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Last Modified: 11-27-2007 1.6 D
Service Category: Steering Section: Steering Column
Model Year: 2008 Model: LX570 Doc ID: RM000000XO500IX
Title: VARIABLE GEAR RATIO STEERING: VARIABLE GEAR RATIO STEERING SYSTEM: SYSTEM DESCRIPTION (2008 LX570)

SYSTEM DESCRIPTION

1. GENERAL DESCRIPTION

(a) The Variable Gear Ratio Steering (VGRS) system controls the steering angle in accordance with vehicle speed. The system is controlled by the steering control ECU which operates the steering actuator mounted on the steering intermediate shaft. The operating angle of the steering actuator is added to the steering angle of the pinion gear in order to vary the turning angle of the front wheels in accordance with vehicle speed.

(b) When the VGRS system is operating normally, the steering wheel can be turned approximately 2.7 turns from lock to lock, with the engine running and the vehicle stopped.

(c) If a malfunction occurs in the VGRS system, steering actuator operation will immediately stop and the input and output shafts will be directly connected to enable the conventional steering mechanism to operate, maintaining the steering function (fail-safe). At the same time, the master warning light will come on to inform the driver of the malfunction.

2. FUNCTIONS OF COMPONENTS

(a) Functions of VGRS system components

Component

Function

Steering Control ECU

Calculates the steering gear ratio based on vehicle speed signals, steering wheel angle and steering wheel angle speed. Drives the steering actuator based on calculation results of steering cooperative control received from the skid control ECU, and steering gear ratio control.

Steering Actuator

Drives the motor using the output current from the steering control ECU to change the output shaft angle.

Rotation Angle Sensor

(Built into Steering Actuator)

Outputs the motor rotation angle to the steering control ECU.

Steering Angle Sensor

Outputs the steering wheel angle to the steering control ECU.

Master Warning Light

Located in the combination meter. Comes on in accordance with system conditions to inform the driver of system malfunctions.

Multi-information Display

Located in the combination meter. Displays a warning message to inform the driver of system malfunctions.