JPH06257558A - Hydraulic system - Google Patents

Abstract

PURPOSE:To simplify the structure of a capacity/cargo switching valve by using one switching valve in performing an operation for switching the capacity of a piston pump from one to another as well as an operation for switching the cargo handling of a cargo actuator from one to another. CONSTITUTION:A vertically moving cylinder 26 is connected to both the suction pipe line 23 and delivery pipe line 24 of a variable displacement pump 21. The delivery pipe line 24 is communicated by a control passage 39 to the control chamber of a control cylinder 19 for regulating the displacement of the pump 21. A capacity/cargo switching valve 22 is disposed in those portions of the delivery pipe line 42 and the suction pipe line 23 which are located downstream of the control passage 49. When the switching valve 22 is in its neutral position Pn, the delivery line 24 is communicated to the suction pipe line 23 by means of a first communicating passage 33 and the pump 21 is operated at zero displacement. The switching valve 22 is switched to a first cargo handling position P1 and the pump 21 is operated at large displacement to raise the rod 29 of the cylinder 26. Further, the valve 22 is switched to a second cargo handling position P2 and pressure oil in an operating chamber 30 is forced to flow back into the suction pipe line 23 from the delivery pipe line 24 through the aperture-equipped second communicating passage 34, to lower the rod 29 of the cylinder 26.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, an industrial vehicle is equipped with a hydraulic system for driving a cargo handling actuator. Conventionally, two systems have been proposed as this hydraulic system.

The first hydraulic system is a power take-off device (PTO) mounted on a transmission of an engine and provided with a switching mechanism, a constant capacity gear pump with a change-over valve linked to the power take-off device, and the gear pump. And a cargo handling actuator connected to the.

The second hydraulic system is a power take-off device (PTO) mounted on the engine transmission.
And a variable displacement piston pump with an opening / closing valve that is interlocked with the power takeoff device, and a cargo handling actuator that is connected to the piston pump via a switching valve.

[0005]

However, since the former hydraulic system operates the cargo handling actuator, the switching operation for activating the power take-off device to drive the constant volume pump and the hydraulic pressure supplied from the pump to the cargo handling actuator. It is necessary to perform two operations, that is, the switching operation of the cargo handling switching valve. Therefore, the switching operation is very troublesome, and
There is a problem that the structure is complicated and the cost of the device cannot be reduced.

Further, the latter hydraulic system has an advantage that the cargo handling operation can be performed by a single operation of only the switching valve. However, since two valves, a displacement switching valve of the variable displacement piston pump and a cargo handling switching valve, are required, there is a problem that the structure is complicated and the cost of the device cannot be reduced.

The object of the present invention is to solve the above problems existing in the prior art, and to perform the switching operation of the displacement of the piston pump and the switching operation of the cargo handling actuator with a single switching valve, and also the switching valve. An object of the present invention is to provide a hydraulic system capable of simplifying the structure of and reducing the cost of the product.

[0008]

In order to achieve the above object, the present invention is directed to a variable displacement swash plate type piston pump, and a cargo handling system connected to a suction port and a discharge port of the piston pump through a suction passage and a discharge passage. Actuator, a control passage for supplying control oil to the control cylinder by communicating the discharge passage of the piston pump with the control chamber of the control cylinder, and the control passage interposed between the suction passage and the discharge passage, and Between a non-carrying position where the piston pump is held at a minimum capacity almost equal to zero capacity to invalidate the operation of the cargo handling actuator, and a cargo handling position where the piston pump is held at a large capacity to drive the cargo handling actuator. A switchable capacity / cargo handling switching valve is provided, and the capacity / cargo handling switching valve is provided in a non-cargo handling position with a communication passage communicating the discharge passage and the suction passage. Release, and a valve body for closing the communication passage at an unloading position.

[0009]

According to the present invention, by taking the above-described means, when the cargo handling actuator in which the capacity / cargo handling switching valve is switched to the zero capacity / non-carrying position is at rest, even if the pump is driven, the discharge oil is almost equal to the zero capacity. Flows from the discharge passage to the suction passage through the communication passage. Therefore, there is almost no increase in pressure in the discharge passage communicating with the oil tank, the pressure in the control passage is maintained at about atmospheric pressure, and the swash plate is returned to the minimum inclination angle (about 0.1 to 4 °) equal to zero capacity by the returning means. ) Is maintained and the clutch (off) function is replaced.

When the capacity / cargo handling switching valve is switched from the non-cargo handling position to the cargo handling position, the valve body closes the communication passage.
The pressure in the discharge passage increases due to the minimum amount of discharge oil. Therefore, the pressure oil is supplied from the control passage to the control chamber of the control cylinder, and is pressed in the direction in which the tilt angle of the swash plate increases due to the movement of the control piston. Therefore, the pump moves from the minimum capacity, which is almost equal to zero, to the steady operation of the maximum capacity when the rising swash plate reaches the maximum inclination angle. By the steady operation of the pump, hydraulic oil is supplied to the cargo handling actuator to operate the actuator.

When the capacity / cargo handling switching valve is switched from the cargo handling position to the non-cargo handling position, the valve body opens the communication passage, so that the hydraulic oil flows from the discharge passage to the suction passage through the communication passage. The pressure in the discharge passage drops to atmospheric pressure. Therefore, the pressure oil is not supplied from the control passage to the control chamber of the control cylinder, and the return means presses the swash plate in the direction in which the inclination angle is minimized. Therefore, the pump is moved to a minimum capacity equal to zero.

According to the present invention, the displacement of the piston pump and the cargo handling actuator can be switched at the same time by operating only the operating lever of the capacity / cargo handling switching valve. Further, in the present invention, since it is not necessary to separately provide a control valve for switching the capacity, the structure of the switching valve is simplified.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic system embodying the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit of a hydraulic system in which the present invention is applied to an industrial vehicle. As a variable displacement hydraulic pump driven by an engine E, a swash plate type piston pump is used. This piston pump will be described with reference to FIG. 3. In front of the center housing 1 (left)
The front housing 2 is joined and fixed to the end surface.
A rear end cover 3 is joined and fixed to a rear (right) end surface of the center housing 1, and a crank chamber 4 is formed inside them. A rotary shaft 5 is supported between bearings 6 and 7 between the opposed end walls of the front housing 2 and the rear end cover 3, and its outer end is connected to a power take-off device (PTO) (not shown) and directly connected to the engine E. It is designed to be rotated.

A cylinder block 8 is attached to the rotary shaft 5.
Are coupled to each other by spline fitting so that they can rotate synchronously, and a plurality of cylinder bores 9 are provided in the cylinder block 8.
Are formed parallel to the rotary shaft 5. A piston 12 moored to a swash plate 11 via a shoe 10 is accommodated in each of the cylinder bores 9 so as to be capable of reciprocating.
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 attached to a direction in which the inclination angle of the swash plate 11 is constantly displaced to a minimum inclination angle (about 0.1 to 4 °) substantially equal to zero volume by a return spring 18 as a return means, that is, a minimum volume position. It is energized. 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 tip end surface of the control piston 20 pushes a sphere moored to a part of the swash plate 11 to push the tilt angle of the swash plate 11 in a direction to increase the tilt angle against the elastic force of the return spring 18. , Piston 12
The stroke can be changed and the discharge volume can be adjusted. Therefore, since the control chamber 19a in the control cylinder 19 is at atmospheric pressure when the hydraulic circuit is stopped, the elastic force of the return spring 18 causes the swash plate 11 to have a minimum inclination angle in FIG. That is, the bias is held at the minimum discharge capacity position. The stopper 2a formed on the front housing 2 regulates the maximum inclination angle of the swash plate 11.

Further, the suction passage 16 and the discharge passage 1 of the variable displacement type swash plate type piston pump 21 configured as described above.
7, a capacity / cargo handling switching valve 22 which will be described later, which is an essential part of the present invention, is disposed. Further, an elevating cylinder 26 as a cargo handling actuator is connected to the suction passage 16 and the discharge passage 17 via a suction pipe line 23, a discharge pipe line 24 and a relief valve 25. The lift cylinder 26 includes a casing 27, a piston 28, and a rod 29. The Pinton side working chamber 30 of the cylinder 26 is in communication with the discharge line 24, and the rod side working chamber 31 is in communication with the suction line 23. The relief valve 25 and the rod-side working chamber 31 (suction line 23) are connected to the oil tank T.

Next, the structure of the capacity / cargo handling changeover valve 22 which is an essential part of the present invention will be described. As shown in FIG.
In the middle of the discharge passage 17 formed in the rear end cover 3, first and second cylindrical valve chambers 17a and 17b are formed.
Are formed so as to be located on the same axis line at a predetermined interval in the vertical direction. Further, the first valve chamber 17 a and the valve chamber 16 a of the suction passage 16 are connected by a first communication passage 33. Further, the first valve chamber 17a and the second valve chamber 17b are communicated with each other by a second communication passage 34 having the same diameter as the first communication passage 33 and located on the same axis. The first and second
In the communication passages 33 and 34, a spool valve 35 as a valve body that opens and closes both communication passages is housed so as to be capable of reciprocating in the vertical direction. The spool valve 35 is provided in the both communication passages 33, 34.
Large-diameter valve portion 36 capable of closing the valve and the valve chamber 16 of the suction passage 16
Insertion hole 37 communicating from a to the outside of the rear end cover 3
It has a large diameter portion 38 penetrating therethrough. The spool valve 35 has a small diameter portion 39 between the large diameter valve portion 36 and the large diameter portion 38. Then, by operating the operation lever 40 attached to the outer end portion of the spool valve 35, the spool valve 35 is reciprocated so that the large diameter valve portion 36 and the small diameter portion 39 move to the first communication passage 33 and the second communication passage. 34 is selectively opened and closed.

The lower end of the large-diameter valve portion 36 is inserted into an atmosphere chamber 41 formed in the lower portion of the rear end cover 3, and a bolt 42 is screwed and fixed in a screw hole 36a formed in the lower end portion. . The head 42a of the bolt 42 is formed in a cylindrical shape, and an annular groove 42b for engaging the locking ring 43 is formed on the outer peripheral surface thereof. Further, on the inner peripheral surface of the atmosphere chamber 41, first to third engaging grooves 41a, 41b, 41c are formed.
Are formed at predetermined intervals. Then, by engaging the locking ring 43 with any one of the engaging grooves,
The spool valve 35 can be held at the neutral (non-loading) position Pn, the first loading (up) position P1, or the second loading (down) position P2. In this embodiment, as shown in FIG. 1, the switching valve 22 is a 4-port, 3-position switching valve.

As shown in FIG. 2, a check valve 45 is interposed in the discharge passage 17 located between the first valve chamber 17a and the second valve chamber 17b. The check valve 45 includes a valve body 46 that opens and closes the valve hole 17c of the discharge passage 17, and the valve body 4
It is composed of a spring 47 for urging 6 toward the closing direction and a lid 48 for supporting the spring 47.

As shown in FIG. 3, the control chamber 19a of the control cylinder 19 is connected by a control passage 49 to the discharge passage 17 upstream of the first valve chamber 17a. Next, the operation of the hydraulic system configured as described above will be described.

When the hydraulic system is in the inoperative state, as shown in FIG. 3, the capacity / cargo handling switching valve 22 has a zero capacity / non-cargo handling position Pn.
Has been switched to. In this state, as shown in FIG. 2, the large-diameter valve portion 36 of the spool valve 35 is held at a position where the first communication passage 33 is opened and the second communication passage 34 is closed. Further, the pressure inside the crank chamber 4 of the variable displacement pump 21 and the pressure inside the discharge passage 17 and the control chamber 19a are both atmospheric pressure. Therefore, the return spring 18 holds the swash plate 11 at a position where the inclination angle is zero.

When the engine E is started in this 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. At this time, the first communication passage 33 allows the first valve chamber 17 a of the discharge passage 17 and the valve chamber 16 of the suction passage 16 to be connected.
Since a is communicated, the pressure in the control passage 49 does not rise. Therefore, the pump 21 continues to operate in the zero capacity state and substitutes for the clutchless function.

In this state, the operating lever 40 is operated to switch the capacity / cargo handling switching valve 22 from the non-cargo handling position Pn to the first cargo handling position P1 in which the piston rod 29 of the cylinder 26 is raised. Then, as shown in FIG. 4, the large-diameter valve portion 36 of the spool valve 35 is moved to a position where both the first communication passage 33 and the second communication passage 34 are closed. For this reason, a small amount of oil is supplied to the discharge passage 17 from the discharge port 15 of the pump 21 that was operating at a capacity close to zero. At this time, there is a check valve 45 in the discharge passage 17, and the pressure in the discharge passage 17 upstream of the valve 45 rises due to the load of the spring 47. As a result, the control passage 49 through the control cylinder 19
Pressure oil is supplied to the control chamber 19a of the
Is ejected and the inclination angle of the swash plate 11 is increased, the pump 21 is increased in discharge capacity, and the discharge pressure is rapidly increased. As a result, the check valve 45 of the discharge passage 17 is opened, high-pressure oil is supplied from the discharge conduit 24 to the working chamber 30 of the cylinder 26, and the piston rod 29 rises. When the rod 29 is moved to the upper limit, the high pressure oil is returned to the oil tank T from the relief valve 25.

When the cargo handling work for raising the piston rod 29 is completed and the cargo handling work for lowering the rod 29 is performed, the operation lever 40 of the capacity / cargo handling changeover valve 22 is operated to move the large diameter valve portion 36. It moves from the position shown in FIG. 4 to the position shown in FIG. Then, the small diameter portion 39 of the spool valve 35 is switched to a position where the first and second communication passages 33 and 34 are opened. For this reason, the oil in the piston-side working chamber 30 is discharged from the discharge conduit 24, the discharge passage 17, the second valve chamber 17b, the second communication passage 34, the first valve chamber 17a, the first communication passage 33, and the valve chamber 16.
The oil is returned to the oil tank T through a, the suction passage 16, and the suction conduit 23. Therefore, the piston rod 29 is lowered, but at this time, the oil recirculation speed becomes a speed according to the passage area (throttle amount) of the gap between the second communication passage 34 and the large diameter portion 36.

When the lowering operation of the piston rod 29 is performed, the discharge passage 17 and the suction passage 16 are connected by the first communication passage 33, so that the pressure in the discharge passage 17 drops sharply. Therefore, the supply of the pressure oil from the control passage 49 to the control chamber 19a is stopped, the swash plate 11 is returned to the inclined position of almost zero capacity by the return spring 18, and the pump 21 shifts to zero capacity operation.

On the other hand, while the piston rod 29 is being raised, the operating lever 40 is operated to move the spool valve 35 to the position shown in FIG.
When switched to the neutral position Pn as shown in FIG. 5, the closed first communication passage 33 is opened by the movement of the large-diameter valve portion 36. Therefore, the pump 21 is switched from the large capacity operation to the zero capacity operation. The check valve 45 prevents the oil in the piston-side working chamber 30 from flowing backward, so that the piston rod 29 is stopped at a predetermined position. In the middle of the descending cargo handling work, the operation lever 40 is operated to operate the spool valve 35.
When the piston rod 29 is switched to the neutral position as shown in FIG. 2, the piston rod 29 is similarly stopped at the predetermined position.

In the above embodiment, the capacity / cargo handling switching valve 2
Only by operating the second operation lever 40, the capacity switching of the piston pump 21 and the operation switching of the lifting cylinder 26 can be simultaneously and easily performed.

Further, in the above embodiment, the first communication passage 33 that communicates the discharge passage 17 and the suction passage 16, the second communication passage 34 that communicates the first valve chamber 17a and the second valve chamber 17b, and both communication passages. The capacity / cargo handling switching valve 22 is constituted by a spool valve 35 that opens and closes 33 and 34. Therefore, capacity switching and cargo handling switching can be performed without separately providing a complicated control valve for capacity switching, and the structure of the switching valve 22 is simplified,
Product cost can be reduced.

Although the switching valve 22 is housed in the rear end cover 3 in the above-described embodiment, in this case, the oil that is recirculated from the discharge passage 17 to the suction passage 16 through the first communication passage 33 in the zero capacity operation state is used. The shortest route is advantageous in reducing power.

The present invention is not limited to the above embodiment, but can be embodied as follows. (1) Instead of the elevating cylinder 26, use a cylinder (not shown) that reciprocates back and forth.

(2) In the above embodiment, the capacity / cargo handling switching valve 2
Although 2 is configured to be switchable between the non-material handling position Pn, the first cargo handling position P1 and the second cargo handling position P2, it should be configured to be switchable only between the two positions of non-cargo handling and cargo handling.

(3) In the above embodiment, the capacity / cargo handling switching valve 2
2 was installed in the rear end cover 3 of the pump 21,
Construct this separately from the pump 21. (4) For example, a hydraulic motor other than the cylinder is used as the cargo handling actuator. In this case, for example, a capacity / cargo handling switching valve having three positions of a neutral position, a forward rotation position and a reverse rotation position may be used.

As the returning means, the tilting shaft of the swash plate is eccentric to the bottom dead center side with respect to the drive shaft, thereby generating a moment in the direction of decreasing the swash plate angle and reducing the load of the return spring. It is also possible to omit it.

[0035]

As described above in detail, according to the present invention, at the non-carrying position of the capacity / cargo handling switching valve, the communication passage communicating the discharge passage and the suction passage is opened by the valve body, and the communication passage is opened at the cargo handling position. It was configured to be closed by the valve body. Therefore, it is possible to easily perform the capacity switching operation of the piston pump and the cargo handling switching operation of the cargo handling actuator with a single capacity / cargo handling switching valve, and simplify the structure of the capacity / cargo handling switching valve to reduce product cost. There is an effect that can be achieved. Further, when the capacity / cargo handling switching valve is in the neutral position and in the lowered position, the pump has almost zero capacity, and power loss can be reduced.

[Brief description of drawings]

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

FIG. 2 is a partial cross-sectional view of a capacity / cargo handling switching valve in a non-cargo handling position.

FIG. 3 is a vertical cross-sectional view of a central portion of a variable displacement piston pump.

FIG. 4 is a partial cross-sectional view of a capacity / cargo handling switching valve in a first cargo handling position.

FIG. 5 is a partial cross-sectional view of a capacity / cargo handling switching valve in a second cargo handling position.

[Explanation of symbols]

11 ... Swash plate, 16 ... Suction passage, 17 ... Discharge passage, 17a
... first valve chamber, 17b ... second valve chamber, 17c ... valve hole, 18 ...
Return spring as return means, 19 ... Control cylinder, 19
a ... control room, 21 ... variable displacement type swash plate type piston pump,
22 ... Capacity / cargo handling switching valve, 23 ... Suction pipe line, 24 ... Discharge pipe line, 26 ... Lifting cylinder as a cargo handling actuator, 33 ... First communication passage, 34 ... Second communication passage, 35 ... As valve body Spool valve, 36 ... Large diameter valve section, 39 ... Small diameter section,
49 ... Control passage, E ... Engine as power source, P
n ... Neutral (non-loading) position, P1 ... 1st loading (up) position, P2 ... 2nd loading (down) position.

Claims (1)

[Claims] 1. A return means for urging the swash plate to a minimum inclination angle equal to zero capacity, and a control cylinder which opposes the swash plate so as to increase the inclination angle of the swash plate to increase the capacity. A variable displacement swash plate type piston pump directly connected to a power supply source, a cargo handling actuator connected to the suction port and the discharge port of the piston pump through a suction passage and a discharge passage, and the discharge of the piston pump. A control passage for communicating the passage with the control chamber of the control cylinder to supply control oil to the control cylinder, and a control passage interposed in the middle of the suction passage and the discharge passage, and having the piston pump equal to almost zero capacity. A non-carrying position for holding the capacity to invalidate the operation of the cargo handling actuator, and a cargo handling position for holding the piston pump at a large capacity and driving the cargo handling actuator. A capacity / cargo handling switching valve that can switch between the two, wherein the capacity / cargo handling switching valve is a valve that opens a communication passage that connects the discharge passage and the suction passage in the non-carrying position and closes the communication passage in the cargo handling position. Hydraulic system with body.