Patent Publication Number: US-3874273-A

Title: Pintle for radial piston machines

Description:
United States Patent 91 Nonnenmacher Apr. 1, 1975 v PINTLE FOR RADIAL PISTON MACHINES [75] Inventor: Gerhard Nonnenmacher,Korntal,  
 Germany [22] Filed: Sept. 28, 1973 [21] Appl. No.: 401,943  
 [30] Foreign Application Priority Data 796,163 1/1936 France 91/498 Primary E.raminerWilliam lL. Freeh Attorney, Agent, or Firm-Michael S. Striker [57] ABSTRACT A radial piston machine wherein the high-pressure control chamber of the pintle is located between two recesses and defines therewith two sealing projections of varying width, either because the width of the control chamber varies in the circumferential direction of the pintle or due to specific configuration of the recesses. This insures that the point of attack of the resultant force furnished by pressure fields which develop between the sealing projections and the internal surface of the rotating cylinder block as a result of leakage of pressurized fluid from the high-pressure control chamber coincides with or is immediately adjacent to the point of attack of the resultant of and neutralizes all forces which tend to move the cylinder block out of axial alignment with the pintle. The cylinder block tends to move out of axial alignment with the pintle due to fluid pressure in certain cylinders of the cylinder block and also due to the pressure which the pistons apply to the surfaces surrounding the respective cylinders.  
 18 Claims, 13 Drawing Figures PINTLE FOR RADIAL PISTON MACHINES BACKGROUND OF THE INVENTION The present invention relates to radial piston ma chines in general, and more particularly to improvements in radial piston machines wherein the position of a slide block with respect to a stationary pintle determines the length of strokes of the pistons which are reciprocable in radially extending cylinders of a piston block which rotates about the pintle.  
  As a rule, the pintle (also called valve) is provided with at least two control chambers which are located diametrically opposite each other and communicate with two axially extending bores of the pintle. The cylinder block has an internal surface which rotates about the peripheral surface of the pintle and is provided with a series of ports, one for each cylinder, which sweep seriatim past and communicate with the two control chambers when the cylinder block rotates, either in response to transmission of torque from a prime mover or in response to admission of pressurized fluid from one of the control chambers, i.e., depending upon whether the machine is used as a pump or as a motor. It is already known to provide the peripheral surface of the pintle with two circumferentially extending recesses which flank the control chambers and define therewith a first pair of elongated sealing projections or ribs which are adjacent to one of the control chambers and a second pair of sealing projections which are adjacent to the other control chamber. When the machine is in use, some pressurized fluid invariably leaks from one of the control chambers (i.e., from the high-pressure chamber) and flows along the adjacent sealing projections toward the recesses which communicate with the interior of the housing of the radial piston machine. Additional fluid leaks along the other pair of sealing projections as well as along sealing rings or carrying rings which flank the recesses in the peripheral surface of the pintle. The fluid which leaks between the sealing projections and sealing elements on the one hand, and the internal surface of the cylinder block on the other hand, establishes pressure fields which oppose the movement of adjacent portions of the internal surface of the cylinder block toward the peripheral surface of the pintle. The pressure fields are more pronounced beween the internal surface of the cylinder block and those sealing projections which are adjacent to the high-pressure control chamber. The control chambers are separated from each other by platforms or lands which constitute non-recessed portions of the peripheral surface of the pintle.  
  When the cylinder block rotates, certain cylinders contain highly pressurized fluid which applies to the surfaces surrounding the respective cylinders a force tending to move the cylinder block toward the pintle. The point of attack of this force travels back and forth about the center of the high-pressure control chamber in and counter to the direction of rotation of the cylinder block. The extent of angular displacement of the point of attack of the just discussed force with respect to the pintle depends on the number of cylinders in the cylinder block, i.e., on the angle between the axes of neighboring pistons. In addition, the pistons apply to the surfaces surrounding the respective cylinders a lateral force which tends to move the cylinder block toward the pintle in the region of that land which is being bypassed by successive pistons WhlCI&#39;l assume their inner end positions at a minimum distance from the axis of the pintle. The resultant of all forces produced by fluid pressure and by the pistons acts on the cylinder block in the region between the aforementioned land and the center of the high-pressure control chamber. The point of attack of such resultant force travels back and forth, i.e., it can move closer to the center of the high-pressure control chamber or closer to the land which is being bypassed by successive pistons which assume their inner end positions.  
  German Offenlegungschrift No. 1,453,629 discloses a radial piston machine wherein the pintle is provided with two circumferentially complete recesses or grooves which flank the control chambers. The fluid which leaks from the high-pressure control chamber toward the recesses establishes very pronounced pressure fields between the internal surface of the cylinder block and those sealing projections which are immediately adjacent to the high-pressure control chamber. The resultant force which is produced by the pressure fields and opposes the movement of cylinder block toward the pintle acts upon the cylinder block at the center of the high-pressure control chamber so that such force cannot neutralize or balance the aforediscussed resultant force which is produced by fluid pressure in the cylinders and by the pistons and tends to move the cylinder block toward the peripheral surface of the pintle. In other words, such pressure fields cannot balance a force which tends to move the cylinder block toward the pintle and Whose point of attack travels back and forth between that land which is adjacent to pistons assuming their inner end positions and the center of the high-pressure control chamber. This is due to the fact that the width of sealing projections which are adjacent to the high-pressure control chamber is constant from end to end.  
 SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved radial piston machine wherein the cylinder block is automatically centered on the pintle.  
  Another object of the invention is to provide a novel and improved pintle for use in radial piston machines of the type wherein the cylinder block is acted upon by a force which tends to move it toward the periphery of the pintle and whose point of attack travels back and forth, as considered in the direction of rotation of the cylinder block.  
  A further object of the invention is to provide a pintle for use in radial piston machines with novel and improved control chambers and/or recesses which insure a complete or practically complete neutralization of all forces tending to move the axis of the rotating cylinder block out of exact alignment with the axis of the pintle.  
  An additional object of the invention is to provide a pintle which insures that all forces acting on the pintle and on the cylinder block are fully balanced or neutralized, at least within each of a succession of unit lengths of time, to thus insure accurate, reliable and automatic centering of the cylinder block on the pintle and to thereby prevent uncontrolled and excessive leakage of pressurized fluid between the peripheral surface of the pintle and the internal surface of the cylinder block.  
  The invention is embodied in a radial piston machine wherein the width of pronounced pressure fields between the peripheral surface of the pintle and the internal surface of the cylinder block varies in the circumferential direction of the pintle in such a way that the point of attack of the resultant force produced by the pressure fields and opposing the movement of the cylinder block out of axial alignment with the pintle coincides with or is closely adjacent to the point of attack of the resultant force (produced by fluid pressure and by the pistons) which tends to move the cylinder block out of axial alignment with the pintle.  
  An important advantage of such configuration of the pronounced pressure fields is that it can be achieved at a reasonable cost, i.e., by the simple expedient of properly configurating the peripheral surface of the pintle. The width of pronounced pressure fields can be varied by properly selecting the configuration of recesses in the peripheral surface of the pintle and/or by properly selecting the configuration of one or both control chambers in the peripheral surface of the pintle.  
  The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved pintle itself, however, both as to 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 FIG. 1 is central vertical sectional view of radial piston machine having a pintle which embodies one form of the invention;  
  FIG. 2 is a developed view of a portion of the pintle in the radial piston machine of FIG. 1;  
  FIG. 3 is a developed view of a portion of a second pintle;  
  FIG. 4 is a developed view of a portion ofa third pintle;  
  FIG. 5 is a developed view of a portion of a fourth pintle;  
  FIG. 6 is a developed view of a portion of a fifth pintle;  
  FIG. 7 is a developed view of a portion of a sixth pin tle;  
  FIG. 8 is a developed view of a portion of a seventh pintle;  
  FIG. 9 is a developed view of a portion of a eighth pintle;  
  FIG. 10 is a developed view of a portion of a ninth pintle;  
  FIG. 11 is a developed view of a portion of a tenth pintle;  
  FIG. 12 is a developed view of a portion of an eleventh pintle; and  
  FIG. 13 is a transverse sectional view as seen in the direction of arrows from the line XIIIXIII of FIG. 12.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a radial piston machine including a housing 1 having a cover 2 which is provided with a bore 3 for a stationary valve or pintle 4. The pintle 4 is held against rotation by a pin 4a and is provided with two axial ports or bores 21, 22, communicating with two peripheral slots or control chambers 19, best shown in FIG. 2. A cylinder block 5 rotates on the pintle 4 and in a friction bearing 6 which is installed in the housing 1. The shaft 7 of the cylinder block 5 is driven by a prime mover (not shown) when the machine is operated as a pump. The cylinder block 5 rotates the shaft 7 when the machine is used as a motor. The cylinder block 5 is formed with radially extending equidistant cylinders 8 for pistons 9 which are received equidistant cylinders 8 for pistons 9 which are received in the cylinders with minimal clearance and are provided with articulately mounted shoes or heads 10 abutting against the internal surface of a slide block 1 1 which is adjustable radially of the pintle 4 to thereby determine the length of piston strokes. The control means for changing the position of the slide block 11 comprises a nut 14 which is rigid with the slide block, a spindle 15 which meshes with the nut 14 and is rotatable in but cannot move axially relative to a bracket 16 of the housing 1, and a handwheel 17 for the spindle 15. A helical spring 18 reacts against the housing 1 and bears against the slide block 11 diametrically opposite the nut 14.  
  Each cylinder 8 has a conical inner end portion 12 which tapers in a direction towrd the periphery of the pintle 4 and communicates with a port 13 of the cylinder block 5. When the cylinder block 5 rotates, the ports 13 communicate seriatim with the control chamber 19, thereupon with the control chamber 20, again with the control chamber 19, and so forth. The control chambers 19, 20 are elongated slots of constant width (see FIG. 2) which extend in the circumferential direction of the pintle 4 in line with the ports 13 and pistons 9 in the cylinder block 5. The control chamber 19 is assumed to constitute a low-pressure chamber and the control chamber 20 is assumed to constitute a highpressure chamber. Thus, when the radial piston machine of FIG. 1 is operated as a pump, pressurized fluid is forced from successive ports 13 into the chamber 20 and the ports 13 thereupon draw fluid from the chamber 19.  
  As shown in FIG. 2, the control chambers 19, 20 are separated from each other by two platforms or lands 23, 24. When the machine is operated as a pump, P cylinder block 5 is assumed to rotate in the directlon indicated by arrow A. The land 23 is adjacent to the ports 13 in register with those pistons 9 which are located at a maximum distance from the pintle 4 and the land 24 is adjacent to those pistons 9 which are nearest to the pintle. I  
  The control chambers 19, 20 are flanked by two C11- cumferentially complete recesses or grooves 25 26 which are configurated in accordance with a feature of the present invention. The width of each of the recesses 25, 26 is constant and these recesses are mirror symmetrical to each other with reference to a plane wlnch is normal to the axis of the pintle 4 and halves the control chambers 19, 20 and lands 23, 24.  
  The recess 25 includes a portion 25a which is parallel to the longitudinal direction of the control chamber 19 and is separated from this control chamber by an elongated sealing projection or rib 29 of constant width. At or close to the median portion of the land 23, the recess 25 includes a relatively short portion 25b which extends axially of the pintle 4 and toward the recess 26, and the portion 25b is followed by a portion 250 which is inclined away from the recess 26 and defines with the control chamber 20 a sealing projection or rib 27 having a width which increases in a direction from the land 23 toward the land 24. At the middle of the land 24, the recess 25 includes a fourth portion 25d which extends axially of the pintle 4 and communicates with the ad acent end of the portion a. the corresponding portions of the recess 26 are shown at 26a, 26b, 26c and 26d. The sealing projections or ribs which the portions 26a and 26c define with the control chambers 19 and 20 are respectively shown at and 28. It will be seen that the sealing projections 29 and 30 are substantially rectangular and that the sealing projections 27, 28 have a triangular or trapezoidal outline.  
  The recesses 25, 26 are respectively adjacent to two circumferentially complete sealing or carrying elements in the form of rings 31, 32. The sealing element 31 extends all the way to the inner axial end of the pintle 4.  
  When the radial piston machine is in use, pressurized fluid leaks from the control chamber 20 toward the recesses 25, 26 by flowing through the gap between the periphery of the pintle 4 and the internal surface of the cylinder block 5. The escaping fluid establishes pronounced pressure fields along the sealing projections 27, 28; such pressure fields oppose the movement of the adjacent portion of the cylinder block 5 toward the periphery of the pintle 4. Due to the fact that the width of sealing projections 27, 28 increases in a direction from the land 23 toward the land 24, the centers of the two pronounced pressure fields are shifted in a direction from the center of the control chamber 20 toward the land 24, i.e., toward the region where the pistons 9 travel when they reach the inner ends of their strokes. The fluid also leaks from the recesses 25, 26 and along the sealing elements 31, 32 to enter the interior of the housing 1. Moreover, and if the fluid pressure in the control chamber 19 is less than the fluid pressure in the recesses 25, 26, the fluid also flows from the recesses 25, 26 toward the control chamber 19 to establish less pronounced pressure fields between the sealing projections 29, 30 and the internal surface of the cylinder block 5. The ability of these less pronounced pressure fields (as well as of the less pronounced pressure fields between the sealing elements 31, 32 and the internal surface of the cylinder block 5) to oppose the movement of the corresponding portions of the cylinder block 5 toward the periphery of the pintle 4 is much less than that of more pronounced pressure fields in the region of the sealing projections 27, 28. The leakage of fluid from the recesses 25, 26 causes the fluid pressure in the recesses 25, 26 to drop so that it matches the fluid pressure in the interior of the housing 1 or in the control chamber 19, whichever pressure is lower. The weaker or less pronounced pressure fields in the region of the sealing elements 31, 32 and sealing projections 29, 30 balance or compensate each other, either completely or substantially, so that the point of attack of the resultant of all forces produced by the pressure fields coincides with or is close to the common center of pronounced pressure fields in the region of the sealing projections 27, 28. Thus, by properly selecting the configuration of recesses 25, 26 (and hence the configuration of sealing projections 27, 28), one can insure that the aforediscussed resultant force acting upon the cylinder block 5 and tending to move the axis of the cylinder block out of exact alignment with the axis of the pintle is balanced by the resultant of forces produced by pronounced pressure fields between the sealing projections 27, 28 and the internal surface f the cylinder block 5.  
  The pintle 4 of FIGS. 1 and 2 is designed for use in radial piston machines wherein the control chamber 20 is always the high-pressure chamber, wherein the control chamber 19 is always the low-pressure chamber, and wherein the piston 9 are nearest to the pintle 4 while traveeling along the land 24.  
  The pintle 35 of FIG. 3 is similar to the pintle 4 and is also used in radial piston machines wherein one of the control chambers (the chamber 36) is always the high-pressure chamber, the other control chamber (37) is always the low-pressure chamber, and the pistons of the cylinder block (not shown) always travel along the land 39 while assuming their inner end positions. The direction of rotation of the cylinder block (when the machine operates as a pump) is indicated by the arrow A. The two lands are shown at 38, 39, the sealing projections which flank the control chamber 36 at 44, 45, the sealing projections which flank the control chamber 37 at 42, 43, the sealing elements at 46, 47 and the circumferentially complete recesses at 40, 41.  
  The recesses 40, 41 are mirror symmetrical to each other with reference to a plane which is normal to the axis of the pintle 35 and halves the control chambers 36, 37 and lands 38, 39. The recess 40 comprises a first portion 40a which extends from the center of the land 39 to the center of the land 38 and is parallel to the longitudinal extension of the control chamber 37, a short portion 40b which extends axially of the pintle 35 toward the recess 41, a third portion 400 which is parallel to the portion 40a, a fourth portion 40d which extends axially of the pintle 35 and away from the recess 41 and is located substantially midway between the ends of the control chamber 36, a fifth portion 40a which is parallel to the portion 40a and extends to the middle of the land 39, and a sixth portion 40f which extends axially of the pintle 35 and communicates with the adjacent end of the portion 40a. The corresponding portions of the recess 41 are respectively shown at 41 a, 41b, 41c, 41d, 41e and 41f. The length of the portions 40b, 40f is substantially half the length of the portion 40d, i.e., the plane of the portion 400! is located substantially midway between the plane of the portion 40c and the plane of the portion 40c.  
  The width of sealing projections 42, 43 is constant from end to end. The sealing projections 44, 45 have narrower portions which are adjacent to the land 38 and wider portions which are adjacent to the land 39. Such configuration of sealing projections 44, 45 insures that the common center of pressure fields which develop between the sealing projections 44, 45 and the internal surface of the cylinder block is shifted in a direction from the center of the high-pressure control chamber 36 toward the land 3&#39;9. This again insures that the forces which act on the cylinder block and tend to move its axis out of axact alignment with the pintle 35 are properly balanced by the force which is produced by pronounced pressure fields in the region of sealing projections 44, 45. The pintle of FIG. 4 is designed for use in a radial piston machine wherein each of the control chambers 53, 54 can constitute a high-pressure chamber or a low-pressure chamber but the direction of eccentricity of the associated cylinder block (not shown) remains unchanged. The double-headed arrow B indicates that the cylinder block can rotate in either direction. The control chambers 53, 54 are separated from each other by platforms or lands 5], 52. lrrespective of the direction of rotation of the cylinder block, the land 51 is adjacent to those pistons which assume their outer end positions (at a maximum distance from the pintle); the pistons are adjacent to the land 52 when they reach their inner end positions.  
  The peripheral surface of the pintle 50 is further provided with two recesses 55, 56 each of which is a circumferentially complete groove. The recess 55 has a first portion 55a which is adjacent to the control chamber 53 and is inclined toward the recess 56 all the way from the center of the land 52 toward the center of the land 51, and a second portion 55b which is inclined in the opposite direction (away from the recess 56). The corresponding mirror symmetrical portions of the recess 56 are shown at 560 and 56b. It will be noted that the distance between the portions 55a, 56a increases in a direction from the land 51 toward the land 52 and that the distance between the portions 55b, 56b decreases in a direction from the land 52 toward the land 51. The sealing projections which respectively flank the control chambers 53, 54 are shown at 57, 58 and 59, 60. The recesses 55, 56 are inwardly adjacent to two circumferentially complete sealing or carrying elements 61, 62. Each of the sealing projections 57-60 has a substantially trapezoidal or triangular outline. The bgses of the projections 57-60 are adjacent to the land If the control chamber 53 constitutes the highpressure chamber, pressurized fluid leaks from the chamber 53 to the recesses 55, 56 and forms pronounced pressure fields along the sealing projections 57, 58. The center of these pressure fields (which can furnish a substantial resistance to movement of the adjacent portion of the cylinder block toward the periphery of the pintle 50) is shifted from the center of the high-pressure chamber 53 toward the land 52. This land is adjacent to the pistons which assume their inner end positions. Fluid which penetrates into the recesses 55, 56 leaks along the sealing elements 61, 62 to establish relatively weak or less pronounced pressure fields. Further less pronounced pressure fields develop between the sealing projections 59, 60 and the internal surface of the cylinder block if the pressure in the chamber 54 is lower than in the recesses 55, 56. The forces produced by all these relatively weak pressure fields are in a state of substantial or exact equilibrium so that the center of the resultant force produced by all pressure fields is only slightly out of line with the resultant force produced by pronounced pressure fields in the region of the sealing projections 57 and 58. The point of attack of the averaged force acting on the pintle 50 is practically identical with the point of attack of the resultant of forces produced by all pressure fields. These two forces are identical or nearly identical.  
  The situation is analogous when the control chamber 54 constitutes the high pressure chamber. The pronounced pressure fields then develop in the region of sealing projections 59, 60 and their centers are shifted from the center of the control chamber 54 toward the land 52. It will be noted that the forces are in virtual or exact equilibrium irrespective of the direction of rotation of the cylinder block.  
  The pintle 65 of FIG. 5 serves the same purpose as the pintle 50 of FIG. 4, i.e., each of its control chambers 68, 69 may constitute the high-pressure chamber or the low-pressure chamber. The control chambers 68, 69 are separated from each other by platforms or lands 66, 67. The pistons which reach the outer ends of their strokes travel past the land 66, and the pistons which reach the inner ends of their strokes (nearest to the pintle 65) travel past the land 67. The two endless recesses 70, 71 are similar to the recesses 55, 56 except that they do not consist of mutually inclined straight portions but rather of arcuate portions having concave sides facing the land 67, convex sides facing the land 66, and nearly straight intermediate portions which are inclined with respect to each other and flank the seal ing projections 72, 73 and 74, 75 which are respectively adjacent to the control chambers 68 and 69. The recess 70 comprises a first arcuate portion 70a which forms part of the circle having its center above the pintle 65, as viewed in FIG. 5, and extending from the center of the chamber 68 to the center of the chamber 69, and a second arcuate portion 7012 which also forms part of a circle having its center of curvature at a level below the pintle 65, as viewed in FIG. 5. The corresponding portions of the recess 71 are respectively shown at 71a and 71b. The distance between the recesses 70, 71 is smallest in the region of the land 66 and greatest in the region of the land 67. Thus, the width of the sealing projections 72, 73 as well as 74, 75 increases in a direction from the land 66 toward the land 67. The two endless elements or rings are shown at 76 and 77; these rings are respectively adjacent to the recesses 70, 71.  
  The manner in which the pressure fields develop when the cylinder block rotates in a clockwise or counterclockwise direction is the same as described in connection with FIG. 4.  
  If desired, the recesses 70 and 71 can be modified so that they consist of portions which resemble sinusoidal curves instead of portions of circles. The configuration of such sinusoidal recesses deviates rather negligibly from the configuration of the recesses 70, 71 and the function of a pintle having such sinusoidal recesses is practically identical to that of the pintle 50.  
  FIG. 6 illustrates a further pintle 80 which is analogous to the pintle 50 of FIG. 4. Each of the two control chambers 83, 84 which are separated from each other by platforms or lands 81, 82 may constitute a highpressure chamber or a low-pressure chamber. The cylinder block (not shown) can rotate clockwise or counterclockwise (see the arrow B) and the pistons which are nearest to the pintle 80 travel past the land 82.  
  The peripheral surface of the pintle 80 is provided with two endless mirror symmetrical recesses 85, 86 which are respectively adjacent to endless sealing elements or rings 91, 92 and respectively define with the control chambers 83, 84 pairs of sealing projections or ribs 87, 88 and 90, 89. The recess 85 comprises portions 85a, 85c which extend in the circumferential di rection of the pintle 80 and portions 85b, 85d which extend in parallelism with the axis of the pintle. The corresponding portions of the recess 86 are shown at 86a 86c and 86b, 86d. The distance between the portions 85a, 86a is less than the distance between the portions 850, 86c and each of these portions extends from the center of the control chamber 83 to the center of the control chamber 84. It will be seen that each of the sealing projections 87-90 comprises a narrower portion of constant width which is nearer to the land 81 and a wider portion of constant width which is nearer to the land 82. The width of the sealing projections 87, 88 increases abruptly substantially midway between the ends of the control chamber 83, and the width of the sealing projections 89, 90 increases abruptly midway between the ends of the control chamber 84.  
  The centers of high pressure fields in the region of those sealing projections which flank the high-pressure control chamber are shifted from the center of the high-pressure control chamber toward the land 82. The manner in which pressure fields develop in the region of the sealing projections, lands and sealing elements is analogous to that described in connection with FIGS. 4 to 6.  
  The pintle 95 of FIG. 7 is analogous to the pintle of FIG. 4, i.e., each of its control chambers 98, 99 can constitute a high-pressure chamber or a low-pressure chamber. The lands are shown at 96, 97, the ringshaped sealing elements at 106, 107, the sealing projections flanking the control chamber 98 at 102, 103, the sealing projections flanking the control chamber 99 at 104, 105, and the two endless recesses at 100, 101. When the radial piston machine embodying the pintle 95 is in use, the pistons reach their inner end positions (nearest to the peripheral surface of the pintle) while travelling along the land 97. The land 96 is located dia metrically opposite the land 97 and is approached by successive pistons which assume their outer end positions.  
  The recess 100 comprises a first portion 100a which is adjacent to the land 96 and is located in a plane which is exactly normal to the axis of the pintle 95, a second portion which is adjacent to the control chamber 98 and is inclined away from the recess 101, a third portion 1006 which is parallel to the portion 100a and is adjacent to the land 97, and a fourth portion 100d which is inclined away from the recess 101. The corresponding portions of the recess 101 are shown at 101a, 101b, 1016 and 10111. It will be noted that the distance between the portions 100a, 101a, as considered in the axial direction of the pintle 95, is less than the distance between the portions 100C, 1016. The width of each of the four sealing projections 102-105, as considered in the axial direction of the pintle 95, increases continuously in a direction from the land 96 toward the land 97. Each ofthese projections has a trapezoidal outline, and the base of each projection is adjacent to the land 97.  
  When the cylinder block (not shown) rotates clockwise or counterclockwise (see the double-headed arrow B), the point of attack of the resultant force produced by all pressure fields between the peripheral surface of the pintle 95 and the cylinder block coincides with or is closely adjacent to the point of attack of the resultant force which urges the cylinder block toward the peripheral surface of the pintle. The pronounced pressure fields develop in the region of those sealing projections which flank the high-pressure control chamber. The point of attack of the resultant force produced by such pronounced pressure fields is located between the center of the high-pressure control chamber and the land 97.  
  The pintle 110 of FIG. 8 is intended to be used in a radial piston machine wherein the cylinder block invariably rotates in the direction indicated by the arrow A but the eccentricity of the slide block can change from one side to the other side of the pintle 110. The peripheral surface of the pintle 110 is provided with two elongated control chambers 113, 114 of constant width, as considered in the axial direction of the pintle. These control chambers are separated from each other by two platforms or lands 111, 112. The land 111 is adjacent to those pistons which dwell in their inner end positions when the axis of the slide block is located above the axis of the pintle (as viewed in FIG. 1) and the land 112 is adjacent to such pistons when the axis of the slide block is located at the opposite side of the axis of the pintle. It is assumed that the machine embodying the pintle is used as a pump.  
  The peripheral surface of the pintle 110 is further provided with two endless recesses 115, 116 which respectively define with the control chambers 113, 114 pairs of sealing projections 117, 118 and 119, 120. Each of these projections is a trapezoid; the bases of the projections 117, 118 are adjacent to the land 111 and the bases of the projections 119, 120 are adjacent to the land 112. The recess 1115 has a first portion 115a which is adjacent to the control chamber 114 and diverges from the corresponding first portion 11611 of the recess 116 in the direction indicated by arrow A, i.e., from the land 111 toward the land 112. A second portion 115b of the recess 111 extends axially of the pintle 110 toward the corresponding portion l16b of the recess 116, a third portion 11.50 of the recess 115 diverges from the corresponding portion 1166 of the recess 116, again in the direction indicated by the arrow A, and a fourth portion 115d of the recess 115 extends axially of the pintle 110 toward the corresponding portion 116d of the recess 116. The portions 116b, 1161) are aligned with the center of the land 112, and the portions 115d, 116d are aligned with the center of the land 111. The two endless sealing elements or rings are shown at 121 and 122.  
  The distance between the portions 115b, 116b, as considered in the axial direction of the pintle 110, equals or closely approximates the distance between the portions 115d, 116a. The length of each of the portions 115b, 115d, 116b, 116d is the same. It will be noted that the width of each of the four sealing projections 117-120, as considered in the axial direction of the pintle 110, increases in the direction indicated by the arrow A.  
  If the control chamber 114 constitutes the highpressure chamber, and if successive pistons travel along the land 112 while such pistons assume their inner end positions, the operation of the: machine embodying the pintle 110 is analogous to that of the machine shown in FIG. 1 (i.e., of the machine embodying the pintle 4 of FIG. 2). A difference between the pintles 4 and 110 is that the width of sealing projections 29, 30 on the pintle 4 is constant and that the recesses 115, 116 diverge from each other adjacent to each of the two control chambers 113, 114. This insures that the forces acting on the pintle 110 are balanced by forces acting on the cylinder block if the eccentricity of the slide block is changed to such an extent that the pistons which are nearest to the peripheral surface of the pintle 110 travel along the land 111 (while the cylinder block continues to rotate in the direction indicated by arrow A).  
  The pintle 125 of FIG. 9 can be used for the same purpose as the pintle 110 of FIG. 8, i.e., the axis of the slide block can be shifted from. the one to the other side of the pintle axis but the direction of rotation of the cylinder block (arrow A) remains unchanged. The control chambers 128, 129 have a constant width, as considered in the axial&#39;direction of the pintle 125, and are separated from each other by platforms or land 126, 127. The pistons which assume their inner end positions travel past the land 126 when the axis of the slide block is located at one side of the axis of the pintle 125, and such pistons travel past the land 127 when the axis of the slide block is located at the other side of the axis of the pintle.  
  The peripheral surface of the pintle 125 is further provided with two endless recesses 130, 131 which are flanked by circumferentially complete sealing elements or rings 136, 137 and respectively define with the control chambers 128, 129 pairs of sealing projections or ribs 132, 133 and 134,135. The recess 130 includes portions 130a, 130b, 1306, 130d which are normal to the axis of the pintle 125 and portions 130e, 130f, 130g, 13011 which are parallel to the axis of the pintle. The corresponding portions of the recess 131 are shown at131a,131b,l31c, 131d, 131e, l31f, 131g and 13111. The portions 130a, 130b, 131a, l3lb are respectively coplanar with the portions 1300, 130d, 1310, 131d, and the distance between the portions 130b, 131b and 130d, 131d exceeds the distance between the portions 130a, 131a and 1300, 131e, as considered in the axial direction of the pintle. The portions 130e, 1316 are aligned with the center of the land 126; the portions 130g, 131g are aligned with the center of the land 127; the portions 13012, 13111 are aligned with the center of the control chamber 128; and the portions 130f, 131f are aligned with the center of the control chamber 129. The width of each of the sealing projections 132135 increases stepwise in the region of the center of the respective control chamber. The wider portions of the sealing projections 132, 133 are adjacent to the land 126, and the wider portions of the sealing projections 134, 135 are adjacent to the land 127.  
  If the control chamber 129 is the high-pressure chamber and if the pistons which reach their inner end positions travel past the land 127, the manner in which the forces acting on the pintle 125 and on the cylinder block balance each other is analogous to that described in connection with FIGS. 1-2 and 3. The difference is that the configuration of the sealing projections 132, I33 is identical with that of the sealing projections 134, 135. Consequently, when the axis of the slide block is moved to the other side of the axis of the pintle 125, i.e., when the pistons which reach their inner end positions travel past the land 126, the forces acting on the pintle 125 and on the cylinder block balance or neutralize each other in the same way as when the pistons which reach their inner end positions travel past the land 127.  
  The pintle 140 of FIG. has a control chamber 143 of constant width, as considered in the axial direction of the pintle, and a control chamber 144 whose width increases in a direction from the land 141 toward the land 142. This pintle 140 is designed for use in a radial piston machine wherein the control chamber 144 always constitutes the high-pressure chamber and the pistons which reach their inner end positions invariably travel past the land 142. The recesses 145, 146 are circumferentially complete grooves each of which is located in a plane extending at right angles to the axis of the pintle 140. The direction in which the cylinder block rotates is indicated by the arrow A, the two endless sealing elements or rings are shown at 151, 152, the sealing projections or ribs which flank the low-pressure control chamber 143 are shown at 147, 148, and the two sealing projections or ribs which flank the highpressure control chamber 144 are shown at 149, 150.  
 The width of the sealing projections 147, 148, as considered in the axial direction of the pintle 140, is constant. The width of the sealing projections 149, 150 increases in a direction from the land 142 toward the land 141. The width of each of the sealing elements 151, 152 is constant.  
  That portion of the cylinder block which is adjacent to the high-pressure control chamber 144 is acted upon by a resultant force which point of attack is located between the center of the control chamber 144 and the land 142. Pressurized fluid leaks primarily from the control chamber 144, along the sealing projections 149, 150, and into the adjacent portions of the recesses 145, 146. Such fluid establishes pronounced pressure fields which resist a movement of the cylinder block toward the control chamber 144. Additional fluid leaks along the sealing projections 147, 148 and along the sealing elements 151, 152 (whence it enters the interior of the housing of the radial piston machine). The forces which are produced by the less pronounced pressure fields in the region of the sealing projections 147, 148 and sealing elements 151, 152 neutralize each other and the point of attack ofthe resultant force with which the pronounced pressure fields in the region of the sealing projections 149, 150 resist the approach of the cylinder block toward the high-pressure control chamber 144 coincides with or is immediately adjacent to the point of attack of the force which tends to move the cylinder block toward the control chamber 144. By suitably configurating and dimensioning the highpressure control chamber 144, one can insure that the cylinder block is invariably centered on the pintle 1.40. Such centering can be achieved at a relatively low cost, i.e., by providing the peripheral surface of the pintle 140 with two parallel recesses 145, 146 of constant width and by machining the control chamber 144 in such a way that its width increases gradually from the land 141 toward the land 142.  
  The pintle 155 of FIG. 11 is similar to the pintle 140 of FIG. 10. The only difference is that the width of the high-pressure control chamber 156 increases stepwise in a direction from the land 141 toward the land 142. The sealing projections which flank the control chamber 156 are shown at 157 and 158; the width of each of these projections increases stepwise in a direction from the land 142 toward the land 141. All other parts of the pintle 155 are denoted by characters identical with those employed in FIG. 10. It will be noted that the width of the right-hand portion of the control chamber 156 substantially exceeds the width of the left-hand portion, and that the width of each of these portions is constant. The abrupt increase in width of the control chamber 156 takes place substantially or exactly midway between the lands 141 and 142.  
  The manner in which the forces acting on the pintle 155 are balanced by forces acting on the cylinder block is identical with the manner described in connection with the pintle 140 of FIG. 10.  
  Referring finally to FIGS. 12 and 13, there is shown a pintle 160 which is similar to the pintle 4 of FIG. 2 except that its peripheral surface is formed with two recesses 225, 225 of finite length. It will be noted that the recesses 225, 226 are interrupted in the region of the land 23. Furthermore, the recess 225 has a first portion 161 which diverges from the corresponding portion 162 of the recess 226 in a direction from the land 23 toward the land 24, a second portion 163 which is parallel to the corresponding portion 164 of the recess 226, and a third or intermediate portion 165 which diverges from the corresponding portion 166 of the recess 226 in a direction from the control chamber 19 toward the control chamber 20. The portions 165, 166 are channels which are machined into the body of the pintle 160 in the region of the land 24. As shown in FIG. 13, the ends of the channel 165 communicate with intermediate parts of the adjacent portions 161, 163 of the recess 225. Analogously, the ends of the channel 166 communicate with intermediate parts of the portions 162, 164 of the recess 226. The width of the sealing projections 29, 30, as considered in the axial direction of the pintle 160, is constant all the way from the land 23 to the land 24. The width of the sealing projections 27, 28 increases continuously from the land 23 toward the land 24.  
  The channels 165, 166 insure that the fluid pressure in the portions 161, 162 of the recesses 225, 226 re spectively equals the fluid pressure in the portions 163, 164. The two circumferentially complete sealing elements or rings are shown at 167 and 168.  
  The operation of the radial piston machine which embodies the pintle 160 is identical or analogous to that of the machine embodying the structure of FIGS. 1 and 2.  
  The pintles of FIGS. 3 to 9 can be modified by replacing their circumferentially complete recesses with recesses which consist of spaced-apart portions adjacent to the two control chambers or by replacing the circumferentially complete recesses with recesses of finite length (see FIGS. 12 and 13). Each recess may com prise two portions in the form of grooves and one or two portions in the form of channels. Referring to FIG. 7, the portions 100a, 1006, and 101a, 1016 may constitute channels and the portions 100b, 100d, 101b, 101:! may constitute grooves. The channels bring about an equalization offluid pressure in the respective grooves. Referring again to FIG. 7, the recesses 100, 101 can be replaced by recesses of finite length wherein the portions 100a, 101a are omitted, the portions 100b, 100d, 101b, 101d constitute grooves, and the portions 100C, 1016 constitute channels.  
  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 claims:  
  1. In a radial piston machine wherein a cylinder block having a plurality of radial cylinders for reciprocable fluid-pressurizing pistons rotates about a stationary pintle whose peripheral surface has highand low-pressure control chambers located substantially diametrically opposite and separated from each other by first and second lands one of which is adjacent to pistons assuming their inner end positions, wherein successive cylinders communicate alternately with said highand lowpressure chambers when said cylinder block rotates. wherein said peripheral surface has only two circumferentially extending endless recesses flanking said control chambers and respectively defining therewith a pair of first and a pair of second sealing projections which are respectively adjacent to said highand low-pressure chambers, and wherein the fluid and the pistons in said cylinders produce a first resultant force acting upon and tending to move said cylinder block toward said pintle in the region between said one land and the center of said high-pressure chamber, the improvement which consists in that the width of said first sealing projections, as considered in the axial direction of said pintle, varies in the circumferential direction of said peripheral surface and the fluid whch leaks from said high-pressure chamber substantially axially of the pintle toward said recesses produces pronounced pressure fields between said first sealing projections and said cylinder block whereby said pronounced pressure fields resist the movement of said cylinder block toward said pintle with a second resultant force, the point of attack of said second resultant force coinciding with or being closely adjacent to the point of attack of said first resultant force as a result of variation of the width of said first sealing projections.  
  2. The improvement as defined in claim 1, wherein each of said sealing projections has a narrower first portion of constant width adjacent to one-half of the respective control chamber and a wider second portion of constant width adjacent to the other half of the respective control chamber, the narrower portion of each first sealing projection being adjacent to the wider portion of a second sealing projection and vice versa.  
  3. The improvement as defined in claim 1 wherein the width of said control chambers, as considered in the axial direction of said pintle, is constant in the circumferential direction of said peripheral surface.  
  4. The improvement as defined in claim 1, wherein the width of said first sealing projections increases constantly from the other of said lands toward said one land, as considered in the direction of rotation of said cylinder block, and wherein the width of said second sealing projections is constant.  
  5. The improvement as defined in claim 1, wherein said recesses are located in parallel planes which are normal to the axis of said pintle.  
  6. The improvement as defined in claim 5, wherein the width of said high-pressure control chamber increases continuously toward said one land.  
  7. The improvement as defined in claim 5, wherein the width of said high-pressure control chamber increases stepwise toward said one land.  
  8. The improvement as defined in claim 1, wherein the width of said first sealing projections increases stepwise from the other of said lands toward said one land, as considered in the direction of rotation of said cylinder block.  
  9. The improvement as defined in claim 8, wherein each of said first sealing projections has a narrower portion of a first constant width adjacent to one half of said high pressure chamber and a wider portion of a second constant width which is adjacent to the other half of said second pressure chamber, and wherein each of said second sealing projections has a constant width which is less than said second constant width but exceeds said first constant width.  
  10. The improvement as defined in claim 1, wherein the width of each of said sealing projections increases in a direction from the other of said lands toward said one land.  
  11. The improvement as defined in claim 10, wherein the distance between said recesses, as considered in the axial direction of said pintle, increases continuously from the central portion of said other land to the central portion of said one land.  
  12. The improvement as defined in claim 10, wherein each of said recesses includes a plurality of arcuate portions each forming part of a circle, the arcuate portions of each of said recesses including a first arcuate portion having a concave side adjacent to said one land and a second arcuate portion having a convex side adjacent to the other of said lands, and wherein each of said sealing projections has a substantially trapezoidal outline.  
  13. The improvement as defined in claim 10, wherein each of said recesses has a first portion adjacent to said one land, a second portion adjacent to the other of said lands, a third portion adjacent to one of said control chambers, and a fourth portion adjacent to the other of said control chambers, said first and second portions of said recesses being respectively parallel to each other, said third portions diverging from each other in a direction from said first towards said second portions, and said fourth portions converging towards each other in a direction from said second towards said first portions, and wherein the distance between said first portions, as considered in the axial direction of said pintle, exceeds the distance between said second portions.  
  14. The improvement as defined in claim 10, wherein each of said recesses includes a plurality of sinusoidal portions including a first portion having a concave side adjacent to said one land and a second portion having a convex side adjacent to the other of said lands, each of said sealing projections having a substantially trapezoidal outline.  
  15. The improvement as defined in claim 10, wherein the width of each of said sealing projections increases stepwise.  
  16. The improvement as defined in claim 15, wherein each of said sealing projections comprises a relatively wide portion of a first constant width extending from said one land to the center of the respective control chamber and a relatively narrow portion of a second constant width extending from the center of the respective control chamber to the other of said lands.  
  17. The improvement as defined in claim 10, wherein the width of each of said sealing projections increases continuously as considered in the direction of rotation of said cylinder block.  
  18. The improvements as defined in claim 17, wherein each of said recesses comprises first and second portions which extend axially of said pintle and are respectively aligned with the center of said one land and with the center of the other of said lands, each of said recesses further comprising a third portion adjacent to one of said chambers and diverging from the third portion of the other recess, and a fourth portion adjacent to the other chamber and diverging from the fourth portion of the other recess.