Rear Suspension, Four-Wheel Drive
Rear suspension, four-wheel driveOverview
A. Upper transverse link
B. Lower transverse link
C. Toe-in link
D. Longitudinal link
E. Steering swivel member
F. Wheel hub
G. Drive shaft
H. Anti-roll bar
Function
The "multi-link" rear suspension comprises a subframe with upper (A) and lower (B) transverse links, one toe-in link (C) and one longitudinal link (D) per wheel. This means that the rear wheels are individually suspended and can move up and down independently.
During oscillation, wheel geometry is altered in a controlled manner. Wheel geometry, or link movement in relation to each other, causes slight oversteering during cornering since the outer rear wheel toe-in approaches 0°. If the front wheels are turned toward the left (overdrive), the right rear wheel turns toward the right and vice versa.
The steering swivel member (E) is made of cast iron. The lower link arm and toe-in link are made of aluminium. The hub is situated in the steering swivel member, fastened with a bolted joint and integrated with the bearing. This unit also includes the wheel speed sensor. The bearing is a double-row, angle-contact bearing.
Toe-in and camber are adjustable by means of off-center bolts in the link arm mountings in the subframe.
The subframe, which is made of painted steel sheeting, is suspended in rubber bushings to insulate against noise and vibrations. The spring elements are located between the lower transverse link and the body.
The transverse links hold the wheel in place laterally in order to properly guide the wheel suspension movements. They are attached to the subframe by rubber bushes and the lower transverse link is attached by rubber bushes to the steering swivel member. The upper transverse and toe-in link are mounted with ball joints in the steering swivel member. The longitudinal link acts as a mounting for the steering swivel member as well as bears longitudinal load. The longitudinal link is attached to the body by a bracket with rubber bushes which act as insulation against noise and vibration and improve comfort. The steering swivel member is also the lower attachment point for the shock absorber.
An anti-roll bar is mounted between the subframe and longitudinal links.
The dampers are telescopic and double-acting. The shock absorbing medium oil, which counteracts foam build-up, is pressurized with gas during manufacture.
Automatic level-regulating shock absorbers
Some models are equipped with automatic level-regulating shock absorbers. These shock absorbers automatically adjust the suspension path based on how heavily the car is loaded.
Function
The rear shock absorber and suspension of the Nivomatic system form a self-regulating hydropneumatic suspension and damping system.
The self-regulating system automatically maintains the optimal chassis level. This level system is unique in that the energy required for chassis position adjustment is taken from the relative movement between the axle and body that occurs during normal driving. Thus, the self-adjusting level system requires no extra energy source.
The rear suspension is compressed by the extra weight. As soon as the vehicle starts to move, the relative movement between the axle and body cause the oil in the low-pressure chamber to be pumped to the gas pad in the high-pressure accumulator (parallel to the chassis spring).
Under the piston rod extension, oil is drawn into the pump through the induction valve. Under compression, the oil is pumped into the high pressure accumulator through an outlet valve. The increased pressure in the high-pressure accumulator acts on the cross-section area of the piston rod to achieve the extra equalization force needed for the system's increased suspension rate, which generates a more constant chassis level. In this situation, the height regulator opens a bypass channel to prevent further oil pressure increase. The oil returns to the low-pressure chamber through a drain opening.