Scroll type compressor having a displaced discharge port
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a scroll type compressor having a seal at the tip of the spiral element. More specifically, the present invention relates to a sealing mechanism to improve durability of the seal. 
     2. Description of the Related Art 
     Gaseous fluid compressors have a wide variety of applications such as in an automobile air conditioning system and/or a refrigeration system. A variety of compressor architectures are available for application compatibility. Among those compressors, scroll type compressors have superior work efficiency and are suitable to be employed in a system requiring a small discharge displacement. Japanese Unexamined Patent Publication No. 3-92591 discloses a typical scroll type compressor. 
     As shown in FIGS. 7 and 8, a conventional scroll type compressor generally includes a fixed scroll 60 having a spiral element 50 that is formed on a end plate 55 and an orbiting scroll 61 is interfitted with the scroll 60. The fixed and orbiting scrolls 60, 61 include spiral elements 50, 51 that are formed on and continuous with the end plate, respectively. The orbiting scroll 61 is eccentrically disposed with respect to the center axis of the fixed scroll 60, and orbits around the above-described axis without self-rotation around its axis while both spiral elements 50, 51 are interfitted to form line contacts. Refrigerant gas is introduced into compression chambers P1, P2 defined by the spiral elements 50, 51 and the end plates 55, respectively. The air-tight compression chambers P1, P2 successively move toward the center portions of the spiral elements 50, 51 according to orbital rotation of the orbiting scroll 61. During the orbiting motion of the scroll 61, the volume of the compression chambers P1, P2 decrease. The compressed gas is discharged to a discharge chamber through a discharge port 54 that is formed in the central portion of the end plate 55 of the fixed scroll 60. 
     A groove 53 is formed in a tip end surface of the orbiting spiral element 51 that contacts with the fixed end plate 55. A seal 52 is accommodated in the groove 53 for improving air tightness within the compression chamber P1 that is defined by both spiral elements 50, 51. While the refrigerant gas is being compressed, the seal 52 is urged against the surface of the fixed end plate, in order to prevent the refrigerant gas leakage from the high pressurized compression chamber P1 to the low pressurized compression chamber P2. Further, as the compression chamber P1 approaches the discharge port, internal pressure thereof increases. Therefore, the seal 52 includes an enlarged portion 52a that is formed at the central end portion thereof. The enlarged portion 52a improves the air tightness of the compression chamber that is approaching the discharge port. 
     As shown in FIG. 7, the center of the discharge port 54 of the above-described conventional scroll type compressor is located on a line H that passes through an initial point E of inner peripheral surface S of the fixed spiral element 50 and a center point O 2  of involute generating circle K for generating an involute curve. The line H is perpendicular to the tangent line drawn at the initial point E of the inner peripheral surface S. Therefore, the compressed refrigerant gas is efficiently discharged from the minimized compression chamber P1 in the final compression stage through clearance defined in the vicinity of the initial point E of the discharge port 54. 
     However, the discharge port 54 is assigned to the fixed location such that the entire discharge port is enabled to be fit within the involute generating circle K. Therefore, a tip portion of the spiral element 51 that forms the minimized compression chamber P1 in the final compression stage covers almost the entire discharge port 54. At this moment, the entire tip portion of the enlarged tip portion 52a confronts against the discharge port 54. The tip portion of the enlarged tip portion 52a tends to bend inward into the discharge port 54 as indicated by a double dotted line in FIG. 8, based upon the suctional action of compressed gas flow. If the tip portion of the seal is repeatedly bent, the tip portion thereof is stressed so that the durability thereof may be lowered. Further, if the above-described case occurs, the tip portion of the enlarged tip portion 52a may hit to the edge of wall portion of the discharge port 54, and may be damaged. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary objective of the present invention to provide an improved scroll type compressor including a seal that is disposed in the distal surface of the spiral element of the orbiting scroll such that stress and wear of the seal are reduced. As a result, the durability of the seal is significantly extended. 
     To achieve the foregoing and other objects and in accordance with the purpose of the present invention, an improved scroll type compressor is provided. The compressor according to the teachings of the invention includes a fixed scroll having a fixed end plate and a fixed involute spiral element and an orbiting scroll having an orbiting end plate and an orbiting involute spiral element. The inner peripheral surface of the spiral element is defined by the locus of points of a curve generated based upon a phantom circle imaginarily located in the fixed end plate. The orbiting spiral element has an end surface with a groove dispersed therein contacting said fixed end plate, a fluid seal being dispersed within said groove. The fixed and orbiting spiral elements being radially and angularly offset and interfit with each other to provide line contacts extending between the fixed and orbiting plates defining a fluid pocket therebetween, which fluid pocket is urged to the center of the fixed and orbiting scrolls by the movement of the orbiting scroll. A discharge port is disposed in the fixed end plate remotely from the center of the phantom circle toward the tip of the fixed spiral element with a predetermined distance so as to minimize cantilever exposure of the terminal tip of the fluid seal over the discharge port. When the discharge port is completely removed from the center of the phantom circle so as not to communicate with the high pressure fluid pocket formed by, and at the center of, the fixed and orbiting spiral elements, then a communicating passage recess is disposed in the fixed end plate for communicating said final compression fluid pocket with said discharge port. Again the discharge port is located at a distance from the center of the phantom circle to minimize the cantilever exposure of the terminal tip of the fluid seal over the combined fluid discharge port and communicating passage. 
     Preferred embodiments of the invention include defining the predetermined portion of the center of the fixed and orbiting scrolls to be the locus of points of the phantom circle (K) that generales the involute curve of the inner peripheral surface of the fixed scroll involute spiral element having an inner terminal and starting point E 1 . The discharge port center (O 1 ) is located at a distance greater than the radius of the involute generating phantom circle (K) and has a smaller radius than the distance between the center (O 1 ) on a line (H) extending between the center of said involute generating circle K and said starting point (E 1 ). Further, the center (O 1 ) of the discharge port is located on the opposite side of the fixed involute inner peripheral surface (S 1 ) with respect to said line (H) and the radius of the discharge port is smaller than the perpendicular distance between the center (O 1 ) and the line (H). The preferred embodiment of the invention has a similarly spiral groove formed on the fixed spiral element of the fixed scroll into which a similar fluid seal is disposed so as to provide a fluid seal between the end surface of the fixed spiral and the orbiting end plate. The grooves and fluid seals of the inner end tips of the fixed and orbiting spiral elements have a wider width than other portions to provide increased fluid sealing in the maximum compression pocket. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The feature of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention, together with objects and advantages thereof, may best understood by reference to the following description of the preferred embodiments together with the accompanying drawings, in which: 
     FIGS. 1 through 6 illustrate an embodiment of a scroll type compressor according to the present invention, wherein: 
     FIG. 1 is a cross-sectional view of a fixed and orbiting spiral elements that are interfitted each other; 
     FIG. 2 is an enlarged cross-sectional view of tip portions of both spiral elements of FIG. 1; 
     FIG. 3 is a cross-sectional view taken along the line 3--3 shown in FIG. 2; 
     FIG. 4 is a perspective view of the tip portion of the spiral element shown in FIG. 2; 
     FIG. 5 is a cross-sectional view showing an entire scroll type compressor; 
     FIGS. 6A, 6B, 6C show an example of a communicating passage formed in the end plate; 
     FIG. 7 is a cross-sectional view showing both spiral elements of a conventional scroll type compressor; and 
     FIG. 8 is a cross-sectional view taken along the line 8--8 shown in FIG. 7. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment according to the present invention will now be described in greater detail, with reference to FIGS. 1 through 5. 
     A scroll type compressor shown in FIG. 5 includes a front housing 2, rear housing 3 and fixed scroll 1 integrally formed within a cylindrically shaped center housing 1e that is disposed between the front and rear housings 2 and 3. A drive shaft 4 is rotatably supported in a front housing 2 through a radial bearing 5. A shaft 6 eccentrically displaced with respect to the center axis of the drive shaft 4 projects axially inward from the inner distal portion of the shaft 4. A balance weight 7 and bushing 8 are rotatably mounted on the eccentric shaft 6. 
     An orbiting scroll 9 is accommodated in the center housing 1e. The orbiting scroll 9 includes an orbiting end plate 9a, an orbiting spiral element 9b that is integrally formed with one surface of the plate 9a, and a cylindrically shaped boss 9c. The boss 9c is integrally formed with the rear central portion of the plate 9a. Further, the boss 9c is in rotational communication with the periphery of the bushing 8, by means of a radial bearing 10, such that the orbiting scroll 9 is able to rotate relative to the bushing 8. As shown in FIGS. 1 and 5, the fixed scroll 1 includes a fixed end plate 1a and a fixed spiral element 1b. Both spiral elements 1b and 9b are interfitted at an offset angle to form movable line contacts. As a result, a plurality of compression chambers P are defined by the fixed and orbiting end plates 1a and 9a, and the fixed and orbiting spiral elements 1b and 9b respectively. 
     As shown in FIG. 5, a well-known anti-spin-mechanism 11 is interposed between a pressure receiving wall 2a of the front housing 2 and the orbiting end plate 9a. The anti-spin-mechanism 11 causes the orbiting scroll 9 to rotate around the center axis of the fixed scroll 1 while limiting the rotation of the orbiting scroll 1 about its own axis. Further, the mechanism 11 transmits thrust reaction force originating from gas compression during the compression stroke from the orbiting scroll 9 to the wall 2a (e.g., referring to Japanese Unexamined Patent Publication No. 2-308990). 
     A suction chamber 12 is formed around the spiral elements 1b and 9b in the center housing 1e. A discharge port 1c is formed at the central portion of the fixed end plate 1a. Each of the compression chambers P is enabled to communicate with a discharge chamber 13 defined by the rear housing 3 and the plate 1a through the discharge port 1c. The discharge port 1c may be shut by means of a discharge valve 13a that is disposed in the discharge chamber 13. Closing or opening operation of the valve 13a is carried out, based upon the correlation of the pressure within the discharge chamber 13 and the pressure within the discharge port 1c. Generally, according to an air conditioning system, the suction chamber 12 communicates with an external suction refrigerant gas passage of cooling device (not shown), via a suction flange (not shown). Further, the discharge chamber 13 communicates with an external discharge refrigerant gas passage (not shown), via a discharge flange (not shown). 
     The orbiting scroll 9 rotates around the center axis of the drive shaft 4 and the refrigerant gas which is fed from a suction port (not shown) to suction chamber 12, is then introduced into the compression chamber P defined between both scrolls 1 and 9. 
     During the course of the orbiting scroll 9&#39;s rotation, the volume of compression chamber P gradually decreases as the rotation progresses. Gas introduced into the compression chamber P is compressed when the chamber P decreases in volume according to the progression of the rotating spiral member. At the same time, as the inner tip portions of the spiral elements 1b and 9b approach each other, the compression chamber P moves toward the central portion of the fixed scroll 1. The compressed refrigerant gas is discharged into the discharge chamber 13, via the discharge port 1c of the fixed plate 1a. 
     As shown in FIG. 1, a seal groove 15 is formed on the distal end surface of the orbiting spiral element 9b of the orbiting scroll 9. The seal groove 15 extends along the orbiting spiral element 9b. As a result, the groove 15 extends in the spiral manner from the center of the orbiting scroll 9 to the periphery thereof. The groove 15 accommodates a seal 14 having a shape corresponding to the groove 15. The seal 14 includes an enlarged tip portion 14a wider in its width W 2  than width W 1  of the remaining portions of orbiting spiral element 9b. As shown in FIG. 5, the fixed spiral element 1b of the scroll 1 has a seal groove 15 that accommodates a seal 14 similar to the above-described scroll 9. 
     FIGS. 2 and 3 show an essential portion of the present invention such as the layout of the discharge port 1c and communicating passage 1d. As shown in FIG. 2, a point O 2  is a center point of involute generating circle K for forming an inner involute curve S 1  of the fixed scroll 1. A point E 1  is defined on the involute generating circle K and is the initial point of inner involute surface S 1 . A straight line H connects between the center O 2  and the initial point E 1 . A center O 1  of the discharge port 1c is located off from the line H opposite to the fixed involute surface S 1  with respect to the line H. As shown in FIG. 3, the communicating passage 1d is engraved in the fixed end plate in the vicinity of the discharge port 1c. The radius of the discharge port, where the point O 1  is the center of the discharge port, is shorter than the distance between the center of the discharge port O.sub. 1 and the line H. Instead of this, the contour line of the passage 1d is arranged to contact with a part of the arc shaped distal surface of the fixed spiral element 1b. 
     An initial point E 9  of an involute inner surface S 9  of the orbiting spiral element 9b rapidly approaches the initial point E 1  of the inner peripheral surface S 1  at the final compression stage while the surface S 9  of the orbiting spiral element 9b is contacting with the surface S 1  of the fixed spiral element 1b. Consequently, a minimized compression chamber Pn is defined between both inner peripheral surfaces S 1  and S 9 . As shown in FIG. 2, however, the discharge port 1c is disposed offset from the line H in a direction opposite the fixed involute surface S 1  and a distance greater than the radius of the involute generating circle K. The minimized compression chamber Pn must communicate with the discharge port 1c through the passage 1d. Therefore, the compression refrigeration gas in the chamber Pn is introduced into the discharge port 1c through the passage 1d, and then discharged into the discharge chamber 13 through the discharge port 1c. 
     According to this embodiment, the enlarged tip portion 14a of the seal 14 covers the discharge port 1c during the final compression stage, as shown in FIGS. 2 and 4. Therefore, the enlarged tip portion 14a is tightly supported by the edge wall of the discharge port 1c in a supporting point T1 located at the middle portion thereof and another supporting point T2 located at the tip portion thereof. In other words, as shown in FIG. 4, the area protruding beyond or cantilevered over a line L connecting between both points T1 and T2 is extremely small. Therefore, this structure prevents the seal 14 sagging into the discharge port 1c because in order to sag the seal material along line L (the longest unsupported portion) would have to stretch. Therefore wear of and damage to the seal 14 are prevented. 
     As described above, according to teachings of the present invention, the discharge port is remotely located with respect to the location of the involute generating circle at the final compression stage location, as shown in FIG. 2. Compare this architecture with that of a conventional compressor, wherein the discharge port 54 is entirely accommodated in the involute generating circle, as shown in FIG. 7. Therefore, according to the present invention, the entire tip portion of the seal 14 does not confront against the discharge port 1c during the final compression stage. Further, since the communication passage 1d communicating the minimized compression chamber (in the final compression stage) with the discharge port, is disposed in the fixed end plate 1a of the fixed scroll 1, the highly pressurized gas is discharged from the passage 1d to the discharge port 1c. Therefore, the durability of the central portion of the seal disposed at the distal surface of the spiral element of the orbiting scroll is significantly increased. 
     Although only one embodiment of the present invention has been described in detail herein, it should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the following modes are applied. 
     According to the above-described embodiment, the communicating passage 1d has an arc shape. If the passage 1d is enabled to communicate the minimized compression chamber in the final compression stage with the discharge port 1c, any shape can be employed for the passage 1d, such as a gutter shape recess as shown in FIG. 6a, a plurality of circular recesses as shown in FIG. 6b and the combination of a recess and groove as shown in FIG. 6c. The present invention can be embodied in a compressor having a generally uniform width seal without an enlarged tip portion 14a. Further, the involute curve for the spiral element can be replaced by another type of curve such as an Archimedes curve. 
     Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.