Abstract:
The invention relates to a piston pump for a motor vehicle braking system having a housing section and a piston guided displaceably in the housing section. The invention further has an intake valve having a valve seat arranged on the piston. The valve seat is configured as a circular sealing edge. A spherical valve body of the intake valve seals against the spherical sealing edge.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/060210 filed on Sep. 26, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a piston pump for a vehicle brake system, having a housing portion and a piston that is dispiaceably guided in the housing portion and has an inlet valve with a sealing seat embodied on the piston. 
     2. Description of the Prior Art 
     The piston pumps used for known vehicle brake systems, particularly anti-lock brake systems (ABS), serve to control the pressure in wheel brake cylinders. In the ABS, the piston pumps are provided for instance for returning brake fluid from one or more wheel brake cylinders to a master cylinder. The ABS often functions in combination with traction control (TC). Another known system, called an electronic stability program (ESP), improves driving safety by a further increment compared to ABS and TC. Wile ABS and TC function in the longitudinal direction of travel, ESP has an influence on transverse dynamics and therefore in principle is transverse traction control. For all these systems as well a further systems for increasing driving safety, piston pumps are employed. 
     Known piston pumps provided for vehicle brake systems comprise among other components a cylinder, which is embodied in a housing and in which a piston is received longitudinally movably. The piston drive is usually effected via an eccentric element, at which the rotary motion of a shaft driven by means of an electric motor is converted into a translational motion of a piston rod of the piston. The piston rod is pressed with its face end against the outer circumference of the eccentric element by means of a prestressing element, for instance in the form of a helical spring. Thus in the final analysis, a reciprocating pumping motion of the piston can be attained. 
     Known piston pumps furthermore as a rule have an inlet valve embodied as a seat valve, for controlling the inflow of fluid. The inflow of fluid from outside the piston pump through the inlet valve is effected in known piston pumps via a suction line, which has a comparatively high flow resistance. As a consequence, known piston pumps used for vehicle brake systems do not have sufficiently effective pressure buildup dynamics, since because of the high flow resistance, they can be filled only relatively slowly. 
     It is the object of the invention to create a piston pump of the type defined at the outset, in which the aforementioned problems are overcome and which have high pressure buildup dynamics. 
     SUMMARY OF THE INVENTION 
     According to the invention, a piston pump is created for a vehicle brake system, having a housing portion and a piston, which piston is guided displaceably in the housing portion and has an inlet valve with a sealing seat embodied on the piston. Also in the piston pump of the invention, the sealing seat is configured as a circular sealing edge, against which a spherical valve body of the inlet valve provides sealing. 
     In the piston pump of the invention, the sealing seat of the inlet valve is configured by means of a sealing edge, against which a ball, as a valve body, provides sealing. In this kind of inlet valve, the sealing diameter is determined solely by the diameter of the associated sealing seat bore, and not by the contact diameter of the ball against a conical seat as is the case in known inlet valves. According to the invention, with a comparatively large sealing seat bore with correspondingly little flow resistance, a small contact diameter of the ball can therefore still be achieved. This small contact diameter means that the ball lifting from the sealing seat, for the same ball stroke, opens up a larger area through which fluid can flow than is the case with a large contact diameter. It is true that with known inlet valves, a larger area through which fluid can flow could be achieved, but the ball stroke would have to be longer for that purpose. That, however, would have an adverse effect on the dynamics of the inlet valve, and the valve would in particular close more slowly. 
     According to the invention, in the piston pump of the invention, the diameter of the circular sealing edge is configured to be preferably between 75% and 90%, and especially preferably 83%, of the diameter of the associated spherical valve body of the inlet valve. With this kind of size of the circular sealing edge, the medium flowing through the inlet valve is carried fluidically with an especially slight pressure drop. 
     Also preferably, the piston is configured with a piston disk portion in which a circular-cylindrical supply conduit portion, forming the circular sealing edge, for brake fluid is embodied. By means of this kind of supply conduit portion, embodied in a piston disk portion and thus especially short, the sealing edge provided according to the invention can be manufactured especially precisely and at the same time economically. 
     Moreover, preferably, the piston is configured with a piston rod portion, oriented toward an eccentric drive, and with a piston disk portion forming the circular sealing edge; in the piston rod portion, a longitudinally oriented first supply conduit portion for brake fluid is formed, and in the piston disk portion, a second supply conduit portion adjoining the first in the flow direction and forming the circular sealing edge is formed. At the second supply conduit portion, the cross-sectional area through which brake fluid flows is configured to be smaller than the corresponding cross-sectional area of the first supply conduit portion. Because of this configuration, with respect to the medium it is to carry, the piston disk portion with its supply conduit portion is a flow portion which although narrow is also in particular shorter; therefore in hydraulic terms, this portion is a baffle. 
     The longitudinally oriented first supply conduit portion embodied in the piston rod portion is preferably configured by means of an axial bore and at least one radial bore. Viewed in cross section, this supply conduit portion can be configured with a comparatively large area and thus fluidically especially favorably. 
     The longitudinally oriented first supply conduit portion embodied in the piston rod portion can alternatively also be configured economically and at the same time with a large volume by means of a radially and axially extending slit. 
     With a view to the aforementioned kinds of configuration, the piston of the invention is especially preferably configured in two parts; with one part of the piston, the piston rod portion oriented toward the eccentric drive is configured, and with the second part of the piston, the piston disk portion forming the circular sealing edge is configured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, exemplary embodiments of a piston pump according to the invention will be described in further detail in conjunction with the accompanying schematic drawings, in which: 
         FIG. 1  shows a longitudinal section through a piston pump of the invention; 
         FIG. 2  is a basic sketch in the form of a longitudinal section through an inlet valve of a piston pump of the prior art; 
         FIG. 3  shows the view as in  FIG. 2  of a first exemplary embodiment of an inlet valve of a piston pump according to the invention; 
         FIG. 4  shows the view as in  FIG. 2  of a second exemplary embodiment of an inlet valve of a piston pump according to the invention; and 
         FIG. 5  is a graph which illustrates the dependency of the size of the area, through which fluid flows, at the inlet valve of  FIGS. 3 and 4  on the diameter of the associated sealing seat opening. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a piston pump  10  according to the invention, which includes two housing portions  12  and  14 ; in the housing portion  12 , a cylindrical bore  16  is embodied, in which a piston  26  is guided displaceably. The piston  26  includes a sealing element in the form of a sealing ring  18 , a receiving means  20  for an inlet valve  22  embodied as a ball seat valve, and a piston rod  62 , which adjoins the sealing ring  18 . The piston rod  62  is embodied in two parts and includes two piston rod elements  28 ,  30 ; the piston rod element  28  is a longitudinally oriented piston rod portion and is received firmly by means of a press fit in the piston rod element  30  that forms a piston disk portion, in order to create a nonpositive connection between the two piston rod elements  28 ,  30 . By the two-part embodiment of the piston rod  62  provided, a piston rod  62  that is economical to produce can be achieved, since an economical rodlike piston rod element  28  is connected to a piston rod element  30  that can be furnished very economically in the form of a plastic injection-molded part, turned part, cast part, or cold-formed part. In the piston rod element  28 , a fluid introduction opening  64 , described in more detail hereinafter, can also be embodied especially economically. 
     The receiving means  20  and the sealing ring  18  together form a one-piece valve cap/sealing ring combination  24 . The piston rod element  30 , for connecting the piston rod  62  to the sealing ring  18 , is received in the sealing ring opening  32  of the sealing ring  18 . 
     The piston pump  10  furthermore has an outlet valve  34 , embodied as a ball seat valve, which is disposed inside an outlet valve cap  36 , and the ball  38  of the ball seat valve  34  is guided in a receptacle  40  embodied in the outlet valve cap  36 . The outlet valve cap  36  may be made in part by metal-cutting machining or cold-forming. A helical spring  42  braced on the cap bottom presses the ball  38  against a valve seat  44 , which is embodied in the housing portion  12  of the piston pump  10  and adjoins an outlet hole  46  embodied in the housing portion  12 . Brake fluid flowing from the outlet hole  46  through the outlet valve  34  flows via a radial conduit  48  between the outlet valve cap  36  and the housing portion  12  in the direction of the pump outlet (not shown). 
     In the cylindrical bore  16  embodied in the housing portion  12 , a prestressing element in the form of a helical spring  50  is also disposed, which rests with one end on the sealing ring  18  and with the other end is braced on the bottom of the housing portion  12 . The helical spring  50  is subject to initial tension, in order to press the two-part piston rod  62 , via the sealing ring  18  on which the piston rod  62  rests with its face end disposed inside the piston pump  10 , against the circumference of the eccentric element of an eccentric drive (not shown). Thus the outer face end of the piston rod element  28  can be kept constantly in contact with the eccentric element. Driving the eccentric element to rotate causes the entire piston  26  to execute an axially reciprocating stroke motion, which effects a delivery of brake fluid in a known manner. 
     The valve seat  52  of the ball inlet valve  22  is embodied as a sealing edge on its face end on the piston rod element  30 . This embodiment according to the invention of the valve seat  52  on the piston rod element  30  of the piston rod  62 , in combination with the one-piece embodiment, according to the invention, of the sealing ring  18  and the receiving means  20  in the form of the valve cap/sealing ring combination  24 , has pronounced advantages. 
     For disassembling the piston pump  10 , the piston rod element  30  received with a clearance fit in the sealing ring opening  32  should be pulled out of the sealing ring opening  32 . The clearance fit provided according to the invention makes problem-free release of the piston rod element  30  from the sealing ring  18  possible. The individual components of the inlet valve  22 , that is, the ball  54  and the helical spring  56 , can then be easily removed from the receiving means  20 . Finally, once the one-piece valve cap/sealing ring combination  24  is pulled out of the cylindrical bore  16 , the helical spring  50  can be removed from the cylindrical bore  16 . The assembly of the piston pump  10  is equally simple; the clearance provided makes unproblematic centering of the piston rod element  30  in the sealing ring opening  32  possible. 
     A snap connection in the form of a snap lug  58  is also embodied on the sealing ring  18  and embraces a shoulder embodied on the piston rod element  30 . By means of the snap lug  58 , the piston rod  62  can be retained on the sealing ring  18  during the assembly of the piston pump  10 , and in particular during the mounting on the cylindrical bore  16 , thus simplifying the assembly of the piston pump  10  of the invention substantially. The thus-attained retention function can alternatively be attained by means of a thermal deformation, after the valve cap/sealing ring combination  24  has been slipped onto the piston rod element  30 . The snap lug  58  takes on only the described retention function that is advantageous for assembly purposes. During the operation of the piston pump  10 , the spring force of the helical spring  50  assures that the valve cap/sealing ring combination  24 , despite the clearance fit that is advantageous for assembly purposes, rests permanently on the piston rod element  30  in the axial direction. Moreover, the snap lug  58  has a protective effect between the cylindrical bore  16  and the piston rod element  30 . A sealing lip  60  is also embodied on the sealing ring  18  of the valve cap/sealing ring combination  24  and closes off the cylindrical space between the piston  26  and the cylindrical bore  16  radially in pressure-tight fashion. 
     In the piston rod element  28 , a fluid introduction opening  64 , as a supply conduit portion, for introducing fluid into the interior of the piston  26  is provided, which in this case is in the form of a slit  66 , radially open on one side, that extends in the axial direction. By means of the slit  66 , fluid from outside the piston rod element  28  can flow with only very slight flow resistance into the interior of the piston  26 . After flowing through the slit  66 , the fluid flows into an axially extending opening  68 , which is embodied in the piston rod element  30  and forms a further supply conduit portion and extends as far as the inlet valve  22 . According to the invention, both the slit  66  and the opening  68  are made quite large, to minimize the flow resistance. The piston pump  10  of the invention can thus be filled quickly, and as a result, good pressure buildup dynamics can be attained. 
     The second piston rod element  30  partially covers the fluid introduction opening  64  in the axial direction of the piston  26 . In this way, according to the invention, the flow course through the piston rod element  30  that forms a piston disk portion can be kept as short as possible, so as to create the least possible flow resistance. The first piston rod element  28  is retained by means of a press fit on the second piston rod element  30 , at the portion  70  of the second piston rod element  30  that partly covers the fluid introduction opening  64 . 
     In an alternative embodiment, not shown, the slit  66  penetrates the piston rod element  28  diametrically and thus once again makes very fast filling of the interior of the piston  26  possible. Also, the second piston rod element  30 , with a covering portion  70 , partially covers the slit  66  in the axial direction of the piston  26 . 
     In a further alternative embodiment, also not shown, the fluid introduction opening  64  is configured in the form of a radial bore, diametrically penetrating the piston rod element  28 , and an axial bore communicating with it in a fluid-carrying mariner. The radial bore is partly covered by a covering portion  70  of the piston rod element  30 . 
     In the piston pump  10  of  FIG. 1 , as noted, the sealing seat or valve seat  52  is also configured as a circular sealing edge  72 , against which the ball  54  provides sealing, as a spherical valve body of the inlet valve  22 . The diameter of the circular sealing edge  72  is 3.3 mm and is thus equal to approximately 83% of the diameter of the ball  54 , which is 4 mm (see also  FIG. 3 ). In an alternative embodiment, the diameter of the circular sealing edge  72  is 3.6 mm, for a diameter again of 4 mm for the ball  54  (see  FIG. 4 ). With this kind of sealing of the ball  54  at the sealing edge  72 , compared to the prior art (see  FIG. 2 ), in which the ball of an inlet valve of the piston pump is sealed against a conical seat, the diameter of the opening  68  is comparatively large, and thus for the same ball stroke, the result is a lesser flow resistance for the inlet valve in this region. At the same time, the area through which fluid flows between the raised ball  54  and the sealing edge  72  (see  FIG. 5 ) is comparatively large for the same ball stroke, so that less flow resistance occurs in this region as well. This is especially true for a diameter of 3.3 mm (see line  74  in  FIG. 5 ) of the sealing edge  72 , compared to a sealing edge  72  that has a diameter of 3.6 mm (see line  76  in  FIG. 5 ). 
     The foregoing relates to the preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.