ELECTRIC POWER STEERING (EPS) CONSTRUCTION AND OPERATION

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Construction

• The EPS consists of the following parts:

― Electric assist and manual steering mechanism

Consists of the steering wheel, steering column, intermediate shaft, steering gear and linkage, reduction gears integrated in the steering column, and EPS motor.

― Control system

Consists of the EPS control module, reduction gear, EPS motor and torque sensor integrated in the steering column, PCM, and vehicle speed/engine speed/condition signals input from the PCM.

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Operation

• The EPS assists the manual steering mechanism operation using the EPS motor to provide supplemental manual power during steering operation, reducing the load on the driver.

Manual steering mechanism operation

• The steering force, generated when the driver operates the steering wheel, is transmitted to the wheels and tires via the steering column, intermediate shaft, and steering gear and linkage.

Control system operation

• The torque sensor detects the steering force (road surface reaction force) according to the steering action of the driver, converts it to an electric signal, and then inputs it to the EPS control module.

• The EPS control module determines optimum assist force per each vehicle speed signal based on the signals from the torque sensor, and outputs current to drive the EPS motor.

Power assist mechanism operation

• The EPS motor is driven by the current from the EPS control module and the force is transmitted to the intermediate shaft via the reduction gears, thus assisting steering operation of the driver.

Component Parts and Function

Part name

Function

Steering wheel

•  Transmits steering force from the driver to the steering column.

Steering column

Torque sensor

•  Detects steering force and outputs it to the EPS control module as an electric signal.

EPS control module

•  Control the current to the EPS motor based on the electric signals from the torque sensor and vehicle speed signals from the PCM.

•  Controls the on-board diagnostic system and fail-safe function when a malfunction is detected in the EPS system.

•  Transmits the steering angle signal via CAN lines to the DSC HU/CM.

EPS motor

•  Generates drive force based on the target current from the EPS control module.

Reduction gear

•  Transmits the drive force from the EPS motor to the intermediate shaft.

Intermediate shaft

•  Transmits the drive force from the reduction gear to the steering gear and linkage.

Steering gear and linkage

•  Transmits the drive force from the intermediate shaft to the wheels and tires.

PCM

•  Outputs vehicle speed signal to the EPS control module via the CAN lines.

Instrument cluster

•  Alerts the driver by illuminating/flashing the EPS warning according to the signals from the EPS control module if the EPS has a malfunction.

Part name		Function
Steering wheel		• Transmits steering force from the driver to the steering column.
Steering column	Torque sensor	• Detects steering force and outputs it to the EPS control module as an electric signal.
	EPS control module	• Control the current to the EPS motor based on the electric signals from the torque sensor and vehicle speed signals from the PCM. • Controls the on-board diagnostic system and fail-safe function when a malfunction is detected in the EPS system. • Transmits the steering angle signal via CAN lines to the DSC HU/CM.
	EPS motor	• Generates drive force based on the target current from the EPS control module.
	Reduction gear	• Transmits the drive force from the EPS motor to the intermediate shaft.
Intermediate shaft		• Transmits the drive force from the reduction gear to the steering gear and linkage.
Steering gear and linkage		• Transmits the drive force from the intermediate shaft to the wheels and tires.
PCM		• Outputs vehicle speed signal to the EPS control module via the CAN lines.
Instrument cluster		• Alerts the driver by illuminating/flashing the EPS warning according to the signals from the EPS control module if the EPS has a malfunction.