Variable swash plate compressor

The present invention relates generally to a swash plate compressor and more particularly to improvements to such a compressor so that the size, energy consumption, and vibrational characteristics are minimized.

Conventional swash plate compressors utilize a rotating swash plate, driven by a drive shaft, to drive a piston. The piston is used to transfer fluid from the low pressure side of an air conditioning system or other device to the high pressure side. Conventional swash plate compressors utilize an elbow to transfer the rotational drive of the drive shaft to the swash plate. The utilization of an elbow, or similar mechanism, to transfer the rotational drive of the drive shaft has several undesirable characteristics. This conventional design transfers undesirable stresses to the swash plate requiring the swash plate to be designed for a higher strength. This adds to the size, weight, and cost of the swash plate compressor. The presence alone of the elbow or similar mechanism adds to the size, weight, complexity and manufacturing cost of the conventional swash plate compressor. In addition, the elbow, as it rotates with the drive shaft, limits the potential travel distance of the piston. The presence of the elbow additionally prevents the use of a double-sided piston to provide pumping action in both directions of piston travel.

It is known that varying the angle of the swash plate relative to the drive shaft allows the swash plate compressor to produce variable fluid transfer rates. One known design utilizes a biasing spring and the crankcase pressure within the compressor to vary the angle of the swash plate. This crankcase pressure can lead to undesirable stresses on the swash plate and can have a negative effect on the vibrational characteristics of the swash plate compressor.

Finally, the piston driving mechanisms in known variable swash plate compressors utilize multiple pivot locations. The swash plate itself typically slides and/or rotates axially on the drive shaft, the elbow joint slides and/or rotates about a pin in the elbow, and the piston joint rotates about its connection with the swash plate. The position and rotation of the swash plate, the elbow, and the piston in relation to each pivot location controls the path of the piston. These multiple pivot locations often result in a variable Top-Dead-Center (“TDC”) of the piston. The TDC of the piston is the distance between the piston face and the piston chamber outlet face at the top of the piston cycle. Variations in the piston TDC result in undesirable variations in the variable swash plate compressor's output.

Therefore, there is a need for a variable swash plate compressor design that reduces the stresses in the swash plate, allows for greater piston travel without increasing the compressor size, (allows for double-sided pistons), reduces undesirable vibrational characteristics, reduces variation in piston TDC, and reduces the size, weight, and manufacturing cost of known variable swash plate compressor designs.

It is therefore an object of the present invention to provide a variable swash plate compressor that reduces the stress in the swash plate, reduces vibrations in the compressor, and reduces the variation in piston TDC. It is a further object of the present invention to provide a variable swash plate compressor that doubles the output of a given size compressor through the use of double-sided pistons. It is a further object of the present invention to provide a variable swash plate compressor that reduces the size, weight, and manufacturing costs associated with conventional swash plate compressor design.

In accordance with the objects of this invention, a variable swash plate compressor is provided. The variable swash plate compressor includes a housing, a drive shaft and a control surface element. The control surface element is attached to and receives a rotational drive force from the drive shaft. The control surface element has a pinnacle element attached thereto.

The variable swash plate compressor also includes a swash plate with a bore located in its center. The control surface element sits within the bore of the swash plate. The swash plate also includes a pocket in which the pinnacle element is seated. The drive shaft transmits a rotational drive force to the swash plate through the control surface element seated in the bore of the swash plate and the pinnacle element seated in the swash plate pocket.

The variable swash plate compressor also includes a double-sided compression piston positioned within a piston chamber formed in the housing. As the double-sided compression piston moves within the piston chamber it alternates between simultaneously drawing fluid into the bottom of the piston chamber through a bottom inlet while forcing fluid within the top of the piston chamber out of the top outlet and simultaneously drawing fluid into the top of the piston chamber through a top inlet while forcing fluid within the bottom of the piston chamber out of the bottom outlet. The double-sided compression piston is moved in this cyclical fashion by remaining in contact with the rotating swash plate such that only axial forces are transmitted between the swash plate and the double-sided compression piston. As the angle between the swash plate and the drive shaft is increased, the travel path of the double-sided compression piston is increased resulting in an increase in the output of the variable swash plate compressor.

The variable swash plate compressor also includes a fulcrum piston assembly for controlling the angle of the swash plate relative to the drive shaft. As the angle of the swash plate relative to the drive shaft is increased, the output of the variable swash plate compressor is increased. The fulcrum piston assembly changes the angle of the swash plate by exerting a force on the swash plate causing it to pivot about the tip of the pinnacle element. The tip of the pinnacle element orbits the axial center of the drive shaft at a distance equal to the distance from the center of the drive shaft to the axial center of the double-sided compression piston. By pivoting the swash plate about a point that orbits over the axial center of the double-sided compression piston, variation in the TDC of the double-sided compression piston is reduced.

Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.

FIG. 1 is a perspective view of a preferred embodiment of a variable swash plate compressor in accordance with the present invention;

FIG. 2 is a cross-sectional view of the variable swash plate compressor illustrated in FIG. 1, the cross-section being taken along the line 2 - 2 in FIG. 1 and in the direction of the arrows, the cross-section illustrating the variable swash plate compressor in its non-idle position;

FIG. 3A is a side view of the drive shaft illustrated in FIG. 2;

FIG. 3B is a top view of the drive shaft illustrated in FIG. 2;

FIG. 4A is a top view of the swash plate illustrated in FIG. 2;

FIG. 4B is a cross-sectional view of the swash plate illustrated in FIG. 4A, the cross-section being taken along the line 4 B— 4 B in FIG. 4 A and in the direction of the arrows;

FIG. 5 is a cross-sectional view of the variable swash plate compressor illustrated in FIG. 1, the cross-section being taken along the line 2 — 2 in FIG. 1 and in the direction of the arrows, the cross-section illustrating the variable swash plate compressor in its idle position; and

FIG. 6 is an illustration of the drive shaft, swash plate, control surface element and pinnacle element illustrated in FIG. 2 .

Referring now to FIG. 1, which is a schematic view of a variable swash plate compressor 10 in accordance with the present invention. The disclosed variable swash plate compressor 10 is preferably for use in automotive air conditioning applications. However, the disclosed variable swash plate compressor 10 may be used in a variety of applications, including non-automotive applications.

Referring now to FIG. 2, which is a cross-sectional view of the variable swash plate compressor 10 in accordance with the present invention. The variable swash plate compressor 10 includes a housing 12 . In the embodiment shown in FIG. 2, the housing 12 is comprised of a top housing section 12 A, a middle housing section 12 B, and a bottom housing section 12 C. A top inlet 14 A located within the top housing 12 A and a bottom inlet 14 B located within the bottom housing 12 C are both in fluid communication with each other and with a pumping chamber 16 located within the middle housing 12 B. The bottom inlet 14 B is in fluid communication with a source of fluid outside the compressor 10 . A double-sided compression piston 18 situated within the pumping chamber 16 moves up and down along its radial axis within the pumping chamber 16 . As the double-sided compression piston 18 moves up, it draws fluid from the bottom inlet 14 B into the bottom of the pumping chamber 16 and simultaneously expels fluid within the top of the pumping chamber 16 into a top outlet 20 A. As the double-sided compression piston 18 moves down, it draws fluid from the top inlet 14 A into the top of the pumping chamber 16 and simultaneously expels fluid within the bottom of the pumping chamber 16 into a bottom outlet 20 B. The top inlet 14 A and the bottom inlet 14 B are in fluid communication with each other to allow both to be supplied with fluid from a single source in communication with the bottom inlet 14 B. In other embodiments, both the top inlet 14 A and the bottom inlet 14 B are in fluid communication with an outside source of fluid independently. The top outlet 20 A and the bottom outlet 20 B are in fluid communication with each other to provide a singe location for fluid to exit the compressor 10 . In other embodiments, the top outlet 20 A and the bottom outlet 20 B may each allow fluid to exit the compressor independently.

The double-sided compression piston 18 is activated through the use of a drive shaft 22 located with the housing 12 . In one embodiment, the drive shaft 22 is imparted with a rotational drive force from a source outside the variable swash plate compressor 10 . Alternatively, the drive shaft 22 may be imparted with a rotational drive force from a source within the variable swash plate compressor 10 . A control surface element 24 is affixed to the drive shaft 22 and rotates in unison with the drive shaft 22 . A pivot element 26 is affixed to the control surface element 24 and travels in a path radially around the axis of the drive shaft 22 . FIGS. 3A and 3B illustrate the assembly of the drive shaft 22 , the control surface 24 and the pivot element 26 . Alternatively, the drive shaft 22 , the control surface element 24 , and the pivot element 26 may all be formed as a single element.

As the drive shaft 22 rotates, it imparts a drive force through the control surface 24 and the pivot element 26 to a swash plate 28 . The swash plate 28 is formed with a bore 30 in which the control surface element 24 sits. The swash plate 28 is additionally formed with a pocket 32 in which the pivot element 26 sits. FIGS. 4A and 4B illustrate the swash plate 28 , the bore 30 and the pocket 32 . Through the bore 30 and the pocket 32 , the rotational drive of the drive shaft 22 is imparted to the swash plate 28 . The pocket 32 is preferably formed in the center plane of the swash plate 28 such that the drive imparted to the swash plate 28 is primarily rotational and such that stresses within the swash plate 28 are minimized.

The swash plate 28 is connected to the double-sided compression piston 18 through the use of a ball joint 36 located within a generally c-shaped opening 38 in the piston 18 . The ball joint 36 prevents the majority of the rotational drive force of the swash plate 28 from being transmitted to the double-sided compression piston 18 . When the swash plate 28 is positioned at an angle β from a position perpendicular to the drive shaft 22 , it moves the double-sided compression piston 18 axially within the pumping chamber 16 as the swash plate 28 rotates with the drive shaft 22 . As the angle β is increased the travel path of the piston 18 is increased and the pumping capacity of the variable swash plate compressor 10 is increased. As the angle β approaches zero and the swash plate 28 becomes approximately perpendicular to the drive shaft 22 , the output of the variable swash plate compressor 10 is minimized (see FIG. 5 ).

The angle β of the swash plate 28 is increased by pivoting the swash plate 28 about the pivot element 26 (see FIG. 6 ). The pocket 32 located within the swash plate 28 and the pivot element 26 are shaped such that the swash plate 28 pivots about the pivot element tip 39 . The pivot element tip 39 is positioned at a distance from the axial center of the drive shaft 22 approximately equal to the distance from the axial center of the double-sided compression piston 18 to the axial center of the drive shaft 22 . This allows variations in the top-dead-center (“TDC”) of the double-sided compression piston 18 to be minimized at all angles β of the swash plate 28 . Minimization of TDC variations allows for greater control of the variable swash plate compressor 10 output.

The angle β of the swash plate 28 is varied through the use of a fulcrum piston assembly 40 . The fulcrum piston assembly is comprised of a fulcrum element 41 and a control piston 42 . The fulcrum element 41 is connected to the control piston 42 through the use of thrust bearings 44 to allow the fulcrum element 41 to rotate with the drive shaft 22 . Fluid pressure in the output chamber 46 controls the position of the fulcrum piston assembly 40 and subsequently the angle β. A control valve 48 , through a connection 49 with the output chamber 46 , increases the pressure in the output chamber 46 during periods where increased compressor capacity is required. During periods where it is desirable for the compressor to remain idle, the control valve 48 allows the fluid pressure in the output chamber 46 to drop and the fulcrum piston assembly 40 drops allowing the swash plate 28 to position itself nearly perpendicular to the drive shaft 22 . The advantage of using this pressure controlled system for adjusting the angle β of the swash plate 28 , as opposed to using known spring biased or crackcase pressure designs, is that the fulcrum piston assembly 40 acts as a damper to minimize vibrations in the rotating swash plate 28 . In another embodiment, the control valve 48 may also be used to allow a bleed line, with a bleed input 50 and a bleed output 52 , to allow portions of fluid from either the top inlet 14 A or the bottom inlet 14 B to be in fluid communication with the crankcase 54 . This allows moving parts within the crankcase 54 to be cooled and lubricated.

Although the present embodiment was described with a single double-sided compression piston 18 , multiple double-sided compression pistons may be used in the variable swash plate compressor 10 . One embodiment makes use of five double-sided compression pistons.

While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.