JP2003065249A - Variable displacement pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent periodic fluctuation of a pump discharge flow amount, and improve responsiveness in a case where a load pressure sensor function is provided. SOLUTION: In a housing 10, a cam ring 21 of a vane pump is arranged to be radially movable, and a differential pressure control valve 31 is arranged in which an axial direction position is controlled by an internal pressure and a load pressure introduced in operation chambers 52a and 52b formed at both ends. A pressure between the internal pressure of the pump and a pressure obtained by reducing the internal pressure is introduced to a first operation chamber 51a arranged to one side of the cam ring, in response to a position of the differential pressure control valve. The load pressure is introduced to the second operation chamber 51b arranged to the other side of the cam ring, and the discharge flow amount is controlled in response to a pump rotating speed. The differential pressure control valve is urged to the inner pressure operation chamber 52a side by a valve pressing spring 33, and a load pressure sensor piston 40 whose tip enters an inside of an internal pressure operation chamber by being urged by the piston pressing spring 41 is abutted to be urged in a reverse direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable displacement pump suitable for use in a power steering device for a vehicle, and more particularly, to a vane pump portion having a rotor rotating in a cam ring and provided in a discharge passage. The present invention relates to a variable displacement pump in which the eccentricity of a cam ring with respect to a rotor is changed according to the pressure difference across an orifice to control the pump discharge flow rate characteristic.

[0002]

2. Description of the Related Art As such a variable displacement pump,
There is a technique disclosed in Japanese Patent No. 2932236 (see Japanese Patent Laid-Open No. 7-243385). This forms the first and second fluid pressure chambers between the cam ring and the pump body that are arranged so that the eccentric amount with respect to the rotor is variable, and urges the cam ring in the direction in which the pump displacement is maximized. A spool type control valve for controlling the fluid pressure supplied to the first fluid pressure chamber according to the differential pressure across the orifice provided in the pump discharge side passage is provided to give a displacement displacement in the direction that maximizes the pump capacity. The fluid pressure on the rear side of the orifice, which is guided to the second chamber at one end of the control valve, is introduced into the second fluid pressure chamber. In this conventional technique, in the spool type control valve, the fluid pressure (pump internal pressure, hereinafter simply referred to as internal pressure) on the front side of the orifice is introduced into the first chamber at the other end, so that the first rotational speed is low when the pump rotational speed is low. By introducing a low pressure (= atmospheric pressure) connected to the reservoir into the first fluid pressure chamber when it is pressed against the chamber side, the eccentric amount of the cam ring is maximized, the pump displacement is maximized, and the pump rotation speed is increased. If it moves to the second chamber side, the internal pressure on the front side of the orifice is introduced into the first fluid pressure chamber to reduce the eccentric amount of the cam ring and reduce the pump capacity.

[0003]

According to the technique of Japanese Patent No. 2932236 as described above, the fluid pressure introduced into the first fluid pressure chamber is low when the pump rotation speed is low, and the pump rotation speed is low. When the speed increases, it varies between the fluid pressures on the front side of the orifice. However, when the pump rotation speed changes rapidly, the fluid pressure introduced into the first fluid pressure chamber also changes rapidly, so the cam ring overshoots. There is a problem in that the pump reciprocates at a certain cycle and the discharge flow rate of the pump also periodically changes. Also, due to this rapid change in fluid pressure, the seal member made of tetrafluoroethylene resin or the like, which is provided between the outer peripheral portion of the cam ring and the inner surface of the pump body, is fatigue-broken in a short time and the durability of the variable displacement pump is improved. There is a problem of decrease.

An object of the present invention is to solve the above problems and to improve the response to the load pressure when the variable displacement pump is provided with the load pressure sensitive function.

[0005]

SUMMARY OF THE INVENTION A variable displacement pump according to the present invention comprises a cam ring rotatably mounted in a housing, and a cam ring rotatably supported by the housing and sliding on an inner surface of the cam ring. A rotor for movably holding a plurality of vanes in contact with each other in a radial direction, an intake port and a discharge port formed in the housing or a member fixed to the housing, and a discharge port provided in a discharge passage communicating with the discharge port And the first working chamber and the second working chamber formed on the outer periphery of the cam ring so as to face each other in the moving direction of the cam ring, and the cam ring is urged toward the first working chamber side where the eccentricity with respect to the rotor is maximum. And a cam pressing means that is axially movable in a valve hole formed in the housing and is actuated by a differential pressure before and after the orifice. In the variable displacement pump including the differential pressure control valve for controlling each pressure acting on the second working chamber, the differential pressure control valve has a small differential pressure before and after the orifice and maximizes the eccentric amount of the cam ring with respect to the rotor. In this state, a pressure obtained by reducing the internal pressure on the front side of the orifice is introduced into the first working chamber.

The fluid pressure introduced into the first working chamber is a minimum of the internal pressure on the front side of the orifice introduced when the differential pressure across the orifice is small and the eccentric amount of the cam ring with respect to the rotor is maximum. Yes, the maximum fluid pressure in the variable displacement pump does not exceed the fluid pressure on the front side of the orifice.

The variable displacement pump according to the present invention includes a cam ring movably provided in the housing, and a plurality of cam rings rotatably supported by the housing in the cam ring and slidably abutting the inner surface of the cam ring. Rotor for movably holding the vanes in the radial direction, an intake port and a discharge port formed in the housing or a member fixed to the housing, an orifice provided in a discharge passage communicating the discharge port with the discharge port, and a cam ring. The first working chamber and the second working chamber formed by partitioning the space between the outer periphery of the cam ring and the housing with a seal member made of a flexible elastic body so as to face each other in the moving direction of the cam ring, and the eccentric amount of the cam ring with respect to the rotor. A cam pressing means for urging the maximum working chamber side, and axial movement in a valve hole formed in the housing. The differential pressure control valve is fitted to the internal pressure working chamber and the load pressure working chamber, which are formed between both ends of the differential pressure control valve and the housing, respectively. In the variable displacement pump in which the load pressure which is the pressure on the rear side is respectively introduced, when the differential pressure control valve is pressed against the inner pressure working chamber side, the pressure reduced from the inner pressure is introduced into the first working chamber. It is characterized in that the internal pressure is introduced into the first action chamber and the load pressure is introduced into the second action chamber when the load pressure action chamber is moved to the first action chamber.

The fluid pressure introduced into the first working chamber has a small differential pressure before and after the orifice. Therefore, the pressure obtained by reducing the internal pressure introduced when the differential pressure control valve is pressed to the internal pressure working chamber side is the minimum. The internal pressure introduced when the differential pressure control valve moves to the load pressure action chamber side is the maximum.

The variable displacement pump according to the present invention comprises a valve pressing spring for urging the differential pressure control valve toward the inner pressure working chamber side, and a tip which is slidably fitted and supported by the housing and protrudes into the inner pressure working chamber. The part further includes a load pressure sensitive piston that can abut one end of the differential pressure control valve in the axial direction, and a piston pressing spring that biases the load pressure sensitive piston toward the differential pressure control valve. Is preferred.

The orifice provided in the discharge passage of the variable displacement pump according to the present invention is preferably a variable orifice whose opening area decreases as the cam ring moves toward the second working chamber.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION First, a first embodiment shown in FIGS. 1 to 4 will be described. The variable displacement pump of this embodiment is used as a working fluid supply source for a power steering apparatus, and includes a housing 10 which is liquid-tightly covered by an end cover 11, and a pump shaft 2 which is provided in the housing 10.
A vane pump unit 20 having a rotor 22 driven to rotate by 6 and a cam ring 21 movable in the radial direction;
Differential pressure control valve 31 for controlling the movement of the cam ring 21
An orifice 54 provided in the discharge passage 53 of the vane pump unit 20 is a main constituent member.

As shown in FIGS. 1 and 2, on a cylindrical inner surface 10a formed in the housing 10, a disk-shaped side plate 12 and a cylindrical adapter 13 which form a part of the housing 10 are provided at the back. They are stacked from the side and integrally fitted and supported. The housing 10 and the end cover 11 fixed to the housing 10 by screws are rotatably supported by the intermediate portion and the rear end portion of the pump shaft 26 coaxially with the inner surface 10a via bearings. A vane pump portion 20 described below is provided between the end cover 11, the side plate 12, and the adapter 13. The vane pump portion 20 is transmitted to the tip of the pump shaft 26 protruding from the housing 10 by transmitting power from the engine. A V-pulley 29 that drives 20 is fixed.

The vane pump portion 20 includes a cam ring 21 provided in the adapter 13, a rotor 22 coaxially spline-coupled to an intermediate portion of a pump shaft 26, and a rotor 2.
2 includes a vane 23 slidably held by a plurality of radial slits and constantly abutting on the cylindrical inner surface of the cam ring 21, and the side surfaces of each of the members 21 to 23 have end covers 11 and It is slidably abutted on the end surface of the side plate 12. The intake port 24 of the vane pump unit 20 is formed on the end surface of the end cover 11,
The working fluid from the reservoir 61 is supplied through the suction passage 14 and the suction port 15. The discharge port 25 is formed on the end surface of the side plate 12, and is guided from the pressure chamber 16 located on the back side to the discharge port 55 through the discharge passage 53 and the conduction hole 34a formed in the housing 10.
An orifice 54 is provided in the middle of the discharge passage 53.

A pin 17 which is provided in parallel with the pump shaft 26 and whose both ends are supported by the end cover 11 and the side plate 12 is engaged with the inner surface of the adapter 13 at a part of the outer periphery of the intermediate portion. The cam ring 21 is movable in the radial direction of the cam ring 21 when a recess 21a formed in a part of the outer peripheral surface is engaged with the pin 17 and swings around the pin 17, and the recess on the outer peripheral surface of the cam ring 21 is provided. 21
The portion opposite to a is slidably sealed by a seal member 50 made of a flexible elastic member such as tetrafluoroethylene resin provided in a groove formed on the inner surface of the adapter 13 and backed up by rubber. There is. Housing 1
Due to the pin 17 and the seal member 50, the space between the adapter 13 and the cam ring 21, which is a part of 0, is opposed to the first working chamber 5 in the moving direction of the cam ring 21.
It is partitioned into 1a and a second action chamber 51b. A plug 18 directed toward the pump shaft 26 is screwed and fixed to the housing 10 on the side of the second action chamber 51b in the moving direction of the cam ring 21, and the cam ring 21 is interposed between the plug 18 and the cam ring 21 and the adapter 13 The first action chamber 51a that maximizes the amount of eccentricity with respect to the rotor 22 by the cam pressing spring (cam pressing means) 28 that passes through
It is elastically biased to the side.

The working fluid from the vane pump portion 20 is discharged from the discharge port 55 through the discharge passage 53 having the orifice 54 and the communication hole 34a. When the variable displacement pump is operating and the working fluid is flowing, the pressure drops before and after the orifice 54 to generate a differential pressure, and the discharge passage 53, the communicating hole 34a and the discharge port 55 on the rear side of the orifice 54 are formed. The pressure inside is the load pressure given by the operating state of the equipment to which the working fluid is supplied, and the pressure inside the discharge passage 53 and the pressure chamber 16 in front of the orifice 54 is the pump internal pressure. This internal pressure is larger than the load pressure by the amount of the differential pressure due to the orifice 54. Therefore, if the load pressure changes, the internal pressure also changes in the same manner. Under normal operating conditions, this differential pressure is considerably smaller than the internal pressure or the load pressure.

As shown mainly in FIG. 1, the pump shaft 26
A spool-shaped differential pressure control valve 31 is inserted into the valve hole 30 formed in the housing 10 in a direction that is three-dimensionally orthogonal to the valve hole 30 from one direction on the left side in the drawing, and is fitted so as to be movable in the axial direction. A union 34 is screwed and fixed to the insertion side of 30, and working chambers 52 a and 52 b are formed between both ends of the differential pressure control valve 31 and the housing 10. The union 34 is formed with a discharge port 55 and a conduction hole 34a for guiding the discharge port 55 to the discharge passage 53. The action chamber 52a opposite to the union 34 is an internal pressure action chamber, and is provided in the pressure chamber 16 via a pump internal pressure introduction passage 56 formed in the housing 10 so as to open to the peripheral surface of the right end portion of the valve hole 30. Internal pressure is always introduced. The working chamber 52b on the side of the union 34 is a load pressure working chamber, and the discharge port 55
The internal load pressure is always introduced through the throttle communication hole 59. The differential pressure control valve 31 has a valve pressing spring 33 interposed between the differential pressure control valve 31 and the union 34, so
In the inoperative state in which the fluid pressure is not elastically urged toward the 2a side, the protrusion 31a at the tip of the differential pressure control valve 31 is located on the right inner end surface of the valve hole 30 on the inner pressure acting chamber 52a side. Abutted.

The introduction passage 57a formed in the housing 10 so as to open to the peripheral surface of the valve hole 30 at a position slightly left of the pump internal pressure introduction passage 56 has a cam ring 21 through a damping orifice 58a formed in the adapter 13. Is communicated with the first working chamber 51a on one side of the outer circumference.
Between the opening portion of the introduction passage 57a opened on the peripheral surface of the valve hole 30 and both side edges of the land portion 31b formed on the outer peripheral portion of the differential pressure control valve 31 corresponding to the opening portion, A pair of variable throttles 62a and 62b whose opening areas change in opposite directions according to the movement of the differential pressure control valve 31 are formed, and one variable throttle (first variable throttle) 62a is provided in the differential pressure control valve 31. The introduction passage 57a communicates with the reservoir 61 opened to the atmosphere through the formed communication passage 32 and the communication conduit 60, and the other variable throttle (second variable throttle) 62b has the internal pressure action chamber 52a and the pump internal pressure introduction passage 56. Introductory route 5 via
7a communicates with the pressure chamber 16. 1 and 4 (a)
As shown in FIG. 2, both the variable throttles 62a and 62b are open at the inoperative position where the differential pressure control valve 31 is in contact with the right inner end surface, so that the introduction passage 57 is provided in the first working chamber 51a.
A pressure (pressure between the internal pressure and the atmospheric pressure) obtained by reducing the internal pressure on the front side of the orifice 54 is introduced via a. If the differential pressure control valve 31 moves from the inoperative position to the load pressure action chamber 52b side, the opening area of the first variable throttle 62a decreases,
Since the opening area of the second variable throttle 62b increases, the pressure introduced into the first working chamber 51a via the introduction passage 57a gradually increases, and as shown in FIG. 4 (b), the first variable throttle 62a.
After is closed, the pressure introduced into the first working chamber 51a becomes the internal pressure in the pressure chamber 16.

Housing 1 on the side of load pressure acting chamber 52b
The load pressure introducing passage 57b formed in a part of 0 is opened in the peripheral surface of the valve hole 30 at a position where it is always opened in the load pressure acting chamber 52b, and the load pressure introducing passage 57b is formed in the adapter 13 and formed in the damping orifice. The second working chamber 51b on the other side of the outer periphery of the cam ring 21 is communicated with the second working chamber 51b via 58b. In the differential pressure control valve 31, the pressure in the load pressure action chamber 52b is stored in the reservoir 6 when the load pressure increases excessively.
1, the differential pressure control valve 31 is set to the load pressure action chamber 5
A pilot relief valve 65 is provided which is moved to the 2b side to minimize the pump discharge flow rate.

When the rotation of the vehicle engine is transmitted to the pump shaft 26 via the drive belt attached to the V pulley 29 and the rotor 22 of the vane pump portion 20 is rotated, the working fluid in the reservoir 61 is sucked into the suction port 15 and It is sucked from the suction passage 14 through the suction port 24 into each vane 23 of the vane pump portion 20, discharged from the discharge port 25 into the pressure chamber 16, and passes through the discharge passage 53 having the orifice 54 and the conduction hole 34a. It is supplied from the outlet 55 to equipment such as a power steering device.

When the pump rotation speed is low, the discharge passage 5
Since the flow rate through the valve 3 is small, and therefore the differential pressure before and after the orifice 54 is small, the differential pressure control valve 31 has
As shown in (a), the valve pressing spring 33 presses the inner pressure working chamber 52a toward the end position, and the first working chamber 51a is introduced into the orifice 5 through the introduction passage 57a.
A pressure obtained by reducing the internal pressure on the front side of No. 4 is introduced, and a pressure lower than this is not introduced into the first working chamber 51a. In this state, the cam ring 21 has the cam pressing spring 2
It is pressed against the side of the first action chamber 51a where the discharge flow rate is maximum by 8 and does not separate. Therefore, the discharge flow rate of the working fluid discharged from the discharge port 55 through the discharge passage 53 and the conduction hole 34a rapidly increases as the pump rotation speed increases, as indicated by the characteristic A in FIG.

If the discharge flow rate increases due to the increase in the pump rotation speed and the differential pressure across the orifice 54 increases, the differential pressure control is performed by the differential pressure between the internal pressure in the internal pressure working chamber 52a and the load pressure in the load pressure working chamber 52b. The force to move the valve 31 against the valve pressing spring 33 toward the load pressure action chamber 52b also increases. If this force exceeds a predetermined value, the differential pressure control valve 31 moves to the load pressure action chamber 52b side against the valve pressing spring 33, and the pressure introduced into the first action chamber 51a via the introduction path 57a. Has increased, FIG.
As shown in (b), the first variable throttle 62a is closed and the pressure introduced into the first working chamber 51a becomes the maximum internal pressure. As a result, the pressure introduced into the first working chamber 51a exceeds a predetermined value, so that the cam ring 21 that has been in contact with the first working chamber 51a side where the discharge flow rate is maximum until then becomes
As the pump rotation speed increases, the amount of eccentricity is reduced in order to keep the differential pressure across the orifice 54 constant.
The discharge flow rate of the working fluid discharged from the discharge port 55 is as shown in FIG.
It becomes almost constant as shown in the characteristic B of 1. Therefore this first
The discharge flow rate characteristics with respect to the pump rotation speed of the variable displacement pump of the above embodiment are as shown by characteristics A and B in FIG.

According to the first embodiment, the fluid pressure introduced into the first working chamber 51a has a small differential pressure before and after the orifice 54. Therefore, the differential pressure control valve 31 causes the internal pressure working chamber 52a of the valve hole 30 to operate. The pressure obtained by reducing the internal pressure introduced when being pressed against the side inner end surface is the minimum, and the differential pressure control valve 31 moves to the load pressure action chamber side to move the first variable throttle 62.
The maximum internal pressure introduced after a is closed is maximum. Therefore, when the minimum and maximum values of the introduced pressure are the low pressure and the internal pressure at the front side of the orifice, respectively, which are connected to the reservoir, the fluctuation range of the pressure is reduced, and even when the pump rotation speed is suddenly changed, Since the fluctuation of the fluid pressure introduced into the working chamber 51a becomes gentle, the cam ring does not overshoot, and thus the discharge flow rate of the pump does not fluctuate periodically. Also, since the fluctuation range of pressure decreases in this way, due to sudden fluctuations in fluid pressure,
The outer periphery of the cam ring 21 and the adapter 1 of the housing 10
The sealing member 50 made of tetrafluoroethylene resin or the like provided between the first and the second parts will not be fatigue-damaged in a short time and the durability of the variable displacement pump will not be deteriorated.

Next, a second embodiment shown in FIGS. 5 to 7 will be described. In the second embodiment, the differential pressure control valve 31 is configured to be operated not only by the differential pressure across the orifice 54 but also by the load pressure, and the discharge passage 53
This embodiment is different from the first embodiment only in that the orifice 54 provided in the first embodiment is a variable orifice whose opening area changes according to the movement of the cam ring 21, so that the difference will be mainly described. The tip of the differential pressure control valve 31 of the second embodiment on the side of the internal pressure working chamber 52a is
The protrusion 31a is not provided.

First, the structure for operating the differential pressure control valve 31 also by the load pressure will be described. As shown in FIG. 5, on one side of the housing 10 on the side of the internal pressure acting chamber 52a, a load pressure sensitive piston 40 having a rod shape having a smaller diameter than the differential pressure control valve 31 and one end of which protrudes into the internal pressure acting chamber 52a.
Is coaxially and slidably fitted and supported on the valve hole 30. The load pressure sensitive piston 40 is biased toward the differential pressure control valve 31 side between the spring receiving member 40a fixed to the other end of the load pressure sensitive piston 40 and the plug 19 coaxially screwed and fixed to the housing 10. The piston pressing spring 41 is interposed, and the pressing force of the piston pressing spring 41 is set to be smaller than the pressing force of the valve pressing spring 33. Therefore, in the non-actuated state in which the fluid pressure is not applied, the differential pressure control valve 31 and the load pressure sensitive piston 40 are in a state where the tips are in contact with each other as shown in FIGS. 5 and 6 (a). Spring 3
The spring bearing member 40a is stopped by abutting the rear end surface of the spring receiving member 40a against the plug 19 by being biased rightward by the difference in the pressing force of 3, 41. The positional relationship between the land portion 31b of the differential pressure control valve 31 and the introduction path 57a in this state is the same as that of FIG. 4A in the first embodiment.

Next, the variable orifice 54A provided in the discharge passage 53 will be described. Second working chamber 5 of housing 10
The plug 18 that is screwed and fixed to the 1b side is larger than that in the first embodiment, and the cylindrical portion 1 of the plug 18 is
A cam pressing piston 27 is fitted in 8a so as to be slidable in the axial direction, and a cam pressing spring (cam pressing means) 28 is provided.
Is urged toward the pump shaft 26. The projection 27a at the tip of the cam pressing piston 27 passes through the adapter 13 in a liquid-tight manner and contacts the outer peripheral surface of the cam ring 21, so that the cam ring 21 is elastically moved toward the first working chamber 51a where the eccentric amount with respect to the rotor 22 is maximum. Is urged to.

The variable orifice 54A is formed by the communication hole 18b formed in the cylindrical portion 18a of the plug 18 and the trailing edge of the cam pressing piston 27, and the cam ring 21 moves to the second working chamber 51b side to move the cam pressing piston 27. As the cam pressing spring 28 moves backward, the communication hole 18
b is gradually closed by the rear edge of the cam pressing piston 27 so that the opening area is reduced. The discharge passage 53 is formed in the housing 10 as in the first embodiment, and discharge passages 53a and 53b for guiding the working fluid discharged from the vane pump portion 20 to the variable orifice 54A and the cam pressing piston 27 from the variable orifice 54A. The working fluid flowing out of the inlet hole 27b is passed through the conduction hole 34 of the union 34.
It is composed of a discharge passage 53c leading to a. Similar to the first embodiment, when the working fluid is flowing, a differential pressure is generated before and after the variable orifice 54A, and the pressure in the discharge passage 53c, the conduction hole 34a, and the discharge port 55 on the rear side of the variable orifice 54A. Is the load pressure given by the operating state of the equipment to which the working fluid is supplied, and the variable orifice 54A
The pressure in the discharge passages 53a, 53b on the front side of and the pressure chamber 16 is the internal pressure of the pump. The configuration of the second embodiment other than this is the same as that of the first embodiment.

When the rotor 22 of the vane pump section 20 is rotated through the drive belt wound around the V pulley 29, the working fluid in the reservoir 61 is sucked into the vane pump section 20, and the discharge passage 53a provided with the variable orifice 54A, 5
It is supplied to equipment such as a power steering device from a discharge port 55 through 3b and 53c and a conduction hole 34a. When the pump rotation speed is low, the differential pressure before and after the variable orifice 54A is small, and the load pressure is also small, the differential pressure control valve 31 is set to the position shown in FIG.
As shown in FIG. 6 (a), the pressure is pushed to the end position on the side of the internal pressure action chamber 52a, and the pressure obtained by reducing the internal pressure on the front side of the variable orifice 54A is introduced into the first action chamber 51a through the introduction path 57a. The cam ring 21 has the first working chamber 5 in which the discharge flow rate is maximized by the cam pressing spring 28.
It is pressed against the side of 1a and does not separate. In this state, the discharge flow rate of the working fluid discharged from the discharge port 55 rapidly increases as the pump rotation speed increases, as indicated by the characteristic A in FIG. 7.

If the discharge flow rate increases due to the increase in the pump rotation speed and the differential pressure across the variable orifice 54A increases,
The force for moving the differential pressure control valve 31 to the load pressure action chamber 52b side against the valve pressing spring 33 by the pressure difference between the internal pressure in the internal pressure action chamber 52a and the load pressure in the load pressure action chamber 52b also increases. To do. When the load pressure is low (for example, when the handle is not operated), the load pressure sensitive piston 40 is in contact with the differential pressure control valve 31 by the urging force of the piston pressing spring 41 and the valve pressing spring 33. Since the pressing force of (1) is offset by the pressing force of the piston pressing spring 41 and is small, the force for urging the differential pressure control valve 31 toward the internal pressure action chamber 52a side is small. Therefore, even when the pump discharge flow rate is relatively small and the generated differential pressure before and after the variable orifice 54A is small, the differential pressure control valve 31 moves against the valve pressing spring 33, and the first action is performed via the introduction path 57a. The pressure introduced into the chamber 51a increases, and as shown in FIG. 6 (b), the first variable throttle 62a is closed and the first working chamber 51a is closed.
The pressure introduced into a becomes the maximum internal pressure. As a result, the pressure introduced into the first working chamber 51a exceeds a predetermined value, so that the first working chamber 5 having the maximum discharge flow rate until then is reached.
The cam ring 21, which has been in contact with the 1a side, is reduced in eccentricity so as to maintain a constant differential pressure across the variable orifice 54A in accordance with an increase in pump rotation speed, and is discharged from the discharge port 55. The discharge flow rate of the working fluid is maintained at a relatively low flow rate as shown by the characteristic C in FIG. In the second embodiment, the throttle area of the variable orifice 54A is reduced as the eccentricity of the cam ring 21 is reduced. Therefore, the characteristic C in FIG. 7 is that the pump discharge flow rate increases as the pump rotation speed increases. Will be reduced.

In this state, when the load pressure is increased by operating the handle, the internal pressure in the internal pressure action chamber 52a is also increased and the load pressure sensitive piston 40 is pressed against the urging force of the piston pressing spring 41. As shown in (c), the differential pressure control valve 31 is separated from the differential pressure control valve 31 (or the pressing force that cancels the pressing force of the valve pressing spring 33 is reduced). The force urging the inner pressure action chamber 52a side increases. As a result, unless the differential pressure before and after the variable orifice 54A becomes large, that is, the pump discharge flow rate does not increase, the differential pressure control valve 31 does not move to the load pressure action chamber 52b side, and therefore acts on the first action chamber 51a. Since the pressure increases from the reduced pressure to the internal pressure, the eccentric amount of the cam ring 21 is not reduced, and the discharge amount is reduced, the discharge flow rate is the characteristic D of FIG.
As shown in, the flow rate is increased to the flow rate required to assist the steering operation. This characteristic D is also a characteristic in which the pump discharge flow rate is reduced as the pump rotation speed increases.

Also in this second embodiment, the above-mentioned first embodiment is used.
As in the embodiment described above, the fluctuation range of the pressure of the fluid pressure introduced into the first action chamber 51a is lower than that of the conventional technique,
Even if the pump rotation speed suddenly changes, the cam ring does not overshoot and the discharge flow rate of the pump does not change periodically, and a seal provided between the outer peripheral portion of the cam ring 21 and the adapter 13 of the housing 10. The member 50 will not be fatigue-damaged in a short time and the durability of the variable displacement pump will not be deteriorated.

In addition to this, in the second embodiment,
The valve hole 3 is provided on one side of the housing 10 that is the inner pressure action chamber 52a side.
The load pressure sensitive piston 40 is provided coaxially with 0, and the load pressure sensitive piston 40 is urged toward the differential pressure control valve 31 by the piston pressing spring 41 to move the differential pressure control valve 31 to the internal pressure action chamber 52a side. If a part of the pressing force of the valve pressing spring 33 that is urged to the valve is canceled and the internal pressure in the internal pressure action chamber 52a that increases and decreases with the load pressure increases, the load pressure sensitive piston 40 resists the valve pressing spring 33. The force for pushing back the differential pressure control valve 31 is configured to be reduced. As a result, the pump rotation speed when the eccentric amount of the cam ring 21 starts to decrease is increased in accordance with the increase of the load pressure, so that the variable displacement pump having the characteristic that the discharge flow rate increases in accordance with the increase of the load pressure can be obtained.

Further, in the second embodiment, the orifice 54 provided in the discharge passage 53 is a variable orifice whose opening area decreases as the cam ring 21 moves to the second working chamber 51b side. Since the throttle area of the orifice 54 is reduced in accordance with the decrease in the amount, the variable displacement pump having the characteristic that the pump discharge flow rate decreases in accordance with the increase in the pump rotation speed after the eccentric amount of the cam ring 21 starts to decrease. can get.

Further, in the case where the differential pressure control valve 31 is moved by the load pressure sensitive piston 40 to increase the discharge flow rate according to the load pressure as in the second embodiment, the differential pressure control valve As the operation stroke of 31 is smaller, the responsiveness of the discharge flow rate to the load pressure is improved, but when the positional relationship between the introduction passage 57a to the first working chamber 51a and the pump internal pressure introduction passage 56 is the same, as in the present invention. When the second variable throttle 62b is opened when the differential pressure control valve 31 is at the end of the stroke on the side of the internal pressure action chamber 52a, the stroke until the first variable throttle 62a is closed is smaller than that of the conventional one. The variable displacement pump having the high responsiveness of the discharge flow rate with respect to the load pressure can be obtained by configuring as in the second embodiment.

[0034]

According to the present invention, the fluid pressure introduced into the first working chamber is the minimum pressure obtained by reducing the internal pressure on the front side of the orifice, and does not exceed the internal pressure on the front side of the orifice even at the maximum. The fluctuation range of the pressure is reduced as compared with the related art in which the minimum value and the maximum value of the introduced pressure are the low pressure and the internal pressure in front of the orifice, which are connected to the reservoir, respectively. Therefore, even if the pump rotation speed changes abruptly, the fluctuation of the fluid pressure introduced into the first working chamber becomes gentle, so that the cam ring does not overshoot and the discharge flow rate of the pump does not fluctuate periodically.

Further, a seal member made of a flexible elastic body is provided to partition the first working chamber and the second working chamber, and the inner pressure working chamber and the load pressure working chamber respectively formed between both ends of the differential pressure control valve and the housing. The internal pressure, which is the pressure on the front side of the orifice of the discharge passage, and the load pressure, which is the pressure on the rear side, are introduced to the internal pressure chamber and the differential pressure control valve reduces the internal pressure to the first operating chamber when pressed against the internal pressure operating chamber side. According to the structure in which the internal pressure is introduced into the first working chamber and the load pressure is introduced into the second working chamber when the pressure is introduced and the load pressure is moved to the working chamber side, The fluid pressure introduced is the minimum of the internal pressure on the front side of the orifice, and the maximum internal pressure on the front side of the orifice. Compared to a pressure of the prior art, the variation range of the pressure is reduced. Therefore, as in the case of the invention of the preceding paragraph, even when the pump rotation speed changes abruptly, the fluctuation of the fluid pressure introduced into the first working chamber becomes gentle, so that the cam ring overshoots and the discharge flow rate of the pump periodically changes. It will not fluctuate. In addition, since the fluctuation range of the pressure decreases in this way, the rapid fluctuation of the fluid pressure causes the seal member made of a flexible elastic body provided between the outer periphery of the cam ring and the housing to fatigue-break in a short time, and the variable capacity type The durability of the pump is not reduced.

A valve pressing spring for urging the differential pressure control valve toward the internal pressure working chamber side and a tip end portion projecting into the internal pressure working chamber slidably fitted and supported by the housing are provided at one end of the differential pressure control valve. According to a load pressure sensitive piston that can abut from the axial direction and a piston pressing spring that biases the load pressure sensitive piston toward the differential pressure control valve, if the load pressure increases, the load pressure sensitive piston The force with which the sensitive piston pushes back the differential pressure control valve against the valve pressing spring is reduced, whereby the pump rotation speed when the eccentric amount of the cam ring starts to decrease is increased in accordance with the increase in load pressure. Therefore, it is possible to obtain the variable displacement pump having the characteristic that the discharge flow rate increases as the load pressure increases. Further, since the stroke of the differential pressure control valve of the present invention is smaller than that of the conventional valve, the response of the discharge flow rate to the load pressure is improved by combining with such a load pressure sensitive piston.

If the orifice provided in the discharge passage is a variable orifice whose opening area decreases as the cam ring moves to the second working chamber side, the throttle area of the orifice decreases as the eccentricity of the cam ring decreases. Therefore, after the eccentricity of the cam ring starts to decrease, a variable displacement pump having the characteristic that the pump discharge flow rate decreases with the increase of the pump rotation speed can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the overall structure of a first embodiment of a variable displacement pump according to the present invention.

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

FIG. 3 is a diagram showing pump discharge flow rate characteristics of the variable displacement pump according to the first embodiment.

FIG. 4 is a partial cross-sectional view illustrating an operating state of the first embodiment.

FIG. 5 is a transverse sectional view showing the overall structure of a second embodiment of the variable displacement pump according to the present invention.

FIG. 6 is a partial cross-sectional view illustrating an operating state of the second embodiment.

FIG. 7 is a diagram showing pump discharge flow rate characteristics of a variable displacement pump according to a second embodiment.

[Explanation of symbols]

10 ... Housing, 21 ... Cam ring, 22 ... Rotor,
23 ... Vane, 24 ... Suction port, 25 ... Discharge port,
28 ... Cam pressing means (cam pressing spring), 30 ...
Valve hole, 31 ... Differential pressure control valve, 33 ... Valve pressing spring, 40 ... Load pressure sensitive piston, 41 ... Piston pressing spring, 50 ... Seal member, 51a ... First working chamber, 51b ... Second working chamber, 53, 53a, 53b, 53
c ... Discharge passage, 54 ... Orifice, 54A ... Variable orifice, 55 ... Discharge port.

Claims (4)

[Claims] 1. A cam ring radially movably provided in a housing, and a plurality of vanes rotatably supported by the housing in the cam ring and slidably abutting an inner surface of the cam ring Rotatably held, suction port and discharge port formed in the housing or a member fixed thereto, an orifice provided in a discharge passage communicating the discharge port with a discharge port, and an outer periphery of the cam ring. A first working chamber and a second working chamber formed to face each other in the moving direction of the cam ring.
The working chamber, a cam pressing means for urging the cam ring toward the first working chamber where the eccentricity with respect to the rotor is maximum, and an orifice fitted in a valve hole formed in the housing so as to be axially movable. In a variable displacement pump provided with a differential pressure control valve that is operated by a differential pressure between the front and the rear to control each pressure acting on the first and second working chambers, the differential pressure control valve includes a differential pressure before and after the orifice. Is small and the amount of eccentricity of the cam ring with respect to the rotor is maximized, a pressure reduced from the internal pressure on the front side of the orifice is introduced into the first working chamber. 2. A cam ring provided in a housing so as to be movable in a radial direction, and a plurality of vanes that are rotatably supported by the housing in the cam ring and that slidably abut the inner surface of the cam ring are moved in a radial direction. Rotatably held, a suction port and a discharge port formed in the housing or a member fixed thereto, an orifice provided in a discharge passage communicating the discharge port with a discharge port, an outer periphery of the cam ring, and A first working chamber and a second working chamber formed by partitioning a space between the housings with a seal member made of a flexible elastic body so as to face each other in the moving direction of the cam ring, and the cam ring having a maximum eccentricity with respect to the rotor. And a cam pressing means for urging it toward the first working chamber, and axially movable in a valve hole formed in the housing. A differential pressure control valve that is fitted into the discharge pressure control valve. The internal pressure working chamber and the load pressure working chamber, which are respectively formed between both ends of the differential pressure control valve and the housing, are provided in front of the orifice of the discharge passage. In a variable displacement pump in which an internal pressure that is a pressure and a load pressure that is a rear pressure are introduced, respectively, when the differential pressure control valve is pressed to the internal pressure action chamber side, the differential pressure control valve is applied to the first action chamber. When the internal pressure is reduced and the load pressure is moved to the load chamber side, the internal pressure is introduced into the first action chamber and the load pressure is introduced into the second action chamber. Variable displacement pump. 3. The variable displacement pump according to claim 2, wherein a valve pressing spring for urging the differential pressure control valve toward the internal pressure action chamber side and a slidably fitted support for the housing. A load pressure sensitive piston whose tip portion projecting into the internal pressure acting chamber can abut one end of the differential pressure control valve in the axial direction; and a piston for urging the load pressure sensitive piston toward the differential pressure control valve. A variable displacement pump that is further equipped with a pressing spring. 4. The variable displacement pump according to any one of claims 1 to 3, wherein the orifice is a variable orifice whose opening area decreases as the cam ring moves toward the second working chamber side. A variable displacement pump.