Signals from External Sensors: Notes

The ICM control unit imports the following signals that are important for dynamic driving systems from external sources:

• Wheel speeds, four signals transmitted via FlexRay from DSC.
• Ride-level heights, four signals, wired directly to ICM control unit.
• Steering wheel angle, transmitted via FlexRay from steering column switch cluster.
• Position of actuators for Active Steering and rear axle slip angle control, transmitted via FlexRay.

The ICM calculates the actual speed  at which the vehicle moves along the driving axis on the road based on the four wheel-speed signals.  If dynamic driving systems intervene and affect the wheel speeds, this is taken into account in the calculation. The status of the ABS control (for example) is also imported in this instance.

The road speed thus determined for the first time in the F01/F02 is now used as the reference for practically all systems in the vehicle. This means that a multiple calculation no longer needs to be performed in many other control units.

The ICM control unit also derives the following information from the wheel-speed signals:

• Distance  travelled
• Wheel tolerance check:  The marginal differences in wheel speeds (e. g. due to differences in tire diameter) are identified and adjusted by the ICM.
• Snow chain detection:  If snow chains are fitted, the driver can enter this information manually via the Central Information Display. The wheel speeds are also used by the HSR control unit to automatically determine whether snow chains are mounted on the rear wheels. The result of this identification is transmitted to the ICM control unit via the FlexRay.

Although, from a theoretical standpoint, it may be more appropriate to assign the ride-height sensors  to the Vertical Dynamics Management, the four ride-height sensors are directly connected to the ICM control unit.

The ICM control unit imports the analog voltage signals of the ride-height sensors. These are converted into the actual ride-level heights in millimeters. To perform this conversion, the ICM control unit must be able to map the voltage signals it receives to reference values as otherwise it will not be able to determine the actual ride-level heights. These reference values are determined by means of a synchronization procedure.

The harmonized ride-level heights are made available by the ICM control unit as bus signals. They are imported from:

• the Vertical Dynamics Management system for the Vertical Dynamics Control and Active Roll Stabilization and also from the
• footwell module for the headlight-range adjustment function.

The ride-level heights are not transmitted as bus signals for the purposes of electronic ride-height control (EHC). Instead, an additional direct line connection exists between the ride-height sensors of the rear axle and the EHC control unit.

The ICM control unit determines the resulting steering lock angle of the front wheels based on the steering wheel angle and location of the Active Steering actuator motor.

As the rear axle can also be steered, a reliable conclusion regarding the driving dynamics cannot be obtained purely on the basis of the steering angle of the front wheels. This is why the ICM control unit also takes the steering angle of the rear wheels into account. The effective steering angle  (of the front and rear wheels) is then determined using both steering angles.

This is a purely theoretical computing value that indicates the steering lock of the vehicle's front wheels that would be required to achieve the same vehicle motion if the rear axle could not be steered. The easiest way for all systems in the vehicle to evaluate the data on the steering wheel movement is to use this effective steering angle.