Patent Abstract:
A swash plate pivot bearing is provided having roller bearing segments ( 15 ) arranged between a hollow cylindrical bearing surface ( 12 ) for a swash plate ( 10 ) in a housing ( 3 ) and a cylindrical bearing surface ( 11 ) on the swash plate ( 10 ), held in curved cages ( 17 ) whereby elements are provided for controlling the cages which prevent the cage ( 17 ) accommodating the roller body ( 16 ) from slipping out from the optimum position thereof in the pivot bearing. The cage control elements are integrated into the roller bearing segments ( 15 ) so that at least one roller body ( 23, 23.1, 23.2 ) of cylindrical form has a positive engagement with the hollow cylindrical bearing surface ( 12 ) and the cylindrical bearing surface ( 11 ). It is thus possible to prevent the escape of roller bearing segments ( 15 ) from the bearing gap ( 22 ) due to the effects of vibration.

Full Description:
BACKGROUND 
   The invention is directed to a swash plate pivot bearing, in particular, for a hydraulic axial piston machine with a variable throughput volume, in which roller-bearing segments are arranged between a hollow-cylindrical bearing surface for a swash plate in a housing and a cylindrical bearing surface on the swash plate. These roller-bearing segments are held in arcuate cages, wherein means for controlling the cage are provided, which prevent the cage holding the roller body from sliding out of its most favorable position in the pivot bearing. 
   Axial piston hydraulic units with variable displacement or variable flow rate use a pivoting swash plate, in order to control the displacement or flow rate of the piston within a rotating cylinder block. A typical type of pivoting swash plate is the cradle-type swash plate, which is held in a housing so that it can pivot by via arcuate roller-bearing segments. For this known construction, a tracking device, which prevents the cage holding the roller body from sliding out of its range of motion set for it, namely from its most favorable position in the pivot bearing, is allocated to the swash plate pivot bearing. If there is no tracking device, such slipping is possible, because the roller bodies perform not only rolling motions, but also sliding motions due to fast pivoting movements and/or vibrations and/or the inertia of the roller-bearing segment, which lead to shifts in the position of the roller-bearing segment. This produces an unfavorable position of the bearing segment or segments towards the load direction. 
   To drive the roller-bearing segments so that they respond to the movement of the swash plate and so that they are moved by the desired degree, in order to guarantee correct roller contact and loading for distribution, the following tracking devices are known: 
   For example, in DE 25 21 312 B1, a swash plate pivot bearing is described, which is distinguished in that on each cage, an elastic rod extending approximately radial to the curvature of the arcuate cage can shift in the radial direction and is hinged so that it can pivot and the rod is supported so that it can pivot with one end fixed in position at one point of the housing and can pivot with its other end on the swash plate and is arranged so that it can move in its longitudinal direction. Other similar tracking devices are described in DE 28 26 928 A1 and in EP 0 182 354 B1. 
   DE 16 53 617 C appears to be somewhat more closely connected to the invention. There, a tracking device is described for a cage of a swash plate pivot bearing, wherein parts thereof are provided with positive-locking elements. For this purpose, the segment-like cage is provided with a rotating pinion, which meshes with bent teeth segments that are fixed with screws, on one side, in the housing and, on the other side, to the sides of the swash plate. 
   All of these tracking devices have the common disadvantages that they have a complicated construction, they are made from many components, and they require additional installation space. Another reason is that the connections have either projections extending perpendicular and into corresponding boreholes in the swash plate and in the housing or openings that slide on pivot pins, which extend perpendicular from the swash plate and the housing. In both cases, the connections are installed after the swash plate was installed, which requires an access opening in the side of the housing. The opening must then be covered by a removable cover with a type of seal between the housing and the cover. Providing an access opening, the cover, and the seal further increases such a pivot bearing. 
   Indeed, roller bodies provided with positive-locking elements are also already known, as U.S. Pat. No. 3,938,865 shows. The means-effect relationships described there, however, are completely different in comparison with the invention. The cylindrical or conical rollers shown in this document have teeth at opposing ends for preventing slip. It is a long-known problem in roller-bearing technology that the friction fit between the inner ring, roller bodies, and outer ring is lost in the unloaded zone. In this zone, the roller bearings reduce their rotational speed. When entering the load zone, they must then be accelerated again abruptly, so that the normal roll-off process can proceed. This causes wear in the roller bodies in the load or acceleration zone, in particular, at a certain load and rotational speed ratio. 
   SUMMARY 
   Starting with the disadvantages of the known state of the art, the invention is based on the objective of structurally simplifying a swash plate pivot bearing of the construction specified above. 
   According to the invention, this objective is met in that the cage control is integrated in the roller-bearing segments, such that at least one cylindrical roller body engages with a positive fit with the hollow-cylindrical bearing surface and the cylindrical bearing surface. 
   Through the positive-fit connection between the roller bodies and both bearing surfaces, it is guaranteed that the cage including the roller body can no longer change its assumed optimal position after setting the desired pivoting. This at least one roller body with a different construction can also be viewed as a control roller body. In this connection, it has proven useful when such a profiled roller body is arranged on both ends of the roller-bearing segment. These can also be load free, so that they have a smaller diameter than the other, non-profiled, supporting roller bodies. Finally, a roller bearing with an increased roller resistance is formed, which prevents the cage from slipping from its most favorable position. As already discussed, this sliding movement always occurs when forces caused by pivoting movements or vibrations act on the roller-bearing segments. This prevents the cage and the supporting roller bodies from wandering from the gap between the swash plate and the housing and prevents damage to connection parts, such as, for example, pistons or sliding blocks. The invention also significantly simplifies the swash plate pivot bearing in production and assembly, because complicated arrangements for tracking the cage are no longer necessary. Consequently, no additional parts have to be produced and connected to the pivot cradle bearing in a complicated way. 
   Additional advantageous embodiment variants of the invention are described in the subordinate claims. 
   For example, in one embodiment it is provided that the roller body is provided with teeth and the two bearing surfaces are provided with associated counter teeth, wherein the roller body is provided with peripheral teeth on the two opposing ends in the axial direction, or in its center part. 
   Attaching the teeth forming the positive connection between the roller body and bearing surfaces is relatively uncomplicated relative to the production of the previously known tracking devices and ensures, in particular, that significant space savings can be realized relative to the known and expensive tracking devices. 
   According to another additional feature, both the hollow-cylindrical bearing surface and also the cylindrical bearing surface should be formed by bearing shells inserted in the housing and on the swash plate. These bearing shells can be produced easily as an add-on part and ensure that both the swash plate and also the housing are not to be provided with expensive positive-locking elements. Here, it has proven advantageous when the bearing shells are constructed as parts formed without cutting and have two sets of counter teeth spaced apart from each other in the axial direction. 
   According to another additional feature of the invention, the bearing shells should be provided at least on one end with a radial directed rim. In this way the segment-like cage including the held roller body is easily prevented from sliding out of the bearing shells in the axial direction. 
   According to another feature of the invention, this rim should be provided with counter teeth. 
   In an improvement of the invention, it is provided that the bearing shells are provided on their peripheral ends with positioning projections angled inward or outward in the radial direction. In this way, their uncomplicated connection to the swash plate and to the housing is realized, in that these positioning projections engage in corresponding recesses on the swash plate and on the housing. 
   A full-type construction, i.e., one without a cage, is also provided. According to this variant of the invention, all of the cylindrical roller bodies should be in positive engagement with the hollow-cylindrical bearing surface and the cylindrical bearing surface in the already described way. The advantage here lies in that due to the lack of a cage, more roller bodies can be arranged, so that the load rating is increased. 
   The invention is explained in more detail in the following embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Shown are: 
       FIG. 1  a longitudinal sectional view through a swash plate bearing according to the invention, 
       FIG. 2  an enlarged representation of a detail from  FIG. 1 , 
       FIG. 3  a perspective view of a bearing shell arranged on the swash plate with cylindrical bearing surface, 
       FIG. 4  a perspective view of a bearing disk arranged in the housing with hollow-cylindrical bearing surface, 
       FIG. 5  a perspective view of a segmented cage, 
       FIG. 6  an enlarged view of a roller body in positive engagement, 
       FIGS. 7 ,  8  a detail view taken from a perspective view of a swash plate bearing, and 
       FIG. 9  a longitudinal section view through an axial piston machine according to the prior state of the art. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   For representing and explaining the overall relationship of a swash plate bearing in the form of an axial piston machine, reference is first made to  FIG. 9 . According to this, the axial piston machine includes a cylinder drum  1 , which is arranged on a shaft  2 , wherein the shaft  2  is a drive shaft or a driven shaft according to the use of the machine as a pump or as a motor. The shaft  2  is supported by bearings  5  and  6  in a housing including the housing parts  3  and  4 . Within the cylinder drum  1 , there are pistons  8 , which are supported on a swash plate  10  via sliding blocks  9 , within cylinder boreholes  7 . The swash plate  10  has a cylindrical bearing surface  11 , which is opposite a hollow-cylindrical bearing surface  12  in the housing part  3 . Both are set apart from each other by the bearing gap  22 . The stroke of the piston  8  in the cylinder boreholes  7  is set in a known way by changing the angular position of the swash plate  10  relative to the axis  13  of the shaft  2 . For this purpose, a not-shown adjustment device attaches, for example, to the lever  14  connected rigidly to the swash plate  10 . In the bearing gap  22  between the bearing surfaces  11  and  12  there is a roller-bearing segment  15 , whose roller bearings  16  are guided and held by a cage  17 . Another roller-bearing segment  15  is arranged in a not-visible way away from this cage, so that the swash plate  10  is doubly supported. The tracking device consists of an elastic rod  18 , which is supported so that it can pivot in the housing part  3  on a fixed bearing point  19  and which is supported so that it can pivot on a bearing point  20  on the cage  17  and can move in its longitudinal direction and which is supported so that it can pivot on the swash plate  10  on a bearing point  21  and can move in its longitudinal direction. Now if the swash plate  10  changes its position with the help of the lever  14 , then the roller-bearing segment  15  is carried along by means of the elastic rod  18 , so that it always assumes an advantageous position in the bearing gap  22 , i.e., is oriented in the direction of force. As already described in detail in the state of the art, such a tracking device requires increased production and assembly expense. 
   Here is where the invention sets in. 
   As can be seen from the  FIGS. 1 to 6 , just like in the prior state of the art, the roller-bearing segment  15  includes the cage  17  with the pocket  24 , in which, however, roller bodies  23 ,  23 . 1 ,  23 . 2  are held in contrast to the state of the art. These roller bodies are in positive engagement with the hollow-cylindrical bearing surface  12  and the cylindrical bearing surface  11 . According to  FIG. 6 , the roller bodies  23 ,  23 . 1 ,  23 . 2  are provided on their two opposite ends with peripheral teeth  25 . These engage with the associated counter teeth  26 ,  27 , which are set, on one side, by the bearing shell  28  and, on the other side, by the bearing shell  29 . Both bearing shells  28 ,  29  are produced as parts formed without cutting and have two sets of counter teeth  26 ,  27 , which are spaced apart from each other in the axial direction and which fit teeth  25  of the roller bodies  23 ,  23 . 1 ,  23 . 2  arranged on both sides. As  FIGS. 3 and 4  show, the bearing shell  29  connected to the swash plate  10  is provided with a rim  31  on both sides directed outward in the radial direction, while the bearing shell  28  arranged in the housing  3  is equipped with a rim  30  directed inward in the radial direction. In addition, the bearing shell  29  is provided with positioning projections  33  directed inward in the radial direction, while the positioning projections  32  for the bearing shell  28  are directed outward. The positioning projections  33  of the bearing shell  29  engage in a not-shown position, in a recess of the swash plate  10 , while the positioning projections  32  of the bearing shell  28  also engage in the housing part  3  in a similarly not-shown way. In this way, a simple connection between the bearing shells  28 ,  29  and the housing part  3  or swash plate  10  is given. In the embodiment according to  FIGS. 1 to 6 , the roller-bearing segment  15  is constructed so that all of the roller bearings arranged in the cage  17  are constructed as roller bodies  23 ,  23 . 1 ,  23 . 2  with peripheral teeth  25 . For the functioning of the solution according to the invention, this needs to be only for one roller body, as  FIGS. 7 and 8  show. 
   As  FIG. 7  shows, the first roller body  23 . 1  and the second roller body  23 . 2 , which, however, is not shown, are provided at the beginning and end of the roller-bearing segment  15  with teeth  25  surrounding the two opposing ends in the axial direction and engaging with the counter teeth  26 ,  27  in positive engagement. As is visible, the counter teeth  26 ,  27  are arranged on the rims  30 ,  31  of the bearing shells  28 ,  29 . The rims  30 ,  31  of the bearing shells  28 ,  29  are provided with the counter teeth  26 ,  27  not over their entire peripheral extent, but instead only at the beginning and end of the roller-bearing segment  15 , so that pivoting about the pivot angle α can be realized. 
   This swash plate pivot bearing shown in  FIG. 8  is distinguished in that the roller body  23 . 1  is provided in its center part with the teeth  25 , which engages, in turn, with the counter teeth  26 ,  27  in a positive engagement. 
   The effect of the cage control according to the invention is explained in more detail below with reference to  FIG. 1 : 
   In the mentioned figure, both bearing shells  28 ,  29  arranged relative to each other so that they can pivot at the point  34  are set so that they assume the same position relative to this point. In this position, however, a hydraulic axial piston machine would not be operable, because the bearing plate  29  connected to the not-shown swash plate  10  is not pivoted. In this case, the pistons  8  could not execute an up and down movement in the axial direction within the rotating cylinder drum  1 , which, however, is irrelevant for the explanation of the invention. 
   As  FIG. 1  further shows, the force F 1  originating from point  34  is supported via a segment, which is bounded on the left side by the point  28 . 1  and on the right side by the point  28 . 2  of the bearing shell  28 , wherein the beginning and the end of the segment run through the center point of the cylindrical roller bodies  23 . 1  and  23 . 2 . Now, as shown in the figure, if the swash plate  10  and thus the bearing shell  29  connected to it is shifted by the angle α in the peripheral direction relative to the bearing shell  28  arranged rigidly, then the roller-bearing segment  15  moves by the same amount, i.e., the points  28 . 1  and  28 . 2  are similarly shifted by the same amount in the clockwise direction. In this way, it is guaranteed that the force F 1  is supported by exactly the same segment, but shifted by an amount, after the pivoting of the swash plate  10  with the bearing shell  29  by the angle α. Wandering of the cage segment  15  from the bearing gap  22  due to vibrations and/or shocks is prevented by the positive-fit connection between the roller bodies  23 ,  23 . 1 ,  23 . 2  and their teeth  25  with the associated counter teeth  26 ,  27  of the bearing shells  28 ,  29 . 
   REFERENCE SYMBOLS 
     1  Cylinder drum 
     2  Shaft 
     3  Housing part 
     4  Housing part 
     5  Bearing 
     6  Bearing 
     7  Cylinder borehole 
     8  Piston 
     9  Sliding block 
     10  Swash plate 
     11  Cylindrical bearing surface 
     12  Hollow-cylindrical bearing surface 
     13  Axis 
     14  Lever 
     15  Roller-bearing segment 
     16  Roller body 
     17  Cage 
     17 . 1  Retaining projection 
     18  Elastic rod 
     19  Bearing point 
     20  Bearing point 
     21  Bearing point 
     22  Bearing gap 
     23  Roller body 
     23 . 1  Roller body 
     23 . 2  Roller body 
     24  Pocket 
     25  Teeth 
     26  Counter teeth 
     27  Counter teeth 
     28  Bearing shell 
     28 . 1  Point 
     28 . 2  Point 
     29  Bearing shell 
     30  Rim 
     31  Rim 
     32  Positioning projection 
     33  Positioning projection 
     34  Point 
   α Pivot angle

Technology Classification (CPC): 5