Asymmetrical suction porting for swash-plate compressor

Abstract: A swash-plate compressor (10) is disclosed having double-acting pistons (22) that reciprocate in aligned sets of horizontally-extending bores (20) of a cylinder block to compress gaseous refrigerant. An improved asymmetrical arrangement (12) of suction intake ports (46) is provided in at least the lowermost piston (22). The suction ports (46) extend longitudinally through operating head ends (23) of the piston (22) and are connected by an open channel (47) so as to provide fluid communication through the piston head end (23). A matching valve disc (48) with a flexible ring (50) is included so as to provide uni-directional flow through the suction ports (46) during the intake stroke. The suction ports (46) are on a constant radius arc spaced 30° apart from one another and are excluded from the lower 120° portion of the piston head end (23) to form the asymmetrical arrangement. Liquid lubricant in a reservoir pool (P) adjacent the bottom of a crankcase (19) is sufficiently spaced from the suction ports (46) so that it is prevented from being drawn through the suction ports (46) and into the cylinder bore (20), thus eliminating slugging within the compressor (10).

Description: The present invention relates to multiple-cylinder axial compressors as specified in the preamble of claim 1, for example as disclosed in FR-A- 997 396. More particularly the present invention concerns an improved intake suction port arrangement in such a compressor providing increased reliability over the service life of the compressor. A variety of refrigerant compressors for use in vehicle air-conditioning systems are currently available. A popular axial-type compressor design includes multiple cylinders with double-acting pistons. In this type of compressor, the cylinders are equally angularly spaced about, and equally radially spaced from, the axis of a central drive shaft. One set of such cylinders is provided at each of two opposing ends of the compressor. A double piston is mounted for reciprocal sliding motion in each set of opposed cylinders. Each piston is reciprocated by a drive plate, more commonly called a swash-plate. During operation of the compressor, rotation of the drive shaft imparts a continuous wave-type reciprocating motion to the swash-plate. This driving of the swash-plate in a nutating path around the drive shaft serves to impart a linear reciprocating motion to the pistons. A thorough description of the operation of this type of compressor is disclosed in United States patent 4,360,321 (Copp, Jr. et al.). In this compressor, the intake of refrigerant fluid into the cylinder and discharge therefrom is controlled by uni-directional reed-type valves located in valve plates at the ends of each cylinder. Annular intake and discharge chambers are provided in the compressor heads at each end of the compressor. A single port accommodates the transfer of fluid from the intake chamber to each cylinder bore, and a second port accommodates the transfer of fluid from each cylinder bore to the discharge chamber. Improvements were previously made in this type of compressor by incorporating intake suction ports into the ends of the pistons themselves. The ports are arranged in an annular array with equi-angular spacing and at a constant radius from a longitudinal axis of each piston. Locating the intake suction ports in the ends of the pistons obviates the need for a separate intake chamber. More particularly, during operation of the improved compressor, refrigerant fluid is communicated into the compressor and directed to the internal cavity of a crankcase surrounding the swash-plate, that is, on the rear side of the pistons. As a piston begins its intake stroke, this refrigerant is sucked through the ports in the piston into a cylinder bore defined between the piston and a discharge valve plate. As the piston then begins its discharge stroke, reed valves block the return flow of the refrigerant through the ports in the piston, thereby forcing the refrigerant to discharge through a discharge port. Whilst this compressor design realizes several advantages over its predecessor, additional improvements are still possible. For example, under certain operating conditions the improved compressor design may suffer from "slugging." Slugging occurs when lubricating liquid enters the cylinder bore compression chamber (i.e. the region defined between each piston and the valve plate). As the piston begins its discharge stroke, it is forced to compress this liquid as well as the refrigerant gas in the chamber. Since the liquid is substantially incompressible, the discharge stroke of the piston is inhibited. Additionally, in a compressor subject to slugging, the compressor components are subjected to higher loads and stress. The trapped liquid slugs cause simulated shock or impact loading, especially as each piston nears the end of its stroke. This action causes not only repeated excess force and torque loading on the components, but greatly increases the noise during operation. Accordingly, a need clearly exists for a design improvement to reduce the adverse effects of slugging. The slugging problem primarily results from the re-location of the suction port assembly in each piston in the new design, referred to above. That is, the equi-angular port placement around the head of the piston necessarily results in the deleterious condition in which liquid pooled in the lubricant reservoir at the bottom of the compressor crankcase is susceptible to being drawn directly into the cylinder bore. To explain further, tiny liquid lubricant droplets are interspersed throughout the refrigerant gas as a mist. This mixture is introduced into the crankcase to provide lubrication for the swash-plate, bearings, and other internal components of the compressor. Gravity causes the liquid particles to collect and accumulate at the bottom of the crankcase. Under certain operating conditions, the liquid lubricant level rises above the lowermost suction ports in each piston, or the lubricant splashes up during hard cornering, braking or the like of the motor vehicle containing the compressor. Consequently, as each piston reciprocates, this liquid is directly drawn from the crankcase reservoir into the cylinder bore. It is accordingly a primary object of the present invention to provide an intake porting assembly in a piston of a refrigerant compressor for use in a vehicle air-conditioning system that reduces the aforesaid slugging. Another object is to provide an intake porting assembly in a piston of an automotive refrigerant compressor that provides improved performance. Still another object of the present invention is to provide an intake porting assembly in a piston of an automotive refrigerant compressor that yields both improved efficiency of operation, increased reliability, reduced stress on component parts and lower noise level over that of prior-art compressor porting systems. An improved suction port arrangement according to the present invention is characterised over FR-A- 997 396 by the features specified in the characterising portion of claim 1. Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following specific description of the invention. The improved compressor includes an intake suction port arrangement that substantially reduces the effects of slugging. In its broadest aspects, the improvement of the present invention relates to the arrangement of the suction ports in each piston of the compressor. More specifically, the suction ports are arranged such that the lowermost ports of the porting assembly, particularly in the lowest pistons of the compressor, are eliminated, but without sacrifice in performance of the compressor. In particular, a plurality of intake/suction ports extend longitudinally through the operating head end of each piston. Uni-directional flow through the ports is assured by a valve disc comprising a flexible ring supported from the centre by a cross-piece. The ring flexes away from the piston to permit fluid to flow during the expansion, intake stroke of the piston from the crankcase through the piston suction ports and into the cylinder bore, i.e, the compression chamber. In contrast, the ring blocks retro-fluid flow through the ports from the cylinder bore to the crankcase during the compression stroke of the respective piston. More specifically, as each piston reciprocates within the cylinder, a constantly changing pressure differential is realized between the crankcase and the compression chamber. During the intake stroke, the volume of the compression chamber increases, thereby creating a low pressure region. Since the crankcase region maintains a relatively constant pressure, a positive pressure differential is realized between the two resulting in a suction force through the ports causing fluid to flow from the crankcase into the compression chamber. On the discharge stroke, the volume of the compression chamber is decreased, thereby resulting in a high pressure region. The resulting negative pressure differential created between the crankcase and the compression chamber causes the fluid in the compression chamber to attempt to return through the suction ports to the crankcase. However, the reed valves cover the suction ports preventing such a reverse flow of fluid. Accordingly, the fluid within the compression chamber is forced into a discharge chamber through a discharge valve provided at the end of the cylinder. The refrigerant fluid then exits the compressor and is used to condition air. The suction port assembly of the present invention is characterized by the ports being connected by a channel and preferably asymmetrically arranged about a central horizontal axis. While consecutive ports are positioned with a constant radial and circumferential spacing, a discontinuity in the spacing is observed at the lower portion of the piston. Several advantages and benefits result from the elimination of ports in the lower part of the piston; that is, about an arc of substantially 120°. Among these benefits is the reduced effects of slugging, thereby yielding enhanced compressor performance. As previously described, slugging occurs when liquid escapes the crankcase and enters the compression chamber. The effects are greatly intensified once the liquid level of the crankcase reservoir rises to a level equal to or above that of one or more of the suction ports. By eliminating the lowermost ports, the liquid lubricant in the crankcase cannot be drawn directly through a port into the compression chamber. In the operation of the compressor, the liquid level in the reservoir remains at a substantially constant level. The present invention takes advantage of this and positions the lowermost ports above the equilibrium liquid level reached under any operating condition, thereby significantly reducing, and all but eliminating, the slugging problem. By reducing the effects of slugging, a number of benefits are realized. For example, the compressor provides a greater throughput and therefore operates at a higher efficiency. Hence, improved cooling capacity of the air-conditioning system is realized. An additional benefit is observed in compressor reliability. As liquid is effectively prevented from being drawn directly into the compression chamber, the piston reciprocates much more freely, thereby reducing stress on internal bearings and other parts. Further, by retaining more liquid within the crankcase, a greater supply of lubricant is provided for the internal parts. The combination of better lubrication and smoother operation directly translates into a longer lasting compressor. Further, shock-loading is eliminated, and the noise of operation is greatly reduced. Still other objects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, there are other different embodiments of the invention and several details of this preferred embodiment are capable of modification in various, obvious aspects all without departing from the scope of the invention as claimed in the appending claims. Accordingly, the drawings and descriptions of this preferred embodiment should be regarded as illustrative in nature and not as restrictive. The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of an entire compressor according to the present invention including a lower piston, an upper suction port within that piston being shown in full line, and a lower suction port being shown in phantom line; and Figure 2 is an exploded perspective view of the piston of Figure 1, showing a novel configuration of a suction port array and a corresponding reed valve. Reference is now made to Figure 1 illustrating a cross-section of a swash-plate type compressor, generally designated by reference numeral 10. The compressor 10 includes an improved intake suction porting assembly 12, at least, in a lower piston 22 (see Figure 2) and constructed in accordance with the present invention. As should be appreciated from a review of the following description, the suction porting assembly 12 of the present invention improves compressor efficiency, reliability and quietness. These advantages result from elimination of ingestion of liquid lubricant into a compression chamber 14 of a cylinder bore 20 on an intake stroke of the piston 22. It should also be appreciated that the present invention is in no way limited to utilization in swash-plate compressors incorporating double-ended pistons of the type described. Rather, the concepts of the present invention can also be adapted to other compressor configurations as well. As is known in the art and shown, for example, in U.S. Patent 4,351,227 (Copp Jr. et al.), the swash-plate compressor 10 includes a front and a rear cylinder block 18F,18R, respectively, in which is provided a crankcase, generally designated by the reference numeral 19. The crankcase 19 contains two oppositely-disposed and aligned sets of axial cylinder bores 20. One bore 20 of each set is provided in each cylinder block 18F and 18R. Only the lower bores 20 in the blocks 18F, 18R are shown in Figure 1. Any suitable number of sets, such as five may be employed. A double-headed piston 22 is slidingly engaged for reciprocal motion within each set of the cylinder bores 20. The reciprocating action of the pistons 22 is utilized to compress the refrigerant. The compressed refrigerant is discharged from a discharge port 24 in each end walls and is subsequently transferred from the compressor 10 for utilization by an air-conditioning system to condition air being directed to a vehicle interior (not shown). The low pressure refrigerant gas is then returned to the compressor 10 to an inlet port 26 to complete the cycle. A central drive shaft 28 is axially aligned within the cylinder blocks 18F, 18R of the crankcase 19. The drive shaft 28 extends externally from the crankcase 19 and is attached through a clutch 30 to a pulley 32. A drive belt 34 is attached to the pulley 32 and to an engine (not shown) of the vehicle. During engine operation, the drive belt 34 transmits power from the engine through the pulley 32 and the drive shaft 28 to the compressor 10. A swash-plate 36 is provided for reciprocating the pistons 22 through attachment to the drive shaft 28. It is observed that, at any particular piston 22, the angle of the swash-plate 36 constantly changes as the swash-plate rotates, thus generating a continuous wave form and thereby imparting the reciprocating motion to each piston 22. Bearings 38 are provided as a part of each piston assembly to minimize the frictional resistance. A constant flow of lubricant fluid is maintained over the bearings and other operating components within the crankcase 19. In operation,low-pressure refrigerant fluid is introduced into an inlet chamber 39 of the compressor 10 through the inlet port 26 and passes into a crankcase chamber 42. The refrigerant fluid is in gaseous form with a liquid lubricant mist interspersed therein. The lubricant coats all the internal components that it contacts, such as the swash-plate 36 and bearings 38. The excess lubricant drops to the bottom of the crankcase 19 forming a pool P of the lubricant where it is then re-circulated, as is known. Reference will now be made to both Figures 1 and 2 in describing the preferred embodiment of the present invention. The suction port assembly 12 is provided in operating head ends 23 of at least the lower double-ended piston 22. Individual suction ports 46 formed in the piston head ends 23 are circular passages that extend longitudinally through each piston head end 23 and are connected on the face of the piston head end 23 by a 360° channel 47. During an intake stroke of the piston 22 refrigerant gas passes through these suction ports 46 and is drawn from the chamber 42 into each of the compression chambers 14 in turn. The ports 46 are annularly arranged on each head end 23 of the piston 22, whereby a constant radius arc is maintained from a central longitudinal axis L (see Figure 2). Additionally, there is equi-angular spacing, i.e. the angular separation in the array of the ports 46, is constant and maintained at substantially 30° between each port in the preferred embodiment. However, in accordance with the invention, the ports 46 are positioned in a horizontally asymmetrical arrangement. That is, there are no ports included in the lowermost portion of each piston head end 23. More particularly, the lowermost ports extend only substantially 30° below the horizontal centre-line of each piston head end 23. Accordingly, the ports are excluded from the lowermost portion of each piston head end 23. More specifically, the exclusion of the ports extends in an arc of substantially 120° about the bottom of the piston; that is 60° each side of bottom dead centre. This spacing is established by empirical means and data calculations, so that under normal operating conditions, the liquid pool P in the crankcase reservoir does not rise to the height of these lowermost ports 46. Hence, the ports are sufficiently spaced above the pool P so that there is no direct drawing of liquid lubricant with the gaseous refrigerant into the lowermost compression chamber 14, and the prior-art slugging problem is essentially avoided. There can be one or multiple ports 46, so long as the diameter of the port(s) is sufficient to provide an aggregate flow volume of the refrigerant to substantially fill the associated compression chamber 14 on the intake stroke. It can be appreciated that, if the diameter of the ports 46 is too small, the throughput of refrigerant is decreased, thereby diminishing the overall performance of the compressor 10. The suction porting assembly 12 includes a unitary reed valve disc 48. This disc 48 has a central support cross-piece and a ring 50 that extends in a circle to coincide with the suction ports 46 and the channel 47. The ring 50 has a width sufficient to cover all of channel 47 and thus all of the suction ports 46. The disc 48 is attached to the piston 22 by a central fastener 52. Further, the combination of the material composition and the thickness of the unitary disc 48 is sufficient to provide adequate strength and memory for the ring 50, whereby proper operation is realized. During the intake stroke of the piston 22, the positive pressure differential between the crankcase 19 and the compression chamber 14 forces the ring 50 to flex open; that is, to lift up and move away from the face of the piston head end 23 and to uncover the channel 47 and the end of each port 46 (see left-hand piston head end 23 shown in Figure 1). This allows the refrigerant gas to pass from the crankcase 19 through the ports 46 into the compression chamber 14. As the discharge stroke begins and a negative pressure differential is realized, the disc 48 flexes back and closes, the ring 50 seating against the face of the piston head end 23 and sealing the suction ports 46 (see right-hand piston head end 23 shown in Figure 1). The presence of the channel 47 allows the pressure to equalize between the individual ports 46 to smooth the flow of refrigerant. As the discharge stroke continue, the refrigerant is pressurized to the designed level within the compression chamber 14. In response, a discharge reed valve 54, provided at the discharge port 24, opens at the proper time to allow the refrigerant to pass from the compression chamber 14 and into a discharge chamber 56. This discharge chamber 56 is an annular cavity provided in each one of both compressor heads 40F and 40R. The chamber 56 is connected to a compressor outlet port (not shown) where the refrigerant is removed from the compressor 10 and directed to the remainder of the automobile air conditioning system to condition the air within the motor vehicle in which the compressor is installed. In summary, various benefits and advantages are realized by the suction porting assembly 12 of the present invention. Among these advantages are smoother piston 22 operation, increased refrigerant throughput, enhanced compressor 10 reliability, and reduced noise. These benefits combine to result in a product providing improved quality, performance, and correspondingly, customer satisfaction.

Claims: A suction port arrangement (12) in a refrigerant compressor (10) of the type having a piston (22) operating in a horizontally-extending cylinder bore (20) of a cylinder block (18F,18R) and including a crankcase (19) having a cavity for a pool (P) of liquid lubricant adjacent the bottom of the crankcase (19), the suction port arrangement (12) comprising a plurality of suction ports (46) extending through an operating head end (23) of the piston (22) so as to provide refrigerant fluid communication for compressing refrigerant fluid in the bore (20); and valve means (48) for providing uni-directional refrigerant fluid flow through the suction ports (46); wherein each suction port (46) is horizontally positioned in the head end (23) so as to be excluded from the lowermost portion of said piston (22) whereby in use the ports are spaced above said pool (P) of lubricant and liquid lubricant from said pool (P) is substantially prevented from flowing through said suction port (46) to eliminate slugging within said compressor; characterised by a channel (47) extending between the suction ports (46) and covered by the valve means (48) to substantially equalise the pressure of refrigerant fluid between the suction ports (46). A suction port arrangement (12) according to claim 1, wherein the suction ports (46) are arranged asymmetrically on the piston head end (23). A suction port arrangement (12) according to claim 2, wherein the suction ports (46) are positioned along a constant radius arc around the head end (23) of the piston (22) with an angle of substantially 30° separating consecutive suction ports (46). A suction port arrangement (12) according to any one of claims 1 to 3, wherein the valve means (48) includes a flexible ring (50) supported from the centre of the piston head end (23).

Inventors: PETTITT EDWARD DOUGLAS, PETTITT, EDWARD DOUGLAS
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1993
Main classification: F04B39
IPC codes: F04B39, F04B27