Abstract:
A venting mechanism for a motor vehicle having an air channel and a grating which covers the flow cross section of the air channel, a flow obstacle being arranged upstream from the grating. In order to equalize the flow in the flow cross section with the lowest possible pressure drop, in particular when only a small installation space is available, the grating has an uneven arrangement of openings so that a high degree of obstruction is achieved in a reduced-flow area of the venting cross section and a low degree of obstruction is achieved in a flow-through area of the ventilation cross section.

Description:
[0001]     This application claims the priority of German patent application 102004003196.716, filed Jan. 22, 2004, the disclosure of which is expressly incorporated by reference herein.  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     This invention relates to a venting mechanism for a motor vehicle.  
         [0003]     Such a venting mechanism is disclosed in European Patent EP 672 551 B1. This venting mechanism has an air channel bordered in the area of its outlet opening by a grating that completely covers the flow cross section. To provide the outflow cross section of the air channel with zones of diffuse outflow at one end and with a direct oncoming flow in the form of streams, the cover grating has nozzle-like openings of identical design distributed uniformly in the respective zones, said openings either becoming wider in the manner of the diffuser in the direction of flow or becoming narrower in the manner of jet nozzles. Diffuser openings and nozzle openings have approximately the same diameters and spacings. A choke is provided to regulate the air flow rate and distribution between two outlet areas. To achieve a uniform flow through the grating, the choke and grating are spaced a great distance apart and an insert of a nonwoven material is arranged in front of the grating.  
         [0004]     The object of this invention is to create a venting mechanism having an air channel which has velocities of flow distributed uniformly over the flow cross section in particular when the available installation space is limited. In particular the flow resistance is to be minimized.  
         [0005]     This object is achieved by a venting mechanism having a grating which covers the entire flow cross section of the air channel situated downstream in the immediate proximity of a flow obstacle, in particular in the wake of the obstacle. The grating has openings distributed uniformly over its area. The uneven distribution of openings results in the grating having different degrees of obstruction over its area. The different arrangement and/or design of the openings of the grating is associated with an equally heterogeneous design of the webs of the grating. The resulting differences in flow cross sections in the area of the grating result in the different degrees of obstruction.  
         [0006]     The inventive grating equalizes the irregularity in flow caused by an upstream flow obstacle. The differences in flow are manifested in velocity of flow distributions and/or uneven distributions of the absolute pressure in the flow cross section. The openings in the grating are provided so that they form a reduced-flow area having a high degree of obstruction and a flow-through area having a low degree of obstruction. The equalization of the flow differences and/or pressure differences in the flow cross section is achieved by said uneven distribution of openings in the grating, whereby the design configuration of flow-through area and reduced-flow area is based on characteristic flow patterns in the wake of the flow obstacle. The reduced-flow area, which has a high degree of obstruction, is assigned to zones of a high absolute pressure, and the flow-through area having a low degree of obstruction is assigned to zones having a low absolute pressure of the flow cross section. An equalization of the flow in the cross section of the air channel is achieved downstream from the grating in the flow cross section.  
         [0007]     Due to the arrangement of the grating in the immediate vicinity of the flow obstacle, an equalization of flow can be achieved while requiring only a small installation space. Due to the targeted design of the flow-through area and the reduced-flow area, no other equalization measures are required in contrast with the state of the art such as a nonwoven insert in front of the grating and a large travel length between the flow obstacle and the grating. This achieves an equalization of flow with a very low flow resistance and with a smaller required installation space than in the state of the art. In addition, due to the arrangement of the grating in the immediate vicinity of the flow obstacle in particular, it is possible to coordinate the arrangement of the flow-through area and the reduced-flow area with the wake of the flow obstacle.  
         [0008]     In a special embodiment of the venting mechanism, in order to achieve different degrees of obstruction of the area of the grating with openings of the same size, which are especially advantageous, e.g., in a special cross-sectional shape and size, in terms of the noise generated, the openings of the grating are arranged with different spacings between them, thereby forming webs of different widths and thus flow-through areas and reduced-flow areas.  
         [0009]     In a special embodiment of the venting mechanism, in order to be able to adjust the degree of obstruction with a low pressure drop in particular, openings of different cross-sectional areas and cross-sectional shapes are designed in the grating. The degree of obstruction of the grating can be adjusted by varying the size of the cross-sectional area of the openings themselves or, in the case of identical sizes of the cross-sectional areas, by varying the shape of the opening, such as the length/width ratios of the openings, for example. Through a corresponding adjustment of the grating, the noise generated by the venting mechanism can be improved.  
         [0010]     A special embodiment of the venting mechanism is equipped with a grating which has different degrees of obstruction inside the reduced-flow area and/or the flow-through area. Openings of different designs and/or spaced different distances apart are provided within the aforementioned areas in the grating. The openings and/or the degree of obstruction may be varied continuously, i.e., steadily, e.g., a longitudinal extent in the area of the grating so that a smooth transition between the reduced-flow area and the flow-through area is possible, whereby the change in the degree of obstruction along the length because of the grating openings is only discretely variable, i.e., is quasi-steady. In the extreme case, however, one or more openings, e.g., slot-shaped openings with a different width of the flow-through area along the longitudinal extent in which it has a great width up to the reduced-flow area in which it has a small width. A plurality of design variants having the same function is conceivable.  
         [0011]     A particular embodiment of the venting mechanism has a bend in the air channel upstream from the grating along a curve which in this case is effective as a flow obstacle. The reduced-flow area is assigned to the cross-sectional area of the air channel on the outside of the curve and/or the geometrically assigned surface area of the grating and the flow-through area is assigned to the cross-sectional area on the inside of the curve. Therefore, this equalizes the increase in velocity and/or pressure along the deflecting wall on the outside of the curve and in the flow cross section arranged in front of it and the low-pressure zone situated in the inside of the curve. Downstream from the grating there is a uniform flow through the flow cross section of the air channel.  
         [0012]     In a special embodiment of the venting mechanism, an interference body is situated in the flow cross section of the air channel upstream from the grating. For equalization of the absolute pressure in the flow cross section, the flow-through area of the grating is assigned to the turbulent area of the interference body and the reduced-flow cross sections are assigned to the flow-through cross sections in addition to the interference body. Downstream from the grating there is a uniform flow of the flow cross section of the air channel.  
         [0013]     In a special embodiment of the venting mechanism, the interference body is a shutoff valve. A reduced-flow area is assigned to an open slot of the shutoff valve and a flow-through area is assigned to an axis of the shutoff valve. Due to the associations of the reduced-flow area and the flow-through area, the turbulent area of the shutoff valve in the area of the pivot axis and the radial increase in velocity of flow are adapted to the open slots. The grating may also be designed based on a special and possibly particularly critical operating point or open angle of the valve through a structural arrangement and design of the openings.  
         [0014]     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  shows a sectional diagram of an embodiment of the venting mechanism of the present invention along the longitudinal extent of the air channel, and  
         [0016]      FIG. 2  shows a sectional diagram of the venting mechanism of  FIG. 1  across the longitudinal extent of the air channel. 
     
    
     DETAILED DESCRIPTION  
       [0017]      FIG. 1  shows a sectional diagram through a venting mechanism having an air channel  1 , which is bordered by its housing  1 . 1  across its longitudinal extent. The air channel  1  has air flowing through it along the arrow shown here. The remaining course of the air channel upstream is not shown in the drawing. The air channel  1  is bordered at the downstream end by the end opening  1 . 2 . Upstream from the end opening  1 . 2 , a grating  2  extending across the entire cross-sectional area of the air channel is arranged across the direction of flow. Due to the arrangement at a distance from the end opening, the grating is additionally covered by air baffles. The grating  2  has openings  2 . 1  and/or  2 . 3  and grating webs  2 . 2  and/or  2 . 4 . The openings  2 . 1  arranged adjacent to the channel wall (shown in cross section in the sectional diagram) have a smaller open cross section than do the openings arranged at a distance from the two sectional channel walls. Likewise, the webs  2 . 2  of the grating  2  arranged close to the sectional channel walls have a greater width than the webs  2 . 4  arranged at a distance from the two sectional channel walls. Due to this difference in the size of the design of the openings  2 . 1  and/or  2 . 3  and the difference in the width of the webs  2 . 2  and  2 . 4 , a reduced-flow area  1 . 3  is created in the lower immediate vicinity of the sectional channel wall  1 . 1  and a flow-through area  1 . 4  is created in the central area of the flow cross section which is at a distance from the two sectional wall areas.  
         [0018]     Upstream from the grating  2  a shutoff valve  3  is arranged in the channel. The shutoff valve  3  is designed as a two-leg shutoff valve with a pivot axis  3 . 1  arranged at the center. To regulate the air flow in the air channel  1 , the shutoff valve  3  is pivotable about its central pivot axis  3 . 1  and can be moved from a closed position, in which it is in contact with both channel walls (shown in cross section in the sectional diagram) of the housing  1 . 1 , to an open position in which it is directed largely along the longitudinal extent of the air channel  1 .  
         [0019]      FIG. 1  shows the shutoff valve  3  in a partially open position between the two end positions, i.e., the closed position on one end and the open position on the other end. Between the closing edge of the shutoff valve  3  and the wall area (shown in cross section in the sectional diagram) of the housing  1 . 1 , an open slot  3 . 2  is exposed on both sides. Due to the flow cross section of the open slots  3 . 2 , which is small in comparison with the full flow cross section of the air channel  1 , there is a great increase in velocity with a ray-like flow developing along the housing walls (shown in cross section in the diagram) of the housing  1 . 1 . In the central cross-sectional area of the flow cross section of the air channel  1 , a wake-like turbulent area is formed due to the coverage of the shutoff valve  3  in the area of the pivot axis  3 . 1 . Due to the increase in velocity along the wall, there is a great increase in the absolute pressure in the immediate vicinity of the wall directly downstream from the shutoff valve  3  in comparison with the absolute pressure in the central area of the cross-sectional flow downstream from the pivot axis  3 . 1 . The grating  2  arranged directly behind the shutoff valve  3  equalizes the flow, i.e., results in uniform velocities of flow over the flow cross section of the air channel  1  downstream from the grating  2  in particular in the cross section of the end opening  1 . 2  due to the great obstruction of the reduced-flow area  1 . 3 , i.e., the great flow resistance there, which is assigned to the area near the wall and thus to the wake of the open slot  3 . 2  and also due to the low velocity of flow of the flow-through area  1 . 4  which is assigned to the pivot axis  3 . 1  and/or the wake of the shutoff valve body. The direct structural assignment of the reduced-flow area  1 . 3  to the zone of a high absolute pressure and the direct assignment of the flow-through area  1 . 4  to the zone of a low absolute pressure make it possible to achieve a uniform flow in a very small installation space and with a low pressure drop.  
         [0020]      FIG. 2  shows a sectional diagram across the longitudinal extent of the air channel  1  along the sectional line II-II in  FIG. 1 . The air channel  1  has a housing  1 . 1  with an approximately rectangular cross section which is rounded in the corners. In the cross section of flow of the air channel  1 , the grating  2  is arranged over the entire cross-sectional area and is connected around the periphery to the wall areas of the housing  1 . 1 . Openings of different sizes, e.g.,  2 . 1  and  2 . 3 , are provided in the surface of the grating  2 . These openings have different spacings and different cross-sectional areas. In the installed position of the upper and lower areas of the grating  2  near the wall, smaller openings  2 . 1  are provided and webs  2 . 2  having a wider area are provided there as well. In the central cross-sectional area at a distance from these two walls along the pivot axis  3 . 1  of the shutoff valve  3  arranged behind the grating, openings of a larger cross section  2 . 3  and webs  2 . 4  with a smaller width in the area of the grating  2  are provided. Rows of openings of a medium cross section are arranged between the rows of openings  2 . 1  of a small cross section and openings  2 . 3  of a large cross section. These form transitional areas between the reduced-flow area  3 . 1  formed by the small openings  2 . 1  and the wide webs  2 . 2  and the flow-through area  1 . 4  formed by the large openings  2 . 3  and the narrow webs  2 . 4 . The openings of the grating  2  are designed to be rectangular with straight edges and to improve the noise pattern they may advantageously be designed with a rounded cross-sectional contour and with rounded edges.  
         [0021]     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.