A hydraulic radial piston motor with a cam disc and a cylinder block with a number of pistons running in cylinders in the block presses rollers against the cam disc in such a way that a torsional moment arises. The rollers are formed with guide members running in slots in guide units which take up tangential forces. The rollers are mounted in roller cages which are formed with hydrostatic bearings. At their outer end each piston is formed with a part-spherical bearing surface and the roller cage has a cooperating part-spherical bearing surface, which allows angular movements between the roller cages and the pistons in all directions. In a hydraulic radial piston motor which includes a housing; a cam disc which has an internal cam surface; a cylinder block havng a plurality of radially disposedcylinders; a plurality of pistons, a respective piston being slidably disposed in a respective cylinder; a plurality of roller cages, each roller cage being located between a respective piston and the cam disc, and each roller cage including an outerbearing surface which is shaped as part of the internal surface of a cylinder; two guide units fixedly joined to the cylinder block, each guide unit including radially inwardly directed guide slots. The guide slots being in register on opposite sides ofeach respective roller cage; a plurality of cam-follower rollers, each cam-follower roller being located in a respective roller cage and having an outer surface which rolls against the internal cam surface of the cam disc, each cam-follower rollerincluding a shaft pin at its opposite ends which mount respective guide bearings, the respective guide bearings being movable in the associated guide slots of the guide units and transmitting tangential forces that act on the cam-follower rollers to theguide units and thus to the cylinder block, the improvement wherein each roller cage and associated piston are separate elements which are movable with respect to one another, each roller cage having an inner bearing surface and each piston having an outer bearing surface constructed such that angular motionstherebetween are possible in all directions, and each roller cage includes a hydrostatic bearing which cooperates with the outer surface of the associated cam-follower roller. The invention relates to a hydraulic radial piston motor with a number of drive rollers running along an internal cam surface in a motor housing and being urged radially outwardly towards the cam surface by a number of pistons slidably disposedin cylinders in a cylinder block arranged in the motor housing. In one embodiment of such a radial piston motor for heavy duty applications, the pistons are completely relieved of tangential forces by the fact that pins projecting from the drive rollerstowards the cylinder block are provided with bearings which run in radially disposed slots in guide units which are fixedly joined to the cylinder block on opposite sides thereof. Either the housing of such a motor may be stationary and the cylinderblock rotates, or the cylinder block may be stationary and the housing rotates. In the first embodiment the motor is usually intended to be connected to a driven shaft. In the second embodiment it is usually intended to be connected to a wheel or acable drum for a winch or the like. According to the invention, the pistons running in the cylinders in the cylinder block are formed on a radially outer portion with a part-spherical bearing surface. The drive rollers running against the cam surface are journalled in roller cageswith a cylindrical bearing seat which is constructed as a hydrostatic bearing and with a part-spherical bearing surface which cooperates with the part-spherical bearing surface of the piston. The roller cage is thus able to tilt in all directions aroundthe center of the spherical bearing. Since the roller cage can tilt in this way relative to the piston, the piston is protected from overturning moments caused by movements of the roller cage due to imperfections of the cam curve and guides for therollers. The pistons of the motor are formed with a throughgoing axial bore which suitably has a greater diameter in its radially outer part than in its radially inner one. The roller cages which support the drive rollers are formed with a guide pinwhich extends down into the outer part of the through-going piston bore having a greater diameter than the radially inner parts thereof. To prevent the roller cages and the pistons from being separated during operation of the motor, the roller cages andthe pistons may be held together by a strong spring which can be attached within the guide pin and to the radially inner part of the piston. The roller cage may be formed so that it surrounds the drive roller over more than 180, the rollerthereby being fixed in its cage. The cage may also be formed with a surrounding angle smaller than 180, whereby the roller cage or the motor is provided with other means for fixing a roller in the roller cage or for guiding the roller. Thecylindrical bearing seat for the roller is formed with a defined hydrostatic supporting surface so as to obtain a suitable balancing of the force against the roller. The supporting surface may be defined by grooves which provide gap sealing. The radialcompressive forces, acting on the roller cage and on the piston, are suitably outbalanced hydrostatically to more than 80%, preferably to between 80 and 95%. In hitherto known embodiments of radial piston motor of the above-mentioned kind, the piston force has been transmitted to each cam-follower roller via a piston rod which is similar in design to a conventional connecting rod. The roller hasheretofore been journalled at its mid-point in a bearing at the outer end of the piston rod and formed with roller ways on either side of the bearing. At its radially inner end, the piston rod has been journalled in the piston. The journalling of theroller means that the length of the roller increases with the width of the bearing in the rod. The width of the roller way in the motor housing becomes wider by a corresponding measure, and its mid-portion is therefore not fully utilized.
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