ELECTRO HYDRAULIC POWER ASSIST STEERING (EHPAS) CONSTRUCTION/OPERATION

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Construction

• The EHPAS system consists of the following parts:

― Manual steering mechanism:

Consists of the steering wheel, steering shaft, steering gear and linkage

― Assist mechanism:

Consists of the motor and gear pump that are incorporated into the electric power steering oil pump.

― Control system:

Integrated with the electric power steering oil pump. The vehicle and engine speed signals input from the PCM, and the steering speed signal from the steering angle sensor are input via the BCM.

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Operation

Power Assist Mechanism Operation

• The steering angle sensor detects the steering speed based on the steering operations of the driver and inputs a steering speed signal to the EHPAS control module (CM) via the BCM. The EHPAS CM uses the steering speed signal, vehicle speed signal, and other vehicle conditions, to determine the proper motor speed.

• Based on the motor speed determined by the EHPAS CM, the current from the motor drive circuit to the EHPAS motor is controlled to within the target current amount and the oil pump operates accordingly.

• The hydraulic pressure created by the oil pump is used to assist the shaft to turn axially. Due to this, the steering operation load on the driver is reduced.

Component Parts/Function

• The EHPAS system consists of the following parts. While each part has a regular function in other systems, only the function during EHPAS control is listed.

Part name

Function

Electric power steering oil pump (with built-in motor, reserve tank, and EHPAS CM)

•  Calculates the proper assist current based on the steering speed signal input from the BCM and the vehicle and engine speed signals input from the PCM via CAN lines, controls the motor, and performs power assist.

•  Controls the on-board diagnostic system and fail-safe function when there is a malfunction in the EHPAS system.

Steering angle sensor

•  Transmits the steering speed to the BCM.

BCM

•  Outputs the steering speed signal to the EHPAS CM via CAN lines.

PCM

•  Outputs the vehicle and engine speed signals to the EHPAS CM via CAN lines.

•  Outputs the engine status (i-stop) signal to the EHPAS CM via CAN lines (MZR 2.0 DISI i-stop).

Instrument cluster

•  The EHPAS warning light illuminates to advise the driver when a system malfunction is detected.

•  Transmits the parking brake position signal to the EHPAS CM via the CAN lines.

Part name	Function
Electric power steering oil pump (with built-in motor, reserve tank, and EHPAS CM)	• Calculates the proper assist current based on the steering speed signal input from the BCM and the vehicle and engine speed signals input from the PCM via CAN lines, controls the motor, and performs power assist. • Controls the on-board diagnostic system and fail-safe function when there is a malfunction in the EHPAS system.
Steering angle sensor	• Transmits the steering speed to the BCM.
BCM	• Outputs the steering speed signal to the EHPAS CM via CAN lines.
PCM	• Outputs the vehicle and engine speed signals to the EHPAS CM via CAN lines. • Outputs the engine status (i-stop) signal to the EHPAS CM via CAN lines (MZR 2.0 DISI i-stop).
Instrument cluster	• The EHPAS warning light illuminates to advise the driver when a system malfunction is detected. • Transmits the parking brake position signal to the EHPAS CM via the CAN lines.