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

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

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.

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

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

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.

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

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

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.

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).

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.

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.