SCREW ROTOR COMPRESSOR HAVING A MOVABLE WALL PORTION

Abstract: The present invention relates to a screw rotor compressor that includes two mutually coacting helical screw rotors and a rotor housing (1). The housing (1) includes a first end wall (2) and a second end wall (3) and a barrel wall (7, 11) that interconnects the end walls. The housing (1) has internally the shape of two mutually intersecting cylinders and the first end wall (2) includes an inlet opening (19). The barrel wall (7, 11) includes an outlet opening (6) adjacent the second end wall (3), and also includes a further opening (9), this further opening extending from the outlet opening (6) towards the first end wall (2) and widening over both cylinder surfaces. The housing (1) also includes a movable or displaceable part (11) which coacts with the opening (9) and which engages the housing in a first position such as to form the mutually intersecting cylindrical surfaces, and which is out of engagement with said housing in a second position and therewith distanced from said further opening. The compressor also includes a maneuvering device for placing the movable part (11) selectively in its first or its second position. The maneuvering device is adapted to actuate a rotatable shaft (12) which is either mounted on the compressor or firmly fixed relative thereto and which is connected to said movable part (11) through the medium of a connecting element (17).

Description: Screw rotor compressor having a movable wall portion The present invention relates to a screw compressor that includes two mutually coacting helical screw rotors housed in a rotor housing. The housing includes first and second end walls that are interconnected by a barrel wall. The housing has an internal configuration that corresponds to two mutually intersecting cylinders and the first end wall includes an inlet opening while the barrel wall includes an outlet opening adjacent the second end wall and further includes an opening which extends from the outlet opening towards the first end wall and widens over both cylinder surfaces. The housing also includes a movable part which coacts with said further opening and which in a first position engages the housing such as to form the mutually intersecting cylindrical surfaces and which in a second position is out of engagement with the housing and therewith spaced from said further opening. The compressor includes a maneuvering device for selective positioning of the movable part either in its first or in its second position. With respect to compressors of this kind it is necessary in many applications to supply compressed working fluid intermittently. In order to avoid the use of complicated, and therewith expensive solutions in respect of these applications, for instance the use of a coupling device or clutch mechanism between the compressor and its drive means, or to avoid the activation and deactivation of said drive means, compressors of this kind are normally provided with means which allow the compressor to idle during those periods when compressed fluid is not required. This is usually achieved by opening a free connection between the high pressure side of the compressor and its low pressure side for return of the working fluid. Such arrangements are described, for instance, in US Patent Specification Nos. 3 527 548, 3 759 636, 4 119 392, 4 799 865 and 4 993 923. The compressor thus taught by US-A1-3 527 548 has hollow axles or shafts whose interiors communicate with the outlet through one opening, and with the inlet. This opening can be closed by a pressure actuated valve against the force of a spring that functions to hold the valve open. The compressor taught by US-A1 -3 759 636 includes in its high pressure end- section a valve which can be opened against an oil pressure through the medium of the outfeed pressure together with a pull spring, said oil pressure acting in the direction op- posite to said outfeed pressure. The valve opens a connection between the compressor outlet and compressor inlet. The compressor taught by US-A1-4 119 392 teaches a female rotor which is shorter than the distance between the end walls and which can be moved axially by a piston that either seals against the high pressure end-wall at full load or leaves a gap to the high pressure end-wall so as to bring the high pressure side into fluid connection with the inlet via the rotor grooves so as to provide an idling facility. US-A1-4 799 865 teaches a compressor that includes an axially movable end- wall at the high pressure end. The end wall is held closed by springs and can be lifted by a piston, or plunger, so as to relieve the load on the compressor. Finally, US-A1-4 993 923 teaches a pressure actuated slide valve that is disposed around the high pressure end of each rotor shaft, said valve providing fluid connection between outlet and inlet when open. A compressor that includes two mutually coacting screw rotors and used as an engine supercharger is known from US Patent Specification US-A1-4 744 734. Arranged at the end of the outlet passageway of this compressor is a disc-shaped throttle valve. The throttle disc is fixed in a shaft that can rotate about its long axis. The compressor also includes a by-pass passageway which has connection with the compressor inlet. Two openings in the housing connects the by-pass with the rotor housing over one of the rotors, and throttle valves pivotally mounted in said passageway function to close and open said connection. Resilient arms fastened in the throttle valve shaft cause the pivotal throttle valves to either close or open the two openings in response to corresponding rotation of the shaft. When the two openings are closed in response to rotation of said shaft, the outlet passageway is opened by the valve disc, and vice versa. The European Patent Application EP-A2-0 484 885 teaches a screw rotor compressor having an inlet at one end and a movable piston in the other axial end of the compressor housing, adjacent the outlet. The piston moves generally perpendicularly to the axes of the screw rotors. Maximum compression is obtained, when the piston is situated closest to the rotors. The size of the outlet opening increases as the piston is moved away from this position, so as to obtain lower compression. One drawback with this latter compressor is that it cannot be made sufficiently compact to suit many purposes. The movable piston by means of which the degree of compression obtained with the compressor is adjusted must have a significant length in its axial direction. It must be possible to move the piston towards and away from a position of abutment in relation to the rotors without sticking or jamming. The forces acting on the piston from the working chamber of the compressor vary and are greatest adjacent the outlet. Another drawback is that the piston may not rotate about its own axis when moved axially in order to change the compression ratio of the compressor. Because the piston is situated above both rotors, any such rotation would cause the piston to come into contact with the rotors and therewith damage the same. One object of the present invention is to eliminate the drawbacks of the solution described in the European Patent Application with respect to changing the compression ratio in a compressor. Another object of the invention is to provide a novel and improved method of short-circuiting the working fluid with respect to idling of a compressor. Still another object of the invention is to provide a simple reliable compressor where the requirements on valve tolerances are low with respect to adjusting the compression ratio. These objects have been achieved in accordance with the present invention by means of a compressor according to the preamble of Claim 1 that includes the modifica- tion in which an operating device or maneuvering device functions to actuate a rotatable shaft which is mounted on the compressor or firmly fixed relative thereto and which is firmly connected to a movable part of the compressor barrel through the medium of a connecting element. Because the valve plate, i.e. the movable part of the barrel wall, is rotatable about an axis, it can be readily rotated out of engagement with the barrel wall and distanced from the rotors. This rotation opens the closed working chambers of the compressor, therewith immediately relieving the compressor of load. The production of compressed fluid is changed immediately, either in one step or ceases almost entirely. When the movable part extends from the outlet opening to the opposite end wall, or preferably terminates a short distance from said wall, all working chambers will come immediately into fluid connection with each other when the movable part is lifted or distanced from abutment with the stationary part of the barrel wall. Losses due to backflow or reflux are 4 reduced to a minimum. Consequently, the movable part need only move to a very small extent in order to provide idling conditions. Only one simple maneuvering device is required to obtain this movement, for instance a motor or a spring which acts on the shaft in some appropriate manner. In one embodiment of the present invention, the opening in which the valve plate is disposed terminates short of the first end wall so that a certain degree of compression will be obtained even when the valve cover is not in engagement with the barrel housing. Another important advantage afforded by the present invention is that the movable part can be fixed through the medium of a connecting element in said shaft. Because the connecting element has a broad and long abutment area with said shaft, the movable part will be positioned exactly in its intended place in the compressor housing in engagement with the barrel housing, and will lie in the vicinity of the rotors with only a small amount of clearance therebetween and in the absence of further guide elements. Attachment of the connecting element on the movable part and in the shaft in- eluding bores whose diameters are larger than the diameters of the screws or other fasteners used, the shaft may be positioned at a wrong angle without any negative effect on the valve function. Although the movable part can be arranged anywhere in the barrel wall, the placement of said movable part perpendicular to the intersection plane of the cylinders is preferred, since this provides a through-passing connection with the grooves of both rotors. The compressor housing is made of a metallic material, for example aluminum. The movable part, however, can be made of some other material, for example a polymeric material. Preferred embodiments of the invention are made apparent in the depending claims. The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 illustrates schematically an inventive compressor from above, where- with a part that is movable relative to the barrel housing is omitted; Figure 2 is a vertical section A-A through the compressor shown in Figure 1 , through its cusps, and shows the part omitted in Figure 1 in place in a first end position, and shows a second end position of said part in broken lines; Figure 3 shows the movable part of the barrel wall from above, with means for moving said part between said two end positions; and Figure 4 is a sectional view of said movable part, taken on the line B-B in Figure 3. The compressor illustrated in Figures 1 and 2 includes a housing 1 which has a first end wall 2 that includes an inlet opening 19 on its inlet side (low pressure side) and a second end wall 3 on its outlet side (high pressure side), and a barrel wall 7, 11 which interconnects said end walls 2, 3. The barrel wall 7 has provided therein a generally triangular outlet opening 6, with the base of the triangle lying adjacent the second end wall 3. The barrel wall comprises two parts, a first stationary main part 7 and a second movable part 11 , this latter part being shown in Figures 2 and 3 and is best seen from Figure 3. The barrel wall 7 includes an opening 9 which is intended to receive the movable part 11. The movable, or displaceable, part 11 has a first end position in which it is received in the opening 9 in the barrel wall 7, as shown in full lines in Figure 2. Figure 2 shows in broken lines a second end position of said movable part 11, i.e. a position in which said movable part is out of engagement with the barrel wall 7. Internally, the compressor housing 1 has the form of two mutually intersecting cylinders in which mutually coacting rotors having helical lobes are arranged. The center line of said rotors 4, 5 is indicated in broken lines in Figure 1 and indicated by the rotor reference signs. In the illustrated embodiment, the opening 9 in the barrel wall 7 is circular and intersects the apex of the generally triangular outlet opening 6. The opening 9 extends towards the first end wall 7, in the illustrated case all the way to said first end wall 2, i.e. to a plane perpendicular to the rotor axes where an inlet pressure is still present. Figure 3 shows the movable or displaceable part 11 from above. As shown in the figure, the arrangement includes a connecting element 17 which connects the movable part 11 with a shaft 12 mounted in bearings 16. The bearings 16 are mounted in some suitable way on the stationary part 7 or on a support fixed in relation to the compressor. One end of the shaft 12 extends beyond the bearing 16 and includes an arm 18. The arm 18 is actuated by a motor 25 or some other means (Figure 1) through the medium of a transmission element 26, so as to cause the shaft 12 to rotate to a limited extent. This rotary movement causes the movable part 11 to be moved between its end positions (Figure 2) or to positions between said end positions. In the cross-sectional view B-B shown in Figure 4, the movable part 11 is perpendicular to the axes of rotors 4, 5. The apex of the mantle housing, i.e. its cusp, on the movable part 11 is referenced 20 and the two areas 21 and 22 which diverge from the cusp 20 are cylindrical in shape and have the same radius of curvature as the cylinders of the stationary part 7. The movable part 11 includes a flange 23 for abutment with a cor- responding recess 8 (Figures 1 and 2) in the barrel wall 7 around the opening 9. The circular side-area 24 of the movable part 11, intended for insertion in the opening 9 in the stationary part 7, preferably tapers conically towards the housing interior. It may alternatively be cylindrical, although in this case there must be sufficient clearance for the movable part 11 to rotate into and out of engagement with the opening 9. The conical configuration enables the movable part 11 to be inserted into the opening 9 with zero clearance, i.e. the conical surfaces may lie in mutual abutment. This means that less stringent requirements are placed on fitting precision. The circular part of the opening 9 will then either be conical or cylindrical in a corresponding manner. In addition to the inlet passageway or opening 19, the first end wall 2 includes a connecting passageway 14 which opens out at one end into the side wall of the opening 9 and the other end of which connects with the compressor inlet. These passageways 14, 19 are both connected to the same source of working fluid. When the movable part 11 is in its one end position, in engagement with the stationary part 7, the passageway 14 is connected to said movable part 11. In the illustrated case, the connecting element 17 has the form of a right-angled block. The shaft 12 includes a flat recess in which one end of the block is received. The connecting element 17 includes two mutually parallel bores for receiving screws 13 or like fasteners that hold the connecting element 17 in a fixed position relative to the shaft 12. Similarly, two mutually parallel further bores extend perpendicularly to the two first mentioned bores for receiving screws 13 or like fasteners that fasten the connecting element to the movable part 11. These bores have diameters that are larger than the diameters of the screws 13. When fastening the connecting element 17 to the shaft 12 and to the movable part 11, the shaft 12 is fitted in the compressor housing and the movable part 11 is placed in its position of engagement with the opening 9. The connecting element is then fastened in the shaft 12 and in the movable part 11 with the aid of said screws. Because the di- ameters of the bores are larger than the diameters of the screws 13, the shaft 12 can be fitted to the compressor at a "wrong angle", both horizontally and vertically relative to the plane of the abutment area 8. This also enables vertical errors to be corrected. A resilient covering may be provided in the recess around the opening 9 in the barrel wall. This covering, or coating, may function as a seal and will preferably com- prise a polymeric material. Such a covering or coating is preferably provided on the flange 23 of the movable part 11, which lies against the recess around the opening 9 on the barrel wall 11. The angle through which the shaft 12 is able to rotate may be restricted either by a stop provided on the compressor or by the extent to which the maneuvering device 25 rotates the shaft 12. When the compressor is running and compresses working fluid, the movable part 11 will be in the position shown in full lines in Figure 2. The passageway 14 is therewith closed to passage of fluid therethrough. Working fluid, normally air, is delivered to the working chambers of the compressor through the inlet opening 19. The rotors 4, 5 mounted in the working chambers and driven by means not shown transport working fluid from the inlet opening 19 to the outlet opening 6 whilst compressing the fluid at the same time. The working fluid leaves the compressor through the outlet opening 6. Depending on the extent to which the opening 9 widens towards the first end wall, the supply of compressed working fluid can be stopped totally or the output pres- sure of the exiting fluid can be lowered when bringing the movable part 11 out of engagement with the barrel wall 7. This is achieved by activating the arm 18 connected to the shaft 12 by means of said maneuvering device 25, such as to rotate the movable part 11 out of its first end position in engagement with the barrel 7 towards its second end position, shown in broken in Figure 2. The working chambers of the compressor are therewith interconnected and short circuit the inlet and outlet via the rotor grooves or reduce the compression zone in the compressor respectively. The passageway 14 is opened at the same time. This causes the pressure in the outlet 16 to fall.

Claims: Claims 1. A screw rotor compressor that includes two mutually coacting helical screws rotors (4,5), a rotor housing (1) which includes a first end wall (2) and a second end wall (3) and a barrel wall (7,11) connecting said end walls (2,3), wherein the housing (1) has the internal shape of two mutually intersecting cylinders, wherein the first end wall (2) includes an inlet opening (19), wherein the barrel wall (7) includes an outlet opening (6) adjacent the second side wall (3) and a further opening (9) which extends from the outlet opening (6) towards the first end wall (2) and widens over both said cylindrical surfaces, a movable part (11) which coacts with the further opening (9) and which in a first position engages the housing (1) to form said mutually intersecting cylindrical surfaces and in a second position is out of engagement with the housing (1) and distanced from the further opening (9), and a maneuvering device (18,26,25) for positioning the movable part (11) selectively in either said first or said second position, characterized in that the maneuvering device (18,26,25) is adapted to actuate a rotatable shaft (12) mounted on the compressor or firmly fixed relative thereto, said shaft being connected to the movable part (11) via a connecting element (17). 2. A compressor according to Claim 1 , characterized in that the rotatable shaft (12) extends at least generally perpendicularly to the intersection plane (the cusps) of said cylinders. 3. A compressor according to Claim 1 or 2, characterized in that the movable part (11) has a circular cross-section in those circumferential parts that do not border on the outlet opening (6). 4. A compressor according to Claim 3, characterized in that the movable part (11) has the shape of a truncated cone. 5. A compressor according to Claim 3 or 4, characterized in that the movable part (11) has a flange which abuts the barrel wall (7) when said movable part is in its first po- sition. 6. A compressor according to Claim 5, characterized in by a sealing coating or covering in the region of the barrel wall (7) against which the movable part (11) abuts in its first position. 7. A compressor according to one or more of Claims 1-7, characterized in that the opening (9) extends up to said first end wall (2). 8. A compressor according to Claim 1, characterized in that the connecting element (17) has a first planar surface that abuts with said movable part (11), a second planar surface which extends perpendicular to the first surface and which abuts a planar recess provided in the shaft (12) and extending parallel to the center line of said shaft. 9. A compressor according to Claim 8, characterized in that the movable part (11) has become fixedly connected to the connecting element (17) subsequent to having placed the movable part (11) in its first position on the barrel surface (7). 10. A compressor according to Claim 8, characterized in that the movable part (11) has become fixedly connected to the fixed shaft (12) subsequent to having placed the movable part (11 ) in its first position on the barrel surface (7).

Inventors: ENGLUND ARNOLD, ENGLUND, ARNOLD
Applicants: ENGLUND ARNOLD, LYSHOLM TECHN AB, ENGLUND, ARNOLD, LYSHOLM TECHNOLOGIES AB
Application year: 1999
Main classification: F04C18
IPC codes: F04C18, F04C28