P46.35-2114-79
Illustration shows MODEL 447.8 |
A1/1 | Instrument cluster (KI) control unit | N30/4 | Electronic Stability Program (ESP) control unit | N80 | Steering column tube module (MRM) control unit | ||
L6/1 | Left front rpm sensor | N62 | PARKTRONIC control unit (PTS) (with CODE EZ7 (Active Parking Assist)) | N93/4 | Gateway for user interface CAN | ||
L6/2 | Right front rpm sensor | N68 | Electrical power steering (ES) control unit | X11 | Diagnostic connector | ||
L6/3 | Left rear rpm sensor | N68b1 | Electric power steering torque sensor | CAN D | Diagnostic CAN | ||
L6/4 | Right rear rpm sensor | N68m1 | Electric power steering actuator motor | CAN E | Chassis CAN | ||
N3/33 | CDI control unit | N73 | Electronic ignition lock (EZS) control unit | CAN HMI | User interface CAN |
S46.35-0006-79
Shown on model 447.6/7 |
A1/1 | Instrument cluster (KI) control unit | N3/34 | ME-SFI control unit (engine 274) | N68m1 | Electric power steering actuator motor | ||
L6/1 | Left front rpm sensor | N3/36 | CDI control unit (engine 622) | N73 | Electronic ignition lock (EZS) control unit | ||
L6/2 | Right front rpm sensor | N30/4 | Electronic Stability Program (ESP) control unit | N80 | Steering column tube module (MRM) control unit | ||
L6/3 | Left rear rpm sensor | N62 | PARKTRONIC control unit (PTS) (with CODE EZ7 (Active Parking Assist)) | X11 | Diagnostic connector | ||
L6/4 | Right rear rpm sensor | N68 | Electrical power steering (ES) control unit | CAN D | Diagnostic CAN | ||
N3/33 | CDI control unit (engine 651) | N68b1 | Electric power steering torque sensor | CAN E | Chassis CAN |
Function requirements, general
Circuit 15 ON
The circuit 15 ON status is sent by the electronic ignition lock (EIS) control unit (N73) via the chassis CAN (CAN E) to the electric power steering (ES) control unit (N68). The engine speed is sent to the electric power steering (ES) control unit (N68) via the chassis CAN (CAN E) by the CDI control unit (N3/33) (engine 651) or by the ME-SFI control unit (N3/34) (engine 274) or by the CDI control unit (N3/36) (engine 622).
Electric power steering (ES), general
The electric power steering (ES) consists of the rack-and-pinion steering gear, the electric power steering torque sensor (N68b1), the electric power steering actuator motor (N68m1) and the electric power steering (ES) control unit (N68). The ES performs continuously variable, 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 power assistance
Steering return is assisted
Diagnosis capability
System diagnosis takes place via the chassis CAN (CAN E), the electronic ignition lock (EIS) control unit (N73), the diagnostic CAN (CAN D) and the diagnostic connector (X11) using Xentry Diagnostics.
The electric power steering (ES) comprises the following subfunctions:
Function sequence for electric power steering (ES)
Function sequence for reducing holding torque
Function sequence for limp-home mode
Function sequence for display in instrument cluster (IC) control unit (A1/1)
Function sequence for electric power steering (ES)
The electric power steering (ES) control unit (N68) requires the following information to calculate the steering power assistance required:
Current steering torque, from electric power steering torque sensor (N68b1)
Current wheel speeds determined by the left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3) and right rear rpm sensor (L6/4) and made available by the Electronic Stability Program (ESP) control unit (N30/4) via the chassis CAN (CAN E)
Steering wheel angle and steering angle rate of change, via the chassis CAN (CAN E) from the steering column tube module control unit (N80)
Current engine speed > 400 rpm, via the chassis CAN (CAN E) from the CDI control unit (N3/33) (engine 651) or from the ME-SFI control unit (N3/34) (engine 274) or from the CDI control unit (N3/36) (engine 622)
The electric power steering (ES) control unit (N68) uses this information to calculate the steering assistance to be provided by the electric power steering (ES) from the stored characteristics map and activates the electric power steering actuator motor (N68m1) accordingly. The direction of rotation of the electric power steering actuator motor (N68m1) depends on the direction of movement of the steering wheel. The assistance provided by the electric power steering (ES) is transmitted from the electric power steering actuator motor (N68m1) to the rack-and-pinion steering gear, thereby supporting the steering torque applied by the driver.
When the vehicle is at a standstill, no electric power steering (ES) is available if the engine and ignition are switched off. With the ECO start/stop function (with code MJ8 (ECO start/stop function)): When the vehicle is at a standstill, reduced electric power steering (ES) is available if the engine was switched off via the ECO start/stop function. The electric power steering (ES) is deactivated after the ignition is switched off. Power steering is active if the vehicle is maneuvered when the engine is off and the ignition is switched on.
During parking space entry, the PARKTRONIC (PTS) control unit (N62) (with code EZ7 (Active Parking Assist)) sends the following signals via the chassis CAN (CAN E) to the electric power steering (ES) control unit (N68):
Status of PARKTRONIC (PTS) control unit (N62)
Vehicle stop signal, at which the vehicle stops at a maneuver point during the parking process
Requested toothed rack position
Function sequence for reducing holding torque
If a holding torque is applied by the driver when driving the vehicle straight ahead, e.g. in a crosswind or on a road surface inclined on one side, this is detected by the electrical power steering (ES) control unit (N68). The applied holding torque is partially compensated for by the electric power steering (ES).
To rule out incorrect compensation (e.g. highway bend with large radius), the electric power steering (ES) control unit (N68) receives the turn rate (vehicle speed about the vertical axis) and the vehicle's lateral acceleration from the Electronic Stability Program (ESP) control unit (N30/4) via the chassis CAN (CAN E). The reduction of the vehicle's holding torque depends on the speed.
Function sequence for limp-home mode
When the electric power steering (ES) is switched on (via circuit 15 ON), the electric power steering (ES) control unit (N68) performs a self-test. If a fault is detected, the electric power steering (ES) is not switched on. The vehicle can be steered with increased force of the hand.
During driving operation, the electric power steering (EPS) control unit (N68) checks the signals from the electric power steering torque sensor (N68b1). If these signals are outside the defined upper or lower limit, the electric power steering (ES) is switched off by the electric power steering (ES) control unit (N68). The vehicle can be steered with increased force of the hand.
Function sequence for display in instrument cluster (IC) control unit (A1/1)
Model 447.6/7 , model 448.7
The electric power steering (ES) control unit (N68) sends the request for a warning message via the chassis CAN (CAN E) to the instrument cluster (IC) control unit (A1/1)
Model 447.8 , model 448.8
The electric power steering (ES) control unit (N68) sends the request for a warning message via the chassis CAN (CAN E) and user interface CAN (CAN HMI) with the interface for the gateway for user interface CAN (N93/4), to the instrument cluster (IC) control unit (A1/1)
In the instrument cluster (IC) control unit (A1/1), the warning message "Power steering defective! Service Required!" is then displayed.
Referenced documents
- gf4635s9997tra Overview of system components of electric power steering (ES)