Slider block radial compliance mechanism

Abstract: The orientation of the elements of a slider block (20) radial compliance mechanism for a scroll compressor (10) is such that the point of application of the actuating force is shifted from a first line extending through the center of gravity of the counterweight (32) and the axis of the crankshaft (30) to a second line parallel to said first line and extending through the axis of the orbiting scroll (10). The result of the changed orientation is an increase in the magnitude of both the sealing force between the scroll elements and the actuating force to move the mechanism.

Description: The present invention relates to a slider block radial compliance mechanism. In a scroll compressor the trapped volumes are in the shape of lunettes and are defined between the wraps or elements of the fixed and orbiting scrolls and their end plates. The ends of the lunettes define points of tangency or contact between the wraps of the fixed and orbiting scrolls. These points of tangency or contact are transient in that they are continuously moving towards the center of the wraps as the trapped volumes continue to reduce in size until they are exposed to the outlet port. These points of tangency or contact represent points of wear and leakage so it is desirable to permit outward radial movement of the orbiting scroll to maintain sealing contact of its wrap with that of the fixed scroll. Further, because the trapped volume may contain a liquid slug of refrigerant and/or oil it is desirable to permit inward radial movement of the orbiting scroll to permit leakage from the trapped volume(s) to relieve any excessive buildup of pressure. One approach has been to use an eccentric bushing mechanism to provide the connection between the crankshaft and the orbiting scroll. Another approach has been to use a swing link connection between the orbiting scroll and crankshaft. Typical radial compliance devices are shown in US-A-3,924,977. In this patent, the centrifugal force of the orbiting scroll is used to activate the mechanism. The line of movement of the orbiting scroll is along the centrifugal force, i.e. along the line extending from the center of gravity of the counterweight through the center of the crankshaft to the center of the orbiting scroll. In particular, US-A-3 924 977 (Figure 20) discloses a swing-link radial compliance assembly where a counterweight affixed to the orbiting scroll is used to counterbalance the centrifugal force and provide a radial sealing force. The swing-link mechanism can be replaced by a sliding block mechanism. In the aforementioned US-A-3 924 977 (Figure 21-23) there is further described a slider block radial compliance mechanism according to the preamble of claim 1. It is an object of this invention to provide an improved radial compliance mechanism permitting a greater sealing force between the scroll elements and an increase in efficiency of a scroll compressor by reducing the leakage. It is a further object of this invention to increase the activating force of a radial compliance mechanism. To achieve this, the slider block radial compliance means of the invention is characterized by the features set forth in the characterizing part of claim 1. Basically, according to the invention, radial compliancy is achieved by locating the recess means receiving the slider block asymmetrically with respect to the plane defined by the crankshaft axis and the center of gravity of the counterweight, the axis of the orbiting scroll being spaced from that plane. The orientation of the elements is changed such that a combination of centrifugal and gas forces are used to activate the mechanism and provide a sealing force between the scroll elements. By changing the orientation of the elements according to the teachings of the present invention, the magnitude of both the sealing force between the scroll elements and the actuating force to move the mechanism are increased. This permits an increase in efficiency due to the reduced leakage resulting from the increased sealing force which also permits the wraps to wear in more quickly. Basically, the common axis of the orbiting scroll and the slider block is displaced perpendicularly so as to be located in parallel with the plane containing the axis of the crankshaft and the counterweight center line/center of gravity. As a result, movement of the slider block and the axis of the orbiting scroll is in a plane spaced from and parallel to the plane containing the axis of the crankshaft and the counterweight center line/center of gravity. The angle formed between the line joining the axis of the crankshaft and the counterweight center line/ center of gravity and the extension of the line joining the center of the orbiting scroll and the axis of the crankshaft influences the value of the resultant sealing force and the centrifugal or actuating force. For a fuller understanding of the present invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings wherein; Figure 1 is a vertical sectional view of a portion of a scroll compressor employing the slider block mechanism of the present invention; Figure 2 is a sectional view of the slider block mechanism taken along line 2-2 of Figure 1; Figure 3 is a sectional view corresponding to that of Figure 2 but with the activating and centrifugal forces acting along the same line as suggested by the PRIOR ART represented by U.S. Patent 3,924,977; Figure 4 is a force diagram corresponding to Figure 2; and Figure 5 is a graph of the sealing forces vs. the offset angle. In Figure 1, the numeral 10 generally indicates a scroll compressor which is only partially illustrated. Scroll compressor 10 includes an orbiting scroll 12 and a fixed scroll 14. Orbiting scroll 12 has a boss 12-2 which is received in bore 20-1 of slider block 20. As best shown in Figure 2, slider block 20 is slidably received in recess 30-1 of crankshaft 30 but a reciprocating motion of slider block 20 in recess 30-1 is the only relative motion permitted between crankshaft 30 and slider block 20 other than generally insignificant movement permitted by the clearances between block 20 and recess 30-1. During operation, as crankshaft 30, counterweight 32 and slider block 20 rotate together about O s the axis of crankshaft 30, centrifugal force contributes to an actuating force which causes slider block 20 to move outwardly in recess 30-1 relative to O s carrying boss 12-2 and, therefore, orbiting scroll 12 with it. As noted above, a preliminary concept of slider block radial compliance is briefly mentioned in U.S. Patent No. 3,924,977. This patent teaches the use of the centrifugal force, F c , of the orbiting scroll to activate the radial sealing mechanism. This is illustrated in Figure 3 which adapts the teachings of U.S. Patent No. 3,924,977 to the slider block mechanism of the present invention. Structure is labeled one hundred higher than corresponding structure in Figures 1 and 2. The line of movement of the orbiting scroll is along the force, F′ c , i.e. the line of movement which represents the actuating force is along the line from O c , the counterweight center line/center of gravity, through O s , the center of crankshaft 130 to O R , the center of orbiting scroll. F c minus the radial gas force F GR is the sealing force, F seal . Slider block 120 thus moves in recess 130-1 along the straight line defined by O c , O s and O R carrying boss 112-2 of the orbiting scroll. Referring now to Figures 2 and 4, and comparing them to Figure 3, it will be noted that the line of movement which represents the axis of relative movement between slider block 20 and crankshaft 30 as well as the location of F′ c is displaced. Specifically, the y-axis always goes through O s and O c and, for the Figure 3 device, also goes through O R . Thus in the Figure 3 device the centrifugal force, F c , acts along the y-axis. In the Figure 2 device, O R is located in and moves in a plane which is parallel to the plane defined by O s , O c and the y-axis. The actuating force, F′ c , is thus displaced with respect to the y-axis. The angle, α formed between the line joining the axis of the crankshaft, O s , and the counterweight center line/center of gravity, O c , and the extension of the line joining the center of the orbiting scroll, O R , and O s represents the vector orientation of the radial gas force, F gr , and the tangential gas force, F gt , relative to the Figure 3 orientation. In Figure 3, the gas forces are along the x and y-axes, but, in Figures 2 and 4, the radial gas force acts along the line between O R and O s while the tangential gas force is perpendicular thereto. Thus, the tangential and radial gas forces each have components along both the x and y-axes. In the Figure 3 configuration, the centrifugal force, F′ c is directly opposed by the radial gas force, F gR , since they both act along the y-axis. The tangential gas force F gT acts along the x-axis. The gas forces are produced by the gas in the trapped volumes between the wraps 14-1 and 12-1 of the fixed and orbiting scrolls 14 and 12, respectively, and oppose F′ c with the net force being the sealing force, F seal . In the configuration of Figures 2 and 4, there is an x and a y component of both F gR and F gT . The y component of the radial gas force, F gRy , is equal to F gR cos α while the y component of the tangential gas force, F gTy , is equal to F gT cos (90-α). As a result, the opposition to F′ c provided by F gR is reduced to F gR cos α while F gT now provides an assist to F' c equal to F gT cos (90-α). The resultant increase in the net effective sealing force is plotted in Figure 5 which clearly shows the increase in F seal with the increase in the offset angle, α. The point at O° represents the Figure 3 configuration for a sealing force of 444.8N (100 pounds of force). The increase in the net sealing force is limited by how much the slider block 20 can be displaced within the crankshaft 30. If for example, is limited to about 30 the value of the net sealing force will be tripled. If should be noted that O R , and therefore the value of α, as well as e, the distance between O R and O s and the orbiting radius of orbiting scroll 12, can change as slider block 20 moves in slot 30-1 due to wear or to a liquid slug trapped between the wraps 12-1 and 14-1. The net tangential gas force acting along the x-axis is equal to F gTX plus F gRx or F gT cos α plus F gR cos (90-α). Since the x-axis component F gT is reduced but the x-axis component of F gR is increased, the net tangential gas forces are less influenced by α than the net radial gas forces. Further, the net tangential gas forces do not have a significant effect on the operation of scroll compressor 10 relative to the net radial gas forces. Movement of slider block 20 is also opposed by a frictional force which is shown in Figure 4 but has no significant influence on the operation of the present invention. The present invention thus teaches the change in orientation from that of Figure 3 to that of Figure 2 such that a combination of centrifugal and gas forces are used to activate the slider block 20 and provide a sealing force between the scroll elements. By changing the orientation from that of Figure 3 to that of Figure 2, the magnitude of F seal , the sealing force between the scroll elements, and of its component F′ c , the activating force to move slider block 20, is increased as illustrated in Figure 5. From the foregoing, it should be clear that F seal which corresponds to the contact force between the wraps 12-1 and 14-1 is, ideally, a small positive number within the boundary of operation so as to maintain a direct contact between the wraps while reducing any friction and wear between them. Thus, as shown in Figure 5 an increase in the offset angle between the line joining O s and O c and the extension of the line joining O R and O s results in a substantial favorable increase in F seal . Although a preferred embodiment of the present invention has been illustrated and described, other changes will occur to those skilled in the art. For example, although orbiting scroll 12 is described and illustrated as having a boss 12-2 which is received in bore 20-1 of slider block 20, slider block 20 could be provided with a boss which is received in a recess in orbiting scroll 12.

Claims: A slider block radial compliance mechanism (20,30-1) in a scroll compressor means (10) having an orbiting scroll means (12) having an axis (O r ), a fixed scroll means (14), crankshaft means (30) having a first and a second end and adapted to rotate about an axis (O s ) of said crankshaft means (30), counterweight means (32) having a center of gravity (O c ) spaced from said axis (O s ) of said crankshaft means (30) and being rotatable with said crankshaft means (30), said slider block radial compliance mechanism (20,30-1) comprising: a recess means (30-1) formed in said first end of said crankshaft means (30) in the direction of said axis (O s ) of said crankshaft means (30), and a slider block means (20) located in said recess means (30-1) and coacting therewith such that substantially only relative reciprocating movement of said slider block means (20) in said recess means (30-1) is possible, the orientation of said recess means being such that said reciprocating movement is parallel to a plane defined by said axis (O s ) of said crankshaft means and said center of gravity (O c ) of said counterweight said slider block means (20) and said orbiting scroll means (12) coacting together such that relative rotary motion about said axis (O r ) of said orbiting scroll means (12) is possible between said slider block means (20) and said orbiting scroll means (12), and said orbiting scroll means (12) is moved with said slider block means (20) when said slider block means (20) moves in relative reciprocating movement in said recess means (30-1), characterized in that said recess means (30-1) is asymmetrically located with respect to a plane defined by said axis (O s ) of said crankshaft means (30) and said center of gravity (O c ) of said counterweight means (32), the said counterweight means (32) being affixed to said crankshaft means (30), said axis (O r ) of said orbiting scroll means (12) being spaced from said plane defined by said axis (O s ) of said crankshaft means (30) and said center of gravity (O c ), such that aid relative reciprocating movement of said slider block means (20) causes said axis (O r ) of said orbiting scroll means (12) to move in a plane spaced from and parallel to said plane defined by said axis (O s ) of said crankshaft means (30) and said center of gravity (O c ) of said counterweight (32). The slider block radial compliance mechanism of claim 1, characterized in that a boss (12-2) is formed on said orbiting scroll means (12) and received in a bore (20-1) formed in said slider block means (20).

Inventors: ETEMAD SHAHROKH, FRASER HOWARD HENRY JR, ETEMAD, SHAHROKH, FRASER, HOWARD HENRY, JR.
Applicants: CARRIER CORP, CARRIER CORPORATION
Application year: 1990
Main classification: F04C29
IPC codes: F04C29, F04C18