Steering: Description and Operation

System Description

System Outline

This vehicle is equipped with an Electronically Controlled Power Steering System (ECPS). Depending on the vehicle speed, the ECPS control unit controls the ECPS valve. The ECPS valve changes the P/S fluid pressure of the pressure side of the power cylinder. By controlling the P/S fluid pressure electrically, it made possible to supply stable P/S fluid pressure to the power cylinder that ensures the steering feel that is not influence the fluctuation of the engine speed, and corresponds to the driving situation.





Flow control valve
This valve stabilizes the oil P/S fluid pressure of the power steering pump output.

ECPS valve assy
The spool valve built in the ECPS valve assy is operated by the stepping motor which is controlled by the ECPS control unit. It changes the P/S fluid pressure to the power cylinder. When this valve closes, the pressure to the power cylinder increases.

Valve body unit
The rotary valve built in the valve body unit is driven by the rotation of the steering wheel. This changes the oil passage between the power steering pump side, power cylinder side, reservoir side, and the ECPS valve side.

Kickback valve
When kickback is occurred from steering rack, the kickback valve in the feed port decreases the kickback to the steering wheel.

VFV (Variable force control valve)
The valve attenuates rapid P/S oil pressure change.

ECPS control unit
The ECPS control unit controls the stepping motor built inside the ECPS valve assy depending on the engine speed signal and the vehicle speed signal from the PCM. When a failure occurs, this unit stores a DTC and sends a signal to the gauge assembly to turn on the ECPS indicator.





Operation when the vehicle stopped (high assist)
When the vehicle is stopped, the ECPS control unit closes the ECPS spool valve. When the steering wheel is turned, the passage between the increase side power cylinder room and the pump opens at the rotary valve. Because the spool valve is closed, all P/S fluid pressure is guided to the increase side power cylinder room passing the variable aperture of vehicle moving (A) at the rotary valve. At the same time, the passage between the decrease pressure side of the power cylinder room and the reservoir opens at the rotary valve, and the P/S fluid inside the decrease side of the power cylinder room returns to the reservoir. By this operation, the power steering system assists with strong force depending on the variable aperture of stationary steering (B) clearance.





Operation when the vehicle moving (duty assist)
The ECPS control unit duty controls the ECPS spool valve depending on the vehicle speed. When the steering wheel is rotated, the P/S fluid amount to the increase side of the power cylinder room changes depending on the clearance of the variable aperture of stationary steering (A), variable aperture of high speed steering (B), and the variable aperture of the ECPS spool valve (C). The assist force is controlled with the synthetic valve of these three aperture clearance. Because the synthetic clearance is larger than the vehicle in stopped condition, the power steering assist force is controlled lower.