JPH07189890A - Axial piston pump - Google Patents

Abstract

PURPOSE:To provide an axial piston pump capable of reducing the size and weight of it by reducing the drum diameter of a housing, facilitating the machining and assembly by reducing the number of part items and also reducing production cost. CONSTITUTION:A cylinder block 8 provided with a cylinder bore 8a is fitted to a rotating shaft 5 synchronous-rotatably, and the base part of a piston 13 stored in the cylinder bore 8a is connected slidably to the slanted surface 9b of an angle-variable swash plate 9 through a shoe 11. Also a return spring 12 to energize the inclined angle of the swash plate 9 in the minimum position is stored in the cylinder bore 8a. Then the center axis O2 of a pivot shaft 10 of the swash plate 9 is provided on the top position T side of the swash plate 9 apart more than the center axis O1 of the rotating shaft 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial piston pump constituting a hydraulic system used in, for example, an industrial vehicle, and more particularly to a pump variable capacity mechanism.

[0002]

2. Description of the Related Art An industrial vehicle is provided with a hydraulic pump driven by an engine, an actuator driven by hydraulic oil discharged from the pump, a discharge passage connecting the hydraulic pump and the actuator, A hydraulic system equipped with a switching valve for switching cargo handling is installed.

As the hydraulic pump, there are one that is started with a maximum capacity and one that is started with a minimum capacity equal to zero capacity. The former pump not only requires an electromagnetic clutch, but also has a large impact at the time of starting, so there is a problem in durability of the electromagnetic clutch and the pump itself. Further, the latter pump has an advantage that the pump itself substitutes the clutch function and the shock at the time of starting is suppressed.

As the minimum displacement starting type axial piston pump, there is a conventional one disclosed in, for example, Japanese Utility Model Laid-Open No. 59-170480. As shown in FIG. 8, this pump has a cylinder block 43 fixedly fitted to a rotary shaft 42 supported by a housing 41, and a piston 4 is provided in a plurality of cylinder bores 43 a of the cylinder block 43.
4 is fitted so that it can slide back and forth. A swash plate 45 is supported by the housing 41 so as to surround the rotary shaft 42 so as to be tiltable around a support shaft 46, and the outer end of the piston 44 is slidably contacted with the swash plate 45. Each piston 4
4 is a coiled spring 4 housed in the cylinder bore 43a
It is pressed against the slope of the swash plate 45 by 7. Further, a mechanism 48 for urging the swash plate 45 to a minimum tilt state equal to zero capacity is mounted near the outer peripheral portion of the housing 41. The mechanism 48 includes a support cylinder 49 fixed to the housing 41, a movable pusher 50 reciprocatingly fitted to the outer circumference of the support cylinder 49, and the pusher 50 is advanced to move the swash plate 45.
And a coiled spring 51 for urging the inclination angle of the coil to the minimum.

In the above-mentioned conventional pump, when the rotary shaft 42 is rotated while the swash plate 45 is in the minimum inclination state, the cylinder block 43 is rotated and the piston 44 is guided by the slope surface of the swash plate 45 and has the minimum stroke. Oil reciprocated and sucked into the cylinder bore 43a from the suction passage 52 is supplied to the actuator from the discharge passage 53. Then, when the cargo handling switching valve (not shown) provided in the discharge passage 53 is switched from the non-cargo handling position to the cargo handling position, the pressure in the discharge passage 53 increases due to the load of the actuator.
The inclination angle of 5 increases, and the discharge capacity increases. That is, the swash plate 45 is located closer to the swash plate 4 than the rotation axis O ₁ of the rotation shaft 42.
5 is supported by the support shaft 46 at a position displaced to the top position side of 5, the swash plate 45 is centered on the axis O ₂ of the support shaft 46 based on the external force received from all the pistons 44.
A rotational moment is generated in the clockwise direction, that is, in the direction of increasing the tilt angle (this principle will be described in the embodiment of the present invention). Therefore, the stroke of the piston 44 is increased and the discharge capacity is increased.

[0006]

In the displacement control mechanism of the piston pump described above, the return spring 5 for biasing the swash plate 45 to the minimum tilt position is provided between the outer peripheral portion of the swash plate 45 and the housing 41.
1, the fixed support cylinder 49, the movable pusher 50, etc. are required. Therefore, there is a problem that the body diameter of the housing 41 becomes large and the entire pump becomes large and heavy. or,
In the conventional pump, since the number of parts such as the return spring 51 increases, there has been a problem that the manufacturing cost cannot be reduced because the machining and assembly are troublesome.

A first object of the present invention is to solve the above-mentioned problems of the prior art and to reduce the body diameter of the housing of the piston pump to reduce the size and weight, reduce the number of parts and reduce the manufacturing cost. It is to provide an axial piston pump that can do.

A second object of the present invention is, in addition to the first object, to provide an axial piston pump capable of rapidly performing a switching operation from the minimum capacity operation to the maximum capacity operation.

[0009]

In order to achieve the first object, the invention according to claim 1 fits a cylinder block having a plurality of cylinder bores on a rotary shaft supported by a housing so as to be synchronously rotatable, A swash plate is housed so as to be tiltable in the front-rear direction with respect to the housing by a support shaft and surrounds the rotary shaft, and the base end of the piston housed in each cylinder bore is circled along the slope of the swash plate. Each of the cylinder bores is slidably slidable along a locus, and the center axis of the support shaft for supporting the swash plate is set closer to the top position side of the swash plate than the center axis of the rotating shaft. Between the top surface and each piston or between the cylinder block and each shoe, the tilt angle of the swash plate is always returned to the minimum tilt angle equal to zero capacity, and the shoe is held in sliding contact with the slope surface of the swash plate. To do Provided a spring respectively, the the discharge passage and the port to open the passage, is provided with switchable capacitance switching valve between a drain port connected to the low pressure side.

Further, in order to achieve the above-mentioned second object, the invention according to claim 2 is characterized in that, when the capacity switching valve is switched to the open port, the discharge passage is temporarily stopped from the discharge passage. A pressure control valve that closes the discharge passage to raise the discharge pressure to a set value and then opens the discharge passage is provided.

[0011]

According to the first aspect of the invention, when the pump is stopped, the inclination angle of the swash plate is kept to a minimum by the return spring. When the pump is started by the power of the engine in this state and the rotating shaft is rotated, the cylinder block is rotated together with the piston. Therefore, a small amount of oil sucked into the cylinder bore from the suction passage is discharged from the discharge passage.

When the pump is in the minimum capacity operation state and the capacity switching valve is held in the drain port, the pressure of the oil sent to the discharge passage is low. For this reason, the pressure in the cylinder bore is also low, and there is no rotational moment around the support shaft that tries to increase the tilt angle acting on the swash plate via the piston, and the minimum capacity operation of the pump is continued. It

After that, when the capacity switching valve is switched from the drain port to the open port, a small amount of oil is supplied to the actuator through the discharge passage, which increases the pressure in the discharge passage. This increase in pressure increases the reaction force received by the multiple pistons in the cylinder bore, so that the swash plate generates a turning moment about its support shaft in the direction of increasing the tilt angle, and the pump is in the minimum capacity state. To a large capacity state.

According to the first aspect of the present invention, there is provided a return mechanism having a dedicated spring for changing the inclination angle of the swash plate from the maximum angle to the minimum angle between the outer peripheral surface of the cylinder block and the inner peripheral surface of the housing. Since there is no need to interpose, the body diameter of the housing is reduced. Further, in the invention described in claim 1, it is not necessary to interpose a conventional return mechanism, and in addition, a spring for anchoring the piston to the swash plate via the shoe returns the swash plate to the minimum inclination angle. Since it also functions as a spring,
The number of parts is reduced and processing and assembling work become easier.

According to the second aspect of the invention, when the displacement switching valve is switched from the drain port to the open port in the minimum displacement operation of the pump, the pressure control valve provided in the discharge passage causes the discharge passage upstream of the control valve. The internal pressure is rapidly increased, the switching operation of the pump from the minimum capacity state to the maximum capacity state is quickly performed, and the actuation start timing of the actuator is accelerated.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an axial piston pump embodying the present invention will be described below with reference to FIGS.

As shown in FIG. 1, a front end cover 2 is integrally formed on the front (left) end surface of the center housing 1, and a rear end cover 3 is joined and fixed to the rear (right) end surface of the center housing 1. A closed working space 4 is formed inside them. A rotary shaft 5 is supported between bearings 6 and 7 between the opposed end walls of the front end cover 2 and the rear end cover 3, and a power take-out device (PTO) (not shown) fitted to the outer ends thereof.
Is directly rotated by the engine E or the like.

A cylinder block 8 is attached to the rotary shaft 5.
Are coupled to each other by a spline 5a so that they can rotate synchronously, and a plurality of cylinder bores 8 are provided in the cylinder block 8.
a is formed so as to be parallel to the rotary shaft 5 and arranged at equal pitches on a circumference centered on the rotary shaft 5. A swash plate 9 is mounted in the working space 4 so as to surround the rotating shaft 5 and to be tiltable in the front-rear direction in a non-rotating state.
As shown in FIG. 3, brackets 9a, 9a are integrally formed on both left and right sides of the swash plate 9, and both brackets 9a, 9a are attached to both side walls of the center housing 1 by the support shaft 1
It is supported by 0 and 10 so as to be rotatable (tilted) about both shafts. The support shaft 10 may be supported by the center housing 1 via a radial bearing (not shown), or may be supported by a hole penetrating the wall of the center housing 1 from the viewpoint of assembly.

The center axis O ₁ of the rotary shaft 5 and the tilt center O ₂ of the swash plate 9 are displaced in the vertical direction as shown in FIG. 2, and the axis O ₂ is located above the axis O ₁ , that is, in the oblique direction. Board 9
Is displaced to the top position T side. The springs 1 in the cylinder bores 8a are pressed against the slopes 9b of the swash plate 9 via the shoes 11 respectively, and the springs 1 in the cylinder bores 8a.
A piston 13 that is biased in the protruding direction by 2 is housed so as to be capable of reciprocating. Further, the cylinder bores 8a are alternately communicated with the suction port 15 and the discharge port 16 which are formed in the valve plate 14 and have an arc shape.

Therefore, when the rotary shaft 5 is rotated, the cylinder block 8 is rotated together with the pistons 13, and each piston 13 is moved along the sloped surface 9b of the swash plate 9.
It is reciprocated in the cylinder bore 8a by the action of the shoe 11 that revolves on a circular orbit centered at. Then, the hydraulic oil is sucked into the cylinder bore 8a from the suction port 15,
The hydraulic oil in the cylinder bore 8 a is discharged from the discharge port 16. A suction passage 17 and a discharge passage 18 communicating with the suction port 15 and the discharge port 16 are formed in the rear end cover 3. The suction passage 17 is connected to the oil tank T.

[0021] As described above, the central axis O ₂ of the support shaft 10 of the swash plate 9 from the center axis O ₁ of the rotary shaft by a predetermined distance displaced upward. Therefore, the swash plate 9 is attached to each cylinder bore 8
Even if the biasing forces of the plurality of coil-shaped return springs 12 housed in a are the same, the inclination angle is always displaced to the minimum inclination angle (about 0.1 to 4 °) equal to zero capacity. Direction, that is, the minimum tilt position. This swash plate 9
If the frictional resistance of each sliding portion is neglected, the minimum inclination angle of is the counterclockwise rotation moment around the support shaft 10 due to the weight of the swash plate 9 in FIG.
The urging force of 2 causes the swash plate 9 to rotate in a clockwise direction about the support shaft 10 in a balanced position. In addition, if there is no displacement of the both axis lines O ₁ and O ₂ ,
The swash plate 9 is completely held at the zero capacity position where the slope 9b is orthogonal to the rotation axis O ₁ .

As described above, each return spring 12 has a function of pressing and holding each piston 13 against the slope 9b of the swash plate 9 via the shoe 11, and a function of biasing and holding the swash plate 9 at the minimum tilt position. Is also used.

An actuator 21 for cargo handling is connected to the discharge passage 18 of the pump P constructed as described above through a discharge conduit 20 as shown in FIG. Discharge line 20
A capacity switching valve 22 that doubles as a cargo handling switching valve is interposed in the discharge passage 18 (also acceptable). The capacity switching valve 22 includes an open port 23a that opens the discharge pipe 20, and the discharge pipe 2
There is provided a valve body 23 that can be switched between a drain port 23b that communicates 0 with the oil tank T, and a spring 24 that constantly urges the valve body 23 to the drain port 23b. Further, an electromagnetic solenoid 25 is operatively connected to the valve body 23, and when excited by a current as a cargo handling switching signal, the valve body 23 is switched from the drain port 23b to the open circuit port 23a. The electromagnetic capacity switching valve 22 can also be switched by a capacity switching lever 26 for manual operation.

The valve body 23 is provided with a pressure control valve 27 for rapidly increasing the pressure in the discharge conduit 20 when the valve body 23 is switched to the open port 23a. As shown in FIG. 5, the control valve 27 includes a valve body 28 that is switched between a closed port 28a that closes the discharge pipeline 20 and a port 28b that opens the discharge pipeline 20, and the valve body 28 is always closed. And a spring 29 for urging the closing port 28a. A pressure sensitive chamber 30 is provided on one end surface side of the valve body 28, and a pilot passage 31 is provided so that the discharge pressure P _d on the upstream side of the valve body acts on the pressure sensitive chamber 30.

As shown in FIG. 4, the discharge pipe 20 is provided with a relief valve 32 for protecting the hydraulic system when the discharge pressure P _d becomes abnormally high. Next, the operation of the hydraulic system mainly including the axial piston pump configured as described above will be described.

As shown in FIGS. 1 and 4, when the actuator 21 in which the capacity switching valve 22 is switched to the drain port 23b (non-loading position) is at rest, the engine E pumps the pump P.
Even if is driven, the increase in the discharge pressure P _d of the discharge line 20 directly connected to the oil tank T is low. Also, in this non-loading state, the swash plate 9 maintains a minimum inclination angle (0.1 to 1 °) equal to zero capacity by the elastic force of the return spring 12 and substitutes the clutch (off) function. Therefore, the starting torque of the pump P is small and the power consumption is small.

From this state, when the capacity switching valve 22 is switched from the drain port 23b to the open port 23a as shown in FIG. 6 by the operation of the electromagnetic solenoid 25 or the cargo handling switching lever 26, the pressure control valve 27 is connected to the discharge conduit 20. Are switched and arranged. Therefore, the discharge pressure P _d on the upstream side of the valve 22 is
Rapidly increases to the set value, and due to the rise of the pressure in each cylinder bore 8a, the swash plate 9 generates a turning moment in the direction of increasing the tilt angle about the support shaft 10, and the pump P is equal to zero. The minimum capacity is quickly changed to the maximum capacity as shown in FIG. For this reason, the pressure in the discharge pipe line 20 becomes high, the valve body 28 of the pressure control valve 27 is switched from the closed port 28a to the open port 28b in FIG. 5, and the supply of hydraulic oil to the actuator 21 is started, and the cargo handling is performed. Work is done.

The reason why the above-described rotational moment is generated will now be described. Since the plurality of cylinder bores 8a communicating with the suction port 15 formed in an arc shape have no pressure fluctuation, they do not cause a moment. But,
The pressure in the plurality of cylinder bores 8a in the discharge stroke communicating with the arc-shaped discharge port 16 rises substantially evenly. The discharge port 16 on the lower side of the rotation axis O ₂ of the support shaft 10 as a boundary
Since the number of cylinder bores 8a communicating with the discharge ports 16 on the upper side is always larger than the number of cylinder bores 8a communicating with the discharge port 16 on the upper side, the reaction force of each piston 13 acting on the slope 9b of the swash plate 9 on the lower side of the support shaft 10 Is greater than the resultant force of the reaction forces of the pistons 13 acting on the slope 9b of the swash plate 9 above the support shaft 10. Therefore, the swash plate 9 receives a turning moment in the clockwise direction in FIG.

After the work such as cargo handling is completed, the capacity switching valve 22 is switched from the open port 23a to the drain hoat 23b, and when the oil supply to the actuator 21 is stopped, the discharge based on the release of the operating load in the discharge pipeline 20 is performed. Due to the decrease in the pressure P _d , the pressure difference in each cylinder bore 8a almost disappears. Therefore, the piston 13 loses the turning moment in the direction of increasing the inclination angle of the swash plate 9, and the return spring 12
The swash plate 9 is gradually displaced by the urging force toward the side where the inclination angle is reduced, and the pump shifts to the minimum capacity equal to zero while continuing the operation.

By the way, in the above embodiment, the capacity switching valve 22
The valve body 23 is provided with the pressure control valve 27. With this arrangement, the pressure in the discharge pipe 20 of the pump rises quickly, and the capacity switching operation is performed quickly. However, even if this pressure control valve 27 is not provided, the pressure P _d in the discharge pipe line 20 is surely increased by the operating load of the actuator 21, so that the above-described pump capacity switching is performed.

In the above embodiment, the return spring 12 is provided in the cylinder bore 8a, and the support shaft 10 of the swash plate 9 is displaced to the top position T side of the swash plate 9 with respect to the central axis O ₁ of the rotary shaft 5. A capacity switching valve 22 was provided in the discharge conduit 20. For this reason, it is not necessary to use the return mechanism 48 shown in FIG. 8 which has been used conventionally, and it is possible to reduce the body diameter of the housing 1 and reduce the size and weight of the pump. Further, the number of parts can be reduced to facilitate the working and assembling, and the cost can be reduced.

The present invention is not limited to the above embodiment, but can be embodied as follows. (1) The pressure control valve 27 is separately provided outside the capacity switching valve 22.

(2) Although not shown, the return spring 12 is provided in the cylinder block 8 and the shoe 11 rather than in the cylinder bore.
To be installed between and. (3) Inside the rear end cover 3, the capacity switching valve 22
To house. In this case, the number of parts of the hydraulic system can be reduced, the assembling can be easily performed, and the cost can be reduced, as compared with the case where the discharge pipe 20 is provided.

[0034]

As described above in detail, according to the invention of claim 1, the body diameter of the housing of the piston pump can be reduced to reduce the size and weight, and the number of parts can be reduced to perform the working and the assembling. The manufacturing cost can be reduced easily.

Further, in the invention described in claim 2, in addition to the effect of the invention described in claim 1, the switching operation from the minimum capacity of the pump to the maximum capacity can be performed quickly.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an axial piston pump according to the present invention in a minimum displacement state.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a plan sectional view showing a mounting structure of a swash plate.

FIG. 4 is a circuit diagram showing a hydraulic system in an unloaded state.

FIG. 5 is a circuit diagram of a closed state of a pressure control valve.

FIG. 6 is a circuit diagram showing a hydraulic system in a cargo handling state.

FIG. 7 is a vertical sectional view of the axial piston pump in a maximum displacement state.

FIG. 8 is a vertical cross-sectional view of a conventional axial piston pump.

[Explanation of symbols]

1 ... Center housing, 2 ... Front end cover, 3
... rear end cover, 5 ... rotary shaft, 8 ... cylinder block, 8a ... cylinder bore, 9 ... swash plate, 9a ... bracket, 9b ... slope, 10 ... spindle, 11 ... shoe, 12 ... return spring, 13 ... piston, 18 Discharge passage, 20 Discharge pipe, 21 Actuator, 22 Volume switching valve, 23
... Valve, 23a ... Open port, 23b ... Drain port,
27 ... Pressure control valve, O ₁ ... Central axis of rotating shaft 5, O ₂ ...
Central axis of the support shaft 10, T ... Top position, P ... Pump.

Claims (2)

[Claims] 1. A rotary shaft supported by a housing is fitted with a cylinder block having a plurality of cylinder bores such that the cylinder block can rotate in a synchronous manner, and the rotary shaft can be tilted forward and backward by a support shaft and surrounds the rotary shaft. The swash plate is housed in each of the cylinder bores, and the base end portion of the piston housed in each cylinder bore is moored via a shoe so as to be slidable on a circular trajectory along the slope of the swash plate. An axial piston pump in which the cylinder block rotates synchronously with the piston, and the slope of the swash plate causes the piston to reciprocate in the cylinder bore to discharge the oil sucked into the cylinder bore from the suction passage to the discharge passage to supply it to the actuator. In, the central axis of the support shaft supporting the swash plate is set to the top position side of the swash plate with respect to the central axis of the rotating shaft, Between the top surface of each cylinder bore and each piston or between each cylinder block and each shoe, the inclination angle of the swash plate is always returned to the minimum inclination angle equal to zero capacity, and the shoe is attached to the slope surface of the swash plate. Axial piston pumps, each of which is provided with a spring for slidingly holding the same, and each of the discharge passages is provided with a capacity switching valve capable of switching between a port that opens the passage and a drain port that is connected to the low pressure side. 2. The discharge passage according to claim 1, wherein when the capacity switching valve is switched to the open port, the discharge passage is temporarily closed to raise the discharge pressure to a set value, and then the discharge passage is opened. Axial piston pump equipped with a pressure control valve.