Abstract:
A device for measuring at least one parameter of a medium flowing in a line, particularly the intake-air volume of an internal combustion engine. Liquid particles contained in the line act upon a measuring element and influence a characteristic curve of the measuring element which is used to determine parameters of the flowing medium. The characteristic curve of the measuring element can be changed disadvantageously by solid-matter particles. In order to reduce the action of solid-matter particles on the measuring element, a protective grating is proposed in which side walls of channels of the protective grating form various angles of intersection with the flow direction. Solid-matter particles are thereby diverted into a path of motion around the measuring element.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for measuring at least one parameter of a medium flowing in a line. 
     BACKGROUND INFORMATION 
     German Published Patent 197 35 891 Application No. describes a measuring body, insertable into a clean channel of an intake line of an internal combustion engine, for determining the mass of the intake air, which has a flow channel and a measuring channel that is essentially inclined in relation to a longitudinal axis of a line, and which subdivides into an S-shaped deflection channel adjoined thereto. A measuring element is arranged in the measuring channel. The measuring element can be constructed as a micromechanical sensor part having a dielectric membrane, as is known, for example, from the German Published Patent Application No. 43 38 891 and U.S. Pat. No. 5,452,610, respectively. Because of the entry of water into the intake line, for example, due to a roadway wet from rain, the measuring element may become contaminated. Natural components of dissolved salts contained in this spray water then cause a drift in the characteristic as the result of the buildup of salt crusts on the membrane of the sensor part. It may be that the inclination of the measuring body forms a screened region, however, dirt or liquid particles nevertheless get into the measuring channel. 
     From German Published Patent Application No. 197 35 664, a device is already known in which the measuring element is positioned within a tubular member through which the medium flows, an upstream end of the tubular member extending into a filter chamber, and there having inlet openings on a lateral surface to reduce the action of dirt particles or water droplets on the measuring element. Particularly in the case of heavily polluted air and a high water content in the intake air of the internal combustion engine, the danger exists that the air filter will become saturated with water which then passes through the filter mat and, in so doing, takes along dirt particles. On the downstream side of the air filter, the actual clean side, the danger now exists that the intake air will again carry along dirt particles and water droplets from the filter surface which then deposit in an undesirable manner on the measuring element, and which lead to measuring errors or a malfunction of the measuring element. By the arrangement of the inlet openings on the lateral surface, the tubular member according to the related art reduces the danger of deposits on the measuring element; however, a correspondingly long design of the tubular member causes an undesirable pressure drop which leads to a decrease in measuring sensitivity. In addition, given a fluid entry of 20 liter/hour resulting during operation of a motor vehicle, the reduction of the action of liquid/solid-matter particles on the measuring element is too small. 
     German Published Patent Application No. 196 52 753 describes a device having a measuring element, the device containing a flow rectifier and a grating for stabilizing a measuring signal. However, no further grating or element is used to protect the measuring element from liquids or solid-matter particles. 
     It has furthermore been proposed to use a repelling grating in a line to separate liquid particles from streaming air or a gas. Such a repelling grating, connected upstream of an inner pipe or in the line, influences the air/water mixture streaming toward the measuring element in such a way that the liquid particles are guided to a pipe wall or a line wall, while the air remains in a center of the inner pipe. 
     A different characteristic appears in response to the throughput of a mixture with air and dust in the line. Because of its still higher inertia compared to a liquid, the dust, in response to a change in the direction of flow forced by the side walls employed, changes its path only by reflection at the side wall, the principle of angle of incidence equal to angle of reflection being valid. Depending on the orientation of the side wall and the point of impact, a certain particle rejection thereby results, that is to say, a certain portion of the particles striking on the repelling grating is deflected by a reflection in the direction of the wall. The remaining part, after two reflections at the side walls, once more exhibits the main flow direction, and thus can strike, unhindered, on the measuring element downstream of the repelling grating. 
     SUMMARY OF THE INVENTION 
     In comparison, the device of the present invention has the advantage that the deflection of solid-matter particles and liquid particles is improved in a simple manner by varying the orientation of the side walls with respect to the main flow direction over their extension in the main flow direction. 
     It is advantageous to influence the path of motion of the solid-matter particles in the streaming medium by the formation of the side walls in such a way that it runs past the measuring element, since in this manner, the measuring element is not soiled. 
     The possibility of positive or negative angles of intersection of the side walls with the flow direction has the advantage that it permits more variations in the design. 
     The continuous curve of a channel has the advantage that the danger of a separation of the flow possibly arising is reduced, whereby otherwise an increased signal noise is caused. 
     The use of a tubular member in the line of the device has the advantage that additional protection is attained for the measuring element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an example of a device according to the present invention in a pipe stub. 
     FIG. 2 shows an axial cross-section in the longitudinal direction in FIG.  1 . 
     FIG. 3 shows a uniflow-current channel according to the related art. 
     FIG. 4 a  is a first illustration of an axial cross-section through a uniflow-current channel constructed according to the present invention. 
     FIG. 4 b  is a second illustration of an axial cross-section through a uniflow-current channel constructed according to the present invention. 
     FIG. 5 a  shows a further exemplary embodiment of the device according to the present invention in partial representation. 
     FIG. 5 b  shows another further exemplary embodiment of the device according to the present invention in partial representation. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a device  1  for measuring at least one parameter, particularly an air-volume flow, of a medium flowing in line  2 , especially the intake-air volume of an internal combustion engine. 
     Parameters of a flowing medium are, for example, the air-volume flow for ascertaining an air mass, a temperature, a pressure or a flow velocity, which are determined by suitable sensors. It is possible to use device  1  for measuring further parameters. This can be carried out by using two or more sensors, one sensor also being able to ascertain two or more parameters. Line  2  has a wall  3 . The medium flows in line  2  in main flow direction  6 , indicated by an arrow. Line  2  has an inner wall  7 . Provided in line  2  is, for example, a tubular member  8  running with radial clearance with respect to line  2  and circumflowed by the medium. Tubular member  8  has a flow-through channel  11  and a protective grating  15  situated in the region of its upstream end. Plastic, metal, ceramics or glass can be used as material for protective grating  15 . For example, plate-shaped protective grating  15  made of plastic can be produced by injection molding or by introducing grating openings  44  using a material-removing method. Downstream, somewhat removed from protective grating  15 , a flow direction  12  prevails in flow-through channel  11 . Flow direction  12  runs, let us say, parallel to main flow direction  6 . Line  2  has a center line  27  which, for example, is also the center line of tubular member  8 . 
     For instance, a measuring member  19  extends into tubular member  8 . For example, measuring member  19  is partially inserted through an insertion opening  31  in wall  3  and an insertion opening  22  in a wall of tubular member  8 , and projects with a free end into flow-through channel  11 . One skilled in the art is familiar with such a measuring member  19  from German Published Patent Application No. 197 35 891, which is intended to be part of this disclosure. The air volume drawn in by the internal combustion engine is arbitrarily alterable by a throttle valve (not shown), positioned downstream of tubular member  8  in the intake manifold of the internal combustion engine. 
     To ascertain the intake-air mass of the internal combustion engine, measuring member  19  is provided which has an essentially elongated and rectangular-shaped design and which extends along a longitudinal axis  21 . Longitudinal axis  21  runs essentially perpendicular to center line  27 , and consequently also to main flow direction  6 . In this context, a connector end of measuring member  19  accommodating the electrical connections, e.g. in the form of blade contacts, remains, for instance, outside of line  2 . Provided in known manner in measuring member  19  is a measuring element  23  that is in contact with the air flowing through flow-through channel  11  and by which the air-volume flow drawn in by the internal combustion engine is determined. For example, measuring element  23  can be a temperature sensor as is known from German Patent No. 42 28 484, a pressure sensor as is used in the German Published Patent Application No. 31 35 794, or an air-volume sensor, which ascertains the corresponding parameters. Selected here as an example for the various sensors is an air-volume sensor which, for instance, is arranged in measuring member  19  that, for example, has an inlet opening  20  into which the medium flows. For example, measuring element  23  can be constructed in known manner in the form of at least one temperature-dependent resistor. In particular, it is possible, as is described, for example, in the German Published Patent Application No. 43 38 891 and the U.S. Pat. No. 5,452,610, respectively, to construct measuring element  23  as a micromechanical component which has a dielectric membrane upon which resistor elements are formed. It is also conceivable to introduce measuring element  23  into line  2  or tubular member  8  without measuring member  19 . Located on tubular member  8  are, for instance, at least two braces  33  which are used to support tubular member  8  in line  2 . 
     In addition to supporting tubular member  8  in the air flow between line  2  and tubular member  8 , braces  33  cause an increase in the pressure drop, so that the air quantity flowing through flow-through channel  11  increases, and secondly, braces  33 , in an intended manner, bring about a rectification of the intake-air flow. Tubular member  8  can also be arranged in line  2  without braces  33 , e.g., it is secured to measuring member  19 . 
     A design of protective grating  15  is clarified more precisely in the following FIGS. 2,  4  and  5 . To that end, only briefly: 
     Liquid droplets deposit on protective grating  15  and are conducted to an inner wall  7  of line  2  or of tubular member  8 , and thereby move past inlet opening  20  of measuring member  19  or past measuring element  23 . 
     Further downstream of protective grating  15 , a flow direction  12 , which is nearly parallel to the center line of tubular member  8 , prevails in flow-through channel  11 . 
     FIG. 2 shows an axial cross-section in the longitudinal direction in FIG.  1 . The same reference numerals as in FIG. 1 are used for identical or equally-acting parts. Protective grating  15  can be seen having side walls  36  which run inclined by a specific deflection angle with respect to center line  27 . Side walls  36  are, for example, parallel to plug-in axis  21  and perpendicular to plug-in axis  21 , or stand perpendicular one upon the other and are arranged in any orientation about center line  27 . Side walls  36  form channel openings  44  which, at least transverse to flow direction  6 ,  12 , are triangular, or are round or oval, or are four-cornered as in this exemplary embodiment. The medium flows in through channel openings  44  and, viewed downstream, leaves protective grating  15  diverted in a different direction  45 , indicated by an arrow, after protective grating  15 . For example, it is also possible to provide no tubular member  8 , so that, for instance, protective grating  15  extends over the entire cross-section of line  2 . Measuring member  19  has a front surface  48  against and around which the medium flows first. A lower surface  55  is formed by the free radial end of measuring member  19 . 
     A channel  43 , formed by two side walls  36 , has, for example, a first section  49  in  0 which side wall  36  forms an angle of intersection α with flow direction  12 . In a second section  50 , side wall  36  of channel  43  forms an angle of intersection β with flow direction  12  which is larger than angle of intersection α. 
     FIG. 3 shows a channel  43  of a protective grating  15  according to the related art. The medium flows into channel opening  44  of channel  43  in main flow direction  6 . Distributed uniformly over the cross-section of channel opening  44  are twenty lines  53  which show paths of motion of one particle each in channel  43 . A part of the particles is reflected once at only one side wall  36  and thereupon leaves channel  43  again downstream in a direction  45 . Direction  45  runs at an angle δ to flow direction  12 . Angle δ is different from zero. A certain portion of lines  53  shows paths of motion in channel  43  with double reflection, one reflection each at each of side wall  36 , so that these particles leave a channel outlet again downstream approximately parallel to flow direction  12 , and thus are able to strike unhindered on measuring element  23  provided downstream. 
     FIGS. 4 a  and  b  show two examples of the design according to the present invention of protective grating  15  of device  1 . FIG. 4 a  shows a channel  43  of protective grating  15  which has, for example, a first section  49  and a second section  50  downstream. The side-wall sections bounding first section  49  form with flow direction  12  an angle of intersection α which here, for example, is 25 degrees. The side-wall sections bounding second section  50  form with flow direction  12  an angle of intersection β which, for example, is 35 degrees. The number of paths of motion of individual representing lines  53  which, upon emergence from channel  43 , run parallel to flow direction  6 ,  12  downstream of channel  43  has been reduced compared to the related art according to FIG.  3 . Improvement of the protection of measuring element  23  from striking particles is thereby ensured. 
     FIG. 4 b  shows an exemplary embodiment of channel  43  having an angle of intersection β which, in this case, is 45°. The angles of intersection can be positive and negative, i.e. all or only a part of them can be negative. 
     FIGS. 5 a  and  b  show further exemplary embodiments of channel  43 . FIG. 5 a  shows a channel  43  whose upper side wall  56  forms an equal angle of intersection with flow direction  12  in all sections. Lower side wall  57  opposite upper side wall  56  has, for example, two sections. First section  49  forms an angle of intersection a with flow direction  12 , and the second section forms an angle of intersection β with flow direction  12  deviating from angle of intersection α. The difference with respect to the channel formation according to FIG. 4 a  is that lines  53 , which are reflected in the region of upper side wall  56  in second section  50 , are reflected with an equal angle of intersection α. 
     FIG. 5 b  shows a channel  43  whose side wall  36  is continuously curved, so that a different angle of intersection α, β, γ is formed with flow direction  12  at each location of the side wall, the danger of a separation of the flow possibly arising thereby being reduced.