Actuator motors with "ripple-counter" system

General

On the E38 seat/steering column memory (SM/LSM), the actuator motors for seat and steering column are no longer switched on and off by means of power transistors or relays installed in the control unit. Activation takes place by means of a control module (ripple-count module or RC module) mounted on the motor.

Each actuator motor is equipped with an RC module. The motor and module form one component.

This module contains the electronic circuitry to drive the motors as well as the electronic circuitry to record the motor speed and motor position.Each RC module can, therefore switch on "its" motor independently and move to a specified position.

Link between control unit SM/LSM and RC module

The relevant RC module is connected to the control unit SM/LSM by means of a simple data link. Following information is transferred via this data link:

• From control unit SM/LSM to RC module: Required direction and required speed.
  
• From RC module to control unit SM/LSM: Position reached; information whether motor stationary or running; information concerning the status of the output stage (short-circuit yes of no).
  

Activation of actuator motors with RC module

Following functions serve the purpose of activating the actuator motors:

• Switching on and off the actuator motors with power transistors contained in the RC module. Relays rendered unnecessary.
  
• Speed control of actuator motors by driving the relevant actuator motor with pulse width-modified pulses (pulse width modulation).
  
• Short-circuit and overload protection integrated in RC module.
  
• Limiting the start-up current by uniform "start-up" of the switch-on pulse width.
  
• Automatic cutout of motor when drive operation completed.
  

Acquisition of motor position with RC module

The position of the motor shaft is achieved by counting the "current ripple" (current changes or magnetic field fluctuations of a DC motor) or by counting pulses produced by a pulse generator. Feedback potentiometer required up until now are no longer needed.