Power steering apparatus for vehicle

• US 5,513,720 A
• Filed: 04/26/1995
• Issued: 05/07/1996
• Est. Priority Date: 10/23/1991
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Original Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Inventors: Yamamoto, Youichi, Yoshida, Hiroaki, Tanaka, Tadao, Momose, Nobuo, Harara, Mitsuhiko, Takeo, Tsuyoshi
• Primary Examiner(s): HILL, MITCHELL
• Application Number:
  US08/429,016
• Time in Patent Office: 377 Days
• Field of Search: 180/79.1, 180/142, 180/141, 180/143, 180/147, 180/148, 180/149, 180/DIG. 3, 180/DIG. 4, 180/DIG. 7
• US Class Current: 180/421
• CPC Class Codes: B62D 6/02 responsive only to vehicle speed

Abstract

A power steering apparatus for a vehicle including a steering mechanism having a torsion bar, a rotary valve connected to an oil pump and disposed between an input shaft and an output shaft, a valve driving mechanism having a pressed portion projected on either the input shaft or the output shaft and a plunger on the one shaft of the input shaft or output shaft on which the pressed portion is not projected for pressing the pressed portion, setting a target assist force of an assist force of an assist force obtained by rotating the rotary valve in the torsion direction of the torsion bar and an assist force obtained by rotating the rotary valve in the reverse direction to the torsion direction, a plunger driving mechanism for driving the plunger so that the preset assist force is obtained, controlling the pressure itself of the rotary valve to the operation angle of the rotary valve, whereby varying the steering force of the steering wheel over a wide range of steering condition with a reduced burden to the driver.

Claims

1. A power steering apparatus for a vehicle comprising:

a steering mechanism including an input shaft connected to a steering wheel side and an output shaft connected to steered wheels, rotatably supported coaxially in a housing and elastically connected to be rotatable relative to each other, for steering the steered wheels according to steering operation of said steering wheel;

valve means for controlling supply of a fluid to a power cylinder exerting an assist force on said output shaft according to relative rotation between said input shaft and said output shaft;

a pressed portion disposed to be projected to at least one side of said input shaft and said output shaft in a radial direction of the shaft;

a large-diameter portion disposed at least the other side of said input shaft or said output shaft and having a chamber for rotatably containing said pressed portion;

first and second hydraulic pressure chambers formed independent of each other between said housing and said large-diameter portion;

a first plunger slidably engaged with a hole formed in said large-diameter portion and opening to said first hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said first hydraulic pressure chamber for applying a rotational force to said input shaft or said output shaft;

a second plunger slidably engaged with a hole formed in said large-diameter portion and opening to said second hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said second hydraulic pressure chamber for applying a rotational force to said input shaft or said output shaft;

first and second annular oil passages connected individually to said first and second hydraulic pressure chambers; and

control valves for controlling hydraulic pressures to said first and second hydraulic pressure chambers for driving said first and second plungers through said first and second annular oil passages.

2. A power steering apparatus for a vehicle comprising:

a steering mechanism including an input shaft connected to a steering wheel side and an output shaft connected to steered wheels, rotatably supported coaxially in a housing and elastically connected to be rotatable relative to each other, for steering the steered wheels according to steering operation of said steering wheel;

valve means for controlling supply of a fluid to a power cylinder exerting an assist force on said output shaft according to relative rotation between said input shaft and said output shaft;

a pressed portion disposed to be projected to at least one side of said input shaft and said output shaft in a radial direction of the shaft;

a large-diameter portion disposed at least the other side of said input shaft or said output shaft and having a chamber for rotatably containing said pressed portion;

first and second hydraulic pressure chambers formed independent of each other between said housing and said large-diameter portion;

a first plunger slidably engaged with a hole formed in said large-diameter portion and opening to said first hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said first hydraulic pressure chamber for applying a rotational force to said input shaft or said output shaft;

a second plunger slidably engaged with a hole formed in said large-diameter portion and opening to said second hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said second hydraulic pressure chamber for applying a rotational force to said input shaft or said output shaft;

first and second annular oil passages connected individually to said first and second hydraulic pressure chambers;

control valves for controlling hydraulic pressures to said first and second hydraulic pressure chambers for driving said first and second plungers through said first and second annular oil passages; and

a fluid change-over circuit having a fixed mode for driving simultaneously said first and second plungers for regulating rotation of said input shaft or output shaft and a rotation mode for driving one of said first and second plungers for exerting a rotational force on said input shaft or said output shaft, whereby selecting one of said modes according to operation condition of the vehicles.

3. A power steering apparatus for a vehicle comprising:

a steering mechanism including an input shaft connected to a steering wheel side and an output shaft connected to steered wheels, rotatably supported coaxially in a housing and elastically connected to be rotatable relative to each other, for steering the steered wheels according to steering operation of said steering wheel;

valve means for controlling supply of a fluid to a power cylinder exerting an assist force on said output shaft according to relative rotation between said input shaft and said output shaft;

a pressed portion disposed to be projected to at least one side of said input shaft and said output shaft in a radial direction of the shaft;

a large-diameter portion disposed at least the other side of said input shaft or said output shaft and having a chamber for rotatably containing said pressed portion;

first and second hydraulic pressure chambers formed independent of each other between said housing and said large-diameter portion;

a first plunger slidably engaged with a hole formed in said large-diameter portion and opening to said first hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said first hydraulic chamber for applying a rotational force to said input shaft or said output shaft;

a second plunger slidably engaged with a hole formed in said large-diameter portion and opening to said second hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said second hydraulic pressure chamber for applying a rotational force to said input shaft or said output shaft;

first and second annular oil passages connected individually to said first and second hydraulic pressure chambers;

control valves for controlling hydraulic pressures to said first and second hydraulic pressure chambers for driving said first and second plungers through said first and second annular oil passages;

operation condition detection means for detecting operation condition of the vehicle; and

control means for controlling operation of said control valves in response to detection signal detected by said operation condition detection means.

4. The power steering apparatus for a vehicle of claim 3 wherein said operating condition detection means includes:

a vehicle speed sensor for detecting a traveling speed of the vehicle;

a steering wheel angle sensor for detecting a steering angle of said steering wheel; and

a torque sensor for detecting a torque applied to said steering wheel.

5. The power steering apparatus for a vehicle of claim 3 wherein an instruction control voltage outputted from said control means to a solenoid for operating said control valves is gradually increased at the beginning of control over said control valves and gradually decreased towards ending of control over said control valves.

6. The power steering apparatus for a vehicle of claim 3, wherein said control means has a steering force control function for driving at least said first or second plunger in the same direction as the steering direction of said steering wheel in a low-speed area of the vehicle less than a predetermined value for applying a rotational force of the same direction to said input or output shaft, whereby controlling operation of said control valves to assist steering of said steering wheel.

7. The power steering apparatus for a vehicle of claim 6, wherein said control means has a determination function for effecting the steering force control function, and the determination function compares a steering torque detected by said operation condition detection means and a preset control determination torque threshold value to effect the steering force control function when the steering torque exceeds the torque threshold value.

8. The power steering apparatus for a vehicle of claim 7, wherein said control means has steering direction determination means for comparing a steering torque of said steering wheel with a control determination threshold value corresponding to a steering direction of said steering wheel, and a steering wheel angular velocity calculated from a steering wheel angle detected by said operation condition detection means with a preset threshold value of steering wheel angular velocity corresponding to a steering direction of said steering wheel to determine whether the steering direction of said steering wheel is at right steering condition or a left steering condition;

and

said steering force control function is set to effect right steering control or left steering control according to the steering direction of said steering wheel determined by said steering direction determination means.

9. The power steering apparatus for a vehicle of claim 8 wherein said steering direction determination means is set so that the steering torque of said steering wheel and the steering wheel angular velocity are compared with the steering direction determination threshold value set in the reverse direction to a steering direction to be determined and the steering wheel angular velocity threshold value to determine the steering direction.

10. The power steering apparatus for a vehicle of claim 9, wherein said steering counter-force control function determines a torque difference from a target steering torque determined from the vehicle speed and the steering wheel angle detected by said operation condition detection means and a steering torque of said steering wheel detected by said operation condition detection means and drives said first and second plungers so that the steering torque approaches the target steering torque according to the torque difference.

11. The power steering apparatus for a vehicle of claim 8, wherein said steering direction control function drives said first or second plunger to even further assist steering of said steering wheel when a torque difference determined from a preset target steering torque and a steering torque of said steering wheel detected by said operation condition detection means is greater than a previous torque difference determined from the target steering torque and the previously detected steering torque, or reduces the assist to steering of said steering wheel with the passage of time when the torque difference is a negative value or the torque difference is smaller than the previous torque difference.

12. The power steering apparatus for a vehicle of claim 3, wherein said control means has a steering counter-force control function for driving at least said first or second plunger in the reverse direction to the steering direction of said steering wheel in a high-speed area of the vehicle more than a predetermined value for applying a rotational force of the reverse direction to said input or output shaft, whereby controlling operation of said control valves to regulate steering of said steering wheel.

13. The power steering apparatus for a vehicle of claim 12 wherein said steering counter-force control function has phase advance control means for positively increasing the steering wheel angle relative to the steering torque of said steering wheel by setting a target torque necessary for operation of said steering wheel by positive feedback of the steering wheel angular velocity.

14. The power steering apparatus for a vehicle of claim 3 wherein said control means has a centering control function for driving at least said first or second plunger in the reverse direction to the steering direction of said steering wheel in a low-speed area of the vehicle less than a predetermined value for applying a rotational force of the reverse direction to said input or output shaft, whereby controlling operation of said control valves to return said steering wheel to a neutral position.

15. The power steering apparatus for a vehicle of claim 14, wherein said centering control function has return direction determination means for determining a return direction of said steering wheel from a positive or negative condition of the steering wheel angle when an absolute value of steering wheel angle detected by said operation condition detection means exceeds a predetermined steering angle.

16. The power steering apparatus for a vehicle of claim 3, wherein said control means has a steering force control function for driving at least said first or second plunger in the same direction as the steering direction of said steering wheel in a low-speed area of the vehicle less than a predetermined value for applying a rotational force of the same direction to said input or output shaft, whereby controlling operation of said control valves to assist steering of said steering wheel, and

a steering counter-force control function for driving at least said first or second plunger in the reverse direction to the steering direction of said steering wheel in a high-speed area of the vehicle more than a predetermined value for applying a rotational force of the reverse direction to said input or output shaft, whereby controlling operation of said control valves to regulate steering of said steering wheel.

17. The power steering apparatus for a vehicle of claim 3, wherein said control means has a steering force control function for driving at least said first or second plunger in the same direction as the steering direction of said steering wheel in a low-speed ahead of the vehicle less than a predetermined value for applying a rotational force of the same direction to said input or output shaft, whereby controlling operation of said control valves to assist steering of said steering wheel;

and

a centering control function for driving at least said first or second plunger in the reverse direction to the steering direction of said steering wheel in a low-speed area of the vehicle less than a predetermined value for applying a rotational force of the reverse direction to said input or output shaft, whereby controlling operation of said control valves to return said steering wheel to a neutral position.

18. The power steering apparatus for a vehicle of claim 17 wherein said control means has a determination function for determining execution of one of said steering force control function and said centering control function, and said determination function compares a steering torque detected by said operation condition detection means and a preset control determination torque threshold for beginning execution of one of said two functions when the steering torque exceeds the torque threshold value.

19. The power steering apparatus for a vehicle of claim 18 wherein the control determination threshold value has a first torque threshold value for determining execution of said steering force control function, and a second torque threshold value for determining execution of said centering control function, the second torque threshold value being set greater than the first torque threshold value.

20. The power steering apparatus for a vehicle of claim 18 wherein the control determination threshold value has a first torque threshold value for determining execution of said steering force control function, and a second torque threshold value for determining execution of said centering control function, and said centering control function is effected when the steering torque of said steering wheel continues within the second torque threshold value for a predetermined length of time.

21. The power steering apparatus for a vehicle of claim 3 wherein said control means has a steering force control function for driving at least said first or second plunger in the same direction as the steering direction of said steering wheel in a low-speed area of the vehicle less than a predetermined value for applying a rotational force of the same direction to said input or output shaft, whereby controlling operation of said control valves to assist steering of said steering wheel;

a steering counter-force control function for driving at least said first or second plunger in the reverse direction to the steering direction of said steering wheel in a high-speed area of the vehicle more than a predetermined value for applying a rotational force of the reverse direction to said input or output shaft, whereby controlling operation of said control valves to regulate steering of said steering wheel; and

a centering control function for driving at least said first or second plunger in the reverse direction to the steering direction of said steering wheel in a low-speed area of the vehicle less than a predetermined value for applying a rotational force of the reverse direction to said input or output shaft, whereby controlling operation of said control valves to return said steering wheel to a neutral position.