1. Suspension Systems - 2 Topics covered in this presentation:
Suspension system variants
Rear suspension system
Suspension levelling system
Active suspension

2. Wishbone Suspension
The suspension must be designed in such a way as to keep the wheel upright for maximum tyre contact (vehicle control) and to minimize tyre wear.
Upper wishbone
The upper wishbone is short and the lower wishbone is longer.
Both wishbones pivot points and lengths are calculated to provide the best operating angle for a given suspension movement.
Lower wishbone

3. Kerb Height Adjustment
The definition of kerb height is the distance of a specified point on the vehicle to the ground when at rest.
The kerb height is only adjustable on some vehicles.
If kerb height is adjustable the manufacturer will give checking specification and loading details. Some vehicles are required to be fully laden or with driver, always check on level ground.
Spring tension can change kerb height, e.g. weak or broken springs.
There are many different adjustment methods, most common is a bolt fitted to a torsion bar.
Height adjustment raises or lowers the frame and body in relation to the ground.

4. MacPherson Strut
This is a very popular and efficient form of suspension. It has one control arm and a strut assembly. A coil spring and shock absorber will normally form parts of the strut assembly.
Strut assembly
Coil springs may be mounted on the control arm instead of being around the strut. On this type, the shock absorber connects the knuckle to the frame.
Frame
Shock absorber
This type of suspension strut is often also used on rear suspension systems.
Knuckle
Control arm
Coil spring

5. MacPherson Strut Suspension
The top of the strut is bolted to a reinforced section of the frame structure.
Steering knuckle
The lower end of the strut is attached to a steering knuckle.
Strut
The control arm is also attached to the steering knuckle.
Frame
The control arms are mounted on a cradle section of the frame.
Control arm
An anti-roll bar links the two control arms together to reduce sway (body roll).
Cradle
Anti-roll bar

6. Solid Rear Axle Suspension
This type of rear suspension is typical for a rear-wheel drive vehicle.
Shock absorber
Coil springs
The axle is inside a solid housing.
The shock absorbers are mounted between the solid axle and the frame.
Axle housing
Stabilizer bar
The springs are arranged between the axle housing and the frame of the vehicle.
Trailing arm
Trailing arms, or links, hold the rear axle in position.
A stabilizer bar and track bar are included to add vehicle stability.

7. Semi-Independent Suspension
This solid (not driven) axle can flex or twist, so that the two wheels are partially independent of each other.
Panhard rod
Coil springs and shock absorbers are mounted on control arms.
Chassis mount
Shock absorber
Control arms are connected to the frame structure and help to maintain stability.
Solid axle
Coil spring
Control arm
Panhard rod prevents sway and stops the axle moving from side to side.
Chassis mounts

8. Independent Rear Suspension
Coil spring and shock absorber
Having independent suspension on all four wheels improves ride smoothness.
The same strut types used in front suspension can also be used for the rear suspension.
Lower ball joint
Trailing arm
This is sometimes known as “McPherson strut” suspension.
Trailing arms control forces generated during normal driving. Not only under acceleration and braking but when driving over bumps and turning.
Chassis mounting points
Lower arm

9. Suspension Levelling System
Diagnostic connector
This system is used to assist a conventional suspension system.
Compressor
Compressor mounting bracket
Special shock absorbers are used with separate air chambers.
Height sensor
Height sensors are mounted on the frame and linked to the axle housing to check the height of the vehicle.
A compressor supplies air pressure to power the system.
Harness
This is electrically controlled via cables and harness.
Shock absorber
Link
If the load increases, the sensor can turn the compressor on, increasing pressure, or release air from the system if the load reduces.

10. Complete Levelling System
Diagnostic connection
This system operates on air springs.
Electronic control unit
Compressor and vent solenoid
Compressor relay
Rear height sensor
Rear air springs
Height sensors
Front air springs
The electronic control unit (computer) uses signals from the height sensors to operate the air compressor or vent solenoid (inflate or deflate the air springs).

11. Electronic Height Control
The microcontroller program can be modified for any of the following:
Use air shock absorbers to control the vehicle height.
Automatically control the kerb height for changes of loading.
Increase shock absorber stiffness to improve cornering response.
Adjust shock absorber stiffness for a softer ride on rough roads.
Compensate for body roll, squat or dive.
Modify suspension response for different speeds or acceleration.

12. Active Suspension System
ECU
This uses hydraulic cylinders in place of the springs.
A hydraulic pump supplies the cylinders with pressure.
Pressure sensor
Hydraulic pump
Sensors
Pressure sensors send signals to an electronic control unit (ECU).
Outlet valve
When a wheel goes down, the inlet valve is opened to increase pressure in the cylinder.
Inlet valve
Fluid Reservoir
When a wheel moves up, the outlet valve is opened to reduce pressure.
Hydraulic cylinder
The system response is very fast.
A back-up pressure reservoir/accumulator is normally incorporated.