JPH0335516B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable displacement hydraulic pump, and more particularly, a control plunger that adjusts the amount of displacement of a variable control element, and a control plunger that biases the variable control element in the direction of maximum displacement in opposition to the plunger. The present invention relates to a variable displacement hydraulic pump comprising a bias means for controlling the discharge pressure to a predetermined discharge amount characteristic by applying a control pressure of self-discharge fluid to the plunger.

In general, this type of hydraulic pump uses a control valve that includes a valve body with a spool chamber, a spool that is freely movable inside the spool chamber of the valve body, and a pressing body that presses the spool in one direction. When the self-discharge pressure of the pump exceeds a predetermined pressure set by the pressing body, the spool is moved to open a control passage provided between the valve body and the control plunger, and the control pressure is increased. , the control plunger is actuated to operate the plunger, and the variable control element is controlled to a neutral position by the operation of the plunger, thereby controlling the capacity under pressure compensation.

By the way, the capacity control is a pressure compensator control (PC control) that uses one control valve to reduce the discharge amount to zero at a predetermined pressure, as shown in FIG.
Although not shown, using the two control valves,
2-pressure, 2-capacity control that controls low-pressure, large-capacity and high-pressure, small-capacity, or a combination of one or more control valves and a feedback mechanism, as shown in FIG. There are constant horsepower control and long ramp control, which are performed by feedback from the engine.

However, these capacity controls are performed by setting the pressing force of the pressing body facing the spool of the control valve, and once the capacity control characteristics are set, the discharge amount with respect to the discharge pressure is determined. Therefore, it is not possible to control the discharge amount to a low value that is less than the set discharge amount.

Therefore, when an actuator such as a hydraulic cylinder or a hydraulic motor is operated in a circular motion by the fluid discharged from the variable displacement hydraulic pump configured as described above, the set displacement can be controlled even during no load or low load. According to the characteristics, the maximum discharge amount is discharged, resulting in wasteful power consumption.

For example, in a hydraulically operated power shovel,
Even when there is no load, such as when the shovel is stationary on the ground, if the pump is driven, its discharge volume will reach its maximum, resulting in the problem of wasted power consumption.

Therefore, in order to solve the above-mentioned problems of a hydraulic pump device that uses a control plunger to control the discharge pressure-discharge rate characteristic to a prescribed displacement characteristic, the inventors of the present invention have developed Separately from the control valve to be controlled, a control valve device having a spool operated by an external operating pressure and a guide sleeve operated in response to displacement of a variable control element is provided, and the spool is operated by the external operating pressure. The control pressure of the self-discharging fluid is applied to the control plunger to control the variable control element, and the pump discharge rate is set to a low discharge rate within the range of the volume control characteristic and lower than the set discharge rate. He invented and applied for a device (Japanese Patent Application No. 56-26619).

However, in the previous invention, the pump discharge amount can be arbitrarily controlled to a low discharge amount by adjusting the external operating pressure, but the spool and the operating circuit for the external operating pressure acting on the spool are each simple. Since it has one configuration, the discharge amount control for the external operating pressure is limited to one type, and the maximum flow rate value for this low discharge control is also set by the maximum value of the external discharge pressure and the working surface of the spool, and can be changed arbitrarily. It cannot be done.

By the way, when connecting multiple actuators to one hydraulic pump and operating one or more actuators among these multiple actuators, the rate of change in discharge amount with respect to pressure change in external operating pressure must be changed. It is required that each actuator can be used differently, such as by increasing or decreasing the speed change of the actuator depending on the work conditions. It is preferable to set the maximum speed, that is, the maximum flow rate in flow rate control by adjusting the external operating pressure, to be able to arbitrarily change the maximum speed.

It is an object of the present invention to arbitrarily control the pump discharge rate to a low discharge rate lower than the set discharge rate by adjusting the external operating pressure within a predetermined discharge pressure-discharge rate characteristic. - Even if the discharge pressure changes within the range of the discharge rate characteristics, in other words, even if the load changes, the discharge rate can be maintained constant, and the discharge rate can be controlled by multiple types of control using the external operating pressure. It is possible to change the maximum flow rate value in multiple stages.

That is, the present invention provides a variable displacement hydraulic pump that is controlled to a predetermined discharge pressure-discharge rate characteristic, and includes a sensing spool having at least two working surfaces with different working areas on which external operating pressure acts, and an external operating pressure pump. An operating valve device is provided that includes a pressing means that opposes the pressure and a guide sleeve that operates in response to the displacement of the variable control element, and the operating passage provided with the variable pressure reducing mechanism is connected to the spool through a switching mechanism. Each working surface is selectively connected to each working chamber that faces, and by controlling the external operating pressure, multiple types of discharge rate control are performed within a predetermined range of discharge pressure-discharge rate characteristics. It is something to do.

That is, the present invention uses at least two sensing spools, each spool's working chamber having a
The basic idea is to introduce an external operating fluid that adjusts the pressure using a variable pressure reduction mechanism, and to make it possible to change the control characteristics of the discharge amount control for pressure adjustment into multiple types, thereby making it possible to meet the above-mentioned requirements. .

Next, an embodiment of the pump device of the present invention will be described based on the drawings.

The hydraulic pump shown in FIG. 1 is a swash plate type axial piston pump in which the swash plate serves as a variable control element.

In FIG. 1, reference numeral 1 denotes a housing including a front cover 1a and an end cap 1b, and a drive shaft 4 is connected between the front cover 1a and the end cap 1b via a pair of bearings 2 and 3. A cylinder block 5 is spline-coupled to the drive shaft 4, and the swash plate 6 is supported within the housing 1.

The cylinder block 5 has a large number of pistons 7
A shoe 9 supported by a retainer 8 is attached to the head of each piston 7, and each shoe 9 is in contact with the swash plate 6.

Further, the swash plate 6 is supported by the trunnion shaft 10 so as to be tiltable within a certain range of inclination angle, and the swash plate 6 is supported at a predetermined position on the swash plate 6, that is, deviated by 90 degrees with respect to the trunnion shaft 10. upper position,
Connecting rods 11 and 12 are pin-coupled to the lower position offset by 180 degrees with respect to the above position, and the rod 1
1 and 12, a bias plunger 13 that presses the swash plate 6 in the direction of maximum inclination and a control plunger 14 that adjusts the angle of inclination of the swash plate 6 are connected.

The bias plunger 13 has a smaller diameter than the control plunger 14,
It is movably supported by a cylinder 15 fixed to the housing 1, and a spring 16 is interposed between the end face of the recessed part of the cylinder 15 and the head part of the bias plunger 13. The chamber 13a communicates with the discharge passage 17 of the pump via a communication passage 18, so that the self-discharge pressure of the pump acts on the back surface of the bias plunger 13.

Further, the control plunger 14 is movably supported by a cylinder 19 fixed to the housing 1, and a control passage 26 extending from a control valve device 20 and an operating valve device 40, which will be described later, is communicated with the rear chamber 14a. The control pressure of the self-discharging fluid of the pump is controlled by the control plunger 14.
It is designed to act on the back of the body.

Therefore, when no control pressure is applied to the control plunger 14, even if the pump discharge pressure is zero, the swash plate 6 reaches its maximum inclination angle as shown in FIG. 1, and the maximum discharge amount can be obtained. Furthermore, when a control pressure is applied to the control plunger 14, the inclination angle of the swash plate 6 is adjusted to the neutral direction, so that a discharge amount commensurate with the inclination angle can be obtained.

The control valve device 20 is for controlling pump characteristics to predetermined discharge pressure-discharge rate characteristics, and basically consists of a valve body 21 having a spool chamber 21a.
, a spool 22 which is freely movable inside the spool chamber 21a of the main body 21, and a pressing body 23 made of a spring that determines the capacity control characteristics of the pump, and one end of the spool 22 communicates with the discharge passage 17. The first passage 25 is connected to apply pump discharge pressure, and the spool 22
The pressing body 23 is disposed on the other end side, while the control plunger 1 is disposed on the valve body 21.
A control passage 26 that communicates with 4 is connected thereto.

In the pump shown in FIGS. 1 to 3, the capacity characteristics of the pump are controlled to the PC characteristics as shown in FIG. 4, and the spool 22 is a PC valve.

In this configuration, the spool 22
In other words, when the pump discharge pressure is lower than the pressure set by the pressing body 23, the control passage 26 opens and communicates with a communication passage 27 to the operating valve device 40, which will be described later. The variable orifice O formed between the land and the opening edge of the control passage 26 on the first passage 25 side is configured to be closed.

Further, when the discharge pressure becomes higher than the pressure set by the pressing body 23, the spool 22 moves by overcoming the pressing force of the pressing body 23,
Open the variable orifice O and open the first passage 25.
from the control passage 26 to one of the pump's self-dispensing fluids.
The control plunger 14 is actuated to adjust the swash plate 6 to the neutral position to compensate for a predetermined discharge pressure as shown in FIG.

Next, an operating valve device 4 is installed separately from the control valve device 20 described above in the pump configured as described above.
0 will be explained.

This operating valve device 40 operates within the range of the pump capacity control characteristics set by the control valve device 20.
A valve body 41 which can arbitrarily obtain a pump discharge rate lower than a set discharge rate, and which is separate from or integrated with the valve body 21, an action surface 42a having a different action area on which external operating pressure acts, A pair of first and second sensing spools 42, 4 with 43a
3, a guide sleeve 44 that operates in accordance with the tilting movement of the swash plate 6, and a pressing body 45 that opposes the movement of the spools 42 and 43.

More specifically, the guide sleeve 44 is movably supported in a sleeve hole formed in the main body 41, and spool holes with different diameters are formed in the guide sleeve 44, and a first sensing sensor with a small diameter is formed in the small diameter spool hole. The spool 42 is also connected to the large diameter second sensing spool 4 in the large diameter spool hole.
3 are arranged in series and supported so that they can move freely, and the spools 4
On the back side of each of 2 and 43, the working surface 4 is provided.
2a, 43a face external operating pressure action chambers 46, 4
7 is formed.

Further, the guide sleeve 44 includes the first
A first port 48 communicating with the passage 25, a second port 49 communicating with the communication passage 27, and a third port 51 communicating with the drain passage 50 are provided,
Spring case 52 housing the pressing body 45
A spring 53 is provided between the two and pressed outward. Further, the second sensing spool 43 is of a two-land type, and the first land 43b connects the second port 49 communicating with the communication passage 27, in other words, the control passage 26, with the first passage 25, In other words, it is possible to switch between the discharge passage 17 and the drain passage 50.

That is, the second port 49 and the first land 43b of the second sensing spool 43 have a zero lap, and the operation of the spool 43 creates two variable orifices O ₁ and O ₂ , that is, the first port 48 . A first passage communicating with the first passage 25
The variable orifice O ₁ and the second variable orifice O ₂ communicating with the third port 51, in other words the drain passage 50, are selectively formed.

Note that the second port 49 and the spool 43
Although the first land 43a was set to zero lap,
It can also be underlap. According to the test results, underlap was preferable.

Further, the second sensing spool 43 is arranged in series with the first sensing spool 42, and when an external operating fluid is introduced into the action chamber 47 formed on the back side of the second sensing spool 43. , operates independently of the first sensing spool 42, but the first sensing spool 4
External operating pressure acts on the back surface of the spool 42.
, the second variable orifice opens one of the first and second variable orifices O ₁ and O ₂ and communicates the second port 49 with one of the discharge passage 17 and the drain passage 50. be.

The first and second sensing spools 42, 4
3 may be arranged in parallel instead of in series as described above, but since the control valve device 20 becomes larger accordingly, it is preferable to arrange them in series.

Furthermore, in the above configuration, each of the spools 4
2, 43 is lower than the pressing force by the pressing body 45, the pressing body 45
Due to the action, each of the spools 42, 43 is moving to the left in FIG. 3, and in this state, the first variable orifice _O1 is opened and the second variable orifice _O2 is closed. The control passage 26 is connected from the orifice O ₂ to the first passage 2
It communicates with the discharge passage 17 via 5. Further, when the external operating pressure becomes higher than the pressing force, the spools 42 and 43 move to the right in FIG. 3, and the first variable orifice O ₁ closes.
The second variable orifice O ₂ opens and the control passage 26 communicates with the drain passage 50 .

Further, the external operating pressure may be applied manually or electrically to the hydraulic pump 60 for an auxiliary circuit, which is driven by a drive source such as a motor or an engine that drives the drive shaft 4 of the pump. An operation passage 62 equipped with a pressure reducing valve (hereinafter referred to as a pressure reducing valve) as one variable pressure reducing mechanism 61 that operates.
The passage 62 is connected to one of the switching passages 64 and 65 via the switching valve 63 to each of the spools 4.
It is selectively connected to each of the working chambers 46 and 47 of 2 and 43.

The fluid discharged from the hydraulic pump 60 is controlled by the pressure reducing valve 61 to a desired secondary pressure according to the operation of the pressure reducing valve 61, and this secondary pressure is used as an external operating pressure. the action chamber 46,
47 through one of the passages 64, 65, and acts on each of the spools 42, 43 individually.

Further, the response of the guide sleeve 44 to the swash plate 6 uses a feedback link mechanism, in which a link 70 is pivotally connected to the valve body 41 via a pin 71, and a
A roller 73 is rotatably attached via a pin 72, and this roller 73 is brought into contact with the head 44a of the guide sleeve 44. The link 70 is pivotally connected to the swash plate 6 via a pin 74 as shown by the dotted line in FIG.

The link 70 swings counterclockwise about the pin 71 when the swash plate 6 tilts from the neutral position to the maximum inclination direction, and the roller 73 moves the guide sleeve 44 toward the pressing body 45. It moves in the direction.

Next, the operation of the hydraulic pump incorporating the operating valve device 40 configured as described above will be explained.

When the drive shaft 4 is stopped, no pressure acts on either the bias plunger 13 or the control plunger 14, and no tilting moment acts on the swash plate 6.
is the maximum angle of inclination due to the spring 16. The variable orifice O of the control valve device 20 and the second variable orifice O ₂ of the operating valve device 40 are fully closed by the pressing forces of the respective pressing bodies 23 and 44, and the first variable orifice O of the control valve device 20 is fully closed.
O ₁ is open.

Therefore, if the drive shaft 4 is driven in this state, the pump will discharge at the maximum discharge amount,
A portion of the discharge fluid is introduced from the discharge passage 17 through the first passage 25, through the first port 48 of the operating valve device 40 and the first variable orifice _O1 , and into the communication passage 27 from the second port 49. , the control plunger 14 via the control passage 26
The control pressure acts on the plunger 14, causing the plunger 14 to move forward and tilting the swash plate 6 in the neutral direction.

At this time, the link 70 of the feedback mechanism also operates due to the tilting of the swash plate 6, and the roller 73 of the link 70 separates from the guide sleeve 44 of the operating valve device 40. It moves away from the pressing body 45 by the action of the spring 53, and as a result, the opening area of the first variable orifice _O1 decreases, and when the swash plate 6 reaches the neutral position, the second variable orifice O1 moves away from the pressing body 45. With orifice O ₂ also closed,
The first variable orifice _O1 is fully closed, and the swash plate 6 is held at the neutral position.

In the above state, no external operating pressure is applied, there is no load, and the pump discharge amount is zero. That is, when there is no load, feathering operation can be performed without applying external operating pressure.

In the above configuration, the cylinder 15 supporting the bias plunger 13 allows the plunger 1 to be placed in the back chamber 13a of the plunger 13.
Stopper means (not shown) for regulating the movement of 3.
By providing this, the swash plate 6 can be held in a state tilted by a predetermined angle in the direction of the maximum tilt angle position with respect to the neutral position, that is, the zero tilt angle position. That is, this tilted position becomes the minimum tilted position, and the minimum discharge amount can be compensated according to the tilted angle.

Therefore, even in feathering operation, the discharge pressure decreases due to the increase in load.
Even in the case of PC control exceeding the set pressure of 0, the minimum discharge amount can be compensated, leakage from the hydraulic circuit for operating the actuator can be compensated for, and the minimum tilt angle position of the swash plate 6 can be reliably maintained. be.

Further, from the state described above, when the desired external operating pressure obtained by operating the pressure reducing valve 61 is applied to, for example, the second sensing spool 43 of the operating valve device 40 and the spool 43 is operated, the second sensing spool 43 is operated. 1
With the variable orifice O ₁ closed, the second variable orifice O ₂ is opened, and the second port 49 communicates with the drain passage 50 , and the communication passage 27
and the drain passage 50 communicate with each other, and the control passage 26
The back chamber 14a of the control plunger 14 communicates with the drain passage 50 via the control plunger 14.

Therefore, the pressing force of the control plunger 14 is removed, and the swash plate 6 tilts again from the minimum tilt angle position to the maximum tilt angle direction. The feedback mechanism also operates due to this tilting,
The guide sleeve 44 moves to the right in FIG. 3 against the spring 53, reducing the opening area of the second variable orifice O ₂ and causing the inclination angle of the swash plate 6 to become larger than necessary. This suppresses the effect of increasing the angle of inclination and maintains the angle of inclination commensurate with the amount of movement of the second sensing spool 43 caused by the external operating pressure. That is, the swash plate 6
When the inclination angle becomes larger than necessary, the first variable orifice O ₁ opens, and the control pressure of the self-discharged fluid from the first passage 25 acts on the control plunger 14 through the above-described path, and the swash plate 6
This suppresses the tilting of the

As described above, the desired external operating pressure can be applied to the second
By acting on the sensing spool 43, the swash plate 6 is controlled to a predetermined inclination angle, and within the range of the discharge pressure-discharge rate characteristic set by the operation valve device 40, the pump discharge rate is adjusted to the fifth level. It is possible to control the control characteristics as shown by the solid line in the figure.

Furthermore, by causing the external operating pressure to act on the first sensing spool 42 by operating the switching valve 63, control characteristics different from those of the second sensing spool 43, with the same operation as described above, can be obtained. In other words, it is possible to control the control characteristics as shown by the dotted line in FIG. This selection of control characteristics can be performed by switching the switching valve 63, and as is clear from FIG. The rate of change can be changed.

Therefore, when operating one or more actuators among a plurality of actuators,
The rate of change in the speed of the actuator relative to the amount of operation of the pressure reducing valve 61 can be changed, making it possible to use the actuator differently depending on the type of actuator and working conditions.

Furthermore, the pressure reducing valve 61 allows the maximum value of the pump discharge amount corresponding to the external operating pressure to be changed even when the external operating pressure is operated to the maximum. Therefore, there is no need to provide a stopper means to control the operating position. In both cases, the maximum speed of the actuator can be controlled in two stages.

The pump discharge rate is controlled under the control of the external operating pressure, and within the range of the discharge pressure-discharge rate characteristic set by the control valve device 20, the pump discharge rate is lower than the set discharge rate. Choose based on quantity. That is, within the range of a predetermined discharge pressure-discharge rate characteristic set by the control valve device 20, the discharge rate is arbitrarily controlled to a low value lower than the set discharge rate, and when the load is low, the speed of the actuator is set to a low speed. It goes without saying that power loss due to adjustment can be eliminated and safety can be ensured.

Furthermore, the swash plate 6 is controlled not by applying an external operating pressure to the control plunger 14, but by applying the control pressure of the self-discharged fluid of the pump, so that the load may fluctuate. Even if the pump discharge pressure changes, the inclination angle of the swash plate 6 can be kept constant, in other words, the discharge amount can be kept constant.

That is, since the tilting moment of the swash plate 6 changes depending on the discharge pressure of the pump, when applying a constant external operating pressure adjusted to a desired value to the control plunger 14, the tilting moment of the swash plate 6 changes. Due to changes in the tilting moment, the inclination angle of the swash plate 6 changes, and the pump discharge amount also changes, but when the control pressure of self-discharge fluid is applied, the control pressure is proportionally controlled by the change in the pump discharge pressure. Therefore, even if the tilting moment of the swash plate 6 changes,
The inclination angle of the swash plate 6 can be kept constant, and the pump discharge amount can also be kept constant.

Furthermore, if the load increases while the discharge amount is controlled to be low as described above, the pump discharge pressure also increases, but this pump discharge pressure is equal to the discharge pressure set by the pressing body 23 of the control valve device 20. If it increases further, the control valve device 20 operates as described above, and the pump discharge amount is controlled to a discharge amount that corresponds to the discharge pressure. That is, the pump discharge pressure is the discharge pressure set by the control valve device 20.
When the set discharge pressure of the discharge rate characteristic is reached, the pump discharge rate is PC-controlled based on the above-described discharge pressure-discharge rate characteristic, regardless of the external operating pressure.

Incidentally, in the embodiment described above, the control valve device 2
The operating valve device 40 is incorporated into a hydraulic pump designed to perform PC control based on the control valve device 20.
It may be formed separately and independently from the PC.
In addition to the hydraulic pump that performs control, the present invention may also be applied to, for example, a hydraulic pump that performs constant horsepower control as shown in FIG.

In this case, a constant horsepower control valve 80 is installed as shown in FIGS. 6 and 7.

The constant horsepower control valve 80 shown in FIGS.
It is interposed between the control valve device 20 which serves as a valve and the operation valve device 40, and uses a guide sleeve 81, and supports the guide sleeve 81 freely in a sleeve hole provided in the valve body 41, and A spool 82 is movably supported by the guide sleeve 81, one end side of the spool 82 is connected to the first passage 25 communicating with the discharge passage 17,
Constant horsepower springs 83 and 84 are arranged at the other end, and the guide sleeve 81 is provided with a control port 85 and a communication port 86, and the control port 85 is connected to the control passage 26.
is connected to the communicating path 27, and a third
While forming a variable orifice _O3 , a roller 75 is provided in the middle of the link 70 via a pin 76, and the feedback mechanism is used to form a feedback mechanism for constant horsepower control.

In addition, in FIGS. 6 and 7, the same reference numerals are used for parts having the same configuration as in FIGS. 2 and 3.

Even in the case of the above configuration, by selecting the switching valve 63, the external operating pressure is transferred to the first and second operating chambers 46, 47 of the operating valve device 40.
By acting on one of the sensing spools 42 and 43, the constant horsepower control valve 80 controls the discharge amount with two types of control characteristics within the range of the discharge pressure-discharge amount characteristics controlled as shown in FIG. , 5th
It is possible to control the control characteristics according to the solid and dotted lines shown in the figure.

Note that when the pump discharge pressure is lower than the pressure set by the constant horsepower springs 83 and 84, the constant horsepower control valve 80 is moved to the normal position (the left position in FIG. 7) by the action of the springs 83 and 84. In this state, the third variable orifice O ₃
is closed, and the control passage 2 is opened via the control port 85.
6 communicates with the communication passage 27, and the control passage 26 communicates with the second port 49 of the operation valve device 40 via the communication passage 27, and the control passage 26 communicates with the second port 49 of the operating valve device 40 in response to the operation of the spools 42 and 43. , the first passage 2
5 and one of the drain passages 50.

On the other hand, if the pump discharge pressure is equal to the constant horsepower spring 8,
3, 84, the spool 82 overcomes the springs 83, 84 and moves, the third variable orifice _O3 opens, and the pump is transferred from the first passage 25 to the control passage 26. A portion of the self-discharged fluid is introduced under controlled pressure to actuate the control plunger 14 and adjust the inclination angle of the swash plate 6.

At this time, the link 70 is also connected to the swash plate 6.
The roller 35 moves the guide sleeve 81 in the direction of the constant horsepower springs 83 and 84.
1, the opening area of the third variable orifice _O3 is reduced, and the inclination angle of the swash plate 6 is adjusted to the inclination angle corresponding to the discharge pressure.

In addition to the hydraulic pumps that perform PC control and constant horsepower control as described above, the present invention may be applied to hydraulic pumps that perform two-pressure and two-capacity control, and may also be applied to other hydraulic pumps that perform long ramp control, throttling mechanisms, etc. The present invention may be combined and applied to a hydraulic pump that performs constant speed control that controls the discharge amount to be constant regardless of changes in the rotational speed of the drive shaft 4. Further, the pump is not limited to an axial piston pump, and may be a variable displacement vane pump.

In short, as long as the variable displacement hydraulic pump uses the control plunger 14 and is controlled to a predetermined discharge pressure-discharge rate characteristic, it does not matter what type of pump it is or what control method it uses.

Further, although the bias plunger 13 is used as a bias means for biasing the variable control element such as the swash plate 6 in the maximum displacement direction, a bias spring may also be used.

Furthermore, in the embodiment described above, two first and second sensing spools 42 and 43 are provided, and each of these spools 42 and 43 is formed with working surfaces 42a and 43a having different areas, respectively.
Two sensing spools may be integrated into one sensing spool, and two working surfaces may be formed on one sensing spool.

Further, the number of the working surfaces may be two or more.

As described above, according to the present invention, the predetermined discharge pressure -
While capacity control can be performed using the discharge rate characteristics, the pump discharge rate can be controlled to a low discharge rate lower than the set discharge rate within the range of the above characteristics by adjusting the external operating pressure. Feathering control can be performed to reduce the pump discharge amount to zero or the minimum discharge amount, eliminating unnecessary power loss and enabling energy-saving pump operation.Furthermore, at low loads, the actuator can be controlled at a speed according to its operating conditions. This makes it possible to operate the actuator with high safety.

Furthermore, by using a sensing spool with at least two working surfaces, the discharge amount can be controlled by external operating pressure, allowing for multiple types of control characteristics.
In other words, it is possible to change the control characteristic to a different rate of change in the discharge amount with respect to a change in the external operating pressure.

Therefore, when operating one or more actuators, even if the amount of operation of the variable pressure reducing mechanism 61 that adjusts the external operating pressure is the same, the speed of the actuator relative to the amount of operation can be changed, depending on the type of actuator and the operation. Control can be used depending on the conditions.

Furthermore, the variable pressure reducing mechanism 61 allows the maximum value of the pump discharge amount corresponding to the external operating pressure to be changed even when the external insertion pressure is maximized, and as a result, while using one variable pressure reducing mechanism, Even without a stopper means for controlling the operating position, the maximum value of the operating speed of the actuator can be controlled in multiple stages.

Furthermore, the present invention does not apply an external operating pressure to the control plunger 14 to adjust the displacement amount of the variable control element, but instead provides an operating valve device 40 and controls the operation of the operating spool 42 in response to the external operating pressure. Since the control pressure of the self-discharged fluid is applied to the control plunger 14 to adjust the displacement amount of the variable control element, the pump discharge amount, which is controlled to a low discharge amount, is independent of changes in the discharge pressure. Therefore, the discharge amount can be controlled to be constant without being affected.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the device of the present invention;
Fig. 2 is a symbol diagram, Fig. 3 is an enlarged sectional view of main parts, Fig. 4 is a discharge pressure-discharge rate characteristic diagram of the embodiment shown in Figs. 1 to 3, and Fig. 5 is an external operation Pressure
A characteristic diagram of discharge amount, FIG. 6 is a second diagram showing another example.
FIG. 7 is an enlarged sectional view of the main part thereof, and FIG. 8 is a discharge pressure-discharge amount characteristic diagram of the embodiment shown in FIGS. 6 and 7. 6... Swash plate, 13... Bias plunger, 1
4...Control plunger, 42, 43...
Sensing spool, 42a, 43a... working surface, 44... guide sleeve, 45... pressing means, 46, 47... working chamber, 61... variable pressure reduction mechanism, 62... operating passage, 63... switching mechanism.

Claims (1)

[Claims] 1. A control plunger 14 that adjusts the displacement amount of the variable control element 6, and a bias means 13 that biases the variable control element 6 in the maximum displacement direction against the plunger 14, and controls the control pressure of the self-discharged fluid. In a variable displacement hydraulic pump which is controlled to a predetermined discharge pressure-discharge rate characteristic by acting on the plunger 14, a sensing spool having at least two working surfaces with different working areas on which external operating pressure acts; An operating valve device including a pressing means 45 that opposes external operating pressure and a guide sleeve 44 that operates in response to the displacement of the variable control element 6 is provided, and an operating passage 62 equipped with a variable pressure reducing mechanism 61 is connected to a switching mechanism. 63 to the respective working chambers 46 and 47 facing each working surface of the spool, and by controlling the external operating pressure, a plurality of types of discharge pressure/discharge amount characteristics can be controlled. A variable displacement hydraulic pump characterized by the ability to control the discharge amount.