Abstract:
A hydraulic dual axial piston machine includes a first driving unit and a second driving unit arranged one behind the other in the direction of the axis of a drive shaft and oriented opposite each other. The first and second driving units each have a respective swashplate and single actuating piston. The first and second actuating pistons exert load on a pivot cradle in a functionally identical manner to increase or decrease a pivot angle of the respective swashplate. The first and second actuating pistons are spaced apart from a central plane of the swashplates which extends through the axis of the drive shaft such that dimensions of a housing in the direction of the pivot axes of the swashplates are minimally influenced.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/DE2011/001367, filed on Jun. 24, 2011, which claims the benefit of priority to Serial No. DE 10 2010 026 454.7, filed on Jul. 8, 2010 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a hydraulic dual axial piston machine having a first drive unit and having a second drive unit which are arranged one behind the other in the direction of the axis of a drive shaft and so as to be oriented oppositely to one another. The first drive unit is equipped with a first swashplate, which for the purpose of varying the inclination relative to the axis of the drive shaft can be pivoted about a first pivot axis, and with a single first actuating piston, which extends at least approximately parallel to the axis of the drive shaft and which, at a first end, engages on the first swashplate for the purpose of pivoting the latter in one direction and which, at a second end, delimits an actuating chamber into which control fluid flows for the purpose of pivoting the first swashplate in one direction and out of which control fluid can be displaced in the event of a pivoting movement of the first swashplate in the other direction. The second drive unit is equipped with a second swashplate, which for the purpose of varying the inclination relative to the axis of the drive shaft can be pivoted about a second pivot axis parallel to the first pivot axis, and with a single second actuating piston, which extends at least approximately parallel to the axis of the drive shaft and which, at a second end, engages on the second swashplate for the purpose of pivoting the latter in a functionally identical manner to the first actuating piston on the first swashplate and which, at a second end, delimits an actuating chamber into which control fluid flows for the purpose of pivoting the second swashplate in one direction and out of which control fluid can be displaced in the event of a pivoting movement of the second swashplate in the other direction. 
     A dual pump of said type, with a back-to-back arrangement of the two component pumps, is known from practice and from the repair manual RDE 93100-11-R/07/07 from Bosch Rexroth AG. Here, the two regulating valves for the adjustment of the component pumps are arranged, on a central part of the housing, in the same plane and so as to be offset both in the longitudinal direction and also in a transverse direction. Furthermore, the regulating valves are oriented oppositely to one another, such that for each regulating valve, the arrangement with respect to the component pump with which it is associated is the same. The actuating pistons are also offset with respect to one another as viewed perpendicularly to the longitudinal direction of the dual pump. This means that the position of the actuating pistons with respect to the exertion of force on the two swashplates by the pump pistons presently performing a delivery stroke is different in the case of one swashplate than in the case of the other swashplate. 
     The disclosure is based on the object of further developing a hydraulic dual axial piston machine of the known type such that substantially identical conditions are present with regard to the two drive units. 
     This is achieved in that the first actuating piston and the second actuating piston, which exert load on the pivot cradle in a functionally identical manner and which thus either both act in the direction of an increase or both act in the direction of a decrease in the pivot angle of the respective swashplate, are arranged, so as to be spaced apart from a central plane of the swashplates which is perpendicular to the pivot axes and which extends through the axis of the drive shaft, at least approximately in alignment with one another. Identical conditions thus prevail for both drive units with regard to the locations at which force is exerted on the swashplates by the pump pistons and by the first and second actuating pistons. As a result of the arrangement spaced apart from a plane which is perpendicular to the pivot axes and which extends through the axis of the drive shaft, the actuating pistons are situated within the housing in such a region that the maximum dimensions of the housing in the direction of the pivot axes of the swashplates, and perpendicular thereto, are influenced at most to a small extent. 
     Advantageous embodiments of a hydraulic dual axial piston machine according to the disclosure emerge from the description below. 
     SUMMARY 
     If the dual axial piston machine has, for each drive unit, an actuating piston which acts as a pivoting-out piston and to the actuating chamber of which pressure medium is supplied in the event of a pivoting movement of the corresponding swashplate in one direction, and an actuating piston which acts as a pivoting-in piston and to the actuating chamber of which pressure medium is supplied in the event of a pivoting movement of the corresponding swashplate in the opposite direction, it is advantageously the case that the two pivoting-out pistons are arranged in alignment with one another and the two pivoting-in pistons are arranged in alignment with one another. 
     In axial piston machines, feedback elements are often provided, the purpose of which is to input the pivot angle of a swashplate alone, or together with the high pressure, into the regulating means of the axial piston machine. It is known for such a feedback element to be provided on an actuating piston, because the position of the actuating piston correlates with the pivot angle of the swashplate. 
     A feedback element of said type is provided in particular if the axial piston machine is to be adjusted in a torque-regulated manner, or proportionally to an input signal. In the case of torque regulation, the feedback element is also provided with a small piston which is subjected to the working pressure and which, depending on the position of the actuating piston and thus of the swashplate, engages on a lever at a different distance from an axis of rotation and exerts a torque on said lever. The valve piston of a regulating valve is supported counter to said torque on the same arm, or on a second arm, of the lever at a fixed distance from the axis of rotation, said valve piston being subjected to a constant or remote-controlled variable force which seeks to increase the swept volume. The swept volume of the axial piston machine is then set in each case such that torque equilibrium prevails at the lever. 
     In the case of a proportional adjustment of the swept volume, the feedback element varies the preload of a spring which exerts load on a valve piston of the regulating valve, said valve piston being acted on counter to the spring by an input force generated predominantly by an electromagnet or a hydraulic pressure. Depending on the magnitude of the input force, the spring force and thus the position of the actuating piston and thus of the swashplate must vary such that, when the valve piston is in the zero position, the spring force and input force maintain the equilibrium. 
     For a dual axial piston machine, it is known for there to be arranged on the first actuating piston a first elongate feedback element by means of which the position of the first actuating piston and thus the pivot angle of the first swashplate is input into a controller of a first regulating valve, and for there to be arranged on the second actuating piston a second elongate feedback element by means of which the position of the second actuating piston and thus the pivot angle of the second swashplate is input into a controller of a second regulating valve. According to one embodiment, it is now the case that the first feedback element and the second feedback element are in each case situated such that the longitudinal axis of the first feedback element and the longitudinal axis of the first actuating piston span a first plane and the longitudinal axis of the second feedback element and the longitudinal axis of the second actuating piston span a second plane which differs from the first plane. The positioning of the feedback elements is determined for example by a guide in the housing or on the respective regulating valve or by means of a particular arrangement on the actuating piston if the latter is not rotatable about its longitudinal axis. 
     It is provided in particular, according to one embodiment, that the first feedback element and the second feedback element are situated such that the first plane and the second plane are at least approximately perpendicular to one another. Small deviations from the mutually perpendicular profile of the two planes may arise for example as a result of a pivoting movement of the actuating piston which is superposed on the linear movement. 
     It is now particularly preferable, according to another embodiment, for the first plane to be perpendicular to the pivot axes of the swashplates, while the second plane runs parallel to the pivot axes of the swashplates. 
     According to another embodiment, the two feedback elements are of different lengths. One feedback element interacts, as already described above, with one regulating valve. Different lengths of the feedback elements now make it possible to compensate for different housing dimensions and resulting different spacings, resulting from the mounting configuration, between the regulating valves and the actuating pistons. 
     If it is the intention for the dual axial piston machine to be of very short construction, it may be the case, if the regulating valves are arranged spatially close to the actuating pistons and the actuating pistons are arranged in alignment, that the accessibility to adjusting devices on the regulating valves is associated with difficulties, even if the regulating valves are arranged more or less in alignment with one another. It may therefore be expedient if, according to one embodiment, the mounting surfaces for the regulating valves on the outside of the housing of the dual axial piston pump are rotated relative to one another about the axis of the drive shaft. This may also be advantageous if no feedback element is provided. 
     For different housing dimensions, the two planes which are parallel to the axis of the drive shaft and in which the mounting surfaces are situated may have different spacings to the axis of the drive shaft. 
     It is preferable for the plane in which one mounting surface is situated to run parallel to the pivot axes of the swashplates and to the axis of the drive shaft, and for the plane in which the second mounting surface is situated to be perpendicular to the pivot axes of the swashplates. 
     If feedback elements are provided, then it is preferable for the first mounting surface to run at least approximately perpendicular to the longitudinal axis of the first feedback element and for the second mounting surface to run at least approximately perpendicular to the longitudinal axis of the second feedback element. Equivalent valve axes of the two regulating valves are offset with respect to one another in the circumferential direction of the housing. 
     An exemplary embodiment of a hydraulic dual axial piston machine according to the disclosure is illustrated in the drawings. The disclosure will now be explained in more detail on the basis of the figures of said drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  shows an external view of a dual pump, one component pump of which has an actuating piston with feedback element mounted in the manner according to the disclosure, 
         FIG. 2  shows a plan view of only the drive units of the dual pump in the direction of the pivot axes of the two swashplates and perpendicular to the axis of the two drive shafts, 
         FIG. 3  shows a plan view of only the drive units of the dual pump in a direction perpendicular to the pivot axes of the two swashplates and perpendicular to the axis of the two drive shafts, 
         FIG. 4  shows a perspective view of an arrangement of drive unit, actuating piston and a regulating valve of the component pump configured according to the disclosure, and 
         FIG. 5  shows a circuit diagram of one component pump. 
     
    
    
     DETAILED DESCRIPTION 
     In the dual axial piston pump shown, it is the case not simply that two single axial piston pumps are mounted on one another in a back-to-back position, but rather that a common main part  13  of a housing  12  is provided for the two component pumps  10  and  11 . The main part  13  can be regarded as being constructed from two housing pots  14  and  15  which, with the bases thereof, form a single central block  16  from which the walls of the housing pots project in opposite directions. At the free edge, the housing pot  14  is closed off by a cover  17 , and the housing pot  15  is closed off by a cover  18 . Within each of the two spaces closed off in each case by a housing pot and a cover there is situated a drive unit  19  or  20  respectively of a component pump. Each drive unit includes a drive shaft  21  or  22  respectively. Said two drive shafts have a common axis  23  and are rotatably mounted in each case in one of the covers and in the central block or in an insert ring (not illustrated in any more detail) which is inserted into said central block. Approximately centrally, the two drive shafts  21  and  22  are coupled to one another in a rotationally conjoint manner by means of an internally toothed coupling sleeve  24  into which they protrude with externally toothed shaft stubs. The drive shaft  21  extends through the cover  17  and has, on the outside, an externally toothed drive journal  25  for coupling to a drive motor, for example a diesel engine. 
     Here, a “back to back” arrangement means that the two drive units  19  and  20  of the two component pumps  10  and  11  are, in terms of basic construction, constructed mirror-symmetrically with respect to a plane running in the region of the central block  16  and perpendicularly to the axis  23 . 
     The drive unit  19  includes a cylinder drum  30  which is connected rotationally conjointly to the drive shaft  21  and in which bores running in the axial direction are situated so as to be distributed at equal angular intervals about the axis  23 , each of which bores receives a pump piston  31 . The pump pistons  31  project at one end side out of the cylinder drum  30  and bear via slide shoes  32  against a swashplate  33 . During the suction stroke in which the working chambers behind the pump pistons are connected to a tank line, to a charge-pressure line which conducts a charge pressure of for example 3 bar, or to a low-pressure line which conducts a feed pressure of for example 30 bar, the slide shoes are held against the swashplate  33 , and pulled out of the bores of the cylinder drum  30 , by a retaining plate  34  which, at bores, engages behind shoulders of the slide shoes. The retaining plate in turn is held against the swashplate by two hold-down segments  35  of said swashplate. 
     The swashplate  33  has, centrally, an aperture in which the drive shaft  21  extends through the swashplate. On each side of the drive shaft, the swashplate  33  has a convex bearing surface  36  of circular cylindrical shape. Both bearing surfaces have the same central axis which constitutes the pivot axis  37  of the swashplate. By means of the bearing surfaces, the swashplate can be pivoted, in corresponding bearing shells of the cover  17 , about the pivot axis  37 . 
     The drive unit  20  includes a cylinder drum  40  which is connected rotationally conjointly to the drive shaft  22  and in which bores running in the axial direction are situated so as to be distributed at equal angular intervals about the axis  23 , each of which bores receives a pump piston  41 . The pump pistons  41  project at one end side out of the cylinder drum  40  and bear via slide shoes  42  against a swashplate  43 . During the suction stroke in which the working chambers at the pump pistons are connected to a tank line, to a charge-pressure line which conducts a charge pressure of for example 3 bar, or to a low-pressure line which conducts a feed pressure of for example 30 bar, the slide shoes are held against the swashplate  43 , and pulled out of the bores of the cylinder drum  30 , by a retaining plate which, at bores, engages behind shoulders of the slide shoes. The retaining plate in turn is held against the swashplate by two hold-down segments  45  of said swashplate. 
     The swashplate  43  has, centrally, an aperture in which the drive shaft  22  extends through the swashplate. On each side of the drive shaft, the swashplate  43  has a convex bearing surface  46  of circular cylindrical shape. Both bearing surfaces have the same central axis which constitutes the pivot axis  47  of the swashplate. By means of the bearing surfaces, the swashplate can be pivoted, in corresponding bearing shells of the cover  18 , about the pivot axis  47 . The pivot axes  37  and  47  intersect the shaft axis  23 . 
     The two end positions of each swashplate  33 ,  43  are predefined by means of stop screws  50  and  51  screwed into the housing main part  13 . 
     The axes of the stop screws run in a skewed configuration with respect to the shaft axis  23 . The stop screw  50  of one component pump is situated on one side, and the stop screw  51  of said component pump is situated on the other side, of a plane spanned by the axes  23  and  37  or  47  respectively, and said stop screws are situated at equal distances from the shaft axis  23 , resulting in a type of diagonal arrangement of the two stop screws at diagonally opposite corners of the housing  12  which has a square basic cross-sectional shape. The stop screw  50  of one component pump interacts with a stop surface on one hold-down means  35  or  45  respectively, and the other stop screw  51  interacts with a stop surface on the other hold-down means  35  or  45  respectively of a swashplate. 
     In  FIGS. 2 and 3 , the swashplate  43  of the component pump  11  is shown in one end position, specifically in or close to the zero position in which it bears against the stop screw  50  associated therewith and in which that surface of the swashplate against which the slide shoes  42  bear is perpendicular or approximately perpendicular to the shaft axis  23 . In said position of the swashplate  43 , the pump pistons  41  do not perform a stroke as the cylinder drum  40  rotates. The swept volume of the component pump  11 , that is to say the amount of pressure medium delivered by the component pump per revolution, is then zero. The swashplate  33  of the other component pump  10  is pivoted to a maximum extent and bears against the associated stop screw  51 . In said position of a swashplate, the swept volume of a component pump is then at a maximum. 
     For the adjustment of the swashplate  33  into any desired intermediate position between the two end positions, there are provided, as actuating pistons, a pivoting-out piston  55  and a pivoting-in piston  56  which are arranged in the two corners, which are not occupied by the stop screws  50  and  51 , of the housing  12  and the longitudinal axes  57  and  58  of which run parallel to the shaft axis  23  when the swashplate  33  is in the zero position. The pivoting-in piston  56  has a piston collar  59  with a relatively large effective surface, by means of which said pivoting-in piston is guided sealingly, and in such a way that the sealing action is maintained, in a slightly pivotable manner in a sleeve  53  which is fixed with respect to the housing and arranged parallel to the shaft axis. In the sleeve, the piston collar delimits an actuating chamber to which pressure medium is supplied via a regulating valve  60  shown in  FIG. 1  for the purpose of decreasing the pivot angle of the swashplate  33  and from which pressure medium can be discharged via the regulating valve  60  when the pivot angle of the swashplate  33  is to be increased. 
     Formed in one piece with the piston collar  59  is a piston rod  61  which is articulatedly connected to a hold-down means  35  and thus to the swashplate  33 . 
     The pivoting-out piston  55  also has a piston collar  62  by means of which it is guided sealingly, and in such a way that the sealing action is maintained, in a slightly pivotable manner in a sleeve  54  which is fixed with respect to the housing and arranged parallel to the shaft axis. In the sleeve, the piston collar  62  delimits an actuating chamber which, in a way which is not illustrated, is subjected permanently to the pump pressure of the component pump  10 . The cross-sectional area of the piston collar  62  is significantly smaller than that of the piston collar  59 , such that a pressure significantly lower than the pump pressure in the actuating chamber delimited by the piston collar  59  is sufficient to pivot the swashplate  33  back counter to the action of the pivoting-out piston  55 . Formed in one piece with the piston collar  62  is a piston rod  63  which is articulatedly connected to the other hold-down means  35  of the swashplate  33 . 
     In order that the swashplate  33  assumes the position of maximum pivot angle as a preferential position in the unpressurized state, there interacts with the pivoting-out piston  55  a pivoting-out spring  65  formed as a helical compression spring, said spring being pushed onto the piston rod  63  and being supported at one side on a shoulder, situated close to the hold-down means  35 , of the pivoting-out piston  55  and being supported at the other side on a spring plate  66 , which surrounds the piston rod  63 , on the housing  12 . 
     Via the pivoting-out piston  55 , the pivoting-out spring  65  exerts load on the swashplate  33  in the direction of larger pivot angles. 
     In that length of the piston rod  63  which is always situated between the piston collar  62  and the spring plate  66 , the piston rod has a thickened region with a transverse bore in which an elongate feedback element  67  is fastened. The position of the feedback element  67  on the piston rod  63  is such that the maximum retraction of the piston collar into the corresponding sleeve in order to attain the zero position of the swashplate  33  is not hindered, nor does the feedback element  67  abut against the spring plate  66  when the swashplate is at the maximum pivot angle. In the housing main part there is situated a corresponding cutout in which the feedback element  67  can move freely. A longitudinal axis  68  of the feedback element is perpendicular to the longitudinal axis of the pivoting-out piston  55 . The feedback element has a housing  69  which, at its distal end remote from the piston rod  63 , is formed as a dihedron  70  and is guided with the latter in a slot of the regulating valve  60 . Said guidance and the position of the regulating valve  60  on the housing  12  have the result that, in the component pump  10 , the feedback element  67  is positioned such that the longitudinal axis  68  thereof and the longitudinal axis of the pivoting-out piston  55  span a plane which runs perpendicular to the pivot axis  37  of the swashplate  33 . 
     For the adjustment of the swashplate  43  of the component pump  11  into any desired intermediate position between the two end positions, there are provided, as actuating pistons, a pivoting-out piston  75  and a pivoting-in piston  76  which are arranged in the two corners, which are not occupied by the stop screws  50  and  51 , of the housing  12  and the longitudinal axes  77  and  78  of which run parallel to the shaft axis  23 , and are aligned with the longitudinal axes  57  and  58  of the corresponding actuating pistons of the component pump  10 , when the swashplate  43  is in the zero position. The two pivoting-in pistons  56  and  76  and the two pivoting-out pistons  55  and  75  are identical to one another. Accordingly, the pivoting-in piston  76  has a piston collar  79  with a relatively large effective surface, by means of which said pivoting-in piston is guided sealingly, and in such a way that the sealing action is maintained, in a slightly pivotable manner in a sleeve which is fixed with respect to the housing and arranged parallel to the shaft axis. In the sleeve, the piston collar delimits an actuating chamber to which pressure medium is supplied via a regulating valve  80  shown in  FIGS. 1 and 4  for the purpose of decreasing the pivot angle of the swashplate  43  and from which pressure medium can be discharged via the regulating valve  80  when the pivot angle of the swashplate  43  is to be increased. 
     Formed in one piece with the piston collar  79  is a piston rod  81  which is articulatedly connected to a hold-down means  45  and thus to the swashplate  43 . 
     The pivoting-out piston  75  also has a piston collar  82  by means of which it is guided sealingly, and in such a way that the sealing action is maintained, in a slightly pivotable manner in a sleeve  74  which is fixed with respect to the housing and arranged parallel to the shaft axis. In the sleeve, the piston collar  82  delimits an actuating chamber which, in a way which is not illustrated, is subjected permanently to the pump pressure of the component pump  11 . The cross-sectional area of the piston collar  82  is significantly smaller than that of the piston collar  79 , such that a pressure significantly lower than the pump pressure in the actuating chamber delimited by the piston collar  79  is sufficient to pivot the swashplate  43  back counter to the action of the pivoting-out piston  75 . Formed in one piece with the piston collar  82  is a piston rod  83  which is articulatedly connected to the other hold-down means  45  of the swashplate  43 . 
     In order that the swashplate  43  assumes the position of maximum pivot angle as a preferential position in the unpressurized state, there interacts with the pivoting-out piston  75  a pivoting-out spring  85  formed as a helical compression spring, said spring being pushed onto the piston rod  83  and being supported at one side on a shoulder, situated close to the hold-down means  45 , of the pivoting-out piston  75  and being supported at the other side on a spring plate  86 , which surrounds the piston rod  83 , on the housing  12 . Via the pivoting-out piston  75 , the pivoting-out spring  85  exerts load on the swashplate  43  in the direction of larger pivot angles. 
     In that length of the piston rod  83  which is always situated between the piston collar  82  and the spring plate  86 , the piston rod has a thickened region with a transverse bore in which an elongate feedback element  87  is fastened. The position of the feedback element  87  on the piston rod  83  is such that the maximum retraction of the piston collar into the corresponding sleeve in order to attain the zero position of the swashplate  43  is not hindered, nor does the feedback element abut against the spring plate  86  when the swashplate is at the maximum pivot angle. In the housing main part there is situated a corresponding cutout in which the feedback element  87  can move freely. The feedback element  87  has a housing  89  which, at its distal end remote from the piston rod  83 , is formed as a dihedron  90  and is guided with the latter in a slot  91  of the regulating valve  80  (see  FIG. 4 ). 
     The function of the feedback element  87  is the same as that of the feedback element  67 .  FIG. 4  shows the longitudinal bore  92  in the pivoting-out piston  75 , via which longitudinal bore a small piston situated in the housing  89  can be subjected to pump pressure. 
     In a manner known per se, depending on the configuration of feedback element and regulating valve, only the position of the swashplate (adjustment of swashplate proportional to a setpoint signal), or the product of the position and the pump pressure (torque regulation), is input into a controller of the regulating element via the feedback element. The latter case applies here. 
     More details in this regard emerge from the circuit diagram in  FIG. 5 , which shows an illustration of the component pump  11  of the dual pump. Said figure shows, in a housing  12 , the drive unit  20  with cylinder drum  40 , drive shaft  22 , swashplate  43 , the pivoting-out piston  75  which delimits an actuating chamber  101 , the restoring spring  85  on the pivoting-out piston, and the pivoting-in piston  76  which delimits an actuating chamber  102 . A high-pressure duct  103  and a low-pressure or suction duct  104  run in the housing. The actuating chamber  101  is permanently connected via a duct  105  to the high-pressure duct  103 . The regulating valve  80  is constructed on the housing  12 . Said regulating valve is composed of a torque-regulating component valve  106  and of a pressure-regulating component valve  107  which, when in a rest position, produces a pass-through connection, via a first input and its regulating output, between a regulating output of the component valve  106  and a control line  108  which leads to the actuating chamber  102  in the pivoting-in piston  76 . A second input of the component valve  107  is connected to the high-pressure duct  103 . Likewise, an input of the component valve  106  is connected to the high-pressure duct  103 , while a second input of said component valve is open to the interior of the housing  12 , which is at tank pressure. A regulating piston of the component valve  107  is loaded in a direction for a decrease in the pivot angle of the swashplate  43  by the pressure in the high-pressure line  103 , and is loaded in the opposite direction by an adjustable spring. 
     In the housing  95  of the valve  80  there is mounted a two-armed lever  115 , one lever arm of which is acted on by the abovementioned small piston  116  which is guided in the housing  89  of the feedback element  87  and which, via the duct  105 , the actuating chamber  101  and the bore  92  in the pivoting-out piston  75 , is subjected to the pressure in the high-pressure duct  103 . The distance by which the engagement point is remote varies with the pivot angle of the swashplate  43 . The other arm of the lever is situated between one end of the regulating piston of the component valve  106  and an adjustable spring  117  which acts at least approximately oppositely on the lever arm. Furthermore, the regulating piston is loaded in the direction of the other lever arm by an adjustable spring  118 . The spring  117  and the spring  118 , which is set so as to be weaker than the spring  117 , generate a fixed torque on the lever  115  in one direction. Via the effective surface of the small piston  116 , the high pressure in the duct  103  exerts a torque on the lever  115  which opposes the fixed torque and which is dependent on the position of the pivoting-out piston  75  or generally on the pivot angle of the swashplate  43 . At a given pressure, the equilibrium with the torque generated by the two springs can be maintained only at a particular pivot angle. In the event of the equilibrium being disrupted by a change in pressure, the valve piston of the component valve  106  is moved out of its regulating position, such that pressure medium flows into the actuating chamber  102  or pressure medium can flow out of the actuating chamber  102  until a different pivot angle is attained at which equilibrium between the torques acting on the lever  115  prevails again. 
     It is possible in  FIG. 1  to see the regions of the identical housings  94  and  95  in which the two component valves  106  and  107  are accommodated. The adjusting screws  119  for the springs  117  and  118  are likewise visible in  FIG. 1 . 
     Said guidance in the slot of the regulating valve  80  and the position of the regulating valve  80  on the housing  12  have the result that, in the component pump  11 , the feedback element  87  is positioned such that the longitudinal axis  88  thereof runs substantially parallel to the pivot axis  47  of the swashplate  43 . The longitudinal axis  88  of the feedback element  87  and the longitudinal axis  77  of the pivoting-out piston  75  span a plane which runs parallel to the pivot axis  47  of the swashplate  43 . 
     Since the piston collars are guided by the sleeves and the other ends of the actuating pistons are articulatedly connected to the swashplates, it is the case that, during an adjustment of the swashplates, the various actuating pistons  55 ,  56 ,  75  and  76  perform a small pivoting movement, which is superposed on the linear movement, in a plane perpendicular to the pivot axes  37  and  47  of the swashplates. The pivoting movement also has an effect on the position of the feedback elements. 
     The feedback element  67  of the component pump  10  can be guided precisely with its dihedron  70  in a slot, which corresponds to the slot  91 , of the regulating valve  60 , because the dihedron  70  remains in the pivoting plane during a pivoting movement of the pivoting-out piston  55 , and the slot is also situated in the pivoting plane. However, the position of the distal end of the feedback element in the direction of the axis  23  is determined not only by the movement component of the pivoting-out piston in said direction but rather also to a relatively great extent by the pivot angle of the pivoting-out piston. This also has an effect on the regulation. The effect is however so slight as to be insignificant in many applications. 
     In the case of the feedback element  87  of the component pump  11 , the position of the distal end of the feedback element along the axis  23  is virtually not influenced by the pivoting of the pivoting-out piston  76 . The regulation is thus more precise. However, the guide for the feedback element  87  must now be configured such that the pivoting-out piston  75  can pivot without constraint. In the present case, this is achieved by virtue of the width of the slot  91  being greater than the thickness of the dihedron  90  to such an extent that the feedback element  87  can jointly participate in the entire upward and downward movement of the pivoting-out piston  75  without a change in direction. Since the width of the slot  91  is slightly greater than the thickness of the dihedron  90 , the longitudinal axis  88  of the feedback element  87  can deviate slightly from parallelism with respect to the pivot axis  47  of the swashplate  43 . 
     Since it is sought to use two identical regulating valves  60 , the width of the corresponding slot in the valve  60  is equal to the width of the slot  91  in the valve  80 . Likewise, the dihedron  70  is of equal thickness to the dihedron  90 . The further guidance between the slot in the valve  60  and the feedback element  67  has no effect on regulation quality. 
     It would also be possible to select a smaller width of the slot  91  and a smaller thickness of the dihedron  90 , such that the pivoting-out piston  75 , during an adjustment, also performs a small rotational movement about its axis  77 . It is finally also conceivable for the slot  91  to be slightly curved so as to correspond exactly to the movement path of the feedback element  87 , and for the guide surfaces on the feedback element to be configured correspondingly. The guidance could then be precise, and the feedback element would reliably maintain its orientation. 
     The different orientation of the two feedback elements  67  and  87  when the two pivoting-out pistons  55  and  75  are in an aligned arrangement is associated with an offset arrangement of the two valves  60  and  80 . For this purpose, the housing main part has a first mounting surface  125 , which is oriented perpendicular to the longitudinal axis  68  of the feedback element  67 , and a second mounting surface  126 , which is oriented perpendicular to the longitudinal axis  88  of the feedback element  87 . The spacing of the plane in which the mounting surface  126  is situated from the axis  23  is slightly larger than the spacing of the plane in which the mounting surface  125  is situated from the axis  23 . Correspondingly, the feedback element  87  is slightly longer than the feedback element  67 . This permits the offset mounting despite different spatial requirements in the different directions within the housing  12 . 
     It can now be seen from  FIG. 1  that the axes of the two component valves  106  of the two regulating valves  60  and  80  are angularly offset with respect to one another to a considerable extent about the axis  23 . Also, the two adjusting screws  119  which are situated at the ends, which face toward one another, of the component valves  106  are thus readily accessible. The adjustment of the corresponding springs (see  FIG. 5 ) poses no difficulties. Here, “valve axis” is to be understood physically to mean a valve bore with a valve piston situated therein, and is to be understood geometrically to mean the central axis of said parts.