Patent Publication Number: US-2015075363-A1

Title: Hydrostatic Axial Piston Machine Utilizing A Bent-Axis Construction

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Application No. 102013108409.5 filed Aug. 5, 2013, which is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a hydrostatic axial piston machine utilizing a bent-axis construction. The axial piston machine has a drive shaft rotatable around an axis of rotation and is provided with a drive flange, a cylinder drum rotatable around an axis of rotation, with the cylinder drum including a plurality of piston bores arranged concentric to the axis of rotation of the cylinder drum, a longitudinally displaceable piston in each cylinder bore and a driving device for driving the cylinder drum. 
     2. Description of Related Art 
     In axial piston machines that utilize a swashplate construction, the longitudinally displaceable pistons in the cylinder drum are each supported by a sliding shoe on a swashplate. However, on account of the high inertial forces of the pistons and the sliding shoes located on the pistons during operation, axial piston machines that utilize a swashplate construction are limited with regard to the maximum allowable speeds of rotation. The limited maximum allowable speed of rotation of an axial piston machine that utilizes a swashplate construction has disadvantages in terms of its use as a hydraulic motor. 
     Axial piston machines that utilize a bent-axis construction have significantly higher maximum allowable speeds of rotation than axial piston machines that utilize a swashplate construction. Axial piston machines that utilize a bent-axis construction have advantages in terms of their use as hydraulic motors. 
     In hydrostatic axial piston machines that utilize a bent-axis construction, the longitudinally displaceable pistons located in the cylinder drum are generally fastened directly or indirectly to the driving flange of the driving shaft by a ball-and-socket joint. The piston forces are supported via the pistons on the driving flange that is located on the driving shaft and generate a torque. In axial piston machines that utilize a bent-axis construction, during rotation there is naturally no driving of the cylinder drum with the pistons located in it. An additional driving device is necessary to drive the cylinder drum. 
     In bent-axis axial piston machines in which the driving device for the cylinder drum is a driving joint located between the drive shaft and the cylinder drum, one disadvantage is that it is not possible to transfer a torque through the axial piston machine because the driving joint is located at the intersection of the axis of rotation of the cylinder drum with the axis of rotation of the drive shaft. In known bent-axis axial piston machines that utilize a driving joint for driving the cylinder drum, it is not possible to provide torque transfer. Therefore, the applications of such axial piston machine are limited. For known bent-axis machines in which torque transfer is to be provided, additional components (such as transfer cases) are necessary to allow universal use of the axial piston machine. 
     Therefore, it is an object of this invention to provide an axial piston machine utilizing a bent-axis construction of the general type described above but which can be used for universal applications. 
     SUMMARY OF THE INVENTION 
     To accomplish this object, the invention teaches that the drive shaft is a hollow shaft. A torque bar runs through the hollow shaft to provide transfer of a torque from a drive flange side end of the axial piston machine to a cylinder drum side end of the axial piston machine, The hollow drive shaft makes it possible to route a torque bar through the drive shaft, by means of which a torque transfer can be achieved on the axial piston machine. Preferably, a torque which is independent of the torque of the drive shaft can be transferred through the axial piston machine from a drive flange side end of the axial piston machine to a cylinder drum side end of the axial piston machine without having to use a complex power divider. As a result of the possibility of the transfer of the torque via the hollow drive shaft and, thus, the torque bar routed through the axial piston machine, the axial piston machine of the invention utilizing the bent-axis construction is suitable for universal applications in which a torque transfer through the axial piston machine is required, e.g. to drive an additional user. 
     It is particularly advantageous if, as in one development of the invention, the torque bar does not have a mechanical connection to the drive shaft. If the torque bar that runs through the axial piston machine does not have a fixed connection to the drive shaft of the axial piston machine, the arrangement has additional advantages with regard to the universal applicability of the axial piston machine of the invention because there can be different speeds of rotation and/or different directions of rotation on the drive shaft (in the form of a hollow shaft) and on the torque bar that runs through the hollow drive shaft. Therefore, two different torques with different speeds of rotation and/or different directions of rotation can be present on the drive shaft and the torque bar. 
     The drive shaft is advantageously provided on the drive flange side end with a torque transmission means for the transmission of torque. Using the torque transmission means, a torque can easily be introduced into the axial piston machine operating as a pump, or, a torque can be taken from the axial piston machine operating as a motor. 
     In one advantageous development of the invention, the cylinder drum includes a longitudinal recess concentric to the axis of rotation of the cylinder drum. The torque bar and/or the drive shaft provided with the drive flange can extend through the recess and, thus, through the cylinder drum. Due to the longitudinal recess in the cylinder drum located concentric to the axis of rotation of the cylinder drum, to achieve a torque transfer it becomes possible to route the torque bar and/or the drive shaft in the form of a hollow shaft (inside which hollow shaft the torque bar is located) through the cylinder drum and the axial piston machine to the cylinder drum side end of the axial piston machine. 
     This arrangement makes it possible to achieve additional advantages if, as in one development of the invention, the drive shaft for the transfer of the torque is provided on the cylinder drum side end with additional torque transmission means for the transmission of torque. Therefore, on the drive shaft that extends through the cylinder drum and through the axial piston machine, an additional possibility for the transfer of a torque is achieved with the axial piston machine of the invention. The transfer of the torque on the drive shaft to the cylinder drum side end of the axial piston machine makes it possible, when the axial piston machine utilizing a bent axis construction is used as a hydraulic motor, to divert and tap the torque on both sides of the drive shaft. The universal application of the axial piston machine of the invention is consequently further improved and applications become possible in which a torque can be tapped on both sides of the drive shaft and/or a torque for the drive of an additional user can be conducted through the axial piston machine. When the axial piston machine utilizing the bent-axis construction of the invention is used as a hydraulic pump, the additional torque transfer capability on the drive shaft makes it possible to locate and drive a plurality of axial piston machines operating as hydraulic pumps one behind the other without having to use a complex transfer case. In addition, the ability to transfer an additional torque on the drive shaft makes it possible to position a plurality of axial piston machines utilizing the bent-axis construction one behind another as hydraulic motors, to increase the torque output. In view of the capability to drive an additional torque with the drive shaft routed through the axial piston machine and provided with torque transmission means on both ends, the universal applicability of the axial piston machine utilizing the bent-axis construction of the invention is further improved and the axial piston machine utilizing the bent-axis construction of the invention can be used for applications in which a torque transfer capability on the drive shaft makes it possible to tap torque on both sides of the drive shaft or to conduct a torque through the axial piston machine via the drive shaft for the drive of an additional user. On the drive flange end, the drive shaft is generally provided with splined shaft teeth as the torque transmission means. On the opposite, cylinder drum side end of the drive shaft, splined shaft teeth or a polygon connection or a feather key connection can also be provided as torque transmission means for the transfer of the torque in an axial piston machine of the invention to both sides when it is used as a hydraulic pump or as a hydraulic motor or for the output of the torque when the axial piston machine is used as a hydraulic motor. 
     In the axial piston machine of the invention, the drive shaft can be mounted in a cantilevered fashion in the housing. With a cantilevered mounting of this type, the mounting of the drive shaft in the housing is located on one side of the cylinder drum in the vicinity of the drive flange side end of the drive shaft. 
     In one preferred development of the invention, the drive shaft is mounted in a housing of the axial piston machine on both sides of the cylinder drum. The longitudinal recess in the cylinder drum and the resulting possible routing of the drive shaft through the cylinder drum makes it possible to mount the drive shaft provided with the drive flange on both sides of the cylinder drum in the housing. This achieves a broad bearing base for the drive shaft. As a result of which, a compact length of the axial piston machine of the invention becomes possible, compared to a unilateral cantilevered mounting of the drive shaft provided with the drive flange. 
     The driving device for the cylinder drum can be formed by connecting rods located at least partly in the pistons and connected in an articulated manner with the piston and with the drive flange by a ball-and-socket joint. The driving of the cylinder drum by connecting rods makes possible a simple construction of the cylinder drum driving device and makes it possible to route the torque bar for a torque transfer through the axial piston machine through the hollow drive shaft. For driving the cylinder drum, the connecting rods are supported on the piston inside walls of the piston bores of the cylinder drum. 
     In one alternative configuration of the invention, the driving device for driving the cylinder drum is formed by the longitudinally displaceable pistons in the piston bores of the cylinder drum, which pistons are for this purpose tapered or spherical and are provided with a tapered or spherical generated surface. The driving of the cylinder drum by the pistons makes possible a simple construction of the driving device of the cylinder drum and makes it possible to route the torque bar for a torque transfer through the axial piston machine through the hollow drive shaft. For driving the cylinder drum, the pistons can be supported with the tapered or spherical segments on the inside walls of the piston bores of the cylinder drum. 
     It is particularly advantageous if, as in one development of the invention, the driving device for the cylinder drive is formed by a driving joint located between the cylinder drum and the drive shaft or the drive flange, such as a constant velocity joint. The driving of the cylinder drum by a driving joint located between the cylinder drum and the drive flange makes possible a simple construction of the driving device of the cylinder drum and makes it possible to route the torque bar for a torque transfer through the axial piston machine through the hollow drive shaft. If the drive linkage is a constant velocity joint, the result is a rotationally synchronous drive of the cylinder drum with the drive flange. A high uniformity of the rotational motion during the drive of the cylinder drum is thereby achieved, which is advantageous for applications of the axial piston machine of the invention as a hydraulic motor. 
     In one configuration of the invention, the drive flange can be shaped in one piece on the drive shaft. In addition, it is alternatively possible to make the drive flange and the drive shaft separate pieces, in which case the drive flange is fastened torque-tight on the drive shaft. The drive flange is thereby separate from the drive shaft and can be connected torque-tight to the drive shaft by a suitable torque connection, such as a shaft-hub connection formed by splined shaft teeth. 
     In one advantageous development of the invention, a spherical guide formed by a spere and a spherical cap for the bearing of the cylinder drum is located between the drive shaft and the cylinder drum. For a spherical guide formed by a spherical segment on the drive shaft and a segment of the cylinder drum in the shape of a hollow sphere, it becomes possible in a simple manner to center and support the cylinder drum on an axial piston machine of the invention that allows for a transfer of torque. 
     The axial piston machine of the invention can be a constant displacement machine with a fixed displacement volume. 
     Alternatively, the axial piston machine of the invention can be a variable displacement machine with a variable displacement volume. 
     The invention further relates to a power split transmission with any of the axial piston machine embodiments discussed above. The construction of the drive shaft as a hollow shaft through which a torque bar runs, in an axial piston machine utilizing a bent-axis construction, the torque bar can be operated at a speed of rotation that is independent of the speed of rotation of the drive shaft and/or can be operated in the same or different direction of rotation as the drive shaft. This provides particular advantages with a power split transmission because the torque of the hydrostatic branch of the power split transmission can be present on the drive shaft and the torque of the mechanical branch of the power split transmission can be present on the torque bar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional advantages and details of the invention are described in greater detail below with reference to the exemplary embodiments illustrated in the accompanying schematic figures, in which like reference numbers identify like parts throughout. 
         FIG. 1  is a longitudinal cross-section of a first embodiment of a bent-axis machine of the invention; and 
         FIG. 2  is a longitudinal cross-section of a second embodiment of a bent-axis machine of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A hydrostatic axial piston machine  1  in the form of a bent-axis machine is illustrated in  FIG. 1 . The machine  1  has a housing  2 , which includes a housing pot  2   a  and a housing cover  2   b.  In the housing  2 , a drive shaft  4  provided with a drive flange  3  is rotationally mounted by bearings  5   a,    5   b  so that it can rotate around an axis of rotation R. In the illustrated exemplary embodiment, the drive flange  3  is formed in one piece with the drive shaft  4 . 
     Located axially next to the drive flange  3  in the housing  2  is a cylinder drum  7 , which is provided with a plurality of piston bores  8  arranged concentrically to an axis of rotation R., of the cylinder drum  7 . There is a longitudinally displaceable piston  10  in each piston bore  8 . 
     The axis of rotation R t  of the drive shaft  4  intersects the axis of rotation R z  of the cylinder drum  7  at the intersection point S. 
     The axial piston machine  1  illustrated in  FIG. 1  is a constant displacement machine with a fixed displacement volume. The axis of rotation R z  of the cylinder drum  7  is at a constant angle of displacement or pivot angle a with respect to the axis of rotation R t  of the drive shaft  4 . 
     For control of the feed and discharge of hydraulic fluid in the displacement chambers V formed by the piston bores  8  and the pistons  10 , the cylinder drum  7  is in contact with a control surface  15  formed on the housing cover  2   b.  The control surface  15  is provided with kidney shaped control bores (not illustrated in detail) which form an admission connection  16  and a discharge connection of the axial piston machine  1 . For connection of the displacement chambers V formed by the piston bores  8  and the pistons  10  with the control bores located in the housing cover  2   b,  the cylinder drum  7  is provided with a control opening  18  at each piston bore  8 . 
     The pistons  10  are each fastened to the drive flange  3  in an articulated manner. For this purpose, between each piston  10  and the drive flange  3 , there is an articulated connection  20  in the form of a spherical joint. The articulated connection  20  in the illustrated exemplary embodiment is in the form of a ball-and-socket joint which is formed by a spherical head  10   a  of the piston  10  and a spherical shell  3   a  in the drive flange  3  in which the piston  10  is fastened with the spherical head  10   a.    
     The pistons  10  each have a collar segment  10   b,  by means of which the piston  10  is located in the piston bore  8 . A piston rod  10   c  of the piston  10  connects the collar segment  10   b  with the spherical head  10   a.    
     To make possible a compensating movement of the pistons  10  during rotation of the cylindrical drum  7 , the collar segment  10   b  of the piston  10  is located in the piston bore  8  with some clearance or play. For this purpose, the collar segment  10   b  of the piston  10  can be spherical. To create a seal between the pistons  10  and the piston bores  8 , sealing means  21 , such as a piston ring for example, are located on the collar segment  10   b  of the piston  10 . 
     A driving device (not illustrated in detail) is provided to drive the cylinder drum  7  during operation of the axial piston machine  1 . 
     In the illustrated exemplary embodiment, the cylinder drum  7  includes a central longitudinal recess  11  which is concentric with the axis of rotation R z , of the cylinder drum  7 . The drive shaft  4  extends through this recess. The drive shaft  4  routed through the axial piston machine  1  is supported by bearings  5   a,    5   b  on both sides (bilateral) of the cylinder drum  7 . The drive shaft  4  is supported by the bearing  5   a  in the housing pot  2   a  and by the bearing  5   b  in the housing cover  2   b.    
     The drive shaft  4 , on the drive flange side end, includes torque transmission means  12 , for example splined gear teeth, to transmit a drive torque or to tap an output torque. 
     On the axial piston machine  1  shown in  FIG. 1 , the drive shaft  4  is a hollow shaft having a longitudinal boring  30  located concentrically and coaxially with the axis of rotation R. A torque bar  31  is located in the longitudinal boring  30  concentric to the axis of rotation R t  and extends through the drive shaft  4 . By means of the torque bar  31 , a torque M t  can be transmitted and a torque transfer through the axial piston machine  1  can be achieved. The torque bar  31  has no mechanical operative connection to the drive shaft  4 . 
     The drive shaft  4  and the torque bar  31  can therefore rotate at different speeds of rotation and/or in different directions of rotation. 
     In the exemplary embodiment illustrated in  FIG. 1 , the drive shaft  4  includes torque transmission means  12  to transmit or tap the torque only on the drive flange side end. The cylinder drum side end of the drive shaft  4  ends in the vicinity of the housing cover  2   b.  There is a through hole  14  for the drive shaft  4  in the housing cover  2   b  and located concentric to the axis of rotation R t  of the drive shaft  4 , to extend the torque bar  31  through the axial piston machine  1 . 
     There is a spherical guide  25  between the cylinder drum  7  and the drive shaft  4  for bearing and centering of the cylinder drum  7 . The spherical guide  25  is formed by spherical segment  26  of the drive shaft  4 , on which is located the cylinder drum  7  with a segment  27  in the shape of a hollow sphere in the vicinity of the central longitudinal recess  11 . The midpoint of the segments  26 ,  27  lies at the intersection S of the axis of rotation R t  of the drive shaft  4  and the axis of rotation R z  of the cylinder drum  7 . 
     In the illustrated exemplary embodiment, the hollow spherical segment  27  is on a sleeve-shaped element  40  located in the central longitudinal recess  11  of the cylinder drum  7 . The element  40  is secured to the axial drum  7  in the longitudinal direction of the cylinder drum  7  in the axial direction and in the peripheral direction. For axial securing, the element  40  is in contact with one end surface on a diametric shoulder  11   a  of the longitudinal recess  11 . It is secured against rotation by securing means  45  which, in the illustrated exemplary embodiment, are formed by a connecting pin located between the sleeve-shaped element  40  and the cylinder drum  7 . The drive shaft  4  that runs through the axial piston machine  1  also extends through the sleeve shaped element  40 . For this purpose, the inside diameter of the sleeve-shaped element  40  is provided with a contour that is aligned with the longitudinal recess  11  of the cylinder drum  7 . 
       FIG. 2  illustrates an additional exemplary embodiment of an axial piston machine employing a bent-axis construction, wherein components that are identical with those illustrated in  FIG. 1  are identified by the same reference numbers. 
     In the exemplary embodiment illustrated in  FIG. 2 , the drive shaft  4  extends through the axial piston machine  1  and through the housing  2  and extends out through the housing cover  2   b.  On the cylinder drum side end extending out of the housing cover  2   b,  the drive shaft  4  is provided with additional torque transmission means  13 . The torque transmission means  13  on the shaft stump of the drive shaft  4  that extends out of the housing cover  2   b  are preferably splined gear teeth or a polygon-shaped profile or a feather key connection. The drive shaft  4  therefore makes it possible to achieve an additional transfer of torque through the axial piston machine  1 . With the torque transmission means  13  on the drive shaft  4 , an additional torque can be conducted through the axial piston machine  1 . Or, on an axial piston machine  1  in the form of a hydraulic motor, a bilateral output is possible. 
     In  FIGS. 1 and 2 , the driving device for the driving of the cylinder drum  7  is a driving joint, such as a constant velocity joint, which is located in the vicinity of the spherical segments  26  of the drive shaft  4  and the hollow spherical segment  27  of the cylinder drum  7 . 
     The invention is not limited to the illustrated exemplary embodiments. 
     Alternatively to the exemplary embodiments illustrated in  FIGS. 1 and 2 , which are constant displacement machines, the axial piston machine can also be in the form of variable displacement machines. In a variable displacement machine, the angle of inclination a of the axis of rotation R z  of the cylinder drum  7  with respect to the axis of rotation R t  of the drive shaft  4  can be varied to vary the displacement volume. For this purpose, the control surface  15  with which the cylinder drum  7  is in contact is on a rocker body which is located so that it can pivot in the housing  2 . 
     The axial piston machine  1  can be in the form of a hydraulic motor or a hydraulic pump. 
     As an alternative to a driving device having a driving joint between the drive shaft  4  and the drive flange  3  and the cylinder drum  7 , the cylinder drum  7  can be driven by the pistons  10  or additional connecting rods. 
     Instead of the bilateral mounting of the drive shaft  4  in the housing  2 , the drive shaft  4  can be cantilever mounted in the housing  2 , in which case the two bearings  5   a,    5   b  are located in the drive flange side area of the drive shaft  4  and, therefore, in the housing pot  2   a.  Only the through hole  14  is located in the housing cover  2   b,  to be able to route the torque bar  31  through the axial piston machine  1 . 
     The design of the drive shaft  4  in the form of a hollow shaft with a torque bar  31  that extends through the hollow shaft makes it possible to achieve a transfer of torque through the axial piston machine  1  by means of the torque bar  31 , and by means of the torque bar  31  to transfer the torque M t  inside the axial piston machine  1  through the axial piston machine  1 . The torque bar  31  and the drive shaft  4  can have different speeds of rotation and/or different directions of rotation. The transfer of a torque by the torque bar  31  located in the interior of the drive shaft  4  results in the universal applicability of the axial piston machine  1  of the invention and makes possible special advantages in the use of the axial piston machine  1  of the invention in a power split transmission. 
     The additional torque transfer capability on the drive shaft  4  illustrated in  FIG. 2  provided on both sides with torque transmission means  12 ,  13 , makes it possible in an axial piston machine  1  of the invention operated as a hydraulic pump to locate a plurality of hydraulic pumps one behind another and to drive them by means of a torque transfer on the drive shaft  4 . The torque transfer capability of the drive shaft  4  provided with torque transmission means  12 ,  13  on both sides also makes it possible, on an axial piston machine  1  of the invention operated as a hydraulic motor, to locate a plurality of hydraulic motors one behind another and to increase the output torque by means of a transfer of the torque. The torque transfer capability of the drive shaft  4  provided with the torque transmission means  12 ,  13  on both ends makes it possible, on an axial piston machine  1  of the invention used as a hydraulic motor alternatively to tap an output torque on both ends of the drive shaft  4 . This arrangement produces advantages in a traction drive, in which the drive shaft is connected with different driven wheels or different driven axles of the vehicle. 
     It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.