Patent Publication Number: US-6663354-B2

Title: Hydrostatic axial piston machine with a control port, a cradle supported swashplate and a swashplate actuating piston

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application corresponds to German Application No. 100 55 262.5 filed Nov. 8, 2000, herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to axial piston machines and, more particularly, to a hydrostatic axial piston machine having a cylinder block in which there are bores to hold reciprocating pistons, and with a swashplate on which the reciprocating pistons are supported and in which there are control ports to supply the bores with hydraulic medium. 
     2. Technical Considerations 
     DE 196 42 022 A1 describes an axial piston machine. The field of application of the machine disclosed therein, with a control system and hydraulic fluid supply system in the swashplate, is limited because the intake and delivery volume is constant. 
     It is an object of the present invention to provide an axial piston machine of the general type described above but with an expanded range of potential applications. 
     SUMMARY OF THE INVENTION 
     The invention provides an axial piston machine in which the swashplate is adjustable. It thereby becomes possible to increase the transformation range of a hydrostatic transmission in which the axial piston machine of the invention is used by regulating not only the primary side (i.e., adjustment of the delivery volume of the pump) but also the secondary side (i.e., adjustment of the intake volume of the motor). 
     In one advantageous configuration of the invention, the swashplate includes a pivoting cradle mounted in friction bearings in a cradle receptacle. Hydraulic fluid channels empty into the cradle receptacle and, regardless of the rotational position of the cradle, are in connection with feed channels in the cradle that are connected to control ports. The bores in the cylinder block are, therefore, supplied with hydraulic fluid via the adjustable cradle. As a result of the hydraulic fluid channels that emerge in the cradle receptacle, the friction bearing system of the cradle can also be pressurized with hydraulic fluid to achieve a hydrostatic relief of the cradle. 
     Pivot means can be provided to pivot the cradle. The pivot means can comprise an actuator piston that is oriented substantially perpendicular to the axis of rotation of the cylinder block and substantially perpendicular to the axis of rotation of the cradle and that is actively connected with the cradle. If the actuator piston has a toothed rack segment that engages a toothed segment on the back side of the cradle, there is a constructively simple and functionally reliable active connection between the actuator piston and the cradle in which the actuator piston is tangentially engaged with the back side of the cradle. 
     The invention teaches that it is appropriate if the actuator piston is located between two friction bearing segments of the cradle receptacle and is centered with respect to the cradle. 
     The cylinder block advantageously has an external bearing system. An external bearing system minimizes the dimensions of the axial piston machine of the invention in the radial direction. In this case, it is advantageous if the cylinder block bearing system has two helical roller bearings in an O-arrangement. 
     In one particularly advantageous configuration of the invention, the axial piston machine is configured as a hub drive, in particular a wheel hub drive, whereby the cylinder block forms a rotating hub, a housing that surrounds the cylinder block serves as the hub carrier, and the cylinder block bearing system is realized in the form of a hub bearing system. The cylinder block can include a wheel fastening flange and a rim centering device. 
     In an additional advantageous configuration of the invention, a brake is connected between the cylinder block and the housing. The brake can be a wet-running, hydraulically-relieved, spring-loaded, multiple-disc brake. In this case, the brake can be cooled by hydraulic fluid, as a result of which it can absorb a high braking power. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional advantages and features of the invention are explained in greater detail below with reference to the exemplary embodiment of the invention illustrated in the accompanying schematic drawings, in which: 
     FIG. 1 is a longitudinal section through a hydrostatic axial piston machine of the invention taken along the line I—I in FIG.  2 . In FIG. 2, the cradle  7  is in the minimum position in which the pistons located in the cylinder drum have their minimum stroke, e.g., zero stroke. In FIG. 1, the cradle  7  is in position other than the minimum position. 
     FIG. 2 is a cross section through the axial piston machine, illustrated in FIG. 1, taken along line II—II in FIG. 1 in the area of the cradle receptacle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the exemplary embodiment shown in FIGS. 1 and 2, the hydrostatic axial piston machine of the invention is in the form of a wheel hub motor. However, it is to be understood that the invention is not limited to use as a wheel hub motor. As shown in FIG. 1, a cylinder block  1  forms a rotating hub and is rotationally mounted by means of a cylinder block bearing system  2  that acts as a hub bearing system in a surrounding housing  3  which performs the function of a hub carrier. The cylinder block bearing system  2  includes two bearing assemblies which include helical roller bearings  2   a  and  2   b , e.g., conical roller bearings, in an O-arrangement, e.g., the bearing  2   a  is mounted between an outer ring  2   aa  and an inner ring  2   ab , and the bearing  2   b  is mounted between an outer ring  2   ba  and an inner ring  2   bb.    
     A rim centering device  1   a  and a wheel fastening flange  1   b  are shaped onto the cylinder block  1  for holding and fastening at least one wheel rim. In the cylinder block  1 , there are a plurality of concentric bores  4  in each of which a reciprocating piston  5  can move longitudinally. The pistons  5  are supported by means of a slipper  6   a  and an annular disc  6   b  on a swashplate that is configured in the form of a cradle  7 . The cradle  7  is mounted on friction bearings  7   b  (shown only in FIG. 2) in a cradle receptacle  8  which is located in a closing cover that is connected with the housing  3 . 
     Between the cylinder block  1  and the housing  3 , there is a wet-running, spring-loaded, multiple-disc brake  9 . The brake  9  can be released by means of a hydraulically pressurized annular piston  10 . The invention teaches that the bores  4  are supplied with hydraulic medium via the adjustable cradle  7  and the cradle receptacle  8 . For this purpose, the cradle  7  is provided on its end surface facing the reciprocating pistons  5  with control ports  11 ,  12  (FIG.  2 ), each of which is connected to a respective supply channel  13 ,  14  in the cradle  7 . 
     The supply channels  13 ,  14  each end at the back side of the cradle  7  in groove-shaped expanded channels  13   a  and  14   a , respectively, which are located in the area of a friction bearing segment of the cradle receptacle  8 . The expanded channels  13   a  and  14   a  ensure that, regardless of the position of the pivoting cradle  7 , the supply channels  13 ,  14  are always connected with hydraulic fluid connecting channels  15  and  16 , respectively, which empty in the cradle receptacle  8 . Hydraulic fluid travels via channels in the annular disc  6   b , the slippers  6   a , and the reciprocating pistons  5  into the bores  4  of the cylinder block  1 , and is also discharged via the same path. 
     The friction bearing segments of the cradle receptacle  8  are also supplied with hydraulic fluid by the hydraulic fluid connecting channels  15  and  16  to achieve a hydrostatic relief of the cradle  7 . 
     Between two parallel friction bearing segments of the cradle  7 , there is a central gearing segment  7   a  on the back side of the cradle  7  for adjustment of the cradle  7  in the cradle receptacle  8 . The gearing  7   a  interacts with a toothed rack segment  17   a  of an actuator piston  17  that is oriented perpendicular to the axis of rotation of the cylinder block  1  and perpendicular to the axis of rotation of the cradle  7 . The double-acting actuator piston  17 , which is located in a bore  18  of the cradle receptacle  8 , is centrally located with reference to the cradle  7  (FIG.  2 ). The actuator piston  17  is, therefore, located between the two friction bearing segments of the cradle receptacle  8 . 
     In this exemplary embodiment, the cradle  7  of the axial piston machine pivots only to one side. The axial piston machine can thereby be set from a maximum intake volume to a minimum intake volume and back again. However, it is also possible to equip the axial piston machine with a cradle  7  that pivots to both sides, in which case the axial piston machine would be reversible (change in direction of rotation). 
     It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.