I was recently asked for my opinion on fitting aftermarket coilover suspension to a 360 – my response was that it would be a bad idea. The 360 was fitted with a very sophisticated active suspension system for its day. In my opinion, replacing the electronic dampers with passive units would be a step backwards.
The active suspension system is made up of variable shock absorbers (dampers) controlled by an ECU which receives data from three accelerometers. The following diagram shows the components and their location in the car:
The main components are the electronic dampers which were designed and manufactured specifically for the 360 by Boge. The dampers contain a small electronic valve inside the top of the unit (see diagram below). In simple terms, this valve changes the flow of oil inside the damper which in turn varies the damping force and thus the stiffness of the suspension.
The valve has three settings which are determined by the amount of electrical current passing through the valve. When no current is passed through the valve the damper is at it’s maximum setting, with 0.9 Amps it is at a medium setting and with 1.8 Amps at the lowest setting. The following diagrams show the damping characteristics for the different settings. The charts display stem speed (x-axis) vs damping force (y-axis). The characteristics are different for compression and extension and are slightly different between front and rear on the car. You can see from the charts that the damping force is about four times greater in the hardest setting than in the softest setting.
At the heart of the system operation is the damper ECU (part number 175222) located under the dashboard. The ECU receives data from three accelerometers – located behind the front bumper, inside the front compartment and in the engine bay. These accelerometers allow the ECU to determine how the car body is moving in a vertical and lateral direction. The ECU also receives signals from the ABS sensors (for wheel speed), gearbox (road speed) and the brake pedal.
The ECU controls the damping in a number of ways:
- Front Vertical Damping
- Rear Vertical Damping
- Transverse Damping (including controls to minimise body roll)
- Longitudinal Damping (separate maps for with/without braking)
Depending on whether sport driving mode is selected the ECU gives priority to comfort or traction. In sport mode the suspension is noticeably firmer and body roll is much reduced.
The ECU also performs onboard diagnostics of the entire system – in the event that a problem is detected an error message (below) is displayed on the dashboard. As well as storing diagnostic results, the ECU also stores data such as driving speed, acceleration (lateral and longitudinal), wheel speeds and level of braking. This information can be accessed via an SD2 machine which makes resolving any issues fairly easy for someone with the correct equipment.
Finally, the damper ECU also provides information to the Motronics in the form of vibration data collected from the accelerometers. This data allows the Motronics to differentiate between engine speed anomalies caused by road vibrations and those caused by genuine misfires. In the event road surface vibration influences the engine speed the error code P1606 or P1607 (road roughness signal) is stored in the Motronic and the “Check Engine” light is displayed. Continued P1606/7 errors can be caused by faulty accelerometers.
Other posts in this category: Suspension