Abstract:
An axial piston machine, especially an air-conditioning compressor for motor vehicles, including a power unit which is rotatably driven by a shaft and in which the rotary movement is converted, via a swash plate, a wobble plate, or a pivot ring, into a fore-and-aft movement of pistons that suction in and compress pressure media. The shaft is mounted in a forward, first axial bearing, among other things.

Description:
The present invention relates to an axial piston machine, in particular to an air-conditioning compressor for motor vehicles, having a power unit which is rotationally driven by a shaft and in which the rotational motion is converted via a pivot ring, a swash plate or a wobble plate, or via a gear unit performing essentially the same function, into a reciprocating motion of pistons which draw in and compress pressure media, the shaft being supported, inter alia, in a front, first axial bearing. 
     BACKGROUND 
     Axial piston machines of this kind are generally known. A disadvantage associated with these machines is that, in the unpressurized state or at low housing pressures and high axial accelerations, the shaft can potentially lift off from the front axial bearing. 
     In addition, axial piston machines are known which have a second, rear axial rolling-contact bearing at the opposite end of the shaft. The second axial rolling-contact bearing leads to an increase in the component part costs and in the manufacturing costs for a machine of this kind, and must also exhibit suitable adjustability characteristics. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to devise an axial piston machine which will overcome these disadvantages. 
     The present invention provides an axial piston machine having a power unit which is rotationally driven by a shaft and in which the rotational motion is converted via a pivot ring, a swash plate or a wobble plate, or via a gear unit performing essentially the same function, into a reciprocating motion of pistons which draw in and compress pressure media, the shaft being supported, inter alia, in a front, first axial bearing, in accordance with the present invention, an elastic, resilient, one-piece axial fixing and bearing device, which preloads the shaft against the front first axial bearing, acting on the shaft in the area of the rear end opposite the front axial bearing. An axial piston machine is preferred in which the axial fixing and bearing device is braced, on the one hand, axially against the shaft and, on the other hand, axially against a housing component, for example against a valve-plate device, a cylinder block, or a cylinder head. 
     In addition, an axial piston machine is preferred in which an axial fixing and bearing device is designed as a molded plastic part, in particular one made of PA 6.6 material. 
     An axial piston machine is also preferred in which the axial fixing and bearing device has an axial annular contact surface F 1  for the shaft and an axial annular contact surface F 2  for the valve-plate device, the cylinder block, or the cylinder head, contact surfaces F 1  and F 2  being joined to one another by an annular surface F 3  that is curved in an approximately tulip shape and is resilient in the axial direction. Equally preferred is an axial piston machine in which, radially outside of contact surface F 2 , the axial fixing and bearing device has a frustoconical, thin-walled outer peripheral surface F 4  which rests radially in a recess of the cylinder block, the cylinder head, or the valve-plate device. 
     The present invention provides that the molded plastic part is subject to a slight degree of intentionally permitted wear that is due to the purposeful use of elastic and plastic characteristics, while taking into consideration the creep behavior which is used to adjust the molded plastic part to its axial installed length. Here, the advantage is derived that, in comparison to known axial bearings, no adjustment procedures are required when using the molded plastic part according to the present invention. It is generally an advantage of the present invention that the one-piece axial fixing and bearing device element eliminates the need for a second axial bearing, as well as for a resilient contact-pressure device and for a vibration damping in the axial direction. 
     In addition, an axial piston machine is preferred in which the axial fixing and bearing device is used as a shipping brace. Here, the advantage is derived that, in the unpressurized and non-operating state, the shaft is secured against axial displacements caused by impacts, and the molded plastic part counteracts any lifting off from the front axial bearing, both in the unpressurized state, as well as during operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in the following with reference to the figures, which show: 
         FIG. 1  a cross section through one portion of an axial piston machine, including the installed axial fixing and bearing device; 
         FIG. 2  the axial fixing and bearing device in a plurality of three-dimensional representations. 
     
    
    
     DETAILED DESCRIPTION 
     Located within a compressor housing  1  in  FIG. 1  is a drive shaft  3  whose rotational motion sets a driving pin  5  into rotation, which, in turn, sets a so-called pivot ring  7  into rotation. In this context, pivot ring  7  in this machine may assume various angular positions and thus vary the displacement volume of the compressor. Sliding shoes  9 , which are disposed within a piston brace  11  of a piston  13 , glide on rotating pivot ring  7 . Piston shoes  9  execute wobbling movements within brace  11  of piston  13 , the rotational motion of pivot ring  7  being converted into a reciprocating motion of pistons  13 . Pistons  13 , in turn, reciprocate within a cylinder block  15  and, in the process, draw in a refrigerant, compress it and expel it into the high-pressure zone of an air-conditioning system. Since pistons  13  apply corresponding axial forces to pivot ring  7  and thus to shaft  3  during this suction and compression work, these axial forces must be absorbed via an axial bearing  17  in the front shaft region. In most operating modes, the axial forces act in such a way that axial bearing  17  is always pressed against housing part  19  by the axial forces occurring in the shaft. However, in the unpressurized state of the operation or at low housing pressures and at high axial accelerations of pistons  13 , shaft  3  can potentially lift off from bearing  17 . Therefore, in accordance with the present invention, a molded plastic part  21 , thus the so-called axial fixing and bearing device, is located between shaft end  23  opposite axial bearing  17 , and a housing part, in this case valve plate  25 . Molded plastic part  21  preloads the shaft against bearing  17  and thus counteracts any lifting of shaft  3  off of bearing  17 . In this context, due to its elastic characteristics and a slight degree of intentionally permitted wear, which occurs as the result of plastic deformation and deliberately utilized creep behavior, molded plastic part  21  is designed to be a component that is readily adaptable to the axial length of the installation space between shaft end  23  and valve-plate device  25 . Molded plastic part  21  is designed in such a way that an axial, approximately annular contact surface F 1  is provided for shaft end  23 , and an axial, very narrow, annular-shaped contact surface F 2  for valve-plate device  25 , both contact surfaces F 1  and F 2  being joined to one another by a resilient annular part F 3  that is curved in an approximately tulip shape and is resilient in the axial direction. Due to the elasticity of the elastomer material, which, for example, may be rubber, plastic, or a mixture of the two, this curved, resilient annular part F 3  produces the axial contact force for pressing shaft  3  against front axial bearing  17 . Starting from bearing surface F 2  on the valve plate, molded plastic part  21  continues radially outwardly, merging into frustoconical, thin-walled peripheral surface F 4 , which rests radially in a recess  27  of cylinder block  15 . The radial centering of molded part  21  is thereby provided as well, so that it may have sufficient clearance at its central opening  29  from a shaft bushing  31 , with the result that no frictional forces are produced there during rotation. Molded plastic part  21  advantageously eliminates the need for providing a second axial bearing or an additional resilient contact-pressure device at rear shaft end  23 , as required in related art methods. Thus, molded plastic part  21  fulfills both functions: that of axial fixing through generation of an axial force and that of an axial bearing. The design as a molded plastic part  21  is conceived to be very simple and economical. 
       FIG. 2  shows a variant of the molded plastic part, thus of axial fixing and bearing device  21 , three-dimensionally and in three views. Axial, annular contact surface F 1  for shaft  3 , respectively shaft end  23  from  FIG. 1 , is discontinuous here in the area of central opening  29  due to four cut-in grooves  33 , so that pockets for a lubricant passage are formed, as are lubricating slots as well. 
     Bearing surface F 2 , which rests against valve plate  25  in  FIG. 1 , is a narrow annular surface F 2  here, as shown in cross section in  FIG. 1 . 
     Thus, a slight amount of intentionally permitted wear occurs at the surface in order to facilitate adaptation to the axial length of the installation space of molded plastic part  21 . The axial resilience is provided in this case by an approximately frustoconical intermediate surface F 3 , which joins together the two bearing surfaces F 1  and F 2 . The relatively thin-walled fourth collar F 4 , thus the frustoconical annular surface, then effects the centering action in recess  27  of cylinder head  15  from  FIG. 1 . The approximately tulip-shaped peripheral surface F 3 , as shown in  FIG. 1 , may be realized by a stepped configuration of surfaces F 3 . 1 , F 3 . 2 , F 3 . 3  and F 3 . 4 , as is apparent in the middle and bottom illustrations in  FIG. 2 . It is merely important that the arched or conical shape be designed for an appropriate deflection motion and spring action. 
     Thus, the advantages of the present invention are evident in the axial fixing of compressor shaft  3 , in a cost reduction achieved by eliminating the need for a second axial bearing, as well as for the adjusting procedures associated therewith, and, therefore, ultimately in a simplified assembly. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  compressor housing 
           3  drive shaft 
           5  driving pin 
           7  pivot ring 
           9  sliding shoes 
           11  piston brace 
           13  piston 
           15  cylinder block 
           17  axial bearing 
           19  housing part 
           21  molded plastic part 
           23  shaft end 
           25  valve plate 
         F 1  axial annular contact surface 
         F 2  conically formed contact surface 
         F 3  resilient annular part 
         F 4  frustoconical, thin-walled outer peripheral surface 
           27  recess of cylinder block  15   
           29  central opening of molded part  21   
           31  shaft bushing 
           33  cut-in grooves