ELECTRO HYDRAULIC POWER ASSIST STEERING (EHPAS) CONSTRUCTION/OPERATION

Construction

• The Electro hydraulic power assist steering (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:

Consists of the EHPAS control module incorporated into the electric power steering oil pump, the P/S angle sensor installed on the steering gear and linkage, and the vehicle and engine speed signals input from the PCM.

Operation

Power Assist Mechanism Operation

• According to the steering action of the driver, the P/S angle sensor detects the steering speed, and then outputs a steering speed signal to the EHPAS control module. The EHPAS control module uses the steering speed signal, vehicle speed signal, and other vehicle conditions, to determine the proper motor speed.

• Based on the motor seed determined by the EHPAS control module, 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.