GF46.35-P-0002MCU Electric Steering, Function
GF46.35-P-0002MCU Electric Steering, Function
With CODE (V26) Power steering, EPS (FFO)
1 Vehicle speed
2 Steering torque
3 Request, steering wheel reset
4 Request, steering power assistance
5 Steering angle, steering speed
6 Engine speed
7 Warning lamp request
A1 Instrument cluster
A1e18 Electric steering indicator lamp
B23 Power steering torque sensor
M19 Power steering motor
N3/10 ME-SFI [ME] control unit
N47-5 ESP control unit
N49 Steering angle sensor
N68 Steering assist control unit
CAN Controller Area Network (data bus/CAN bus) (CAN)
General
The electric steering is based on a conventional rack and pinion steering gear which is assisted by the power steering motor. The steering power assistance takes place steplessly and speed-dependent.
Functions
^ Power steering assistance
^ Steering reset assistance
^ "active center feeling" function
Function requirements
^ Circuit 15 On
^ Engine speed > 500 rpm
^ No overvoltage or undervoltage
The steering assist control unit requires the following information to calculate the steering power assistance:
^ Steering torque from torque sensor
^ Vehicle speed via CAN from ESP control unit
^ Steering angle and steering speed via CAN from steering angle sensor
^ Engine speed via CAN from motor electronics control unit
Steering power assistance
By turning the steering wheel a torque on the control rod is produced by which is recorded by the torque sensor and passed on to the power steering control unit. By means of the steering torque determined, the steering angle and vehicle speed the assistance torque is established by the steering assist control unit and the power steering motor actuated accordingly. This assists the driver's steering torque at the drive pinion of the rack-and-pinion steering via a worm gear. The direction of rotation of the power steering motor depends on the direction of motion of the steering wheel.
The steering power assistance is at a maximum at low speeds and when the vehicle is stationary and decreases as the vehicle speed increases.
Once the engine is switched off and the vehicle stops the steering power assistance is deactivated in steps after approx. 3 s.
Steering reset assistance
The steering reset is introduced due to the shaft kinematics (after-run). As a result the power steering motor is excited passively and operates as a generator. On the basis of this signal the power steering control unit detects the assistance requirement and assists the return force by the corresponding energizing of the power steering motor.
"active center feeling" function
When the steering wheel center position is detected and in the absence of steering movements, the power steering motor is energized by the power steering control unit so that an adequate torque is produced in order to hold the steering in the center position.
As a result the driver has an improved "feel" for the center position of the steering.
Limp-home function
The steering assist control unit permanently checks all input signals for plausibility. In the event of a faulty component the power steering assistance is switched off, a fault is stored in the power steering control unit and the electric steering indicator lamp in the instrument cluster is actuated.
Actuation takes place by the power steering control unit via CAN. The steering then continues to function as a conventional rack-and-pinion steering.
