CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 13/513,477 filed Jun. 19, 2012, which is a 35 USC 371 application of PCT/EP 2010/065320 filed Oct. 13, 2010, which claims priority to both of German Patent Application 10 2009 047 326.2 filed Dec. 1, 2009 and German Patent Application 10 2010 039 691.5 filed Aug. 24, 2010, the entire contents of all of which are incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a control valve for metering a fluid for a delivery pump. 
         [0003]    Control valves, particularly for metering a fluid for a downstream delivery pump, are known on the market. For instance, they are used in common rail fuel systems of motor vehicles as a quantity control valve, for controlling the fuel flow fed into the common rail from a high-pressure delivery pump. Such quantity control valves can be embodied as electromagnetic control valves, in which an electromagnet and a spring act on a valve element of the control valve. See German Patent Disclosure DE 198 34 121 A1, for example. 
       SUMMARY 
       [0004]    The control valve of the invention has the advantage that flow forces at the valve element, when the control valve is actuated in the opening direction, are reduced without lessening the robustness of the control valve. As a result, the excitation of acoustic waves can be reduced as well. 
         [0005]    For example, a control valve which is used as a quantity control valve for metering a quantity of fuel for a piston high-pressure delivery pump of an internal combustion engine functions as follows: 
         [0006]    In an intake phase of the high-pressure delivery pump, the valve element disposed in a flow channel and embodied for instance as a valve plate is, as a consequence of pressure differences that occur beyond the valve element, put into an open position, as in a normal inlet valve actuated by a pressure difference, for instance as in DE 198 34 121 A1. This open position of the control valve can be reinforced by an electromagnetically actuated valve needle. If in an ensuing delivery stroke of the high-pressure delivery pump the pressure ratios are reversed, then by the action of the valve needle on the valve element, the control valve can continue to remain temporarily in the open position. In this phase, a partial backflow of the fuel already located in the high-pressure delivery pump takes place. The flow of fuel through the control valve is then the opposite of its “normal” flow direction. The backflowing fuel—without the provision according to the invention—then leads to a pressure on an axial end face of the valve element. This pressure has to be compensated for, at least from time to time, by the action of the valve needle. 
         [0007]    The invention proceeds from the thought that the pressure which during the backflow acts on the axial end face of the valve element can be lessened by means of a bit. Thus the actuation force that has to be furnished by the valve needle can be reduced, and an electromagnet of the control valve does not need to be as strong. The impact speed of the valve needle or the valve element on a stop that limits its motion can be reduced as well. In this way, the control valve is also made less expensive, and it operates more quietly. 
         [0008]    The shield is preferably disposed such that it essentially shields the axial end face of the valve element from the backflowing fuel but itself does not substantially hinder the backflowing fuel. For instance, the valve element is embodied as a valve plate around which the backflowing fuel is guided with little loss by means of the shield. The valve plate has two axial terminal positions. First, a seat of repose, which the valve plate strikes when the control valve is closed, and second, a stop for an open position of the control valve. In this open position, the valve plate in most instances of use is disposed quite close to the shield. There it can either touch the shield, or a gap remains; specifically, a constriction is opened up between the valve plate and the shield. This constriction does not represent the flow direction of the fuel, however; instead—in some embodiments of the invention—it forms a kind of channel to a region that is filled with fuel but essentially has no flow through it, as will be explained hereinafter. The stop for the open position of the control valve is not absolutely necessary. 
         [0009]    The control valve is more simply constructed if the shield has an encompassing and for instance annular shield portion. The result is a structurally simple embodiment of the shield. The shield can almost always be used in a quantity control valve and can optionally also be used in existing embodiments without structural changes. As a result, the control valve is made simpler, and its production is made less expensive. 
         [0010]    One embodiment of the control valve provides that the shield portion is conical. Thus the control valve can be embodied such that the flow losses of the flowing fuel are reduced especially markedly. This pertains to both the delivery direction and the backflow. 
         [0011]    It is additionally proposed that the shield or at least the shield portion is a molded sheet-metal part. A molded sheet-metal part of this kind is especially easy to produce and especially inexpensive. 
         [0012]    A further embodiment of the control valve provides that it includes at least one channel, which connects a flow region located outside the shield, in which region upon a backflow a comparatively low static pressure prevails, with a region located inside the shield. Preferably, the channel is oriented essentially orthogonally to the backflow. The channel can also be embodied in various ways and/or at various and virtually arbitrary portions of the flow channel, as will be explained further hereinafter. As a result, the electromagnetic actuating device, which moves the valve needle, can be made smaller. Consequently the power needed by the electromagnet can e lowered still more, and less heat, for instance in the armature winding, is generated. 
         [0013]    An embodiment of the control valve provides that the channel is formed in at least some regions by a preferably radially encompassing gap between the valve element and the shield or the shield portion. The encompassing gap or channel is formed for instance whenever the valve element is in its opening position. The elements of the control valve are dimensioned such that the suction jet effect ensues with a desired intensity and in a desired direction, without a separate channel having to be produced. In this way, the channel can be implemented especially simply and inexpensively. 
         [0014]    A further embodiment of the control valve provides that the channel is formed in at least some regions by at least one opening in the shield and/or in the shield portion. The opening can be oriented radially or diagonally or parallel to an axis of the control valve and can moreover have various kinds of cross-sectional shapes. For instance, the opening can be embodied as a bore. This provides many possibilities for connecting the region located inside the shield fluidically with the flow channel, so that—adapted to a particular structural form of the control valve—the desired suction jet effect ensues. It is equally possible for a plurality of openings to be provided, which are for instance arranged radially symmetrically to the axis of the control valve. In that case, the channel is accordingly always present, regardless of the position of the valve element. This has functional advantages. 
         [0015]    A further embodiment of the control valve provides that the channel is formed in at least some regions by at least one opening in the valve element. For instance, the valve element has an essentially rotationally symmetrical and disklike geometry, and the flow or backflow flowing through the flow channel flows radially, in at least some portions, around an axial face of the valve element. In that case, the channel can be formed by axial openings in the vicinity of the edge of the valve element. This embodiment has the advantage that along the flow channel, no additional throttle restriction is required, and as a result, corresponding throttle losses in the suction direction are avoided. 
         [0016]    A still further embodiment of the control valve provides that the flow region located outside the shield, into which region the channel discharges, is shaped such that the backflow is deflected. As a result, the channel discharges into the radially inner region of the crooked flow, in which region a pressure gradient can be established in the radial direction. The result in the radially inner flow region is a comparatively low pressure, which can be transmitted by means of the channel to the region located inside the shield. A further advantageous alternative version of the control valve is thus formed. 
         [0017]    The control valve of the invention functions especially well if the backflow is guided essentially orthogonally to the channel. As a result, it is attained among other things that the function of the channel is essentially independent of the flow direction in the flow channel, so that when the flow direction changes, either no redistribution, or only a comparatively slight redistribution, of fluid through the channel occurs. As a result, hydraulic losses can be avoided. 
         [0018]    the control valve is structurally especially simple if at least some elements of the control valve, in particular the valve needle, valve element and/or shield, have an essentially rotationally symmetrical shape. A rotationally symmetrical shape is an especially favorable embodiment for a control valve, and the shield of the invention can likewise be adapted well to this shape. Accordingly, the flows in the region of the control valve, and especially in the region of the valve plate, have an essentially rotationally symmetrical behavior. 
         [0019]    The control valve can be used especially advantageously if it is a quantity control valve for metering fuel in a fuel system of an internal combustion engine. Then the operating frequency of the control valve and the incident pressures and the prevailing pressure differences are all especially high. The control valve of the invention is advantageously suited to such operating conditions and to similar operating conditions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Exemplary embodiments of the invention will be described below in conjunction with the drawings. In the drawings: 
           [0021]      FIG. 1  shows an overview of a fuel system with a high-pressure pump, a common rail system, and a quantity control valve; 
           [0022]      FIG. 2  shows a control valve in a sectional view in a first embodiment, showing flow speeds; 
           [0023]      FIG. 3  shows a control valve in a sectional view in a second embodiment, showing flow speeds; 
           [0024]      FIG. 4  shows a control valve of  FIG. 3 , showing a static pressure distribution; 
           [0025]      FIG. 5  shows a control valve in a sectional view in a third embodiment, showing a static pressure distribution; 
           [0026]      FIG. 6  shows a control valve in a sectional view in a fourth embodiment, showing a static pressure distribution; 
           [0027]      FIG. 7  shows a control valve in a sectional view in a fifth embodiment, showing a static pressure distribution; and 
           [0028]      FIG. 8  shows a control valve in a sectional view in a sixth embodiment, showing a static pressure distribution. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    For functionally equivalent elements and sizes in all the drawings, even in different embodiments, the same reference numerals are used. 
         [0030]      FIG. 1  shows a fuel system  1  of an internal combustion engine in a highly simplified illustration. A high-pressure pump  2  (not further shown) embodied as piston pump communicates upstream with a fuel tank  6 , via a suction line  3 , a prefeed pump  4 , and a low-pressure line  5 . Downstream, a high-pressure reservoir  8  (“common rail”) is connected to the high-pressure pump  2  via a high-pressure line  7 . A control valve  10  embodied as a quantity control valve, having an electromagnetic actuating device  11 —hereinafter called an electromagnet  11 —is disposed hydraulically between the low-pressure line  5  and the high-pressure pump  2  and forms the inlet valve of the high-pressure pump. Other elements, such as the outlet valve of the high-pressure pump  2 , are not shown in  FIG. 1 . It is understood that the quantity control valve  10  can be embodied together with the high-pressure pump  2  as a structural unit. 
         [0031]    In operation of the fuel system  1 , the prefeed pump  4  pumps fuel from the fuel tank  6  into the low-pressure line  5 . In the process, the quantity control valve  10  determines the quantity of fuel delivered from the high-pressure pump  2  to the high-pressure reservoir  8  by remaining intermittently open in compulsory fashion during a delivery stroke. 
         [0032]      FIG. 2  shows a portion of the quantity control valve  10  on the intake side of the high-pressure pump  2 . It can be seen that the quantity control valve  10  has a housing  12 , a valve needle  14 , a platelike valve element  16 , a valve seat  17  (“seat of repose”) cooperating with the valve element, and a shield  24 . In terms of the drawing, the high-pressure pump  2  is disposed to the right of the control valve  10 , and the low-pressure line  5  coming from the prefeed pump  4  is disposed on the left. A flow channel  20  is located in the upper or middle region of  FIG. 2  and has a passage for the fuel that in terms of the drawing is substantially horizontal. The flow channel  20 , over its course, has various cross-sectional shapes and cross-sectional areas. 
         [0033]    The shield  24  includes a central portion  23  and an annular shield portion  25 , which here is embodied conically and in some regions forms a radially inner wall of the channel  20 , which at least at this point is annular. It is also conceivable to produce the shield  24  as a molded sheet-metal part. However, that is not shown in  FIG. 1 . A region  26  located radially inside the shield  24  here forms a “fluid chamber” and is surrounded by the shield  24 , with its shield portion  25  and central portion  23 , and by the valve element  16 . The region  26  is filed with fuel and communicates with the flow channel  20  via a constriction  27 , which is also formed between the valve element  16  and the shield portion  25  when the valve element  16  is in the open position, as shown in  FIG. 2 . The constriction  27  is embodied in  FIG. 2  as a radially encompassing gap and simultaneously forms a channel  28 . 
         [0034]    The elements of the control valve  10  here have an essentially rotationally symmetrical shape around a center line  18 . In the drawing, only half of a sectional view is shown. This applies to  FIGS. 3-8  described below as well. 
         [0035]    The sectional view in FIG.  2 —as in  FIGS. 3-8  described below—corresponds to a simulation model for calculating flow speeds and pressure distributions and in the present instance does not show any stop for the valve needle  14  or the valve element  16  for the open position of the control valve  10 . Such a stop could be created for instance by means of a radially symmetrical shaping of the central portion  23 , so that the valve element  16  in the open position shown can sit directly on the central portion  23  of the shield  24 . A helical spring (not shown), which urges the valve element  16  in the direction of the closed position, can be accommodated in this region  26  as well. However, neither is absolutely necessary. 
         [0036]    The view in  FIG. 2  corresponds—as mentioned above—to a control valve or quantity control valve  10  located in the open position. The valve seat  17  identifies a closed position, not described in further detail, of the valve element  16 . The valve needle  14  and the valve element  16  are axially movable and are located in an extreme right-hand position in terms of the drawing. The shield  24  is secured to the housing. 
         [0037]    The high-pressure pump  2  and the quantity control valve  10  function as follows: In an intake phase of the high-pressure pump  2 , fuel is fed from left to right in the drawing. This corresponds to the “normal” flow direction through the control valve  10 . The function of the quantity control valve  10  is then essentially equivalent to that of a normal, spring-loaded inlet intake valve, of the typical known kind in piston pumps. In an ensuing pumping phase, a fuel pressure is built up in the high-pressure pump  2 . As a result, some of the previously aspirated fuel flows back in the direction of the arrows  22  (backflow), as long as the valve element  16  is compelled to be in the open position shown by of the action by the valve needle  14 , which in turn is put into this position by the electromagnetic actuating device  11 . 
         [0038]    In the flow channel  20 , above all during the backflow just described, various flow speeds of the backflowing fuel arise as a consequence of hydraulic effects. The various flow speeds are illustrated in  FIG. 2  by different degrees of blackening. There are regions of relatively low flow speeds  30 , medium flow speeds  32 , and relatively high flow speeds  34 . Additional degrees of shading in  FIG. 2  and the attendant flow speeds are shown without reference numerals. Identical degrees of blackening of the shadings do not necessarily mean identical flow speeds. Because of the black-and-white illustration here, the drawing in  FIG. 2  is not reversibly unambiguous in each case. More simply, and in general, it should be noted that regions of relatively high flow speeds are located predominantly near the middle of a given cross section of the flow channel  20 . 
         [0039]    It can be seen that the backflow indicated by the arrows  22  stays essentially away from an axial end face  36  of the valve element  16 , because of the action of the shield  24  or the shield portion  25 . The flow is accordingly steered around the valve element  16 . As a result the pressure of the fuel exerted on the axial end face  36  is comparatively low. The pressure loss as fuel passes through the flow channel  20  is comparatively slight overall. 
         [0040]      FIG. 3  shows an similar embodiment of the control valve  10  to  FIG. 2 , in which the housing  12 , the valve element  16 , the shield  24  and the shield portion  25  have a different geometry from  FIG. 2 . The geometries of the flow channel  20 , the constriction  27 , the channel  28 , and the fuel-filled region  26  are different as well. In particular, in the vicinity of the constriction  27  or channel  28 , the flow channel  20  has a throttle restriction  38 , which narrows the cross section for the backflow. The flow speeds of the fluid or fuel are shown similarly to  FIG. 2 . Accordingly, the aforementioned limitations in terms of the drafting of the drawing apply here as well. 
         [0041]    The basic function of the control valve  10  of  FIG. 3  is comparable to that of  FIG. 2 ; however, the flow speeds and the hydraulic effects and pressures are different in some locations as a consequence of the different geometries. In particular, the region of the throttle restriction  38  has a higher fluid speed, compared to the other portions of the flow channel  20 . As a consequence, a static pressure of the fuel in the region of the constriction  27  is comparatively low. Thus a suction effect on the fuel located in the region  26  arises in the direction of the arrow  40 . As a consequence, the hydraulic pressure in the region  26  decreases, and the axial force acting on the axial end face  36  of the valve element  16  decreases accordingly. Overall, the axial end face  36  is thus relieved in two ways. First, by the action of the shield portion  25 , which keeps the backflow essentially away from the axial end face  36 . Second, by the suction effect and the attendant reduction in the hydraulic pressure in the region  26 . In a manner similar to the embodiment of the control valve  10  of  FIG. 2 , the pressure loss as the fuel passes through the flow channel  20  is comparatively slight. 
         [0042]    Unlike what is shown in  FIG. 2 , the shield portion  25  “clasps” the valve element  16  in the radial direction, and correspondingly, the channel  28  is oriented differently relative to the center line  18 , namely essentially axially. For the generation of the suction jet effect this is of little importance, as long as the flow speeds of the backflow in the region of the throttle restriction  38  are high enough. 
         [0043]      FIG. 4  shows a control valve  10  of  FIG. 3 , showing a static pressure distribution of the flowing fuel, instead of flow speeds. In the drawing, the same limitations in terms of drafting mentioned in the description of  FIG. 2  apply accordingly. The external (hydraulic) operating conditions of the control valve  10  of  FIG. 4  correspond to those of  FIG. 3 . In an upper portion, in terms of the drawing in  FIG. 4 , of the flow channel  20 , a relatively high pressure  46  prevails; in a region at the left bottom and in the region  26 , a medium pressure  44  prevails; and in a region on the left in the drawings, a relatively low pressure  42  prevails. It is understood that the “medium pressure  44 ” is not necessarily a precise mean value of the relatively high pressure  46  and the relatively low pressure  42 , but instead can be substantially below that. 
         [0044]    Below, in conjunction with  FIGS. 5-8 , further static pressure distributions during the backflow of the fluid are presented in further embodiments of the control valve  10 . Similarly to  FIGS. 2-4 , they are embodied essentially rotationally symmetrically. In terms of the drafting of the drawing, the limitations mentioned in the description of  FIG. 2  apply accordingly. It is common to all of  FIGS. 5-8  that in the right-hand part of the drawing—unlike in FIGS.  2 - 4 —additional regions of the flow channel  20 , some with radially extending flows, are also visible. 
         [0045]    The basic function of the control valve  10  in  FIGS. 5-8  is comparable to that in  FIGS. 3 and 4 ; that is, besides the effect of the shield  24  or shield portion  25 , a suction effect by means of the channel  28  also ensues. The flow speeds and the hydraulic effects and pressures sometimes differ, as a consequence of the different geometries. Similarly to  FIGS. 2-4 , the pressure loss as the fuel passes through the flow channel  20  is comparatively slight in each case. 
         [0046]    It is also common to the embodiments of  FIG. 5-8  that the shield portion  25  additionally forms a stop for the valve element  16 , in each case toward the right in terms of the drawings. As a result, a stroke limitation of the valve element  16  takes place. In  FIGS. 5-8 , the constriction  27  shown in  FIGS. 2-4  becomes a possibly persistent residual gap. The residual gap might lead to small leaks in the region  26 , but this can be compensated for by the action of the channel  28 . 
         [0047]      FIG. 5  shows a third embodiment of the control valve  10 , in which the housing  12 , the valve element  16 , the shield  24  and the shield portion  25  have a different geometry from  FIGS. 2 and 3 . The geometries of the flow channel  20 , the channel  28 , and the fuel-filled region  26  are different as well. The residual gap of the constriction  27  occurs in  FIG. 5  at a stop of the valve element  16  on the shield portion  25  and is fluidically inactive, in the state shown in the drawing. 
         [0048]    The channel  28  here is formed by a series of axial openings—such as bores—in the vicinity of the edge of the valve element  16 , of which only one is visible in the sectional view of  FIG. 5 . The throttle restriction  38  is located in the region of the valve seat  17  of the valve element  16  and in a bypass around the channel  28 , which channel—in a manner similar to the other FIGS.  2 - 8 —is oriented essentially orthogonally to the backflow. 
         [0049]    Along the flow channel  20  in  FIG. 5 , a pressure reduction ensues in the backflow direction  22 , from a relatively high pressure  46  via a medium pressure  44  to a relatively low pressure  42  in the left part of the drawing. In the region  26 , a relatively low pressure  42  prevails. Similarly to  FIG. 2  or  FIG. 3 , the pressure loss as the fuel passes through the flow channel  20  is comparatively slight overall. Since the channel  28  discharges into the region  42  of high flow speed and thus relatively low static pressure, the suction effect already described ensues again and leads to a pressure reduction in the region  26 . 
         [0050]      FIG. 6  shows a fourth embodiment of the control valve  10 , in which the channel  28  is extended all the way through the shield portion  25  and radially outward into the channel  20 . The throttle restriction  38  is formed her by two encompassing luglike shapings of the shield portion  25 . The pressure distribution shown is approximately comparable—except for the surroundings of the throttle restriction  38 —to  FIG. 4 ; see reference numerals  42 ,  44  and  46  in the drawing. Since the channel  28  discharges into the region of the throttle restriction  38  having a high flow speed and thus a relatively low static pressure, the result again is the suction effect already describe above, which leads to a pressure reduction in the region  26 . 
         [0051]      FIG. 7  shows a fifth embodiment of the control valve  10 , in which in a flow region at top right in the drawing, the backflow is deflected at approximately a right angle. The channel  28  discharges then into the radially inner region of the crooked flow, in which a pressure gradient can therefore be established in the radial direction. This is illustrated in the drawing by an arrow  48 . Thus in the radially inner flow region, a comparatively low pressure ensues, which continues by means of the channel  28  into the region  26  located inside the shield  24 . 
         [0052]      FIG. 8  shows a sixth embodiment of the control valve  10 , in which the channel  28  is formed by one or more axially oriented openings in the shield  24 . The function is analogous to the other embodiments. 
         [0053]    It is understood that  FIGS. 2-8  are merely examples of the control valve  10 . The described actions of the shield  24  and/or the suction effect can also be implemented with different geometries from  FIGS. 2-8 . In particular, combinations of the embodiments shown in  FIGS. 2-8  are also possible according to the invention. 
         [0054]    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.
A control valve is provided, in particular for metering in a fluid for a delivery pump which is arranged downstream. The control valve has a flow channel, an axially movable valve needle, and a valve element which can be loaded by the valve needle in an opening direction and is arranged in the flow channel. If the valve element is actuated in the opening direction by the valve needle, the fluid can flow back through the flow channel at least temporarily counter to the opening direction of the valve element. Upstream of the valve element as viewed in the backflow direction, the flow channel has a fluidically active shield which keeps the backflow at least partially free of a face of the valve element.