Electric Power Steering (Eps) Construction/Operation - Mazda RX-8 2004 Service Highlights

ELECTRIC POWER STEERING (EPS) CONSTRUCTION/OPERATION

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.
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.
06–13–4
ELECTRIC POWER STEERING (EPS)
PCM
-VEHICLE SPEED SIGNAL
-ENGINE SPEED SIGNAL
EPS CONTROL MODULE
BALL SCREW
EPS MOTOR
STEERING
TORQUE SENSOR
FORCE
SIGNAL
RACK AND PINION MECHANISM
STEERING GEAR AND LINKAGE
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CHU0613S002