ELECTRIC POWER STEERING SYSTEM

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Outline

• A column-assist type electric power steering (EPS) has been adopted with a motor installed to the steering column to assist in the steering force.

• The EPS achieves smooth handling performance from low to high speed and excellent steering feel by the vehicle speed response control.

• The size and weight of the system have been reduced by integrating the EPS control module (CM) and the EPS motor.

• The automatic configuration function and the steering wheel angle neutral position auto-learning function have been adopted.

Purpose, Function

• The EPS system makes up for the steering force required when the driver operates the steering wheel using the EPS motor to reduce the load on the driver.

Construction

• The EPS consists of the following mechanisms.

― Manual steering mechanism:

Consists of the steering wheel, steering column, intermediate shaft, and steering gear and linkage.

― Electric assist mechanism:

Consists of the EPS motor and reduction gear.

― Control mechanism:

Consists of the EPS CM and torque sensor.

• The EPS CM communicates with the PCM, DSC HU/CM, start stop unit, SAS control module, and instrument cluster via CAN communication.

Part name

Functions

EPS CM

•  Calculates the optimum assist force based on the signals from the torque sensor, EPS motor, PCM, DSC HU/CM, and SAS control module, and outputs the EPS motor drive current.

•  After the vehicle begins moving, the system performs self-learning of the steering angle neutral position based on the signals from the DSC HU/CM and the SAS control module, and outputs it as a steering angle (estimated absolute steering angle) signal to CAN.

•  Outputs an power steering malfunction indication on/flash request signal and a power steering warning buzzer request signal to CAN when there is a malfunction in the EPS system.

PCM

•  Transmits a vehicle speed signal, engine speed signal, and i-stop condition signal to the EPS CM via CAN communication.

DSC HU/CM

•  Transmits a vehicle wheel speed signal to the EPS CM via CAN communication.

Start stop unit

•  Transmits the signal from the steering angle sensor to the EPS CM as a steering angle (absolute steering angle) signal via CAN communication.

SAS control module

•  Transmits the vehicle lateral-G (vehicle lateral acceleration speed) and yaw rate (vehicle turning angle speed) to the EPS CM via CAN communication.

Instrument cluster

•  Turns on/flashes the power steering malfunction indication based on the power steering malfunction indication on/flash request signal and power steering warning buzzer request signal output by the EPS CM, and activates the power steering warning buzzer to alert the driver that there is a malfunction the EPS system.

Part name	Functions
EPS CM	• Calculates the optimum assist force based on the signals from the torque sensor, EPS motor, PCM, DSC HU/CM, and SAS control module, and outputs the EPS motor drive current. • After the vehicle begins moving, the system performs self-learning of the steering angle neutral position based on the signals from the DSC HU/CM and the SAS control module, and outputs it as a steering angle (estimated absolute steering angle) signal to CAN. • Outputs an power steering malfunction indication on/flash request signal and a power steering warning buzzer request signal to CAN when there is a malfunction in the EPS system.
PCM	• Transmits a vehicle speed signal, engine speed signal, and i-stop condition signal to the EPS CM via CAN communication.
DSC HU/CM	• Transmits a vehicle wheel speed signal to the EPS CM via CAN communication.
Start stop unit	• Transmits the signal from the steering angle sensor to the EPS CM as a steering angle (absolute steering angle) signal via CAN communication.
SAS control module	• Transmits the vehicle lateral-G (vehicle lateral acceleration speed) and yaw rate (vehicle turning angle speed) to the EPS CM via CAN communication.
Instrument cluster	• Turns on/flashes the power steering malfunction indication based on the power steering malfunction indication on/flash request signal and power steering warning buzzer request signal output by the EPS CM, and activates the power steering warning buzzer to alert the driver that there is a malfunction the EPS system.

Structural View

L.H.D.

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R.H.D.

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System Wiring Diagram

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Operation

1. Steering force (1) generated by the driver's steering wheel operation is detected by the torque sensor built into the steering column and shaft, and it is output (2) to the EPS CM as a steering torque signal.

2. The EPS CM calculates optimum assist force based on the steering torque signal (2) from the torque sensor and the vehicle speed signal (3) and engine speed signal (4) from the PCM, and EPS motor position information (5) from the EPS motor, and outputs (6) electric current to drive the EPS motor.

3. The EPS motor drive force (assist torque) generated by the EPS motor drive current (6) from the EPS CM is transmitted (7) to the intermediate shaft via the reduction gear to assist the driver's steering operation.

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