Vehicle Dynamics Control (VDC)
- VDC prevents the vehicle from breaking away when oversteering or understeering.
- It ensures that the vehicle does not deviate from the course specified by the driver (within physical limits).
- Brake forces are produced selectively at the individual wheels to correct any deviations.
- Furthermore, reduction of the drive torque takes place in order to increase driving stability.
- The electronic stability program control unit processes the following measured quantities to determine the vehicle behavior:
- Yaw velocity
- Steering angle
- Brake pressure
- Engine torque
- Transmission stage
- Lateral acceleration
- Wheel speed
- Differentiation is made between the following intervention types:
Intervention in the case of oversteer
- If the vehicle begins to oversteer, brake pressure is built up at the outer front wheel.
- The resulting reduction in lateral force at the outer front wheel generates a yawing moment which counteracts the tendency of the vehicle to rotate inward.
- The vehicle speed decreases as a result of the brake force at the front wheel, which also enhances stability.
Intervention in the case of understeer
- If the vehicle understeers, the maximum possible lateral force at the front axle has been exceeded.
- In other words, the vehicle pushes via the front axle to the outer edge of the curve.
- The resulting instability is counteracted by means of a reduction in drive torque and the following brake interventions at up to 3 wheels:
- Brake pressure buildup at inside rear wheel (stage 1)
- Stage 1 and in addition brake pressure buildup at outside rear wheel (stage 2)
- Stage 2 and in addition brake pressure buildup at inside front wheel (stage 3)
- Depending on the brake force, a torque is generated which causes the vehicle to rotate inward with a simultaneous reduction in speed.
- This has a considerable stabilizing effect. The electronic stability program control unit sends a signal to reduce the drive torque over the CAN communication to the ECM, which then reduces the engine power accordingly.
- A pending shift operation is suppressed for the duration of control intervention.
- To do so, the electronic stability program control unit sends a signal over the CAN communication to the ECM, which forwards the information over the CAN communication to the TCM. The latter control unit suppresses the shift operation.