Patent Publication Number: US-3874272-A

Title: Radial piston machine

Description:
United States Patent 1 1 [111 3,874,272 Bosch i 51 Apr. 1, 1975 RADIAL PISTON MACHINE Primary ExaminerWilliam L. Freeh [75] Inventor. Paul Bosch, Ludwigsburg, Germany Attorney g or Firm MiChael S. Striker [73] Assignee: Robert Bosch GmbH, Stuttgart,  
  Germany 22 Filed: July 18, 1973 ABSTRACT [21] Appl. No.: 380,164 A radial piston machine wherein the cylinder block rotates about a stationary pintle having in its external surface a high-pressure chamber and a low-pressure [30] Forelgn Apphcamn Priority Data chamber, and wherein the cylinder block has radially July 22, 1972 Germany .i 2236125 outwardly extending Cylinder bores travelling Seriatim in register with the chambers and with lands provided [52] US. Cl. 91/498 the pintle between the two Chambers The lands of [51] lllt. Cl. F0lb 13/06 the pintle are p i with recesses i the f of [58] Fleld of Search 91/487, 485, 6.5, 507 cutouts or cavities which are in temporary communi cation with successive cylinder bores when the cylin- [56] References C&#39;ted der block rotates so that the pressure fields which de- UNITED STATES PATENTS velop in the region of the recesses communicating 2.944529 7/1960 Wiggermann 9l/6.5 with cylinder bores containing pressurized fluid op- 3()82.696 3/1963 Henrichsen 91/487 pose radial movements of the cylinder block. The re- 3.i7i,36i 3/1965 Boulet 91/487 cesses in the lands of the pintle can be rep1aced or g I 5%3 provided in addition to recesses in the internal surface 1mm 3,520,229 7/1970 Slimm et a1 .7 9l/6.5 of the cylmder blocki FOREIGN PATENTS OR APPLICATIONS United Kingdom 91/498 14 Claims, 6 Drawing Figures FHENTEU APR 1 19?? SHEET 1 OF 2 RADIAL PISTON MACHINE BACKGROUND OF THE INVENTION The present invention relates to radial piston machines, and more particularly to improvements in radial piston machines of the type wherein a cylinder block having radially extending cylinder bores rotates about a stationary valve or pintle whose periphery is provided with a highpressure chamber and a low-pressure chamber.  
  It is already known to provide a radial piston machine with a pintle having in its external surface two arcuate chambers separated from each other by lands. The inner end portions of the cylinder bores orbit along a path which is adjacent to the chambers and to the lands so that each cylinder bore communicates first with one of the chambers, thereupon travels along one of the lands, then communicates with the other chamber, thereupon travels along the other land, and again communicates with the one chamber. A drawback of presently known radial piston machines of the just outlined character is that the forces which develop when a piston moves in the cylinder block radially inwardly, i.e., toward the inner end portion of the respective cylinder bore, tend to flex the pintle away from the respective inner end portion and simultaneously tend to move the adjacent portion of the cylinder block radially of and away from the pintle. At the same time, the portion of the cylinder block which is located opposite the piston dwelling in its inner end position tends to move nearer to the adjacent portion of the external surface on the pintle. While the liquid which fills the clearance between the internal surface of the cylinder block and the external surface of the pintle opposes such radial displacements of the cylinder block, its resistance is not always sufficient to insure accurate centering of the cylinder block so that pressurized liquid is likely to leak in the region where a piston assumes its inner end position and the losses due to friction between the cylinder block and the pintle opposite such region are extremely high.  
  It is further known to reduce the effect of forces which tend to move the cylinder block radially of the pintle by providing the lands between the high-pressure and low-pressure chambers of the pintle with recesses in the form of cutouts or cavities. The pintle contains a system of valve elements serving to connect the higher-pressure chamber with the recess or recesses which are located opposite a piston in its inner end position. This results in the establishment of highpressure fields which are capable of counteracting some but not all of the forces tending to move the cylinder block radially of the pintle. In addition to unsatisfactory neutralization of radial forces, the just described radial piston machine exhibits the serious drawback that the valve elements in the pintle contribute excessively to the initial and maintenance cost of the machine. The maintenance cost is high because the channels wherein the pressurized fluid flows between the high-pressure chamber and selected recesses are likely to be clogged by impurities in the fluid to thereby reduce the effectiveness of the centering action upon the cylinder block and to cause excessive wear upon the neighboring surfaces of the cylinder block and pintle.  
 SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved radial piston machine wherein the forces tending to move the cylinder block radially of the pintle are balanced or neutralized with greater accuracy and with a higher degree of reliability than in presently known machines.  
  Another object of the invention is to provide a novel and improved pintle and a novel and improved cylinder block for use in radial piston machines of the just outlined character.  
  A further object of the invention is to provide a radial piston machine whose pintle and cylinder block are simpler than in the aforementioned radial piston machines wherein the pintle is provided with valve elements, and wherein the balancing of radial forces acting on the cylinder block is achieved in a simpler, less expensive and more reliable way than in heretofore known machines.  
  An additional object of the invention is to provide a radial piston machine wherein the radial forces acting on the cylinder block are neutralized to such an extent that the combined area of surfaces provided on the pintle and serving to guide the cylinder block can be reduced sufficiently to greatly reduce losses due to fric tion when the cylinder block is caused to rotate relative to the pintle.  
  Still another object of the invention is to provide a radial piston machine which can stand longer periods of use than heretofore known machines because the wear upon the neighboring surfaces of the cylinder block and pintle iswa&#39; small fraction of such wear in conventional machines, and wherein the leakage of fluid between the cylinder block and the pintle is a small fraction of leakage in presently known machines.  
  One feature of the invention resides in the provision of a radial piston machine which can be used as a pump or as a motor and comprises a rotary cylinder block having a cylindrical internal surface and radially extending equidistant cylinder bores including end portions (e.g., in the form of round ports) terminating in the internal surface of the block, and a stationary valve or pintle having a cylindrical external surface surrounded by the internal surface of the cylinder block, a high-pressure chamber and a low-pressure chamber machined into the external surface in such positions as to register with and to be swept seriatim by the end portions of successive cylinder bores when the cylinder block rotates relative to the valve. The external surface of the valve includes two portions which constitute lands between the two chamber, and the lands are providcd with recesses in the form of cutouts or cavities which are offset relative to the chambers, as considered in the axial direction of the cylinder block. Each recess is in temporary communication with that cylinder bore whose end portion travels in the region of the respective land whereby the pressure fields which develop in the recesses communicating with the high-pressure chamber (by way of the end portions of the cylinder bores) are capable of at least partially counteracting the radial forces which tend to move the cylinder block toward or away from the valve.  
  The aforementioned recesses are more effective than the valve elements in the pintles of conventional radial piston machines but their machining into the external surface of the valve can be carried out at a fraction of the cost of such valve elements.  
  Another feature of the invention resides in the provision of recesses in the form of cavities or cutouts which are machined into the internal surface of the cylinder block to perform substantially the same function as the recesses in the lands of the valve. The recesses in the cylinder block can be provided in addition to or as a substitute for recesses in the lands of the valve.  
  The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved radial piston machine itself, however, both as of its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.  
 BRIEF DESCRIPTION OF THE DRAWING the cylinder block substantially as seen in the direction of arrow V in FIG. a.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. I and 2, there is shown a radial piston machine which comprises a housing 1 provided with a separable cover or lid 2. The cover 2 is formed with a bore 3 for a cylindrical valve or pintle 4 which is secured to the cover by means of a pin 3a. The pintle 4 is surrounded by a cylinder body or block 5 which is rigid (e.g., integral) with a shaft 7. The shaft 7 is driven by thc bloek 5 when the machine is operated as a motor, and the shaft 7 drives the block 5 when the machine is operated as a pump. A shoulder of the block 5 abuts against a bearing 6 mounted in the housing 1 and surrounding the shaft 7.  
  The block 5 is provided with radially extending cylinder bores 8 for pistons or plungers 9 each of which has a shoe l0 abutting against the cylindrical internal surface of a floating control ring 11 which surrounds the block 5. The pistons 9 are reciprocable in the respective cylinder bores 8 with minimal clearance. The inner part ofcach cylinder bore 8 is surrounded by a conical surface 12 and terminates in a circular end portion or port 13 as well as in two grooves 14, 15 which are disposed diametrically opposite each other with reference to the center of the respective port 13 and are located in a plane which includes the common axis of the cylinder block 5 and pintle 4.  
  The means for changing the position of the control ring 11 radially of the block 5 and for thereby changing the strokes of the pistons 9 comprises a nut 16 which is secured to and extends radially outwardly ofthe control ring 11, a spindle 17 which meshes with the nut 16 and is rotatable in a bell I8 ofthe housing I, and a hand wheel 19 which is secured to the outer end portion of the spindle 17. The latter is held against axial movement so that, when the hand wheel 19 is rota ed, the nut 16 moves the control ring 11 radially oft e cylinder block 5 and thereby changes the strokes of the pistons 9. A helical spring 20 reacts against the housing 1 and biases the control ring 11 upwardly, as viewed in FIG. 1, i.e., in the axial direction of the spindle 17.  
  The pintle 4 is formed with two axially parallel holes 23, 24 one of which terminates in an inlet and the other of which terminates in an outlet for a fluid medium, e.g., oil. The inner end portions of the holes 23, 24 respectively communicate with arcuate control chambers 21, 22 which are machined into the cylindrical external surface of the pintle 4 and register with the cylinder bores 8. Thus, when the cylinder block 5 rotates about the pintle 4, successive ports 13 sweep past the control chambers 21, 22 so that the pistons 9 can draw fluid into the respective cylinder bores 8 while moving radially outwardly and that the pistons can expel fluid from the respective bores 8 during movement toward the axis of the pintle 4. The control chambers 21, 22 are of identical length, as considered in the circumferential direction of the pintle 4, and are separated from each other by two axially parallel lands 29, best shown in FIG. 2. Each of the lands 29, 30 constitutes a portion of the cylindrical external surface of the pintle 4. The control chamber 21 is flanked by two narrow sealing ribs 25, 26 which extend in the circumferential direction of the pintle 4 between the lands 29, 30, and the control chamber 22 is flanked by two similar sealing ribs 27, 28. The width of the control chamber 21 and sealing ribs 25, 26 respectively equals or approximates that of the control chamber 22 and sealing ribs 27, 28.  
  In accordance with a feature of the invention, the land 29 between the control chambers 21, 22 is provided with four substantially rectangular recesses in the form of cutouts or cavities 31, 32, 33 and 34 which are respectively provided with narrow and short channels or extensions 35, 36, 37, 38. The extensions 37, 38 are adjacent to the path of successive grooves 14 and the extensions 35, 36 are adjacent to the path of successive grooves 15. The arrow A denotes in FIG. 2 the direction in which the cylinder block 5 rotates relative to the periphery of the pintle 4. The cutouts 31, 32 are outwardly adjacent to the sealing ribs 25, 27 and the cutouts 33, 34 are outwardly adjacent to the sealing ribs 26, 28. The arrangement is such that successive ports 13 and the corresponding grooves l4, 15 can establish communication between the control chamber 21 and cutouts 31, 33 and thereupon between the control chamber 22 and cutouts 32, 34. The pintle 4 is further provided with a first auxiliary sealing rib 31 which is outwardly adjacent to the cutouts 31, 32 and merges into the land 29, and with a second auxiliary sealing rib 33 which is outwardly adjacent to the cutouts 33, 34 and alsomerges into the land 29. The length of each of the extensions 35-38, considered in the axial direction ofthe pintle 4 (i.e., vertically, as viewed in FIG. 2), may but need not equal the corresponding dimension of the groove 14 or 15.  
  The land 30 between the control chambers 22, 21 is also provided with four recesses in the form of cutouts or cavities 39, 40, 41, 42 which respectively communicate with channels in the form of small bores 49, 45, 50, 46. The cutouts 39, are outwardly adjacent to the sealing ribs 25, 27 and the cutouts 41, 42 are outwardly adjacent to the sealing ribs 26, 28 (as considered in the axial direction of the pintle 4). The cutouts 40 and 42 are respectively located behind the cutouts 39, 41, as considered in the direction of rotation of the cylinder block 5 (arrow A).Thc bores 46, 50 are respectively provided with inlets 44, 48 which are adjacent to the path of movement of successive grooves 14, and the bores 45, 49 respectively have inlets 43, 47 which are adjacent to the path of movement of successive grooves 15. An auxiliary sealing rib 39 of the pintle 4 is outwardlyadjacent to the cutouts 39, 40, and a similar auxiliary sealing rib 41&#39; is outwardly adjacent to the cutouts 41, 42. The auxiliary sealing ribs 39, 4] merge into the land 30. The bores 45, 46 can cooperate with successive ports 13 and the associated grooves 14, l5 to establish communication between the control chamber 22 and the cutouts 40, 42. The bores 49, 50 can cooperate with successive ports 13 and the associated grooves 14, to establish communication between the control chamber 21 and the cutouts 39, 41. Thus, successive grooves 14 and the corresponding ports 13 will connect first the chamber 22 with the cutout 42 and thereupon the chamber 21 with the cutout 41, and successive grooves 15 and the associated ports 13 will connect the chamber 22 first with the cutout 40 and thereupon the chamber 21 with the cutout 39.  
  The control chamber 21 communicates with a tapering triangular pilot notch 51 which extends into the land and insures a gradually increasing communication between successive ports 13 and the chamber 21 when the cylinder block 5 rotates. The control cham ber 22 communicates with a similar tapering triangular pilot notch 52 which extends into the land 29 and insures a gradually increasing communication between successive ports 13 and the chamber 22. The length of the pilot notch 51 (as considered in the circumferential direction ofthe pintle 4) is selected in such a way that a port 13 begins to communicate with the control chamber 21 only after the corresponding grooves 14,  
 15 have moved beyond the inlets 44, 43 of the bores 46, 45. Analogous, the length of the pilot notch 52 is such that a port 13 begins to communicate with the control chamber 22 only after the respective grooves 14, 15 have advanced beyond the extensions 37, of the cutouts 33, 31. As shown in FIG. 2, the grooves 14, 15 are positioned in such a way that the groove 14 respectively communicates with the extensions 37, 38 when the associated groove 15 registers with the extensions 35, 36, and that the groove 14 respectively rcgisters with the inlets 44, 48 when the groove 15 respec tively registers with the inlets 43, 47.  
 The operation:  
  When the cylinder block 5 rotates in the direction indicated by arrow A, the end portions or ports 13 of successive cylinder bores 8 orbit about the axis of the pintle 4 and sweep seriatim along the control chamber 21, land 29, control chamber 22, land 30, control chamber 21, etc. By following the orbital movement of a single port 13 and the associated grooves 14, 15, it will be seen that, when the port 13 reaches the land 29, the grooves 14, 15 respectively move into register with the extensions 37, 35 before the port 13 moves beyond the control chamber 21, i.e., the port 13 and the associated grooves 14, 15 establish communication between the control chamber 21 and the cutouts 31, 33. The communication between the control chamber 21 and Cutouts 31, 33 is of short duration but suffices toinsure an equalization of pressure of fluid in the chamber 21 and cutouts 31, 33. 1f the control 21 is connected to the suction (low-pressure) opening of the pintle 4, the pressure in the cutouts 31,33 increases negligibly so that pressure fields developing in the region of these cutouts do not contribute significantly to balancing of forces which tend to move the cylinder block 5 radially of the pintle 4.  
  As the cylinder block 5 continues to rotate, the port 13 and the associated grooves 14, 15 respectively move out of register with the control chamber 21 and cutouts 33, 31. At such time, the corresponding piston 9 changes the direction ofits movement in the respective cylinder bore 8. The port 13 then reaches the pilot notch 52 and thus begins to communicate with the control chamber 22 which contains pressurized fluid. Thus, there begins to take place an equalization of pressures between the interior of the chamber 22 and the adjacent bore 8. Shortly thereafter, the grooves 14, 15 respectively reach the extensions 38, 36 so that the cutouts 34, 32 receive pressurized fluid and the pressure therein rises to a maximum vallue at the time when the port 13 is in full or substantial register with the control chamber 22 but the grooves 14, 15 continue to comm unicate with the extensions 38, 36. When the grooves 14, 15 respectively advance beyond the extensions 38, 36, the pressure of fluid in the cutouts 34, 32 gradually decreases due to leakage of fluid between the periphery of the pintle 4 and the cylinder block 5. The pressure of fluid in the cutouts 34, 32 riises again when the next groove 15 begins to communicate first with the pilot notch 52 and thereupon directly with the control chamber 22.  
  When the port 13 begins to advance beyond the control chamber 22, the grooves 1.4, 15 respectively communicate with the inlets 44, 43 of the bores 46, 45 before the communication between the control chamber 22 and port 13 is interrupted. There takes place an.  
 equalization ofpressures between the control chamber 22 and the cutouts 42, which respectively communicate with the bores 46, 45. The pressure in the cutouts 42, 40 begins to decrease as soon as the grooves 14, 15 respectively advance beyond the inlets 44, 43, i.e., as soon as the port 13 is sealed from the bores 46, 45. The same procedure is repeated when the next port 13 begins to advance beyond the control chamber 22 so that the grooves 14, 15 which are associated with the next port 13 move past the inlets 44,43.  
  The port 13 moves along the land 30 when the corresponding piston 9 reaches the inner end of its stroke. The pressurized fluid in the cutouts 42, 40 then balances theforce which tends to urge the cylinder block 5 against the pintle 4 whenever a piston 9 reaches the inner end of its stroke, The drop offluid pressure in the cutouts 42, 40 is slower than in the cutouts 34, 32 which are disposed diametrically opposite the cutouts 42, 40 with reference to the axis of the pintle 4. This is due to the fact thatthe clearance between the cylinder block 5 and the pintle 4 in the region of the cutouts 42 40 is smaller than in the region of the cutouts 34, 32. Consequently, the fluid in the cutouts 42, 40 can, on the average, offer a greater resistance to radial displacement of the cylinder block 5 than the fluid in the cutouts 34, 32. The widths of the gaps between the cylinder block 5 and pintle 4 automatically assume such values that the forces acting On the pintle 4 balance or neutralize each other.  
  When the port 13 advances beyond the control chamber 22, it moves into register with the pilot notch 51 of the control chamber 21. In the meantime, the corresponding piston 9 has changed the direction of its movement so that it travels radially outwardly to draw fluid into the respective bore 8. The pressure in the bore 8 begins to approach that in the control chamber 21 and the cutouts 41, 39 begin to receive fluid from the control chamber 21 by way of the port 13, grooves 14, 15, inlets48, 47 and bores 50, 49. The pressure fields in the region of the cutouts 41, 39 correspond to those in the region of the cutouts 33, 31, i.e., they are relatively weak and do not offer a substantial resistance to radial displacement of the cylinder block 5. When the grooves 14, 15 advance beyond the inlets 48, 47, the cylinder block has completed one full revolution.  
  It will be noted that the pressure fields in the region of the cutouts at one end of the control chamber 21 or 22 develop subsequent to development of such pressure fields in the region of cutouts at the other end of the respective control chamber. In spite of continuous fluctuations of fluid pressure in the cutouts, the arrangement of FIG. 2 insures a highly satisfactory neutralization of forces which act upon the pintle 4 and further insures that the pressure fields in the region of cutouts are capable of withstanding the tendency of the cylinder block 5 to move radially of the pintle. Due to the aforedescribed symmetric distribution of cutouts with reference to the axis of the pintle 4, the machine operates satisfactorily irrespective of the direction of rotation of the cylinder block 5 and irrespective of whether the control chamber 21 or 22 contains pressurized fluid.  
  Another advantage of the structure shown in FIG. 2 is that the pressure fields in the region of cutouts can stand substantial radial forces which tend to move the cylinder block 5 relative to the pintle 4 and which tend to flex the pintle so that the combined area of the sealing ribs 25-28, lands 29, 30 and auxiliary sealing ribs 31, 33, 39&#39;, 41 can be made small. This reduces the losses due to friction.  
  The cutouts or recesses 31-34 and 39-42 form two groups of cutouts one of which is provided in the land 29 and the other of which is provided in the land 30. Each group comprises two cutouts (31, 33 and 40, 42) which can communicate with successive cylinder bores 8 before such bores communicate with the other two cutouts (32, 34 and 39, 41 All of the cutouts are offset relative to the control chambers 21, 22, as considered in the axial direction of the pintle 4.  
  FIG. 3 illustrates the cylindrical external surface of a modified valve or pintle 104. The control chambers are shown at 56 and 57, the narrow sealing ribs for the chambers 56 and 57 at 58, 59 and 60, 61, and the lands at 62 and 63. The land 62 is provided (as considered in the direction of arrow A) with recesses or cutouts 64, 65 having channels or extensions 70, 71 located in the path of movement of successive grooves 14, and  
 with recess or cutouts 66. 67 having channels or extensions 72, 73 located in the path of movement of successive grooves 15. The cutouts 64, 66 can communicate with the control chamber 56 and the cutouts 65, 67 can communicate with the control chamber 57. The auxiliary sealing ribs for the cutouts 64, 65 and 66, 67 are respectively shown at 68 and 69. The length of the extensions 70, 71 and 72, 73, as considered in the circumferential direction of the pintle 104, is selected in such a way that they can register fully or to a substantial extent with the grooves 14 and 15.  
  The land 63 of the pintle 104 is provided with recesses or cutouts 74, 76 which can communicate with the control chamber 57 by way of their channels or extensions 78, 80, successive grooves 14, 15 and the corresponding ports 13. The land 63 is further provided with recesses or cutouts 75, 77 having channels or extensions 79, 81 which can communicate with the control chamber 56 by way of successive grooves 14, 15 and the associated ports 13. The pilot notches of the chambers 56, 57 are respectively shown at 84 and 85. The auxiliary sealing ribs for the cutouts 74, and 76, 77 are respectively shown at 82 and 83. The extensions 70, 7l, 78, 79 and 72, 73, 80, 81 begin to communicate with the respective grooves 14, 15 when the corresponding ports 13 are still in some communication or begin to communicate with the respective control chamber 56, 57. Thus, the length of intervals during which the cutouts communicate with the respective control chambers is relatively short.  
  it will be noted that the pilot notches 84, 85 taper counter to the direction (arrow A) of rotation of the cylinder block (not shown in FIG. 3). The length of pilot notches 84, 85 is selected in such a way that, when a port 13 travels for example toward the control chamber 57 (see the position of the port 13 in FIG. 3), the corresponding grooves l4, 15 move beyond the extensions 70, 72 before the port 13 reaches the tip of the pilot notch 85. The same applies for the extensions 78, 80 and the pilot notch 84.  
  The distance between the extensions 71, 78 or the extensions 73, 80 which can be communicatively connected to the chamber 57 is a whole multiple of the distance between the centers of two neighboring ports 13 in the cylinder block, as considered in the circumferential direction of the pintle 104. The same applies for the extensions 79, 70 or 81, 72 which can communicate with the control chamber 56. The remainder of the hydraulic machine which embodies the pintle 104 of FIG. 3 is assumed to be identical with that of the machine shown in FIG. 1.  
  The sequence in which the pressure fields develop in the region of cutouts 64-67 and 74-77 is analogous to that for the pressure fields in the region of cutouts shown in FIG. 2. In contrast to the operation of the embodiment of FIGS. 1-2, the equalization of pressure in all cutouts which are associated with the control chamber 56 or 57 takes place simultaneously. The pressure fields which develop in the region of the cutouts 65, 74 resp. 67, 76 which can be connected to the control chamber 57 are spaced apart a distance which is less than considered in the circumferential direction of the pintle 104. Therefore, such pressure fields have components which are added to each other and act in directions normal to a symmetry plane extending midway across the lands 62 and 63. These components balance the forces which tend to urge the cylinder block toward the pintle 104 in the region of the highpressure control chamber.  
  The force which tends to move the cylinder block toward the pintle 104 at the inner dead center position of a piston is balanced by the corresponding component of the pressure field in the region of that cutout which is located opposite such piston. That component of the last mentioned pressure field which acts in the same direction as the force acting to move the cylinder block toward the pintle 104 in the region of a piston dwelling in its innermost position is automatically reduced (prior to being fully neutralized) due to the fact that the gap in the region of the respective cutout increases with the result that the pressure field becomes weaker until the forces acting on the cylinder block balance each other. This also neutralizes the forces acting on the pintle I04 because the latter takes up radial stresses acting on the cylinder block.  
  As a rule, pressure fields develop only in the region of those cutouts which communicate with the highpressure control chamber of the pintle, i.e., only such pressure fields exert a pronounced influence on the balance of forces acting on the cylinder block. The pressure fields which develop in the region of the cutouts in communication with the low-pressure (suction) chamber are normally negligible. However, if the direction of rotation of the cylinder block remains unchanged while the direction of fluid flow changes the low-pressure chamber becomes the high-pressure chamber and vice versa. Due to aforedescribed symmetric distribution of cutouts in the periphery of the pintle 4 or 104. the forces acting on the cylinder block are balanced again whereby the previously negligible pressure fields contribute significantly to a balancing of forces which act upon the cylinder block, and vice versa.  
  The combined area of relatively small sealing ribs 58-61, lands 62, 63 and auxiliary sealing ribs 68, 69, 82, 83 suffices for satisfactory guidance of the cylinder block and counteracts the unbalanced hydrostatic forces. At the same time, the losses due to friction are minimal.  
  FIG. 4 shows a further valve or pintlc 204 having two elongated control chambers 86, 87, two lands 92, 93, and scaling ribs 88, 89 and 90, 91 which respectively flank the control chambers 86, 87. The land 92 has four rectangular recesses or cutouts 94, 95, 96 and 97 of different sizes. The smaller cutouts 95, 97 can communicate with the control chamber 87 by way of successive ports l3 and associated grooves l4, l5, and the larger cutouts 94, 96 can communicate in the same way with the control chamber 86. The larger outer cutouts 94, 96 are respectively flanked by auxiliary sealing ribs 98, 99. The cutouts 94, 96 respectively communicate with channels or bores I00, 10] having inlets I, I01 which are respectively adjacent to the path of successive grooves l4, 15. The channels 95, 97 respectively include channels or extensions 102, 103 located in the path of movement of successive grooves l4, l5.  
  When a port I3 travels along the land 92 from the control chamber 86 toward the control chamber 87, the associated grooves l4. 15 respectively communicate with the inlets 100. 101 so that the control chamber 86 is in communication with the cutouts 94, 96 by way of the respective bores I00, 101. The port 13 thereupon begins to communicate with a pilot notch [04 of the control chamber 87 shortly before the grooves 14, I5 reach the extensions I02. 103 of the cutouts 95, 97. The port 13 begins to communicate with the pilot notch I04 after the grooves l4, move beyond the inlets I00, 101. The grooves 14, 15 communicate with the extensions 102, 103 while the corresponding port 13 communicates with the control chamber 87.  
  The land 93 is identical with the land 92. It is provided with two smaller recesses or cutouts I06, I08 having channels or extensions I11, I12 and with two larger recesses or cutouts 105, I07 communicating with channels or bores 109, HO having inlets I09, I10. Successive grooves 14 communicate first with the inlet 109&#39; to thereby connect the control chamber 87 with the cutout 105. and thereupon with the extension 111 to thereby connect the control chamber 86 with the cutout 106. Analogously, successive grooves 15 communicate first with the inlet to connect the control chamber 87 with the cutout I07, and thereupon with the extension 2 to connect the control chamber 86 with the cutout 108. The pilot notch 113 of the control chamber 86 begins to communicate with a port 13 after the respective grooves 14, I5 advance beyond the inlets 109, I10, and the port I3 communicates with the control chamber 86 while the respective grooves l4, l5 overlie the extensions ll], H2. The larger outer cutouts I05, 107 of the land 93 are flanked by auxiliary sealing ribs 114, I15. It will be noted that the pilot notch 113 extends counter to the direction of rotation (arrow A), of the cylinder block.  
  The manner in which the pressure fields are built up in a machine embodying the pintle 204 of FIG. 4 is analogous to that described with reference to FIG. 2. If the cylinder block (not shown) rotates in the direction indicated by arrow A, and if the control chamber 87 is the high-pressure chamber, a port 13 travels along the land 93 of the pintle 204 when the corresponding piston is nearest to the axis of the pintle. The pressure fields in the region of the cutouts I05 and 107 develop whenever the grooves l4, 15 associated with a port 13 which is still in communication with the high-pressure chamber 87 reach the inlets 109&#39;, 110. Such pressure fields are capable of offering a substantial resistance to radial movement of the cylinder block toward the periphery of the pintle 204, and are much more pronounced than the pressure fields in the region of cutouts 95, 97. The cutouts 95, 97 are located diametrically opposite the cutouts I05. 107 and intermittently receive pressurized fluid from the control chamber 87 by way of the pilot notch 104, successive ports I3, associated grooves l4, l5 and the extensions I02, 103. The pressure fields in the region of the cutouts I05, 107 compensate for the force whiclh tends to move the cylinder block toward the land 93 due to the fact that the piston sweeping past the land 93 pressurizes the fluid in the respective cylinder bore. Moreover, the pressure fields in the region of cutouts I05, I07 counteract the pressure fields in the region of cutouts 95, 97. The intensity ofsuch pressure fields is adjusted automatically in that the gap between the pin&#39;tle 204 and the cylinder block increases wherever the forces are unbalanced whereby the leakage of pressurized fluid increases and the magnitude of the respective pressure fields decreases accordingly. By properly dimensioning the cutouts in the lands 92, 93, one can achieve an extensive balancing of forces and thus an accurate centering of the cylinder block on the pintle.  
  It will be noted that the larger cutouts 105, 107 in the land 93 communicate with the high-pressure chamber 87 because a piston moves past the land 93 while it pressurizes the fluid in the respective cylinder bore. If the control chamber 86 is the high-pressure chamber, the pistons move radially inwardly during travel toward the land 92 so that pronounced pressure fields develop in the region of the large cutouts 94. 96. Thus, pronounced pressure fields are always established in the region of those larger cutouts which are in communication with successive ports 13 while the respective pistons approach, reach and leave their inner dead-center positions. In this manner, one achieves a highly satisfactory balancing of forces irrespective of the direction of fluid transport, as long as the cylinder block rotates in the same direction. Such balancing of forces renders it possible to greatly reduce the combined area of surfaces (on the sealing ribs and lands) for guidance of the cylinder block which, in turn, results in a substantial reduction of losses due to friction.  
  The recesses or cutouts 94-97 and 105108 are located centrally of the lands 92, 93. as considered in the circumferential direction of the pintle 204.  
  FIGS. 5a and 5b illustrate a portion of a modified radial piston machine with a presently preferred configuration of cylinder bores in a cylinder block 120 which enhance the balancing of remaining forces acting upon the cylinder block in the region of the high-pressure chamber in the valve or pintle 121. The cylinder block 120 has an axial bore bounded by an internal surface 120 which surrounds the pintle 121. The cylinder bores 122 of the block 120 extend radially outwardly from the internal surface 120. The pintle 121 has two control chambers 123, 124 which are separated from each other by lands 123 (one shown in FIG. 5a).  
 Each cylinder bore 122 has an inner end portion or port 125 and the cylinder block 120 has internal shoulders 126 between the main portions of the bores 122 and the respective ports 125. Each port 125 communicates with a rectangular recess or cavity 127 which is machined into the internal surface 120 and extends in the circumferential direction of the pintle 121. The neighboring cavities 127 are separated from each other by narrow webs 129. The width of a land 123 on the pintle 121 equals the distance between the centers of two neighboring ports 125, as considered in the circumferential direction of the pintle. The length ofeach cavity 127 equals the width of a land 123 minus the width of a web 129, as considered in the circumferential direction of the pintle 121. As a rule, the length of a cavity 127 is between 8571 and 95% of the width of a land 123&#39;. The width of a cavity 127, as considered in the axial direction of the pintle 121. is selected in axial direction of the pintle 121, is selected in such a way that the pressure field developing in the region of such cavity can counteract the remaining force which develops in response to pressurization of fluid in the respective bore 122.  
  When a cylinder bore 122 travels from the highpressure chamber (e.g., control chamber 123) toward the low-pressure chamber and the respective &#39;port 125 moves along the land 123&#39; of FIG. 5a, the cavity 127 insures that the bore 122 continues to communicate with the high-pressure chamber. Consequently, the force which the fluid in the bore 122 exerts against the shoulder 126 and which tends to urge the cylinder block 120 against the periphery of the pintle 121 remains intact as long as the adjacent portion ofthe internal surface 120 continues to overlie the high-pressure chamber 123. Such portion of the surface 120&#39; is subjected to the action of forces V,, which tend to move the cylinder block 120 away from the pintle 121 and which are opposed by lluid pressure acting against the shoulder 126. In other words, that portion of the cylinder block 120 which extends between the centers of two neighboring ports 125 or between two neighboring webs 129 is acted upon simultaneously by a first force (shoulder 126) tending to move the cylinder block toward the pintle 121 and by a second force which tends to move the cylinder block away from the pintle. The  
 second force acts upon that portion of the internal surface (in the region of the respective port which continues to overlie the high-pressure chamber 123. Shortly after a cavity 127 moves into full register with the land 123&#39;, it begins to communicate with the low-pressure chamber 124 so that the force which tends to move the cylinder block 120 away from the pintle 12] decreases simultaneously with the force which tends to move the cylinder block toward the pintle.  
  When a port 125 moves along the other land of the pintle 121 (on its way from the low-pressure chamber 124 toward the high-pressure chamber 123), there develops a force which tends to move the cylinder block 120 away from the pintle as soon as the adjacent portion of the internal surface 121) begins to overlie the chamber 123. Since the length of a cavity 127 closely approximates the width of a land 123&#39; (ie, the distance between the centers of two neighboring ports 125 minus the width of a web 129), the respective bore 122 begins to communicate with the high-pressure chamber 123 practically simultaneously with the generation of a force which tends to move the cylinder block 120 away from the pintle 121, whereby the fluid acting on the corresponding shoulder 126 urges the cylinder block toward the pintle and balances the aforementioned separating or lifting force. The two forces act along the same line but in opposite directions so that they can neutralize each other.  
  Each recess or cavity 127 includes two mirror symmetrical portions 128 (sec particularly FlG. 512) one of which extends forwardly and the other of which ex-&#39; tends rearwardly of the respective port 125, as considered in the direction of rotation of the cylinder block 120.  
  The preceding description indicates that the forces which tend to move the cylinder block toward and away from the pintle neutralize each other in the region of those cylinder bores where the pistons are in the process of changing the direction of their movement. The cavities 1277 evidently do not influence such forces while they are in full register with the highpressure chamber of the pintle.  
  The improved pintle and cylinder block are susceptible of many additional modifications without departing from the spirit of the invention. For example, the ports of the cylinder bores can be configurated in such away that the cavities 127 of FIGS. 5a and 5/) can be dispensed with. Also, the cutouts in the lands of the pintle need not have a rectangular or square shape, the extensions of the cavities can be replaced by bores, and the bores can be replaced by extensions. The cylinder block 120 of FIGS. 5a and 5b can be used in combination with the pintle 4, 104 or 204.  
  Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.  
  What is claimed as new and desired to be protected by letters patent is set forth in the appended:  
  1. In a radial piston machine, a combination comprising a rotary cylinder block having a cylindrical external 13 surface and radially extending cylinder bores including end portions tcrminatins in said internal surface; and a valve having a cylindrical external surface surrounded by said internal surface, a high-pressure chamber and a low-pressure chamber provided in said external surface, said chambers being in register with and being swept seriatim by successive end portions when said block rotates relative to said valve and said external surface including two portions constituting lands between said chambers, said external surfaces further having at least two recesses in each of said lands, offset in axial direction of said block relative to said chambers and respectively located to opposite sides of the path of the end portions of successive cylinder bores, each of said recesses being in temporary communication with that cylinder bore whose end portion travels in the region of the respective land.  
  2. A combination as defined in claim 1, wherein said internal surface is provided with grooves, at least one for each cylinder bore and each communicating with the respective cylinder bore, said cylinder bores being arranged to communicate with said recesses by way of the respective grooves.  
  3. A combination as defined in claim 1. wherein said recesses include a first group of recesses in one of said lands and a second group of recesses in the other of said lands, each group of recesses including at least one first recess which communicates with successive cylinder bores while the end portions of the respective cylinder bores simultaneously communicate with one of said chambers and at least one second recess which communicates with successive cylinder bores while the end portions of the respective cylinder bores communicate with the other ofsaid chambers, said lands further having first and second channels which respectively establish communication between said first and second recesses and successive cylinder bores, the distance be tween said first channels or said second channels, as considered in the circumferential direction of said valve, being a whole multiple of the distance between the centers of the end portions of two neighboring cylinder bores in said block.  
  4. A combination as defined in claim I, wherein said recesses include a first and a second group respectively provided in the one and the other of said lands and the recesses of each group include at least one first recess which communicates with successive cylinder bores while the end portions of the respective cylinder bores communicate with said high-pressure chamber and at least one second recess which communicates with successive cylinder bores while the end portions of the respective cylinder bores communicate with said lowpressure chamber, the distance between said first recesses, as considered in the circumferential direction of said valve, being less than 180 degrees.  
  5. A combination as defined in claim 1, wherein said valve further comprises sealing ribs flanking said chambers and auxiliary sealing ribs flanking said recesses, said sealing ribs constituting with said lands the sole means for guiding said internal surface while said cylinder block rotates relative to said valve.  
  6. A combination as defined in claim 1, wherein said recesses include a first and a second group of four recesses each respectively provided in the one and the other of said lands, each of said groups including a first pair of recesses which communicate with successive cylinder bores during the last stage of communication of the corresponding end portions with one of the chambers and a second pair of recesses which communicate with successive cylinder bores during the initial stage of communication of the corresponding ports with the other of said chambers.  
  7. A combination as defined in claim 6, wherein one pair of said recesses ofeach group is located behind the other pair of recesses of the respective group, as considcred in the direction of rotation of said cylinder block.  
  8. A combination as defined :in claim 6, wherein one pair of recesses of each of said groups is nearer to the path of said end portions than the other pair of recesses of the respective group.  
  9. A combination as defined in claim 1, wherein said valve is further provided with channels by means of which said recesses communicate with the end portions of successive cylinder bores.  
  10. A combination as defined in claim 9, wherein at least some of said channels are bores.  
  11. A combination as defined in claim 9, wherein at least some of said channels are extensions of said recesses.  
  12. A combination as defined in claim I, wherein the recesses in each of said lands include at least one first recess and at least one larger second recess said second recesses being arranged to communicate with those cylinder bores whose end portions simultaneously register with said high-pressure chamber,  
  13. A combination as defined in claim 12, wherein said recesses are located substantially centrally of the respective lands, as considered in the circumferential direction of said valve.  
  14. In a radial piston machine, a combination comprising a rotary cylinder block [having a cylindrical internal surface and radially extending cylinder bores including end portions terminating in said internal surface; and a valve having a cylindrical external surface surrounded by said internal surface, a high-pressure chamber and a low-pressure chamber provided in said external surface, said chambers being swept seriatim by successive end portions when said block rotates relative to said valve and said external surface including two portions constituting lands between said chambers, each of said lands being provided with at least one recess adjacent to one side of the path of the end portions of successive cylinder bores, and with at least one second recess adjacent to the other side of said path, said internal surface having a pair of grooves for each of said cylinder bores and the grooves of each pair being in communication with the respective cylinder bores, one groove of each pair being .arranged to communicate with said first recesses and the other groove of each pair being arranged to communicate with said second recesses when said cylinder block rotates and said cylinder bores travel in the region of the respective lands.