The Shock Absorber
The illustration shows a front shock absorber.
The damping force in the four shock absorbers is altered individually using control valves, which are affected by solenoids. Valves and solenoids are located in the lower end of the shock absorbers.
The suspension module (SUM) controls the current to the solenoids. Lower current gives lower damping forces, high current higher damping forces.
The valves are sprung so that they return to their original position if there is no flow through the solenoids. This results in the shock absorbers functioning as conventional passive shock absorbers if the valves are not affected by the solenoids.
The solenoids are diagnosed by the Suspension module (SUM).
Exploded view of the shock absorber
| 1 | High pressure side | 6 | Check valve |
| 2 | Splash guard | 7 | Low pressure side |
| 3 | Check valve | 8 | Solenoid |
| 4 | Lubrication duct | 9 | Control valve |
| 5 | Oil duct |
The shock absorbers are oil hydraulic with gas pressure to prevent deposit build-up. The design is of the 3 tube shock absorber type with three shock absorber tubes instead of two as in traditional shock absorbers. The extra tube creates an oil duct past the piston on the high pressure side so that the oil flow can always travel the same way in the control valve.
Oil flow in the shock absorber
- Piston's movement
- Oil flow
The flow always travels in the same direction through the oil duct and control valve (C) due to check valves in the piston (A) and in the bottom of the shock absorber cylinder (B). When the shock absorber is depressed, the oil flows up through the check valve in piston the (A). When the shock absorber is pulled out, the oil flows through the check valve at the bottom (B). In both cases, the oil flows the same direction through the oil duct and through the control valve (C).
Control valve
| 1 | Low pressure section | 6 | Valve seat |
| 2 | Pilot valve | 7 | High pressure section |
| 3 | Solenoid | A | Main flow |
| 4 | Fail-safe valve | B | Pilot flow |
| 5 | Main cone | C | Fail-safe-flow |
Damping becomes harder or softer depending on the pressure in the shock absorber and on the ease of oil flow through the shock absorber. This is controlled by the varying opening area in the control valve. The area is determined by the distance between the valve seat (6) and the main cone (5). The main flow of oil (A) travels through this.
A smaller flow travels through the pilot valve at the same time and produces a counter pressure to the main cone. The solenoid that is controlled by the Suspension module affects the pilot valve and, depending on the solenoid's force, obtains different counter pressures in the valve. In the event of any faults, the control valve shifts to passive position and the fail-safe valve controls the counter pressure with a ball and spring instead, then as the fail-safe flow. The valve is installed so that the shock absorber functions safely. This passive position cannot be set using any of the selectable driving modes.