Abstract:
A device for measuring at least one parameter of a medium flowing in a line, in particular the intake air mass of an internal combustion engine in which fluid particles and solid particles in the line influence a characteristic curve behavior of a measuring element which is used to determine a parameter of the flowing medium. A protective screen according to the invention deflects fluids and solid particles away from the measuring element in such a way that they are conveyed against an inner wall of the line. In addition, the device stabilizes the flowing medium by generating longitudinal eddies in a flow direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 00/03046 filed on Sep. 5, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention is based on a device for measuring at least one parameter of an air flow mass flowing in an air intake line of an internal combustion engine. 
     2. Description of Prior Art 
     DE 44 07 209 C2 has disclosed a measuring body that can be inserted into a clean conduit of an intake line of an internal combustion engine to measure the mass of intake air, a so-called air mass sensor, which has a flow conduit that is essentially made up of a measurement conduit, which tapers in the main flow direction, and an adjoining S-shaped deflection conduit. A measuring element is disposed in the tapering measurement conduit. The measuring element can be embodied as a micromechanical sensor part with a dielectric membrane, as has been disclosed, for example, by DE 43 38 891 A1 and U.S. Pat. No. 5,452,610. The penetration of water into the intake line, for example due to travel on a road wet with rain, can result in contamination of the measuring element. Natural amounts of dissolved salts contained in this splashed water then cause a measurement characteristic curve deviation due to the buildup of salt encrustation on the membrane of the sensor part. 
     DE 197 35 664 A1 discloses a device in which the measuring element is disposed inside a tubular body that the medium flows through, in which an upstream end of the tubular body extends into a filter chamber and has inlet openings there on a circumference surface in order to reduce the action of dirt particles or water droplets on the measuring element. Particularly with severely contaminated 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 laden with water which then penetrates the filter mat and thereby carries dirt particles along 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 carry along dirt particles and water droplets from the filter surface which will then be undesirably deposited on the measuring element and lead to incorrect measurements or to a failure of the measuring element. Through the placement of inlet openings on the circumference surface, the tubular body according to the prior art does in fact reduce the danger of deposits on the measuring element, but this embodiment produces an undesirable pressure drop which leads to a reduction of the measurement sensitivity. 
     U.S. Pat. No. 5,507,858 has also disclosed using a screen-like perforated plate in a housing which is connected to a line in order to separate out fluid particles from the air or a gas medium flowing in the line. This housing, though, has two outlets, one for the gas or the air and a second for the fluid. A perforated plate or wire mesh that is circulated around in an approximately longitudinal direction, however, also has the property that a more or less favorable through flow perpendicular to the openings of the perforated plate or wire mesh occurs depending on the angle at which it is set. The through flow capacity of the openings is also a function of the degree of turbulence, the speed of the flowing medium, and the surface roughness of the screen used. Thus the air mass sensor positioned downstream of the wire mesh or the perforated plate produces considerable divergences from a reference without a screen in particular speed ranges, i.e. the measurement of the mass of the flowing medium is supplied under certain circumstances with large tolerances from component to component. 
     DE 196 47 081 A1 describes screens with different screen opening cross sections. These screens, however, are used to achieve a uniform speed profile and not as a protective screen for a measuring element disposed downstream. 
     SUMMARY OF THE INVENTION 
     The device according to the invention has the advantage over the prior art that a measuring element can be simply protected from fluid and solid particles and consequently, a measurement characteristic curve deviation is prevented by virtue of the fact that a screen surface—which is disposed in the line upstream of the measuring element, upstream of a measuring body, or upstream of a tubular body containing the measuring element or the measuring body and which constitutes at least one protective screen—influences the medium flowing toward the measuring element, a gas/fluid mixture, in such a way that the fluid particles and solid particles are conveyed toward a tubular wall or a line wall. As a result, the gas also remains in a center of the line or tubular body and deviations in the measurement signal of the measuring element are reduced through conditioning of the flowing medium by virtue of the fact that longitudinal eddies are produced in a flow direction. 
     An advantageous embodiment of the protective screen is a configuration of one or more cones, wherein the cone tip(s) is/are aligned counter to a main flow direction and the cone(s) is/are disposed symmetrically around a line parallel to the center line of the line itself because as a result, the flowing medium once again flows in the main flow direction after passing through the protective screen. In this connection, it is advantageous that this line passes through a center of the measuring element or an inlet opening of the measuring body. 
     Another advantageous embodiment of the protective screen is a combination of side screens which enclose an acute angle with one another. 
     In this connection, it is advantageous if at least one longitudinal axis of a damming region extends parallel to a longitudinal axis of the measuring element and both of these axes intersect a center line of the line because as a result, the flowing medium once again flows in the main flow direction after passing through the protective screen. 
     In the embodiment of the protective screen with its screen surfaces, it is advantageous to have a center line of the screen openings to extend inclined in relation to the main flow direction because this causes a deflection of the fluid particles and solid particles. 
     At high flow speeds and a high fluid content, it is advantageous to enlarge the screen surface area by virtue of the fact that at least two protective screens are inserted into the line, where the one protective screen partially protrudes into the downstream end of the other protective screen. 
     At high flow speeds, it is advantageous for there to be a smaller cone angle or smaller protective screen internal angle; at low flow speeds, it is advantageous for there to be a larger cone angle or protective screen internal angle. 
     When there are pulsations in the flow, it is advantageous to also dispose a protective screen with an attack edge or attack tip counter to the return flow direction downstream of the measuring element in the line. 
     The insertion of a tubular body into the line in addition to the protective screen offers further advantages in the reduction of the action of solid particles and fluid on the measuring element. 
     Notches and triangular wedges in the attack edge of the protective screen are an advantageous modification to stabilize or condition the flowing medium so that a reproducible measurement of the air mass is possible. 
     Deviations that occur during the measurement of air mass in different flow testing stands are minimized. Jumps in the air mass characteristic curve are sharply reduced. 
     In this connection, it is advantageous to dispose the wedges or notches uniformly along the attack edge and upstream, at the level of the measuring element or the inlet opening of the measuring body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are described herein below and are depicted in a simplified fashion in the drawings, in which: 
     FIG. 1 shows an exemplary embodiment of the device according to the invention, 
     FIG. 2 shows a protective screen in an enlarged detail from FIG. 1, 
     FIGS. 3 a, b  show different possible placements of the protective screen in the line, 
     FIG. 4 shows a device viewed in the main flow direction, 
     FIGS. 5 a-e  show exemplary embodiments for different operating conditions, 
     FIGS. 6 a, b  show flow lines upstream and downstream of a protective screen, 
     FIG. 7 shows a disposition of a tubular body in the line, 
     FIGS. 8 a, b  show a protective screen and a device with notches, and 
     FIGS. 9 a, b  show a protective screen and a device with wedges. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a device  1  for measuring at least one parameter, in particular of an air mass flow, of a medium flowing in a line  3 , in particular the intake air mass flow of an internal combustion engine. Parameters of a flowing medium include, for example, the air mass flow for determining an air mass, a temperature, a pressure, or a flow speed, which are determined by means of suitable sensors. It may be necessary to use the device  1  for measuring other parameters. The line  3  has an external wall surface  6  and an internal wall surface  8 . The medium flows in the line  3  in the main flow direction  12 , which is indicated by arrows. The line  3  has a center line  16 . For example, a measuring body  20  extends in the line  3 . The measuring body  20  can, for example, be a temperature sensor of the kind disclosed by DE 42 28 484 C2, a pressure sensor of the kind used in DE 31 35 794 A1, or an air mass sensor which determines the corresponding parameter. An air mass sensor has been selected here as an example for the different sensors, which is disposed for example in the measuring body  20 . 
     For example, the measuring body  20  has an inlet opening  22  into which the medium flows and a bypass conduit connected to it. A measuring element  34  is disposed in the bypass conduit  23 . A measuring body  20  of this kind is known to the specialist from DE 197 35 891 A1, which is incorporated into this disclosure by reference. 
     The air mass taken in by an internal combustion engine can be changed arbitrarily by means of a throttle valve, not shown, that is disposed in the intake tube of the engine, in a line end  50  downstream of the line  3 . 
     The measuring body  20 , which is essentially embodied as oblong and block shaped and extends along the longitudinal axis  26 , is provided for determining the intake air mass of the internal combustion engine. The longitudinal axis  26  extends essentially perpendicular to the center line  16  and thereby also to the main flow direction  12 . The measuring body  20  is, for example, partially inserted through an insertion opening  29  in the wall  6  and protrudes with a free end  31  into the line  3 . A connector end of the measuring body  20  that contains the electrical connections, for example in the form of connector tabs, thereby remains outside the line  3 . In a known manner, the measuring body  20  contains a measuring element  34  which remains in contact with the air flowing through the line  3  and determines the air mass taken in by the internal combustion engine. In a known manner, the measuring element  34  can be embodied in the form of temperature-dependent resistors. In particular, it is possible to embody the measuring element, as has been disclosed for example by DE 43 38 891 A1 and U.S. Pat. No. 5,452,610, as a micromechanical component with a dielectric membrane, on which resistance elements are embodied. 
     In order to prevent the measuring element  34  from being undesirably acted on by solid particles or fluid, a protective screen  38  is disposed at least partially upstream of the measuring element  34  inside the line  3  and serves as a first means  37  for manipulating the flowing medium. 
     The protective screen  38  has, for example, two screen surfaces  46 . In this instance, the screen surfaces  46  are constituted, for example, by means of two side screens  44  which, when combined, comprise the protective screen  38 . Each side screen  44  has for example a flat, arc-shaped, or elliptically oval form. The geometry of the protective screen  38  can also be conically embodied so that the protective screen  38  is constituted by one screen surface  46 . A cone tip  41  (FIG. 6 b ) or an attack edge  40  in a contact the line of the side screen  44  of the protective screen  38  is aligned counter to the main flow direction  12 . These parts  40 ,  41  constitute a damming region  39  of the protective screen because the flowing medium cannot flow through the attack edge  40  or the attack tip  41  but instead is dammed up there. The attack edge  40  extends, for example, through the center line  16 . For example, the attack edge  40  is also perpendicular to the center line  16 ; however, it can also be oriented otherwise. 
     The attack edge  40  constitutes a damming region longitudinal axis  68 , which protrudes perpendicularly up from the plane of the drawing. Preferably, at least one attack tip  41  is also aligned with the center line  16 . The protective screen  38  is preferably symmetrical to a line extending parallel to the center line  16 . This line extends, for example, through a center point of the measuring element  34  or the inlet opening  22 . 
     The protective screen  38  here has a V-shaped cross section, for example, and is aligned with its side screens  44 , for example, so that the side screens  44  protrude perpendicularly up from the plane of the drawing. The side screens  44  are combined so that they enclose a protective screen internal angle β between themselves, which is an acute angle. The for example flat side screen  44  encloses an attack angle χ with the main flow direction  12 . A flow rectifier can also be installed in the line  3  downstream of the measuring body  20 . 
     On the upstream end, the protective screen  38  can be integrated into a ring, for example, which contains a second flow rectifier for the medium flowing in the line  3 . 
     FIG. 2 shows a protective screen  38  in an enlarged detail from FIG.  1 . In FIG.  2  and the FIGS. that follow, parts which are the same or function in the same manner are provided with the same reference numerals as in FIG.  1 . The protective screen  38  has screen openings  53 , which have an opening center line  54 . The screen openings  53  do not necessarily have to have a straight opening center line  54 . The opening center line  54  encloses an angle δ with the center line  16  of the line  3 . 
     The opening center lines  54  of the screen openings  53  do not have to be parallel to one another. Consequently, for example, the screen openings  53  that are disposed in the vicinity of the inner wall  8  can have a greater angle δ than the screen openings  53  that are disposed in the vicinity of the center line  16 . As a result, the screen openings  53  can be suitably adapted to a speed profile of the flowing medium. 
     The screen openings have a particular screen opening distance  60  from one another. The screen opening distance  60  does not necessarily have to be equal for all of the screen openings  53 . 
     DE 196 47 081 A1, which is incorporated into this disclosure, describes screens with different screen opening cross sections. The screen openings can be adapted to the flowing medium in order to obtain a uniform and/or focused flow. 
     The inclination of the side screen  44  gives the side screen  44  a downstream end  63 . Between the downstream end  63  and the inner wall  8  of the line  3 , for example, an open outlet opening  66  is provided which is embodied either by virtue of the fact that the downstream end  63  terminates spaced apart from the inner wall  8  or by virtue of the fact that the downstream end  63  does in fact extend to the inner wall  8 , but the outlet opening  66  is recessed into the screen  38 ,  44  or the inner wall  8 . 
     The screen  38 ,  44  can be embodied both as a small gage wire mesh or as a thin plate that has screen openings  53  disposed in a screen pattern. Plastic, metal, ceramic, or glass can be used as a material for both the wire mesh and the plate-shaped protective screen. The plate-shaped protective screen made of plastic can be produced, for example, through injection molding or through producing the screen openings by means of a material-removing process. The plate-shaped protective screen made of metal can be produced out of sheet metal, for example, by means of stamping, erosion, drilling, etc.; the edge elements (slats) encompassing the screen openings can also be somewhat inclined in relation to the screen surface  46  by means of bending. A protective screen  38  which has a high degree of surface roughness increases the wetting with fluid and therefore increases adhesion. A fluid film is produced which permits fluid particles which strike against it to slide off. The thermal capacity and electrostatic action of the material of the protective screen  38  also influences the action of fluid particles or solid particles. An angular form of the slats that constitute the protective screen  38  yields a greater contact surface area than round slats. 
     If the intake air coming into the line  3  contains dirt particles and fluid droplets, then part of these settle on the screen surface  46  and move predominantly toward the downstream end  63  of the protective screen  38 ; this occurs both on a front surface  70  of the screen surface  46  oriented counter to the flow direction  12  and on a rear surface  71  oriented in the flow direction  12 . From the downstream end  63 , this deposited fluid is carried along by the intake air, for example from the front surface  70  into the outlet opening  66  and predominantly adheres to the inner wall  8 . The intake air carries the fluid, which also contains extremely fine dirt particles and is in the form of extremely fine fluid droplets or a thin fluid film, further along the inner wall in the flow direction  12 , past the measuring body  20  and measuring element  34  to the tube end  50  downstream of the measuring body  20 . 
     Depending on the fluid quantity contained in the air, the protective screen  38  can be embodied in several structural variants. The surface roughness and surface form, the protective screen interior angle β, the mesh width, and the material can be considered as potentially changeable in this connection. The surface roughness and consequently in general, the material of the protective screen as well as the form of the screen wire or the slats, influences the adhesion of fluid droplets to the protective screen  38 ,  44  by means of the contact angle. The attack angle χ of the protective screen  38 ,  44  permits fluid particles to be deflected depending on the flow speed; the attack angle χ should become flatter as the particle speed increases. Finally, the mesh width determines the size of the droplets to be deflected. 
     FIGS. 3 a  and  3   b  show different possible placements of the protective screen  38  in the line  3 . 
     FIGS. 3 a  and  3   b  show a top view of the device, looking into the line  3  in the direction of the longitudinal axis  26 . The protective screen  38  according to FIG. 1 has been rotated here by 90° around the center line  16 . 
     FIG. 3 a  shows a protective screen  38 , which is disposed, for example, entirely upstream of the measuring body  20  and the measuring element  34  in the main flow direction  12  and does not extend out to the inner wall  8 . The outlet opening  66  is then constituted by a free region between the downstream end  63  of the side screen  44  and the inner wall  8 . 
     FIG. 3 b  shows another possible placement. The protective screen  38  is disposed only partially upstream of the measuring body  20  and the measuring element  34 , and in this instance, for example, extends out to the inner wall  8 . The outlet opening  66  is then embodied, for example, in the screen  38 ,  44 , but can also be provided in the inner wall  8 . 
     The embodiments in both FIG. 3 a  and FIG. 3 b  cause fluid particles and solid particles to be conveyed past the measuring body  20  or measuring element  34 . 
     FIG. 4 shows a device  1 , for example according to FIG. 3, viewed in the main flow direction  12 . 
     The measuring element  34  is disposed, for example, downstream of the inlet opening  22  in the bypass conduit  23  of the measuring body  20 . The attack edge  40  of the protective screen  38  in this instance extends, for example, parallel to the longitudinal axis  26  of the measuring body  20 . Thus the attack edge  40  constitutes the damming region  39  and has a damming region longitudinal axis  68  extending parallel to the longitudinal axis  26 . The protective screen  38  in this example extends inside the line  3  only part way in the cross section of the line  3 . It is sufficient, for example, if the inlet opening  22  is protected from the medium flowing in the main flow direction  12  by the protective screen  38 . 
     FIGS. 5 a  to  5   e  show exemplary embodiments for different operating conditions of the protective screen  38 . A configuration of multiple protective screens  38 , in this case a configuration of two of them, is used when there is a high fluid content in the flowing medium (FIG. 5 a ). Fluid particles or solid particles which are not deflected by the screen that is struck first by the flow in the main flow direction  12  are deflected by the second protective screen  38 . The second protective screen  38  is disposed, for example, partially inside the first protective screen. However, this is not required. If the two protective screens  38  are slid together so tightly that a drainage occurs between the respective side screens  44 , then this increases the adhesion of the fluid particle grains  44  because of the greater contact surface area. 
     The protective screen internal angle β and therefore the attack angle χ do not necessarily have to be equal. Consequently, the attack angle χ of the downstream protective screen can be adapted to the speed which has been changed by the preceding protective screen  38 . 
     This multiple configuration is also possible with any other form of the protective screen  38 , for example a protective screen  38  with four side screens that are arranged in the form of a W or through the use of conical protective screens  38 . Other combinations of protective screens  38  with different geometries are also conceivable. 
     When there are pulsations in the medium flow, this produces a return flow  74  which can bring fluid particles and dirt particles back from the zone downstream of the inlet opening  22  toward the zone upstream of the inlet opening  22 , counter to the main flow direction  12 . In the exemplary embodiment according to FIG. 5 b , therefore, a protective screen  38  embodied comparably to the ones according to FIGS. 1 and 3 is provided, which is disposed downstream of the measuring element  34  and has an attack edge  40  oriented counter to the return flow direction  74 , which minimizes such effects. The protective screen internal angle β of the protective screen  38  for the return flow does not have to be identical to that of the other protective screen  38  for the main flow direction  12 . This is useful since the speed profile, speed, and fluid content differ between the return flow and the main flow. 
     An optimal form of the protective screen  38  also depends on the flow speeds of the medium in the line  3 . In flow engineering, usually a small attack angle χ is used at high flow speeds. Consequently, a for example small protective screen angle β is used here as well for the protective screen  38  (FIG. 5 c ) and at low flow speeds, a greater protective screen internal angle β is used (FIG. 5 d ). A greater span of the protective screen  38  in the main flow direction  12  with a small protective screen internal angle β is produced because the intent is to achieve a particular coverage of the line  3  in the cross section, i.e. a protective action. 
     At high flow speeds and a high fluid content, the screen surface  46  can also be enlarged by virtue of the fact that in principle, at least two protective screens are inserted into the line  3  next to each other in a W shape, which have a common attack edge  40  approximately at the level of the center line  16  (FIG. 5 e ) and are comprised of four side screens  44 ,  44 ′. The for example two screen surfaces  44 ′ closer to the center line  16  are for example curved in this instance. 
     The screen surfaces  44  closer to the wall  6  broaden the speed profile of the flowing medium and slow down the flow speed. Thus the speed of the flowing medium can be greater without the flow speed downstream of the protective screen  38  for the measuring element  34  being too great. The screen surfaces  44 ,  44 ′ can also be conical, i.e. the protective screen  38  is comprised for example of two or more cones, whose cone tips are not oriented counter to the main flow direction  12 , i.e. they point downstream. The protective screen internal angle β of the side screens  44 ′ in this example can differ from the protective screen internal angles β of the side screens  44 ,  44 ′. Thus the speed profile can be influenced in a concerted manner in the center of the line  3  and at the edge. 
     FIG. 6 a  shows flow lines  78  that constitute a speed profile, upstream and downstream of a protective screen  38  in terms of the main flow direction  12 , which protective screen corresponds, for example, to the one from FIG. 3 a  or  3   b.    
     The flowing medium strikes the attack edge  40  and the side screen  44  of the protective screen  38 . The screen openings  53  deflect the flow direction of the medium during a certain flow section and focus it in a manner that corresponds to the action of an optical lens system. Downstream of the deflected flow section, the flow lines  78  once again run approximately parallel to the center line  16 . 
     FIG. 6 b  shows the flow lines  78  for another exemplary embodiment of a protective screen  38 . The protective screen  38  is a cone, for example, and has a cone outer surface  81  and an attack tip  41 . The cone outer surface  81  is for example flat, but can also be curved. When the protective screen  38  is acted on by a flowing medium, it acts as a collecting line, similar to an optical lens, i.e. the flow lines of the incoming flow upstream of the screen are focused downstream of it, and consequently the flow speed there is increased. 
     FIG. 7 shows the disposition of a tubular body  82 , which the medium circulates around, in the line  3 , which body extends, for example, spaced radially apart from the line  3  and has a smaller cross section than the line. The measuring body  20  extends in the tubular body  82  and the measuring element  34  is disposed inside the tubular body  82 . The tubular body  82  is affixed in the line  3 , for example by means of struts  83 . The protective screen  38  is disposed upstream of the tubular body  82 . It is also conceivable to dispose the protective screen  38  in the tubular body  82 . 
     As described above for the line  3 , in this instance as well, the intake air carries the fluid, which also contains extremely fine dirt particles and is in the form of extremely fine fluid droplets or a thin fluid film, further along the inner wall in the flow direction  12 , past the measuring body  20  and measuring element  34  to the tube end  50  downstream of the measuring body  20 , from which the clinging fluid detaches and is carried by the surrounding flowing intake air to the engine. 
     FIGS. 8 a, b  show the protective screen  38  made up of at least two side screens  44 , with a notch  85  in the attack edge  40 . 
     In order to condition and stabilize the through flow of the protective screen  38 , the notches  85  generate, as a second means  84  for stabilizing the flowing medium, a so-called longitudinal eddy flow  88  (FIG. 8 a ), whose course is schematically depicted with lines. The longitudinal eddy flow  88  is produced as in a delta wing of an airplane, by circulation around the front edges. Several notches  85  can be provided along the entire attack edge  40 . Ideally, the notches  85  are disposed, for example, only in the central region of the attack edge  40 , e.g. in five to ten different positions. For example, the distances between the individual notches  85  are preferably uniform (FIG. 8 b ). The notches  85  extend to a depth t in the direction of the measuring body  20  and have an opening angle α (FIG. 8 b ). 
     Dimensions of the notches  85  must be adapted to respectively occurring flow speeds. In a speed range from 0 to 50 m/s, for example, notches of approximately t=2 mm deep and an opening angle of α=45° . . . 90° must be provided. 
     For generating longitudinal eddies  88 , it is likewise conceivable to attach small pyramid-shaped or conical wedges  92  to the attack edge  40 , as an element  91  with a stabilization attack edge  93 , whose point is oriented counter to the main flow direction. 
     FIG. 9 a  shows a protective screen  38  with a wedge  92 . Dimensions and disposition along the attack edge  40  similar to the notches  85  should also be used with the pyramid-shaped or conical wedges  92  (FIG. 9 b ). A side surface of the wedge  92 , which the medium flows against, can also be curved, for example. Lateral to the main flow direction  12 , the wedge  92  has a width b. Preferably, widths of b=0.5 . . . 1 mm are provided. In order to generate particularly powerful longitudinal eddies, even greater widths b must be used. 
     The foregoing relates to preferred exemplary embodiments of the invention, it 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.