Power steering apparatus

• US 6,227,328 B1
• Filed: 05/20/1999
• Issued: 05/08/2001
• Est. Priority Date: 09/26/1997
• Status: Expired due to Fees

• Current Assignee: Koyo Seiko Co., Ltd. (Toyota Motor Corporation)
• Original Assignee: Koyo Seiko Co., Ltd. (Toyota Motor Corporation)
• Inventors: Shimizu, Yoshinobu
• Primary Examiner(s): Johnson, Brian L.
• Assistant Examiner(s): YEAGLEY, DANIEL S
• Application Number:
  US09/308,619
• Time in Patent Office: 719 Days
• Field of Search: 180/421, 180/422, 180/423, 180/441, 180/442, 180/446, 701/41, 701/42
• US Class Current: 180/422
• CPC Class Codes: B62D 5/065 characterised by specially adapted means for varying pressurised fluid supply based on need, e.g. on-demand, variable assist

Abstract

A power steering apparatus is provided which is adapted to generate a steering assist force by a hydraulic pressure generated by a pump driven by an electric motor. The apparatus includes: a steering angle detection section (11, S1, S4) for detecting an absolute steering angle on the basis of a steering angle midpoint and a relative steering angle; a first control section (31, S6, S8 to S10) for actuating the electric motor in response to the steering angle detection section detecting an absolute steering angle of not smaller than a first threshold value; and a second control section (31, S6, S11, S9, S10) for actuating the electric motor in response to a steering angle change becoming not smaller than a second thresold value which is smaller than the first threshold value when the absolute steering angle detection is not carried out by the steering angle detection section.

Claims

1. A power steering apparatus adapted to generate a steering assist force by a hydraulic pressure generated by a pump driven by an electric motor, the apparatus comprising:

steering angle detection means for detecting an absolute steering angle on the basis of a steering angle midpoint and a relative steering angle;

first control means for actuating the electric motor in response to the steering angle detection means detecting an absolute steering angle that is not smaller than a first threshold value; and

second control means for actuating the electric motor in response to a steering angle change being not smaller than a second threshold value, which is smaller than the first threshold value, when absolute steering angle detection is not carried out by the steering angle detection means due to the steering angle midpoint being undetected.

2. A power steering apparatus as set forth in claim 1, wherein

the steering angle detection means includes a steering angle sensor for outputting relative steering angle data, and midpoint detection means for determining the steering angle midpoint on the basis of the relative steering angle data outputted from the steering angle sensor,

the power steering apparatus further comprising means for judging whether or not the absolute steering angle detection to be carried out by the steering angle detection means, on the basis of whether or not the steering angle midpoint has been determined by the midpoint detection means.

3. A power steering apparatus as set forth in claim 2, further comprising

means for actuating the electric motor on a condition that the absolute steering angle reaches a third threshold value which is greater than the second threshold value if the absolute steering angle is at a level within a predetermined range around the steering angle midpoint, and actuating the electric motor in response to the steering angle change reaching a fourth threshold value which is smaller than the third threshold value if the absolute steering angle is at a level out of the predetermined range, when the absolute steering angle detection is carried out by the steering angle detection means.

4. A power steering apparatus as set forth in claim 2, further comprising:

vehicle speed detection means for detecting a vehicle speed; and

means for switching between an absolute steering angle based motor actuation control and a steering angle change based motor actuation control in accordance with whether or not the absolute steering angle detection is carried out by the steering angle detection means, when the vehicle speed detected by the vehicle speed detection means is lower than a predetermined level.

5. A power steering apparatus as set forth in claim 1, further comprising:

means for actuating the electric motor on a condition that the absolute steering angle reaches a third threshold value which is greater than the second threshold value, if the absolute steering angle is at a level within a predetermined range around the steering angle midpoint, and actuating the electric motor in response to the steering angle change reaching a fourth threshold value which is smaller than the third threshold value if the absolute steering angle is at a level out of the predetermined range, when the absolute steering angle detection is carried out by the steering angle detection means.

6. A power steering apparatus as set forth in claim 5, further comprising:

vehicle speed detection means for detecting a vehicle speed; and

means for switching between an absolute steering angle based motor actuation control and a steering angle change based motor actuation control in accordance with whether or not the absolute steering angle detection is carried out by the steering angle detection means, when the vehicle speed detected by the vehicle speed detection means is lower than a predetermined level.

7. A power steering apparatus as set forth in claim 1, further comprising:

vehicle speed detection means for detecting a vehicle speed; and

means for switching between an absolute steering angle based motor actuation control and a steering angle change based motor actuation control in accordance with whether or not the absolute steering angle detection is carried out by the steering angle detection means, when the vehicle speed detected by the vehicle speed detection means is lower than a predetermined level.

9. A method as set forth in claim 5, further comprising the steps of:

actuating the electric motor on a condition that the absolute steering angle reaches a third threshold value which is greater than the second threshold value, if the absolute steering angle is at a level within a predetermined range around the steering angle midpoint, when the absolute steering angle detection is carried out by the steering angle detection means; and

actuating the electric motor in response to the steering angle change reaching a fourth threshold value which is smaller than the third threshold value, if the absolute steering angle is at a level out of the predetermined range.

8. An electric motor actuation control method to be applied to a power steering apparatus having a steering angle detection means for detecting an absolute steering angle on the basis of a steering angle midpoint and a relative steering angle, and having an electric motor for driving a pump for generating a steering assist force, the method comprising:

a first control step of actuating the electric motor in response to the steering angle detection means detecting an absolute steering angle that is not smaller than a first threshold value; and

a second control step of actuating the electric motor in response to a steering angle change being not smaller than a second threshold value, which is smaller than the first threshold value, when absolute steering angle detection is not carried out by the steering angle detection means due to the steering angle midpoint being undetected.