Abstract:
The invention relates to a device for determining at least one parameter of a medium flowing in a line, in particular the intake air mass of an internal combustion engine. The solid particles contained in the line act on a measuring element and influence a characteristic curve behavior of the measuring element, which is used to determine parameters of the flowing medium. In order to reduce the action of solid particles on the measuring element, the measuring element is disposed in a line or a tubular body downstream of a protective screen, and an element for influencing movement paths of the solid particles is disposed in the line, on an inner wall. By intentionally influencing the movement paths of the solid particles, their action on the measuring element is considerably reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 01/01192, filed Mar. 29, 2001. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is based on a device for determining at least one parameter of a medium flowing in a line, and particularly for measuring a parameter of a flow into an internal combustion engine. 
   2. Description of the Prior Art 
   DE 197 35 891 A1 has disclosed a measuring body, which can be inserted into a clean conduit of an intake line of an internal combustion engine and is used to determine the mass of intake air; the measuring body has a flow conduit and a measurement conduit, which is essentially inclined in relation to a longitudinal axis of a line and is comprised of an S-shaped deflection conduit adjoining said line. A measuring element is disposed in the measurement conduit. As has been disclosed, for example, by DE 43 38 891 A1 and U.S. Pat. No. 5,452,610, the measuring element can be designed as a micromechanical sensor part with a dielectric membrane. The measuring element can become contaminated by solid particles that penetrate through the air filter and by water permeation through the air filter into the intake line, e.g. as a result of roads that are wet with rain. Natural components of dissolved salts contained in this sprayed water then cause a drift in the characteristic curve due to the buildup of salt encrustation on the membrane of the sensor part. 
   The inclination of the measuring body does in fact produce a protected leeward region, but a part of these solid particles or fluid particles still get into the measurement conduit. 
   DE 197 35 664 A1 has already disclosed a device in which the measuring element is disposed inside a tubular body that the medium flows through, where an upstream end of the tubular body extends into a filter chamber and has inlet openings disposed there on a circumferential surface in order to reduce the action of dirt particles or water droplets on the measuring element. Particularly with very dirty air and a high water content in the intake air of the internal combustion engine, there is the danger that the air filter will become saturated with water, which then seeps through the filter mat and entrains dirt particles with it. On the downstream side of the air filter, the actually clean side, there is now the danger that the intake air will once again entrain dirt particles and water droplets from the filter surface, which will then be undesirably deposited on the measuring element and will lead to erroneous measurements or to a failure of the measuring element. The tubular body according to the prior art does reduce the danger of deposits by placing inlet openings on the circumferential surface, but a correspondingly long design of the tubular body produces an undesirable pressure drop, which results in a reduction in measuring sensitivity. In addition, the reduction of an action of fluid/solid particles on the measuring element can hardly be assured with a very high fluid influx of approx. 20 liters/hour. 
   DE 196 52 753 A1 has disclosed a device with a measuring element, which contains a flow rectifier and a screen in order to stabilize a measurement signal. However, no additional screen or element is used to protect the measuring element from fluids or solid particles. 
   The use of a deflecting screen in a line has also been proposed for separating fluid particles from a flowing air or gas. A deflecting screen of this kind, which is connected upstream of an inner tube or in the line, influences the air/water mixture flowing toward the measuring element in such a way that the fluid particles are conveyed against a tube wall or a line wall while the air remains in a center of the inner tube. 
   A different behavior is produced when a mixture of air and dust passes through a deflecting screen in the line. The dust does not form a wall film like a fluid, but is reflected against the line wall, where the principle of the angle of incidence being equal to the angle of reflection applies. Since the measuring element is disposed a certain distance from the deflecting screen, a certain portion of the reflected solid particles collide with the measuring element disposed downstream of the deflecting screen. 
   SUMMARY OF THE INVENTION 
   The device according to the invention  4 , has the advantage over the prior art that the protection of a measuring element from solid particles is improved in a simple manner by exerting influence on the movement paths of the solid particles. 
   It is advantageous to influence the movement paths of the solid particles by means of a protrusion that is broad in the axial direction because this conveys the solid particles past the measuring element by means of intentionally adjusted reflection. 
   It is also advantageous to influence the movement paths of the solid particles by means of a step so that the solid particles are reflected backward. 
   It is particularly advantageous to dispose an element for influencing the movement paths of the solid particles in a tubular body because this makes use of a protective action of the tubular body and the element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Several exemplary embodiments of the invention are shown in a simplified fashion in the drawings and are explained in detail in the subsequent description, in conjunction with the drawings, in which: 
       FIG. 1  shows a first exemplary embodiment of a device according to the invention, and 
     FIGS  2  and  3  show additional exemplary embodiment of the device according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a device  1  for determining at least one parameter, in particular an air volume flow, of a medium flowing in a line  3 , in particular of the intake air of an internal combustion engine. Parameters of a flowing medium include, for example, the air volume flow for determining an air mass, a temperature, a pressure, a concentration of a component of the medium, or a flow speed, which are determined by means of suitable sensors. It is possible to use the device  1  for determining other parameters. This can take place by virtue of the fact that two or more sensors are used; one sensor can also determine two or more parameters. The line  3  has a wall  6  having an inner surface  9 . The medium flows in the line  3  in the main flow direction indicated by the arrow  12 . For example, a tubular body  15  is provided in the line and extends spaced radially apart from the line  3 ; the medium circulates around this tubular body  15 . The tubular body  15  has a through flow conduit  22  and a protective screen  25  disposed in the vicinity of its upstream end. Plastic, metal, ceramic, or glass can be used as materials for the protective screen  25 . The plate-shaped protective screen  25  made of plastic can be manufactured, for example, by injection molding or by producing screen openings  29  using a material-removing process. 
   A flow direction  32  prevails in the through flow conduit  22  downstream from the protective screen  25 , somewhat removed from it. The flow direction  32  runs approximately parallel to the main flow direction  12 . The tubular body  15  has a center line  35 , which for example is also the center line of the line  3 . 
   For example, a measuring body  39  extends in the tubular body  15 . The measuring body  39  is partially inserted through a first insertion opening  40  in the wall  6  and a second insertion opening  42  in the wall  16  of the tubular body  15  and protrudes into the through flow conduit  22 , for example with a free end. 
   Such a measuring body  39  is known to the specialist from DE 197 35 891 A1, which is incorporated by reference into this disclosure. The air volume aspirated by the internal combustion engine can be changed at will by means of a throttle valve, not shown, which is disposed in the intake tube of the internal combustion engine, downstream of the tubular body  15 . 
   In order to determine the intake air mass of the engine, the measuring body  39  is provided, which is essentially oblong and block-shaped and extends along a longitudinal axis  41 . The longitudinal axis  41  extends essentially perpendicular to the center line  35  and therefore also perpendicular to the main flow direction  12 . 
   A plug end of the measuring body  39 , which contains electrical connections, e.g. in the form of plug connector tabs, remains outside of the line  3 , for example. At least one measuring element  45  is disposed in a known manner in the measuring body  39 , in this example a measuring element  45  that contacts the air flowing through the through flow conduit  22 . The measuring element  45  can, for example, be a temperature sensor of the kind known from DE 42 28 484 C2, a pressure sensor of the kind used in DE 31 35 794 A1, or an air volume sensor that determines the corresponding parameters. 
   As an example for the different sensors, an air volume sensor is selected here by way of example, which is used to determine the air volume aspirated by the internal combustion engine. 
   The measuring element  45  is disposed, for example, in the measuring body  39 , which has an inlet opening  49  into which the medium flows. 
   The measuring element  45  can be embodied in a known manner, for example in the form of at least one temperature-dependent resistor. In particular, it is also possible, as demonstrated in DE 43 38 891 A1 and U.S. Pat. No. 5,452,610, to design the measuring element  45  as a micromechanical component that has a dielectric membrane upon which resistor elements are embodied. It is also conceivable to insert the measuring element  45  into the line  3  or into the tubular body  15  without the measuring body  39 . 
   The protective screen  25  has slats  52 , which are inclined at a particular deflection angle in relation to the center line  35 . The slats  52  constitute screen openings  29  and conduits  63  downstream of the protective screen  25 . Fluid droplets adhere to the protective screen  25  and are conveyed by the inclined conduits against the inner wall surface  9  of the line  3  or a wall  16  of the tubular body  15  and then travel past the inlet opening  49  of the measuring body  39  or past the measuring element  45 . The gas/solid particle mixture flows through the screen openings  29  deflected in a different direction  56  downstream of the protective screen  25 , the new direction  56  being indicated by an arrow. 
   The movement path of a solid particle is indicated in  FIG. 1  by lines  60 . The movement paths  60  and the direction  56  of the solid particles extend from each conduit  63  of the protective screen  25  parallel to one another and collide with an inner wall of the tubular body  15  or the line  3 . According to the law of reflection, the solid particles are reflected there and subsequently dispersed in a line  3  according to the prior art over an entire cross section of the through flow conduit  22  or the line  3 . As a result, the solid particles also travel into the inlet opening  49  of the measuring body  39  and can then collide with the measuring element  45 , which can be damaged as a result. 
   In order to prevent solid particles from traveling into the inlet opening  49 , an element  70  is provided upstream of the measuring body  39 , in the vicinity of the gas/solid particle mixture flowing in the direction  56 , which influences the movement paths  60  of the solid particles. In this exemplary embodiment, the element  70  is disposed, for example, directly downstream of the protective screen  25  and is a protrusion  73  of the wall  16 , which is broad in the axial direction, i.e. in direction  32 . For example, a contour  76  of the protrusion  73  is a continuously curved surface that is convexly curved in relation to the center line  35 . The protrusion  73  has an apex point  79 . Solid particles that collide with the protrusion  73  before the apex point  79 , in terms of the flow direction, are reflected by a smaller reflection angle and therefore flow past the inlet opening  49 . Solid particles that collide with the protrusion  73  downstream of the apex point  79 , are reflected by a greater reflection angle, for example past the lower end of the measuring body  39  and also do not travel into the inlet opening  49  of the measuring body  39 . 
     FIG. 2  shows another exemplary embodiment of the device  1  embodied according to the invention. Parts that are the same or function in the same manner are provided with the same reference numerals in the following Figs. as they were in the preceding Figs. 
   In this exemplary embodiment, the element  70 , which influences the movement path  60  of the solid particles, has a step  82  directed counter to the flow of the gas/solid particle mixture, with an edge  83  against an inner wall  19  of the tubular body  15 . The edge  83  of the step  82  can form any angle with the longitudinal axis  41 . The solid particles, which would otherwise be reflected toward the inlet opening  49  by being reflected against a flat inner wall  9 ,  19 , are reflected backward at the edge  83 . As a result, the measuring element  45  is protected from solid particles. 
     FIG. 3  shows another exemplary embodiment of the device  1  embodied according to the invention. By contrast with  FIG. 1 , no tubular body  15  is used in this exemplary embodiment. For example, but not necessarily, the protective screen  25  extends over the entire cross section of the line  3 . A protrusion  73  provided on the inner wall  19  has been selected as the element  70 . However, a step  82  can also be disposed on the inner wall  9  of the line  3 . 
   The foregoing relates to preferred exemplary embodiments of the invention, if 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.