ELECTRO HYDRAULIC POWER ASSIST STEERING CONTROL MODULE CONSTRUCTION/OPERATION

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Construction

• The EHPAS control module (CM) is built into the electric power steering oil pump.

• The module calculates the proper assist current based on the steering speed signal from the BCM, and the vehicle and engine speed signals from the PCM via CAN communication, and then outputs the control current to the motor.

• If each of the conditions is met, the system switches from normal control to parking brake control, and the control current to the motor is reduced.

• The system switches from normal control to EHPAS i-stop control based on the engine status (i-stop) signal from the PCM, and the control current to the motor is stopped.

• The EHPAS CM determines the power steering fluid temperature by the thermistor in its circuit board and corrects the target rotation to the motor based on the change in fluid temperature.

Function Table

Control item	Function
Motor current control	• Normal control ― Calculates the proper assist current based on the steering speed and vehicle and engine speeds, and outputs a control current to the motor. • Parking brake control ― If each of the conditions continues to be met for 0.5 s, control current to the motor is reduced, and motor rotation is decelerated. • EHPAS i-stop control (MZR 2.0 DISI i-stop) ― If the engine stop control permit conditions are met, the control current to the motor is stopped, stopping the motor. ― If the engine restart control permit conditions are met, the control current to the motor is output and the motor is started.
On-board diagnostic function	• A function that allows important parts of the control system to perform self-diagnosis. In case a malfunction occurs, the EHPAS warning light illuminates to advise the driver, and at the same time a DTC is stored in the EHPAS CM. • When a malfunction is determined as a result of the on-board diagnosis, system control is suspended or limited to prevent any dangerous occurrence while driving.

Control item

Function

Motor current control

• Normal control

― Calculates the proper assist current based on the steering speed and vehicle and engine speeds, and outputs a control current to the motor.

• Parking brake control

― If each of the conditions continues to be met for 0.5 s, control current to the motor is reduced, and motor rotation is decelerated.

• EHPAS i-stop control (MZR 2.0 DISI i-stop)

― If the engine stop control permit conditions are met, the control current to the motor is stopped, stopping the motor.

― If the engine restart control permit conditions are met, the control current to the motor is output and the motor is started.

On-board diagnostic function

• A function that allows important parts of the control system to perform self-diagnosis. In case a malfunction occurs, the EHPAS warning light illuminates to advise the driver, and at the same time a DTC is stored in the EHPAS CM.

• When a malfunction is determined as a result of the on-board diagnosis, system control is suspended or limited to prevent any dangerous occurrence while driving.

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Operation

Motor current control

Normal control

• The proper assist current is calculated based on the steering speed from the BCM and the vehicle and engine speed signals from the PCM, and then the current output to the motor is controlled so that the motor speed is as specified according to the following table.

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Parking brake control

• When the vehicle is stopped (the following conditions continue for 0.5 s), the system switches from normal control to parking brake control, motor rotation is decelerated, and motor control current is reduced.

― Steering speed signal is 0 degree per s

― Vehicle speed is 0 km/h

― Parking brake signal is On

― Motor operating current is less than 30 A

― Control-based temperature and metal-based temperature are less than 105 °C

― Engine speed signal exceeds 450 rpm

• If a malfunction is detected in the system, parking brake control is canceled.

EHPAS i-stop control (MZR 2.0 DISI i-stop)

• When engine stop control permit conditions are met based on the engine status (i-stop) signal from PCM, the control current to the motor is stopped.