GF46.35-P-0001CE Electric Power Steering (ES), Function
GF46.35-P-0001CE Electric Power Steering (ES), Function
MODEL 204.0 /2 with ENGINE 274.9
MODEL 204.9
A1 Instrument cluster
A1p13 Multifunction display
A91b1 Electric power steering torque sensor
A91m1 Electric power steering actuator motor
L6/1 Left front axle speed sensor
L6/2 Right front axle speed sensor
L6/3 Left rear axle speed sensor
L6/4 Right rear axle speed sensor
N3/9 CDI control unit (with diesel engine)
N3/10 ME-SFI [ME] control unit (with gasoline engine)
N10/1 Front SAM control unit with fuse and relay module
N30/4 Electronic Stability Program control unit
N49 Steering angle sensor
N62 Parking system control unit (with code (230) Exclusive Parking Assist)
N68 Electrical power steering control unit
N73 Electronic ignition switch control unit
N80 Steering column module control unit
X11/4 Diagnostic connector
CAN B Interior CAN
CAN D Diagnostic CAN
CAN E Chassis CAN
1 Rack-and-pinion steering gear
2 Belt drive housing
A91b1 Electric power steering torque sensor
A91m1 Electric power steering actuator motor
N68 Electrical power steering control unit
Function requirements, general
^ Circuit 15 ON
The "circuit 15 ON" status is sent by the electronic ignition lock control unit via the chassis CAN to the electrical power steering control unit. The engine rpm is sent to the electrical power steering control unit over the chassis CAN by the ME-SFI [ME] control unit (with gasoline engine) or the CDI control unit (with diesel engine).
Electric power steering (ES), general
The ES consists of the rack-and-pinion steering gear, the electric power steering torque sensor, the electric power steering actuator motor and the electrical power steering control unit.
The ES performs stepless, speed-dependent regulation of the power steering.
The advantages compared to hydraulic power steering are:
- Improved steering feel
- Fuel saving
- Hydraulic fluid not required
- Compact design
- Speed-dependent steering servo
- Steering return is assisted
- Diagnosis capability
The ES comprises the following subfunctions:
^ Power steering function sequence
^ Steering assistance function sequence
^ Function sequence for reducing holding torque
^ Function sequence for limp-home mode
^ Display on instrument cluster function sequence
Power steering function sequence
The electrical power steering control unit requires the following information to calculate the steering power assistance required:
- Current steering moment, from electric power steering torque sensor
- Current wheel speeds, determined by the left front axle rpm sensor, right front axle rpm sensor, left rear axle rpm sensor and right rear axle rpm sensor and made available on the chassis CAN by the Electronic Stability Program control unit
- Steering angle and steering speed, from the steering angle sensor in the steering column tube module control unit via the chassis CAN
- Current engine speed greater than 400 rpm, from ME-SFI control unit (with gasoline engine) or CDI control unit (with diesel engine) via chassis CAN
The electric power steering control unit uses this information to calculate the steering force support to be applied from the stored characteristics map and activates the electric power steering actuator motor accordingly.
The direction of rotation of the electric power steering actuator motor depends on the direction of movement of the steering wheel.
The steering force assistance is transmitted from the electric power steering actuator motor to the rack-and-pinion steering gear, thereby supporting the steering moment applied by the driver.
When the vehicle is at a standstill, no steering force support is available if the engine and ignition are switched off If the vehicle is switched off using the ECO start/stop function, reduced steering force assistance is available when the vehicle is stationary. The steering force support is deactivated after the ignition is switched off. Steering assistance is active if the vehicle is maneuvered when the engine is off and the ignition is switched on.
Steering assistance function sequence
The steering assistance function helps the driver to achieve an optimum steering reaction in critical driving situations.
Steering assistance is provided with the aid of the electric power steering control unit and Electronic Stability Program control unit.
The following functions are performed here:
- Driver support through countersteering for a vehicle with oversteer
- Driver support for braking on varying road surfaces
The current vehicle status is sensed by the Electronic Stability Program control unit.
If necessary, the message "Steering assistance torque request" is transmitted via chassis CAN to the electrical power steering control unit, which actuates the electric power steering actuator motor accordingly.
During a parking operation, the parking system control unit (with code (230) Exclusive Parking Assist) sends the following signals to the electrical power steering control unit:
- Current status of parking system control unit
- Vehicle stop signal, at which the vehicle stops at a maneuver point during the parking process
- Requested toothed rack position
The following signals are sent by the electrical power steering control unit to the parking system control unit (with code (230) Exclusive Parking Assist):
- Current status of the electrical power steering control unit
Function sequence for reducing holding torque
If a holding torque is applied by the driver when driving the vehicle straight ahead, e.g. for a crosswind or on a road surface inclined on one side, the electrical power steering control unit detects it.
The applied holding torque is partially compensated for by the electric power steering.
In order to prevent incorrect compensation (e.g. on freeway bends with a large radius), the electrical power steering control unit receives the rotational speed (vehicle speed about the vertical axis) as well as the lateral acceleration of the vehicle from the Electronic Stability Program control unit via the chassis CAN.
The reduction of the vehicle's holding torque depends on the speed.
Function sequence for limp-home mode
When the ES is switched on (via "circuit 15 ON"), the electric power steering control unit carries out a self-test. If a fault is detected, the steering force assistance is not switched on.
The vehicle can be steered with increased force of the hand.
During driving operation, the electrical power steering control unit checks the signals from the electric power steering torque sensor.
If these signals are outside the defined upper or lower limit, the ES is switched off by the electrical power steering control unit.
The vehicle can be steered with increased force of the hand.
Display on instrument cluster function sequence
The electrical power steering control unit control unit transmits the request for a warning message via chassis CAN to the instrument cluster.
The instrument cluster's multifunction display then shows the warning message "Power steering defective! Visit workshop!".
