Continuously Controlled Chassis Concept (Four-C)

The suspension module (SUM) controls the Four-C function.

The suspension module (SUM) regulates and optimizes the damping forces of the vehicle so that the compromise between ride comfort, road grip and steering characteristics is considerably better than with traditional shock absorbers.

By measuring the vertical movement of the wheels and the car body and correlating this with the information received via the Controller area network (CAN), the suspension module (SUM) calculates the required damping force.

The suspension module (SUM) constantly assesses the driving style by monitoring the brake pressure and steering wheel angle. The suspension module (SUM) receives information via the Control area network (CAN) about:

• the torque desired by the driver from the engine control module (ECM)
• the brake pressure signal from the brake control module (BCM)
• the steering wheel angle signal from the steering wheel angle sensor module (SAS).

The Four-C function minimizes the damping forces in relation to the actual speed and driving situation The suspension module (SUM) regulates each shock absorber individually. For example when driving straight ahead, there is so called "Skyhook control". This can be likened to the car body being mounted to a damper connected to the sky. The driver experiences this as a feeling that the car is floating over the road. When cornering, the system stiffens the suspension (by employing considerable damping) to give a sporty feeling. If there is sudden under- or oversteer, the damping is reduced to optimize grip. Optimal grip is always the priority of the system, even during heavy braking or when the ABS system engages.

On uneven surfaces, such as unmade roads, the position of the shock absorbers changes rapidly. The suspension is then controlled by the Four-C function to ensure that the pressure of the wheels on the road surface is as even as possible to maintain contact with the road in all situations.

The damping forces are controlled individually for all four wheels and are updated 500 times per second.

Information about the rear chassis height is transmitted from the suspension module (SUM) to the central electronic module (CEM) via the control area network (CAN). This information is used by the Gas Discharge Lamp (GDL) system.

The following applies to vehicles with R line: 

• The intensity of the lighting in the keypad is manually controlled via the rheostat. The signal is transmitted from the light switch module (LSM) to the suspension module (SUM) via the control area network (CAN) and then on to the keypad via a directly connected cable
• The intensity of the lighting in the keypad on the dashboard is also automatically regulated via a signal from the twilight sensor on the climate control module (CCM). The signal is transmitted from the climate control module (CCM) to the suspension module (SUM) via the control area network (CAN) and then on to the keypad via a directly connected cable.

The following applies to vehicles without R line: 

• The intensity of the lighting in the switch is controlled by the climate control module (CCM).

If the Four-C function is not working, the shock absorbers act like standard passive shock absorbers. In the event of a fault in the system, a text message is displayed in the driver information module (DIM) indicating that a service is required.

The suspension module (SUM) transmits a signal via the control area network (CAN) to the central electronic module (CEM) indicating that it is active. This is so that a diagnostic trouble code (DTC) can be stored in the central electronic module (CEM) if the suspension module (SUM) does not respond on the control area network (CAN).

The Four-C function is not active when the vehicle is stationary. The function is activated automatically when the vehicle speed exceeds 1 km/h.