Principle of Operation
EPS controls servo assistance for steering. In addition to the measuring the driver's steering torque, the EPS Control Module also monitors further inputs such as
- Vehicle speed
- Steering angle velocity
- Steering angle
- Dynamic Driving Control (Sport) button
- Internal system temperature
The EPS calculates an assistance setpoint. The electric motor is activated via the integrated power electronics and the torque is transmitted through the worm gear to the driven gear (attached to the steering column output shaft).
The Servotronic function (vehicle speed dependent steering assistance) is also integrated. The corresponding assistance and damping characteristics are stored in the EPS Control Module. The required assistance torque is gradually increased when the engine is started and reduced (with a delay) when the engine is switched off.
General Information
The mass balance spring (arrow) should be disconnected when work is performed on the upper steering column.
| CAUTION | The mass balance spring is under extreme tension. Be careful not to bend the spring tab mounting retainers. |
Note. Only the ignition starter switch, the lock cylinder and the Steering Angle Sensor (LWS) can be replaced as separate components on the upper steering column.
Scheme 52
If slow or sudden inflation pressure loss occurs in a RFT, it is still mobile because of the additional high temperature rubber reinforcements that strengthen the side wall.
These reinforcements prevent side wall damage when the tire is deflated and also provides support during extreme loads (even when negotiating curves). In addition, the special RFT wheel (rim) grips the tire for sufficient steering, braking and accelerating power.
The Tire Deflation Warning (RPA) function is performed by the DSC Control Module. When a tire loses air pressure, the radius and dynamic rolling circumference is reduced. This increases the rotational speed as compared to the other tires on the vehicle. The RPA function measures the number of wheel revolutions from the four DSC wheel speed sensors and performs a diagonal comparison for a speed average.
If there is a difference, this is recognized as pressure loss. The RPA can inform the driver after a short drive, approx. 1-3 minutes, from a vehicle speed > 10 mph via an indicator light (red) in the Instrument Cluster.
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Initialization/Operation
The system must be initialized when the tire inflation pressures are changed or when the wheels/tires are replaced.
The RPA switch (1) in the center console switching center must be pressed to start initialization (as follows on the next page).
Scheme 54
With KL 15 "on", press the RPA switch until the RPA indicator light in the Instrument Cluster illuminates in "yellow".
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After a short drive (approx. 1-3 minutes), from a vehicle speed > 10 mph, the system learns the new wheel speed sensor reference values and the RPA indicator light (yellow) goes out.
When an inflation pressure loss is determined, the RPA indicator light illuminates in "red". The driver is informed of a RPA system failure by the "yellow" illuminated RPA indicator light.