Shock Absorbers: Notes

The Adaptive Damping (AD) shock absorbers are monotube, nitrogen gas and oil filled units, which are integrated with a conventional coil spring (front suspension) or an air spring (rear suspension) to form the spring and shock absorber assemblies. The shock absorbers are continuously variable, which allows the damping force to be electrically adjusted when the vehicle is being driven. The shock absorbers provide the optimum compromise between vehicle control and ride comfort.

The shock absorbers have an electrical connector on the end of the piston rod, in the center of the top mount.

In each shock absorber, the damping adjustment is achieved by a solenoid operated variable orifice, which opens up an alternative path for oil flow within the damper. When de-energized the bypass is closed and all the oil flows through the main (firm) valve. When energized the solenoid moves an armature and control blade, which work against a spring. The control blade incorporates an orifice which slides inside a sintered housing to open up the bypass as required. In compression, oil flows from the lower portion of the damper through a hollow piston rod, a separate soft (comfort) valve, the slider housing and orifice and into the upper portion of the damper, thereby bypassing the main (firm) valve. In rebound the oil flows in the opposite direction.

In the firm setting oil flows through the main (firm) valve only, but when the bypass is opened by any amount the oil flows through both valves in a pressure balance. When fully energized the solenoid moves the armature and therefore the slider to the maximum extension and opens the orifice completely. The damper operates continuously between these two boundary conditions.

The solenoid in each damper is operated by a separate 526 Hz Pulse Width Modulation (PWM) signal from the ISCM. The ISCM continuously varies the current of the PWM signals between a minimum of 0 A and a maximum of 1.5 A (i.e. between the maximum firm setting when de-energized and the maximum soft setting when fully energized) to independently increase and decrease the damping of each damper as required.