The Automotive Chassis and Principle

1.1  General Characteristics of Wheel Suspensions

1.2  Independent Wheel Suspensions-General

1.2.2 Double Wishbone Suspensions
1.2.3 McPherson Struts and Strut Dampers
1.2.4 Rear Axle Trailing-Arm Suspension
1.2.5 Semi-Trailing-Arm Rear Axle
1.2.6 Multi-Link Suspensions

1.3  Rigid and Semi-Rigid Crank Axles

1.3.1 Rigid Axles
1.3.2 Semi Rigid Crank Axles

1.4  Front-Mounted Engine, Rear-Mounted Drive

1.4.1 Advantages and disadvantages of the front-mounted engine, rear-mounted drive design
1.4.2 Non-driven front axles
1.4.3 Driven rear axles

1.5  Rear and Mid Drive

1.6  Front-Wheel Drive

1.6.1 Types of design
1.6.2 Advantages and disadvantages of front-wheel drive
1.6.3 Driven front axles
1.6.4 Non-driven rear axles

1.7  Four-Wheel Drive

1.7.1 Advantages and disadvantages
1.7.2 Four-wheel drive vehicles with overdrive
1.7.3 Manual selection four-wheel drive on commercial and all-terrain vehicles
1.7.4 Permanent four-wheel drive; basic passenger car with front-wheel drive
1.7.5 Permanent four-wheel drive, basic standard design passenger car
1.7.6 Summary of different kinds of four-wheel drive

2.

This translation of fourth German edition  is published by Butterworth Heinemann as the second
English edition of The Automotive Chassis. translated from the German by AGET limited.

Chassis and Vehicle Overall
Wheel Suspensions and Types of Drive
Axle Kinematics and Elastokinematics
Steering - Spring - Tires

1.1 General Characteristics of Wheel Suspensions

The suspensions of modern vehicles need to satisfy a number of requirements whose aims
partly conflicts because of different operating conditions (load/unload, accelerating/braking,
level/uneven road, straight running/cornering).

The forces and moments that operate in the wheel contact area must be directed into the body.
The kingpin offset and disturbing lever force arm in the case of longitudinal forces, the castor offset in the case of the lateral forces and the radial load moment arm in the case of the vertical forces are important elements whose effects interact as a result of the angle of the steering axis.

Sufficient vertical spring travel, possibly combined with the horizontal movement of the wheel
away from an uneven area of the road. The build-up and size of the later wheel forces are
determined by specific toe-in and camber changes of the wheels depending on the jounce and
movement of the body as a result of the axle kinematics (roll steer) and operative forces
(compliance steer).

• independent movement of each of the wheels on the axle (not guaranteed in the case of rigid axles.)
• small, unsprung masses of the suspension in order to keep wheel load fluctuating as low as possible.

It consists of at least one trailing arm on each side. The arm is guided by two (or even three)

transverse control arms. The trailing arm simultaneously serves as a wheel hub carrier and 

(on four-wheel steering) allows the minor angle movements required to steer the rear wheels.

The main advantages are its good kinematic and ealstokinematic characteristics.

1. GGG 40 Cast Iron. Trailing arms. They absorb all longitudinal forces and braking moments as well as transferring them via the points.
2. The centers of which also form the radius arm axes on the body. The lateral forces generated at the center of the tire contact are absorbed at the sub-frame 5, which is fastened to the body with four rubber bushes (items 6 and 7) via the transverse control arms 3 and 4. 
3. The upper arms 3 carry the minibloc spring 11 and the joints of of the anti-roll bar 8.  Consequently, this is the place where the majority of the vertical forces are transferred between the axle and the body.

The shock absorbers which carry the additional polyurethan springs 9 at the top, are fastened in a good position behind the axle center at the ends of the trailing arms. For reasons of noise, 

the differential 10 is attached elastically to the sub-frame 5 at three points (with two rubber

bearings at the front and one hydro bearing at the back). 

When viewed from the top and the back, the transverse control arms are positioned at an angle

so that, together with the different rubber hardness of the bearings at the point 2, they achieved 

the desired elastokinematic characteristics.

a.  toe-in under braking forces

b.  lateral force compliance understeer during cornering

c.  prevention of torque effects

d.  lane change and straight running stability

For reasons of space, the front eyes 2 are pressed into parts 1 and bolted to the attachment

bracket. Elongated holes are also provided in this part so toe-in can be set. The upper 

transverse arm is made of aluminium for reasons of weight (reduction of unsprung masses.)

Five arm rear axle in the BMW 3 series Touring. 

 Four Bar Twist Beam Axle. Renault.

With two torsion bar springs both for the left and right axle sides (items 4 and 8). The V-shape

profile of the cross member 10 has arms with different lengths, it resistant to bending but less

torsionally stiff and absorbs all moments generated by vertical, later, and braking forces. It also

partially replaces the anti-roll bar. 

At 23.4 mm, the rear bars 8 are thicker than front ones (20.8 mm, items 4). On the outside, 

8 grips into the trailing links 1 with the serrated profile 13 and on the inside they grip into the 

connector 12, which transmits it to the front bars 4, subjecting them to torsion. 

In the case twist-beam axles, both sides of the wheels are connected by means of a flexurally

rigid, but torsionally flexible beam. On the whole, these axles save a great deal of space and 

elastokinematic balance because of  the functional duality of the function in the components and require the existence of adequate clearance in the region of the connecting beam. They are  mainly used as a form of rear wheel suspension in front-wheel drive vehicles. 

Independent Suspension :

• Longitudinal link and semi-trailing arm axles, which require hardly any overhead room and consequently permit a wide luggage space with a level floor, but which can have considerable diagonal springing.
• Wheel controlling suspension and shock-absorber strut, which certainly occupy much space in terms of height, but which require little space at the side and in the middle of the vehicle.(can be used for the engine or axle drive).
• Double wishbone suspensions.
• Multilink suspensions, which have up to five guide links per wheel and which offer the greates design scope with regard to the geometric definition of the kingpin offset, pneumatic trail, kinematic behavior with regard to toe-in, camber and track changes, breaking/staring torque behavior and elastokinematic properties.

Driven. rigid steering axle with dual joint made by the company GKN Birfield AG for four-wheel

drive special-purpose vehicles, tractors and construction machinery.

The dual joint is the center over the bearings 1 and 2 in the region of the fork carriers; these are

protected against fouling by the radial sealing rings 3. Bearing 1 serves as a fixed bearing and

bearing 2 as a movable bearing. The drive shaft 4 is also a sun gear for the planetary gear with

the internal-geared wheel 5. 

Vertical, lateral, longitudinal forces are transmitted by both tapered-roller bearings 6 and 7.

Steering takes place about the steering axis EG.

Top view of the dual joint.

The wheel end of the axle is turned about point P in the middle of the steering pivot during

steering. The individual joints are constrained at points A and B so that point A is displaced to

position A', P is displaced to P' and B is displaced along the drive axle by the distance X to B'.

In order assimilate the variable bending angle  resulting from the longitudinal displacement

of point B, the mid-point of the joint P is displaced by the distance Y. The adjustment value Y

depends on the distance between the joints and the steering angle at which constant velocity

is to exist. Where large steering angle can be reached (up to 60 degrees), there should be

constant velocity at the maximum steering angle. 

The adjustment Y and the longitudinal displacement X should be taken into consideration in the

design of the axle.