Abstract:
An axial piston machine having bent axis construction, having a drive shaft rotatably supported in a housing and ending in a drive flange comprising a face on the drive shaft side, is disclosed in which ball races are formed for receiving piston heads. The piston heads are rotatably retained in the ball races by means of deformable rings. The axial piston machine having bent axis construction possesses characteristics so that pressure relief of the ball head is ensured for all cases. The rings at the inner surface comprise at least one groove running so as to connect the ring faces to each other.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2009/008869, filed Dec. 11, 2009, which claims the benefit of priority to application Ser. No. DE 10 2009 005 390.5, filed Jan. 21, 2009 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to an axial piston machine having bent axis construction. 
     Known axial piston machines of this type have a drive mechanism which, as essential components, comprises a rotatably supported drive shaft with an integrally formed drive flange, a cylinder barrel with longitudinally displaceable pistons guided in axially extending cylinder bores, and a control element. After the formation of a neck, the pistons, which are guided in a longitudinally displaceable manner in the cylinder bores, each have at the free end a spherical piston head, which is received in a manner which allows rotary motion in a spherical cup formed in the drive flange. A retraction disk, which fits behind the piston heads and thus prevents them from sliding out of the spherical cups, is provided for all the piston heads. However, the production and installation of the retraction disk is an involved process. During production, the retraction hole walls must be made in such a way that friction and wear are kept low during functional operation. To allow releasable fastening of the retraction disk, additional bores are required in the disk to accept screws. Additional threaded holes are required in the drive disk to accept the fastening screws. 
     One known way of countering this is to replace the retraction plate by individual bearing metal rings, which hold the spherical piston heads in a manner which allows rotation. DT 20 61 906 or DT 24 02 066 A1 each show such a solution. Here, the spherical cup is provided with a widened portion into which a bearing metal ring is pressed. 
     It is the underlying object of the disclosure to refine an axial piston machine having bent axis construction in such a way that pressure relief of the spherical head is ensured in all cases. 
     SUMMARY 
     This object is achieved, in the case of an axial piston machine having bent axis construction having the features of the preamble, by additional provision of the features in the characterizing part of claim  1 . 
     In an axial piston machine having bent axis construction according to the disclosure, at least one groove extending so as to connect the ring faces to each other is provided on the inner surface of the retraction rings. 
     Introducing a groove into a retraction ring can be accomplished in a particularly simple and rapid manner. A retraction ring embodied in this way makes possible pressure relief to the leakage oil space during the changeover process. The relief groove, as it is called, leads to an improvement in hydrostatic relief and to a reduced friction effect. 
     Advantageous embodiments of an axial piston machine having a bent axis construction according to the disclosure is set forth below. 
     According to a particularly preferred embodiment of the present disclosure, the groove extends in a spiral shape. The groove can be produced by turning by means of a simple tool directly during the production of the ring. The tool is fixed and the ring is cut by turning. This is a simple and economical way of producing the spiral groove. 
     Other possibilities for the shape of the relief groove are also conceivable, with one or more grooves extending axially, for example. 
     The inside diameter of the ring preferably widens radially at the piston head end, ensuring that pivoting of the pistons relative to the drive flange is not limited by the ring. 
    
    
     
       BRIEF DESRCIPTION OF THE DRAWINGS 
       One illustrative embodiment of an axial piston machine having bent axis construction according to the disclosure is illustrated in the drawings. The disclosure will now be explained in greater detail with reference to the figures of these drawings, in which 
         FIG. 1  shows a longitudinal section through a drive mechanism of an axial piston machine according to the disclosure, 
         FIG. 2  shows a longitudinal section through a spherical piston head corresponding to a detail A in  FIG. 1 , 
         FIG. 3  shows a longitudinal section through a drive flange portion from the end of the drive flange to a radial widened portion of two spherical cups, and 
         FIG. 4  shows a longitudinal section through a retraction ring. 
     
    
    
     DETAILED DESCRIPTION 
     The drive mechanism  1  of an axial piston machine having bent axis construction, which drive mechanism is illustrated in  FIG. 1 , comprises, as essential components, a rotatably supported drive shaft  2  with an integrally formed drive flange  3 , a cylinder barrel  4  with longitudinally displaceable pistons  6  guided in axially extending cylinder bores  5 , and a control element  7 . The cylinder barrel  4  is arranged between the drive flange  3  and the control element  7  and, at the control-element end, is supported by a concave bearing surface  8  on the facing convex control surface  9  of the control element  7 . At the drive-flange end, the cylinder barrel  4  is supported on the drive flange  3  by way of a centering journal  10  in such a way as to be rotatable and, in particular, to allow adjustment of the working stroke of the pistons  6 , so as to be pivotable. 
     The centering journal  10  projects into a central cylinder bore  11  and is pressed against the drive flange  3  by a compression spring  12 , which is arranged between the centering journal  10  and the cylinder barrel  4 . The cylinder bores  5 , which extend axially and in a manner uniformly distributed around a pitch circle in the cylinder barrel  4  open via ducts  13  into the concave bearing surface  8  of the cylinder barrel  4  and, when the barrel  4  is rotated, connect the cylinder bores  5  to a pressure and suction connection (not shown) via kidney-shaped control ports (not shown). The pistons  6 , which are guided in a longitudinally displaceable manner in the cylinder bores  5 , are embodied with a conical shape. After the formation of a piston neck  14 , the ends of the pistons  6  facing away from the cylinder barrel have, at each of the free ends thereof, spherical heads  15 , which are received rotatably in spherical cups  16  formed in the drive flange  3  and are fixed by means of retraction rings  17 .  FIG. 2  shows a detail A from  FIG. 1 , which comprises a spherical head  15  fixed rotatably in a spherical cup  16  by means of a retraction ring  17 . The spherical head  15  has an apex  20  and an equator  21 . The center of the equator  21  corresponds to the center of the spherical head  15 . The equator  21  includes an angle of 90° with the piston axis  22  and divides an upper hemisphere  23  including the apex from a lower hemisphere  24 . The spherical cup  16  extends beyond the upper hemisphere  23  of the spherical head  15 . The upper hemisphere  23  fits accurately into the spherical cup  16 . At the level of the equator  21  of the spherical head  15 , the inside diameter of the spherical cup  16  recedes radially and thereby becomes larger. The shape of the spherical cup  16  from the radial backward step  30  to an opening of the spherical cup  16  is illustrated in  FIG. 3 . A cylindrical transition  31  connects the radial backward step  30  and a second radial backward step  32 . From this backward step  32 , the spherical cup  16  has a spherical shape with a widened inside radius  33  as far as the face of the drive flange  3  and ends with a circular opening  34 , which is chamfered frustoconically at an angle of 30°. Insertion of the piston head  15  into the spherical cup  16  gives rise to an annular gap  36  between the spherical cup  16  and the piston head  15  from the equator  21 , and the retraction ring  17  is pressed into said gap in order to hold the piston head  15  rotatably in the spherical cup  16 . 
     According to  FIG. 4 , the retraction ring  17  has a frustoconical chamfer  40  at an angle of 30° on the inner edge facing the piston, said chamfer having a depth of 5 mm. The retraction ring has a V-shaped spiral groove  41 , which enables operating fluid to flow from the inner annular face  42  situated on the piston head side to the outer annular face  43  situated on the piston neck side when pressed in. 
     According to  FIG. 2 , each piston head  15  has a pocket-shaped opening  25 , from which there starts a spiral groove  26  ending in an encircling annular groove  27  above the equator  21 . The pocket-shaped opening  25  in the apex  20  of the piston head  15  is connected via a restrictor  28  and an adjoining piston through bore  29  to a working space  18  in the cylinder bore  5 . The spherical cup  16  also has a pocket-shaped recess  35 , which extends symmetrically with respect to the longitudinal axis of the spherical cup  16  and has a larger diameter than the diameter of the pocket-shaped opening  25  in the apex  20  of the spherical head  15 . 
     The axial piston machine operates in a known manner, which will not therefore be described further. 
     That area of the concave spherical cup surface which corresponds to the pivoting angle range of the axial piston machine forms a bearing surface  45 , on which the spherical head surface is supported by way of a mating bearing surface as a defined relief surface  46  by virtue of a pressure field  49  formed in a bearing gap  48 . The relief surface  46  of a hydrostatic bearing  47  resulting therefrom is bounded by the encircling groove  27  on the upper hemisphere  23 . 
     To build up the pressure field  49 , operating medium flows from the working space  18 , through the piston through bore  29 , via the restrictor  28  and into the pocket-shaped opening  25  in the piston head  15 . Upstream of the restrictor  28 , the prevailing pressure is the supply pressure, while a defined feed pressure is established at the relief surface  46 . The pressure field  49  absorbs the piston force and thus prevents metallic contact between the spherical head  15  and the concave spherical cup surface  45 . If the piston force increases, the bearing gap  48  becomes smaller. The feed pressure rises until the pressure difference across the restrictor  28  is virtually zero, i.e. the feed pressure corresponds approximately to the supply pressure. The bearing  47  is now hydrostatically relieved. If the piston force decreases, the bearing gap  48  becomes larger, the feed pressure falls and approaches the supply pressure until the bearing  47  is hydrostatically relieved at approximately equal pressures. 
     During the changeover process from high pressure to low pressure, the supply pressure falls abruptly while the feed pressure is still very high. The spherical head  15  is now pressed into the retraction ring  17  and operating fluid can flow out into a leakage oil space  50  via the spiral groove  41  in the retraction ring  17 . The feed pressure falls and, as pressure equilibrium is approached, the spherical bearing  47  is hydrostatically relieved. 
     The shape of the groove in the retraction ring is not limited to a spiral but it is important that the faces of the ring should be connected via the groove. The connection exists even when there is at least one axially extending groove, for example.