Lubricating mechanism for a piston assembly of a slant plate type compressor

Abstract: A slant plate type compressor (10) having a lubricating mechanism for a piston assembly (71) is disclosed. The compressor (10) includes a housing (20) having a cylinder block (21) provided with a plurality of cylinders (70) and a crank chamber (22) adjacent the cylinder block (21). A piston (72) slides within each cylinder (70) and is reciprocated by a wobble plate (60) driven by a cam rotor (40) mounted on a drive shaft (26). Each of pistons (72) is connected to each of periphery located outer ends of the wobble plate by a connecting rod (73). The piston (72), at least one piston ring (81) disposed on an outer peripheral surface of the piston and the connecting rod (73) form the piston assembly. The piston (72) and connecting rod (73) are connected by a ball-socket connection (73a). During the compression stroke, the lubricating mechanism having a conduit (74) formed in the piston supplies a lubricating oil to a gap (g) created within the ball-socket connection (73a) from the cylinder chamber (70D) together with the pressure dropped refrigerant gas.

Description: The present invention relates to a refrigerant compressor according to the precharacterizing portions of claims 1 and 2, respectively. In particular, the invention relates to a slant plate type piston compressor, such as a wobble plate type piston compressor, having a lubricating mechanism for a piston assembly for use in an automotive air conditioning system. A wobble plate type compressor of this kind is disclosed in US-A-4,594,055 and includes a piston assembly having a piston and connecting rod which connects a wobble plate and the piston. The piston is provided with a spherical concavity at its bottom side for receiving a ball portion formed at one end of the connecting rod. After receiving the ball portion, a bottom end peripheral portion of the spherical concavity is radially inwardly bent by using a caulking apparatus in order to firmly grasp the ball portion, but the ball portion is allowed to slidably move along an inner surface of the spherical concavity. Therefore, a slight amount of gap is created between the inner surface of the spherical concavity and the outer surface of the ball portion. The above-mentioned manner of connection is generally called a ball-socket connection. Accordingly, it is required to supply the lubricating oil to the gap in order to smoothly move the ball portion along the inner surface of the spherical concavity without abnormal wearing of the inner surface of spherical concavity and the outer surface of the ball portion. In Japanese Utility Model Application Publication No. 01-71178, a mechanism for supplying the lubricating oil to the gap from the cylinder chamber during the compression stroke is disclosed. However, in this Japanese '178 application, during the compression stroke, the lubricating oil is supplied to the gap from the cylinder chamber together with the refrigerant gas of high pressure. Therefore, a smooth movement of the ball portion within the spherical concavity is prevented by the undesirable high pressure of the refrigerant gas, thereby causing abnormal wearing of the inner surface of the spherical concavity and the outer surface of the ball portion. Furthermore, as a measure to an environmental issue, when R134a is employed as the refrigerant of the compressor, the above-mentioned defect becomes worse because that lubricating ability of R134a is lower than lubricating ability of CFC as the conventional refrigerant. The US-A-1,332,760 discloses an engine piston for use in an internal combustion motor, wherein the piston comprises a spherical concavity formed at its bottom and so as to receive a ball portion of the connecting rod. A conduit connects the spherical concavity with the outer peripheral surface of the piston at a location between peripheral grooves receiving piston rings. Document GB-A-321,761 also discloses a piston for an internal combustion engine which includes a spherical concavity receiving the ball portion of a connecting rod; in this document a conduit connects the spherical concavity with the bottom of an angular groove receiving the piston ring. It is an object of the present invention to provide a slant plate type compressor having an improved lubricating mechanism. This object is achieved by a refrigerant compressor as defined in claim 1 or claim 2. Figure 1 is a vertical longitudinal sectional view of a wobble plate type refrigerant compressor according to a first embodiment of this invention. Figure 2 is an enlarged partial sectional view of a piston assembly shown in Figure 1. Figure 3 is an enlarged partial sectional view of the piston assembly shown in Figure 2. In the drawing, the flow of the refrigerant gas and lubricating oil is illustrated. Figure 4 is a view similar to Figure 2 illustrating a second embodiment of this invention. With reference to Figure 1, the construction of a slant plate type compressor, specifically a wobble plate type refrigerant compressor 10 in accordance with a first embodiment of the present invention is shown. Compressor 10 includes cylindrical housing assembly 20 including cylinder block 21, front end plate 23 at one end of cylinder block 21, crank chamber 22 formed between cylinder block 21 and front end plate 23, and rear end plate 24 attached to the other end of cylinder block 21. Front end plate 23 is mounted on cylinder block 21 forward (to the left side in Figure 1) of crank chamber 22 by a plurality of bolts (not shown). Rear end plate 24 is mounted on cylinder block 21 at is opposite end by a plurality of bolts (not shown). Valve plate 25 is located between read end plate 24 and cylinder block 21. Opening 231 is centrally formed in front end plate 23 for supporting drive shaft 26 by bearing 30 disposed in the opening. The inner end portion of drive shaft 26 is rotatably supported by bearing 31 disposed within central bore 210 of cylinder block 21. Bore 210 extends to a rearward end surface of cylinder block 21 to dispose valve control mechanism 19 as disclosed in Japanese Patent Application Publication No. 01-142276. Cam rotor 40 is fixed on drive shaft 26 by pin member 261 and rotates with shaft 26. Thrust needle bearing 32 is disposed between the inner end surface of front end plate 23 and the adjacent axial end surface of cam rotor 40. Cam rotor 40 includes arm 41 having pin member 42 extending therefrom. Slant plate 50 is adjacent cam rotor 40 and includes opening 53 through which passes drive shaft 26. Slant plate 50 includes arm 51 having slot 52. Cam rotor 40 and slant plate 50 are connected by pin member 42, which is inserted in slot 52 to crate a hinged joint. Pin member 42 is inserted in slot 52 to create a hinged joint. Pin member 42 is slidable within slot 52 to allow adjustment of the angular position of slant plate 50 with respect to the longitudinal axis of drive shaft 26. Wobble plate 60 is nutatably mounted on slant plate 50 through bearings 61 and 62. Fork-shaped slider 63 is attached to the outer peripheral end of wobble plate 60 and is slidably mounted about sliding rail 64 held between front end plate 23 and cylinder block 21. Fork shaped slider 63 prevents rotation of wobble plate 60 and wobble plate 60 nutates along rail 64 when cam rotor 40 rotates. Cylinder block 21 includes a plurality of peripherally located cylinder chambers 70 in which pistons 72 reciprocate. Each piston 72 is connected to wobble plate 60 by a corresponding connecting rod 73. Each piston 72 and connecting rod 73 substantially compose piston assembly 71 as discussed below. Rear end plate 24 includes peripherally located annular section chamber 241 and centrally located discharge chamber 251. Valve plate 25 is located between cylinder block 21 and rear end plate 24 and includes a plurality of valved suction ports 242 linking suction chamber 241 with respective cylinders 70. Valve plate 25 also includes a plurality of valved discharge ports 252 linking discharge chambers 251 with respective cylinder chambers 70. Suction ports 242 and discharge ports 252 are provided with suitable reed valves as described in U.S. Patent No. 4,011,029 to Shimizu. Suction chamber 241 includes inlet portion 241a which is connected to an evaporator of the external cooling circuit (not shown). Discharge chamber 251 is provided with output portion 251a connected to a condenser of the cooling circuit (not shown). Gaskets 27 and 28 are located between cylinder block 21 and the inner surface of valve plate 25, and the outer surface of valve plate 25 and rear end plate 24 respectively, to seal the mating surfaces of cylinder block 21, valve plate 25 and rear end plate 24. Disk-shaped adjusting screw member 32 is disposed in a central region of bore 210 located between the inner end portion of drive shaft 26 and valve control mechanism 19. Disk-shaped adjusting acrew member 32 is screwed in to bore 210 so as to be in contact with the inner end surface of drive shaft 26 through washer 33, and adjusts an axial position of drive shaft 26 by tightening and loosing thereof. Disk-shaped adjusting screw member 32 and washer 33 include central holes 32a and 33a respectively in order to obtain passageway 150, which provides communication between crank chamber 22 and suction chamber 241 via valve control mechanism 19, as substantially disclosed in above-mentioned Japanese '276 Patent Application Publication. The opening and closing of passageway 150 is controlled by the contracting and expanding of bellows 193 of valve control mechanism 19 in response to crank chamber pressure. During operation of compressor 10, drive shaft 26 is rotated by the engine of the vehicle through electromagnetic clutch 300. Cam rotor 40 is rotated with drive shaft 26, rotating slant plate 50 as well, which causes wobble plate 60 to nutate. Nutational motion of wobble plate 60 reciprocates pistons 71 in their respective cylinders 70. As pistons 71 are reciprocated, refrigerant gas which is introduced into suction chamber 241 through inlet portion 241a, flows into each cylinder 70 through suction ports 242 and then compressed. The compressed refrigerant gas is discharged to discharge chamber 251 from each cylinder 70 through discharge ports 252, and therefrom into the cooling circuit through outlet portion 251a. The capacity of compressor 10 is adjusted to maintain a constant pressure in suction chamber 241 in response to change in the heat load of the evaporator or change in the rotating speed of the compressor. The capacity of the compressor is adjusted by changing the angle of the slant plate which is dependent upon the crank chamber pressure. An increase in crank chamber pressure decreases the slant angle of the slant plate and thus the wobble plate, decreasing the capacity of the compressor. A decrease in the crank chamber pressure increases the angle of the slant plate and the wobble plate and thus increases the capacity of the compressor. Valve control mechanism 19 maintains a constant pressure at the outlet of the evaporator during capacity control of the compressor. With reference to Figure 2 additionally, piston assembly 71 includes connecting rod 73 which includes a pair of ball portions 73a and 73b formed at both ends thereof respectively and cylindrical-shaped piston 72 which is connected to ball portion 73a formed at the rear (to the right in Figures 1 and 2) end of connecting rod 73 as a manner described bellow. Piston 72 includes depressed portion 721 formed at the bottom (to the left in Figures 1 and 2) thereof. A central region of depressed portion 721 is further depressed so as to define spherical concavity 722 which receives ball portion 73a therewithin. After receiving ball portion 73a, the bottom end peripheral portion 722a of spherical concavity 722 is radially inwardly bent by using a caulking apparatus (not shown) in order to firmly grasp ball portion 73a, but ball portion 73a is allowed to slidably move along an inner surface of spherical concavity 722. Therefore, a slight amount of gap "g" is created between the inner surface of spherical concavity 722 and the outer surface of ball portion 73a. The above-mentioned manner of connection between the ball portion and the spherical concavity is generally called a ball-socket connection. The outer peripheral end of wobble plate 60 and ball portion 73b formed at the other end of connecting rod 73 are connected by the ball-socket connection as well. Piston 72 is provided with two annular grooves 701 and 702 at its outer peripheral surface near top and bottom portions thereof. Conical shaped piston rings 81 and 82 identical to ring 81, which are formed of resin, fit into grooves 701, 702 respectively to seal the outer peripheral surface of piston 72 and an inner surface of cylinder 70. Conduit 74 is radially formed in piston 72. One end of conduit 74 is open to the certain portion of the outer peripheral surface of piston 72 located between grooves 701 and 702, and the other end is open to the inner surface of spherical concavity 722. It should be understood that although only one piston assembly is shown in Figure 1, in the embodiment shown there are plural, for example, five such sockets arranged peripherally around the wobble plate to respectively receive the five pistons employed in the disclosed embodiment. The effect of the piston assembly of the present invention is as follows. With reference to Figure 3 additionally, during the compression stroke, a small part of the compressed refrigerant gas in space 700 which is defined by piston 72 and the inner peripheral surface of cylinder 70 flows into gap "G1" created between the inner peripheral surface of piston ring 81 and the bottom surface of groove 701, and pushes piston ring 81 radially outwardly by its pressure force. Thereby, the refrigerant gas in gap "G1" further flows into space 701 defined by piston 72, cylinder 70 and piston rings 81, 82 with a pressure drop due to the throttling effect of gap "G1". Furthermore, a small part of the refrigerant gas in space 710 radially inwardly pushes piston ring 82 by its pressure force, and flows into crank chamber 22 with a further pressure drop due to the throttling effect of gap "G2" created between the outer peripheral surface of piston ring 82 and the inner surface of cylinder 70. Still furthermore, the remaining great part of the refrigerant gas in space 710 flows into gap "g" created between the inner surface of spherical concavity 722 and the outer surface of ball portion 73a through conduit 74, and then the refrigerant gas in gap "g" flows to crank chamber 22 with a further pressure drop due to the throttling effect of gap "g". As a result, during the compression stroke of the compressor, pressure Pb in midway pressure space 710 is given by Pa > Pb > Pc, where Pa is the pressure in space 700 and Pc is the pressure in crank chamber 22. Accordingly, during the compression stroke, the lubricating oil accumulated at an adjacent outer peripheral surface near top portion of piston 72 flows to space 710 through gap "G1" together with the pressure dropped refrigerant gas. Further, a great part of the lubricating oil in space 710 conducted into gap "g" through conduit 74 by virtue of the pressure difference between Pb, the pressure in space 710, with Pc, the pressure in crank chamber 22. The remaining small part of the lubricating oil in space 710 is conducted to crank chamber 22 by virtue of the pressure difference between Pb with Pc. Thereby, ball portion 73a of connecting rod 73 can smoothly move along the inner surface of spherical concavity 722 without abnormal wearing of the inner surface of spherical concavity 722 and the outer surface of ball portion 73a even though R134a is employed as the refrigerant of the compressor. Figure 4 shows a certain portion of a wobble plate type refrigerant compressor including a piston assembly in accordance with a second embodiment of this invention in which the same numerals are used to denote the same elements shown in Figure 2. In the second embodiment, conduit 74 having a small diameter portion 741a at its one end is radially formed in piston 72. One end of small diameter portion 741a is open to the inner surface of spherical concavity 722 and the opposite end of conduit 741 is open to the center of the bottom surface of annular groove 701. Therefore, during the compression stroke, a great part of the refrigerant gas in gap "G1" flows into gap "g" through conduit 741 with a pressure drop due to the throttling effect of small diameter portion 741a and then the refrigerant gas in gap "g" flows to crank chamber 22 with further pressure drop due to the throttling effect of gap "g". The remaining small part of the refrigerant gas in gap "G1" flows to crank chamber 33 via space 710 and gap "G2" with a pressure drop due to the throttling effect of gaps "G1" and "G2". Accordingly, during the compression stroke, a great part of the lubricating oil accumulated at the adjacent outer peripheral surface near top portion of piston 72 is conducted into gap "g" via a part of gap "G1" and conduit 741 by virtue of the pressure difference between Pa, the pressure in space 700 with Pc, the pressure in crank chamber 22. Thereby, ball portion 73a of connecting rod 73 can smoothly move along the inner surface of spherical concavity 722 without abnormal wearing of the inner surface of spherical concavity 722 and the outer surface of ball portion 73a even though R134a is employed as the refrigerant of the compressor as well as the first embodiment of this invention. In the above-mentioned two embodiments, the present invention is applied to the slant plate type compressor with the capacity control mechanism, however, of course, the present invention can be also applied to the fixed capacity slant plate type compressor.

Claims: A refrigerant compressor (10) including a compressor housing (20), said compressor housing (20) including a cylinder block (21), front end plate (23) disposed on one end of said cylinder block (21), a rear end plate (24) disposed on an opposite end of said cylinder block (21), said rear end plate (24) having a discharge chamber (251) and a suction chamber (241) formed therein, said cylinder block (21) having a plurality of cylinders (70) formed therein, a crank chamber (22) disposed forward of said plurality of cylinders (70) and enclosed within said cylinder block (21) by said front end plate (23), a piston (72) slidably fitted within each of said cylinders (70) and reciprocated by a drive mechanism, said drive mechanism including connecting rods (73) to reciprocate said pistons (72) in said cylinders (70), said connecting rod (73) including a ball portion (73a) formed at its (73) one end, said piston (72) including a spherical concavity (722) formed at its (72) bottom end so as to firmly receive said ball portion (73a) of said connecting rod (73) with allowing said ball portion (73a) of said connecting rod to slidably move along an inner surface of said spherical concavity (722), at least one annular groove (701, 702) being provided on the outer peripheral surface of each of said pistons (72), at least one piston ring (81, 82) disposed within said at least one annular groove (701, 702) having an outer diameter larger than the outer diameter of said piston (72) at normal temperatures, characterized by: at least one conduit (74) being formed at each of said pistons (72), one end of said conduit (74) being open to a certain portion of the outer peripheral surface of each of said pistons (72) being forwardly apart from said at least one groove (701, 702) and the other end of said conduit (74) being open to the inner surface of said spherical concavity (722); and wherein a passage for a lubricant is formed between a space (700) in the cylinder (70) on the rear end plate side of the piston (72) and the crank chamber (22) through a gap (G1) between an inner peripheral surface of said at least one piston ring (81, 82) and a bottom surface of said at least one annular groove (701, 702), through the conduit (74, 741) and a gap (g) between the inner surface of said spherical concavity (722) and an outer surface of said ball portion (73a). The refrigerant compressor according to the preamble of claim 1, characterized by: at least one conduit (741) including a throttling portion (741a) being formed at each of said pistons (72), one end of said conduit (741) being open to the bottom surface of said at least one annular groove (701, 702) of each of said pistons (72) and the other end of said conduit (741) being open to the inner surface of said spherical concavity (722). The refrigerant compressor according to claim 2, characterized in that a passage for a lubricant is formed between a space (700) in the cylinder (70) on the rear end plate side of the piston (72) and the crank chamber (22) through a gap (G1) between the inner peripheral surface of said at least one piston ring (81, 82) and the bottom surface of said at least one annular groove (701, 702), through the conduit (741) and the gap (g) between the inner surface of said spherical concavity (722) and the outer surface of said ball portion (73a).

Inventors: SHIMIZU SHIGEMI C O SANDEN COR, TERAUCHI KIYOSHI C O SANDEN CO, SHIMIZU, SHIGEMI, C/O SANDEN CORPORATION, TERAUCHI, KIYOSHI, C/O SANDEN CORPORATION
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1990
Main classification: F04B27
IPC codes: F04B27, B65D81, F16J1