# Patent

## Title
Wabble plate type variable displacement compressor

## Abstract

A wabble plate type variable displacement compressor has a wabble plate rotation preventing mechanism including an inner ring axially movable relative to a main shaft, an outer ring connected to the wobble plate, a plurality of balls placed between guide grooves of the inner and outer rings and performing power transmission, and a sleeve axially movably engaged with the inner ring, provided so as to be axially movable together with the inner ring. A shape differs between the axial cross-sectional profiles of substantially concave spherical surfaces formed respectively in the inner periphery of the outer ring and the outer periphery of the sleeve such that the closer to the axial opposite ends of the contact portion between both the surfaces the position is, the greater the clearance between these surfaces. Implementation of the wabble plate rotation preventing mechanism in such a compressor can provide excellent durability and silent performance.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 12/809,457, filed Jun. 18, 2010, which was the National Stage of International Patent Application No. PCT/JP2008/072473, filed Dec. 11, 2008, which claims the benefit of Japanese Patent Application No. 2007-339454, filed Dec. 28, 2007, the disclosures of which are incorporated herein by reference in their entirety.


TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wabble plate type variable displacement compressor, and specifically, to a wabble plate type variable displacement compressor which incorporates therein a new rotation preventing mechanism for the wabble plate.
BACKGROUND ART OF THE INVENTION
For example, as a compressor provided in a refrigeration circuit for an air conditioning system for vehicles, a wabble plate type variable displacement compressor is known wherein a rotational movement of a swash plate rotated together with a rotational main shaft and supported changeably in angle relative to the main shaft is converted into a wabble movement of a wabble plate, and by transmitting the wabble movement to a piston connected to the wabble plate, the piston is reciprocated. In this wabble plate type variable displacement compressor, because it is necessary to prevent the rotation of the wabble plate connected to the piston, a rotation preventing mechanism of the wabble plate is incorporated. With respect to the rotation preventing mechanism of the wabble plate, various improvements for making the compressor small, improving the durability and the silent performance, facilitating processing, cost down, etc., have been investigated.
For example, in Patent documents 1, 3 and 4, a structure provided with a Birfield type constant velocity universal joint as a wobble plate rotation preventing mechanism is disclosed. In this structure, since wabble parts and a swash plate are supported by an outer ring of a Birfield type constant velocity universal joint provided as a wobble plate rotation preventing mechanism, and ultimately supported by a main shaft via a cage of an internal part of the constant velocity universal joint (a cage for regulating positions of a plurality of balls for performing power transmission), and further, via an inner ring of the constant velocity universal joint, the number of interposed parts increases and the accumulated play becomes great, and therefore, there is a problem insufficient in vibration, noise and durability.
Further, although the Birfield type constant velocity universal joint disclosed in Patent documents 1, 3 and 4 theoretically has a structure performing a rotational power transmission between inner and outer rings by a plurality of balls, actually it is a multiple restriction structure, and it is difficult to achieve uniform and continuous contact of the plurality of balls, and therefore, a contact pressure of specified balls may locally increase. Further, because the rotational power transmission between inner and outer rings is performed in the shear direction of balls by ball guide grooves formed on each of inner and outer rings on both sides of a cage, the contact surface between the balls and the guide grooves may have a large inclination relative to the power transmission direction. By this, when a predetermined power is transmitted, the contact load generated as a vertical reaction force becomes high. Therefore, in order to ensure a sufficient transmission ability, it is necessary to employ a sufficiently large ball size (ball diameter), and from these reasons, it is difficult to make the structure further small-sized, and it is difficult to apply it to a small displacement compressor.
Further, since the support for the rotational main shaft of the compressor in the internal mechanism described in Patent documents 2, 3 and 4 is provided on one side relative to the main mechanism portion (a cantilever supporting is employed), whirling of the main shaft becomes great, and it is disadvantageous on durability, vibration and noise.
Further, in the compression mechanism disclosed in Patent documents 3 and 4, since the inner ring of the constant velocity universal joint is supported slidably in the axial direction at a condition being prevented with rotation, it is necessary to make the main shaft thick in order to ensure the rigidity of the main shaft provided to the housing to be sufficiently great, and it may cause increase of the weight of the main shaft and the weight of the product.
Further, in the constant velocity universal joint mechanism disclosed in Patent documents 3 and 4, machining of grooves for regulating the positions of a plurality of balls operating for power transmission is complicated, and the mechanism may be disadvantageous on cost.
Furthermore, in the compression mechanism disclosed in Patent document 2, since there is no support in the radial direction due to the main shaft in the main mechanism portion and play in the wabble portion in the radial direction tends to become great, by this play, problems on durability, vibration and noise may occur.
Patent document 1: U.S. Pat. No. 5,112,197
Patent document 2: U.S. Pat. No. 5,509,346
Patent document 3: U.S. Pat. No. 5,129,752
Patent document 4: JP-A-2006-200405
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
Paying attention to the problems in the above-described conventional technologies, a wabble plate type variable displacement compressor is previously proposed by the applicant of the present invention which uses a constant velocity universal joint small-sized, good in durability and silent performance, easy-to-machine and inexpensive, that has achieved to realize uniform and continuous contact of a plurality of balls operating for power transmission while suppressing play in the radial direction and rotational direction of the inside of the constant velocity universal joint provided as a wabble plate rotation preventing mechanism (Japanese Patent Application No. 2006-327988).
In this proposal, as the rotation preventing mechanism of the wabble plate, a mechanism is provided, which comprises (a) an inner ring provided in a housing movably in an axial direction although rotation is prevented, supporting a rotational main shaft via a bearing at an inner diameter portion to rotate relatively and to move relatively in an axial direction and having a plurality of guide grooves for guiding a plurality of balls provided for power transmission, (b) a sleeve functioning as a wabble central member of the wabble movement of the wabble plate, provided on the rotational main shaft to rotate relatively thereto and to move in an axial direction and engaged with the inner ring movably in an axial direction together with the inner ring, (c) an outer ring having a plurality of guide grooves for guiding the balls at positions opposing respective guide grooves of the inner ring, supported on the sleeve wabblingly, supporting the wabble plate fixedly on an outer periphery and supporting the swash plate rotatably via a bearing, and (d) a plurality of balls held by the guide grooves formed in the inner ring and the outer ring at a condition of opposing each other and performing power transmission by being compressed between the guide grooves.
By this proposal, a wabble plate type variable displacement compressor made small-sized, good in durability and silent performance, easy-to-machine and inexpensive, has become possible, but, even in this proposed mechanism, matters to be further improved are still left, Namely, in the fitting portion (fitting portion of arc surfaces with each other having substantially same shapes) between the sleeve provided on the rotational main shaft as a member for supporting a wabble center of the wabble plate and the outer ring of the rotation preventing mechanism assembled on the sleeve wabblingly, while a radial component force of a compression reaction force and a transmission reaction force of the rotational torque transmitted by the contact of an arm, etc, provided at a rotor side rotated together with the rotational main shaft are received, sliding accompanied with the wabble movement of the wabble plate is generated. Therefore, although it is preferred that this sliding section is sufficiently lubricated in order to maintain excellent durability and silent performance, because this sliding section is positioned at a central portion of the rotated parts, it is difficult to achieve a sufficient lubrication stably. Moreover, with respect to the contact between the spherical surface formed on the outer periphery of the sleeve and the spherical surface formed in the inner periphery of the outer ring as a wabble member, because it becomes a contact of partial spherical surfaces having substantially same shapes, there is a fear that an excessive surface pressure may be generated locally on the respective ends of the contact surfaces. By these, left is a fear on this sliding section that may cause seizure or abrasion.
Accordingly, paying attention to the problems left in the new wabble plate rotation preventing mechanism using a specified constant velocity universal joint mechanism which was previously proposed by the applicant of the present invention, an object of the present invention is to provide a wabble plate type variable displacement compressor which can suppress the seizure and abrasion of the above-described sliding section of the rotation preventing mechanism and which can have further excellent durability and silent performance.
Means for Solving the Problems
To achieve the above-described object, a wabble plate type variable displacement compressor according to the present invention has pistons inserted reciprocally into cylinder bores, a swash plate rotated together with a rotational main shaft and supported changeably in angle relative to the main shaft, a wabble plate which is connected to the pistons, in which a rotational movement of the swash plate is converted into a wabble movement of the wabble plate, and which transmits the wabble movement to the pistons to reciprocate the pistons, and a rotation preventing mechanism of the wabble plate, and is characterized in that
the rotation preventing mechanism comprises (a) an inner ring provided in a housing movably in an axial direction although rotation is prevented, supporting the rotational main shaft via a bearing at an inner diameter portion to rotate relatively and to move relatively in an axial direction and having a plurality of guide grooves for guiding a plurality of balls provided for power transmission, (b) a sleeve functioning as a wabble central member of the wabble movement of the wabble plate, provided on the rotational main shaft to rotate relatively thereto and to move in an axial direction and engaged with the inner ring movably in an axial direction together with the inner ring, (c) an outer ring having a plurality of guide grooves for guiding the balls at positions opposing respective guide grooves of the inner ring, supported on the sleeve wabblingly, and connected with the wabble plate fixedly on an outer periphery of the outer ring, and (d) a plurality of balls held by the guide grooves formed in the inner ring and the outer ring at a condition of opposing each other and performing power transmission by being compressed between the guide grooves,
a relative shape difference in axial cross-sectional profile is provided between a substantially concave spherical surface formed in an inner periphery of the outer ring functioning as a wabble member for wabblingly connecting the wabble plate in the rotation preventing mechanism and a substantially convex spherical surface formed on an outer periphery of the sleeve functioning as the wabble central member, and
the shape difference is set such that the closer to axial opposite ends of a contact portion between the substantially concave spherical surface and the substantially convex spherical surface a position of the contact portion is located, the greater a clearance between both surfaces becomes. Where, the outer ring may be structured so as to rotatably support the swash plate via a bearing. Alternatively, the swash plate may be structured so as to be supported rotatably by the wabble plate via a bearing.
In the rotation preventing mechanism of the wabble plate thus constructed, first, by the structure where the outer ring of the rotation preventing mechanism is supported wabblingly by the sleeve and the sleeve is supported rotatably and movably in the axial direction relative to the rotational main shaft, it becomes possible to make play in the radial direction between the rotational main shaft and the whole of the wabble mechanism portion small, and increase of reliability and reduction of vibration and noise may become possible. Further, the inner ring is supported in the housing movably in the axial direction and prevented with rotation, and by the bearing provided in the inner diameter portion of this inner ring, the rotational main shaft, for example, the rear end portion of the rotational main shaft, is supported. Therefore, the rotational main shaft is rotatably supported at both sides of the compression main mechanism portion (that is, inboard type supporting), a sufficiently high rigidity can be easily ensured, the whirling of the main shaft may be suppressed small, and therefore, it becomes possible to make the diameter of the main shaft small, improve the reliability and reduce vibration and noise. Further, because the whirling of the main shaft is suppressed, the deflection of the swash plate rotated together with the main shaft may be suppressed small, and the rotational balance of the whole of the rotational portion may be improved. Further, by optimizing the formation of the guide grooves formed on the inner ring and the outer ring which oppose each other, uniform and continuous contact of the balls held between the guide grooves becomes possible, and therefore, it becomes possible to improve the reliability and reduce vibration and noise. Furthermore, the guide grooves of balls may be formed so that balls can roll between a pair of guide grooves separated from each other accompanying with the movement of the intersection of both guide grooves, complicated shapes are not required for the guide grooves themselves, and therefore, the machining therefor is facilitated and becomes advantageous on cost. In such a structure according to the present invention, basically, the plurality of balls operating for power transmission perform power transmission at a condition where they are nipped and supported between guide grooves facing to each other in the compression direction. By this, an actual contact area can be ensured sufficiently large, it becomes possible to reduce the contact surface pressure, and it becomes advantageous on reliability. Further, because the contact surface pressure can be reduced, it becomes possible to make the diameter of balls small and it becomes also possible to make the whole of the rotation preventing mechanism small-sized.
Then, by the structure in which a relative shape difference in axial cross-sectional profile is provided between a substantially concave spherical surface formed in an inner periphery of the outer ring functioning as a wabble member for wabblingly connecting the wabble plate in the rotation preventing mechanism and a substantially convex spherical surface formed on an outer periphery of the sleeve functioning as the wabble central member, and the shape difference is set such that the closer to axial opposite ends of a contact portion between the substantially concave spherical surface and the substantially convex spherical surface a position of the contact portion is located, the greater a clearance between both surfaces becomes, the surface pressure at the end portions of the sliding section (ends of the contact surface) for the wabble movement due to the contact of the spherical surfaces to each other is reduced, and an excessive surface pressure, that has been feared at this end portion, may be prevented from being generated. Although it is difficult that a sufficient lubrication is provided to this sliding section stably because this sliding section is positioned at a central portion of the rotational parts, by preventing occurrence of an excessive surface pressure, a fear of occurrence of seizure and abrasion may be removed, and excellent durability and silent performance may be realized.
In this wabble plate type variable displacement compressor according to the present invention, it is preferred that the above-described shape difference is set such that the clearance at the axial opposite ends of the contact portion becomes 20 microns (micron meters) or more. If the clearance is less than 20 microns, because there is a fear that the effect for preventing occurrence of an excessive surface pressure cannot be sufficiently obtained, it is preferred to set it at 20 microns or more in order to obtain this effect securely.
As described above, in the present invention, for example, the following structures can be employed in order to provide a desirable relative shape difference in axial cross-sectional profile between the substantially concave spherical surface formed in the inner periphery of the outer ring functioning as a wabble member and the substantially convex spherical surface formed on the outer periphery of the sleeve functioning the wabble central member.
Namely, a structure may be employed wherein an axial cross-sectional profile of the substantially concave spherical surface formed in the inner periphery of the outer ring is formed from a main circular-shape portion at an axial central section formed as an arc which is a part of a circle and linear-shape portions provided at both axial ends of the main circular-shape portion so as to become tangents relative to the main circular-shape portion. At these linear-shape portions, it becomes possible to form a desirable clearance between it and the substantially convex spherical surface formed on the outer periphery of the sleeve.
Alternatively, a structure may be employed wherein an axial cross-sectional profile of the substantially concave spherical surface formed in the inner periphery of the outer ring and an axial cross-sectional profile of the substantially convex spherical surface formed on the outer periphery of the sleeve are both formed as arcs each of which is a part of a circle, a radius of curvature of an arc of the axial cross-sectional profile of outer ring side is set greater than a radius of curvature of an arc of the axial cross-sectional profile of sleeve side, and a center of curvature of the arc of the axial cross-sectional profile of outer ring side is offset relative to a center of curvature of the arc of the axial cross-sectional profile of sleeve side. Since the radius of curvature of the arc of the axial cross-sectional profile of outer ring side is set greater than the radius of curvature of the arc of the axial cross-sectional profile of sleeve side at a condition where the position of the center of curvature is offset at a predetermined amount, the closer to the axial end between the both spherical surfaces the position is, the greater the clearance becomes in accordance with the difference between the radii of curvature, and the above-described desirable clearance is formed between both spherical surfaces.
Alternatively, a structure may be employed wherein an axial cross-sectional profile of the substantially concave spherical surface formed in the inner periphery of the outer ring is formed from a main circular-shape portion at an axial central section formed as an arc which is a part of a circle and tangential circular-shape portions connected to both axial ends of the main circular-shape portion so as to become tangential circles relative to the main circular-shape portion and so that a radius of curvature of each of the tangential circles becomes greater than a radius of curvature of the main circular-shape portion. In each of the tangential circular-shape portions at both axial ends, it becomes possible to form a desirable clearance between it and the substantially convex spherical surface formed on the outer periphery of the sleeve.
In such a wabble plate type variable displacement compressor according to the present invention, it is possible to employ a structure wherein the outer ring and the wabble plate in the above-described wabble plate rotation preventing mechanism are formed integrally. By this integration, it becomes possible to further decrease the number of parts, and it becomes advantageous also in cost for manufacture and assembly.
Further, a structure may be employed wherein the guide grooves opposing each other of the inner ring and the outer ring of the above-described rotation preventing mechanism are formed at a relative angle of 30 to 60 degrees relative to a center axis of the rotational main shaft, and guide grooves opposing each other for forming a single ball guide are disposed so as to be symmetric relative to a plane perpendicular to the main shaft and passing through a wabble center of the wabble plate at a condition where a relative angle between an axis of the inner ring and an axis of the outer ring is zero. By the structure where the guide grooves opposing each other are disposed at a crossed axes angle within a predetermined range and both guide grooves formed in the directions crossed with each other are disposed symmetrically relative to the plane passing through the wabble center of the wabble plate, it becomes possible that the balls held between the guide grooves are brought into contact with both guide grooves at a uniform and continuous condition, the vibration and noise at this portion may be greatly reduced, and the reliability may be greatly improved.
Further, in this constitution, a structure may be employed wherein two ball guides adjacent to each other among a plurality of ball guides of the above-described rotation preventing mechanism are referred to be a pair of ball guides, and the pair of ball guides are disposed in parallel to each other. By such a structure, because the play in the rotational direction in the rotation preventing mechanism portion is schematically decided by a relationship between the distance between the bottoms of the pair of guide grooves provided on the inner and outer rings and the diameter of the balls, setting and management of an actual clearance between the bottoms of the guide grooves and the balls are facilitated, and it becomes possible to suppress the play to be small by setting a proper clearance.
In this constitution, a structure may be employed wherein the pair of ball guides disposed in parallel to each other are disposed symmetrically relative to a plane including a center axis of the rotational main shaft, and a structure also may be employed wherein a guide groove forming one ball guide of the pair of ball guides, which are disposed in parallel to each other, is disposed so that its axis is positioned on a plane including a center axis of the rotational main shaft. In the former structure, a rotation preventing mechanism, in which a rotational direction may not be selected, can be formed, and it becomes possible to reduce the contact load of the balls, and in the latter structure, it becomes possible to further reduce the contact load by setting the power transmission direction at a specified direction.
Further, in the above-described rotation preventing mechanism, a structure may be employed wherein two ball guides disposed on both sides of the rotational main shaft approximately symmetrically relative to the rotational main shaft among the plurality of ball guides are referred to be a pair of ball guides, and the pair of ball guides are disposed in parallel to each other. By this structure, because the play in the rotational direction in the rotation preventing mechanism portion is schematically decided by a relationship between the distance between the bottoms of the pair of guide grooves provided on the inner and outer rings and the diameter of the balls, it becomes possible to set and manage actual clearances in both ball guides simultaneously at desirable clearances, by disposing two ball guides symmetrically disposed in parallel to each other. As a result, the setting and management of the clearances are facilitated, and it becomes possible to suppress the play to be small.
In this structure, it is preferred that the above-described pair of ball guides, which are disposed in parallel to each other, are disposed so that axes of guide grooves forming the pair of ball guides are positioned on a plane including a center axis of the rotational main shaft. By disposing the pair of ball guides on the plane including the center axis of the rotational main shaft, it becomes possible to minimize the ball contact load without selecting the power transmission direction.
Although the above-described wabble plate type variable displacement compressor according to the present invention can be applied to a wabble plate type variable displacement compressor used in any field, in particular, it is suitable for use in the field for vehicles highly requiring making small-sized, increase of reliability, improvement of durability and silent performance, and cost down, especially, for use in an air conditioning system for vehicles.
Effect According to the Invention
Thus, in the wabble plate type variable displacement compressor according to the present invention, as compared with the wabble plate rotation preventing mechanism using the conventional constant velocity universal joint, uniform and continuous contact of a plurality of balls operating for power transmission can be achieved while the play can be suppressed small, a rotation preventing mechanism small-sized, excellent in durability and silent performance, good in rotational balance, easy in machining and inexpensive can be realized, and a wabble plate type variable displacement compressor, having an excellent performance which has not been achieved by the conventional technologies, can be provided. And, by providing a relative shape difference in axial cross-sectional profile between the substantially concave spherical surface formed in the inner periphery of the outer ring functioning as a wabble member in the wabble plate rotation preventing mechanism of this compressor and the substantially convex spherical surface formed on the outer periphery of the sleeve functioning as a wabble central member, and by setting the shape difference such that the closer to axial opposite ends the position is, the greater the clearance between both surfaces becomes, occurrence of an excessive surface pressure at the end portions of the sliding section for the wabble movement can be effectively prevented, a fear of occurrence of seizure and abrasion can be removed, and further excellent durability and silent performance can be realized.



BRIEF EXPLANATION OF THE DRAWINGS
FIG. 1 is a vertical sectional view of a wabble plate type variable displacement compressor according to an embodiment of the present invention.
FIG. 2 is a vertical sectional view of the wabble plate type variable displacement compressor depicted in FIG. 1, showing an operational condition different from that depicted in FIG. 1.
FIG. 3 is an exploded perspective view of a main portion including a wabble plate rotation preventing mechanism of the wabble plate type variable displacement compressor depicted in FIG. 1.
FIG. 4 shows an example of the structure of the wabble plate type variable displacement compressor depicted in FIG. 1, FIG. 4(A) is a partial, vertical sectional view thereof, and FIG. 4(B) is a partial elevational view thereof.
FIG. 5 is a partial elevational view showing another example of the structure of the wabble plate type variable displacement compressor depicted in FIG. 1.
FIG. 6 is a schematic partial sectional view showing an example of the wabble plate rotation preventing mechanism of the wabble plate type variable displacement compressor depicted in FIG. 1.
FIG. 7 is a schematic partial sectional view showing another example of the wabble plate rotation preventing mechanism of the wabble plate type variable displacement compressor depicted in FIG. 1.
FIG. 8 is a schematic partial sectional view showing a further example of the wabble plate rotation preventing mechanism of the wabble plate type variable displacement compressor depicted in FIG. 1.
FIG. 9 is a partial elevational view showing a further example of the structure of the wabble plate type variable displacement compressor depicted in FIG. 1.
FIG. 10(A) and FIG. 10(B) are partial elevational views showing further examples of the structure of the wabble plate type variable displacement compressor depicted in FIG. 1, and FIG. 10(A) and FIG. 10(B) show examples different from each other.
FIG. 11(A) and FIG. 11(B) are partial elevational views showing still further examples of the structure of the wabble plate type variable displacement compressor depicted in FIG. 1, and FIG. 11(A) and FIG. 11(B) show examples different from each other.



EXPLANATION OF SYMBOLS
1: wabble plate type variable displacement compressor
2: housing
3: front housing
4: rear housing
5: rotational main shaft
5a: center axis
6: rotor
7: hinge mechanism
8: swash plate
9: cylinder bore
10: piston
11: connecting rod
12: wabble plate
13: suction chamber
14: valve plate
15: suction hole
16: discharge hole
17: discharge chamber
21: rotation preventing mechanism of wabble plate
22, 23, 29, 33: bearing
24, 24a, 24b, 24c: sleeve
25: ball
26: guide groove of inner ring
27: inner ring
28: guide groove of outer ring
30, 30a, 30b, 30c: outer ring
31, 32: thrust bearing
41: ball guide
42, 43: axis of guide groove
44: plane passing through wabble center
45: pair of ball guides
46: axes of guide grooves formed on inner and outer rings
47: plane including center axis of rotational main shaft
51a, 51b, 51c: substantially concave spherical surface of outer ring
52: main circular-shape portion
53: linear-shape portion
54a, 54b, 54c: substantially convex spherical surface of sleeve
55: plane including wabble center
56: main circular-shape portion
57: range of main circular-shape portion
58: tangential circular-shape portion
61: pair of ball guides
62: power transmission direction of outer ring
63: one ball guide
64: axis of guide groove
65: plane including center axis of rotational main shaft
66: power transmission direction of inner ring
71: pair of ball guides
72: axis of guide groove
81: pair of ball guides
82: axis of guide groove
83: plane including center axis of rotational main shaft
84: wabble plate integrated with outer ring
THE BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, desirable embodiments of the present invention will be explained referring to figures.
First, an embodiment of the whole structure of a wabble plate type variable displacement compressor according to the present invention will be explained referring to FIGS. 1-5, and next, referring to FIGS. 6-8, embodiments will be explained wherein a relative shape difference in axial cross-sectional profile is provided between a substantially concave spherical surface formed in an inner periphery of an outer ring functioning as a wabble member in a wabble plate rotation preventing mechanism and a substantially convex spherical surface formed on an outer periphery of a sleeve functioning as a wabble central member.
FIG. 1 shows a wabble plate type variable displacement compressor according to an embodiment of the present invention, and shows its entire structure in the operation state at the condition of the displacement achieving its maximum discharge. FIG. 2 shows the operation state of the wabble plate type variable displacement compressor depicted in FIG. 1 at the condition of the displacement achieving its minimum discharge. FIG. 3 shows a main portion including a wabble plate rotation preventing mechanism in the wabble plate type variable displacement compressor depicted in FIG. 1 as an exploded perspective view.
In FIGS. 1 and 2, a wabble plate type variable displacement compressor 1 has a housing 2 disposed at the central portion, a front housing 3 and a rear housing 4 disposed on both sides of the housing 1 as its housings, and a rotational main shaft 5 inputted with a rotational drive power from outside is provided over the range from the portion of housing 2 up to the position extending through front housing 3. A rotor 6 is fixed to rotational main shaft 5 so as to be rotated integrally with main shaft 5, and a swash plate 8 is connected to rotor 6 via a hinge mechanism 7, changeably in angle and rotatably together with rotational main shaft 5. Piston 10 is reciprocally inserted into each cylinder bore 9, and piston 10 is connected to wabble plate 12 via connecting rod 11. The rotational movement of swash plate 8 is converted into the wabble movement of wabble plate 12, the wabble movement is transmitted to piston 10 via connecting rod 11, and piston 10 is reciprocated. Fluid to be compressed (for example, refrigerant) is sucked from suction chamber 13 formed in rear housing 4 into cylinder bore 9 through suction hole 15 formed on valve plate 14 (a suction valve is omitted in the figure) accompanying with the reciprocating movement of piston 10, and after the sucked fluid is compressed, the compressed fluid is discharged into discharge chamber 17 through discharge hole 16 (a discharge valve is omitted in the figure), and therefrom, sent to an external circuit.
It is necessary that the above-described wabble plate 12 performs a wabble movement at a condition where its rotation is prevented. Hereinafter, the remaining portions of compressor 1 will be explained mainly with respect to the rotation preventing mechanism of this wabble plate 12, referring to FIGS. 1 to 3.
Rotation preventing mechanism 21 of wabble plate 12 is formed from a mechanism comprising (a) an inner ring 27 provided in housing 2 movably in the axial direction although its rotation is prevented, supporting rotational main shaft 5 via a bearing 22 (radial bearing) at its inner diameter portion to rotate relatively and to move relatively in the axial direction and having a plurality of guide grooves 26 for guiding a plurality of balls 25 provided for power transmission, (b) a sleeve 24 functioning as a wabble central member of the wabble movement of wabble plate 12, provided on rotational main shaft 5 to rotate relatively thereto and to move in the axial direction and engaged with inner ring 27 movably in the axial direction together with inner ring 27, (c) an outer ring 30 having a plurality of guide grooves 28 for guiding balls 25 at positions opposing respective guide grooves 26 of inner ring 27, supported on sleeve 24 wabblingly, connected with wabble plate 12 fixedly on its outer periphery and supporting swash plate 8 rotatably via a bearing 29 (radial bearing), and (d) a plurality of balls 25 held by guide grooves 26, 28 formed in inner ring 27 and outer ring 30 at a condition of opposing each other and performing power transmission by being compressed between guide grooves 26, 28. Thrust bearings 31, 32 are interposed between wabble plate 12 and swash plate 8 and between rotor 6 and front housing 3, respectively. Further, although inner ring 27 is supported in housing 9 movably in the axial direction, its rotation is prevented. As means for preventing the rotation, a general rotation regulating means such as a key or a spline may be used (not depicted). Furthermore, although the rear end of rotational main shaft 5 is supported by bearing 22 provided on the inner diameter portion of inner ring 27, because rotational main shaft 5 is supported also at the side of front housing 3 through the compression main mechanism portion rotatably via bearing 33 (radial bearing), it is radially supported on both sides (inboard supporting).
In rotation preventing mechanism 21 of wabble plate 12 constructed as described above, outer ring 30 is wabblingly supported by sleeve 24 through the spherical surface contact (the detailed structure of this portion will be described later), and sleeve 24 is supported by rotational main shaft 5 rotatably and movably in the axial direction, and by this structure, it is possible to make play in the radial direction between rotational main shaft 5 and the whole of the wabble mechanism portion small, thereby improving the reliability and reducing vibration and noise.
Further, in the above-described embodiment, since rotational main shaft 5 is supported in the condition of inboard supporting on both sides of the compression main mechanism portion by bearing 22 provided in the inner diameter portion of inner ring 27 and bearing 33 provided on front housing 3 side, a sufficiently high rigidity can be ensured even if the diameter of main shaft 5 is relatively small, the whirling of main shaft 5 can also be suppressed, making small-sized can be easily achieved, and improvement of reliability and reduction of vibration and noise may be possible. Further, as the result of suppressing the whirling of rotational main shaft 5, the whole of the rotational portion rotated together with rotational main shaft 5 can be suppressed to be small, and therefore, the rotational balance of the whole of the rotated portion becomes remarkably good. Where, in the above-described structure, it is possible to extend rotational main shaft 5 rearward and to replace it for a structure being supported directly by housing via a bearing.
Moreover, in the above-described embodiment, by the engagement of the spherical surface (concave spherical surface) formed in the inner diameter side of inner ring 27 with the spherical surface (convex spherical surface) formed in the outer diameter side of sleeve 24, a mutual supporting between both members is performed. By adjusting a clearance in this supporting portion, it is possible to absorb a relative whirling of the inner and outer rings caused by the dispersion of the positions of the guide grooves for a plurality of balls operating for power transmission, whereby the uniform and continuous contact of balls 25 is further improved, and it is more advantageous with respect to reliability, vibration and noise.
Where, although outer ring 30 and wabble plate 12 are formed as separate members and they are fixed to each other in the above-described embodiment, it is possible to form them integrally. By this integration, the number of parts may be further decreased, and the assembly may be facilitated.
FIG. 4 shows a condition where the relative angle between the inner and outer rings is zero in rotation preventing mechanism 21 of wabble plate 12. As depicted in FIG. 4(A), guide grooves 26, 28 formed on inner ring 27 and outer ring 24 of rotation preventing mechanism 21 are disposed at relative angles (relative angles within a range of 30 to 60 degrees) relative to the center axis of rotational main shaft 5. Guide groove 26 formed on inner ring 27 (the axis of guide groove 26 is indicated by symbol 42) and guide groove 28 formed on outer ring 30 (the axis of guide groove 28 is indicated by symbol 43), which form one ball guide 41 and oppose each other, are disposed so as to be symmetric relative to plane 44 which is perpendicular to rotational main shaft 5 and passes through the wabble center of wabble plate 12, at a condition where the relative angle between the axis of inner ring 27 and the axis of outer ring 30 is zero. Ball 25 is regulated and supported on the intersection of axis 42 of guide groove 26 and axis 43 of guide groove 28. Further, as depicted in FIG. 4(B), a structure can be employed wherein two ball guides adjacent to each other among a plurality of ball guides 41 of rotation preventing mechanism 21 are referred to be a pair of ball guides, and respective ball guides 41 in the pair of ball guides 45, in other words, axes 46 of the guide grooves formed on the inner and outer rings in this portion, are disposed in parallel to each other. In such a structure, as aforementioned, because the play in the rotational direction in the rotation preventing mechanism portion is schematically decided by a relationship between the distance between the bottoms of the pair of guide grooves provided on the inner and outer rings and the diameter of the balls, setting and management of an actual clearance are facilitated, and it becomes possible to suppress the play to be small by setting a proper clearance. A plurality of balls 25 operating for power transmission are supported in the compression direction between guide grooves 26, 28 facing each other through the respective balls, and perform power transmission. Since ball 25 is held by guide grooves 26, 28 facing each other so as to be embraced and come into contact with both guide grooves 26, 28, the contact area between ball and the respective guide grooves 26, 28 may be ensured to be sufficient large, it becomes possible to reduce the contact surface pressure, and a structure remarkably advantageous in reliability, vibration and silent performance may be realized. Further, it is also possible to make the diameter of balls 25 small, and the whole of the rotation preventing mechanism may be made small.
Further, the load applied to ball, which is provided as a moment whose center is rotational main shaft 5, is generated as a perpendicular reaction force of the actual contact surface. The smaller the inclination of the normal line of the contact surface relative to the direction of the moment is, the smaller the contact load becomes, and as depicted in FIG. 5, by a structure where the pair of ball guides 45 disposed in parallel as described above are disposed symmetrically relative to plane 47 including center axis 5a of rotational main shaft 5, in other words, by a structure where axes 46 of two sets of guide grooves formed on the inner and outer rings are disposed symmetrically relative to plane 47 including center axis 5a of rotational main shaft 5, the mechanism is made as a rotational preventing mechanism which does not select the rotational direction, and it is possible to minimize the ball contact load.
In the present invention, a relative shape difference in axial cross-sectional profile is provided between a substantially concave spherical surface formed in the inner periphery of outer ring 30 functioning as a wabble member for wabblingly connecting wabble plate 12 in wabble plate rotation preventing mechanism 21 and a substantially convex spherical surface formed on the outer periphery of sleeve 24 functioning as a wabble central member, and the shape difference is set such that the closer to axial opposite ends of a contact portion between the substantially concave spherical surface and the substantially convex spherical surface a position of the contact portion is located, the greater a clearance between both surfaces becomes. The clearance between both surfaces at both axial ends of the contact portion is set at 20 microns or more. Concrete structural examples for giving such a shape difference will be explained referring to FIGS. 6-8 depicting for explanation of only the relationship between the outer ring and the sleeve.
In the example depicted in FIG. 6, the axial cross-sectional profile of substantially concave spherical surface 51a formed in the inner periphery of outer ring 30a functioning as a wabble member is formed from a main circular-shape portion 52 at an axial central section formed as an arc which is a part of a circle and linear-shape portions 53 provided at both axial ends of main circular-shape portion 52 so as to become tangents relative to the main circular-shape portion 52. At these linear-shape portions 53, it becomes possible to form a desirable clearance between it and substantially convex spherical surface 54a formed on the outer periphery of sleeve 24a functioning as a wabble central member. In this case, radius of curvature R1 of main circular-shape portion 52 of outer ring 30a other than linear-shape portion 53 and radius of curvature R2 of substantially convex spherical surface 54a of sleeve 24a may be substantially same, and the center of curvature C1 thereof may be same. In such a structure, by forming linear-shape portions 53 on both sides of main circular-shape portion 52 of substantially concave spherical surface 51a, the clearance between linear-shape portions 53 and substantially convex spherical surface 54a of sleeve 24a can be increased as the position is closer to both axial ends, and by setting this clearance properly, occurrence of an excessive surface pressure at the end portions of the sliding section for the wabble movement can be effectively prevented, a fear of occurrence of seizure and abrasion can be removed, and a compressor excellent in durability and silent performance can be realized.
In the example depicted in FIG. 7, the axial cross-sectional profile of substantially concave spherical surface 51b formed in the inner periphery of outer ring 30b functioning as a wabble member and the axial cross-sectional profile of substantially convex spherical surface 54b formed on the outer periphery of sleeve 24b functioning as a wabble central member are both formed as arcs each of which is a part of a circle, radius of curvature R3 of the arc of the axial cross-sectional profile of outer ring side is set greater than radius of curvature R4 of the arc of the axial cross-sectional profile of sleeve side, and center of curvature C2 of the arc of the axial cross-sectional profile of outer ring side is offset by δ relative to center of curvature C3 of the arc of the axial cross-sectional profile of sleeve side on a same axis in plane 55 including the wabble center. Since radius of curvature R3 of the arc of the axial cross-sectional profile of outer ring side is set greater than radius of curvature R4 of the arc of the axial cross-sectional profile of sleeve side at a condition where the position of center of curvature C2 is offset at a predetermined amount δ, the closer to the axial end between the both spherical surfaces the position is, the greater the clearance becomes in accordance with the difference between the radii of curvature, and a target clearance in the present invention is formed between both spherical surfaces. By setting this clearance properly, occurrence of an excessive surface pressure at the end portions of the sliding section for the wabble movement can be effectively prevented, a fear of occurrence of seizure and abrasion can be removed, and a compressor excellent in durability and silent performance can be realized.
In the example depicted in FIG. 8, the axial cross-sectional profile of substantially concave spherical surface 51c formed in the inner periphery of outer ring 30c functioning as a wabble member is formed from main circular-shape portion 56 at an axial central section formed as an arc which is a part of a circle (the range of this main circular-shape portion 56 is indicated by symbol 57) and tangential circular-shape portions 58 connected to both axial ends of main circular-shape portion 56 so as to become tangential circles relative to the main circular-shape portion 56 and so that radius of curvature R5 of each of the tangential circles becomes greater than radius of curvature R6 of the main circular-shape portion 56. In each of the tangential circular-shape portions at both axial ends, it becomes possible to form a desirable clearance between it and the substantially convex spherical surface formed on the outer periphery of the sleeve. In the example depicted, the center of curvature of main circular-shape portion 56 and the center of radius of curvature R7 (center of curvature) of substantially convex spherical surface 54c formed on the outer periphery of sleeve 24c functioning as a wabble central member are positioned at same, and center of curvature C5 of tangential circular-shape portions 58 is not necessary to be positioned on a same axis in plane 55 including the wabble center relative to center of curvature C4. At the positions of these tangential circular-shape portions 58 located on both axial sides of main circular-shape portion 56, a target clearance in the present invention is formed between the tangential circular-shape portions 58 and substantially convex spherical surface 54c formed on the outer periphery of sleeve 24c. By setting this clearance properly, occurrence of an excessive surface pressure at the end portions of the sliding section for the wabble movement can be effectively prevented, a fear of occurrence of seizure and abrasion can be removed, and a compressor excellent in durability and silent performance can be realized.
Thus, in new wabble plate rotation preventing mechanism 21 according to the present invention, further by employing the structure wherein a relative shape difference in axial cross-sectional profile is properly provided between a substantially concave spherical surface formed in the inner periphery of outer ring 30a, 30b or 30c functioning as a wabble member and a substantially convex spherical surface formed on the outer periphery of sleeve 24a, 24b or 24c functioning as a wabble central member, and a desirable shape difference is set such that the closer to axial opposite ends of a contact portion between the substantially concave spherical surface and the substantially convex spherical surface the position is, the greater the clearance between both surfaces becomes, the surface pressure at the end portions of the sliding section (ends of the contact surface) for the wabble movement due to the contact of the spherical surfaces to each other is reduced, and occurrence of an excessive surface pressure at these end portions may be prevented. Although it may be difficult that a sufficient lubrication is provided to this sliding section stably because this sliding section is positioned at a central portion of the rotational parts, as aforementioned, by preventing occurrence of an excessive surface pressure as described above, occurrence of seizure and abrasion may be prevented securely, and excellent durability and silent performance may be realized for this sliding section. As a result, excellent durability and silent performance can be realized as the whole of the compressor.
In the present invention, as an embodiment other than the embodiment depicted in FIGS. 1-5, for example, as depicted in FIG. 9, by offsetting one ball guide 63 mainly operating in power transmission direction of outer ring 62 among the pair of ball guides 61, in other words, axis 64 of the guide groove in the ball guide 63, onto plane 65 including center axis 5a of rotational main shaft 5, it is possible to further reduce the contact load in the specified restricted power transmission direction. Where, in FIG. 9, arrow 66 indicates power transmission direction of inner ring.
Further, as depicted in FIG. 10 (A) or (B) (FIGS. 10 (A) and (B) depict examples different from each other), a structure can also be employed wherein two ball guides disposed on both sides of rotational main shaft 5 approximately symmetrically relative to rotational main shaft 5 among a plurality of ball guides are referred to be a pair of ball guides, and the pair of ball guides are disposed in parallel to each other, in other words, axes 72 of guide grooves formed on inner ring 27 and outer ring 30 forming the pair of ball guides 71 are disposed in parallel to each other. By this structure, because the play in the rotational direction in the rotation preventing mechanism portion is schematically decided by a relationship between the distance between a set of bottoms of the pair of guide grooves provided on inner and outer rings 27, 30 and the diameter of the balls, it becomes possible to set and manage the clearances in both ball guides simultaneously at desirable clearances, by disposing two ball guides symmetrically disposed in parallel to each other. Consequently, the setting and management of the clearances are facilitated, and it becomes possible to suppress the play to be small.
Further, in this structure where the pair of ball guides are disposed in parallel to each other, as depicted in FIG. 11(A) or (B) (FIGS. 11 (A) and (B) depict examples different from each other), a structure can be employed wherein the pair of ball guides 81, which are disposed in parallel to each other, are disposed so that axes 82 of guide grooves forming the pair of ball guides are positioned on plane 83 including center axis 5a of rotational main shaft 5. In such a structure, the ball contact load is minimized without selecting the power transmission direction. Where, in FIG. 11(B), a structure of a case of wabble plate 84 integrated with an outer ring is exemplified.
INDUSTRIAL APPLICATIONS OF THE INVENTION
The wabble plate type variable displacement compressor according to the present invention can be applied to a wabble plate type variable displacement compressor used in any field, and especially, it is suitable for use in the field for vehicles highly requiring making small-sized, increase of reliability, improvement of durability and silent performance, and cost down, in particular, for use in an air conditioning system for vehicles

## Claims

1. A wabble plate type variable displacement compressor, comprising:
pistons inserted reciprocally into cylinder bores;
a swash plate rotated together with a rotational main shaft and supported changeably in angle relative to said main shaft;
a wabble plate which is connected to said pistons, in which a rotational movement of said swash plate is converted into a wabble movement of said wabble plate, and which transmits said wabble movement to said pistons to reciprocate said pistons, and
a rotation preventing mechanism of said wabble plate, wherein:
said rotation preventing mechanism comprises (a) an inner ring provided in a housing movably in an axial direction although rotation is prevented, and having a plurality of guide grooves for guiding a plurality of balls provided for power transmission, (b) a sleeve functioning as a wabble central member of said wabble movement of said wabble plate, provided on said rotational main shaft to rotate relatively thereto and to move in an axial direction and engaged with said inner ring movably in an axial direction together with said inner ring, (c) an outer ring having a plurality of guide grooves for guiding said balls at positions opposing respective guide grooves of said inner ring, supported on said sleeve wabblingly, and connected with said wabble plate fixedly on an outer periphery of said outer ring, and (d) a plurality of balls held by said guide grooves formed in said inner ring and said outer ring at a condition of opposing each other and performing power transmission by being compressed between said guide grooves,
a relative shape difference in axial cross-sectional profile is provided between a substantially concave spherical surface formed in an inner periphery of said outer ring functioning as a wabble member for wabblingly connecting said wabble plate in said rotation preventing mechanism and a substantially convex spherical surface formed on an outer periphery of said sleeve functioning as said wabble central member, and
said shape difference is set such that the closer to axial opposite ends of a contact portion between said substantially concave spherical surface and said substantially convex spherical surface a position of said contact portion is located, the greater a clearance between both surfaces becomes.

2. The wabble plate type variable displacement compressor according to claim 1, wherein said shape difference is set such that said clearance at said axial opposite ends of said contact portion becomes 20 microns or more.

3. The wabble plate type variable displacement compressor according to claim 1, wherein an axial cross-sectional profile of said substantially concave spherical surface formed in said inner periphery of said outer ring is formed from a main circular-shape portion at an axial central section formed as an arc which is a part of a circle and linear-shape portions provided at both axial ends of said main circular-shape portion so as to become tangents relative to said main circular-shape portion.

4. The wabble plate type variable displacement compressor according to claim 1, wherein an axial cross-sectional profile of said substantially concave spherical surface formed in said inner periphery of said outer ring and an axial cross-sectional profile of said substantially convex spherical surface formed on said outer periphery of said sleeve are both formed as arcs each of which is a part of a circle, a radius of curvature of an arc of said axial cross-sectional profile of outer ring side is set greater than a radius of curvature of an arc of said axial cross-sectional profile of sleeve side, and a center of curvature of said arc of said axial cross-sectional profile of outer ring side is offset relative to a center of curvature of said arc of said axial cross-sectional profile of sleeve side.

5. The wabble plate type variable displacement compressor according to claim 1, wherein an axial cross-sectional profile of said substantially concave spherical surface formed in said inner periphery of said outer ring is formed from a main circular-shape portion at an axial central section formed as an arc which is a part of a circle and tangential circular-shape portions connected to both axial ends of said main circular-shape portion so as to become tangential circles relative to said main circular-shape portion and so that a radius of curvature of each of said tangential circles becomes greater than a radius of curvature of said main circular-shape portion.

6. The wabble plate type variable displacement compressor according to claim 1, wherein said outer ring is formed integrally with said wabble plate.

7. The wabble plate type variable displacement compressor according to claim 1, wherein said guide grooves opposing each other of said inner ring and said outer ring of said rotation preventing mechanism are formed at a relative angle of 30 to 60 degrees relative to a center axis of said rotational main shaft, and guide grooves opposing each other for forming a single ball guide are disposed so as to be symmetric relative to a plane perpendicular to said main shaft and passing through a wabble center of said wabble plate at a condition where a relative angle between an axis of said inner ring and an axis of said outer ring is zero.

8. The wabble plate type variable displacement compressor according to claim 7, wherein two ball guides adjacent to each other among a plurality of ball guides of said rotation preventing mechanism are referred to be a pair of ball guides, and said pair of ball guides are disposed in parallel to each other.

9. The wabble plate type variable displacement compressor according to claim 8, wherein said pair of ball guides disposed in parallel to each other are disposed symmetrically relative to a plane including a center axis of said rotational main shaft.

10. The wabble plate type variable displacement compressor according to claim 8, wherein a guide groove forming one ball guide of said pair of ball guides, which are disposed in parallel to each other, is disposed so that its axis is positioned on a plane including a center axis of said rotational main shaft.

11. The wabble plate type variable displacement compressor according to claim 7, wherein two ball guides disposed on both sides of said rotational main shaft approximately symmetrically relative to said rotational main shaft among a plurality of ball guides of said rotation preventing mechanism are referred to be a pair of ball guides, and said pair of ball guides are disposed in parallel to each other.

12. The wabble plate type variable displacement compressor according to claim 11, wherein said pair of ball guides, which are disposed in parallel to each other, are disposed so that axes of guide grooves forming said pair of ball guides are positioned on a plane including a center axis of said rotational main shaft.

13. The wabble plate type variable displacement compressor according to claim 1, wherein said compressor is used in an air conditioning system for vehicles.

14. A wabble plate type variable displacement compressor, comprising:
pistons inserted reciprocally into cylinder bores;
a swash plate rotated together with a rotational main shaft and supported changeably in angle relative to said main shaft, said rotational main shaft is extended rearward and supported directly by a housing;
a wabble plate which is connected to said pistons, in which a rotational movement of said swash plate is converted into a wabble movement of said wabble plate, and which transmits said wabble movement to said pistons to reciprocate said pistons; and
a rotation preventing mechanism of said wabble plate,
wherein said rotation preventing mechanism comprises (a) an inner ring provided in said housing movably in an axial direction although rotation is prevented, and having a plurality of guide grooves for guiding a plurality of balls provided for power transmission, (b) a sleeve functioning as a wabble central member of said wabble movement of said wabble plate, provided on said rotational main shaft to rotate relatively thereto and to move in an axial direction and engaged with said inner ring movably in an axial direction together with said inner ring, (c) an outer ring having a plurality of guide grooves for guiding said balls at positions opposing respective guide grooves of said inner ring, supported on said sleeve wabblingly, and connected with said wabble plate fixedly on an outer periphery of said outer ring, and (d) a plurality of balls held by said guide grooves formed in said inner ring and said outer ring at a condition of opposing each other and performing power transmission by being compressed between said guide grooves.