Abstract:
The invention relates to a piston pump for a vehicle braking system, with a housing section and a piston, which is guided in the housing section in a slidable manner. An accommodating member for accommodating an intake valve is provided in the housing section, and a sealing element adjoins the accommodating member to seal the piston against the housing section. A piston rod adjoins the sealing element which is embodied in one piece with the accommodating member.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/054956 filed on May 22, 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 section and a piston that is guided displaceably in the housing section, a receiving element for receiving an inlet valve, a sealing element adjoining the receiving element for sealing off the piston from the housing section, and a piston rod adjoining the sealing element. 
     2. Description of the Prior Art 
     The piston pumps for known vehicle brake systems, in particular anti-lock systems (ABS), serve to control the pressure in wheel brake cylinders. In the ABS, the piston pumps are intended 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). Another known system, the electronic stability program (ESP), improves driving safety by a further increment compared to ABS and TC. While ABS and TC act in the longitudinal travel direction, ESP affects the transverse dynamics and in principle is therefore transverse traction control. For all these systems and for other systems for increasing driving safety, piston pumps are used. 
     Known piston pumps intended for vehicle brake systems comprise among other things a cylinder, which is embodied in a housing and in which a piston is received longitudinally movably. The piston drive is usually effected by an eccentric drive, in which the rotary motion of a shaft driven by a drive motor is converted to a translational motion of the piston. In the process, the piston rod is pressed with its face end against the outer circumference of the eccentric element of the eccentric drive by 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. 
     Moreover, known piston pumps, to control the fluid inflow, have an inlet valve embodied as a seat valve; in the cylinder, between the inlet valve and the piston, a sealing element is also provided, which is guided longitudinally movably in the cylinder. The piston of known piston pumps is mounted with its face end, disposed inside the cylinder, on the sealing element, so that a reciprocating piston motion is transmitted directly to the sealing element. On the end of the sealing element toward the inlet valve, a valve seat of the inlet valve embodied as a seat valve is embodied, and for the fluid inflow, a bore extending through the sealing element is provided, which extends as far as the valve seat, so that fluid flows through the inlet valve that is open in the intake phase. The barrier body of the inlet valve embodied as a seat valve is pressed via a spring element against the valve seat embodied on the sealing element, and the barrier body, the spring element, and the end, embodied as a valve seat, of the sealing element are received in a receiving element in the form of an inlet valve cap. The inlet valve cap serves as a brace for the spring element and as a guide for the barrier body. Around the inlet valve cap, there is a prestressing element in the form of a helical spring, which presses against a bracing body embodied on the inlet valve cap that is received in a recess embodied in the sealing element, in order to transmit the spring force, transmitted to the bracing body, to the piston mounted on the sealing element by way of the sealing element. In this way, prestressing can in the final analysis be transmitted to the piston, in order to press the piston against the eccentric element of the eccentric drive. 
     Thus viewed overall, many pump components are disposed in the cylinder of known piston pumps. As a consequence, assembling and disassembling know piston pumps is comparatively complex. Moreover, because of the many pump components provided, known piston pumps cannot be manufactured especially economically. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The object of the invention is to disclose a piston pump for a vehicle brake system that can be assembled and disassembled with little effort or expense and that can furthermore be manufactured economically. 
     This object is attained according to the invention with the piston pump, recited at the outset, for a vehicle brake system in which the sealing element is embodied in one piece with the receiving element. 
     According to the invention, the sealing element is embodied in one piece with the receiving element. This has the advantage that unlike the piston pumps known from the prior art, the functions of the sealing element and of the receiving element serving to receive the inlet valve are taken on by only a single component. Thus according to the invention, compared to the known embodiments, one less component is used, and as a consequence, the assembly and disassembly of the piston pump of the invention can be done very simply, and the chain of tolerances is reduced markedly. Moreover, by using one less component according to the invention, the manufacturing costs for the piston pump can be reduced markedly. Finally, because it uses one less component, the piston pump of the invention can be markedly smaller than known pumps. 
     In an advantageous refinement of the invention, 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 piston pump possible. Thus particularly for disassembling the piston pump, the piston rod adjoining the sealing element has to be removed from the sealing element. Next, the inlet valve, which is preferably embodied as a seat valve, can be removed together with its individual components, including in particular a barrier body and a spring element, without major effort or expense from the receiving element embodied in one piece with the sealing element. Finally, the sealing element, which is received longitudinally movably in the cylinder of the piston pump and on which the receiving element is embodied in one piece, can be removed from the cylinder without problems. 
     In a further advantageous refinement of the invention, a prestressing element, preferably in the force 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 section. The prestressing force transmitted from the prestressing element to the sealing element always retains the piston in an outer position. 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 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 piston pump of the invention can be used in conjunction with eccentric drives, which are preferably used in brake systems for driving the piston pumps. 
     In a practical refinement of the invention, the sealing element is embodied in the form of a sealing ring with a sealing ring opening, and the piston rod is received in the sealing ring opening, and preferably the piston rod is received in the sealing ring opening with a clearance fit. By means of a clearance fit, the piston rod can be centered in the sealing ring opening without problems. Moreover, a clearance fit makes a requisite problem-free release of the piston rod from the sealing ring opening for disassembly purposes possible. 
     In a further advantageous refinement of the invention, a snap connection is embodied between the sealing element and the piston rod, for premounting the piston rod on the sealing element. The snap connection, which is preferably embodied on the sealing element, for instance embraces a shoulder embodied on the piston rod. By the snap connection according to the invention, during the assembly of the piston pump and in particular during the assembly on the cylinder, the piston rod can be held on the sealing element by way of the snap function furnished according to the invention. Moreover, by the snap connection according to the invention, the inner wall of the cylinder is protected from the outer diameter of the piston. By the snap connection of the invention, any contact of the piston with the inner wall of the cylinder is precluded so that damage to the inner wall of the cylinder or the piston is avoided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of a piston pump of the invention are described in further detail below in conjunction with the appended schematic drawings. 
         FIG. 1  is a longitudinal section through a piston pump of the invention; 
         FIG. 2  is a longitudinal section through a piston pump of the prior art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a piston pump  10  according to the invention. The piston pump  10  includes two housing sections  12  and  14 , and in the housing section  12 , a cylinder bore  16  is embodied, in which a piston  26  is displaceably guided. The piston  26  includes a sealing element in the form of a sealing ring  18 , a receiving element  20  for an inlet valve  22  that is embodied as a ball seat valve and is embodied in one piece with the sealing ring  18  and in the present case as an inlet valve cap, and a piston rod  62  that 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 connection by nonpositive engagement between the two piston rod elements  28 ,  30 . Because of the two-part embodiment of the piston rod  62  as provided, a piston rod  62  that can be manufactured economically is attained, since according to the invention, an economical rodlike piston rod element  28  is connected to a piston rod element  30  that can be furnished extremely economically, in the form of a plastic injection-molded part, a part turned on a lathe, a cast part, or a cold-forged part. 
     The receiving element  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 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 manufactured partially by metal-cutting machining or cold-forging. A helical spring  42  braced on the cap bottom presses the ball  38  against a valve seat  44 , which is embodied in the housing section  12  of the piston pump  10  and which adjoins an outlet hole  46  embodied in the housing section  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 a radial conduit  48  between the outlet valve cap  36  and the housing section  12 . 
     A prestressing element in the form of a helical spring  50  is also disposed in the cylinder bore  16  embodied in the housing section  12 ; it rests with one end on the sealing ring  18  and is braced with its other end on the bottom of the housing section  12 . The helical spring  50  is subjected to prestressing, in order to press the two-part piston rod  62  against the circumference of the eccentric element of an eccentric drive (not shown), via the sealing ring  18  on which the piston rod  62  rests with its face end disposed inside the piston pump  10 . Thus the outer face end of the piston rod element  28  can be kept in constant contact with the eccentric element. By driving the eccentric element to rotate, the entire piston  26  is driven to an axially reciprocating stroke motion, which in a known manner causes pumping of brake fluid. 
     The valve seat  52  of the ball inlet valve  22 , which seat can be produced for instance by ball stamping, is embodied 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 conjunction with the one-piece embodiment of the sealing ring  18  according to the invention, with the receiving element  20  designed as an inlet valve cap, in the form of the valve cap/sealing ring combination  24 , offers pronounced advantages in the assembly and disassembly of the piston pump  10 . For disassembly of the piston pump  10 , the piston rod element  30 , received in the sealing ring opening  32  with a clearance fit, 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 here. The individual components of the seat valve  22 , that is, the ball  54  and the helical spring  56 , can then easily be removed from the receiving element  20 . Finally, after the one-piece valve cap/sealing ring combination  24  is pulled out of the cylinder bore  16 , the helical spring  50  can be removed from the cylinder bore  16 . The assembly of the piston pump  10  is correspondingly simply designed; the clearance fit provided enables problem-free centering of the piston rod element  30  in the sealing ring opening  32 . 
     A snap connection in the form of a snap lug  58 , which embraces a shoulder embodied on the piston rod element  30 , is also embodied on the sealing ring  18 . 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 assembly in the cylinder bore  16 , thereby 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, which 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 in the axial direction on the piston rod element  30 , despite the clearance fit that is advantageous for assembly purposes. Moreover, the snap lug  58  has a protective action between the cylinder bore  16  and the piston rod element  30 . On the sealing ring  18  of the valve cap/sealing ring combination  24 , a sealing lip  60  is also embodied, which closes off the cylinder chamber between the piston  26  and the cylinder bore  16  radially in pressure-tight fashion. 
     Finally, the piston pump  10  has a radial bore  66 , embodied in the piston rod element  30 , and a central axial bore  68 , through which fluid from outside the piston pump can flow through the inlet valve  22 . 
       FIG. 2  shows a sectional view of a piston pump  64  of the prior art. Unlike the piston pump  10  of the invention, in the known piston pump  64 , the receiving element  20  and the sealing ring  18  in particular are separate components, which makes the disassembly and assembly of the known piston pump  64  markedly more difficult and, unlike the piston pump  10  of the invention, involves a longer chain of tolerances. Moreover, no contact protection between the cylinder bore  16  and the piston  26  is provided. 
     The foregoing relates to the preferred exemplary embodiment 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.