear axles of the vehicle. By monitoring the wheel

orientation and position during the compliance tests bending effects, such as, toe compliance,

camber compliance and caster change, under lateral, longitudinal and aligning torque forces can

be determined. each compliance test applied +/-250 lb per wheel at the tire contact patch. This is

the lower load that would normally be applied and was limited by the light vertical loads on the

tires.

The key factors of getting results, that are possible on a K & C rig test is that both kinematic and

compliance tests are run cyclically.

The Graphs obtained after the K & C rig test of a vehicle suspension system comparing with the

Kinematics software WinGeo are as follows

1. CAMBER ANGLE AND VERTICAL DISPLACEMENT

.




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2. TOE AND VERTICAL DISPLACEMENT

3. CASTER AND VERTICAL DISPLACEMENT




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4. STEER CAMBER CHANGE

Note:

Kinematic and compliance rig, with exception of two or three notable points is verysimilar to the overall characteristics of a wheel predicted by kinematic software

(WinGeo).

It is very important when K & C measured data is comparing with predictions that the

wheel travel is relative to the wheel as opposed to relative to the ground.

5. THE RELATION SHIP BETWEEN THE SUSPENSION SYSTEM , THE TYRE

AND FULL VEHICLE DYANAMICS PERFORMANCE

5.1 CAMBER [6]

Camber causes tire wear if the alignment is not proper.

Excessive positive camber causes scuffing and wear on the outside edge of the tire and

vice versa if excessive negative camber as shown in the figure 5.1




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Fig : 5.1

To optimize a tire‟s performance ina turn the suspension should provide a slight camber angle inthe direction of rotationPositive camber tilts the tire and forms a cone shape that causes the

wheel to roll away or pull outward towards the point of curve.Camber angle is difficult to

achieve in practice and the car makers set the camber angle with in the design area ashown in the

graph [5].

Camber

angle Design area

0

Rebound 0 Bump

5.2 CASTER [2]

Negative Caster provides low steering in to the corners, easy steering out of the corner, more

straight line stability, high tire print area during turn, good turn in in response, good directional

stability, good steering feel. So most street cars are made with 4-6 degrees negaive caster.Higher

the caster angle more the front tire tilt,cause camber-type tire wear.




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Castor versus Camber

Camber dosen’t improve turn-in as the positive caster dose. Camber is not generally good for

tire wear.Camber in one wheel dose not improve directional stability. Camber adversely affects

braking and acceleration efforts.

5.3 BUMP STEER [5]

As the suspension moves between bump/rebound, small amount of steer change may be

introduced due to suspension geometry.

It is desirable to add an understeer characterstics as follows.

V

+ve toe -ve toe

Inside renound outside bump

-ve toe +ve toe

Dotted lines are roll steer exaggerated. The above schematic representation is showing that under

steer charcterstics which are desirable to have in vehicle. And the suspension curves are as

follows.

Steer or Toe - - - - Front

Degrees Rare

0

Rebound 0 Bump




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6.SUMMARY

All the parts which perform the function of isolating the vehicle from the road shocks are

collectively called a suspension system.The role of the suspension system is to allow the

relative motion between the wheel and the vehicle body.

There are two types of suspension systems : Dependent in which the left and right

wheels are connected and Independent in which the left and right wheels are

disconnected. Solid axle is the most common dependent systemWhere as, McPherson

strut and Double wishbone are independent suspension systems.

The suspension parameters such as Camber, Caster, Roll centre, Instant center, steeraxis

inclination, Bump movements and wheel recession can be calculated by using existing

suspension suspension system and laboratory tests such as Kinematics and Compliancerig test which has been developed specifically for measure the suspension parameters, as

loads are applied to an existing suspension.

The orientation of tire and wheel with respect to the vehicle is expressed by employing

three co-ordinate frames and calculated.

The coefficients of the leading diagonal matrix [C] directly relates the displacement or

rotation to the associated forces or torques applied at the Degree of freedom.

7.CONCLUSION

It has been revealed through systematic research and investigation into various automotive

suspension system configurations and the methodologies to design and analysis, Solutions are

deviced to increase the performance of the vehicle.

Instant centers and roll centers, which rely on four bar theory are a useful concepts in

understanding the suspension behavior. A through understanding of four bar theory is necessary

to calculate those centers from measured datas. And also the importance of installing the

suspension parameters to the vehicle using laboratory tests like K & C rig are known.

I became obvious from this research and investigation that consistant test followed by momentry

analysis thinking in different angles to find innovate and optimize solutions.




Vehicle Dynamics

1

REFERENCES

1. Michell Blundell and Damian hall ., “The Multibody systems approach to vehicle

Dynamics” , Elsevier butterworth – Heinemann publishers , 2004 , pp 131-175.

2. Reza N . Jazar . , “Vehicle Dynamics – Theory and applications” , Springer publishers ,

pp 456-510.

3. Heinz heisler . , “ Vehicle and engine technology “ , Elsevier butterworth – Heinemann

publishers , second edition, 1999 , pp 141-159.

4. Geoffrey P Howard . , “ Car suspension and handling” , Third edition, SAE publishers,

pp 20-50.

5. Michell Blundell . , “M02MAE- Vehicle refinement” , Class notes , suspension systems.

6. James D Halderman . , “Auomotive technology”, third edition , Chapters 85, 86 and 87.

7. Robert simons, Thimothy sutherlands and michel keena ., “Suspension geometry: theory

vs K & C Measurements” , SAE technical paper series, 2008-01-2948.

Documents

Suspension (Repaired)