Electrical power steering (ES) driving mode, function

P46.35-2007-06

A91 Electromechanical control unit (ES)

A91b1 Electrical power steering (ES) torque sensor

A91m1 Electrical power steering (ES) actuator motor

N68 Electrical power steering (ES) control unit

Function requirements:

 Circuit 15 ON

 Engine speed > 300 rpm

A high power steering assistance is desired at low vehicle speeds and when the vehicle is stationary. By contrast, power steering assistance is not desired at high vehicle speeds. For rapid steering maneuvers specific power steering assistance can improve vehicle dynamics.

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The electrical power steering (ES) control unit (N68) requires the following input signals to calculate the power steering assistance required:

 The steering torque currently applied from the electrical power steering (ES) torque sensor (A91b1)

 The current wheel speeds from the ESP and BAS control unit (N47-5) via the Controller Area Network bus class C (engine compartment) (CAN-C)

 The steering angle and steering speed from the steering angle sensor (N49) in the steering column module (N80) via the CAN C

 The current engine speed from the ME-SFI [ME] control unit (N3/10) or CDI control unit (N3/9) via the CAN C

 The current rotor position of the electrical power steering (ES) actuator motor (A91m1) from the motor position sensor in the electromechanical control unit (ES) (A91)

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When the driver makes a steering movement, the electrical power steering (ES) control unit (N68) calculates the current and rotation direction to be applied to the electrical power steering (ES) actuator motor (A91m1) based on the performance map using the input signals. The electrical power steering (ES) actuator motor (A91m1) is energized accordingly. The electrical power steering (ES) actuator motor (A91m1) actively intervenes in the steering operation via a worm gear. A current-recording resistance in the electrical power steering (ES) control unit (N68) checks the actual current.

 The maximum power steering assistance is required when the vehicle is stationary. As the vehicle speed increases the power steering force decreases continuously. During rapid steering maneuvers and at high speeds power steering assistance can take place depending on all input signals.