Power steering apparatus

• US 20060237256A1
• Filed: 04/10/2006
• Published: 10/26/2006
• Est. Priority Date: 04/11/2005
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Takahashi, Toru, Sasaki, Mitsuo
• Granted Patent: US 7,735,596 B2
• Time in Patent Office: Days
• US Class Current: 180/442
• 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 includes a hydraulic power cylinder, and a reversible pump driven by a motor and connected by left and right fluid passages with left and right pressure chambers of the power cylinder. The first and second fluid passages are so arranged that pressure losses in the first and second passages are substantially equal to each other.

Claims

1. A power steering apparatus comprising:

a hydraulic power cylinder including first and second fluid pressure chambers to assist a steering mechanism;

a reversible pump including first and second outlets to supply a hydraulic pressure to the power cylinder;

a first fluid passage connecting the first outlet of the reversible pump with the first pressure chamber of the power cylinder;

a second fluid passage connecting the second outlet of the reversible pump with the second pressure chamber of the power cylinder,

a motor to drive the reversible pump in one of forward and reverse directions;

a steering load sensing section to ascertain a steering load of the steering mechanism; and

a motor controlling section to control the motor in accordance with the steering load;

wherein the first and second fluid passages are made substantially equal in pressure loss to each other.

2. The power steering apparatus as claimed in claim 1, wherein a difference between the pressure loss of the first fluid passage and the pressure loss of the second fluid passage is smaller than or equal to 0.5N·

m in terms of a steering torque.

3. The power steering apparatus as claimed in claim 1, wherein the power steering apparatus further comprises a correcting section to make the pressure losses of the first and second fluid passages (91, 92) substantially equal to each other.

4. The power steering apparatus as claimed in claim 3, wherein the correcting section includes a bend formed in at least one of the first and second fluid passages;

one of the first and second fluid passages is a longer passage longer than the other, and the other of the first and second fluid passages is a shorter passage shorter than the longer passage; and

the number of bends in the longer passage is smaller than the number of bends in the shorter passage.

5. The power steering apparatus as claimed in claim 3, wherein the motor controlling section is configured to produce a motor drive signal to drive the motor in accordance with the steering load;

and the correction section is configured to modify the motor drive signal to increase a pump discharge pressure for one of the first and second fluid passages which is greater in pressure loss than the other passage.

6. The power steering apparatus as claimed in claim 3, wherein the correcting section includes a variable flow restriction disposed in one of the first and second fluid passages and arranged to vary an opening area of the variable flow restriction in accordance with a temperature condition to equalize the pressure losses of the first and second fluid passages.

7. The power steering apparatus as claimed in claim 6, wherein one of the first and second fluid passages is a heat-affected passage disposed in surroundings including a heat source so that a temperature of a hydraulic fluid in the heat-affected passage tends to be higher than that in the other of the first and second fluid passages;

and the variable flow restriction is disposed in the heat-affected passage.

8. The power steering apparatus as claimed in claim 6, wherein the power steering apparatus further comprises a temperature condition sensor to sense a temperature condition affecting a kinetic viscosity of the hydraulic fluid, and the variable flow restriction is arranged to vary the opening area in accordance with the temperature condition sensed by the temperature condition sensor.

9. The power steering apparatus as claimed in claim 3, wherein the correcting section is configured to vary the pressure loss in at least one of the first and second fluid passages in accordance with an operating condition affecting a kinetic viscosity of the hydraulic fluid.

10. The power steering apparatus as claimed in claim 3, wherein the correcting section is configured to equalize temperature conditions of the first and second fluid passages.

11. The power steering apparatus as claimed in claim 10, wherein the correcting section includes a cooling device to decrease an oil temperature in one of the first and second fluid passages to equalize the oil temperatures in the first and second fluid passages.

12. The power steering apparatus as claimed in claim 10, wherein the correcting section includes a heating device to increase an oil temperature in one of the first and second fluid passages to equalize the oil temperatures in the first and second fluid passages.

13. The power steering apparatus as claimed in claim 10, wherein the correcting section includes a heat conducting device disposed between the first and second fluid passages and arranged to conduct thermal energy from one to the other of the first and second fluid passages.

14. The power steering apparatus as claimed in claim 13, wherein the heat conducting device is a heat exchanger disposed between the first and second fluid passages.

15. The power steering apparatus as claimed in claim 10, wherein the correcting section comprises a control valve disposed in a connection passage connecting the first and second fluid passages, and a circulation command section to open the control valve and to drive the motor to circulate the hydraulic fluid through the connection passage between the first and second passages.

16. The power steering apparatus as claimed in claim 9, wherein the correcting section comprises a heat insulating member provided for one of the first and second fluid passages which is closer to a heat source.

17. The power steering apparatus as claimed in claim 3, wherein the correcting section comprises a flow restriction disposed in a shorter passage which is one of the first and second fluid passages and which is shorter than the other.

18. The power steering apparatus as claimed in claim 1, wherein the first and second fluid passages are substantially equal in length.

19. The power steering apparatus as claimed in claim 1, wherein the number of bends in the first fluid passage is equal to the number of bends in the second fluid passage.

20. The power steering apparatus as claimed in claim 1, wherein the first and second fluid passages are equal in material.

21. The power steering apparatus as claimed in claim 8, wherein the first and second fluid passages are asymmetric with respect to an imaginary median plane bisecting the power cylinder into left and right equal halves.

22. The power steering apparatus as claimed in claim 1, wherein the number of bends in a longer passage which is a longer one of the first and second fluid passages is smaller than the number of bends in a shorter passage which is a shorter one of the first and second fluid passages.

23. The power steering apparatus as claimed in claim 1, wherein the cross sectional size of a longer passage which is a longer one of the first and second fluid passages is greater than the cross sectional size of a shorter passage which is a shorter one of the first and second fluid passages.

24. The power steering apparatus as claimed in claim 1, wherein a flow restriction is provided in a shorter passage which is a shorter one of the first and second fluid passages.

25. The power steering apparatus as claimed in claim 1, wherein the hydraulic power cylinder includes a cylinder tube, a piston received slidably in the cylinder tube and arranged to separate the first and second pressure chambers, a first rod extending in the first pressure chamber from the piston, and a second rod extending in the second pressure chamber from the piston;

one of the first and second fluid passages is a low-loss passage which is smaller in pressure loss than the other passage, and one of the first and second rods is a thicker rod having a cross sectional size greater than that of the other; and

the low loss passage is connected with the pressure chamber in which the thicker rod extends.

26. A power steering apparatus comprising:

a hydraulic power cylinder including first and second fluid pressure chambers to assist a steering mechanism;

a reversible pump including first and second outlets to supply a hydraulic pressure to the power cylinder;

a first fluid passage connecting the first outlet of the reversible pump with the first pressure chamber of the power cylinder;

a second fluid passage connecting the second outlet of the reversible pump with the second pressure chamber of the power cylinder,

a motor to drive the reversible pump in one of forward and reverse directions;

a steering load sensing section to ascertain a steering load of the steering mechanism; and

a motor controlling section to deliver a motor drive signal to control the motor in accordance with the steering load,

the motor controlling section being configured to modify the motor drive signal to increase a pump discharge pressure discharged from the reversible pump into one of the first and second fluid passages which is greater in pressure loss than the other.

27. An apparatus comprising:

a hydraulic power cylinder including first and second fluid pressure chambers to assist a steering mechanism;

a reversible pump including first and second outlets to supply a hydraulic pressure to the power cylinder;

a first fluid passage connecting the first outlet of the reversible pump with the first pressure chamber of the power cylinder;

a second fluid passage connecting the second outlet of the reversible pump with the second pressure chamber of the power cylinder,

a motor to drive the reversible pump in one of forward and reverse directions;

a steering load sensing section to ascertain a steering load of the steering mechanism; and

a motor controlling section to deliver a motor drive signal to control the motor in accordance with the steering load,

the first and second fluid passages being so arranged that an oil temperature in the first fluid passage is substantially equal to an oil temperature in the second fluid passage.

28. The apparatus as claimed in claim 27, wherein the first and second fluid passages are arranged so that thermal surroundings of the first fluid passage and thermal surrounds of the second fluid passage are approximately equal to each other.

29. The apparatus as claimed in claim 28, wherein the first and second fluid passages are placed near a heat source in an engine compartment of a vehicle.

30. The apparatus as claimed in claim 27, wherein the power steering apparatus comprises a temperature adjusting device adjusting an oil temperature of at least one of the first and second fluid passages to equalize temperature conditions of the first and second fluid passages.

31. The apparatus as claimed in claim 30, wherein the temperature adjusting device includes a cooling device to cool one of the first and second fluid passages to equalize the temperature conditions of the first and second fluid passages.

32. The apparatus as claimed in claim 30, wherein the temperature adjusting device includes a heating device to heat one of the first and second fluid passages to equalize the temperature conditions of the first and second fluid passages.

33. The apparatus as claimed in claim 30, wherein the temperature adjusting device includes a heat conducting device to conduct heat from one of the first and second fluid passages to the other to equalize the temperature conditions of the first and second fluid passages.

34. The apparatus as claimed in claim 33, wherein the heat conducting device is a heat exchanger provided between the first and second fluid passages.

35. The apparatus as claimed in claim 33, wherein the heat conducting device includes a connection valve disposed in a connecting passage connecting the first and second fluid passages, and arranged to open the connection passage to circulate the hydraulic fluid between the first and second fluid passages to equalize temperature conditions of the first and second fluid passages.

36. The apparatus as claimed in claim 35, wherein the power steering apparatus further comprises a circulation command section to open the connection valve and drive the motor in accordance with a temperature condition of at least one of the first and second fluid passages.

37. The apparatus as claimed in claim 36, wherein the power steering apparatus further comprises a circulation command section to open the connection valve and drive the motor when a difference between oil temperatures in the first and second fluid passages is greater than or equal to a predetermined value.

38. The apparatus as claimed in claim 30, wherein the first and second fluid passages are placed in an engine compartment of a vehicle, and the temperature adjusting device includes a heat insulating member provided for one of the first and second fluid passages which is closer to a heat source in the engine compartment.

39. The apparatus as claimed in claim 27, wherein the apparatus is a vehicle including a heat source disposed in an engine compartment of the vehicle, and the first and second fluid passages are disposed in the engine compartment so that at least one of the first and second fluid passages is thermally affected by the heat source.

40. A apparatus comprising:

a hydraulic power cylinder including first and second fluid pressure chambers to assist a steering mechanism;

a reversible pump including first and second outlets to supply a hydraulic pressure to the power cylinder;

a first fluid passage connecting the first outlet of the reversible pump with the first pressure chamber of the power cylinder;

a second fluid passage connecting the second outlet of the reversible pump with the second pressure chamber of the power cylinder,

a motor to drive the reversible pump in one of forward and reverse directions;

a steering load sensing section to ascertain a steering load of the steering mechanism; and

a motor controlling section to deliver a motor drive signal to control the motor in accordance with the steering load,

one of the first and second fluid passages being a hotter passage which is to be placed in surroundings tending to make an oil temperature in the hotter passage higher than an oil temperature in the other of the first and second fluid passages, and the pressure loss of the hotter passage is greater than the pressure loss of the other of the first and second fluid passages.

41. The apparatus as claimed in claim 40, wherein the power steering apparatus further comprises a variable flow restriction disposed in the hotter passage and arranged to decrease an opening size with an increase in an oil temperature in the hotter passage.

42. The apparatus as claimed in claim 41, wherein the power steering apparatus further comprises a throttle controlling section to control the opening degree of the variable flow restriction in accordance with a parameter representing an oil temperature in the hotter passage.

43. A apparatus comprising:

a hydraulic power cylinder including first and second fluid pressure chambers to assist a steering mechanism;

a reversible pump including first and second outlets to supply a hydraulic pressure to the power cylinder;

a first fluid passage connecting the first outlet of the reversible pump with the first pressure chamber of the power cylinder;

a second fluid passage connecting the second outlet of the reversible pump with the second pressure chamber of the power cylinder,

a motor to drive the reversible pump in one of forward and reverse directions;

a steering load sensing section to ascertain a steering load of the steering mechanism; and

a motor controlling section to deliver a motor drive signal to control the motor in accordance with the steering load,

one of the first and second fluid passages being arranged to vary a pressure loss in the passage in accordance with a temperature condition of the passage.