Steering: Description and Operation

SYSTEM OUTLINE

The ECU of the PPS (Hydraulic reaction type) controls the hydraulic pressure applied to the hydraulic reaction chamber in the gear box control unit to change the steering force and provide optimum steering feeling at any vehicle speed and under any steering conditions.

PPS OPERATION
When the ignition SW is turned on, the starting current flows from the ABS-IG fuse to TERMINAL 4 of the PPS ECU. The vehicle speed sensor monitors the vehicle speed and transmits control signals to TERMINAL 5 of the ECU.

When the vehicle speed is low, the PPS ECU sends a higher-current from TERMINAL 1 of the ECU to TERMINAL 1 of the PPS solenoid to TERMINAL 2 to TERMINAL 2 of the ECU to TERMINAL 6 to GROUND, increasing the solenoid valve opening angle to provide comfortable steering operation. When the vehicle speed is high, the PPS ECU decreases the solenoid valve opening angle by reducing the current to the valve to provide responsive steering feeling.

System Diagram:

SYSTEM DIAGRAM


SYSTEM DESCRIPTION

LEXUS LS430 uses the rack and pinion type steering gear, and the vehicle speed sensing hydraulic reaction type electronically controlled Progressive Power Steering (PPS) system.

The PPS (Progressive Power Steering) is vehicle speed sensing type power steering, which increases/ decreases steering effort in accordance with vehicle speed.

The power steering ECU assy sends a control signal to the steering gear (PPS linear solenoid valve assy) based on a vehicle speed signal. This system enables obtainment of a heavy steering feeling when driving at high speeds.

1. Power steering ECU assy
The power steering ECU assy receives a vehicle speed signal from the combination meter.
It then sends a signal to the PPS linear solenoid valve assy.

2. PPS linear solenoid valve assy
The PPS linear solenoid valve assy controls power steering fluid pressure by receiving a signal from the power steering ECU assy.