ELECTRIC POWER STEERING SYSTEM

id061300701600

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

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

• A steering column with a tilt/telescoping mechanism has been adopted allowing fine adjustment of the steering wheel position according to the driving posture of the driver.

• A steering column and shaft with a shock-absorbing mechanism has been adopted.

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

Specifications

Item

Specification

Steering wheel

Outer diameter

(mm {in})

372 {14.6}

Lock to lock

(turns)

2.82

Steering column and shaft

Shaft type

Collapsible

Joint type

Cross-shaped joint

Tilt amount

(mm {in})

45 {1.8}

Telescope amount

(mm {in})

70 {2.8}

Steering gear and linkage

Type

Rack-and-pinion

Rack stroke

(mm {in})

149.2 mm {5.874 in}

Power steering system

Power assist type

Electric motor assist (Column assist type)

Item	Specification
Steering wheel	Outer diameter	(mm {in})	372 {14.6}
Lock to lock	(turns)	2.82
Steering column and shaft	Shaft type	Collapsible
Joint type	Cross-shaped joint
Tilt amount	(mm {in})	45 {1.8}
Telescope amount	(mm {in})	70 {2.8}
Steering gear and linkage	Type	Rack-and-pinion
Rack stroke	(mm {in})	149.2 mm {5.874 in}
Power steering system	Power assist type	Electric motor assist (Column assist type)

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, electronically controlled brake unit, SAS control module, instrument cluster, and CMU via CAN communication.

Part name

Functions

EPS CM

•  Calculates the optimum assist force based on the signals from the torque sensor, EPS motor, PCM, electronically controlled brake unit 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 electronically controlled brake unit 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 request signal to CAN when there is a malfunction in the EPS system.

PCM

•  Transmits an electric motor speed signal to the EPS CM via CAN communication.

Electronically controlled brake unit

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

SAS control module

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

Instrument cluster

•  Alerts the driver that there is a malfunction in the EPS system by turning on the electric power steering warning indication based on the electric power steering warning light/electric power steering warning indication on request signal output by the EPS CM.

CMU

•  Alerts the driver that there is a malfunction in the EPS system by turning on the electric power steering warning indication based on the electric power steering warning light/electric power steering warning indication on request signal output by the EPS CM.

Part name	Functions
EPS CM	• Calculates the optimum assist force based on the signals from the torque sensor, EPS motor, PCM, electronically controlled brake unit 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 electronically controlled brake unit 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 request signal to CAN when there is a malfunction in the EPS system.
PCM	• Transmits an electric motor speed signal to the EPS CM via CAN communication.
Electronically controlled brake unit	• Transmits a vehicle wheel speed signal, vehicle speed signal, vehicle lateral-G (vehicle lateral acceleration speed) and yaw rate (vehicle turning angle speed) to the EPS CM via CAN communication.
SAS control module	• Transmits the signal from the steering angle sensor to the EPS CM as a steering angle (absolute steering angle) signal via CAN communication.
Instrument cluster	• Alerts the driver that there is a malfunction in the EPS system by turning on the electric power steering warning indication based on the electric power steering warning light/electric power steering warning indication on request signal output by the EPS CM.
CMU	• Alerts the driver that there is a malfunction in the EPS system by turning on the electric power steering warning indication based on the electric power steering warning light/electric power steering warning indication on request signal output by the EPS CM.

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, the vehicle speed signal (3) from the electronically controlled brake unit, electric motor speed signal (4) from the PCM, and EPS motor position signal (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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