Abstract:
A valve device for switching or metering a fluid includes a housing, a flow channel defined by the housing, and a valve body arranged in the flow channel. The valve body has a sealing section which contacts a housing-side sealing seat when the valve device is closed. The sealing section at least slightly protrudes beyond a surface of the valve body facing the sealing seat.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2012/050220, filed on Jan. 9, 2012, which claims the benefit of priority to Serial No. DE 10 2011 005 485.5, filed on Mar. 14, 2011 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a valve device and to a method of producing a valve device. 
     Valve devices, for example flow-rate control valves of a fuel system of an internal combustion engine, are known commercially. Such valve devices often have a valve body which can be loaded for example into an open position by a valve needle. When the valve device is in the closed state, the valve body abuts, by way of a sealing portion, against a sealing seat on the housing. The valve body is for example of plate-shaped form, whereby it may have a relatively low mass. 
     In many flow-rate control valves, the valve device is open during the suction phase of a high-pressure fuel pump. In the subsequent, so-called return-flow phase, the valve device continues to be forcibly held open for a certain time period for example by means of a valve needle which is loaded by a spring force. During the delivery phase of the high-pressure fuel pump that follows the return-flow phase, it is for example the case that an electromagnet is energized, whereby the valve needle can lift from the valve body and the valve device can thus close, often with the assistance of a valve spring. 
     Patent publications from this technical field are for example DE 10 2008 043 237 A1, DE 10 2007 034 038 A1, DE 10 2007 028 960 A1, DE 10 2005 022 661 A1, DE 10 2004 061 798 A1, DE 2004 016 554 A1, DE 101 24 238 A1, EP 1 701 031 A1, EP 1 471 248 A1 and EP 1 296 061 A2. 
     SUMMARY 
     The problem addressed by the disclosure is solved by means of a valve device and by means of a method of producing a valve device. Advantageous refinements are specified in the subclaims. Features of importance for the disclosure can also be found in the following description and in the drawings, wherein the features may be of importance for the disclosure both individually and also in different combinations, without this being explicitly pointed out again. 
     The valve device according to the disclosure has the advantage that tolerances or wear on a sealing portion and/or on a sealing seat cannot lead, or can lead only to an insignificant extent, to changes in a flow force exerted on a valve body when the valve device is open. Furthermore, a lifting of the valve body during the opening of the valve device can take place in a particularly uniform and defined manner. Furthermore, the valve device according to the disclosure can be produced inexpensively. 
     The disclosure is based on the consideration that a valve body in a flow duct of the valve device is loaded not only by the forces of a valve needle and of a valve spring but also by hydraulic flow forces. In particular in the case of flow-rate control valves, such as is used for example in a fuel system of an internal combustion engine or of a motor vehicle, the hydraulic flow forces are relatively large and thus also have an effect on the function of the flow-rate control valve. 
     According to the disclosure, a sealing portion arranged on the valve body is designed such that it projects at least slightly beyond a surface, which faces toward the associated sealing seat which is fixed with respect to the housing, of the valve body, for example in the manner of an axially extending annular collar. In this way, the precondition is met that mechanical tolerances in an area surrounding a sealing region formed by the sealing portion and the sealing seat cannot, or can only slightly, change the flow forces acting on the valve body. This is of significance in particular during the so-called “return-flow phase” of the flow-rate control valve, in which a fluid stream is to be conveyed, in as unhindered a manner as possible, from a delivery chamber of the fuel pump controlled by the flow-rate control valve back into the low-pressure region. Here, the valve body is preferably held in the open position only by the valve needle or by a spring which exerts load on the valve needle. 
     One refinement of the disclosure provides that the valve body and the sealing portion are produced in one piece. In this way, the valve body and the sealing portion can be produced in a particularly precise, durable and inexpensive manner. 
     It is also provided that the sealing seat is of substantially planar form in an area surrounding the sealing region. Thus, the valve device according to the disclosure has only a single hydraulically acting “sealing contour”, specifically on the sealing portion of the valve body. Furthermore, the sealing seat can be produced in a particularly simple manner and with narrow tolerances. 
     A further refinement of the disclosure provides that the functional elements of the valve device are of substantially rotationally symmetrical form and the sealing portion is part of a radially encircling annular web or collar. Said geometry is particularly expedient from a flow aspect, in particular in flow-rate control valves. Furthermore, it is achieved in this way that the sealing region has a substantially constant area which is virtually independent of any radial offset of the valve body in relation to a longitudinal axis of the valve device and/or independent of wear on the sealing portion. Thus, the opening of the valve device can take place in a uniform and defined manner, and the flow rate of the fluid medium (fuel) can be set in a particularly precise manner. 
     The disclosure is particularly expedient if, in the flow duct, there is arranged a fluidically active shield which can at least partially shield the valve body from a flow of the fluid in the event of a return flow of the fluid when the valve body is forcibly raised from the sealing seat. In this way, the valve body together with the sealing portion can, when raised from the sealing seat, be removed from the region of the most intense flow. Correspondingly, the valve body is subjected to relatively little loading in a closing direction by hydraulic flow forces. In this way, a further precondition is met that any mechanical tolerances of the valve body or of the sealing portion cannot, or can only negligibly, change said flow forces. In this way, the valve device operates in a particularly precise and durable manner. 
     A further refinement of the valve device provides that, in an area surrounding the sealing region, a delimiting wall of the flow duct has a rounding or a bevel. The fluid (fuel) that flows radially inward or radially outward in the sealing region when the valve device is open can be diverted into or out of the axial direction with particularly low flow losses by means of the rounding or the bevel. In this way, the hydraulic efficiency of the valve device can be further improved. 
     It is additionally proposed that the valve body has an axial and approximately spherical-cap-shaped recess against which a valve needle can abut. In this way, a concave deformation of the valve body at the abutment point of the valve needle, such as arises during operation of the valve device, can be structurally anticipated, so to speak. The precision and the durability of the valve device can thus be additionally increased. 
     Also proposed is a method for producing the valve body of the valve device, wherein the valve body is produced by extrusion such that a material displaced by the extrusion—in particular from the region of the spherical-cap-shaped recess—contributes at least partially to the formation of the radially encircling annular web. In this way, the valve body can be manufactured in a particularly inexpensive manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the disclosure will be explained below with reference to the drawing, in which: 
         FIG. 1  shows a simplified schematic diagram of a fuel system of an internal combustion engine of a motor vehicle; 
         FIG. 2  shows a simplified sectional illustration through a first embodiment of a valve device from  FIG. 1 , in an open state; 
         FIG. 3  shows a simplified sectional illustration of a second embodiment of the valve device, in a closed state; and 
         FIG. 4  shows a simplified sectional illustration of a third embodiment of the valve device, in a closed state. 
     
    
    
     DETAILED DESCRIPTION 
     In all of the figures, even in the case of different embodiments, the same reference signs have been used for functionally equivalent elements and dimensions. 
       FIG. 1  shows a fuel system  10  of an internal combustion engine in a highly simplified illustration. From a fuel tank  12 , fuel is supplied to a high-pressure pump  24  (not explained in any more detail here) by means of a pre-feed pump  16  via a suction line  14 , via a low-pressure line  18  and via a valve device  22 , in the present case a flow-rate control valve, which can be actuated by an electromagnet  20 . The high-pressure pump  24  is connected, downstream, to a high-pressure accumulator  28  via a high-pressure line  26 . Other elements, such as for example outlet valves of the high-pressure pump  24 , are not shown in  FIG. 1 . It is self-evident that the valve device  22  or the flow-rate control valve may be formed as a structural unit together with the high-pressure pump  24 . For example, the flow-rate control valve may be an inlet valve of the high-pressure pump  24 . Furthermore, the flow-rate control valve may also have some other actuation device instead of the electromagnet  20 , for example a piezo actuator or a hydraulic actuation means. 
     During the operation of the fuel system  10 , the pre-feed pump  16  delivers fuel from the fuel tank  12  into the low-pressure line  18 . Here, the flow-rate control valve determines the fuel flow rate supplied to a delivery chamber of the high-pressure pump  24 . 
       FIG. 2  shows a first embodiment of the valve device  22  from  FIG. 1  in a simplified sectional illustration. Those elements of the valve device  22  that are illustrated in the drawing are designed to be substantially rotationally symmetrical about a longitudinal axis  29 , and comprise a housing  30  with a substantially planar sealing seat  32 , against which a sealing portion  34  of an approximately plate-shaped valve body  36  can bear when the valve device  22  is closed. In  FIG. 2 , however, the valve device  22  is open, that is to say the valve body  36  is raised axially from the valve seat  32 . A valve needle  37  exerts load on the valve body  36  in the direction toward the right in the drawing. Here, an end portion of the valve needle  37  rests in a spherical-cap-shaped recess  39  of the valve body  36 . In the valve device  22  there is formed a flow duct  38  through which, in the open position shown, fluid, in the present case fuel, flows in the direction of arrows  40 . A fluidically active shield  42  is arranged in the flow duct  38  upstream of the valve body  36  such that it can at least partially shield the valve body  36  from a flow of the fluid when said valve body is forcibly raised from the sealing seat  32  during a return flow of the fluid. 
     The sealing seat  32  and the sealing portion  34  are of areal form and are parallel to one another and together form a sealing region  44 . The sealing portion  34  projects a distance  48  beyond a surface  46 , which faces toward the sealing seat  32 , of the valve body  36 . The valve body  36  thus has, in a radially outer portion, a radially encircling annular web  49  or axially extending collar. A radial gap (without reference sign) is formed between the valve body  36  or the annular web  49  and the shield  42  such that the valve body  36  can be moved axially without being hindered by the shield  42 .  FIG. 2  does not illustrate a valve spring, which is arranged to the right of the valve body  36  in the drawing and which guides the valve body  36 . 
     It can be seen that, during the return-flow phase of the valve device  22  illustrated in  FIG. 2 , the fuel flows substantially from right to left (that is to say from the high-pressure pump  24  back into the low-pressure line  18 ), corresponding to the arrows  40 . Here, the flow initially runs approximately horizontally, and is subsequently diverted radially inward in front of the valve body  36  and the shield  42 . The flow is subsequently diverted axially again in the lower left-hand region of the drawing. 
     It can also be seen that the valve body  36  and likewise the sealing portion  34  are remote from the region of the most intense flow owing to the fluidically active shield  42 . Correspondingly, mechanical tolerances of the valve body  36 —in particular in an area surrounding the sealing portion  34 —have no influence or relatively little influence on flow forces that act on the valve body  36 . Tolerances of the distance  48  are also of relatively little significance. 
     Overall, the sealing portion  34  has an annular contour. From this, it is evident that a possible radial play of the valve body  36  with respect to the longitudinal axis  29  does not change a contact surface formed between the sealing seat  32  and the sealing portion  34  when the valve device  22  is in the closed state. Thus, a subsequent lifting of the valve body  36  from the sealing seat  32  can take place in a uniform and precise manner, regardless of the possible radial play. Said state of the valve device  22  is however not shown in  FIG. 2 . 
       FIG. 3  shows a further embodiment, similar to  FIG. 2 , of the valve device  22 . Here, the valve device  22  is situated in the closed state, that is to say the valve body  36  abuts axially by way of the sealing portion  34  against the sealing seat  32  which is fixed with respect to the housing. In the drawing, a boundary wall  50  of the flow duct  38  has a rounding  52  below the sealing region  44 . 
     The rounding  52  has the effect, when the valve device  22  is open, that the hydraulic flow flowing in the flow duct  38  can be diverted from the radial direction into the axial direction—or vice versa—with particularly low losses. The rounding  52  may alternatively also be in the form of a bevel or an upstream edge. This is however not shown in  FIG. 3 . 
     In the present case, the valve body  36  has been produced by means of extrusion such that a material displaced by the extrusion—in particular from the region of the spherical-cap-shaped recess  39 —has contributed partially to the formation of the annular web  49 . 
       FIG. 4  shows a further embodiment, similar to  FIG. 3 , of the valve device  22 . By contrast to  FIG. 3 , the embodiment of  FIG. 4  has an upstream edge  54  instead of the rounding  52 .