Screw compressor

Abstract: A screw compressor to enable prevention of contact between a slide valve and screw rotors. The screw compressor comprising a capacity controlling slide valve (3) provided for advance and (or) retreat through a piston rod (6) by a piston (5) operated by fluid pressure arranged on the discharge side to adjust the size of a diametral opening of screw rotors (1,2) on the suction side, the screw compressor including projections (8) extending in parallel with axes of the screw rotors (1,2) from a position distanced from the screw rotors (1,2) at the end on the suction side of the slide valve (3), and a support portion (10) which comes in relative slidable contact with surfaces (9) of the projections (8) on the axial side of the screw rotors (1,2) which advance and retreat along with the slide valve (3) to support the projections (8).

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a screw compressor provided with a capacity controlling slide valve. Prior Art: A screw compressor provided with a capacity controlling slide valve 21 shown in FIGS. 7 and 8 has been heretofore well known (Japanese Patent Publication No. 7-62477). The slide valve 21 is coupled to a piston rod 23 of a hydraulic cylinder 22 arranged on the discharge side, and is provided for advance and (or) retreat along with a piston 25 through the piston rod 23 extending through a discharge port 24. As is known, the slide valve 21 comes in sliding contact with the internal surface of a casing opposite to, that is, on the back side of a pair of male and female screw rotors 26, 27, for advance and (or) retreat. The slide valve 21 operates to adjust the size of an opening in a diametral direction on the suction side of the screw rotors 26, 27. It is noted that only the opening 29 in the diametral direction of the one screw rotor 26 is shown in FIG. 8. In the compressor, a side cover 31 on the discharge side formed with a discharge axial port 30 is provided with a projection 32 for controlling the diametral movement of the slide valve 21 (which is shown by the cross hatching in FIG. 7). The surface on the slide valve 21 side of the projection 32 comprises the guide surface which slidably contacts with the slide valve 21. In the case of the aforementioned conventional compressor, compressed gas from the discharge port 24 moves into a fine clearance between the slide valve 21 and the internal surface of the casing 28 behind the slide valve 21. The pressure caused by the compressed gas exerts on the back of the slide valve 21 as shown by the arrow A in FIG. 8. The diametral movement on the discharge side of the slide valve 21 can be controlled by the projection 32 with respect to the back pressure exerting on the slide valve 21. On the other side, however, the slide valve 21 cannot be prevented from being flexed towards the screw rotors 26,27, on the suction side, as shown by the arrow B in FIG. 8. This poses problems in that the back pressure causes the contact between the slide valve 21 and the screw rotors 26, 27, the damage of the slide valve 21, and the screw rotors 26,27 resulting therefrom, the abnormal noises, the lowering of performance, and the like. SUMMARY OF THE INVENTION A screw compressor comprising the features summarized in the pre-characterizing clause of claim 1 is known from document JP-A-57-195890. In this known screw compressor, the support portion is disposed on the diametric outer side of the projecting portion. The support portion has a cylindrical inner guiding surface which is in relative slidable contact with a surface of the projecting portion. The projecting portion comprises a guide member which is inserted into a long hole formed lengthwise in the support portion and which has a head section which is in relative slidable contact with a further guiding surface on the diametric outer side of the support portion. Thereby, the slide valve is given a turn stop, and its projecting portion is prevented from being floated from the cylindrical inner guiding surface of the support portion. It is an object of the present invention to provide a screw compressor which enables prevention of contact between the slide valve and the screw rotors while restricting the movement of the slide valve in the rotational direction of the central axis thereof and while relieving the pressures at the at least one guiding surface. This object is achieved by the screw compressor according to claim 1. Details of the present invention and other objects thereof will become apparent from the ensuing description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a screw compressor according to a first embodiment of the present invention; FIG. 2 is a sectional view taken on line II-II of FIG. 1; FIG. 3 is a sectional view taken on line III III of FIG. 1; FIG. 4 is a sectional view of a screw compressor according to a second embodiment of the present invention; FIG. 5 is an enlarged sectional view of a V portion of FIG. 4; FIG. 6 is a perspective view of a slide member of FIG. 4; FIG. 7 is a view of showing the discharge side of a conventional screw compressor; and FIG. 8 is a fragmentary sectional view of the compressor shown in FIG. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be explained hereinafter with reference to the drawings. FIGS. 1 to 3 show a screw compressor according to a first embodiment of the present invention. A mutual relationship between screw rotors 1, 2, a slide valve 3, and a casing 4 is similar to the case of a compressor shown in FIGS. 7 and 8. The slide valve 3 is coupled to a piston 5 arranged on the discharge side through a piston rod 6. 6. In FIG. 1, in the first case where the piston 5 is moved to the right to increase the capacity of the compressor, pressure oil is guided to a space on the left side of the piston 5. Conversely, in the second case where the piston 5 is moved to the left to decrease the capacity of the compressor, pressure oil in the space on the left side lets escape outside the space. Since a force for pressing the slide valve 3 toward the discharge side is always exerted on the slide valve 3 by means of a spring not shown, in the second case, pressure of a discharge port 7 is further applied by the spring force during the operation of the compressor so that the slide valve 3 moves leftward. Further, the compressor includes two projections 8 extending in parallel with axes of the screw rotors 1, 2 from a position distanced from the screw rotors 1, 2 provided at an axial end of the slide valve 3 on the suction side which advance and (or) retreat along with the slide valve 3 and a support portion 10 of the casing which is in relative slidable contact with surfaces 9 of the projections 8 on the axial side of the screw rotors 1, 2 supporting the projections 8. The slide valve 3 is kept in the so-called opposite-end support state through the piston 5 restricted in the diametral movement on the discharge side and through the projections 8 supported by the support portion 10 so as to restrict the diametral movement thereof. In FIG. 3, the aforesaid surfaces 9 are placed in contact with two guiding surfaces 10a, 10b positioned on the upper side of the support portion 10 and at a part distanced to left and right from the axis of the slide valve 3. With such a constitution as described, the movement of the elide valve 3 in the rotational direction of the axis thereof is restricted. Accordingly, back pressure exerts on the slide valve 3 similar to the case of the aforementioned compressor, but the slide valve 3 is not flexed toward the screw rotors 1, 2 sides even on the suction side as well as the discharge side so as to overcome the contact trouble between the slide valve 3 and the screw rotors 1, 2. Note, for the portions of the piston 5 and the piston rod 6, the construction of the hydraulic cylinder may be employed similar to the case of the aforementioned compressor. FIGS. 4 to 6 show a screw compressor according to a second embodiment of the present invention. Parts common to those of the screw compressor according to the first embodiment shown in FIGS. 1 to 3 are indicated by the same reference numerals, description of which is omitted. On the screw compressor are mounted an O-ring 11 as one example of a seal member provided in the outer peripheral portion of the piston 5, and in addition, an annular slide member 12 in the outer peripheral portion of the piston 5 and at a position distanced from the O-ring 11. The slide member 12 is formed from a member which is small in sliding friction during the sliding such as fluorocarbon resin, for example, polytetrafluoroethylene. Further, the periphery of the piston 5 is sealed by the O-ring 11. The slide member 12 is not aimed at sealing. Accordingly, in the state where the piston 5 is not inclined as shown in FIG. 5, the sliding member 12 need not be placed in contact with the inner wall surface surrounding the periphery of the sliding member 12. On the other hand, when the great force exerts on the piston 5 to incline the latter so that the piston 5 is excessively inclined, the O-ring 11 becomes deformed. Therefore, there is a possibility that the piston 5 comes in contact with the aforesaid inner wall surface to increase the sliding friction so that the piston 5 is not operated smoothly, as the case may be. However, in the present screw compressor, the sliding member 12 is provided Therefore, when the piston 5 starts to incline, the sliding member 12 comes in contact with the aforesaid inner wall surface before the angle of inclination becomes large to thereby prevent the angle of inclination from being increased. Furthermore, since the sliding friction between the sliding member 12 and the aforesaid inner wall surface is small, the smooth operation of the piston 5 is maintained. While in FIG. 5, an example is shown in which the O-ring 11 and the sliding member 12 are arranged on left-hand and right-hand, respectively, it is to be noted that the present invention is not limited thereto but the present invention includes the screw compressor in which the O-ring 11 and the sliding member 12 are arranged on right-hand and left-hand, respectively. In the screw compressor according to the invention, there occurs no contact between the slide valve and the screw rotors caused by the back pressure of the slide valve. This brings forth the effect of the avoidance of damage given to the slide valve and the screw rotors caused by the aforesaid contact, and the solution of abnormal noises, while maintaining the performance of the compressor. The two (or more) guiding surfaces of the support portion which the projections contact are provided at a positions distanced from the axis of the slide valve. With this, there provides a further effect, in addition to the effect just mentioned above, in that as compared with the case where a narrow single surface is formed for the support portion to contact the projections, the displacement of the slide valve in the rotational direction of the axis thereof is also solved while relieving pressure applied to the contact surface. The second embodiment provides a further effect, in addition to the effects mentioned above, in that even if the excessive force exerts on the piston to incline the latter, the smooth operation of the piston is assured.

Claims: A screw compressor comprising a casing (4), a pair of male and female screw rotors (1, 2) meshed with each other, a slide valve (3) for adjusting the size of a suction opening in a diametral direction of said screw rotors (1, 2), wherein said slide valve (3) has a central axis and comprises a projecting portion (8) being provided at an axial end of said slide valve (3) on the suction side thereof and extending from a position distanced from said screw rotors (1, 2) in parallel with the axes of said screw rotors (1, 2) so that said projecting portion (8) advances and retreats along with said slide valve (3), and a support portion (10) of said casing (4) which is in relative slidable contact with surfaces (9) of said projecting portion (8) by at least one guiding surface (10a, 10b) and supports said projecting portion (8), characterized in that said support portion (10) comprises two guiding surfaces (10a, 10b) provided at positions distanced at opposite sides from the central axis of said slide valve (3), and in that said projecting portion comprises two projections (8), wherein one of said two projections (8) is placed in contact with one of said two guiding surfaces (10a, 10b) and the other of said two projections (8) is placed in contact with the other of said two guiding surfaces (10a, 10b). The screw compressor according to claim 1, further comprising: a piston (5) arranged on the discharge side of said slide valve (3) and coupled to said slide valve (3) through a piston rod (6), said slide valve (3) being operated by fluid pressure; a seal member (11) provided in the outer peripheral portion of said piston (5); and an annular slide member (12) provided at a position distanced from said seal member (11) in the outer peripheral portion of said piston (5).

Inventors: MATSUKUMA MASAKI, SUZUKI KATSUYUKI, TSUBOI NOBORU, MATSUKUMA, MASAKI, SUZUKI, KATSUYUKI, TSUBOI, NOBORU, Matsukuma, Masaki, Harima Plant in Kobe Steel,Ltd., Suzuki, Katsuyuki, Harima Plant in Kobe Steel,Ltd., Tsuboi, Noboru, Harima Plant in Kobe Steel, Ltd.
Applicants: KOBE STEEL LTD, KABUSHIKI KAISHA KOBE SEIKO SHO ALSO KNOWN AS KOBE STEEL LTD.
Application year: 1998
Main classification: F04C29
IPC codes: F01C1, F04C18, F04C2, F04C28