JPH084658A - Variable displacement type piston pump - Google Patents

Abstract

PURPOSE:To provide constant flow rate control and cost reduction in manufacture by eliminating the use of a switching valve for volume control. CONSTITUTION:A cylinder block 8 provided with a cylinder bore 10 is fitted onto a driving shaft 5 so as to rotate synchronously, and the basic end part of a piston 11 stored in the bore 10 is brought into sliding contact with the sloped surface of a swash plate 17 whose angle is variable through a shoe 27. Between a front housing 2 and the swash plate 17, a return spring 28 which forces its inclined angle to the minimum position is placed. The swash plate 17 is supported by a supporting shaft 34 and an eccentric shaft 35. The position of the central axis O3 of the eccentric shaft 35, namely, the inclining center O3 of the swash plate 17 is set so as to be displaced downwards from the axis O1 of the driving shaft 5.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A hydraulic system for an industrial vehicle includes a variable displacement hydraulic pump driven by an engine, and a cargo handling actuator such as a lifting cylinder or a hydraulic motor driven by hydraulic oil discharged from the pump. .
Further, a switching valve for switching between non-cargo handling and cargo handling is provided in the discharge passage connecting the hydraulic pump and the actuator.

The displacement control of a conventional variable displacement hydraulic pump is
This is performed by mechanically changing the tilt angle of the swash plate housed inside the housing by an operation handle provided outside the housing to change the stroke of the working piston.

Further, as a displacement control mechanism of a conventional variable displacement pump, a control cylinder capable of changing the tilt angle of a swash plate of a hydraulic pump is provided, and a displacement switching valve for supplying control oil to the control cylinder is provided as a discharge pipe line. The one provided in the above has also been proposed.

[0005]

In the former displacement control mechanism of the hydraulic pump, since it is necessary to directly change the inclination angle of the swash plate by manually operating the operation handle, even when the engine speed fluctuates. There is a problem that a capacity control mechanism for controlling the discharge flow rate of the pump to be substantially constant cannot be incorporated. Also, in order to protect the circuit when an excessive load acts on the cargo handling actuator and the pressure in the discharge pipe becomes abnormally high, it is necessary to use a relief valve that operates at a large set pressure. There was also the problem of large losses.

The latter hydraulic pump displacement control mechanism is
By operating the displacement switching valve, the piston of the control cylinder adjusts the tilt angle of the swash plate to adjust the discharge capacity. For this reason, a displacement control valve that controls the discharge capacity to a constant value regardless of the engine speed is provided, and if the pressure in the discharge pipe becomes abnormal, the tilt angle of the swash plate is decreased to reduce the discharge capacity. It is also possible to reduce power consumption by reducing the size of the relief valve for circuit protection. However, the latter pump requires a dedicated capacity switching valve for switching the discharge capacity and a control cylinder, which increases the number of parts and complicates the structure, and the manufacturing and assembly work is troublesome and the cost is reduced. There was a problem that I could not do it.

A first object of the present invention is to solve the above-mentioned problems of the prior art and to discharge when the discharge pressure becomes abnormal and a capacity control mechanism for controlling the discharge capacity to be substantially constant irrespective of the engine speed. Provided with a variable displacement piston pump that can incorporate a capacity control mechanism that reduces the capacity to protect the circuit and power loss, simplifies the structure by reducing the number of parts, and reduces the manufacturing cost. To do.

A second object of the present invention is, in addition to the first object, to provide a variable displacement piston pump capable of further reducing the cost by simplifying the structure of the position adjusting means of the tilt center of the swash plate. To do.

A third object of the present invention is, in addition to the above-mentioned first object, that the size of the housing in the axial direction is shortened to reduce the size,
An object is to provide a variable displacement piston pump that can achieve weight reduction.

A fourth object of the present invention is, in addition to the first object, is to provide a variable displacement piston pump capable of changing the discharge direction of a discharge fluid. In addition to the first object, a fifth object of the present invention is to provide a variable displacement piston pump capable of further reducing the cost by simplifying the structure of the position adjusting means for the tilt center of the swash plate. is there.

A sixth object of the present invention is, in addition to the first object, to provide a variable displacement piston pump capable of controlling the discharge capacity to be substantially constant even if the engine speed changes. is there.

[0012]

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 drive shaft supported by a housing so as to be synchronously rotatable, A swash plate is housed in the housing so as to surround the drive shaft, and the swash plate is supported in the cylinder bore by a hinge mechanism so as to be capable of reciprocal tilting in the same direction as the axial direction of the drive shaft. The base end of each of the working pistons is moored slidably on a circular locus along the slope of the swash plate via a shoe and a retainer, and the cylinder block is rotated synchronously with the working piston by the rotation of the drive shaft. In a variable displacement piston pump in which a working piston is reciprocated in a cylinder bore to perform a pumping action, the swash plate is tilted with respect to the hinge mechanism. It is provided with a means for adjusting a direction toward or away from the location to the central axis of the drive shaft.

In order to achieve the second object, the position adjusting means for adjusting the tilt center of the swash plate according to the second aspect of the present invention includes a support shaft rotatably supported by the housing, and The eccentric shaft is formed at a position eccentric to the support shaft and is rotatably supported by the swash plate.

According to a third aspect of the present invention, in order to achieve the third object, the position adjusting means of the tilt center of the swash plate in the first aspect is used, and the tilt center of the swash plate is orthogonal to the central axis of the drive shaft. The position is adjustable in the direction.

According to a fourth aspect of the present invention, in order to achieve the fourth object, the position adjusting means of the tilt center of the swash plate in the first aspect of the present invention acts on each swash plate from each working piston by a pump action. There are two positions, a position where the turning moment based on the total force of the force receives the turning moment in the direction to increase the tilt angle of the swash plate and a position where the swash plate decreases the tilt angle and receives the turning moment in the opposite direction. Adjustable in one position.

According to a fifth aspect of the present invention, in order to achieve the fifth object, a pair of support shafts according to the first or fourth aspect are provided with position adjusting means for tilting center of the swash plate on both left and right sides of the swash plate. And a pair of movable bearings that respectively support both support shafts and are reciprocated by being guided by the guide surface of the housing, and a switching lever for synchronously switching the positions of both movable bearings. There is.

In order to achieve the sixth object, the invention according to claim 6 is the one according to any one of claims 1 to 5, wherein the housing is provided with a control cylinder for adjusting the inclination angle of the swash plate. A capacity for communicating the control chamber with the discharge passage of the pump through the control passage, providing a throttle in the discharge passage, and detecting the differential pressure of the discharge pressure before and after the throttle in the control passage to adjust the opening of the control passage. A control valve is provided.

[0018]

According to the first aspect of the invention, when the means for adjusting the position of the tilt center of the swash plate is actuated during the operation of the pump, the total force of the reaction forces of the respective working pistons acting on the swash plate by the pump action. The rotation moment around the tilt center acting on the swash plate changes based on Therefore, the inclination of the swash plate is changed,
The discharge capacity of the pump is changed.

According to the invention described in claim 2, in addition to the operation of the invention described in claim 1, when the support shaft is rotated, the eccentric shaft is revolved around the center axis of the support shaft, and the swash plate is tilted. The center position is adjusted. In this invention, since the means for adjusting the position of the tilt center of the swash plate is composed of the support shaft and the eccentric shaft, the number of parts can be reduced and the structure can be simplified. In addition to the action of the invention described in claim 1, since the tilt center of the swash plate is moved in the direction orthogonal to the central axis of the drive shaft, the mooring position of the working piston with respect to the swash plate and the slope thereof varies in the drive shaft direction. do not do. Therefore, the position of the tilt center is smoothly adjusted, and it is not necessary to increase the axial dimension of the housing.

In the invention according to claim 4, when the tilt center is alternately switched by sandwiching the center axis of the drive shaft by the position adjusting means of the tilt center of the swash plate, the tilt direction of the swash plate is changed to the center axis of the drive shaft. The ejection direction of the fluid is switched by reversing with the straight line orthogonal to.

According to the fifth aspect of the present invention, when the switching lever is operated, both movable bearing members are reciprocated along the guide surface of the housing, and the position of the swash plate is changed via the both support shafts. In the invention according to claim 4, the structure of means for changing the tilt center of the swash plate is simplified.

Further, in the invention according to claim 6, when the rotational speed of the drive shaft fluctuates and the differential pressure between the discharge pressures before and after the throttle increases, the control passage is closed and the drain passage is opened. And the discharge capacity is reduced. Therefore, the discharge flow rate of the pump is kept substantially constant.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A first embodiment of a variable displacement piston pump embodying the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the front housing 2 is joined to the front (left) end surface of the center housing 1, and the rear end cover 3 is joined to the rear (right) end surface of the center housing 1. These are not shown. They are fastened together by bolts. The center housing 1, the front housing 2 and the rear end cover 3 form a closed working space 4. A drive shaft 5 is supported by bearings 6 and 7 between the opposing end walls of the front housing 2 and the rear end cover 3, and an engine or the like is driven by a power take-out device (PTO) (not shown) fitted to the outer ends of the drive shaft 5. It is designed to be rotated directly.

A cylinder block 8 is connected to the drive shaft 5 by a spline 9 so as to be rotatable synchronously and movable along the axial direction of the drive shaft 5, and a plurality of cylinder bores 10 are provided in the cylinder block 8. Are formed so as to be parallel to the drive shaft 5 and located at the same pitch on the same circumference centered on the drive shaft 5, and the working pistons 11 are inserted into the respective bores 10.

A valve plate 12 is fixed to the rear end cover 3 in correspondence with the cylinder block 8. The plate 12 is formed with an arc-shaped suction port 13 and a discharge port 14, and the end cover 3 has a suction port 1
A suction passage 15 and a discharge passage 16 are formed so as to correspond to 3 and the discharge port 14. The bore 10 in the cylinder block 8 that rotates integrally with the drive shaft 5 is alternately connected to the suction port 13 and the discharge port 14.

A swash plate 17 is tiltably supported by the center housing 1 via a hinge mechanism 18 which will be described in detail later. The drive shaft 5 passes through a hole 19 formed in the swash plate 17 at substantially the center thereof. There is. A pressing spring 21 is housed in a housing chamber 20 formed in the center of the cylinder block 8 so as to surround the drive shaft 5. The spring force acts on the cylinder block 8 via the spring bearing 22, and also acts on the shoe retainer 26 via the spring bearing 23, the pin 24 and the pivot 25. Therefore, the shoe 27 on the shoe retainer 26 is pressed against the swash plate 17, and the cylinder block 8
The piston 11 pressed by the valve plate 12 and connected to the shoe 27 can reciprocate by a distance corresponding to the tilt angle of the swash plate 17. The hydraulic oil is sucked into the cylinder bore 10 through the suction passage 15 and the suction port 13 by the reciprocating movement of the piston 11, and the hydraulic oil in the bore 10 is discharged from the discharge port 1.
4 and the discharge passage 16 are discharged to the outside.

A return spring 28 as a return means is interposed between the end wall of the housing 2 and the outer periphery of the upper portion of the swash plate 17. The spring force of the return spring 28 acts on the upper front surface (the left side in FIG. 1) of the swash plate 17 via the spring receiver 29. The swash plate 17 is always displaced by the return spring 28 to a minimum inclination angle (about 0.1 to 1 °) which is almost equal to zero capacity,
That is, it is biased to the minimum capacity position.

Next, the hinge mechanism 18 of the swash plate 17 will be described in detail. As shown in FIG. 3, brackets 31 are integrally formed on both right and left sides of the swash plate 17 so as to be curved. or,
As shown in FIG. 4, bearings 32 and seal rings 33 are provided on both side walls of the center housing 1 so as to correspond to both brackets 31.
A pair of support shafts 34 are supported via. Both support shafts 34
The eccentric shafts 35 are formed integrally with each other, and both eccentric shafts 3
Both brackets 31 of the swash plate 17 are supported on the bearing 5 by bearings 36. A discharge capacity switching lever 38 is connected to the outer end of the support shaft 34 via a connecting fitting 37. The connecting fitting 37 is fastened to the support shaft 34 with bolts 39, and a rotation preventing pin 40 is interposed between the support shaft 34 and the connecting fitting 37.

As shown in FIGS. 1 and 4, the center axis O1 of the drive shaft 5 is located above the center axis O2 of the support shaft 34, and the center axis O3 of the eccentric shaft 35 is in operation when the pump is operating at the minimum capacity.
The tilt center O3 of the swash plate 17 is held at the same height as the axis O1 of the drive shaft 5. Further, in FIG. 5, when the switching lever 38 is rotated counterclockwise from the solid line position, the tilting center O3 of the swash plate 17 is displaced by the support shaft 34 below the axis O1. When the position of the tilt center O3 is changed, the rotational moment acting on the swash plate 17 is changed, the tilt angle of the swash plate is changed, and the discharge capacity is changed, as described later. As shown in FIG. 5, the switching lever 38 is provided with locking fittings 38A, 38 attached to the center housing 1.
B is locked in two positions.

Next, during operation of the pump, the drive shaft 5
A control mechanism for keeping the discharge volume substantially constant when the number of rotations fluctuates will be described. A control cylinder 41 is cantilevered on the rear end cover 3, and a control piston 42 is accommodated in the cylinder 41 in parallel with the drive shaft 5 and capable of reciprocating in the same direction. The tip end surface of the control piston 42 pushes the spherical body 43 moored to a part of the swash plate 17 to push the tilt angle of the swash plate 17 against the elastic force of the return spring 28 to increase the operation. Piston 1
Change the stroke of 1 and adjust the discharge volume. When the hydraulic circuit is stopped, the control chamber 44 in the control cylinder 41
Is the atmospheric pressure, the elastic force of the return spring 28 biases and holds the swash plate 17 at the position where the tilt angle is minimum in FIG. 1, that is, at the minimum capacity position. That is, the base end surface of the control piston 42 is locked by the stopper 45 formed on the inner peripheral surface of the control cylinder 41, whereby the minimum inclination angle of the swash plate 17 is set. The stopper 46 formed on the front housing 2 regulates the maximum tilt angle of the swash plate 17.

The suction passage 15 of the pump 51 constructed as described above is connected to the oil tank 53 through the suction pipe line 52. A valve housing 54 is fixed to the rear end cover 3, and a discharge passage 55 communicating with the discharge passage 16 is formed in the housing 54. As shown in FIG. 6, a hydraulic motor 57 as a cargo handling actuator is connected to the discharge passage 55 via a discharge conduit 56. A cargo handling switching valve 58 is interposed in the discharge pipeline 56.

A throttle 5 is provided in the passage 55 of the housing 54.
9 is provided, and a valve 60 that controls the operation of the control piston 42 by the pressure difference across the throttle 59 is housed.
As shown in FIG. 6, the capacity control valve 60 has a valve body 62 that opens and closes a control passage 61 that connects the discharge passage 16 and the control chamber 44.
And a port 63 that always opens the passage 61 in the valve body 62.
And a spring 64 for urging the spring. Further, pressure sensing chambers 65 and 66 that receive the discharge pressure before and after the throttle 59 are formed at both ends of the valve body 62, and when the pressure difference increases, the valve body 62 moves against the biasing force of the spring 64. Then, the control passage 61 is closed, and the control chamber 44 communicates with the drain passage 67. As a result, in the control valve 60, when the rotation speed N of the engine E increases and the rotation speed of the drive shaft 5 increases,
The supply of oil to the control chamber 44 is reduced, the discharge capacity of the pump is reduced, and as a result, the discharge capacity Q of the pump is controlled to be substantially constant even if the rotation speed changes (see FIG. 7).

As shown in FIG. 6, the pump 51 and the throttle 5
Between 9 and 9, a preloading valve 7 for obtaining pilot pressure
1 is provided. Further, the discharge pipe 56 is provided with a relief valve 72 for protecting the hydraulic system when the discharge pressure becomes abnormally high. The preload application valve 71 is shown in FIG.
As shown in FIG. 7, the spool 73, the spring 74 that normally urges the spool 73 to the closed position, and the pressure in the discharge passage 16 are applied to the spool 7.
3 and a pilot passage 76 that acts on the pressure-sensitive chamber 75 formed on one end surface thereof.

Next, regarding the hydraulic system mainly composed of the variable displacement piston pump 51 constructed as described above,
The operation will be described. 1 and 6 show the stopped state of the hydraulic system. In this state, the pressure inside the pump 51 is kept equal to the atmospheric pressure, and the swash plate 17 is kept at the minimum inclination angle. Further, in FIG. 6, the cargo handling switching valve 58 is held in the non-cargo handling position, and the valve body 62 of the control valve 60 is held by the port 63 that opens the control passage 61 by the spring 64. Further, the switching lever 38 is at the minimum capacity position, that is, the swash plate 17
The tilt center O3 of the drive shaft is held at a position that coincides with the axis O1 of the drive shaft 5.

When the drive shaft 5 is rotated by the engine E in this state, the working piston 11 reciprocates together with the cylinder block 8 with a minimum stroke, and the suction port 13
The hydraulic oil drawn from the discharge port 14 is discharged through the discharge passage 16
To discharge. At this time, the discharge passage 1 is opened by the preload applying valve 71.
The pressure in 6 is maintained at the set value P1, but since the tilt center O3 of the swash plate 17 is on the central axis O1 of the drive shaft 5, no rotational moment acts on the swash plate 17. Further, since the pressure of the set value P1 or less is applied to the control chamber 44, the swash plate 17 has the minimum inclination angle (0.1 to 0.1) due to the elastic force of the return spring 28.
(1 °) position, the minimum capacity operation equal to zero capacity is continued, and the minimum tilt angle is maintained to replace the clutch (off) function. Therefore, the starting torque of the pump 51 is small and the power consumption is small.

When the switching lever 38 is rotated in this state, the support shaft 34 is rotated and the eccentric shaft 35 is rotated counterclockwise in FIGS. Therefore, the tilt center O3 of the swash plate 17 is displaced downward from the axis O1. As a result,
The pressing force of the working piston 11 acting on the slope of the swash plate 17 above the tilt center O3 of the swash plate 17 becomes larger than the pressing force acting below the tilt center O3, and the swash plate 17 is shown in FIG. It is rotated to an intermediate tilt position as shown by the chain line. As shown in FIG. 4, since there is no pressure fluctuation in the plurality of cylinder bores 10 communicating with the suction port 13 formed in an arc shape,
It does not cause a moment. The pressure in the plurality of cylinder bores 10 communicating with the arc-shaped discharge port 14 rises substantially evenly during the discharge stroke. When the number of cylinder bores 10 communicating with the upper discharge port 14 is greater than the number of cylinder bores 10 communicating with the lower discharge port 14 with the tilt center O3 of the swash plate as a boundary, the eccentric shaft 3 is formed.
Each piston 1 acting on the slope of the swash plate 17 above 5
The reaction force (resulting force) of 1 becomes larger than the reaction force (resulting force) of each piston 11 that acts on the slope of the swash plate 17 below the eccentric shaft 35. Therefore, the swash plate 17 is centered on the eccentric shaft 35 as shown in FIG.
At the counterclockwise rotation moment,
The tilt angle increases.

The intermediate inclination angle of the swash plate 17 is a position where the turning moment of the hydraulic oil acting on the swash plate 17 and the urging force of the return spring 28 are balanced. When the cargo handling switching valve 58 is held in the non-cargo handling position, the pressure in the control chamber 44 is low and the pressing force of the control piston 42 does not act on the swash plate 17.

The eccentric shaft 35 is the central axis O2 of the support shaft 34.
Since it is rotated in the counterclockwise direction by 90 ° about, the tilt center O3 of the swash plate 17 is also displaced to the front side. However, the biasing force of the spring 21 causes each shoe 27 to pass through the spring receiver 23, the pin 24, the pivot 25, and the shoe retainer 26.
Therefore, the shoe 27 is constantly pressed against the slope of the swash plate 17.

Next, when the cargo handling switching valve 58 is switched to the cargo handling position, the discharge passage 1 is driven by the load of the hydraulic motor 57.
6, 55, the pressure in the discharge pipe 56 rises. Then
Since the control oil is sent from the control passage 61 to the control chamber 44,
The control piston 42 is advanced, the tilt angle of the swash plate 17 is increased, and is held at the maximum tilt position as shown in FIG. Therefore, a large amount of oil is supplied from the discharge pipe line 56 to the motor 57, and actuators such as a compressor and a cylinder are operated,
Cargo handling work is performed.

By the way, when the engine speed increases while the vehicle is running, the drive shaft 5 speed increases. Therefore, the amount of hydraulic oil discharged from the discharge port 14 increases,
Since the pressure difference before and after the throttle 59 becomes large and the control valve 60 is switched to the position where the control passage 61 is closed and the drain passage 67 is opened, the inclination angle of the swash plate 17 is reduced and the discharge capacity is reduced. As a result, the actual discharge capacity of the pump is controlled to be substantially constant.

If an excessive load acts on the hydraulic motor 57 and the pressure in the discharge pipe line 56 rises above the set value P3 as shown in FIG. 8, the relief valve 72 shown in FIG. Is activated to prevent damage to the hydraulic system.

Further, when the cargo handling switching valve 58 is switched from the cargo handling position to the non-cargo handling position, the pressure in the discharge conduit 56 decreases, so that the swash plate 17 is shown by a chain line in FIG. Is displaced into position. Therefore, pump 5
1 operates at an intermediate capacity, so power loss is reduced. When the switching lever 36 is switched from the intermediate capacity position shown by the chain line in FIG. 5 to the zero capacity position shown by the solid line, the eccentric shaft 35 is switched to the position shown by the solid line in FIG. The turning moment due to the hydraulic oil is lost, and the swash plate 17 is returned to the minimum tilt position shown by the solid line in FIG. 1 by the spring 28.

In the first embodiment, the swash plate 17 is attached to the support shaft 34.
And the tilt center O3 of the swash plate 17 supported by the eccentric shaft 35.
Is configured to be displaceable downward from the axis O1 of the drive shaft 5.
Therefore, only by operating the switching lever 38, the displacement of the pump can be controlled by changing the tilt angle of the swash plate 17 without using a complicated and expensive switching valve. Further, it is possible to provide a control valve 60 for controlling the discharge oil amount to be substantially constant even if the engine speed changes. Also, the discharge line 5
It is also possible to provide a pressure cut control valve (not shown) for reducing the discharge capacity by reducing the pressure in the control chamber 44 of the control piston 42 when the pressure in 6 abnormally rises. By providing this control valve, the set value of the relief valve 72 can be set to P2 lower than P3 as shown in FIG. 8, and power loss can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, a swash plate 17 and a columnar support shaft 8 which are integrally formed concentrically with a square columnar movable bearing body 81.
Supported by 2. That is, the movable bearing 81 is fitted in the guide groove 83 formed in the housing 1 so as to be able to reciprocate vertically, and the support shaft 82 is inserted into the bracket 31 of the swash plate 17. The switching lever 38 can reciprocate the movable bearing 81 in the vertical direction. In this embodiment, the position of the tilt center O3 can be vertically displaced by moving the swash plate 17 in the vertical direction, so that the displacement of the swash plate 17 in the direction of the axis O1 of the drive shaft 5 is eliminated.
As compared with the first embodiment, fluctuations in the discharge capacity of the pump are prevented.

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, the axis of the support shaft 82 that supports the swash plate 17 when the pump is stopped, that is, the tilt center O3 of the swash plate coincides with the center axis O1 of the drive shaft 5. or,
The tilt center O3 of the swash plate 17 is moved to the axis O by the switching lever 38.
It can be changed from 1 upward or downward. Further, the control cylinder 41, the control piston 42, the return spring 28, etc. are omitted.

In the third embodiment, when the drive shaft 5 is rotated, the swash plate 17 is held at the minimum inclination angle by the spring (not shown), so that the swash plate 17 is started with the minimum capacity. Switching lever 38
When the support shaft 82 is switched upward by the above, the swash plate 17 receives a rotational moment in the clockwise direction by the hydraulic oil, and its inclination angle is displaced to the maximum inclination angle, and the pump operates at the maximum displacement. Further, when the support shaft 82 is displaced below the axis O1, the swash plate 17 receives a turning moment in the counterclockwise direction and is tilted in the opposite direction, and when the discharge direction of the hydraulic oil is reversed, the swash plate 17 is maximized. It becomes capacity operation.

Also in the third embodiment, the discharge capacity can be easily changed with a simple structure. Further, in this embodiment, the switching lever 38 can also be used as a cargo handling switching lever. This pump can be used as an inexpensive pump when the function of controlling the flow rate to be constant regardless of the fluctuation of the rotation speed is not required, such as a dump truck.

Next, a fourth embodiment of the present invention will be described with reference to FIGS. 11 and 12. In this embodiment, the return spring 2
8 biases the swash plate 17 toward the maximum capacity position. The drive shaft 5 is connected to the engine E via an electromagnetic clutch (not shown).

Therefore, in this embodiment, when the electromagnetic clutch is turned on with the pump stopped as shown in FIG.
The pump 51 is started with the maximum capacity. Then, the switching lever 38 is operated to displace the tilt center O3 of the swash plate 17 below the axis O1 of the drive shaft 5 as shown in FIG. Therefore, the swash plate 17 receives a rotational moment in the counterclockwise direction about the center O3, and the swash plate 17 is rotated in the direction in which the inclination angle is reduced against the biasing force of the spring 28. Therefore, the pump operates at minimum capacity as shown in FIG.

Next, a fifth embodiment of the present invention will be described with reference to FIGS. 13 and 14. In this embodiment, a pair of left and right arc-shaped support shafts 91 are integrally provided on the back surface of the swash plate 17, and the movable bearing body 9 having a guide groove 92 for the support shafts 91 is provided.
Reference numeral 3 is in contact with the inner wall surface of the front housing 2 so as to be capable of reciprocating in a direction orthogonal to the axis O1. Further, the switching lever 38 is connected to the movable bearing body 93, and the tip end thereof penetrates the front housing 2 and is led out to the outside.

In this embodiment, when the switching lever 38 is reciprocated in the vertical direction, the bearing body 93 is reciprocated in the vertical direction along the guide surface 94 of the front housing 2, and the tilt center O3 of the swash plate 17 is driven by the drive shaft. 5 is displaced in a direction away from the axis O1. Therefore, the discharge capacity of the pump can be changed with a simple configuration.

The present invention is not limited to the above embodiment, but can be embodied as follows. (1) The switching lever 38 can be operated by a wire (not shown).

(2) In the third and fourth embodiments, the position of the tilt center O3 of the swash plate 17 is adjusted by the eccentric shaft 35. The technical ideas other than the claims that can be understood from the above embodiments will be described below along with their effects.

In claim 1, an arcuate support shaft 91 is formed on the back surface of the swash plate 17, and the support shaft 91 is reciprocally movable in a direction orthogonal to the axis O1 of the drive shaft 5.
Variable displacement piston pump engaged with the guide groove 92 of FIG.

In the case of this pump, in addition to the action and effect of the first aspect of the invention, displacement can be properly performed by eliminating displacement of the tilt center O3 of the swash plate 17 in the direction of the axis O1.

[0057]

As described above in detail, according to the invention described in claim 1, the displacement control mechanism for controlling the displacement to be substantially constant irrespective of the engine speed and the displacement when the discharge pressure becomes abnormal. It is possible to incorporate a capacity control mechanism for reducing the circuit protection and power loss, and to reduce the number of parts to simplify the structure and reduce the manufacturing cost.

According to the invention of claim 2, in addition to the effect of the invention of claim 1, the number of parts of the position adjusting means for the tilt center of the swash plate can be reduced to simplify the structure. According to the invention of claim 3, in addition to the effect of the invention of claim 1, the axial dimension of the housing can be shortened to reduce the size and weight.

According to the invention described in claim 4, in addition to the effect of the invention described in claim 1, the discharge direction of the discharge fluid can be changed. According to the invention of claim 5, claim 1 or 4
In addition to the effects of the invention described above, the structure of the position adjusting means for the tilt center of the swash plate can be simplified to further reduce the cost.

According to the sixth aspect of the invention, in addition to the effect of any one of the first to fifth aspects of the invention, the discharge capacity can be controlled to be substantially constant even if the engine speed changes.

[Brief description of drawings]

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

FIG. 2 is a vertical cross-sectional view of the pump in a maximum capacity state.

FIG. 3 is an exploded perspective view showing a hinge mechanism of a swash plate.

FIG. 4 is a sectional view showing a hinge mechanism of a swash plate.

FIG. 5 is a front view showing a hinge mechanism of a swash plate.

FIG. 6 is a circuit diagram showing a hydraulic system in an unloaded state.

FIG. 7 is a graph showing the relationship between engine speed and discharge capacity.

FIG. 8 is a graph showing the relationship between discharge pressure and discharge volume.

FIG. 9 is a cross-sectional view of a pump showing a second embodiment of the present invention.

FIG. 10 is a vertical sectional view of a pump showing a third embodiment of the present invention.

FIG. 11 is a vertical sectional view of the pump of the fourth embodiment in the maximum displacement state.

FIG. 12 is a vertical sectional view of a pump of a fourth embodiment in a minimum capacity state.

FIG. 13 is a partial vertical cross-sectional view of the pump of the fifth embodiment in the minimum capacity state.

FIG. 14 is an exploded perspective view showing a hinge mechanism of a swash plate according to a fifth embodiment.

[Explanation of symbols]

1 ... Center housing, 2 ... Front housing, 3 ...
Rear end cover, 5 ... Drive shaft, 8 ... Cylinder block, 10 ... Cylinder bore, 11 ... Working piston, 16 ...
Discharge passage, 17 ... Swash plate, 18 ... Hinge mechanism, 26 ... Retainer, 27 ... Shoe, 28 ... Return spring, 31 ... Bracket, 34 ... Spindle, 35 ... Eccentric shaft, 38 ... Switching lever, 4
1 ... Control cylinder, 44 ... Control chamber, 56 ... Discharge pipe line, 5
7 ... Hydraulic motor as an actuator, 58 ... Cargo handling switching valve, 59 ... Throttle, 60 ... Capacity control valve, 61 ... Control passage, 81 ... Movable bearing body, 82 ... Support shaft, 83 ... Guide groove, 9
1 ... Support shaft, 92 ... Guide groove, 93 ... Movable bearing body, 94 ... Guide surface, O1 ... Central axis of drive shaft, O3 ... Tilt center of swash plate.

Claims (6)

[Claims] 1. A drive shaft supported by a housing is fitted with a cylinder block having a plurality of cylinder bores such that the cylinder block can rotate synchronously, and a swash plate is housed in the housing so as to surround the drive shaft. The swash plate is supported by a hinge mechanism so as to be capable of reciprocal tilting in the same direction as the axis of the drive shaft, and the base end of each working piston housed in each cylinder bore is attached to the swash plate's slope through a shoe and a retainer. A variable displacement piston moored along a circular locus along which the cylinder block and the working piston are synchronously rotated by the rotation of the drive shaft so that the working piston reciprocates in the cylinder bore to perform a pumping action. In the pump, for adjusting the position of the tilting center of the swash plate with respect to the hinge mechanism in a direction toward or away from the central axis of the drive shaft. Variable displacement piston pump provided with a stage. 2. The position adjusting means for tilting center of the swash plate according to claim 1, the support shaft being rotatably supported by the housing and the eccentric position with respect to the support shaft. A variable displacement piston pump comprising an eccentric shaft rotatably supported. 3. A variable displacement piston according to claim 1, wherein the position adjusting means for adjusting the tilt center of the swash plate is capable of adjusting the position of the tilt center of the swash plate in a direction orthogonal to the central axis of the drive shaft. pump. 4. The position adjusting means for adjusting the tilt center of the swash plate according to claim 1, wherein the rotational moment based on the total force of the reaction forces acting on the swash plate from each working piston by the pump action changes the tilt angle of the swash plate. A variable displacement piston pump configured to be adjustable to two positions, a position for receiving a turning moment in an increasing direction and a position for a swash plate to decrease its tilt angle and receive a turning moment in the opposite direction. . 5. The position adjusting means for tilting center of the swash plate according to claim 1 or 4, wherein a pair of support shafts provided on both left and right sides of the swash plate support both the support shafts, and a guide surface of the housing. A variable displacement piston pump including a pair of movable bearing bodies that are guided and reciprocated by a movable bearing body and a switching lever that synchronously switches the positions of the movable bearing bodies. 6. The control cylinder according to claim 1, wherein the housing is provided with a control cylinder for adjusting the inclination angle of the swash plate, and the control chamber of the cylinder communicates with the discharge passage of the pump through the control passage. The discharge passage is provided with a throttle, and the control passage is provided with a displacement control valve that senses a pressure difference between the discharge pressure before and after the throttle and adjusts the opening of the control passage.