Abstract:
A flow guide element is provided for guiding a flow of a fluid medium which is particularly suitable for use in an intake tract of an internal combustion engine. The flow guide element includes a flow tube having an elbow for diverting the flow. In the region of the elbow there is situated, in this case, at least one flow baffle having at least one deflector. The deflector is penetrated by an opening, going right through the flow baffle, in at least one area.

Description:
BACKGROUND INFORMATION 
     The present invention relates to flow guide elements such as the ones used in various fields of natural science and technology. These flow guide elements are used as a part of flow guide systems which are used to guide flowing fluid media, especially gases or liquids over a specified path, for instance, to supply gases to a process or drain off exhaust gases from this process. 
     One important field of application of a flow guide is motor vehicle technology, and within that field, especially the area of guiding gaseous media. A first important example in the field of motor vehicle technology is the area of air guidance in connection with air filters in the intake tract of internal combustion engines. The air taken in, in this instance, has to be guided from the air filter to the internal combustion engine by using several partially straight, partially curved pieces of tubing. 
     A second example, in which flow guide elements are important, is air mass meters such as may also be used in the intake tract of internal combustion engine, for example. One important measuring principle is the so-called hot-film air mass meter, like the one described in German Patent Application No. DE 102 53 970, for example. In such devices, which may be inserted as plug-in sensors into the intake tract, for example, a part of the air is guided through a so-called bypass channel, which is curved several times, to a sensor chip on which the air mass throughput may be determined, using heating elements and temperature sensors. German Patent Application No. DE 102 53 970, for instance, describes the method of functioning of such hot-film air mass meters. 
     Depending on the field of application, such flow guide elements or systems, which are composed of these elements, are subject to various requirements. Thus, in the intake tract, especially in the area of the air filters, besides an intake air quantity that is stable in time and as free from fluctuations as possible, a high air throughput is of decisive importance. In other systems, by contrast, such as the hot-film air mass meters mentioned, the emphasis of requirements (besides as high a throughput as possible, which is subject to a signal level swing) is especially on high stability of the flow of the fluid medium. 
     In order to do justice to these requirements, even today, in many flow systems, especially in air flow systems, guide blades are used in order to divert the flow in as lossfree a manner as possible, and without flow separation. Such guide blades are used under various designations, and are also designated as auxiliary wings or sheet metal diverters. 
     One example of such guide blades is described in German Patent Application No. DE 102 53 970. In the system described there, in order to improve the flow conditions in the bypass channel of the hot-film air mass meter, a guide blade is proposed (there designated by reference numeral 50), which guides the flow and counteracts flow separation of the flow of the partial media flow from the channel walls of the measuring channel. Other examples may be found in the constructions of many current motor vehicle air filters. 
     An important disadvantage of this design approach is that the geometry and the position of the guide blades has to be adapted very carefully to be effective. Unfortunately, this constructive adaptation is not always possible, since the flow topology in air guidance systems frequently changes rapidly with flow speed. In this case it may happen that the guide blades or sheet metal baffles themselves cause additional separations and interferences. 
     SUMMARY OF THE INVENTION 
     A flow guide element to guide the flow of a fluid medium is therefore provided, which substantially avoids the disadvantages of known flow guide elements described above. The flow guide element is particularly suitable for use in the intake tract of an internal combustion engine, but may also be used for other types of flow guide elements in the fields of natural science and technology, especially in the field of method technology and/or automobile construction. 
     The flow guide element provided includes a flow tube (by analogy, however, several flow tubes being able to be included too), having an elbow for diverting the flow. By “elbow” one should basically understand, in this context, any formed element which is designed to change the main flow direction of the fluid medium. The flow tube may basically also have any cross section, round cross sections and/or multiangular cross sections being preferred for construction reasons, however. 
     In the region of the elbow, in this instance, there is situated at least one flow baffle having at least one deflector. Thus, “flow baffles” are to be taken as being elements basically formed at will, which are situated in the flow, that is, within the flow cross section of the flow tube, and which are designed by their deflectors to favor the diversion of the flow. 
     To this extent, the provided flow guide element corresponds, for instance, to the guide blades in the bypass of an hot-film air mass meter described in German Patent Application No. DE 102 53 970, that was described above. By contrast to known flow guide elements, the flow guide element provided is, however, designed in such a way that the deflector has an opening in at least one area that passes through the flow baffle. 
     By “opening” one should understand an opening which passes transversely through the flow guide element, in this context. It is particularly preferred if this opening is situated approximately perpendicular to the local flow direction of the fluid medium, preferably having a deviation from a right angle of not more than 20°. 
     A basic idea of the flow guide element provided using the openings is to avoid flow separations in the areas of the flow baffle by the deliberate introduction of longitudinal swirls. By longitudinal swirl one should understand a swirl having a swirl axis which is directed essentially in the main flow direction (or rather in the local main flow direction of the fluid medium. 
     Because of pressure differences, the air, or rather the fluid medium flows through between the leading edge (also called the luff side, below) and the side facing away from the flow (also called the lee side below), and generates strong longitudinal swirls on the lee side. These longitudinal swirls ensure a reinforced pulse exchange between rapid fluid (external current) and slow fluid (fluid in the separation area), and in this way diminish or avoid separations at the rear side of the flow baffle. 
     Because of the at least partial permeability of the flow baffle, a “soft” effect is ensured. The diverting effect may be weakened locally by partial perforation. Because of this, the flow baffle becomes relatively insensitive to its positioning and its geometry. Because of the pressure drop of the flow through the flow baffles or the guide blades with increasing flow speed, the diverting action increases with increasing flow speed. This effect correlates with the physical fact that the separation tendency generally decreases with increasing flow speed and increasing Reynolds number. 
     In this context it is particularly preferred if the flow baffle includes a sheet metal flow baffle. However, the term “sheet metal” should not necessarily be limited to mean a metallic material, although metals and sheet metals are preferably used. In particular, perforated sheet metals that are commercially available may be used in this context. 
     In particular, the sheet metal baffle may have a rectangular shape, for instance, having a first rectangular side, which essentially corresponds to a diameter and/or a chord of the flow tube, and a second side, the longitudinal side, which corresponds to the longitudinal extension of the sheet metal guide in the flow tube. 
     In this context, the thickness of the sheet metal baffle is preferably constant and it is preferably smaller by an order of magnitude than the extension of the sheet metal guide in the lateral direction. 
     Instead of sheet metal baffles having constant thickness, which are preferably made of a deformable material, other types of flow baffles may also be used, such as guide blades, guide wings or similar shapes, as described above, for instance, having a wing cross section. 
     The opening preferably has a round shape, in particular a circular or oval shape, and/or a multiangular shape, especially a rectangular shape and/or a slotted shape. 
     A plurality of openings may be situated in a matrix shape, in this instance, a matrix being understood to be a uniform geometrical positioning in a plane. However, this does not have to be a row and column arrangement, but every other row may be offset by half a column width compared to the remaining rows, for instance. 
     The “density” of the distribution of the openings may also be designed to be variable, and may vary, for instance, corresponding to the pressure conditions at the deflector. One example which implements this idea in a simple way is that the flow baffle includes at least one first area provided with openings, and at least one second area not provided with openings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows the problem of the formation of separation regions in the area of elbows. 
         FIG. 1B  shows the reduction of the problem by the use of sheet metal baffles. 
         FIG. 2A  shows the problem of the formation of separation regions to the lee of sheet metal baffles. 
         FIG. 2B  shows the avoidance of this problem by the use of perforated sheet metal baffles, according to the present invention. 
         FIG. 3  shows one exemplary embodiment of a continuously perforated sheet metal for use as a sheet metal baffle. 
         FIG. 4  shows a stylized, perspective representation of the swirl formation at a partially perforated sheet metal baffle. 
         FIGS. 5A to 5C  show alternative specific embodiments of perforated sheet metal baffles. 
         FIG. 6A  shows a semitransparent, perspective representation of the flow in an elbow of an air filter. 
         FIG. 6B  shows the air filter according to  FIG. 6A  having a sheet metal baffle. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIGS. 1A and 1B , the known problem of the formation of separation regions  110  is shown in the region of elbows  112  of flow tubes  114 . The fluid medium, in this instance, flows at a (local) main flow direction  116  through flow tube  114 . Directly after being diverted in the region of elbow  112 , there is formed a separation region  110 , in the embodiment in  FIG. 1A  not having flow baffles, in which a very slow flow and a partial backflow prevail. 
     In this region, the flow, which is symbolically made clear in  FIGS. 1A and 1B  by flow lines  118 , is compressed, and the flow cross section becomes narrower. The throughput of flowing fluid medium through flow tube  114  is reduced thereby. An additional problem is that separation regions  110  may be unstable laterally, whereby fluctuations in the throughput may occur. 
       FIG. 1B  shows the arrangement shown in  FIG. 1A , but in this case two flow sheet metal baffle  120  have been accommodated inside flow tube  114 . These flow sheet metal baffles  120  have deflectors  122 . As may be seen in the stylized representation in  FIG. 1B , these sheet metal baffles  120  contribute the formation of separation region  110  being at least largely avoided. 
     However, in  FIG. 2A  a problem is shown that is frequently observed in practice. On leeward side  124  of flow sheet metal baffle  120 , in this case, there is formed a separation region  110 . Consequently, sheet metal baffle  120  does not directly contribute to the solution of the problem, described above, of the formation of separation regions  110 , but it may, under unfavorable flow conditions, even augment the problem, or solve it only partially. 
     By contrast, in  FIG. 2B  an embodiment according to the present invention of a flow sheet metal baffle  120  is shown. In this case, flow sheet metal baffle  120  has several openings  130  at its upstream end. Because of the pressure differences between luff side  128  and lee side  124  of flow sheet metal baffle  120 , longitudinal swirls  132  form on the leeward side behind these openings  130 . These longitudinal swirls  132  ensure a thorough mixing of the flow on leeward side  124  of guide blade  120  and thus they prevent the formation of separation region  110 . 
     Instead of only one flow sheet metal baffle  120 , as shown in  FIG. 2B , exemplary embodiments are also possible, however, in which several such flow sheet metal guides  120  may be inserted. As a result, the exemplary embodiment shown in  FIG. 1B  may also be modified in such a way that both flow sheet metal baffles  120  have such openings  130 . 
     In  FIGS. 3 to 5C , various exemplary embodiments of flow sheet metal baffles  120  are shown having openings  130 , such as may be used in air filters (see below). Thus,  FIG. 3  shows a top view of a sheet metal guide  120  that is completely interspersed with openings  130 . Sheet metal baffle  120  is thus designed in this exemplary embodiment completely as a perforated sheet metal, which may be made of aluminum, for example. 
     Openings  130  are circular in this exemplary embodiment, and are situated in a matrix type, every other row being offset by one-half of a column distance. The sheet metal may have a thickness of 0.7 mm, for example, and the holes may have a diameter of 1 mm, and the sheet metal preferably has a rectangular shape having an edge length of 20 to 25 mm and a length of ca. 80 mm. The exact measurements of holes  130  usually depend strongly on the installation situation. 
     In a perspective representation,  FIG. 4  shows the flow against a sheet metal baffle  120 . We have selected the view direction onto leeward side  124  of sheet metal baffle  120 . 
     By contrast to the embodiment in  FIG. 3 , flow sheet metal baffle  120 , in the representation according to  FIG. 4 , has a first area  134  that is provided with openings  130 , as well as a second area  136  in which no openings  130  are situated. Sheet metal baffle  120 , in this context, is differently curved along its longitudinal extension, and has the greatest curvature in first area  134 . This example in  FIG. 4  is an example to show that the distribution and the density of openings  130  is able to be optimized, so as to achieve an optimum flow guide effect, on the one hand, and effectively to avoid the formation of separation regions  110 , on the other hand. 
     In  FIGS. 5A to 5C , various examples of sheet metal baffles  120  are shown that are alternative to  FIG. 4 . Thus,  FIG. 5A  shows an arrangement in which, similarly to  FIG. 4 , in a first area  134 , which is situated at the flow end, rectangular openings  130  are situated. These rectangles are formed in an extended manner, having a longer side along the main flow direction and a narrow side perpendicular to it. Again, to this first area  134  a second area  136  adjoins downstream, which is not perforated. 
     By contrast, in  FIG. 5B  an exemplary embodiment of a sheet metal baffle  120  is shown in which openings  130  are not situated in the middle of sheet metal guide  120 , but at its edges. In this context, sheet metal baffle  120  is pictured in the state of being inserted into flow tube  114 . Openings  130  are recesses in the form of rectangles in the edges of flow sheet metal baffle  120 , in this instance. 
     In  FIG. 5C , by contrast, openings  130  are developed as a row of holes, which extend along the lower edge of flow sheet metal baffle  120  along its longer edge. 
     The examples in  FIGS. 5B and 5C  show that the “density” of openings  130  is able to be varied not only, as in examples  4  and  5 A, in the flow direction, but also perpendicular to this flow direction. In this way, for instance, using commercially available CFD simulation software (CFD=computational fluid dynamics), the design and distribution of openings  130  may easily be optimized in flow sheet metal baffles  120 . 
     As was described above, the flow guide element may be used in technology in various ways, especially in the field of automotive technology. One example (not shown below) of such an application is the modification of the flow baffle (reference numeral 50) of German Patent Application No. DE 102 53 970, in such a way that it has additional openings  130 . 
     An additional example shown in  FIGS. 6A and 6B  is to design the air guidance in an air filter  138  appropriately.  FIG. 6A , in this context, shows a half transparent, perspective representation of an usual air filter  138 , flow lines  118  having been calculated using a CFD simulation in flow tube  114 .  FIG. 6B , on the other hand, shows an air filter  138  designed according to the present invention, in which a flow sheet metal baffle  120  having openings  130  has been inserted. 
     Air filter  138  has a filter unit  140 , an adjoining flow tube  114  and a connection piece  142 . In flow tube  114 , directly ahead of connection piece  142 , a hot-film air mass meter  144  is situated (which is abbreviated below as HFM). 
     From the representation of flow lines  118  in  FIG. 6A  one may see that in this design of air filter  138 , in the region of elbow  112 , or rather immediately after it, a large separation region  110  has been formed. This separation region  110  not only borders on the throughput, and thus on the entire intake air quantity, but also represents a source of unreliabilities of measurements of hot-film air mass meter  144 , because of the direct spatial vicinity to HFM  144  and the usually occurring instabilities of separation region  110 . 
     By contrast, in the design of air filter  138  according to  FIG. 6B  (shown only symbolically in  FIG. 6B ) a flow sheet metal baffle  120 , according to the design shown in  FIG. 4 , is inserted into flow tube  114 , in the area of elbow  112 . Openings  130  are situated at the flow side, in this instance. As may be seen in  FIG. 6B , flow sheet metal baffle  120 , in this context, extends downstream up to the vicinity of hot-film air mass meter  144 . By way of this flow sheet metal baffle  120 , separation region  110  may be considerably diminished, and the flow quality may be considerably improved.