Eps Control Unit
The EPS control unit (1) processes the following signals:
- from the torque sensor (steering torque and rotational direction)
- from odometer signal sensor (vehicle speed)
- the engine speed from the engine control unit (as an additional reference)
- EPS control unit
- X51: Electric motor
- X50: Battery positive, ground
- X60: Ter. 15, odometer signal, torque signal, diagnostic plug, EPS telltale,
- X52: Torque sensor
The control unit allocates an appropriate assistance torque to each steering torque event, which the electric motor then transfers to the torsion steering column.
The speed-dependent steering assistance provides a high degree of steering assistance for parking the vehicle and little assistance at high speeds. At a standstill, with ignition ON and the engine not running, the EPS is deactivated to prevent the battery discharging.
7.1.5 Eps Control Unit
Safety Functions
The EPS control unit is capable of recognising its own malfunctions. Malfunctions from connected units, such as sensors and motors, or cable fractures and short circuits are likewise recognised.
In the event of a malfunction, the control unit deactivates via a safety relay and via the power electronics. The deactivation function is designed in tandem to ensure safe deactivation, even if there is a malfunction in the final stage transistors or the relay.
Safety functions of the EPS control unit which lead to deactivation:
| Components | Cause of fault |
|---|---|
| Torque sensor | Incorrect connection, short circuit, cable fracture, malfunction |
| Odometer signal | Incorrect connection, short circuit, cable fracture, malfunction |
| Engine speed signal | Incorrect connection, short circuit, cable fracture, signal level incorrect |
| Electric motor | Incorrect connection, short circuit, coil short circuit |
| Control unit | CPU faulty, safety relay faulty |
Overload Protection
The control unit has an integrated overload protection. If the current to the electric motor exceeds a limit in a defined period of time, the current is reduced to a value that allows safe steering.
For example, this is the case when the steering wheel is turned to full lock at a standstill. This precaution both protects against thermal overload and prevents the battery from discharging.