Principle of Operation
Principle of Operation
EDC-K is a microprocessor controlled damper adjusting system. The system consists of mechanical, hydraulic and electrical/electronic subsystems. Acceleration sensors record the driving/road surface conditions and the control module receives the sensor frequency signals for evaluation. The sensor signals are compared with each other for plausibility. The control module logic activates the damper valves according to internal programmed maps to dampen body and wheel movement as needed.
The driver can use the Controller and Control Display menu to select between comfort and sports programs. The system is diagnosable with the DISplus. In the event of sensor faults, the system is switched to a "safe state" by supplying fixed power to the damper valves. In the event of a system failure (no power), the dampers are mechanically sprung to the firmest setting.
The EDC-K function is divided into 3 blocks:
- Control Module
- Sensors and program selection option
- Actuators - 4 electronically adjustable dampers
The input signals for the system are generated by:
In addition to the forces calculated in each measured movement, there are vertical, longitudinal, transversal, copy and tolerance control logic.
EDC-K Electronic System Overview
Vertical Dynamics Control
Vertical Dynamics Control responds to vertical (up/down) body movements based on wheel/body acceleration and speed. A distinction is made between a low frequency body vibration (approx. 1 Hz) and a high frequency wheel vibration (approx. 10 to 15 Hz). Because the body speed cannot be measured, a characteristic value is calculated from the acceleration signals. This value is adapted based on the vehicle speed, frequency ranges and road surfaces.
The higher frequency vibrations of the axle are calculated as the wheel dynamics value based on the wheel speed signal inputs. The value is determined from the irregularities of the wheel rotation when driving over bumps. This control operation takes place separately for both axles.
Longitudinal Dynamics Control
The Longitudinal Dynamics Control responds to acceleration and braking body movements (forward/backward). The vehicle speed signals are monitored by the control module: two direct wheel speed inputs from the DSC control module and three digital inputs from the PT-CAN Bus. Two of the signals on the PT-CAN Bus correspond to the 2 wheel speed signals from DSC and the third signal is the averaged vehicle speed.
The EDC-K control module assesses the plausibility of these signals. A Longitudinal Dynamics value is calculated from the wheel speed signal, which represents the level of acceleration or deceleration. The dampers are adjusted (on both axles) to the harder setting to counter act the longitudinal movement.
Transversal Dynamics Control
The Transversal Dynamics Control responds to transversal movement (dive and squat - front to back roll). This value is calculated from the steering angle sensor and the vehicle speed signals. The onset of "yaw" movement is detected very early from the steering angle sensor signal. A harder damper setting to support the vehicle as it enters a curve is activated at an early stage. The front and rear axles are separately controlled.
Copy Control
The Copy Control function responds to the compression and rebound of the body (encountering bounces on one side of the vehicle) while driving straight ahead. Through comfortable damper tuning, EDC-K responds to one sided unevenness due to the road surface. This prevents a side to side rolling motion while driving straight ahead.
Once vehicle "copying" is detected, a harder damping combination is applied to the front and rear axles. Detection is based on the evaluation of the right and left vertical acceleration signals from the front axle.
Tolerance Adaptation
The damper force is diminished as part of the operating time function. Diminishing damper forces are compensated by current (amperage) reductions which are calculated by the tolerance control. This also individually compensates for mechanical damper wear on each axle.
Control Strategy
All of the dampers are controlled simultaneously until a single damper control in particular is required. For stability reasons, the smallest desired output current of the four damper controls (hardest damper setting) is set.
Plausibility Monitoring and Safety Concept
The EDC-K inputs and outputs are checked for plausibility. Depending on the type of fault, restricted operation of the damper control system will occur while a high degree of safety and comfort is maintained.
The control display informs the driver when an EDC-K system fault has occurred. There are two different shutdown options in the event of faults.
- In partial operation, medium damping is set by a fixed current at the front and rear axle valves.
- When the entire system is shut down, the de-energized valves instantly switch (spring loaded) and remain in the "hard damping" setting.
In the event of system faults, the chassis and suspension is set to a safe condition that is acceptable to the driver The valves, sensors, electric circuits and EDC-K control module are fault monitored.