Radial piston motor
United States Patent 3,874,274 Knoblauch Apr. 1, 1975 [54] RADIAL PISTON MOTOR FOREIGN PATENTS OR APPLICATIONS Inventor Rainer Knoblauch, Stuttgart, 796,163 l/l936 France 91/498 Germany 1,043,083 10/1958 Germany 91/498 Assigneez Robert Bosch GmbH, Stuttgart, 570,252 6/1945 United Kmgdom 91/492 Germany Primary Examiner-William L. Freeh 1 Flledi 1973 Attorney, Agent, or FirmMichae1 S. Striker [21] Appl. No.: 408,796  
 [57] ABSTRACT 30 F v A P D t A radial piston motor wherein the angle through 1 0 12 pglca Ion y a a 2251792 which the cylinder block must rotate relative to the ermany pintle to move a port which communicates with a cylinder for a piston in the inner or outer end position into register with one of the control Chambers in the 58 d 498 492 peripheral surface of the pintle depends on the friction l 0 care 7 coefficient between the shoes: of pistons and the slide 56] R f Ct d block. This insures that the forces which act on the l I e erences l e shoes do not interfere with smooth starting of the cyl- UNITED STATES PATENTS inder block 2,431,175 11/1947 Hoffer 91/498 3,408,948 11/1968 Boyd 91/493 9 6 Drawmg F&#39;gures PATENTED 5 sum 1 ur 3 Fig.1  
 PATENTED APR 1 HEEI 2 of 3 RADIAL PISTON MOTOR BACKGROUND OF THE INVENTION The present invention relates to radial piston machines in general, and more particularly to improvements in radial piston motors of the type wherein the pistons are provided with articulately connected shoes travelling along the internal surface of an eccentric annular slide block while the cylinder block rotates about a stationary pintle.  
  It is already known to provide the peripheral surface of the pintle with two control chambers which are located diametrically opposite each other and are separated from each other by lands. One of the lands is adjacent to those pistons which assume their inner end positions and the other land is adjacent to the pistons assuming their outer end positions.  
  A serious drawback of presently known radial piston motors is that they cannot start without a certain delay and without an abrupt acceleration of the cylinder block. Smooth and undelayed starting of the cylinder block is opposed by friction between the relatively movable parts, especially between the shoes or heads of the pistons and the internal surface of the slide block whose eccentricity with respect to the pintle and cylinder block determines the length of piston strokes. Friction between the shoes and the slide block develops mainly as a result of fluid pressure acting on the pistons in the cylinders or bores of the cylinder block.  
 In accordance with a presently known proposal, friction between the slide block and the shoes of the pistons is reduced by insuring that the shoes are hydrostatically relieved to the maximum possible extent. Such proposal is not entirely satisfactory because, as the area of hydrostatically relieved portions of the shoes increases, the noise which is generated by orbiting shoes SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved radial piston motor which is constructed and assembled in such a way that friction between the shoes of its pistons and the slide block cannot adversely influence the acceleration of the cylinder block during starting.  
 Another object of the invention is to provide a novel and improved valve or pintle for use in the radial pisto motor.  
  A further object of the invention is to provide a radial piston motor wherein the forces which act upon the shoes as a result of fluid pressure upon the pistons and which tend to interfere with smooth starting of the cylinder block are either eliminated or reduced to a fraction of similar forces in conventional motors.  
  An additional object of the invention is to provide a radial piston motor which can be started with qradual and undelayed acceleration of its rotary parts.  
  The invention is embodied in a radial piston machine, particularly in a radial piston motor, which comprises a rotary cylinder block having a cylindrical internal surface, radially extending cylinders and ports extending between the cylinders and the internal surface, an eccentric annular slide block which spacedly surrounds the cylinder block, pistons which are reciprocably mounted in the cylinders and have outer end portions in the form of articulately mounted shoes or heads frictionally engaging the internal surface of the slide block so that the pistons move radially between inner and outer end positions in response to rotation of the cylinder block relative to the slide block, and a pintle having a cylindrical peripheral surface which is surrounded by the internal surface of the cylinder block and is formed with highand low-pressure control chambers located diametrically opposite each other and with first and second lands which separate the control chambers from each other.  
  One of the lands is in register with successive pistons which assume their inner end positions, and the other land is in register with successive pistons which assume their outer end positions. The width of the lands as considered in the circumferential direction of the pintle is selected in such a way that a port which registers with a piston assuming one of its end positions is completely sealed from the control chambers and remains sealed from at least one of the control chambers (e.g., from the high-pressure control chamber) while the cylinder block rotates relative to the pintle through an angle alpha whose magnitude is a function of the friction coefficient between the slide block and the shoes of the pistons.  
  Such selection of the angle alpha prevents the development of forces which oppose the starting of the cylinder block within the angle alpha. This is attributed to the fact that the cylinders of the cylinder block remain sealed from the control chamber or chambers while the cylinder block turns through the angle alpha so that the pressure in such cylinders equals zero. Consequently,  
 the forces which tend to resist a smooth and immediate acceleration of the cylinder block cannot develop at all or are sufficiently small to be completely balanced by useful forces which transmit to the cylinder block a torque to start the operation of the radial piston motor.  
  The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved radial piston motor 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 a longitudinal vertical sectional view of a radial piston motor which embodies one form of the invention;  
  FIG. 2 is a fragmentary transverse vertical sectional view as seen in the direction of arrows from the line IIII of FIG. 1;  
  FIG. 3 is a diagrammatic end elevational view showing the path along which the centers of articulate connections between the pistons and their shoes orbit about the pintle;  
  FIG. 4 illustrates a shoe and the forces acting thereon;  
  FIG. is a diagram illustrating variations in the starting force of the radial piston motor at different friction coefficients between the shoes and the slide block;  
 and 1 FIG. 6 is a view similar to that of FIG. 2 but showing a modified pintle.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a radial piston motor which comprises a housing 1 having a cover 2 provided with a centrally located bore 3 for a stationary valve or pintle 4. The means for holding the pintle 4 against rotation in the housing 1 comprises a pin 4a. A cylinder block 5 is rotatable on the pintle 4 and has an output shaft 5a which extends from the housing 1. A portion of the cylinder block 5 is mounted in a friction bearing 6 which is installed in a bore provided therefor in the left-hand wall of the housing 1, as viewed in FIG. 1.  
  The cylinder block 5 is formed with a set of equidistant radially extending cylinders 7 for reciprocable pistons 8 each of which is provided with a swiveling outer end portion here shown as a head or shoe 9 engaging the cylindrical internal surface 36 of a ring-shaped slide block 10. The means for moving the slide block 10 radially of the pintle 4 to thereby change the length of strokes of the pistons 8 comprises a spindle nut 11 which is rigid with the slide block and meshes with a feed screw 12. The latter is rotatable in a bracket 13 of the housing 1 and is provided with a hand wheel 14. A helical spring 15 reacts against the housing 1 diametrically opposite the spindle nut 11 and bears against the slide block 10.  
  Each cylinder 7 has a conical inner end portion which communicates with a port 16 extending radially outwardly from the cylindrical internal surface of the cylinder block 5. The ports 16 are in register with two elongated control chambers 17, 18 which are machined into the peripheral surface of the pintle 4 diametrically opposite each other and are separated from each other by platforms or lands 25, 26 (see also FIG. 2). The control chambers 17, 18 respectively communicate with axially parallel bores or ports 23, 24 in the pintle 5. The bore 23 is assumed to admit, and the bore 24 is as sumed to serve for evacuation of a hydraulic fluid. The land 25 is formed with an axially parallel recess or groove 27 which communicates with a centrally located bore 28 in the housing 1. The bore 28 communicates with an annular internal compartment 1a of the housing 1 byway of one or more radially extending channels 29. The recess or groove 27 communicates with successive ports 16 when the cylinder block 5 rotates in response to admission of pressurized fluid to the control chamber 17. The arrangement is such that a port 16 communicates with the recess or groove 27 while it is sealed from the control chambers l7, l8, i.e., while such port completely overlies the land 25.,The other land 26 is formed with a radially extending recess in the form of a bore or passage 30 which communicates with the bore 28 in the housing 1 by way of an axially parallel bore or passage 31 in the pintle 4. The purpose of the recess or bore 30 is the same as that of the recess or groove 27. A port 16 communicates with the recess or bore 30 while it is completely sealed from the adjacent end portions of the control chambers 17 and 18.  
  The peripheral surface of the pintle 4 is further formed with, substantially triangular pilot notches 32 and 33 which are machined into the land 25 and respectively communicate with the control chambers 17 and 18. Two additional pilot notches 34, 35 are machined into the land 26 and respectively communicate with the control chambers 17 and 18. The length of the lands 25, 26 and control chambers 17, 18, as considered in the circumferential direction of the pintle 4, is selected in such a way that a port 16 begins to communicate with the control chamber 17 or 18 when the cylinder block 5 completes a movement through an angle a starting from that position in which the axis of such port coincides with the line AA shown in FIG. 2. The line AA is located in a symmetry plane which includes the axis of the pintle 4 and extends midway between the control chambers 17 and 18. As shown in FIG. 2, the plane including the line AA and the axis of the pintle 4 halves the groove 27 and the bore 30. When the upper port 16 of FIG. 2 is moved clockwise through the angle a; it begins to communicate with the control chamber 18 through the medium of the pilot notch 33; if the port is rotated counterclockwise, it begins to communicate with the control chamber 17 by way of the pilot notch 32 as soon as the cylinder block 5 completes a movement through the angle a. The same applies for the lower port 16 of FIG. 2 and the control chambers 18, 17. A port 16 assumes the position shown in the upper half of FIG. 2 when the corresponding piston 8 reaches the inner end of its stroke, and a port 16 assumes the position shown in the lower part of FIG. 2 when the corresponding piston 8 reaches the outer end of its stroke. The magnitude of the angle a depends on the friction coefficient p. between the shoes 9 and the slide block 10. The relationships will be explained in connection with FIGS. 3-5.  
  FIG. 3 illustrates the radial piston motor of FIG. 1 in a greatly simplified view. There are shown the pintle 4, a piston 8 and the articulate connection or universal joint 9a for itsshoe 9, the internal surface 36 of the slide block 10, and the path 37 of the center M of a joint 9a between the piston 8 and the respective shoe 9. The path 37 is a circular path whose center is spaced apart from the axis M of the pintle 4 and whose radius is shown at R. The eccentricity of the slide block 10 with respect to the pintle 4 is shown at e, and the center of the path 37 is shown at M The line AA intersects the axis M and center M A line m which connects the center M with the axis M makes an angle 7 with a line r which connects the center M .of the path 37 (i.e., the axis of the slide block 10) with the center M The extent of angular displacement of a piston 8 from a position corresponding to that of the port 16 shown in the upper half of FIG. 2 is indicated at d). The relationship between the angles 7 and d can be expressed as follows:  
  sin &#39;y e/R sin and &#39;y= arc sin (e/R sin (b).  
  For starting the radial piston motor, the eccentricity e is increased to its maximum value so that the value of e can be considered to constitute a constant.  
  FIG. 4 illustrates the forces which act upon a shoe 9. In this Figure F represents the piston forcewhich equals p. 0.785 11,} wherein d is the diameter of a piston 8 and p is the cylinder pressure. F is the force which is applied by a shoe 9 and equals F /cosy; F E is a relieving force which equals 5. F 6 is that portion of a shoe 9 which is totally relieved hydrostatically; R is the frictional force which equals 1. (F F H is the driving force which develops as a result of angular displacement of the piston and equals F tan &#39;y; and F is the starting force which equals H minus R. The force F can be determined in accordance with the following equations:  
 F 0.785 (1 p/cos y [tan &#39;y,u (l e)].  
  The values e, R, p-and ii, are known and constant so that the friction coefficient u is a parameter which can be varied to determine the magnitude of the starting force F.  
  The diagram of FIG. 5 indicates the changes in starting force F of a shoe 9. The force F is measured along an angle (1) of 180 at the high pressure side of the pintle 4. Of the aforementioned constants, p 100 bar, 6 0.50, e 4.5 millimeters, and d 18 millimeters. The diagram shows that, when the friction coefficient 1. 0.03, the starting force of a shoe 9 would be negative in the region between 06 and l74l90 and would thus interfere with starting of the radial piston motor. In other words, if the friction coefficient is 0.03, the platforms or lands25, 26 must be configurated in such a way that a port 16 begins to communicate with the high-pressure chamber only after it has advanced beyond the dead-center position through an angle a of 6. In such range of angular positions, the pressure in the port 16 equals the pressure in the interior of the housing 1 (see the recess or groove 27 in the land 25), and such pressure normally equals or closely approches atmospheric pressure, i.e., it is much lower than the fluid pressure in high-pressure control chamber 17. A negative starting force cannot develop because p equals zero. Even if the pressure in the housing 1 exceeds atmospheric pressure, it is still small when compared with the working pressure in chamber 17 so that the starting force which develops in the aforediscussed range of angular positions of the shoe is negligible. The situation is analogous when the port 16 communicates with the low-pressure side.  
  In the illustrated embodiment, the starting forces are positive in the range between 6 and 174. In this range, the port 16 must communicate with the high-pressure control chamber. The diagram of FIG. 5 further shows that, when the friction coefficient is 0.1 l, the starting force would be positive only in the range between 25 and 155 The angle a (FIG. 2) would have to equal 25 to thereby avoid the development of negative starting forces. As a rule, the exact magnitude of the angle &#39;7 a will be determined empirically (but as a function of t) because its magnitude depends to a certain extent on a host of variables which cannot always be calculated with a requisite degree of accuracy.  
  Referring again to FIG. 1, the peripheral surface of the pintle 4 is further formed with two pairs of elongated grooves 19, 20 and 21, 22 which respectively flank the high-pressure control chamber 17 and the low-pressure control chamber 18. The grooves l9-22 define with the respective control chambers pairs of sealing projections or ribs 119, 120 and 121, 122 which are surrounded by the cylindrical internal surface of the cylinder block. When the motor is in use, some pressurized fluid leaks from the control chamber l7 along the sealing projections 119, and establishes between such projections and the internal surface of the cylinder block 5 pressure fields which serve to counteract the forces tending to move the cylinder block radially toward the pintle in the region of the high-pressure control chamber. The pressure fields in the region of sealing projections 121, 122 counteract the forces which tend to move the cylinder block radially when the control chamber 18 constitutes a highpressure control chamber.  
  The manner in which the structure of FIG. 1 is operated as a motor to drive the output shaft 5a of the cylinder block 5 is well known in the art and need not be described here.  
  FIG. 6 illustrates a modified pintle 40 for use in a radial piston motor wherein the cylinder block 5 invariably rotates in a single direction. All such parts which are identical with or clearly analogous to the corresponding parts shown in FIG. 2 are denoted by similar reference characters. The peripheral surface of the pintle 40 is formed with a high-pressure control chamber 41 and a low-pressure control chamber 42 located diametrically opposite the chamber 41. The low-pressure chamber 42 communicates with elongated pilot notches 43, 44 which are respectively machined into the lands 45 and 46. The notch 43 has an extension 47 which extends circumferentially of the pintle 40. The land 46 is further formed with a short pilot notch 48 which communicates with the high-pressure control chamber 41. The effective width of the lands 45, 46 is selected in such a way that a port 16 can be completely sealed from both control chambers during travel from register with one control chamber toward register with the other control chamber. The line A-A coincides with the axes of those pistons (not shown in FIG. 6) which assume their inner or outer end positions. When a piston moves from the upper dead center position (adjacent to the land 45), it begins to communicate with the high-pressure control chamber 41 after the cylinder block 5 advances through an angle a. Analogously, a port 16 ceases to communicate with the control chamber 41 when it assumes the angular position shown in the lower part of FIG. 6, i.e., when the cylinder block 5 must advance through an angle a before the corresponding piston moves its axis into register with the line A-A. Thus, a port 16 communicates with the high-pressure control chamber 41 while the cylinder block 5 covers an angle minus 2a. The angle a is determined in the same way as described in connection with FIGS. 2 to 5.  
  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.  
 pistons reciprocably mounted in said cylinders and having outer end portions frictionally engaging said slide block so as to move radially between inner and outer end positions in response to rotation of said cylinder block; and a pintle having a cylindrical peripheral surface surrounded by said internal surface and provided with highand low-pressure control chambers located diametrically opposite each other and first and second lands separating said chambers from each other, one of said lands being in register with successive pistons assuming said inner end positions and the other of said lands being in register with successive pistons assuming said outer end positions, the width of said lands as considered in the circumferential direction of said pintle being such that a port which registers with a piston assuming one of said end positions is completely sealed from said control chambers and remains sealed from at least one of said control chambers while said cylinder block rotates relative to said pintle through an angle a whose magnitude is a function of the friction coefficient between said slide block and said outer end portions of said pistons, each of said pistons further comprising a second end portion articulately connected with the respective outer end portion and the starting force F of said outer end portions of said pistons during starting of said cylinder block equaling F= 0.785 (1,? p/cos (arc sin (e/R sin 01)) {tan (arc sin (e/R sin 01)) u (1 6)} E wherein d is the diameter of a piston, p is the fluid pressure in said high-pressure control chamber, e is the eccentricity of said slide block, R is the radius of the circular path along which the centers of articulate connections between said end portions and said second portions of said pistons orbit about said pintle, u is the friction coefficient, and e is the hydrostatically relieved area of each of said end portions.  
  2. A combination as defined in claim 1, wherein said one control chamber is said high-pressure control chamber.  
  3. A combination as defined in claim 1, wherein each of said pistons comprises a second portion and a universal joint between said second portion and the respective end portion.  
  4. A combination as defined in claim I, wherein each of said ports is located diametrically opposite another port of said cylinder block.  
  5. A combination as defined in claim 1, wherein said cylinder block is arranged to rotate in a single direction.  
  6. A combination as defined in claim 1, wherein at least one of said lands is provided with a recess wherein the fluid pressure is lower than in said high-pressure control chamber and which communicates with a port while such port registers with said one land and is sealed from said control chambers.  
  7. A combination as defined in claim 6, further comprising a housing supporting said pintle and said slide block and surrounding said cylinder block, said housing having an internal space communicating with said recess.  
  8. A combination as defined in claim 7, wherein said recess is an axially parallel groove in said one land.  
 9. A combination as defined in claim 7, wherein said recess is a radial bore in said pintle.