Semi-spherical shoe

The invention relates to a semi-spherical shoe and more particularly, to a semi-spherical shoe which is preferred to be interposed between a piston of a swash plate compressor and a swash plate.

The use of the semi-spherical shoe in a swash plate compressor which is provided with a semi-spherical surface and a flat end face is known in the art.

In the prior art practice, the entire semi-spherical surface of the semi-spherical shoe has been formed substantially to a uniform surface roughness. The semi-spherical shoe has its semi-spherical surface fitted into a semi-spherical recess formed in the piston and thus is disposed in sliding contact therewith. However, the entire semi-spherical surface is not disposed in sliding contact with the semi-spherical recess in the piston, but it is known that an annular region which is disposed toward the axial center of the semi-spherical shoe is disposed in sliding contact with the semi-spherical recess. Thus, the semi-spherical surface of the semi-spherical shoe includes a sliding contact region which is disposed in sliding contact with the semi-spherical recess in the piston, and a non-sliding contact region which is not disposed in sliding contact with the semi-spherical recess in the piston as is known in the art.

In the conventional semi-spherical shoe, the entire semi-spherical surface, thus, both the sliding contact region and the non-sliding contact region are formed to the same surface roughness. However, it is found by a study of a conventional semi-spherical shoe by the present inventor that a fine roughness of the semi-spherical surface has been effective in view of the sliding response. On the contrary, when the surface roughness of the semi-spherical surface is fine, the semi-spherical surface repels a lubricant oil, and thus there results a disadvantage that the lubricant oil is less susceptible to be guided toward the sliding contact region.

In view of the foregoing, the present invention provides a semi-spherical shoe including a semi-spherical surface which is fitted into a semi-spherical recess formed in one of members and an end face which is disposed in sliding contact with a flat surface formed on another member, in which a non-sliding contact region of the semi-spherical surface which is not disposed in sliding contact with the semi-spherical recess has a roughness which is greater than the roughness of a sliding contact region of the semi-spherical surface which is disposed in sliding contact with the semi-spherical recess.

With this arrangement, the greater surface roughness of the non-sliding contact region area than the surface roughness of the sliding contact region of the semi-spherical surface prevents a lubricant oil from being repelled by the non-sliding contact region, and allows the lubricant oil to be smoothly supplied to the sliding contact region through the non-sliding contact region. Because the sliding contact region has a fine surface roughness, there is provided a semi-spherical shoe which exhibits an excellent sliding response.

FIG. 1 is a cross section of one embodiment of the present invention;

FIG. 2 is a front view of the semi-spherical shoe shown in FIG. 1;

FIG. 3 is an enlarged view of the semi-spherical shoe shown in FIG. 1;

FIG. 4 shows the disposition of the semi-spherical shoe shown in FIG. 1 during the operation of a swash plate compressor;

FIG. 5 is a cross section of a second embodiment of the invention;

FIG. 6 is a cross section of a third embodiment of the invention; and

FIG. 7 is a cross section of a fourth embodiment of the invention.

Several embodiments of the invention shown in the drawings will now be described. Referring to FIGS. 1 to 3 , there is shown a semi-spherical shoe 1 which is disposed within a swash plate compressor which is in itself known in the art.

A swash plate compressor comprises a piston 2 which is disposed for reciprocating motion in the vertical direction as viewed in FIG. 1, and a flat swash plate 3 which is disposed for rotation by a rotary shaft. The piston 2 has an end face 2 A, in which a semi-spherical recess 2 B is formed. In this embodiment, the semi-spherical recess 2 B is formed to exhibit a uniform curvature over the entire region thereof.

The semi-spherical shoe 1 includes a semi-spherical surface 1 A and a flat end face 1 B. At its top end, as viewed in FIG. 1, the semi-spherical surface 1 A is slightly notched in a direction perpendicular to an axis C to define a shallow recess 1 C which is arcuate in section. The end face 1 B is formed with a substantially conical opening 1 D toward the center or in alignment with the axis. The recess 1 C formed at the top has a depth which is chosen to be on the order of about one-third the depth of the opening 1 D in the end face 1 B.

The semi-spherical shoe 1 is disposed so that the semi-spherical surface 1 A is fitted into the semi-spherical recess 2 B in the piston 2 while the end face 1 B abuts against the swash plate 3 . When the semi-spherical shoe 1 is interposed between the semi-spherical recess 2 B and the swash plate 3 , a region of the semi-spherical surface 1 A which is located adjacent to a boundary 1 E between the semi-spherical surface 1 A and the end face 1 B is exposed in a space between the end face 2 A of the piston 2 and the swash plate 3 (see FIG. 1 ).

A space 4 is defined by the recess 1 C and the semi-spherical recess 2 B in the piston 2 while a space 5 is defined by the opening ID and the swash plate 3 . These spaces 4 and 5 function as temporary reservoir chambers for the lubricant oil.

When the swash plate 3 rotates, the piston 2 is driven through the semi-spherical shoe 1 for reciprocating motion. At this time, the end face 1 B of the semi-spherical shoe 1 slides relative to the swash plate 3 while the semi-spherical surface 1 A slides relative to the semi-spherical recess 2 B. During this process, the lubricant oil which is stored in the spaces 4 and 5 permeates into sliding contact regions of the semi-spherical surface 1 A and the end face 1 B, thus lubricating and cooling these regions.

In the present embodiment, the semi-spherical surface 1 A includes a sliding contact region 1 a and non-sliding contact regions 1 b , 1 b ′ having different surface roughnesses.

Specifically, the semi-spherical surface 1 A of the semi-spherical shoe 1 is not entirely in sliding contact with the semi-spherical recess 2 B in the piston 2 , but only the annular region located adjacent to the top recess 1 C or the sliding contact region 1 a is disposed in sliding contact with the semi-spherical recess 2 B. In other words, regions of the semi-spherical surface 1 A except for the sliding contact region 1 a , namely, a region between the sliding contact region 1 a and the recess 1 C (or non-sliding contact region 1 b ), and a region located between the boundary 1 E and the sliding contact region 1 a (or non-sliding contact region 1 b ′) are not in sliding contact with the semi-spherical recess 2 B.

In the present embodiment, the sliding contact region 1 a of the semi-spherical surface 1 A has a roughness which is finer than the non-sliding contact regions 1 b , 1 b ′. Stated differently, the roughness of the non-sliding regions 1 b , 1 b ′ is greater than the roughness of the sliding contact region 1 a.

More specifically, in the present embodiment, the surface roughness of the sliding contact region 1 a is chosen to be equal to or less than 0.8 μmRz (or more preferably 0.2 μmRz). By contrast, the surface roughness of the non-sliding contact regions 1 b , 1 b ′ is chosen to be equal to or less than 1.6 μmRz (or more preferably 0.4 μmRz). It is desirable that the roughness of the sliding contact region 1 a be chosen to be equal to or less than 1.6 μmRz while the roughness of the non-sliding contact regions 1 b , 1 b ′ be chosen to be 3.2 μmRz.

The roughness of the non-sliding contact regions 1 b , 1 b ′ is achieved by a cutting operation. In addition to the cutting operation, a forging operation or a laser machining may be used to achieve a greater surface roughness of the non-sliding contact regions 1 b , 1 b ′ than the surface roughness of the sliding contact region 1 a.

In the present embodiment, a region of the end face 1 B of the semi-spherical shoe 1 which is located toward the axis (or opening 1 D) is formed to bulge into the swash plate 3 as compared with the boundary 1 E which defines the outer periphery of the semi-spherical shoe. A flat surface which is located toward the axis defines a region which is used as a sliding contact region 1 F disposed in sliding contact with the swash plate 3 .

On the other hand, a region extending from an outer edge 1 F′ of the sliding conduct region 1 F to the boundary 1 E is formed to depict a gentle arc in section, thus defining a non-sliding contact region 1 G which is not disposed in sliding contact with the swash plate 3 .

In the present embodiment, when forming the non-sliding contact region 1 G, the outer edge 1 F′ of the sliding contact region 1 F is located nearer the axis C as compared with a distance R (or radius) by which a top edge 1 a ′ or the edge located toward the recess 1 C of the sliding contact region 1 a of the semi-spherical surface 1 a is spaced from the axis C (see FIG. 3 ).

When an imaginary line L is drawn parallel to the axis C so as to intersect with the edge 1 a ′, a point X where the line L intersects with the non-sliding region 1 G, the sliding contact region 1 F and the boundary 1 E are chosen such that denoting a distance by which the sliding contact region 1 F and the boundary 1 E are spaced apart axially (or a bulge of the sliding contact region 1 F) by C 1 and a distance by which the sliding contact region 1 F and the pointer X are spaced apart vertically by C 2 , the inequality C 2 /C 1 ≦0.3 is satisfied.

In this manner, in the present embodiment, a region of the end face 1 B located toward the axis (or sliding contact region 1 F) bulges beyond the boundary 1 E which defines the outer periphery.

In actual use of the semi-spherical shoe 1 , a maximum load P applied to the piston 2 along the axis thereof is supported by the swash plate 3 which assumes its most skewed position and the sliding contact region 1 F of the end face 1 B, as shown in FIG. 4 . Accordingly, the semi-spherical shoe 1 which is interposed between the semi-spherical recess 2 B of the piston 2 and the swash plate 3 assumes a very stable position. In the condition shown in FIG. 4, part of the sliding contact region 1 a of the semi-spherical surface 1 A becomes exposed in a space between the end face 2 A of the piston 2 and the swash plate 3 , whereby the lubricant oil is guided into the region of sliding contact between the sliding contact region 1 a and the semi-spherical recess 2 B.

As mentioned above, in the semi-spherical shoe 1 of the present embodiment, the non-sliding contact regions 1 b , 1 b ′ have a surface roughness greater than the surface roughness of the sliding contact region 1 a , and thus the non-sliding contact regions 1 b , 1 b ′ have a reduced tendency to repel the lubricant oil. Accordingly, the lubricant oil can be smoothly supplied to the sliding contact region 1 a through the non-sliding contact regions 1 b , 1 b′.

On the other hand, the reduced surface roughness of the sliding contact region 1 a achieves an excellent sliding response when it slides relative to the semi-spherical recess 2 B in the piston 2 .

Thus it will be seen that since the non-sliding contact regions 1 b , 1 b ′ having a greater surface roughness are effective to draw the lubricant oil into the sliding contact region 1 a in the present embodiment, there is provided a semi-spherical shoe 1 having an excellent sliding response as compared with the conventional semi-spherical shoe 1 in which the semi-spherical shoe 1 A has a uniform roughness over the entire region thereof

As mentioned above, in the present embodiment, a region of the end face 1 B located toward the axis (or the sliding contact region 1 F) bulges to a greater degree than at the outer periphery (the non-sliding contact region 1 G). As a consequence, the position of the semi-spherical shoe 1 during the operation of the swash plate compressor becomes stabilized, providing a good lubricating and cooling effect upon the sliding regions by the lubricant.

Second Embodiment

FIG. 5 shows a second embodiment of the invention in which the opening 1 D formed in the end face shown in the first embodiment is omitted. In other respects, the arrangement is similar to the first embodiment. Again, a similar functioning and effect can be achieved as a achieved in the first embodiment.

Third Embodiment

FIG. 6 shows a third embodiment of the present invention in which the recess 1 C shown in the second embodiment is provided by a opening 1 C of a greater depth. In other respects, the arrangement is similar to the second embodiment. Again, a similar functioning and effect can be achieved as achieved in the first embodiment.

Fourth Embodiment

FIG. 7 shows a fourth embodiment of the present invention in which the recess 1 C shown in the second embodiment is replaced by a flat surface 1 C which extends perpendicular to the axis. In other respects, the arrangement is similar to the second embodiment. Again a similar functioning and effect can be achieved as achieved in the first embodiment.

Above described embodiments illustrate the application of the present invention to the semi-spherical shoe of the swash plate compressor, but it should be understood that the shoe of the present invention can be used with a wobble plate oil pump. In addition, the shoe according to the present invention can also be used with a mechanical component having a semi-spherical recess into which the semi-spherical shoe is fitted.

As described above, in accordance with the invention, there is obtained an advantage that a semi-spherical shoe having an improved sliding response as compared with the prior art can be obtained.