Patent Publication Number: US-2005123413-A1

Title: Radial piston pump

Description:
The present invention concerns a radial piston pump with a pump body, in which pistons and cylinders are placed radially to a driving eccentric, by means of which, a piston during a suction thrust can draw in a fluid through an intake port which is built into the cylinder in accord with the principal concept of claim  1 .  
      Radial piston pumps have been extensively used in motor vehicles for transporting lubricating oil, pumping fuel, and as pressure generating means for hydraulically operated servomechanisms. Such pumps find further use as hydraulic pumps for power steering, shock absorbers, clutches and continuous transmissions, automatically controlled transmissions, and hydraulically operated driving and auxiliary equipment, and for operational machines and the like. Radial piston pumps are predominately installed in cases where a higher pressure level is necessary.  
      Serving as pumps of the displacement type, radial piston pumps do not deliver a pumped medium in continuous flow, but irregularly, in partial volumes per revolution of a drive eccentric. The cyclically transported volumes give rise to pressure variations and pulsations, both at the intake and output ports of the pump. The said pulsations inlet and outlet overlap, due to the opening and closing of the of the pump chambers, that is to say, the cylinders. The impacts are particularly severe if, during operation with volute spring activated inlet and outlet valves, suddenly spaces are made available which exhibit large pressure differentials. Beyond this, as a rule, large pressure swings also occur, if a system operates at high pressure, or if a cylinder is partially filled.  
      If pressure in a cylinder attains an opening pressure of the annular volute spring of a valve, then the valve lifts away from its seat, and the hydraulic fluid, for example pressurized oil, is pushed into a reserve tank. If the pressure in the cylinder falls below the closure pressure of the spring loaded valve, then this valve impacts once again on the seat and causes thereby a loud hammering noise. This performance repeats itself at every rotation of the drive eccentric, in accord with the number of piston-cylinder combinations of a pump.  
      The noise is just that much louder, as the opening and closure process becomes more dynamic. Also influencing the said hammering noise are the related opening pressures and closing pressures and as well, the rate of increase of pressure at the instant of opening generates noise. If these values are very high, then the spring loaded valve will be lifted instantaneously very far from its seat and accordingly return to its seated position with considerable force. The pressure impacts of all pistons produce a general noise, which resounding from the body of the pump, radiates as audible air-borne noise.  
      In order to both reduce and mitigate the peaks of the pressure impacts, and also to reduce the noise generation of the radial piston pump, there is proposed in DE A 43 36 673, a radial piston pump, which has a plurality of pistons set into corresponding cylinder borings in a pump housing, wherein each piston is loaded by a spring, which spring abuts against a detent. The drive shaft is axially affixed to an eccentric, upon which a slide bushing is placed. Between one inner slide ring, which is pushed onto the said slide bushing, and a concentric outer slide ring, is located a damping element, which, for example, is designed as a flat, compression spring. Upon rotation of the eccentric, in this way, the respective piston which is expelling oil under pressure can, to some extent, act resiliently against the assigned section of the slide ring, so that the pressure spike normally occurring at the beginning of the pressure thrust can be reduced in intensity.  
      In another published embodiment, the damping element possesses the shape of slotted annular spring, wherein, equally distributed projections supportingly oppose one another across the inner and outer diameters of said annular spring. The supporting projections permit sufficient clearance between them, so that the particular piston making the thrust can resiliently modify itself.  
      In yet another embodiment an elastic ring is inserted between the two slide rings. The said elastic ring can well be made of rubber and be vulcanized onto both sides of the slide ring. Instead of a rubber ring, this disclosure also allows that, between the inner and the outer slide rings, an annular ring may be inserted, which is again vulcanized, but consists of a combination of multiple straight sections.  
      In DE A 101 26 151 a slide ring for a radial piston pump is described, which consists of an inner ring and a thereto coaxially arranged outer ring, between which a damping element is interposed. The damping element is constructed as being of “gone piece” and has on both sides, respectively, a bulged rim, which lies against the side rim of the inner ring against the outer circumference thereof, and at the rim of the outer ring within the inner circumference thereof, whereby, between the two said bulged rims, a connecting structure is provided, which, for example, can be formed by an additional damping ring, which is connected with the said bulged rim by means of fabricated webs. In addition, it is possible, that by appropriate formation of the damping element between the inner ring and the outer ring, chambers are created, into which a filling fluid may be introduced, so that the rigidity of the sliding rings can be made variable.  
      With these measures, the possibility is at hand, to reduce the noise issuing from the pump during its operation. However, this does not completely set aside the said noise, since this is generated by differing noise sources.  
      The intake ports commonly open into the operational cylinders of conventional radial piston pumps. Through these ports, upon one directional movement of the corresponding piston, fluid is drawn into the said cylinder. These ports are fabricated to be rectangular, to fit the similar rectangular suction conduit. This means, that the ports have, respectively, one straight line under edge, two side edges running perpendicularly to the said under edge, and again a straight line upper edge. What is disadvantageous with this right angled intake port geometry, is, however, that by means of the straight line port upper edge, the intake port is abruptly shutoff, when the piston in the respective cylinder carries out its pressure generating thrust. When this occurs, a largely accelerated pressure gradient (curve slope) occurs in the cylinder. Because of this sharp rate of increase in pressure, the noise level of the radial piston pump reacts in a manner negative to allowable sound levels.  
      Thus, the purpose of the present invention is, to achieve a further reduction in the noise level of a suction throttled radial piston pump.  
      This purpose is accomplished with the stated features in the characterization section of claim  1 ; advantageous embodiments are described in the subordinate claims.  
      The present invention is initiated from a radial piston pump with a pump body, in which pistons and cylinders are placed in radial distribution about a drive eccentric, wherein the pistons, upon respective suction producing movements, draw fluid through intake ports, which respectively open into the said cylinders. Upon a reverse motion of the said pistons with corresponding pressure expulsion, the said fluid is transported into a reserve tank. In accord with the present invention, contrarily, provision is now made, that the geometry of the intake ports is so specified, that upon the pressure thrust of a piston, a lower pressure increase rate is achieved inside the cylinder.  
      In the case of a particularly advantageous embodiment, the geometry of the intake port calls for a straight-lined under edge and a curved upper edge, into which upper edge both side edges (right and left) make a smooth transition.  
      By means of this geometry of the intake ports the advantage is achieved, that no hard striking closure of the intake port occurs during the piston upon its pressure thrust. Accordingly, when compared with the conventional radial piston pump with its right angled intake ports, a softer pressure increase is achieved along with a lower pressure rise rate, which leads to an improvement of the produced noise level of the radial piston pump.  
      Intake port geometric fabrication of intake ports can be carried out by means of various production methods. These methods would include milling, contour turning, eroding, boring, etc. Especially, by means of contour turning, almost any desired “show-window” geometry can be excised at neutral costs.  
      The particularly favorable embodiment for the geometry of the intake port is principally an example for an intake port contour, by means of which the noise level of the pump can be lessened.  
      Further advantageous formulations of the geometry of the intake port become evident in the following description and the subordinate claims. 
    
    
      In the following, the invention will be more closely described and explained with the aid of the drawing, in which advantageous embodiments are presented. There is shown in:  
       FIG. 1 a  cross section through a conventional radial piston pump with the arrangement of the essential components,  
       FIG. 2 a  large scale drawing of the geometry of an intake port in a conventional radial piston pump,  
       FIG. 3 a  first example of an invented geometry for the intake port of a radial piston pump, and  
       FIGS. 4-9  are further advantageous geometries for the intake port of a radial piston pump. 
    
    
       FIG. 1  shows a cross section through a conventional, suction throttled radial piston pump, wherein the pump body is designated by reference number  1 , in which a multiplicity of radially aligned cylinders  2  are provided. The number  4  defines a slide ring arrangement, which, in a known manner, is comprised of one inner ring, one outer ring and a provided spring interposed therebetween. The slide ring placement circularly encompasses an eccentric  5 , the rotational movement of which converts to a translational movement of the piston  3  in the cylinders  2 . No.  7  denotes an annular suction groove in the pump body, whereby in each cylinder  2 , an intake port is made.  
      The number  6  defines a zone line, which surrounds one of the intake ports  12 .  FIG. 2  demonstrates now an enlarged presentation of the said zone  6  with the intake port  12 . The intake port  12  possesses a straight line under edge  9 , an upper edge  2  above which also is in straight line design, and two side edges  11 ,  11 ′ connected thereto. In this case, a right angled geometry has been accomplished. In the case of a pressure thrust of the piston  3 , which moves itself back and forth in the cylinder  2 , the upper edge  8  of the intake port closes with a severe impact, whereby a higher pressure rise gradient is created in the cylinder. By means of these high pressure increase gradients, the noise level of the pump becomes negative to acceptable levels.  
       FIG. 3  shows an especially favored embodiment of an invented geometry for the intake port in each cylinder  2  of a radial piston pump. In the case of this embodiment example, as the  FIG. 3  indicates, the under edge  9  of the intake port  13  is made as a straight line. Instead of the upper edge being made parallel to the said under edge  9 , with side edges running perpendicularly thereto, a curvature is introduced, which, on one end, begins at the under edge  9 , and curvingly terminates thereon on the other end. In accord with the placement of this curvature  10 , the geometry of the thereto constructed intake port  13  is semicircularly, semi-elliptically, or convexly bowed upward at this or some other curvature.  
      By this curvature of the intake port  13 , no sudden closure of the said intake port  13  occurs upon the pressure thrust, so that a more gradual build up of pressure takes place, which leads to a diminishing of the pressure rise gradient in the cylinders and thereby a clear reduction of the noise level of the pump.  
      It could be quickly determined in a practical application, that, because of the novel geometry of the intake port, especially the curved outline of the intake port in  FIG. 3 , a substantial improvement of the noise level, especially at a speed of rotation in a range of 1000 to 2000 RPM can be achieved.  
      Further advantageous geometries for an intake port are presented in FIGS.  4  to  9 .  
       FIG. 4  shows a triangular geometry for an intake port  14  with a straight under edge and with two straight line, side sections  20 ,  21  which angularly run together.  
       FIG. 5  shows a geometry for an intake port  15 , again with a straight under edge  9 , with two side edges  11 ,  11 ′ which are perpendicular thereto, and which sides edges continue to form upper edge sections  22 ,  22 ′. The said upper edge sections  22 ,  22 ′ accordingly run parallel to the under edge  9 . These sections  22 ,  22 ′ are joined midway by a connecting apex  23 , the curve of which extends away from the under edge  9 .  
       FIG. 6  shows a geometry for an intake port  16 , again with a straight line under edge  9  and with two, straight line edges  11 ,  11 ′ which are perpendicular to said under edge  9 . The upper edge  23  connects the edges  11 ,  11 ′ with a smooth bend toward the under edge  9 .  
       FIG. 7  shows the geometry for an intake port  17 . which is circular in shape.  
       FIG. 8  shows the geometry for an intake port  18  with a straight line under edge  9  and having two side edges  11 ,  11 ′ perpendicular thereto. The side edges  11 ,  11 ′ are curvingly extended toward the center into slanted sections  25 ,  25 ′, which run at an angle departing from the under edge  9 . These sections  25 ,  25 ′ join in an apex  26 , which is curved away from the under edge  9 .  
       FIG. 9  shows the geometry for an intake port  19 , with a straight under edge  9 , with two side edges  11 ,  11 ′ perpendicular thereto. The upper edge comprises two sections  27 ,  27 ′, curving in the direction of the said under edge  9 , which are joined by an apex  28  which extends away from the under edge  9 .  
      The geometries presented in  FIGS. 3-9  for an intake port in the cylinder of a radial piston pump possess all the same advantage, that being, namely, to avoid a impact type closure of the said intake ports caused by the piston  3  in the course of a pressure thrust and thus, contrarily, to lead to a repressed buildup of pressure with a small pressure increase gradient. Further geometric shapes, especially the combination of a plurality of radii of curvature can be easily conceived. A volume reflux, caused by this kind of intake port geometries in the proportional range, or a transport back flow, can be compensated for by the exact adjustment of the relevant components for the maintenance of transport flow, that is to say, by means of a radial piston pump with lateral intake suction by changes of the (1) the suction groove diameter, (2) the eccentric, and (3) the height of the piston.  
      Reference Numbers  
       1  Pump body  15  Intake port  
       2  Cylinder  16  Intake port  
       3  Piston  17  Intake port  
       4  Slide ring arrangement  18  Intake port  
       5  Eccentric (a cam disk)  19  Intake port  
       6  Limit line of intake port  20  Section  
       7  Suction groove  21  Section  
       8  Upper edge  22  (and  22 ′) Section  
       9  Under Edge  23  Curvature  
       10  Curvature  24  Circle (circumference of  
       11  (and  11 ′) side edge port)  
       12  Intake port  25  (and  25 ′) Section  
       13  Intake port  26  Curvature  
       14  Intake port  27  (and  27 ′) Section  
       28  Curvature