Abstract:
The invention concerns a technically optimized radial piston engine comprising a cam ring and a cylinder block arranged so as to rotate about an axis of rotation relative to the cam ring and having a plurality of cylinders oriented in the radial direction of the cylinder block. A piston capable of being radially displaced is located in each cylinder, resting on the cam ring via a roller. Said roller is mounted on the piston so as to rotate about an axis parallel to that of the cylinder block and rests axially, relative to its axis of rotation in the cylinder, against roller guides arranged on its surfaces. Said radial piston engine is characterized in that the roller guides are integrally mobile with the roller associated with them, in the piston stroke direction, and thereby driven by the roller both when the piston performs a loaded stroke and an idle stroke, without any contact occurring between the roller guides and the cam ring. The pistons are rotationally fixed by a torsional stop which is separate from the roller guide.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a radial piston engine with roller guides for axial guidance of the rollers, via which the pistons are braced against the cam ring. 
     2. Discussion of the Background 
     From British Patent GB B 2238086 there is known a radial piston engine corresponding to the preamble of claim  1 , wherein the object was to reduce the manufacturing complexity previously associated with axial positioning of the rollers and thus to lower the manufacturing and assembly costs. This object was supposedly achieved in that, in each of the spaces between the roller end faces and the cylindrical inside face as the roller guide, there is disposed a wedge piece, whose cross section viewed in piston displacement direction is a circular segment, and which positions the roller axially in the cylinder relative to the cam. ring. The wedge pieces disclosed in the cited patent can be divided substantially into three different designs. 
     In a first design, each wedge piece has on the side facing the roller a plane surface which bears on the end face of the roller and on the side facing away from the roller a cylindrical surface which is in contact with the inside face of the cylinder. In addition, this wedge piece is accommodated in the space between roller, piston and cylindrical inside face, without being rigidly connected to any of these components. By virtue of the fact that the wedge piece is freely movable in piston displacement direction relative to the roller, the piston urges the wedge pieces toward the cam ring during a load stroke. In the process, the wedge pieces do not yet come into contact with the cams formed on the cam ring. In the ensuing idle stroke of the piston, however, the wedge pieces strike the cams formed on the cam ring. This recurring striking contact between the cams and the wedge pieces as well as the friction occurring therebetween can lead to severe wear of the wedge pieces. A further disadvantage of this design is that the width of the cam ring must be at least sufficiently large that the cam ring in addition to the roller also provides a contact face for the two laterally disposed wedge pieces. Aside from large total weight of the radial piston engine, a broad cam ring results in high manufacturing costs due to the greater manufacturing complexity associated with precision machining of the cam ring. 
     In a second design, each of the two wedge pieces has on the side facing the roller a driver-like projection, which extends toward the other wedge piece in an opening provided in the piston between piston and roller. Since in this case the wedge pieces are driven back into the cylinder by the roller during an idle stroke of the piston, striking contact between the wedge pieces and the cams basically cannot occur. Due to the high relative velocity between the roller and the driver-like projections of the wedge pieces in contact with the outside circumference of the roller, however, severe abrasion can take place on the driver-like projections. With increasing abrasion of the driver-like projections, the space available for play of the wedge pieces in piston displacement direction could ultimately increase to the point that striking contact could occur between the wedge pieces and the cams. A further disadvantage of this design is that driver-like projections must be formed on the roller guides and recesses must be formed on the piston, thus increasing the manufacturing complexity and thus the manufacturing costs. 
     In addition, the friction between the roller and the wedge pieces in the two foregoing designs occurs over the entire end face of the roller. This relatively large-area frictional contact necessitates precision machining of the friction faces of both components, once again resulting in high manufacturing costs. 
     At that time a further assumption was that, by virtue of the recurring contact of the rollers with the cam ring, the rollers and thus the respective piston automatically assume a particular angular position in the cylinder or relative to the cam ring, which is critical for reliable operation of the radial piston engine. In certain cases, however, for example during initial operation of the radial piston engine, when hydraulic fluid is fed to the cylinders for the first time, it is conceivable that the pistons and thus the rollers may be inserted so far into the respective piston that contact between roller and curved path does not yet occur. To ensure the necessary angular position of the piston in the cylinder in those cases, one of the two wedge pieces has, in a third design, on the side facing the cylindrical inside face, an elongated slot, into which a bolt, clamp or the like extending through the cylinder wall engages and in this way prevents turning of the piston in the cylinder and thus of the roller relative to the cam ring. The presence of the slot leads to weakening of the wedge piece in question, however, and thus to shortening of the useful life of the wedge piece, which is subjected to severe stresses and strains during operation of the radial piston engine. In addition, sliding contact takes place between the wedge piece and the bolt or clamp, which appears disadvantageous as regards good roller guidance. Furthermore, such a structural feature means high manufacturing complexity. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the disadvantages encountered in conventional radial piston engines, the object of the present invention is therefore to provide an optimally engineered radial piston engine, which is characterized by greater manufacturing simplicity and at the same time functionally reliable operation. 
     This object is achieved by the inventive subject matter according to the features of claim  1 , which is characterized in particular in that the roller guides disposed on the front sides of the rollers are rigidly connected to the respective roller with respect to sliding in piston displacement direction. 
     Since the respective roller urges the roller guides in piston displacement direction, in other words both during the load stroke and during the idle stroke, the roller guides can be dimensioned such that they do not project beyond the outside circumference of the respective roller, thus ensuring that striking contact does not take place between the roller guides and the cam ring. This ultimately leads to longer useful life of the roller guides and thus to functionally reliable operation of the radial piston engine on the whole. In addition, material economies are achieved in the manufacture of the roller guides. 
     If the roller guides do not come into contact with the cam ring, the width of the cam ring can be further reduced to a width which corresponds at most to the width of the rollers. In this way, not only is the total weight of the radial piston engine lessened, but also manufacturing complexity and thus the manufacturing costs are considerably reduced with regard to precision machining of the curved paths of the cam ring. 
     By suitable structural measures, such as by formation of a cylindrical projection on the roller guide, which projection is inserted in a corresponding recess on the front side of the roller, the relative velocities at the friction faces of roller and roller guides and thus the wear of the two components can also be reduced. Because of the reduced wear, the play developed between roller and roller guides is kept to a minimum, even after prolonged operating time. This contributes to functionally reliable and dependable operation of the radial piston engine on the whole. 
     Further advantageous features of the inventive radial piston engine are subject matter of the dependent claims. 
     The roller and roller guides can be rigidly connected with respect to sliding in displacement direction by simple manufacturing techniques. For example, the roller guides can be provided on the side facing the end face of the roller with a cylindrical projection, which is insertable into a central cylindrical recess formed on the end face of the roller. Likewise, it would naturally also be conceivable for the roller guides to be provided on the side facing the front side of the roller with a recess into which a projection formed on the front side of the roller is insertable. Of course, the opening and the projection engaged therewith could also have conical shape. If the diameter of the openings and projections are dimensioned such that they are small compared with the outside diameter of the roller, or in other words such that the projections and the openings are concentrated on a central region around the axis of rotation of the roller, and if the projections are engaged with the respective openings in such a way that play is present between the annular face of the roller around the opening and of the face around the projection of the roller guide, the circumferential velocities present at the outside circumference of the projection and at the inside circumferential wall of the opening during operation of the radial piston engine are reduced, as is therefore the relative velocity between roller and roller guides. Moreover, since no friction occurs at the two spaced-apart faces of roller and roller guide, reduction of frictional abrasion of both components is achieved. 
     The surfaces of the roller guides in contact with the cylindrical inside face preferably have cylindrical shape for simplicity, thus achieving optimal guidance of the piston-roller system in the cylinder. Since the roller is normally not subjected to compressive loads in axial direction, it would also be conceivable, however, to give the surface of the roller guide bearing on the cylindrical inside face rotationally symmetric shape or to construct it as a spherical segment relative to the axis of rotation of the roller. In this case, rigid connection between roller guide and roller would even be possible both in piston displacement direction and in the direction of rotation of the roller. This would have the advantage that, during operation of the radial piston engine, friction between roller and roller guides would no longer take place and the friction occurring between roller guide and cylindrical inside face would be considerably reduced. 
     Heretofore it has been assumed that the roller is constantly in contact with the curved paths of the cam ring, whereby the angular position of the piston in the cylinder and accordingly the orientation of the roller relative to the curved path is automatically predetermined. As already explained in the introduction, however, it is possible for the contact between roller and cam ring to be separated. In this case it is possible according to the present invention to prevent turning of the piston in the cylinder by means of an antirotation device disposed separately from the roller guide and thus to maintain a particular orientation of the roller relative to the cam ring. 
     For this purpose, the piston can be provided on the end portion facing away from the roller with a flattened part oriented perpendicular relative to the axis of rotation of the cylinder block, which flattened part bears on a corresponding contact face of the antirotation device, thus unambiguously predetermining the angular position of the piston in the cylinder and of the roller relative to the curved path. Another effective expedient has proved to be providing the cylinder with at least two cylinder portions of different inside diameters and the piston accordingly with at least two piston portions of different diameters matching the corresponding cylinder diameters. In this case, the antirotation device is provided in the cylinder portion with the smaller inside diameter and the flattened part is provided accordingly on the piston portion with the smaller diameter. By this expedient, on the one hand a large face for admission of pressure is retained on the piston and on the other hand only little material is removed from the piston in order to form the flattened part. The additional antirotation device creates better guidance of the piston in the cylinder compared with the conventional antirotation device mentioned in the introduction, since according to the present invention large-area sliding contact takes place between piston and antirotation device. 
     The antirotation device preferably has a cross section which, viewed in piston displacement direction, is a circular segment, with an arc corresponding to the cylindrical inside face and a chord corresponding to the flattened part. 
     Since the cylinder block in any case is normally provided with axial inlet ports, through which the hydraulic fluid enters the respective cylinder spaces, the manufacturing complexity with regard to fixing the antirotation device in the cylinder can be reduced in that the antirotation device is fixed in the cylinder by means of a pin, which is inserted through the inlet port into a blind hole in the cylinder block aligned with the inlet port. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     Further features and advantageous embodiments of the present invention will become clear from the description hereinafter of preferred embodiments with reference to the drawing, wherein 
     FIG. 1 shows a longitudinal section of a preferred embodiment of the inventive radial piston engine; 
     FIG. 2 shows a cross section through the cylinder block in FIG. 1 along line II—II; 
     FIG. 3 a  shows a section on larger scale through the cylinder block in FIG. 2 along line III—III; 
     FIG. 3 b  shows a perspective view of the piston; 
     FIG. 4 shows a section through the cylinder block along line IV—IV in FIG. 1; 
     FIG. 5 shows a perspective view of the roller guide; 
     FIG. 6 shows a section through the cylinder block along line VI—VI in FIG. 1; 
     FIG. 7 shows a perspective view of the antirotation device; 
     FIGS. 8 a  and  8   b  show modifications of the roller guide in FIG. 5; 
     FIGS. 9 a  and  9   b  show modifications of the connection between roller guide and roller in FIG. 5; and 
     FIGS. 10 a  and  10   b  show modifications of the cylinder block in FIG. 3 a.   
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1 to  6  there will be described a preferred embodiment of the inventive radial piston engine. Radial piston engine  2  comprises, as illustrated in FIG. 1, substantially two housing parts  4  and  6  as well as a cam ring  8  disposed between the two housing parts  4  and  6 . The two housing parts  4  and  6  and cam ring  8  are coaxially connected to one another in fluid-tight manner by means of bolts  10 . On the inside face of cam ring  8  there is formed a curved path  12  with a plurality of cams  14 , as can be seen in particular in FIG.  2 . 
     Inside cam ring  8  there is disposed a cylinder block  18  which can rotate around a longitudinal axis of rotation  16 . As is evident in FIGS. 1 and 2, cylinder block  18  is provided with a central opening  20  having an internal toothing. In this opening  20  there is accommodated in axial sliding relationship an end portion  22  of a driven shaft  24 , which is equipped with an external toothing corresponding to the internal toothing of opening  20 . By means of a bearing assembly  30 , driven shaft  24  is mounted to rotate relative to the two housing parts  4  and  6  and to cam ring  8 . Bearing assembly  30  comprises two tapered roller bearings  32  and  34 , which are mounted in housing part  4  and can transmit large axial and radial forces. The other end portion  26  of driven shaft  24  projects out of housing part  4  and is provided with a shaft flange  28  for fastening to a drive element (not shown) of a device to be driven, such as a gear of a loader. 
     In cylinder block  18  there is also formed a plurality of cylinders  36  directed radially outward in a star pattern relative to axis of rotation  16 , which cylinders have cylinder axis  37  perpendicular relative to axis of rotation  16 . As is evident in the enlarged illustration in FIG. 3 a , cylinder  36  has a cylinder portion  38  of large inside diameter disposed radially outward relative to axis of rotation  16 , as well as a cylinder portion  40  with small inside diameter disposed radially inward. Cylinder portion  38  is open at the substantially cylindrical outside circumferential face  42  of cylinder block  18 . Furthermore, there is formed in cylinder block  18  an inlet port  43 , which is parallel to longitudinal axis of rotation  16  and opens into cylinder portion  40 , and via which hydraulic fluid is supplied and removed during operation of radial piston engine  2 . 
     In cylinder  36  there is accommodated a piston  44  which, as shown in FIG. 3 b , has piston portions  46  and  48 . Piston portion  46  has a diameter corresponding substantially to the inside diameter of cylinder portion  38 . Piston portion  48  has on its outside circumference two flattened parts  48   a  and  48   b  which, as is evident in FIG. 6, are oriented perpendicular to axis of rotation  16 . The diameter of the outside circumference of piston portion  48  corresponds to the inside diameter of cylinder portion  40 . Flattened part  48   b  defines a contact face, which bears on a correspondingly provided contact face  50   b  of an antirotation device  50 , to be described in more detail hereinafter. Flattened portion  48   a  faces inlet port  43 . 
     When cylinder  36  is supplied with hydraulic fluid via inlet ports  43  during operation of radial piston engine  2 , pistons  44  are pressurized selectively to the effect that they execute a displacement movement toward cam ring  8 . In the process they are each braced via a corresponding roller  54  against curved path  12  formed on cam ring  8 . As shown in FIG. 1, axial width B of the cam ring in this embodiment of radial piston engine  2  corresponds substantially to the axial length of rollers  54 . On the end portion of each piston portion  46  facing cam ring  8  there is formed a bearing  56 , in which there is accommodated the respective roller  54 , mounted to rotate relative to piston  44  around an axis of rotation  58 . 
     As shown in FIGS. 1,  3   a ,  4  and  5 , a roller guide  60  is disposed at each of the two front sides  54   a  and  54   b  of roller  54 , whereby the axial position of roller  54  in cylinder  36  and thus relative to piston  44  and curved path  12  is predetermined. Roller guides  60  are each disposed in a space formed between end faces  54   a  and  54   b  of roller  54 , piston  44  and the cylindrical inside face of cylinder  36 . FIG. 5 shows a perspective view of roller guide  60  which, viewed in piston displacement direction, has a cross section substantially in the form of a circular segment. On the chord side facing front side  54   a  or  54   b  of roller  54 , each roller guide  60  has a cylindrical projection  62  which is axial relative to axis of rotation  58  and which is engaged with a corresponding central recess  54   c  or  54   d  on front sides  54   a  and  54   b  of roller  54 . Cylindrical arc side  63  of each roller guide  60  bears on the cylindrical inside face of cylinder  36 . The length of axial projection  62  is somewhat greater than the depth of recess  54   c  and  54   d , and so play exists between the face of roller guide  60  around central projection  62  and each annular face on front sides  54   a  and  54   b  of roller  54  around central recess  54   c  and  54   d.    
     By virtue of the type of connection of roller guides  60  with roller  54  described hereinabove, roller guides  60  are driven in piston displacement direction by respective roller  54  during operation of radial piston engine  2 , or in other words during a displacement movement of the piston. Since, as described hereinabove, the width of the cam ring corresponds to the length of the rollers, striking contact between the roller guides and the cam ring does not occur during operation of the radial piston engine according to this embodiment, regardless of whether the roller guides project beyond the roller in piston displacement direction. In addition, the wear of both components due to the relative velocity that occurs between roller guides and roller during operation of the radial piston engine can be reduced considerably, since the friction between the two components occurs in a range in which the relative velocity is quite low. 
     As is evident in FIG.  6  and has already been mentioned hereinabove, there is provided at the cylindrical inside face of cylinder portion  40  opposite inlet port  52  a so-called antirotation device  50 , which has the function of preventing turning of piston  44  in cylinder  38  around a cylinder axis  37 . The critical factor here is that a particular angular position of piston  44  relative to cylinder axis  37  and thus of roller  54  relative to curved path  12  is maintained. Antirotation device  50  is fastened to cylinder block  18  by means of a pin  76 , such as a tapered pin, straight pin or grooved pin in the manner shown in FIG. 3 a  or FIG.  6 . FIG. 7 shows a perspective view of antirotation device  50  which, viewed in piston displacement direction, has in common with roller guide  60  a cross section in the form of a circular arc, wherein cylindrical arc side  50   a  bears on the cylindrical inside face of cylinder portion  40  and chord side  50   b  bears on flattened part  48   b  formed on piston portion  48  of piston  44 . In contrast to roller guide  60 , which in this embodiment of the radial piston engine is provided with a projection  62 , there is formed in antirotation device  50  a cylindrical opening  78 , in which there is seated the part of pin  76  which projects out of blind hole  84 , disposed in cylinder block  18  in such a way as to be aligned with inlet port  43 . 
     Reference symbol  66  denotes a fluid-control unit, by means of which, via inlet ports  43 , hydraulic fluid is supplied to the respective cylinder spaces or removed from the respective cylinder spaces during operation of radial piston engine  2 . Fluid-control unit  66  is disposed in fluid-tight relationship in housing part  6  such as to rotate therewith. In order to be able to distribute hydraulic fluid to the respective cylinder spaces, fluid-control unit  66  is provided with two separate circumferential grooves  68  and  70 , which are in communication with fluid channels  72  and  74  respectively. During operation of radial piston engine  2 , fluid channels  72  and  74  come alternately into communication with axial inlet ports  43 , which are formed in cylinder block  18  and each of which communicates with one of the cylinder spaces. 
     During operation of radial piston engine  2 , pistons  44  are actuated by means of hydraulic fluid via fluid channels  68 ,  70 ,  72  and  74 , inlet ports  43  and the cylinder spaces in such a way that they are urged radially outward relative to axis of rotation  16 . In the process they are braced via the respective roller  54  against curved path  12  of cam ring  8 , whereby cylinder block  18  is ultimately caused to perform a rotary movement around axis of rotation  16 . The direction of rotation is selected by the mode of actuation. Because of the positive connection of driven shaft  24  to cylinder block  18 , a torque is transmitted to driven shaft  24 . This shaft is braced via tapered roller bearings  32  and  34  of bearing assembly  30 . A drive element such as a gear of a loader (not illustrated in more detail here), which is connected via flange portion  28  to drive shaft  24 , therefore receives a torque. 
     FIGS. 8 a  and  8   b  show modifications of the roller guides described in connection with the foregoing embodiment of the inventive radial piston engine. 
     Roller guide  90  illustrated in FIG. 8 a  differs from roller guide  60  shown in FIG. 5 in that, at the upper outside face facing cam ring  8 , it is rounded in a manner corresponding to the outside circumference of roller  54  and is designed to ensure that it does not project beyond the outside circumference of the roller in piston displacement direction. Since roller guide  90  in this case does not project beyond the outside circumference of roller  54 , and since in addition it is rigidly connected to roller  54  with respect to sliding in piston displacement direction, roller guide  90  could also be used—of course, only together with inventive roller  54 —for a conventional radial piston engine with a cam ring, in which the cam ring has a width which is greater than the length of roller  54 . 
     Whereas surfaces  63  of roller guides  60  in contact with the cylindrical inside face were of cylindrical structure hereinabove for the sake of simplicity, roller guide  92  shown in FIG. 8 b  is provided on the side facing the cylinder face with a surface  93  which is rotationally symmetric or has the form of a spherical segment relative to axis of rotation  58  of roller  54 . Since the roller and thus also the roller guides normally do not experience particularly large axial loads during operation of the radial piston engine, the service life of the roller guides should not be shortened by giving the structure of the roller guides the form of a spherical segment. In order constantly to achieve reliable axial positioning of the rollers in this case, however, it is necessary that the extent to which the pistons are displaced during operation of the radial piston engine is sufficiently limited that axis of rotation  58  of each roller  54  is still disposed inside the cylinder even at maximum piston displacement. This restriction is not necessary in the roller guides mentioned hereinabove, however, because they are in contact over a large area. 
     In the special case shown in FIG. 8 b , roller guides  92  could be connected positively and nonpositively to roller  54  not only in piston displacement direction but also in the direction of rotation of roller  54 , so that friction no longer develops between roller and roller guide. Because of the small, substantially only linear contact of roller guide  92  on the cylindrical inside face, the friction occurring between roller guide  92  and cylindrical inside face would also be considerably reduced. Since roller guides  90  and roller  54  then can no longer turn relative to one another, the positive and/or nonpositive connection between roller guide and roller could also be achieved in any other manner. It would even be conceivable to construct the roller and the roller guides in one piece, or in other words to provide the roller guides on the roller. 
     FIGS. 9 a  and  9   b  show further options for connecting the roller guides to the roller. 
     Whereas in the preferred practical example of inventive radial piston engine  2  described hereinabove there were formed on each roller guide a projection  62  and on the roller corresponding recesses  54   c  and  54   d , roller guide  94  according to FIG. 9 a  is provided with a recess  95  and roller  96  with a corresponding projection  97 . In this example also, play is present between the oppositely disposed faces on roller guide and roller around the recess or around the projection, whereby the friction developed between these components occurs in a range in which small relative velocities exist between roller and roller guides. However, the present invention is not limited merely to this arrangement; it would naturally also be conceivable for the roller guides to be directly in contact with the roller in the conventional sense, or in other words without play. 
     Roller guide  98  in FIG. 9 b  is characterized by a conical projection  99 , which is engaged with a corresponding central recess  101  of conical shape on roller  100 . In this case the roller guide is engaged with the roller without play but, as is also the case in the foregoing examples, the area of contact between roller  100  and roller guides  98  is relocated into a central region relative to axis of rotation  58 . 
     In the preferred embodiment there is provided an antirotation device  50 , which prevents turning of piston  44  in cylinder  36  and thus turning of roller  54  relative to curved path  12 . Since the rollers are normally constantly in contact with the curved path, however, whereby the angular position of the roller and thus of the piston is automatically determined, it is not absolutely necessary to provide an antirotation device. This case is shown in FIG. 10 a . Here the structure of the cylinder and piston is simplified substantially, since special manufacturing steps do not have to be performed either for piston  102  or for the cylinder block. 
     It is also possible by another relatively simple structural modification to the piston and cylinder block, however, as shown for example in FIG. 10 b , to provide an antirotation device  106  for piston  104  without having to form the piston and cylinder as stepped structures. 
     At this juncture it should be pointed out that all features described hereinabove, especially in connection with the geometry of the roller guide, the connection between roller guides and rollers, and also the antirotation device for the pistons, can be combined with one another to the extent technically possible. 
     The present invention therefore creates a technically optimized radial piston engine with a cam ring and a cylinder block, which is disposed to rotate relative to the cam ring around an axis of rotation and which has a plurality of cylinders aligned in the radial direction of the cylinder block. In each cylinder there is disposed a piston which can be displaced in radial direction, and which is braced via a roller against the cam ring. The roller is mounted in a bearing provided on the piston such that it can rotate around an axis of rotation parallel to the axis of rotation of the cylinder block while being braced axially in the cylinder relative to its axis of rotation via roller guides disposed at its front sides. The inventive radial piston engine is characterized in particular in that the roller guides are rigidly connected with the respective roller with respect to sliding in piston displacement direction and accordingly are urged in piston displacement direction by the respective roller both during a load stroke and during an idle stroke of the piston, whereby the roller guides do not come into contact with the cam ring.