ICM: Integrated chassis management
The ICM control unit serves as a central signal provisioning point and distributes the signals created in the vehicle. In addition to the dynamic handling characteristic elements such as longitudinal acceleration, lateral acceleration and yaw rate, a driving speed is created as reference. Relevant wheel speeds supplied by the DSC are used to do this. Taking into account the different kinematic relationships, different steering angles are calculated from the absolute rack position calculated by the EPS. These include:
- Steering angle of steering wheel
- Steering angle on front axle
- Absolute steering angle
All deviations are ironed out before output signals are sent. Suitable monitoring systems are in place to check that all output signals are correct. For example, the steering angles are checked for plausibility against a steering angle calculated from the yaw rate.
Additional functions are integrated in the ICM, whereby the control unit is responsible for data preparation and calculations. The EPS serves merely as the actuator for executing the control variable.
Two examples of this are outlined in brief below:
Limit range feedback:
This ICM function dramatically improves steering within the limit range. The objective is to make the positive characteristics of hydraulically assisted steering movements available for EPS as well. The reason for this is that the steering feedback during oversteer and untersteer is suppressed by the increased friction and inertia in the EPS. In addition, the increased friction makes active feedback a necessity, which leads to even poorer feedback within the limit range.
During untersteer, the steering servo assist, feedback and damping action are reduced in accordance with the reduced self-aligning torque of an oversteered front axle. This is perceptible to the driver as a "softening" of the steering in the same manner as with conventional steering. During oversteer, the front axle is subjected to an additional torque in the stabilizing direction applied by the EPS unit. This action is supported by an additional reduction in feedback and damping action. An oversteer intervention makes steering into the oversteer lighter and the vehicle stabilizes itself in a driving situation that opposes the oversteer forces.
Predicting steering power:
This function uses physical driving variables to analyze the current driving situation. Driving situations using intensive steering power are thereby identified in advance. Energy management is informed of the expected steering power demand.