JPH0261638B2 - - Google Patents

Description

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

Power steering devices are attached to various machines such as agricultural tractors and automobiles, and the power steering devices are required to have various output characteristics depending on their uses. 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 install a flow rate control valve and control the valve opening according to operating conditions, etc.
A variable displacement pump has been proposed in which the discharge flow rate itself of the pump is set to an arbitrary value within a certain range regardless of the rotational speed of the pump. 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. 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 that regulates the flow rate, and the differential pressure across the orifice is transferred to the oil chamber 1 above and below the cam piston 5 via the passages 12 and 13.
It is designed to lead to numbers 4 and 15.

The cam piston 5 is displaced according to this differential pressure,
When 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 (the volume of the working chamber) decreases. The amount of change) also becomes smaller, and as a result, the pump discharge amount is feedback-controlled to a constant value.

By controlling the energization of the electromagnetic urging device 8, that is, controlling the urging force, the flow rate characteristics of the pump can be changed as shown in the graphs of FIGS. 2A, B, and C. In other words, the cam piston 5 always adjusts the orifice 1 that occurs at a certain specific discharge flow rate.
The discharge flow rate is constant regardless of the rotational speed of the rotor 2 because the rotor 2 stands still at a point where the differential pressure around 1 and the biasing force of the electromagnetic biasing device 8 are balanced. By switching the biasing force of the device 8 into three stages and relatively displacing the equilibrium point,
It can be adjusted in three stages as shown in graphs A, B, and C.

However, this electromagnetic urging device 8 complicates the structure of the pump itself, and requires the provision of an energization control device, so it is of a so-called externally operated type and cannot automatically control the flow rate. There was a problem.

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

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, and a plurality of vanes 28 are slidably provided on the rotor 23 at equal intervals in the radial direction.
A cylindrical cam surface 26 is provided on which the cam ring 25 slides, and a portion of the cam ring 25 is rotatably supported by a pin 27 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 is:
It changes by rotating the cam ring 25 around the pin 27, and as the amount of eccentricity increases,
The discharge flow rate increases.

Further, the body 22 is provided with a discharge port 29 that opens to a high pressure section in the cam ring 25 and a suction port 30 that opens to a low pressure section, located on the side surface of the rotor 23. A cylinder 40 is provided in the body 22, and a piston 3 is slidably attached to the cylinder 40.
A first pressure chamber 32 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.

An orifice 35 is also provided in the passage 34 to communicate with the actuator of the power steering device. The second pressure chamber 33 communicates with the passage 34 downstream of the orifice 35 by a passage 36 . Therefore, a differential pressure across the orifice 35 acts on the piston 31. The tip of the piston rod 41 provided on the piston 31 comes into contact with an arm 42 provided integrally on the cam ring 25, and the cam ring 25
is rotated about the pin 27 in a direction in which the amount of eccentricity decreases. A cylinder 43 is provided in the body 22, and a piston 44 is housed therein to provide a third pressure chamber 45. A compression spring 46 is interposed between the arm 42 and the piston 44, and the cam ring 25 is moved against the piston 31. and force it to push back.

A valve 48 is provided in the body 22.
This valve 48 has a spool 50 inside the cylinder 49.
This spool 50 has an annular groove 54 formed between the first land 51 and the second land 52, and comes into contact with the left side wall 49a of the cylinder to keep the spool 50 stationary at position A (position A). (See Figure 4) A protrusion 53 is provided, and a return spring 55 is interposed between the cylinder right side wall 49b and the spool 50. Land 5 of cylinder 49
The left chamber 56 separated by the first pressure chamber 3
A passageway 60 communicating with the left ventricle 56 is opened, thereby applying absolute pump discharge pressure to the left ventricle 56. The cylinder 49 is provided with an annular recess 57.
A passage 58 communicating with the third pressure chamber 45 opens at position A of the cylinder 49, and the land 5 opens at position A of the cylinder 49.
1 and 52, a passage 59 is opened that branches from a low pressure (tank pressure) storage space 63.

As shown in FIG. 4, in position A, spool 50 connects passage 58 with passage 59 on the low pressure side via recess 57, and in position B, connects passage 58 with passage 60 on the high pressure side via recess 57. . 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 from position A to position B. There is.

According to the above configuration, the relationship between the rotational speed (Nrpm) of the rotor 23 and the discharge flow rate (Ql/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 surface 26, fluid is discharged to the discharge port 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 is the piston 31
acts on both end surfaces of the piston rod 41 and arm 4.
2 to rotate the cam ring 25 against the spring 46 in a direction in which the amount of eccentricity with respect to the rotor 23 is reduced. However, in the low speed rotation range of the rotor 23, this differential pressure cannot overcome the biasing force of the spring 46, and the eccentricity does not change.
That is, 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 (region a in characteristic E in FIG. 5).

In contrast, the rotational speed of the rotor 23 increases,
When the discharge flow rate becomes larger, the orifice 35
The piston 31, which responds to the differential pressure between the front and rear, overcomes the biasing force of the spring 46 and rotates the cam ring 25 with respect to the piston 27, thereby reducing the amount of eccentricity with respect to the rotor 23. Therefore, the volume of the working chamber formed between the cylindrical cam surface 26, 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
The discharge flow rate is always almost constant because it 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 discharge flow rate are balanced (region b of characteristic E in Fig. 5). .

The above flow rate characteristics are the characteristics when the valve 48 is in position A. On the other hand, when the pressure on the downstream side of the passage 34, that is, the load pressure of the power steering increases, and the pressure upstream of the orifice 35 increases accordingly, this pump discharge absolute pressure acting on the left chamber 56 increases to a predetermined level. When the value is exceeded, the spool 50 overcomes the biasing force of the spring 55 and moves to the right in FIG. When the valve 48 is switched to position B, this pump discharge pressure acts on the third pressure chamber 45 from the left chamber 56 via the recess 57 passage 58, and the piston 44 receives this absolute pressure and moves inside the cylinder 43. It moves to 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 balances this load.

Furthermore, when this variable capacity vane pump is installed in the power steering system of an agricultural tractor,
If installed so that it is directly driven by the engine, the output that energizes the steering gear can be kept to a constant value during normal operation, and when a large output is required due to the wheels being buried in dirt, etc. , it is possible to automatically provide sufficient power assist according to the steering load.

Further, in the case of an automobile, high output can be applied when the steering load is large, such as when stationary or at low speed, and output can be lowered when the steering load is small, such as when driving at high speed.

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 6
A spool 67 is slidably housed in a cylinder 66, and this spool 67 is connected to the first and second lands 5.
1, 52 and a third land 68, and annular recesses 69 and 54 are provided between them. With the spool 67 biased by the spring 55 and stationary at position A, a passage 60 communicating with the discharge passage 29
In order to connect the cylinder 66 with a passage 58 communicating with the third pressure chamber 45, annular recesses 70 and 71 are provided in the cylinder 66, respectively, and the passage 58 is opened in the recess 71. Furthermore, due to an increase in the pump discharge absolute pressure, the spool 67 moves to the right side in FIG.
An annular recess 72 is provided to connect the passage 58 and the passage 59, 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 A to B, 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, the biasing force of the spring 46 that opposes the differential pressure across the orifice 35 decreases, and the pump maximum discharge flow rate decreases as shown by characteristic G in FIG. 5.

As described above, according to the present invention, it is possible to automatically change the maximum value of the pump discharge flow rate in response to the steering load, and relatively diverse pump output characteristics can be adjusted without installing an electromagnetic biasing device or the like. can get.

[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, FIG. 4 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, 28... Vane, 29... Pump discharge passage,
30... Suction passage, 35... Orifice, 46...
...Spring, 44...Piston, 45...Third
Pressure chamber, 48...valve.

Claims (1)

[Claims] 1. 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 that is in sliding contact with the vanes, and a cam ring that has the cylindrical cam surface is placed at the center of the rotor. In a variable capacity vane pump supported on the body so that the amount of eccentricity between the cam ring and the cam ring is variable, a spring is provided to bias the cam ring in the eccentric direction, a hydraulic piston is provided to adjust the initial load of the spring, and the pump discharge passage is provided with a hydraulic piston to adjust the initial load of the spring. An orifice is provided in the middle of the orifice, and a piston is provided that presses the cam ring against the biasing force of the spring in response to the differential pressure before and after the orifice, and the hydraulic piston is provided with a high pressure or A variable capacity vane pump characterized by being equipped with a switching valve that selectively introduces low pressure.