GB2215781A - Swashplate and sliding shoe assembly for an air conditioning compressor - Google Patents

Description

SWASHPLATE AND SLIDING SHOE ASSEMBLY4 157 8 1 FOR AN AIR-CONDITIONING

COMPRESSOR The present invention is concerned with improvements in an automotive air conditioning compressor and is related to the invention described in British Patent Application No. 88i9680.3, filed on 18 August, 1988.

Prior art swashplate compressor designs may be seen by referring to U.S. patent 4,381,178; 4,413,955; 4,408,962 and 3,380,651. The designs shown in these prior art references include cylinder bodies in which axially arranged cylinders are machined in angularly spaced relationship about the axis of the compressor. Each cylinder receives a compressor piston, each piston comprising a pair of piston heads joined by a bridge to form an integral, double acting piston. The margin of a swashplate is received within a piston cavity located between each piston head adjacent the bridge. A sliding swashplate shoe engages the swashplate and is held in place within the piston recess thereby providing a sliding drivable connection between the swashplate and each piston. As the swashplate rotates, the rotary motion of the swashplate is translated into reciprocating motion of the pistons.

The swashplate in the prior art constructions is formed of cast iron or powdered metal, the shoe engaging surfaces of which are machined following the forging operation. The swashplate is joined to a central driveshaft received through a central opening the hub of the swashplate. The swashplate and the drive shaft nay be joined by a drive pin as shown in the 1178 patent and in the 1955 patent, or by a key and slot connection as shown in the 1651 patent or by a friction force fit as shown in the 1962 patent. The drive pin or the key way driving connection introduces complexity into the compressor assembly and requires expensive machining 2 operations. The machining operations, aside f rom the -cost and the special machine tools that are required during manufacture, establish stress points which are potential causes of structural failure of the compressor during operation when the swashplate is subjected to high f orces. In the prior art designs that emplby a press fit between the shaft and the hub of the swashplate, such as in the design of the 1962 patent, high stresses are developed as the shaft is pressed into the central opening of the swashplate hub. This requires a relatively large swash-plate hub.

The machined surface of the swashplate, as seen in each of the prior art references mentioned above, is engaged by shoes. Each shoe has a recess in which is fitted a drive ball. In turn the ball is received in a recess in the adjacent piston. The ball is formed of high carbon steel, and the shoe is formed of a material having suitable bearing characteristics. Provision is made for establishing an oil film between the shoe and the adjacent surface of the swashplate engaged by the shoe.

Because of the machining operation that the swashplates of prior art designs require, it is necessary in those designs to provide a substantial relief near the hub of the swashplate. This reduces the axial dimension of the finished swashplate and reduces the strength of the swashplate. Because of the presence of the relief adjacent the hub of the swashplate, it is necessary to increase the axial effective width of the swashplate to maintain sufficient strength to withstand the substantial axial forces imposed on the swashplate by the pistons during operation. This avoids breakage of the swashplate as the drive shaft is inserted during manufacture into the central opening of the swashplate hub with a press fit as shown in the 1962 patent.

3 With a view to mitigating the shortcomings described above with respect to the prior art constructions, the present invention provides an air conditioning compressor having a swashplate assembly comprising a die cast aluminium alloy swashplate with bearing surfaces disposed in a plane angularly oriented with respect to the swashplate axis, a swashplate hub, a hub opening formed centrally in the hub and thrust bearing surfaces on each axial side of said hub; and a drive shaft having a knurled portion and received in said hub opening with a force fit, the degree of dimension interference that establishes said force fit being reduced due to the presence of said knurled portion, whereby a driving connection between said swashplate and said drive shaft is established with minimal stress on said swashplate.

A practical embodiment of the invention uses a die cast swashplate rather than a forged swashplate. The material used is die cast aluminium alloy 390, which is comprised of 16 to 18 percent silicon. The shoe engaging surfaces of the swashplate following the die cast operation do not require grinding. Because no machining of the swashplate hub diameters is required, as in the case of prior art designs, it is not necessary to provide deep reliefs or recesses adjacent the hub of the swashplate for purposes of tool clearance during the machining operation. The swashplate is capable of withstanding the stresses that are developed as the drive shaft is press fitted into a central opening formed in the hub of the swashplate.

All of the critical dimensions of the finished swashplate can be achieved during the die casting operation with the exception of the swashplate OD and shoe faces the end surf aces of the hub that are engaged by the thrust bearings and the central bore. A simple turning operation is required to machine these surfaces and to provide the necessary axial dimension of the hub.

4 Before the drive shaft is press f itted into the hub of the swashplate, the shaft is formed with the knurled. portion. The knurl can be a standard knurl conforming to SAE standard specifications. The knurl extends only for a portion of the length of the swashplate hub. Because of the use of a knurl portion it is not necessary to provide a high degree of interference as the shaft is press fitted into the swashplate hub. This in turn eliminates the high forces that would otherwise be created during manufacture. It is thus possible to employ a die cast aluminium silicon alloy material, previously described, since high stresses are avoided during the manufacture of the swashplate and shaft assembly. This stress avoidance is in addition to the stress avoidance, described above, that is achieved by the elimination of a deep tooling recess adjacent the hub of the swashplate which would be required if a finished machining operation were to be needed.

The improved design eliminates also the need for using a shoe and ball sub-assembly. A sliding driving connection is provided between the swashplate and each of the pistons]Sy means of a generally semicircular powered metal cast shoe having a semispherical bearing surface received in a semispherical pocket formgd in the piston. One surface of the powered metal shoe forms' a bearing surface that slidably engages the sliding surface of the swashplate. No finish machining of the shoes is required except for grinding of the shoe face because it is possible to manufacture the shoes using a powered metal process in which the material is approximately 90 percent iron, 2 percent nickel and approximately 5 percent copper. The bearing surface of the shoes can be held to approximately 26 microns using the powered metal process and the porosity of the shoe itself is conducive to the development of a lubricating oil film. This feature of the invention improves both the performance and substantially reduces the cost because of the simplicity of its manufacture and the reduction in the number of parts.

The improvements of the design of the invention make it possibleto provide a swashplate as sembly that has bette7r detail because of the die cast operation employed in its manufacture. The die cast aluminium alloy and the powered metal shoes provide better wear surfaces than the forgings of the prior art designs, and the reduction in the number of machining operations substantially reduces the cost. The shallow relief that it required because of the die cast operation, in contrast to a forging operation, improves the durability of the assembly. 15 The invention will now be described further, by way of example, with reference to the drawings, in which: Figure 1 is a cross-sectional assembly view of a 20 compressor assembly embodying the invention, Figure 2 is an end view of one of the two cylinder blocks that form a part of the assembly of Figure 1.

Figure 3 is an end view showing the opposite end of the cylinder block of Figure 2. Figure 4 is a side elevation view of a swashplate and shaft assembly which form a part of the assembly of 30 Figure 1.

Figure 5 is an end view of the structure of Figure 4 as seen from the plane of section line 5-5 of Figure 4.

Figure 6 is a side view of a piston adapted to be received in a cylinder of the cylinder block of Figures 2 and 3.

6 Figure 7 is a - plan view of the front of the valve plate used-in the assembly.

Figure 8 is an edge or end view of the plate of Figure 7 as seen from the plane of section 10-10 of Figure 7.

Figure 9 is a plan view of an inlet valve reed positioned at each axial end of the cylinder blocks.

Figure 10 is a plan view of the outlet or discharge valve reed located at each axial end of the cylinder blocks.

Figure 11 is an end view of the rear casting head or housing for the assembly. It shows the interior porting and passage arrangement at the end wall of the opening in the casting head.

Figure 12 is a sectional view taken along the plane of section line 12-12 of Figure 11.

Figure 13 is an end view of the front casting head of the housing showing the interior of the end wall of the front head together with the porting and passage structure.

Figure 14 is a sectional view taken along the plane of section line 14-14 of Figure 13.

Figure 15 is a plan view of the gasket for the discharge reed valve and valve plate at each end of the cylinder blocks, and Figure 16 is an edge or end view of the gasket as seen from the plane of section line 16-16 of Figure 15.

In Figure 1 reference character 10 designates generally a cast housing for an air conditioning compressor.

Housing 10 includes a rear housing part 14 and a front housing part 16, each of which is formed-of die cast aluminium alloy. Housing part 14 has a cylindrical interior 18 and an integral end "wall 20 that forms a part of the die casting. Mounting bosses 22 and 24 are formed as part of the die casting, and mounting bolts are received in bolt openings formed in the bosses 22 and 24.

A die cast aluminium cylinder body 26, in which is formed a plurality of cylinder openings, is itself of cylindrical shape and is fitted within the opening 18 with a very small clearance between the inner diameter of the cylindrical opening 26 of the housing 14 and the outer diameter of the cylinder body 26.

One of the cylinder openings in the-cylinder body 26 is shown at 28. A compressor piston 30 is slidably received in the cylinder opening 28.

The front compressor head comprises the companion housing part 16. Like the housing part 14, housing part 16 has a circular central opening as seen at 32. A cylinder body 34, which itself is of cylindrical shape, is received in the cylindrical opening 32 with a minimum clearance between its outer diameter and the inside diameter of the cylindrical opening 32.

An inlet valve plate in the form of a circular spring steel disc is identified by reference numeral 36. That disc will be described with reference to Figure 9.

Adjacent the disc 36 is a front valve plate 38, which has formed in it valve openings that register with reed valve elements of the inlet valve disc 36. The valve plate 38 will be described with reference to Figure 9.

8 A front discharge valve plate 40, which will be described with reference to Figure 10, is located directly adjacent valve plate 38. It is f ormed" with reed valve elements that register with valve openings formed in valve plate 38.

A front gasket plate 42 is disposed between the f ront discharge valve plate 40 and the end surface 44 of the opening 32 formed in the housing part 16. Surface 44 is a machined surface on the inner face of the end wall 46 of the housing part 16.

As seen in Figure 1, the cylinder block 30 is assembled in abutting relationship with respect to the cylinder identified by block 34, the abutting surfaces being common reference numeral 48. As seen in Figure 1, cylinder opening 28 is aligned with cylinder opening 50 in cylinder block 34 thus forming a common cylinder for the reciprocating piston 30.

A swashplate shaft 52 is journalled by bushing 54 in cylinder block 34 and by bushing 56 in cylinder block 26. Shaft 52 extends through end plate opening 58 in the end plate 46. A fluid seal 60 seals the interior of the housing as the shaft 52 rotates in shaft opening 58.

A stationary sleeve shaft extension 62 is formed on the end plate 46 and provides a support for an electromagnetic clutch, now shown.

As seen in Figure 1 and in Figure 6, the piston comprises two juxtaposed bosses 94 and 96, which are machined to provide semi-spherical pocket recesses 98 and 100 for swashplate shoes 102 and 104, respectively.

The shoes are formed of sintered powder metal, which may comprise about 97% iron, 2% nickel and.5% copper. The shoes are provided with a flat bearing surface that slidably engage surfaces 106 and 108, respectively, on 1 the swashplate and shaft assembly shown in Figure 1 and in Figure 4. The bearing surface is formed in the sintering process. Finish machining is not required except for grinding of the face. A smoothness of 26 microns or less can be achieved by sintering.

The die cast aluminium-silicon alloy swashplate is disposed, as seen best in Figure 4, at an angle relative to the axis of the shaft. The swashplate itself, which is designated by reference character 111, includes a hub 113 that is press fitted on the shaft 52 and that is locked in place by standard SAE serrations 114 formed on the shaft 52 prior to the assembly of the swashplate 111 on the shaft by the press fitting operation. The serrations extend f or only a part of the depth of the swashplate hub. As the shaft 52 rotates, the swashplate 106, due to the sliding engagement with the shoes 102 and 104, causes the piston 30 to reciprocate in the cylinder defined by cylindrical openings 28 and 50 in the cylinder blocks 26 and 34, respectively. Thrust forces on the swashplate are accommodated by the radial needle bearing assemblies 110 and 112, which respectively engage the cylinder blocks 26 and 34 whereby the thrust on the swashplate hub is absorbed by the cylinder blocks.

The shoes 102 and 104, which are formed of sintered metal, have flat bearing surfaces that are porous enough to carry a lubricating oil film thus establishing a non-abrasive sliding bearing relationship with respect to the swashplate surfaces 106 and 108 as the pistons are reciprocated.

The swashplate is provided with very shallow recesses or reliefs 115 and 117 on either side of the swashplate. This is in contrast to the deep relief s that would be required if the swashplate were to be forged, as in prior art designs.

As best seen in Figure 6, the piston 30 is formed of a unitary die casting. It includes a bridge portion 115 of reduced depth with respect to the diameter of the ends of the piston. The bridge portion is formed during the die casting operation with an upper surface 116 that is situated below the centre line 118 of the piston. This permits sufficient clearance for the outer margin of the swashplate 111 thereby preventing interference during operation of the compressor. This die casting operation eliminates complex machining operations that are common to reciprocating pistons of swashplate compressors of the kind illustrated in the prior art disclosures mentioned in the specification.

As seen in Figure 6, the piston is a double acting piston that is provided with piston ends 120 and 122 of equal diameter. Each end 120 and 122 has a piston seal groove 124 and 126 which receives a piston seal ring.

The rear housing part wall 20 of the housing part 14 has inlet and outlet pressure cavities that are formed in it during the die casting operation. The low pressure inlet cavity shown at 128 encircles the shaft 52 as best seen at numeral 128. It is separated from the high pressure cavity 130 by a cylindrical baffle 1 32. The outlet port, which is a high pressure discharge port,-is shown in Figures 1 and 11 by reference numeral 134.'. The upper extremity of the cylindrical baffle wall 132, as, seen in Figure 12, registers with and forms a continuation of separator walls 136 and 138 which isolate the outlet passage from the inlet passage 128. Located in the outlet port 134 is a pulsation damper tube or muffler, preferably made of plastic material. This is indicated in Figure 1 by reference numeral 140.

It includes a cylindrical end piece 142 received in the discharge port 134. It includes also a reduced diameter extension 146 that is received in the high pressure cavity 130. The left hand end of the extension 146, as seen in Figure 1, is received in discharge passage 150 of the rear cylinder block 26. This is seen best by referring to Figure 2.

When high pressure discharge gas is distributed to the discharge port 150 of the cylinder block 26, it passes into the discharge passage 130 formed in the die cast end plate of the housing part 14. But before the gas be transferred to the discharge opening 134 it must reverse in its directional flow toward the left hand opening of the extension 146 of the damper 140. The flow passage in the extension 146 is of less area than the flow area of the opening 134. This circuitous flow path for the discharge gas results in a dampening of undesirable pressure pulsations in the delivery of the refrigerant.

In Figure 11 the inlet opening for the refrigerant is shown at 152. It should be noted in Figure 11 that communication between opening 152 and the arcuate region of the inlet passage 128 is interrupted by a bridge 154. The plane of the inner surface of the bridge 154 is common to the plane of the inner surface of the baffle wall 132. Gases that enter the port 152, therefore, pass directly through openings 156 in reed valve plate 36 as see in Figure 9.

The low pressure refrigerant then passes through opening 158 of the rear valve plate 38 shown in Figure 7. The refrigerant gas then is passed through openings 158 that are cast in the cylinder body 26 as seen in Figure 2.

The gases then accumulate in the region 160. From there the refrigerant gases pass into each of the other cast low pressure passages 162 and 164 as seen in Figure 2.

The right hand end of each of these cast passages seen in Figure 2 communicates with the low pressure passage 128 that is cast in the end wall 20 of the housing part 14, as previously described.

As seen in Figure 11 there is a second bridge 166 which bridges the baffle wall 132 with the outer housing wall. The inner surface of this bridge 166 is lower relative to the base of the inlet passage 128 than the machined surface-of the bridge 154. Thus direct communication is permitted between opening 152 and opening 168 formed in the valve plate of Figure 7.

The valve reed disc of Figure 9 includes a flexible cantilever valve part 170 which registers with the opening 168 and permits one-way flow through the opening 168 when the piston for the associated cylinder adjacent to it undertakes its intake stroke. The bridge 166 acts as a partial baffle that prevents transfer of a so- called slug of refrigerant in liquid form into the adjacent cylinder and permits relative equal distribution of refrigerant to each of the other cylinders. It does this by assuring that most of the refrigerant, perhaps 80 percent of the inlet flow, is transferred to the cavity 160 and distributed from there through the internal flow intake passages 162 and 164 and 158 from which it is transferred to the cast intake passage 128 formed in the end plate 20 of the housing portion 14.

As seen in Figure 11, there are multiple cantilever valve elements at 172, 174, 176 and 178 as well as at 170. These valve elements or reeds register with valve plate openings 180, 182, 184, and 186 as well as with opening 158. The cylinder block 26, as seen in Figure 2, has 5 cylinder openings which accommodate 5 compressor pistons and each cylinder is served by a separate one of the valve reeds shown in Figure 9. As each piston 130 is stroked in a left hand direction as seen in Figure 1, refrigerant is drawn through the valve plate opening and past its associated valve reed. Refrigerant is then drawn from the opening 128 in the case of cylinders 188, 190, 192 and 194 which are identified in Figure 2. In the case of cylinder 196 shown in-Figure 2, refrigerant is drawn directly from the opening 152 across the bridge 168.

The discharge reed assembly of Figure 10 includes a plu wality of reed valve elements separately identified by characters 198, 200, 202, 204,and 206.

Each of these valve elements registers with high pressure discharge openings 208, 210, 212, 214, and 216, as seen in Figure 7. Each of these openings serves as a discharge port for the high pressure refrigerant as the pistons for the respective cylinders are stroked in a right hand direction, as seen in Figure 1. The discharge reeds shown in Figure 10 permit one-way flow of high pressure gases into the discharge flow path 130 previously described with reference to Figure 11. A baffle wall 132 is separated at 218 to permit communication between passage 130 and the discharge passage 134.

The cylinder block 34 is identical and inter-changeable with cylinder block 26. The valve plate, the inlet reeds and the discharge reeds described with reference to the rear housing part 14 are identical to those that function with respect to the front housing part 16.

Like the rear housing part 14, the front housing part 16 shown in Figure 13 is provided,with cast high pressure and low pressure passages. The high pressure passage shown at 220 corresponds to high pressure passage 130 of the rear housing part. Low pressure passage 222 of Figure 13 corresponds to low pressure passage 128 of the rear housing part.

A baffle wall 224,- which corresponds to the baffle wall 132 of the rear housing part 14, separates passages 220 and 222. The wall 224 is discontinuous as shown at 226 to provide communication between passage 220 and the outlet opening 228 as seen in Figure 1.The region 230, 14 seen in Figure 1 and in Figure 13, which is the high pressure region, is separated from the low pressure inlet passage 222 by bridge portions 232 and 234 of the baffle wall 224.

Fluid that is discharged by the pumping pistons passes from discharge passage 220 and into the region 230, whereupon it passes through internal crossover passage 236 seen only in Figure 1. This passage corresponds to passage 150 that was described with reference to the rear cylinder block of Figure 2. Passage 150 and passage 236 register at their juncture to form a continuous passage that communicates with the discharge opening 142 seen in Figure 1. This internal crossover passage eliminates the need for providing a separate crossover tube as in some prior art arrangements, and it may be formed during the die casting operation with minimal finish machining operations being required.

Figure 15 shows a gasket or seal plate that is interposed between the valve plate and the inner machined surface of the front and rear housing parts.

The gasket of Figure 13, which was described with reference to Figure 1 and identified by reference numeral 140, includes an opening 220 with a high pressure opening 186 in the valve plate of Figure 7. It includes also openings 222, 224, 226, and 228 which register with cast end openings in the front cylinder block, which in turn correspond to the cast end openings previously described with reference to the cylinder block 26 shown in Figure 2. These respectively are shown at 150, 158, 160, 162 and 164. The corresponding openings in the valve plate 28 of Figure 7 are shown in Figure 7 at 150t, 1581, 161, 1621 and 164t.

Figure 15 shows at 230 an embossment which encircles the axis of the shaft 52 and which envelopes the opening 220. The embossment forms a continuous ridge which - 15 registers with valve plate locations opposite the machined inner surface of the baffle wall 225, as shown in Figure 13. It registers also with themachined surface of the bridge portions 232 and 234 of the baffle wall 225. Thus the embossment forms an effective seal that isolates the high pressure cast passage 220 from the low pressure cast passage 222. The gasket or seal of Figure 15 includes also an inner embossment ring 232 which prevents passage of high pressure refrigerant from the high pressure discharge port for the cylinders from the region of the bearing 54 and the shaft opening 58.

A similar gasket or seal plate is used to seal the high pressure and low pressure passages in the end plate 20 of the rear housing part 14.

The valve plate for the front cylinder block is identical to the valve plate for the rear cylinder block. Simi-larly, the inlet valve reeds and the discharge valve reeds for the front and rear cylinder blocks are identical, one with respect to the other.

This inter-changeability, as well as the inter-changeability of the cylinder blocks themselves, simplifies both the design and the manufacture and assembly of the components, thus making it possible to_ achieve reduced manufacturing costs and improved reliability during operation following assembly.

Radial arms, one of which is shown at 234 in Figure 15, support the hub of the gasket on which the embossment 232 is formed.

Near the radially outer margin of the gasket of Figure are straps 236 which provide rigidity to the disc but which are displaced out of the plane of the gasket thereby permitting free flow of refrigerant gas through the valve plate openings and past the inlet valve reeds.

The relative position of the straps 236 with respect to - 16 the plane of the gasket can be seen by referring to Figure 1 where the gasket is shown in cross section.

As- seen in Figure 11 the rear housing part 14 has four external bosses 237, 238, 240, and 243.- Similarly, the front housing part 16 has bossfes 244, 242, 248 and 246, which register with the bosses237, 238, 240, and 243 of the front housing part 16. Each of these bosses has a bolt opening to permit entry of a clamping bolt. When the bolts are tightened following assembly of the components, the cylinder blocks are brought into registry, one with respect to- the other, and a predetermined load is applied to the gasket. Effective seals thus are established. The left hand margin of the housing part 14 is received within the right hand margin of the housing part 16, as seen in Figure 1, and an 11011 ring seal 250, which is received in an 11011 ring groove in the housing part 14, establishes a fluid tight seal between the mating parts.

The previously mentioned shoes that engage the surfaces 106 and 108 of the swashplate are formed of powdered metal that may be heat treated to a hardness of over 40 Rockwell C. It is possible, therefore, to eliminate the necessity for using a se parate shoe on the. movable slipper element as in prior art designs such as tho. se shown in the prior art references mentioned in- the preceding portion of this specification. The shoes themselves may or may not be tumbled after they are finished. In addition to the inter-changeability of the parts -- for example, the inlet valve disc, the discharge valve disc and the valve plate -- pre-assembly of the valve plate with the gasket and the two reed valve discs can be achieved by locater pins which are received in pin openings formed in valve plate 38 illustrated in Figure 7. These pins are received with a force fit in pin openings 254 and 256 as seen in Figure 7. Corresponding openings 258 and 260 are formed in the 17 - discharge valve of Figure 10, and these register with the locater pins. Similarly, locat er pip openings 258 and260 are formed in the gasket as formed in Figure 15, and these also register with the locater pins.

On the opposite side of the valve plate pin openings 262 and 264, as seen in Figure 9, register viith the valve pins. Thus the valve plate, the inlet valve disc, the discharge valve disc and the gasket can be preassembled to simplify the manufacturing operation. After this pre-assembly procedure the sub-assembly is inserted into registering pin locater openings 266 and 268, shown in Figure 3 for the rear housing part. Corresponding pin openings 270 and 272 for the front housing part can be seen in Figure 13. These locater pins establish proper angular registry of the assembled parts, one with respect to the other. No fasteners are required and the manufacturing cost and assembly cost and improved reliability by a simplified assembly is achieved.

Manufacturing operations are simplified further by the piston construction as explained previously. The piston construction has a bridge area that does not require f inished machining. The bridge area is formed during the die casting operation and it permits the swashplate outside diameter at maximum displacement to extend beyond the bosses for the slippers. There is no need for machining a relief area in the bridge surface as in the prior art constructions, examples of which are shown in the references described in this specification. it is permissible with this design for the swashplate to engage the bridge surface with a running engagement on the midpoint surfaces of the bridge.

The improved design further provides improved reliability and simplified manufacturing operations by reason of the die casting process for forming the swashplate itself. It is normal practice in the design of a - 18 swashplate compressor to use a cast forge process or by using a forging process without casting. The depth between the face of the shoe and the relief in the hub of the swashplate is sufficiently shallow in the present design to assure sufficient strength. The presence of the refrigerant in the region of the swashplate provides sufficient lubrication because sufficient lubricating oil is present. The refrigerant gas permits an oil film to be developed continuously over the surfaces engaged by the shoes.

The bearings 54 and 56 for the shaft 52 are steel backed sleeve bearings which can be assembled with no further machining being required after installation. These are located, as seen in Figure 1, adjacent radial needle bearings 112 and 110 respectively. The cage for the radial rollers of the bearings 112 and 110 rotate in the usual fashion between two thrust washer rings. This establishes a centrifugal pumping action which draws lubricant and refrigerant from the inboard ends of the sleeve bearings. A pressure differential exists between the swashplate chamber and the inlet annulus that is cast in each of the end plates f or the housing parts. The existence of this pressure differential creates a pressure differential across the bearings themselves and this is aided by the centrifugal action of the rotating cages of the radial needle bearings, which act as thrust bearings. Thus the cages of the radial needle bearings, which act as thrust bearings, and the j ournal bearings are lubricated thereby further improving the reliability of the compressor.

Claims (5)

1. An air conditioning compressor having a swashplate assembly comprising a die cast aluminium alloy swashplate with bearing surfaces disposed in a plane angularly oriented with respect to the swashplate axis, a swashplate hub, a hub opening formed centrally in the hub and thrust bearing surfaces on each axial side of said hub; and a drive shaft having a knurled portion and received in said hub opening with a force fit., the degree of dimension interference that establishes said force fit being reduced due to the presence of said knurled portion, whereby a driving connection between said swashplate and said drive shaft is established with minimal stress on said swashplate.

2. An air conditioning compressor as claimed in Claim 1, wherein said swashplate assembly includes multiple, generally semispherical shoes, said shoes being formed of sintered powdered metal, each shoe having a bearing surface engageable with said bearing surfaces on said swashplate, said shoes being adapted to be engageable with reciprocating pistons adapted to move axially with respect to the axis of said drive shaft.

3. An air conditioning compressor as claimed in Claim 1 or 2, wherein said drive shaft is f ormed of steel and said knurled portion extends for substantially less than the full length of said hub opening.

4. An air conditioning compressor as claimed in Claim 2 or 3, wherein each side of said swashplate is formed with a bearing surface and said shoes engage each bearing surface at directly opposite locations whereby each pair of said shoes is adapted to establish a driving connection between one of said pistons and said swashplate.

5. An air conditioning compressor constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated iri the accompanying drawings.

1 i i i i i Published 1989 atThe Patent Office, State House, 86'71 High Holborn, LondonWClR 4TP. Further copies maybe obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington, Rent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con- 1/87