Scroll type compressor

Abstract: So as to decrease fluctuations in gas pressures acting on the external surface of the end plate 11 by decreasing the area ratio of the high pressure chamber 44 disposed on the outside of the end plate of the fixed scroll to the back pressure chamber 45, a scroll type compressor has the opening 13b of the discharge port 13 to the high pressure chamber 44 provided in the end plate 11 so as to coincide with the center of the spiral-shaped lap 12.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to a scroll type compressor. Fig. 3 shows an example of a conventional scroll type compressor. As shown in Fig. 3, a scroll type compressor mechanism C is arranged at the upper area inside a sealed housing 8, and an electric motor M is laid out at the lower area of this housing. The scroll type compressor mechanism C is composed of a fixed scroll 1, a rotating scroll 2, a rotation preventive mechanism 3, such as Oldham's coupling (link), that permits the revolution of the rotating scroll 2 but prevents its rotation around its own axis, a frame 6 to which the fixed scroll 1 and the electric motor M are attached, an upper bearing 71 and a lower bearing 72 for supporting a rotary shaft 5, a rotation bearing 73 and a thrust bearing for supporting the rotating scroll 2, and the like. The fixed scroll 1 is equipped with an end plate 11 and a spiral-shaped lap 12 erected on the internal surface of said plate 11, and supported by the frame 6 movably along the axial direction for its free movement through a spring 18. The rotating scroll 2 is provided with an end plate 21 and a spiral-shaped lap 22 erected on the internal surface of said plate 21, and a drive bush 25 is rotatably fitted inside a boss 23 erected on the outer surface of said end plate 21 via a rotation bearing 73. An eccentric pin 53 protruding from the upper end of the rotary shaft 5 is rotatably fitted inside an eccentric hole provided on this drive bush 25. A balance weight 84 is mounted on the upper end of the rotary shaft 5. The fixed scroll 1 and the rotating scroll 2 are engaged with each other with a eccentric throw corresponding to the radius of revolution and with an angular shift of 180° between them. With this engagement, a plurality of compression chambers 24 are formed with a point symmetry with respect to the center axis P of the spiral-shaped lap 12 of the fixed scroll 1. A discharge port 13 is provided at the center area of the end plate 11 of the fixed scroll 1, and one end of this discharge port 13 is communicated to an innermost chamber 26 (formed immediately before the point where the base ends of spiral-shaped laps 12 and 22 depart from the corresponding side spiral-shaped laps 22 and 12, respectively). Cylindrical bosses 46 and 47 are provided concentrically on the outer surface of the end plate 11, and the tips of these bosses 46 and 47 are slidably engaged via a seal 42 to a partition plate 41 which is fixed to the sealed housing 8 with an interposed space to the end plate 11. Thus, a high pressure chamber 44 is formed in the central area on the outside of end plate 11, and an annular back pressure chamber 45 is formed around this high pressure chamber. A discharge port 13 opens to this high pressure chamber 44, while a negative pressure chamber 45 communicates gas via a through hole 19 to a compression chamber which is in the process of compression. The rotating scroll 2 is driven via a turning drive mechanism, such as the rotary shaft 5, an eccentric pin 53, a dry bush 25, a boss 23 and the like by the electric motor M, whereas the rotating scroll 2 makes a revolution motion on a circular orbit with a revolution turning radius while the rotation around its own axis is prevented by the rotation preventive mechanism 3. Then, the gas enters into the sealed housing 8 through a suction pipe 82, and after cooling down the electric motor M, it passes through a channel 85 provided on the frame 6 and also through a suction chamber 16 from a suction channel 15 and is sucked into the compression chambers 24 from the external end openings of the spiral-shaped laps 12 and 22. The gas reaches an innermost chamber 26 located in the central area while it is compressed as the volume of the compression chamber 24 decreases due to the revolution of the rotating scroll 2. It then passes through the discharge port 13 therefrom to discharge into the high pressure chamber 44, and enters into a discharge cavity 48 through a hole 43 provided on the partition plate 41, and is finally discharged to the outside via a discharge pipe 83. At the same time, lubricating oil 81 which is stored at the inner bottom of the housing 8 is sucked up by a centrifugal pump 51 installed in a lower portion inside the rotary shaft 5, and after lubricating the lower bearing 72, the eccentric pin 53, the upper bearing 71, the rotation preventive mechanism 3, the rotation bearing 73, the thrust bearing 74, and the like through an oiling port 52, it returns to the bottom of the sealed housing 8 via a chamber 61 and an oil discharge port 62, and is stored therein. Further, because the discharged gas under high pressure is introduced into the high pressure chamber 44 under the revolution motion of the rotating scroll 2 and the medium pressure gas in the process of compression is introduced into the back pressure chamber 45, the end plate 11 is pressed downward by the gas pressures inside these high pressure chamber 44 and back pressure chamber 45. The tip surfaces of spiral-shaped laps 12 and 22 are pressed with an adequate contact pressure against the internal surfaces of end plates 21 and 11, so as to maintain each of a plurality of compression chambers 24 in sealed conditions. Also, the high pressure chamber 44 and back pressure chamber 45 are formed with the point-symmetry with respect to the center axis P of the spiral-shaped lap 12 as a center: This is because, if the center of urging pressure forces acting on the end plate 11 due to gas pressures do not coincide with the center axis P of the spiral-shaped lap 12, an overturning moment occurs which prevents the tip surfaces of the spiral-shaped laps 12 and 22 from being pressed with a uniform contact pressure against the internal surfaces of the end plate 21 and 11, thereby causing the defective sealing of the compression chambers 24. This conventional scroll type compressor makes an adequate pressing force acting on the end plate 11 by appropriately setting the pressure receiving areas of the high pressure chamber 44 and back pressure chamber 45, but in order to decrease fluctuations of the pressuring forces which accompany pressure changes in the compression chamber 24 to a minimum level, the pressure receiving area of the high pressure chamber 44 should preferably be made smaller than that of the back pressure chamber 45; or in other words, it is preferred that the area ratio of the high pressure chamber 44 be made smaller. However, because the discharge port 13 is provided at a position shifted sideways from the center axis P of the spiral-shaped lap 12 and the pressure receiving area of the high pressure chamber 44 is set to a large size so as to include this discharge port 13, the area ratio of the high pressure chamber 44 is large and the pressing force acting on the end plate 11 fluctuates greatly. As a result, if the pressing force becomes too small, the sealing of the compres sion chambers 24 becomes insufficient; and on the other hand if the pressing force becomes excessive, frictional forces between the tip surfaces of the spiral-shaped laps 12 and 22 and the internal surfaces of the end plates 21 and 11 increases, thereby causing such troubles as power loss of the compressor. Such an arrangement is also disclosed in the prior art document GB-A-2 194 291. OBJECT AND SUMMARY OF THE INVENTION An object of this invention is to solve the above-described problems. The gist of this invention resides in a scroll type compressor comprising the features of claim 1. In this invention, because the opening of the discharge port to the high pressure chamber is positioned at the center of the spiral-shaped lap, not only the pressure receiving area of the high pressure chamber which is formed around the center axis of this spiral-shaped lap can be made smaller, but also the pressure receiving area of the back pressure chamber can be expanded. As a result, it is possible to decrease fluctuations in pressing forces onto the end plates due to the gas pressures in the high pressure chamber and the back pressure chamber. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial sectional view of a scroll type compressor according to a first embodiment of this invention; Fig. 2 is a partial sectional view of scroll type compressor according to a second embodiment of this invention; and Fig. 3 is a sectional view showing a conventional scroll type compressor. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 is a partial sectional view of a scroll type compressor according to the first embodiment of the present invention. The discharge port 13 is inclined, and its opening 13a on one end; namely, an opening to the innermost chamber 26 is shifted sideways from the center axis P of the spiral-shaped lap 12. Its other opening 13b on the other end; namely, an opening to the high pressure chamber 44 is arranged so that its center coincides with the center axis P of the spiral-shaped lap 12. Such various items as the channel area and the opening 13a and 13b of the discharge port 13 are set so that the flow resistance of gas passing through this port may become smaller than a permissible level. The high pressure chamber 44 and the back pressure chamber 45 are formed concentrically around the center axis of the spiral-shaped lap 12, and the diameter of the high pressure chamber 4 is set equal to that of the opening 13b and made smaller than that of the conventional high pressure chamber shown in Fig. 3. The other structural features are similar to those of the conventional one shown in Fig. 3. The same symbols are given to the corresponding members and their explanations are omitted. In this way, because the center of the opening 13b to the high pressure chamber interior 44 of the discharge port 13 coincides with the central axis P of the spiral-shaped lap 13, the high pressure chamber 44 may be formed so as to include the opening 13b around the center axis P as its center. Therefore, because the pressure receiving area of the high pressure chamber 44 can be made smaller and the pressure receiving area of the back pressure chamber 45 can be expanded accordingly, the area ratio of the back pressure chamber 45 can be increased. Thus, it is possible to decrease the fluctuations of pressing forces against the end plate 11 due to the gas pressures inside the high pressure chamber 44 and the back pressure chamber 45. Although the center of the opening 13b is made to coincide with the center axis P in the above embodiment, this invention is by no means restricted to this arrangement. The opening 13b can be formed as much closer as possible to the center axis P so as to include the center axis. Furthermore, the discharge port 13 can also be provided on the end plate 21 of the spiral scroll 2, and the high pressure chamber 44 and back pressure chamber 45 can be arranged on the outside of end plate 21. Fig. 2 shows another embodiment, wherein vertical holes are bored from the internal surface and external surface of the end plate 11 so that these holes are communicated mutually with each other inside the end plate 11. The discharge port 13 can be machined more easily this way. Other structures and actions are identical to those of the first embodiment shown in Fig. 1, and the same symbols are given to the corresponding members, and their explanations are omitted. In this invention, because the opening to the high pressure chamber of the discharge port provided in the end plate is positioned at the center of the spiral-shaped lap, the pressure receiving area of the high pressure chamber can be made smaller, and moreover the pressure receiving area of the back pressure chamber can be expanded, so the area ratio of the back pressure chamber increases. Because it is possible to reduce fluctuations in pressing pressure forces against the end plate due to the gas pressures inside the high pressure chamber and the back pressure chamber in this manner, not only the sealing conditions of the compression chambers can be maintained favorably, but also power consumption losses of the compressor can be prevented.

Claims: A scroll type compressor, comprising a fixed scroll (1) and an orbiting scroll (2), each having a spiral-shaped wrap (12, 22) set up on internal surface of an end plate (11, 21) thereof, said fixed scroll and orbiting scroll being caused to engage each other with an angular displacement and in an eccentric manner so as to form a plurality of compression chambers (24) with a point-symmetry with respect to the central axis of the spiral-shaped wrap of said fixed scroll, said fixed scroll being so supported as can freely move along the direction of its axis, and a high pressure chamber (44) is arranged on external surface of the end plate of said fixed scroll, said high pressure chamber having a discharge port (13) opened thereto on the center portion of the end plate and a back pressure chamber (45) is arranged around said high pressure chamber so as to conduct gas undergoing compression into said back pressure chamber, characterized in that said high pressure chamber (44) and back pressure chamber (45) are formed concentrically around said central axis of the spiral-shaped wrap (12) of said fixed scroll (1), one opening (13a) of said discharge port (13) being shifted from the central axis of said spiral-shaped wrap at the side of the innermost compression chamber (26) of said end plate of said fixed scroll and the other opening (13b) of said discharge port (13) being arranged in the position of central axis at the side of said high pressure chamber (44) of said and plate of said fixed scroll and both said openings (13a, 13b) being arranged to communicate with each other by a passage (13) inclined to said central axis of said spiral-shaped wrap. The scroll type compressor according to claim 1, characterized in that the diameter of said high-pressure chamber (44) is equal to the corresponding other opening (13b) of said discharge port (13). The scroll type compressor according to claim 2 characterized in that a pressure receiving area of said back pressure chamber (45) is greater than a pressure receiving area of said high pressure chamber (44).

Inventors: TAKEDA KIMIHARU, TAKEDA, KIMIHARU, Takeda, Kimiharu, c/o Mitsubishi Jukoyo K.K.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: F04C27
IPC codes: F04C29, F04C18, F04C27