JP4194742B2 - Power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power steering apparatus for a vehicle, and more particularly to a technique for suppressing excessive vibration of wheels.
[0002]
[Prior art and problems to be solved by the invention]
2. Description of the Related Art Conventionally, a power steering apparatus that assists a steering force with hydraulic pressure is frequently used as a steering apparatus for a vehicle. This power steering device outputs a steering assist force by supplying hydraulic oil discharged from a hydraulic pump to a hydraulic cylinder. Between the hydraulic pump and the hydraulic cylinder, a steering direction and a steering are output. A hydraulic control valve that controls the supply of hydraulic oil to the hydraulic cylinder according to the resistance is interposed.
[0003]
In this type of power steering apparatus, the steering wheel excessively vibrates during traveling due to the accuracy of the components of the steering system, and this vibration is transmitted to the steering wheel via a cylinder rod of a hydraulic cylinder, for example. Shimmy phenomenon may occur. Therefore, a damper valve for preventing the occurrence of the shimmy phenomenon is provided in a hydraulic circuit connecting the hydraulic control valve and the hydraulic cylinder.
[0004]
The damper valve is interposed in hydraulic circuits 103 and 104 that individually connect the hydraulic control valve 101 and the left and right oil chambers 102a and 102b of the hydraulic cylinder 102, as shown in FIG. A check valve 105 that allows the flow of hydraulic oil to the hydraulic cylinder 102 side, and a throttle check valve 106 that allows the flow of hydraulic oil from the hydraulic cylinder 102 to the hydraulic control valve 101 side with a predetermined resistance. I have. According to the damper valve 100, when the cylinder rod 102c of the hydraulic cylinder suddenly moves to the left and right due to excessive vibration of the steering wheel, a small amount of hydraulic oil corresponding to the amount of movement moves to the check valve 105 and the throttle check valve 106. By preventing the passage of the sheet, the shimmy phenomenon is prevented from occurring.
However, since the conventional damper valve 100 includes the check valve 105 and the throttle check valve 106, there is a problem that the number of parts is large, the structure is complicated, and the manufacturing cost is high.
[0005]
On the other hand, the hydraulic control valve 101 tunes (resonates) with the pulsation of the hydraulic pump 107, the vibration of the engine, the vibration of the vehicle body frame system, etc., so that the hydraulic pressure of the hydraulic oil supplied from the hydraulic control valve 101 to the hydraulic cylinder 102 during steering. Fluctuates, and hydraulic vibration is generated in the oil chambers 102a and 102b of the hydraulic cylinder 102, resulting in an inconvenience that the steering wheel excessively vibrates.
Therefore, tuning of related parts such as steering system mount rigidity and hydraulic control valve characteristics has been performed, but the countermeasures by such tuning are considerably restricted in relation to the steering feeling. There was a problem that the excessive vibration of the ring could not be effectively suppressed.
[0006]
The present invention has been made in view of the above problems, and effectively suppresses the occurrence of a shimmy phenomenon or excessive vibration of a steered wheel due to vibration of a hydraulic control valve with a simple structure. It is an object of the present invention to provide a power steering device that can be used.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a power steering apparatus according to the present invention includes a hydraulic pump, a hydraulic cylinder that outputs a steering assist force by hydraulic fluid supplied from the hydraulic pump, and the hydraulic pump and the hydraulic cylinder. In a power steering apparatus provided with a hydraulic control valve that intervenes and controls supply and discharge of hydraulic oil to and from the hydraulic cylinder according to steering,
A buffer chamber facing the oil chamber of the hydraulic cylinder;
The oil chamber and the buffer chamber are normally shut off in a state that allows leakage of hydraulic oil, and a check valve is provided to connect the oil chamber and the buffer chamber when the oil pressure in the oil chamber exceeds a predetermined pressure. ,
The buffer chamber is formed as a recess in the inner wall of the cylinder wall of the hydraulic cylinder ;
The check valve includes a movable valve that moves to the buffer chamber side when the oil pressure in the oil chamber exceeds a predetermined pressure, and communicates the oil chamber with the buffer chamber. And a valve housing attached to the inner wall,
The movable valve of the check valve moves only within the valve housing, and the buffer chamber is arranged so as not to spatially overlap the check valve in the direction in which the movable valve moves (claim). Item 1).
[0008]
According to the power steering apparatus having the above-described configuration, when hydraulic vibration is generated in the oil chamber due to excessive vibration of the steered wheels or vibration of the hydraulic control valve, the check valve is moved between the oil chamber and the buffer chamber due to rapid hydraulic fluctuation. The hydraulic vibration is attenuated by alternately repeating the interruption and communication between the two. That is, when the oil pressure in the oil chamber exceeds a predetermined pressure due to the hydraulic vibration of the oil chamber, the check valve causes the oil chamber and the buffer chamber to communicate with each other, and a part of the hydraulic oil in the oil chamber flows into the buffer chamber. If the oil pressure in the oil chamber drops below the oil pressure in the buffer chamber from this state, the hydraulic oil that has flowed into the buffer chamber leaks from the buffer chamber to the oil chamber, and the oil pressure in the oil chamber is reduced. By reducing the decrease and repeating this operation, the hydraulic vibration is attenuated.
[0009]
The buffer chamber, since formed as recesses on the inner wall of the cylinder wall of the hydraulic cylinder, it is possible to simplify the structure than the case of separately forming the buffer chamber and the cylinder wall.
[0010]
The power steering apparatus, the movable valve of the check valve, optionally provided with a small hole to allow the leakage of hydraulic oil in a state of blocking the oil chamber and the buffer chamber (claim 2).
In this case, the hydraulic oil in the buffer chamber can be easily and reliably returned to the oil chamber by the small hole in a state where the oil chamber and the buffer chamber are blocked by the check valve.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view of an essential part showing an embodiment of a power steering apparatus of the present invention. This power steering apparatus is of a ball screw type, and includes an input shaft 1 connected to a steering wheel of a vehicle, and a ball screw 3 connected to the input shaft 1 via a torsion bar 2. .
[0013]
The torsion bar 2 has an upper end connected to the input shaft 1 via a pin 4 and a lower end connected to a ball screw 3 via a serration 5 so as to be integrally rotatable. The input shaft 1 is introduced into the housing 7 through the dust seal 6 and is rotatably fitted to the housing 7 via a roller bearing 9 and is relatively rotatable to the ball screw 3 via a bush 10. It is mated. The ball screw 3 is supported by the housing 7 via a ball bearing 11.
A ball nut 13 is fitted to the ball screw 3 via a large number of balls 12. A rack 15 is formed on the outer periphery of the ball nut 13, and a sector gear 16 formed on the output shaft 14 is engaged with the rack 15.
A pitman arm (not shown) is attached to the output shaft 14, and this pitman arm is connected to a steering wheel of the vehicle via a link.
[0014]
In the above configuration, when the input shaft 1 rotates in accordance with the rotation operation of the steering wheel, the rotation of the input shaft 1 is transmitted to the ball screw 3 through the torsion bar 2, and the ball nut 13 is rotated by the rotation of the ball screw 3. but moves in the axial direction. As a result, the output shaft 14 rotates through the rack 15 and the sector gear 16 to steer the steered wheels.
In order to assist the steering force of the steered wheels, a hydraulic cylinder 20 and a hydraulic control valve 30 that controls driving of the hydraulic cylinder 20 are provided inside the housing 7.
The hydraulic cylinder 20 includes a cylinder 21 formed by a part of the housing 7 and a piston 22 formed by a ball nut 13. Inside the cylinder 21, a pair of partitions partitioned by the piston 22 is provided. Oil chambers 23 and 24 are formed.
[0015]
The hydraulic control valve 30 is a known valve that supplies hydraulic oil from the hydraulic pump P to the oil chambers 23 and 24 in accordance with the steering direction and the steering resistance. The hydraulic control valve 30 has a valve member 31 interposed between the housing 7 and the input shaft 1, and the valve member 31 is connected to the ball screw 3 so as to be integrally rotatable. The hydraulic control valve 30 includes an input port 32 connected to the hydraulic pump P, a return port 33 connected to the reserve tank T, a first output port 34 connected to one oil chamber 23, and the other And a second output port 35 communicating with the oil chamber 24.
[0016]
The ports 32, 33, 34, and 35 communicate with each other via an oil passage between the input shaft 1 and the valve member 31, and the oil passage is connected to the input shaft 1 and the valve along with the torsion bar 2 being twisted. The opening degree is adjusted by relative rotation with the member 31. That is, since there is no steering resistance in the straight traveling state, the torsion angle of the torsion bar 2 is zero, the input port 32 and the return port 33 communicate with each other, and the hydraulic oil that is supplied from the hydraulic pump P to the hydraulic control valve 30 Is recirculated to the reserve tank T as it is. For this reason, hydraulic pressure does not act on the piston 22. When the steering resistance increases with steering, the torsion bar 2 is twisted according to the steering resistance, and the valve member 31 integrated with the ball screw 3 rotates relative to the input shaft 1. As a result, the opening of the oil passage between the input port 32 and the return port 33 is reduced, and hydraulic oil is supplied from the input port 32 to one of the oil chambers 23 and 24 according to the steering direction and the steering resistance. Then, the hydraulic oil in the other oil chamber is returned to the reserve tank T through the return port 33. Thereby, a steering assist force corresponding to the steering direction and the steering resistance acts on the ball nut 13.
[0017]
In the power steering apparatus having the above-described configuration, a thick portion 21b is formed at the center portion of the end wall 21a facing the one oil chamber 23 of the cylinder 21, and the thick portion 21b includes a thick portion 21b. A buffer chamber A is formed facing the oil chamber 23. The buffer chamber A is formed of a hole having a circular cross section, the inner back side thereof is closed, and the side facing the oil chamber 23 is opened. Thus, by forming the buffer chamber A inside the end wall 21a of the cylinder 21, the structure can be simplified as compared with the case where the buffer chamber A is configured separately from the cylinder 21.
[0018]
Further, the oil chamber 23 and the buffer chamber A are normally shut off from the opening side of the buffer chamber A, and the oil chamber 23 and the buffer chamber A are communicated when the oil pressure of the oil chamber 23 exceeds a predetermined pressure. A check valve 40 is provided.
Referring also to FIG. 2, the check valve 40 includes a cylindrical valve housing 41, a movable valve 42 inserted in the valve housing 41 in a state in which movement in the axial direction is permitted, and a valve housing. 1, a valve seat 43 provided at one end, a coil spring 44 that urges the movable valve 42 toward the valve seat 43, and a spring receiving portion that receives one end of the coil spring 44 at the other end of the valve housing 41. 45.
[0019]
The valve housing 41 has a press-molded cylindrical shape, and the outer periphery thereof is press-fitted into the inner periphery of the buffer chamber A.
The movable valve 42 is a press-molded cap type, and is provided with a pressure receiving portion 42 a that receives hydraulic oil supplied to the oil chamber 23, and is provided around the pressure receiving portion 42 a and is in close contact with the valve seat 43. A conical cylindrical seal portion 42b, a peripheral wall portion 42c extending from the seal portion 42b toward the spring receiving portion 45, and a small hole 42d formed in the central portion of the pressure receiving portion 42a are provided. A gap is provided between the peripheral wall portion 42c and the inner periphery of the valve housing 41 to allow the hydraulic oil to pass therethrough. The small hole 42d allows the hydraulic oil introduced into the buffer chamber A to leak into the oil chamber 23 in a state where the seal portion 42b is in close contact with the valve seat 43, and the leakage of the hydraulic oil is easy and reliable. Can be tolerated.
[0020]
The valve seat 43 is annular, and the outer periphery thereof is fitted in the inner peripheral groove of the valve housing 41. A conical seating surface on which the seal portion 42 b of the movable valve 42 is seated is formed on the inner surface of the valve seat 3.
The spring receiving portion 45 is integral with the valve housing 41, and partially protrudes inward from the other end portion of the valve housing 41.
The coil spring 44 is wound in a conical shape, and is interposed between the spring receiving plate 45 and the movable valve 42 in a state where the large diameter side abuts against the spring receiving portion 45 and is elastically contracted. is there. The biasing force of the coil spring 44 normally causes the movable valve 42 to be seated on the valve seat 43 against the pressure of the hydraulic oil supplied to the oil chamber 23, and hydraulic vibration is generated in the oil chamber 23. When the hydraulic pressure suddenly rises and the hydraulic pressure exceeds a predetermined pressure, the movable valve 42 is set to a value that separates from the valve seat 43.
[0021]
With the above configuration, when hydraulic vibration occurs in the oil chamber 23 due to excessive vibration of the steering wheel or vibration of the hydraulic control valve 30, the sudden movement of the hydraulic valve causes the movable valve 42 of the check valve 40 to move from the valve seat 43. The operation of separating and sitting on the valve seat 43 is repeated to attenuate the hydraulic vibration. That is, when the hydraulic pressure of the oil chamber 23 exceeds a predetermined pressure due to the hydraulic vibration of the oil chamber 23, the movable valve 42 of the check valve 40 separates from the valve seat 43 against the biasing force of the coil spring 44, and the oil chamber 23 and the buffer chamber A are communicated with each other, a part of the hydraulic oil in the oil chamber 23 flows into the buffer chamber A, and the oil pressure increase in the oil chamber 23 is alleviated. Further, in this state, when the oil pressure in the oil chamber 23 is lower than the oil pressure in the buffer chamber A, the hydraulic oil that has flowed into the buffer chamber A passes through the small hole 42d formed in the movable valve 42 of the check valve 40. The oil pressure in the oil chamber 23 is reduced. Therefore, the hydraulic vibration can be attenuated by repeating the above operation. For this reason, it is possible to effectively prevent the steering wheel from excessively vibrating due to the shimmy phenomenon or the hydraulic control valve 30 being synchronized with the vibration of the vehicle body system. it can.
In the above-described embodiment, the movable valve 42 is urged by the coil spring 44, but a disc spring may be used instead of the coil spring 44. Further, the buffer chamber and the check valve 40 may be provided facing the oil chamber 23 on the hydraulic control valve 30 side, or a pair may be provided facing each of the oil chambers 23 and 24.
[0022]
FIG. 3 is a cross-sectional view of an essential part showing a reference example of the power steering apparatus of the present invention . In this reference example , the movable valve of the check valve 40 is constituted by a ball 46 and a buffer chamber A is provided inside the check valve 40. In the check valve 40, the cylindrical valve housing 41 is screwed into the end wall 21 a of the cylinder 21 at the front end side and is covered with a cap 47 at the rear side. The inner periphery of the cap 47 is screwed into the outer periphery of the valve housing 41, and the opening end thereof is in close contact with the end wall 21 a of the cylinder 21 via the packing 48. Further, the seating surface of the valve seat 43 is formed with concave grooves 43a at a plurality of positions along the circumferential direction so that a gap can be partially formed with the ball 46 seated thereon. With the ball 46 seated on the seat 43, the hydraulic oil in the buffer chamber A can leak into the oil chamber 23 through the concave groove 43a. The rear end of the coil spring 44 is received by the inner bottom portion of the cap 47.
Also in this reference example , when the hydraulic vibration is generated in the oil chamber 23, the operation of the ball 46 of the check valve 40 moving away from the valve seat 43 or sitting on the valve seat 43 is repeated, so that the hydraulic vibration Can be attenuated.
[0023]
FIG. 4 is a cross-sectional view of a main part showing another reference example . In this reference example , an accumulator 50 is provided in communication with the oil chamber 23 of the hydraulic cylinder 20.
The accumulator 50 is made of an elastic material such as rubber that can be expanded and contracted, and hydraulic oil flows from the oil chamber 23 into the accumulator 50. The accumulator 50 can attenuate the hydraulic vibration by expanding or contracting when the hydraulic vibration is generated in the oil chamber 23. That is, when the hydraulic pressure of the oil chamber 23 exceeds a predetermined pressure due to the hydraulic vibration of the oil chamber 23, the hydraulic oil in the oil chamber 23 further flows into the accumulator 50 while expanding the accumulator 50. The rise is mitigated. In this state, when the oil pressure in the oil chamber 23 is lower than the oil pressure in the accumulator 50, the expanded accumulator 50 is contracted, and the working oil that has flowed into the accumulator 50 is returned to the oil chamber 23, 23 is alleviated. Therefore, the hydraulic vibration can be attenuated by repeating the above operation.
The accumulator 50 may be a diaphragm type. The accumulator 50 may be provided in communication with the oil chamber 23 on the hydraulic control valve 30 side, or a pair of accumulators 50 may be provided in communication with the oil chambers 23 and 24, respectively.
[0024]
【The invention's effect】
As described above, according to the power steering apparatus of the first aspect, when hydraulic vibration occurs in the oil chamber, the check valve is repeatedly opened and closed to supply the hydraulic oil in the oil chamber to the buffer chamber, The hydraulic vibration can be damped by returning the supplied hydraulic oil to the oil chamber. For this reason, it is possible to effectively suppress the occurrence of the shimmy phenomenon or excessive vibration of the steering wheel due to the vibration of the control valve with a simple structure.
[0025]
Further, the buffer chamber so to form a recess in the inner wall of the cylinder wall of the hydraulic cylinder, it can be further simplified structure.
[0026]
According to the power steering apparatus of the second aspect , since the movable valve of the check valve is provided with a small hole that allows leakage of hydraulic oil in a state where the oil chamber and the buffer chamber are shut off, the reverse valve With the oil valve and the buffer chamber blocked by the stop valve, the hydraulic oil can be easily and reliably returned to the oil chamber through the small hole.
[0027]
According to the power steering apparatus according to the reference example, the hydraulic vibration generated in the oil chamber by the accumulator can be damped, so that the excessive vibration of the steered wheels caused by the shimmy phenomenon and the vibration of the control valve can be reduced with a simple structure. It can be effectively suppressed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a power steering apparatus of the present invention.
FIG. 2 is an enlarged cross-sectional view of a main part of a buffer chamber portion.
3 is a cross-sectional view of a main part showing a reference example . FIG. 4 is a cross-sectional view of a main part showing another reference example . FIG. 5 is a schematic view showing a conventional power steering apparatus.
[Explanation of symbols]
20 hydraulic cylinder 21 cylinder 21a end wall 30 hydraulic control valve 40 check valve 42 movable valve 42d small hole 43 valve seat 50 accumulator A buffer chamber P hydraulic pump

Claims (2)

A hydraulic pump, a hydraulic cylinder that outputs a steering assist force by hydraulic oil supplied from the hydraulic pump, and a hydraulic cylinder that is interposed between the hydraulic pump and the hydraulic cylinder, and supplies and discharges hydraulic oil to and from the hydraulic cylinder according to steering. In a power steering apparatus provided with a hydraulic control valve for controlling
A buffer chamber facing the oil chamber of the hydraulic cylinder;
The oil chamber and the buffer chamber are normally shut off in a state that allows leakage of hydraulic oil, and a check valve is provided to connect the oil chamber and the buffer chamber when the oil pressure in the oil chamber exceeds a predetermined pressure. ,
The buffer chamber is formed as a recess in the inner wall of the cylinder wall of the hydraulic cylinder ;
The check valve includes a movable valve that moves to the buffer chamber side when the oil pressure in the oil chamber exceeds a predetermined pressure, and communicates the oil chamber with the buffer chamber. And a valve housing attached to the inner wall,
The movable valve of the check valve moves only within the valve housing, and the buffer chamber is arranged so as not to spatially overlap the check valve in the moving direction of the movable valve. Taking device.   The power steering apparatus according to claim 1, wherein the movable valve of the check valve is provided with a small hole that allows leakage of hydraulic oil in a state where the oil chamber and the buffer chamber are shut off.

Images