JPH08100759A - Variable displacement piston pump - Google Patents

Abstract

PURPOSE: To operate an actuator quickly when cargo handling work is started by reducing load to be applied to an engine when no cargo handling work is performed to reduce power loss. CONSTITUTION: An inclination angle of a swash plate 7 is 0 deg. due to elastic force of a restoration spring 16 when no cargo handling work is performed. Also, a solenoid 36 which presses a control piston 21 by operating a main switch 37 and elongates a control piston 21 arbitrarily to set an inclination angle of the swash plate 7 to 2-5 deg. is provided. As a result, it is possible to keep pressure in a bore 5 at atmospheric pressure so far as the main switch 37 is not turned on and reduce load on an engine. Consequently, it is possible to improve fuel consumption, power efficiency of a hydraulic motor connected with the engine, and drivability.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Generally, in a swash plate type variable displacement piston pump, a piston is reciprocally housed in a bore of a cylinder block which rotates integrally with a shaft. The shaft is connected to the engine, and when the engine is driven, the cylinder block is rotated via the shaft, and the piston reciprocates a distance corresponding to the tilt angle of the swash plate. Along with this, hydraulic oil is sucked and discharged from the suction port and the discharge port on the valve plate that are in sliding contact with the cylinder block. The inclination angle of the swash plate is constantly urged by the elastic force of the spring or the like in a direction in which the inclination angle is minimized. The tilt angle of the swash plate is changed by a control cylinder provided in the pump.

That is, when the engine is stopped, the inclination angle of the swash plate is kept at the minimum inclination angle. At this time, the inclination angle of the swash plate is about 2 to 5 °. When the engine is driven and the shaft is rotated, the piston reciprocates. At this time, since the swash plate has a small inclination angle of 2 to 5 °, the stroke of the piston is also very small, but a small amount of hydraulic oil is discharged from the pump and discharged to the tank. Then, by switching the cargo handling switch, the discharge passage to the tank is closed and the working oil discharged from the pump is supplied to the cargo handling actuator (for example, a lifting cylinder). This allows
The control piston of the control cylinder extends when the hydraulic pressure of the discharged hydraulic oil (hereinafter referred to as the discharge pressure) rises due to the load and exceeds the set pressure. That is, the control piston tilts the swash plate toward the maximum tilt side against the elastic force of the spring. As a result, the stroke of the piston increases, the amount of hydraulic oil supplied to the lifting cylinder increases, and the lifting cylinder rises.

[0004]

However, the above-mentioned swash plate type variable displacement piston pump has the following problems.

(1) The inclination angle of the swash plate is always 2 to 5 in order to secure the pilot pressure for extending the control piston regardless of whether the cargo handling work is performed or not.
Since it is maintained at °, negative pressure and positive pressure always act inside the bore. As a result, the load applied to the engine is large especially when the engine is started. Further, even during non-carrying work, the piston constantly reciprocates, and the hydraulic oil is discharged from the pump, which slightly increases the load on the engine. As a result, engine power loss increases and drivability deteriorates.

(2) In the extension operation of the control piston, after the switching operation of the cargo handling switch, the working oil is supplied to the lifting cylinder, and the pressure in the pipeline between the lifting cylinder and the pump becomes a predetermined pressure or more. It will be done after. Therefore, the swash plate type variable displacement piston pump described above has a long time lag after the loading / unloading switch is switched from the non-loading state to the loading state. That is, the responsiveness of the lifting cylinder at the start of cargo handling is poor. In order to shorten the time lag after switching the cargo handling switch, it can be solved by keeping the swash plate angle at the time of non-handling as large as possible, but in this case, the power loss at the time of non-handling becomes large.

The present invention has been made to solve the above problems, and a first object thereof is to make it possible to reduce the power loss by reducing the load applied to the engine during non-cargo handling. It is to provide a positive displacement piston pump.

A second object of the present invention is to provide a variable displacement piston pump capable of quickly operating an actuator at the start of cargo handling work.

[0009]

In order to achieve the above-mentioned object, in the invention described in claim 1, the shaft is integrally rotated with the shaft connected to the drive source, and the piston is housed in a plurality of bores so as to be capable of reciprocating. The cylinder block, the swash plate that can be tilted back and forth with respect to the axial direction of the shaft, the returning means that urges the swash plate in the direction of the minimum tilt angle, and the swash plate that faces the bore of the cylinder block and is stored in the tank. A suction passage for sucking the oil into the bore and a discharge passage for discharging the oil sucked into the bore to the cargo handling actuator side, and a direction in which the swash plate tilt angle increases due to the pressure of the oil discharged from the discharge passage. A control cylinder for urging a swash plate and a control cylinder provided in the middle of the discharge passage, when the pressure of oil discharged from the discharge passage is less than a preset set pressure. Communicating between the tank, whereas, when the pressure of oil discharged from the discharge passage of the set pressure is
A switching valve that communicates between the control cylinder and the discharge passage, and a control cylinder forcibly operating means for forcibly operating the control cylinder regardless of the pressure of the oil discharged from the discharge passage to increase the inclination angle of the swash plate. The point is to have and.

According to another aspect of the present invention, there is provided a cylinder block which integrally rotates with a shaft connected to a drive source and accommodates a piston in a plurality of bores so that the piston can reciprocate, and front and rear with respect to an axial direction of the shaft. A tiltable swash plate, a return means for urging the swash plate in the direction of the minimum tilt angle, a suction passage that faces the bore of the cylinder block, and that sucks the oil stored in the tank into the bore. A discharge passage for discharging the oil sucked into the cargo handling actuator, a control cylinder for urging the swash plate in a direction in which the pressure of the oil discharged from the discharge passage increases, and a discharge for the control cylinder. The control cylinder forcing means for forcibly operating regardless of the pressure of the oil discharged from the passage to increase the inclination angle of the swash plate, and the control cylinder forcing means. Between the actuating means and the control cylinder, and its gist that between interposed a valve body which holds communicating with communicating holding, or control cylinder and the tank between the control cylinder and the discharge passage.

According to the third aspect of the invention, the tilting angle of the swash plate is maintained at approximately 0 ° by the returning means when the shaft is not rotating and the control cylinder forcing means is not operating. Use as a summary.

The gist of the invention according to claim 4 is that the control cylinder forcing operation means is a solenoid for expanding and contracting by a switch operation to operate the control cylinder.

According to a fifth aspect of the present invention, the restoring means is composed of a spring, and the swash plate is forcibly returned in a direction in which the inclination angle is reduced by the elastic force of the spring.

In a sixth aspect of the invention, the gist of the returning means is that the tilt center portion of the swash plate is eccentric to the bottom dead center side with respect to the shaft axis.

[0015]

According to the invention described in claim 1, when the drive source is driven, the cylinder block is rotated integrally with the shaft. At this time, the swash plate is held at the minimum tilt position by the returning means. The tilt angle of the swash plate at this minimum tilt position is 0
Set close to °. Therefore, the piston does not reciprocate,
Since the pressure in the discharge passage is the drain pressure (tank pressure), the switching valve connects the control cylinder and the tank. As a result, the control cylinder is not activated and the tilt angle of the swash plate is still 0 °.

Here, when operating the cargo handling actuator to carry out the cargo handling work, the control cylinder forcibly operating means forcibly activates the control cylinder to increase the inclination angle of the swash plate. As a result, the piston reciprocates, and oil is supplied from the discharge pipe line to the cargo handling actuator. When oil is supplied to the cargo handling actuator, a load is applied to the discharge pipeline, so that the pressure in the pipeline is increased and the pressure reaches the set pressure. as a result,
The switching valve communicates between the control cylinder and the discharge passage to further operate the control cylinder. As a result, the tilt angle of the swash plate is further increased, the discharge amount of oil discharged from the discharge pipe line is increased, and the cargo handling actuator is operated.

As described above, since the control cylinder is forcibly operated by the control cylinder forcibly operating means, the minimum tilt angle of the swash plate can be set small. As a result, it is possible to reduce the load on the drive source during non-carrying work.

According to the second aspect of the invention, when the drive source is driven, the cylinder block is rotated integrally with the shaft. At this time, the swash plate is held at the minimum tilt position by the returning means. The tilt angle of the swash plate at this minimum tilt position is
Set so that it is close to 0 °. Therefore, in this case, the piston is not reciprocated. Further, since the control cylinder forced actuation means is not actuated, the valve body holds the control cylinder and the tank in communication with each other.

Here, when operating the cargo handling actuator to carry out the cargo handling work, the control cylinder forcibly operating means forcibly activates the control cylinder via the valve element to increase the inclination angle of the swash plate. At this time,
The valve body holds the control cylinder and the tank in a non-communication state, and also maintains the control cylinder and the discharge passage in a communication state. That is, oil is supplied to the control cylinder and separated from the tank, and the control piston presses the swash plate in the direction in which the tilt angle increases due to the cooperation of the pressing force of the control cylinder forcing operation means and the oil pressure. . As a result, the stroke of the piston increases, the amount of oil to the cargo handling actuator increases, and the cargo handling actuator operates. As described above, in the present invention, since the power for operating the control cylinder is generated by the power of the control cylinder forced actuation means and the oil pressure, the power of the control cylinder forced actuation means can be set small. Further, since the valve body is moved by the control cylinder forced actuation means and at the same time the discharge passage communicates with the control chamber, the actuator can be quickly actuated.

According to the third aspect of the invention, when the shaft is not rotating and the control cylinder forcibly operating means is not operating, the tilting angle of the swash plate is maintained at approximately 0 ° by the returning means. That is, the tilt angle of the swash plate is maintained at approximately 0 ° during the non-cargo handling work. This makes it possible to reduce the load applied to the drive source during non-cargo handling work.

According to the fourth aspect of the invention, the solenoid is expanded and contracted by the switch operation, and the control cylinder is forcibly operated. That is, when carrying out the cargo handling work, the tilt angle of the swash plate is increased by operating the switch to extend (or contract) the solenoid, and a large amount of oil is supplied to the cargo handling actuator.

According to the fifth aspect of the invention, the swash plate is surely biased in the direction of the minimum tilt angle by the elastic force of the spring. According to the invention described in claim 6, the tilt center portion of the swash plate is eccentric to the bottom dead center side with respect to the shaft axis. As a result, the moment due to the compression reaction force acting on the swash plate when the piston discharges the oil in the bore becomes larger on the top dead center side. As a result, it is possible to urge the swash plate in the direction of the minimum tilt angle only by the compression reaction force of the piston without using a spring or the like.

[0023]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the front housing 1
Is connected and fixed to the front end surface (the left end surface in the figure) of the center housing 2. The rear housing 3 is connected and fixed to the rear end surface of the center housing 2. The shaft 4 is rotatably supported between the front housing 1 and the rear housing 3. The shaft 4 is connected to the engine E via a power take-off device (PTO) not shown.

Cylinder block 6 having a plurality of bores 5
Are connected to the shaft 4 by spline connection so as to rotate integrally therewith. The swash plate 7 is engaged with the front housing 1 so that the front-back inclination angle with respect to the axis of the shaft 4 changes. More specifically, the arcuate sliding surface 7a of the swash plate 7 is slidably engaged with the concave guide surface 1b formed on the inner wall of the front housing 1. Therefore, the center position of the arc forming the sliding surface 7a becomes the tilt center portion P of the swash plate 7, and the swash plate 7 tilts back and forth around the tilt center portion P. The piston 8 is accommodated in the bore 5 so as to be able to reciprocate, and is slidably engaged with the swash plate 7 via the shoe 9 and the retainer 10. The tilting center P of the swash plate 7
Is on the center line of the shaft 4.

In this embodiment, there is no valve plate interposed between the rear housing 3 and the cylinder block 6 for ensuring the slidability and wear resistance between the cylinder block 6 and the rear housing 3. In this embodiment, the rear housing 3 and the cylinder block 6 are made of an aluminum alloy (Al-Si alloy) instead of the valve plate, and the rear end surface of the cylinder block 6 is Ni-P plated (or Ni) with a film thickness of 20 to 40 μm. -P + Ni-B plating). Thereby, the slidability between the rear housing 3 and the cylinder block 6 can be secured without interposing the valve plate.

The suction passage 14 and the discharge passage 15 are formed in the rear housing 3. Each of the bores 5 has a suction passage 14 or a discharge passage 15 as the cylinder block 6 rotates.
And communicate with each other. Return spring 1 as return means
6 is interposed between the swash plate 7 and the front housing 1,
The end portion of the swash plate 7 is biased in the direction in which the tilt angle of the swash plate 7 is minimized (clockwise in FIG. 1). In this embodiment, the minimum inclination angle of the swash plate 7 when the shaft 4 is not rotated is set to 0 ° (a slight error may occur from the set angle of 0 ° due to a processing error, an assembly error, or the like. ).

The control cylinder 20 is cantilevered on the inner wall of the rear housing 3. The control piston 21 is reciprocally housed in a control chamber 22 that penetrates in the same direction as the axial direction of the shaft 4. When the control piston 21 extends from the control chamber 22 and presses the swash plate 7, the swash plate 7 rotates counterclockwise in the figure against the elastic force of the return spring 16. That is, as the control piston 21 extends, the tilt angle of the swash plate 7 increases and the stroke of the piston 8 changes. Swash plate 7
The inclination angle on the maximum side of is restricted by a stopper 1a formed in the front housing 1.

The suction passage 14 and the tank T for storing hydraulic oil are connected via a suction pipe line 31. The discharge passage 15 and the lifting cylinder 32 as an actuator are connected via a discharge pipe line 30.
A cargo handling switching valve 33 is provided in the middle of the discharge conduit 30.

The cargo handling changeover switch 35 is switched between two positions of a cargo handling mode position and a non-carrying mode position. When the cargo handling changeover switch 35 is held in the cargo handling mode position, the discharge passage 15 and the lifting cylinder 32 are communicated with each other via the spool A of the cargo handling changeover valve 33. That is, by setting the cargo handling changeover switch 35 to the cargo handling mode position, the piston rod of the lifting cylinder 32 can be extended. Further, when the cargo handling changeover switch 35 is held in the non-cargo handling mode position, the cargo handling changeover valve 3
The discharge passage 15 and the lifting cylinder 32 are communicated with each other via the spool B of No. 3. That is, by setting the cargo handling changeover switch 35 to the non-cargo handling mode position, the piston rod of the lifting cylinder 32 can be contracted.
Since the return passage is provided with the throttle, it is possible to prevent the lifting cylinder 32 from suddenly descending due to its own weight. Further, when the piston rod of the lifting cylinder 32 is lowered, the relief valve 34 can prevent unnecessary pressure from acting on the lifting cylinder 32.

The accommodation chamber 23 is formed in the rear housing 3. The drain hole 24 communicates between the storage chamber 23 and the tank T. The control passage 25 connects the accommodation chamber 23 and the control chamber 22 of the control cylinder 20. The ON / OFF valve 26 as a control valve is housed in the housing chamber 23 of the rear housing 3 so as to be capable of reciprocating. The drain passage 27 and the high pressure passage 28 have an ON / OFF valve 26.
Is formed. The ON / OFF valve 26 is always rearward (rightward in the figure) due to the elastic force of the spring 29.
Is urged by.

When the ON / OFF valve 26 moves to the right in FIG. 1, the control passage 25 and the drain hole 24 communicate with each other via the drain passage 27. That is,
The control room 22 and the tank T communicate with each other. Also, ON /
When the OFF valve 26 moves to the left in the figure against the elastic force of the spring 29 and the high pressure passage 28 and the control passage 25 communicate with each other, the OFF valve 26 and the discharge passage 30 are connected via the high pressure passage 28. The communication with the control passage 25 is established. That is, the discharge conduit 30 and the control chamber 22 communicate with each other.

The ON / OFF valve 26 is a spring 29.
The timing of moving to the left against the elastic force of is when the pressure of the hydraulic oil discharged from the discharge passage 15 (hereinafter, referred to as discharge pressure) exceeds a predetermined set pressure. That is, when the discharge pressure becomes stronger than the elastic force of the spring 29. Therefore, when the discharge pressure exceeds the set pressure, the discharge pipeline 3 is passed through the high pressure passage 28 and the control passage 25.
0 and the control chamber 22 communicate with each other, and high-pressure hydraulic oil is supplied into the control chamber 22. In this case, the pressure of the hydraulic oil supplied into the control chamber 22 causes the control piston 21
Extends to increase the tilt angle of the swash plate 7.

A solenoid 36 as a control cylinder forcibly operating means is attached and fixed to the rear end surface of the rear housing 3 at a portion facing the control chamber 22. When the main switch 37 is turned on, the solenoid 36 causes the rod 38 to extend and the control piston 21
The rear end face is pressed to force the control piston 21 to extend from the control chamber 22. In this embodiment, the extension amount of the rod 38 is set so that the inclination angle of the swash plate 7 is 2 to 5 °. Further, the contraction of the rod 38 can be performed by turning off the main switch 37.

Next, the operation of this embodiment will be described.
First, when the engine is started, the main switch 37 is turned off and the cargo handling changeover switch 35 is held in the non-cargo handling mode position. After confirming the positions of both switches 37 and 35, the engine is started and the shaft 4 is rotated. At this time, since the tilt angle of the swash plate 7 is held at 0 ° which is the minimum angle by the elastic force of the return spring 16, the piston 8
The stroke is also zero. Therefore, in this state, even if the shaft 4 is rotated, the inside of the bore 5 is at atmospheric pressure, and the pump does not suck or discharge the hydraulic oil (see FIGS. 1 and 2). At this time, the control room 22 is turned on / off.
The communication state with the tank T is maintained via the drain passage 27 of the valve 26. Therefore, the inside of the control chamber 22 is maintained at the drain pressure.

Next, when carrying out the cargo handling work, first, the main switch 37 is turned on to extend the rod 38 of the solenoid 36 (see FIG. 3). As a result, the control piston 21 is forcibly extended from the control chamber 22 and the swash plate 7
Is increased to 2-5 °. As a result, the piston 8
Reciprocates with a stroke according to the inclination angle of the swash plate 7, and a small amount of hydraulic oil from the tank T is sucked into the bore 5 and a small amount of hydraulic oil is discharged from the discharge passage 15. The hydraulic oil discharged from the discharge passage 15 has a discharge pipe line 30.
After passing through the spool B of the cargo handling switching valve 33, it is supplied to the lifting cylinder 32. At this time, since the load is not applied to the lifting cylinder 32, the discharge pressure is low and does not reach the set pressure yet. Therefore, at this time, the control chamber 22 is still at the drain pressure.

By switching the cargo handling changeover switch 35 to the cargo handling mode position, the hydraulic oil discharged from the discharge passage 15 is supplied from the spool A of the cargo handling changeover valve 33 to the lifting cylinder 32. Lifting cylinder 32
By supplying the hydraulic oil to, the pressure in the discharge pipe line 30 increases. Accordingly, when the discharge pressure reaches the set pressure, O
The N / OFF valve 26 moves in the forward direction against the elastic force of the spring 29, so that the hydraulic oil flows from the high pressure passage 28 to the control chamber 2
2 (see FIG. 4). Therefore, the control piston 21 is pressed by the hydraulic oil supplied to the control chamber 22, and the tilt angle of the swash plate 7 is further increased (at this time, the stroke of the control piston 21 is maximized).
As a result, the stroke of the piston 8 is maximized and the discharge capacity of the pump is increased, so that the lifting cylinder 32 can carry out cargo handling work.

When a series of cargo handling operations is completed, the cargo handling changeover switch 35 is switched and held at the non-cargo handling mode position, and the lifting cylinder 32 is lowered. As a result, the discharge pressure becomes lower than the set pressure, the ON / OFF valve 26 is biased rightward by the elastic force of the spring 29, and
The swash plate 7 is biased by the return spring 16 toward the minimum tilt angle side. At this time, the swash plate 7 is connected to the rod 38 of the solenoid 36.
It is urged toward the minimum tilt side until it comes into contact with. This allows
The control piston 21 is pressed toward the contraction side by the swash plate 7, and the hydraulic oil in the control chamber 22 is discharged from the drain hole 24 to the tank through the control passage 25 and the drain passage 27.

Thereafter, the main switch 37 is turned off and the rod 38 of the solenoid 36 is contracted. As a result, the swash plate 7 is further urged by the return spring 16, the inclination angle becomes zero, and the discharge pressure becomes the drain pressure.

As described above, the following effects can be obtained by configuring the variable displacement piston pump in this embodiment. Conventionally, the inclination angle of the swash plate is set to 2 to 5 ° in order to secure the pilot pressure for operating the control cylinder even during the non-carrying work (when the engine is stopped). On the other hand, in this embodiment, during non-loading work,
Due to the elastic force of the return spring 16, the tilt angle of the swash plate 7 is 0 °
And Further, the solenoid 36 for pressing the control piston 21 by operating the main switch 37 and arbitrarily extending the control piston 21 to set the inclination angle of the swash plate 7 to 2 to 5 ° is provided. As a result, unless the main switch 37 is turned on, the inside of the bore 5 can be kept at atmospheric pressure,
The load on the engine can be reduced. As a result, it is possible to improve fuel efficiency, improve power efficiency of a hydraulic motor or the like connected to the engine, and improve drivability.

The rear housing 3 and the cylinder block 6 are made of an aluminum alloy (Al-Si alloy), and the rear end surface of the cylinder block 6 has a film thickness of 20 to 40 μm.
The surface treatment of Ni-P plating (or Ni-P + Ni-B plating) was performed with m. As a result, the slidability and wear resistance between the rear housing 3 and the cylinder block can be ensured without interposing the valve plate, and the number of members can be reduced, and the cost can be reduced. .

(Second Embodiment) Next, a second embodiment of the present invention will be described. In the present embodiment, the same members as those in the first embodiment will be described with the same member numbers, and detailed description thereof will be omitted.

As shown in FIG. 5, the control piston 51 of the control cylinder 50 is housed in the control chamber 52 so as to be capable of reciprocating. The control spool 53 is reciprocally housed in the control chamber 52 on the rear end side of the control piston 51. When the control spool 53 moves forward in the control chamber, the control chamber 52 is separated into the first control chamber 52a and the second control chamber 52a.
The control room 52b is divided into two parts. The control spring 54 is interposed between the rear end surface of the large diameter portion 55 of the control piston 51 and the control spool 53.
The control spool 53 and the control spool 53 are always urged in a direction in which they repel each other. The elastic force of the control spring 54 is weaker than that of the return spring 16 (shown in FIG. 1). Therefore, the tilt angle of the swash plate 7 is 0 ° during the non-carrying work as in the above embodiment.

The control communication passage 56 is formed in the control spool 53 and communicates with the control chamber 52 which is divided into two as the control spool 53 moves. The control chamber 52 and the tank T are connected via a drain passage 57. Further, the control chamber 52 and the discharge conduit 30 are connected by a high pressure passage 58. A solenoid 59 as a control cylinder forcibly operating means is attached and fixed to the rear housing 3 at a portion facing the rear end surface of the control spool 53.

In this embodiment, when the main switch 37 is turned on, the rod 60 of the solenoid 59 extends and the discharge pipe 30 and the lifting cylinder 32 communicate with each other via the spool A of the cargo handling switching valve 33. It Further, by turning off the main switch 37, the rod 60 of the solenoid 59 contracts, and the discharge pipe line 30 and the lifting cylinder 32 communicate with each other via the spool B of the lifting cylinder 32. Furthermore, in this embodiment,
A back pressure valve 61 is provided in the discharge conduit 30 between the discharge passage 15 and the cargo handling switching valve 33. This back pressure valve 61 is used for the control cylinder 5 at the start of cargo handling work.
Secure 0 pilot pressure.

Next, the operation of this embodiment will be described.
At the time of starting the engine E, the main switch 37 is turned off also in this embodiment as in the first embodiment. That is, the inclination angle of the swash plate 7 is maintained at 0 °. As a result, the load on the engine E is reduced as described above.
Next, when carrying out cargo handling work, the main switch 37 is turned on. As a result, as shown in FIG.
60 of the rod is extended and the cargo handling switching valve 3
The discharge passage 15 and the lifting cylinder 32 communicate with each other via the spool A of No. 3.

When the rod 60 is extended, the control spool 53 is pressed by the rod 60 to close the drain passage 57 and open the high pressure passage 58. The inclination angle of the swash plate 7 at this time is 2 to 5 °. As a result, the hydraulic oil is discharged from the discharge passage 15. At this time, since the discharge conduit 30 is shut off by the back pressure valve 61, all the hydraulic oil discharged from the discharge passage 15 flows into the control chamber 52 via the high pressure passage 58. Further, the hydraulic oil passes through the control communication passage 56 to pass from the first control chamber 51a to the second control chamber 5
It flows to the 1b side and presses the control piston 51. As a result, the control piston 51 is extended and presses the swash plate 7 in a direction in which the tilt angle increases.

Then, as shown in FIG. 7, even when the extension amount of the rod 60 becomes maximum and the movement of the control spool 53 stops, the control piston 51 continues to move due to the pressure of the hydraulic oil. As shown in FIG. 8, when the extension amount of the control piston 51 reaches the maximum, a large amount of hydraulic oil is discharged from the discharge passage 15, and the discharge pressure between the discharge passage 15 and the back pressure valve 61 increases. The discharge pressure is the back pressure valve 61.
When the pressure becomes equal to or higher than the set pressure of, the discharge passage 15 is communicated with the lifting cylinder 32, and the lifting cylinder 32 is lifted.

When a series of cargo handling work is completed, the main switch 37 is turned off. As a result, as shown in FIG. 9, the rod 60 of the solenoid 59 is contracted, the elastic force of the control spring 54 moves the control spool 53 rearward, and the drain passage 57 is opened and the high pressure passage 5 is opened.
8 is closed. As a result, the hydraulic oil in the control chamber 52 is discharged to the tank, and the pressure in the control chamber 52 becomes the drain pressure, so that the control piston 51 is contracted. That is, the inclination angle of the swash plate 7 becomes 0 °.

As described above, since the variable displacement piston pump is constructed in this embodiment, the following effects can be obtained. (1) Similar to the first embodiment, since the inclination angle of the swash plate 7 can be set to 0 ° at the time of starting the engine and at the time of non-carrying work, the load on the engine can be reduced and other hydraulic motors connected to the engine can It is possible to improve power efficiency and drivability.

(2) By simply turning on the main switch 37, the tilt angle of the swash plate 7 can be rapidly increased and the lifting cylinder 32 can be quickly extended. (3) The rod 60 of the solenoid 59 extends and the movement of the control spool 53 starts, and at the same time, the high-pressure passage 58 and the control chamber 52 communicate with each other, and hydraulic oil is supplied to the control chamber 52. As a result, the control piston 51 is extended by the cooperation of the pressing force of the rod 60 and the pressure of the hydraulic oil. As a result, in the present embodiment, even if the inexpensive solenoid 59 having a small capacity is used, the swash plate 7 can be reliably operated.
Can be tilted.

The present invention can also be configured as follows. (1) In the second embodiment, as shown in FIG.
A diaphragm 70 should be provided in the middle of the high-pressure passage 58 to embody it. With this configuration, the amount of hydraulic oil supplied to the control chamber 52 can be made constant, and the control piston 51 will not be pushed too much. as a result,
It is possible to reduce the amount of hydraulic oil leaked between the control chamber 52 and the control piston 51 into the pump casing. Further, the extension speed of the control piston 51 can be made constant, and it is possible to prevent the swash plate 7 from abruptly tilting. As a result, the load on the engine E can be reduced.

(2) As a control cylinder forced actuation means, by operating a lever or the like. Thus, the control pistons 21 and 51 may be manually (mechanically) extended.

(3) In the above embodiment, the returning means is constituted by the spring, and the elastic force of the spring forcibly urges the swash plate toward the minimum tilt angle side. In contrast,
The returning means may be configured as shown in FIG. That is, the sliding surface 7a of the swash plate 7 should be formed at a position eccentric to the bottom dead center side with respect to the axis of the shaft 4. With this configuration, the moment based on the compression reaction force that acts on the swash plate 7 when the piston 8 discharges the oil in the bore 5 can be increased at the top dead center side. As a result, without using a spring or the like, only the compression reaction force of the piston 8
The swash plate 7 can be biased in the direction of the minimum tilt angle, and the number of pump parts can be reduced.

[0055]

According to the invention described in claim 1, since the control cylinder forcibly actuating means forcibly actuates the control cylinder, the minimum tilt angle of the swash plate can be set small. As a result, it is possible to reduce the load on the drive source during non-carrying work, which in turn reduces the power loss of the drive source and improves drivability.

According to the second aspect of the invention, the capacity and stroke of the control cylinder forcing actuation means can be set small and the cargo handling actuator can be actuated quickly.

According to the third aspect of the present invention, since the inclination angle of the swash plate is set to approximately 0 °, it is possible to reduce the load applied to the drive source during non-carrying work. According to the invention described in claim 4, the control cylinder can be easily operated by the switch operation.

According to the fifth aspect of the present invention, the elastic force of the spring can surely bias in the minimum tilt direction. According to the sixth aspect of the present invention, the swash plate can be biased in the direction of the minimum tilt angle only by the compression reaction force of the piston without using a spring or the like, so that the number of parts can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view and schematic hydraulic circuit diagram of a variable displacement piston pump according to a first embodiment of the present invention.

FIG. 2 is a partial sectional view and a schematic hydraulic circuit diagram of a control cylinder in the first embodiment.

FIG. 3 is a partial cross-sectional view and a schematic hydraulic circuit diagram of the control cylinder in a state where the main switch is turned on from the state of FIG.

FIG. 4 is a partial cross-sectional view and a schematic hydraulic circuit diagram of the control cylinder in a state where the cargo handling changeover switch is turned on from the state of FIG.

FIG. 5 is a partial cross-sectional view and a schematic hydraulic circuit diagram of a control cylinder in a second embodiment embodying the present invention.

6] The main switch is turned on from the state of FIG. 5,
FIG. 3 is a partial cross-sectional view and a schematic hydraulic circuit diagram of the control cylinder in a state where the rod of the solenoid has started to expand.

FIG. 7 is a partial cross-sectional view and a schematic hydraulic circuit diagram of the control cylinder in a state where the rod is further extended from the state of FIG.

8 is a partial cross-sectional view and a schematic hydraulic circuit diagram of the control cylinder with the control piston further extended from the state of FIG. 7.

9 is a partial sectional view and a schematic hydraulic circuit diagram of the control cylinder in a state where the rod is contracted from the state of FIG.

FIG. 10 is a partial cross-sectional view of another example of a control cylinder in which a high pressure passage is provided with a throttle.

FIG. 11 is a cross-sectional view of another example of a variable displacement piston pump in which the tilt center position of the swash plate is eccentric.

[Explanation of symbols]

4 ... Shaft, 5 ... Bore, 21, 51 ... Piston, 6 ...
Cylinder block, 7 ... Swash plate, 14 ... Suction passage, 15 ...
Discharge passage, 16 ... Returning means, T ... Tank, 20, 50 ...
Control cylinder, 26 ... Switching valve, 32 ... Cylinder for raising and lowering through actuator for cargo handling, 36, 59 ... Solenoid as control cylinder forced actuation means,
37 ... Main switch as switch, 53 ... Control spool as valve body, P ... Tilt center part, E ... Engine as drive source

Front page continuation (72) Minoru Wataru, 2-chome, Toyota-cho, Kariya city, Aichi prefecture Toyota Industries Corporation

Claims (6)

[Claims] 1. A cylinder block that rotates integrally with a shaft that is connected to a drive source and that houses a piston in a plurality of bores so that the piston can reciprocate; and a swash plate that can tilt forward and backward with respect to the axial direction of the shaft. A return means for urging the swash plate in the minimum inclination direction, a suction passage that faces the bore of the cylinder block and sucks the oil stored in the tank into the bore, and loads the oil sucked into the bore. For discharging to the actuator side, a control cylinder for urging the swash plate in a direction in which the pressure of the oil discharged from the discharge passage increases the tilt angle of the swash plate, and a discharge cylinder provided in the middle of the discharge passage. When the pressure of the oil discharged from the passage is less than a preset set pressure, the control cylinder and the tank are communicated with each other, while the pressure of the oil discharged from the discharge passage is set. When the pressure is equal to or higher than the pressure, the switching valve that connects the control cylinder and the discharge passage and the control cylinder are forcibly operated irrespective of the pressure of the oil discharged from the discharge passage to change the inclination angle of the swash plate. A variable displacement piston pump with increasing control cylinder forced actuation means. 2. A cylinder block that integrally rotates with a shaft that is connected to a drive source and that houses a piston in a plurality of bores so that the piston can reciprocate; and a swash plate that can tilt forward and backward with respect to the axial direction of the shaft. A return means for urging the swash plate in the minimum inclination direction, a suction passage that faces the bore of the cylinder block and sucks the oil stored in the tank into the bore, and loads the oil sucked into the bore. Of the oil discharged from the discharge passage, the control cylinder for urging the swash plate in the direction in which the swash plate tilt angle increases due to the pressure of the oil discharged from the discharge passage, A control cylinder forcibly operating means for forcibly operating regardless of pressure to increase the inclination angle of the swash plate; A variable displacement piston pump having a valve body interposed between the control cylinder and the discharge passage, or between the control cylinder and the tank. 3. The tilt angle of the swash plate is maintained at approximately 0 ° by the returning means when the shaft is not rotating and the control cylinder forcing actuation means is not actuated.
Alternatively, the variable displacement piston pump according to claim 2. 4. The variable displacement piston pump according to claim 1, wherein the control cylinder forced actuation means is a solenoid that expands and contracts by a switch operation to actuate the control cylinder. 5. The variable displacement piston according to claim 1, wherein the returning means is composed of a spring, and the swash plate is returned in a direction in which the tilt angle is forcibly reduced by the elastic force of the spring. pump. 6. The variable displacement piston pump according to claim 1, wherein the returning means is configured such that a tilt center portion of the swash plate is eccentric to a bottom dead center side with respect to a shaft axis center. .