ELECTRIC POWER STEERING (EPS) CONSTRUCTION/OPERATION


BHE061301034T04

Construction

• The EPS (Electric Power Steering) consists mainly of manual steering and electric assist mechanisms, and a control system.

– Manual steering mechanism:
Consists of the steering wheel, steering shaft, steering gear and linkage
– Electric assist mechanism:
Consists of the EPS motor and ball screw built into the steering gear and linkage.
– Control system:
Consists of a torque sensor, and vehicle speed and engine speed signals input from the EPS control module and PCM

1
PCM
2
Vehicle speed signal
3
Engine speed signal
4
EPS control module
5
Steering force signal
6
Torque sensor
7
Ball screw
8
EPS motor
9
Steering gear and linkage
10
Rack and pinion mechanism

Operation

• EPS assists the manual steering mechanism operation with the EPS motor, supplementing manual power during vehicle steering and reducing the load on the driver.

Manual Steering Mechanism Operation

• The steering input force, formed when the driver operates the steering wheel, is converted from a rotational movement to a linear movement by the rack and pinion mechanism of the steering gear and linkage. This linear movement is transmitted via the inner and outer ball joints to the steering knuckle and the tires are steered to the left or right.

Power Assist Mechanism Operation

• According to the steering action of the driver, the torque sensor detects the steering force for the road surface resistance and then inputs a steering force signal to the EPS control module. The EPS control module uses this steering force signal, correcting for vehicle speed and other conditions, to determine the proper power assist force
• Based on the assist force determined by the EPS control module, the current from the motor drive circuit to the EPS motor is controlled to within the target current amount and the motor operates accordingly.
• The operating force generated by the EPS motor rotates the ball screw integrated with the motor and thereby assists the rack to turn axially. Due to this, the steering operation load on the driver is reduced.

Function of Component Parts

Part name

Function

Steering gear and linkage
Torque sensor
• Detects the steering force signal and inputs it to the EPS control module.
EPS motor
• Generates an assist force based on the control current from the EPS control module.
EPS control module
• Determines the control current for the EPS motor based on the steering force signal from the torque sensor, vehicle speed signal from the PCM and other signals.
• Inputs an idle increase request signal to the PCM via CAN communication lines.
• Controls the on-board diagnostic system and fail-safe function when an abnormality is detected in the EPS system.
PCM
Vehicle speed signal
• Inputs the vehicle speed signal to the EPS control module via CAN communication lines.
Engine speed signal
• Inputs the engine speed signal to the EPS control module via CAN communication lines.
Instrument cluster
EPS warning light
• The light illuminates to inform the driver when a system malfunction is detected.