Electric power steering device

Abstract

To provide an electric power steering device that can reliably detect the abnormality of a steering angle sensor and prevent the generation of a wrong decision. When both the two differences (|θa−θr |, |θa−θe|) between an absolute steering angle value θa obtained from a steering angle sensor and a relative steering angle value θr estimated from the rotating angle sensor of a motor, and an estimated steering angle value ee estimated from the induced voltage of the motor respectively exceed predetermined values (threshold values), the steering angle sensor is determined to be failed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an external appearance of an electric power steering device according to the present invention;

FIG. 2 is a block diagram showing a specific structure of a microcomputer of FIG. 1;

FIG. 3 is a diagram for explaining a deviation between a relative steering angle θr or an estimated steering angle value θe and a true steering angle value;

FIG. 4 is an example of a flowchart showing the flow of a failure deciding process of a steering angle sensor in a first embodiment;

FIG. 5 is a control block diagram of a central processing unit of the first embodiment;

FIG. 6 is an example of a flowchart showing the flow of a failure deciding process of a steering angle sensor in a second embodiment;

FIG. 7 is a control block diagram of a central processing unit of the second embodiment;

FIG. 8 is a diagram for explaining the meaning of the estimation of a true steering angle;

FIG. 9 is an example of a flowchart showing the flow of a failure deciding process of a steering angle sensor in a third embodiment;

FIG. 10 is a control block diagram of a central processing unit of the third embodiment;

FIG. 11 is an example of a flowchart showing the flow of a failure deciding process of a steering angle sensor in a fourth embodiment; and

FIG. 12 is a control block diagram of a central processing unit of the fourth embodiment.

Claims

1. An electric power steering device, comprising: a steering wheel to which steering torque is input;a steering shaft being integral with the steering wheel;a torque sensor that detects steering torque of the steering wheel;a motor that applies assist load to the steering shaft; anda controller that drives the motor in accordance with magnitude of the steering torque,wherein the controller comprises:an absolute steering angle calculating part that calculates an absolute steering angle θa in accordance with a signal from a steering angle sensor;a relative steering angle calculating part that calculates a relative steering angle θr in accordance with a motor rotating angle sensor value from a motor rotating angle sensor of the motor;a steering angular velocity estimating part that estimates a steering angular velocity from voltage between terminals of the motor and a motor current;an estimated steering angle calculating part that calculates an estimated steering angle θe by integrating the steering angular velocity; anda comparing part that compares the difference between the absolute steering angle θa and the relative steering angle θr or the estimated steering angle θe with predetermined values respectively set thereto,wherein the steering angle sensor is decided to be abnormal, when following conditions are met: the difference between the absolute steering angle θa and the relative steering angle θr exceeds the corresponding predetermined value; andthe difference between the absolute steering angle θa and the estimated steering angle θe exceeds the corresponding predetermined value.

2. The electric power steering device according to claim 1, wherein the absolute steering angle θa is corrected by using an initial value θa0 of the absolute steering angle θa at a certain time,the relative steering angle θr is corrected by using an initial value θr0 of the relative steering angle θr at the substantially same time, andthe estimated steering angle θe is corrected by using an initial value θe0 of the estimated steering angle θe at the substantially same time.

3. The electric power steering device according to claim 1, further comprising a wheel rotating speed sensor, wherein an estimated value θ0 of true steering angle is estimated in accordance with a wheel rotating speed obtained by the wheel rotating speed sensor at a certain time,the relative steering angle θr is corrected by using the difference (θ0−θr0) between the estimated value θ0 at the certain time and the initial value θr0 of the relative steering angle θr at the substantially same time andthe estimated steering angle θe is corrected by using the difference (θ0−θe0) between the estimated value θ0 of the true steering angle at the certain time and the initial value θe0 of the estimated steering angle θe at the substantially same time.

4. The electric power steering device according to claim 1, further comprising a neutral angle estimating unit, wherein the relative steering angle θr is corrected by using the initial value θr0 of the relative steering angle θr at a time when the estimation of a neutral angle of the absolute steering angle by the neutral angle estimating unit is completed andthe estimated steering angle θe is corrected by using the initial value θe0 of the estimated steering angle θe at the substantially same time.

5. An electric power steering device comprising: a steering wheel to which steering torque is input;a steering shaft being integral with the steering wheel;a torque sensor that detects steering torque of the steering wheel;a motor that applies assist load to the steering shaft; anda controller that drives the motor in accordance with magnitude of the steering torque,wherein the controller comprises:a first steering angular velocity calculating art that calculates a steering angular velocity ωa in accordance with a signal from a steering angle sensor;a second steering angular velocity calculating part that calculates a steering angular velocity ωm in accordance with a motor rotating angle sensor value from a motor rotating angle sensor of the motor;a steering angular velocity estimating part that estimates a steering angular velocity ωe from voltage between terminals of the motor and a motor current; anda comparing part that compares difference between the steering angular velocity ωa by the steering angle sensor and the steering angular velocity ωm by the motor rotating angle sensor or the steering angular velocity ωe estimated from the voltage between the terminals of the motor and the motor current with predetermined values respectively set thereto,wherein the steering angle sensor is decided to be abnormal when the following conditions are met: when the difference between the steering angular velocity ωa and the steering angular velocity ωm exceeds the corresponding predetermined value andwhen the difference between the steering angular velocity ωa and steering angular velocity ωe exceeds the corresponding predetermined value.