VARIABLE DISPLACEMENT WOBBLE PLATE TYPE COMPRESSOR

Abstract: A variable displacement wobble plate type compressor is provided with an inclined plate (12) which is hinged to a rotor (10) fixed on a drive shaft (7) and supports a wobble plate (15). The inclined plate is formed with a central hole (124) for penetrarion on the drive shaft. The inner surface of the central hole partly contacts the outer surface of the drive shaft to restrict radial movement of the inclined plate while permitting the angle of the inclined plate to be varied.

Description: This invention relates to a wobble plate compressor with a variable displacement mechanism for permitting easy change of angle of an inclined plate which supports the wobble plate. A wobble plate compressor, with a variable displacement mechanism, which changes the stroke of pistons by changing the inclined angle of inclination of the wobble plate and thus the volume of cylinders, is well known. US-A-3,062,020 and US-A-4,061,433, disclose such a compressor with an inclined plate, with which a wobble plate is adjacently disposed, hinged with a rotor fixed on a drive shaft. Variation in the angle of the inclined plate is controlled by the difference between crank chamber pressure and suction chamber pressure. In this structure of rotor and inclined plate, both parts are only connected by a hinge mechanism and, therefore, a change in the locus of the inclined plate to vary its angle is not stabilized. One solution to the above mentioned disadvantage is to use a slider element, as shown in US-A-4,061,433. That slider element is slidably disposed on the drive shaft and coupled with the inclined plate through a pin extending from the slider element. Therefore, the change of angle of the inclined plate is determined by the sliding motion of the slider element. Furthermore, in axial piston type compressors, the point of action of the piston pressure on the inclined plate is shifted from the top dead point of piston and eccentrically located in the direction perpendicular to the direction of maximum angle of inclination of the plate. In Figure 1 of the accompanying drawings it is shown that S is an inclined surface of the plate, D is a top dead point of the piston, 0 is a driving axis line, P1 is the direction of the maximum angle of inclination of the inclined plate, P2 is the direction perpendicular to P1 and F is the mean piston pressure. The piston pressure F acts on the inclined surface S eccentrically from a supporting point. Thus a moment should be generated to rotate the inclined plate around the axis P2 passing through the plate. Also, another moment should be generated to rotate the inclined plate around the axis P1 passing through plate. Thus, the supporting structure for the inclined plate requires high rigidity. In the supporting structure shown in US-A-4,061,433, if the strength of the supporting mechanism is to be improved, the supporting structure must become complicated and large, so that the size of the compressor would become larger. It is primary object of this invention to provide a wobble plate compressor, with a variable displacement mechanism, which is simple and compact in construction, low in cost, and with high durability. EP-A-0035867 shows a wobble plate compressor with a variable displacement mechanism, the compressor including a compressor housing provided with a crank chamber and a cylinder block in which a plurality of cylinders are formed, a drive shaft rotatably supported in the housing, a rotor fixed on the drive shaft and having a variably inclined plate provided with a central hole for penetration by the drive shaft and which rotates with the drive shaft, a wobble plate adjacent to the inclined plate, and caused by the rotation of the inclined plate to nutate about the drive shaft, the wobble plate being coupled with a plurality of pistons each of which is reciprocatably fitted with a respective one of the cylinders, and means for restricting the radial movement of the inclined plate about the drive shaft while permitting variation in the inclination thereof; the central hole of the inclined plate being of elongate cross section in a plane perpendicular to the axis of the drive shaft, so that the longer dimension of the cross section accomodates pivotal the movement of the plate relatively to the shaft; whereas the present invention is characterised in that the shorter dimension of the cross section provides a fit against the shaft; and in that radial movement of the inclined plate about the drive shaft is restricted solely by contact of the inner surface of the central hole with the outer surface of the drive shaft. Some examples of compressors constructed in accordance with the invention are illustrated in the accompanying drawings, in which:­ Figure 1 is an explanatory view illustrating relevant forces applied to an inclined surface of an inclined plate; Figure 2 is a cross-sectional view of one example of compressor; Figure 3 is a perspective view of an inclined plate of the compressor shown in Figure 2; Figure 4 is a cross-sectional view of another example of compressor; Figure 5 is a cross-sectional view of a further example of compressor, illustrating the main portion of a variable displacement mechanism; Figure 6 is a cross-sectional view of the inclined plate used in the compressor of Figure 5; Figure 7 is a cross-sectional view of a still further example compressor illustrating the main portion of a variable displacement mechanism. Figures 2 and 3 show a wobble plate compressor 1 which includes a front end plate 2, and a cylinder casing 3 having a cylinder block 31, a valve plate 4, and a cylinder head 5. The front end plate 2 is fixed on one end opening of the cylinder casing 3 by securing bolts (not shown). An axial hole 21, is formed through the centre of the front end plate 2 for penetration of a drive shaft 7. A radial bearing 8 is disposed in the axial hole 21 to support the drive shaft 7 rotatably. An annular sleeve portion 22 projects from the front end plate 2 and surrounds the drive shaft 7 for defining a seal cavity 23. The cylinder casing 3 is provided with a cylinder block 31 and a crank chamber 32. The cylinder block 31 has a plurality of equiangularly spaced cylinders 33. A cam rotor 10 is fixed on the drive shaft 7 by a pin 103. A thrust needle bearing 11 is disposed between the inner wall surface of the front end plate 7 and the adjacent axial end surface of the cam rotor 10. An arm portion 101 of the cam rotor 10 extends in the direction of the cylinder block 31. An elongate hole 102 is formed in the arm portion 101. An inclined plate, provided by a cylindrical member 12 with a flange portion 121 is disposed around the drive shaft 7. A second arm portion 122 is formed on the outer surface of the flange portion 121 of the cylindrical member 12 and faces the arm portion 101 of the cam rotor 10. A hole 123, formed in the arm portion 122, is aligned with the elongate hole 102. A pin 14, inserted through the hole 123, is slidably movable within the elongate hole 102. A ring-shaped wobble plate 15 is mounted on the outer surface of the cylindrical member 12 and prevented from axial movement by the flange portion 121 and by a snap ring 16 disposed on the cylindrical member 12. Also, a thrust needle bearing 17 is disposed in a gap between the flange portion 121 and the wobble plate 15. The other end of the drive shaft 7 is rotatably supported through a radial bearing 18 in a central bore in the cylinder block 31. A sliding shaft 151 is attached on the outer periphral portion of the wobble plate 15 and projects towards the bottom surface of the cylinder casing 3 where it is slidably disposed in a groove 321, to prevent the rotation of the wobble plate 15. One end of each of a plurality of piston rods 19 is universally connected to a receiving surface 152 of the wobble plate 15. The other end of the piston rod 19 is universally connected to a piston 20 which is slidably disposed in its cylinder 33. Suction ports 41 and discharge ports 42 are formed through the valve plate 4. A suction reed valve (not shown) is disposed on the valve plate 4. A discharge reed valve (not shown) is also disposed on the side of the valve plate 4 opposite to the suction reed valve. The cylinder head 5 is connected to the cylinder casing 3 through a gasket and the valve plate 4. A partition wall 51 extends axially from the inner surface of the cylinder head 5 and divides the interior of the cylinder head 5 into two chambers: a suction chamber 52 and a discharge chamber 53. The suction chamber 52 is connected with an external fluid refrigerant circuit through a fluid inlet port 60 formed in the cylinder head 5. The discharge chamber 53 is also connected with the external fluid circuit through a fluid outlet port 61 formed in the cylinder head 5. The crank chamber 32 of the cylinder casing 3 and suction chamber 52 of the cylinder head 5 are connected with one another to control the angle of inclination of the cylindrical member 12 and wobble plate 15. The connection and control method for varying the angle of the cylindrical member 12 and wobble plate 15 is disclosed in US-A-3,062,020. In the above described compressor, a central hole 124 formed through the cylindrical member 12 has an elongate shape, as shown in Figure 3. That is an inner diameter of the central hole 124 in the direction along the X-axis, which is indicated by "1" in Figure 3, is just a little greater than the outer diameter of the drive shaft 7, however, the diameters of both elements should be selected to cause a good fit therebetween. On the other hand, the inner diameter of the central hole 124 of the cylindrical member 124 extending along the Y-axis is greater than the outer diameter of the drive shaft 7. This enlarged portion of the central hole 124 permits the varying inclined angle of the cylindrical member 12 and wobble plate 15. The inner surfaces of the wider side parts of the central hole 124 are formed as curved surfaces 124a, 124b to provide at least one contact portion against the outer peripheral surface of the drive shaft 7. These contact portions between the curved inner surfaces 124a, 124b and the outer peripheral surface of the drive shaft 7 are continuously shifted in accordance with the varying inclined angle of the cylindrical member 12. The wobble plate 15 generates its wobbling motion owing to rotation of the drive shaft 7, and the centre of the wobbling motion of the wobble plate 15 should be aligned on the geometrical centre C of the wobble plate 15, such as the axis of the drive shaft 7, to take account of the inertia force of the cylindrical member and wobble plate, vibration of the compressor or a balance of force analysis. Therefore, the radial movement of the cylindrical member 12 should be restricted to determine the position of the centre (C) of the wobbling motion of the wobble plate 15, because the cylindrical member 12, while rotating, supports the wobbling plate 15. The contact portion between the curved surfaces 124a, 124b and the outer surface of the drive shaft 7, and also fit between the short diameter of the central hole 124 and the outer surface of the drive shaft 7 restrict the radial movement of the cylindrical member 12. Therefore, the wobbling motion centre (C) is normally aligned on the central axis of the drive shaft 7, even if the inclined angle of the cylindrical member and wobble plate is varied. In the above explained structure of the central hole, the lower curved surface 124b is normally urged against the outer surface of the drive shaft 7 owing to the compression gas force acting against the pistons 20 to cause the secure contact, but the upper curved surface 124a only touches the outer surface of the drive shaft 7. Therefore, the upper surface of the central hole 124 may be formed as a flat surface 124c, as shown in Figure 4. Figures 5 and 6 show another modification of the inner surface of the wider part of the central hole 124. In these Figures, similar parts are represented by the same reference numbers as in the example shown in Figure 2, and any description of the similar parts is omitted to simplify the description. Each upper and lower surface of the wider part of the central hole 124 is formed as two straight parts which have different angles relatively to the central axis of the cylindrical member 12. That is, the upper surface consists of two straight parts 124c, 124d and a connecting point 124e between the two parts 124c, 124d functions as a contact point on the outer surface of the drive shaft 7. Also, the lower surface consists of two parts 124f, 124g and, a connecting point 124h between the two parts 124f, 125g functions as a contact point on the outer surface of the drive shaft 7. These two parts are formed parallel to the opposed parts on the opposite side of the drive shaft. Therefore, the angle of the two straight parts should determine the maximum and minimum inclined angle of the cylindrical member 12 which is thus restricted by the contact between the two contact points of the wider part of the central hole 124, and by the fit between the inner surface of the narrower part of the central hole 124 and the drive shaft 7. The straight portions for restricting the inclined angle of the cylindrical member 12, and the corresponding contact points, may be formed on a separate ring member 70 which is fixed on the inner peripheral surface of the cylindrical member 12, as shown in Figure 7. In this construction, the manufacture of the inner surface of the cylindrical member can be easily carried out and the manufacturing cost of the cylindrical member can be small.

Claims: 1. A wobble plate compressor with a variable displacement mechanism, the compressor including a compressor housing (3) provided with a crank chamber (32) and a cylinder block (31) in which a plurality of cylinders (33) are formed, a drive shaft (7) rotatably supported in the housing, a rotor (10) fixed on the drive shaft and having a variably inclined plate (12) provided with a central hole (124) for penetration by the drive shaft (7) and which rotates with the drive shaft, a wobble plate (15) adjacent to the inclined plate, and caused by the rotation of the inclined plate to nutate about the drive shaft, the wobble plate being coupled with a plurality of pistons (20) each of which is reciprocatably fitted with a respective one of the cylinders, and means for restricting the radial movement of the inclined plate about the drive shaft while permitting variation in the inclination thereof; the central hole (124) of the inclined plate (12) being of elongate cross section in a plane perpendicular to the axis of the drive shaft, so that the longer dimension of the cross section accomodates pivotal movement of the plate relatively to the shaft; characterised in that the shorter dimension of the cross section provides a fit against the shaft; and in that radial movement of the inclined plate (12) about the drive shaft (7) is restricted solely by contact of the inner surface of the central hole (124) with the outer surface of the drive shaft (7). 2. A compressor according to claim 1, wherein the inner surface (124a,124b) of the wider part of the hole is curved to provide a contact portion with the outer surface of the drive shaft. 3. A compressor according to claim 1, wherein an inner surface (124c,124d) of the wider part of the hole is formed by two straight portions, (124c, 124d) for engagement with the shaft to restrict the inclined angle of the inclined plate (12) each of which straight portions is at a different angle to a central axis of the plate, a connection point (124e) between the two straight portions being arranged to contact the outer surface of the drive shaft. 4. A compressor according to claim 3, wherein the straight portions (124c, 124d) and the corresponding contact point, are formed on a separate ring member (70) fixed on the inner peripheral surface of the inclined plate.

Inventors: TERAUCHI, KIYOSHI
Applicants: SANDEN CORPORATION
Application year: 1986
Main classification: F04B1
IPC codes: F04B27