VARIABLE CAPACITY VANE PUMP

Abstract

Variable capacity vane pump 1 supplying working fluid to power steering device of vehicle has pump housing 2 formed from bottomed cylindrical-shaped front housing 5 and rear housing 6 closing the front housing, pump element 3 accommodated in pump housing, communicating with inlet passage 23 and with outlet passage 30 and sucking and discharging working fluid, and flow amount control valve 33 controlling an amount of working fluid discharged by pump element. Pressure-sensitive valve 50, which changes a flow passage cross-sectional area of the outlet passage so that the discharge amount of the pump element is increased with increase in load pressure of power steering device, is set at some midpoint of the outlet passage and at bottom wall portion 5b of front housing. It is therefore possible to suppress increase in size of device while reducing energy loss when variable capacity vane pump is mounted in power steering device.

Description

TECHNICAL FIELD

The present invention relates to a variable capacity vane pump applied to, for instance, a hydraulic power steering device of a vehicle.

BACKGROUND ART

A variable capacity vane pump generally has a pump housing having therein a pump element accommodation space, a pump element driven and rotating by an engine and sucking and discharging working fluid, an outlet passage leading the working fluid discharged by the pump element to an oil-supply portion, an orifice provided at some midpoint of the outlet passage, and a flow amount control valve controlling a discharge amount of the working fluid discharged by the pump element on the basis of a pressure difference of the working fluid between front and back sides of the orifice.

The pressure difference between front and back sides of the orifice changes according to the discharge amount of the pump element, and this discharge amount is determined on the basis of an engine rotation speed. That is, the variable capacity vane pump is configured to control the flow amount of the working fluid on the basis of the engine rotation speed.

However, in a case where such a variable capacity vane pump is applied to a power steering device of a vehicle, the working fluid is discharged to the power steering device even at straight-ahead driving of the vehicle at which almost no steering assist force by hydraulic pressure is required. This may therefore cause energy loss.

Thus, as a variable capacity vane pump that is capable of reducing the energy loss when being mounted in the power steering device, the following variable capacity vane pump has been disclosed in Patent Document 1.

When briefly explaining this variable capacity vane pump, the variable capacity vane pump disclosed in Patent Document 1 has, in addition to the above pump configuration, a bypass passage connecting an upstream side and a downstream side of the orifice and a pressure-sensitive valve provided on the bypass passage and opening and closing the bypass passage according to a load pressure of the power steering device.

The pressure-sensitive valve opens the bypass passage during a steering operation in which the load pressure of the power steering device is increased, while the pressure-sensitive valve closes the bypass passage at straight-ahead driving at which the load pressure is low. With this valve working, since a pump discharge amount at the straight-ahead driving can be reduced regardless of the engine rotation speed, the energy loss of the power steering device can be reduced.

CITATION LIST

Patent Document

Patent Document 1: Japanese Unexamined Patent Publication No. JP2003-176791

SUMMARY OF THE INVENTION

In the variable capacity vane pump, however, flow passages are complicated by the fact that the bypass passage is provided, and this results in increase in size of the power steering device.

The present invention was made in view of the above technical problem. An object of the present invention is therefore to provide a variable capacity vane pump that is capable of suppressing the increase in size of the power steering device while reducing the energy loss when being mounted in the power steering device.

A variable capacity vane pump supplying working fluid to a power steering device of a vehicle, comprises: a pump housing formed from a first housing having a cylindrical portion and a bottom wall portion provided so as to close one end opening of the cylindrical portion and a second housing provided so as to close the other end opening of the cylindrical portion, the pump housing forming a pump element accommodation space inside the pump housing between the first and second housings; a drive shaft inserted and rotatably supported in the pump housing; a rotor accommodated in the pump element accommodation space and driven and rotated by the drive shaft, the rotor being provided with a plurality of slits in a radial direction of the rotor; vanes provided in the slits so as to extend and retract; a ring-shaped cam ring movably provided in the pump element accommodation space and forming a plurality of pump chambers together with the rotor and the vanes; an inlet port provided in the pump housing and opening to a suction section where a volume of each of the pump chambers gradually increases with rotation of the rotor; an outlet port provided in the pump housing and opening to a discharge section where the volume of each of the pump chambers gradually decreases with rotation of the rotor; an inlet passage provided in the pump housing and introducing the working fluid stored in a reservoir tank to the inlet port; an outlet passage provided in the pump housing and introducing the working fluid discharged from the outlet port to an outside of the pump housing; a first fluid pressure chamber and a second fluid pressure chamber each provided at an outer peripheral side of the cam ring, the first fluid pressure chamber being located on a side where a volume of the fluid pressure chamber is decreased when the cam ring moves in a direction in which an eccentric amount of the cam ring with respect to the rotor is increased, and the second fluid pressure chamber being located on a side where the volume of the fluid pressure chamber is increased when the cam ring moves in the direction in which the eccentric amount of the cam ring with respect to the rotor is increased; a first valve accommodation hole formed at the bottom wall portion of the first housing and at some midpoint of the outlet passage; a first valve body movably provided in the first valve accommodation hole, the first valve body being configured so that movement of the first valve body is controlled by a pressure difference between a suction pressure acting on one end side of the first valve body and a discharge pressure introduced from the outlet passage and acting on the other end side of the first valve body, and the first valve body changes a flow passage cross-sectional area of the outlet passage according to the movement of the first valve body; a second valve accommodation hole provided in the pump housing; a high pressure chamber provided at one end side of the second valve accommodation hole and formed so as to communicate with the outlet port; a control pressure chamber provided at the other end side of the second valve accommodation hole and formed so as to communicate with a downstream side, with respect to the first valve accommodation hole, of the outlet passage; and a second valve body movably provided in the second valve accommodation hole and controlling a pressure in the first fluid pressure chamber by a pressure difference between a pressure in the high pressure chamber and a pressure in the control pressure chamber.

According to the present invention, it is possible to suppress the increase in size of the power steering device while reducing the energy loss when the variable capacity vane pump is mounted in the power steering device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a variable capacity vane pump according to embodiments of the present invention.

FIG. 2 is a longitudinal cross section of the variable capacity vane pump.

FIG. 3 is a sectional view taken along a line A-A of FIG. 2.

FIG. 4 is a longitudinal cross section of an essential part of the variable capacity vane pump.

FIG. 5A is an enlarged view of the essential part of the variable capacity vane pump shown in FIG. 4, of a case where a pressure difference between a discharge pressure and a suction pressure which act on a first valve body is small. FIG. 5B is an enlarged view of the essential part of the variable capacity vane pump shown in FIG. 4, of a case where the pressure difference is large.

FIG. 6 is a perspective view showing a state in which the first valve body of the present embodiment is inserted in a front housing.

FIGS. 7A and 7B show the first valve body of the present embodiment. FIG. 7A is a perspective view of the first valve body. FIG. 7B is a side view of the first valve body.

FIG. 8 is a sectional view taken along a line B-B of FIG. 4.

FIG. 9 is a graph showing a relationship between a pump revolution speed (revolutions per minute of a pump) and a discharge flow amount in the variable capacity vane pump.

FIG. 10 is a schematic diagram showing rate of change of a flow passage cross-sectional area of an outlet passage according to movement of the first valve body.

FIG. 11 is a graph showing a relationship between a spring-load and a displacement of an uneven or unequal pitch spring, which can be used as a coil spring, according to a second embodiment of the present invention.

FIG. 12 is a graph showing a relationship between a spring-load and a displacement of a tapered spring, which can be used as the coil spring, according to the second embodiment of the present invention.

FIG. 13 is a graph showing a relationship between a pressure of hydraulic fluid and an orifice opening area when the hydraulic fluid acts on the first valve body, according to the second embodiment of the present invention.

FIG. 14 is a longitudinal cross section of an essential part of the variable capacity vane pump according to a third embodiment of the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Embodiments of a variable capacity vane pump of the present invention will be explained below with reference to the drawings. Each embodiment shows an example in which the variable capacity vane pump is mounted in a power steering apparatus of a vehicle.

As shown in FIGS. 1 to 3, the variable capacity vane pump 1 has a pump housing 2 having therein a cylindrical pump element accommodation chamber 2a as a pump element accommodation space and a pump element 3 accommodated in the pump element accommodation chamber 2a. The pump element 3 is driven and rotated by a drive shaft 4 that is inserted in the pump element accommodation chamber 2a, then a pumping action is performed.

As shown in FIGS. 1 and 2, the pump housing 2 has a bottomed cylindrical-shaped front housing 5 as a first housing and a rear housing 6 as a second housing that closes an opening of the front housing 5. Both these front and rear housings 5 and 6 are tightened and fixed together by bolts 7.

As shown in FIGS. 2 and 3, the pump element (or pump component) 3 has a substantially ring-shaped adapter ring 8 fitted and fixed to an inner circumferential surface of a cylindrical portion 5a of the front housing 5, a substantially ring-shaped cam ring 9 movably provided in a substantially oval-shaped inner space inside the adapter ring 8, a rotor 10 provided at an inner circumferential side of the cam ring 9 and rotating integrally with the drive shaft 4 and a substantially disc-shaped pressure plate 11 disposed at a bottom wall portion 5b of the front housing 5 and sandwiching the cam ring 9 and the rotor 10 together with the rear housing 6.

As shown in FIG. 3, the adapter ring 8 is provided, at a lower portion of an inner circumferential surface 8a thereof, with a plate seal member 12. This plate seal member 12 has the function of sealing a gap between the adapter ring 8 and the cam ring 9, and also serves as a rolling surface on which the cam ring 9 moves while rolling in the inner space of the adapter ring 8.

The adapter ring 8 is also provided, in a position radially opposite to the plate seal member 12 on the inner circumferential surface 8a of the adapter ring 8, with a seal member 13 that seals a gap between the adapter ring 8 and the cam ring 9, like the plate seal member 12.

The cam ring 9 defines a first fluid pressure chamber 14 and a second fluid pressure chamber 15 between the adapter ring 8 and the cam ring 9 through the both seal members 12 and 13. The cam ring 9 is configured to move in right and left directions in FIG. 3 by a pressure difference between the first fluid pressure chamber 14 and the second fluid pressure chamber 15. With this movement, an eccentric amount of the cam ring 9 with respect to the rotor 10 is changed.

The cam ring 9 is forced or pressed all the time in a direction in which the eccentric amount with respect to the rotor 10 becomes a maximum by a return spring 16 that is elastically connected to an outer circumference of the cam ring 9.

Further, a position holding pin 17 to hold a position of the cam ring 9 is provided at a counterclockwise direction side of the plate seal member 12 in FIG. 3, i.e. in a position on the second fluid pressure chamber 15 side, between the adapter ring 8 and the cam ring 9. This position holding pin 17 also serves as a rotation stopper that restrains an excessive rotation of the cam ring 9 with respect to the adapter ring 8 in addition to the function of holding the position of the cam ring 9.

The rotor 10 is configured to rotate in a counterclockwise rotation (an arrow direction) in FIG. 3 as the drive shaft 4 rotates by an engine (not shown). The rotor 10 has, at substantially regular intervals in a circumferential direction at an outer circumference of the rotor 10, a plurality of slits (slots) 18 formed by being cut and extending in a radial direction. Substantially flat plate vanes 19 are each accommodated in the slits 18 so as to be able to move or extend/retract in the radial direction of the rotor 10.

Each vane 19 is forced all the time in a direction of an inner circumferential surface of the cam ring 9 by pressure of working oil that is working fluid introduced into a back-pressure chamber 20 formed at an inner end portion of each slit 18 of the rotor 10.

The vanes 19 form a plurality of pump chambers 21 by partitioning an annular space between the cam ring 9 and the rotor 10 by adjacent two vanes 19 and 19.

As shown in FIGS. 2 and 3, an arc-shaped first inlet port 22 is formed on an inner end surface 6a of the rear housing 6 which faces the pump element accommodation chamber 2a, and more specifically, the first inlet port 22 is located at a section of the inner end surface 6a of the rear housing 6 which corresponds to a suction section (suction area) where a volume of each pump chamber 21 gradually increases with rotation of the rotor 10. This first inlet port 22 communicates with a reservoir tank T that stores the working fluid through an inlet passage 23 formed in the rear housing 6 by e.g. drilling. With this structure, the working fluid stored in the reservoir tank T is introduced into the first inlet port 22 through the inlet passage 23, and is introduced or sucked into each pump chamber 21 by a pump suction action taken in the suction section.

Further, as shown in FIG. 2, a second inlet port 24 having the substantially same shape as the first inlet port 22 is formed by cutting between a bottom surface of the front housing 5 and one end surface 11a of the pressure plate 11. The second inlet port 24 communicates with a seal ring groove 26 that is a seal member accommodation space through a return passage 25 that is a low pressure communication passage formed in the front housing 5.

The seal ring groove 26 is formed into a ring-shape on an outer circumferential side of the drive shaft 4. The seal ring groove 26 accommodates therein a seal ring 27 that is a seal member sealing a gap between the front housing 5 and the drive shaft 4. With this structure, leak of the working fluid coming from the pump element accommodation chamber 2a through the drive shaft 4 to the outside of the pump housing 2 is restricted or prevented. Further, this excess or redundant working fluid is returned to the second inlet port 24 through the return passage 25.

In addition, as shown in FIGS. 2 and 3, an arc-shaped outlet port 28 is formed on the one end surface 11a of the pressure plate 11, and more specifically, the outlet port 28 is located at a section of the one end surface 11a of the pressure plate 11 which corresponds to a discharge section (discharge area) where the volume of each pump chamber 21 gradually decreases with rotation of the rotor 10. The outlet port 28 communicates with a recessed pressure chamber 29 formed at the bottom wall portion 5b of the front housing 5. This pressure chamber 29 serves to force the pressure plate 11 to the rotor 10 side by pressure inside the pressure chamber 29.

The outlet port 28 is configured so that, as shown in FIGS. 2 and 3, the working fluid is supplied to a rotary valve of a power steering device (not shown) through an outlet passage 30 formed at the bottom wall portion 5b of the front housing 5.

The outlet passage 30 is provided, at some midpoint thereof (in a predetermined position in the outlet passage 30), with a metering orifice 32 whose cross section is substantially circular. By the metering orifice 32, a pressure difference of the working fluid occurs in the outlet passage 30.

Further, as shown in FIGS. 2 and 3, a flow amount control valve 33 is provided at an upper end portion of the front housing 5. The flow amount control valve 33 has a control valve accommodation hole 34 as a second valve accommodation hole formed at the front housing 5 so as to be orthogonal to the drive shaft 4, a control valve body 35 as a second valve body slidably accommodated in the control valve accommodation hole 34, a plug 36 closing an opening at an axial direction one end side of the control valve accommodation hole 34 and a valve spring 37 forcing or pressing the control valve body 35 toward the plug 36.

In the control valve accommodation hole 34, as shown in FIG. 3, a high pressure chamber 38 which is provided between the plug 36 and the control valve body 35 and into which pressure (a discharge pressure) of an upstream side of the metering orifice 32 is introduced, a control pressure chamber 39 which is provided at an axial direction another end side of the control valve accommodation hole 34 and accommodates the valve spring 37 and into which pressure (a control pressure) of a downstream side of the metering orifice 32 is introduced, and a low pressure chamber 41 which is formed at an outer peripheral side of the control valve body 35 and into which a pump suction pressure from the inlet passage 23 through a low pressure passage 40 is introduced, are provided. These pressure chambers 38, 39 and 41 are defined by first and second land portions 35a and 35b of the control valve body 35.

Between the outlet passage 30 and the control pressure chamber 39, a dumper orifice 42 to drop or lower a fluid pressure of the working fluid introduced into the control pressure chamber 39 and reduce an influence of pulsation is provided.

The control valve body 35 is configured to move in the axial direction according to a pressure difference between pressure in the high pressure chamber 38 and pressure in the control pressure chamber 39.

More specifically, in a case where the pressure difference between the high pressure chamber 38 and the control pressure chamber 39 is relatively small and the control valve body 35 is positioned at the plug 36 side by a spring force of the valve spring 37, a communication passage 43 connecting the first fluid pressure chamber 14 and the control valve accommodation hole 34 opens to the low pressure chamber 41. With this communication, a suction pressure is introduced into the first fluid pressure chamber 14 from the low pressure chamber 41.

On the other hand, in a case where the pressure difference between the high pressure chamber 38 and the control pressure chamber 39 is relatively great and the control valve body 35 moves to a right side in FIG. 3 against a pressure of the control pressure chamber 39 and the spring force of the valve spring 37, the communication between the low pressure chamber 41 and the first fluid pressure chamber 14 is gradually interrupted, then the high pressure chamber 38 communicates with the first fluid pressure chamber 14 through the communication passage 43. With this communication, a high pressure is introduced into the first fluid pressure chamber 14 from the high pressure chamber 38.

That is, the pressure of the low pressure chamber 41 or the pressure of the high pressure chamber 38 is selectively introduced into the first fluid pressure chamber 14.

As for the second fluid pressure chamber 15, the pump suction pressure is introduced into the second fluid pressure chamber 15 all the time. When the suction pressure from the low pressure chamber 41 is introduced into the first fluid pressure chamber 14, the cam ring 9 moves (rolls) to a position in which the eccentric amount of the cam ring 9 with respect to the rotor 10 becomes a maximum by an urging force of the return spring 16, and a pump discharge amount becomes a maximum.

On the other hand, when the high pressure of the high pressure chamber 38 is introduced into the first fluid pressure chamber 14, the cam ring 9 moves (rolls) in a direction in which the eccentric amount of the cam ring 9 is decreased, i.e. the cam ring 9 moves (rolls) to the second fluid pressure chamber 15 side, by the high pressure of the high pressure chamber 38 against the urging force of the return spring 16, and the pump discharge amount is reduced.

The control valve body 35 is provided with a relief valve 44 inside the control valve body 35. This relief valve 44 is configured to open when the pressure in the control pressure chamber 39 becomes a predetermined pressure or higher, i.e. when a load pressure of the power steering device side becomes a predetermined pressure or higher, and return the high pressure working fluid to the inlet passage 23 through the low pressure chamber 41 and the low pressure passage 40.

As shown in FIG. 4, in an immediately upstream position of the metering orifice 32 on the outlet passage 30, a pressure-sensitive valve 50, which changes a flow passage cross-sectional area of a downstream side of the metering orifice 32 in response to the load pressure of the power steering device side, is provided.

The pressure-sensitive valve 50 has, especially as shown in FIGS. 5A and 5B, a bottomed cylindrical-shaped pressure-sensitive valve accommodation hole 51 as a first valve accommodation hole formed at the bottom wall portion 5b of the front housing 5 by cutting, a cylindrical pressure-sensitive valve body 52 (a spool valve) as a first valve body slidably accommodated in the pressure-sensitive valve accommodation hole 51 and a coil spring 53 as a spring member forcing or pressing the pressure-sensitive valve body 52 toward the pressure plate 11.

As shown in FIGS. 4, 5A, 5B and 8, the pressure-sensitive valve accommodation hole 51 is formed parallel to the drive shaft 4, and has a stepped diameter shape. The pressure-sensitive valve accommodation hole 51 has a large diameter hole portion 51a formed at an axial direction one end opening side of the pressure-sensitive valve accommodation hole 51 and accommodating the pressure-sensitive valve body 52 and a small diameter hole portion 51b formed at an axial direction another end bottom side of the pressure-sensitive valve accommodation hole 51 and accommodating the coil spring 53.

Further, a ring-shaped stepped surface 51c orthogonal to the axial direction is formed at a connecting portion between the large diameter hole portion 51a and the small diameter hole portion 51b. This stepped surface 51c serves as a stopper of the pressure-sensitive valve accommodation hole 51 side which restrains or limits movement of the pressure-sensitive valve body 52 to the small diameter hole portion 51b side when a moving amount of the pressure-sensitive valve body 52 to the small diameter hole portion 51b side is a predetermined value or greater.

Since the pressure-sensitive valve accommodation hole 51 is formed parallel to the drive shaft 4, the pressure-sensitive valve body 52 and the coil spring 53 move along the axial direction of the drive shaft 4.

The pressure-sensitive valve accommodation hole 51 communicates with the metering orifice 32 in a substantially middle position in the axial direction of the large diameter hole portion 51a.

Further, the pressure-sensitive valve accommodation hole 51 is formed so that the opening of the pressure-sensitive valve accommodation hole 51 communicates with the discharge section (the discharge area) indicated by a dashed line in FIG. 6, and overlaps the discharge section (the discharge area) in a circumferential direction of the drive shaft 4.

As shown in FIGS. 7A and 7B, the pressure-sensitive valve body 52 is a so-called spool valve formed into the cylindrical shape. The pressure-sensitive valve body 52 has a land portion 54 provided at the axial direction one end side of the pressure-sensitive valve body 52 so as to be able to slide on an inner peripheral surface of the large diameter hole portion 51a, a guide portion 55 provided at the axial direction another end side of the pressure-sensitive valve body 52 so as to be able to slide on the inner peripheral surface of the large diameter hole portion 51a like the land portion 54 and a passage forming portion 56 formed integrally with an axial direction outer end of the guide portion 55 and forming a passage for introducing the working fluid into an after-mentioned pressure receiving chamber 63.

The coil spring 53 is formed so as to have characteristic of a substantially linear spring constant.

The land portion 54 has one end surface 54a formed into a ring-shaped flat surface as a stopper. This one end surface 54a contacts the stepped surface 51c of the stopper of the pressure-sensitive valve accommodation hole 51 side, thereby limiting further movement of the pressure-sensitive valve body 52 to the one end side.

The guide portion 55 guides the movement of the pressure-sensitive valve body 52 by the sliding contact with the inner peripheral surface of the pressure-sensitive valve accommodation hole 51 together with the land port ion 54, and suppresses wobbling movement or backlash of the pressure-sensitive valve body 52.

The passage forming portion 56 is formed into a cylindrical shape whose diameter is slightly smaller than that of the guide portion 55. The passage forming portion 56 has four passage grooves 57 as groove portions at substantially 90 degree positions in a circumferential direction. Each of the passage grooves 57 is formed by cutting in a radial direction of the pressure-sensitive valve body 52 so as to have a relatively large rectangular shape in cross section. That is, most of the another end side of the pressure-sensitive valve body 52 in the circumferential direction is cut, and four protrusions 58 whose cross sections are substantially triangular shapes remain.

Further, an annular groove 60 formed by cutting in the circumferential direction is provided on an outer peripheral surface of a small diameter portion 59 between the land portion 54 and the guide portion 55 of the pressure-sensitive valve body 52. This annular groove 60 has four communication holes 59a connecting an inside and an outside of the pressure-sensitive valve body 52 at substantially 90 degree positions in the circumferential direction. The annular groove 60 communicates with the inside of the pressure-sensitive valve body 52 through each of the communication holes 59a.

In addition, a disc-shaped partition wall 61 is formed as an integral part inside the pressure-sensitive valve body 52 at a portion on the one end side with respect to the communication holes 59a. As shown in FIGS. 4, 5A, 5B and 8, the partition wall 61 partitions an inside space of the pressure-sensitive valve accommodation hole 51 into a pressure suction chamber 62 on the one end side which is isolated from the outlet passage 30 and a pressure receiving chamber 63 on another side which communicates with the outlet passage 30 through the passage grooves 57 and into which the discharge pressure is introduced.

As shown in FIGS. 5A, 5B and 8, the pressure suction chamber 62 communicates with the seal ring groove 26 through a low pressure introduction passage 64 formed on a bottom surface of the pressure-sensitive valve accommodation hole 51. The low pressure (the suction pressure) is introduced into the pressure suction chamber 62 from this low pressure introduction passage 64.

As shown in FIGS. 4, 5A, 5B and 8, at the one end portion of the pressure-sensitive valve body 52 where the pressure suction chamber 62 is formed, a cylindrical spring retaining groove 65 as a spring retaining portion is formed. This spring retaining groove 65 is formed from one end surface 61a of the partition wall 61 and an inner peripheral surface of the land portion 54. The inner peripheral side of the spring retaining groove 65 accommodates and retains a part of the coil spring 53, and the one end surface 61a of the partition wall 61 which is a groove bottom elastically contacts one end portion of the coil spring 53. On the other hand, the other portion of the coil spring 53 elastically contacts a bottom surface of the pressure-sensitive valve accommodation hole 51 (the small diameter hole portion 51b). With this structure, as explained above, the coil spring 53 forces or presses the pressure-sensitive valve body 52 toward the pressure plate 11.

The pressure receiving chamber 63 is formed at an inner peripheral side of the pressure-sensitive valve body 52 at a portion on another end side with respect to the partition wall 61. As shown by arrows in FIGS. 5A and 5B, the pressure receiving chamber 63 is configured so that after pressure of hydraulic fluid introduced from the passage forming portion 56 acts on the other end surface 61b of the partition wall 61, the hydraulic fluid flows out to a downstream side of the metering orifice 32 through the communication holes 59a and the annular groove 60.

The pressure-sensitive valve body 52 is configured to move in the axial direction by a pressure difference between pressure in the pressure receiving chamber 63 and pressure in the pressure suction chamber 62, and close a part of the metering orifice 32 with an outer peripheral surface of the land portion 54 according to the movement of the pressure-sensitive valve body 52, then changes the flow passage cross-sectional area of the metering orifice 32.

More specifically, in a case where the pressure difference between pressure in the pressure receiving chamber 63 and pressure in the pressure suction chamber 62 is relatively small, as shown in FIG. 5A, the pressure-sensitive valve body 52 is positioned on a left side in the drawing where the protrusions 58 contact the pressure plate 11 by an urging force of the coil spring 53. In this case, since the land portion 54 closes or covers substantially half of the metering orifice 32, the flow passage cross-sectional area of the metering orifice 32 is decreased to almost half of its initial size.

On the other hand, in a case where the pressure difference between pressure in the pressure receiving chamber 63 and pressure in the pressure suction chamber 62 is increased and the pressure-sensitive valve body 52 moves to a right side in the drawing by overcoming the urging force of the coil spring 53, as shown in FIG. 5B, an overlap amount between the metering orifice 32 and the land portion 54 is gradually decreased, and the flow passage cross-sectional area of the metering orifice 32 gradually becomes large according to the decrease of the overlap amount. Here, when the one end surface 54a of the land portion 54 contacts the stepped surface 51c of the pressure-sensitive valve accommodation hole 51, the overlap amount is 0 (zero), and the flow passage cross-sectional area becomes a maximum.

Here, the pressure-sensitive valve body 52 is installed so that in assembly of the variable capacity vane pump 1, after the pressure-sensitive valve body 52 is inserted into the pressure-sensitive valve accommodation hole 51 with the coil spring 53 already installed from the opening side (the large diameter hole portion 51a side) to the bottom side of the pressure-sensitive valve accommodation hole 51, the pressure-sensitive valve accommodation hole 51 is closed or covered with the pressure plate 11.

Working or Operation and Effect of the Present Embodiment

According to the variable capacity vane pump 1, for instance, during straight-ahead driving of the vehicle at which no steering assist force is required, since most of the working fluid supplied to the rotary valve (not shown) is returned to the reservoir tank T without being used for the steering assist, the load pressure of the power steering device side is in a low pressure state. Then, since the fluid pressure of the working fluid in the outlet passage 30 that communicates with the power steering device is also kept at the low pressure state, a closure amount of the metering orifice 32 by the pressure-sensitive valve body 52 (the land portion 54) is large, and the flow passage cross-sectional area is small. That is, this state is the same as a case where a throttle amount of a variable orifice is increased.

Therefore, a pressure difference between fluid pressure at the upstream side and fluid pressure at the downstream side of the metering orifice 32 becomes large, and the flow amount control valve 33 works in response to this pressure difference so as to make the cam ring 9 move (roll) in a direction in which the eccentric amount of the cam ring 9 with respect to the rotor 10 is small, then as indicated by a broken line in FIG. 9, the pump discharge amount is decreased.

On the other hand, during steering operation in which steering assist force is required, since the working fluid supplied to the rotary valve (not shown) is provided into a power cylinder which is a closed space without returning to the reservoir tank T, the load pressure of the power steering device side is increased.

Then, since the fluid pressure of the working fluid in the outlet passage 30 is also increased, the pressure-sensitive valve body 52 (the land portion 54) moves to the axial direction one end side (FIG. 5B), and the closure amount of the metering orifice 32 becomes small, then the flow passage cross-sectional area becomes large. That is, this state is the same as a case where a throttle of a variable orifice is eased or loosened.

Therefore, the pressure difference between fluid pressure at the upstream side and fluid pressure at the downstream side of the metering orifice 32 becomes small, and the flow amount control valve 33 works in response to this pressure difference so as to make the cam ring 9 move (roll) in a direction in which the eccentric amount of the cam ring 9 with respect to the rotor 10 is large, then as indicated by a solid line in FIG. 9, the pump discharge amount is increased.

Accordingly, during the steering operation, as indicated by the solid line in FIG. 9, the discharge amount of the working fluid fed to the power steering device is kept at a relatively high amount state.

Here, various elements or components such as the pump element 3, the inlet passage 23 and the outlet passage 30 are installed inside the variable capacity vane pump 1 of the present embodiment. It is thus difficult to provide further elements or components in the variable capacity vane pump 1.

As a space where no element is installed, it is a space C indicated by a two-dot chain line in FIG. 4. However, since the drive shaft 4 is inserted in the space C, there is a necessity to avoid interference with the drive shaft 4. Because of this, the space C is a dead space for installation of a mechanism having a sophisticated operation. And, this results in increase in an entire size of the device by the fact that the mechanism is externally added or a size of the pump housing 2 is increased, in order to add the further elements or components to the variable capacity vane pump 1.

Therefore, in the present embodiment, by utilizing the pressure-sensitive valve 50 that performs a linear movement, installation of the further element (the pressure-sensitive valve 50) in the dead space becomes possible, and a discharge amount suitable for the power steering device can be obtained.

Especially in the present embodiment, since the pressure-sensitive valve 50 is set so as to move along the axial direction of the drive shaft 4, interference with the drive shaft 4 can be avoided.

Further, the pressure-sensitive valve accommodation hole 51 is located so as to overlap the discharge section (the discharge area) in the circumferential direction of the drive shaft 4. Therefore, a flow passage to lead the discharge pressure to the pressure-sensitive valve accommodation hole 51 can be shortened, thereby further saving space.

Moreover, the pressure-sensitive valve body 52 is the spool valve, and the control of the flow passage cross-sectional area of the metering orifice 32 can be performed only by changing the overlap amount between the land portion 54 and the metering orifice 32. It is therefore possible to prevent the mechanism from being complicated and suppress an increase in size of the device due to the complicated mechanism.

Hence, according to the variable capacity vane pump 1 of the present embodiment, increase in size of the device can be suppressed while reducing energy loss when being mounted in the power steering device.

Further, since the other end side of the pressure-sensitive valve accommodation hole 51 is formed so as to communicate with the discharge section through the passage grooves 57, introduction of the discharge pressure can be easily done.

In addition, in the present embodiment, in a case where the fluid pressure of the working fluid flowing in the outlet passage 30 is low, the land portion 54 closes or covers substantially half of the metering orifice 32, and a closure area of the metering orifice 32 by the land portion 54 is gradually decreased with increase of the fluid pressure from this half-closure state.

That is, regarding change of the flow passage cross-sectional area according to the movement of the pressure-sensitive valve body 52, as shown in FIG. 10, the change of the flow passage cross-sectional area is a maximum when the pressure-sensitive valve body 52 (the land portion 54) starts to move in a Y-direction (a valve opening direction) with a substantially diameter line X being a base point (or a reference line), and the change of the flow passage cross-sectional area is gradually small as the pressure-sensitive valve body 52 (the land portion 54) moves toward a top of the arrow Y from this reference line. In other words, rate of change of the flow passage cross-sectional area depends on a circular shape in cross section of the metering orifice 32, and is gradually decreased with increase of the pressure of the working fluid flowing in the outlet passage 30.

With this, the rate of change of the flow passage cross-sectional area is large immediately after performing the steering operation from the straight-ahead driving, and the flow amount of the working fluid is rapidly increased by this change of the rate of change. A steering response can therefore be improved. Further, the rate of change of the flow passage cross-sectional area is small immediately after returning the steering operation to the straight-ahead driving, and the flow amount of the working fluid is gently decreased. An odd or awkward feeling of the steering operation can therefore be suppressed.

Furthermore, the pressure-sensitive valve body 52 is installed by inserting the pressure-sensitive valve body 52 from the opening side (the large diameter hole portion 51a side) of the pressure-sensitive valve accommodation hole 51 and closing or covering the pressure-sensitive valve accommodation hole 51 with the pressure plate 11. Therefore, a sealing member or a covering member such as a sealing plug (a plug) is not necessary, thereby reducing cost.

Moreover, since the pressure-sensitive valve accommodation hole 51 is provided close to the drive shaft 4, connection of the pressure-sensitive valve accommodation hole 51 with the seal ring groove 26 that communicates with the suction section can be easily made. As a result, introduction of the suction pressure into the pressure suction chamber 62 located apart from the suction section becomes possible.

In addition, since the passage grooves 57 cut in the radial direction of the pressure-sensitive valve body 52 are formed at the passage forming portion 56 of the pressure-sensitive valve body 52, even when the passage forming portion 56 contacts the pressure plate 11, the working fluid can be introduced into the pressure receiving chamber 63 from the passage grooves 57. Especially, since each of the passage grooves 57 is formed so that an inlet area for introducing the working fluid is large, the working fluid can be efficiently introduced.

In the present embodiment, as described above, the one end surface 54a of the land portion 54 is formed into the flat surface, and by the fact that this surface contacts the stepped surface 51c of the pressure-sensitive valve accommodation hole 51, the movement of a predetermined distance or more, of the pressure-sensitive valve body 52 to the one end side is limited. With this structure, it is possible to avoid a problem of changing a linear characteristic of the coil spring 53 which is caused by excessive compression of the coil spring 53. Further, since a gap between the one end surface 54a of the land portion 54 and the stepped surface 51c of the pressure-sensitive valve accommodation hole 51 is sealed by the contact, the working fluid on the high pressure side is prevented from returning to the low pressure side, thereby improving pump efficiency.

Moreover, in the present embodiment, it is possible to suppress lean or inclination of the coil spring 53 by the spring retaining groove 65 formed at the one end portion of the pressure-sensitive valve body 52. And, since a coil length of the coil spring 53 is elongated by a length equivalent to a depth of the spring retaining groove 65, change of spring characteristics (the linear characteristic) due to the compression of the coil spring 53 can be further suppressed.

Further, when considering a maximum load applied to the pressure-sensitive valve body 52 then comparing a direction (a right direction in FIGS. 5A and 5B) in which the area of the metering orifice 32 is increased and a direction (a left direction in FIGS. 5A and 5B) in which the area of the metering orifice 32 is decreased, since the discharge pressure of the outlet passage 30 is increased up to a relief pressure at the maximum, a load in a direction in which the area of the metering orifice 32 is increased is greater. That is, in a case where slidability (sliding performance) of the pressure-sensitive valve body 52 becomes worse and the pressure-sensitive valve body 52 is fixed due to foreign matter etc., the possibility that the pressure-sensitive valve body 52 is fixed with the one end surface 54a of the land portion 54 contacting the stepped surface 51c of the pressure-sensitive valve accommodation hole 51 is strong. Since the pressure-sensitive valve accommodation hole 51 and the pressure-sensitive valve body 52 etc. are configured so that the flow passage cross-sectional area of the metering orifice 32 becomes a maximum in this state, even if the fixation between the one end surface 54a and the stepped surface 51c occurs, a disadvantage is only that an energy-saving effect cannot be obtained, but steering assist performance can be maintained. As a consequence, continuity of safe operation can be secured.

In the present embodiment, the hydraulic fluid flowing in the outlet passage 30 directly flows out to the downstream side of the metering orifice 32 while applying the pressure of hydraulic fluid to the pressure-sensitive valve body 52. Therefore, as compared with a configuration in which a position control of the pressure-sensitive valve body 52 is carried out by exerting the hydraulic fluid to the pressure-sensitive valve body 52 through a different flow passage, configuration of the flow passage formed in the pump housing 2 can be simplified. As a consequence, the device can be simplified.

Second Embodiment

FIGS. 11 to 13 show a second embodiment of the present invention. A basic structure of the second embodiment is the same as that of the first embodiment. However, in the second embodiment, as the coil spring 53, a spring (a nonlinear spring) having a nonlinear spring constant is used.

That is, the coil spring 53 of the present embodiment is formed so that at least one parameter of design parameters such as a coil diameter, a pitch and a line diameter is formed so as to vary along the axial direction of the coil spring 53. With this design, a relationship between a spring-load F and a displacement X from an initial length (hereinafter, simply called “displacement X”) is nonlinear.

FIGS. 11 and 12 each show, as an example, a relationship between the spring-load F and the displacement X of the coil spring 53 of the present embodiment. The coil spring 53 of FIG. 11 is a so-called dual pitch spring (or a two stage spring) whose pitch is different between one end side and the other end side of the spring. The coil spring 53 of FIG. 12 is a so-called tapered spring whose coil diameter widens from one end side to the other end side of the spring.

Working or Operation and Effect of the Second Embodiment

In the first embodiment, since the coil spring 53 has the linear characteristic, a pressure P of the hydraulic fluid acting on the pressure-sensitive valve body 52 and the moving amount of the pressure-sensitive valve body 52 to the small diameter hole portion 51b side are substantially proportional. For this reason, a characteristic of change of an opening area S (hereinafter, simply called “orifice opening area S”) of the metering orifice 32 with increase in the pressure P is greatly affected by the cross section (the circular shape) of the metering orifice 32. Therefore, the relationship between the pressure P and the orifice opening area S is univocally or uniquely determined so that, when the orifice opening area S is changed from a minimum value S_min to a maximum value S_max, the orifice opening area S most greatly changes at a start of movement of the pressure-sensitive valve body 52, while change of the orifice opening area S is gradually small as the pressure P is increased (see a dashed line in FIG. 13).

In contrast to this, in the present embodiment, since the coil spring 53 has the nonlinear characteristic, the relationship between the pressure P and the moving amount of the pressure-sensitive valve body 52 to the small diameter hole portion 51b side is not proportional. Then, according to or by a certain pressure region, the pressure-sensitive valve body 52 greatly moves, or the moving amount is small.

Thus, the characteristic of change of the orifice opening area S with increase in the pressure P is greatly affected not only by the cross section (the circular shape) of the metering orifice 32 but also by the spring characteristics of the coil spring 53. Therefore, the characteristic of change of the orifice opening area S with increase in the pressure P is an irregular or abnormal characteristic as shown by a solid line in FIG. 13.

This characteristic of change can be adjusted or changed freely to some extent by changing the coil spring 53 to another spring having a different nonlinear characteristic.

Hence, according to the present embodiment, since the present embodiment has the same basic structure as that of the first embodiment, the same effects as those of the first embodiment can be obtained. Further, since the characteristic of change of the orifice opening area S with increase in the pressure P can be readily adjusted to a desired value by the coil spring 53 having the nonlinear characteristic, flexibility of tuning can be increased.

Third Embodiment

FIG. 14 shows a third embodiment of the present invention. A basic structure of the third embodiment is the same as that of the first embodiment. However, in the third embodiment, a structure of the pump housing 2 is changed. In the following explanation, the same element or component as that of the first embodiment is indicated by the same reference sign, and its detailed explanation will be omitted.

That is, as shown in FIG. 14, the pump housing 2 of the present embodiment is formed by a flat plate-shaped front housing 5 as a first housing and a bottomed cylindrical-shaped rear housing 6 as a second housing. An opening of the rear housing 6 is closed or covered with an inner end surface, on the rear housing 6 side, of the front housing 5, then the pump element accommodation chamber 2a is formed in the pump housing 2.

According to or by the change of structure of the pump housing 2, the adapter ring 8 forming the pump element 3 is fitted and fixed to an inner circumferential surface of a cylindrical portion 6b of the rear housing 6. Further, the pressure plate 11 is disposed at a bottom wall portion 6c of the rear housing 6 so as to sandwich the cam ring 9 and the rotor 10 together with the front housing 5.

In addition, one end portion 4a, on the front housing 5 side, of the drive shaft 4 supported by the pump housing 2 protrudes to the outside of the pump housing 2, and a pulley 66 as a drive shaft transmission unit is provided at this protruding portion. The pulley 66 drives and rotates the drive shaft 4 by transmitting power of the engine which is transmitted through a belt (not shown) to the drive shaft 4.

Furthermore, according to or by the change of structure of the pump housing 2, a setting position of the flow amount control valve 33 of the present embodiment is changed to an upper end portion of the cylindrical portion 6b of the rear housing 6.

Moreover, according to or by the change of structure of the pump housing 2, a setting position of the pressure-sensitive valve 50 is also changed. That is, the pressure-sensitive valve accommodation hole 51 of the pressure-sensitive valve 50 of the present embodiment is disposed in a position at some midpoint of the outlet passage 30 (in a predetermined position in the outlet passage 30) and on the pulley 66 side of the front housing 5 with respect to the rotor 10 in the axial direction of the drive shaft 4.

The other structure and connecting configuration of the flow amount control valve 33 and the pressure-sensitive valve 50 are the same as those of the first embodiment. Thus, their explanation will be omitted here.

Working or Operation and Effect of the Third Embodiment

Since the basic structure of the third embodiment is the same as that of the first embodiment, it is possible to increase the pump discharge amount during steering operation in which large steering assist force is required, and decrease the pump discharge amount during straight-ahead driving of the vehicle at which no steering assist force is required, by the pressure-sensitive valve 50. Therefore, the pump discharge amount is properly adjusted according to an operating condition, thereby reducing energy loss of the pumping operation.

Also in the present embodiment, in terms of avoidance of interference with the drive shaft 4 and a bearing (not shown) supporting the drive shaft 4, a space C (indicated by a two-dot chain line in FIG. 14) close to the drive shaft 4 in the front housing 5 is a dead space for installation of a mechanism having a sophisticated operation. However, by utilizing the pressure-sensitive valve 50 that performs the linear movement and arranging this pressure-sensitive valve 50 in the space C, increase in size of the device due to the arrangement of the pressure-sensitive valve 50 can be suppressed.

The present invention is not limited to the above embodiments, and includes all design modifications and equivalents belonging to the technical scope of the present invention.

For instance, in each of the embodiments, the cross section of the metering orifice 32 is circular. However, as long as the rate of change of the flow passage cross-sectional area is gradually decreased according to the movement of the pressure-sensitive valve body 52 with increase of the pressure of the working fluid flowing in the outlet passage 30, the metering orifice 32 could be formed into rhombus in cross section.

In the above explanation, the pressure-sensitive valve 50 changes the flow passage cross-sectional area of the metering orifice 32 provided in the outlet passage 30. However, the metering orifice 32 could be removed, then the outlet passage 30 could be configured so that its flow passage cross-sectional area is directly changed.

Further, in each of the embodiments, the hydraulic fluid flowing in the outlet passage 30 directly flows out to the downstream side of the metering orifice 32 while applying the pressure of hydraulic fluid to the pressure-sensitive valve body 52. However, the pressure-sensitive valve 50 could be set as a pilot valve, and a pilot flow passage that branches off from the outlet passage 30 could be further provided, then by moving the pressure-sensitive valve body 52 by a pilot pressure of the hydraulic fluid flowing into the pilot flow passage, the hydraulic fluid flowing in the outlet passage 30 indirectly flows out to the downstream side of the metering orifice 32.

Furthermore, in each of the embodiments, although the stopper limiting the movement of the pressure-sensitive valve body 52 to the one end side is provided on the pressure-sensitive valve body 52 side (the one end surface 54a) and on the pressure-sensitive valve accommodation hole 51 side (the stepped surface 51c), the stopper might be provided at at least either of the pressure-sensitive valve body 52 or the pressure-sensitive valve accommodation hole 51.

Moreover, in each of the embodiments, the cam ring 9 moves or rolls on an upper end surface of the plate seal member 12, then the eccentric amount of the cam ring 9 with respect to the rotor 10 is changed. However, as long as the cam ring 9 is provided movably in the pump element accommodation chamber 2a, the configuration of the cam ring 9 is not limited to this. For instance, the cam ring 9 could be provided so as to move or roll with the position holding pin 17 being a rolling fulcrum, and the eccentric amount of the cam ring 9 with respect to the rotor 10 is changed by this rolling.

Claims

1. A variable capacity vane pump supplying working fluid to a power steering device of a vehicle, comprising:

a pump housing formed from a first housing having a cylindrical portion and a bottom wall portion provided so as to close one end opening of the cylindrical portion and a second housing provided so as to close the other end opening of the cylindrical portion, the pump housing forming a pump element accommodation space inside the pump housing between the first and second housings;

a drive shaft inserted and rotatably supported in the pump housing;

a rotor accommodated in the pump element accommodation space and driven and rotated by the drive shaft, the rotor being provided with a plurality of slits in a radial direction of the rotor;

vanes provided in the slits so as to extend and retract;

a ring-shaped cam ring movably provided in the pump element accommodation space and forming a plurality of pump chambers together with the rotor and the vanes;

an inlet port provided in the pump housing and opening to a suction section where a volume of each of the pump chambers gradually increases with rotation of the rotor;

an outlet port provided in the pump housing and opening to a discharge section where the volume of each of the pump chambers gradually decreases with rotation of the rotor;

an inlet passage provided in the pump housing and introducing the working fluid stored in a reservoir tank to the inlet port;

an outlet passage provided in the pump housing and introducing the working fluid discharged from the outlet port to an outside of the pump housing;

a first fluid pressure chamber and a second fluid pressure chamber each provided at an outer peripheral side of the cam ring, the first fluid pressure chamber being located on a side where a volume of the fluid pressure chamber is decreased when the cam ring moves in a direction in which an eccentric amount of the cam ring with respect to the rotor is increased, and the second fluid pressure chamber being located on a side where the volume of the fluid pressure chamber is increased when the cam ring moves in the direction in which the eccentric amount of the cam ring with respect to the rotor is increased;

a first valve accommodation hole formed at the bottom wall portion of the first housing and at some midpoint of the outlet passage;

a first valve body movably provided in the first valve accommodation hole, the first valve body being configured so that movement of the first valve body is controlled by a pressure difference between a suction pressure acting on one end side of the first valve body and a discharge pressure introduced from the outlet passage and acting on the other end side of the first valve body, and the first valve body changes a flow passage cross-sectional area of the outlet passage according to the movement of the first valve body;

a second valve accommodation hole provided in the pump housing;

a high pressure chamber provided at one end side of the second valve accommodation hole and formed so as to communicate with the outlet port;

a control pressure chamber provided at the other end side of the second valve accommodation hole and formed so as to communicate with a downstream side, with respect to the first valve accommodation hole, of the outlet passage; and

a second valve body movably provided in the second valve accommodation hole and controlling a pressure in the first fluid pressure chamber by a pressure difference between a pressure in the high pressure chamber and a pressure in the control pressure chamber.

2. The variable capacity vane pump as claimed in claim 1, wherein:

the first valve body is provided so as to move along an axial direction of the drive shaft.

3. The variable capacity vane pump as claimed in claim 1, wherein:

the first valve accommodation hole is provided so that an opening side of the first valve accommodation hole communicates with the discharge section.

4. The variable capacity vane pump as claimed in claim 3, wherein:

the first valve accommodation hole is provided so as to overlap the discharge section in a circumferential direction of the drive shaft.

5. The variable capacity vane pump as claimed in claim 4, wherein:

the first valve body is inserted into the first valve accommodation hole from the opening side of the first valve accommodation hole.

6. The variable capacity vane pump as claimed in claim 4, wherein:

the pump housing has: a seal member accommodation space formed into a ring-shape on an outer circumferential side of the drive shaft and accommodating therein a seal member that seals a gap between the pump housing and the drive shaft; a low pressure communication passage connecting the seal member accommodation space and the suction section; and a low pressure introduction passage connecting one end side of the first valve accommodation hole and the seal member accommodation space.

7. The variable capacity vane pump as claimed in claim 1, wherein:

the first valve body is a spool valve that has a land portion and changes the flow passage cross-sectional area of the outlet passage by changing an overlap amount between the land portion and the outlet passage.

8. The variable capacity vane pump as claimed in claim 7, wherein:

a groove portion is formed at the other end side of the first valve body by cutting in a radial direction of the first valve body.

9. The variable capacity vane pump as claimed in claim 7, further comprising:

a spring member forcing the first valve body to the other end side of the first valve body, and wherein

the first valve body has, at one end portion thereof, a stopper that limits the movement of the first valve body to the one end side of the first valve body.

10. The variable capacity vane pump as claimed in claim 9, wherein:

the spring member is a coil spring, and

the first valve body has, at the one end side thereof, a spring retaining portion that accommodates and retains a part of the spring member.

11. The variable capacity vane pump as claimed in claim 9, wherein:

the first valve body is configured so that when the movement of the first valve body is limited by the stopper, the flow passage cross-sectional area of the outlet passage is a maximum.

12. The variable capacity vane pump as claimed in claim 7, wherein:

the outlet passage is configured so that rate of change of the flow passage cross-sectional area of the outlet passage is gradually decreased with increase of the discharge pressure acting on the other end side of the first valve body.

13. The variable capacity vane pump as claimed in claim 1, further comprising:

a spring member provided in the first valve accommodation hole and forcing the first valve body, and wherein

the spring member has a nonlinear spring constant.

14. The variable capacity vane pump as claimed in claim 1, wherein:

the first valve body directly introduces the working fluid acting on the other end side of the first valve body to the downstream side of the outlet passage.

15. The variable capacity vane pump as claimed in claim 1, wherein:

the first valve accommodation hole is provided so that a bottom side of the first valve accommodation hole communicates with the inlet passage.

16. A variable capacity vane pump supplying working fluid to a power steering device of a vehicle, comprising:

a pump housing formed from a first housing formed into a flat plate and a second housing having a cylindrical portion and a bottom wall portion provided so as to close one end opening of the cylindrical portion, the other end opening of the cylindrical portion being closed by the first housing, the pump housing forming a pump element accommodation space inside the pump housing between the first and second housings;

a drive shaft inserted and rotatably supported in the pump housing;

a drive shaft transmission unit provided at a protruding portion of the drive shaft which protrudes to an outside of the pump housing and transmitting external power to the drive shaft;

a rotor accommodated in the pump element accommodation space and driven and rotated by the drive shaft, the rotor being provided with a plurality of slits in a radial direction of the rotor;

vanes provided in the slits so as to extend and retract;

a ring-shaped cam ring movably provided in the pump element accommodation space and forming a plurality of pump chambers together with the rotor and the vanes;

an inlet port provided in the pump housing and opening to a suction section where a volume of each of the pump chambers gradually increases with rotation of the rotor;

an outlet port provided in the pump housing and opening to a discharge section where the volume of each of the pump chambers gradually decreases with rotation of the rotor;

an inlet passage provided in the pump housing and introducing the working fluid stored in a reservoir tank to the inlet port;

an outlet passage provided in the pump housing and introducing the working fluid discharged from the outlet port to an outside of the pump housing;

a first fluid pressure chamber and a second fluid pressure chamber each provided at an outer peripheral side of the cam ring, the first fluid pressure chamber being located on a side where a volume of the fluid pressure chamber is decreased when the cam ring moves in a direction in which an eccentric amount of the cam ring with respect to the rotor is increased, and the second fluid pressure chamber being located on a side where the volume of the fluid pressure chamber is increased when the cam ring moves in the direction in which the eccentric amount of the cam ring with respect to the rotor is increased;

a first valve accommodation hole formed in a position on a drive shaft transmission unit side of the first housing with respect to the rotor in an axial direction of the drive shaft and at some midpoint of the outlet passage;

a first valve body movably provided in the first valve accommodation hole, the first valve body being configured so that movement of the first valve body is controlled by a pressure difference between a suction pressure acting on one end side of the first valve body and a discharge pressure introduced from the outlet passage and acting on the other end side of the first valve body, and the first valve body changes a flow passage cross-sectional area of the outlet passage according to the movement of the first valve body;

a second valve accommodation hole provided in the pump housing;

a high pressure chamber provided at one end side of the second valve accommodation hole and formed so as to communicate with the outlet port;

a control pressure chamber provided at the other end side of the second valve accommodation hole and formed so as to communicate with a downstream side, with respect to the first valve accommodation hole, of the outlet passage; and

a second valve body movably provided in the second valve accommodation hole and controlling a pressure in the first fluid pressure chamber by a pressure difference between a pressure in the high pressure chamber and a pressure in the control pressure chamber.

17. The variable capacity vane pump as claimed in claim 16, wherein:

the first valve body is provided so as to move along an axial direction of the drive shaft.

18. The variable capacity vane pump as claimed in claim 16, wherein:

the first valve accommodation hole is provided so that an opening side of the first valve accommodation hole communicates with the discharge section.

19. The variable capacity vane pump as claimed in claim 18, wherein:

the first valve accommodation hole is provided so as to overlap the discharge section in a circumferential direction of the drive shaft.

20. A variable capacity vane pump supplying working fluid to a power steering device of a vehicle, comprising:

a pump housing formed from a first housing having a cylindrical portion and a bottom wall portion provided so as to close one end opening of the cylindrical portion and a second housing provided so as to close the other end opening of the cylindrical portion, the pump housing forming a pump element accommodation space inside the pump housing between the first and second housings;

a drive shaft inserted and rotatably supported in the pump housing;

a rotor accommodated in the pump element accommodation space and driven and rotated by the drive shaft, the rotor being provided with a plurality of slits in a radial direction of the rotor;

vanes provided in the slits so as to extend and retract;

a ring-shaped cam ring movably provided in the pump element accommodation space and forming a plurality of pump chambers together with the rotor and the vanes;

an inlet port provided in the pump housing and opening to a suction section where a volume of each of the pump chambers gradually increases with rotation of the rotor;

an outlet port provided in the pump housing and opening to a discharge section where the volume of each of the pump chambers gradually decreases with rotation of the rotor;

an inlet passage provided in the pump housing and introducing the working fluid stored in a reservoir tank to the inlet port;

an outlet passage provided in the pump housing and introducing the working fluid discharged from the outlet port to an outside of the pump housing;

a first fluid pressure chamber and a second fluid pressure chamber each provided at an outer peripheral side of the cam ring, the first fluid pressure chamber being located on a side where a volume of the fluid pressure chamber is decreased when the cam ring moves in a direction in which an eccentric amount of the cam ring with respect to the rotor is increased, and the second fluid pressure chamber being located on a side where the volume of the fluid pressure chamber is increased when the cam ring moves in the direction in which the eccentric amount of the cam ring with respect to the rotor is increased;

a first valve accommodation hole formed at the bottom wall portion of the first housing and at some midpoint of the outlet passage;

a first valve body movably provided in the first valve accommodation hole, the first valve body being configured so that movement of the first valve body is controlled by a pressure difference between a suction pressure acting on one end side of the first valve body and a discharge pressure introduced from the outlet passage and acting on the other end side of the first valve body, the first valve body changes a flow passage cross-sectional area of the outlet passage according to the movement of the first valve body, and the working fluid acting on the other end side of the first valve body flows out of the first valve body;

a second valve accommodation hole provided in the pump housing;

a high pressure chamber provided at one end side of the second valve accommodation hole and formed so as to communicate with the outlet port;

a control pressure chamber provided at the other end side of the second valve accommodation hole and formed so as to communicate with a downstream side, with respect to the first valve accommodation hole, of the outlet passage; and

a second valve body movably provided in the second valve accommodation hole and controlling a pressure in the first fluid pressure chamber by a pressure difference between a pressure in the high pressure chamber and a pressure in the control pressure chamber.