1. VGRS (Variable Gear Ratio Steering) System
General
The steering gear ratio will be changed in accordance with the vehicle speed a
a - 
a + 
VGRS system is adopted only for the 3UZ-FE model as standard equipment
Basic construction and operation is same as ’05 LX470
Low Ratio (Quick)
High Ratio (Slow)
Vehicle speed low
Vehicle speed high

2. Rotational Position Sensor (for motor)
VGRS System
Major Difference from ’05 LX470
Item
’06 GS430
’05 LX470
Rotational Position Sensor (for motor)
Resolver
Three Hall ICs
System Warning
Warning Message
VGRS Warning Light
Communication
CAN,
Serial Communication
[Major Difference]
Resolver is used as rotational position sensor for motor
Warning message is displayed on the multi information display (VGRS warning light is discontinued)
CAN communication is used

3. VGRS System System Diagram VGRS ECU Steering Angle Sensor
VGRS Actuator
VGRS
ECU
Serial Communication
Lock Mechanism
Spiral Cable
Motor
Skid Control ECU
CAN
Resolver
Temp. Sensor
Engine ECU (ECM)
CAN communication is used
CAN
DLC3
BEAN
Gateway ECU
Serial Communication
EPS ECU
Combination Meter

4. VGRS system not operates
Steering Gear Ratio
Confidential
Slow 19
VGRS system not operates 17
Steering Gear Ratio 15
Lock to Lock : 3.2
At very low speed: Quick gear ratio to reduce the driver's steering angle
At low or middle speed: Optimum steering gear ratio to vehicle responds with more agility and handles more easily
At high speed: Slow gear ratio to ensures a stable vehicle response
Quick
100 (62)
200
(124)
Km/h (mile)
Lock to Lock : 2.7
Vehicle Speed

5. VGRS System System Operation VGRS ECU VGRS Actuator Motor Gear Map
Steering Angle Sensor
VGRS Actuator
Motor
Rack & Pinion
Gear
Control Signal
(Target Operating Angle)
VGRS ECU
Steering Angle
Map
Calculate actuator target operating angle
Actuator Operating Angle
Skid Control ECU
Vehicle Speed
Vehicle Speed

6. VGRS System System Operation
VGRS ECU adds the supplemental assist with steering speed to reduce delay of vehicle response
Normal Operation
Actuator Output
In order to operate this control, serial communication with steering angle sensor is used
(Serial communication speed is faster than the CAN communication)
Assist

7. VGRS Actuator Assembly
VGRS System
VGRS Actuator
VGRS Actuator
Spiral Cable
Steering Wheel
Lock Mechanism
Motor
Do not overhaul the VGRS actuator
Rack & Pinion
VGRS Actuator Assembly
Reduction Mechanism

8. VGRS System VGRS ECU Spiral Cable Flexible flat cable is used
Spiral Cable (Flexile Flat Cable)
VGRS ECU
Control Signal, Power Source
Rotational angle and rotational direction of the motor
Motor

9. Service Point (VGRS System)
Spiral Cable
Before installing VGRS actuator, secure the neutral position of this cable
2 turns
Lock
After 2 turns
Neutral Position
Mark
Same as spiral cable for driver’s airbag
1. Turn the cable clockwise until it becomes harder to turn
2. Then turn the cable counterclockwise about 2 turns
Slit

10. Lock Holder (Motor Shaft)
VGRS System
Lock Mechanism
Locks the motor shaft
Lock Mechanism
A – A Cross Section
Lock Holder (Motor Shaft)
Solenoid A A
Lock mechanism locks the motor shaft
Motor Shaft
Return Spring
Lock Lever
(Housing)

11. VGRS System Lock Mechanism Lock / unlock operation Solenoid “ON”
Solenoid “OFF”
Solenoid ON (Unlock): System is normal
Solenoid OFF (Locked by return spring force): Engine is stopped or system fail
Unlock
Lock

12. Rotation Angle Sensor (Resolver)
VGRS System
Motor
A compact high-output low-noise brush-less motor
Rotation Angle Sensor (Resolver)
Brush-less Motor
Motor Shaft
Magnet
Coil
Rotation angle sensor (resolver) outputs 2 signals with which the phase lagged 90 degrees
Motor rotation angle can be detected by comparing the 2 signal waveforms
Reduction Mechanism

13. VGRS System Reduction Mechanism
The strain wave gearing type reduction mechanism
Motor
Stator Gear
Stator Gear
Flexible Gear
Wave Generator
Flexible Gear
Driven Gear
Strain wave gearing type reduction mechanism is compact and high precision, few components, and higher reduction ratio
Wave Generator
Driven Gear
Output Shaft

14. Wave Generator (input)
VGRS System
Reduction Mechanism
Components
Stator Gear (input)
Driven Gear (output)
Wave Generator (input)
Flexible Gear
Stator Gear (Input): Coupled to the housing of the VGRS actuator
Flexible Gear:Flexible metal body
Gear teeth are meshed with the inside of both stator gear and driven gear
Driven Gear (Output): Coupled to the output shaft of the VGRS actuator
Wave Generator (Input): Consists an oval-shaped cam and bearing, and rotated by the motor
Steering Wheel
Rack & Pinion

15. The difference of number of teeth
VGRS System
Reduction Mechanism
Number of teeth
Stator Gear (input)
Driven Gear (output)
Wave Generator (input)
Flexible Gear
The difference of the number of teeth is used for the reduction mechanism
100
100
102
The difference of number of teeth

16. VGRS System Reduction Mechanism Construction Meshing Not meshing
Stator Gear
Flexible Gear
Wave Generator
Meshing
Ball Bearing is between flexible gear and wave generator
Flexible gear is oval shaped by wave generator
Not meshing
View from stator gear side
(Steering wheel side)

17. VGRS System Reduction Mechanism Operation of strain wave gearing
Motor Shaft
Flexible Gear
(100 teeth)
Wave Generator
Stator Gear
(102 teeth)
Ball Bearing
(Between flexible gear and wave generator)
View from stator gear side
(Steering wheel side)

18. View from stator gear side
VGRS System
Reduction Mechanism
Operation of strain wave gearing
[Operation of strain wave gearing]
1. Flexible gear is flexed into an oval shape by wave generator
2. Flexible gear teeth meshes with stator gear teeth and driven gear
3. During wave generator rotation, the meshed area of the flexible gear and stator gear / driven gear moves in sequence
4. After the wave generator makes one turn, the flexible gear is shifted by 2 teeth because the flexible gear has 2 fewer teeth than the stator gear
5. The driven gear and flexible gear have the same number of teeth, so their rotational movements are identical
6. The flexible gear is shifted by 2 teeth = The driven gear shifted by 2 teeth (= Actuator output)
Stator gear fixed
View from stator gear side
(Steering wheel side)

19. VGRS System Reduction Mechanism Operation of strain wave gearing
Stator Gear
(102 teeth)
Flexible Gear (100 teeth)
Shifts by
2 teeth
Wave generator makes
one turn
Every time motor rotates, stator gear and flexible gear (driven gear) shifts by two teeth
This shift is used as actuator output
Click!
Movie
Driven Gear (100 teeth)

20. VGRS System Reduction Mechanism Reduction gear ratio Gear Ratio 50 : 1
Flexible gear rotates one turn
Wave generator (motor) rotates 50 turns
Reduction Gear Ratio: 50
Gear Ratio 50 : 1
Motor
Flexible Gear

21. M VGRS System Operation Vehicle speed is low (quick ratio)
Add steering angle M
[Vehicle speed is low (quick ratio)]
When the steering wheel is turned to the left, motor rotates the clockwise and adds steering angle
Click!
Movie

22. M VGRS System Operation Vehicle speed is mid. (normal ratio) No assist
[Vehicle speed is middle (normal ratio)]
When the steering wheel is turned to the left, motor does not operates and no assist
Click!
Movie
No assist

23. Reduces steering angle
VGRS System
Operation
Vehicle speed is high (slow ratio) M
[Vehicle speed is high (slow ratio)]
When the steering wheel is turned to the left, motor rotates the counterclockwise and reduces steering angle
Click!
Movie
Reduces steering angle

24. VGRS System Warning Message
VGRS warning message for the system malfunction
Master warning light is light up when the VGRS warning message is displayed
Warning Message

25. VGRS System Diagnosis 29 DTCs for VGRS system DTC Detection Item C1591
VGRS Actuator Neutral Position Calibration Undone
C1592
VGRS Actuator Neutral Position Calibration Incomplete
C1593
VGRS Actuator Standard Position Malfunction
C1595
Lost Communication with Steering Angle Sensor Module
C1597
Lost Communication between VGRS and EPS
C15A1
VGRS Actuator Malfunction
C15A2
C15A3
C15A4
C15A5
C15A6
C15A9
Lock Holder Deviation Detection
C15AA
Lock Mechanism Release Incomplete
C15AB
Lock Mechanism Insertion Malfunction

26. VGRS System Diagnosis 29 DTCs for VGRS system DTC Detection Item C15B1
VGRS ECU Malfunction
C15B2
C15B3
C15B4
C15C1
Steering Angle Sensor Malfunction
C15C2
Steering Angle Sensor B+ Malfunction
C15C3
Brake System Control Module Malfunction
C15C6
IG Power Supply Voltage Malfunction
C15C7
DC Motor Power Source Voltage Malfunction
C15C8
Power Supply Relay Failure
U0100
Lost Communication With ECM/PCM "A"
U0122
Lost Communication With Vehicle Dynamics Control Module
U0123
Lost Communication With Yaw Rate Sensor Module
U0126
Lost Communication With Steering Angle Sensor Module
U0131
Lost Communication With Power Steering Control Module

27. Initialization and Calibration
VGRS System
Initialization and Calibration
Item
Steering Angle Sensor Initialization
Calibration
Replacement
VGRS ECU
VGRS Actuator 
Repairing steering system parts
Reconnect the battery terminal 
Reconnect the connectors
Steering Angle Sensor
Skid Control ECU
[Steering Angle Sensor Initialization]
- Restore the neutral position of steering wheel
- Center the steering wheel position
[Calibration]
- Initialize and calibrate the VGRS actuator angle
- Center the steering wheel position (when steering wheel is still off-center after completing the steering angle sensor initialization)

28. Service Point (VGRS System)
Initialization and Calibration
Steering angle sensor initialization
Drive the vehicle on a straight road at 35 km/h (22 mph) or more for 5 sec. or longer
Neutral position of steering wheel is restored
Steering wheel is automatically centered
Perform normal cornering 2 to 3 times
[Steering Angle Sensor Initialization]
If steering angle sensor initialization is not completed, VGRS system is stopped
1. Drive the vehicle on a straight road at 35 km/h (22 mph) or more for 5 sec. or longer
Note: Steering wheel will still off-center
Neutral position of steering wheel is restored in this step
2. After performing normal cornering 2 to 3 times, the steering wheel position is automatically corrected
3. Confirm the steering angle sensor initialization is completed
Access the VGRS data list using the Intelligent Tester II (Hand-held Tester) and confirm the “Straight Angle Valid Flag” parameter reads VALID
Note: If INVALID, return to first step (If INVALID returns again, check for DTCs and perform VGRS system calibration)
Using IT II, Confirm the steering angle sensor initialization is completed

29. Service Point (VGRS System)
Initialization and Calibration
Calibration
Face the tire straight ahead
IG/ON Engine OFF
Using IT II, perform calibration in accordance with the “Steering Angle Adjust”
Confirm the steering wheel from lock to lock is 2.7-turn
[Calibration]
1. Face the tire straight ahead, IG/ON, Engine OFF
2. Using Intelligent Tester II (Hand-held Tester), perform calibration in accordance with the “Steering Angle Adjust” from the VGRS DIAGNOSTIC MENU
3. Turn the steering wheel from lock to lock to check that it rotates approx. 2.7 turns
4. Perform the actuator sensor learning confirmation procedure to confirm the system calibration has been completed properly
5. Drive vehicle to confirm steering wheel is centered
Perform the actuator sensor learning confirmation
Click for Detail
Drive vehicle to confirm steering wheel is centered

30. Service Point (VGRS System)
Initialization and Calibration
Actuator sensor learning confirmation (detail)
Start the engine
Continue the turning for 3 sec.
Turn the steering wheel to the left 90 and then back to center
Repeat 15 times
While turning, stop the engine
Turn the steering wheel to the right 90 and then back to center
Hold the steering wheel for 3 sec.
Turn the steering wheel slowly to the left
[Actuator sensor learning confirmation]
1. Start the engine
2. Turn the steering wheel from center to the left 90° and then back to center
3. Turn the steering wheel from center to the right 90° and then back to center
4. Hold the steering wheel in the centered position for 3 sec.
5. Perform the following check procedure
a. Turn the steering wheel slowly to the left
b. While turning the steering to the left, turn off the engine
c. Continue to turn the steering wheel slowly to the left 3 sec.
6. Repeat step1 to 5 for 15 times
Note: DTC C15A9 requires that the fault occurs 5 consecutive times to set
The confirmation procedure must be performed multiple times to ensure the condition does not repeat
7. Check that the DTC is not output
Note: If C15A9 is set, repeat the calibration for a second time (If C15A9 is set again, replace the VGRS actuator)
Check that the DTC is not output

31. Reference (VGRS System)
Components
Wave Generator
Flexible Gear
Motor M
Output
(Rack & Pinion)
Steering Wheel
Actuator Housing
Driven Gear
Stator Gear