JPS6050992B2 - Variable displacement hydraulic pump - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a variable displacement hydraulic pump, in which one pressure reducing pump can handle two pressures from low pressure large capacity to high pressure small capacity as shown in Figure 2.・This is to provide a hydraulic pump that has the function of allowing two-capacity control and small-capacity control as shown in Fig. 4 to be arbitrarily selected by simply operating a switching valve, in other words, capable of multiple control. .

(Prior Art) Conventionally, when performing two-pressure/two-capacity control using one variable displacement hydraulic pump, the low pressure side pressure P is determined based on the characteristics shown by curves A and B shown in Fig. 6. , and high pressure side pressure Po
It is controlled by setting the high pressure side pressure P.
Not only does it have the disadvantage that it is very difficult to set o, but when this high pressure side pressure P2 changes, the discharge amount Q corresponding to the pressure changes,
This has the disadvantage that it is easy to change, the accuracy varies, and stable control cannot be performed.

In addition, the relief pressure (maximum discharge pressure) PA-PB is also high, and the required horsepower within the range of the low pressure side pressure P and the high pressure side pressure P2 is large, so it also has the disadvantage of large power loss and heat generation. There is.

That is, since the two-pressure/two-capacity control using the method explained above is performed based on the characteristics shown in curves A and B, in other words, the characteristics close to the constant flow characteristics, the discharge amount at the high-pressure side pressure Po Q is not stable, and the above-mentioned drawbacks occur.

However, in view of the above-mentioned problems, the present inventor has continued his research and has made numerous proposals to date.
Rapid traverse of the actuator using one hydraulic pump (
It is a liquid that can control two actuators and two volumes to change between (light load) and transport (heavy load), and can easily and stably perform both high pressure and small volume settings with high precision. Patent application No. 47-86507 for pressure pump (
Japanese Patent Application Publication No. 49-4190) and Patent Application No. 82871-1982
(Japanese Unexamined Patent Publication No. 52-6105).

Hereinafter, these items will be briefly explained. The former type, as shown in FIG. A control pilot plunger 62 is provided in series at an intermediate position, and the back chamber 1 of the pilot plunger 62 is connected to the discharge line 63, and the back chamber h of the operating plunger 61 is connected to the tank line 64 of the discharge line 63. A pressure control valve 65 for high pressure is provided, which is switched and connected at a set pressure on the high pressure side.

Note that 66 is a spring that presses the controllable connecting element 60 to the maximum inclination position, and in the pressure control valve 65, 67 is a spool, and 68 is a pressure setting pressure body. Thus, the one shown in FIG. 7 is of a self-pressure control type using discharge pressure, and the pilot plunger 62 overcomes the pressing force of the spring 66 and moves the variable control element 60 back to the intermediate position. When the discharge pressure reaches the set pressure on the high pressure side, the spool 67 of the pressure control valve 65 switches, and the operating plunger The back chamber h of 61 and the discharge line 63 are connected, and discharge pressure is introduced into the back chamber h, and the plunger 61
The rightward movement causes the controllable element 60 to return to its neutral position.

On the other hand, the latter mentioned above is as shown in FIG. A variable control element 70, an operating plunger 71, and a pilot plunger 72 are provided in the same manner as shown in FIG. Switch according to the set pressure and repeat! Separate pressure control valves 76 and 77 are provided for low pressure and high pressure to be passed through, and a discharge line 78 is connected to the connection passage 73 for low pressure and the connection passage 7 for high pressure.
4 and a switching valve 79 for selectively communicating with the rear chamber i of the pilot plunger 72.

As mentioned above, this device is of the switching control valve type, and when the switching valve 79 is set to the position shown in FIG. 8, the pressure control valve 76 for low pressure is activated to perform low pressure and large capacity operation. Also, when the position of the switching valve 79 is reversed, the pilot plunger 7
The discharge pressure acts on the rear chamber 1 of No. 2, causing the variable control element 70 to move back to the intermediate position, and the pressure control valve 77 for high pressure acts to enable high pressure, small capacity operation.

(Problems to be Solved by the Invention) However, as described above, there are two hydraulic pumps that employ a self-pressure control system to perform two-pressure and two-capacity control, and hydraulic pumps that employ a control system that uses a switching valve. If the pumps and pumps are formed separately, it is not possible to adapt to machining conditions that vary depending on the size and material of the workpiece, for example, and two types of portal hydraulic pumps must always be prepared.

That is, according to each of the specialized pumps, the tool linked to the actuator is applied to the workpiece in 1st speed feed mode, and after the load pressure on the actuator due to the machining load increases, the tool is switched to 1st slow feed mode. If you want to machine the workpiece using this 1-slow feed, you can also reduce the speed of the tool linked to the actuator just before the workpiece to create a 1-slow feed to move this tool to the workpiece without impact. It is not possible to arbitrarily select between the two types of operation depending on the needs, such as when the pump is applied to the pump to perform processing, and it is necessary to prepare the two types of pumps described above.This invention has the following features: This invention has been invented to solve the above-mentioned problems in hydraulic pumps. (Means for solving the problems) The structure of the present invention consists of an operation plunger 21 that controls the variable control element 11 to a neutral position, and This is a hydraulic pump in which the discharge amount is made variable by adjusting the position of the variable control element 11 with pilot plungers 21 and 24 that place the variable control element 11 in an intermediate position, and the pump discharge pressure and the first pressure are applied at both ends. It has a first spool 22 opposed to the body 30, and has a low pressure pressure that switches the control passage 34 communicating with the back pressure chamber K of the pilot plunger 24 from the tank line 40 to the discharge line 36 as the pump discharge pressure increases. control valve 25
a, and a second spool 23 at both ends that opposes the pump discharge pressure and the second pressing body 31, and the back pressure chamber b of the operation plunger 21 is connected from the tank line 40 to the discharge line by increasing the pump discharge pressure. 36 is provided with a pressure control valve 25b for high pressure which is connected to the back pressure chamber k of the pilot plunger 24 in the middle of the control passage 34. 3
4, a switching valve 37 for switching communication between the primary side connected to the low pressure pressure control valve 25a and the discharge line 36;
By providing this, it is possible to easily select and perform two-pressure control using a self-pressure control system or a switching valve control system by simply switching the switching valve 37 as necessary using one hydraulic pump. I made it.

(Function) By switching the switching valve 37, the secondary side of the control passage 34 and the primary side of this control passage 34 are communicated (see Fig. 1), and the pressure is increased to 2 pressures and 2 volumes by self-pressure. To explain the effect when performing control, the pump discharge pressure is
When the pressure is lower than the pressure set by the first pressing body 30 of the low pressure pressure control valve 25a, the pressing force of the first pressing body 30 is equal to the pressing force due to the pump discharge pressure acting on the first spool 22. In addition, the tank line 40 and the control passage 34 are connected, and thus the control passage 3
4, the back pressure chamber k of the pilot plunger 24 is released to the tank line 40, and at this time, the back pressure chamber b of the operation plunger 21 is opened by the high pressure pressure control valve 25b. and said tank line 40
Since the plungers 24 and 21 are in communication with each other, the plungers 24 and 21
, the pressing force that causes the variable control element 11 to move back toward the neutral direction does not work, and as a result, the variable control element 11 maintains the maximum inclination angle, and low-pressure, large-capacity operation is performed.

Next, when the pump discharge pressure rises below the predetermined pressure set by the second pressing body 31 and above the pressure set by the first pressing body 30, the high pressure pressure control valve 25b is activated. While the back pressure chamber b of the operation plunger 21 is still connected to the tank line 40, the low pressure pressure control valve 25a switches and connects the control passage 34 to the discharge line 36, so that the no. The pump discharge pressure (control pressure) from the discharge line 36 acts on the back pressure chamber k of the pilot plunger 24, and as a result, the variable control element 11 is moved back to the intermediate position by the pilot plunger 24. .

Therefore, the operation is switched to high pressure and small capacity operation.

Furthermore, the pump discharge pressure is controlled by the high pressure pressure control valve 25b.
When the pressure becomes higher than the pressure set in , the pressing force due to the pump discharge pressure acting on the second spool 23 of the high pressure pressure control valve 25b overcomes the pressing force of the second pressing body 31. , this control valve 25b is connected to the operating plunger 2
1 back pressure chamber b is switched and connected to the discharge line 36, and as a result, the operation plunger 21 is operated by the pump discharge pressure (control pressure) acting on the back pressure chamber b, and the variable control element 11 is moved back to the neutral position.

As described above, the low pressure, large capacity operation and the high pressure, small capacity operation can be switched at will.

Next, a case of two-pressure, two-capacity control by switching the switching valve 37 will be described.

In the case of low-pressure, small-capacity operation, the switching valve 37 is set to the same switching position as in the case of self-pressure control described above.

Therefore, when switching from low-pressure, small-capacity operation to high-pressure, small-capacity operation, the switching valve 37 is placed in a switching position (see FIG. 3) such that the secondary side of the control passage 34 and the discharge line 36 are communicated with each other. Let it happen.

As a result, the pump discharge pressure acts on the back pressure chamber k of the pilot plunger 24, and the variable control element 11 is moved back to the intermediate position by the plunger 24.

That is, by switching the switching valve 37, the low-pressure, small-capacity operation is switched to the high-pressure, small-capacity operation. Further, in operation in this switching position of the control valve 37, when the pump discharge pressure reaches the predetermined pressure of the high pressure pressure control valve 25b, the pressure control valve 25b operates in the same manner as in the case of free control. Then, the variable control element 11 is moved back to the neutral position by the operating plunger 21.

- (Example) Hereinafter, an example of the pump of the present invention will be described based on FIG. 1.

The hydraulic pump shown in FIG. 1 is a swash plate type axial plunger pump, and 1 is a hollow housing body, and a cover 2 is fixed to one side of the housing body.

A main shaft 5 is pivotally supported inside the housing main body 1 via bearings 3 and 4, and a cylinder block 7 can be rotated integrally with the main shaft 5 via a spline portion 6 formed at an intermediate portion thereof. Fixed. This block 7 is provided with a large number of pistons 8 that reciprocate with a predetermined stroke, and a shoe 10 supported by a retainer 9 is attached to the tip of each piston 8. The swash plate 11, which constitutes a variable control element, is contacted through the swash plate 11, which constitutes a variable control element.

The swash plate 11 is swingable around a trunnion shaft 12 within a certain angle of inclination, and the shoe 10
A spring 13 is interposed between the back surface of the housing body 1 which is in contact with the inner surface of the housing body 1, and acts to maintain the tilt angle of the swash plate 11 at the maximum position at all times.

Therefore, when the main shaft 5 is driven to rotate the cylinder block 7 in this state, each piston 8 reciprocates, and this reciprocating movement provides the maximum discharge amount.The inclination angle of the swash plate 11 can be changed. Therefore, an arbitrary discharge amount can be obtained, and the inclination angle of the swash plate 11 is determined by the operating pressure introduced to the back side of the operating plunger 21.
In FIG. 1, 14 is a valve plate, 15 is a spring, and 16 is a receiver for the spring 15.

In the pump shown in FIG. 1, the operating plunger 21 is incorporated into the pump housing body 1 constructed as described above, and the operating plunger 21 is controlled. , 23 for low pressure and high pressure, respectively.

The plunger 21 is provided in the housing body 1. It is inserted into the cylinder chamber a freely movably, and one end thereof contacts the swash plate 11 as described above, and the other end forms a rear chamber between it and the inner wall of the cylinder chamber a. A pilot plunger 24 is movably housed in this rear chamber and is in contact with the rear surface of the plunger 21. This pilot plunger 24 sets the discharge amount during high pressure control, and consists of a large diameter part 24a and a small diameter part 24b.
The large diameter portion 24a partitions the back chamber into a front chamber (back chamber of the operating plunger 21) b and a rear chamber (back pressure chamber of the pilot plunger 24) k.

Further, each pressure control valve 25a, 25b is connected to a valve block 25.
Inside are the spools 22, 23 and the pressing bodies 30, 31.
Specifically, each spool 22, 23 has a spool hole 26 provided in the valve block 25.
. It is made to move.

On the back side of each of these spools 22, 23, pressing bodies 30, 31 made of coil springs or the like to counter the movement are provided.
1 opposes the discharge pressure introduced into the spool holes 26, 27, and prevents movement of each of the spools 22, 23 until the discharge pressure exceeds a certain pressure.

Also, the spools 22, 23 by the pressing bodies 30, 31
The pressing forces of the spools 22,
The pressure P2 during high pressure control is set by the pressing bodies 31 corresponding to the respective pressing bodies 30 and 31, and these pressing bodies 30 and 31 adjust the pressing force and set the discharge pressure at which the spools 22 and 23 move to a predetermined value. Pressure adjustment screws 32 and 33 are provided to set the value.

Furthermore, the valve block 25 is connected with control passages 34 and 35 that open when the spools 22 and 23 move, and among these passages 34 and 35, the control passage 34 of the low pressure control spool 22 is connected to the back chamber. The control passage 35 of the high-pressure control spool 23 is communicated with the rear chamber k, and the control passage 35 of the high-pressure control spool 23 is communicated with the front chamber b, and a 4-boat 3-position open center is connected in the middle of the low-pressure side control passage 34 of the control passages 34 and 35. An electromagnetic switching valve 37 is installed, and of the two inlet boats in this switching valve 37, the primary side of the control passage 34 is communicated with the second inlet boat P2, and the first inlet boat P1 is communicated with the discharge line 36. Furthermore, the back chamber k of the pilot plunger 24 is connected to the second outlet boat P4 of the two outlet boats.
Tank line 39 communicating with tank T to exit boat P3
are connected to each other.

Further, the first position of the switching valve 37 is the first inlet boat P1.
and the second exit boat P, and the second entrance boat P.
2 and the first outlet boat P3, the second position is open and all the boats are connected and released to the tank line 39, and the third position is closed between the second inlet boat P2 and the second inlet boat P3. The first entrance boat P1 and the first exit boat P3 are closed off by communicating with the exit boat P4.

Note that this switching valve 37 has three positions and two positions as described above, and the second neutral position may be omitted, but if this second position is provided, it is effective when the tool is idle, for example. No-load operation is possible.

Further, although an electromagnetic switching valve is mainly used as the switching valve 37, a manual switching valve may also be used. When using a 3-position electromagnetic switching valve, solenoids Sl and S2 may be provided on both sides, and when using a 2-position electromagnetic switching valve, one of the solenoids Sl and S2 may be of a spring type.

Further, in FIG. 1, 40 and 41 are tank lines established in the tank T, and the tank line 40 is connected to the spool hole 26.
, 27 secondary sides 26a, 27a, and also tank line 4
1 communicates with the accommodation chambers 30a, 31a of the pressing bodies 30, 31. Next, a description will be given of the operation when performing complex control using the pump having the structure described above.

This composite control is a composite characteristic control in which two pressures and two volumes are automatically obtained by self-pressure, and two pressures and two volumes are obtained by operating the switching valve 37. It can be arbitrarily selected by switching the valve 37.

First, a case will be explained in which automatic two-pressure/two-capacity control is performed using self-pressure.

In this self-pressure control method, the switching pressure between low pressure large capacity and high pressure small capacity is preset by pressure adjusting screws 32 and 33. Therefore, when adopting this self-pressure control method, among the solenoids Sl and S2, the solenoid S1 on the right in Fig. 1 is energized, and the switching valve 37 is set to the position shown in Fig. 1. As a result of this, the low pressure side control passage 34 is directly connected to the rear chamber k of the rear chamber via the stamp valve 37, and the pressure line 38 communicating with the discharge line 36 is closed; In this state, both the pilot plunger 24 and the operation plunger 21 are located at the left end, and in this state, the oblique position 11 is at the maximum inclination angle, and the pump discharge amount is at the maximum.

However, when the main shaft 5 is rotated in the levered state, the piston 8 provided in the cylinder block 7 reciprocates, and fluid is discharged at the maximum flow rate. Flows from the spools 22 and 23 into the pressure lines 28 and 29, and is introduced into the spool holes 26 and 27 of the low pressure and high pressure pressure control valves 25a and 26a, respectively.
These spools 22 are pressed to the right, respectively.
, 23 are pressed to the left by the pressing bodies 30, 31, respectively, so the spools 22, 23 do not move until the discharge pressure reaches a predetermined pressure that overcomes this pressing force. However, as mentioned above, the pressing force of the pressing body 30 is smaller than that of the pressing body 31, so if the discharge pressure from the discharge line 36 overcomes the pressing force of the pressing body 30, the spool 22 will move to the right. , the passage 34 opens, enters the rear chamber k of the rear chamber through the passage 34, moves the operating plunger 21 to the right via the pilot plunger 24, and reduces the inclination angle of the swash plate 11. be.

5. In other words, when the pump is operated at low pressure as shown in curve C shown in FIG. As described above, the spool 22 moves to push the operating plunger 21 to the right side iθ, thereby reducing the inclination angle of the swash plate 11, and the discharge amount becomes Q1 at the discharge pressure P1.

Note that this discharge amount is determined by the stroke of the pilot plunger 24, and the maximum stroke of this plunger 24 is the stroke until the large diameter portion 24a comes into contact with the stepped portion c in the front chamber b of the back chamber 35. be. However, the second
In the C curve shown in the figure, the coordinate R.

, OR2 to the coordinates Rl, PlQ2 shows a state in which the tool interlocked with the actuator is being fed at a speed of 40 to the workpiece, and at this coordinate R1 the tool comes into contact with the workpiece, and the The spool 22 begins to open,
Pressure line 28 is associated with passageway 34. In addition, in the range from the coordinate R1 to the coordinate R2, P''1Q1, the pilot plunger 24 is operated so that the pressure in the passage 34 is lower than the solenoid valve 37.
Since it joins the rear chamber k through , it begins to move together with the operating plunger 21, and the operating plunger 21 finally comes into contact with the step in the front chamber b of the rear chamber at the coordinate R2. Furthermore, in the range from coordinate R2 to coordinate R3, P2Ql,
The tool is still in contact with the workpiece and is waiting until the pressure necessary for machining is reached, and when the tool reaches the coordinate R3 and reaches a pressure state sufficient to machine the workpiece, it begins machining. It will be completed. Also, from coordinate l to coordinate R4,
In the range of P''20, after the machining is completed, the actuator reaches the stroke end, the pressure oil becomes clogged, and the pressure increases, and when the predetermined pressure rises, the spool 23 opens and the pressure line 29 opens. Since it communicates with the passage 35 and is machined on the back side of the operating plunger 21, the plunger 2
1 pushes the swash plate 11 to the neutral position and connects the discharge line 36.
This makes the flow rate zero.

Therefore, the large capacity Q2, small capacity Q1, low pressure P1 and high pressure P2 are adjusted by adjusting the adjusting screws 32 and 33. The opening of the passage 35 forms an orifice between the land of the spool 23 and the spool hole 27, and the pressure is reduced by this orifice.
This reduced pressure acts on the front chamber k of the rear chamber.

However, this reduced pressure is a pressure that only opposes the rotational moment of the swash plate and the spring 13. Therefore, if the orifice opening area increases slightly, the reduced pressure will also increase slightly, but this... The angle of the swash plate 11 is immediately reduced by a force corresponding to the increase, and this effect is instantaneous.

In other words, it functions as a servo machine. That is, the rotational moment of the swash plate 11 is set to take a substantially constant value regardless of the position of the swash plate angle, and the reduced pressure acting on the rear chamber b is caused by this rotational moment and the spring as described above. It is determined by the sum of 13. Therefore, as the swash plate angle becomes smaller, the reduced pressure increases by the compressive force of the spring 13. 04Thus, by repeating the above action, the inclination angle of the swash plate 11 becomes smaller, and finally due to the operation of the spool 23, The inclination angle becomes close to zero, and the discharge amount becomes zero at the discharge pressure Pc.

As described above, according to the operation shown in FIG. 1, the discharge pressure flow rate characteristics shown in the curve C in FIG. can.

In addition, the low pressure P1 and high pressure P in these operations
As mentioned above, 2 can be set arbitrarily. Next, a case will be described in which two-pressure/two-capacity control is performed by operating the directional switching valve, instead of using the self-pressure control described above.

In this case, the above-mentioned switching pressure between low pressure large capacity and high pressure small capacity is arbitrarily selected by switching operation of the switching valve 37, and as described later, for example, the speed of the tool linked to the actuator is adjusted just before the workpiece. This is effective when decelerating the machine to a 1-delay feed and performing machining without impact.
Is the switching of the switching valve 37 performed manually?
Alternatively, the limit switch L provided in the movement path of the tool as shown in FIG.
This is done by operating the electromagnetic switching valve 37 with S.

Thus, in the two-pressure/two-capacity control by this operation, the right solenoid S1 is energized as in the case of the self-pressure control described above, and the switching valve 37 is set to the position shown in FIG.

When the discharge pressure reaches a predetermined pressure, that is, a predetermined pressure that does not reach the pressing force of the pressing body 30, the left solenoid S2 is energized to switch the switching valve 37 to the position shown in FIG. By this switching, the pressure line 38 is communicated with the rear chamber k of the rear chamber through the secondary side 34b of the control passage 34, the discharge pressure is directly introduced into the rear chamber k from the pressure line 38, and the pilot plunger 24 is immediately moved. This movement moves the operating plunger 21 to the right and reduces the angle of inclination of the swash plate 11. In this case, the ax fluid pressure applied to the pilot plunger 24 is applied through an orifice formed between the spool 22 and the passage 34 as the spool 22 moves against the pressing body 30, as shown when the solenoid S1 is energized. Since the pilot plunger 24 and the operating plunger 21 interlocked therewith are applied directly from the discharge line 36 instead of being applied by the force of the spring 13 and the rotational moment of the swash plate, Therefore, the swash plate 11 is set at a predetermined angle. The discharge amount at this time is a small volume Q
1, the tool interlocked with the actuator is retarded and approaches the workpiece, and the tool hits the workpiece without any impact, creating a high pressure P2 and starting machining again. There is a situation where this happens. As described above, since the discharge line 36 is also connected to the spool hole 27 of the pressure control valve 25b for high pressure via the pressure line 29, the spool 23 in the spool hole 27 is prevented from moving. However, the pressing force of the pressing force 31 provided opposite to this spool 23 has a discharge pressure of P2.
The pressure is overcome and the spool 23 is not allowed to move until it reaches .

In this state, if the discharge pressure reaches P2, the spool 2
3 pushes the pressing body 31 and moves to open the passage 35. Therefore, an orifice is formed between the spool hole 27 and the passage 35 at the opening of this passage 35, and the reduced discharge pressure P2 is applied to the front chamber b through this orifice, and the same operation plan as described above is applied. The jar 21 moves to raise the swash plate 11.

As a result, the inclination angle of the swash plate 11 becomes smaller and finally becomes zero, resulting in the discharge amount becoming zero. Therefore, according to the operation described above, the control from low pressure large capacity to high pressure small capacity can be switched at any pressure position, and can be effectively applied to the machining of the above-mentioned workpiece.

Next, an example of application of this operating method will be explained with reference to FIG.

What is shown in FIG. 3 is the rod 5 of the actuator 50.
1, a tool 52 is attached to the tool 52, and this tool 52 is applied to a machine tool that processes a workpiece A.
6 is connected to the actuator 50 via an electromagnetic switching valve 53, and the tool 52 is moved relative to the workpiece A via the actuator 50 by switching the switching valve 53. In this case, the solenoid SO of the electromagnetic switching valve 53
2 and the solenoid S1 of the electromagnetic switching valve 37 are electrically linked.

Then, along the movement path of this tool 52, the workpiece A
A limit switch LS for controlling the switching valve 37 is set near the switch valve 37 so that the tip of the tool 52 is the workpiece A.
The structure is such that the contact point closes when the object approaches the object. Therefore, as an operation program for the tool 52,
To explain the case where the tool 52 is set to be fast fed when it approaches the workpiece, and decelerated and switched to slow feed when it reaches just in front of the workpiece A, the limit switch is connected to the switching valve 37. left solenoid S2
, so that when the switch field is closed, the solenoid S2 is energized. When the operation is started in this manner, the tool 52 is first rapidly fed under low pressure and large capacity as described above, and approaches the workpiece A.
Due to this approach the said limit switch? When the switching valve 37 is closed, the switching valve 37 is switched, and the speed is immediately reduced to slow feed under high pressure and small capacity.

Therefore, the tool 52 contacts the workpiece A without any impact, and then machining begins.

Further, the discharge pressure is further increased by the start of this machining, but when the machining is completed, the high-pressure actuator control valve 25b operates as described above and moves the operation plunger 21, and the discharge amount is zero and the tool 52 is It is held in the completed position. Also, after completing this work, the electromagnetic switching valve 5
3, the tool 52 returns to its original position, but even in this return stroke, its speed can be freely controlled.
That is, the slow feed is performed while the tool 52 is present on the workpiece A, and the fast feed is performed when the tool 52 leaves the workpiece A. This can be easily carried out using the limit switch LS. Further, if rapid feeding is desired throughout the return stroke, the solenoid SO1 of the electromagnetic switching valve 53 and the solenoid S1 of the electromagnetic switching valve 37 may be electrically linked. The operations described above are all two-pressure/two-capacity control, but by operating the switching valve 37, the discharge pressure/flow rate characteristics shown in FIG. 4 can be obtained.

7. In other words, the one shown in FIG. 4 is for performing only the slow feeding of the tool 52 described above with a high pressure and small capacity.

The operation in this case is carried out by switching the switching valve 37 as shown in FIG. It is introduced into the rear chamber k of the rear chamber from the switching valve 37, and the pilot plunger 24 is moved by its discharge pressure. Note that since the discharge pressure increases in accordance with the load, the discharge pressure is low at the beginning of operation, but the rotation moment of the swash plate 11 is required to move the pilot plunger 24 and the operation plunger 21 It is determined according to the sum of the pressure force of the spring 13 and the pressure force of the spring 13, and its value is small, so that the pilot plunger 24 can be moved even if the discharge pressure is low, that is, even if the pressure is caused by piping resistance or the like.

However, if the swash plate 11 is at its maximum inclination at the beginning of operation,
The maximum discharge amount Q2 is instantaneously reached upon the start of operation, but the swash plate 11 is immediately raised by introducing the discharge pressure into the rear chamber k, and the discharge amount is controlled to a small capacity.

Thereafter, as the load increases, the pressure is increased while maintaining the discharge amount Q1, and when this discharge pressure reaches a predetermined pressure, the high pressure control valve 25b operates as described above.
The operating plunger 21 is moved to control the swash plate 11 to the neutral position. Further, the discharge amount of the small capacity explained above is determined by the stroke of the pilot plunger 24 as described above, and a screw is provided in the small diameter portion 24b of this plunger 24, and an adjusting body is screwed into this screw. However, if this adjustment body is brought into contact with the stepped portion c in the back chamber, it is possible to make any changes.

In addition, in each of the embodiments described above, two pressure control valves were provided to achieve two-stage control of low pressure large capacity PlQ2 and high pressure small capacity P2Ql as shown in FIG. Increase the number of valves to two or more and open them sequentially using these pressure control valves! each passage is provided, and each of these passages is communicated with the rear chamber of the operating plunger,
It is also possible to easily implement multi-stage control in which the flow rate of the hydraulic pump is reduced in multiple stages as the pressure increases.

5 Furthermore, although all of the embodiments described above are swash plate type axial piston pumps, the same applies to all other variable displacement piston pumps and variable displacement vane pumps. That is, in this case, the tilting yoke, eccentric ring, or four-cam ring is the variable control element, and the plunger 21 is brought into contact with this variable control element. As described above, the present invention provides an operation plunger 2 for controlling the variable control element 11 to the neutral position.
1 and a pilot plunger 24 for setting the variable control element 11 to a neutral position, these plungers 21, 24 are provided.
This hydraulic pump has a discharge amount variable by adjusting the displacement position of a variable control element 11, and has a first spool 22 at both ends that opposes the pump discharge pressure and a first extrusion body 30, A pressure control valve 25a for low pressure switches the control passage 34 that communicates with the back pressure chamber k of the plunger 24 from the tank line 40 to the discharge line 36 as the pump discharge pressure increases, and a pressure control valve 25a for low pressure that communicates with the pump discharge pressure and a second pressure at both ends. A pressure control valve 25b for high pressure is provided, which has a second spool 23 opposed to the body 31, and switches the back chamber b of the operation plunger 21 into communication from the tank line 40 to the discharge line 36 as the pump discharge pressure increases. On the other hand, in the middle of the control passage 34, a secondary side connected to the back pressure chamber k of the pilot plunger 24 in the control passage 34 is connected to the pressure control valve 25a for low pressure in the control passage 34. By providing a switching valve 37 for switching communication between the primary side and the discharge line 36, two-pressure/two-capacity control of low-pressure large capacity and high-pressure small capacity can be performed.
Pressure/2 volume control is done by simply switching the switching valve 37.
It is possible to freely select between automatic control and control using external force. In other words, when machining a workpiece with a tool, the tool is applied to the workpiece at 0 speed feed, and the discharge pressure increases due to this load or machining load, and then the tool is automatically slowed down by one. There are two cases: when the tool is fed at 1st speed and then the speed is reduced to 7slow feed just before the workpiece, and when the tool is brought into contact with the workpiece without impact. This selection can be easily made simply by operating the switching valve 37. Both the two-pressure/two-volume control using self-pressure control and the two-pressure/two-volume control using operation described above have advantages, and which one is appropriate depends on the size and material of the workpiece. According to the invention, it is possible to select the optimum control method corresponding to these changes, and a pump with high versatility can be provided.

Moreover, according to the present invention, the low pressure and high pressure can be freely determined in the two-pressure/two-capacity control, and the two pressure control valves and the switching valve 37 are used, and the circuit configuration described above is used. Since the control method can be selected between two pressures and two volumes, the structure can be configured without complicating the structure.Furthermore, it can be configured in the low pressure to high pressure range, from low pressure large capacity control to high pressure small capacity control. Since the required horsepower is small, power loss and heat generation are also small, and losses due to relief valves can be eliminated.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view showing an embodiment of the hydraulic pump of the present invention, Fig. 2 is a characteristic diagram of two-pressure/two-capacity control, Fig. 3 is a schematic explanatory drawing showing an application example, and Fig. 4 is a high-pressure and small-pressure pump. Characteristic diagram for capacity,
FIG. 5 is a characteristic diagram in the case of no-load large capacity, FIG. 6 is a characteristic diagram of conventional two-pressure/two-capacity control, and FIGS. 7 and 8 are explanatory diagrams of the conventional example. DESCRIPTION OF SYMBOLS 11... Swash plate, 13... Spring, 21... Operation plunger, 22, 23... Spool, 25a, 25b.
...Pressure control valve, 28, 29...Pressure line, 30,
31... Pressing body, 34, 35... Passage, b... Front chamber, k... Rear chamber, 37... Switching valve.

Claims (1)

[Claims] 1. An operating plunger 21 for controlling the variable control element 11 to a neutral position and a pilot plunger 24 for controlling the variable control element 11 to an intermediate position are provided, and these plungers 21
, 24, the displacement of the variable control element 11 is adjusted to make the discharge amount variable. , a pressure control valve 25a for low pressure that switches the control passage 34 communicating with the back pressure chamber of the pilot plunger 24 to the discharge line 36 from the tank line 40 as the pump discharge pressure increases; It has a second spool 23 that opposes the second pressing body 31,
A pressure control valve 25b for high pressure is provided to switch the back pressure chamber b of the operation plunger 21 from the tank line 40 to the discharge line 36 as the pump discharge pressure increases, and a high pressure control valve 25b is provided in the middle of the control passage 34. The secondary side connected to the back pressure chamber of the pilot plunger 24 in the passage 34 is connected to the pressure control valve 2 for low pressure in the control passage 34.
A variable displacement hydraulic pump characterized in that a switching valve 37 is provided at 5a to switch the connection between the primary side and the discharge line 36.