JP2004239077A - Axial swash plate type hydraulic pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an axial swash plate type hydraulic pump for improving mechanical efficiency and the service life of the pump by preventing seizure by securing superior slidability by securing lubricating oil of the whole sliding surface between a cylinder and a piston. <P>SOLUTION: The piston of the axial swash plate type hydraulic pump is composed of a cylindrical piston body part, an inserting end taper part for diametrally contracting in the inserting direction from the piston body part and a projecting end taper part for diametrally contracting in the projecting end direction from the piston body part, and the superior slidability is secured by the wedge effect of the taper part. The superior slidability is secured by preventing partial contact occurring when a piston shaft becomes eccentric to a cylinder hole shaft by arranging an annular oil groove on an outer peripheral wall of the piston body part. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an axial swash plate type hydraulic pump, and more particularly to a hydraulic pump suitably used as a high pressure hydraulic source for construction machines such as a hydraulic shovel.
[0002]
[Prior art]
An axial type swash plate type hydraulic pump of this type includes a swash plate disposed in a casing so as to be tiltable with respect to a drive shaft, a rotor attached to the drive shaft and rotating opposite to the swash plate, It has a piston that is inserted into the cylinder hole of the rotor, and a shoe that pivotally supports the protruding end of the piston via a spherical bearing so as to swing freely, and slides the sliding surface of the swash plate in the circumferential direction. When the rotor is driven to rotate, the change in the distance between the shoe and the rotor, which occurs according to the tilt angle of the swash plate, is taken as the reciprocating stroke of the piston. It is possible to discharge a high volume of high pressure hydraulic oil.
[0003]
The piston of such a hydraulic pump is slidably fitted in a cylinder hole with a small gap, and an oil film of hydraulic oil is formed in the gap, so that the piston and the cylinder hole are in contact with each other. Lubrication of the contact surface (sliding surface) and sealing of the liquid in the cylinder hole are performed.
However, in the swash plate type hydraulic pump, when the shoe slides along the swash plate, it acts in the direction perpendicular to the cylinder axis as a component force of the friction force along the rotation direction of the rotor and the pressing force from the swash plate. Therefore, the piston shaft slightly tilts with respect to the cylinder shaft, and there is a problem that the contact resistance at the contact portion increases because the piston hits the wall of the cylinder hole.
[0004]
In order to avoid such a problem, there is an example in which a tapered portion for reducing the contact area and reducing the contact resistance is used at the protruding end side of the piston (hereinafter, referred to as “protruding end”). (For example, see Patent Document 1).
[0005]
[Patent Document 1]
JP 10-176652 A
[Problems to be solved by the invention]
When the protruding end of the piston is tapered, a lubricating action by a so-called wedge effect is exerted. More specifically, when the piston moves in the direction of immersion into the cylinder hole, lubricating oil is applied to the contact portion between the cylinder body wall and the tapered portion and the cylinder hole wall from the gap formed by the cylinder hole and the piston body. The hydraulic oil is supplied so as to be scraped, and the hydraulic oil forms an oil film to improve the lubrication state in the contact portion and reduce the contact resistance.
[0007]
However, according to the above-described prior art, the contact resistance is reduced in a region where the portion slides due to the tapered end of the piston, but the effect is not sufficient as a whole.
Also, since the pressure distribution in the gap between the cylinder hole and the piston is not uniform due to the inclination of the piston with respect to the cylinder hole axis, the piston is pressed against one side of the cylinder hole wall in a direction from a high working pressure to a low working pressure. In some cases, the piston shaft may be eccentric with respect to the cylinder hole axis.
[0008]
In such a case, direct metal contact occurs between the piston and the cylinder hole wall, smooth lubrication is not performed, and galling and seizure may occur between the piston and the cylinder hole wall.
Advantageous Effects of Invention The present invention can secure good lubricity by securing lubricating oil on the entire sliding surface between a cylinder and a piston, prevent seizure, and improve mechanical efficiency and life of a pump. An object of the present invention is to provide an axial type swash plate type hydraulic pump.
[0009]
[Means for Solving the Problems]
According to the present invention, in order to solve the above-described problems, a piston is provided so as to be freely inserted into and retracted from a cylinder hole of a rotor that rotates integrally with a drive shaft, and a pressure having a capacity corresponding to a tilt angle of a swash plate is provided. An axial type swash plate type hydraulic pump for discharging oil, wherein the piston has a cylindrical piston main body, an insertion end tapered part whose diameter decreases in an insertion direction from the piston main body, and protrudes from the piston main body. An axial type swash plate type hydraulic pump is provided, comprising: a protruding end taper portion whose diameter is reduced in an end direction.
[0010]
While the piston body slides on the cylinder hole wall, each of the insertion end taper portion and the projecting end taper portion of the piston performs wedge effect lubrication near the contact portion between the piston and the cylinder hole wall during reciprocation of the piston. In addition, the entire sliding surface of the piston body is maintained in a smooth lubricated state.
Here, even if the piston is most protruded from the cylinder hole, the maximum of the piston that can be generated from the difference between the outer diameter of the piston main body and the inner diameter of the cylinder hole so that the tapered end of the piston does not contact the cylinder hole wall. When the taper angle of the tapered portion at the insertion end is larger than the inclination angle (Claim 2), and when the annular groove is formed near the bottom of the cylinder hole, the piston is in the state most immersed in the cylinder hole. Also, it is desirable that the boundary between the piston main body and the insertion end tapered portion exists on the sliding surface between the piston and the cylinder hole (claim 3) in order to reduce the resistance.
[0011]
For the same reason, the tapered angle of the tapered end of the protruding end is larger than the maximum inclination angle of the piston that can be caused by the difference between the outer diameter of the piston body and the inner diameter of the cylinder hole so that the tapered end of the piston does not contact the cylinder hole wall. The resistance is reduced because the boundary between the piston main body and the tapered end of the protruding end exists on the sliding surface between the piston and the cylinder hole even when the piston is set to a large value and the piston is most protruded from the cylinder hole. (Claim 4).
[0012]
Further, according to the fifth aspect of the present invention, the outer peripheral wall of the piston body has an annular oil groove. Even when the piston makes a partial contact with the cylinder hole wall, the lubricating oil is supplied through the annular oil groove, the pressure distribution can be made uniform, and the lubricating state can be maintained.
Such an annular oil groove is desirably located substantially at the center of the piston body in consideration of the axial distribution of the lubricating oil (claim 6).
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.
First, the configuration of an axial type swash plate type hydraulic pump 1 according to the present invention will be described with reference to FIGS.
The hydraulic pump 1 includes a casing 4 including a rear casing 2 and a front casing 3. Inside the casing 4, the rotor 6 is driven to rotate by the drive shaft 5 and is tiltable with respect to the drive shaft 5. Swash plate 8 is accommodated.
[0014]
The rotor 6 is spline-coupled to the shaft 5, rotates integrally with the shaft 5, and has a plurality of bottomed cylinder holes 20 (in the present embodiment, as shown in FIG. 8 are arranged at equal intervals in the direction), and are pierced with the opening facing the swash plate 8.
The cylinder hole 20 has a cylinder main hole portion 20a with which a piston 30 described later in detail slides, and a cylinder hole annular groove portion 20b formed near the bottom surface 20c of the cylinder hole 20 and having a larger diameter than the cylinder main hole portion 20a. Have.
[0015]
A piston 30 is reciprocally fitted into each of the cylinder holes 20. In a state where the piston 30 is most immersed in the cylinder hole (a state immersed at the top dead center position), a part thereof (hereinafter referred to as a “protruding end”). 33) protrudes from the cylinder hole 20 to the swash plate 8 side.
A concave portion 33a is formed on the end surface of the protruding end tapered portion 33, and the piston 30 swings on the shoe 10 (only two are shown in FIG. 1) via a substantially spherical joint 10a fitted into the concave portion 33a. It is freely pivoted.
[0016]
The shoe 10 includes a pedestal 10b integrally formed with the above-described joint 10a, and is held by an annular pressing plate 11, and the pedestal 10b is mounted on the swash plate 8 slidably in the circumferential direction of the rotor 6. Is done.
The swash plate 8 is in contact with the swash plate tilt angle adjusting pistons 7A and 7B at two symmetrical points on the peripheral edge, and the pistons 7A and 7B are connected to the cylinder holes 2c and 2d formed in the rear casing 2. The tilt angle of the swash plate 8 can be adjusted by controlling the oil pressure to expand and contract the respective pistons.
[0017]
An oil passage 61 is opened in each cylinder hole bottom surface 20c. The oil passage 61 is formed between the suction port 2a or the discharge port 2b installed in the rear casing 2 or the discharge port 2b and the rear casing 2 as the rotor rotates. The communication is made alternately via the installed valve plate 9.
An outline of the operation of the swash plate type hydraulic pump 1 configured as described above will be described below.
[0018]
First, when the swash plate tilt angle adjusting pistons 7A and 7B are expanded and contracted and the tilt angle of the swash plate 8 abutting on them is adjusted to a predetermined angle, the stroke of the reciprocating motion of the piston 30 is changed by the tilt angle. Therefore, the discharge amount (capacity) of the hydraulic pump 1 per unit time is determined from the tilt angle and the rotation speed of the rotor 6.
When the drive shaft 5 is rotated by an engine (not shown) or the like, the rotor 6 also rotates integrally with the piston 30 inserted in the cylinder hole 20. As the rotor 6 rotates, the shoe 10 slides in the circumferential direction along the sliding surface of the swash plate 8, and the swash plate is inclined with respect to the drive shaft 8. Will move back and forth. Therefore, with the rotation of the rotor 6, the piston 30 repeats a reciprocating motion of insertion (advance) and projection (retreat) into the cylinder hole 20.
[0019]
At this time, the oil passage 61 opening to the cylinder hole bottom surface 20c with the rotation of the rotor 6 communicates via the valve plate 9 with the suction port 2a during the retreat of the piston 30 and with the discharge port 2b during the forward movement of the piston 30. Thereby, the hydraulic oil is sucked into the cylinder hole 20 and the high-pressure hydraulic oil is discharged.
Next, the piston 30 of the hydraulic pump 1 according to the present invention will be described in detail with reference to FIGS.
[0020]
As shown in FIG. 3, the piston 30 includes a piston main body 31 and an insertion end taper portion 32 and a projecting end taper portion 33 integrally formed at both ends thereof.
The piston body 31 is formed in a hollow cylindrical body for weight reduction and oil supply to the shoe 10 and the like, and this part is always inserted into the cylinder hole 20. Two annular oil grooves 31a and 31b are formed on the outer peripheral wall of the piston main body 31 at positions substantially symmetrical on both sides of the substantially central position.
[0021]
The insertion end taper portion 32 is located on the insertion end side of the piston main body portion 31, and its outer shape is reduced in diameter in the insertion direction. Further, the protruding end taper portion 33 is located on the protruding end side of the piston main body portion 31, and its outer shape is reduced in diameter toward the discharge end direction.
The outer diameter of the piston body 31 is suitably set so that a gap of about 1/1000 with respect to the inner diameter of the main cylinder hole 20a is formed around the piston body 31 so that an oil film thickness required for lubrication can be secured. Is done. For example, when the inner diameter of the cylinder hole is 36 mm, the gap is about 36 microns.
[0022]
As shown in FIG. 4, the boundary 34 between the piston body 31 and the insertion end tapered portion 32 is in a state where the piston 30 is most immersed in the cylinder hole 20 in consideration of the maximum tilt angle of the swash plate 8 (top dead center). (A point position), it is located at a position retracted by a distance L1 (for example, 1 to 2 mm) from the insertion side edge (step portion) 20d of the cylinder main hole portion 20a, and the piston body portion 31 and the protruding end taper portion 33 As shown in FIG. 5, the boundary 35 is, when the piston 30 projects most from the cylinder hole 20 (the bottom dead center position) in consideration of the maximum tilt angle of the swash plate 8, from the cylinder hole opening edge 20 f. It is set to be located at a position advanced (inserted) by a distance L2 (for example, 1 to 2 mm). With this setting, as described above, the piston body 31 always comes into sliding contact with the cylinder wall 20e without coming off the main cylinder hole 20a.
[0023]
The above-mentioned distances L1 and L2 are set as small as possible so that the boundaries 34 and 35 can be located on the main cylinder hole 20a in consideration of machining errors and assembly errors.
The length of the piston body 31, the insertion end taper 32, and the protrusion end taper 33 are set in consideration of the maximum stroke length, the depth of the cylinder main hole 20a, the groove width of the annular groove 20b, and the like.
[0024]
Regarding the taper angles of the insertion end taper portion 32 and the projecting end taper portion 33, even when the piston 30 is in the most inclined state with respect to the axis of the cylinder hole 20, the respective taper portions 32 and 33 are in sliding contact with the cylinder hole wall 20e. In other words, it is necessary that the inclination angle is larger than the maximum inclination angle α of the piston 30, and about twice as much as α in consideration of suppressing leakage of high-pressure hydraulic oil in the cylinder hole 20. Is preferred.
[0025]
Here, the maximum inclination angle α of the piston 30 can be calculated in consideration of the difference between the inner diameter of the main cylinder hole 20a and the outer diameter of the piston main body 31, and furthermore, these processing errors. Assuming the state shown, it can be easily obtained by giving the length of the piston main body 31. Note that the maximum inclination angle in this embodiment is a constant value from the state where the piston 30 is most immersed in the cylinder hole 20 (FIG. 4) to the state where the piston 30 is most protruded (FIG. 5).
[0026]
Next, the operation and effect of the piston 30 formed as described above will be described.
Here, the state of an oil film formed on the sliding contact surface by the piston 40 having no insertion end taper is considered. At this time, the annular groove portion 20b is filled with hydraulic oil that also acts as lubricating oil. As shown in FIG. 6, when the piston 40 is inclined with respect to the cylinder hole 20, that is, when the piston 40 is inserted toward the insertion end (the direction of arrow V) while sliding on the cylinder hole wall 20 e. In FIG. 6, a wedge-shaped space that expands toward the insertion end, above the piston 40 and toward the insertion end from the boundary 44 between the piston body 41 and the protruding end taper 43 in FIG. S1 is formed.
[0027]
Here, at the uppermost point 44a of the boundary 44 in FIG. 6, a gap C1 is formed between the piston 40 and the cylinder hole wall 20e, and the upper end edge 42a of the piston insertion end 42 in FIG. If a gap C2 is formed between the piston 30 and the piston 20e, the pressure P1 of the wedge-shaped space S1 becomes higher as the piston 30 enters the insertion end side. The pressure P1 is higher than the pressure PL of the space S2 formed above the piston 40 in FIG. 6 on the protruding end tapered portion 43 side with the gap C1 as a boundary, and the gap C1 is smaller than the gap C2. Therefore, the lubricating oil in the wedge-shaped space S1 is swept toward the gap C1 by the pressure distribution and reaches the gap C1, so that a stable oil film is formed in the gap C1 and a good lubricating state is maintained. You.
[0028]
On the other hand, the so-called wedge effect does not act on the piston insertion end 42 having no taper, and in the worst case, an oil film is interposed between the insertion end 42 and the cylinder main hole end edge 20d. There is also a risk that undesired metal contact will occur.
On the other hand, the piston 30 of the hydraulic pump 1 according to the embodiment of the present invention has the insertion end taper portion 32 at the insertion end in addition to the projection end taper portion 33 as shown in FIG. The wedge effect acts on the boundary 34 on the insertion end taper portion 32 as well as the boundary 35 on the end taper portion 33 side, and the contact resistance is reduced.
[0029]
Further, the increase in the contact resistance due to the eccentricity of the piston 30 with respect to the cylinder hole 20 is considered as follows.
That is, when the piston 40 moves in the insertion direction of the cylinder hole 20 and the piston 40 is inclined with respect to the axis of the cylinder hole 20, the pressure P1 of the upper space S1 of the piston 40 in FIG. Since the pressure becomes larger than the pressure P2, a differential pressure between the pressures P1 and P2 acts on the piston 40, and the entire piston 40 is pressed downward in FIG. 6, and as shown in FIG. 20g does not coincide with the center 40a of the piston 40, and the piston 40 slides on the cylinder hole wall 20e in an eccentric state.
[0030]
Even in such a case, when the piston 40 is relatively rotating around the axis of the cylinder hole 20, the lubricating oil flows around the gap portion 22 because the narrow gap portion 22 near the sliding contact portion is a low pressure portion. However, when the piston 40 is not rotating with respect to the cylinder hole 20, such an effect is not obtained, and the piston 40 and the cylinder hole wall 20e make direct metal contact without lubricating oil, and the contact resistance increases. There is a risk of doing so.
[0031]
In the piston 30 according to the present embodiment, the lubricating oil is supplied through the two annular oil grooves 31a and 31b substantially at the center of the piston body 30 due to the effect of the differential pressure due to the non-uniform pressure distribution. Is uniform, so that direct metal contact does not occur and the contact resistance does not increase.
Due to the above-described operation and effect, in the hydraulic pump 1 according to the present embodiment, galling or seizure does not occur between the piston 30 and the cylinder hole wall 20e.
[0032]
In the present embodiment, the annular groove 20b is formed near the bottom surface 20c of the cylinder hole 20, but the annular groove 20b may be omitted. In that case, it is preferable to provide an insertion end taper portion having a length that is approximately one-third of the inner diameter of the cylinder hole 20, for example, to obtain a better wedge effect than the insertion end surface of the piston.
Further, in this embodiment, each boundary between the piston main body 31 and the insertion end taper 32 and between the piston main body 31 and the protruding end taper 33 is defined by the intersection of a simple cylindrical shape and a conical shape (taper). However, the portion may be formed by a so-called crowning having a curved surface.
[0033]
Further, in the present embodiment, the number of the annular oil grooves 31a and 31b at the approximate center of the piston main body 31 is two, but is not limited to two, and may be one or three or more.
[0034]
【The invention's effect】
According to the present invention, the piston is formed of a cylindrical piston body, an insertion end taper that reduces the diameter from the piston body in the insertion direction, and a protruding end taper that reduces the diameter from the piston body toward the protruding end. With this configuration, the contact (sliding) resistance can be sufficiently reduced by the wedge effect at the protruding end and the insertion end, and preferably, when an annular oil groove is formed on the outer peripheral surface of the piston main body, the pressure distribution can be reduced. Even if the pressure is not uniform and the piston is pressed against the cylinder hole wall due to the pressure difference, the lubricating oil is supplied through the annular oil groove, the pressure distribution is uniformed, and the lubrication state can be maintained. The contact resistance between the cylinder hole and the piston is reduced, galling and seizure are prevented, and mechanical efficiency and life can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view showing an axial type swash plate type hydraulic pump according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view of the rotor 6 as seen from the direction of arrows II-II in FIG.
FIG. 3 is an enlarged partial sectional view of a cylinder and a piston of the axial type swash plate type hydraulic pump shown in FIG. 1;
FIG. 4 is an enlarged partial cross-sectional view schematically showing a positional relationship between a piston and a cylinder at a top dead center according to an embodiment of the present invention (hatching is omitted in the figure).
FIG. 5 is an enlarged partial cross-sectional view schematically showing a positional relationship between a piston and a cylinder at a bottom dead center according to an embodiment of the present invention (hatching is omitted in the figure).
FIG. 6 is an enlarged partial sectional view for explaining a lubricating state of a conventional piston.
FIG. 7 is an enlarged partial cross-sectional view schematically showing a positional relationship between a conventional piston and a cylinder hole (hatching is omitted in the figure).
[Explanation of symbols]
Reference Signs List 1 axial swash plate type hydraulic pump 4 casing 5 drive shaft 6 rotor 8 swash plate 10 shoe 20 cylinder hole 20a cylinder main hole 20b cylinder hole annular groove 20c cylinder hole bottom surface 30 piston 31 piston body 31a annular oil groove 31b annular Oil groove 32 Insertion end taper 33 Projection end taper 34 Boundary 35 Boundary

Claims (6)

An axial type swash plate type hydraulic pump comprising a piston which is inserted and retractably inserted into a cylinder hole of a rotor which rotates integrally with a drive shaft, and discharges a pressure oil having a capacity corresponding to the tilt angle of the swash plate. ,
The piston is
A cylindrical piston body,
An insertion end tapered portion that is reduced in diameter in the insertion direction from the piston body;
A projecting end taper portion that reduces in diameter in a projecting end direction from the piston body;
An axial type swash plate type hydraulic pump characterized by comprising: In a state where the piston protrudes most into the cylinder hole, the insertion end tapered portion has a taper angle equal to or larger than a maximum inclination angle of the piston that can be caused by a difference between an outer diameter of the piston body and an inner diameter of the cylinder hole. The axial type swash plate type hydraulic pump according to claim 1, wherein: The cylinder hole has a cylinder main hole in which the piston body slides, and a ring groove formed near the bottom of the cylinder hole and having a larger diameter than the cylinder main hole, and the piston is most immersed in the cylinder hole. In the state, the boundary between the piston main body and the insertion end tapered portion is located in the cylinder main hole, and the insertion end tapered portion projects toward the annular groove. 3. The axial type swash plate type hydraulic pump according to 2. In a state where the piston projects most from the cylinder hole, a boundary between the piston body and the protruding end taper is located in the cylinder hole, and the protruding end taper has an outer diameter of the piston body. The axial type swash plate type hydraulic pump according to any one of claims 1 to 3, wherein the axial type swash plate type hydraulic pump according to any one of claims 1 to 3, having a taper angle equal to or greater than a maximum inclination angle of the piston which can be caused by a difference in cylinder bore inner diameter. The axial type swash plate type hydraulic pump according to any one of claims 1 to 4, wherein an annular oil groove is provided on an outer peripheral wall of the piston body. The axial type swash plate type hydraulic pump according to claim 5, wherein the annular oil groove is formed at a substantially central position of the piston body.

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