Control and Modulation of Steering

Both the basic steering system and the optional Integrated Active Steering on the F01/F02 incorporate the Servotronic  function. That speed-sensitive power assistance function is effected by way of the Servotronic valve on the steering gear.

The Servotronic valve is always controlled by the ICM control unit regardless of the equipment options fitted. Accordingly, the Servotronic function algorithm is stored on the ICM control unit.

Similarly regardless of equipment options, the steering system also always incorporates a proportional control valve which is controlled by the ICM control unit. With the aid of that valve, the power steering pump's volumetric flow rate can be electronically adjusted. For that reason it is also referred to as the "electronic volumetric flow control"  valve (EVV valve).

That valve too is controlled by the ICM control unit. Depending on the degree of power assistance demanded at the time, the volumetric flow rate delivered by the power steering pump is split between the steering valve and a bypass circuit. The ratio of that split can be infinitely varied. The less power assistance is required, the more hydraulic fluid is diverted into the bypass circuit. As the hydraulic fluid does not have to do any work in the bypass circuit, less power is required to drive the power steering pump. Consequently, the proportional control valve helps to reduce  fuel consumption and CO ₂  emissions. 

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

Courtesy of BMW OF NORTH AMERICA, INC.