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Variable capacity hydrostatic axial piston machineVariable capacity hydrostatic axial piston machine description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070251377, Variable capacity hydrostatic axial piston machine. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]The invention relates to a variable capacity hydrostatic axial piston machine according to the features of claim 1. [0002]Variable capacity hydrostatic machines which, for example, are used as hydraulic motors, have a cylinder drum which is mounted such that it can rotate about its central longitudinal axis and has cylinder bores distributed on its circumference, in which pistons can be displaced. The cylinder drum is mounted in the housing of the axial piston machine such that it can pivot about a pivot axis running transversely with respect to its axis of rotation, so that the central longitudinal axis of the cylinder drum forms an adjustable angle with the axis of the drive shaft. The pistons are supported in an articulated manner on the drive flange of the drive shaft at the adjustable angle. The spherical piston heads are in this case pivotably mounted in spherical shells, which are formed in the drive flange or in piston shoes fitted there. In order to be able to insert the spherical heads of the pistons into the spherical shells and to hold them axially there during the operation of the machine, they are generally retained by a retaining device which engages behind the spherical heads, for example by a perforated plate screwed on. An axial piston machine of this type is known, for example from EP 1 251 271 A2. [0003]Also known are spherical joint connections having a spherical shell which encloses an angle which is greater than 180.degree.. In order to be able to insert the spherical head, the latter has lateral flats or recesses, so that it can be inserted at an angle deviating from the working position and is held in the working position by the spherical shell. Spherical joints of this type are described, for example, in DE-OS 2 307 641. [0004]It is an object of the invention to specify an axial piston machine of the type described at the beginning having improved spherical guidance of the pistons in the drive flange. SUMMARY OF THE INVENTION [0005]According to the invention, this object is achieved 10 with a variable capacity hydrostatic axial piston machine which has a drive shaft with a drive flange having an end face oriented towards displacement pistons, in which end face spherical shells for holding substantially spherical piston heads are formed. The calotte of the spherical shells in this case go beyond the semisphere and have a circular opening with a smaller diameter than the spherical shell diameter. The spherical calotte of the piston heads have a recess having a smaller diameter than that of the circular opening of the spherical shells so that at the vertex of the piston a spherical section making up less than the semisphere and, spaced apart from the latter by the recess a retaining collar having a larger diameter than the circular opening of the spherical shell are formed. A transverse groove is formed in the circular opening of the spherical shell in such a way that the piston head with the retaining collar can be threaded into the spherical shell through the transverse groove and is retained there in the working position of the piston. [0006]With the invention, for example a piston shoe can be dispensed with and overall space for a larger domed sphere can be obtained, at the same time a smaller total overall length being achieved. The larger domed sphere in this case permits a high level of balance of the hydrostatic load from the piston force, so that only a small part of the piston force has to be transmitted mechanically via the frictional contact. [0007]The retaining collar preferably forms a spherical layer, which begins approximately in the middle of the spherical dome of the piston heads and extends approximately from the middle of the spherical dome beyond the latter by about 1/8 to 1/4, preferably about 1/6, of the sphere diameter, which means that the height of this spherical layer is between 1/8 and 1/4 of the sphere diameter, preferably 1/6 of the sphere diameter. Therefore, the part of the solid sphere on the piston side is eliminated. The piston rod can adjoin the retaining collar directly. [0008]The recess is preferably rotationally symmetrical in relation he piston longitudinal axis. Therefore, economical manufacturing by turning is possible. The same advantage results during the production of the transverse grooves if they are formed rotationally symmetrically in relation to the axis of the drive shaft and form a circular ring around the latter. [0009]The particular advantage of the invention resides in the fact that in order to thread them into the spherical shells the pistons can be set at an angle to the end face of the drive flange which is smaller than the smallest such angle occurring during the operation of the axial piston pump. [0010]Therefore, the threading of the pistons can be carried out in blique position which does not occur during the operation of the machine so that the piston heads are retained securely in the spherical shells. The difference between the mounting and operating positions of the piston may be enlarged further by mounting grooves being provided in the end face of the drive flange which make threading possible at a minimum angle between the end face of the drive flange and the piston longitudinal axis. [0011]The pistons preferably have a bore in the longitudinal direction through which hydraulic pressure is led from the cylinder chamber to the spherical dome of the piston head for the purpose of balancing the hydrostatic load on the mounting. This load relief is optimized by the fact that, firstly, in order to limit the hydrostatic balancing force, a circumferential groove is formed in the spherical section of the piston head and is surrounded on the outside by an annular spherical layer as a sealing surface, and secondly, a spiral groove is formed in the spherical section of the piston head from the bore as far as the circumferential groove. BRIEF DESCRIPTION OF THE DRAWINGS [0012]Further features and advantages of the invention emerge from the following figure description. [0013]In the drawing: [0014]FIG. 1 shows an exemplary embodiment of the invention with the mounting position of the piston; [0015]FIG. 2 shows the exemplary embodiment from FIG. 1 with the piston mounted; [0016]FIG. 3 shows an exemplary embodiment of the piston; [0017]FIG. 4 shows the piston from FIG. 3 in a perspective view; and [0018]FIG. 5 shows the mounting of the piston in a sectional illustration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0019]In FIG. 1, an exemplary embodiment of the invention is shown in the state in which the piston is being mounted and threaded into the associated spherical shell of the drive flange. The drive shaft 1 of the variable capacity axial piston machine has a drive flange 2, on whose end face 3 the pistons 4 are pivotably mounted. For this purpose spherical shells 5 are formed in the end face 3 of the drive flange 2 and accommodate the spherical heads 6 of the displacement pistons 4. The spherical shells 5 go beyond the semisphere. They comprise an angle which is greater than 180.degree. and open towards the pistons with a circular opening 7 which is smaller than the spherical shell diameter. [0020]The mounting of the piston is made possible by the fact that a transverse groove 11 passing through the circular opening 7 is formed and in the example illustrated, as a circumferential groove forms a circular ring around the longitudinal axis of the drive shaft. The specially designed head 6 having the retaining collar 10 is pushed into the spherical shell obliquely in the axial direction through this transverse groove 11. The retaining collar 10 and the groove dimensions are configured in such a way that the mounting of the pistons is possible only with the illustrated highly oblique position of the piston axis in relation to the shaft axis. The angle between the end face 3 of the drive flange 2 and the piston axis can be kept particularly small by the fact that mounting grooves 12 running radially from the shaft axis to the spherical shells 5 are provided in the end face 3 of the drive flange 2, so that an extreme oblique position can be achieved which deviates considerably from the working position of the pistons, in which only smaller oblique positions occur, equivalent to a considerably larger angle between the piston axis and the end face 3. Continue reading about Variable capacity hydrostatic axial piston machine... Full patent description for Variable capacity hydrostatic axial piston machine Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Variable capacity hydrostatic axial piston machine patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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