Abstract:
The invention concerns a hydraulic axial piston machine with a housing, in which a cylinder drum having at least one cylinder is arranged to be rotatable around an axis, in which cylinder is located a piston that is supported on a swashplate, whose inclination angle is adjustable in an adjustment plane. It is endeavoured to keep the cost of manufacturing individual parts of the axial piston machine small. For this purpose it is provided that on the side facing away from the cylinder drum ( 4 ) the swashplate ( 12 ) has a spherical bearing surface ( 15 ), which rests on a spherical supporting surface ( 16 ) in a bottom part ( 3 ) of the housing ( 2 ) and comprises an inclination protection ( 31 - 34 ), which counteracts an inclination of the swashplate ( 12 ) perpendicularly to the adjustment plane.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Patent Application No. PCT/DK2008/000349 filed on Oct. 8, 2008 and German Patent Application No. 10 2007 048 316.5 filed Oct. 9, 2007. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention concerns a hydraulic axial piston machine with a housing, in which a cylinder drum having at least one cylinder is arranged to be rotatable around an axis, in which cylinder is located a piston that is supported on a swashplate, whose inclination angle is adjustable in an adjustment plane. 
       BACKGROUND OF THE INVENTION 
       [0003]    Such an axial piston machine is, for example, known from DE 196 08 228 A1. Here, the swashplate is formed as a section of a cylinder and lies in a correspondingly formed bearing shell. For adjusting the inclination angle, the swashplate can be tilted around an axis that extends in parallel to the axis of the cylinder. 
         [0004]    U.S. Pat. No. 1,533,399 shows a further axial piston machine, in which the swashplate is also formed by a section of a cylinder, whose cover surface has a worm wheel toothing that engages in a worm shaft. When the worm shaft is turned, the inclination of the swashplate is changed. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is based on the task of keeping the cost of manufacturing individual parts of an axial piston machine small. 
         [0006]    With a hydraulic axial piston machine as mentioned in the introduction, this task is solved in that on the side facing away from the cylinder drum the swashplate has a spherical bearing surface, which rests on a spherical supporting surface in a bottom part of the housing and comprises an inclination protection, which counteracts an inclination of the swashplate perpendicularly to the adjustment plane. 
         [0007]    With this embodiment, both the swashplate and the bottom part with its supporting surface can be made by means of turning. For this purpose, an element, which will eventually form the supporting surface, is simply fixed in a lathe and worked. The same applies for the bottom part. The blank required for manufacturing the swashplate is only slightly larger than the finished swashplate, that is, the material losses are relatively small. A spherical bearing surface can be inclined in all directions in a spherical supporting surface. As, however, a change of the relative alignment between the swashplate and the bottom part of the housing is only desired in one direction, the inclination protection is provided, which prevents an inclination in all other directions. For this purpose, it is sufficient, if the inclination protection can adopt forces acting perpendicularly to the adjustment plane. 
         [0008]    Preferably, the swashplate has an asymmetric design. This is simply achieved in that a segment is removed from the swashplate, or that the swashplate is chamfered on the side opposite the bearing surface. The asymmetric design has the advantage that the swashplate does not need substantially more space than is absolutely required for the adjustability. 
         [0009]    Preferably, a pin connected to the swashplate projects through an opening in the supporting surface, the opening having, at least in the adjustment plane a larger extension than the pin. Then, the pin can be used to adjust the inclination of the swashplate. As it projects through the supporting surface, the adjustment can be made from a position, where no other elements of the axial piston machine are interfering. 
         [0010]    Preferably, an adjustment arrangement acts upon the pin. The inclination of the swashplate can be set manually by means of the pin. However, a larger accuracy can often be achieved, if an adjustment arrangement is used. 
         [0011]    It is preferred that the adjustment arrangement has at least one adjusting screw. Rotation of the adjusting screw will change its position in the bottom plate. The adjusting screw acts upon the pin. The change of the adjusting screw position changes the angle alignment of the pin in relation to bottom plate and thus also the inclination of the swashplate. 
         [0012]    Preferably, the adjustment arrangement has two adjusting screws acting upon the pin from opposite sides. Thus, the pin can be fixed in two directions, particularly between the two adjusting screws. If the angle alignment of the swashplate, that is, the inclination angle, has been set, this state can be permanently fixed by the two adjusting screws. Alternatively, an adjustment can be achieved by means of only one screw, which then acts upon the pin in two directions (pull and pressure). 
         [0013]    Preferably, the pin is part of a locking device. Thus, the pin cannot only be used to change the inclination angle of the swashplate, but also to retain the inclination angle after a change. 
         [0014]    It is preferred that the pin is screwed into the swashplate and comprises a head that can be clamped to the bottom part. When the swashplate has then assumed the desired inclination angle, the pin is screwed further into the swashplate, so that the head is clamped to the bottom part. In this connection, it is possible that auxiliary elements are located between the head and the bottom part, for example a washer or a support arrangement, which again comprises a pair of spherical faces, which can be displaced in relation to each other. 
         [0015]    Preferably, the opening is surrounded by a sealing, which is located between the bearing surface and the supporting surface. The sealing then prevents hydraulic fluid from reaching the opening and thus ensures the tightness of the machine in this area. 
         [0016]    Preferably, the inclination protection has at least one groove, which is located in one of the parts bearing surface and supporting surface, and in which at least one guide pin is guided, which is located in the other of the parts bearing surface and supporting surface. The interaction between the groove and the guide pin ensures that the swashplate can only change in relation to the bottom part of the housing in one plane. Other changes, also rotational movements of the swashplate in relation to the bottom part, are not possible. 
         [0017]    Preferably, the guide pin is fixedly connected to the part allocated to it. This simplifies the mounting. The guide pin can, for example, be glued onto or injected into the swashplate. 
         [0018]    Preferably, the groove is divided into at least two sections along the adjustment plane. This firstly ensures that the supporting surface or the bearing surface remains as large as possible. Secondly, the sections of the groove can also be used as inclination angle limitations, so that a too large inclination of the swashplate is avoided. If this is not required, the groove can also be continuous. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In the following, the invention is described on the basis of preferred embodiments in connection with the drawings, showing: 
           [0020]      FIG. 1  is a hydraulic axial piston machine in a section, 
           [0021]      FIG. 2  is an enlarged section from  FIG. 1 , 
           [0022]      FIG. 3  is a modified embodiment of a swashplate-bottom part arrangement in a perspective view, 
           [0023]      FIG. 4  is the arrangement of  FIG. 3  from another visual angle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0024]      FIG. 1  shows a hydraulic axial piston machine  1  with a housing  2  that comprises a bottom part  3 . A cylinder drum  4  is rotatably supported in the housing  2 . The rotation occurs around an axis  5 , which is at the same time the axis of a shaft  6 , which is unrotatably connected to the cylinder drum  4 . 
         [0025]    Several cylinders  7  are arranged in the cylinder drum, the axes of the cylinders  7 , which are not shown in detail, being arranged eccentrically to the axis  5 . Preferably, the axes of the cylinders  7  are located on a circle around the axis  5 . 
         [0026]    Via a valve plate  8 , at which the cylinder drum  4  rests under insertion of slide shoes  9 , the cylinders  7  are supplied with pressurised hydraulic fluid, or pressure-less fluid is discharged from the cylinders  7 , when the axial piston machine works as a motor. When the axial piston machine works as a pump, pressurised fluid leaves the cylinders  7  through the valve plate  8 , and fluid is sucked in through the valve plate  8 , depending on the rotation angle position of the cylinder drum  4 . 
         [0027]    The sectional view of  FIG. 1  divides the valve plate  8  into two halves, each having a control kidney. Therefore, these are not visible in the present sectional view. 
         [0028]    In each cylinder  7  is arranged a piston  10 , which is supported via a slide shoe  11  on a swashplate  12 . Via a holddown plate  13  the slide shoes  11  are held in contact with the swashplate  12 , or rather with a control surface  14  of the swashplate  12 . When the cylinder drum  4  rotates, the pistons  10  are moved axially in relation to the cylinder drum  4  by the control surface  14  and the holddown plate  13 . Such an embodiment of an axial piston machine  1  is known in principle. 
         [0029]    The swashplate  12  has, on the side facing the cylinder drum  4 , the plane control surface, on which the sliding shoes  11  rest, and on the side facing away from the cylinder drum  4 , a spherical bearing surface  15 , which rests in an accordingly spherical supporting surface  16  at the bottom part  3 . The radii of the bearing surface  15  and the supporting surface  16  are adjusted to each other, so that an extensive bearing of the bearing surface  15  on the supporting surface  16  occurs. Both the bearing surface  15  and the supporting surface  16  can be made by means of turning, which is a relatively simple manufacturing process. 
         [0030]    As can be seen, particularly from  FIG. 2 , the swashplate is made to be asymmetrical, that is, at the lower end (the direction relates to the view in  FIG. 2 ) a part  17  is missing. In this area, the swashplate  12  can be swung to its other extreme position. 
         [0031]    A pin  18  is screwed into the swashplate  12 . The pin  18  projects through an opening  19  in the supporting surface  16 , so that it extends outwards from the bottom part  3 . The pin  18  has a head  20 , which has a torque application surface  21 , for example a hexagon socket. The opening  19  is an oblong hole, that is, in one direction it has an extension, which is larger than the diameter of the pin  18 . Vertically to that, the extension of the opening  19  corresponds to the diameter of the pin  18 . Thus, the pin  18  only permits the swashplate  12  to swing in relation to the bottom part  3  in one direction. 
         [0032]    The head  20  acts upon a supporting disc  22 , which has a plane first surface  23  and a spherical second surface  24 , the spherical surface  24  interacting with a bearing shell  25 , which has a corresponding spherical surface on the side facing the supporting disc  22  and a plane surface on the part facing the bottom part  3 . Accordingly, it is possible, when screwing the pin  18  into the supporting disc  22 , to fix the supporting disc  22  in relation to the bottom part  3 , thus retaining an already set inclination or angle position. 
         [0033]    The pin  18  simultaneously acts as adjustment element for the inclination angle of the swashplate  12 . Adjustment screws  26 ,  27  are inserted in the bottom part  3  from sides opposite each other, the adjustment screws  26 ,  27  acting upon the pin  18  via adjustment pins  28 ,  29 . However, it is also possible that the adjustment screws  26 ,  27  act directly upon the pin  18 . If, for example, the adjustment screw  26  is screwed somewhat out of the bottom part  3  and the adjustment screw  27  is screwed somewhat into the bottom part  3 , the pin  18  is swing somewhat downwards, thus changing the inclination angle of the control surface  14  of the swashplate in relation to the axis  5 . 
         [0034]    A sealing  30  is arranged between the bearing surface  15  and the supporting surface  16 , the sealing  30  surrounding the opening  19 , thus preventing fluid from escaping from the inside of the axial piston machine  1  into the environment. 
         [0035]    The embodiment of the swashplate  12  with a spherical bearing surface  15  that is supported in a correspondingly spherical supporting surface  16  in principle permits an inclination of the swashplate  12  in all directions. Also a rotational movement of the swashplate  12 , for example around the axis  5 , would be possible. However, it is endeavoured to ensure that the swashplate  12  can only move in an adjustment plane. In the  FIGS. 1 and 2 , the adjustment plane corresponds to the drawing plane. The control surface  14  extends laterally to the drawing plane and thus laterally to the adjustment plane. The inclination of the swashplate  12  and thus of the control surface  14  shall only be changeable in parallel to the drawing plane, that is, in parallel to the adjustment plane. 
         [0036]    For this purpose, the swashplate  12  has two guide pins  31 ,  32 , which are led through the bearing surface  15  and connected to the swashplate  12 . The guide pins  31 ,  32  can, for example, be pressed into the swashplate  12 , glued into the swashplate  12  or otherwise fixed there. The guide pins  31 ,  32  are guided in grooves  33 ,  34 . 
         [0037]    The grooves  33 ,  34  have a width that corresponds to the width of the guide pins  31 ,  32 . Thus, the guide pins  31 ,  32  fill the grooves  33 ,  34  in a direction laterally to the adjustment plane, that is, laterally to the drawing plane. Along the adjustment plane, however, the grooves  33 ,  34  have an extension, which is larger than the corresponding extension of the guide pins  31 ,  32 . Accordingly, together with the grooves  33 ,  34 , the guide pins  31 ,  32  ensure that the inclination of the swashplate  12  in relation to the axis  5  can change in the adjustment plane, another movement of the swashplate  12 , however, being impossible. Particularly an inclination of the swashplate  12  laterally to the adjustment plane is prevented. 
         [0038]    Of course, it is also possible to arrange the guide pins  31 ,  32  in the bottom part  3  and the grooves  33 ,  34  in the bearing surface  15 . 
         [0039]    The above mentioned control kidneys have different pressures, which again attempt to incline the swashplate  12 . This is prevented by the pins  31 ,  32 , which interact with the grooves  33 ,  34 , where they are supported at the lateral flanks. 
         [0040]    In  FIG. 1 , the swashplate  12  is shown in its one extreme position, and in  FIG. 2  in its other extreme position. The extreme positions, that is, the maximum or minimum possible inclination angle, respectively, occur in that the guide pins  31 ,  32  butt against frontside limitations of the grooves  33 ,  34 . 
         [0041]    The  FIGS. 3 and 4  show perspective exploded views of a modified embodiment of the swashplate  12  and the bottom part  3 , in which corresponding elements have the same reference numbers as in  FIGS. 1 and 2 . 
         [0042]    It appears from  FIG. 3  that the opening  19  is made as an oblong hole, so that here the pin  18  has a certain movability. The supporting disc  22  can be inserted immediately into the opening  19 . A part of its circumference then projects somewhat laterally over the opening  19 . 
         [0043]    A further difference is that the grooves  33 ,  34  are made to be coherent in the supporting surface  16 . Thus, they form a common groove. 
         [0044]    Here, the asymmetric design of the swashplate  12  is realised in a different manner. A cylinder-shaped blank is used, which receives the spherical bearing surface  15  on its frontside. The opposite frontside of the blank is then bevelled to form the control surface  14 . 
         [0045]    Also here, the guide pins  31 ,  32  together with the groove  33 ,  34  form an inclination protection, so that the swashplate  12  is only movable in one direction in relation to the bottom part  3 , namely in the direction, in which the guide pins  31 ,  32  can slide in the groove  33 ,  34 . 
         [0046]    In many cases the inclination angle of the swashplate  12  must only be varied in a small area, for example by ±3°. With the change of the inclination angle, the displacement of the axial piston machine  1  can be changed. 
         [0047]    With the embodiments shown until now, it is not provided that the inclination angle of the swashplate  12  can be continuously changed. On the contrary, with these embodiments an inclination angle is prespecified and then changed from time to time, if a need occurs. 
         [0048]    However, it is also possible to change the inclination angle of the swashplate  12  during operation, for example, if the adjustment screws  26 ,  26  are activated by a motor, or the pin  18  is otherwise displaced by a drive, for example a small electric, hydraulic or pneumatic motor. The change of the displacement, that is, the change of the inclination of the swashplate  12 , can then be controlled on the basis of many parameters. If the axial piston machine  1  is used as pump in a reverse osmosis system, such parameters could, for example, be the temperature or the salt content of the water. 
         [0049]    The guiding of the swashplate  12  in the bottom part  3  by means of the guide pins  31 ,  32  and the grooves  33 ,  34  has the advantage that also an adjustment during operation requires only little force to change the inclination angle of the swashplate  12 . The reason for this is that the pressure from the piston acts relatively uniformly in both inclination directions. In principle, the adjustment arrangement only has to overcome frictional forces, which occur on the one side between the bearing surface  15  and the supporting surface  16  and on the other side between the guide pins  31 ,  32  and the side walls of the grooves  33 ,  34 . Thus, the adjustment of the inclination angle of the swashplate could also be made by a motor, in which a relatively small torque is sufficient. 
         [0050]    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.