Vehicle steering system

Abstract

A vehicle steering system for steering vehicle wheels includes a steering wheel, a steering power assisting unit for providing assisting power when the steering wheel is steered, a transfer ratio control mechanism for controlling the ratio of a steering angle of the steering wheel to a steered angle of the vehicle wheels according to a vehicle condition; a steering torque sensor, a motor control circuit for controlling the driving motor so as to cancel the steering torque applied to the steering wheel when the steering torque sensor detects a steering torque applied to the steering wheel until the transfer ratio control mechanism starts operation. The transfer ratio control mechanism includes a transfer ratio changing mechanism and a driving motor for driving the transfer ratio changing mechanism.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings:

FIG. 1 is a block diagram of a vehicle steering system according to a preferred embodiment of the invention;

FIG. 2 is a block diagram showing a main portion of the vehicle steering system according to the preferred embodiment;

FIG. 3 is a block diagram showing a transfer ratio control mechanism;

FIG. 4 is a root cause analysis diagram;

FIG. 5A is a graph showing a steering torque characteristic;

FIG. 5B is a graph showing an output angle characteristic of the transfer ratio control mechanism; and

FIG. 6 is a flow diagram of a control operation of the transfer ratio control mechanism.

Claims

1. A vehicle steering system for steering vehicle wheels comprising: a steering wheel;a steering power assisting unit for providing assisting power when said steering wheel is steered;a transfer ratio control mechanism, including a transfer ratio changing mechanism and a driving motor for driving said transfer ratio changing mechanism, for controlling a ratio of a steering angle of said steering wheel to a steered angle of said vehicle wheels according to a vehicle condition;a steering torque sensor; anda motor control circuit for controlling said driving motor so as to cancel the steering torque applied to said steering wheel when said steering torque sensor detects a steering torque applied to said steering wheel until said transfer ratio control mechanism starts operation.

2. A vehicle steering system as in claim 1, wherein said torque sensor detects the torque applied to said steering wheel when said steering wheel is turned from a prescribed angular position.

3. A vehicle steering system as in claim 1, wherein said torque sensor detects the torque applied to said steering wheel when said steering wheel is turned when the steering speed is zero.

4. A vehicle steering system as in claim 1, wherein: said motor control circuit calculates a target angle for said driving motor to turn; andsaid torque sensor detects the torque applied to said steering wheel before the target angle is given to said driving motor.

5. A vehicle steering system as in claim 1, wherein said motor control circuit continuously provides a torque to cancel the steering torque after said transfer ratio control mechanism has started.

6. A vehicle steering system as in claim 5, wherein the direction of the torque to cancel the steering torque is changed when the direction of the steering torque changes.

7. A vehicle steering system for steering a steering wheel of a vehicle to thereby steer a vehicle wheel, said system comprising: a steering power assisting means for providing assisting steering power when said steering wheel is steered;a transfer ratio changing mechanism for changing a ratio of a steering angle of said steering wheel to a steered angle of said vehicle wheel according to a vehicle condition;a steering torque sensor for detecting a steering torque applied to said steering wheel;a control circuit for controlling said transfer ratio changing mechanism so as to cancel the steering torque applied to said steering wheel when the steering torque is detected until said transfer ratio control mechanism starts operation.

8. A vehicle steering system as in claim 7, wherein said transfer ratio changing mechanism comprises a gear mechanism connected between said steering wheel and said vehicle wheel so as to change the ratio of a steering angle of said steering wheel to a steered angle of said vehicle wheel.

9. A vehicle steering system as in claim 8, wherein: said transfer ratio changing mechanism further comprises a motor for driving said gear mechanism to change the ratio according to the vehicle condition; andsaid control circuit controls said motor to cancel the steering torque a steering torque sensor for detecting a steering torque when the steering torque is detected until said transfer ratio control mechanism starts operation.

10. A vehicle steering system for steering a steering wheel of a vehicle to thereby steer a vehicle wheel, said system comprising: a steering power assisting means for providing assisting steering power when said steering wheel is steered;a transfer ratio control mechanism, including an input shaft connected to said steering wheel and an output shaft connected to said vehicle wheel, for changing a ratio of a turning angle of said input shaft to a turning angle of said output shaft according to a vehicle condition;a steering torque sensor for detecting a steering torque applied to said steering wheel;a control circuit for controlling said transfer ratio changing mechanism so as to cancel the steering torque when the steering torque is detected until said transfer ratio control mechanism starts operation.