JP2672093B2 - Variable displacement pump controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control device for a variable displacement pump, and more particularly to a control device for controlling a discharge flow rate of a variable displacement pump, which corresponds to a load of an actuator. In addition to load-sensitive control for increasing and decreasing the discharge flow rate, the discharge flow rate of the variable displacement pump can be controlled according to the opening degree of the variable throttle provided between the variable displacement pump and the actuator. The present invention relates to a control device for a variable displacement pump, which can miniaturize the pump itself as much as possible and achieve energy saving. BACKGROUND OF THE INVENTION Conventionally, variable displacement hydraulic pumps have been widely used as means for feeding pressure oil to an actuator in a pressure oil supply system that constitutes various hydraulic drive devices. That is, this type of hydraulic pump is provided with a mechanism for controlling the discharge flow rate of the pressure oil. For example, a so-called load-sensitive control mechanism that increases / decreases the pump discharge amount according to the load of the actuator is used as the control mechanism. Therefore, in a normal hydraulic drive device, when the load received by the actuator is small, the drive speed of the actuator is fast, and when the load is large, the speed is often controlled slow, and the hydraulic pump is also controlled. In response to this, the discharge pressure and the discharge flow rate are changed. Therefore, for example, when the actuator is driven at a high load and at a low speed, the opening of the variable throttle provided between the hydraulic pump and the actuator is narrowed, and the flow rate of the pressure oil is restricted, while the high pressure oil is applied to the actuator. Will be supplied. However, in the conventional load sensitive control mechanism that adjusts the discharge flow rate of the hydraulic pump so that the differential pressure before and after the variable throttle is constant, the differential pressure becomes large when the opening of the variable throttle is large. Since it hardly occurs, the hydraulic pump remains at the maximum flow rate. Therefore, since a high load is dealt with in such a state, the prime mover for driving this hydraulic pump also has a maximum discharge flow rate at the maximum discharge pressure as shown by h in FIG. In other words, it is necessary to install the one capable of exerting corner horsepower. In fact, as mentioned above, it is sufficient to achieve the control at a high speed when the load is large, while the speed is slow when the load is small.
In the conventional load-sensitive control mechanism, since a prime mover capable of exerting corner horsepower is installed, a considerable burden is imposed economically and energy saving is achieved today.
It exposes various inconveniences. [Object of the Invention] The present invention has been made to overcome the above-mentioned inconvenience, and in a device for controlling the discharge flow rate of a variable displacement pump, the discharge flow rate of the variable displacement pump is changed according to the load of an actuator. In addition to the load sensitive control mechanism, the discharge flow rate can be controlled according to the opening degree of the variable throttle interposed between the variable displacement pump and the actuator, thereby driving the variable displacement pump. It is an object of the present invention to provide a control device for a variable displacement pump that enables downsizing. [Means for Achieving the Object] In order to achieve the above object, according to the present invention, the discharge flow rate of the variable displacement pump is adjusted by tilting a cam lever provided on the variable displacement pump and swingably supported. A control device for increasing / decreasing, wherein a return piston that abuts on the cam lever via an elastic force of an elastic body in order to tilt the cam lever to a maximum discharge flow position, and a discharge pressure oil of the variable displacement pump that is fed back By this action, in order to tilt the cam lever to the minimum discharge flow rate position, a power piston that faces the return piston and abuts the cam lever, and a power piston that is fitted to the power piston and resists the elastic force of the elastic body. And the servo spool that applies the action force of the discharge pressure oil to the end portion of the power piston by the displacement. By the action of the discharged pressurized fluid of the variable displacement pump, in order to displace the servo spool,
A shift spool that comes into contact with an end of the servo spool, and the variable displacement pump that is accommodated so as to be displaceable with respect to the servo spool and has one end abutting the shift spool and the other end introduced into the servo spool. Of the discharge pressure oil, a spool for displacing the servo spool against the elastic force of the elastic body by its reaction, and a variable throttle arranged between the variable displacement pump and the actuator. When the hydraulic pressure on the upstream side becomes higher than the hydraulic pressure on the downstream side by a predetermined amount or more due to displacement according to the pressure difference between the upstream side and the downstream side of the variable throttle, the variable spool is provided at the end of the shift spool. And a differential spool for applying the action force of the discharge pressure oil of the displacement pump. [Operation] In the present invention, when the actuator (90) is driven with the opening of the variable aperture (89) set to a predetermined amount, when the load on the actuator (90) decreases, the variable aperture (89) The differential pressure before and after increases, which causes the differential spool (72) to be displaced and shift spool (6
The pressure of the discharge pressure oil of the variable displacement pump (11) is applied to 0). The shift spool (60) displaces the servo spool (32) by the discharged pressure oil, and the displacement of the servo spool (32) applies the pressure of the discharge pressure oil to the end portion of the power piston (26). . Therefore, the power piston (26) tilts the cam lever (18) against the pressing force of the return piston (24), and reduces the flow rate of the discharge pressure oil of the variable displacement pump (11). When the load on the actuator (90) increases, the variable throttle (8
Since the differential pressure before and after 9) becomes small, the differential spool (7
2) is displaced to cut off the supply of pressure oil discharged from the variable displacement pump (11) to the shift spool (60). Therefore, the variable capacity pump (1
The flow rate of discharge pressure oil in 1) increases. As a result, within the predetermined horsepower range of the prime mover of the variable displacement pump (11),
Since the flow rate of the discharge pressure oil of the variable displacement pump (11) is adjusted according to the load, a fixed amount of pressure oil set according to the opening of the variable throttle (89) is supplied to the actuator (90). That is, so-called load sensitive control is achieved. On the other hand, the pressure of the discharge pressure oil of the variable displacement pump (11) is applied to the spool (52). When this pressure becomes higher than a predetermined value, the reaction causes the servo spool (32) to cause the elastic body (58, 58a) to move. ) Is displaced against the resilience of the power piston (26), whereby the pressure of the discharge pressure oil is applied to the end of the power piston (26). Therefore, irrespective of the differential pressure before and after the variable throttle (89), when the pressure of the discharge pressure oil exceeds a predetermined value, the power piston (26) tilts the cam lever (18), and the variable displacement pump (11). To reduce the flow rate of discharge pressure oil. In this case, since the flow rate of the discharge pressure oil decreases as the discharge pressure increases, the variable displacement pump (11)
The prime mover is not required to have a corner horsepower determined by the product of the maximum discharge pressure and the maximum discharge flow rate. [Embodiments] Next, preferred embodiments of a control device for a variable displacement pump according to the present invention will be described in detail below with reference to the accompanying drawings. In FIG. 2, reference numeral 10 indicates a control device for a variable displacement pump according to the present invention. The control device 10 of this variable displacement pump has a control mechanism 12 and a differential valve section 14, and the control mechanism 12
In addition, the differential valve section 14 is a body that constitutes the variable displacement pump 11.
It is located in 16. First, a cam lever 18 at a predetermined portion in the body 16 is pivotally supported by a shaft member 20 so as to be tiltable. As schematically shown in the figure, the shaft member 20 is provided at the base end of the cam lever 18.
A connecting portion 18a is formed so as to be orthogonal to the connecting portion 18a, and an arm member 21 is swingably attached to the connecting portion 18a via a pin or the like. The tip of the arm member 21 is a variable displacement pump.
Combined with 11. Therefore, the discharge flow rate of the variable displacement pump 11 is controlled via the arm member 21 as the cam lever 18 tilts. Therefore, the tip portion 22 of the cam lever 18 is clamped by the return piston 24 and the power piston 26. In this case, the return piston 24 is a chamber defined by the body 16.
The hemispherical tip end portion 22 of the cam lever 18 is constantly pressed in the direction of arrow A by the coil spring 30 arranged in the 28. In this case, the passage 28 communicates with the chamber 28. On the other hand, the power piston 26 is also slidably fitted in the chamber 31 defined by the body 16. The diameter of the power piston 26 is in this case chosen larger than the diameter of the return piston 24. The power piston 26 is provided with a hole portion 33 penetrating in the axial direction thereof, and the servo spool 32 is fitted into the hole portion 33. The power piston 26
One end of the abuts on the hemispherical tip 22 of the cam lever 18. An annular chamber 34 is defined on the outer peripheral surface of the power piston 26. The annular chamber 34 communicates with the passage 29 through a passage 36 and also communicates with the annular chamber 40 defined by the servo spool 32 through a passage 41. An oil chamber 42 is defined at the other end of the power piston 26, and communicates with the hole 33 via a passage 44 defined therein. In this case, the area where the pressure oil acts to displace the power piston 26 in the oil chamber 42, that is, the area of the surface 43 that defines the oil chamber 42 is selected to be considerably larger than the cross-sectional area of the return piston 24. Keep it. Next, the above-mentioned servo spool 32 will be described.
One end of the servo spool 32 has the power piston 26.
It is slidably fitted in the hole portion 33 formed in. in this case,
A land 46 is formed at the one end, and a small diameter portion 47 is formed near the land 46. That is, this small diameter portion 47
The annular chamber 40 is defined by the hole 33 and the hole 33. A plurality of holes 48 are formed in the small diameter portion 47, and the holes 48 communicate with a passage 50 defined in the servo spool 32 coaxially. A spool 52 is inserted and arranged in the passage 50. In fact, the other end of the servo spool 32 faces the chamber 56 defined by the body 16. That is, the flange portion 54 is formed inside the chamber 56, and one end of the coil spring 58 interposed inside the chamber 56 engages with the flange portion 54. A coil spring 58a shorter than the coil spring 58 is further provided inside the chamber 56. In this case, the servo spool 32 is biased in the direction of arrow C in the figure by the elastic force of the coil spring 58. Further, a chamber 66 is defined in the body 16 coaxially with the chamber 56, and the shift spool 60 is slidably fitted in the chamber 66. The body 16 further defines a chamber 68 communicating with the chamber 66 and having a diameter smaller than that of the chamber 66.
Communicates with 29. Here, the differential valve unit 14 will be described. The differential spool 72 constituting the differential valve portion 14 is slidably fitted inside the passage 29, and includes a column portion 74a and this column portion 74a.
It includes a cylindrical portion 74b having a slightly larger diameter and a land 76 formed on the cylindrical portion 74a. On the other hand, a flange portion 78 is formed at an end portion of the differential spool 72, and the flange portion 78 is inserted into the chamber 80 defined by the body 16 and is interposed in the chamber 80. It engages with one end of the coil spring 82. Therefore, the differential spool 72 has a coil spring 82.
As a result of being urged upward in the figure by the resilience force, the land 76 blocks the communication between the passage 70 and the passage 29. The reference numeral 81 indicates the passage 29 and the chamber 56.
Shows a passage communicating with each other. Next, the configuration of the hydraulic circuit in the control device according to the present invention will be schematically described. The tank 64 connected to the passage 62 is connected to the suction side of the variable displacement pump 11 via a pipe line 84. On the other hand, the conduit 86 extending from the discharge side of the variable displacement pump 11 is a relief valve.
While being connected to 85, it branches into conduits 87 and 88 on the way. A variable throttle 89 is provided on the way of the pipe 87, and the pipe 87 is connected to the actuator 90 and communicates with the chamber 80 constituting the differential valve portion 14 via the pipe 92. . A tank 94 is arranged downstream of the actuator 90.
On the other hand, the conduit 88 communicates with the passage 29 via a port 96 defined in the body 16. The reference numeral 98 indicates a tank arranged downstream of the relief valve 85. The control device for a variable displacement pump according to the present invention is basically constructed as described above. Next, its operation and effect will be explained. When the variable displacement pump 11 is driven, the hydraulic oil in the tank 64 is pressurized by the variable displacement pump 11 to become pressure oil having a predetermined pressure and is supplied to the actuator 90 via the pipe line 87. A part of this pressure oil is introduced into the chamber 80 via the pipe line 92, and pushes the differential spool 72 in cooperation with the elastic force of the coil spring 82, and pushes it upward in the drawing. On the other hand, the pressure oil supplied from the variable displacement pump 11 is branched and introduced into the passage 29 from the port 96 via the pipe line 88.
That is, the pressure oil in the passage 29 is introduced into the chamber 28 and pushes the return piston 24 together with the elastic force of the coil spring 30 to push it in the direction of arrow C. Further, the pressure oil in the passage 29 acts to push the differential spool 72 downward in the drawing, and the pressure oil introduced from the passage 29 into the annular chamber 34 via the passage 36 is passed from the passage 41 to the servo spool 32. It reaches the annular chamber 40 defined by the above, is further guided to the passage 50 through the hole 48, and acts on one end of the spool 52. It is assumed that the throttle opening of the variable throttle 89 arranged in the pipe line 87 is sufficiently large, and therefore the pressure difference of the pressure oil on the upstream side and the downstream side of the variable throttle 89 can be almost ignored. And will be described below. In this case, the discharge pressure of the variable displacement pump 11 and the pressure of the pressure oil downstream of the variable throttle 89 become equal. Therefore, the pressure oil supplied from the passage 29 to the differential spool 72 and the pressure applied to the chamber 80 from the pipe 92 are substantially equal to each other, so that only the elastic force of the coil spring 82 assists. As a result, the differential spool 72 is displaced upward in the figure. As a result, the land 76 releases the closed state with respect to the passage 70, and the chamber 68 communicates with the passage 81 through the gap defined by the side surface of the passage 70 and the cylindrical portion 74b forming the differential spool 72. Since the passage 81 communicates with the tank 64 from the passage 62 through the chamber 56, the pressure oil in the chamber 68 flows back to the tank 64. Therefore, the shift spool 60 is not displaced and exerts no force on the servo spool 32.
Therefore, when the load received by the actuator 90 is small and therefore the discharge pressure of the variable displacement pump 11 is low, the cam lever 18 is tilted in the direction of arrow A in the figure, that is, the maximum discharge of the variable displacement pump 11. Therefore, when the load of the actuator 90 is increased while the opening of the variable throttle 89 remains in the above-described state, the variable position is set in accordance with the flow rate position. The discharge pressure of the displacement pump 11 increases. At this time, the pressure oil supplied from the variable displacement pump 11 to the port 96 via the pipe 88 is introduced into the annular chamber 40 of the servo spool 32 from the passage 29 via the passage 36 and the annular chamber 34. Further, this pressure oil reaches the passage 50 from the hole 48 formed in the small diameter portion 47, acts on one end of the spool 52, and tends to displace the spool 52 in the arrow C direction. However, since the spool 52 comes into contact with the shift spool 60 and is restricted and cannot be displaced, the reaction force of the pressure acting on the spool 52 causes the servo spool 32 to resist the elastic force of the coil spring 58 in the arrow D direction. Acts to displace. When the reaction force overcomes the elastic force of the coil spring 58 as the pressure of the pressure oil rises to a predetermined value, the servo spool 32 is displaced in the direction of arrow D in the drawing, and the coil The compression of only the spring 58 is started (see point b in FIG. 1), and after a predetermined amount of displacement, the coil spring 58a is contacted (see point c in FIG. 1). Then, the coil springs 58 and 58a are compressed (see the range of points c to d in FIG. 1). During the course of these processes, the land 46 formed at one end of the servo spool 32 brings the annular chamber 40 and the passage 44 into communication with each other. Therefore, the pressure oil in the annular chamber 40 is introduced into the oil chamber 42 through the passage 44. Here, since the area of the surface 43 on which the pressure oil acts on the power piston 26 is selected to be sufficiently larger than the cross-sectional area of the return piston 24, the power piston 26 follows the servo spool 32 in the arrow D direction. The cam lever 18 is tilted in the direction of arrow B against the elastic force of the coil spring 30 that presses the return piston 24. And finally, the land 46
Thereby, the passage 44 is closed and the power piston 26 is stopped. Due to the tilting of the cam lever 18 in the direction of arrow B, the discharge flow rate of the variable displacement pump 11 is reduced, and the pressure of the pressure oil is reduced accordingly, and a new equilibrium state is obtained. On the other hand, in this equilibrium state, if the pressure of the pressure oil decreases and the equilibrium is broken, the servo spool 32 is displaced in the arrow C direction by the elastic force of the coil springs 58 and 58a. Therefore, the land 46 is displaced to open the passage 44, and the pressure oil in the oil chamber 42 is discharged to the outside through the passage 44 and the hole 33. Therefore, the power piston 26 is displaced in the arrow C direction until the passage 44 is blocked by the land 46. As a result, the return piston 24 in combination with the elastic force of the coil spring 30 tilts the cam lever 18 in the direction of arrow A to increase the discharge flow rate of the variable displacement pump 11, and the equilibrium state is again reached. . That is, as shown in FIG. 1, the change in the pump discharge amount Q with respect to the discharge pressure Pb depends on the spool 52 and the coil spring.
Since it is determined by the equilibrium with the reaction force of 58, 58a, the discharge pressure Pb
The change in the pump discharge amount Q is as indicated by a, b, c and d in the above-mentioned figure. Therefore, a drive source with corner horsepower is not required. Next, a case where the opening of the variable aperture 89 is reduced to a relatively small amount will be described. In this case, for example, the actuator 90
Corresponds to the case where the is driven at a relatively high load and at a low speed. That is, since the opening degree of the variable throttle 89 is small, the pressure difference of the pressure oil is generated between the upstream side and the downstream side thereof. Therefore, in the pressure oil acting on both ends of the differential spool 72, the passage 29
The pressure of the pressure oil introduced via the
On the downstream side, that is, higher than the pressure of the pressure oil in the chamber 80. When the force acting on the differential spool 72 and the upper end reaches the resultant force of the force acting on the lower end and the elastic force of the coil spring 82, the differential spool 72
Is displaced downward in the figure, and the land 76 connects the passage 29 and the passage 70. As a result, the pressure oil introduced through the passage 29 is introduced into the chamber 68. In this case, the cross-sectional area of the shift spool 60 is selected to be sufficiently larger than the cross-sectional area of the spool 52. Therefore, even if the discharge pressure of the variable displacement pump 11 is low, the pressure of the pressure oil introduced into the chamber 68 acts to move the servo spool 32 in the direction of arrow D against the elastic force of the coil spring 58. . Therefore, the servo spool 32 is displaced, and the cam lever 18 is moved in the same process as described above.
Tilts in the direction of arrow B, and the discharge flow rate of the variable displacement pump 11 decreases via the arm member 21. Therefore, as described above, the reduction of the discharge flow rate also reduces the differential pressure between the upstream side and the downstream side of the variable throttle 89. The elastic force of the coil spring 82 becomes dominant due to the decrease in the differential pressure, and the differential spool 72 is displaced upward in the figure and stops at a new equilibrium position. For this reason,
The communication state between the passage 70 and the passage 29 is partially throttled by the land 76, and the pressure of the pressure oil in the chamber 68 decreases. As a result, the elastic force of the coil spring 58 displaces the servo spool 32 in the direction of arrow C, Push the shift spool 60. Eventually, the pressure oil in the chamber 42 of the power piston 26 is led out from the passage 44 and the hole 33. Therefore, the cam lever 18 tilts in the direction of arrow A, the discharge flow rate of the variable displacement pump 11 increases, and finally,
The pressure is stabilized in a predetermined equilibrium state so that the pressures on the upstream side and the downstream side of the variable throttle 89 are constant. Further, in this state, when the discharge pressure of the variable displacement pump 11 further increases due to the increase of the load, regardless of the state of the differential spool 72, the pressure oil acting on the spool 52 causes the same process as in the first case. The discharge flow rate is controlled. Thus, the differential pressure generated by the opening of the variable throttle 89 is controlled to be constant, in other words, the flow rate corresponding to the differential pressure set by the variable throttle 89 is controlled to be constant. Become. Therefore, the variable throttle is adjusted in advance to the flow rate required by the load corresponding to the load of the actuator 90.
By adjusting 89, the variable displacement pump 11 can be controlled to the discharge flow rate found at the opening. Therefore, especially when the actuator is required to operate at a relatively high load and a low speed, in terms of driving force compared with the conventional load sensitive control that controls the discharge flow rate of the hydraulic pump exclusively according to the load. It will be easily appreciated that it is more efficient. Next, FIG. 3 shows another embodiment of the control device for the variable displacement pump according to the present invention. In this case, the first
The same reference numerals as in the embodiment of FIG. Therefore, in this embodiment, the bypass line 100 is connected to the line 87, and the bypass line 100 has an orifice.
A tank 106 is provided while a 102 and a variable throttle 104 are interposed. Further, the orifice 102 and the variable diaphragm 104
The space between them is branched and connected to the chamber 80 through the pipe 108. In this case, the positions of the orifice 102 and the variable diaphragm 104 may be reversed. In this embodiment, the pressure oil is supplied to the tank 1 via the variable throttle 104.
Since it recirculates to 06, the pressure of the pressure oil drops considerably downstream of the orifice 102, and the pressure difference of the pressure oil acting on the upper and lower ends of the differential spool 72 in the figure becomes large. Therefore, by finely adjusting the opening of the variable throttle 104, the differential spool 72 responds sharply, and the discharge flow rate control of the variable displacement pump 11 can be achieved by that much. [Advantages of the Invention] As described above, according to the present invention, the differential spool that is displaced in accordance with the differential pressure generated between the upstream side and the downstream side of the variable throttle interposed between the variable displacement pump and the actuator. By providing the variable displacement pump, the flow rate of the discharge pressure oil of the variable displacement pump is adjusted in accordance with the load within a predetermined horsepower range of the prime mover of the variable displacement pump. A so-called load sensitive control is achieved in which a quantity of pressure oil is supplied to the actuator. Also, when the pressure of the discharge pressure oil of the variable displacement pump becomes higher than a predetermined value, the power piston tilts the cam lever via the servo spool regardless of the differential pressure before and after the variable throttle, and the discharge of the variable displacement pump In order to reduce the flow rate of pressure oil, the prime mover of the variable displacement pump is not required to have a corner horsepower determined by the product of the maximum discharge pressure and the maximum discharge flow rate.
Therefore, the drive efficiency of the variable displacement pump is improved,
It is extremely effective in saving the power, and in addition to being able to promote miniaturization of the driving power source, further energy saving can be achieved. As described above, the present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to these embodiments, and various improvements and design changes can be made without departing from the gist of the present invention. Of course.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the discharge pressure Pd and the pump discharge amount Q, FIG. 2 is a schematic vertical sectional view showing a control device of a variable displacement pump according to the present invention, and FIG. It is a schematic longitudinal cross-sectional view showing another embodiment of the control device for the variable displacement pump according to the present invention. 10 …… Control device, 12 …… Control mechanism 14 …… Differential valve section, 18 …… Cam lever 24 …… Return piston, 26 …… Power piston 32 …… Servo spool, 40 …… Annular chamber 52 …… Spool, 60 …… Shift spool 72 …… Differential spool

Claims (1)

(57) [Claims] A control device for increasing / decreasing a discharge flow rate of the variable displacement pump by tilting a cam lever provided on a variable displacement pump and swingably supported, wherein the cam lever is tilted to a maximum discharge flow position,
The return piston, which comes into contact with the cam lever via the elastic force of the elastic body, and the action of the discharge pressure oil of the variable displacement pump, which is fed back, cause the return piston to tilt in order to tilt the cam lever to the minimum discharge flow position. A power piston that opposes and abuts against the cam lever, and a power piston that is fitted to the power piston and is displaced against the elastic force of the elastic body, thereby exerting the action force of the discharge pressure oil on the end portion of the power piston. A servo spool to be applied, a shift spool that comes into contact with an end of the servo spool in order to displace the servo spool by the action of feedback pressure oil of the variable displacement pump that is fed back, and can be displaced with respect to the servo spool. And one end of which abuts against the shift spool and the other end of which is introduced into the servo spool. The spool is arranged between the variable displacement pump and the actuator, and a spool for displacing the servo spool against the elastic force of the elastic body by the reaction of the discharge pressure oil of the variable displacement pump. The variable throttle and the displacement of the variable throttle according to the pressure difference between the upstream side and the downstream side of the variable throttle, and when the hydraulic pressure on the upstream side becomes higher than the hydraulic pressure on the downstream side by a predetermined amount or more, the end portion of the shift spool. And a differential spool for applying the action force of the discharge pressure oil of the variable displacement pump, to the controller of the variable displacement pump.