Patent Publication Number: US-6662707-B1

Title: Axial piston engine

Description:
The invention relates to an axial piston machine according to the precharacterising clause of claim  1  or  2 . 
     An axial piston machine of this type is described in DE-A 21 01 213. In this previously known axial piston machine, the restraint device for supporting the retracting device is formed by holding plungers which are mounted to be radially displaceable in radial guide holes in the housing and are prestressed radially inwards by springs, the plungers having at their inner ends oblique faces which are inclined towards the adjacent retracting device relative to the associated radial plane and engaging, with these oblique faces, behind the outer border of a perforated disc forming the retracting device. This known restraint device has the following disadvantages owing to the oblique faces. If the inclination of the oblique faces is too great, there is the risk of the perforated disc pressing the holding plungers outwards owing to the axial tensile force of the pistons, with the result that the holding plungers lose their stability and are able to exert only a reduced restraining force on the perforated disc, or none at all. In such a case, there is the risk of the perforated disc being overstressed by the axial tensile force of the pistons and, for example, warped. It should be borne in mind here that the holding plungers are particularly inclined to yield outwards owing to vibrations which are present when the axial piston machine is in operation and to the radial force components which act on the oblique faces. If, in contrast, the inclination of the oblique faces is too small, there is the risk of the holding plungers jamming on the perforated disc, with the result that the rotary operation would be impaired and, because of wear, an inadequate service life would have to be expected. 
     Another major disadvantage of the known axial piston machine is that, owing to the fact that they project into the housing interior space, the holding plungers interfere with the mounting or demounting of the components arranged in the housing interior space. 
     The object on which the invention is based is to construct a restraint device of the type specified at the outset such that reliable functioning and a long service life can be obtained. 
     This object is achieved by the features of claims  1  or  2 . 
     In the inventive configuration according to claim  1 , the restraint device cooperates with a nonrotating component, namely the swash plate, the retracting device cooperating with a supporting device engaging behind it and connected to the swash plate. This gives rise to another support for the retracting device, namely on the swash plate, on which mutual support can be achieved in a simple and stable manner with relatively large supporting areas, with the result that low wear coupled with reliable support is ensured even with a rotating retracting device. 
     In the configuration according to claim  2 , the restraint device is not mounted on the housing, but on the swash plate. This likewise enables the above-described advantages to be achieved, and in addition simple production is possible since the constructional features for the arrangement and mounting of the restraint device on the swash plate can be formed on the latter in a simple and cost-effective manner. This is due not only to the fact that the swash plate is a relatively small component, but is also a component with a high degree of processing, on which the additional features for the arrangement of the restraint device can be realised efficiently in one procedure. claims  3  to  25  contain advantageous developments of the invention. 
     According to a development of the invention, when the axial piston machine is in operation, the restraint device is displaced in a self-acting manner or automatically from a release position releasing the retracting device into a working position engaging behind the retracting device and, once the operation has been stopped, is automatically displaced into its release position again, the displacement into the working position being effected by the pressure of an adjoining or adjacent pressure space which is present or a pressure line and the displacement into the release position being effected by the force of a spring. By pressurising the restraint device with an internal pressure which is present when the axial piston machine is in operation or an external pressure, for example from an adjacent axial piston machine, it is possible in a simple manner to produce a pushing-in force which is greater than the retracting or pushing-against force required, so that in operation the position of the restraint device in its working position is reliably ensured. Owing to the automatic movement of the restraint device into its release position, it is not necessary, during mounting or demounting, for any special attention to be paid or any adjusting work performed to move the restraint device into its release position. This ensures simple and rapid mounting or demounting, while ensuring a stabilised retracting device and reliable operation. 
     In the case of an axial piston machine of the present type, suction forces act on the pistons in pump operation or when the axial piston machine in motor operation performs a braking function, which forces try to lift the slide shoes and thus the retracting device off from the swash plate. In the configuration according to the invention, such axial loads are not damaging even if they overload the retracting device, since the latter finds additional support and stabilisation on the restraint device and is able to take up the loads without damage. 
     The retracting device is to be arranged in the region of the lateral half of the axial piston machine in which the pistons perform a suction stroke, this region extending approximately over 180°. A restraint device arranged preferably centrically in the region of this lateral half, or a plurality of restraint devices arranged on this lateral half, are, in the case of an axial piston machine adapted for pump operation, also able to function in cases where the axial piston machine performs a motor operation owing to a braking function. In the case of axial piston machines movable in both directions of rotation, one or more restraint devices are to be arranged in each case in the region of the two lateral halves. 
     A particularly stable support for the retracting device arises when the area on the restraint device provided for the support is a radial area relative to the axis of rotation of the axial piston machine. 
     An advantageous embodiment for a restraint device is a stop peg of preferably circular cross-section which is mounted to be displaceable in a radial guide hole in the housing between the working position and the release position. It is advantageous to provide the pin in its outer end region with a flange on which a spring, in particular a helical spring, arranged between the flange and an inner hole shoulder is able to engage and pressurise the stop peg into its release position. For the pneumatic or hydraulic displacement of the pin into its working position, the hole space located radially outside relative to the stop peg can be connected by a channel to the housing interior space or to a space exhibiting a pressure when the axial piston machine is in operation. When the hole space is connected to the housing interior space, the channel can run in the housing wall or longitudinally in the stop peg. In order to provide twice the operational reliability or in order to be able to selectively connect the hole space either to the housing interior space or to the pressure space, it is advantageous to provide two corresponding channels, in each of which is arranged a nonreturn valve which automatically closes under the effect of the pressure which becomes established in each case in the pressure space or of a closing spring. 
     It is furthermore advantageous to arrange, on the relevant lateral half, or on both lateral halves, of the axial piston machine, in each case only one stop peg parallel to the pivot axis of the swash plate. Such a housing design may be selectively used for immovable or movable swash plates. In this case, it is also advantageous to round the stop peg convexly at its side facing towards the retracting device so as to prevent constraints arising in the case of a pivotable swash plate. 
     It is also advantageous to arrange the stop peg such that between it and the retracting device there is a small spacing which is merely dimensioned to be of such a size that, in the event of an overload and deformation of the retracting device within its elastic range, the retracting device abuts against the stop peg before it is deformed beyond its yield point. 
     In addition, it is advantageous if the supporting device is actuated by the restraint device such that the supporting device engages behind the retracting device only when the restraint device is situated in its working position, and otherwise releases it. On actuation of the restraint device, therefore, not only is the swash plate anchored in the housing, but additionally it is ensured that the retracting device is secured to the swash plate. In the demounting position, in which the restraint device is not actuated, not only is the swash plate then released relative to the housing, but additionally the securing of the retracting device with respect to the swash plate is released. The demounting can thus be effected without problems. In this configuration, the supporting device may, for example, have a rotary shaft which is interlocked with the restraint device and is rotated on actuation of the restraint device. It is possible to arrange on the rotary shaft an eccentric projection which engages behind or releases the retracting device depending on the rotary position of the rotary shaft. 
    
    
     The invention and further advantages obtainable by means of the invention will be explained in more detail below with reference to a number of advantageous exemplary embodiments and simplified drawings, in which: 
     FIG. 1 shows an axial piston machine according to the invention, in partial axial section; 
     FIG. 2 shows a modified configuration of an axial piston machine according to the invention, in partial axial section; 
     FIG. 3 shows the section III—III in FIG. 2; 
     FIG. 4 shows the partial section IV—IV in FIG. 3; 
     FIG. 5 shows a hydraulic circuit diagram for a detail of the axial piston machine according to the invention; 
     FIG. 6 shows a further modified configuration of an axial piston machine according to the invention, in partial axial section; 
     FIG. 7 shows the section VII—VII in FIG. 6; 
     FIG. 8 shows the partial section VIII—VIII in FIG. 7; 
     FIG. 9 shows the detail IX in FIG. 8, in an enlarged representation; and 
     FIG. 10 shows the detail X in FIG. 7, in an enlarged representation. 
    
    
     The main parts of the axial piston machine, denoted generally by  1 , are a housing  2  with a housing wall  2   a , which can be seen in section in the drawing, and which encloses a housing interior space  3  in which a cylinder drum  5  with a plurality of cylinder bores  6 , preferably distributed over a part of a circle and longitudinally directed, is arranged on a shaft  4 , with a plurality of pistons  7  which are mounted to be axially displaceable in the cylinder bores  6 , with a plurality of slide shoes  8  which are connected, to be pivotable but axially fixed, to spherical piston heads  9  at one end of the pistons  7 , with a swash plate  11  against whose oblique face  12  the slide shoes  8  bear and are axially supported, the swash plate  11  being mounted to be pivotable in a pivot bearing (not shown) about a pivot axis  14  running at right angles to the longitudinal centre axis of the axial piston machine  1  or the axis of rotation  13  of the shaft  4 , and being lockable in the respective pivoting position, with a retracting device  15 , the purpose of which is to ensure the contact of the slide shoes  8  with the oblique face  12 , a restraint device  16  which is intended to stabilise the retracting device  15 , and with a control plate  17  which bears against the cylinder drum  5  at the side facing away from the swash plate  11  and, by means of control slots  18  arranged in the control plate  17  and cylinder bore holes  19  in the cylinder drum  5  which cooperate therewith, controls the delivery of the medium, in the present case hydraulic medium, of the axial piston machine  1 . A spring  21  prestressing the cylinder drum  5  against the control plate  17  ensures a leaktight contact between the cylinder drum  5  and the control plate  17 . 
     The retracting device  15  is formed by a perforated disc  22  with holes  23  present for the slide shoes  8 , the hole borders of which surround the slide shoes in the region of tapered slide-shoe heads with play and, with their side facing towards the swash plate  11 , bear against a base flange  24  of the associated slide shoe  8 , so that the base flange  24  is held with little play between the oblique face  12  and the perforated disc  22 . The perforated disc  22  itself bears, at its side facing away from the swash plate  11 , against a locating face of the shaft  4  or of an add-on piece or of the cylinder drum  5 , with the result that it is supported in the axial direction facing away from the swash plate  11 . The locating face  25  may also be formed on a supporting ring  26  fixed on the shaft  4 . In the case of a pivotably mounted swash plate  11 , the locating face  25  is a face in the shape of a spherical-ring section, on which the perforated disc  22  is supported by an inner supporting ring  27  which bears, with a tangential or concave bearing face in the shape of a spherical-ring section, against the locating face  25 . 
     The restraint device  16  is formed by a cylindrical or stepped-cylindrical stop pin or stop peg  31  which is mounted to be radially displaceable with little play in a radial guide hole or a guide bore  32  in the housing wall  2   a , the radial centre axis  33  of which runs at right angles to the axis of rotation  13  and parallel to the pivot axis  14  and is offset relative to the latter on the side opposite the control plate  17 . The stop peg  31  is movable between a radially pushed-in working position (shown in the drawing), in which its radially inner pin end  34  overlaps a locating face  11   a , facing towards the control plate  17 , on the swash plate  11  and thus is able to axially support the swash plate  11 , and a radially pushed-out release position, in which the pin end  34  is pushed out of the housing interior space  3  or releases the swash plate  22  for axial mounting or demounting. In the present exemplary embodiment, the radial locating face  11   a  is formed by a recess  11   b ,here a blind bore, in the swash plate  11 . In the present exemplary embodiment, the recess  11   b  is situated in the central region of the swash plate  11 , and the depth t of the recess  11   b  can be a few millimetres, e.g. 3 to 5 mm. To allow for play b, the cross-sectional size of the recess  11   b  is dimensioned larger than the cross-sectional size of the stop peg  31 , so that the latter engages with play b in the recess  11   b , as illustrated in FIG.  1 . Preferably, the centre axis  33  of the stop peg  31  is arranged coaxially with the pivot axis  14 , in which case the recess  11   b  can be of circular design. If the centre axis  33  is offset axially and possibly also radially relative to the pivot axis  14 , a shape of the locating face  11   a  curved in the shape of a circular arc about the pivot axis  14  is required, in which case the recess  11   b  can be formed by an elongated hole curved in the shape of a circular arc. In the pushed-in working position, the stop peg  31  can bear, with its end face, against the bottom of the recess  11   b  and thereby radially support the swash plate  11  or be at a small distance therefrom so as to allow play. In the exemplary embodiment according to FIG. 1, in which the restraint device  16  directly supports the swash plate  11  and directly engages on the swash plate  11 , it is necessary to fix the perforated disc  22  to the swash plate  11  in order to allow the restraining action of the restraint device  16  to take effect on the slide shoes  8  as well. In the present configuration, therefore, to fix the slide shoes  8  to the swash plate  11  provision is made for an additional restraint device, namely a supporting device  16   a , which, while allowing for play a, prevents the perforated disc  22  in a form-fitting manner from lifting off from the sliding face  12 . In the present exemplary embodiment, the supporting device  16   a  is formed by two supporting parts  16   b , arranged diametrically opposite each other in a mirror-image fashion and connected to the swash plate  11 , which, in the present exemplary embodiment, are formed with an axial supporting-part leg  16   c , arranged radially beside the retracting device  15  or beside the perforated disc  22 , and a supporting-part leg  16   d , projecting radially inwards from the supporting-part leg  16   c , these being integrally joined to each other. The supporting parts  16   b  may also be integrally joined to the swash plate  11  and project from it, for example axially. In the present configuration, the supporting parts  16   b  are separate parts which bear, with a plane bottom face  16   e , against the plane sliding face  12  of the swash plate  11  and are screwed up to the swash plate  11  by headed screws  16   f  which each pass through the supporting-part leg  16   c  in a through-hole and engage in a threaded hole in the swash plate  11 . The radial spacings between the supporting-part leg  16   c  and the perforated disc  22  on the one hand and the housing wall  2   a  on the other hand are each dimensioned to be of such a size that, even in oblique positions of the swash plate  11 , a radial spacing is always present. A small axial spacing a is present between the supporting-part leg  16   d  and the retracting device  15 , here the perforated disc  22 . The bearing face of the supporting-part leg is a plane face, with the result that a low surface pressure and low wear, as well as a long service life are ensured. 
     As can be seen from FIG. 3, the supporting parts  16   b  —as viewed along the axis of rotation  13 —are curved to correspond to the peripheral border of the round perforated disc  22 , with the result that a greater overlapping area at the supporting-part leg  16   d  is achieved. From FIG. 3, it can also be seen that each supporting part  16   b  can be screwed up with a plurality of, in particular two, headed screws  16   f.    
     The radially inwardly directed movements of the stop peg  31  are limited by a stop  35 . This working position is determined by a step face  37  of the stepped guide bore  32  and a step face  38  of the radially outwardly divergently stepped stop peg  31 . A closure plug  39  is screwed into the guide bore  32 , made from outside, and sealed. To seal the stop peg  31 , provision is made for one or two annular seals  41  which are arranged and act, between the wall of the guide bore  32  and the outer circumferential surface of the stop peg  31 , in an annular groove on one or both sides of the step faces  37 ,  38 . 
     The stop peg  31  is prestressed into its release position by the force of a spring  40  which, in the present exemplary embodiment, is formed by a helical spring which engages on a flange  31   a  at the outer end of the stop peg  31  and bears against a step face  32   a  of an outer bore widening  32   b  of the guide bore  32 . 
     The purpose of the restraint device  16  and the supporting device  16   a  is to axially support the retracting device  15  against overloads resulting from tensile forces directed towards the right in the drawing, which are produced by the pistons  7  during a suction stroke and the resultant of which is indicated by the arrow Fr. For adequate support, it is therefore sufficient if the restraint device  16 —as viewed axially—is arranged on the side of the axial piston machine  1  on which the pistons  7  perform the suction strokes. In the case of an axial piston machine  1  with a pivotable swash plate  11 , as is the case in the present exemplary embodiment, the restraint device  16 , here the stop peg  31 —as viewed along the axis of rotation  13 —is arranged in the region of the pivot axis  14 . In this case, the supporting face  31   b  on the stop peg  31 , which supporting face in the working position of the stop pin  31  is opposite the retracting device  15  and preferably extends radially relative to the axis of rotation  13 , is situated in alignment with the pivot axis  14 . In order to avoid constraints on the stop pin  31  during the pivoting of the swash plate  11 , it is advantageous to round the supporting face  31   b  convexly relative to the centre axis  33  of the stop pin  31 . These features are fulfilled highly advantageously in a simple manner by a cylindrical shape of the stop pin  31 . The axial supporting force of the housing is denoted by Fg. 
     Within the framework of the invention, the spacing b may also be omitted, since no significant relative movement takes place between the swash plates  11  and the stop peg  31 . The spacing a and/or b is at most of such a size that, in the event of a large axial load, the retracting device  15  abuts against the supporting face  31   b  and the locating face  11   a  abuts against the stop pin  31  before the retracting device  15  is deformed beyond its elastic deformation range or beyond its yield point. This ensures that it is only in the case of load peaks that the retracting device  15 , here the perforated disc  22 , can come into contact with the supporting-part leg  16   d  and, indirectly via the swash plate  11 , into contact with the supporting face  31   b  and then be actively supported on the housing  2  via the stop peg  31 . When the overload ceases, the retracting device  15  returns to its starting position again owing to its elasticity. As a result, friction in particular between the retracting device  15  and the supporting-part leg  16   d  and between the locating face  11   a  and the supporting face  31   b  is avoided in the case of normal loading of the axial piston machine  1 , with the result that frictional wear is reduced or where load peaks do not occur is avoided. 
     In the case of an axial piston machine  1  whose swash plate  11  is pivotable beyond the zero position, a restraint device  16  is to be arranged accordingly on the opposite side in a mirror-image fashion, the restraint device coming into operation when the direction of rotation is reversed. 
     The hole space situated radially outside the stop peg  31  forms, when the axial piston machine  1  is in operation, a secondary pressure space  42  which is connected by a channel  43 ,  44  to a primary pressure space in which, when the axial piston machine  1  is in operation, there prevails a pressure which is transmitted through the channel  43 ,  44  into the pressure space  42  and at the outer end of the stop peg  31  produces a radially inwardly directed pushing force which overcomes the force of the spring  40  and displaces the stop peg  31  into its working position. 
     The primary pressure space may, for example, be the housing interior space  3  in which, when the axial piston machine  1  is in operation, there arises a sufficient leakage pressure to be able to produce the above-mentioned pushing force. It should be borne in mind here that this interior space pressure produces an opposite force at the end face of the pin end  34  and therefore the effective differential area between the outer and inner end face of the stop pin  31 , or the interior space pressure, is to be dimensioned with an appropriate size. In this case, a channel connection is required between the secondary pressure space  42  and the housing interior space  3 , and this may be formed by a channel running in the housing wall  2   a  or by a bore  43   a  running longitudinally through the stop peg  31 . In another configuration, the pressure space  42  may be connected, by a channel  44  running in the housing wall  2   a  and formed, for example, by a longitudinal bore, to a pressure line of the axial piston machine, which line exhibits a working or control pressure in operation, or to an adjacent hydraulic unit (external pressure), it being necessary for this working or control pressure or external pressure to be of a sufficient size to produce the pushing force which overcomes the force of the spring  40 . In this case, too, the opposite force produced by the interior space pressure at the inner end face of the stop peg  31  is to be taken into account and the differential area between the outer and inner end face of the stop peg  31  or the working or control or external pressure is to be dimensioned with an appropriate size. 
     For reliable operation, in each case one of the two channels  43 ,  44  is sufficient. For the purpose of improving the adaptability of the axial piston machine  1  to both above-mentioned pressure sources, it is possible for both channels  43 ,  44  to be present at the same time, in which case only one or both channels can be connected to the associated pressure source. In the latter case, a nonreturn valve  45 ,  46  whose valve body  47 ,  48  closes in the direction of the associated pressure source is to be arranged in both channels  43 ,  44 . The valve bodies  47 ,  48  may be prestressed into their closing position by a spring or they may be arranged to be freely movable without a spring. 
     If the channel  44  is not connected and the housing interior space  3  is used as the primary pressure space  49 , the pressure present in the housing interior space  3  in operation is transmitted through the channel  43  into the secondary pressure space  42 , where it produces at the outer end of the stop peg  31  the pushing-in force for displacing the stop peg  31  into its working position. In this case, the nonreturn valve  46  closes automatically by its valve body  48  moving up against the associated valve seat under the pressure which is present. If, in contrast, the channel  44  is connected to a primary pressure source, then the stop peg  31  is displaced by this pressure into its working position, in which case the valve body  47  of the nonreturn valve  45  closes automatically at the associated valve seat  52 , with the result that the pressure in the housing interior space  3  remains unaffected and no leakage losses occur. 
     The nonreturn valves  45 ,  46  delimit a closed pressure space system in which the pressure has to be relieved before the stop pin  31  can be displaced into its release position, for example for demounting the swash plate  11  or the retracting device  15 . This may be effected, for example, by an at least slight opening of the closure plug  39 . Another measure for the automatic relief or delayed relief of the pressure space system consists in connecting the pressure space system to the return system or the tank by a small or throttled channel, it being necessary for the throttle to be dimensioned as small as possible to avoid power losses. Such a relief channel  53  with a throttle  54  may be arranged, for example, in the closure plug  39 , as shown in outline in the drawing. 
     Furthermore, it is advantageous, particularly with a larger movement stroke of the stop pin  31 , to aerate and deaerate the annular space between the step faces  37 ,  38  or to connect it by a channel to a substantially unpressurised line for the hydraulic medium. This may be effected by a channel  55 , illustrated in outline, which extends from the annular space, for example, to the tank for the hydraulic medium. 
     In the exemplary embodiment according to FIG. 2, in which the same or comparable parts are provided with the same reference symbols, the supporting device  16   a  is of the same design as in the exemplary embodiment according to FIG. 1, but in contrast to FIG. 1 the restraint device  16  is not arranged on the housing  2  but on the swash plate  11  and is mounted to be displaceable between a radially pushed-in release position and a radially pushed-out working position, in which the stop peg  31  engages behind a locating face  2   b  on the housing  2  and is thereby axially supported in the direction of the pistons  7 . Here, too, the at least one stop peg  31  is prestressed into its release position by a spring  40  and can be pressurised into its working position by a pressure in a pressure space  42  adjoining the stop peg  31 . In this configuration, too, the round stop peg  31  is designed as a stepped piston with a piston  56  and a piston shaft  57  projecting radially outwards therefrom. The piston  56  is mounted to be displaceable in a blind bore  58 , arranged approximately radially and in the central region of the swash plate  11  and emerging at the peripheral surface thereof, and is prestressed in the direction of the bottom of the blind bore  58  in each case by the spring  40  designed as a helical spring surrounding the piston shaft  57 . The spring  40  acts on the one hand against the piston annular surface and on the other hand against an abutment shoulder  59 , which may be formed, for example, by a securing ring which is inserted in an internal groove in the wall of the blind bore  58 . The depth of the blind bore  58  and the lengths of the piston  56  and of the piston shaft  57  are coordinated with one another such that, in the pushed-in release position (at the top of FIG.  3 ), the stop peg  31  is at a distance from the inner surface of the housing wall  2   a  and in the pushed-out working position the stop peg  31  engages behind an approximately radial locating face  2   b  which faces away from the pistons  7  in the axial direction and thereby forms an abutment, providing the supporting force Fg, for the piston forces Fr. In this configuration, too, the locating face  2   b  may be formed by a recess  2   c  or blind bore in the inner circumferential surface of the housing wall  2   a . As already in the exemplary embodiment according to FIG. 1, in the configuration according to FIGS. 2 to  4 , likewise, the supporting force of the housing  2  is denoted by F and also acts on the supporting-part leg  16   d  owing to the transmitting action of the supporting device  16   a.    
     The secondary pressure space  42  arranged in the bottom of the blind bore  58  is connected by at least one and, in the present configuration, likewise two channels  61 ,  62  to a primary pressure space in each case. For both of the above-mentioned channels  61 ,  62  a common channel  63  extends, for example, secantly through the swash plate  11 , this channel intersecting a widened channel section  64  running transversely or axially, in which a valve cartridge  65  is firmly inserted, for example screwed. The channels  61 ,  62  extend opposite each other from the valve space of a shuttle valve  66  in which a valve body, e.g. a valve ball  67 , is mounted to be movable coaxially with the channels  61 ,  62  and is able to alternately close and open the openings thereof to the channels  61 ,  62 . The channel denoted by  61  opens into the housing interior space  3 , whereas the channel denoted by  62  is connected by a throttled channel connection  68 , which passes axially through an associated slide shoe  8  and a piston head  9 , to the associated piston space and thus to a hydrostatic pressure relief, known per se, for the slide shoe  8  and the associated piston head  9 . The pistons  7  are preferably designed as hollow pistons. In the above-described configuration, the stop peg  31  can be selectively pressurised both by the working pressure and by the housing interior space pressure and pushed out into its working position, the valve body  67  automatically closing in each case the channel  61 ,  62  containing a lower pressure. In operation, the working pressure can perform the pressurising of the pressure space  42 . In contrast, the housing interior space pressure can perform the pressurising when the working pressure drops, for example immediately after the axial piston machine  1  has been shut off, it being possible for a housing interior space pressure which still exists for a certain time even after shut-off to keep the stop peg  31  in its pushed-out working position. 
     In the pushed-out working position, the pushing-out movement of the stop peg(s)  31  is limited by stop against the abutment  59  such that the stop peg  31  is at a radial distance c from the bottom of the recess  2   b  and thus no radial stresses exist between the swash plate  11  and the housing wall  2   b.    
     After a relatively long stoppage period or in the event of demounting of the axial piston machine  1 , the spring  40  can displace the stop peg  31  into its release position, in which the swash plate  11  can be demounted without problems. As already explained with regard to the first exemplary embodiment, it is sufficient, for an effective axial restraint of retracting device  15 , if a stop peg  31  is present preferably in the central region of the suction-or pressure-stroke section of the pistons  7 . For the purpose of symmetrical support or in the case of those axial piston machines in which the swash plate  11  is movable beyond its O position, for example for the purpose of a reversal of the direction of rotation, it is advantageous to provide on both sides of the axis of rotation  13  a restraint device  16  and also a supporting device  16   a , as illustrated in FIG.  2 . In this case, both channels  63  intersect the channel  64  containing the valve cartridge  65  for the purpose of connection to the channels  61 ,  62 . The valve cartridge  65  has, in the region of the valve space, one or more radial connecting holes which open into the channel(s)  63 . FIG. 5 shows schematically the hydraulic control of the restraint device(s), a throttle  69 ,  71  for the purpose of throttling the working pressure or the housing interior pressure being arranged in each of the channels  61 ,  62 . Within the framework of the invention, the restraint device(s)  16  may be arranged centrically or—as can be seen from FIG.  3 —offset by an amount d and thus eccentrically. Moreover, within the framework of the invention, it is also possible for the pivot axis  14  and the centre axis  31  of the restraint device  16  to be arranged coaxially with each other (not shown). Furthermore, within the framework of the invention, it is also possible for two mutually oppositely arranged round stop pegs  31  to be able to form the pivot bearing of the swash plate  11  if the recesses  2   c ,  11   b  which receive the stop pegs  31  are bearing recesses and in particular are formed by bearing bores. This applies both to the configuration according to FIG.  1  and to that according to FIGS. 2 to  4 . 
     It is also possible within the framework of the invention (FIG. 3) to arrange the hole  66 , through which the shaft  4  passes, in the swash plate  11  eccentrically in the housing  2  on the side, see (c), on which the pivot axis  14  and/or the centre axis  31  are offset. In this case, the eccentricity c may be smaller than the offset amount d and preferably be about half the size. 
     In the configuration according to FIG. 4, the swash plate  11  has, on its rear side  2 , bearing faces  11   c , lid which enclose an obtuse angle W with each other and are preferably plane, and with which it bears, in its position of minimum and maximum pivoting angle, against the facing end wall  2   d  of the housing  2 . In this case, the swash plate  11  can bear against and be axially supported on the end wall  2   d  not only in its pivoting end positions, but, with the vertex  67 , also in optional intermediate positions, with the result that the pivot bearing or the pivot bearings, which are present on both sides, of the swash plate  11  are relieved and thus can be designed less sturdily. The bearing contact of the bearing faces  11   c ,  11   d  is advantageous particularly when two stop pegs  31  form the pivot bearing, as shown in outline in FIG.  4 . 
     FIGS. 6 to  10  show a further exemplary embodiment of an axial piston machine  1  according to the invention. This exemplary embodiment largely corresponds to the exemplary embodiments described with reference to FIGS. 2 to  4 . Corresponding reference symbols have been assigned to parts which are the same or act the same, so that in this regard repetitive description is unnecessary. 
     The difference from the exemplary embodiment explained with reference to FIGS. 2 to  4  is that the supporting device  16   a  does not continuously engage behind the retracting device  15 , but only when the restraint device  16  is situated in its extended working position. When, in contrast, the restraint device  16  is situated in its normal unextended position, the supporting device  16   a  releases the retracting device  15 . This substantially facilitates the demounting of the axial piston machine  1 . 
     In the exemplary embodiment illustrated in FIGS. 6 to  10 , the supporting device  16   a  comprises in each case a rotary shaft  80 . Arranged on, or formed in one piece with, the rotary shaft  80  is an eccentric projection  81  which is plate-shaped in the exemplary embodiment. The rotary shaft  80  is in engagement with the stop peg  31  of the restraint device  16 . When the stop peg  31  is displaced from the normal position illustrated in FIG. 7 into the working position illustrated in FIG. 6, this translational movement of the stop peg  31  brings about a rotary movement of the rotary shaft  80  and thus a rotation of the eccentric projection  81  on each rotary shaft  80 . The eccentric projection  81  is arranged here such that it engages behind the retracting device  15  only when the stop peg  31  of the restraint device  16  is situated in its working position, as illustrated in FIG.  6 . When, in contrast, the stop peg  31  is situated in its normal position illustrated in FIG. 7, the eccentric projection  81  of the two rotary shafts  80  does not engage behind the retracting device  15 , so that the retracting device  15  and the components connected thereto can be demounted without problems. 
     As is apparent both from FIG. 9, which illustrates the detail IX in FIG. 8 in enlarged form, and from FIG. 10, which illustrates the detail X in FIG. 7 in enlarged form, the stop peg  31  has a toothing  82  which meshes with a toothing  83  on the rotary shaft  80 . In the exemplary embodiment, the toothing  82  of the stop peg  31  is designed in the manner of a toothed rack on a flattened area  84  of the stop peg  31 . Alternatively, however, the toothing  82  could also be formed by grooves running around the circumferential surface of the stop peg  31 . The rotary shaft  80  is designed, in the region in which it is in engagement with the stop peg  31 , as a toothed wheel with teeth  85  distributed around the periphery. Through the toothing  83 , the rotary shaft  80  is operatively connected to the assigned stop peg  31  such that in the event of a displacement or translational movement of the stop peg  31  the rotary shaft  80  performs a rotary movement. 
     In the exemplary embodiments described with reference to FIGS. 6 to  10 , it is particularly advantageous that both an anchoring of the swash plate  11  on the housing  2  and of the retracting device  15  on the swash plate  11  is brought about automatically or in a self-acting manner by the actuation of the restraint device  16 . As soon as a housing interior pressure has become established in the housing interior space  3 , or a system pressure is available via the channel connection  68 , the restraint device  16  according to the invention is actuated and brings about the anchoring described. In the event of demounting, this anchoring is automatically removed, thereby considerably simplifying maintenance work.