Abstract:
The invention relates to a pump having a valve through which a fluid can optionally flow. The valve is embodied by a cavity for displaceably guiding a spherical blocking body, and a valve seat that is spatially adapted to the spherical shape of the blocking body. A free space protruding radially outwards from the spherical body is located downstream, directly behind the valve seat, for temporarily receiving the fluid which flows through the valve seat.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/060052 filed on Sep. 21, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a pump, in particular a piston pump, having a valve through which a fluid can selectively flow and which has a receptacle for movably guiding a spherical blocking body and has a valve seat adapted three-dimensionally to the spherical shape of the blocking body. 
     2. Description of the Prior Art 
     Piston pumps are used, among other purposes, in known vehicle brake systems, especially anti-lock brake systems (ABS). There, they serve to control the pressure in wheel brake cylinders. In the ABS, they are provided for instance for returning brake fluid from one or more wheel brake cylinders to a master cylinder. Often, the ABS functions in combination with traction control (TC), which likewise makes use of piston pumps. A further known system, known as an electronic stability program (ESP), improves the driving safety by a further increment over ABS and TC by varying the crosswise dynamics of the vehicle. In this system as well, piston pumps are employed. 
     Known pumps used particularly for vehicle brake systems have valves, for controlling the fluid flow direction through the pump, which are as a rule embodied as check valves acted upon springs and serve as inlet and outlet valves. Preferably, the check valves acted upon by springs are embodied in the form of ball-seat valves, including a blocking body in the form of a ball and a valve seat adapted three-dimensionally to the spherical shape of the blocking body. In the case of the ball-seat valves acting as an outlet valve, the ball is usually guided in a receptacle embodied in an outlet valve cap of the known piston pumps. When fluid flows out through an outflow bore embodied in the piston pumps, the ball opens the outlet region in accordance with the following principle. The ball migrates tangentially out of the sealing seat in the direction of the outlet valve cap bottom and the outflow bore. The ball in this case opens only minimally, since a dynamic pressure develops upstream of the ball. In addition, the ball is drawn into the outflow groove, directly adjoining the valve seat, by the outflow of the fluid. Overall, in the pump interior of known piston pumps, a high dynamic pressure develops, which results in high stress on components. Moreover, because of what is described above, known piston pumps have high driving torque and accordingly a high system output. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The object of the invention is to disclose a pump which can be used in particular for vehicle brake systems and in which during operation, only a slight stress on components occurs, and which furthermore has only slight driving torque and a low system output. 
     This object is attained according to the invention by the pump referred to at the outset, in which directly downstream of the valve seat, a free space protruding radially outward from the spherical blocking body is embodied for the sake of briefly receiving fluid passing through the valve seat. 
     As a result of the free space embodied according to the invention, when fluid flows through the valve, an outflow cross section develops, which is markedly increased compared to the outflow cross sections of known pumps. A throttling effect resulting from an overly small outflow cross section is thus avoided according to the invention. In this way, in the pump according to the invention no dynamic pressure develops, which is associated with a markedly reduced stress on the system and its components. 
     In an advantageous refinement of the invention, downstream of the valve seat, an outflow line is provided, and the free space is embodied essentially diametrically opposite the outflow line. Fluid from the pump according to the invention can flow through the opened valve into the outflow line and thus be carried out of the pump. Thus according to the invention, a valve-controlled pump outlet can be created with which no dynamic pressures that put stress on components are associated. 
     In a practical refinement of the invention, the free space is formed by a concave cavity of the component that forms the receptacle. The component forming the receptacle may for instance be an outlet valve cap. 
     Preferably, the free space is formed by a convex peripheral shaping of the component forming the receptacle. A convex peripheral shaping of the component forming the receptacle can be achieved with little production effort or expense. Alternatively, the free space can also be formed by a phase designed on the component forming the receptacle. In the same way as a convex peripheral shaping, a phase can also be attained with little production effort and hence economically. 
     In a further practical refinement of the invention, the free space has a depth which amounts to at least 25% of the diameter of the spherical blocking body. By means of a free space depth thus specified according to the invention, the throttling effect known from the prior art associated with the dynamic pressure can be effectively prevented, and at the same time, known fundamental functions of the valve, especially a fluidically optimal outflow before the equator of the ball can be maintained. For that purpose, the free space according to the invention should preferably have a maximum height that amounts to at least 25% of the diameter of the spherical blocking body. 
     In an alternative practical refinement of the invention, the valve seat has a valve seat opening with a predetermined mean diameter, and the free space has a depth which amounts to at least 33% of the predetermined mean diameter, in order in particular to maintain the known fluidically advantageous fundamental functions of the valve. For that purpose, the free space should according to the invention preferably have a maximum height which amounts to at least 33% of the predetermined mean diameter. 
     In an especially practical refinement of the invention, the pump has a piston, which is guided displaceably in a housing portion of the piston pump, and the piston has a receiving part for receiving an inlet valve, a sealing element, adjoining the receiving part, for sealing the piston off from the housing portion, and a piston rod, adjoining the sealing element, and the sealing element is embodied in one piece with the receiving part. 
     Accordingly, the sealing element is embodied in one piece with the receiving part. This has the advantage that in a distinction from pumps known from the prior art, which are used especially for vehicle brake systems, the functions of the sealing element and of the receiving part provided for receiving an inlet valve are performed by only a single component. Thus according to the invention, compared to the known versions, one less component is needed, and as a consequence, assembly and disassembly of the pump of the invention can be done quite simply, and the chain of tolerances is shortened markedly. Moreover, by the economy from using one less component achieved according to the invention, the production costs of the pump can be reduced markedly. Finally, the pump according to the invention, because of the economy of one component, can be made markedly smaller than known pumps. 
     Preferably, the inlet valve has a valve seat, which is embodied on the piston rod. This structural embodiment according to the invention makes simple assembly and disassembly of the pump possible. For instance, for disassembling the pump, the piston rod adjoining the sealing element can be removed from the sealing element. Next, the inlet valve, which is preferably embodied as a seat valve, can be removed along with its individual components, for instance including a blocking body and a spring element, from the receiving part embodied in one piece with the sealing element without major effort. Finally, the sealing element, on which the receiving part is embodied in one piece and which is received longitudinally movably in the cylinder of the pump, can easily be removed from the cylinder. 
     In a further advantageous refinement of the invention, a prestressing element, preferably in the form of a helical spring, is provided, which rests on the sealing element and with which the piston is forced in the direction out of the housing portion. The prestressing force transmitted from the prestressing element to the sealing element keeps the piston in an outer position at all times. In this way, according to the invention, the outer face end of the piston can be pressed against the eccentric element of an eccentric drive, in order thus to convert a translational driving motion, furnished by the eccentric drive, into a reciprocating pumping motion of the piston. By means of the prestressing element, the pump of the invention can be used in conjunction with eccentric drives that are preferentially used in brake systems for driving the pumps. 
     In a practical refinement of the invention, the sealing element is embodied in the form of a sealing ring having a sealing ring opening, and the piston rod is received in the sealing ring opening, and the piston rod is preferably received with a clearance fit in the sealing ring opening. By means of a clearance fit, the piston rod can be centered in the sealing ring opening without problems. Moreover, a clearance fit makes problem-free release of the piston rod from the sealing ring opening, which is necessary for disassembly purposes, possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, exemplary embodiments of a pump according to the invention are described in further detail in conjunction with the schematic drawings, in which: 
         FIG. 1  shows a longitudinal section through a pump according to the invention; 
         FIG. 2   a  shows a longitudinal section of the receptacle and of the valve seat of an outlet valve of a piston pump known from the prior art; 
         FIG. 2   b  is a three-dimensional view of the outflow region, resulting from  FIG. 2   a , for the outlet valve; 
         FIG. 3   a  shows a longitudinal section of the receptacle and of the valve seat of an outlet valve of a piston pump according to the invention; and 
         FIG. 3   b  is a three-dimensional view of the outflow region, resulting from  FIG. 3   a , for the outlet valve. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a pump according to the invention in the form of a piston pump  10 . The piston pump  10  includes two housing portions  12  and  14 , and in the housing portion  12 , a cylinder 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, which receiving means  20  is embodied in one piece with the sealing ring  18  and in the present case is embodied as an inlet valve cap; 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 received firmly in the piston rod element  30  by means of a press fit, in order to create a nonpositive connection between the two piston rod elements  28 ,  30 . Because of the two-part embodiment of the piston rod  62  provided, a piston rod  62  that is economical to produce can be attained, since according to the invention an economical rodlike piston rod element  28  is connected to a piston rod element  30  which can be furnished quite economically in the form of a plastic injection-molded part, a turned part, a cast part, or a cold-formed part. 
     The receiving means  20 , designed as an inlet valve cap, 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 a 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 manufactured 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 which 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 in the direction of the pump outlet (not shown) via an outflow bore in the form of a radial conduit  48  between the outlet valve cap  36  and the housing portion  12 . 
     A prestressing element in the form of a helical spring  50  is also disposed in the cylinder bore  16  embodied in the housing portion  12 ; it rests with one end on the sealing ring  18  and is braced with the other end on the bottom of the housing portion  12 . The helical spring  50  is prestressed, 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 always 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 in a known manner causes brake fluid to be pumped. 
     The valve seat  52  of the ball inlet valve  22 , which can be made for instance by ball embossing or stamping, is embodied on the face end of 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  with the receiving means  20  designed as an inlet valve cap, in the form of a valve cap/sealing ring combination  24 , offers marked advantages in assembly and disassembly of the piston pump  10 . For disassembly of the piston pump  10 , the piston rod element  30 , received with a clearance fit in the sealing ring opening  32 , must be drawn 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 here. The individual components of the inlet valve  22 , that is, the ball  54  and the helical spring  56 , can then be removed easily from the receiving means  20 . Finally, after the one-piece valve cap/sealing ring combination  24  is removed from the cylinder bore  16 , the helical spring  50  can be removed from the cylinder bore  16 . Assembling the piston pump  10  proves to be correspondingly simple; the clearance fit provided enables problem-free centering of the piston rod element  30  in the sealing ring opening  32 . 
     Also on the sealing ring  18 , a snap connection in the form of a snap lug  58  is embodied, which 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 mounting on the cylinder bore  16 , thus simplifying the assembly of the piston pump  10  of the invention substantially. The retention function thus attained according to the invention 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 . According to the invention, 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  rests permanently on the piston rod element  30  in the axial direction, despite the clearance fit that is advantageous for assembly purposes. Moreover, the snap lug  58  has a protective effect between the cylinder 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 ; it closes off the cylinder chamber between the piston  26  and the cylinder bore  16  in a radially pressure-tight fashion. 
     Finally, the piston pump  10  has a radial bore  96 , embodied in the piston rod element  30 , and a central axial bore  98 , through which fluid from outside the piston pump can flow through the inlet valve  22 . 
       FIG. 2   a  shows an outlet valve cap or a receptacle and a valve seat of the outlet valve of a known piston pump, and a three-dimensional view of the outflow region that results for the outlet valve is shown in  FIG. 2   b.    
       FIG. 3   a  shows the outlet valve cap  36  and the valve seat  44  of the outlet valve  34  of the piston pump  10  of the invention, and a three-dimensional view of the outflow region that results for the outlet valve  34  is shown in  FIG. 3   b.    
     In  FIGS. 2   a ,  2   b ,  3   a  and  3   b , the regions that when there is a flow through the outlet valve  34  are filled with flowing fluid are indicated schematically by dotted shading. 
     A circular-cylindrical receptacle  40  (shown in  FIG. 3   a ), in which the ball  38  ( FIG. 1 ) is guided in  FIGS. 2   a  through  3   b , of the outlet valve  34  is embodied in the outlet valve cap  36  of the piston pump  10  of the invention. In the outlet valve cap  36  of the piston pump  10  of the invention, a free space protruding radially outward from the ball  38  is embodied, in order, when there is a flow through the outlet valve  34 , to briefly receive the fluid passing through the valve seat  44  and an outflow cross section face  80 . The free space  84  is embodied essentially diametrically opposite an outflow line  48  leading out of the receptacle  40 , and fluid from the piston pump  10  of the invention can flow via the opened outlet valve  34  into the outflow line  48  and thus can flow out of the piston pump. 
     The free space  84  (see  FIG. 3   a ) is formed by a concave cavity  82  of the outlet valve cap  36  and can alternatively also be embodied as a chamfer, a convex radius, or a groove. 
     The free space  84 , which is increased in size compared to the prior art (see  FIG. 2   a ), has the consequence that a throttling effect from a backup of fluid downstream of the valve seat  44  is prevented. As a result, the dynamic pressure in the pump interior is lowered, which results in reduced system stress and component stress and consequently effects a reduction in the driving torque and the system output. The free space  84  embodied in the outlet valve cap  36  has no effect on the fundamental functions of the ball seat valve, and in particular an outflow upstream of the ball equator is achieved. A minimal opening, known from the prior art, of the ball, because of the dynamic pressure developing downstream of the ball, is avoided by the free space  84  of the invention. In particular, this prevents the ball from being drawn into an outflow groove  86  (see  FIG. 2   a ), as is the case in the known version, by the outflow of brake fluid and the associated local pressure reduction. 
     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. 
     The free space  84 , according to the invention, has a depth  88 , which amounts to at least 25% of the diameter of the ball, and also has a height  90 , which amounts to at least 25% of the diameter of the spherical blocking body. By means of this kind of dimensioning, specified according to the invention, of the free space  84 , the throttling effect known from the prior art, with the associated dynamic pressure, can be effectively prevented, and at the same time, known fundamental functions of the outlet valve  34 , in particular a fluidically optimal outflow before the ball equator, can be maintained. Alternatively, the advantageous dimensions of the free space  84  can also be referred to the mean diameter  92  of the valve seat opening  94 ; in the present case, a free space depth  88 , which amounts to at least 33% of the mean diameter, and a free space height  90 , which amounts to at least 33% of the predetermined mean diameter, represent advantageous dimensions of the free space  84 .