JPS59110882A - Variable volume vane pump - Google Patents

Abstract

PURPOSE:To maintain delivery constant irrespective of rotation of rotor, by containing a rotor rotatably in a tubular cam face of cam ring having adjustable eccentricity and varying the eccentricity of cam ring automatically in accordance to delivery of pump. CONSTITUTION:Upon rotation of rotor 23 in a tubular cam face 26, fluid is delivered through a delivery port 29 to produce differential pressure corresponding to delivery across an orifice 35 in a path 34. It will function on both end faces of piston 31 but it is low in low rotation area of rotor 23 to block sliding of piston 31 by spring 46 force. While under high rotation area, the piston 31 is moved to the right against the spring 46 by increased differential pressure to displace the cam ring 25 around a pin 27. Consequently eccentricity of cam ring 25 against rotor 23 is reduced to reduce delivery per unit rotation of pump.

Description

DETAILED DESCRIPTION OF THE INVENTION -1 The present invention relates to a variable capacity vane pump used in a power steering device.

Power steering devices are installed on various machines such as tractors and automobiles, and various output characteristics are required for the power steering device depending on the application. This required output characteristic is responded to by changing the discharge flow rate from the pump that feeds pressure oil into the power cylinder. For this purpose, it is common to provide a flow rate control valve and control the valve opening according to operating conditions, etc., but as disclosed in Japanese Patent Application Laid-Open No. 53-140605, the discharge flow rate itself of the pump can be adjusted to the rotation speed of the pump. A variable displacement pump has been proposed that can set the value to any value within a certain range. This variable displacement pump will be explained below based on FIG. 1.

A rotating shaft 3 of a rotor 2 is supported in the housing 1, and a plurality of vanes 4 are disposed on the rotor 2 so as to be slidable in a radial manner, and the tips of the vanes 4 are in sliding contact so as to surround the rotor 2. A cam piston 5 having a cylindrical cam surface 6 is formed, and the cam piston 5 is movably housed in the housing 1 so that the amount of eccentricity between the cylindrical cam surface 6 and the center of the rotor 2 is variable. do. The cam piston 5 has a plunger 5a extending outside the housing 1. The plunger 5a is slidably inserted into the electromagnetic force device 8, and the cam piston 5 and the rotor 2 are connected in accordance with the electromagnetic force. The amount of eccentricity is variably controlled. The pump discharge passage 10 is provided with an orifice 11 for regulating the flow rate, and the differential pressure across the orifice is guided to oil chambers 14 and 15 above and below the cam piston 5 through passages 12 and 13.

The cam piston 5 is displaced in accordance with this differential pressure, and as the differential pressure increases, the cam piston 5 moves in a direction that reduces the amount of eccentricity of the cam surface 6.

When the eccentricity of the cylindrical cam surface 6 decreases, the stroke amount (the difference between the maximum and minimum protrusion amounts) of the vanes 4 of the rotor 2 in the radial direction decreases, so the discharge amount per stroke (volume of the working chamber) decreases. The amount of change) also becomes smaller, thereby feedback controlling the pump discharge amount to a constant value.

-3- - By controlling the energization to the electromagnetic urging device 8, that is, controlling the urging force, the flow rate characteristics of the pump are changed as shown in Fig. 2A.
, B, and C can be changed to J: sea urchin.

That is, the cam piston 5 always stands still at a point where the differential force before and after the orifice 11 that occurs at a certain discharge flow rate and the biasing force of the electromagnetic biasing device 8 are balanced, regardless of the rotational speed of the rotor 2. With the discharge flow rate constant, the maximum discharge flow rate at this time can be determined by changing the biasing force of the electromagnetic biasing device 8 into three stages and relatively displacing the equilibrium point.
, B, and C.

However, this electromagnetic biasing device 8
In addition to complicating the structure, it is necessary to provide an energization control device 11, which is a so-called externally operated type, and there are problems such as not being able to automatically control the flow rate.

The present invention provides a spring that biases the cam ring of a variable capacity vane pump in an eccentric direction, and acts a piston that responds to the differential pressure before and after the orifice in opposition to this spring, and also provides switching that responds to the absolute pressure of the pump discharge. By installing a hydraulic device that changes the initial load of the spring in response to the pressure oil selectively guided through the switching valve, the discharge flow rate can be controlled to a constant value, and the steering load can be reduced. The purpose is to automatically change this maximum discharge flow rate when the flow rate increases.

Embodiments of the present invention will be described below based on the accompanying drawings.

As shown in FIG. 3, the body 22 of the vane pump 21 supports a rotating shaft 24 of a rotor 23, a plurality of vanes 28 are slidably provided on the rotor 23 at equal intervals in the radial direction, and a cam ring 25 is provided with a rotor 23. Cylindrical cam surface 26 with which 23 comes into sliding contact
At the same time, a part of this cam ring 25 is attached to the bin 2.
7, it is rotatably supported on the body 22. Therefore, the amount of eccentricity between the center of the cylindrical cam surface 26 and the center of the rotating shaft 24 changes as the cam ring 25 is rotated around the pin 27, and the greater the amount of eccentricity, the greater the discharge flow rate. Become.

Further, the body 22 is provided with a discharge port 29 that opens to a part of the high pressure -5 in the cam ring 25, and a suction boat 3o that opens to a low pressure part, located on the side surface of the rotor 23. The body 22 is provided with a cylinder 40, a piston 31 is slidably housed in the cylinder 40, and the first pressure chamber 3
2 and a second pressure chamber 33 are separated from each other, and the first pressure chamber 32 is communicated with a passage 34 branched from the discharge port 29.

The passage 34 is also provided with an orifice 35 to communicate with the actuator of the power steering device. The second pressure chamber 33 is connected to the passage 34 downstream of the orifice 35 by a passage 36 . Therefore, a differential pressure before and after the orifice 35 acts on the screw 31.
5 is rotated about the bin 27 in a direction in which the amount of eccentricity decreases. The body 22 is provided with a cylinder 43 and a piston 44.
The third pressure chamber 45 is provided by accommodating the arm 4.
A compression spring 46 is interposed between the cam ring 2 and the piston 44, and urges the cam ring 25 to be pushed back against the piston 31.

A valve 48 is provided in the body 22.

This valve 48 has a spool 50 movably housed in a cylinder 49, and an annular groove 54 is formed between a first land 51 and a second land 52, and the spool 50 abuts against the left side wall 498 of the cylinder. A projection 53 is provided to keep the spool 50 stationary at position A (see FIG. 4), and a return spring 55 is installed between the cylinder right side wall 49b and the spool 50. A left chamber 56 separated by a land 51 of the cylinder 49 has a first pressure chamber 3.
A passage 60 communicating with the left ventricle 5G is opened, thereby applying absolute pump discharge pressure to the left ventricle 5G. The cylinder 49 is provided with an annular recess 57, and the third pressure chamber 45 is provided in this annular four part 57.
A passage 58 communicating with the cylinder 49 is opened, and a passage 59 located between the lands 51 and 52 and branching from a low pressure (tank pressure) storage space 63 is opened at the position Δ of the cylinder 49.

As shown in FIG. 4, in position A, the spool 50 connects the passage 58 with the passage 59 on the low pressure side through the fourth part 57, and in the position B, connects the passage 58 with the passage 60 on the high pressure side through the recess 57. Connect with. In addition,
When the pressure in the left chamber 56, that is, the absolute pump discharge pressure, exceeds a certain value, the spool overcomes the biasing force of the spring 55 and moves to the right in Fig. 3, switching to the position Ahs + B. .

According to the above configuration, the rotation speed (Nrpm) of the rotor 23
The relationship between the discharge flow rate 1 (Qf/min) and the discharge flow rate 1 (Qf/min) can be changed as shown in graphs E and F in FIG.

That is, when the rotor 23 is rotated within the cylindrical cam 26, fluid is discharged to the discharge boat 29, and a pressure difference is generated before and after the orifice 35 of the passage 34 according to the discharge flow rate. This differential pressure acts on both end surfaces of the piston 31 and attempts to rotate the cam ring 25 against the spring 46 via the piston rod 41 and the arm 42 in a direction in which the amount of eccentricity with respect to the rotor 23 becomes smaller. However, in the low speed rotation range of the rotor 23, this differential pressure cannot overcome the force of the spring 46, and the eccentricity does not change, causing the Zunawa-8
- The cam ring 25 is held at the maximum eccentric position, and the discharge flow rate increases in proportion to the increase in the rotational speed of the rotor 23 (the fifth
area a in characteristic E in the figure).

On the other hand, when the rotational speed of the rotor 23 increases and the discharge flow rate further increases, the piston 31, which responds to the differential pressure before and after the orifice 35, overcomes the biasing force of the spring 46 and rotates the cam ring 25 relative to the bottle 27. to reduce the amount of eccentricity with respect to the rotor 23. Therefore, the cylindrical cam surface 2
6. The volume of the working chamber formed between the rotor 23 and the adjacent vanes 28 becomes smaller than before the rotation of the cam ring 25, and the discharge flow rate per unit rotation of the pump becomes smaller. In this way, the cam ring 25 always stands still at a point where the differential pressure before and after the orifice 35 and the biasing force of the spring 46 that occur at a certain specific discharge flow rate are balanced, so the discharge flow rate is always approximately constant (fifth b area of characteristic E in the figure).

The flow rate characteristics described above are the characteristics when the valve 48 is in position A. On the other hand, the pressure downstream of the passage 34,
In other words, when the power steering load -9- pressure increases and the pressure upstream of the orifice 35 increases accordingly, when the absolute pump discharge pressure acting on the left chamber 56 exceeds a predetermined value, the spool 50 It overcomes the urging force of 55 and moves to the right in Figure 3. When the valve 48 is switched to position B, the pump discharge pressure is transferred from the left chamber 56 to the third pressure chamber 57 through the passage 58. ! I5, the piston 44 receives this absolute pressure and moves inside the cylinder 43 toward the left in FIG. 3 until it comes into contact with the stopper 61, thereby compressing the spring 46. As a result, the initial load of the spring 46 increases, and the pump discharge flow rate increases as shown by characteristic F so that the biasing force of the piston 31, that is, the differential pressure across the orifice 35 is balanced with this load.

Furthermore, when this variable capacity vane pump is installed in the power steering system of an agricultural tractor, if it is installed so that it is directly driven by the engine, the output powering the steering system can be held to a constant value during normal operation. , and when a large output is required, such as when the wheels are buried in earth and sand, sufficient power assistance can be automatically provided in accordance with the steering load.

Furthermore, in the case of automobiles, high output can be applied when the steering load is large, such as when twisting or at low speeds, while output can be lowered when the steering load is low, such as when cutting at high speeds.

In the next embodiment, the valve 65 shown in FIG. 6 is provided in place of the valve 48 in the variable displacement vane pump of the embodiment shown in FIG. This valve 65 has a spool 67 slidably housed in a spool 66, and this spool 67 has first and second lands 51, 52 and a third land 68,
Annular quadrants 69 and 54 are provided between them. Spool 6
7 is biased by a spring 55 and remains stationary at position A, an annular recess is formed in the cylinder 66 to connect a passage 60 communicating with the discharge passage 29 and a passage 58 communicating with the third pressure chamber 45. 70 and 71 are respectively provided, and the passage 58 is opened in the recess 71. Further, due to an increase in the pump discharge absolute pressure, the -11- spool 67 moves to the right side in FIG. is provided, and the passage 59 is opened in the recess 72. That is, as shown in FIG. 7, in position A, valve 65 connects passage 60 and passage 58, and in position B, valve 65 connects passages 59 and 58. Note that these positions A and B are switched by sensing the pump discharge pressure acting on the passage 60.

According to the above configuration, when the steering load increases and the pump discharge absolute pressure exceeds a predetermined value, the valve 65 automatically switches its position from 8 to 8, and the piston 44 is actuated by this pump discharge absolute pressure to spring. From the state in which the spring 46 is contracted, tank pressure acts on the spring 46 to move it to the right in FIG. 3, lowering the initial load of the spring 46. In other words, orifice 35
The biasing force of the spring 46 that opposes the differential pressure between the front and rear ends decreases, and the maximum discharge flow rate of the pump decreases as shown by characteristic G in FIG.

As described above, according to the present invention, the -12- maximum value of the pump discharge flow can be automatically changed in accordance with the steering load, and relatively various types of Pump output characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional variable displacement vane pump, and FIG. 2 is a graph showing the flow rate characteristics of this pump. FIG. 3 is a sectional view showing an embodiment of the present invention, and FIG.
The figure is a hydraulic circuit diagram of the valve portion, and FIG. 5 is a graph showing the flow rate characteristics of this pump. FIG. 6 is a sectional view of a valve portion of another embodiment, and FIG. 7 is a hydraulic circuit diagram of the valve portion. 22...Body, 23...Rotor, 24...Rotating shaft, 25...Cam ring, 26...Cylindrical cam surface, 2
8... Vane, 29... Pump discharge passage, 30...
・Suction passage, 35... Orifice, 46... Spring, 44... Piston, 45... Third pressure chamber, 4
8... Valve. Patent applicant Kayaba Kogyo Co., Ltd. -13- Figure 1 a Figure 2 Q ('/mIn) Figure 4 Figure 6 453- Figure 5 Figure 7

Claims (1)

[Scope of Claims] A rotor that supports a plurality of vanes in a radially slidable manner, a body that supports a rotating shaft of the rotor, and a cylindrical cam surface in sliding contact with the vanes, the cylindrical cam surface having A variable capacity vane pump in which a cam ring is supported on the body so that the amount of eccentricity with respect to the center of the rotor is variable, a spring is provided to bias the cam ring in an eccentric direction, and a hydraulic piston is provided to adjust the initial load of the spring. [On the other hand, an orifice is provided in the middle of the pump discharge passage, and a piston is provided that presses the cam ring against the biasing force of the spring in response to the differential pressure after the orifice 1)a, and the hydraulic piston A variable displacement pump characterized by being provided with a switching valve that selectively introduces high pressure or low pressure in response to the absolute pressure in a discharge passage.