Electrical Power Steering System (EPS)

GENERAL INFORMATION

- The steering wheel has three spokes. All vehicles are equipped with SRS (Supplemental Restraint System).

- The steering column has a shock absorbing mechanism and a tilt steering mechanism.

- Improved fuel consumption by reduction of engine load, and weight saving by decrease of the number of parts have been achieved with the introduction of the electric power steering system.

- Vehicle-speed sensitive electric power steering (whole range type) has been adopted.
This system allows a light steering force during stationary steering maneuver or low speed driving, and a moderate steering force during medium or high speed driving.

- For vehicles with this system, the electric power steering-ECU controls the motor current according to the vehicle speed and steering force of the steering wheel.

- CAN* communication has been adopted in order to communicate with another ECUs for obtaining necessary information related to this control, achieving wiring harness saving and secure data communication.
NOTE:
*: For more information about CAN (Controller Area Network), Controller Area Network (CAN).

CONSTRUCTION DIAGRAM





SPECIFICATIONS





DESCRIPTION ON SYSTEM





To improve operational reliability, the dual-circuit system has been adopted for the torque sensor. If any malfunction occurs in the electric power steering system, the fail-safe function of the electric power steering-ECU is activated, and the output current of the electric power steering-ECU applied to the motor is turned off. At the same time, the steering system enters manual mode, and informs a driver of the system malfunction by illuminating the warning light on the combination meter. The warning light illuminates when the following malfunctions occur: open circuit in the electric power steering system wiring harness, poor connection, malfunctions in the electric power steering-ECU, motor, or sensors.

ELECTRICAL PARTS AND FUNCTIONS





SYSTEM CONFIGURATION





NOTE:
Dashed lines indicate CAN-bus lines.

STEERING GEAR





The torque sensor which detects a operated force of the steering wheel is installed in the steering gear. When the steering wheel is turned, the steering force is detected by the torque sensor. At the same time, 2-way supply voltage signal (main and sub) are input to the electric power steering-ECU.

MOTOR





The motor is installed in the steering gear. The steering motor is applied with a control current sent from the electric power steering-ECU and generates the assist torque to the steering gear according to the steering operation.

ELECTRIC POWER STEERING-ECU





The electric power steering-ECU is attached below the glove box, which is integrated with an input interface circuit, a microcomputer, an output drive circuit, a fail-safe relay, and a motor line relay etc.
It is also integrated with a self-diagnostic function, and illuminates the warning light and sets DTC to the Data link connector.

CAN COMMUNICATION

The electric power steering-ECU performs the data transfer with another ECUs through CAN communication.






NOTE:
Indicates items which send and receive data through CAN communication.

FAIL-SAFE FUNCTION

If the electric power steering-ECU detects any malfunction, it illuminates the warning light, deactivates the electric power steering function, and then switches the steering system into manual mode.

DIAGNOSTIC FUNCTION

Electric power steering-ECU has the following functions for easier system checks.

- DTC set

- Service data output
All
the above items can be diagnosed using scan tool.

DIAGNOSTIC TROUBLE CODE SET

There are 28 diagnostic items. Since all the diagnostic results are recorded in volatile memory (EEPROM*), they are stored in the memory even though the battery terminals are disconnected.
NOTE:

- *: EEPROM (Electrical Erasable &
Programmable ROM) Special type of memory that can be programmed or erased electrically.

- For each diagnostic item, refer to the Workshop Manual.

SERVICE DATA OUTPUT

Using scan tool, the input data sent from the sensors and motors can be read.
NOTE:
For each service data item, refer to the Workshop Manual.

OPERATION

IGNITION SWITCH ON

Ignition supply voltage is applied to the electric power steering-ECU, and the ECU enters standby mode.





1. When the engine is started, the engine speed signal sent from the engine control module (ECM) is input to the electric power steering-ECU.

2. After starting the engine, the electric power steering-ECU judges the engine status
"ENGINE SPEED ON" when the engine speed reaches 500 r/min, then the power assist function is ready.

STEERING WHEEL OPERATION





3. When the steering wheel is operated, the torque sensor integrated into the gear box detects the steering torque and outputs the torque sensor signal
(main and sub), which varies with the steering force, to the electric power steering-ECU.

4. The electric power steering-ECU outputs the current in proportion to the torque sensor signal to the motor.

5. The motor outputs the rotational torque (assist torque) in proportion to the current intensity and assists the power steering gear.

FAIL-SAFE FUNCTION OPERATION

During the fail-safe mode, the electric power steering operates as a manual steering system.