Abstract:
The invention relates to a piston pump for conveying fluids. The piston pump includes a piston, and a pressure chamber located between an intake valve and a discharge valve. The intake valve is arranged between the pressure chamber and a low-pressure zone of the piston pump. The intake valve has a valve body, a closing element, a device for preloading the closing element, and a device for fastening the intake valve to the piston. The fastening device encompasses at least two fastening elements which protrude from the valve body toward the piston. The fastening elements are positioned at a distance from one another, and are fitted with inlets therebetween for supplying fluid. The invention further relates to a piston pump having an intake valve without a spring-biased element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/054952 filed on May 22, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a piston pump for conveying fluids, and in particular to a piston pump for conveying liquids in vehicles, such as brake fluid or fuel. 
     2. Description of the Prior Art 
     Piston pumps in various embodiments are known from the prior art. In vehicles, piston pumps are used for instance as fuel pumps, or as pumps for supplying pressure to brake systems. A known piston pump, between an inlet valve and an outlet valve, has a work or pressure chamber, in which a pressure is built up by means of a linear motion of a piston. In order to have the most compact possible construction, the fluid is delivered to the inlet valve through a plurality of radial bores and a longitudinal bore in the piston. However, this requires metal-cutting machining of the piston, which is very complicated. It has furthermore been found that because of the delivery by the piston and the attendant relatively long travel distances for delivering the fluid, flow losses occur. Hence the known piston pump is relatively complicated in its construction and expensive to manufacture. 
     ADVANTAGES AND SUMMARY OF THE INVENTION 
     The piston pump of the invention has the advantage over the prior art that it requires only very little structural space and can be manufactured economically. Moreover, the piston pump of the invention has markedly reduced flow losses. As a result, the efficiency of the piston pump can be improved. Metal-cutting machining of the piston is furthermore unnecessary in the piston pump of the invention. The piston pump of the invention can be manufactured very economically and has only a small number of parts. As a result, the assembly costs can also be lowered by reducing the required number of assembly steps. This is attained according to the invention in that the piston pump has a piston and a pressure chamber that is disposed between an inlet valve and an outlet valve. The inlet valve is disposed between the pressure chamber and a low-pressure zone of the piston pump. The inlet valve includes a valve body with a valve seat, a closing element, a prestressing device for prestressing the closing element, and a fixation device for fastening the inlet valve to the piston. The fixation device includes at least two fixation lugs, protruding from the valve body in the direction of the piston, which are spaced apart from one another and between which, inflow openings for the inflow of the fluid are located. As a result, it is no longer necessary for inflow bores or the like to be provided in the piston. The inflow of fluid is effected according to the invention through the inflow openings between the valve body and the piston. A cross section of the inflow opening can be varied, for instance by varying a length of the fixation lugs or varying a spacing of the fixation lugs, or varying the number of fixation lugs. 
     Preferably, the fixation lugs are each spaced equally apart from one another along a circumference of the valve body. It should be noted that especially preferably, three or four fixation lugs are provided. As a result, an adequate cross-sectional area for the inflow of fluid can be furnished between the various fixation lugs. 
     In an especially preferred feature of the invention, each of the fixation lugs includes one step. The step serves as a stop for a face end of the piston, so that upon mounting of the valve body onto the piston, a defined position of the valve body on the piston is always obtained. As a result, errors in assembly can also be avoided. Moreover, as a result of the graduation, a press fit between the piston and the valve body can be achieved. 
     To make especially economical production possible, the piston is preferably a cylindrical roll of a solid material, in particular a metal material. 
     To make fast and simple assembly possible, a fastening of the fixation lugs to the piston is preferably done by nonpositive engagement, in particular via a press fit. 
     The valve body is especially preferably made from a plastic material. As a result, production costs can be reduced, since the valve body can be produced economically by an injection-molding process. 
     In a preferred feature of the invention, the prestressing device of the inlet valve is a spring, in particular a spiral spring, which is braced on a cage disposed on the valve body. The cage is preferably formed in one piece with the valve body. As a result, the number of parts can be reduced. 
     In an alternative feature, the prestressing device includes many elastic prestressing lugs, which retain the closing element. By elastic deformation of the prestressing lugs, the inlet valve can be opened. Beyond a predetermined opening pressure, the prestressing lugs deform, and they close the inlet valve again once the opening pressure has dropped below the predetermined value. For holding the closing element, the prestressing lugs preferably have an undercut. Also preferably, the prestressing lugs are formed in one piece with the valve body. 
     The present invention further relates to a piston pump for conveying fluids, including a piston and a pressure chamber that is located between an inlet valve and an outlet valve. The inlet valve includes a valve body, a closing element, and a prestressing device for prestressing the closing element; the prestressing device of the inlet valve includes many elastic prestressing elements. The elastic prestressing elements take on a function of a restoring spring for the inlet valve. The prestressing elements preferably have an undercut for holding the closing element and are moreover preferably formed in one piece with a valve body of the inlet valve. The prestressing elements are preferably made from a plastic material. 
     A closing element of a piston pump of the invention is preferably a ball or a plate. 
     Also preferably, a sealing element for sealing off the pressure clamber from a low-pressure zone of the piston pump is additionally disposed on the valve body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred exemplary embodiments of the invention are described below in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic sectional view of a piston pump in a first exemplary embodiment of the invention; 
         FIG. 2  is a view, partly in section, of a piston preassembled with an inlet valve; 
         FIG. 3  is a perspective view of  FIG. 2 ; 
         FIG. 4  is a perspective view of an inlet valve; 
         FIG. 5  is a perspective view of the inlet valve of  FIG. 4  from a different direction; and 
         FIG. 6  is a schematic sectional view of a piston pump in a second exemplary embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A piston pump  1  in a first exemplary embodiment of the invention will be described below with reference to  FIGS. 1 through 5 . 
     As can be seen from  FIG. 1 , the piston pump  1  includes a piston  2 , which is made from a solid material as a cylindrical roll. The piston  2  is guided movably back and forth (double arrow X in  FIG. 1 ) on a housing  22  in a sleeve  22   a  and is driven for instance by means of a cam for example (not shown). The piston pump  1  furthermore includes an inlet valve  4 , an outlet valve  16 , and a pressure chamber  3  disposed between the inlet valve  4  and the outlet valve  16 . 
     The inlet valve  4  includes a valve body  5 , which is made from a plastic material. The inlet valve  4  furthermore includes a closing element  6 , which in this exemplary embodiment is a ball. The closing element  6  either seals off a valve seat  7  that is formed on the valve body  5  or opens the valve seat. The closing element  6  is prestressed against the valve seat  7  by means of a cylindrical spring  8 . The cylindrical spring  8  is braced on a cage  9  that is formed integrally with the valve body  5 . The cage includes three arms  9   a ,  9   b ,  9   c , which can be seen particularly in  FIGS. 2 and 5 . Each of the arms  9   a ,  9   b ,    9   c has a respective projection  90   a ,  90   b ,  90   c , that protrudes inward, against which the cylindrical spring  8  is braced. The inlet valve  4  furthermore includes a fixation device  10 , for fastening the inlet valve  4  to the piston  2 . As can be seen from  FIGS. 1 and 4 , the fixation device  10  includes many fixation elements. In this exemplary embodiment, the fixation device  10  includes four fixation elements  11 ,  12 ,  13 ,  14 . The fixation elements  11 ,  12 ,  13 ,  14  protrude axially from the valve body  5  in the direction of the piston  2  and are connected to the piston  2  via a press fit. The fixation elements  11 ,  12 ,  13 ,  14  each have a respective step  11   a ,  12   a ,  13   a ,  14   a , for forming a stop for an end face  2   a  of the piston  2 . The fixation elements  11 ,  12 ,  13 ,  14  are each spaced equally apart from one another. As a result, one inflow opening  15  is formed between each two adjacent fixation elements  11 ,  12 ,  13 ,  14 , so that a total of four inflow zones are formed. 
     As can be seen from  FIG. 1 , the inlet valve separates the pressure chamber  3  from a low-pressure zone  20 . The low-pressure zone  20  in this exemplary embodiment forms an annular conduit, to which fluid is delivered, as indicated by the arrow A, via an intake conduit  19 . 
     In the intake phase of the piston pump, the fluid thus flows through the four inflow openings  15 , which are formed between the fixation elements  11 ,  12 ,  13 ,  14 , and past the open closing element  6  into the pressure chamber  3 . This is represented in  FIG. 1  by the arrow B. 
     The outlet valve  16  includes both a closing element  17  and a spring  18 . The outlet valve  16  is embodied as a check valve, and it opens as soon as a predetermined pressure in the pressure chamber  3  is reached. The fluid can then be delivered through the opened outlet valve  16  into the pressure conduit  21  and from there for instance to the wheel brakes of a vehicle. 
     The function of the piston pump  1  of the invention is as follows. In the intake phase, the outlet valve  16  is closed and the inlet valve  4  is open. Since the inlet valve  4  is completely fastened to the pressure chamber end of the piston  2 , the inlet valve  4  moves together with the piston  2  away from the outlet valve  16 . In the intake phase, fluid is thus delivered through the intake conduit  19 , the inflow openings  15 , and the opened inlet valve into the pressure chamber  3 . This is represented in  FIG. 1  by the arrows A and B. At bottom dead center, the direction of motion of the piston  2  reverses, and the pressure buildup phase begins. In it, the inlet valve  4  is closed, and the pressure buildup takes place in the pressure chamber  3  counter to the closed outlet valve. As soon as a predetermined opening pressure, which is determined by the prestressing force of the outlet valve spring  18  and the contrary pressure applied, is reached, the outlet valve  16  opens, and the fluid that is under pressure can flow out of the pressure chamber  3  into the pressure conduit  21  via the opened outlet valve  16 . 
     The piston pump of the invention thus has an especially simple construction. The inflow of fluid to the pressure chamber  3  is thus effected through the inflow openings  15  between the inlet valve  4  and the piston  2 . The inlet valve  4  can be premounted as a preassembled structural unit onto the piston  2 . Thus a structural unit including the inlet valve  4  and the piston  2  can be furnished in the form of a preassembled unit. Since the valve body  5  and the fixation device  10  as well as the cage  9  are embodied in one piece, the number of components can be reduced. This reduces the number of assembly steps required. The valve body  5  may for instance be produced by injection molding. 
     According to the invention, the flow losses upon the inflow of the fluid into the pressure chamber  3  can furthermore be reduced, since the inflow no longer takes place via the bores that are present in the piston in the prior art. As the piston  2 , a needle roll, which can be furnished simply and inexpensively, can for instance be used. 
     The piston pump  1  of the invention can be used as both a pressure pump and a suction pump. 
     Below, in conjunction with  FIG. 6 , a piston pump  1  in a second exemplary embodiment of the invention will be described. Elements that are identical or function identically are identified by the same reference numerals as in the first exemplary embodiment. 
     The second exemplary embodiment corresponds essentially to the first exemplary embodiment, but in a distinction from it, the inlet valve  4  is constructed differently. The inlet valve  4  of the second exemplary embodiment no longer has any spring element. Instead, the inlet valve  4  of the second exemplary embodiment has a plurality of elastic prestressing elements  30 , which each include an inward-pointing prestressing lug  31 . A closing element  6  of the second exemplary embodiment is moreover embodied as a plate. The elastic prestressing elements  30  are formed in such a way that when the closing element  6  lifts from its valve seat  7  in the valve body  5 , an elastic deformation of the prestressing elements  30  or prestressing lugs  31  takes place. The elastic deformation can take place both at the prestressing lugs  31  and in the zone of connection between the prestressing lugs  31  and the valve body  5 . The travel distance of the closing element  6  in the axial direction upon opening is relatively short. The closure of the inlet valve  4  is then effected via the restoring force of the prestressing elements  30 , which return to their outset position again, and in the process they press the closing element  6  against the valve seat  7 . 
     The inflow of the fluid is effected, as in the first exemplary embodiment, through the inflow openings  15  between the fixation elements  11 ,  12 ,  13 ,  14  of the fixation device  10 . The piston pump of the second exemplary embodiment has a very compact construction, especially in the axial direction. Moreover, by dispensing with a spring element for the inlet valve, the number of parts is reduced still further. The prestressing elements  30  are again formed in one piece with the valve body  5 , so that this component can be produced for instance by plastic injection molding. 
     Otherwise, the second exemplary embodiment is equivalent to the first exemplary embodiment, so that the description of the latter can be referred to. 
     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.