Patent Publication Number: US-9850757-B2

Title: Axial piston machine utilizing a bent-axis construction

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Application No. DE 102014104951.9 filed Apr. 8, 2014, which is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a hydrostatic axial piston machine utilizing a bent-axis construction having a drive shaft located inside a housing so that it can rotate around an axis of rotation, a drive flange located inside the housing so that it can rotate around an axis of rotation, and a cylinder barrel located inside the housing of the axial piston machine so that it can rotate around an axis of rotation. The cylinder barrel has a plurality of piston bores, in each of which is located a longitudinally displaceable piston. The pistons are fastened to the drive flange in an articulated manner by ball joint connections formed by a spherical cap-shaped receptacle socket in one end surface of the drive flange and a ball head in an operative connection with the piston. 
     Description of Related Art 
     In hydrostatic axial piston machines utilizing a bent-axis construction, the longitudinally displaceable pistons located in the cylinder barrel are generally fastened to the drive flange of the drive shaft by a ball joint. The piston forces are transmitted by the piston to the drive flange located on the drive shaft and generate a torque. In axial piston machines utilizing a bent-axis construction, it is necessary to fasten the pistons to the drive flange in an articulated manner. For this purpose, a ball joint connection is used that consists of a spherical cap-shaped receptacle socket in one end surface of the drive flange and a ball head located on the piston and inserted into the receptacle socket of the drive flange. 
     In operation, the ball heads of the pistons must be held in place in the respective receptacle sockets of the drive flange. 
     WO 2004/109107 A1 describes a hold-down plate with openings for the piston heads and spherical caps formed on the openings threaded over the pistons and bolted to the drive flange. 
     Because of the need for the hold-down plate, which is complex and expensive to manufacture on account of the spherical caps and the threaded connectors that are required to bolt the hold-down plate to the drive flange, axial piston machines of this type are complex and expensive to construct. 
     To eliminate the effort required for the construction of the additional hold-down plate, EP 0 567 805 B1, EP 1 071 884 B1, DE 40 24 319 A1 and EP 0 697 520 B1 teach that the ball heads can be positively secured in the spherical cap-shaped receptacle sockets. The spherical cap-shaped receptacle socket has a wrapping angle greater than 180 degrees, so that the receptacle sockets wrap around the ball equator, and the ball heads have a cylindrical surface area, e.g., by flattening or machining of the ball head, so that the ball head is inserted into the spherical cap-shaped receptacle socket in a defined position by the cylindrical surfaces, and can then be secured in the receptacle socket by tilting. The manufacture of the components is thereby simplified and makes possible an easy assembly of the pistons with the ball heads in the receptacle sockets of the drive flange. 
     In EP 0 567 805 B1 and EP 1 071 884 B1, the cylindrical surfaces are oriented parallel to the longitudinal axis of the pistons so that during assembly, the pistons are threaded into the receptacle sockets coaxially to the axis of rotation of the drive flange. When the pistons are tilted to the working angle, the piston heads are locked in position in the receptacle shells. In bent-axis machines in the form of variable displacement machines, when the pistons are locked in position in the receptacle sockets in this manner, the coverage of the ball heads in the receptacle sockets can become too small as the pivoting angle of the cylinder barrel decreases. Thus, these methods of locking the ball heads of the pistons in the drive flange are suitable only under certain conditions for use in variable displacement machines with a variable pivoting angle of the cylinder barrel. These locking mechanisms are not suitable for use in variable displacement machines with a pivoting angle of 0° because the pistons can no longer be securely held in the receptacle sockets and can fall out of the receptacle sockets. 
     In DE 40 24 319 A1 and EP 0 697 520 B 1, the cylindrical surfaces are oriented at an angle with respect to the longitudinal axis of the pistons. The angle of inclination of the cylindrical surfaces is such that this angle does not occur during operation of the axial piston machine. Therefore, this locking mechanism is suitable for use on variable displacement machines and makes it possible to lock the pistons in the receptacle sockets of the drive flange even at a pivoting angle of 0°. For the installation of the pistons in the drive flange, the pistons must be tilted sharply, in which case it may be necessary to provide a recess (which is complex and expensive to manufacture) on each receptacle socket as an opening or recess for the piston rod of the piston. Depending on the installation angle of the pistons, this recess in the receptacle socket of the drive flange necessary for the installation of the pistons can extend to the equator of the ball, as a result of which the surface area of the spherical cap-shaped receptacle socket is significantly reduced. 
     In the axial piston machines described in EP 0 567 805 B1, EP 1 071 884 B1, DE 40 24 319 A1 and EP 0 697 520 B1, as a result of the wrapping angle of more than 180° of the spherical cap-shaped receptacle sockets, there is a correspondingly high thickness of the drive flange. This takes up a correspondingly large amount of space in the axial direction of the axial piston machine because the rotating cylinder barrel with the end surface containing the piston outlet openings may not come into contact with the end surface of the drive flange in which the receptacle sockets are located. 
     Therefore, it is an object of this invention to provide an axial piston machine utilizing a bent-axis construction in which the locking of the pistons in the drive flange is easier to manufacture and makes it possible to reduce the axial dimensions of the axial piston machine. 
     SUMMARY OF THE INVENTION 
     This problem is solved according to the invention in that the receptacle sockets are each in the form of hemispheres that extend to the equator of the ball. A retaining web is shaped on one end surface of the drive flange, in the vicinity of the receptacle sockets, that extends beyond the ball equator of the hemisphere to grip the ball head over an angle greater than 180°. In the axial piston machine of the invention, the receptacle sockets in the form of a hollow sphere in the drive flange are only hemispheres that extend to the equator of the ball. To secure the ball heads in these hemispheric receptacle sockets in a positive or form-fitting manner, on the end surface of the drive flange, in the vicinity of the receptacle sockets, there is a retaining web that projects beyond the end face of the drive shaft and extends beyond the ball equator of the hemisphere. The wrapping of the ball heads beyond the ball equator occurs only in the vicinity of the retaining web, so that only the retaining web located on the end surface of the drive flange secures the pistons in the receptacle sockets and forms the retaining mechanism for the pistons. As a result of the spatial limitation of the retention of the ball heads to the area of the retaining web located on the end surface of the drive flange, it becomes possible to reduce the thickness of the remaining area of the end surface of the drive flange with respect to the retaining web, so that an open space or recess is created and the cylinder barrel with the end surface containing the piston outlet openings can be brought closer to the drive flange. This makes it possible to reduce the axial space requirement of the axial piston machine. Compared to known axial piston machines that employ a bent-axis construction, in the axial piston machine of the invention, on account of the spatial limitation to the retaining web of the retention of the pistons in the receptacle sockets, the construction effort and expense can also be reduced. 
     In one advantageous embodiment of the invention, the retaining web forms two retaining segments on each receptacle socket, which are located opposite one another on the receptacle socket and extend beyond the hemisphere. With two opposed retaining segments, it becomes possible in a simple manner to grasp the ball head in the vicinity of the equator to hold the ball head in the receptacle socket in a positive or form-fitting manner. 
     With regard to a reduced construction effort and expense, it is particularly advantageous if the retaining web is formed by a circular ring-shaped elevation on the end surface of the drive flange. A ring-shaped elevation on the end surface requires little additional construction effort or expense. In addition, breaks between the segments of the ring-shaped elevation can be formed in a simple manner during the manufacture of the hemispheric receptacle sockets in the drive flange so that two retaining segments located opposite each other can be formed on each receptacle socket. 
     It is particularly advantageous if the center point of the circular ring-shaped elevation that forms the retaining web is located on the axis of rotation of the drive flange. As a result of this concentric orientation of the circular ring-shaped elevation and the axis of rotation of the drive flange, the contour of the circular ring-shaped elevation can be easily and economically manufactured by lathe turning. 
     The circular ring-shaped elevation is advantageously located in the vicinity of a reference circle on which the centers of the hemispheres are located. In this manner, a secure retention of the ball heads in the receptacle sockets by the retaining web can be achieved. This measure also creates a corresponding open space or recess that makes it possible to move the cylinder barrel close to the drive flange to achieve compact axial dimensions of the axial piston machine. 
     With regard to the simple manufacture of the axial piston machine, it is particularly advantageous if the retaining web is formed in one piece with the end surface of the drive flange. If the retaining web is formed with an appropriate machining allowance on a blank of the drive flange, the drive flange and the retaining web can be easily and economically manufactured as a lathe-turned part by machining on a lathe. 
     To be able to install the ball heads in the corresponding receptacle sockets, in one advantageous development of the invention, each ball head is provided with two grooves located opposite each other. The distance between the groove bases of the two grooves is less than the width of the opening formed by the two retaining segments on the respective receptacle socket. This makes it possible in a simple manner to thread the ball heads into the receptacle socket utilizing the two grooves between the retaining segments, thereby achieving a simple installation of the pistons in the receptacle sockets. 
     The width of the grooves is advantageously greater than the width of the retaining web. As a result of the two opposed grooves, which like the retaining web have only a small width, the ball half (hemisphere) of the ball head that transmits the piston force is reduced only negligibly in terms of surface area by the relatively small width of the two grooves, so that high cylinder forces can be transmitted. 
     The grooves can be oriented perpendicularly or parallel to the longitudinal axis of the piston. It is particularly advantageous if the grooves on the ball head are inclined at an angle with respect to the longitudinal axis of the piston. Depending on the angle of inclination of the grooves, it is possible in the axial piston machine of the invention to omit the recesses in the receptacle sockets for the piston rods for installation of the pistons. This is because with the end surface of the drive flange set back with respect to the retaining web, a corresponding open space is already created for the piston rods for installation of the pistons. If, with a correspondingly high angle of inclination of the grooves, a recess is necessary to provide the necessary open space on the inside of the drive flange in the vicinity of the receptacle sockets for the piston shaft of the piston to make it possible to install the pistons in the drive flange, in the axial piston machine of the invention, compared to known axial piston machines, the depth of the recess is smaller and, thus, so is the recess in the end surface of the drive flange. Preferably, the grooves are not oriented perpendicular to the longitudinal axis of the pistons, as a result of which, compared to perpendicularly oriented grooves, there are smaller recesses in the receptacle sockets for the piston rods for the installation of the pistons. On account of smaller recesses for the piston rod of the pistons, the surface area of the spherical cap of the receptacle socket in which the piston force is transmitted is reduced only slightly in the axial piston machine of the invention. In addition, because the grooves are oriented at an angle, the locking of the pistons in the drive flange is suitable for bent-axis machines with a pivoting angle of 0°. 
     The angle of inclination of the grooves is advantageously selected so that the angle of inclination is different from the tilting angles of the pistons that occur during operation of the axial piston machine. The angle of inclination is advantageously selected so that during installation, the inclination of the pistons toward the axis of rotation of the drive flange is greater than the maximum inclination of the pistons that occurs during operation, so that during operation of the axial piston machine the pistons can be securely and positively held with the ball heads in the receptacle sockets of the drive flange. 
     On the drive flange on each receptacle socket there is advantageously a recess for a piston rod of the piston, to achieve an easy installation of the piston in the drive flange with grooves oriented at an angle. 
     In one advantageous embodiment of the invention, a spherical guide is located between the drive flange and the cylinder barrel for the guidance of the cylinder barrel. With a spherical guide of this type, which is preferably formed by a spherical segment of the drive flange or of the drive shaft and a segment of the cylinder barrel in the form of a hollow sphere, a simple, economical and space-saving guidance and mounting of the cylinder barrel can be achieved. 
     The recesses are advantageously formed on the radially outer portion of the receptacle socket in the end surface of the drive flange. On an axial piston machine with a spherical guidance of the cylinder barrel, recesses located on the radially outer portion make possible a simple installation of the pistons by tilting the pistons radially outwardly. 
     If the drive flange is provided with a bevel on the outer edge of the end surface having dimensions such that the bevel forms the recess for the piston rod of the piston, the optional recess for the piston rod of the piston can be manufactured as an opening or recess without additional manufacturing effort or expense. 
     The grooves in the ball heads of the pistons can run in a straight line. 
     Particular advantages become possible if the grooves follow a bent path. Compared to grooves that run in a straight line, grooves that follow a bent path make it possible for the load-bearing half (hemisphere) of the ball head to have a larger area so that higher piston forces can be transmitted. 
     The grooves advantageously have a first section that is oriented at an inclination with respect to the longitudinal axis of the piston and a second section that is bent with respect to the first section, in particular perpendicularly to the longitudinal axis of the piston. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional advantages and details of the invention are described in greater detail below on the basis of the exemplary embodiments illustrated in the accompanying schematic figures, in which like reference numbers identify like parts throughout. 
         FIG. 1  illustrates an axial piston machine of the invention employing a bent-axis construction in a longitudinal section; 
         FIG. 2  is an enlarged detail from  FIG. 1 ; 
         FIG. 3  is a plan view of the end surface of the drive flange; 
         FIG. 4  is a section along line B-B in  FIG. 3 ; 
         FIG. 5  is a section along line A-A in  FIG. 4 ; 
         FIGS. 6 a -6 d    are illustrations illustrating the installation of the pistons; 
         FIGS. 7 a -7 d    are views in perspective illustrating the installation of the pistons; 
         FIGS. 8 a -8 d    are additional views in perspective illustrating the installation of the pistons; 
         FIGS. 9 a -9 c    are multiple views along a line C-C in  FIG. 3  at different angles of inclination of the pistons; 
         FIGS. 10 a -10 c    are multiple views in perspective of a piston installed in the receptacle socket; 
         FIG. 11 a    shows a first embodiment of a piston; and 
         FIG. 11 b    shows a second embodiment of the piston. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A hydrostatic axial piston machine  1  of the invention in the form of a bent-axis machine is illustrated in  FIG. 1 . The axial piston machine  1  has a housing  2  that includes a housing assembly  2   a  and a housing cover  2   b  that is fastened to the housing assembly  2   a . Located in the housing are a drive flange  3  and a drive shaft  4  that can rotate around an axis of rotation R t  that corresponds to a longitudinal axis L of the axial piston machine  1 . In the illustrated exemplary embodiment, the drive shaft  4  is mounted by bearing devices  5   a ,  5   b  so that it can rotate around the axis of rotation R t . In the illustrated exemplary embodiment, the drive flange  3  is formed in one piece with the drive shaft  4 . 
     A cylinder barrel  7  is located in the housing  2  axially next to the drive flange  3 . The cylinder barrel  7  rotates around an axis of rotation R Z  and is provided with a plurality of piston bores  8  which, in the illustrated exemplary embodiment, are located concentric to the axis of rotation R Z  of the cylinder barrel  7 . A piston  10  is located so that it can move longitudinally 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 barrel  7  at the intersection point SP. 
     The drive shaft  4  is equipped on the drive flange end with torque transmission means  12 , such as splines, for the introduction of a drive torque or the tapping of an output torque. 
     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 barrel  7  is in contact with a control surface  15 , which is provided with kidney-shaped control bores (not illustrated in any detail) which form an inlet connection  16  and an outlet 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, the cylinder barrel  7  is provided with a control opening  18  at each piston bore  8 . 
     The axial piston machine illustrated in  FIG. 1  is a variable displacement machine with a variable displacement volume. On the variable displacement machine, the angle of inclination α, and thus the pivoting angle of the axis of rotation R Z  of the cylinder barrel  7 , is variable with reference to the axis of rotation R t  of the drive shaft  4  to vary the displacement volume. The control surface  15  with which the cylinder barrel is in contact is located on a cradle body  19  located in the housing  2  so that it can rotate around a pivoting axis that lies at the intersection point SP of the axis of rotation R t  of the drive shaft  4  and the axis of rotation R Z  of the cylinder barrel  7  and is oriented perpendicularly to the axes of rotation R t  and R Z . 
     Depending on the position of the cradle body  19 , the angle of inclination α of the axis of rotation R Z  of the cylinder barrel  7  varies relative to the axis of rotation R t  of the drive shaft  4 . The cylinder barrel  7  can be pivoted into a null position where the pivoting angle is 0°, in which the axis of rotation R Z  of the cylinder barrel  7  is coaxial with the axis of rotation R t  of the drive shaft  4 . Starting from this null position, the cylinder barrel  7  can be pivoted to one or both sides, so that the axial piston machine illustrated in  FIG. 1  can be a unilaterally or bilaterally pivotable variable displacement machine. A device for pivoting the cradle body  19 , and thus the cylinder barrel  7 , is not illustrated in detail in  FIG. 1 . 
     The pistons  10  are each fastened to the drive flange  3  in an articulated manner. 
     Between the respective piston  10  and the drive flange  3 , there is a ball joint connection  20  in the form of a spherical joint  20 . The ball joint  20  (illustrated in greater detail in  FIG. 2 ) is formed by a ball head  10   a  of the piston  10  and a spherical cap-shaped (hollow spherical shaped) receptacle socket  3   a  which is formed in the end surface  3   b  of the drive flange facing the cylinder barrel  7 , in which the piston  10  with the ball head  10   a  is fastened. 
     The pistons  10  can also each have a longitudinal bore  13  that runs through the piston  10 , is in communication with the displacement chamber V, and extends through the ball head  10   a , to hydrostatically relieve the ball joint  20 . 
     The pistons  10  each have a collar section  10   b , with which the piston  10  is positioned in the piston bore  8 . A piston rod  10   c  of the piston  10  connects the collar segments  10   b  with the ball head  10   a.    
     To make possible an equalization movement of the pistons  10  in the event of a rotation of the cylinder barrel  7 , the collar segment  10   b  of the piston  10  is located in the piston bore  8  with some play. 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, are located on the collar segment  10   b  of the piston  10 . 
     For mounting and centering of the cylinder barrel  7 , a spherical guide  25  is located between the cylinder barrel  7  and the drive flange  3  or the drive shaft  4 , respectively. The spherical guide  25  is formed by a spherical segment  26  of the drive flange  3  or of the drive shaft  4  on which the cylinder barrel  7  is located and has a hollow spherical segment  27 . The center of segments  26 ,  27  lies at the intersection point SP of the axis of rotation R t  of the drive shaft  4  and the axis of rotation R Z  of the cylinder barrel  7 . In the illustrated exemplary embodiment, the hollow spherical segment  26  is located on the end surface of a sleeve-like bushing  50 , which is located and fastened in a central longitudinal bore  11  of the cylinder barrel  7  and, therefore, in the interior of the cylinder barrel  7 . 
     To drive the cylinder barrel  7  during operation of the axial piston machine  1 , a drive device (not illustrated in detail) couples the drive shaft  4  and the cylinder barrel  7  in the direction of rotation. The drive device can be, for example, a drive linkage, such as a constant velocity joint. 
     On the axial piston machine  1  employing the bent-axis construction (as illustrated in greater detail in  FIGS. 3 to 5 ) the spherical cap-shaped receptacle sockets  3   a  are each in the shape of hemispheres that extend only to the equator of the ball. The centers M of the spherical shell-shaped receptacle sockets  3   a  (hemispheres) therefore lie in the plane generated by the end surface  3   b  of the drive flange  3 . The spherical cap-shaped receptacle sockets  3   a  in the form of hemispheres wrap around the ball head  10   a  by 180°.  FIG. 3  shows a plan view of the end surface  3   b  of the drive flange  3  in the vicinity of a receptacle socket  3   a  (the corresponding piston  10  is not shown). 
     To positively secure the ball heads  10   a  of the pistons  10  in the hollow spherical shaped receptacle sockets  3   a  (hemispheres), a retaining web  30  is formed on the end surface  3   b  of the drive flange  3  in the vicinity of the receptacle sockets  3   a  and, as illustrated in  FIG. 5 , extends beyond the ball equator of the hemisphere to wrap around and grasp the ball head  10   a  over an angle of greater than 180°. The retaining web  30  is provided on the inner contour with a ball contour  31  that continues the spherical contour of the spherical cap-shaped receptacle sockets  3   a.    
     The retaining web  30  forms two retaining segments  30   a ,  30   b  on each receptacle socket  3   a  which, as illustrated in  FIGS. 3 and 5 , are located opposite each other on the receptacle socket  3   a  and are each provided with the ball contour  31 . 
     The retaining web  30  is formed by a circular ring-shaped encircling elevation  32  on the end surface  3   b  of the drive flange  3 . The circular ring-shaped elevation  32 , and thus the retaining web  30 , are concentric to the axis of rotation R t  of the drive flange  3 , so that the center of the circular ring-shaped elevation  32  that forms the retaining web  30  is located on the axis of rotation R t  of the drive flange  3 . 
     The circular ring-shaped elevation  32  is located on the end surface  3   b  of the drive flange  3  in the vicinity of a reference circle diameter T k  on which the centers M of the hemispheric shaped receptacle sockets  3   a  are located. 
     The circular ring-shaped elevation  32  is located facing the cylinder barrel  7  on the end surface  3   b  of the drive flange  3 . 
     The retaining web  30  has a width B in the radial direction that is significantly less than the diameter of the hemisphere, for example, a maximum of ⅓ of the diameter of the hemisphere and, thus, of the diameter of the ball head  10   a . The radially outside peripheral surface  30   d  of the retaining web  30  is at a radially inward distance from the radially outside peripheral surface  3   d  of the drive flange  3 . 
     In the illustrated exemplary embodiment, the retaining web  30  is formed in one piece on the end surface  3   b  of the drive flange  3 . The contour of the drive flange  4  is therefore provided with the retaining web  30  and thus the ring-shaped elevation  32  that projects out of the end surface  3   b . Preferably, the retaining web  30  is formed as early as on a blank of the drive flange  3  with a certain amount of excess material so that the contour of the retaining web  30  can be economically produced in a lathe turning operation of the drive flange  3 . 
     In the axial piston machine  1 , the retention of the piston heads  10   a  in the hemispheric shaped receptacle sockets  3   a  is limited to the area of the retaining web  30 . Because the encircling retaining web  30  is at some distance radially inwardly from the radially outer peripheral surface  3   d  of the drive flange  3 , an open space is created that makes it possible to bring the cylinder barrel  7  with the end surface  7   a  containing the piston outlet openings close to the end surface  3   a  of the drive flange  3 , so that it becomes possible for the axial piston machine  1  to have compact dimensions in the axial direction of the longitudinal axis L.  FIG. 2  illustrates one possible small distance s between the cylinder barrel  7  containing the end surface  7   a  containing the piston outlet openings and the centers M of the hemispheric receptacle sockets  3   a  which are located on the end surface  3   b  of the drive flange. To achieve the smallest possible distance s, the end surface of the retaining web  30  facing the cylinder barrel  7  is provided in the radially outer area with a bevel  33  that is inclined toward the end surface  3   b  of the drive flange  3 . 
     To be able to introduce the pistons  10  with the piston heads  10   a  into the receptacle sockets  3   a , each ball head  10   a  (as illustrated in  FIG. 5 ) is provided with two grooves  40   a ,  40   b  located opposite each other. The grooves  40   a ,  40   b  are places where material has been removed from the ball surface in the vicinity of the equator area of the ball heads  10   a . The distance D between the cylindrical groove bases of the two grooves  40   a ,  40   b  oriented parallel to one another is less than the opening width E between the two retaining segments  30   a ,  30   b  of the retaining web  30  on the respective receptacle socket  3   a.    
     The groove widths F of the grooves  40   a ,  40   b  (as illustrated in  FIG. 4 ) are each greater than the width B of the retaining web  30 . 
     The grooves  40   a ,  40   b  are inclined on the ball head  10   a  with a longitudinal axis L N  with respect to the longitudinal axis L K  of the piston  10 . In the illustrated exemplary embodiment, the longitudinal axis L N  of the grooves  40   a ,  40   b  is inclined with respect to the longitudinal axis L K  of the piston  10  by an angle of inclination β M  that forms an installation angle β M . The installation angle β M  is less than 90°. 
     In  FIGS. 1 to 11   a , the grooves  40   a ,  40   b  run in a straight line. 
     The angle of inclination β M  of the grooves  40   a ,  40   b  is such that the angle of inclination β M  for the installation of the pistons  10  is different from the maximum tilting angles  131  of the pistons  10  that occur during operation of the axial piston machine  1 . 
     For installation of the pistons  10  into the receptacle sockets  3   a , on the drive flange  3  on each receptacle socket  3   a  there is a recess  45  for the piston rod  10   c  of the piston  10 . In the illustrated exemplary embodiment, the recesses  45  are located on the radially outer portion of the receptacle sockets  3   a  in the end surface  3   b  of the drive flange  3  and extend from the receptacle socket  3   a  radially outwardly toward the radially outer peripheral surface  3   d  of the drive flange  3 . The recesses  45 , viewed looking inwardly in the radial direction, have a depth that increases starting from the radially outer peripheral surface  3   d  toward the receptacle socket  3   a.    
     On the outer edge between the radially outer peripheral surface  3   d  and the end surface  3   b , the drive flange  3  is also provided with a bevel  46 . The recesses  45  extend into the area of the bevel  46 . 
     The process of installing the pistons  10  into the receptacle sockets is illustrated in greater detail in  FIGS. 6 a  to 8 d   . The indices “a” to “d” in  FIGS. 6 a  to 8 d    correspond to the same installation positions. 
     For installation of the piston  10  in the receptacle socket  3   a , the piston  10  is introduced into the receptacle socket  3   a  at the installation angle β M  illustrated in  FIGS. 6 a , 7 a , and 8 a   . Because when the pistons  10  are tilted at the installation angle β M  the longitudinal axis L N  of the grooves  40   a ,  40   b  is oriented parallel to the retaining web  30 , the piston  10  with the two grooves  40   a ,  40   b  can be inserted into the receptacle socket  3   a  between the two retaining segments  30   a ,  30   b  of the retaining web  30 , as illustrated in  FIGS. 6 b , 7 b , 8 b , and 6 c , 7 c , 8 c   . When the piston  10  is inserted all the way into the receptacle socket  3   a  at the installation angle β M , the piston rod  10   b  comes into contact with the recess  45 . If the ball head  10   a  has been introduced all the way into the receptacle socket  3   a , the piston can be tilted back starting from the installation angle β M  to the angle of inclination β 1  (as illustrated in  FIG. 6 c    by the arrow  60  and in  FIGS. 6 d , 7 d , and 8 d   ) so that the ball head  10   a  is positively secured in the receptacle socket  3   a  by the retaining web  30 . 
     During operation of the axial piston machine  1 , the maximum tilting angles β 1  occur on the pistons  10  (as illustrated in  FIGS. 6 d  and 9 a  to 9 c   ) so that the piston head  10   a  is reliably secured in the receptacle socket  3   a  during operation of the axial piston machine  1 . 
       FIGS. 10 a  to 10 c    are views in perspective of the pistons  10  secured in the receptacle socket  3   a.    
       FIG. 11 b    illustrates a second embodiment of a piston  10  in which the grooves  40   a ,  40   b  in the piston head  10   a  follow a bent path. The grooves  40   a ,  40   b  have a first segment oriented with a longitudinal axis L N  at the angle of inclination β M  at an inclination with respect to the longitudinal axis L K  of the piston  10 . A second segment of the grooves  40   a ,  40   b  is also bent with respect to the first segment and in the illustrated exemplary embodiment is oriented with a longitudinal axis L N2  perpendicular to the longitudinal axis L K  of the piston  10 . Because of the bent second segment of the grooves  40   a ,  40   b , the ball end of the ball head  10   a  that is opposite the piston shaft  10   c  has a dimension t 2  from the outer edge of the grooves  40   a ,  40   b  that is greater than the dimension t 1  of a straight path of the grooves  40   a ,  40   b  ( FIG. 11 a   ), so that the load-bearing ball half that is opposite the piston rod  10   c  and transmits the piston forces in the receptacle socket  3   a  has an enlarged surface area. 
     The invention has a series of advantages. 
     The locking of the pistons  10  of the invention in the receptacle sockets  3   a , on account of the hemispheric shaped receptacle sockets  3   a  and the retaining web  30  on the end surface  3   b  of the drive flange  3 , which projects out of the end surface  3   b  of the drive flange  3 , requires little extra manufacturing effort or expense. In addition, a compact axial dimension of the axial piston machine of the invention can be achieved with the locking of the piston  10  in the drive flange  3  of the invention. As a result of the presence of the two inclined grooves  40   a ,  40   b , the locking of the pistons  10  is appropriate for use on variable displacement machines with a variable displacement volume and makes pivoting angles of 0° possible. The two grooves  40   a ,  40   b  on the piston heads  10   a , compared to flattened areas on the piston heads  10   a  to manufacture cylindrical surfaces, on account of the small groove width F of the grooves  40   a ,  40   b , results in a slight reduction of the ball surface area on the load-bearing ball half that is opposite the piston rod  10   c.    
     The invention is not limited to the illustrated exemplary embodiments. The axial piston machine  1 , instead of being constructed as a variable displacement machine, can alternatively be constructed as a constant displacement machine. In a constant displacement machine, the angle of inclination α of the axis of rotation R Z  of the cylinder barrel  7  is constant and fixed with respect to the axis of rotation R t  of the drive shaft  4 . The control surface  15  with which the cylinder barrel  7  is in contact can be formed on the housing  2 . 
     It goes without saying that the bushing  50  can be constructed in one piece with the cylinder barrel  7 . 
     The drive flange  3  can be in the form of a component that is separate from the drive shaft  4  and is connected with the drive shaft  4  in a torque-tight manner. 
     The bevel  46  on the drive flange  3  can be enlarged so that the additional recesses  45  for the installation of the pistons  10  can be eliminated. 
     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 breath of the appended claims and any and all equivalents thereof.