ROTARY VANE COMPRESSOR

Abstract: A flat-piston compressor has a body (1) containing a piston chamber bounded by an enclosing wall (2) and two end walls (3, 4). A rotor (5) is disposed eccentrically within the piston chamber and mounted rotatably. The rotor (5) has a diametric slot (55) wherein a flat piston (7) is received so as to be radially moveable therein. The rotor (5) and the flat piston (7) divide the piston chamber into working chambers for the compression of the medium. The medium is conducted out of the working chambers via outlet ducts (91) in the rotor (5). Backflow through the outlet ducts (91) is completely eliminated by the combination of features that self-acting valves (92) in the outlet ducts (91) prevent backflow while in closed position, and that the inner surface (21) of the enclosing wall of the body (1) conforms closely, within the angle ( alpha ), to the enclosing surface (53) of the rotor (5) preventing backflow during the periods when the valves (92) are closing.

Description: ROTARY VANE COMPRESSOR The present invention is concerned with a flat-piston compressor, comprising a body consisting of an enclosing wall and two end walls which form a piston chamber, a rotor mounted to rotate in the piston chamber and disposed eccentrically within the piston chamber so that the enclosing wall of the rotor touches the inside surface of the enclosing wall of the pump body, said rotor having a diametric slot wherein a flat piston is received so as to be radially moveable therein, said rotor and flat piston dividing the piston chamber into working chambers for the compression of a medium and for the transmission thereof from an inlet aperture to an outlet aperture. In order to limit power losses due to backflow, compressors of this type may be fitted with a valve on the outlet side. EP-A-0255920 presents a flat-piston compressor having self-acting valves in the body. It is intended to be used as a suction pump. In a flat-piston compressor having a self-acting valve or valves in the body on the outlet side and a split piston, substantial power losses arise, particularly at high speeds, due in part to backflow through the valve during its closure phase and in part to friction between the flat piston and the body. Such a compressor cannot compete in efficiency with certain other types of compressor and has therefore only been used in certain special applications where efficiency is of secondary importance. Self-acting valves are very commonly used in reciprocating piston compressors. That a valve is self-acting means that it is opened and closed by pressure differences in the working medium. S lf-acting valves used in compressors are usually constructed of a seat, a stop, a valve plate, and springs. The valve plate is free to move between the seat and the stop. The valve is open when the valve plate is in contact with the stop and closed when it is in contact with the seat. The purpose of the springs is to reduce backflow by expediting the valve's closing phase. In flat-piston compressors with a self-acting valve in the body on the outlet side, problems have been experienced, particularly at high speeds, in limiting the backflow through the valve to an acceptable volume of medium per unit time. With valve springs the backflow can be reduced but not eliminated. More rigid springs afford efficiency gains from reduced backflow but losses from higher back pressure. The purpose of the present invention is to make available a flat-piston compressor without valve springs which is completely free from backflow. According to the invention this is achieved by the combination of the following features: that the rotor is provided with outlet ducts opening from its casing surface for the egress of the medium from the working chambers and self-acting valves arranged when in closed position to prevent backflow of the medium through the outlet ducts; and that the cross-section of the inner surface of the body's enclosing wall is formed so as to conform closely, within a certain angle, to the enclosing surface of the rotor in order to prevent backflow of the medium through the outlet ducts during the periods when the self-acting valves are closing. An example of embodiment of the invention will be described hereafter with reference to the attached drawings. Fig. 1 shows an axial section through a flat-piston compressor according to the invention. Fig. 2 shows a section on the line I-I in Fig. 1. The flat-piston compressor comprises a body 1 with a piston chamber defined by an enclosing wall 2 and two parallel end walls 3 and 4. A circular cylindrical rotor 5 is positioned eccentrically within the piston chamber. The axis of the rotor 5 is indicated by 51. The rotor 5 has a shaft 52 which is mounted in bearings 60, 61 in the end wall 4. The rotor 5 has a central cavity 54 which is open towards the end wall 3. The end wall 3 supports a shaft journal 31 extending into the central inner region of the body 1 and carrying on its free end a rolling bearing 32 whose axis is indicated by 321. The rotor 5 has a diametric slot 55 passing through the axis 51 of the cup-shaped rotor 5. A flat piston 7 is received in the diametric slot 55 in the rotor 5. The flat piston 7 consists of a piston plate 71 which extends with little play through the diametric slot 55 in the rotor 5 so as to be radially moveable with respect to the rotor 5 within said diametric slot 55. The piston disk 71 is equal in width to the distance between the end walls 3 and 4 of the body 1. The generally flat and rectangular piston plate 71 has two axial edges 72 which move parallel with the inner surface 21 of the enclosing wall 2 and further has radial edges 73, 74 which run close to and parallel with the inner surfaces of the end walls 3 and 4. The inner surface 21 of the enclosing wall of the body 1 is shaped so that within an angle α, whose bisector 22 intersects the axis 51 of the rotor 5 and the axis 321 of the rolling bearing 32 and whose apex lies on the axis 51 of the rotor 5, said inner surface 21 conforms closely to the rotor 5 and over the remaining sector conforms to the path described by the axial edges 72 of the flat piston 7 as the rotor 5 rotates. The end of the flat piston 7 nearer to the end wall 7 is provided with a guide slot 75 which in open towards end wall 3 and whose side walls 76 are flat and parallel and lie in planes perpendicular to the principal plane of the piston plate 71. The distance between the side walls 76 is equal to the outer diameter of the rolling bearing 32, so that the piston plate 71 can be translated relative to the rolling bearing 32. The flat piston 7 is symmetrical about a plane which includes the axis 321 of the rolling bearing 32 and which is perpendicular to the principal plane of the piston plate 71. The flat-piston compressor has an inlet aperture 81 in the enclosing wall 2 of the body 1 and an outlet aperture 82 in the end wall 3. On the inner surface 21 of the enclosing wall the inlet aperture 81 extends in the direction of rotation of the rotor 5 as shown by the arrow 56 from where angle α ends to approximately 90 degrees from the bisector 22 of angle α. Regarded in an axial direction, the cross-sectional area of the outlet aperture 82 is covered by the central cavity 54 of the rotor 5. For the egress of the medium from the working chamber the rotor 5 is provided with two outlet ducts 91 opening from the enclosing surface 53 of the rotor 5 and located one on each side of the diametric slot 55. The outlet ducts 91 are located immediately ahead of the diametric slot 55 in the direction of rotation as indicated by the arrow 56. The outlet ducts 91 are oriented radially inwards into the rotor 5 and lead from the working chambers into the central cavity 54 of the rotor, which discharges from the rotor 5 to the outlet aperture 82. The two outlet ducts 91 are each fitted with a self-acting valve 92 to prevent backflow of the medium through the outlet ducts 91. A self-acting valve 92 has a seat 94 and a stop 95, between which a valve plate 93 is free to move and so arranged that when it is in contact with the seat 94 and covering the seat port 96 the valve is closed, and when it is in contact with the stop 95 the valve is open. The valve plate 93 is acted on not only by the pressure difference on either side thereof but also by the centrifugal force which acts in a radially outward direction during the rotation of the rotor. If the piston plate 71, in the course of the rotation of the rotor 5 in the direction indicated by the arrow 56, is in the position illustrated in Fig. 2, as soon as the rotor 5 has passed through an angle 12 a new working chamber begins to expand, being bounded by the inner surface 21 of the enclosing wall of the body 1, the rotor 5, the end walls 3 and 4, and the flat piston 7. This chamber immediately comes into communication with the inlet aperture 81. During the continued rotation of the rotor 5, the volume of the working chamber expands continuously, while medium flows into the working chamber. The working chamber reaches its maximum volume when the rotor 5 has rotated through 270 degrees. Immediately thereafter, the working chamber ceases to be in communication with the input aperture 81 and internal compression begins as the volume of the working chamber decreases. When the pressure inside the working chamber exceeds the pressure inside the central cavity 54 of the rotor 5 sufficiently to overcome the centrifugal force acting on the valve plate 93, the self-acting valve 92 opens and medium passes through the outlet duct, which is in communication with the working chamber. As the rotor 5 continues to rotate, all of the medium in the working chamber is forced out through the outlet duct 91 and thence via the central cavity 54 out of the outlet aperture 82. When the seat port 96, which has been in contact with the working chamber, is entirely within the angle α. the inner surface 21 of the enclosing wall of the body 1 forms a seal with the radially outward portion of the seat 94, after which medium can no longer flow in either direction through the outlet duct 91. Thus, provided the self-acting valve 92 is fully closed by the centrifugal force acting on the valve plate 93 while the seat port 96 is entirely within angle α, backflow cannot occur during the closure phase of the self- acting valve 92. Because the rolling bearing 32 supports the flat piston 7 by its guide slot 75. the flat piston 7 is fixed radially in its own plane, but being moveable in the direction normal thereto it is able to follow the rotor 5 as it rotates, while being moveable relative to the rotor 5 in the radial direction only. As the rotor 5 rotates, the path of the axially oriented edges 72 of the flat piston 7 will be uniquely determined. Thus if the cross-sectional shape of the inner surface 21 of the enclosing wall of the body 1, outside the angle α: conforms with the path described by the axial edges 72, the flat piston 7 will form a seal directly with the enclosing wall surface 21. If the cross-sectional shape of the inner surface 21 of the enclosing wall of the body 1, even outside the angle α, diverges somewhat from the path described by the axial edges 72, being e.g. a circular arc, the gap between the flat piston 7 and the enclosing wall surface 21 can be bridged with conventional blades which are free to move radially in slots in the flat piston 7. The enclosing wall surface 21 is preferably cylindrical, but it will be apparent to one skilled in the art that one might choose a more or less conical form or a form defined by a curved generatrix. The expert will also see that the operating range of the flat-piston compressor comprises pressures from far below to far above atmospheric pressure. The above example of embodiment shows a flat-piston compressor in which backflow is prevented, in which friction between the flat piston and the enclosing wall of the body is eliminated, and in which the degree of compression is automatically adapted for optimal efficiency regardless of the pressures on the inlet and the outlet sides. However, the invention is not limited to this embodiment but may be modified within the terms of the Claims presented hereafter.

Claims: CLAIMS 1. A flat-piston compressor comprising a body ( 1 "> consisting of an enclosing wall (2) and two end walls (3, 4) forming a piston chamber, a rotor (5) mounted to rotate in the piston chamber and disposed eccentrically within the piston chamber of the body (1 ) so that the enclosing wall (53) of the rotor (5) touches the inside surface (21 ) of the enclosing wall of the body (1), said rotor (5) having a diametric slot (55) wherein a flat piston (7) is received so as to be radially moveable therein, and said rotor (5) and flat piston (7) dividing the piston chamber into working chambers for the compression of the medium and for the transmission thereof from an inlet aperture (81) to an outlet aperture (82); c h a r a c t e r i s e d b y the combination of features that the rotor (5) is provided with outlet ducts (91) opening from its casing surface (53) for the egress of the medium from the working chambers and with self- acting valves (92) arranged when in closed position to prevent backflow of the medium through the outlet ducts (91), and that the cross-section of the inner surface (21) of the enclosing wall of the body (1) is formed so as to conform closely, within a certain angle (α), to the enclosing surface (53) of the rotor (5) in order to prevent backflow of the medium through the outlet ducts (91 ) during the periods when the self-acting valves (92) are closing. 2. A flat-piston compressor as claimed in Claim 1, c h a r a c t e r i s e d in that the rotor (5) is provided with a shaft (52) which extends out through one end wall (4), said shaft (52) being mounted rotatably in bearings (60. 61) which are directly or indirectly supported by said end wall (4), and that the outlet ducts (91) of the rotor (5) discharge directly or indirectly out of the rotor (5) to an outlet aperture (82) in the other end wall (3). 3. A flat-piston compressor as claimed in Claim 1 or 2, c h a r a c t e r i s e d in that the outlet ducts (91) in the rotor (5) for the egress of the medium from the working chambers are at least two in number, whereof at least one opens on each side of the diametric slot (55) in the rotor (5). 4. A flat-piston compressor as claimed in any of Claims 1-3, characterised in that the outlet ducts (91) discharge into a central cavity (54) in the rotor (5) and that said central cavity (54) is open to the end wall (3) and discharges to the outlet aperture (82) in the end wall (3). 5. A flat-piston compressor as claimed in any of Claims 1-4, characterised in that a bearing arrangement (31, 32, 75) is disposed to support the flat piston (7) to be radially fixed in its own plane and to support said flat piston (7) to permit translation thereof in a direction generally normal to the principal plane of said flat piston (7). 6. A flat-piston compressor as claimed in Claim 5, c h a r a c t e r i s e d in that the bearing arrangement (31, 32, 75) includes a stationary-mounted rolling bearing (32) which is axially parallel to the axis (51) of the rotor (5) and that the rolling bearing (32) is received in a guide slot (75) in the flat piston (7) to be moveable therein and is supported by a journal (31 ) which is directly or indirectly supported by the end wall (3). 7. A flat-piston compressor as claimed in Claim 6, characterised in that the rotor (5) is provided with a central cavity (54) which is open towards the end wall (3) in order to permit the rolling bearing (32) which supports the flat piston (7) to be located close to the centre of gravity of the flat piston (7). 8. A flat-piston compressor as claimed in any of Claims 5-7, characterised in that the cross-sectional shape of the inner surface (21) of the enclosing wall of the body (1) is formed so that within an angle (α) it conforms closely to the enclosing surface (53) of the rotor (5) and elsewhere conforms to the path described by the axial edges (72) of the flat piston (7) as the rotor (5) rotates.

Inventors: SVENSSON GOESTA, SVENSSON, GOESTA
Applicants: SVENSSON GOESTA, SVENSSON, GOESTA
Application year: 1999
Main classification: F04C18
IPC codes: F01C21, F04C18, F04C29