Abstract:
A hydraulic rotary motor, in particular to a stewing gear for elevating plant such as excavator grabs, etc., comprising a housing in which a rotor is rotatably received as well as a ring piston having an inner toothed arrangement and an outer toothed arrangement which is seated between the rotor and the housing so that displacement chambers are formed between the ring piston and an outer toothed arrangement of the rotor and/or an inner toothed arrangement of the housing, with a first motor connector being rotatably fixedly connected to the housing and a second motor connector being rotatably fixedly connected to the rotor. The hydraulic rotary motor is characterized in that the rotor is axially and radially supported at the housing via plain bearings and the second motor connector connected to the rotor is solely supported via the plain bearings at the housing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a hydraulic rotary motor, in particular to a slewing gear for elevating plant such as excavator grabs, etc., comprising a housing in which a rotor is rotatably received as well as a ring piston having an inner toothed arrangement and an outer toothed arrangement which is seated between the rotor and the housing so that displacement chambers which can be filled with pressure fluid are formed between the ring piston and an outer toothed arrangement of the rotor and/or an inner toothed arrangement of the housing, with a first motor connector being rotatably fixedly connected to the housing and a second motor connector being rotatably fixedly connected to the rotor. 
         [0003]    2. Description of the Prior Art 
         [0004]    Such a hydraulic rotary motor is known from DE 33 42 131 A1. DE 37 29 049 C1, DE 2 365 057 or DE 196 05 879 A1 also show hydraulic rotary motors of this type in which a ring piston orbits in a gyrating manner and in this process interacts with an inner toothed arrangement at the housing and with an outer toothed arrangement at the rotor to drive the rotor in a rotary manner relative to the housing. Typically, such rotary motors are used as slewing gears for elevating plant of excavators, part-load cranes or logging cranes, wherein, when used, for example, for an excavator grab, the first motor connector fixed to the housing is connected to the excavator arm, whereas the excavator grab is installed at the second motor connector connected to the rotor. The excavator grab can be rotated in a manner known per se relative to the excavator arm via the rotary movement of the rotor relative to the housing. 
         [0005]    With such hydraulic rotary motors of the initially named kind, the rotor is typically seated rotationally fixedly, but longitudinally displaceably on a drive shaft whose end exiting the housing forms the second motor connector for the fastening of the elevating plant. To intercept the forces and torques introduced onto the motor by the elevating plant, the motor shaft is supported on both sides of the rotor via tapered roller bearings at the housing. DE 33 42 131 or DE 37 29 049, for example, show this. Axial forces and bending torques introduced into the motor shaft should thereby largely be kept away from the rotor so that it can run smoothly and precisely in the ring-shaped housing gap in which the ring piston is received and so that the sealing of the displacement chambers does not experience any impairment by bearing forces or reaction forces onto the rotor. However, what is disadvantageous with this support of the motor shaft via tapered roller bearings is, however, the large axial construction length of the motor which hereby arises. In addition, static overdeterminations result since, in addition to the shaft support, the rotor itself must be guided precisely so that the displacement chambers do not experience any excessive leaking. In addition, the production and assembly effort is relatively high due to the corresponding components. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention wants to provide a remedy here. It has the underlying object of providing an improved rotary motor of the said kind which avoids disadvantages of the prior art and further develops the latter in an advantageous manner. A compact rotary motor of simple construction and short axial design should preferably be provided which can be manufactured in a cost-favorable manner by a low production effort and use of material. 
         [0007]    This object is solved in accordance with the invention by a hydraulic rotary motor in accordance with claim  1 . Preferred aspects of the invention are the subject of the dependent claims. 
         [0008]    In the rotary motor in accordance with the invention, a separate support of the motor shaft by the known tapered roller bearings is omitted. It is rather the case that the forces and torques introduced from the motor connector connected to the respective elevating plant are directly intercepted via the rotor itself. In accordance with the invention, the rotor is supported axially via plain bearings and radially at the housing. The second motor connector connected to the rotor for the fastening of the elevating plant is supported via the rotor and the plain bearings at the housing supporting it. By the omission of separate shaft bearings in the form of tapered roller bearings or other roller bearings and by the interception of the forces and torques via the rotor itself and corresponding plain bearings free of roller bearings, the axial construction length of the motor can be substantially shortened, on the one hand. On the other hand, the production effort and the use of material are reduced by the dispensing with of the separate roller bearings for the motor shaft, whereby cost savings can be achieved. The second motor connector connected to the rotor can in particular be rigidly connected to the rotor and be supported exclusively via the plain bearings engaging at the rotor. 
         [0009]    In a further development of the invention, the rotor can be seated rigidly on an output shaft whose end exiting the housing forms the second motor connector for the fastening of the elevating plant. The rotor can be pressed onto the output shaft or be rigidly connected to it in another suitable manner. 
         [0010]    To achieve a particularly compact arrangement, a motor shaft can be fully dispensed with. The rotor itself replaces the motor shaft in this connection and itself forms the motor connector for the fastening of the elevating plant which can advantageously be fastened directly to the rotor. For this purpose, the rotor can have suitable fastening means, in particular bores for the reception of bolts for the fastening of the elevating plant. The rotor expediently has a stub-shaped shoulder whose end face forms the installation surface for the elevating plant. 
         [0011]    The rotor advantageously forms a ring in whose inner cut-out a rotary brake, preferably a multi-disk brake, can be arranged. A particularly compact arrangement is hereby achieved, on the one hand. On the other hand, the braking forces are introduced from a housing section directly into the rotor which is particularly suitable for this due to its high-strength material. 
         [0012]    In a further development of the invention, the rotor can have a disk section which has two axially plain bearing surfaces on oppositely disposed sides with which the rotor is axially supported in opposite directions in a housing gap into which the ring piston is also inserted. The rotor can additionally have two shaft sections which project axially in the manner of a hollow shaft stub at both sides from the said disk section. In a further development of the invention, radial plain bearing surfaces are provided at the shaft sections and the rotor is supported at these on the rims of the housing gap. A stiff support of the rotor can hereby be achieved both with respect to axial forces and to radial forces and corresponding torques. 
         [0013]    The plain bearing surfaces can generally be formed by bearing inserts which are used on the housing side and/or on the rotor side. However, in a further development of the invention, the plain bearing surfaces can be formed directly by the material or by the surface of the rotor and of the housing section adjacent thereto. If the housing is produced from gray-cast iron, good plain bearing properties can be achieved directly by the housing material. 
         [0014]    The bearing of the rotor advantageously dispenses with the conventional distributor plates or pressing plates which are guided movably in the housing and are known, for example, from the construction in accordance with DE 33 42 131. The production effort and use of material can thereby be further reduced. 
         [0015]    To ensure a sufficient lubrication of the plain bearing support of the rotor, an oil guiding system and/or a passage system is provided in accordance with a further aspect of the invention, in particular in the housing, which guides hydraulic oil out of the displacement chambers and/or out of the pressure supply passages of the motor to the bearing positions of the rotor and/or to the drive shaft connected thereto. Communication passages to the pressure passages for the improvement of the oil supply of the plain bearing surfaces can in particular be provided via which the displacement chambers of the motor are filled with oil and the motor is ultimately driven. The oil supply of the bearing positions via a passage system in the housing which guides hydraulic oil from the displacement chambers and/our from the pressure supply passages of the motor to the bearing positions also has considerable advantages, however, in the lubrication of rotors conventionally supported via roller bearings or of the drive shafts of such motors. In accordance with an advantageous embodiment of the invention, ring grooves can in particular be provided in the radial plain bearing surfaces of the rotor or in the corresponding radial plain bearing surfaces of the housing which are connected to a respective one of the pressure passages for the supply of the displacement chambers. The respective ring groove ensures the distribution of the oil over the total periphery. To utilize the oil pressure available from the pressure passages also for the lubrication of the axial plain bearing surfaces, transverse bores can be provided in the housing which connect the said axial plain bearing surfaces with one of the aforesaid ring grooves. Alternatively or additionally, oil bores could also lead directly from the pressure passages for the supply of the displacement chambers to the axial plain bearing surfaces. 
         [0016]    A first set of oil supply passages is advantageously provided in the housing which are connected to a pressure passage for the supply of the displacement chambers for reverse action and a second set of oil supply passages is provided which are connected to a pressure passage for the supply of the displacement chambers for forward action. 
         [0017]    For this purpose, two ring grooves can be formed in levels in the housing lying above one another and can each have a wave-shaped or S-shaped contour, with the wave-shaped or S-shaped contours of the two ring grooves being arranged offset with respect to one another. The ring grooves can hereby be spot drilled individually through the feed bores in the bulges without the respective other ring groove being connected as well. The wave-shaped design can advantageously be effected in casting technology, for example by insertion of correspondingly shaped tube cores. 
         [0018]    Alternatively or additionally, preferably approximately tubular insert sleeves with infeed apertures open to a respective one ring passage can advantageously be inserted into the feed bores connected to the ring passage. In this connection, the feed bores can as such penetrate both ring grooves so that a wave-shaped or S-shaped ring passage contour can be dispensed with. 
         [0019]    The at least one ring groove can be made open toward an inner peripheral surface of the housing, at which inner peripheral surface the rotor and/or the drive shaft connected to it is/are radially supported to ensure a lubrication at this support position. 
         [0020]    Alternatively, the ring groove can also be made closed completely in the interior of the housing and be connected via feed bores to at least one support of the rotor and/or the drive shaft connected to it. 
         [0021]    It has proved to be particularly advantageous for the lubrication of the axial plain bearing surfaces for transverse bores to be provided in the meshing noses of the rotor which open onto the axial plain bearing surfaces of the rotor. Oil can thereby flow from the one side of the rotor to the other in order to ensure a sufficient oil supply on both sides of the meshing noses of the rotor on which the axial plain bearing surfaces are provided. 
         [0022]    In a further development of the invention, plate-shaped recesses can be formed in the axial plain bearing surfaces of the rotor which form pressure pockets or better distribute the oil located there. These plate-shaped recesses are in particular arranged on the side of the rotor which intercepts the tensile forces introduced from the elevating plant. The plate-shaped recesses are advantageously in communication with the transverse bores in the meshing noses of the rotor so that they are fed with oil from the other side of the rotor. 
         [0023]    To introduce sufficient oil into the aforesaid transverse bores in the meshing noses of the rotor, distributor grooves connected to the transverse bores can be provided in the axial plain bearing surfaces, with these distributor grooves in particular being arranged on the side of the rotor disposed opposite the aforesaid plate-shaped recesses. 
         [0024]    To ensure a circulating oil pressure and thus an exchange of oil due to circulating pressure differences in the radial plain bearing surfaces, in a further development of the invention, axial grooves for the oil distribution can be provided—in particular offset by 180—in the radial plain bearing surfaces of the housing and/or of the rotor and/or of the shaft connected thereto. 
         [0025]    An oil guiding system or passage system is advantageously also provided for the lubrication of the ring piston for this. To transport the oil onto the axial surfaces of the ring piston, the ring piston thickness can reduce toward the edges of the outer toothed arrangement, with bevels, for example in the form of a chamfer toward the outer meshing noses, in particular being provided at the rims of the axial plain bearing surfaces of the ring piston. This facilitates the oil being able to move onto the plain bearing surfaces of the ring piston. The outwardly conical shape of the piston moreover ensures a flooding and centering of the ring piston. Furthermore, the parallelism and angle defects have a smaller effect. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention will be explained in more detail in the following with reference to preferred embodiments and to associated drawings. There are shown in the drawings: 
           [0027]      FIG. 1  is a schematic sectional view through a rotary motor in accordance with a first preferred embodiment of the invention in which the rotor of the motor received in the housing itself forms that motor connector connectable with the elevating plant; 
           [0028]      FIG. 2  is a schematic sectional view of a hydraulic rotary motor in accordance with an alternative embodiment of the invention in which the motor connector is formed for the fastening of a elevating plant of a motor shaft to which the rotor is rigidly connected; 
           [0029]      FIG. 3  is a schematic plan view of the ring piston with an inner and outer toothed arrangement and the rotor cooperating therewith and the housing of the rotary motors cooperating therewith from  FIGS. 1 and 2 ; 
           [0030]      FIG. 4  is an axial section through the rotor of the rotary motors of  FIGS. 1 and 2  which shows the transverse bores in the meshing noses for the oil supply of the plain bearing surfaces; 
           [0031]      FIG. 5  is a plan view of the meshing noses of the rotor and the distributor grooves introduced therein and the transverse bores connected thereto; 
           [0032]      FIG. 6  is a plan view of the side of the meshing noses of the rotor on the opposite side in comparison with  FIG. 5  which shows the plate-like recesses introduced therein and the transverse bores connected thereto; 
           [0033]      FIG. 7  is an axial section through the ring piston of the motors from  FIGS. 1 and 2  which shows the ring piston thickness reducing toward the outer contour of the ring piston; 
           [0034]      FIG. 8   1 s a sectional view along the line A-A in  FIG. 2  which shows lubrication grooves formed in the bearing cover of the housing; 
           [0035]      FIG. 9  is a sectional view of the rotary motor in accordance with  FIG. 2  which shows a relief bore between an axial bearing surface of the motor shaft and an oil leakage space between the ring piston and the housing; 
           [0036]      FIG. 10  is a sectional view of the housing in the region of a pressure passage for the feeding of the displacement chambers for a rotary direction which shows a ring distributor passage in the housing and oil feed passages in communication therewith into which the sleeve-like inserts with infeed bores are inserted; 
           [0037]      FIG. 11  is a sectional view of the housing similar to  FIG. 10  along the line A-A in  FIG. 13 , with the ring distributor passages lying above one another each being made offset in wave shape in the embodiment in accordance with  FIG. 11  so that the oil feed bores can be spot drilled directly into the respective ring distribution passage; 
           [0038]      FIG. 12  is a sectional axial section through the housing cover which shows the position of the ring distribution passages from  FIG. 11  and the connection of the lower ring distributor passage via a feed bore to the axial plain bearing surface of the rotor; 
           [0039]      FIG. 13  is a sectional axial section of the housing similar to  FIG. 12  which shows the connection of the upper ring distributor passage to the axial plain bearing surface at the rotor; 
           [0040]      FIG. 14  is a schematic sectional view of the housing with a ring distributor passage in accordance with an alternative embodiment of the invention which is not open to the inner cut-out of the housing, whereby corresponding seals are no longer required; 
           [0041]      FIG. 15  is a schematic sectional view of a rotary motor similar to  FIG. 2 , with here the oil supply of the plain bearing surfaces for the rotor or the shaft being fed from a pressure passage for the pressure supply of the elevating plant connectable to the rotary motor; and 
           [0042]      FIG. 16  is a schematic sectional view of a rotary motor similar to  FIG. 15 , with here the rotor side loaded on tensile forces introduced from the elevating plant being fed with pressure oil from the pressure supply passage which is provided for the supply of the elevating plant attachable to the rotary motor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    The rotary motor  1  shown in  FIG. 1  comprises a substantially cup-shaped housing  2  which consists in the drawn embodiment substantially of three parts, namely the motor head  3 , the rotor housing ring  4  and the bearing cover  5 . As  FIG. 1  shows, the bearing cover  5  is set on the rotor housing ring  4  and is screwed via screw connections  6  to the radially projecting flange  7  of the motor head  3  so that an annular rotor gap  8  is formed between the bearing cover  5  and the motor head  3 . The ring piston  9  is received in the said rotor gap  8  as is—radially inside this ring piston  9 —the substantially likewise disk-shaped rotor  10 . In more precise terms, a disk section  11  of a rotor/shaft unit is seated with an exact fit between the bearing cover  5  and the motor head  3 . Shaft sections  12  and  13  are shaped in a projecting manner at both sides of the disk section  11  and their outer periphery runs with an exact fit on inner peripheral surfaces of the bearing cover  5  or of the motor head  3 . 
         [0044]    As  FIG. 3  shows, the ring piston  9  is provided with an inner toothed arrangement  14  and with an outer toothed arrangement  15  and interacts therewith, on the one hand, with an outer toothed arrangement  16  of the rotor  10  and, on the other hand, with an inner toothed arrangement  17  of the rotor housing ring  4  in a manner known per se. The ring piston  9  can be driven in an orbiting gyratory manner by pressure fluid charging of the displacement chambers  18  formed between the ring piston  9  and the rotor  10  or the rotor housing ring  4 , whereby said ring piston drives the rotor  10  via the toothed arrangements relative to the rotor housing ring  4  and thus to the housing  2  as is described in detail in DE 33 42 131 A1 to which reference is made in this respect. 
         [0045]    As  FIG. 1  shows, the rotary motor fully dispenses in this embodiment of the invention with a separate motor shaft which is replaced by the rotor  10 . The end face  19  of the shaft section  13  of the rotor  10  exiting the housing  2  forms a motor connector  20  to which an elevating plant  21  such as an excavator grab can be attached. For this purpose, bolts  22  are provided in the rotor  10 . The other motor connector  23  is formed in a manner known per se by the motor head  3  of the housing  2  with which the rotary motor  1  can be attached, for example, to the arm of an excavator. 
         [0046]    As  FIG. 1  furthermore shows, the rotor  10  is made as a ring. A rotary brake  25  in the form of a multi-disk brake is arranged in the hollow inner space  24  of the rotor  10  and does not extend axially beyond the rotor and ensures a particularly compact design of the motor. The inner peripheral surface of the rotor  10  supports, for example via a spline profile, a set of the multiple disks of the rotary brake  25  whose other set of multiple disks is rotationally fixedly supported at a sleeve-like catch piece  26  which is itself likewise fastened rotationally fixedly to the housing  2 . The multiple disks of the rotary brake  25  can be pressed onto one another via a brake piston  27  in the intermediate space between the said catch piece  26  and the rotor  10  and the braking effect can hereby be effected. 
         [0047]    As  FIG. 1  shows, the rotary motor  1  dispenses fully with roller bearings. The forces and torques introduced by the elevating plant  21  are intercepted solely via the rotor  10  itself and the plain bearings supporting it at the housing  2 . The rotor  10  comprises for this purpose, on the one hand, axial plain bearing surfaces  28  and  29  which are formed by the oppositely disposed flat sides of the disk section  11  of the rotor  10 . On the other hand, the rotor  10  comprises radial plain bearing surfaces  30  and  31  which are formed by the outer peripheral surfaces of the shaft sections  12  and  13  of the rotor  10 . It is understood that corresponding plain bearing surfaces are provided at the housing  2  which cooperate with the said axial plain bearing surfaces  28  and  29  and with radial plain bearing surfaces  30  and  31 . 
         [0048]    Roller bearings are also dispensed with in the embodiment of the rotary motor  1  shown in  FIG. 2 . The forces and torques introduced from the elevating plant  21  are also intercepted here solely via plain bearings. The rotor  10  is in particular also axially supported at the housing  2  here via axial plain bearing surfaces  28  and  29  on the flat sides of its disk section  11 . In contrast to the embodiment of  FIG. 1 , the ring-shaped rotor  10  is, however, pressed onto a drive shaft  32  in this embodiment. The rotor  10  is rigidly connected to the drive shaft  32  so that both axial forces and bending torques and radial forces from the drive shaft  32  are introduced into the rotor  10  or are, vice versa, intercepted by the latter. The radial plain bearing surfaces  30  and  31  are provided in the embodiment of  FIG. 2  at the shaft sections  12  and  13  of the drive shaft  32  which axially adjoin the rotor  10 . Since the rotor  10  is seated on the drive shaft  32  in the embodiment of  FIG. 2 , it is not the rotor  10  itself which forms the motor connector for the fastening of the elevating plant. The motor connector  20  is formed by the end face  19  of the end of the drive shaft  32  exiting the housing  2  (cf.  FIG. 2 ). 
         [0049]    For the oil supply of the axial and radial plain bearing surfaces  28 ,  29 ,  30  and  31 , various oil passages are formed in the rotor  10  and in the housing  2  through which the oil is guided in a sufficient amount to the said plain bearing surfaces. 
         [0050]    On the one hand, such passages are provided in the rotor  10  in order to have sufficient oil on both axial plain bearing surfaces  28  and  29 . As  FIG. 4  shows, transverse bores  34  are provided in the meshing noses  33  of the rotor  10  which connect the axial plain bearing surface  28  on the upper side of the rotor  10  to the axial plain bearing surface  29  on the lower side of the rotor  10 . Oil can thereby be guided onto the lower bearing surface from the upper side of the rotor  10 . In addition, a pressure compensation or a higher pressure can be generated on the lower axial plain bearing surface  29 , whereby the operating loads are compensated to a specific degree which are introduced by tensile forces via the elevating plant  21 . 
         [0051]    As  FIG. 5  shows, distributor grooves  35  are provided in the axial plain bearing surface  28  on the upper side of the rotor  10  which extend approximately tangentially to the peripheral direction and are connected to the aforesaid transverse bores  34 . This improves a continuous oil flow to the lower support position and a corresponding pressure build-up. In a further development of the invention, the distributor grooves  35  are made very narrow so that the axial pressure remains low. The width of the distributor grooves  35  can amount to less than 1 mm. 
         [0052]    On the side opposite the distributor grooves  35 , the transverse bores  34  passing through the meshing noses  33  open into plate-shaped recesses  36 , as  FIG. 6  shows. These large-area pressure pockets improve the lubrication of the lower axial plain bearing surface  29  and can support or ensure a sliding of the rotor  10  with respect to the bearing cover  5  even at higher operating loads. The axial plain bearings can hereby be relieved hydraulically against the main direction of force, i.e. the tensile forces introduced via the elevating plant  21 . 
         [0053]    It is possible by the oil supply of the axial plain bearing surfaces  28  and  29  from the inside via the said transverse bores  34  to form the outer contour of the rotor  10  and the inner contour of the ring piston  9  without chamfers or other bevels. Such bevels or slight chamfers toward the pressure chamber would likewise per se ensure a pressure supply of the plain bearing surfaces  28  and  29  and ensure a certain sliding of the rotor  10  or of the ring piston  9  in the oil bath. On the other hand, this results in a leak in the chamber region which is avoided in the sharp-edge design. Nevertheless, the inner supply of the axial plain bearing surfaces  28  and  29  via the transverse bores  34  ensures that no interruption of the oil film occurs. 
         [0054]    The plain bearing surfaces  28  and  29  are advantageously fed via feed bores from pressure passages which are provided either for the pressure supply of the displacement chambers  18  or for the pressure supply of an attached elevating plant in the housing  2 . For this purpose, ring distributor passages  37  and  38  are advantageously introduced in the motor head  3 , as  FIGS. 10 to 14  show, which are arranged at different vertical levels and are in each case connected to one of the oil supply passages for in each case one direction of rotation. As  FIGS. 12 and 13  show, feed bores  39  and  40  lead from the said ring distributor passages  37  and  38  to the axial plain bearing surface  28 . The oil led there can then be guided in the previously described manner via the transverse bores  34  formed in the meshing noses  33  to the oppositely disposed axial plain bearing surface  29 . 
         [0055]    As  FIG. 10  shows, the ring distributor passages  37  to  38  on the inner peripheral surface of the housing  2  which supports the radial plain bearing surface  30  of the rotor  10  are made open toward the inner side so that they can be introduced by mechanical working and ensure a lubrication of the radial plain bearing surfaces there. Every second feed bore  39  to  40  can be connected by spot bores to the respective ring distributor passage  37  or  38  respectively. In this process, the feed bores  39  and  40  can be drilled through or into both ring distributor passages  37  and  40  and then sleeve-shaped inserts  50  can be inserted into the feed bores which have an infeed bore at a respectively matching height and thus connect the respective feed passage  39  and  40  to the desired ring distributor passage  37  or  38 , cf.  FIG. 10 . 
         [0056]      FIG. 11  shows an alternative embodiment of the ring distributor passages  37  to  38 . Here, each ring distributor passage  37  or  38  is made in a technical casting manner such that the feed bore  39  to  40  can be directly spot drilled offset to the respective other passage.  FIG. 12  and  FIG. 13  show this in section. As  FIG. 11  shows, the two passages each have a shaft contour offset to one another so that a respective bulge  51  of the one ring distributor passage  37  can be spot drilled without hitting the other ring distributor passage  38 . 
         [0057]    Alternatively to the inwardly open design, the ring distributor passages  37  and  38  can also be made closed completely in the interior of the housing  2 , as  FIG. 14  shows, e.g. by a suitable casting technology. This has the advantage that no seals have to be provided on the inner peripheral surface of the housing  2 . The ring distributor passages  37  and  38  are here also advantageously made in wave shape and directly spot drilled so that the feed bores  39  and  40  communicate with the respective ring distributor passage  37  or  38 . 
         [0058]    Alternatively or additionally, a lubrication of the plain bearing surfaces can also take place from the pressure passage  41  in the housing  2  which is provided for the pressure supply of the elevating plant  21  attached to the rotary motor  1 . As  FIG. 15  shows, a pressure lead  42  can, for example, charge a ring space between the housing and the drive shaft  32  which thereby acts so-to-say as a piston and effects a pressure relief. The pressure lead  42  is preferably connected to the closing force pressure lead  41  so that when closing force is applied, the pressure relief is ensured. 
         [0059]    As  FIG. 9  shows, an oil supply of the plain bearing surfaces can also take place from the oil leakage space  43  which is formed between the ring piston  9  and the rotor housing ring  4 . The oil leakage space  43  is advantageously charged with a relatively low pressure, which can actually serve the foaming of the oil and can be effected via control valves, but advantageously also ensures the lubrication. 
         [0060]    The axial grooves  44  which accept the shaft sections  12  and  13  of the rotor  10  or of the drive shaft  32  are advantageously arranged offset to one another by 180—in the inner peripheral surfaces of the bearing cover  5  and/or of the motor head  3 . It can thereby be achieved that an oil exchange takes place in the radial plain bearing surfaces  30  and  31  by the peripheral oil pressure. 
         [0061]    In order also to achieve a lubrication of the ring piston  9 , provision can be made in an advantageous further development of the invention, as  FIG. 7  shows, that the thickness of the ring piston  9  reduces toward its outer contour. A corresponding flattening or beveling  45  ensures that oil from the oil leakage space  43  can spread over the upper side or lower side of the ring piston  9 . The ring piston  9  so-to-say is flooded and is sufficiently lubricated at its upper side and lower side. In addition the parallelism and angle errors have a lower effect.