Steering Column: Description and Operation
Steering Column Memory (LSM):
Functional Description:
The steering column memory (LSM) represents an extension of the seat- mirror memory. The position of the steering wheel (inclination and longitudinal adjustment) can be set in an optimum driving position by means of two electric motors. The switch mounted on the left-hand side of the steering column is used for this purpose. The control unit activates the motors via a relay corresponding to the required adjustment direction. A set steering column position can be stored by the LSM control unit. The voltage values of the feedback potentiometers serve as data for the control unit indicating the relevant status of the steering column. The corresponding voltage is stored fail-safe in an EEPROM. A certain steering column position can be programmed and called up via the keypad (three position keys, one memory key) of the SM/SPM system. The LSM system also includes an entrance/exit function.
System components:
- Electrically adjustable steering column with two electric motors for inclination and longitudinal adjustment.
- Two feedback potentiometers flanged onto the electric motors
- Steering column switch for operation
- Wire harness LSM
Note: The steering column memory control unit is only installed in conjunction with the seat/mirror memory. This steering column memory function is not possible in vehicles without a seat/mirror memory, only manual adjustment is possible in this case. A relay module (without self-diagnosis capabilities!) is installed instead of the LSM control unit.
Location of the control Unit:
In the E31, the control unit is mounted above the heater/air conditioning unit. The control unit is accessible after removing the heater outlet in the centre console or the MID and the radio.
Entrance/Exit Function:
To provide convenient entrance and exit for the driver, at the end of a trip, the steering column is moved to the topmost inclination position (= entrance/exit position). The drive position is reassumed when the vehicle is used once again.
In order to detect whether the driver wishes to enter/exit the vehicle (en- try/exit position) or whether he wishes to drive (drive position), the control It nit uses the following inputs for evaluation: Driver's door, hand brake, terminal R, terminal 15. Certain signals must be applied at these inputs in order to inform the control unit whether the steering column is in the drive position or entry/exit position. The table below shows the 10 combinations relevant for
the control unit:
Definition of Potentiometer Voltages:
To ensure perfect operation of the LSM, the following potentiometer voltage progressions are defined for the adjustment procedure:
During positive direction of movement of the drives, the voltages of the corresponding feedback potentiometer must increase and decrease in negative direction of movement. Positive direction of movement is defined as: Inclination adjustment up, longitudinal adjustment towards the driver.
Adjustment procedure:
The effective adjustment range (manual and memory adjustment) is restricted in order to relieve the load on the mechanical limit stops of the steering column. The drive motors are switched off before reaching the mechanical limits.
The mechanical limits are determined by the control unit in an adjustment procedure. Call: Via diagnosis request or during initial operation of the system.
Procedure: After a delay period of approx. 6 seconds, the following directions of movement are each activated for 6 seconds one after the other.
1. Inclination down
2. Longitudinal adjustment forward (towards driver)
3. Inclination up
4. Inclination down
5. Longitudinal adjustment back
On completion of the adjustment procedure, the steering column stops in the "zero position", the assumed position is stored as the zero position in the EEPROM of the control unit. The adjustment procedure has a duration of approx. 50 seconds.