Rear suspension (Rear suspension): Description and operation

REAR SUSPENSION

General

The rear suspension is of the independent type and is a four-link system which comprises the following main components:

• Two coil springs
• Two damper units
• Two upper pivot arms
• Two trailing arms
• Two lower links
• Two adjustable track control arms
• Two swivel hubs
• One anti-roll bar
• Two anti-roll bar links
• Peripheral subframe

The rear suspension system consists of a spring/damper unit at each rear wheel. Each spring/damper combination is mounted between the vehicle’s body and upper suspension arm.

There are two grades of suspension configuration, Standard and Sports. The Sports version has a lower (10 mm) and stiffer suspension than for the Standard.

Damper and Spring Unit

Two damper and spring units control the damping of the rear suspension. The coil springs support the weight of the vehicle, maintain ride height and absorb road shock. When additional load is placed on the coil springs (e.g. through acceleration), or when the vehicle passes over bumps in the road, the springs compress to absorb the change and ensure ride comfort is maintained.

The coil spring is retained in a compressed condition between the strut spring seat and the top (body) mounting. The coil springs and the upper ball joints support the weight of the vehicle which is transmitted through the springs to the upper control arms and then through the upper ball joints.

Isolators are fitted at each end of the spring/damper units to reduce noise transmitted from the suspension to the body. The upper spring isolator has a locating tag on its top surface which is used to orientate it correctly by locating it through a hole in the front of the subframe turret.

The damper units assist in absorbing the energy stored in the coil spring after passing a bump to quickly terminate the reciprocating motion of the suspension and return the coil spring to the rest position.

Each damper is gas and oil filled and is of twin tube construction. The twin tube construction allows the damper piston to operate against hydraulic fluid in an inner tube. The damper unit is fully displaced on rebound and uses rod displaced valving during compression.

As the suspension travels through the bump and rebound phases, the hydraulic fluid in the inner tube of the damper unit is forced through tiny holes inside the piston and the base valve, this changing pressure in the hydraulic fluid slows down the piston and consequently slows down spring and suspension movement. The damper units provide velocity sensitive hydraulic damping, the amount of resistance depending on the speed of the suspension and the number and size of the holes in the piston and base valve. The faster the suspension moves, the more resistance the damper units will provide. As a result, the damper units reduce:

• Bounce
• Body roll or sway
• Brake dive
• Acceleration squat

An oil cavity between the inner and outer tubes is used as a reserve tube to store excess hydraulic fluid. A low pressure charge of nitrogen gas in the reserve tube provides resistance to fluid entering the reserve tube and with the hydraulic fluid under pressure, aeration of the fluid is greatly reduced to provide better ride comfort and improved handling. Besides minimising oil cavitation this two-tube design helps eliminate the effect of damage to the outer tube affecting piston operation.

A compression valve is included in the base of the piston inner pressure tube to control fluid movement between the inner and outer chambers during the compression cycle. The diameter of the piston and inside diameter of the pressure tube is 30 mm (1.18 in.).