JP2000080977A - Piston pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of negative pressure in the vicinity of the sliding surface of a valve plate when hydraulic oil flows from the discharge port of the valve plate to the cylinder port of a cylinder block. SOLUTION: This piston pump is provided with a piston 8 housed in the cylinder 7 of a cylinder block 6 for sucking/discharging hydraulic oil, and a valve plate 5 having suction and discharge ports. In the sliding surface 5D of the valve plate 5 in the vicinity of the lower dead point of the piston 8, a notch is provided to extend from the end part of the discharge port to the suction port side, and a cylinder port 7A is provided in the end surface 6A of the cylinder block 6 so as to be communicated with any of the suction and discharge ports of the valve plate 5. In this case, between the end part of the suction port of the valve plate 5 in the vicinity of the lower dead point of the piston 8 and the notch, an oil sump part 5E is formed in the shape of a recess and capable of housing oil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston pump provided in a hydraulic shovel or the like, and more particularly to a piston pump having a notch on a sliding surface of a valve plate extending from an end of a discharge port to a suction port. .

[0002]

2. Description of the Related Art Conventionally, this type of piston pump has
There is one disclosed in Japanese Utility Model Laid-Open No. 5-6161. This prior art has a plurality of cylinders, a rotatable cylinder block, and a plurality of pistons housed in each of the cylinders for sucking and discharging hydraulic oil, and the end faces of the cylinder block are slidably contacted with each other. A valve plate having a suction port for sucking oil and a discharge port for discharging hydraulic oil, and the above-mentioned end surface that slides on the valve plate of the cylinder block,
It has a plurality of cylinder ports which communicate with corresponding ones of the cylinders and which can selectively communicate with either the suction port or the discharge port of the valve plate as the cylinder block rotates.

[0003] The sliding surface of the valve plate on which the end surface of the cylinder block slides comes into contact with a position corresponding to the vicinity of the bottom dead center of the piston from the end of the discharge port formed on the valve plate. There is a V-shaped groove or notch extending to the side of the port. Further, a V-shaped groove, that is, a notch, which can communicate with each of the above-described notches of the valve plate, is formed at the tip of each of the cylinder ports in the rotation direction of the cylinder block.

In the prior art configured as described above, with rotation of the cylinder block, the cylinder port formed on the end face of the cylinder block is switched from a position facing the suction port of the valve plate to a position facing the discharge port. At the time of the replacement operation, the notch formed on the sliding surface of the valve plate and the notch formed on the end of the cylinder port on the end face of the cylinder block gradually overlap each other within a very short time. Therefore, the area of the opening that connects the discharge port of the valve plate and the cylinder port of the cylinder block changes so as to gradually increase, and high-pressure hydraulic oil in the discharge port of the valve plate passes through the cylinder port to the cylinder. It gradually flows in, and the high-pressure hydraulic oil described above diffuses in these notches according to the shapes of the notches in the valve plate and the notches in the cylinder port. As a result, the pressure change in the cylinder becomes relatively gentle, and the generation of pump noise and vibration when such high-pressure hydraulic oil flows in shock is suppressed.

[0005]

FIG. 5 is a view for explaining a problem in the above-mentioned prior art, and is a cross-sectional view of a main part of a sliding surface portion between a valve plate and a cylinder block. In FIG. 5, reference numeral 20 denotes a fixedly held valve plate, 20A denotes a suction port formed in the valve plate 20, and 20B denotes a valve plate 2 similarly.
0 is a discharge port, 21 is a cylinder block whose end surface 21A is in sliding contact with the valve plate 20, and 21B is a cylinder port communicating with a cylinder (not shown) formed in the cylinder block 21. Cylinder block 2
As described above, on the sliding surface 20C of the valve plate 20 with which the first end surface 21A is in sliding contact, the position corresponding to the vicinity of the bottom dead center of the piston extends from the end of the discharge port 20B formed in the valve plate 20. A notch 20D extending toward the suction port 20A is provided. The notch 21D that can communicate with the notch 20D of the valve plate 20 is also formed at the tip of the cylinder port 21B in the rotation direction of the cylinder block 21 indicated by the arrow 21C in FIG.

In this prior art, the high-pressure hydraulic oil at the discharge port 20B of the valve plate 20 is supplied to the notch 20D of the valve plate 20.
5 flows into the notch 21D of the cylinder block 21 and further flows into the cylinder port 21B through the sliding surface 20C of the valve plate 20 according to the shape of the notch 21D of the cylinder block 21 as shown by an arrow 22 in FIG. High pressure hydraulic oil is applied to the cylinder port 21 at an angle
It flows into B. Thereby, the sliding surface 20C of the valve plate 20
, A negative pressure is generated, and cavitation is generated by the negative pressure. That is, bubbles 23 are generated. This bubble 23
There is a concern that erosion (crushing) may occur on the sliding surface 20 </ b> C of the valve plate 20 or the cylinder wall surface due to the impact at the time of collapse.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned situation in the prior art, and has as its object to slide a valve plate when high-pressure hydraulic oil flows from a discharge port of a valve plate to a cylinder port of a cylinder block. An object of the present invention is to provide a piston pump capable of preventing generation of a negative pressure near a moving surface.

[0008]

In order to achieve this object, an invention according to claim 1 of the present invention has a plurality of cylinders, a rotatable cylinder block, and a cylinder block which is housed in each of the cylinders and operates. A plurality of pistons for performing suction and discharge of oil, and a valve plate having an end port of the cylinder block slidably contacted and having a suction port for sucking the hydraulic oil and a discharge port for discharging the hydraulic oil; A notch extending from the end of the discharge port to the suction port side is provided on a sliding surface of the valve plate near the bottom dead center where the end surface of the cylinder block slides, and slides on the valve plate of the cylinder block. The end face communicates with each of the corresponding ones of the cylinders, and any one of the suction port and the discharge port of the valve plate is rotated with the rotation of the cylinder block. A piston pump having a plurality of cylinder ports that can selectively communicate with the piston, wherein the end of the suction port located near the bottom dead center of the piston of the valve plate and the notch have a concave shape. Formed,
It has a configuration in which an oil reservoir that can store oil is provided.

According to the first aspect of the present invention, as the cylinder block rotates, the cylinder port formed on the end face of the cylinder block faces the discharge port from the position facing the suction port of the valve plate. During the switching operation, the notch formed on the sliding surface of the valve plate and the groove formed on the tip of the cylinder port of the cylinder block gradually overlap within a very short time, increasing the opening area. Let it. As a result, the influx of hydraulic oil from the discharge port of the valve plate to the cylinder port is suppressed, and the generation of pump noise and vibration is suppressed. At this time, a part of the hydraulic oil flowing into the cylinder port from the discharge port is accommodated in the oil reservoir, and the oil accommodated in the oil reservoir is sucked out by the jet flowing into the cylinder port from the notch, As a result, oil can be supplied also to the portion approaching the sliding surface of the valve plate, and therefore, the generation of negative pressure near the sliding surface of the valve plate can be prevented, and the occurrence of cavitation, that is, the generation of air bubbles, can be prevented. Can be prevented.

The invention according to a second aspect of the present invention is the invention according to the first aspect, wherein the oil reservoir is formed in a curved shape.

According to the second aspect of the present invention, the flow of the oil sucked by the jet from the notch can be made smooth along the curved surface.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a piston / pump according to the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing an embodiment of the piston pump of the present invention, FIG. 2 is a front view of a valve plate corresponding to the view taken along the line II of FIG. 1, and FIG. 3 is an embodiment shown in FIG. FIG. 7A is a view for explaining a relative operation between a sliding surface of a valve plate and a sliding surface of a cylinder block, in which FIG.
FIG. 3 is a front view of a main part mainly showing a valve plate portion.

In FIG. 1, reference numeral 1 denotes a casing forming an outer shell of a piston pump provided in a hydraulic excavator or the like. The casing 1 includes a cylindrical casing main body 2 having a closed portion 2A at one end in the axial direction, and a rear casing 3 that closes an open end of the casing main body 2. A rotating shaft 4 is inserted in the casing 1 in the axial direction thereof, and the rotating shaft 4 is rotatably supported between the closing portion 2A side and the rear casing 3 side.
A cylinder block 6 is spline-coupled to the rotating shaft 4, and the cylinder block 6 rotates integrally with the rotating shaft 4. A plurality of cylinders 7 are formed around the axis in the cylinder block 6, and each of the cylinders 7 accommodates a piston 8 for sucking and discharging hydraulic oil.

A valve plate 5 is fixed to the inner surface of the rear casing 3 described above, and the valve plate 5 has a sliding surface 5D which is in sliding contact with the end surface 6A of the cylinder block 6. Further, the valve plate 5 is formed with a suction port 5A and a discharge port 5B which are always in communication with a pair of inflow / outflow passages (not shown) provided in the rear casing 3 and have eyebrows as shown in FIG. Discharge port 5B of valve plate 5 corresponding to the bottom dead center side of piston 8
Is formed with a notch 5C extending toward the suction port 5A.

The end surface 6A of the cylinder block 6 which is in sliding contact with the sliding surface 5D of the valve plate 5 communicates with the corresponding one of the cylinders 7 described above.
Cylinder port 7 that can selectively communicate with either suction port 5A or discharge port 5B of valve plate 5 with rotation of
A is formed.

A swash plate 10 is provided in the casing 1 at a position facing the valve plate 5. Further, a spring 11 is arranged between the cylinder block 6 and the rotating shaft 4. The spring force of the spring 11 is applied to the cylinder block 6, whereby the cylinder block 6 is pressed against the valve plate 5. The spring force of the spring 11 is applied to the retainer 14 via the rod 12 and the bush 13, whereby the shoe 8A rotatably connected to the piston 8 is pressed against the swash plate 10.

As shown in FIGS. 2 and 3A, between the end of the suction port 5A located near the bottom dead center of the piston 8 of the valve plate 5 and the notch 5C. An oil reservoir 5E is formed in a recessed shape and is capable of storing oil. The oil sump 5E is entirely formed in a curved surface shape, for example, a substantially hemispherical shape. Also, this oil sump 5E
For example, the dimension of the length of the opening is set to about 80 to 90% of the difference between the outer diameter and the inner diameter of the valve plate 5, and the depth is set to, for example, １ ／ of the thickness of the valve plate 5. This is set as above. By setting as described above, the oil sump 5E can contain a sufficient amount of oil to be supplied near the sliding surface 5D of the valve plate 5.

In this embodiment configured as described above,
When the cylinder block 6 rotates together with the rotation shaft 4, the piston 8 reciprocates a stroke according to the inclination angle of the swash plate 10. Further, each cylinder port 7A of the cylinder block 6 is sequentially connected to a suction port 5A and a discharge port 5B of the valve plate 5. As a result, the hydraulic oil is supplied to the rear casing 3
Of the valve plate 5 through an inflow passage (not shown)
A is sucked into the cylinder 7 from A, and then the hydraulic oil in the cylinder 7 is discharged through a discharge port 5B of the valve plate 5 to an outflow passage (not shown) of the rear casing 3.

FIG. 3A shows a state in which each of the cylinder ports 7A of the above-described cylinder block 6 is switched and connected from the suction port 5A of the valve plate 5 to the discharge port 5B.
This will be described with reference to FIG.

When the end 7B of the end of the cylinder port 7A communicates with the end of the notch 5C of the discharge port 5B, the inside of the cylinder 7 is in a low pressure state.
The high-pressure hydraulic oil flows into the cylinder 6 through the notch 5C, and raises the pressure in the cylinder 7. At this time, most of the hydraulic oil passing through the notch 5C flows into the cylinder port 2A as shown by an arrow 15 in FIG. A part of the hydraulic oil is stored in the oil reservoir 5E along the wall surface of the cylinder port 7A and the like. In the state where the oil is stored in the oil sump 5E, as shown by the arrow 15 in FIG. 3A, when the jet of the hydraulic oil flows into the cylinder port 5A from the notch 5C, the oil sump The oil contained in the portion 5E is sucked out as shown by the arrow 16 and the valve plate 5
Can also be supplied to the part approaching the sliding surface 5D of
Therefore, generation of negative pressure in the vicinity of the sliding surface 5D of the valve plate 5 can be prevented, and generation of cavitation, that is, generation of bubbles can be prevented.

According to the present embodiment configured as described above,
As the cylinder block 6 rotates, the cylinder port 7A formed on the end face 6A of the cylinder block 6
From the position facing the suction port 5A of the discharge port 5B.
The notch 5C formed in the sliding surface 5D of the valve plate 5 at the time of the operation of switching to the position opposing to the above gradually increases the opening area within a very short time. Thereby, the valve plate 5
Of the operating oil from the discharge port 5B to the cylinder port 7A is suppressed, and the generation of pump noise and vibration is suppressed.

At this time, the oil contained in the oil reservoir 5E is sucked out by the jet flow from the notch 5C with the inflow of the hydraulic oil from the notch 5C of the valve plate 5, and as described above, the valve is opened. Supplied near the sliding surface 5D of the plate 5, the generation of negative pressure near the sliding surface 5D can be prevented, and the occurrence of cavitation, that is, the generation of bubbles can be prevented. Therefore, it is possible to reliably prevent erosion that is likely to occur due to the impact when the bubble is crushed, that is, erosion on the sliding surface 5D of the valve plate 5 or the wall surface of the cylinder 7.

Further, since the oil reservoir 5E is set to have a curved surface, the flow of oil sucked by the jet from the notch 5C can be made to be a smooth flow along the curved surface. The operation of sucking oil from the portion 5E can be performed favorably.

Further, the present embodiment has a simple structure in which the oil reservoir 5E is simply formed in the valve plate 5 which is usually provided, and therefore can be realized at a relatively low manufacturing cost.

[0025]

As described above, according to the present invention, when the high-pressure hydraulic oil flows from the discharge port of the valve plate to the cylinder port of the cylinder block, the force of the jet of the hydraulic oil is increased. Can be weakened through the notch of the valve plate, and hydraulic oil can be supplied also near the sliding surface of the valve plate, thereby preventing the generation of negative pressure near the sliding surface of the valve plate, Cavitation due to this negative pressure, that is, the generation of air bubbles can be prevented, and the erosion that is likely to occur with the impact when the air bubbles are crushed, that is, the erosion of the sliding surface of the valve plate or the wall surface of the cylinder is reliably generated. Can be prevented.

Further, since the valve plate has a simple structure in which a recessed oil reservoir is provided in a valve plate equivalent to the conventional one, it can be realized at a relatively low manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a piston pump of the present invention.

FIG. 2 is a front view of the valve plate corresponding to the direction of the arrow II in FIG. 1;

3A and 3B are diagrams for explaining a relative operation between a valve plate and a sliding surface of a cylinder block provided in the embodiment shown in FIG. 1; FIG. FIG. 3B is a main part front view mainly showing a valve plate portion.

FIG. 4 is a diagram for explaining a problem in the prior art, and is a cross-sectional view of a main part of a sliding surface portion between a valve plate and a cylinder block.

[Explanation of symbols]

 Reference Signs List 1 casing 4 rotary shaft 5 valve plate 5A suction port 5B discharge port 5C notch 5D sliding surface 5E oil sump 6 cylinder block 6A end face 7 cylinder 7A cylinder port 8 piston 15 arrow 16 arrow

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuya Sakairi 650 Kandamachi, Tsuchiura-shi, Ibaraki F-term in the Tsuchiura Plant of Hitachi Construction Machinery Co., Ltd.

Claims (2)

[Claims] Claims: 1. A rotatable cylinder block having a plurality of cylinders and housed in each of the cylinders,
A plurality of pistons for sucking and discharging hydraulic oil, and a valve plate having an end surface of the cylinder block slidably contacted and having a suction port for sucking the hydraulic oil and a discharge port for discharging the hydraulic oil, wherein the piston A notch extending from the end of the discharge port to the suction port side is provided on a sliding surface of the valve plate near the bottom dead center where the end surface of the cylinder block slides, and the valve plate slides on the valve plate of the cylinder block. A plurality of cylinder ports that communicate with corresponding ones of the cylinders and that can selectively communicate with one of the suction port and the discharge port of the valve plate with the rotation of the cylinder block are provided on the contacting end face. A piston pump having a recess between the end of the suction port located near the bottom dead center of the piston of the valve plate and the notch. It is formed in a shape, a piston pump, characterized by comprising an oil reservoir which can accommodate the oil. 2. The piston pump according to claim 1, wherein said oil reservoir is formed in a curved shape.