EP0162157B1

EP0162157B1 - A screw compressor incorporating a slide valve

Info

Publication number: EP0162157B1
Application number: EP19840303436
Authority: EP
Inventors: Shoji Yoshimura
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1984-05-21
Filing date: 1984-05-21
Publication date: 1988-08-10
Also published as: DE3473326D1; EP0162157A1

Description

The present invention relates to a compressor incorporating a slide valve. Discussion of Prior Art
A prior type compressor incorporating a slide valve will be described with reference to Figures 1 to 8 of the accompanying drawings in which:

Figure 1 is a vertical section of a conventional slide valve type screw compressor;
Figure 2 is a sectional view taken on line I-I of Figure 1.
Figures 3 and 4 are a plan view and a front view of a conventional slide valve;
Figure 5 is a diagrammatic illustration showing rotational positions of rotors in phase (a) to (f), seen from an end on the suction side of the screw compressor;
Figures 6(a) to 6(f) are developed sectional views taken on line X-X of Figure 5 (in which the line of section is indicated in Figure 5(a) alone);
Figure 7 is an illustration similar to Figure 6 but showing the conventional slide valve in a shifted position;
Figure 8 is a graph showing variations in suction volume.

As illustrated in Figures 1 and 2, a screw compressor is generally provided with a pair of male and female screw rotors 5 and 6 (hereinafter referred to simply as "rotors" for brevity) which are rotatable in meshed state within a compression chamber 8 in a casing 7. One end face of the compression chamber 8 is partly cut away at a position corresponding to tooth grooves of the rotors 5 and 6 to provide an opening 10 (an axial port) in communication with a suction port 11 through a suction casing 7a. The other end face is similarly provided with an opening, although different in shape, for communication with a discharge port 12. Further, provided beneath the compression chamber 8, partly in overlapped relation therewith, is a longitudinal slot in communication with the suction port 11, which mounts a slide valve 31 (of a length L,) which is slidable in the axial direction of the rotors. The slide valve 31 is provided with curved surfaces each of an arcuate shape in section which form part of the inner wall surface of the compression chamber 8, and its forward movement (leftwards in Figure 1) is limited by a fixed stop 31 a which is located in a forward position.
In this sort of screw compressor, a gas which is sucked in through the suction port 11 is enclosed and compressed in the compression chamber 8 between the rotors 5 and 6 and the casing 7, and then sent toward the discharge port 12, while the slide valve 32 is retractable to open a radial port 13 of a variable area in the wall of the compression chamber 8 for communicating the compression chamber 8 with the suction port 11, permitting volumetric control through adjustment of the initial closing position of the rotors 5 and 6.
As shown in Figures 3 and 4, the conventional slide valve 31 has the end face 33 on the side of the suction port formed by a flat surface which is disposed perpendicular to the sliding direction, so that it has been difficult to preclude an abrupt and discontinuous variation in the volume of a closed space (hereinafter referred to simply as "suction volume" for brevity) at an initial closing point even if the radial port 13 is opened little by little in the initial stage of a volumetric control.
Now, the above-mentioned discontinuous variations are explained more particularly with reference to Figures 5 and 6 which show at (a) to (f) sequential phases of the rotation of the rotors.
More specifically, Figure 5 shows at (a) to (f) varying conditions at the end of the compression chamber on the side of the suction port 11 in relation with rotation of the rotors. As the operation proceeds from phase (a) to (f), the rotors 5 and 6 are rotated in the arrowed directions, gradually compressing a closed space 14 which is indicated by a hatched area. In this instance, the closed space 14 is the one which is formed when the aforementioned radial port 13 is in closed state (so that the latter does not appear in Figure 5), and, for simplification of explanation, there is shown a case where the width W of a lower projection 18 which forms the opening 10 in the end 5 face 17 or which closes the ends of the screw root ends of the rotors 5 and 6 is equal to the width w of the curved surfaces 2 of the slide valve 31 (see Fig. 2).
Shown at (a) to (f) of Figure 6 are developed views of sections taken along line X-X of Figure 5, which correspond to phases (a) to (f) of Figure 5. As shown there, an end face 33 of the slide valve 31 is positioned on the side of the suction port 11 and outside the compression chamber 8, closing the radial port 13 with the curved surfaces 2. (Therefore, the radial port 13 does not appear in Figure 6). The hatched areas in Figure 6 indicate a closed space 14 corresponding to the hatched areas in Figure 5, which is gradually shifted upward from phase (a) to (f) of Figure 6. On the other hand, the closed space 14 reaches an end face 19 on the discharge side and the end of the discharging side is closed while the end face 19 is rotated through a predetermined angle, so that the volume of the closed space 14 is reduced to compress the gas gradually from phase (a) to (f) of Figure 6.
Referring to Figure 7, the slide valve 31 is shown in a position which is slightly moved from that of Figure 6 with its end face 31 located a little closer to the discharging side (the upper side in the figure) than the end face 17 of the compression chamber 8, with the radial port 13 in a slightly opened state, illustrating variations of the closed space in this position from phase (a) to (f) corresponding to the phases shown in Figure 6. In this case, a portion corresponding to the closed space 14 is in communication with the suction port 11 through the radial port 13 as indicated by a dotted area in phases (a) to (d) of Figure 7, so that it is only in and after phase (e) that a closed space 15 is formed as indicated by a hatched area. Namely, the lowermost point M (a closing point) of a V-shaped hatched area, at which the male and female rotors 5 and 6 contact with each other, is gradually shifted inward across the end face 17 of the compression chamber 8 and it is only when the closing point M reaches the end face 33 of the slide valve 31 that a closed space 15 is formed.
Therefore, the suction volume corresponds to the closed space 14 in phase (a) in the position of Figure 6 and to the closed space 15 in phase (e) in the position of Figure 7. Thus, the suction volume is abruptly and discontinuously varied or stepwise from the volume in phase (a) of Figure 6 to the volume in phase (e) of Figure 7 (same as that of the closed space in phase (e) of Figure 6) upon opening the radial port 13 only to a slight degree. Even if the radial port 13 is further minimised, the result is that the position of the lowermost point M comes nearer to the end face 17 but the closed space 15 is not yet formed in phase (d) of Figure 7 and is formed also in phase (e) of the same figure, resulting likewise in a suction volume which is varied discontinuously from the state in phase (a) of Figure 6.
If the radial port 13 is widened by shifting the slide valve 31 toward the discharge end, the position of the lowermost point M which represents the initial closing point is shifted upward to reduce the suction volume continuously.
As is clear from the foregoing description, the suction volume is varied as indicated by curve II of Figure 8, in which the horizontal axis represents a distance 1 of displacement of the slide valve 31, namely, the distance between the end faces 17 and 33 in the particular embodiment shown, and the vertical axis represents the rate (%) of the suction volume at various distances 1 of displacement to the suction volume in the state shown in Figures 5 and 6 (a state in which the radial port 13 is closed).
As seen therefrom, curve II consists of a vertical portion AB and an inclined portion BC. The point A represents a state in which the end faces 17 and 33 are located in the same plane (distance of displacement 1 = 0) with the radial port 13 closed, the point B represents a state in which opening of the radial port 13 has just been initiated or when the distance in phase (e) of Figure 7 is infinitesimal, and the point C represents a state in which the radial port 13 has been further widened continually. Thus, upon opening the radial port 13, the curve II is varied discontinuously from point A to B.
On such a discontinuous variation, a compressing gas which is relatively dense like air shows an inferior response to the variation due to a greater friction resistance, so that an apparent suction volume is varied continuously in response to displacement of the slide valve 31 as indicated by curve III (broken line) in Figure 8. Namely, actually the suction volume can be controlled from the maximum value by gradually shifting the slide valve 31.
However, in a case where a light gas like hydrogen and helium is employed as a compressing gas, the gas has a low frictional resistance and shows a quick response to the afore-mentioned discontinuous variation, so that the apparent suction volume is varied discontinuously as indicated by curve II. Consequently, it has been difficult for the conventional screw compressor to control the suction volume of a light gas continuously in the initial state of the control.
A slide valve type screw compressor of the type generally shown in Figures 1 to 8 above is illustrated in French patent specification 2279951, but in addition to the above described features, this French specification shows a compressor in which the slide valve includes a part which is retractably protrudable into the suction casing. (See Figure 1).

SUMMARY OF THE INVENTION

With the foregoing in view, the present invention has as its object the provision of a slide valve type screw compressor which can vary a suction volume theoretically in a continuous manner throughout a range of volumetric control including an initial point of the control no matter whether or not the compressing gas is a light (less dense) gas.
According to the present invention, there is provided a slide valve type screw compressor having a slide valve with a generally chevron-shape transverse cross section consisting of a pair of arcuately curved surfaces forming part of the wall of a compression chamber which compression chamber accommodates a pair of intermeshed male and female screw rotors, said slide valve being slidable in the axial direction of said rotors for communicating said compression chamber with a suction port through an opening with an adjustably variable area for volumetric control of said compressor, and the fore end of said slide valve is retractably protrudable into a suction casing disposed on the side of said suction port characterised in that the opposite outer corner portions of the fore end of said curved surfaces of the slide valve are chamfered at a predetermined angle to the axis whereby the fore end of the curved surfaces of the slide valve is generally wedge shaped with an apex of the wedge facing forwards.
The above and other objects, features and advantages of the present invention will become apparent from the following description and appended claims, taken in conjunction with Figures 9 to 26 of the accompanying drawings which show by way of example a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

Figures 9 and 10 are a plan view and a front view of a screw compressor slide valve according to the present invention;
Figure 11 is a vertical section of the slide valve type screw compressor embodying the present invention;
Figures 12(a) to 12(f) are views similar to Figures 6(a) to 6(f) but showing the rotational positions in the screw compressor according to the invention;
Figures 13(a) to 13(c) are developed sectional views taken on line X-X mentioned above, showing the extent of opening of the radial port in relation with the position of the slide valve;
Figures 14 to 25 are fragmentary plan and front views of slide valves of modified constructions; and
Figure 26 is a view similar to Figure 13 but showing a slide valve with a different cut angle.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to Figures 9 and 10, there is shown a screw compressor slide valve 1 (with a length L 08) according to the present invention, which is substantially the same as the slide valve 31 of Figures 3 and 4 in construction except for its shape of the end face 33 on the suction side.
More particularly, the slide valve 1 is provided with a surface of chevron shape in section consisting of arcuately curved surfaces 2 formed on opposite sides of an apex 26, which constitute part of the wall of the compression chamber 8 as stated hereinbefore, and has end faces 3 on the suction side shaped such that the lines of intersection 4 with the curved surfaces 2 are inclined in the direction of screw threads of rotors 5 and 6 to form a wedge shape fore end. The slide valve 1 is received in a suction casing 7a which is provided with a stopper 23 to permit the valve end on the suction side (or the fore end of the valve) to protrude retractably into the suction casing 7a.
Figure 11 shows a screw compressor incorporating the slide valve according to the invention, which is the same in construction as the screw compressor of Figures 1 and 2 except that the slide valve 1 and stopper 23 are employed in place of the slide valve 31 and fixed valve 31 a, respectively. The component parts which are common to the example shown in Figures 1 and 2 are designated by common reference numerals, and their description is omitted to avoid unnecessary repetitions. Further, the reference numeral of the slide valve 1 is indicated in brackets in Figure 2 so that the latter can serve also as a side view of the compressor of Figure 11.
Now, variations in suction volume which are caused by shifts of the slide valve 1 are explained by way of phases (a) to (f) shown in Figure 12.
As described hereinbefore, the lines of intersection 4 are inclined in the direction of screw threads of rotors 5 and 6, so that each intersecting line 4 is disposed parallel with a line 22 of a screw thread (which comes out in a straight line in a developed view). Consequently, as the slide valve 1 is gradually shifted upward in Figure 12, a radial port 13 is opened on the opposite sides of the slide valve 1 in a manner similar to the rotor grooves which are moving toward the centre (in the direction of arrows V) on the end face 17.
Shown in Figures 13(a) to 13(c) is an example of the varying condition of the radial port 13, which is observed, for instance, when the slide valve 1 alone is moved upward in the state of Figure 12(c). As clear therefrom, the radial port 13 is in fully closed state and does not appear in Figure 13(a), but it is gradually widened from Figure 13(b) to 13(c). Consequently, the closed space 16 of Figures 13(a) and 13(b) is uncovered in Figure 13(c), resuming a state prior to dosing.
Therefore, in Figures 12(a) to 12(f) which show the radial port 13 in the initial stages of the opening operation, the portion which corresponds to the closed space 14 of Figures 5 and 6 is indicated by a dotted area 21 in Figure 12(a). This area 21 is in communication with the suction port 11 through radial ports 13, and not yet closes in a gas. However, in phases (b) to (f), a closed space 16 which extends toward the centre is formed beyond the radial ports 13 as indicated by hatching.
The volume of the closed 16 space (or the suction volume) in phase (b) of Figure 12 at the initial closing point can be adjusted to approach the volume of the closed space 14 in phase (a) of Figures 5 and 6 (the maximum suction volume) by minimising the radial ports 13. That is to say, as the slide valve 1 is shifted upward in the drawing from the fully closed position to open the radial ports 13, the suction volume is continuously reduced from the maximum value at the fully closed position (the value in phase (a) of Figures 5 and 6).
The variations in suction volume in the case of the slide valve 1 are plotted by curve IV in the graph of Figure 8, from which it will be seen that the suction volume is reduced from the point A smoothly and linearly in response to increases in the distance of shift of the slide valve 1. In this graph, 1 = 0 means a position of the slide valve 1 immediately before opening the radial ports 13.
Although the width w of the curved surface 2 of the slide valve 1 is shown and described as being equal to the width W of the lower projection 18 on the end face 17, the invention is not limited to this particular arrangement and can produce similar effects, for example, in a case where w > W except for a change in the initial position of the slide valve 1 for the volumetric control. On the contrary, in a case where w < W, there occurs a slight discontinuous variation at an initial point of the volumetric control but it is far smaller than the discontinuous variation from point A to B of Figure 8.
Further, the fore end portion as a whole of the slide valve 1 is shaped in an inclined form in the foregoing embodiment with the lines of intersection 4 of the end face 3 disposed in the direction of screw threads of the rotors 5 and 6. However, if desired, the corner portions of the curved surfaces 2 on the side of the suction port may be partly cut off, or the intersecting lines 4 may be disposed in the same direction at an angle different from the lead angle of the screw threads of the rotors. In such a case, similarly a slight discontinuous variation occurs to the suction volume.
The cutting angle 13 (beta) of the end face 3 of predetermined angle is greater than the lead angle (a) of the screw threads of said rotors (5, 6).

3. A slide valve type screw compressor as claimed in claim 1, characterised in that said opposite corner portions (4) at said front end of said curved surfaces (2) are chamfered along a zig-zag line.
4. A slide valve type screw compressor as claimed in claim 1, characterised in that said opposite corner portions (4) at said front end of said curved surfaces (2) are chamfered down to a level halfway through the thickness of said slide valve (1).
5. A slide valve type screw compressor as claimed in claim 1, characterised in that said slide valve (1) is provided with a fore extension on the front of said wedge section.
6. A slide valve type screw compressor as claimed in claim 1, characterised in that said suction casing (7a) is provided with a stopper member (23) thereby.to limit displacement of said slide valve (1) when said wedge section protrudes into said suction casing (7a).

Claims

1. Schraubenkompressor der Steuerschieber- bauart mit einem einen allgemein V-formigen Querschnitt aufweisenden Steuerschieber (1), der aus einem Paar von bogenformig gekrümmten Flachen (2) besteht, welche einen Teil einer Wand eines ein Paar von miteinander in Eingriff stehen- den Außen-(6) und Innen-(5)-Schraubenrotoren aufnehmenden Verdichtergehäuses (8) bildet, wobei der Steuerschieber (1) in axialer Richtung der Rotoren (5, 6) zur Verbindung des Verdichtergehäuses (8) mit einem Ansaugkanal (11) durch eine Öffnung (13) mit einem einregelbar verän- derlichen Flächenbereich zur volumetrischen Steuerung des Kompressors verschiebbar und das vorwartige Ende des Steuerschiebers (1) zuruckziehbar in ein auf der Seite des Ansaugka- nals (11) angeordnetes Sauggehause (7a) vor- schiebbar ist, dadurch gekennzeichnet, daß die einander gegenuberliegenden Kantenteile (4) des vorwärtigen Endes der gekrümmten Flächen (2) des Steuerschiebers (1) unter einem vorbestimm- ten Winkel zur Achse abgeschragt sind, so daß das vorwärtige Ende der gekrummten Flächen (2) des Steuerschiebers allgemein keilförmig mit einem vorwärts gerichteten Scheitelpunkt (26) ausgestaltet ist.

2. Schraubenkompressor der Steuerschieber- bauart nach Anspruch 1, dadurch gekennzeichnet, daß der vorbestimmte Winkel größer ist als der Steigungswinkel (33) der Schraubgewinde der Rotoren (5, 6).

3. Schraubenkompressor der Steuerschieber- bauart nach Anspruch 1, dadurch gekennzeichnet, daß die einander gegenüberliegenden Kantenteile (4) am vorwartigen Ende der gekrümmten Flächen (2) längs einer Zick-Zack-Linie abgeschragt sind.

4. Schraubenkompressor der Steuerschieber- bauart nach Anspruch 1, dadurch gekennzeichnet, daß die einander gegenüberliegenden Kantenteile (4) am vorwartigen Ende der gekrümmten Flachen (2) bis zur halben Höhe in der Dicke des Steuerschiebers (1) hinunter abge- schrägt sind.

5. Schraubenkompressor der Steuerschieber- bauart nach Anspruch 1, dadurch gekennzeichnet, daß der Steuerschieber (1) an der Frontseite des Keilabschnitts mit einer vorderen Verlängerung versehen ist.

6. Schraubenkompressor der Steuerschieber- bauart nach Anspruch 1, dadurch gekennzeichnet, daß das Sauggehäuse (7a) mit einem die Verlage- rung des Steuerschiebers (1), wenn der Keilab- schnitt in das Sauggehause (7a) hineinragt, begrenzenden Anschlag (23) ausgestattet ist.