Abstract:
An axial piston machine includes a housing part, a drive shaft, which is mounted in the housing part, and a cylinder drum, which is connected to the drive shaft in a rotationally fixed manner and which accommodates a plurality of pistons. Each of the pistons bound a working chamber and are supported on a swashplate. The working chambers can be connected in alternation to a high-pressure channel and to a low-pressure channel, which extend in the housing part. An insert part is rigidly inserted into the housing part. A control surface of the insert part is directly opposite the cylinder drum. The insert part has a high-pressure channel section and a low-pressure channel section, which have approximately kidney-shaped opening areas in the control surface. The other openings of the high-pressure and low-pressure channel sections opposite the opening area in the control surface are formed radially on the insert part.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2011/003927, filed on Aug. 5, 2011, which claims the benefit of priority to Serial No. DE 10 2010 045 867.8, filed on Sep. 17, 2010 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to an axial piston machine as described below and to an insert part which is suitable for such an axial piston machine. 
     An axial piston machine is known, for example, from DE 10 2006 062 065 A1 195 36 997 C1 and datasheet RDE 93220-04-R/02.08 by Bosch Rexroth AG and can be embodied as a single or double axial piston machine and as a pump or motor. In these known solutions, the axial piston machine is embodied with a housing in which at least one cylinder drum with a multiplicity of pistons which each bound one working chamber is rotatably mounted. These pistons are each supported by means of a piston foot on a swash plate whose attitude angle determines the piston stroke. 
     The working chamber which is bounded in each case by a piston can be alternately connected to a high pressure duct and to a low pressure duct via a control disk which is arranged at the end of the housing. The cylinder drum is connected in a rotationally fixed fashion to a drive shaft which, depending on the type of machine (motor, pump), acts either as an output shaft or as a drive shaft. 
     In the abovementioned axial piston machines, the housing has a housing part which is for example pot shaped or double pot shaped and in whose pot bottom the high pressure ducts and low pressure ducts are formed, it being possible to connect said high pressure ducts and low pressure ducts in series to the working chambers of the cylinder drum via the control disk which is fixed with respect to the rotating cylinder drum. In other axial piston machines, the part of the housing in which the pressure ducts are formed can also be embodied in a plate shape. 
     In the control disk, a plurality of comparatively small pressure kidneys which lie on a common pitch circle and between each of which a material web is arranged are formed. On the low pressure side, each control disk is embodied with a suction kidney which extends over a circumferential angle range which is relatively large compared to the small pressure kidneys. 
     U.S. Pat. No. 7,257,948 B1 presents a double axial piston machine in which a charging pump which is embodied as an internally toothed gearwheel machine is arranged between two pump units. The charging pump is arranged here between two disks which are fixedly connected to the housing. The disks here have the pressure kidneys described above and a suction kidney and form at the same time the housing of the axial piston machine in this region, i.e. they are not radially surrounded by the housing or a housing part. On the drum side, each disk bears against the assigned cylinder drum. 
     It is disadvantageous here that the disks are not surrounded by a housing, with the result that bearing faces of the disks against the charging pump are at risk of soiling. 
     DE 195 36 997 C1 presents a double axial piston pump having two pump units in a swash plate configuration in which the housing has a disk-shaped central housing part in which the two drive shafts of the two units are connected to one another in a rotationally fixed fashion. An impeller wheel or impeller of a charging pump, by means of which a charging pressure can be applied for both units to the pressure medium on the low pressure side, is mounted in this region between the two shafts. In order to mount the impeller wheel, the housing part is embodied on the side of a first unit with an insert ring which is mounted after the impeller wheel is inserted into the housing part. In this insert ring, high pressure duct sections and low pressure duct sections which are assigned to the cylinder drum of the first unit are formed, said duct sections having a pressure medium conducting connection on the side of the central housing part to a high pressure duct and low pressure duct arranged in the housing part. In the second pump unit, these high pressure duct sections and low pressure duct sections are formed in the wall of the housing part. 
     Working chambers of the two cylinder drums can be alternately connected to the high pressure duct section and the low pressure duct section of the housing or the insert ring via a control disk which is arranged on the end side of the central housing part (second pump unit) or on the end side of the insert ring (first pump unit). In the control disk, a plurality of comparatively small pressure kidneys which are located on a common pitch circle are formed on the high pressure side, in each case a material web being arranged between said pressure kidneys. On the low pressure side, each control disk is embodied with a suction kidney which extends over a circumferential angle range which is relatively large in comparison with the small pressure kidneys. 
     The two control disks are of a very thin configuration here and bear with an axial bearing face, which has been ground with high precision, on a likewise precise axial bearing face of the insert ring or of the central housing part. On the drum side, the control disks are likewise fabricated and ground in a very precise spherically convex fashion. 
     During operation of the axial piston machine, comparatively high pressures are applied to the high pressure ducts in the central housing part, in the region of the pressure kidneys and of the material webs adjoining the latter. It is problematic here that as a rule the housing part is manufactured from ductile graphite, and that precisely in this region one zone is present which is problematic with respect to the casting front profile and in which cavity points can occur during hardening of the casting. In the case of high stresses owing to a high hydraulic pressure, damage or deformation of the housing part can then occur in the region where cavities are present, with the result that the running time of the axial piston machine is reduced. 
     A disadvantage of the solution is that the control disk, the insert ring and the housing part against which the control disk bears can only be fabricated at very high cost with the required precision and pressure resistance and take up a relatively large amount of space in the axial direction. 
     In contrast with the above, the disclosure is based on the object of providing an axial piston machine with a shortened overall length and simplified fabrication and in which the risk of damage by pressure loading is reduced. 
     This object is achieved by means of an axial piston machine having the features described below. The object is also achieved by an insert part having the features described below. 
     Further advantageous refinements of the disclosure are described below. 
     SUMMARY 
     The axial piston machine according to the disclosure has a housing part in which a cylinder drum which is connected to a drive shaft in a rotationally fixed fashion is mounted. The cylinder drum has a multiplicity of pistons which each bound one working chamber and are supported on a swash plate. In this context, during one rotation of the drum the working chambers can alternately be connected to a high pressure duct and to a low pressure duct via a high pressure duct section and a low pressure duct section of an insert part which is fixed to the housing or fixedly arranged in the housing, said pressure ducts extending in the housing part. The expression “extending in the housing part” also includes here the fact that the ducts also extend in further parts which are recessed into the housing part. According to the disclosure, the insert part is located with a control face directly opposite the cylinder drum, wherein the high pressure duct section and the low pressure duct section have approximately kidney-shaped mouth regions in the control face. The insert part bears directly against the cylinder drum if the lubrication film which is formed between the insert part and the cylinder drum during operation is considered to be insignificant for the approach. 
     The insert part combines the function of an insert ring and the function of a control disk in a single, compact component by virtue of the fact that in the insert part the high pressure duct section tapers from a kidney-shaped mouth region to a circular-cylindrical mouth, and by virtue of the fact that by means of the insert part the working chambers of the cylinder drum are placed in a pressure medium conducting connection with the high pressure duct and the low pressure duct. This embodiment in a single part results in a lower degree of expenditure on fabrication, since instead of the conventional insert ring with a control disk now only one insert part has to be fabricated and processed. As a result of the fact that the insert ring and the control disk are fabricated in one piece as an insert part, the need to fabricate bearing faces between the two conventional parts (insert ring, control disk) is also eliminated. It is particularly advantageous here that the difficult fabrication or processing of the thin control disk is eliminated. The use of an insert part which is embodied in one piece in this way compared to a control disk which bears directly against the housing also contributes to higher pressure resistance of the housing since highly stressed regions around the high pressure connection are, according to the disclosure, not embodied in the housing or housing part but rather in the insert part, and the insert part can be dealt with significantly better in terms of shaping and reshaping. Finally, this configuration makes it possible to make the housing part comparatively thin-walled, while in the region of the zones which are stressed with high pressure the housing part is formed by the insert part. Given the same pressure resistance, relatively large duct cross sections are therefore also possible, which have a positive effect on the flow conditions in the machine and the efficiency of the machine. The specified advantages mean that the installation space and in particular the overall length of the total axial piston machine are shortened compared to the conventional solutions since they require very voluminous housings in order to make available the necessary pressure resistance. 
     In one preferred development of the disclosure, the high pressure duct section has an approximately circular-cylindrical mouth at its other end opposite the mouth region in the control face. 
     The control face of the insert part therefore bears against an end face of the cylinder drum in such a way that flat contact is formed between the insert part and the cylinder drum and the working chambers can be connected in a pressure-medium-tight fashion to the high pressure duct section or to the low pressure duct section in the insert part via the mouth region. The flat contact between the control face and the end face is embodied here in such a way that the cylinder drum can rotate together with the drive shaft without too much leakage between the cylinder drum and the insert part. In each case just a lubrication film is formed between the end face of the cylinder drum and the control face of the insert part. 
     In one advantageous development, a mouth region or the mouth regions has/have a fine adjustment geometry, in particular an adjustment groove which ends in the control face. The groove advantageously extends here approximately along a pitch circle which can be covered by both the mouth region and insert-part-side openings of the working chambers during the rotation of the cylinder drum. If the axial piston machine operates with different rotational directions of the drive shafts, it is additionally advantageous if fine adjustment geometries are provided on the mouth regions for both directions of rotation. 
     The control face is preferably of spherical configuration. It can be of concave or convex configuration. However, a planar control face is also possible. 
     In an advantageous development, the control face is embodied as an annular face which is raised with respect to a surface of the insert part facing the rest of the cylinder drum, in which annular face the mouth regions are located. As a result, just one small defined face bears against the cylinder drum, as a result of which the working chambers can be connected particularly reliably and in a way which can be checked satisfactorily, and in a pressure-medium-tight fashion to the high pressure duct section or the low pressure duct section in the insert part, with the exception of the leakage which is necessary to form the lubrication film. 
     In order to prevent pressure damage to the insert part or to the mouth regions, in one advantageous development of the disclosure in the mouth region of the high pressure duct section or of the low pressure duct section, one or more material webs ( 33 ) run between the radially inner boundary and the radially outer boundary. 
     In one particularly advantageous development, an end-face-side surface of the material webs is stepped back with respect to the control face. In this way, the surface of the material webs does not end flush with the control face and the recesses or control kidneys which are adjacent to the material webs have a pressure medium conducting connection directly to one another at the control face. 
     The low pressure duct section of the insert part preferably has a mouth region toward the housing part, in a circumferential face. 
     The mouth of the high pressure duct section is preferably formed in a circumferential face on the insert part. 
     The configuration of the axial piston machine can be simplified if a locating receptacle, into which a pressure bushing which extends into the housing part and in which the high pressure duct changes from the insert part into the housing part is inserted, is formed in the mouth of the high pressure duct section. As a result of the bushing, the position of the insert part with respect to the housing part can also be secured. It is particularly advantageous if the pressure bushing is stepped here with the result that such a load bearing face for the high pressure is provided that a force in the direction of the insert part acts on the pressure bushing. 
     In order to support the insert part axially against the housing, the insert part has a radial backstep via which an axial bearing face against the housing is formed. The insert part can also be centered radially in the housing by means of the radial backstep. 
     According to the disclosure it is preferred if a receptacle, into which a sliding bearing or roller bearing is inserted, is formed in the insert part, the drive shaft being mounted in the insert part and therefore in the housing part by means of said sliding bearing or roller bearing. 
     In one particular embodiment of the disclosure, the insert part is a steel casting, wherein preferably nitrated steel casting is used. It is also possible for the insert part to be a forged part or to be formed in a metal cutting fashion from a solid material and nitrated. Instead of a preferably used steel casting, ductile graphite or gray casting, in principle it is also possible to manufacture the housing from a simpler material, for example from lightweight metal. 
     An axial piston machine having the features disclosed herein can, in particular, also be embodied as a double axial piston machine with two units which are accommodated in a common housing part and which include at least one drive shaft and in each case a cylinder drum, wherein each unit is assigned an insert part according to at least one embodiment disclosed herein. 
     If each cylinder drum is assigned in each case a drive shaft, said drive shafts are preferably connected to one another in a rotationally fixed fashion at their opposite end sections via a coupling bushing, wherein the coupling bushing is preferably mounted in a rotatable fashion by means of a roller bearing or sliding bearing which is arranged in a receptacle of the two insert parts. In this context, the drive shafts can have external toothing which engages in internal toothing on the coupling bushing. The end sections of the shafts are preferably kept short here, as a result of which bending of the drive shaft can be compensated and is transmitted to the coupling bushing only to a limited degree. If the two drive shafts have identical end sections accommodated in the bushing, the two units can be mounted in two variants (on the left/on the right). 
     A charging pump, via which a charging pressure can be applied to a pressure medium flowing in on the low pressure side, can be arranged in the region between the cylinder drums, and wherein an impeller wheel of the charging pump forms an axial gap seal at least in certain sections with one or both insert parts. 
     It is preferred if the impeller or impeller wheel is connected to the coupling bushing in a rotationally fixed fashion. In this context it may, for example, be embodied in one piece with the bushing or be integrally formed onto the bushing. 
     The insert part according to the disclosure has a high pressure duct section with an end-side mouth region and an approximately circular-cylindrical radial mouth and is embodied in one piece. A blank of the insert part can be a casting which is formed in one piece here or can be composed from blanks of an insert ring and a control plate which are connected to one another in a materially joined fashion, for example by fusing or welding. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred exemplary embodiment of the disclosure will be explained in more detail below with reference to the drawings, in which: 
         FIG. 1  shows a detailed illustration in a partial section along the longitudinal axis of a double axial piston pump, 
         FIG. 2  shows a detailed illustration of the double axial piston pump according to  FIG. 1  in an enlarged illustration, 
         FIG. 3  shows a perspective illustration of a first insert part of the double axial piston pump according to  FIGS. 1 and 2 , 
         FIGS. 4 and 5  show sectional views of the first insert part of the double axial piston pump according to  FIG. 3 , 
         FIG. 6  shows a perspective illustration of a second insert part according to the disclosure of the double axial piston pump according to  FIGS. 1 and 2 , 
         FIG. 7  shows a sectional view of the second insert part of the double axial piston pump according to  FIG. 6 , and 
         FIG. 8  shows a plan view of an upper side of the insert part which is valid for both insert parts. 
     
    
    
     DETAILED DESCRIPTION 
     Since the basic configuration of a double axial piston pump is sufficiently known from the prior art, for example such as from DE 195 36 997 C1, in the text which follows only the components which are essential to understanding the disclosure, and in particular a central region of the machine, are explained. 
     The double axial piston pump  1  according to  FIG. 1  has a multi-component housing, of which only the central, double-pot-like housing part  2  with housing sections  2   a ,  2   b  and  2   c  is shown partially in  FIG. 1 . The housing section  2   b  is a central part from which the housing sections  2   a  and  2   c  project in opposite directions. Two pump units  66  and  68  are arranged in the housing. A drive shaft  4  of the pump unit  66  is arranged and mounted in the housing section  2   a  and  2   b , and a drive shaft  5  of the pump unit  68  is arranged and mounted in the housing section  2   b  and  2   c . The approximately cylindrical housing sections  2   a  and  2   c , which are fitted onto the central housing section  2   b , form, together with external covers (not illustrated), a receptacle chamber for two cylinder drums  10 ,  11 . The drive shafts  4 ,  5  have external toothing which engages in corresponding internal toothing (neither illustrated) of a cylinder drum  10 ,  11  in each case. 
     The cylinder drums  10 ,  11  have here a multiplicity of cylinder drilled holes  12  which are located on a common pitch circle and in each of which a piston  14  is guided. The latter bounds, together with the cylinder drilled hole  12 , a working chamber  16  whose volume is dependent on the piston stroke. A piston foot (not illustrated), remote from the working chamber  16 , of each piston  14  is connected in an articulated fashion to a sliding shoe (not illustrated). The latter bears against a swash plate (not illustrated either) which is mounted in a rotationally fixed fashion in the housing sections  2   a  and  2   c , wherein the attitude angle of a bearing face on which the sliding shoes can slide determines the piston stroke. Depending on the configuration of the double axial piston pump  1 , this attitude angle of the swash plates can be made either adjustable or invariable. 
     Each cylinder drum  10 ,  11  has, on its end side shown in  FIG. 1 , an end wall  26  in which a plurality of ducts  27 , lying on a common pitch circle, are formed, which ducts  27  open, at one end, in each case in one of the working chambers  16  and, at the other end, in the outer end face  28  of the cylinder drums  10 ,  11 . Both end faces  28  are of concavely spherical configuration. Each end face  28  of the cylinder drums  10 ,  11  of each pump unit  66 ,  68  bears, according to the disclosure, in a sliding fashion on insert parts  30 ,  31  which are mounted fixed to the housing and in each of which pressure kidneys  32  and a comparatively large suction kidney  34  are formed in a manner known per se. During the rotation of the cylinder drums  10 ,  11 , the pressure kidneys  32  and the suction kidneys  34  alternately have a pressure medium conducting connection to the working chambers  16 . The specific configuration of the insert parts  30 ,  31  is explained later on the basis of  FIGS. 3 to 8 . 
     The pump housing part  2  or, to be more precise, the central housing section  2   b  is subjected to considerable pressure forces during the operation of the axial piston pump, in particular in the regions adjoining the insert parts  30 ,  31 . According to the disclosure, these pressure forces are taken up by the insert parts  30 ,  31 , which are adapted to this pressure loading in terms of their geometry and material selection. As a result, it is possible to configure the central housing section  2   b  with a comparatively simple configuration which is easy to deal with in terms of casting technology. 
     In the central housing section  2   b , there are two high pressure connections P 1 , P 2 , wherein the first pump unit is assigned to the high pressure connection P 1 , and the other pump unit is assigned to the high pressure connection P 2 . A tank connection (not shown in more detail) is common to both pump units. The high pressure connection P 1 , P 2  of one unit  66 ,  68  is connected here to the abovementioned pressure kidneys  32  via, in each case, one high pressure duct (HP duct)  46  and one high pressure duct section (HP duct section)  52  arranged in the insert part  30 ,  31 . The low pressure connection T of one unit  66 ,  68  is connected to the abovementioned suction kidney  34  via a low pressure duct (LP duct) (not illustrated) and a low pressure duct section (LP duct section)  54  arranged in the insert part  30 ,  31 . In each case a pressure bushing  62  is inserted into both HP ducts  46 . The two pressure bushings  62  are embodied in a step with an annular face  114 , relieved of loading via, in each case, one relief drilled hole  113  toward the interior of the housing, on the step and are subjected to high pressure in such a way that a resultant of the pressure force, which acts radially into the interior of the double axial piston pump  1 , occurs. An end section (at the bottom in  FIG. 1 ) of the pressure bushings  62  bears here in a precisely fitting fashion on a locating face of the insert parts  30 ,  31  in such a way that the latter are fixed in position, in particular with respect to the angular position, by means of the pressure bushings  62 . 
     The drive shafts  4 ,  5  have, on their end sections, external toothings  102  which mesh with an internal toothing of the coupling bushing  80 . In this way, the drive shafts  4 ,  5  are connected to one another in a rotationally fixed fashion via the coupling bushing  80 . The coupling bushing  80  is radially mounted by means of two sliding bearings  86 ,  87  in the two insert parts  30 ,  31 . It also has two radially extended annular webs  88 ,  89 , of which the annular web  88  is supported axially on an annular shoulder  90  of the sliding bearing  87 , and the annular web  89  is supported axially on an annular shoulder  91  of the sliding bearing  86 . 
     As is described, for example, in DE 195 36 997 C1, double axial piston machines of this type are embodied with a charging pump  82 . In the specific solution, this charging pump  82  is formed by an impeller which is connected in a rotationally fixed fashion to the drive shafts  4 ,  5  via the coupling bushing  80  and via which a charging pressure is applied to the pressure medium on the suction side. An impeller wheel  84  is integrally formed on in one piece to the coupling bushing  80  here via the annular web  89 . Pressure medium is sucked in from a suction chamber T via the impeller wheel  84  and fed into a charging pressure chamber  104 . The charging pressure chamber  104  is connected via the suction-side LP duct sections  54  of the insert parts  30 ,  31  to the suction kidneys  34  thereof. 
       FIG. 2  shows an enlarged partial illustration of the exemplary embodiment according to  FIG. 1  in the region of the two pressure bushings  62 . It is possible to see part of the impeller wheel  84  and of the coupling bushing  80 . The coupling bushing  80  forms two hubs  100 ,  101  to the left and right in  FIG. 2  in the region of which hubs  100 ,  101  the external toothing  102  of the drive shafts  4 ,  5  meshes with the internal toothing of the coupling bushing  80 . According to this illustration, the insert parts  30 ,  31  have at their end side in each case a circumferential guide collar  108 ,  109 , which protrudes with respect to the impeller wheel  84  and in each case covers the external circumference of the impeller wheel  84  in certain sections and forms a sealing gap therewith. The radial sealing gaps seal the charging pressure side of the impeller, on the one hand, with respect to a suction side of the impeller and, on the other hand, with respect to that in the interior of the housing in which the cylinder drum of the one unit is located. The hubs  100  and  101  of the impeller dip into the two sliding bearings  86 ,  87 , which are each fitted into a receptacle  148 ,  149  of the insert parts  30 ,  31  and are supported axially with an annular end face  124 ,  125  of their annular shoulders  90 ,  91  in a radial extension of the receptacle  148 ,  149 . The plan faces lying opposite the annular shoulders, on the annular webs  88  and  89 , serve as an axial guiding means for the coupling bushing together with the impeller. Otherwise, there is a certain degree of play between the axial end faces of the impeller and the insert parts  30 ,  31 . The flat annular chamber, brought about as a result of this, between the impeller and the insert part  30  and therefore the corresponding side face on the impeller are relieved of loading by the charging pressure by a drilled hole  85  in the impeller. Alternatively, the flat annular chamber can also be relieved of loading through the insert part  30  to the interior of the housing through a drilled hole  83  which is indicated by dashed lines in  FIG. 1 . 
     The two identical pressure bushings  62  are subjected to the high pressure on an excess face radially toward the inside (at the bottom of  FIG. 2 ), with the result that they are always acted on in the direction of the associated insert part  30 ,  31 . The end section of the pressure bushings  62  which is embodied with an annular end face  126  dips into a corresponding radial locating receptacle  130  of the insert parts  30  and  31 , with the result that the insert parts  30 ,  31  are secured with respect to the angular position. Their radial centering occurs in each case by means of their circular-cylindrical external circumferential faces  166 ,  168  with which they are inserted into a continuous locating drilled hole  160  in the central housing section  2   b.    
     Details of the two insert parts  30  and  31  are explained with reference to  FIGS. 3 to 8 . Here,  FIG. 3  shows the basic configuration of the insert part  30  in an overview, and  FIGS. 4 and 5  show the insert part  30  in a section and in an enlarged section, respectively.  FIG. 6  shows the basic configuration of the somewhat larger insert part  31 , and  FIG. 7  shows the insert part  31  in a section.  FIG. 8  shows a plan view which applies with the exception of the arrangement of the adjustment grooves  36  for the two insert parts  30 ,  31 . The adjustment grooves are indicated in the form in which they are present in the insert part  30  in  FIGS. 3 to 5 . In the case of the insert part  31 , the adjustment grooves are located at the respective other ends of the control kidneys since the direction of rotation of the cylinder drum which bears against the insert part  31  is, with respect to the insert part  31 , opposed to the direction of rotation of the other cylinder drum with respect to the insert part  30 . 
     The insert parts  30 ,  31  are constructed from a comparatively high-strength material, for example from nitrated steel casting, while the housing part  2  can be manufactured from a material with a comparatively small pressure resistance, for example from lightweight metal casting or the like. 
       FIGS. 3 to 5  explain in the text which follows the configuration of the insert part  30  according to the disclosure in unit  66 . 
       FIG. 3  shows the insert part  30  with a drum-side end section  140  and an impeller-side annular section  142 , which is set back radially with respect to the drum-side end section  140 . The locating receptacle  130  for the pressure bushing  62  (cf.  FIG. 1 or 2 ) is formed in at least one of the two sections  140  and  142 . On an upper side of the insert part  30  or on that side of the drum-side end section  140  which is on the right in  FIGS. 4 and 5 , an annular spherical control face  144  is formed in such a way that it is slightly raised with respect to another upper side  146 . According to the disclosure, in the mounted state of the insert part  30  this control face  144  bears against the end face  28  of the cylinder drum  10  (cf.  FIGS. 1 and 2 ). The narrow annular shape of the control face  144  makes it possible to form, between the cylinder drum  10  and the insert part  30 , a defined bearing or contact zone which brings about a good seal and which forms a sliding film with the operating fluid when the parts rotate with respect to one another. The control face  144  is fabricated and ground very precisely here. The same applies for the end face  28 , lying opposite the latter, of the cylinder drum  10 . Compared to the prior art (cf. DE 195 36 997 C1) in which two individual parts—an insert ring and a thin control disk—perform the function of the insert part  30  which is in one piece according to the disclosure, the insert part  30  has the advantage that both the original shaping, that is to say the molding, and the subsequent processing steps are simplified owing to the size and compactness of the insert part  30 . 
     The axial HP mouth region  56  and the axial LP mouth region  58  are formed in the control face  144 . In this context, three pressure kidneys  32  are formed, separated by material webs  33 , in the HP mouth region  56 . A surface of the material webs  33  is lowered somewhat with respect to the control face  144 , as a result of which during operation all three pressure kidneys  32  of the insert part  30  are connected to one another in a pressure medium conducting fashion. The LP mouth region  58  is formed by a large suction kidney  34 . 
     Each mouth region  56 ,  58  has in each case an adjustment groove  36 , as a result of which pressure surges during operation of the double axial piston pump  1  can be reduced. Depending on the direction of rotation, the adjustment groove is located at one or other end of the mouth regions. 
       FIG. 4  shows a section of the insert part  30  according to  FIG. 3 , from which the profile of the HP duct section  52  and of the LP duct section  54  is very clear. Accordingly, both duct sections  52 ,  54  are embodied in an angular shape, wherein the mouth regions  56 ,  58  each open in the axial direction in the control face  144  of the end section  140 . It is clearly apparent that the control face  144  is made very narrow at the locations of the mouth regions  56  and  58  and in addition is not formed parallel to the other upper side  146  of the insert part  30 . A mouth  132  which is oriented toward the pressure connection P (cf.  FIGS. 1 and 2 ) and a mouth region  134  which is oriented toward the suction connection T open radially in a circumferential wall in the junction region between the control-side end section  140  and the annular section  142  which is set back radially with respect thereto. 
     A receptacle  148  for the sliding bearing  86  according to  FIGS. 1 and 2  is provided in the insert part  30  via an axial drilled through-hole. Furthermore, on the impeller side a radial backstep  150  of the receptacle  148  is provided in which the annular shoulder  90  of the sliding bearing  86  can dip (cf.  FIGS. 1 and 2 ). 
     The guide collar  108  (already explained in  FIG. 2 ) which engages around the impeller  84  in certain sections in the circumferential direction is formed in the region of the end face of the annular section  142 . 
     For defined axial positioning of the insert part  30  in the housing section  2   b , the radial step in the insert part  30  is embodied from the end section  140  toward the annular section  142  in a perpendicular direction with respect to the central axis, as a result of which a bearing face is formed in the form of an annular end face  141 . This bearing is ground precisely in the same way as the control face  144  or the end face  28  (cf.  FIG. 1 ). 
     The insert part  30  according to  FIG. 2  is radially centered and mounted in the housing section  2   b  in the axial locating drilled hole  160  provided for this purpose, via an external circumferential face  168 . 
       FIG. 5  shows, for the sake of better illustration of a region of the control face  144 , a section through the insert part  30  according to  FIG. 4  in an enlarged illustration. A symmetrical central part of the receptacle  148  according to  FIG. 4  is cut away here. A dot-dash curve A, which is at a tangent to the control face  144 , indicates that the control face  144  is formed a section of a spherical surface. The radius of the dot-dash curve A corresponds here to the radius of the corresponding sphere. In this illustration it is clearly apparent that within the HP mouth region  56  a radial diameter of a pressure kidney  32  is somewhat reduced with respect to a material web  33 , which results in the lowering of the control-face-end surface of the material webs  33  with respect to the control face  144 , which has already been mentioned in  FIG. 3 . The LP mouth region  58  is formed by a large suction kidney  34  and does not have such a lowered portion. In the exemplary embodiment shown, the surface of the material webs  33  is formed so as to be planar and perpendicular with respect to the central axis of the insert part  30 . In order to increase the pressure resistance of the control face  144 , this surface can alternatively be formed from a face which is concentric with respect to the control face  144  and has a slightly reduced radius. In order to reduce a notch effect between the wall of the control face  144  and the upper side  146  of the insert part, the upper side  146  merges with the wall of the control face  144  via a supporting annular step  120 . 
       FIGS. 6 and 7  explain in the text which follows the configuration of the herein disclosed insert part  31  of the unit  68 . 
       FIG. 6  shows the insert part  31  of the unit  68  which is similar in principle to the insert part  30  of the unit  66  according to  FIGS. 1 to 5 . Features which are of identical configuration therefore have the same reference symbols for the insert part  30 . 
     A drum-side end section  140  has a HP mouth region  56  with a pressure kidney  32 , reinforced by material webs  33 , and an LP mouth region  58 , with a suction kidney  34 . On the right-hand side of the drum-side end section  140  in  FIG. 7 , the annular spherical control face  144  is formed slightly raised with respect to the other upper side  146 . One surface of the material webs  33  is somewhat lowered with respect to the control face  144 , as a result of which the pressure kidney  32  of the insert part  31  is not interrupted directly in the control face. The LP mouth region  58  is formed by a large suction kidney  34 . Each mouth region  56 ,  58  also has in each case an adjustment groove  36  in a way analogous to the insert part  30 . 
     In the illustration according to  FIG. 6 , it is also possible to see the locating receptacle  130  for the pressure bushing  62  of the unit  68  (cf.  FIG. 2 ). This locating receptacle  130  opens in an annular section  154  which is significantly longer compared to the insert part  30  and is set back in the radial direction compared to the end section  140  of the insert part  31 . 
     According to the disclosure, in the mounted state of the insert part  31  the control face  144  of the insert part  31  bears against the end face  28  of the cylinder drum  11  (cf.  FIGS. 1 and 2 ). In this context, the same advantages are obtained compared to the prior art as already presented with respect to the insert part  30  in the description according to  FIG. 3 . 
     In the illustration according to  FIG. 6 , a cutout  156  is shown which opens toward the suction chamber, with the result that the pressure medium can flow to the impeller wheel  84  (cf.  FIGS. 1 and 2 ) via this cutout  156 . 
     On the impeller wheel side, according to the sectional illustration in  FIG. 7  an end recess is in turn formed in the end face of the annular section  154 , the circumferential walls of which end recess form the guide collar  109  for a section of the impeller wheel  84 , with the result that the latter forms, as already mentioned, a sealing gap in the radial direction by means of the guide collar  108  on the insert part  30  and the guide collar  109  on the insert part  31 . An axial drilled through-hole forms a receptacle  149  for the sliding bearing  87  (cf.  FIG. 2 ) in the insert part  31 . Furthermore, a radial backstep  151  of the receptacle  149  is provided on the impeller side, in which backstep the annular shoulder  91  of the sliding bearing  87  (cf.  FIG. 2 ) can dip. 
     For defined axial positioning of the insert part  31  in the housing section  2   b , the radial step of the insert part  31  is embodied so as to be perpendicular to the central axis from the end section  140  to the annular section  154 , as a result of which a bearing face in the form of an annular end face  141  is formed in a way analogous to the insert part  30  of the unit  66 . This bearing is ground precisely, like the control face  144  or the end face  28  of the cylinder drum  11  of the unit  68  (cf.  FIG. 1 ). According to  FIG. 2 , the insert part  31  bears with its annular end face  141  against the housing part  2 . 
     The insert part  31  according to  FIG. 2  in the housing section  2   b  is centered and mounted radially in the axial locating drilled hole  160  provided for this purpose, by means of an external circumferential face  166 . 
       FIG. 8  shows a plan view of the upper side of the insert parts  30 ,  31  which is valid for both insert parts  30 ,  31  and which faces the respective end faces  28  of the cylinder drums  10  and  11 . The control face  144 , the other upper side  146  which is set back axially somewhat, the mouth regions  56  and  58 , the pressure kidney  32  and material webs  33 , the adjustment grooves  36  and the suction kidney  34  are depicted in a way analogous to  FIGS. 3 to 7 . In this context, the adjustment grooves are each located at that end of the mouth regions as a function of the direction of rotation that the ducts  27  in the cylinder drum can slowly build up the pressure in the working chamber starting from the suction kidney  34  via the groove  36  of the pressure kidney and can slowly reduce the pressure starting from the pressure kidney via the groove  36  of the low pressure kidney. 
     An axial piston machine having a housing and a cylinder drum is disclosed, wherein an insert part having an HP duct section is arranged in the housing, said HP duct section changing from an approximately kidney-shaped drum-side HP mouth region into an approximately circular-cylindrical housing-side mouth, wherein the insert part bears directly against the cylinder drum. Furthermore, an insert part for such an axial piston machine is disclosed.