Scroll type fluid machine

Abstract: In a low speed rotation, side surfaces of a spiral wrap (2b) of a swivel scroll (2) are brought into pressing contact with side surfaces of a spiral wrap (1b) of a stationary scroll (1) to thereby keep an air tight condition therebetween. When the orbiting swivelling speed of the swivel scroll exceeds the predetermined level, a predetermined gap is kept between the side surfaces of the spiral wrap (2b) of the swivel scroll and the side surfaces of the spiral wrap (1b) of the stationary scroll to thereby prevent the abnormal wear of the spiral wraps and to thereby suppress the increase of the consumption power. A counterweight (10) is provided to a drive bush (5) for generating a centrifugal force Fc which is greater than a centrifugal force Fs applied to the swivel scroll (2) during the orbiting swivelling motion of the swivel scroll and which is directed in an opposite direction to that of the centrifugal force Fs. A spring member (15) is provided for biasing the drive bush (5) in a direction in which the orbiting swivelling radius is increased in a slide direction ϑ. Thus, the swivel scroll (2) is shifted in a direction in which the orbiting swivelling radius is decreased when the orbiting swivelling speed exceeds the predetermined level.

Description: BACKGROUND OF THE INVENTION The present invention relates to a scroll type fluid machine for use as a compressor, an expander or the like. This scroll type compressor according to the prior art is shown in Figs. 3A and 3B. In Figs. 3A and 3B, reference numeral 1 denotes a stationary scroll which is composed of an end plate 1a and a spiral wrap 1b raised from an inner surface of the end plate 1a. Reference numeral 2 denotes a swivel scroll which is composed of an end plate 2a and a spiral wrap 2b raised from an inner surface of the end plate 2a in substantially the same shape of that of the above-described spiral wrap 1b. These stationary scroll 1 and swivel scroll 2 are displaced by a predetermined distance r between their centers O 1 and O 2 , and their phase is displaced by 180° to obtain the engagement combination shown, whereby a plurality of compression chambers 3 are defined about the center of the spiral shape with a point symmetry. A cylindrical boss 4 is projected from an outer central portion of the end plate 2a of the swivel scroll 2. A drive bush 5 is rotatably engaged within the boss 4 through a bearing 6. A slide hole 7 is formed in the drive bush 5. An eccentric pin 9 which eccentrically projects by a predetermined distance r from the axial center O 1 of an end face of a rotary shaft 8 is engaged within this slide hole 7. As shown in Fig. 3B, a cross section of the slide hole 7 is in the form of an oblong shape slanted by an angle  relative to the eccentric direction of the eccentric pin 9. Linear portions 9a formed by cutting both sides of the eccentric pin 9 may slide in contact with and along linear portions 7a of the slide hole 7. When the rotary shaft 8 is rotated, its rotational torque is transmitted to the drive bush 5 through the linear portion 7a of the slide hole 7 from the linear portions 9a of the eccentric pin 9 and is further transmitted to the swivel scroll 2 through the bearing 6 and the boss 4. Thus, the swivel scroll 2 is orbited and swivelled on a circular locus having a radius of a predetermined distance r about a center O 1 of the axis of the rotary shaft 8 and the stationary scroll 1 under the condition that the swivel scroll 2 is prevented from rotating about its own axis by a revolving preventing mechanism (not shown). Then, as gas entrained within the compression chambers 3 is moved toward the center of the spiral shape while reducing their volume, the gas is gradually compressed to reach the central chamber 11 and is discharged through the outlet port 12. In accordance with the orbiting swivelling motion of the swivel scroll 2, a centrifugal force Fs which is directed to the eccentric direction of the eccentric pin 9 is generated by an imbalance weight caused by the swivel scroll 2, the boss 4, the bearing 6, the drive bush 5 and the like. On the other hand, a gas force Fp is applied to the swivel scroll 2 by the gas pressure within the compression chambers 3. The drive bush 5 is moved in the direction of the angle  by a component F of the centrifugal force Fs and the gas pressure Fp in the direction of the angle  so that the orbiting and swivelling radius of the swivel scroll 2 is increased, and side surfaces of the spiral wrap 2b of the swivel scroll 2 are pressed on side surfaces of the spiral wrap 1b of the stationary scroll 1 by the above-described force F. In the above-described scroll type compressor, there is a fear that when the centrifugal force Fs is increased by the increase of the orbiting swivelling speed of the swivel scroll 2, the force for pressing the side surfaces of the spiral wrap 2b of the swivel scroll 2 against the side surfaces of the spiral wrap 1b of the stationary scroll 1 would be excessive so that the side surfaces of the spiral wraps 1b and 2b would be abnormally worn out. When the orbiting swivelling speed of the swivel scroll exceeds the predetermined level, the swivel scroll is moved in a direction that the orbiting swivelling radius is decreased. Accordingly, it is possible to suppress the extra contact pressure between the spiral wrap of the swivel scroll and the spiral wrap of the stationary scroll. SUMMARY OF THE INVENTION According to the present invention, there is provided a scroll type fluid machine comprising: a stationary scroll; a swivel scroll for orbiting swivelling relative to said stationary scroll while being engaged with said stationary scroll with an eccentricity of a predetermined distance relative to said stationary scroll and with a displacement in an angle; a drive bush supported rotatably to said swivel scroll; and an eccentric pin that is eccentric with an axis of a rotary shaft and slidably engages within a slide hole of said drive bush, wherein said drive bush is slidingly moved in a direction perpendicular to an eccentric direction of said eccentric pin to thereby an orbiting swivelling radius of said swivel scroll is changed; said scroll type fluid machine comprising the improvement in which: a counterweight is provided to said drive bush for generating a centrifugal force Fc greater than a centrifugal force Fs applied to said drive bush during the orbiting swivelling motion of said swivel scroll and in a direction opposite to that of the centrifugal force Fs, and a spring member is provided for biasing said drive bush in a direction in which the orbiting swivelling radius is increased in the slide direction whereby when the orbiting swivelling speed exceeds a predetermined level, said swivel scroll is shifted in a direction in which the orbiting swivelling radius is decreased. A displacement limiting means for limiting a displacement in which the orbiting swivelling radius is decreased is provided to said drive bush. The displacement limiting means comprises stepped shouldered portions formed in the slide hole. The spring member is composed of a coil spring. The coil spring is interposed at a stepped groove provided at one end of the slide hole and said eccentric pin. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Figs. 1A and 1B show one embodiment of the invention, Fig. 1A being a longitudinal sectional view of a primary part and Fig. 1B being a cross-sectional view taken along the line B-B; Fig. 2 is an illustration of forces applied to the swivel scroll in the embodiment; and Figs. 3A and 3B show one example of a conventional scroll type compressor, Fig. 3A being a longitudinal sectional view of a primary part and Fig. 3B being a cross-sectional view taken along the line B-B. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described by way of example with reference to Figs. 1A and 1B. A counterweight 10 is mounted on a drive bush 5. The counterweight 10 is moved in an opposite direction to that of a centrifugal force Fs to be applied to a swivel scroll upon the orbiting swivelling motion of the swivel scroll 2 and generates a centrifugal force Fc that is greater than the centrifugal force Fs. As shown in Fig. 1B, a slide hole 70 of the drive bush 5 is composed of a large width portion 71 and a stepped groove 72. Shouldered portions are formed in a boundary therebetween. An eccentric pin 9 is slidably engaged with the large width portion 71, and a spring member 15 made of a coil spring is received in the stepped groove 72. One end of the spring member 15 is brought into contact with the eccentric pin 9. The other end thereof is brought into contact with a bottom 74 of the stepped groove 72 to bias the drive bush 5 in a slide direction, i.e., a direction where the orbiting swivelling radius is increased in the direction of the angle . Thus, when the orbiting swivelling speed of the swivel scroll 2 is less than a predetermined level, the drive bush is moved in the direction in which the orbiting swivelling radius is increased. On the other hand, when the orbiting swivelling speed of the swivel scroll 2 is greater than the predetermined level, the drive bush is moved in the direction in which the orbiting swivelling radius is decreased. The other structure is the same as that of the conventional technology shown in Figs. 3A and 3B, and the same reference numerals are used to designate the like components and members. A force which is applied to the swivel scroll 2 during the operation of the compressor will be explained with reference to Fig. 2. The force Fp which is directed to a direction perpendicular to the eccentric direction of the gas force based upon the gas pressure within each compression chamber 3 is given in equation 1: Fp=(P H -P L )·h·W 1 +(P 1 -P 2 )·h·W 2 where P H is the exhaust pressure, P L is the suction pressure, P 1 is the gas pressure within an inner compression chamber 3, P 2 is the gas pressure within an outer compression chamber 3, h is the height of the spiral wraps 1b and 2b, W 1 is the distance between contact points A and C of the spiral wraps 1b and 2b, and W 2 is the distance between contact points B and D of the spiral wraps 1b and 2b. Incidentally, although the force which is directed perpendicular to the force Fp is generated, this is very small and hence is negligible. On the other hand, the centrifugal force Fs which is directed in the eccentric direction is applied to the center O 2 of the swivel scroll 2, and the centrifugal force Fc is applied in the opposite direction to the centrifugal force Fs. Thus, if a force to the drive bush 5 in a right upward direction along the slide direction  is given by F, the force F is given by equation 2: F=Fs cos+Fp sin-Fc cos+f·x where f·x is the force by the spring member 15, f is the elastic coefficient of the spring member 15 and x is the displacement of the spring member 15. Therefore, when the orbiting swivelling speed of the swivel scroll 2 is less than a predetermined level, the force F is positive, and when the speed is greater than the predetermined level, the factors Fs, Fc, Fp, f·x and the angle  are selected so that the force is negative. More specifically, spring coefficient f of the spring member 15 is selected. Thus, when the orbiting swivelling speed of the swivel scroll 2 is less than the predetermined level, the side surfaces of the spiral wrap 2b are pressed against the side surfaces of the spiral wrap 1b of the stationary scroll 1 by the force F. As a result, the drive bush 5 is slidingly moved in the right upward direction along the direction  within the large width portion 72 of the slide hole 70. Thus, the orbiting swivelling radius is increased, and the spring member 15 is elongated. When the orbiting swivelling speed of the swivel scroll 2 is greater than the predetermined level, the side surfaces of the spiral wrap 2b are separated away from the spiral wrap 1b of the stationary scroll 1 by the force F. Thus, the orbiting swivelling radius is decreased and the spring member 15 is shortened. In response to the increase of the orbiting swivelling speed of the swivel scroll 2, the drive bush 5 is moved in a left downward direction in the direction of the angle . However, the eccentric pin 9 is brought into contact with the stepped shoulder portions 73 of the slide hole 70, the eccentric pin 9 is not moved beyond the shoulder portions 73. Thus, the operation is kept while maintaining a predetermined distance between the spiral wraps 1b and 2b. According to the present invention, the counterweight is provided to the drive bush for generating a larger centrifugal force Fc than the centrifugal force Fs in the opposite direction to the centrifugal force Fs applied to the swivel scroll during the orbiting and swivelling motion of the swivel scroll, and the spring member is provided for biasing the drive bush in the direction the orbiting swivelling radius is increased in the slide direction, whereby when the orbiting swivelling speed of the swivel scroll exceeds the predetermined level, the swivel scroll is moved in a direction that the orbiting swivelling radius is decreased. Accordingly, it is possible to suppress the extra contact pressure between the spiral wrap of the swivel scroll and the spiral wrap of the stationary scroll. Also, in the low speed rotation, the side surfaces of the spiral wrap of the swivel scroll are brought into pressing contact with the side surfaces of the spiral wrap of the stationary scroll to thereby keep an air tight condition therebetween. However, in the case where the orbiting swivelling speed of the swivel scroll exceeds the predetermined level, a predetermined gap is kept between the side surfaces of the spiral wrap of the swivel scroll and the side surfaces of the spiral wrap of the stationary scroll to thereby prevent the abnormal wear of the spiral wraps and to thereby suppress the increase of the consumption power.

Claims: A scroll type fluid machine comprising: a stationary scroll (1); a swivel scroll (2) for orbiting swivelling relative to said stationary scroll while being engaged with said stationary scroll with an eccentricity of a predetermined distance relative to said stationary scroll and with a displacement in an angle; a drive bush (5) supported rotatably to said swivel scroll; and an eccentric pin (9) that is eccentric with an axis of a rotary shaft (8) and slidably engages within a slide hole of said drive bush; said drive bush (5) being slidingly moved in a direction perpendicular to an eccentric direction of said eccentric pin (9) to thereby an orbiting swivelling radius of said swivel scroll (2) being changed; characterized in that a counterweight (10) is provided to said drive bush (5) for generating a first centrifugal force (Fc) greater than a second centrifugal force (Fs) applied to said drive bush (5) during the orbiting swivelling motion of said swivel scroll due to the imbalance weight of various compressor components and in a direction opposite to that of the second centrifugal force (Fs), and a spring member (15) is provided for biasing said drive bush (5) in a direction in which the orbiting swivelling radius is increased in the slide direction whereby when the orbiting swivelling speed exceeds a predetermined level, said swivel scroll is shifted in a direction in which the orbiting swivelling radius is decreased. The scroll type fluid machine according to claim 1, characterized in that a displacement limiting means for limiting a displacement in which the orbiting swivelling radius is decreased is provided to said drive bush (5). The scroll type fluid machine according to claim 2, characterized in that said displacement limiting means comprises stepped shouldered portions (73) formed in the slide hole. The scroll type fluid machine according to claim 1, characterized in that said spring member is composed of a coil spring (15). The scroll type fluid machine according to claim 4, characterized in that said coil spring (15) is interposed at a stepped groove (72) provided at one end of the slide hole and said eccentric pin (6).

Inventors: MIURA SHIGEKI, SHIGEOKA TETSUO, MIURA, SHIGEKI, SHIGEOKA, TETSUO, Miura, Shigeki, c/o Air-Cond.&amp; Refrig. Mach. Works, Shigeoka, Tetsuo, c/o Nagoya Res. &amp; Dev. Center
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1995
Main classification: F04C29
IPC codes: F04C29, F04C18, F04C28