JP2001032767A - Swash plate axial piston type hydraulic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a swash plate axial piston type hydraulic device having a piston composed so that seizure or abrasion will not occur even in high-speed and high-load application. SOLUTION: A swash plate axial piston type hydraulic motor or pump comprises a cylinder block 16 rotatably provided in a fixed housing with a shaft, a piston 18 inserted in plural bores 28 provided in this cylinder block 16 to be capable of axially reciprocating, and a swash plate 22 slidably engaged with a shoe 20 installed on an outer end part of the piston 18 to decide the stroke of the piston 18. An outer circumferential surface of the piston 18 is protruded in a crown form in a length direction of it. Quantity of the crown form is, favorably, +0.6μ-+3μ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a hydraulic motor or a hydraulic pump which is a swash plate type axial piston type hydraulic device.

[0002]

BACKGROUND ART With the miniaturization and high performance of construction machines and agricultural machines, swash plate type axial piston type hydraulic motors and hydraulic pumps which are compact but can be used for high-pressure applications or high-speed high-load applications are widely used. These hydraulic devices may be of the variable displacement type, in which the inclination of the swash plate can be changed during operation as required, and thereby the displacement volume can be changed. There are also things. In the present specification, the present invention will be described by way of example by applying the present invention to a hydraulic motor. However, the hydraulic motor and the oil pump are essentially the same in structure except that the relationship between input and output is essentially reversed. Therefore, the following description also applies to the hydraulic pump.

FIG. 1 shows a basic structure of a typical swash plate type axial piston type hydraulic motor. Such a structure and its operating principle are generally well known and need not be described in detail. Reference numeral 12 denotes a housing of the hydraulic motor 10, and 14 extends from one end of the housing.
A rotating output shaft connected to a load (not shown), 16
A cylinder block, mounted in the housing and rotatably connected to the shaft together with the shaft, 18
A plurality of pistons 22 are provided in the bore of the cylinder block so as to be able to reciprocate in the axial direction and at equal intervals around the shaft, and are provided with slippers or shoes 20 with retainers at the outer ends. A swash plate 24 fixedly provided in the housing at an angle with respect to the axis of the shaft; a fixed valve plate 24 serving to selectively supply and remove hydraulic oil to and from the bore of the cylinder block;
Is an end cover fixed to the other end of the housing. The illustrated hydraulic motor is of a constant displacement type in which the swash plate 22 is preset to have a constant inclination.

[0004]

2. Description of the Prior Art Referring now to FIG. 4, one of the conventional pistons is shown positioned within a corresponding bore 28 of a cylinder block. In order that the content of the present invention may be better understood, the operating principle of the illustrated axial piston type hydraulic motor 10 will be described focusing on the operational relationship between the piston 18 'and the swash plate 22. The piston 18 'is
9 receives the oil pressure P applied to the bore 28 through the bore 9 and performs a certain degree of rotation (rotation) in the bore while receiving the lubricating action of the hydraulic oil in the bore, while axially moving to the right as viewed in the drawing. Try to do a stretching movement. Since the swash plate 22 is inclined with respect to the shaft, the pressing force of the piston acting on the swash plate via the shoe 20 is divided into a force parallel to the swash plate and a force perpendicular to the swash plate. Since the swash plate is fixed in the housing, the force acting parallel to the swash plate causes the piston 18 'to move in the direction of arrow D while sliding on the swash plate together with the shoe 20, and thus together with the cylinder block. The shaft starts to rotate.

During this operation, the piston 18 'receives a reaction force from the swash plate, and as a result, a force R is applied to the piston 18' in a direction perpendicular to the shaft 14. Then, as shown in FIG.
At 0, a line or rolling contact is made with the inner edge of the bore of the cylinder block, and a part of the outer edge of the inner end also comes into line or rolling contact with the inner wall of the bore at 32. In order to avoid stress concentration at such a contact portion that causes seizure and wear of the piston and / or the inner wall of the bore, it is necessary to provide a radius at the inner edge near the bore opening and at the inner end of the piston. Have been done.

However, in high-speed and high-load applications, R acting on the shaft 14 is large, and
At this point, the contact pressure between the outer surface of the piston and the inner wall of the bore becomes very large, and the lubricating effect of the hydraulic oil is not exhibited. As a result, seizure and wear of the inner wall of the piston and the bore still occur. Such a problem has not been solved even by improving the processing accuracy of the inner wall of the bore and the outer peripheral surface of the piston or by surface treatment.

SUMMARY OF THE INVENTION An object of the present invention is to provide a swash plate type axial piston type hydraulic device having a piston configured to solve such a problem and prevent seizure and wear even in high-speed and high-load applications.

[0008]

According to the present invention, there is provided a cylinder block provided rotatably with a shaft in a fixed housing, a piston inserted reciprocally in an axial direction into a bore provided in the cylinder block. A swash plate type axial piston type hydraulic device having a swash plate slidably engaged with a shoe attached to the outer end of the piston to determine the stroke of the piston, for example, a swash plate type axial piston type hydraulic motor or pump About. According to a feature of the present invention, the outer peripheral surface of the piston has a convex crown shape or a middle height in the longitudinal direction.

Preferably, the difference between the diameters of both ends and the center of the piston, that is, the amount of crown is +0.6 μm to +3 μm.
It is.

[0010]

FIG. 2 shows a piston 18 of the present invention positioned in a corresponding one of a plurality of bores 28 in a cylinder block 16. FIG. As described in connection with FIG. 4, the piston 18 receives the hydraulic pressure P applied to the bore 28 through the hole 29 and performs a certain rotation in the bore while being lubricated by the hydraulic oil in the bore. While performing the (rotation) movement, the user intends to make an axial extension movement to the right as viewed in the drawing, that is, toward the swash plate 22.

According to an important feature of the invention, the piston 1
It is noted that the outer peripheral surface 19 of 8 has a convex crown shape or a middle height in the longitudinal direction. As shown in FIG. 3, the difference between the diameters of both ends and the center of the piston, that is, the crown amount is preferably +0.6 μm to +3 μm. It has been experimentally found that piston load and seizure problems do not occur in load applications.

As can be seen from FIG. 2, the piston of the present invention, in contrast to conventional pistons, has its outer surface 19 having a very smoothly curved or large radius of curvature at reference numerals 30 and 32. Surface contact with the bore inner wall, and as a result, the load F at the contact portion is distributed and acts, so that stress concentration is suppressed and the contact pressure strength is reduced, so that seizure and wear of the piston and the bore inner wall do not occur. Become. Moreover, according to the configuration of the present invention, the piston 18 rotates more smoothly in the bore 28 while receiving the lubricating action of the hydraulic oil at the contact portion with the inner wall of the bore.

Since the amount of crown of the piston of the present invention is relatively small, there is almost no problem of performance deterioration of the motor due to leakage or the like.

Those skilled in the art will appreciate that the principle of the present invention is that the swash plate is associated with a well-known inclination adjusting means, and by operating the same, the stroke of the piston is changed according to the desired output torque. It will be appreciated that the invention can be applied not only to a variable displacement type hydraulic device capable of changing the displacement volume but also to a swash plate type axial piston type hydraulic pump having substantially the same structure.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic structure of a typical swash plate type axial piston hydraulic motor.

FIG. 2 is a side view showing a piston of the present invention in a bore of a cylinder block.

FIG. 3 is a schematic diagram more clearly showing the state and amount of a crown applied to the piston of the present invention.

FIG. 4 is a side view showing a conventional piston in a bore of a cylinder block.

[Explanation of symbols]

 Reference Signs List 10 hydraulic motor 12 housing 14 shaft 16 cylinder block 18 piston 22 swash plate

Claims (4)

[Claims] 1. A cylinder block rotatably provided with a shaft in a fixed housing, a piston inserted in a bore provided in the cylinder block to be reciprocally movable in an axial direction, and attached to an outer end of the piston. A swash plate type axial piston hydraulic device having a swash plate slidably engaged with a set shoe and determining a stroke of the piston, wherein an outer peripheral surface of the piston is formed into a convex crown shape in a longitudinal direction. Hydraulic equipment. 2. The amount of the crown is from +0.6 μ to +3.
2. The hydraulic apparatus according to claim 1, wherein the hydraulic pressure is μ. 3. The hydraulic device according to claim 1, wherein the hydraulic device is a swash plate type axial piston hydraulic motor. 4. The hydraulic device according to claim 1, wherein the hydraulic device is a swash plate type axial piston type hydraulic pump.