Patent Abstract:
The invention relates to an axial piston machine having a first group of pistons ( 34.1 ) for delivering into a first hydraulic circuit and a second group of pistons ( 34.2 ) for delivering into a second hydraulic circuit. The pistons ( 34.1 ) of the first group and the pistons ( 34.2 ) of the second group are supported on a common slanted swash plate ( 37 ′) and the slanted swash plate ( 37 ′) can be slanted to a first swivel axis ( 55 ) in order to regulate a first delivery volume of the first group of pistons ( 34.1 ) in the first hydraulic circuit ( 55 ) and to a second swivel axis ( 56 ) in order to regulate a second delivery volume of the second group of pistons ( 34.2 ) in the second hydraulic circuit.

Full Description:
BACKGROUND OF THE INVENTION 
   The invention relates to an axial piston machine having a first group of pistons for delivery into a first hydraulic circuit and having a second group of pistons for delivery into a second hydraulic circuit. 
   From DE 30 26 765 A1 it is known, in an axial piston machine, to provide a first group of pistons and a second group of pistons, which deliver in each case into a separate hydraulic circuit. In order to be able to adjust a different delivery rate each for the first hydraulic circuit and for the second hydraulic circuit, the pistons of the first group and the pistons of the second group are supported in each case on a separate swash plate. The angles of inclination of the two swash plates are adjustable in each case by means of a separate control device. 
   The pistons of the first group and the pistons of the second group are disposed along, in each case, a separate graduated circle, wherein the pistons that are associated with the graduated circle having the smaller diameter are supported on a first swash plate, which is of a hemispherical design at the side remote from the pistons and is mounted in the second swash plate. The first and the second swash plate, for independent adjustment of the delivery rates of the first hydraulic circuit and the second hydraulic circuit, are pivotable separately about a common axis, wherein for displacing the first swash plate in the second swash plate a recess is provided, through which the control device accesses the first swash plate. The first swash plate, for varying the dead centre position, may moreover be inclined slightly about a second axis that is perpendicular to the actual swiveling axis. 
   A drawback of this arrangement is that the second swash plate, whilst it may be mounted in a known manner with a spherical external contour, at the same time has to be designed as a bearing for the first swash plate. A further drawback is that, for adjusting the swivel angle of the inner swash plate, a recess is provided in the second swash plate. As the swash plates have to absorb considerable compressive forces, the required recess may be neither fashioned nor positioned in any desired manner. This leads however to a restriction with regard to the displaceability of the first swash plate, with the result that the volumetric displacement of the corresponding hydraulic circuit is also variable only to a limited extent. 
   Furthermore, by mounting the two swash plates one inside the other, the overall axial length of the axial piston machine is increased. Some of the advantage of using a single axial piston machine to deliver into two hydraulic circuits is therefore sacrificed. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to provide an axial piston machine that is provided for delivery into two hydraulic circuits, the delivery rate of which is individually adjustable, wherein the displaceability is simplified. 
   The axial piston machine according to the invention comprises a first group of pistons for delivering a pressure medium in a first hydraulic circuit. For adjusting the volumetric displacement for the first hydraulic circuit, the swash plate, on which the pistons of the first group are supported, is pivotable about a first swiveling axis. On the same swash plate, moreover, the pistons of the second group for delivering a pressure medium into a second hydraulic circuit are also supported. In order to adjust the volumetric displacement for the second hydraulic circuit, the swash plate is pivotable about a second swiveling axis, by means of which an effective swept volume of the pistons of the second group is adjusted. 
   By virtue of the use of two swiveling axes of the swash plate, the swept volume that is effective in each case for the first hydraulic circuit and for the second hydraulic circuit may be individually adjusted. The possible adjustable swivel angles are in said case not limited by the angle adjusted in each case relative to the other swiveling axis. In particular, by virtue of the individual adjustment of the volumetric displacement by means of a single swash plate acting upon the pistons of both groups, it is also possible to dispose the pistons of both groups on a common graduated circle and still enable an individual volumetric displacement adjustment. 
   Advantageous developments of the axial piston machine according to the invention are represented in the sub-claims. 
   In particular, it is advantageous for the two swiveling axes to be disposed in such a way that they intersect jointly with the centre line of the axial piston machine at one point. This widens the operative range of the piston machine as a reversal of the delivery direction is easily possible owing to the symmetry. It is moreover particularly advantageous for the two swiveling axes not only to intersect jointly with the centre line of the axial piston machine at one point, but for the swiveling axes also to lie at right angles to one another and to the centre line of the piston machine. This virtue of this angle between the two swiveling axes being as large as possible, a particularly large individual adjustment range is achieved for the two hydraulic circuits. 
   The pistons of the first and of the second group are disposed in a longitudinally displaceable manner in corresponding first and second cylinder bores respectively. The first and second cylinder bores are connectable in each case by a pair of kidney-shaped control ports to the first and second hydraulic circuit respectively. In each case, a pair of kidney-shaped control ports is then arranged symmetrically relative to the vertical projection of the corresponding swiveling axis into the plane of the kidney-shaped control ports. 
   A particularly simple bearing arrangement that enables an inclination of the swash plate in any desired direction is moreover achieved by a hemispherical geometry of the swash plate at the side remote from the bearing surface. 
   It is further advantageous for the pistons of the first and second group that are provided for delivery into the first and second hydraulic circuit respectively to be disposed on a common graduated circle. This leads in particular, given use of the same diameter of the cylinder bores and pistons, to an identical volumetric displacement into the two hydraulic circuits. A further result of disposing all of the pistons on one graduated circle only is an improved synchronism of the axial piston machine, with correspondingly less vibration and reduced noise generation. 
   For purposefully adjusting different delivery rates in the first and in the second hydraulic circuit, it may also be advantageous for the pistons, whilst being supported on a common swash plate, to be disposed on different graduated circles. In this way it is possible, e.g. for a second delivery circuit, purposefully to limit the maximum delivery rate in a specific ratio to the other hydraulic circuit. The maximum delivery rate is in said case achieved not through the use of only one limited swivel angle range. The result is a correspondingly fine graduating facility for adjustment of the volumetric displacement since the full range of adjustment for the angle of inclination of the swash plate is maintained. 
   The use of a single swash plate moreover offers the possibility of either using two adjusting devices, which act separately from one another upon the single swash plate, to adjust the inclination of the swash plate in each case relative to a swiveling axis or providing a common adjusting device, which adjusts the swash plate accordingly to its resultant inclination. The use of the common swash plate for both hydraulic circuits moreover provides some freedom with regard to the constructional development of its activation. 

   
     An embodiment of an axial piston machine according to the invention is illustrated in a simplified manner in the drawings and described in detail below. The drawings show: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  a sectional view of an axial piston machine for delivery into two hydraulic circuits; 
       FIG. 2  an enlarged view of the drive mechanism of the axial piston machine according to  FIG. 1 ; 
       FIG. 3  a diagrammatic view with a swash plate inclined about a swiveling axis; 
       FIG. 4  a diagrammatic view with a swash plate inclined about another swiveling axis; and 
       FIG. 5  a plan view of a control plate of the axial piston machine according to the invention. 
   

   In the longitudinal section of a hydrostatic piston machine  1  according to the invention illustrated in  FIG. 1  it is revealed how a common drive shaft  2  is supported by means of a roller bearing  3  at one end of a pump housing  4 . The common drive shaft  2  is additionally supported in a plain bearing  6 , which is disposed in a connection plate  5  that closes the pump housing  4  at the opposite end. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Formed in the connection plate  5  and penetrating the connection plate  5  completely in axial direction is a recess  7 , in which on the one hand the plain bearing  6  is disposed and which on the other hand is penetrated by the common drive shaft  2 . At the side of the connection plate  5  remote from the pump housing  4 , the auxiliary pump  8  is inserted into a radial widening of the recess  7 . For driving the auxiliary pump  8 , the common drive shaft  2  has gearing  9 , which is in mesh with corresponding gearing of an auxiliary pump shaft  10 . The auxiliary pump shaft  10  is supported in the recess  7  by means of a first auxiliary pump plain bearing  11  and in an auxiliary pump connection plate  13  by means of a second auxiliary pump plain bearing  12 . 
   Disposed on the auxiliary pump shaft  10  is a gear wheel  14 , which is in mesh with an internal gear wheel  15 . Via the gear wheel  14  the internal gear wheel  15 , which is disposed rotatably in the auxiliary pump connection plate  13 , is likewise driven by the auxiliary pump shaft  10  and hence ultimately by the common drive shaft  2 . In the auxiliary pump connection plate  13  the suction-side connection and the discharge-end connection for the auxiliary pump  8  are formed. The auxiliary pump  8  is fixed in the radial widening of the recess  7  of the connection plate  5  by means of a cover  16 , which is mounted on the connection plate  5 . 
   The inner race of the roller bearing  3  is fixed in axial direction on the common drive shaft  2 . The inner race lies at one side against a collar  17  of the common drive shaft  2  and is held in this axial position at the other side by means of a locking ring  18 , which is inserted in a groove of the common drive shaft  2 . The axial position of the roller bearing  3  in relation to the pump housing  4  is determined by means of a locking ring  19 , which is inserted in a circumferential groove of the shaft opening  20 . At the other side, the roller bearing  3  lies against a housing shoulder (not shown) of the pump housing  4 . Disposed in the shaft opening  20  in the direction of the outside of the pump housing  4  there is moreover a sealing ring  21  and finally a further locking ring  22 , wherein the locking ring  22  is inserted into a circumferential groove of the shaft opening  20 . 
   Formed on the end of the common drive shaft  2  that projects from the pump housing  4  is drive gearing  23 , via which the hydrostatic piston machine is driven by means of a prime mover (not shown). 
   Disposed in the interior of the pump housing  4  is a cylinder drum  24 , which has a central through-opening  25  that is penetrated by the common drive shaft  2 . By means of a driving spline  26  the cylinder drum  24  is connected to the common drive shaft  2  so as to be locked against rotation but displaceable in axial direction, with the result that a rotational movement of the common drive shaft  2  is transmitted to the cylinder drum  24 . 
   Inserted into a circumferential groove formed in the central through-opening  25  is a further locking ring  27 , against which a first support disc  28  lies. The first support disc  28  forms a first spring bearing for a compression spring  29 . A second spring bearing for the compression spring  29  is formed by a second support disc  30 , which is supported against the end face of the driving spline  26 . The compression spring  29  therefore exerts, on the one hand, on the common drive shaft  2  and, on the other hand, on the cylinder drum  24  a force in an, in each case opposite, axial direction. The common drive shaft  2  is loaded in such a way that the outer race of the roller bearing is supported against the locking ring  19 . 
   The compression spring  29  acts in the opposite direction upon the cylinder drum  24 , which is held with a spherical indentation  31 , which is formed on the end face of the cylinder drum  24 , in abutment with a control plate  32 . The control plate  32  in turn rests with the side remote from the cylinder drum  24  sealingly against the connection plate  5 . By means of the spherical indentation  31 , which corresponds with a matching spherical outward projection of the control plate  32 , the cylinder drum  24  is centered. The control plate  32  may alternatively take the form of a flat disc if, for example, a differently realized centering together with a spherical control plate  32  would lead to an overdetermination. 
   The position of the control plate  32  in radial direction is fixed by the outer circumference of the plain bearing  6 . The plain bearing  6 , for this purpose, is inserted only partially into the recess in the connection plate  5 . 
   Cylinder bores  33  are introduced into the cylinder drum  24  so as to be distributed over a common graduated circle and have disposed therein pistons  34 , which are longitudinally displaceable in the cylinder bores  33 . At the end remote from the spherical indentation  31 , the pistons  34  project partially from the cylinder drum  24 . At this end, there is fastened to each piston  34  a sliding shoe  35 , via which the pistons  34  are supported against a bearing surface  36  of a swash plate  37 . 
   In order to generate a lifting movement of the pistons  34 , the angle that the bearing surface  36  of the swash plate  37  forms with a centre line  40  is variable. For this purpose, the inclination of the swash plate  37  may be adjusted by means of an adjusting device  38 . For taking up the forces that are transmitted by the sliding shoes  35  to the swash plate  37 , the swash plate  37  is supported in the pump housing  4 . 
   For connecting the hydrostatic piston machine  1  to a first hydraulic circuit and to a second hydraulic circuit, a first connection  39  and a second connection  39 ′ are illustrated diagrammatically in the connection plate  5  and connectable in a non-illustrated manner by the control plate  32  to the cylinder bores  33 . 
   An enlarged view of the components that interact in the interior of the pump housing  4  is shown in  FIG. 2 . 
   For executing a swiveling movement, the swash plate  37  is coupled to a slide block  44 , which in a non-illustrated manner rotates the swash plate  37  about an axis lying in the drawing plane. 
   The cylinder bores generally denoted by  33  in  FIG. 1  are divided into a first group of cylinder bores  33 . 1  and a second group of cylinder bores  33 . 2 . As has already been briefly explained in the description pertaining to  FIG. 1 , against the end of each piston  34  remote from the control plate  32  a sliding shoe  35  is disposed. The sliding shoe  35  is fastened by a recess to a spherical head of the piston  34 , so that the sliding shoe  35  is fastened movably to the piston  34  and tensile and compressive forces are transmissible. 
   Formed on the sliding shoe  35  is a sliding surface  45 , by which the sliding shoe  35  and hence the piston  34  are supported on the bearing surface  36  of the swash plate  37 . Formed in the sliding surface  45  are lubricating oil grooves, which are connected by a lubricating oil channel  46 , which is formed in the sliding shoe  35  and continued in the piston  34  as lubricating oil bore  46 ′, to the cylinder bores  33  formed in the cylinder drum  24 . 
   Because the sliding shoes  35  are supported against the bearing surface  36 , the pistons  34  upon rotation of the common drive shaft  2  execute a lifting movement, by means of which the pressure medium situated in the cylinder chambers in the cylinder drum  24  is placed under pressure. The sliding shoes  35  are hydrostatically relieved at the bearing surface  36  of the swash plate  37 . In order to deliver the pressure medium from the cylinder chambers into the first and second hydraulic circuit, first connecting channels  47 . 1  and second connecting channels  47 . 2  are connected to the cylinder bores of the first group  33 . 1  and the cylinder bores of the second group  33 . 2  respectively. The first and second connecting channels  47 . 1  and  47 . 2  extend from the cylinder bores of the first group  33 . 1  and the cylinder bores of the second group  33 . 3  respectively to the spherical indentation  31  formed in an end face  48  of the cylinder drum  24 . 
   In the control plate  32 , which is connected to the connection plate  5  so as to be locked against rotation, a first kidney-shaped control port  50  and a second kidney-shaped control port  51  are formed, which penetrate the control plate  32  in axial direction. 
   Preferably a third kidney-shaped control port and a fourth kidney-shaped control port are further formed in the control plate  32 , these ports not being visible in  FIG. 2  because of the position of the cutting plane. While the first and the second kidney-shaped control port  50  and  51  are connected by the connection plate  5  to the working lines of the first hydraulic circuit, the third and the fourth kidney-shaped control port are connected in a corresponding manner to the working lines of the second hydraulic circuit. The geometric design of the kidney-shaped control ports in the control plate  32  is additionally described below with reference to  FIG. 5 . 
   The first and second kidney-shaped control ports  50  and  51  are at an identical first distance R 1  from the centre line  40  of the cylinder drum  24  that is greater than the distance R 2 , which in turn is identical for the third and fourth kidney-shaped control ports. During a revolution of the common drive shaft  2  the first connecting channels  47 . 1  are connected alternately to the first kidney-shaped control port  50  and the second kidney-shaped control port  51 , so that because of the lifting movement of the pistons  34  disposed in the cylinder bores  33 . 1  of the first group the pressure medium is taken in e.g. through the second kidney-shaped control port  51  and pumped through the first kidney-shaped control port  50  into the discharge-end working line of the first hydraulic circuit. 
   In the illustrated embodiment, the first connecting channels  47 . 1  are disposed in such a way in the cylinder drum  24  that the first distance R 1  of the mouth at the end face  48  is greater than the second distance R 2 , at which the second connecting channels  47 . 2  open out at the end face  48 . The second connecting channels  47 . 2  have a radial direction component and accordingly open out at the end face  48  of the cylinder drum  24  at the second distance R 2 , which corresponds with the distance of the third and fourth kidney-shaped control port from the centre line  40 . Thus, during a revolution of the common drive shaft  2  the cylinder bores of the second group  33 . 2  are connected by the second connecting channels  47 . 2  alternately to the third and fourth kidney-shaped control port. 
   In order during an intake stroke to prevent the sliding shoes  35  from lifting off the bearing surface  36  of the swash plate  37 , a retraction plate  52  is provided, which encompasses the sliding shoes  35  at a shoulder provided for this purpose. The retraction plate  52  has e.g. a spherical, central recess  53 , with which it is supported against a retraction ball  54  that is disposed on the end of the cylinder drum  24  remote from the end face  48 . 
   In  FIG. 3  it is revealed how, proceeding from an axial piston machine of  FIGS. 1 and 2 , with a swash plate  37 ′ an independent adjustment of the delivery rates for the two hydraulic circuits may be achieved. 
   The swash plate  37 ′ is inclinable about a first swiveling axis  55  and about a second swiveling axis  56 . The first and the second swiveling axis  55  and  56  lie in the plane of the bearing surface  36  of the swash plate  37  and, when the axial piston machine is set to zero volumetric displacement in both hydraulic circuits, form an angle of 90° with the centre line  40 . 
   In  FIG. 3  the swash plate  37 ′ is shown inclined about the second swiveling axis  56 . This produces an effective stroke for delivering pressure medium into the second hydraulic circuit. What is meant by an effective stroke, here, is a movement of the pistons  34  that leads to an actual delivery of pressure medium. In order therefore to enable the adjustment of two delivery rates for the first hydraulic circuit and the second hydraulic circuit independently of one another, the third kidney-shaped control port  57  and the fourth kidney-shaped control port  58  are disposed in each case symmetrically relative to a vertical projection  56 ′ of the second swiveling axis  56  into the plane of the kidney-shaped control ports. 
   Thus, the second connecting channels  47 . 2  move during a half revolution of the cylinder drum  24  from the bottom dead centre to the top dead centre substantially along the third kidney-shaped control port  57 , so that the pressure medium is pressed through the third kidney-shaped control port  57  into the discharge-end working line of the second hydraulic circuit. During the second half of a revolution of the cylinder drum  24 , the second connecting channels  47 . 2  accordingly move en route from the top dead centre to the bottom dead centre substantially along the fourth kidney-shaped control port  58  and execute an intake stroke. 
   As may already be seen in  FIG. 3 , the first kidney-shaped control port  50  and the second kidney-shaped control port  51  are in turn formed symmetrically relative to a vertical projection  55 ′ of the first swiveling axis  55  into the plane of the kidney-shaped control ports. In the illustrated, preferred form of construction, the first swiveling axis  55  and the second swiveling axis  56  are disposed at right angles to one another. The first and second kidney-shaped control ports  50  and  51  as well as the third and fourth kidney-shaped control ports  57  and  58  in the control plate  32  are accordingly disposed likewise rotated through 90° relative to one another. 
   A delivery into the first hydraulic circuit does not occur, given the illustrated deflection of the swash plate  37 ′. The position of the first and second kidney-shaped control port  50  and  51  is symmetrical relative to the position of the top and bottom dead centre respectively, so that despite the use of the common swash plate  37 ′ in the first hydraulic circuit only a slight pulsation is produced, so long as the swash plate  37 ′ is not additionally inclined about the first swiveling axis  55 . The arrangement of the first to fourth kidney-shaped control ports  50 ,  51 ,  57  and  58  in the control plate  32  is explained once more in the description pertaining to  FIG. 5 . 
   In the illustrated preferred form of construction, the first swiveling axis  55  and the second swiveling axis  56  are disposed at right angles to one another, wherein both swiveling axes  55  and  56  lie in the plane of the bearing surface  36 . The point of intersection of the first swiveling axis  55  with the second swiveling axis  56  coincides with the point of intersection of both swiveling axes  55  and  56  with the centre line  40 . 
   At its side remote from the bearing surface  36 , the swash plate  37 ′ at least in a region  59  adjoining the bearing surface  36  is of a hemispherical design. As a bearing, a ball bearing or a plain bearing may be provided for supporting the swash plate and enabling rotation thereof. 
   In order to keep the axial overall length of the axial piston machine as low as possible, the hemispherical region  59  is delimited by a flattened area  63  formed preferably parallel to the bearing surface  36 . 
   The adjustment of the inclination of the swash plate  37 ′ may be effected either by means of a separate adjusting device for each swiveling axis  55  and  56 , wherein in  FIG. 1  only the adjusting device for the swiveling axis  55  is shown and the adjusting device for the swiveling axis  56  is not visible in the sectional view, or by means of a common adjusting device, by means of which a resultant angle of inclination of the swash plate  37 ′ is adjusted. 
     FIG. 4  shows the swash plate  37 ′ situated in its neutral position with regard to the second swiveling axis  56 , but inclined with regard to its first swiveling axis  55 . Thus, an effective stroke is produced only for the pistons  34  that are connected by the first connecting channels  47 . 1  during a revolution of the cylinder drum  24  alternately to the first kidney-shaped control port  50  and the second kidney-shaped control port  51 . 
   The pistons that are connectable by the second connecting channels  47 . 2  to the third kidney-shaped control port  57  and the fourth kidney-shaped control port  58 , on the other hand, in the region, where a connection to the respective hydraulic circuit is established, execute merely a slight movement about the bottom dead centre and the top dead centre respectively that in turn produces only a slight pulsation in the working lines of the second hydraulic circuit. 
     FIG. 5  shows the control plate  32  in plan view. In the preferred embodiment, the first swiveling axis  55  and the second swiveling axis  56  are perpendicular to one another. The vertical projections  55 ′ and  56 ′ illustrated in  FIG. 5  in said case form in each case an axis of symmetry for the first and the second kidney-shaped control port  50  and  51  and for the third and the fourth kidney-shaped control port  57  and  58 . 
   The control plate  32  has in the centre a centering opening  62 , by which the position of the control plate in the axial piston machine  1  is defined. The centering opening  62  for this purpose centers the control plate on the plain bearing  6 . Along the projection  55 ′ of the first swiveling axis  55  there extends in radial direction from the centering opening  61  in each case a groove  63 . 1  and  63 . 2 . In each case, a further groove  64 . 1  and  64 . 2  extends in an analogous manner along the projection  56 ′ of the further swiveling axis  56 . The four grooves  63 . 1 ,  63 . 2 ,  64 . 1  and  64 . 2  are connected to one another by an annular groove  60 . 
   The annular groove  60  itself is disposed concentrically with the centering opening  62  and the kidney-shaped control ports. The kidney-shaped control ports  50  and  51  extend in said case along a circular line having a radius that is greater than the radius of the circular line, along which the third and fourth kidney-shaped control port  57  and  58  extend. In the annular groove  60  extending therebetween, four bores  61 . 1  to  61 . 4  are arranged in a uniformly distributed manner. The bores  61 . 1  to  61 . 4  connect the annular groove  60  to the side of the control plate  32  facing the cylinder drum  24 . Thus, leakage pressure medium may be carried off into the interior of the axial piston machine  1 . 
   The generation of an effective stroke for delivering pressure medium into a first and into a second hydraulic circuit through swiveling of the swash plate  37 ′ is not restricted to axial piston machines, in which the pistons  34 . 1  of the first group and the pistons  34 . 2  of the second group are disposed on a single, common graduated circle. The two groups of pistons and cylinder bores may equally well be disposed in one cylinder drum, but on two different graduated circles. 
   Besides the axial piston machine for two separate, closed circuits that is illustrated in the drawings, an axial piston machine for two open circuits or for one closed and one open circuit may also be provided with the adjustment of the volumetric displacement according to the invention. Also, more than two circuits are easily conceivable.

Technology Classification (CPC): 5