Abstract:
The invention concerns a vane cell machine with a stator and a rotor having radially displaceable vanes arranged in guides, said vanes bearing on an inside of the stator and bordering, together with the rotor, the stator and a side wall, work chambers at each axial end of the rotor. It is endeavored to provide a vane cell machine that has a good internal tightness, in which the wear is still kept small. For this purpose, in a radially internal area the side wall comprises an insert that is axially movable in the side wall and has a pressure application surface axially inside and axially outside.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     Applicants hereby claim foreign priority benefits under U.S.C. §119 from German Patent Application No. 10 2011 116 858.7 filed on Oct. 25, 2011, the contents of which are incorporated by reference herein. 
     TECHNICAL FIELD 
     The invention concerns a vane cell machine with a stator and a rotor having radially displaceable vanes arranged in guides, said vanes bearing on an inside of the stator and bordering, together with the rotor, the stator and a side wall, work chambers at each axial end of the rotor. 
     BACKGROUND 
     Such a vane cell machine is, for example, used as amplification pump before or after a pressure converter in a circuit of a reverse osmosis system. In a reverse osmosis system, water, for example saltwater, is pumped through a membrane and purified or desalinated water is then available on the outlet side of the membrane. 
     As, in such a machine, the rotor rotates in relation to the stator and a high pressure rules in the work chambers at least once during each rotation, it must be ensured that the vane cell machine is tight towards the inside and towards the outside. An internal leakage would reduce the efficiency. An external leakage is undesirable anyway. 
     Therefore, the rotor and the side wall must therefore bear on one another with a certain force, in order to keep internal leakages as small as possible. However, this force is not allowed to be too large, as the friction between the side wall and the rotor would thus cause a too large wear. 
     SUMMARY 
     The invention is based on the task of providing a vane cell machine with a good internal tightness and a small wear. 
     With a vane cell machine as mentioned in the introduction, this task is solved in that in a radially internal area the side wall comprises an insert that is axially movable in the side wall and has a pressure application surface axially inside and axially outside. 
     With this embodiment, the side wall is divided into two elements, namely the insert and an element surrounding the insert. The insert then forms some sort of piston in the side plate, said piston being displaceable in the direction of the rotor or in the opposite direction. In this connection, the displacement forces adhere to the pressures acting upon the two pressure application surfaces axially inside and axially outside. When the pressure application surfaces and the pressures acting upon them are adapted to each other accordingly, a hydraulic balance can be achieved, so that the insert and the rotor bear on each other with a force that is chosen so that on the one hand a satisfactory tightness is achieved and on the other hand the wear can be kept small. 
     Preferably, the side wall is made as a plate. A plate is relatively easily manufactured. When the insert is inserted in the plate, the assembled plate can be assembled with the stator as a separate element. With regard to function, the plate with the insert then forms a part of the stator. 
     Alternatively, the side wall can be formed in a housing of the vane cell machine. In this case, no additional element is required apart from the insert, which also has a positive effect on the accuracy during mounting. The smaller the number of parts to be mounted, the smaller the errors that can occur because of tolerances. 
     Preferably, a sealing ring is arranged between the stator and the insert. This sealing ring, for example an O-ring, seals the insert towards the outside. This sealing ring can be arranged in a groove, in order to define its position clearly. The sealing ring is arranged at a position, where adjacent parts are not moving in relation to each other. Thus, the sealing ring provides a simple way of preventing large amounts of fluid from escaping from the stator to the outside. 
     Preferably, the sealing ring is arranged at a radial position of the rotor, at which the forces caused by the pressure of the fluid radially outside the sealing ring are as large as forces caused by the pressure of the fluid on the side of the insert facing the rotor. The forces do not have to be exactly equal. The force acting radially inwards can be somewhat larger than the force acting radially outwards. The sealing ring seals radially inwards. Radially outside the sealing ring, fluid is available between the stator and the insert. On the opposite side of the insert the fluid can penetrate further radially inwards through a gap between the rotor and the insert. In this gap, however, the pressure of the fluid subsides radially from the outside towards the inside. Now, the position of the sealing ring can be determined so that the pressure application surface on the insert is smaller on the axial outside than on the axial inside. In this connection, the pressure application surfaces extend in the radial direction and are exposed to a pressure that acts in the axial direction. The relation between the sizes of the pressure application surfaces is then chosen so that the pressure subsiding in the radial direction acts upon a correspondingly larger pressure application surface on the axial inside of the insert. Simply expressed, when regarding an axial section, the integral of the pressure across the surface on the axial outside of the insert is approximately as large as the pressure integral across the pressure application surface on the axial inside of the insert. 
     Preferably, the insert comprises an axial extension that forms a bearing for a shaft that is connected to the rotor. Thus, it is possible to form the insert so that at the same time it forms the bearing for the shaft of the rotor. The shaft sealing can then be arranged between shaft of the rotor and the insert. In this case, the pressure can act axially inside upon the complete axial extension of the insert. 
     Preferably, the extension comprises a step that forms a bearing surface for the sealing ring. At the same time, the step then defines the radial position of the sealing ring. 
     Preferably, the insert is arranged in a central recess of the side wall and comprises an eccentric bore, through which the rotor is led. When the rotor is provided with a shaft, this shaft is of course led through this eccentric bore of the insert. In a vane cell machine with one work stroke of the vane per rotation of the rotor, the inside of the stator, on which the vanes rest, can have the shape of a hollow cylinder. In order still to realize the radial extension and retraction movement of the vanes, the rotor is eccentrically supported, that is, one point on the circumference of the rotor approaches the inside of the stator and moves away from the inside of the stator again during each rotation. This eccentricity is easily realized by means of the insert. This embodiment has the further advantage that it is easily ensured that the vanes can always rest with their front sides on the element surrounding the insert. Accordingly, the vanes and this element can be adapted to each other with regard to material in such a manner that the wear remains as small as possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention is described on the basis of preferred embodiments in connection with the drawings, showing: 
         FIG. 1  is a schematic longitudinal section through a vane cell machine, 
         FIG. 2  is a section II-II according to  FIG. 1 , 
         FIG. 3  is a partial section through a modified embodiment of a vane cell machine, 
         FIGS. 4   a ,  4   b , and  4   c  are enlarged views of an insert according to  FIG. 3 , 
         FIG. 5  is a schematic view explaining a distribution of pressures on the insert, 
         FIG. 6  is a simplified view according to  FIG. 5  for a different embodiment, and 
         FIG. 7  shows an embodiment modified in relation to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     A vane cell machine  1  comprises a stator  2  in which a rotor  3  is rotatably supported. The rotor is connected to a shaft  4  that is, when the vane cell machine  1  is made as a pump, connected to a drive motor that is not shown in detail. When the vane cell machine  1  works as a motor, an output can be taken at the shaft  4 . 
     The rotor  3  is made of a first material, preferably steel. In the rotor  3  several vanes  5  are distributed in the circumferential direction, each vane comprising a core  6  of steel that is surrounded by an enclosure  7  that is made of a second material that differs from the first material, preferably a plastic material that interacts unfrictionally with the steel of the rotor  3 . The stator  2  is also made of the first material, preferably steel. The enclosure  7  also interacts unfrictionally with the material of the stator  2 , also when the vane cell machine  1  is operated with water. 
     In the following description, steel is used as the first material and a plastic material that interacts unfrictionally with steel is used as the second material. 
     The material for the enclosure  7  can be selected from the group of high-resistant thermo-plastic plastic materials on the basis of polyaryletherketones, in particular polyetheretherketones, polyamides, polyacetals, polyarylethers, polyethyleneterephtalates, polyphenylensulfides, polysulphones, polyethersulphones, polyetherimides, polyamidimides, polyacrylates, phenol-resins, such as novolacquer-resins, and glass, graphite, polytetraflourethylene or carbon, particularly as fibres, can be used as filler. 
     For each vane, the rotor  3  has a guide  8 . Each guide  8  has two substantially radially progressing and axially extending walls  9 ,  10 , between which the vane  5  is guided in the radial direction (in relation to the rotation axis of the rotor). On the radial inside of the vane  5  a chamber  11  is arranged in the guide, fluid getting into said chamber through a gap between the vane  5  and the walls  9 ,  10 . 
     As can be seen from  FIG. 2 , the rotor  3  has an even number of vanes  5 . Between any two diametrically opposed vanes  5 , a rod  12  is positioned. This rod  12  is also made of the friction-reducing plastic material. The rod  12  is dimensioned so that the diametrically opposed vanes  5  bear on the inside  13  of the rotor  3 . A small tolerance is permissible in order to avoid jamming. 
     Any two vanes  5  being adjacent to each other in the circumferential direction border a chamber  14 . As can be seen from  FIG. 2 , the volume of the chamber  14  changes during a rotation of the rotor inside the stator  2 , as known from vane cell machines. 
     The chambers  14  must be tightened at their axial front sides. For this purpose, a side wall  15  is formed at each front side of the vanes  5 . In the present case, the side wall  15  is formed at a plate  16 . The plate  16  is made of steel, so that the vane  5  with its enclosure  7  can rub along the plate  16 . Because of the plastic material of the enclosure  7 , a movement with a relatively low friction occurs here. 
     An insert  17  is inserted in the plate  16 . At least on its surface, the insert is made of a third material that can be equal to the second material. Thus, here the surface of the insert  17  is also made of the friction-reducing plastic material. The insert  17  bears on a front side section  18  of the rotor  3 . 
     The insert  17  is inserted in a central bore  19  of the plate  16 . The insert  17  comprises an eccentric bore  20 , through which the rotor  3  is led. Accordingly, it is possible to dimension the plate  16  with the insert  17  so that during the complete rotation the vanes  5  with their enclosure  7  only bear on the plate  16 , that is, on steel, whereas the rotor  3  with its front side section  18  only bears on the insert  17 , that is, on plastic material. Merely in the area of the radial inner end of the vanes  5  a slight overlapping between vanes  5  and insert  17  can occur, which is, however, uncritical because it is so small. 
     With this embodiment it can be ensured that friction always only occurs between parts, of which one has a surface of steel and the other has a surface of the friction-reducing plastic material, for example polyether ether ketone (“PEEK”). 
     It is possible that fluid under pressure can penetrate axially to the outside between the plate  16  and the insert  17 . Accordingly, an O-ring  22  (or a similar sealing) is arranged between the insert  17  and a front-side housing part  21 . This O-ring  22  can have an axial and/or radial pretension, so that it already tightens during small pressures, for example to avoid a leakage during start-up. 
     The position of the O-ring will be explained in the following. 
     The rotor  3  has several axially extending through channels  33 , which ensure a pressure balance between the axial rotor ends. 
     The insert  17  is movable in the axial direction in relation to the plate  16 , that is, forms some sort of “piston”. The division into insert  17  and plate  16  also simplifies the manufacturing. Thus, the plate  16  and the insert  17  can be made with plane parallel surfaces. The insert  17  can be slightly thicker than the plate  16 . 
       FIG. 3  shows a slightly modified embodiment, in which the same elements have the same reference numbers.  FIG. 4  shows the insert  17  alone, namely in  FIG. 4   a  a front view,  FIG. 4   b  a section A-A according to  FIG. 4   a  and  FIG. 4   c  a side view. 
     The insert  17  is now extended in the axial direction and forms a bearing  23  for the rotor  3 . Accordingly, also the material pair between the rotor  3  (steel) and the bearing  23  on its circumferential surface (PEEK) is made so that here an unfrictional behavior occurs. 
     The position of the O-ring is explained by means of  FIG. 5 . The same and functionally equal elements have the same reference numbers as in the  FIGS. 1 to 4 . 
     The rotor  3  is here made in one piece with the shaft  4 . However, the shaft  4  can also be made as a separate part. 
     Between the insert  17  and the housing part  21  a gap  25  is formed. Further, a gap  26  is provided between the rotor  3  and the insert  17 . The gap  25  can be slightly larger than the gap  26 . In the gap  25  an O-ring  22  is arranged, so that it is ensured that in the pressure-less state the gap  25  can always be kept open. 
     In the gap  25  the insert  17  has a first pressure application surface  27 . In the gap  26  the insert has a second pressure application surface  28 . The first pressure application surface  27  is bordered on the radial inside by the O-ring  22 . Basically, the second pressure application surface  28  is bordered by the shaft  4  or a shaft sealing  29  sealing the shaft  4 . From this it can be seen that the second pressure application surface  28  is larger than the first pressure application surface  27 . The relation between the pressure application surfaces  27 ,  28  can be determined by the position of the O-ring  22 . 
     In the gap  25  between the housing part  21  and the insert  17  a high pressure rules that is symbolized by arrows  30 . This pressure is constant in the radial direction, which is symbolized by the fact that all arrows  30  have the same length. 
     Also in the gap  26  a high pressure rules, which is symbolized by arrows  31 . As a small flow is permitted between the rotor and the insert  17 , the pressure subsides from the radial outside towards the radial inside. This is symbolized by the fact that radially inwards the arrows have a subsiding length. 
     The two pressure application surfaces  27 ,  28  are now dimensioned so that the product of the first pressure application surface  27  and the constant pressure (arrow  30 ) approximately equal to the product of the second pressure application surface  28  and the subsiding pressure in the gap  26 . With this dimensioning it can be achieved that a hydraulic balance occurs across the insert  17 . As the insert is movable in the axial direction in the plate  16 , the position of the insert  17  in relation to the rotor can be adjusted so that a maximum tightness is achieved, yet at the same time the wear is kept small. The movements of the insert  17  in relation to the side plate  16  are, however, very small. 
     The insert  17  and the plate  16  are made as two separate parts, so that the side plate made of the plate  16  and the insert  17  can be made with plane parallel surfaces. 
       FIG. 6  shows a corresponding embodiment of the insert  17  with step  24 . Also here a gap  25  exists between the housing part  21  and the insert  17  and a gap  26  exists between the insert  17  and the rotor  3 . The first pressure application surface  27  is smaller than the second pressure application surface  28 , as the first pressure application surface  27  is bordered radially towards the inside by the O-ring  22 . The step  24  defines the position of the O-ring  22 . In the embodiment according to  FIG. 5  a groove  32  takes over the positioning. 
     Again, the arrows  30 ,  31  symbolize that the pressure in the gap  25  that acts upon the first pressure application surface  27  is constant in the radial direction, whereas the pressure in the gap  26  that acts upon the pressure application surface  28  subsides from the radial outside towards the radial inside. 
       FIG. 7  shows a schematic view of an embodiment that is modified in relation to  FIG. 1 . The same and functionally equal parts have the same reference numbers. 
     In this embodiment, the insert  17  is arranged immediately in the front-side housing part  21 , that is, on the radial outside of the insert  17  the front-side housing part  21  also takes over the function of the plate  16 . 
     In this embodiment, the O-ring  21  between the insert  17  and the front-side housing part is not absolutely necessary. Accordingly, for reasons of clarity, this O-ring is not shown in  FIG. 7 . Of course, it can still be there. This O-ring can then act as “spring” for the generation of an initial force on the insert  17  during start-up, so that already during start-up the insert  17  is pressed against a corresponding surface of the rotor  3 . 
     However, this force can also be generated in a different manner, for example by means of a spring between the insert  17  and the front-side housing part  21 . 
     While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present.