JPH06340271A - Hydraulic power steering gear - Google Patents

Abstract

PURPOSE:To provide the responsive property and stability of steering by providing a means for changing the opening of a second variable throttle section according to running requirements to enlarge the opening in proportion to the increase of vehicle speed while lessening the opening in proportion to the increase of the upstream pressure in a first variable throttle section. CONSTITUTION:The opening of a second variable throttle section 91 of a bypass path 90 affording communication between the high pressure side and low pressure side a flow path between valves 27 is enlarged in proportion to the increase of vehicle speed to be changed for lessening a steering assist force. On the other hand, the opening of the second vehicle throttle section 91 is reduced in proportion to the reduction of the vehicle speed and changed to increase the steering assist force. Further, the opening of a first variable throttle section 80 is reduced in proportion to the increase of steering resistance to increase the upstream pressure in the first variable throttle section 80, so that the opening of the second variable throttle section 91 is lessened and changed to increase the steering assist force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic power steering system capable of applying a steering assist force in accordance with operating conditions such as steering resistance and vehicle speed and steering angle.

[0002]

2. Description of the Related Art A hydraulic actuator that generates a steering assist force and a hydraulic control valve that controls the hydraulic pressure acting on the hydraulic actuator according to the steering resistance are provided. When the steering resistance increases, the hydraulic pressure supplied to the hydraulic actuator increases. However, a hydraulic power steering device that applies a steering assist force according to steering resistance has been conventionally used.

As such a hydraulic control valve, a cylindrical first
A valve member and a second valve member that is inserted into the first valve member so as to be rotatable relative to the first valve member, and a valve between the inner periphery of the first valve member and the outer periphery of the second valve member. The inter-passage is connected to the pump, the tank, and the hydraulic actuator for generating steering assist force, and the opening is changed in the inter-passage to increase the steering assist force as the relative twist angle of both valve members increases. A rotary control valve provided with a throttle portion is used, and the hydraulic pressure acting on the hydraulic actuator is controlled according to the steering resistance by changing the flow passage area of the throttle portion in the inter-valve flow passage according to the steering resistance. There is.

In the hydraulic power steering system as described above, in order to satisfy the high steering response during low speed traveling and the steering stability during high speed traveling, two sets of throttle portions of the inter-valve passage are used. When divided into groups, the flow passage area of the throttle portions belonging to the second set is made larger than the flow passage area of the throttle portions belonging to the first set under constant steering resistance. It has been proposed to provide a variable throttle valve between the tank and the tank for changing the flow passage area of the discharge-side oil passage according to operating conditions such as vehicle speed (Japanese Patent Laid-Open No. 2-30687).
No. 8).

That is, as shown in FIG. 12, the pump 1
00, tank 101, and hydraulic cylinder 1 for generating steering assist force
The inter-valve passages 104 and 105 between the two systems are provided with two systems, and the inter-valve passages 104 of one system are provided with throttle portions A, B, C and D belonging to the first set, and the inter-valve passages of the other system are provided. Channel 10
5, throttle parts A ', B', C ', D'belonging to the second set are provided, and the variable throttle valve 102 is arranged downstream of the intervalve passage 105 of the other system. At the time of right steering, the throttles A, A ', D, D'are opened and at the same time the throttles B, B', C, C'are closed, and at the time of left steering, the throttles A, A ', D'are made according to the steering resistance. , D ′ are closed and the throttle B is
Open B ', C, C'. Then, by closing the variable throttle valve 102 during low speed traveling, the hydraulic pressure acting on the hydraulic cylinder 103 is controlled only by the throttle portions A, B, C and D belonging to the first group, and during high speed traveling the variable throttle valve 102 is controlled. By opening 102, the narrowed portions A ′, B ′ belonging to the second set,
The hydraulic pressure acting on the hydraulic cylinder 103 is also controlled by C'and D '.

As a result, when the vehicle is traveling at a low speed, even if the steering input torque is small and the relative twist angles of both valve members are small, the throttle portion belonging to the first group (A when steering to the left,
Since the flow passage area of B, C) becomes small at the time of D, right steering, the increase rate of the hydraulic pressure for generating the steering assist force with respect to the steering resistance becomes large, and the high responsiveness of steering can be satisfied. Further, at the time of high speed traveling, unless the steering input torque is increased to increase the relative twist angle of both valve members, the throttle parts A ', B', C ', belonging to the second group,
Since the flow passage area of D'is kept large, the increase rate of the hydraulic pressure for generating the steering assist force with respect to the steering resistance is small,
It is possible to satisfy the steering stability.

[0007]

SUMMARY OF THE INVENTION In the above conventional configuration,
When traveling at medium speed, it may not be possible to apply the steering assist force according to the steering resistance. That is, FIG.
In FIG. 3, a solid line P indicates the change characteristic of the flow passage area with respect to the relative twist angle of both valve members in the throttle portion (A, D during left steering, B, C during right steering) belonging to the first set, and one point. The chain line Q shows the change characteristic of the flow passage area with respect to the relative twist angle of both valve members in the throttle portion (A ', D'for left steering, B', C'for right steering) belonging to the second set, and the broken line. R indicates the flow passage area of the variable throttle valve 102. The flow passage area of the variable throttle valve 102 changes depending on the vehicle speed. Since the variable throttle valve 102 is in a fully closed state at low speed running, the steering assist force corresponding to the change characteristic of the flow passage area of the throttle portions A, D or B, C belonging to the first set shown by the solid line P is the steering resistance. It is given according to. In addition, the variable throttle valve 102
Since the flow path area of the second flow path is made larger than the maximum value of the flow path area of the throttle portions A ′, D ′ or B ′, C ′ belonging to the second set when traveling at high speed, Change characteristics of the flow passage area of the throttle portions A ′, D ′ or B ′, C ′ belonging to the set, and the change of the flow passage area of the throttle portions A, D or B, C belonging to the first set shown by the solid line P A steering assist force corresponding to the combined value with the characteristic is applied according to the steering resistance.

However, at the time of traveling at medium speed, the flow passage area of the variable throttle valve 102 is larger than 0 as shown by a broken line R in FIG. Maximum value of flow path area of D'or B ', C' (S)
Will be smaller than. Therefore, until the throttle portions A, D or B, C belonging to the first set are in the fully closed state (see FIG.
(Until the relative twist angle of both valve members becomes θ1), the throttle portions A and D belonging to the first set indicated by the solid line P
Alternatively, a steering assist force corresponding to the combined value of the flow path area change characteristic values of B and C and the flow path area value of the variable throttle valve 102 indicated by the broken line R is applied according to the steering resistance. And the first
After the throttle parts A, D or B, C belonging to the second set are fully closed, the flow passage area of the throttle parts A ′, D ′ or B ′, C ′ belonging to the second set is variable. Until the flow passage area becomes smaller than the flow passage area of the variable throttle valve 102 (the relative twist angle between both valve members is between θ1 and θ2 in FIG. 13), the steering assist force becomes a constant value determined by the flow passage area of the variable throttle valve 102. Will end up. That is, as indicated by the chain double-dashed line in FIG. 14, the steering resistance changes in the relationship between the steering input torque corresponding to the steering resistance and the hydraulic pressure for generating the steering assist force with respect to the relative twist angle of both valve members. Nevertheless, the steering assist force becomes constant. If the area where such steering assist force cannot be controlled according to the steering resistance becomes large,
There is a problem that the steering feeling is reduced.

Further, in the above configuration, the steering assist force increases as the steering resistance increases, but the increase rate of the steering assist force is constant in the small steering resistance range and the large steering resistance range. This is because the rate of change of the flow passage area of the throttle portion of the inter-valve flow passage with respect to the steering resistance is almost constant in the area where the steering assist force is generated, regardless of the magnitude of the steering resistance. Therefore, if the increase rate of the steering assist force is set on the basis of the small steering resistance range, the steering response is lowered in the range of large steering resistance, and if the high steering resistance range is set on the basis of the steering resistance, the steering resistance is small. There is a problem that the stability of steering falls in the range. Therefore, it is conceivable that the rate of change of the flow passage area of the throttle portion with respect to the steering resistance is made different in the range where the relative twist angle of both valve members is large and in the range where the steering assist force is generated. However, for that reason, the shape of the narrowed portion becomes complicated and it is difficult to process in reality. Further, in the above configuration, the flow velocity of the pressure oil passing through the throttle portion of the inter-valve flow passage becomes large as the steering resistance becomes large, so that a large flow noise is generated.

An object of the present invention is to provide a hydraulic power steering system which can solve the above-mentioned problems of the prior art.

[0011]

SUMMARY OF THE INVENTION The present invention has a first valve member and a second valve member which is inserted into the first valve member so as to be relatively rotatable in response to steering resistance. The inter-valve flow path between the valve member and the second valve member is communicated with the pump, the tank and the hydraulic actuator for generating the steering assist force, and the inter-valve flow path is steered as the relative twist angle of both valve members increases. In a hydraulic power steering system in which a throttle portion whose opening degree is changed so as to increase the assisting force is provided, a first variable throttle portion is provided in a flow passage that connects the intervalve passage and the tank. In order to reduce the opening degree of the variable throttle section 1 as the steering resistance increases,
Means for changing the relative twist angle of the two valve members is provided, and a second variable throttle section is provided in a bypass passage that connects the high-pressure side of the inter-valve passage to the low-pressure side.
Means for changing the opening degree of the variable throttle portion in accordance with the operating condition so as to increase as the vehicle speed increases, and to decrease it as the upstream pressure of the first variable throttle portion increases. It is characterized by being provided.

[0012]

According to the structure of the present invention, the relative twist angle of both valve members increases as the steering resistance increases, and the opening degree of the throttle portion of the inter-valve flow passage changes according to the relative twist angle. Change to increase. On the other hand, as the steering resistance decreases, the relative twist angle of both valve members decreases, and the opening degree of the throttle portion of the inter-valve flow passage changes in accordance with the relative twist angle so as to decrease the steering assist force.

Further, as the vehicle speed increases, the opening degree of the second variable throttle portion of the bypass passage connecting the high pressure side of the inter-valve flow path to the low pressure side increases, and the steering assist force changes so as to decrease. On the other hand, as the vehicle speed decreases, the opening degree of the second variable throttle portion decreases, and the steering assist force changes to increase.

Further, as the steering resistance increases, the opening degree of the first variable throttle portion decreases and the upstream pressure of the first variable throttle portion increases, which causes the second variable passage portion of the bypass passage.
The degree of opening of the variable throttle unit is decreased and is changed so as to increase the steering assist force. On the other hand, as the steering resistance decreases, the opening degree of the first variable throttle unit increases and
The upstream pressure of the variable throttle part of becomes small,
The opening degree of the second variable throttle portion of the bypass path increases and changes so as to reduce the steering assist force.

The increase rate of the hydraulic pressure for generating the steering assist force is determined by the combined value of the opening degree of the throttle portion in the intervalve passage and the opening degree of the second variable throttle portion in the bypass passage. As a result, there will be no region where the steering assist force cannot be controlled according to the steering resistance. Therefore, even when the steering resistance is small when the vehicle is traveling at low speed or when the vehicle is stopped, it is possible to increase the rate of increase in the hydraulic pressure that generates the steering assist force and to satisfy the high responsiveness of steering. As long as the steering resistance does not increase, the rate of increase in the hydraulic pressure that generates the steering assist force does not increase, and steering stability can be satisfied. Stability can be obtained.

Then, not only the opening of the throttle portion in the inter-valve flow passage but also the opening of the second variable throttle portion is changed by the change of the steering resistance, so that the inter-valve flow is generated in the area where the steering assist force is generated. Even if the rate of change of the opening of the throttle on the road is constant, the rate of increase of the steering assist force generating hydraulic pressure is increased as the steering resistance increases due to the change of the degree of opening of the second variable throttle. You can As a result, the rate of increase of the steering assist force is made larger in the range of large steering resistance than in the range of small steering resistance, steering response is improved in the range of large steering resistance, and steering stability is improved in the range of small steering resistance. be able to.

The opening degree of the first variable throttle portion provided in the flow passage that connects the intervalve passage and the tank becomes smaller as the steering resistance becomes larger, whereby the upstream of the first variable throttle portion. Since the side pressure increases, the opening decreases as the steering resistance increases in the inter-valve flow path, and the pressure difference between the upstream side and the downstream side of the throttle portion decreases. Thereby, the flow velocity of the pressure oil passing through the throttle portion can be reduced to reduce the flow noise.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

The rack and pinion type hydraulic power steering system 1 shown in FIG. 2 has an input shaft 2 connected to a steering wheel (not shown) of a vehicle, a torsion bar 6 inserted through the input shaft 2, and the input shaft 2. And an output shaft 3 connected through the torsion bar 6. The torsion bar 6 is connected to the input shaft 2 via a pin 4 and is connected to the output shaft 3 via a serration 5. The input shaft 2 is supported by a valve housing 7 via a bearing 8 and is relatively rotatably supported by an inner peripheral surface of a recess formed in the output shaft 3 via a bush 12 that also serves as a seal. The output shaft 3 is rotatably supported by a rack housing 9 via bearings 10 and 11.
A pinion 15 is formed on the output shaft 3, and a steering wheel (not shown) is connected to a rack 16 that meshes with the pinion 15. As a result, the rotation of the input shaft 2 due to steering is transmitted to the pinion 15 via the torsion bar 6, the rotation of the pinion 15 moves the rack 16 in the vehicle width direction, and the movement of the rack 16 causes steering of the vehicle. Done. Oil seals 42 and 43 are interposed between the input / output shafts 2 and 3 and the valve housing 7. In addition, the support yoke 40 that supports the rack 16 has a spring 4
It is pressed against the rack 16 by the elastic force of 1.

A hydraulic cylinder 20 is provided as a hydraulic actuator that applies a steering assist force. The hydraulic cylinder 20 includes a cylinder tube configured by the rack housing 9 and a piston 21 integrated with the rack 16. A rotary hydraulic control valve 30 is provided in order to supply pressure oil to the oil chambers 22 and 23 partitioned by the piston 21 according to the steering direction and steering resistance.

The control valve 30 has a tubular first valve member 3 rotatably inserted in the valve housing 7.
1 and a second valve member 32 inserted into the first valve member 31 so as to be relatively rotatable. The first
The valve member 31 is connected to the output shaft 3 via a pin 29 so as to rotate together. The second valve member 32 is formed integrally with the input shaft 2, and the outer peripheral portion of the input shaft 2 serves as the second valve member 32, whereby the second valve member 32 rotates together with the input shaft 2.

The valve housing 7 has an inlet port 34 connected to the pump 70, an outlet port 36 connected to the tank 71, and a first port 37 connected to one oil chamber 22 of the hydraulic cylinder 20. , And a second port 38 connected to the other oil chamber 23. Each port 34, 36, 37, 38 has its first valve member 31
Between the valve and the second valve member 32, the inter-valve flow path 27
Communicate with each other via. The opening degree of the throttle portion of the inter-valve flow path 27 changes due to the relative rotation of the input shaft 2 and the output shaft 3.

That is, as shown in FIG. 4, eight first recesses 50 are formed on the inner circumference of the first valve member 31 at equal intervals in the circumferential direction, and second recesses 51 are formed on the outer circumference of the second valve member 32. 8 are formed at equal intervals in the circumferential direction. The first recess 50 communicates with the first port 37 via a flow passage 53 formed in the first valve member 31, and a flow passage 54 formed in the first valve member 31.
And those communicating with the second port 38 via the are alternately arranged in parallel along the circumferential direction. The second recess 51, which communicates with the inlet port 34 via the pressure oil supply passage 55 formed in the first valve member 31, and which communicates with the outlet port 36 alternate in the circumferential direction. Parallel to. The second recess 51 communicates with the outlet port 36 via a first variable throttle 80 which will be described later.

The edge of the first recess 50 along the axial direction and the second edge
The space between the recess 51 and the edge along the axial direction is the narrowed portion A,
They are B, C, and D.

The input shaft 2 and the output shaft 3 relatively rotate due to the torsion of the torsion bar 6 due to the resistance transmitted from the road surface through the steering wheel. That is, the first valve member 31 and the second valve member 32 relatively rotate according to the steering resistance. As a result, the opening degree of the throttle portion of the inter-valve flow path 27 changes, and the pressure oil is supplied to the hydraulic cylinder 20 that applies the steering assist force according to the steering direction and the steering resistance. That is, FIG.
Indicates that steering is not being performed, and the inlet port 34
And the outlet port 36 communicate with each other via the inter-valve flow path 27, and the oil flowing from the pump 70 into the control valve 30 flows back to the tank 71, and no steering assist force is generated. When the first valve member 31 and the second valve member 32 rotate relative to each other due to steering resistance generated by steering to the left or right from this state, the circumferential relative position of the second recess 51 with respect to the first recess 50 changes. As a result, the opening degree of the throttle portion of the intervalve flow path 27 changes. That is, the inlet port 34 and the first port 37
The opening of the throttle portion A between the first port 37 and
The opening degree of the throttle portion B between the inlet port 34 and the outlet port 36 is reduced, and the throttle portion C between the inlet port 34 and the second port 38 is reduced.
Becomes smaller, and the second port 38 and the outlet port 36
The opening degree of the narrowed portion D between and becomes large. by this,
Pressure oil having a pressure according to the steering direction and steering resistance is supplied to one oil chamber 22 of the hydraulic cylinder 20, and the other oil chamber 2
The oil flows back from the tank 3 to the tank 71, and the steering assist force to one of the left and right sides of the vehicle acts on the rack 16 by the hydraulic cylinder 20. Further, when steering to the other left or right, the input shaft 2 and the output shaft 3
Rotate relative to each other in the opposite direction, the opening degree decreases in the throttle portion A, the opening degree increases in the throttle portion B, and the throttle portion C increases.
The opening degree becomes larger at, and the opening degree becomes smaller at the throttle portion D. As a result, the steering assisting force to the other of the left and right of the vehicle acts on the rack 16 by the hydraulic cylinder 20.

The second recess 51 in the intervalve flow path 27
Communicates with the space between the inner and outer circumferences of the torsion bar 6 and the input shaft 2 through the flow path 52a formed in the input shaft 2, and the space between the inner and outer circumferences of the torsion bar 6 and the input shaft 2 is Three
Communicates with the outlet port 36 via the first variable throttle unit 80 shown in FIG. That is, a pair of flat surfaces 81 parallel to each other are formed on the outer periphery of the lower end of the input shaft 2, and a stopper surface 82 facing the flat surface 81 at a distance is provided in a recess formed at the upper end of the output shaft 3. When the relative twist angle of the input shaft 2 with respect to the output shaft 3 becomes a constant value, the flat surface 81 abuts the stopper surface 82, and the relative twist angle is prevented from becoming excessive. Four oil passages 83 that open to the outer peripheral flat surface 82 and the inner peripheral surface of the input shaft 2 are formed, and a torsion bar is formed from the oil passages 83 through slits (not shown) formed in the output shaft 3. The pressure oil between the inner and outer circumferences of 6 and the input shaft 2 reaches the outlet port 36. The four oil passages 83 are formed so as to expand in the radial direction from the center of the input shaft 2. The pressure oil flowing out from two of the four oil passages 83 changes from a state where the steering resistance is small as shown in (1) of FIG. 3 to a state where the steering resistance is large as shown in (2) of FIG. Then, the relative twist angle of the input shaft 2 with respect to the output shaft 3, that is, the relative twist angle of the valve members 31, 32 becomes large, so that the flat surface 81 approaches the stopper surface 82 and the outlets of the two oil passages 83. The distance between the stopper surface 82 and the stopper surface 82 becomes narrower, and the space between the flat surface 81 and the stopper surface 82 is narrowed. That is, the opening degree of the first variable throttle portion 80 changes in accordance with the relative twist angle of the valve members 31 and 32 such that the opening degree decreases as the steering resistance increases. As a result, the upstream pressure of the first variable throttle 80 increases as the steering resistance increases. In order to prevent the pressure oil between the inner and outer circumferences of the torsion bar 6 and the input shaft 2 from reaching the outlet port 36 without passing through the first variable throttle 80, as described above, the input shaft 2 outputs It is supported on the inner peripheral surface of the recess formed in the shaft 3 via a bush 12 that also serves as a seal.

The valve housing 7 is provided with an intervalve flow passage 27.
Of the bypass passage 90 connecting the high pressure side to the low pressure side and the opening degree of the second variable throttle portion 91 provided in the bypass passage 90 are changed according to the driving condition so as to be increased as the vehicle speed increases. A throttle valve 92 is provided for changing the pressure so that the upstream pressure of the first variable throttle section 80 becomes smaller as the pressure increases.

That is, the bypass passage 90 is composed of the first passage 90a and the second passage 90b. One end of the first flow passage 90a is connected to the first port 37 of the control valve 30 communicating with the one oil chamber 22 of the hydraulic cylinder 20, and the other end thereof is connected to the throttle valve 92. The second flow passage 90b has one end connected to the second port 38 of the control valve 30 communicating with the other oil chamber 23 of the hydraulic cylinder 20, and the other end connected to the throttle valve 92. By communicating one oil chamber 22 and the other oil chamber 23 of the hydraulic cylinder 20 via the bypass passage 90, the high pressure side of the intervalve passage 27 communicates with the low pressure side. The oil pressure in the inter-valve flow passage 27 is uniform in the state where no steering assist force is generated,
When the steering assist force is generated, there are a high hydraulic pressure portion and a low hydraulic pressure portion depending on the steering direction. The high hydraulic pressure portion is called the high pressure side, and the low hydraulic pressure portion is called the low pressure side.

As shown in FIGS. 5 and 6, the throttle valve 92 has a cylindrical first spool 93 inserted into the valve housing 7 and a cylindrical second spool 93 inserted into the first spool 93. The spool 94, a spring 95 that pushes the first spool 93 downward in the drawing, and a spring (not shown) that pushes the second spool 94 upward in the drawing are provided. A solenoid 96 that applies an electromagnetic force to the second spool 94 is provided below the throttle valve 92.
A control device 97 for controlling 6 according to the vehicle speed is provided, and the second spool 94 thereof moves upward in the figure by the elastic force of the spring as the vehicle speed increases, and moves downward by the electromagnetic force as the vehicle speed decreases. Move to.

A first bypass port 93a communicating with the first flow passage 90a of the bypass passage 90 and a second bypass port 93b communicating with the second flow passage 90b are formed on the outer periphery of the first spool 93. . Each bypass port 93
Each of a and 93b is composed of a circumferential groove formed on the inner circumference and the outer circumference of the first spool 93, and a through hole that connects both circumferential grooves. A recess 98 is formed on the outer periphery of the first spool 93 below the bypass ports 93a and 93b, and an oil passage 100 that connects the recess 98 and the outlet port 36 of the control valve 30 is formed in the valve housing 7. The recess 98 and the inner peripheral hole 94a of the second spool 94 are communicated with each other via a passage (not shown), whereby the first
The pressure at the outlet port 36, that is, the pressure on the downstream side of the first variable throttle 80 acts on the upper and lower end surfaces of the spool 93.

A peripheral groove 94b is formed on the outer circumference of the second spool 94.
Are formed. The circumferential groove 94b is always in communication with the first bypass port 93a and has a large opening between the second groove 94b and the second bypass port 93b due to the relative upward movement of the second spool 94 with respect to the first spool 93. The second variable throttle unit 91 has a smaller opening degree due to the downward movement.

A step surface 101 is formed on the outer circumference of the first spool 93 by making the upper side larger in diameter than the lower side, and the insertion hole of the valve housing 7 into which the first spool 93 is inserted is formed. The inner diameter of 7a is larger on the upper side than on the lower side, so that an annular oil chamber 102 is formed between the outer circumference of the first spool 93 and the inner circumference of the insertion hole 7a. The pressure oil on the upstream side of the first variable throttle 80 is introduced into the oil chamber 102. That is, the valve housing 7 has the oil chamber 102 and the control valve 30.
An oil passage 105 that communicates with the outer space 104 of the input shaft 2 above is formed. Also, on its input shaft 2,
In the space between the inner and outer circumferences of the torsion bar 6 and the input shaft 2, the input shaft 2 is provided upstream of the first variable throttle unit 80.
An oil passage 106 communicating with the outer space 104 is formed. As a result, the upstream pressure of the first variable throttle portion 80 acts on the step surface 101 of the first spool 93, the steering resistance increases, and the upstream pressure of the first variable throttle portion 80 increases as the pressure increases. The first spool 93 moves upward in the drawing against the elastic force of the spring 95, and moves downward in the drawing due to the elastic force of the spring 95 as the steering resistance decreases.

FIG. 5 shows a state in which the opening degree of the second variable throttle portion 91 is small, and FIG. 6 shows a state in which the opening degree of the second variable throttle portion 91 is large. That is, the second spool 94 moves upward as the vehicle speed increases, the opening degree of the second variable throttle portion 91 increases, and the second spool 94 increases as the vehicle speed decreases.
As the spool 94 moves downward and the opening degree of the second variable throttle portion 91 decreases, and the steering resistance increases, the upstream pressure of the first variable throttle portion 80 increases and the first spool 93 moves upward. When the steering resistance decreases, the upstream side pressure of the first variable throttle 80 decreases and the first spool 93 moves downward. The opening degree of the second variable throttle 91 increases.

According to the above construction, the hydraulic circuit shown in FIG. 1 is constructed, and as the steering resistance increases, the relative twist angle of both valve members 31, 32 of the control valve 30 increases.
Depending on the relative twist angle, the throttle portion A of the intervalve flow passage 27,
The opening degrees of B, C, and D change so as to increase the steering assist force. On the other hand, as the steering resistance decreases, both valve members 3
The relative twist angles of Nos. 1 and 32 are reduced, and the openings of the throttle portions A, B, C, and D of the inter-valve flow path 27 are changed so as to reduce the steering assist force according to the relative twist angle. Also,
As the vehicle speed increases, the opening degree of the second variable throttle portion 91 of the bypass 90 that connects the high pressure side of the inter-valve flow path 27 to the low pressure side increases and changes so as to reduce the steering assist force. On the other hand, as the vehicle speed decreases, the second
The opening degree of the variable throttle unit 91 becomes smaller and changes so as to increase the steering assist force. Furthermore, as the steering resistance increases, the opening degree of the first variable throttle section 80 decreases and the upstream pressure of the first variable throttle section 80 increases, which opens the second variable throttle section 91. The degree becomes smaller and the steering assist force changes so as to increase. On the other hand, as the steering resistance becomes smaller, the opening degree of the first variable throttle section 80 becomes larger and the upstream pressure of the first variable throttle section 80 becomes smaller, whereby the second variable throttle section 9 becomes smaller.
The opening degree of 1 increases and changes so as to decrease the steering assist force.

FIG. 7 shows a change in the opening area of the second variable throttle portion 91 with respect to the relative twist angle of both valve members 31 and 32 corresponding to the steering resistance by a broken line, and the intervalve passage 27 with respect to the relative twist angle. Throttle portion (throttle portions B and C when steering to the left or right, throttle portion A when steering to the other left or right,
The change of the opening area in D) is shown by a one-dot chain line. The second
The change in the opening area of the variable throttle portion 91 is shown in the case where the current applied to the solenoid 96 is changed stepwise according to the vehicle speed. The opening area of the second variable throttle unit 91 is constant until the relative twist angle becomes about θa in FIG. 7, but this is the same in the first variable throttle unit 80 until the relative twist angle becomes θa. This is because the pressure oil can hardly be squeezed. The rate of change in the opening area of the throttle portions A, D or B, C of the intervalve flow path 27 changes the relative twist angle at θb in FIG. 7, but the steering assist force is generated up to the relative twist angle up to θb. It is assumed that the hydraulic pressure hardly changes, and a range where the relative twist angle is larger than θb is a substantial steering assist force generation region. In the steering assist force generation region, the throttle portions A and D of the inter-valve passage 27 are formed. Alternatively, the rate of change of the opening area with respect to the relative twist angles of B and C is constant.

The rate of increase of the hydraulic pressure for generating the steering assist force is calculated by the combined value of the opening of the throttles A, D or B, C in the intervalve flow path 27 and the opening of the second variable throttle 91. Is determined. As a result, there will be no region where the steering assist force cannot be controlled according to the steering resistance. Therefore, as shown in the relational characteristic of the hydraulic pressure for generating the steering assist force with respect to the relative twist angle of both valve members 31 and 32 in FIG. 8, the steering assist force is applied even when the steering resistance is small at the time of low speed traveling or stop. It is possible to increase the rate of increase of the hydraulic pressure to be generated to satisfy the high steering responsiveness.On the other hand, at high speed, unless the steering resistance increases, the rate of increase of the hydraulic pressure that generates the steering assist force does not increase. Further, it is possible to satisfy the steering stability, and it is possible to obtain the steering responsiveness and the steering stability according to the steering resistance at the time of traveling at a middle speed.

Then, not only the openings of the throttle portions A, B, C, D in the inter-valve flow passage 27 are caused by the change in the steering resistance,
Since the opening degree of the second variable throttle portion 91 is also changed, even if the opening degree change rate of the throttle portions A, B, C, D in the intervalve flow passage 27 is constant in the steering assist force generation region. Due to the change in the opening degree of the second variable throttle portion 91, the increase rate of the hydraulic pressure for generating the steering assist force can be increased as the steering resistance increases. As a result, the rate of increase of the steering assist force is made larger in the range of large steering resistance than in the range of small steering resistance, steering response is improved in the range of large steering resistance, and steering stability is improved in the range of small steering resistance. be able to.

Further, the opening degree of the first variable throttle section 80 becomes smaller as the steering resistance becomes larger, and the upstream pressure of the first variable throttle section 80 becomes larger accordingly, so that in the intervalve passage 27. When the steering resistance increases, the pressure difference between the upstream side and the downstream side of the throttle portion (throttle portions B and C when steering to the left or right, throttle portions A and D when steering to the other left and right) becomes smaller as the steering resistance increases. As a result, the narrowed portions A, B,
The flow noise can be reduced by reducing the flow velocity of the pressure oil passing through C and D.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the four oil passages 83 forming the first variable throttle portion 80 are formed so as to expand in the radial direction from the center of the input shaft 2, but the first oil passage shown in FIG.
As shown in the modification, it may be constituted by two oil passages 83 'which are parallel to each other. Further, the configuration of the first variable aperture section 80 may be that shown in the second modification of FIGS. 10 and 11. That is, the gap δ between the outer periphery of the lower end of the torsion bar 6 and the inner periphery of the input shaft 2 is made minute, and the recess 120 is formed on the outer periphery of the lower end of the torsion bar 6 so as to face the recess 120. A through hole 121 is formed in the input shaft 2. From the recess 120, through the through hole 121 and the through hole 122 formed in the output shaft 3, the torsion bar 6
The pressure oil between the inner and outer circumferences of the input shaft 2 and the input shaft 2 reaches the outlet port 36. The pressure oil flowing from the recess 120 to the through hole 121 is
When the steering resistance increases and the relative twist angle of the torsion bar 6 with respect to the input shaft 2 increases, the area of the facing portion of the recess 120 and the through hole 121 decreases, so that the outer circumference of the torsion bar 6 and the inside of the input shaft 2 decrease. It is narrowed down with the lap. Others are the same as the above-mentioned embodiment, and the same portions are denoted by the same reference numerals. Further, although the present invention is applied to the rack and pinion type hydraulic power steering device in the above-described embodiments, it can be applied to, for example, a ball screw type hydraulic power steering device. Further, although the opening degree of the second variable throttle portion is changed according to the vehicle speed in the above-mentioned embodiment, it may be changed according to other driving conditions such as steering angle.

[0040]

According to the hydraulic power steering system of the present invention, in the case of applying the steering assist force according to the steering resistance and the driving condition, the region where the steering assist force cannot be controlled according to the steering resistance at the time of traveling at medium speed. It is possible to prevent the steering feeling from being deteriorated. Further, the increase rate of the steering assist force can be made larger in the range where the steering resistance is large than in the range where the steering resistance is small, and the steering response and stability can be improved. Further, the flow noise of the pressure oil when applying the steering assist force can be reduced.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of a hydraulic power steering device according to an embodiment of the present invention.

FIG. 2 is a vertical sectional view of a hydraulic power steering device according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a first variable aperture section according to the embodiment of the present invention.

FIG. 4 is a transverse cross-sectional view of the main part of the control valve according to the embodiment of the present invention.

FIG. 5 is a sectional view of the throttle valve according to the embodiment of the present invention at a low speed and a large steering resistance.

FIG. 6 is a sectional view of the throttle valve according to the embodiment of the present invention at a high speed with a small steering resistance.

FIG. 7 is a diagram showing the relationship between the relative twist angle of both valve members and the opening area of the throttle portion according to the embodiment of the present invention.

FIG. 8 is a diagram showing a relationship between a relative twist angle of both valve members and a hydraulic pressure for generating a steering assist force according to the embodiment of the present invention.

FIG. 9 is a cross-sectional view of a first variable aperture section according to a first modification of the present invention.

FIG. 10 is a vertical cross-sectional view of a hydraulic power steering device according to a second modified example of the present invention.

FIG. 11 is a cross-sectional view of a first variable aperture section according to a second modification of the present invention.

FIG. 12 is a hydraulic circuit diagram of a conventional hydraulic power steering device.

FIG. 13 is a diagram showing the relationship between the relative twist angle of both valve members and the opening area of the throttle in the hydraulic power steering device of the conventional example.

FIG. 14 is a relational diagram of relative twist angles of both valve members of a hydraulic power steering device of a conventional example and hydraulic pressure for generating a steering assist force with respect to input torque.

[Explanation of symbols]

 20 Actuator 27 Inter-valve flow path 31 First valve member 32 Second valve member 70 Pump 71 Tank 80 First variable throttle portion 90 Bypass passage 91 Second variable throttle portion 92 Throttle valve A, B, C, D throttle portion

Claims (1)

[Claims] 1. A first valve member and a second valve member which is inserted into the first valve member so as to be rotatable relative to the first valve member, and between the first valve member and the second valve member. Is connected to the pump, the tank, and the hydraulic actuator for generating steering assist force, and the opening degree is increased in the inter-valve flow path so that the steering assist force increases as the relative twist angle of both valve members increases. In a hydraulic power steering apparatus provided with a throttle portion that changes in a variable amount, a first variable throttle portion is provided in a passage that connects the intervalve passage and the tank, and the opening degree of the first variable throttle portion is increased. Is provided in accordance with the relative twist angle of the valve members so that the steering resistance becomes smaller as the steering resistance increases, and the second passage is connected to the bypass passage that connects the high pressure side of the intervalve passage to the low pressure side. The variable diaphragm part of The opening degree of the second variable throttle portion is changed so as to be increased as the vehicle speed is increased, and is changed so as to be decreased as the upstream pressure of the first variable throttle portion is increased. A control valve for a hydraulic power steering device, which is provided with a means for operating the control valve.