Control and Adjustment of Steering: Notes

The Servotronic  function in the F01/F02 is included in the basic steering and Integral Active Steering (option). This speed-dependent power steering assistance function is implemented by the Servotronic valve at the steering gear.

The Servotronic valve is always activated from the ICM control unit irrespective of the equipment specification. It follows that the ICM control unit also incorporates the logic of the Servotronic function.

Again, regardless of the options fitted, the steering system also contains a proportional valve that is also controlled by the ICM control unit. The volumetric flow in the steering hydraulic circuit can be adjusted electronically assisted by this valve which is why it is also referred to as an "electronic volumetric flow adjustment" valve, or EVV valve for short.

This valve is also controlled by the ICM control unit. The volumetric flow generated by the power steering pump is distributed between a circuit to the steering valve and a bypass circuit according to the level of power steering assistance required. This distribution is infinitely variable. The less power steering assistance is required, the more hydraulic oil is diverted to the bypass circuit. Because the hydraulic oil in the bypass circuit has no task to perform, this means that the power steering pump consumes less power. In this way, the EVV valve contributes to reducing  fuel consumption and CO ₂  emissions. 

Fig 1: Input/Output Signal Diagram - Control Of Steering By ICM

Courtesy of BMW OF NORTH AMERICA, INC.