JP2002206490A - Variable displacement pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the fitting structure of a relief valve for relieving the load pressure, when the load pressure rises excessively high rises, and to prevent generation of chatterings and the like. SOLUTION: A cam ring 21 of a vane pump is provided in a housing 10 freely movably in the radial direction, and the internal pressure before and after a variable orifice 44 provided in discharge passages 43a, 43b, 43c and the load pressure are led into a first and a second working chambers 41a and 41b respectively formed in both sides of the cam ring to freely to change the pump discharge flow. The cam ring is elastically pushed toward the first working chamber side, in which the quantity of deviation becomes maximum, via a cam pushing piston 27 fitting into the second working chamber at a tip thereof to abut against the periphery of the cam ring, and a pilot relief valve 55 for relieving the pressure inside the second working chamber 2, when the pressure inside of the second working chamber, in which the load pressure is led, exceeds the prescribed relief pressure is provided inside of the tip of the cam pressing piston.

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 discharge pump which does not exceed a predetermined flow rate even if the pump rotation speed increases. The present invention relates to a variable displacement pump.

[0002]

2. Description of the Related Art As such a variable displacement pump,
There is a technique disclosed in Japanese Patent Publication No. 2-61638.
This is because the cam ring supported on the body is biased in the eccentric direction by a spring so that the amount of eccentricity with respect to the rotor center of the vane pump is variable, and the piston rod operated by the differential pressure across the orifice provided in the discharge passage is provided. The cam ring is brought into contact with the spring in a direction in which the cam ring is moved against the spring, and a high pressure (internal pressure) or a low pressure is selectively introduced by a switching valve responsive to the internal pressure at the front of the orifice provided in the discharge passage. The initial load of the spring that directly urges the spring is changed. According to this technique, when the pump rotation speed increases and the pump discharge flow rate reaches a certain limit value, the pump flow rate according to the pump rotation speed is adjusted so that the discharge flow rate does not increase even if the pump rotation speed increases further. The discharge flow characteristics can be controlled.

The above-described variable displacement pump of the prior art is
When the load pressure generated at the discharge port is excessively increased, the load pressure is relieved to the reservoir, and a relief valve for reducing the load pressure is not provided, but as a variable displacement pump having such a relief valve, There is a structure as shown in FIG. This is the cam ring 2a of the vane pump section 2.
Is swingably supported on the housing 1 via the pin 2c so that the amount of eccentricity with respect to the center of the rotor 2b is variable, and the amount of eccentricity of the cam ring 2a in the middle of the discharge passage 3a communicating the discharge port 2d with the discharge port 3. A variable orifice 3b whose opening area changes in accordance with the first and second working chambers 4a and 4b for introducing the internal pressure on the front side and the load pressure on the rear side of the variable orifice 3a is provided around the cam ring 2a. 2a are formed facing each other in the moving direction of 2a,
The cam ring 2a has a first working chamber 4a in which the amount of eccentricity with respect to the rotor 2b is maximized by a cam pressing spring 5a via a cam pressing piston 5 whose leading end abuts on the outer peripheral surface thereof.
A relief valve 9a of a direct acting type is provided in the relief passage 9 which is urged to the side and which communicates the discharge passage 3a with the reservoir 51 through the communication conduit 50.

FIG. 5 shows an internal pressure working chamber 8a between a housing 1 and a differential pressure control valve 7 fitted in a valve hole 6 formed in the housing 1 so as to be movable in the axial direction.
And the load pressure action chamber 8b, and the differential pressure control valve 7 is moved by the valve pressing spring 7a to the internal pressure action chamber 8a.
When the differential pressure control valve 7 is pressed against the internal pressure action chamber 8a, the differential pressure control valve 7 introduces a low pressure into the first action chamber 4a and moves to the load pressure action chamber 8b. An internal pressure is introduced into 5a.

[0005]

However, the structure shown in FIG. 5 uses the direct-acting relief valve 9a to relieve the load pressure to the reservoir 51, so that the pump discharge flow rate of the relief valve 9a is reduced. The characteristic from when the cracking pressure is exceeded until the pump discharge flow rate becomes 0 is indicated by the broken line B in FIG.
, The pressure override D increases and the relief characteristics deteriorate, and depending on the operating conditions, problems such as occurrence of an oscillation phenomenon such as chattering may occur. Also, plug 9 is used to attach relief valve 9a.
Since an adapter such as b is required, there is also a problem that the number of parts increases and the cost increases. An object of the present invention is to solve each of these problems.

[0006]

SUMMARY OF THE INVENTION A variable displacement pump according to the present invention includes a cam ring provided in a housing so as to be movable in a radial direction, and a cam ring rotatably supported by the housing in the cam ring and sliding on the inner surface of the cam ring. A rotor for holding a plurality of vanes abuttable so as to be movable in a radial direction, a suction port and a discharge port formed in a housing or a member fixed to the housing, and a discharge passage communicating the discharge port with a discharge port. With an orifice
A first working chamber and a second working chamber for respectively introducing an internal pressure on the front side and a load pressure on the rear side of the orifice are formed on the outer periphery of the cam ring so as to face each other in the moving direction of the cam ring, and a tip portion enters the second working chamber. In the variable displacement pump, the cam ring is elastically biased toward the first working chamber side where the amount of eccentricity with respect to the rotor is maximized via a cam pressing piston which abuts on the cam ring. A pilot-type relief valve is provided for relieving the pressure in the second working chamber when the pressure in the second working chamber into which the load pressure is introduced exceeds a predetermined relief pressure.

[0007] The invention of the preceding paragraph provides a differential pressure control by forming an internal pressure action chamber and a load pressure action chamber between the housing and a differential pressure control valve axially movably fitted into a valve hole formed in the housing. The valve is urged toward the internal pressure working chamber by a valve pressing spring. When the differential pressure control valve is pressed against the internal pressure working chamber, it introduces a low pressure into the first working chamber and moves toward the load pressure working chamber. In this case, it is preferable that the internal pressure be introduced into the first working chamber and the load pressure be introduced into the second working chamber via the pilot orifice.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a variable displacement pump according to the present invention will be described below with reference to FIGS. The variable displacement pump according to this embodiment is used as a working fluid supply source for a power steering device.
1, a vane pump section 20 having a rotor 22 provided in the housing 10 and rotationally driven by a pump shaft 26 and a cam ring 21 movable in a radial direction, and a cam ring 21. The main components are a differential pressure control valve 31 to be controlled and a variable orifice 44 provided in the discharge passages 43a, 43b, 43c of the vane pump section 20.

As shown in FIGS. 1 and 2, an intermediate portion and a rear end portion of a pump shaft 26 are rotatably supported by a housing 10 and an end cover 11 screwed to the housing 10 via bearings. ing. A cylindrical inner surface 10a formed in the housing 10 coaxially with the pump shaft 26
A disk-shaped side plate 12 is fitted on the back side, and a cylindrical adapter 13 is fitted and supported on the front side so as not to rotate, and between the end cover 11, the side plate 12 and the adapter 13. Is provided with a vane pump section 20 described below. A pulley 29 to which power from the engine is transmitted is fixed to a tip of a pump shaft 26 protruding from the housing 10.

The vane pump section 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 which is slidably held by a plurality of radial slits formed on the cam ring 21 and is always in contact with the cylindrical inner surface of the cam ring 21. It is slidably abutted on the end face of the side plate 12. The suction port 24 of the vane pump section 20 is formed on the end face of the end cover 11,
The working fluid is supplied from the reservoir 51 through the suction passage 14 and the suction port 15. The discharge port 25 is formed on an end surface of the side plate 12 and communicates with a pressure chamber 16 located on the back side. The pressure chamber 16 is provided with discharge passages 43 a and 43 provided with a variable orifice 44 in the middle.
It is led to the discharge port 45 formed in the housing 10 through b and 43c.

The pin 17, which is provided in parallel with the pump shaft 26 and has both ends supported by the end cover 11 and the side plate 12, has a part of the outer periphery of the intermediate portion engaged with the inner surface of the adapter 13. The cam ring 21 is movable in the radial direction of the cam ring 21 by a concave portion 21 a formed in a part of the outer peripheral surface being engaged with the pin 17 and swinging about the pin 17. 21
The portion opposite to a is slidably sealed by a Teflon (registered trademark) seal member 40 provided in a groove formed on the inner surface of the adapter 13 and backed up by rubber. A first working chamber 41a and a second working chamber 41b are formed on the outer periphery of the cam ring 21 between the adapter 13 and defined by the pin 17 and the seal member 40, and are opposed to each other in the moving direction of the cam ring 21. I have.

In the moving direction of the cam ring 21, the second working chamber 4
A cylindrical hole 10b extending in the direction of the pump shaft 26 is formed in the housing 10 on the 1b side, and a cylindrical portion 18a of the plug 18 screwed and fixed to the cylindrical hole 10b in a liquid-tight manner.
A cam pressing piston 27 is fitted slidably in the axial direction, and is urged toward a pump shaft 26 by a cam pressing spring 28. The distal end of the cam pressing piston 27 passes through the adapter 13 with a gap, and passes through the second working chamber 41b.
The cam ring 21 comes into contact with the outer peripheral surface of the cam ring 21 to elastically urge the cam ring 21 toward the first working chamber 41a where the amount of eccentricity with respect to the center of the rotor 22 is maximized. When the pressure in the second working chamber 41b, into which the load pressure is introduced as described later, exceeds a predetermined relief pressure, the tip of the cam pressing piston 27 that has entered the second working chamber 41b is supplied with pressure. A pilot relief valve 55 for relief is provided. That is, a center hole 27a opening to the second working chamber 41b is formed at the tip of the cam pressing piston 27, and the center hole 27a is normally closed by the pilot relief valve 55 urged by the spring 56. . When the load pressure exceeds the relief pressure, the pilot type relief valve 55 is pushed, and the pressure is reduced to the small hole 27b of the cam pressing piston 27, the annular chamber 52 formed in the housing 10 on the outer periphery of the cam pressing piston 27, and the relief passage 53. Then, the pressure in the second working chamber 41 b is made to be relieved by the reservoir 51 through the communication pipe 50.

The variable orifice 44 has a communication hole 18b formed in the cylindrical portion 18a of the plug 18 and the cam pressing piston 2
7, the communication ring 18b moves as the cam ring 21 moves toward the second working chamber 41b and the cam pressing piston 27 retreats against the cam pressing spring 28.
Are gradually closed by the trailing edge of the cam pressing piston 27 so that the opening area is reduced. Variable orifice 4
4 is provided between a portion 43b of the discharge passage and a portion 43c following the discharge passage 43, and the working fluid from the vane pump section 20 is supplied to the discharge passage 43 provided with the variable orifice 44 in this manner.
a, 43b, and 43c are discharged from the discharge port 45. In a state in which the working fluid flows by operating the variable displacement pump, the pressure drops before and after the variable orifice 44 to generate a differential pressure, and the discharge passage 43 c and the discharge port 45 in the rear of the variable orifice 44 are disposed. The pressure is a load pressure given by the operation state of the device to which the working fluid is supplied, and the pressure in the discharge passages 43a and 43b on the front side of the variable orifice 44 and the pressure in the pressure chamber 16 is the internal pressure of the pump. This internal pressure is greater than the load pressure by the pressure difference due to the variable orifice 44, and therefore if the load pressure fluctuates, the internal pressure fluctuates as well. Under normal operating conditions, this pressure difference is considerably smaller than the internal or load pressure.

As shown mainly in FIG.
A differential pressure control valve 31 is inserted into a valve hole 30 formed in the housing 10 so as to be three-dimensionally orthogonal to the left side in FIG.
The differential pressure control valve 31 is urged by a valve pressing spring 33 interposed between the valve hole 30 and the bottom of the valve hole 30 toward the plug 19 screwed into the insertion side of the valve hole 30 in a liquid-tight manner. Both ends of differential pressure control valve 31 and housing 10
Between the pressure chamber 16 and the internal pressure working chamber 42a, which is on the plug 19 side, through the pump internal pressure introducing passage 48. Load pressure action chamber 42b
Has a pilot pressure orifice 49 and a load pressure introduction passage 4
The load pressure in the discharge port 45 is constantly introduced via 9a.

A pair of land portions 31 fitted in the valve hole 30 are provided on the outer periphery of the differential pressure control valve 31 with an axial interval therebetween.
a and 31b are formed, and both land portions 31a and 31b are formed.
An annular space 31c is formed between the valve and the valve hole 30. The annular space 31c is always in communication with the reservoir 51 via the communication pipe 50. The land portion 31a on the plug 19 side forms a step portion 31a1 by slightly reducing the diameter of a part on the annular space 31c side.

A valve hole 30 formed near a land 31a of the differential pressure control valve 31 is formed in a part of the housing 10.
The first introduction passage 46a having one end opened to the first working chamber 41a by the movement of the differential pressure control valve 31.
And selectively communicates with the annular space 31c communicated with the internal pressure action chamber 42a into which the internal pressure is introduced. When the differential pressure control valve 31 is pressed against the plug 19 by the valve pressing spring 33 in the inoperative state, the first introduction path 46a is formed in an annular space through a gap between the step portion 31a1 of the land portion 31a and the valve hole 30. 31c and the internal pressure action chamber 42
a is not communicated (see FIGS. 1 and 4 (a)). However, as soon as the differential pressure control valve 31 starts to move toward the load pressure action chamber 42b against the valve pressing spring 33 due to the differential pressure across the variable orifice 44, the internal pressure action chamber 42a
And immediately thereafter, the communication with the annular space 31c through the gap between the step portion 31a1 and the valve hole 30 is interrupted (see FIG. 4 (b)). This first introduction path 46a
Is connected to the first working chamber 41a on one side of the outer periphery of the cam ring 21 via a damping orifice 47a formed in the adapter 13.

The housing 1 on the side of the load pressure action chamber 42b
The second introduction passage 46b formed in a part of the valve opening 30 has one end opened in the valve hole 30 at a position where the second introduction passage 46b always opens in the load pressure action chamber 42b.
The cam ring 21 communicates with a second working chamber 41b on the other side of the cam ring 21 via a damping orifice 47b formed in the cam ring 21.

In an initial state in which the variable displacement pump is not operated, the cam ring 21 is moved to the first working chamber 41 by the cam pressing spring 28 via the cam pressing piston 27.
The eccentricity with respect to the rotor 22 is maximized. In this state, the rotation of the engine of the vehicle is controlled by the pump shaft 2 via the drive belt hung on the pulley 29.
6 and the rotor 22 of the vane pump 20 is rotated, the working fluid in the reservoir 51 is sucked from the suction port 15 and the suction passage 14 between the respective vanes 23 of the vane pump section 20 via the suction port 24, Discharge port 25
Is discharged into the pressure chamber 16 through the discharge passages 43a, 43b, 43c provided with the variable orifices 44.
5 is supplied to equipment such as a power steering device. The load pressure generated on the rear side of the variable orifice 44 is controlled by the load pressure introduction path 4 provided with the discharge passage 43c and the pilot orifice 49.
9a into the load pressure action chamber 42b, and further through the second introduction passage 46b and the orifice 47b.
It is introduced into the working chamber 41b. The internal pressure generated on the front side of the variable orifice 44 is introduced into the internal pressure working chamber 42a through the pump internal pressure introducing passage 48.

When the pump rotation speed is low, the differential pressure between the internal pressure before and after the variable orifice 44 introduced into the internal pressure action chamber 42a and the load pressure action chamber 42b and the load pressure is small.
The differential pressure control valve 31 is pressed against the plug 19 by a valve pressing spring 33, and the first working chamber 41a
Is connected to the reservoir 51 (see FIG. 4A). In this state, no force is generated to move the cam ring 21 against the cam pressing spring 28, so that the cam ring 21 is in the first working chamber where the discharge flow rate is maximized by the cam pressing spring 28 regardless of the pump rotation speed. 41a
Remains pressed to the side. Therefore, the discharge passage 43
The working fluid discharged from the discharge port 45 via a, 43b, and 43c is stably maintained at the maximum discharge flow rate,
It increases sharply as the pump rotation speed increases.

If the discharge flow rate increases due to an increase in the pump rotation speed, the internal pressure action chamber 42a and the load pressure action chamber 42b
The differential pressure between the internal pressure before and after the variable orifice 44 and the load pressure is also increased, and if this differential pressure exceeds a predetermined value, the differential pressure control valve 31 will act against the valve pressing spring 33 against the load pressure action chamber 42b. Side first, the first introduction path 46a
Is communicated with the internal pressure action chamber 42a, and then the land portion 31a
The communication with the annular space 31c via the gap between the step 31a1 and the valve hole 30 is cut off (see FIG. 4B). Thereby, the internal pressure is introduced into the first working chamber 41a,
The pressure difference from the load pressure introduced into the second working chamber 41b increases as the pump rotation speed increases. If the pressure difference exceeds a predetermined value, the cam ring 21 that has been in contact with the first working chamber 41a, at which the discharge flow rate is maximized, becomes
As the pump rotation speed increases, the amount of eccentricity is reduced in order to maintain a constant differential pressure across the variable orifice 44.

In this embodiment, the cam ring 21
As the amount of eccentricity decreases, the throttle area of the variable orifice 44 decreases, so that the pump discharge flow rate decreases as the pump rotation speed increases. As a result, a discharge flow rate characteristic with respect to the pump rotation speed suitable for the power steering device can be obtained.

In the above-described operating state, when the load pressure is increased by operating the handle such as stationary operation and the load pressure introduced into the second working chamber 41b exceeds a predetermined relief pressure, the relief valve 55 is activated. Activating the second working chamber 41
b, the opening 27 a and the small hole 27 b of the cam pressing piston 27 and the annular chamber 5 formed in the housing 10.
2. Relieved by the reservoir 51 via the relief passage 53 and the communication conduit 50. This causes a flow through the pilot orifice 49, so that the load pressure action chamber 42
b and the pressure in the second working chamber 41b decrease, thereby increasing the differential pressure between the first working chamber 41a and the second working chamber 41b acting on both ends of the cam ring 21.
1 moves against the cam pressing spring 28 to reduce the amount of eccentricity with respect to the center of the rotor 22, and the pump discharge flow rate also decreases. Since the load pressure decreases rapidly due to the decrease in the discharge flow rate, a good relief characteristic with a small pressure override C as shown by a solid line A in FIG. 3 is obtained, and no oscillation phenomenon such as chattering occurs.

When the variable displacement pump is not operated, the relief valve 55 is turned on by the cam pressing spring 28.
Provided in the cam pressing piston 27 for pressing the cam ring 21 toward the first working chamber 41a by the pressure, the adapter such as a plug for mounting the relief valve 55 is not required. Therefore, the variable displacement pump is downsized by reducing the number of parts as compared with the prior art, and the manufacturing cost is reduced.

In the above-described embodiment, while the pump discharge flow rate is small, the first working chamber 41a is communicated with the reservoir 51, and after the pump discharge flow rate increases, the internal pressure is introduced into the first working chamber 41a. A valve 31 is provided so that the cam ring 2 can be used while the pump discharge flow rate is small.
Since 1 is pressed against the first working chamber 41a where the discharge flow rate is maximum, the working fluid discharged from the discharge port 45 can be stably held at the state where the discharge flow rate is maximum. However, the present invention can be implemented by omitting the differential pressure control valve 31 and directly introducing the internal pressure and the load pressure into the first working chamber 41a and the second working chamber 41b. Various effects such as prevention of oscillation phenomena such as relief characteristics and chattering, downsizing of the variable displacement pump, and reduction of manufacturing cost can be obtained.

In the above-described embodiment, when the differential pressure control valve 31 is in a non-operating state pressed against the plug 18,
The stepped portion 3 formed in the land portion 31a for communicating the first introduction path 46a with the annular space 31c communicated with the reservoir 51.
Although 1a1 is used, the land 31a may have the same diameter and the step 31a1 may be omitted, and a communication path 32 as shown by a two-dot chain line in FIG. 1 may be used instead. The communication between the annular space 31c and the first introduction passage 46a by the communication passage 32 is performed when the differential pressure control valve 31 starts to move toward the load pressure action chamber 42b against the valve pressing spring 33, and the first introduction passage 46a
Is shut off immediately after communication with the internal pressure action chamber 42a. Instead of such a communication path 32, a cutout may be provided in a part of the land 31a on the annular space 31c side where the stepped portion 31a1 is omitted.

[0026]

According to the present invention, when the load pressure introduced into the second working chamber exceeds a predetermined relief pressure, the pressure in the second working chamber is relieved by the relief valve and reduced, whereby the cam ring is eccentric. Since the volume is reduced, the pump discharge flow rate is also reduced. Since the load pressure sharply decreases due to the decrease in the discharge flow rate, good relief characteristics with small pressure override can be obtained, and oscillation phenomenon such as chattering does not occur.

Further, since the relief valve is provided in the cam pressing piston originally provided in the variable displacement pump premised on the present invention, an adapter such as a plug for mounting the relief valve is not required. Accordingly, it is possible to reduce the number of parts, reduce the size of the variable displacement pump, and to reduce the manufacturing cost.

When the differential pressure control valve is pressed against the internal pressure working chamber, a low pressure is introduced into the first working chamber, and when the differential pressure control valve is moved toward the load pressure working chamber, the internal pressure is introduced into the first working chamber. According to the above configuration, the working fluid discharged from the discharge port can be stably held at the maximum discharge flow rate while the pump discharge flow rate is small.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing pump discharge flow characteristics of a variable displacement pump according to the present invention and the prior art.

FIG. 4 is a partial sectional view illustrating an operation state of the embodiment shown in FIG. 1;

FIG. 5 is a cross-sectional view showing the entire structure of an example of a variable displacement pump according to the related art.

[Explanation of symbols]

10: housing, 21: cam ring, 22: rotor,
23 ... Vane, 24 ... Suction port, 25 ... Discharge port,
27: cam pressing piston, 30: valve hole, 31: differential pressure control valve, 33: valve pressing spring, 41a: first
Working chamber, 41b: second working chamber, 42a: internal pressure working chamber, 4
2b: load pressure action chamber, 43a, 43b, 43c: discharge passage, 44: variable orifice, 49: pilot orifice, 55: relief valve.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tsuyoshi Ikeda 1-1-1, Asahi-cho, Kariya-shi, Aichi Prefecture Toyota Machine Works F-term (reference) DD16 DD35 DD43

Claims (2)

[Claims] 1. A cam ring provided in a housing so as to be movable in a radial direction, and a plurality of vanes rotatably supported by the housing in the cam ring and slidably in contact with an inner surface of the cam ring in a radial direction. A cam rotor having an orifice provided in the middle of a discharge passage communicating the discharge port with a discharge port, a suction port and a discharge port formed in the housing or a member fixed to the housing, A first working chamber and a second working chamber for respectively introducing an internal pressure on the front side and a load pressure on the rear side of the orifice are formed on the outer periphery of the orifice so as to face each other in the moving direction of the cam ring. The cam ring is inserted into the cam ring through the cam pressing piston and the cam ring is shifted to the first position where the amount of eccentricity with respect to the rotor is maximized. In the variable displacement pump elastically biased toward the working chamber, if the pressure in the second working chamber, in which the load pressure is introduced into the distal end of the cam pressing piston, exceeds a predetermined relief pressure, A variable displacement pump provided with a pilot relief valve for relieving pressure in the second working chamber. 2. An internal pressure operation chamber and a load pressure operation chamber are respectively formed between the differential pressure control valve axially movably fitted in a valve hole formed in the housing and the housing, and the differential pressure control valve is also provided. Is biased toward the internal pressure action chamber by a valve pressing spring. When the differential pressure control valve is pressed against the internal pressure action chamber,
Introducing a low pressure into the working chamber and introducing the internal pressure into the first working chamber if moving to the load pressure working chamber side, and introducing the load pressure into the second working chamber via a pilot orifice. Variable displacement pump characterized by the following.