Electric power steering apparatus for vehicle
First Claim
1. An electric power steering apparatus for a vehicle which includes operation force detection means for detecting operation force which is input by a driver so as to steer steerable wheels of the vehicle through rotation operation of a steering wheel;
- an electric motor for generating assist force so as to assist the rotation operation of the steering wheel by the driver; and
control means for controlling operation of the electric motor on the basis of an assist force corresponding to the operation force detected by the operation force detection means, the control means comprising;
vehicle speed detection means for detecting speed of the vehicle;
wheel speed detection means provided for each of front-side left and right wheels and rear-side left and right wheels of the vehicle for detecting speed of the corresponding wheel;
anomaly detection means for detecting an anomaly of the operation force detection means;
steering angle estimation means, operable when the anomaly detection means has detected an anomaly of the operation force detection means, for computing a first steering angle of the steerable wheels through use of the speeds of the front-side left and right wheels among those detected by the wheel speed detection means, computing a second steering angle of the steerable wheels through use of the speeds of the rear-side left and right wheels among those detected by the wheel speed detection means, and estimating the steering angle of the steerable wheels at the time when the vehicle is turning, through use of the first and second steering angles;
axial force estimation means for estimating an axial force through use of the steering angle estimated by the steering angle estimation means and the vehicle speed detected by the vehicle speed detection means, the axial force having a predetermined relation with the steering angle of the steerable wheels and the vehicle speed, and being input to a steering mechanism which steers the steerable wheels of the vehicle;
assist force computation means for determining a target steering force through use of the vehicle speed detected by the vehicle speed detection means, the target steering force having a predetermined relation with the vehicle speed and being input by the driver via the steering wheel, and for computing the assist force for assisting the rotation operation of the steering wheel by the driver, through use of the determined target steering force and the axial force estimated by the axial force estimation means;
operation control means for controlling operation of the electric motor on the basis of the assist force computed by the assist force computation means; and
operation speed detection means for detecting a rotational operation speed of the steering wheel, whereinthe steering angle estimation means includes filter processing means for performing low-pass filter processing for the speeds of the wheels detected by the wheel speed detection means, the low-pass filter processing having a predetermined cutoff frequency, andthe filter processing means performs the low-pass filter processing for the speeds of the wheels detected by the wheel speed detection means, while increasing the cutoff frequency as the rotational operation speed detected by the operation speed detection means increases, and decreasing the cutoff frequency as the detected rotational operation speed decreases.
1 Assignment
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Accused Products
Abstract
A steering angle estimation section calculates a front-wheel-side estimative steering angle and a rear-wheel-side estimative steering angle through use of wheel speeds of respective wheels, and averages these steering angles to thereby obtain an accurate estimative steering angle. It also calculates an estimative steering angle difference between the steering angles. An axial force estimation section calculates a base axial force through use of the estimative steering angle and a vehicle speed, and calculates a correction axial force which applies an axial force difference (hysteresis) to the base axial force in accordance with a turning or returning operation by a driver. The axial force estimation section adds the base axial force and the correction axial force together to thereby calculate an accurate estimative axial force. An assist computation section compares a target steering torque, which changes with the vehicle speed, and the accurate estimative axial force, and subtracts the target steering torque from the estimative axial force, to thereby calculate an assist torque.
17 Citations
13 Claims
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1. An electric power steering apparatus for a vehicle which includes operation force detection means for detecting operation force which is input by a driver so as to steer steerable wheels of the vehicle through rotation operation of a steering wheel;
- an electric motor for generating assist force so as to assist the rotation operation of the steering wheel by the driver; and
control means for controlling operation of the electric motor on the basis of an assist force corresponding to the operation force detected by the operation force detection means, the control means comprising;vehicle speed detection means for detecting speed of the vehicle; wheel speed detection means provided for each of front-side left and right wheels and rear-side left and right wheels of the vehicle for detecting speed of the corresponding wheel; anomaly detection means for detecting an anomaly of the operation force detection means; steering angle estimation means, operable when the anomaly detection means has detected an anomaly of the operation force detection means, for computing a first steering angle of the steerable wheels through use of the speeds of the front-side left and right wheels among those detected by the wheel speed detection means, computing a second steering angle of the steerable wheels through use of the speeds of the rear-side left and right wheels among those detected by the wheel speed detection means, and estimating the steering angle of the steerable wheels at the time when the vehicle is turning, through use of the first and second steering angles; axial force estimation means for estimating an axial force through use of the steering angle estimated by the steering angle estimation means and the vehicle speed detected by the vehicle speed detection means, the axial force having a predetermined relation with the steering angle of the steerable wheels and the vehicle speed, and being input to a steering mechanism which steers the steerable wheels of the vehicle; assist force computation means for determining a target steering force through use of the vehicle speed detected by the vehicle speed detection means, the target steering force having a predetermined relation with the vehicle speed and being input by the driver via the steering wheel, and for computing the assist force for assisting the rotation operation of the steering wheel by the driver, through use of the determined target steering force and the axial force estimated by the axial force estimation means; operation control means for controlling operation of the electric motor on the basis of the assist force computed by the assist force computation means; and operation speed detection means for detecting a rotational operation speed of the steering wheel, wherein the steering angle estimation means includes filter processing means for performing low-pass filter processing for the speeds of the wheels detected by the wheel speed detection means, the low-pass filter processing having a predetermined cutoff frequency, and the filter processing means performs the low-pass filter processing for the speeds of the wheels detected by the wheel speed detection means, while increasing the cutoff frequency as the rotational operation speed detected by the operation speed detection means increases, and decreasing the cutoff frequency as the detected rotational operation speed decreases. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
- an electric motor for generating assist force so as to assist the rotation operation of the steering wheel by the driver; and
Specification