JPH07233782A - Hydraulic system - Google Patents

Abstract

PURPOSE:To lower load acting on an engine, and lessen the capacity of a relief valve for protecting a hydraulic system by switching the capacity of a pump from a large one to a small one when the pressure of hydraulic oil within a pipeline is in excess of a specified value. CONSTITUTION:A going up and down cylinder 26 is connected to a pump equipped with a control cylinder 19 via a discharge pipe-line 24 and a load switching valve 25. A first control valve 28 is provided halfway to a control passage 27 communicating the discharge pipe line 24 with the first control room R1 of the control cylinder 19 wherein the first control valve switches the pump from its minimum capacity to a great capacity with a control piston advanced. A second control valve 37 is provided, which switches the pump from its great capacity to an intermediate capacity by releasing control oil in a second control room R2, moving a control piston 20 backward halfway, and stopping it when the pressure of the control passage 27 is in excess of a set value due to high loading with respect to a drain passage 27 communicating a second control room R2 within the control cylinder 19 with an oil tank T.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic system which is widely used in various industrial machines, industrial vehicles and the like, and in particular includes a variable displacement swash plate type piston pump equipped with a swash plate tilt angle adjusting mechanism.

[0002]

2. Description of the Related Art As a swash plate type variable displacement piston pump used in a hydraulic system, the applicant of the present application has proposed a minimum displacement starting type which replaces the clutch (off) function. In this pump, an operating piston in a cylinder block that rotates integrally with a rotary shaft reciprocates a distance corresponding to the tilt angle of a swash plate. Further, the working oil is sucked and discharged through the suction port and the discharge port on the valve plate which are in sliding contact with the cylinder block. Further, the tilting angle of the swash plate is always biased by the return spring so as to be minimized. When the control cylinder for changing the inclination angle of the swash plate is operated by the high-pressure control oil introduced from the discharge pipe line, the swash plate is moved in the direction of increasing the inclination angle to maximize the discharge capacity. This pump is a simple switch on and off operation such as cargo handling command,
Substantial capacity control can be achieved. Moreover, with a simple structure, the capacity of the pump can be swiftly switched from the minimum (nearly zero) capacity to the maximum capacity during the switching operation from the unloaded state to the loaded state.

[0003]

In the hydraulic system equipped with the above-mentioned pump, the pressure in the discharge pipe is reduced due to, for example, the engine changing to high speed rotation or the actuator being subjected to an excessive cargo handling load. Even if it becomes abnormally high, the inclination angle of the swash plate is kept at the maximum. For this reason, it is necessary to dispose a relief valve having a large capacity corresponding to the maximum capacity of the piston pump in the discharge conduit. Also, if the pump continues to operate with the maximum capacity and abnormally high pressure, only the leak of hydraulic oil from the relief valve is sufficient, so a large load acts on the engine, and the engine may stop unexpectedly.
There is a problem of shortening the life. In addition,
If the relief pressure of the relief valve is set low so that the engine does not stop, the power of the actuator is also reduced and the cargo handling work is restricted.

Further, in the conventional pump, when the engine speed increases in the cargo handling state, the discharge capacity of the pump increases, so that the amount of oil supplied to the actuator increases and the cargo handling speed changes. There was also a problem.

A first object of the present invention is to solve the above-mentioned problems existing in the prior art, and when a high load acts on the cargo handling actuator so that the pressure of the hydraulic oil in the discharge pipe becomes equal to or higher than a set value. In addition, the capacity of the pump is switched from a large capacity to an intermediate capacity to continue the cargo handling work, the load on the power source is suppressed, its abnormal stop is prevented, and the durability of the power source can be improved. An object of the present invention is to provide a hydraulic system capable of reducing the valve capacity.

A second object of the present invention is, in addition to the first object, to provide a hydraulic system capable of maintaining the speed of cargo handling work substantially constant when the rotational speed of the pump increases. Especially.

[0007]

The invention according to claim 1 is
Return means for urging the swash plate to a minimum tilt angle equal to zero capacity,
A variable displacement type swash plate type piston pump provided with a control cylinder that opposes this in a direction to increase the inclination angle of the swash plate to increase the capacity, and to the pump via a discharge pipe line and a cargo handling switching valve. An actuator for cargo handling that is connected with the control passage for communicating the discharge pipeline with the control chamber of the control cylinder to supply control oil from the discharge pipeline into the control chamber;
A drain passage communicating between the control chamber of the control cylinder and the low pressure chamber side, and the control passage is interposed in the middle of the control passage, and when the pressure in the discharge pipeline becomes equal to or higher than the first set value, the control passage is moved to the low pressure chamber side. The first control valve for switching the communication from the communicating drain port to the connecting port, supplying control oil from the control passage to the control cylinder to advance the control piston, and switching the pump from the small capacity to the large capacity, and the drain passage. When the pressure in the discharge pipe line becomes equal to or higher than the second set value which is higher than the first set value, the drain passage is switched from the closed port to the connection port to discharge the control oil in the control chamber and control it. A second control valve that retracts the piston and reduces the pump capacity,
The second control valve is operated, and the control piston is provided with an intermediate position restricting means for holding the control piston at an intermediate position while retracting.

Further, in the invention according to claim 2, in claim 1, the first control valve is a first pressure sensing chamber for sensing the pressure in the discharge pipe line, and the pressure in this pressure sensing chamber is a first set value. In the case of the above, it is constituted by the first spool valve that switches the control passage from the drain port to the connection port against the biasing force of the first spring, and the second control valve senses the pressure in the discharge pipeline. It is composed of a second pressure sensing chamber and a second spool valve that opens the drain passage against the biasing force of the second spring when the pressure in the pressure sensing chamber becomes equal to or higher than the second set value. .

According to a third aspect of the present invention, in the second aspect, the first and second spool valves are integrally formed, and the first pressure sensing chamber and the second pressure sensing chamber are combined into one pressure sensing chamber. The first spring and the second spring are housed in one low pressure chamber.

Further, in the invention according to claim 4, in claim 2 or 3, the intermediate position regulating means of the control piston is configured such that the control chamber side opening of the drain passage is opened at an intermediate position of the inner peripheral surface of the control chamber. The opening is closed by the outer peripheral surface of the piston while the control piston is being retracted to prevent the control piston from moving backward.

Further, the invention of claim 5 is the same as claim 1.
In any one of 4 to 4, the discharge pipe is provided with a throttle, and the control passage detects the pressure difference before and after the throttle, and when the differential pressure increases, the amount of control oil supplied to the control chamber is increased. A reducing third control valve is provided.

Further, the invention according to claim 6 is the same as claim 5.
In the third control valve, when the pressure difference between the pressure sensing chamber that senses the pressure on the front side of the throttle and the pressure sensing chamber that senses the pressure on the rear side of the throttle increases in the discharge pipe, And a third spool valve that reduces the passage area of the control passage against the biasing force of.

[0013]

According to the first aspect of the present invention, when the cargo handling actuator in which the cargo handling switching valve is switched to the non-cargo handling position is at rest, the hydraulic oil having a capacity equal to zero capacity is discharged from the discharge pipeline to the cargo handling switching valve even when the pump is driven. It is returned to the oil tank through the drain passage. For this reason, there is almost no increase in the pressure in the discharge pipe communicating with the oil tank, and the pressures in the control passage and the control chamber of the control cylinder are maintained at substantially atmospheric pressure. The swash plate replaces the clutch (off) function by maintaining a minimum tilt angle (about 0.1 to 4 °) equal to zero capacity by the returning means.

When the cargo handling switching valve is switched from the non-cargo handling position to the cargo handling position, the drain passage of the cargo handling switching valve is closed, so that the load in the cargo handling actuator causes a small amount of pressure in the discharge pipe from the pump to operate. Raised by oil.

When the pressure in the discharge line exceeds the first set value, the first control valve is switched from the drain port to the connection port. Therefore, the control oil is supplied from the discharge pipe line to the control chamber of the control cylinder through the control passage, and is pushed in the direction in which the tilt angle of the swash plate increases as the control piston advances. Therefore, the pump shifts from the minimum capacity equal to zero to the normal operation of the maximum capacity when the rising swash plate reaches the maximum tilt angle. By the steady operation of the pump, hydraulic oil is supplied to the cargo handling actuator to operate the actuator.

When the pressure of the hydraulic oil in the discharge pipe becomes equal to or higher than the second set value due to the stroke end of the cargo handling actuator during the cargo handling work of the actuator, the second control valve is switched from the closed port to the connection port. As a result, the control oil in the control chamber is discharged to the low pressure chamber side through the drain passage. Therefore, the control piston is retracted, the swash plate is moved by the returning means in the direction of decreasing the tilt angle, and the capacity of the pump is reduced. When the means for holding the control piston in the intermediate position is operated during the capacity reducing operation, the control piston is held in the intermediate position, the pump is held in the intermediate capacity operation, and the cargo handling work is continued.

When the pressure of the hydraulic oil in the discharge pipe line becomes equal to or lower than the second set value, the second control valve is switched from the connection port of the drain passage to the closed port. Hydraulic oil pressure is first
Above the set value, the first control valve is held in the connection port, so that the oil in the discharge pipe is supplied to the control chamber through the control passage to move the control piston in the direction to increase the tilt angle of the swash plate, and the pump operates. Switching to large capacity operation again.

When the cargo handling switching valve is switched to the non-cargo handling position, the pressure in the discharge pipe line falls below the first set value, and the first control valve is switched from the connection port to the drain port.
The oil in the control chamber is discharged to the low pressure chamber side, the swash plate is shifted to the minimum tilt angle, and the pump is switched to the minimum capacity operation.

According to the first aspect of the invention, the pump is switched from the large capacity operation to the intermediate capacity operation when the pressure of the hydraulic oil in the discharge pipeline becomes equal to or higher than the second set value. The capacity of the provided relief valve can be reduced. Further, since an abnormally high load does not act on the power source such as the engine, the power source can be prevented from being inadvertently stopped and the maximum power of the pump can be reduced.

According to the second aspect of the invention, when the pressure in the first pressure sensing chamber exceeds the first set value, the first spool valve resists the biasing force of the first spring and the first control valve causes the drain to drain. You can switch from a port to a connection port. Therefore, pressure oil is supplied from the control passage to the control chamber, and the pump is switched from the minimum capacity to the large capacity. When the pressure in the second pressure sensing chamber exceeds the second set value, the second spool valve opens the drain passage against the biasing force of the second spring. Therefore, the control oil in the control chamber is discharged from the drain passage to the low pressure chamber side, the control piston is retracted, and the capacity of the pump is reduced. In the present invention, the configurations of the first and second control valves can be simplified.

In the invention according to claim 3, since the first and second spool valves are integrally formed, the structure of the first and second control valves is simplified as compared with the invention according to claim 2. can do.

Further, when the second control valve is switched to the position for opening the drain passage, the control piston is moved to the intermediate position. Therefore, the control chamber side opening of the drain passage is closed by the outer peripheral surface of the control piston, and the control oil is prevented from flowing out. As a result, the backward movement of the piston is stopped, the swash plate is held at an intermediate tilt angle,
The pump operates at medium capacity. Since the first control valve is held at the connection port, oil is supplied to the control chamber and the control piston moves forward, but since oil is discharged from the drain passage, the position of the piston is almost constant. Held in position.

According to the fourth aspect of the invention, the means for holding the control piston at the intermediate position can be simplified by setting the opening position of the drain passage to a specific position.
Further, in the invention of claim 5, when the engine speed is increased and the discharge capacity of the pump is increased, the pressure difference before and after the throttle provided in the discharge pipe line is increased. Therefore, the amount of control oil supplied from the control passage to the control chamber is reduced by the third control valve, the control piston is retracted, the tilt angle of the swash plate is reduced, and the discharge capacity is reduced. Therefore, when the engine speed fluctuates, the displacement of the pump is kept almost constant,
The loading / unloading speed of the actuator becomes almost constant.

Further, in the invention according to claim 6, when the pressure difference between before and after the throttle in the discharge conduit increases, the third spool valve reduces the passage area of the control passage against the biasing force of the third spring. . According to the present invention, the configuration of the third control valve can be simplified.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a hydraulic system in which the present invention is applied to an industrial vehicle will be described below with reference to FIGS.

FIG. 4 shows a variable displacement hydraulic pump driven by an engine. A swash plate type piston pump is used as this pump, and a front housing 2 is joined and fixed to the front (left) end surface of the center housing 1. A rear end cover 3 is joined and fixed to the rear (right) end surface of the center housing 1, and a crank chamber 4 is formed inside them. The front housing 2
A rotary shaft 5 is supported by bearings 6 and 7 between the opposite end walls of the rear end cover 3 and the rear end cover 3, and its outer end is connected to a power take-off device (PTO) (not shown) so that it can be directly rotated by the engine. Has become.

A cylinder block 8 is connected to the rotary shaft 5 by spline fitting so that the cylinder block 8 can rotate synchronously.
A plurality of cylinder bores 9 are formed in the cylinder block 8 in parallel with the rotary shaft 5. A piston 12 moored to a swash plate 11 via a shoe 10 and a retainer 10A is housed in each of the cylinder bores 9 so as to be capable of reciprocating. The swash plate 11 is supported by the front housing 2 by an unillustrated shaft pin so that the tilt angle can be changed.
Further, the bore 9 in the cylinder block 8 that rotates integrally with the rotating shaft 5 is alternately communicated with the arc-shaped suction port 14 and discharge port 15 that are provided through the valve plate 13. As a result, the hydraulic oil is sucked into the cylinder bore 9 from the suction port 14, and the hydraulic oil in the cylinder bore 9 is discharged from the discharge port 15. A suction passage 16 and a discharge passage 17 that communicate with the suction port 14 and the discharge port 15 are formed in the rear end cover 3.

The swash plate 11 is always urged by a return spring 18 as a returning means to a direction in which the tilt angle is displaced to a minimum tilt angle (about 0.1 to 4 °) equal to zero capacity, that is, a minimum capacity position. There is. A control cylinder 19 is supported by the rear end cover 3 in a cantilever manner, and a control piston 20 is housed in the cylinder 19 so as to be reciprocable in the same direction in parallel with the rotary shaft 5. The control piston 20
The tip end surface of the piston pushes the swash plate 11 so as to increase the inclination angle of the swash plate 11 against the biasing force of the return spring 18, thereby changing the stroke of the piston 12 and changing the discharge capacity. adjust. Therefore, since the control chambers R1 and R2 in the control cylinder 19 are at atmospheric pressure when the hydraulic circuit is stopped, the control piston 20 moves to the most retracted position via the swash plate 11 by the urging force of the return spring 18. Be stopped. Therefore, the swash plate 11 is biased and held at the minimum tilt position, that is, the minimum capacity position in FIG. The stopper 2a formed on the front housing 2 regulates the maximum tilt angle of the swash plate 11.

Further, the valve housing 2 is provided on the side surface of the rear end cover 3 of the variable displacement pump 21 configured as described above.
2 is bonded and fixed. The suction passage 16 is connected to an oil tank T as a low pressure chamber via a suction pipe line 23. A discharge conduit 24 is connected to the discharge passage 22 a of the valve housing 22 that communicates with the discharge passage 17. An elevating cylinder 26 as a cargo handling actuator is connected to the discharge conduit 24 via a cargo handling switching valve 25. A relief valve V for protecting the hydraulic circuit is provided in the middle of the discharge pipe line 24.

As shown in FIG. 1, the control cylinder 19
A large-diameter inner peripheral surface 19a slidingly contacting the outer peripheral surface 20a of the control piston 20 and a valve hole 19b having a smaller diameter than the inner peripheral surface.
And a housing hole 19c having a larger diameter than the valve hole 19b are formed in series. A rod portion 20b having a diameter smaller than that of the valve hole 19b is formed at the inner end of the control piston 20. The valve hole 19 is provided at the end of the rod portion 20b.
A valve portion 20c having the same diameter as b is integrally formed. Further, a first control chamber R1 is formed inside the accommodation hole 19c of the control cylinder 19, and a second control chamber R2 is formed between the inner end face of the control piston 20 and the inner bottom face of the control cylinder 19. Both control chambers R1 and R2 have the valve hole 19
b formed between b and the outer peripheral surface of the rod portion 20b
The control chambers R1 and R2 are shut off with the valve portion 20c fitted in the valve hole 19b.

The discharge passage 22a formed in the valve housing 22 and the first control chamber R1 of the control cylinder 19 communicate with each other by the control passage 27 formed in the housing 22 and the rear end cover 3. The first control valve 2 for controlling the discharge capacity of the pump 21 is provided in the middle of the control passage 27.
8 are interposed. Further, the second control chamber R2 and the suction passage 16 (shown as an oil tank T in FIGS. 1 to 3) serving as a low pressure chamber are communicated with each other by a drain passage 29 formed in the control cylinder 19, the rear end cover 3 and the valve housing 22. There is. A second control valve 37 that controls the discharge capacity of the pump 21 is disposed in the middle of the drain passage 29.

As shown in FIG. 1, the first control valve 28 is a first spool valve which is reciprocally accommodated in a first spool accommodating chamber 30A formed in the control passage 27 in the valve housing 22. Has 31. A first drain port 32 is formed in the first spool valve 31 to connect the control passage 27 to the oil tank T. An annular first connection port 33 is formed on the right side of the first spool valve 31. The first spool valve 31 is always biased by the first spring 34 to a position where the control passage 27 communicates with the first drain port 32. Further, the first pressure-sensitive chamber 35 defined by the right end surface of the first spool valve 31 and the bottom surface of one side of the first spool accommodating chamber 30A has the first pilot passage 27.
It is communicated with the discharge conduit 24 by a. First spring 34
The first low-pressure chamber 36 that accommodates the oil is communicated with the first drain port 32 and the oil tank T.

Therefore, when the pressure Pc of the control passage 27 acting on the first pressure sensing chamber 35 by the first pilot passage 27a becomes larger than the first set value P _C1 , the first spring 34
The first spool valve 31 is switched from the first drain port 32 to the first connection port 33 against the urging force of. The pressure Pc of the control oil in the control passage 27 is determined by the discharge pipe line 24.
Is equal to or lower than the pressure of the hydraulic oil by the flow path resistance of the control passage 27.

The second control valve 37 includes a valve housing 22.
Inside, there is a second spool valve 38 that is reciprocally accommodated in a second spool accommodating chamber 30B formed in the middle of the drain passage 29. In the second spool valve 38, the second connection port 39 having a throttle 39a for communicating the second control chamber R2 and the control passage 27, and the communication between the control passage 27 and the second control chamber R2 are cut off, and A second drain port 40 that connects the control chamber R2 and the oil tank T is formed. Further, the second spool valve 38 is always biased by the second spring 41 to the position where the second drain port 40 is closed. The second pressure sensing chamber 42 defined by the lower end surface of the second spool valve 38 and the bottom portion of the second spool accommodating chamber 30B is connected to the control passage 27 by the second pilot passage 27b. The second low-pressure chamber 43 that houses the second spring 41 is communicated with the oil tank T.

Therefore, when the pressure Pc of the control passage 27 acting on the second pressure sensing chamber 42 through the second pilot passage 27b becomes equal to or higher than the second set value P _C2 , the urging force of the second spring 41 is resisted. The second spool valve 38 and the second connection port 39
To the second drain port 40, the oil in the second control chamber R2 can be discharged from the drain passage 29 to the oil tank T.

The opening 29a of the drain passage 29 on the side of the second control chamber R2 is set in the middle of the inner peripheral surface 19a of the control cylinder 19, that is, at the intermediate position of the reciprocating stroke of the control piston 20, as shown in FIG. ing. This setting constitutes the intermediate position regulating means K of the control piston 20. During the backward movement of the control piston 20, the opening 29a is closed by the outer peripheral surface 20a of the piston 20 to prevent the control oil in the second control chamber R2 from being discharged through the drain passage 29, so that the control piston 20 is moved to the intermediate position. It is possible to stop at. This operation will be described later.

The relief valve V provided in the discharge conduit 24 is operated when the second set value P _C2 of the second control valve 37 is slightly higher than the second set value P _C3 to protect the hydraulic circuit. To do. Next, the operation of the hydraulic system configured as described above will be described.

In the inoperative state of the hydraulic system with the engine stopped, the pressure in the crank chamber 4 of the pump 21 shown in FIG. 4 and the discharge passage 17, the first and second control chambers R1 and R2 are shown.
The internal pressure is atmospheric pressure. Therefore, the return spring 18 holds the swash plate 11 at a position where the inclination angle is the minimum. Further, in the same state, the spool valve 31 of the first control valve 28 is held in the first drain port 32 by the first spring 34 as shown in FIG. Further, the second spool valve 38 of the second control valve 37 is held in the second connection port 39 by the second spring 41, and the cargo handling switching valve 25 is held in the non-charging position (drain port).

When the engine is started in this stopped state,
The rotary shaft 5 of the pump 21 is rotated via the power take-out device. Therefore, the pump 21 is started in the minimum capacity state in which the discharge oil amount is equal to zero as shown in FIG. At this time, a small amount of oil is supplied to the discharge pipe line 24 and the control passage 27, but since the control passage 27 communicates with the oil tank T through the first drain port 32 of the first control valve 28, the control passage 27
Therefore, the control oil is not supplied into the first control chamber R1 of the control cylinder 19. Therefore, the pump 21 continues to operate with only a small amount of oil discharged in the zero capacity state, and substitutes the function of the clutch (off).

Now, in this zero capacity / non-loading state, the loading / unloading switching valve 25 is switched to the loading / unloading position and the discharge conduit 24 is opened.
When a very small amount of hydraulic oil corresponding to almost zero capacity of the pump is supplied to the lifting cylinder 26 from the above, the pressure in the discharge pipe line 24 increases. Then, when the control pressure Pc acting on the first pressure sensitive chamber 35 through the first pilot passage 27a becomes equal to or higher than the first set value P _C1 , the first spool valve 31 causes the first spring 3 to move.
Moved against the force of 4. Therefore, the first spool valve 31 is switched from the first drain port 32 to the first connection port 33 as shown in FIG. Then, the control oil is supplied from the control passage 27 to the first control chamber R1 of the control cylinder 19, and is also supplied to the second control chamber R2 through the gap g. Therefore, the control piston 20 is advanced, the tilt angle of the swash plate 11 is increased, the discharge capacity of the pump 21 is increased, and the discharge pressure is rapidly increased. As a result, the hydraulic oil of high pressure Ph is supplied from the discharge pipe line 24 to the lifting cylinder 26, and the lifting cylinder 26 performs the lifting cargo handling work.

During the forward movement of the control piston 20, the valve portion 20c is fitted into the valve hole 19b so that both control chambers R
The communication due to the gap g between 1 and R2 is blocked. In synchronization with this, the opening 29a formed by the outer peripheral surface 20a of the control piston 20
Is closed and the second control valve 37 is held in the second connection port 39, the second pilot passage 27
b through the drain passage 29 and the control oil to the second control chamber R2
Is supplied to. As a result, the control piston 20 continues the forward movement until the stroke end. In the state shown in FIG. 2, the swash plate 11 shown in FIG. 4 is held at the maximum inclination angle in contact with the stopper 2a.

Then, for example, when the lifting cylinder 26 is moved to the stroke end, or when a very large load acts on the cylinder 26, the pressure of the hydraulic oil in the discharge pipe line 24 causes the second set value P shown in FIG. Cross _C2 . Then,
High-pressure control oil acts on the inside of the second pressure-sensitive chamber 42 of the second control valve 37 through the control passage 27 and the second pilot passage 27b. Since the second connection port 39 has the throttle 39a, the second spool valve 38 is moved against the urging force of the second spring 41 in FIG. 2, and the second spool valve 38 moves from the second connection port 39 to the second drain port 39. Switched to port 40, Figure 3
The second control chamber R2 communicates with the oil tank T through the drain passage 29 as shown in FIG.

Therefore, since the control oil in the second control chamber R2 is returned to the oil tank T through the drain passage 29, the control piston 20 is retracted by the return spring 18 together with the swash plate 11. When the control piston 20 is moved to the intermediate position of its stroke as shown in FIG. 3, the opening 29a of the drain passage 29 is closed by the outer peripheral surface 20a of the piston 20. Then, the drainage of the control oil through the drain passage 29 is blocked, the control piston 20 is stopped at the intermediate position, and the pump 21 is operated at the intermediate capacity.

Since the first control valve 28 is held in the connection port 33, oil is supplied from the control passage 27 to the first control chamber R1, and the control piston 20 moves forward against the urging force of the return spring 18. . However, when the opening 29a is opened,
Since the pressure in the second control chamber R2 drops, the piston 20
Is set back. The piston 20 is repeatedly moved back and forth, and the piston 20 is held at a position substantially corresponding to the opening 29a as shown in FIG.

[0045] is reduced cargo handling load, when the circuit pressure falls below a second set value P _C2, the second pressure sensing chamber 42 from the control passage 27 through the second pilot passage 27b second set value P _C2 following intermediate pressure Pn acts. Therefore, the second spool valve 38 is switched from the state shown in FIG. 3 to the second connection port 39 shown in FIG. 2 by the second spring 41, and the second control chamber R
The pressure of 2 rises due to the pressure oil from the port 39 and the drain passage 29 and the leakage pressure oil from the first control chamber R1, and the control piston 20 moves forward by the hydraulic pressure of both chambers R1 and R2 to reach the maximum capacity again. .

The gap g of the valve portion 20c is closed from the maximum capacity to the intermediate capacity, and when the second control valve 37 is switched to the second drain port 40, the pressure in the second control chamber R2 is quickly increased. Helps lower and improve capacity responsiveness.

When the cargo handling switching valve 25 is switched to the non-cargo handling position in the state shown in FIG. 3, the pressure in the discharge pipe line 24 is changed to that shown in FIG.
As indicated by the chain line H, the first set value P _C1 or less,
The first control valve 28 is switched to the first drain port 32. Therefore, the control oil in the first control chamber R1 and the second control chamber R2 is discharged to the oil tank T, and the control piston 20 and the second control chamber R2 are discharged.
The spool 38 of the control valve 37 is returned to the original position shown in FIG. 1, the swash plate 11 is displaced to the tilted position of almost zero displacement, and the pump 21 shifts to zero displacement operation (see the chain line H ′ in FIG. 5).

When the pump 21 shown in FIG. 2 is in a large-capacity operating state, for example, when the lifting cylinder 26 is at the stroke end and the cargo handling switching valve 25 is still held at the cargo handling position, the chain line I in FIG. As shown by, the pressure Pc of the control oil rises above the third set value P _C3 . At this time, as described above, after the pump 21 is switched to the intermediate capacity operation, the relief valve V that has been closed due to the abnormally high pressure in the discharge pipe line 24 is opened, and the pressure in the discharge pipe line 24 is further increased. Is blocked and the hydraulic circuit is protected.

In the first embodiment, the second control valve 37 is provided in the middle of the drain passage 29, and when the pressure Pc in the control passage 27 reaches the second set value P _C2 , the second spool valve 38 is set to the second spool valve 38. It can be switched to the drain port 40. Therefore, the pump 21 is switched from the large capacity operation to the intermediate capacity operation, the load acting on the engine is reduced, and the inadvertent stoppage thereof is prevented. In addition, if the lifting cylinder 26 is in the middle of the cargo handling work, the work can be continued although the work speed is reduced. Further, when the lifting cylinder 26 is at the stroke end, the hydraulic oil leaks from the relief valve V to the oil tank, but compared with the pump 21 leaking during operation at maximum capacity operation, Power can be reduced. Further, since the relief valve V is operated only when the pump 21 operates at the intermediate capacity, the capacity of the relief valve V can be reduced according to the intermediate capacity.

Next, a second embodiment of the present invention will be described with reference to FIGS.
It will be described based on. In the second embodiment, the above-mentioned first
In the embodiment, the first control valve 28 and the second control valve 37 are united. As shown in FIG. 6, a united spool valve 51 is reciprocally accommodated in a spool accommodating chamber 30c formed in the valve housing 22. The spool valve 51 is provided with a first connection port 33 of the control passage 27, a first drain port 32 (also serving as the second drain port 40), and a second connection port 39. The first spring 34, the spring receiver 52, and the second spring 4 are provided at the left end of the spool valve 51.
1 is interposed. Furthermore, the first low-pressure chamber 36 and the second low-pressure chamber 43 that accommodate both springs 34 and 41 are communicated with the first (2) drain port 32 (40) and the oil tank T. Pressure sensing chamber 5 in which the first and second pressure sensing chambers 35 and 42 formed on the right end surface side of the spool valve 51 are combined
Control oil is supplied to 3 from a pilot passage 27c, which is a combination of the first and second pilot passages 27a and 27b.

Therefore, as shown in FIG. 6, the spool valve 51
Is the first (2) drain port 32 with respect to the control passage 27
When the cargo handling switching valve 25 is switched to the cargo handling position while being held at (40) and the pump 21 is in the zero capacity state, control oil is supplied from the pilot passage 27c to the pressure sensing chamber 53. Thereafter, when the pressure Pc of the control oil reaches the first set value P _C1 , the spool valve 51 moves to the first set value P _C1 as shown in FIG.
It is moved against the biasing force of the spring 34, and the first connection port 3
Switched to 3. At the same time, the second control room R2 has the passage 2
9, communicating with the pressure sensitive chamber 53 by the second connection port 39,
Therefore, the control oil is supplied from the control passage 27 and the drain passage 29 into the first control chamber R1 and the second control chamber R2, and the pump 21 is switched from the zero capacity operation to the large capacity operation.

When the elevating cylinder 26 is operated, for example, to the stroke end during the large capacity operation of the pump 21,
The pressure of the hydraulic oil in the discharge pipe line 24 exceeds the second set value P _C2 . Then, the pressure is supplied to the pressure sensing chamber 53 from the pilot passage 27c. A throttle 39 for the second connection port 39
Since a is provided, the spool valve 51 is moved against the urging force of the second spring 41, as shown in FIG. 8, and is switched from the second connection port 39 to the drain passage 29. Therefore, the oil in the second control chamber R2 is discharged from the drain passage 29 and the drain port 32 to the oil tank through the first and second low pressure chambers 36 and 43, and the pump 21 is switched from the large capacity to the intermediate capacity.

In the second embodiment, since the first and second control valves 28 and 37 are mainly constituted by the common spool valve 51, the structure is simplified and the manufacturing cost is reduced as compared with the first embodiment. can do. The rest of the configuration and effects are similar to those of the first embodiment.

Next, a third embodiment of the present invention will be described with reference to FIGS.
It will be described based on 5. The structure of the pump 21 used in the third embodiment is shown in FIG. FIG. 9 shows the maximum tilt angle of the swash plate 11, but an adjustment bolt 54 for regulating the position of the right end surface of the piston 20 and adjusting the minimum tilt angle is screwed into the rear end cover 3. 55 is bolt 5
4 fixing nut. The other configuration of the pump 21 is the first
It is similar to the embodiment.

Since the first and second control valves 28 and 37 provided in the rear end cover 3 are combined in substantially the same manner as the control valves 28 and 37 of the second embodiment described above, different configurations will be described. .

As shown in FIG. 10, the first and second springs 3
The right ends of 4, 41 are supported by a fixed spring receiver 56, and the biasing force of the springs 34, 41 can be adjusted by an adjusting bolt 57 screwed into the valve housing 22 to change the opening / closing timing of the spool valve 51. 58 is bolt 5
7 is a fixing nut. Further, in the third embodiment, the drain passage 29 is connected to the drain groove 29b having an annular groove formed on the inner peripheral surface of the spool accommodating chamber 30C. Due to the movement of the spool valve 51, at the position where the first drain port 32 corresponds to the drain port 29b, the second control chamber R
2 is connected to the oil tank T through the drain passage 29. In the third embodiment, the second connection port 39 having the throttle 39a provided on the spool 51 in the second embodiment is omitted.

As shown in the hydraulic circuit of FIG. 12, a fixed throttle 59 is provided in the middle of the discharge pipe 24.
The discharge pressure P _{d1 on} the front side of 9 acts on the pressure sensitive chamber 53 through the pilot passage 27c, and the discharge pressure P _d2 on the rear side of the throttle 59 acts on the first control chamber R1 through the control passage 27.

In the third embodiment, the pressure difference between the discharge pressures P _d1 and P _d2 before and after the throttle 59 is detected to detect the first pressure from the control passage 27.
A third control valve 60 for adjusting the control oil pressure supplied to the control chamber R1 and controlling the discharge capacity to a constant value when the engine speed increases is provided in the middle of the control passage 27.

The control valve 60 will be described with reference to FIG. 10. In the spool housing chamber 30D provided in the rear end cover 3 and the valve housing 22, a third spool valve 61 is reciprocally housed. This spool valve 61 has a throttle 59
It has a port 62 for connecting the control passage 27 connected to the rear discharge pipe line 24B. Further, the spool valve 61 is biased by a spring 63 in a direction to hold the connection port 62. Further, the spool valve 61 has a drain port 6
4 is formed and communicates with the oil tank T through the drain passage 65. The discharge pressure P _d1 is introduced into the pressure sensitive chamber 66 formed on the left end surface side of the spool valve 61 from the discharge conduit 24A on the front side of the throttle 59 through the pilot passage 67. Then, the pressure of the pressure sensitive chamber 68 accommodating the spring 63 and the spring 6
The spool valve 61 is reciprocated by the difference between the resultant force of the urging forces of No. 3 and the pressure of the pressure sensing chamber 66, and the capacity control as described later is performed.

Next, the operation of the hydraulic system according to the third embodiment described above will be described. 10 and 12 show the pump 2
1 is operated in the minimum capacity state, the spool valve 51 closes the control passage 27, and the first (2) drain port 3
2 (40) communicates with the first control chamber R1 via the control passage 27. Further, the spool valve 51 is held at a position to close the drain passage 29, and the third control valve 60 is held in the control passage 2
7 and the drain port 64 is closed.

When the rotational speed of the pump 21 increases in the minimum capacity operation of the pump 21 in the non-load handling state, the discharge volume (flow rate) of the pump gradually increases as shown by the broken line in FIG. In the minimum capacity state, the cargo handling switching valve 25 shown in FIG.
Is switched from the non-loading position to the loading position, the pressure P _{d1 on the} front side of the throttle 59 in the discharge conduit 24 rises, and the pressure oil is supplied from the pilot passage 27c to the pressure sensing chamber 53.
The spool valve 51 is moved against the biasing force of the first spring 34. Then, the spool valve 51 becomes the first drain port 32.
To the first connection port 33, pressure oil is supplied to the first control chamber R1 from the discharge conduit 24B on the rear side of the throttle 59 through the control passage 27, and the tilt angle of the swash plate 11 is increased by the forward movement of the piston 20. The pump 21 operates in a large capacity. (See FIGS. 9 and 13) In the large-capacity operating state of the pump 21 shown in FIG. 13, for example, when the engine speed increases and the discharge capacity of the pump 21 increases, the discharge pressures P _d1 and P _d before and after the throttle 59 are increased. The difference in _d2 increases. Therefore, the spool 61 of the third control valve 60 is moved to the side that reduces the opening degree of the control passage 27 against the biasing force of the spring 63. Then, the hydraulic pressure supplied from the control passage 27 to the first control chamber R1 decreases, the piston 20 retracts, and the discharge capacity of the pump 21 decreases. As a result, even if the rotation speed of the pump rises above the set rotation speed, the pump 21
The discharge capacity Q of is maintained substantially constant as shown in FIG. In FIG. 15, T1 shows the mode of increase of the discharge capacity Q in the process of increasing the rotation speed n of the pump when the cargo handling load is small and the discharge pressure of the pump 21 is low. When the rotation speed n reaches the set rotation speed n1, the capacity Q becomes constant as indicated by T2.

Further, when the elevating cylinder 26 reaches, for example, the stroke end while the pump 21 is operating with a large capacity, the pressure P _d in the discharge pipe line 24 rises abnormally, so that the spool valve 51 shown in FIG. And, as shown in FIG. 14, the control passage 27 is closed and switched to the first drain port 32 connecting the drain passage 29.
The control oil in 2 is returned to the oil tank T through the drain passage 29. Therefore, the control piston 20 is retracted until the opening 29a is closed, the discharge capacity of the pump 21 is reduced to an intermediate capacity, and an excessive load on the engine is prevented. When the piston 20 is retracted, the oil in the first control chamber R1 flows into the second control chamber R2 through the gap on the outer peripheral surface side of the rod portion 20b, so that the piston can be retracted. Further, when the cargo handling load is large and the pressure in the discharge conduit 24 is high, a high pressure is applied to the pressure sensing chamber 53, so that the control passage 27 before and after the spool valve 51 as shown in FIG.
Is closed, but some pressure is supplied to the control passage 27 through the clearance on the outer circumference of the spool valve 51. If the rotation speed of the pump 21 increases in this state, the third
Since the control valve 60 operates independently, the spool valve 61 is switched to the drain port 64 by the increase in the differential pressure before and after the throttle 59, and the pressure in the control passage 27 'between the spool valves 51 and 61 decreases. At this time, since there is a clearance C between the inner peripheral surface of the spool accommodating chamber 30c and the outer peripheral surface of the spool valve 51, the control pressure oil in the first control chamber R1 is controlled by the control passage 27, the first connection port 33, and the clear run. It is led to the control passage 27 'between the spool valves 51 and 61 through C. Therefore, the pressure in the control chamber R1 gradually decreases, the inclination angle of the swash plate 11 decreases, and the discharge capacity of the pump decreases.

On the other hand, when the rotation speed of the hydraulic pump 21 is reduced while the pressure in the discharge pipe 24 is high, the differential pressure before and after the throttle 59 becomes small, and the spool valve 61 is connected to the connection port 62.
Is switched to. Therefore, the pressure oil is supplied from the discharge conduit 24A to the first control chamber R1 through the control passage 27 and the clear run C, and the discharge capacity of the pump 21 is increased.

Since the above-described operation is repeated, the discharge capacity is controlled to be substantially constant even if the rotation speed of the pump 21 increases under high pressure. In FIG. 15, T3 indicates a mode in which the discharge capacity Q increases in the process of increasing the pump rotation speed n when the cargo handling load is large and the discharge pressure of the pump 21 is high. When the rotation speed n reaches the set rotation speed n2, the flow rate Q becomes constant as shown at T4. However, the first control room R1
The control oil inside is leaked through the clearance C,
Since the pressure oil is also supplied into the control chamber R1 via the clearance C, the response of the constant volume control is low and slower than that of the constant volume control at medium pressure.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In this embodiment, in the first embodiment,
Connection point J between control passage 27 and second pilot passage 27b
27e in the control passage 27d from the first control room R1 to the first control room R1
Is provided. Also, the rod portion 20b of the control piston 20
And the valve section 20c are omitted, and the first and second control chambers R1,
It has a structure in which R2 is one control room R. Other configurations are similar to those of the first embodiment.

In the fourth embodiment, when the pump is operating at maximum capacity, the pressure in the discharge conduit 24 rises abnormally, and the pressure in the second pressure sensing chamber 42 causes the second control valve 37 to connect to the connection port 39.
To the drain port 40. Then, since the control passage 27 has the throttle 27e, the pressure oil is slowly supplied to the control chamber R, and the oil is discharged from the control chamber R through the drain passage 29, so that the pressure in the control chamber R decreases. To do. As a result, the piston 20 is retracted to the intermediate position as shown in FIG. 16, and the pump has the intermediate capacity. Other functions and effects of this embodiment are similar to those of the first embodiment.

Next, a fifth embodiment of the present invention will be described with reference to FIGS. In this embodiment, the above-mentioned second
The first control chamber R1 and the second control chamber R2 in the embodiment are combined into one control chamber R, and the throttle 59 and the third control valve 6 are provided.
0 is omitted. The first connection port 33 formed on the united spool valve 51 communicates with the pressure sensing chamber 53. The pressure sensing chamber 53 and the connection port 33 are arranged in the middle of the control passage 27. The other structure of this embodiment is the same as that of the second embodiment.

Therefore, in the fifth embodiment, as shown in FIGS. 17 and 18, when the pump 21 has the minimum capacity and is in the unloaded state, the control passage 27 and the drain passage 29 are closed by the spool valve 51, and the first passage The drain port 32 is open.

Here, when the cargo handling switching valve 25 is switched from the non-cargo handling to the cargo handling position, the pressure in the discharge conduit 24 rises. When the pressure inside the pressure sensing chamber 53 becomes equal to or higher than the first set value P _C1 , the spool valve 51 is moved to the right in FIG. 18 against the biasing force of the first spring 34. Then, as shown in FIG. 19, the control passage 27 is opened by the first connection port 33, and the first drain port 32 is closed. Therefore, high-pressure oil is supplied from the discharge conduit 24 to the control chamber R through the control passage 27, so that the control piston 20 is pushed in the direction of increasing the tilt angle of the swash plate 11. In this way, the pump 21 is switched from the minimum capacity to the large capacity.

After that, the pressure in the discharge conduit 24 exceeds the second set value P _C2 due to the stroke end of the lifting cylinder 26 or the like. Then, the pressure in the pressure-sensitive chamber 53 is further increased, so that the spool valve 51 has both springs 34,
It is further moved to the right against the urging force of 41. Then, the control passage 27 is closed as shown in FIG.
When the drain port 40 is opened, the oil in the control chamber R flows from the drain passage 29 to the suction passage 16. As a result, the control piston 20 retracts to the position where it closes the opening 29a, the tilt angle of the swash plate 11 becomes smaller, and the pump is switched from the large capacity to the intermediate capacity. In the state shown in FIG. 20, the control passage 27 is closed by the spool, but a small amount of control oil is supplied to the control chamber R from the clearance C on the outer circumference of the spool 51 between the connection port 33 and the passage 27. Therefore, oil leaking from the outer peripheral surface of the control piston 20 can be replenished to hold the piston 20 at the intermediate position.

The other operation and effect of the fifth embodiment is the second one.
It is similar to the embodiment. Next, a sixth embodiment of the present invention will be described with reference to FIG. In this embodiment, a second control valve 37 is provided in the drain passage 29 communicating with one control chamber R. Further, when the second control valve 37 is operated in the control cylinder 19, it is operated by a signal from the pressure detector 70 and the control device 71, and an intermediate position restricting means for restricting the backward movement of the control piston 20 on the way. Is provided as an electromagnetic actuator 72.

In this embodiment, when the pressure in the discharge conduit 24 exceeds the second set value P _C2 , the drain passage 29 is opened by the second control valve 37 and the control piston 20 is retracted. Further, the pressure detector 70 detects the pressure, the rod 73 of the actuator 71 moves forward, and the retracted position of the piston 20 is restricted to the intermediate position. Therefore, the pump is switched from the large capacity to the intermediate capacity, and the stall of the engine is prevented.

The other actions and effects of the fifth embodiment are the first.
It is similar to the embodiment. Further, the present invention is not limited to the above embodiment, but can be embodied as follows.

(1) Although the return spring 18 is used as the return means in the above embodiment, the return center of the swash plate 11 is replaced by the bottom dead center of the swash plate 11 with respect to the axis of the rotary shaft 5 (not shown). Eccentric to the side. Then, the swash plate 11 is configured to return to the minimum tilt angle by the moment generated by the spring for biasing the piston 12 provided in the cylinder bore 9.

(2) The control valves 28, 37, 60 are arranged as a unit in the middle of the discharge pipe line 24. (3) In addition to the cylinder 26, for example, a hydraulic motor or the like should be used as the cargo handling actuator.

(4) In the third embodiment, the first control room R
The pressure leading to 1 is set to the pressure P _{d1 on} the front side of the throttle 59, and the pressure P _d2 on the rear side of the throttle is guided to the pilot passages 27c and 67. In this case as well, the same operational effect is obtained.

(5) In the fifth embodiment, the above-mentioned third
Use of volume control valve 60. In this case, the discharge capacity is controlled to be substantially constant even if the rotation speed of the pump increases. (6) An operation signal from the pressure detector when a solenoid valve (not shown) is used instead of the first control valve 28 and the pressure of the hydraulic oil in the discharge pipe line 24 becomes equal to or higher than the first set value. To open the control passage 27. In addition, the second control valve 37
Instead of using a solenoid valve (not shown), when the pressure of the hydraulic oil in the discharge conduit 24 exceeds the second set value, the drain passage 29 is opened by the operation signal from the pressure detector. To do.

The technical ideas other than the claims that can be understood from the above-described embodiments will be described below along with their effects. Valve hole 19 formed in control cylinder 19 according to claim 2.
A valve portion 20a formed at the base end portion of the control piston 20 is inserted in b, a first control chamber R1 is partitioned behind the valve portion, and a second control chamber R2 is partitioned in front of the valve portion. The control passage 27 is connected, the drain passage 29 is connected to the second control chamber R2, and the second spool 38 of the second control valve 37 is connected.
Is the second connection port 3 for supplying control oil to the second control room R2
Hydraulic system with 9.

In addition to the operation of the invention of claim 2, this hydraulic system can supply control oil to both control chambers R1 and R2.
The forward movement of the control piston 20 can be performed quickly.

[0080]

As described above in detail, since the invention according to claim 1 has the structure described in the claims, it has the following excellent effects.

(1) Since the substantial operation (discharging) of the pump is always started from the minimum capacity substantially equal to zero, the starting torque is small, and power saving and rapid load fluctuation can be suppressed.

(2) Since the capacity without load can be maintained at the minimum capacity equal to zero, the power cutoff mechanism such as the clutch can be omitted. (3) While the cargo handling actuator is operating,
When the pressure of the hydraulic oil in the discharge pipe becomes equal to or higher than the set value, the capacity of the pump can be switched from the large capacity to the intermediate capacity, and the capacity of the relief valve for protecting the hydraulic system can be reduced.

(4) It is possible to suppress the load on the power source, prevent its abnormal stop, and improve the durability of the power source. Furthermore, in addition to the effect of the invention described in claim 1, the invention described in claim 2 can simplify the configuration of the first and second control valves.

According to the third aspect of the invention, the first and second spool valves are integrally formed. Therefore, in addition to the effect of the first or second aspect of the invention, the first and second control valves are provided. The configuration can be further simplified.

Furthermore, the invention according to claim 4 is the same as claim 2
Alternatively, in addition to the effect of the invention described in 3, the means for holding the control piston in the intermediate position can be simplified. Further, in addition to the effect of any one of the first to fourth aspects of the invention, in the fifth aspect of the invention, the discharge capacity of the pump is held substantially constant when the engine speed fluctuates, and the cargo handling of the actuator is performed. The work speed can be kept almost constant.

Further, in the invention described in claim 6, in addition to the effect of the invention described in claim 5, the structure of the third control valve can be simplified.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of a hydraulic system according to the present invention in a non-loading state, which schematically illustrates a part thereof.

FIG. 2 is a circuit diagram of a hydraulic system in a cargo handling state.

FIG. 3 is a circuit diagram of an operating state of a second control valve of the hydraulic system.

FIG. 4 is a vertical cross-sectional view of a central portion of a variable displacement pump.

FIG. 5 is a graph showing the displacement control operation of the variable displacement pump.

FIG. 6 is a sectional view showing a control valve of a second embodiment of the hydraulic system according to the present invention in a non-loading state.

FIG. 7 is a sectional view showing a control valve of a second embodiment in a cargo handling state.

FIG. 8 is a sectional view of the control valve of the second embodiment in a cargo handling state.

FIG. 9 is a vertical sectional view of a pump according to a third embodiment of the present invention.

FIG. 10 is a partially enlarged sectional view of the capacity control mechanism.

FIG. 11 is a partially enlarged sectional view of the capacity control mechanism.

FIG. 12 is a circuit diagram of a hydraulic system according to a third embodiment in a non-load handling state.

FIG. 13 is a circuit diagram of a hydraulic system of a third embodiment in a cargo handling state.

FIG. 14 is a circuit diagram of a hydraulic system of a third embodiment in a cargo handling state.

FIG. 15 is a graph showing the relationship between the rotational speed of the pump and the flow rate.

FIG. 16 is a cross-sectional view of essential parts of a fourth embodiment of the present invention.

FIG. 17 is a sectional view of a variable displacement pump according to a fifth embodiment of the present invention.

FIG. 18 is a sectional view showing a control valve of a fifth embodiment.

FIG. 19 is a sectional view showing a control valve of a fifth embodiment.

FIG. 20 is a sectional view showing a control valve of a fifth embodiment.

FIG. 21 is a cross-sectional view of essential parts of a sixth embodiment.

[Explanation of symbols]

11 ... Swash plate, 16 ... Suction passage as low pressure chamber, 17, 2
2a ... Discharge passage, 18 ... Return spring as return means, 1
9 ... Control cylinder, 19a ... Inner peripheral surface, 21 ... Pump, 2
3 ... Suction pipe line, 24 ... Discharge pipe line, 26 ... Lifting cylinder as a cargo handling actuator, 27 ... Control passage, 27a
(27b) ... first (second) pilot passage, 27c ... pilot passage, 28 (37) ... first (second) control valve, 3
1 (38) ... first (second) spool valve, 32 (40) ...
1st (2nd) drain port, 33 (39) ... 1st (2nd) connection port, 34 (41) ... 1st (2nd) spring, 3
5 (42) ... first (second) pressure-sensitive chamber, 36 (43) ... first
(Second) low-pressure chamber, 51 ... spool valve, 53 ... pressure-sensitive chamber, K
... Control piston intermediate position regulating means, R1 (R2) ... First (2) control chamber, T ... Oil tank as low pressure chamber.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideaki Igarashi 2-chome, Toyota-cho, Kariya-shi, Aichi Stock company, Toyota Industries Corporation (72) Inventor Wataru Minami 2-chome, Toyota-cho, Kariya-shi, Aichi Company Toyota Loom Works

Claims (6)

[Claims] 1. A return means for urging the swash plate to a minimum tilt angle substantially equal to zero capacity, and a control cylinder facing the return means for pushing in a direction to increase the tilt angle of the swash plate to increase the capacity. A variable displacement piston pump provided, a cargo handling actuator connected to the pump through a discharge pipeline and a cargo handling switching valve, and the discharge pipeline and the control chamber of the control cylinder are communicated with each other from the discharge pipeline. A control passage for supplying control oil into the control chamber, a drain passage communicating between the control chamber of the control cylinder and the low-pressure chamber side, and a pressure inside the discharge pipe which is interposed in the middle of the control passage. When the value exceeds the set value, the control passage is switched from the drain port communicating with the low pressure chamber side to the connection port, the control oil is supplied from the control passage to the control cylinder to advance the control piston, and the pump is moved. Small To a large capacity, and a drain control valve that is interposed in the drain passage and closes the drain passage when the pressure in the discharge pipeline becomes equal to or higher than a second preset value higher than the first preset value. To the connection port,
Drain the control oil in the control chamber and retract the control piston,
A hydraulic system comprising a second control valve for reducing the displacement of the pump, and an intermediate position regulating means for holding the control piston at an intermediate position while the second control valve is operated to retract the control piston. 2. The first control valve according to claim 1, wherein the first control valve senses the pressure in the discharge pipe line, and the first pressure sensing chamber is a first pressure sensing chamber when the pressure in the pressure sensing chamber is equal to or higher than a first set value. The first control valve is configured by a first spool valve that switches the control passage from the drain port to the connection port against the biasing force of the first spring, and the second control valve is a second pressure sensing chamber that senses the pressure in the discharge pipe line. A hydraulic system including a second spool valve that opens the drain passage against the biasing force of the second spring when the pressure in the pressure-sensitive chamber exceeds a second set value. 3. The first and second spool valves according to claim 2, wherein the first and second spool valves are integrally formed, and the first pressure sensing chamber and the second pressure sensing chamber are in one pressure sensing chamber. Is a hydraulic system housed in one low-pressure chamber. 4. The intermediate position regulating means of the control piston according to claim 2, wherein the control chamber side opening of the drain passage is opened at an intermediate position of the inner peripheral surface of the control chamber, and the control piston is retracted through the opening. A hydraulic system configured to close by the outer peripheral surface of the piston on the way to prevent the backward movement of the control piston. 5. The control oil according to any one of claims 1 to 4, wherein a throttle is provided in the discharge pipe line, and the control oil is detected when a pressure difference before and after the throttle is sensed to increase the differential pressure. A hydraulic system provided with a third control valve for reducing the amount of supply to the control room. 6. The third control valve according to claim 5, wherein the third control valve includes a pressure-sensitive chamber that senses pressure on the front side of the throttle in the discharge pipe, a pressure-sensitive chamber that senses pressure on the rear side of the throttle, and a pressure difference before and after the throttle. And a third spool valve that reduces the passage area of the control passage against the biasing force of the third spring.