JPH09280159A - Axial piston type hydraulic pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent vibration and noise, etc., due to pulsation, to improve the efficiency and life of a pump. SOLUTION: One side of an oil hole 17, positioned on the movable locuses of respective cylinder ports 8A, is provided on one-side of a directional control valve part of a valve plate 14, and the other side of an oil hole 18 is provided on the other side of a directional control valve part. Also, a communication path 19 is formed on a rear casing 4 so that the oil holes 17 and 18 can be constantly communicated, and also a check valve 21 for allowing the flow of a pressurized oil from one side oil hole 17 to another side oil hole 18, and checking a reverse direction flow, is provided on the halfway of the path 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial piston type hydraulic pump used as, for example, a swash plate type pump, an oblique type pump and the like.

[0002]

2. Description of the Related Art Generally, as a hydraulic pump for supplying pressure oil to a hydraulic cylinder for a working device such as a hydraulic excavator or a hydraulic motor for turning or traveling, a casing and a rotary rotatably provided in the casing. A shaft, and is provided so as to rotate integrally with the rotary shaft located inside the casing;
A cylinder block formed with a plurality of cylinders spaced apart from each other in the circumferential direction and extending in the axial direction, and slidably fitted in each cylinder of the cylinder block. It is composed of a plurality of pistons that move to suck and discharge hydraulic oil, and a valve plate that is provided between the casing and the end surface of the cylinder block and that has suction ports and discharge ports that communicate with the cylinders. Axial piston type hydraulic pumps are widely known.

In this type of conventional hydraulic pump, when the rotary shaft is rotationally driven by a drive source such as an engine, the cylinder block is rotated in the casing together with the rotary shaft. As a result, the piston reciprocates in each cylinder of the cylinder block, and the working oil sucked into the cylinder from the suction port is pressurized by the piston and discharged to the discharge port as pressure oil.

The operation of the cylinder block, piston and valve plate will now be described. When the cylinder port of each cylinder communicates with the suction port of the valve plate, the direction in which the piston projects from the beginning to the end of the suction port To the suction stroke for sucking the working oil into the cylinder from the suction port. On the other hand, when the cylinder port of each cylinder communicates with the discharge port, the piston moves in the direction in which the piston enters the cylinder from the start end to the end of the discharge port to discharge the hydraulic oil in the cylinder into the discharge port. It is a process. And
By rotating the cylinder block to repeat this operation (stroke), the hydraulic oil sucked into the cylinder from the suction port in the suction stroke is pressurized in the discharge stroke and discharged to the discharge port, and this pressure oil is discharged to the hydraulic cylinder or the like. The power is supplied to the hydraulic motor.

As another conventional technique, for example, in the hydraulic pump disclosed in Japanese Utility Model Laid-Open No. 58-120882, a return port having a small diameter is provided between the intake port and the discharge port, and the return port is connected between the return ports. Are configured to communicate with each other.

[0006]

By the way, in the above-mentioned axial piston type hydraulic pump according to the prior art, the pressure in the cylinder which sucks the hydraulic oil through the suction port of the valve plate during the suction stroke is reduced to the pressure in the discharge port. The pressure becomes lower than that. In addition, the pressure in the cylinder tends to be negative because the volume in the cylinder is slightly expanded before the piston reaches the bottom dead center after the suction stroke. When the cylinder port of each cylinder begins to communicate with the discharge port, high pressure oil in the discharge port rapidly flows (backflows) into the low pressure cylinder via the cylinder port, causing a large pressure fluctuation. However, there is a problem that pulsation is generated in the piston due to this pressure fluctuation, and vibration or noise is generated from the casing via the swash plate or the like. Further, pulsation also occurs in a hose pipe or the like connected to the discharge port, and noise and vibration are also generated from the hose pipe side.

On the other hand, in the discharge stroke, the pressure in the cylinder that has discharged the hydraulic oil through the discharge port becomes higher than the pressure in the suction port, and the pressure in each cylinder ends the discharge stroke and the piston moves upward. The pressure in the cylinder is further reduced by slightly reducing the volume in the cylinder before reaching the dead point. The high pressure oil remaining in the cylinder may flow back into the suction port through the cylinder port when it starts communicating with the suction port, so that the working oil from the suction port smoothly flows into the cylinder. There is a problem that the efficiency of the pump is lowered because the pump cannot be sucked.

Further, as described above, the pressure oil that flows backward from the discharge port into the cylinder and the pressure oil that flows backward from the cylinder into the suction port becomes a jet flow that is rapidly ejected into the cylinder and the suction port. This jet flow may cause erosion or the like on the inner wall portions of the cylinder port and the suction port of each cylinder, resulting in a problem that pump efficiency and life are significantly reduced.

Therefore, as a countermeasure for preventing the occurrence of pulsation and erosion, in the above-mentioned other prior art, a cylinder whose inside has a low pressure due to a suction stroke and a cylinder whose inside has a high pressure due to a discharge stroke have been described. , It is possible to reduce the pressure difference between the discharge port or the suction port and the inside of the cylinder by temporarily connecting the small diameter return port and replenishing the high pressure hydraulic oil into the low pressure cylinder. There is.

However, in this case, since the cylinder whose internal pressure is high due to the discharge stroke and the cylinder whose internal pressure is low due to the suction stroke are momentarily communicated with each other,
There is a problem that sufficient pressure oil cannot be replenished from the high-pressure side cylinder into the low-pressure side cylinder, and pump efficiency and life cannot always be sufficiently improved.

Further, in another conventional technique, it is necessary to process the three members of the valve plate, the cylinder block, and the casing, and there is a problem that the number of processing steps increases.

The present invention has been made in view of the above-mentioned problems of the prior art, and provides an axial piston type hydraulic pump capable of effectively preventing vibration and noise due to pulsation and reliably improving pump efficiency and life. It is intended to be provided.

[0013]

In order to solve the above-mentioned problems, the present invention provides a casing, a rotating shaft rotatably provided in the casing, and the casing so as to rotate integrally with the rotating shaft. A cylinder block having a plurality of cylinders formed therein, and a plurality of pistons slidably inserted into the cylinders of the cylinder block and reciprocating in the cylinders as the cylinder block rotates. , A valve plate which is provided between the casing and the cylinder block and which faces the intake port and the discharge port with the rotating shaft interposed therebetween and which has one side of the switching valve portion and the other side of which the switching valve portion is formed. It is applied to axial piston type hydraulic pumps.

The feature of the structure adopted by the invention of claim 1 is that the oil hole on one side provided in the switching valve portion on one side and the oil hole on the other side provided in the switching valve portion on the other side are provided. An oil hole, a communication passage that communicates the oil hole on one side with the oil hole on the other side, and pressure oil is provided in the middle of the communication passage from the oil hole on one side toward the oil hole on the other side. It is provided with a backflow preventing means for allowing the flow and preventing the reverse flow.

With this configuration, even if high pressure oil remains in the cylinder that has reached the switching valve portion on one side after the discharge stroke, for example, this cylinder is still on the switching valve portion on one side. Communicates with the oil hole on one side, so that the pressure oil remaining inside the cylinder can be discharged from the oil hole on one side toward the oil hole on the other side via the communication passage. On the other hand, in the cylinder that has completed the suction stroke and reached the switching valve portion on the other side, the volume in the cylinder slightly expands until the piston reaches the bottom dead center, and the cylinder tends to have a negative pressure. However, at this time, the cylinder on the switching valve portion on the other side communicates with the oil hole on the other side, so that the pressure oil via the communication passage flows into the cylinder from the oil hole on the other side,
It is possible to prevent negative pressure in the cylinder.

Further, when the cylinder communicates with the discharge port while communicating with the oil hole on the other side by the backflow prevention means provided in the middle of the communication passage, the pressure in the cylinder communicates with the oil hole on the one side. Even if the pressure becomes higher than the pressure in the cylinder, the pressure oil can be prevented from flowing backward from the cylinder communicating with the oil hole on the other side to the oil hole on the one side through the communication passage.

Further, in the invention described in claim 2, the switching valve portion on the one side is disposed on the top dead center side where each piston reciprocating in each cylinder switches from the discharge stroke to the suction stroke. The switching valve portion on the other side is disposed on the bottom dead center side where each piston switches from the suction stroke to the discharge stroke.

With this structure, the high pressure oil can be discharged from the cylinder at the top dead center side to the cylinder at the bottom dead center side, and the pressure in the cylinder at the bottom dead center side is increased. The pressure difference between the cylinder and the discharge port can be reduced.

On the other hand, in the invention described in claim 3, the oil hole on the one side is connected to a tank line communicating with the tank, and an oil hole on the one side from the tank is formed in the middle of the tank line. It is composed of an oil liquid replenishing means for allowing the oil liquid to be replenished toward it and preventing a reverse flow.

With this configuration, the cylinder is in communication with the oil hole on one side and is in slight communication with the suction port at the initial stage of the suction stroke, even if the suction flow rate of the oil liquid from the suction port is insufficient. It is possible to replenish the oil liquid from the tank and prevent negative pressure in the cylinder.

Further, in the invention described in claim 4, between the oil hole on the other side and the discharge port, an oil passage communicating between the two is provided, and in the middle of the oil passage, the oil passage on the other side is provided. The pressure oil discharge means is configured to allow the pressure oil to be discharged from the oil hole toward the discharge port and prevent the flow in the opposite direction.

With this configuration, the cylinder communicates with the oil hole on the other side at the initial stage of the discharge stroke and slightly communicates with the discharge port, so that the pressure oil flows into the cylinder from the discharge port and the inside of the cylinder. Even if the volume of the cylinder is reduced and the pressure in the cylinder becomes high, the pressure oil in the cylinder can be discharged to the discharge port through the oil passage, and the pressure in the cylinder can be prevented from becoming excessive.

[0023]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

1 to 5 show a variable displacement type swash plate type hydraulic pump as an axial piston type hydraulic pump according to the first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a casing which forms an outer shell of a swash plate type hydraulic pump. The casing 1 is a cylindrical casing body 2 and a front casing 3 for closing an opening on one end side of the casing body 2. And a rear casing 4 that closes the other end side opening of the casing body 2. Further, the front casing 3 is formed with an insertion hole 3A in the axial direction through which a rotary shaft 5 described later is inserted.

A rotary shaft 5 is rotatably supported by the casing 1 via bearings 6. The rotary shaft 5 projects to the outside through, for example, the insertion hole 3A of the front casing 3, and a prime mover such as an engine (not shown). It is driven to rotate.

Reference numeral 7 denotes a cylinder block which is located inside the casing 1 and is integrally rotated with the rotary shaft 5 by spline coupling. The cylinder block 7 includes:
A plurality of (8 in this example) cylinders 8 spaced apart in the circumferential direction,
.. are formed in the axial direction, and cylinder ports 8A communicating with the respective cylinders 8 and opening in an oval shape on the sliding surface 7A side of the cylinder block 7 are formed as shown in FIG. There is.

Here, the cylinder block 7 has a sliding surface 7A.
2 slides in a direction indicated by an arrow A shown in FIG. 2 with respect to a valve plate 14 described later, and at this time, each cylinder port 8A extends along a suction port 15 and a discharge port 16 described later and a movement locus R.
As shown in the drawing, the suction port 15 and the discharge port 16 are sequentially communicated with and blocked. Each cylinder port 8A extends at a constant angle .theta.1 in the circumferential direction of the cylinder block 7 as shown in FIG.

[0029] Reference numerals 9, 9, ... Show a plurality of pistons slidably inserted in the respective cylinders 8. The respective pistons 9 reciprocate in the respective cylinders 8 as the cylinder block 7 rotates. The intake stroke and the discharge stroke are repeated in each cylinder 8. A spherical portion 9A is formed at the tip of each piston 9 protruding from the cylinder block 7.

.. are spherical portions 9 of each piston 9.
Each shoe 10 is slidably fitted to the spherical portion 9A by a plurality of shoes provided on the outer peripheral side of A, and each piston 9 is swung on the swash plate 11 described later through the spherical portion 9A. Supports freely.

Reference numeral 11 denotes a swash plate provided between the front casing 3 and the cylinder block 7, and the front surface side (cylinder block 7 side) of the swash plate 11 is a sliding surface on which the shoes 10 rotate while slidingly contacting each other. 11A, and the back side is a semi-cylindrical tilting sliding portion 11B slidably fitted in a concavely curved guide groove 12 formed in the front casing 3. Further, the swash plate 11 is provided with an insertion hole 11C formed in the central portion side and having a diameter increased from the front surface side to the back surface side, and a side surface of the tilt sliding portion 11B. A tilting mechanism insertion hole 11D into which a part of the mechanism is inserted is formed. The tilting angle of the swash plate 11 is changed by the tilting drive mechanism so that the stroke amount of each piston 9 is appropriately adjusted to variably control the displacement (discharging amount) of the hydraulic pump. .

Reference numeral 13 denotes an annular shoe retainer fixed to the sliding surface 11A of the swash plate 11 while engaging with the outer peripheral side of each shoe 10, and the shoe retainer 13 is provided on the sliding surface 11A of the swash plate 11. It allows each shoe to make a circular motion and compensates for each piston 9 reciprocating in each cylinder 8 as the cylinder block 7 rotates.

Reference numeral 14 denotes a valve plate fixed to the rear casing 4 of the casing 1 and having a sliding surface 14A on one side surface.
As shown in FIG. 2, the valve plate 14 has an eyebrow-shaped suction port 1
5 and the discharge port 16 are provided so as to extend in the circumferential direction so as to be substantially symmetrical positions. Further, when the cylinder block 7 rotates in the arrow A direction with respect to the valve plate 14, the discharge port 16 is formed with a notch 16A that extends in the circumferential direction at the starting end side that is the upstream side in the rotation direction. The cylinder port 8A of each cylinder 8 and the discharge port 16 are formed in a substantially triangular shape so as to gradually communicate with each other.

Further, between the suction port 15 and the discharge port 16 of the valve plate 14, one switching valve portion 14B is provided at the top dead center side where each piston 9 switches from the discharge stroke to the suction stroke. A switching valve portion 14C on the other side is provided on the bottom dead center side where the piston 9 faces the switching valve portion 14B on the one side with the rotary shaft 5 interposed therebetween and each piston 9 switches from the suction stroke to the discharge stroke. When each cylinder 8 sliding on the valve plate 14 reaches the one-side switching valve portion 14B, the communication with the discharge port 16 is cut off, and when it reaches the other-side switching valve portion 14C. The communication with the suction port 15 is cut off.

Here, in the intake stroke in which the piston 9 strokes from the top dead center position to the bottom dead center position, each cylinder port 8A communicates with the intake port 15, and the hydraulic oil is introduced into the cylinder 8 through the intake port 15. Is sucked. Then, in the discharge stroke in which the piston 9 strokes from the bottom dead center position to the top dead center position, each cylinder port 8A moves to the discharge port 1
The hydraulic fluid in the cylinder 8 is discharged through the discharge port 16 in communication with the hydraulic fluid 6.

Further, the suction port 15 and the discharge port 1
Numeral 6 always communicates with a suction passage and a discharge passage (both not shown) formed in the rear casing 4, and the discharge passage is connected to a hydraulic cylinder, a hydraulic motor (neither is shown) or the like via a hose pipe or the like. Is done.

The suction port 15 and the discharge port 16 are intermittently communicated with the cylinder port 8A of each cylinder 8 by the rotation of the cylinder block 7 with respect to the valve plate 14, and the oil from the suction passage is discharged. While sucking the liquid into each cylinder 8, the pressure oil discharged from each cylinder 8 is supplied to a hydraulic actuator such as a hydraulic cylinder or a hydraulic motor through a discharge passage.

Reference numeral 17 denotes an oil hole on one side formed in the switching valve portion 14B on one side of the valve plate 14, and the oil hole 17 is the center of the movement locus R of each cylinder port 8A as shown in FIG. It is located on the line and is formed as a small diameter hole in the plate thickness direction of the valve plate 14. The oil hole 17 is circumferentially separated from the end of the discharge port 16 by an angle θ1 of the cylinder port 8A so that it communicates with the cylinder port 8A when the cylinder port 8A of each cylinder 8 is blocked from the discharge port 16. Is provided. Further, the oil hole 17 on the one side communicates with the oil hole 18 on the other side via a communication passage 19 described later.

Reference numeral 18 denotes an oil hole on the other side formed in the switching valve portion 14C on the other side of the valve plate 14, and the oil hole 18 is also the center of the movement locus R of each cylinder port 8A as shown in FIG. It is located on the line and is formed as a small diameter hole in the plate thickness direction of the valve plate 14. The oil hole 18 is separated from the end of the suction port 15 in the circumferential direction by the angle θ1 of the cylinder port 8A so that it communicates with the cylinder port 8A when the cylinder port 8A of each cylinder 8 is blocked from the suction port 15. Is provided. The oil hole 18 on the other side communicates with the oil hole 17 on the one side via a communication passage 19 described later.

Reference numeral 19 denotes a communication passage formed in the rear casing 4. The communication passage 19 is, as shown in FIG.
7 has a diameter larger than 7, and has one end communicating with the oil hole 17 and extending in the axial direction of the rear casing 4, and the other end communicating with the oil hole 18 extending in the axial direction of the rear casing 4. Of the oil passage 19B and another oil passage 19C extending in the radial direction so as to connect the oil passages 19A and 19B with each other. A stepped hole 20 that opens to the bottom side of the rear casing 4 is formed between the oil passages 19A and 19C. The stepped hole 20 is a reverse flow prevention means that is inserted from the bottom side of the rear casing 4 and is attached. It is closed by a stop valve 21.

Reference numeral 21 denotes a check valve which is inserted into the stepped hole 20 of the rear casing 4 from the bottom side, and the check valve 21 is shown in FIG.
As shown in FIG. 2, a valve cylinder 22 formed in a tubular shape and the valve cylinder 2
A lid 23 for fixing 2 in the stepped hole 20, and the valve cylinder 22
A valve body 24 accommodated therein and a spring 25 for biasing the valve body 24 toward the opening 22A side of the valve cylinder 22 with a weak spring force are generally configured. Here, the valve cylinder 22 communicates with the oil passage 19A through an opening 22A formed of a small diameter hole, and a valve body 23 is axially slidably arranged in the large diameter cylinder 22B. Further, a through hole 22C penetrating in the radial direction is provided in the cylinder portion 22B, and an oil passage 19C communicates with the inside of the valve cylinder 22 through the through hole 22C.

Further, the bottomed tubular valve body 24 inserted into the valve barrel 22 has a spring 25 disposed therein.
By abutting one end of 5 on the bottom surface 23A of the lid 23, the valve body 24 is normally urged toward the opening 22A of the valve cylinder 22 in the valve closing direction.

When the pressure in the oil hole 17 on one side is higher than the pressure in the oil hole 18 on the other side, pressure oil is supplied from the oil passage 19A communicating with the oil hole 17 on one side to the check valve 21. Flows in and the valve body 24 in the valve cylinder 22 is pushed toward the lid body 23 against the spring 25 by the pressure at this time, so that the check valve 21 opens and the pressure oil flows into the valve cylinder 22. Oil passage 1 from the inside through the through hole 22C
It flows to 9C.

On the other hand, when the pressure in the oil hole 18 on the other side is higher than the pressure in the oil hole 17 on the one side, a valve is opened from the oil passage 19C communicating with the oil hole 18 on the other side through the through hole 22C. Although the pressure oil flows into the cylinder 22, the force against the spring 25 is not applied and the valve body 24 is biased toward the opening 22A side of the valve cylinder 22.
The check valve 21 is closed so that the pressure oil does not flow backward from the oil hole 18 side to the oil hole 17 side.

The swash plate type hydraulic pump according to the present embodiment has the above-mentioned structure. First, when the rotating shaft 5 is rotated by the prime mover, the cylinder block 7 splined to the rotating shaft 5 is integrally formed. Is rotated. As a result, the piston 9 inserted into each cylinder 8 rotates together with the cylinder block 7, and its spherical portion 9A is
While being guided by the shoe presser 13 via the, the sliding surface 11A of the swash plate 11 is rotated. At this time, the sliding surface 1 of the swash plate 11
Since 1A has a predetermined tilt angle, the piston 9 moves into the cylinder 8 while the cylinder block 7 makes one rotation, and the piston 9 comes into the cylinder 8 at the top dead center position and the cylinder 8 extends to the bottom dead center. Strokes to and from the point position.

Here, while the cylinder port 8A communicates with the suction port 15 during a half rotation in which each piston 9 strokes from the top dead center position to the bottom dead center position, the suction passage (through the suction port 15) Cylinder 8 (not shown)
This is the suction stroke for sucking the oil liquid inside. On the other hand, during the half rotation in which the piston 9 strokes from the bottom dead center position to the top dead center position, while the cylinder port 8A communicates with the discharge port 16, the discharge port 16 is pressurized while the oil liquid sucked into the cylinder 8 is pressurized. The discharge process is to discharge from a discharge passage (not shown). In this way, the rotary shaft 5 is rotationally driven to reciprocally move the piston 9 in the cylinder 8, whereby the suction stroke and the discharge stroke are repeated, and the pump action is performed.

On the other hand, in order to variably control the discharge capacity of the pump, the displacement capacity in the cylinder 8 is changed by appropriately tilting the swash plate 11 along the guide groove 12 by the tilting drive mechanism. It is designed to be controlled.

Next, the operation of replenishing the pressure oil through the oil hole 17 on one side, the oil hole 18 on the other side and the communication passage 19 will be described with reference to FIG.
Will be described in detail with reference to FIG.

First, each cylinder 8 has a cylinder block 7
While continuing to rotate in the direction of arrow A, the cylinder port 8A of the cylinder 8 located on the top dead center side is blocked from the discharge port 16 at this time and communicated with the oil hole 17 on one side.
Then, in this cylinder 8, the pressure oil that has become high in pressure due to the discharge stroke so far is passed through the communication passage 19 to the oil hole 1 on the other side.
It is discharged toward 8.

On the other hand, the cylinder 8 located on the bottom dead center side is
The cylinder port 8A is blocked from the suction port 15 and communicates with the oil hole 18 on the other side. Then, the cylinder 8 finishes the suction stroke, and the volume in the cylinder 8 is slightly expanded until the piston 9 reaches the bottom dead center, so that the cylinder 8 tends to have a negative pressure.

However, while the oil hole 17 on one side communicates with the cylinder 8 on the top dead center side, the pressure oil in this cylinder 8 is discharged into the communication passage 19, and the oil hole 18 on the other side and the lower side. While communicating with the cylinder 8 on the dead center side, the pressure oil in the communication passage 19 is supplied to the cylinder 8 on the bottom dead center side via the oil hole 18 on the other side. The inside of the cylinder 8 on the side is prevented from having a negative pressure tendency, and the cylinder 8 is preliminarily slightly pressurized.

Next, when each cylinder 8 further moves in the direction of arrow A as shown in FIG. 5, the cylinder port 8A of the cylinder 8 on the bottom dead center side communicates with the oil hole 17 on one side and the discharge port. The 16 notches 16A are communicated with the tip of the notch 16A. At this time, pressure oil flows from the discharge port 16 into the cylinder 8 on the bottom dead center side, and at the top dead center side communicating with the oil hole 17 on one side through the oil hole 18 on the other side and the communication passage 19. The pressure oil tries to flow in the opposite direction to the cylinder 8. However, the check valve 21 provided in the middle of the communication passage 19 prevents this backflow and prevents the pressure in the discharge port 16 from decreasing.

Further, the inside of the cylinder 8 on the bottom dead center side is pre-pressurized by the pressure oil supplied from the cylinder 8 on the top dead center side, and the pressure difference with the discharge port 16 becomes small, so that the discharge stroke is reached. Discharge port 1 in the started cylinder 8
6, the amount of pressure oil flowing in (backflowing) via the notch 16A of 6 is greatly reduced, and the pulsation of the piston 9, the hose pipe (not shown), etc. is reduced, and the sudden discharge in the discharge port 16 is reduced. Pressure fluctuations are prevented.

Thus, in this embodiment, the oil hole 17 is formed in the switching valve portion 14B on one side and located on the center line of the movement locus R of each cylinder port 8A, and the oil hole 18 is formed in the switching valve portion 14C on the other side. Is formed, and the oil holes 17 and 18 are communicated with each other through the communication passage 19, and the check valve 21 is provided in the middle of the communication passage 19, so that the inside of the cylinder 8 that reaches the switching valve portion 14B on one side is formed. Even if high pressure oil remains in the cylinder, the cylinder port 8A of the cylinder 8 communicates with the oil hole 17 on the one side on the switching valve portion 14B on the one side, and the communication passage 19 and the oil hole 18 on the other side. It is possible to replenish the pressure oil from the communication passage 19 into the cylinder 8 on the switching valve portion 14C on the other side through the passage. On the other hand, communication passage 1
Due to the check valve 21 provided in the middle of 9, the pressure oil does not flow from the cylinder 8 on the bottom dead center side toward the cylinder 8 on the top dead center side.

As a result, the inside of the cylinder 8 can be preliminarily pressurized on the switching valve portion 14C on the other side, so that the discharge port 1
It is possible to prevent the pressure oil from flowing back from the inside of the cylinder 6 to the inside of the cylinder 8, prevent a rapid pressure change in the cylinder 8, and generate pulsation in the pressure oil and the like in the cylinder 8 and the hose pipe (not shown). Can be prevented. Further, the vibration and noise of the casing 1 and the like due to the pulsation of the pressure oil can be significantly reduced, and the backflow of the pressure oil from the discharge port 16 into the cylinder 8 can be made substantially zero. It is possible to reduce the pressure loss in the port 16 and improve the pump efficiency.

By supplying the pressure oil remaining in the cylinder 8 on the top dead center side to the cylinder 8 on the bottom dead center side, it is possible to reduce the pressure in the cylinder 8 on the top dead center side. It is possible to prevent the pressure oil from flowing out (backflowing) into the suction port 15 from the inside of the cylinder 8 which has passed through the point, and smoothly suck the oil liquid into the cylinder 8 from the suction port 15 to improve the pump efficiency. You can

Further, the pressure oil flowing from the discharge port 16 into the cylinder 8 passing through the bottom dead center and the pressure oil flowing out from the cylinder 8 passing through the top dead center into the suction port 15 are significantly reduced. Since the jet flow due to these pressure oils is eliminated, it is possible to reliably prevent the inner wall portions of the cylinder port 8A and the suction port 15 of each cylinder 8 from being eroded by the jet flow, and the life of the hydraulic pump. Can be significantly improved.

The communication passage 19 for communicating between the oil holes 17 and 18 can be formed by making a simple hole in the rear casing 4, and the check valve 21 can be easily formed from the bottom side of the rear casing 4. Since it can be attached, the number of processing steps can be reduced and the workability during assembly can be improved.

Next, FIGS. 6 and 7 show a second embodiment of the present invention. In this embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. It shall be. However, the feature of this embodiment is that the tank pipe 32 that connects the oil hole 17 on one side to the tank 31 is provided, and the inside of the cylinder 8 communicating with the oil hole 17 on one side is provided in the middle of the tank pipe 32. The check valve 33 is provided as an oil replenishing means for preventing a negative pressure.

Here, as shown in FIG. 6, the tank pipe 32 is provided between the oil hole 17 on one side and the check valve 21 and is branched from the communication passage 19. The check valve 33 provided in the middle of the above allows the oil liquid to flow from the tank 31 toward the oil hole 17 on one side and blocks the reverse flow.
In this case, the check valve 33 has substantially the same structure as the check valve 21 and prevents the oil hole 17 side from having a negative pressure tendency.

Then, as shown in FIG. 7, the cylinder 8 on the top dead center side communicates with the oil hole 17 on one side, and the suction port 15
When the cylinder 8 is slightly communicated with the cylinder 8, the internal volume of the cylinder 8 in which the suction stroke has started is expanded, and the oil liquid flows into the cylinder 8 from the suction port 15. However, inhalation port 1
When the communication area between the cylinder 5 and the cylinder port 8A is small, the amount of the oil liquid supplied from the suction port 15 is insufficient with respect to the expansion of the volume in the cylinder 8, and the inside of the cylinder 8 tends to have a negative pressure. At this time, the check valve 33 is opened and the oil liquid is replenished from the tank 31, so that the pressure drop in the cylinder 8 is prevented.

Thus, in this embodiment having the above-mentioned structure, the same effects as those of the first embodiment can be obtained, but particularly in this embodiment, the oil hole 17 and the tank 31 on one side are provided. Since the tank pipe 32 for communicating with the cylinder 8 is provided, and the check valve 33 is provided in the middle of the tank pipe 32, the inside of the cylinder 8 is in the initial stage of the intake stroke in which the cylinder 8 and the intake port 15 are slightly communicated with each other. Can be prevented from becoming a negative pressure tendency, the generation of bubbles in the cylinder 8 and the decrease in pressure can be prevented, and the pump efficiency can be improved.

Next, FIGS. 8 to 12 show a third embodiment of the present invention. In this embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. It shall be. However, the feature of this embodiment is that the oil passage 41 that connects the oil hole 18 on the other side and the discharge port 16 is provided, and the inside of the cylinder 8 that communicates with the oil hole 18 on the other side is provided in the middle of the oil passage 41. The check valve 42 is provided as a pressure oil discharge means for preventing an excessive pressure higher than the pressure in the discharge port 16.

Here, the oil passage 41 is, as shown in FIG.
One end side is located between the oil hole 17 and the check valve 21 on the other side and connected to the communication passage 19, and the other end side is open in the discharge port 16. Further, the check valve 42 provided in the middle of the oil passage 41 has substantially the same structure as the check valve 21, and allows the oil liquid to flow from the oil hole 17 on the other side toward the discharge port 16 and reverses the check. Stop the flow in the direction.

The swash plate type hydraulic pump according to this embodiment has the above-mentioned structure, and its operation will be described below.

First, when the angle formed by the center of the cylinder port 8A and the end of the suction port 15 with respect to the center of the rotary shaft 5 is defined as the cylinder rotation angle, the cylinder 8 is set to the suction port 1.
When it reaches the switching valve portion 14C on the other side by breaking the communication with 5, the cylinder rotation angle of the cylinder 8 on the bottom dead center side becomes an angle θA, and the cylinder 8 communicates with the oil hole 18 on the other side. Because of the previous state, the pressure in the cylinder 8 substantially matches the pressure in the suction port 15.

Next, when the cylinder 8 rotates in the direction of arrow A as shown in FIG. 9 and the cylinder rotation angle becomes the angle θB, the cylinder 8 communicates with the oil hole 18 on the other side. At this time, since the oil hole 17 on one side communicates with the cylinder 8 on the top dead center side, the pressure oil in the cylinder 8 on the top dead center side communicates with the oil hole 18 on the other side via the communication passage 19. It flows into the cylinder 8 and the pressure in the cylinder 8 on the bottom dead center side rises.

Further, when the cylinder 8 rotates in the direction of arrow A as shown in FIG. 10 and the cylinder rotation angle becomes the angle θC, the cylinder 8 communicates with the oil hole 18 on the other side and the discharge port 16 of the other side. It communicates with the notch 16A. At this time, the high pressure oil in the discharge port 16 is notched in the notch 16 in the cylinder 8.
Flowing in from A, the pressure in the cylinder 8 rises further. Further, since the cylinder 8 is in the discharge stroke in which the internal volume is reduced and the communication area between the cylinder 8 and the discharge port 16 is small, the oil liquid in the cylinder 8 is compressed and the pressure becomes higher.

When the cylinder 8 rotates in the direction of arrow A as shown in FIG. 11 and the cylinder rotation angle becomes the angle θD, the cylinder 8 is disconnected from the oil hole 18 on the other side and the discharge port 16 is disconnected. The pressure in the cylinder 8 becomes substantially equal to the pressure in the discharge port 16 by communicating with the cylinder with a sufficient communication area.

Here, when the swash plate type hydraulic pump is started, etc., the pressure in the discharge port 16 at a steady state (for example, 350 k
pressure lower than that of g / cm ² (for example, 100 kg / c)
m ² ). At this time, in the case where the oil passage 41 is not provided, the cylinder internal pressure with respect to the cylinder rotation angle shows that the cylinder 8 has an angle θ as shown by a characteristic line 43 shown by a solid line in FIG.
When the position C is reached, the pressure in the cylinder 8 is temporarily higher than the pressure in the discharge port 16 and becomes an overpressure state.
Pulsation occurs in the pressure oil and the like, and vibration and noise are generated from the casing 1 and the like.

Therefore, in the present embodiment, the oil passage 41 that connects the discharge port 16 and the oil hole 18 on the other side is provided, and the check valve 42 is provided in the middle of the oil passage 41.
When the pressure inside the cylinder 8 is higher than the pressure inside the discharge port 16, the check valve 42 opens and the pressure oil inside the cylinder 8 is discharged into the discharge port 16 through the oil passage 41, and inside the cylinder 8 12 is prevented from becoming an excessive pressure as indicated by a characteristic line 44 shown by a dotted line in FIG.

Thus, in this embodiment having the above-described structure, it is possible to obtain the same effect as that of the first embodiment. However, particularly in this embodiment, the discharge port 16 and the oil hole on the other side are obtained. Since an oil passage 41 communicating with 18 is provided and a check valve 42 is provided in the middle of the oil passage 41,
It is possible to prevent excessive pressure in the cylinder 8 at the initial stage of the discharge stroke in which the cylinder 8 slightly communicates with the notch 16A of the discharge port 16 and to prevent vibration and noise.

Next, FIG. 13 shows a fourth embodiment of the present invention. In this embodiment, the same components as those in the third embodiment are designated by the same reference numerals and the description thereof will be omitted. To do. However, the feature of this embodiment is that the oil hole 17 on one side is connected to the tank 31.
A check valve 52 as an oil liquid replenishing means is provided in the middle of a tank pipe line 51 connected to the oil pipe, and a pressure oil discharge means is provided in the middle of an oil passage 41 connecting the oil hole 18 on the other side to the discharge port 16. The check valve 42 is provided.

The check valve 52 has substantially the same structure as the check valve 33 described in the second embodiment, and allows the oil liquid to flow from the tank 31 toward the oil hole 17 side. It is configured to block the reverse flow.

Thus, in this embodiment having the above-described structure, the same operational effect as that of the first embodiment can be obtained, but particularly in this embodiment, the check valve 52 is provided midway.
The oil passage 17 on one side is communicated with the tank 31 by the tank conduit 51 provided with the oil passage 41 and the oil hole 18 on the other side and the discharge port 16 are connected by the oil passage 41 provided with the check valve 42 in the middle. Since the cylinder 8 on the top dead center side is slightly communicated with the suction port 15, the negative pressure inside the cylinder 8 can be prevented, and the cylinder 8 on the bottom dead center side discharges. It is possible to prevent the inside of the cylinder 8 from being in an overpressure state when it slightly communicates with the notch 16A of the port 16, and it is possible to reliably prevent generation of vibration and noise.

In each of the embodiments described above, the case where the variable displacement type swash plate type hydraulic pump is used as the axial piston type pump has been described as an example, but the present invention is not limited to this, and the fixed displacement type hydraulic pump is used. May be applied to swash plate type hydraulic pump,
It may be applied to the oblique shaft type hydraulic pump.

In each of the above embodiments, the case where eight cylinders 8 and cylinder ports 8A are formed in the cylinder block 7 has been shown as an example, but the present invention is not limited to this, and may be about seven. Further, it may be nine or more.

Further, in each of the above embodiments, each cylinder 8
Although the cylinder port 8A is illustrated as an example in which the cylinder port 8A is formed in an oval shape, the cylinder port 8A may have an elliptical shape or a circular shape.

[0079]

As described above in detail, according to the invention of claim 1, one side oil hole provided in the one side switching valve portion,
An oil hole on the other side provided in the switching valve section on the other side, a communication passage that communicates the oil hole on the one side and the oil hole on the other side, and the one side provided in the middle of the communication passage. Since the configuration is provided with a backflow prevention unit that allows the pressure oil to flow from the oil hole toward the oil hole on the other side and blocks the reverse flow, for example, after the discharge stroke is reached, it reaches the switching valve section on the one side. When high pressure oil remains in the cylinder, the pressure oil remaining inside the cylinder can be discharged from the oil hole on one side to the oil hole on the other side through the communication passage, and the suction stroke is completed. Even if the cylinder that has reached the switching valve portion on the other side has a negative pressure tendency, the pressure oil from the communication passage can be replenished into this cylinder, and the negative pressure in the cylinder can be reliably prevented. . Also, due to the backflow prevention means provided in the middle of the communication passage, the pressure inside the cylinder communicating with the oil hole on the other side becomes higher than that on the cylinder communicating with the oil hole on the one side, and The pressure oil can be prevented from flowing out toward the oil hole.

By increasing the pressure in the cylinder on the switching valve section on the other side in advance, the pressure oil from the discharge port flows into the cylinder that has reached the discharge port from the switching valve section on the other side. Can be suppressed, rapid pressure changes in the discharge port and cylinder can be prevented, and pulsation of pressure oil in the cylinder and hose piping can be effectively reduced, reducing pressure loss and reducing pump pressure. It is possible to improve efficiency.

Further, it is possible to prevent the pressure oil from being jetted into each cylinder and the suction port when each cylinder starts to communicate with the discharge port and the suction port, and to prevent the jet flow from being generated by these pressure oils. As a result, it is possible to reliably prevent the inner wall portions of the cylinder port and the suction port of each cylinder from being eroded, and it is possible to significantly extend the life.

On the other hand, according to the second aspect of the present invention, the one-side switching valve portion is disposed on the top dead center side where each piston reciprocating in each cylinder switches from the discharge stroke to the suction stroke. However, the switching valve section on the other side is arranged at the bottom dead center side where each piston switches from the suction stroke to the discharge stroke, so that a high pressure is applied from the top dead center side cylinder to the bottom dead center side cylinder. The pressure oil can be discharged, and the pressure in the cylinder at the bottom dead center side can be increased to reduce the pressure difference between the cylinder and the discharge port.

According to the third aspect of the present invention, the tank line for communicating the oil hole on one side with the tank and the oil hole on the one side provided in the middle of the tank line for communicating with each other. Since it is configured to include oil liquid replenishing means for preventing negative pressure in the cylinder, the cylinder communicates slightly with the oil port on one side at the initial stage of the suction stroke, and slightly communicates with the suction port. Even if the suction flow rate of the oil liquid from the tank is insufficient, the oil liquid can be supplied from the tank, the negative pressure inside the cylinder can be prevented, and the occurrence of bubbles and pressure drop in the cylinder can be prevented. It can prevent and improve pump efficiency.

According to the invention described in claim 4,
An oil passage communicating between the oil hole on the other side and the discharge port; and pressure oil discharge means for preventing an excessive pressure in the cylinder provided in the oil passage and communicating with the oil hole on the other side. With the configuration, the cylinder communicates with the oil hole on the other side slightly while communicating with the oil hole on the other side in the initial stage of the discharge stroke, pressure oil flows into the cylinder from the discharge port, and the volume inside the cylinder decreases. Even if the pressure in the cylinder becomes high,
The pressure oil in the cylinder can be discharged to the discharge port through the oil passage, the pressure in the cylinder can be prevented from becoming excessive, and vibration and noise can be surely prevented.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a swash plate type hydraulic pump according to a first embodiment of the present invention.

2 is an enlarged cross-sectional view taken along the line II-II in FIG. 1 showing a valve plate having an intake port and a discharge port.

FIG. 3 is an enlarged cross-sectional view taken along line III-III in FIG. 1 showing a cylinder block having a cylinder port and the like.

FIG. 4 is an enlarged vertical sectional view showing the check valve in FIG.

5 is a sectional view similar to FIG. 2, showing a state in which each cylinder port has begun to communicate with an intake port and a discharge port.

FIG. 6 is a sectional view similar to FIG. 2, showing a valve plate and the like of a swash plate type hydraulic pump according to a second embodiment of the present invention.

FIG. 7 is a sectional view similar to FIG. 2, showing a state in which each cylinder port starts to communicate with an intake port and a discharge port.

FIG. 8 is a sectional view similar to FIG. 2, showing a valve plate and the like of a swash plate hydraulic pump according to a third embodiment of the present invention.

9 is a sectional view similar to FIG. 2, showing a state in which each cylinder port communicates with an oil hole on one side and an oil hole on the other side.

FIG. 10 is a sectional view similar to FIG. 2, showing a state in which each cylinder port starts to communicate with an intake port and a discharge port.

FIG. 11 is a sectional view similar to FIG. 2, showing a state in which each cylinder port further communicates with an intake port and a discharge port.

FIG. 12 is a characteristic diagram showing the relationship between the cylinder pressure on the side of bottom dead center and the cylinder rotation angle according to the third embodiment of the present invention.

13 is a sectional view similar to FIG. 2, showing a valve plate and the like of a swash plate type hydraulic pump according to a fourth embodiment of the present invention.

[Explanation of symbols]

 1 Casing 5 Rotating shaft 7 Cylinder block 8 Cylinder 8A Cylinder port 9 Piston 14 Valve plate 14B One side switching valve section 14C Other side switching valve section 15 Suction port 16 Discharge port 17 One side oil hole 18 Other side oil hole 19 Communication Passage 21 Check Valve (Backflow Prevention Means) 31 Tank 32, 51 Tank Pipeline 33, 52 Check Valve (Oil Liquid Supply Means) 41 Oil Passage 42 Check Valve (Pressure Oil Discharge Means)

Claims (4)

[Claims] 1. A casing, a rotating shaft rotatably provided in the casing, a cylinder block provided in the casing so as to rotate integrally with the rotating shaft, and a plurality of cylinders formed in the casing. Plural pistons that are slidably inserted into the cylinders of the cylinder block and reciprocate in the cylinders as the cylinder block rotates, and suction ports and discharges provided between the casing and the cylinder block. An axial piston type hydraulic pump comprising a switching valve portion on one side opposed to a port with a rotary shaft interposed therebetween and a valve plate on which a switching valve portion on the other side is formed, wherein the switching valve portion on the one side is provided. Oil hole on one side, an oil hole on the other side provided in the switching valve section on the other side, a communication passage communicating the oil hole on the one side and the oil hole on the other side, and the communication passage The one side provided in the middle of Axial piston type hydraulic pump, characterized in that towards the oil hole to the oil hole of the other side has a configuration and a reverse flow preventing means for preventing the flow of reverse allowed to flow the pressure oil. 2. The switching valve section on the one side is disposed on the top dead center side where each piston that reciprocates in each cylinder switches from the discharge stroke to the suction stroke, and the switching valve section on the other side is arranged respectively. 2. The axial piston type hydraulic pump according to claim 1, wherein the piston is arranged at the bottom dead center side where the suction stroke is switched to the discharge stroke. 3. The oil hole on one side is connected to a tank line communicating with a tank, and an oil liquid is replenished from the tank toward the oil hole on one side in the middle of the tank line. 3. The axial piston type hydraulic pump according to claim 2, wherein an oil liquid replenishing means for allowing the above-mentioned flow and blocking the reverse flow is provided. 4. An oil passage communicating between the oil hole on the other side and the discharge port is provided, and an oil passage communicating between the oil hole and the discharge port is provided between the oil hole on the other side and the discharge port. 4. The axial piston type hydraulic pump according to claim 2 or 3, which comprises pressure oil discharge means for allowing pressure oil to be discharged and blocking a reverse flow.