Sensor arrangement for determining at least one parameter of a fluid medium flowing through a channel

Abstract

Sensor arrangement (10) for determining at least one parameter of a fluid medium flowing through a channel (26), in particular an intake air mass flow of an internal combustion engine, wherein the sensor arrangement (10) comprises a sensor housing (34), in particular a plug-in sensor (12) inserted or insertable into a flow tube, in which the channel (26) is formed, and at least one sensor chip arranged in the channel (26) for determining the parameter of the fluid medium, wherein the sensor housing (34) has an inlet (16) into the channel (26) which points against a main flow direction (18) of the fluid medium, and at least one outlet (30) from the channel (26) in a surface (28) of the sensor housing (34), wherein the surface (28) of the sensor housing (34) has several recesses (60) upstream of the outlet (30) in the main flow direction (18), characterized in thatthat the surface (28) of the sensor housing (34), viewed in the main flow direction (18), has a downstream step (40) adjacent to the outlet (30) with a shear edge (44) and an upstream step (42) adjacent to the outlet (30) with a shear edge (46), wherein the downstream step (40) and the upstream step (42) form a chimney-like projection (48) from the surface (28) and the downstream step (40) and the upstream step (42) delimit the outlet (30) on all sides.

Description

State of the art

[0001] Numerous methods and devices for determining at least one flow property of fluid media, i.e., liquids and / or gases, are known from the prior art. The flow properties as a possible parameter can be any physical and / or chemical measurable properties that qualify or quantify the flow of the fluid medium. In particular, this can be a flow velocity and / or a mass flow and / or a volume flow.

[0002] The invention is described below in particular with reference to so-called hot-film air mass meters, such as those known, for example, from Konrad Reif (ed.): Sensors in Motor Vehicles, 1st edition 2010, pages 146-148. Such hot-film air mass meters are generally based on a sensor chip, in particular a silicon sensor chip, for example with a sensor membrane as the measuring surface or sensor area over which the flowing fluid medium can flow. The sensor chip generally comprises at least one heating element and at least two temperature sensors, which are arranged, for example, on the measuring surface of the sensor chip, with one temperature sensor being mounted upstream of the heating element and the other temperature sensor downstream of the heating element.From an asymmetry of the temperature profile recorded by the temperature sensors, which is influenced by the flow of the fluid medium, a mass flow and / or volume flow of the fluid medium can be inferred.

[0003] Hot-film air mass meters are typically designed as plug-in sensors that can be permanently or replaceably inserted into a flow tube. For example, this flow tube can be the intake tract of an internal combustion engine.

[0004] A partial flow of the medium flows through at least one main channel provided in the hot-film air mass meter. A bypass channel is formed between the inlet and the outlet of the main channel. In particular, the bypass channel is designed such that it has a curved section for deflecting the partial flow of the medium entering through the inlet of the main channel. The curved section further transitions into a section in which the sensor chip is arranged. The latter section represents the actual measuring channel in which the sensor chip is arranged.

[0005] Such hot-film air mass meters must meet a variety of requirements in practice. In addition to the goal of reducing the overall pressure drop across the hot-film air mass meter through suitable fluidic design, one of the main challenges is to further improve the signal quality and the robustness of the devices against contamination by oil and water droplets, as well as soot, dust, and other solid particles. This signal quality refers, for example, to the mass flow of the medium through the measuring channel leading to the sensor chip, as well as, where appropriate, to reducing signal drift and improving the signal-to-noise ratio.Signal drift refers to the deviation, for example, of the mass flow of the medium, in the sense of a change in the characteristic curve relationship between the actual mass flow and the output signal determined during calibration during production. When determining the signal-to-noise ratio, the sensor signals output in rapid temporal succession are considered, whereas characteristic curve or signal drift refers to a change in the mean value.

[0006] In conventional hot-film air mass meters of the type described, a sensor carrier with a sensor chip attached or inserted thereon usually projects into the measuring channel. For example, the sensor chip can be glued into the sensor carrier or bonded to it. The sensor carrier can, for example, form a unit with a metal base plate, to which electronics, a control and evaluation circuit (for example with a circuit carrier, in particular a printed circuit board) can also be glued. For example, the sensor carrier can be designed as an injection-molded plastic part of an electronic module. The sensor chip and the control and evaluation circuit can be connected to one another, for example by bonding. The electronic module created in this way can, for example, be glued into a sensor housing, and the entire plug-in sensor can be closed with covers.

[0007] DE 198 15 656 A1 discloses a sensor arrangement for determining at least one parameter of a fluid medium flowing through a channel, in particular an intake air mass of an internal combustion engine. The sensor arrangement has at least one sensor chip arranged in the channel for determining the parameter of the fluid medium. The sensor chip is accommodated in a sensor carrier projecting into the channel. The channel leads to an outlet opening opening into a flow tube on an outer surface of the sensor arrangement. On the outer surface of the sensor arrangement having the outlet opening, at least one elevation is provided in the vicinity of the outlet opening.

[0008] DE 197 38 337 A1 discloses a hot-film air mass meter with a step downstream of the outlet.

[0009] In such hot-film air mass meters, a boundary layer forms continuously on the outer surface up to the bypass outlet. The wide velocity range that the hot-film air mass meter must cover means that at certain velocities, the bypass outlet lies in a laminar-turbulent boundary layer transition. This transition region is characterized by poor reproducibility and nonlinear behavior. This leads to poorer tunability and complex behavior in pulsating flow, which encompasses the transition region.

[0010] For this reason, hot-film air mass meters were developed that feature a step with a separation edge, forming a chimney-like projection, upstream and downstream of the bypass outlet. The step in the wall contour forces the regeneration of a turbulent boundary layer, thus minimizing interactions between the boundary layer at the bypass outlet and any transition region present upstream, thus enabling more precise alignment to the target characteristic curve.

[0011] Despite the numerous advantages of the current state-of-the-art methods for matching the target characteristic curve, they still have potential for improvement in other functional aspects. For example, the height of the chimney-like projection required for boundary layer regeneration in the latter state-of-the-art increases with increasing air mass flow. This contradicts the demand for the shortest possible sensor housing.

[0012] DE 10 2006 045 657 A1 discloses a plug-in sensor for determining a parameter of a fluid medium flowing in a main flow direction, comprising a plug-in part that can be inserted into the flowing fluid medium. At least one flow channel with at least one inlet opening and at least one outlet opening is provided in the plug-in part, and at least one sensor for determining the parameter is accommodated in the at least one flow channel. The plug-in part has a release element in the form of a step on at least one side. Disclosure of the invention

[0013] Therefore, a sensor arrangement for determining at least one parameter of a fluid medium flowing through a channel is proposed, which can at least avoid the disadvantages of known methods and strategies and in which, during a flow, a restart of the boundary layer immediately upstream of the bypass outlet is forced even at higher air mass flows, so that reproducible conditions are present during the adjustment.

[0014] The sensor arrangement for determining at least one parameter of a fluid medium flowing through a channel, in particular an intake air mass flow of an internal combustion engine, comprises a sensor housing, in particular a plug-in sensor that is inserted or can be inserted into a flow tube in which the channel is formed, and at least one sensor chip arranged in the channel for determining the parameter of the fluid medium. The sensor housing has an inlet into the channel, which faces opposite a main flow direction of the fluid medium, and at least one outlet from the channel in a surface of the sensor housing. The surface of the sensor housing has a plurality of recesses upstream of the outlet, as viewed in the main flow direction.

[0015] The depressions can be spaced apart from one another. The depressions can be designed as grooves. The depressions can be formed perpendicular to the main flow direction. In particular, the depressions extend parallel to a direction that is perpendicular to a top and a bottom of the sensor housing. The depressions can have a section-wise cross-section. In other words, the depressions can be concave in the sensor housing and have a cross-section in the shape of a circular section. The depressions are arranged in the sensor housing such that the centers of their section-wise circular shape all lie on a common circular path. The circular path has, for example, a radius of 10.3 mm. On this circular path, the centers of the section-wise circular shape of the depressions are spaced apart from one another by 15°.In other words, the distance between two adjacent centers on the circular path is 15°. The recesses can have a depth of 0.4 mm to 0.8 mm, for example, 0.6 mm.

[0016] According to the invention, the surface of the sensor housing has, downstream of the outlet in the main flow direction, a downstream step adjacent to the outlet with a separation edge and, upstream of the outlet, an upstream step with a separation edge, wherein the downstream step and the upstream step form a chimney-like projection from the surface and the downstream step and the upstream step delimit the outlet on all sides. The downstream step can protrude from the surface by 0.5 mm to 5 mm, preferably from 0.75 mm to 3 mm, and more preferably from 1.2 mm to 2.2 mm. The downstream step and / or the upstream step can protrude perpendicularly from the surface. The separation edge can have a dimension in the main flow direction of 0.2 mm to 0.4 mm, and preferably from 0.25 mm to 0.35 mm.The downstream stage and / or the upstream stage may extend at least partially perpendicular to the main flow direction. The outlet may be located at a position on the surface where the fluid flowing in the main flow direction is turbulent. The outlet may have a rectangular opening cross-section.

[0017] In the context of the present invention, the main flow direction is understood to mean the local flow direction of the fluid medium at the location of the sensor or sensor arrangement, whereby local irregularities, such as turbulence, may be disregarded. In particular, the main flow direction can thus be understood to mean the local averaged transport direction of the flowing fluid medium at the location of the sensor arrangement. The averaged transport direction refers to a transport direction in which the fluid medium predominantly flows on average over time.

[0018] For the purposes of the present invention, a downstream arrangement refers to the arrangement of a component at a location that the fluid medium reaches later in the main flow direction than a reference point. For example, a downstream arrangement of a stage relative to the outlet means that the fluid medium reaches the stage later in time than the outlet.

[0019] Analogously, within the scope of the present invention, an upstream arrangement of a component is understood to mean an arrangement of the component at a location that the fluid medium flowing in the main flow direction reaches earlier in time than a reference point. For example, an upstream arrangement of a stage with respect to an outlet means that the fluid medium reaches the stage earlier in time than the outlet.

[0020] In the context of the present invention, a step is understood to mean a projection from the surface of the sensor housing.

[0021] In the context of the present invention, a separation edge is understood to mean a component with a sharp edge or a component with a very small radius of curvature that is designed to cause a flow separation or a flow separation of the fluid medium.

[0022] For the purposes of the present invention, turbulent flow is defined as a mostly three-dimensional, seemingly random, unsteady motion of fluid particles. The flow is turbulent if its Reynolds number is greater than the critical Reynolds number, i.e., greater than approximately 2300.

[0023] A fundamental idea of ​​the present invention is to provide groove-shaped depressions in the wall contour upstream of the bypass outlet. This forces the regeneration of a turbulent boundary layer even with relatively flat or short chimney-like projections. This minimizes interactions between the boundary layer at the bypass outlet and any transition region present upstream, thus enabling a more precise alignment to the target characteristic curve.

[0024] The sensor arrangement according to the invention thus enables a particularly optimized shape for the outlet of a hot-film air mass meter, which forces a new flow of the boundary layer immediately upstream of the outlet, so that reproducible conditions are present during calibration. This allows for smaller tolerances to be achieved in this operating range. In addition, the optimized outlet contour significantly simplifies the adjustment of the pulsation behavior. Since the pulsation behavior is essentially determined by the bypass channel length, shifting the outlet position is an effective means of adjusting the pulsation behavior. With conventional hot-film air mass meters, however, shifting the outlet position would also change the position in the boundary layer and thus the pressure prevailing at the outlet, resulting in complex causal relationships.Thanks to the optimized design of the sensor arrangement according to the invention, the position in the boundary layer is not changed, making this influencing parameter negligible when adjusting the pulsation behavior. This makes the pulsation behavior much easier to adjust. In particular, the bypass outlet is extended in a chimney-like manner, meaning it no longer sits flush with the adjacent walls, as is the case with the prior art. Consequently, the wall contour is no longer continuous, but exhibits a jump immediately before and after the bypass outlet.

[0025] The groove-like depressions in the wall contour upstream of the bypass outlet force subcritical separations, which lead to a reattachment of the flow to the wall contour. This ensures that the flow breaks off at the chimney-like, extended bypass outlet, even at higher air mass flows, and a new turbulent boundary layer forms. Short description of the drawings

[0026] Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are schematically illustrated in the figures. They show: Fig. 1 a perspective view of a sensor arrangement and Fig. 2 a schematic plan view of the sensor arrangement in the area of ​​the outlet. Embodiments of the invention

[0027] The Fig. 1 shows a sensor arrangement 10 for determining a parameter of a fluid medium flowing through a channel. In this exemplary embodiment, the sensor arrangement 10 is configured as a hot-film air mass meter and can, in particular, detect an intake air mass flow of an internal combustion engine. In this exemplary embodiment, the sensor arrangement 10 comprises a plug-in sensor 12, which can be inserted, for example, into a flow tube, in particular an intake tract of the internal combustion engine. A channel structure 14 is accommodated in the plug-in sensor 12, through which a representative quantity of the fluid medium can flow via an inlet opening or inlet 16, which, when inserted, faces a main flow direction 18 of the fluid medium.

[0028] Fig. 1 shows a section of the plug-in sensor 12 in the area of ​​the channel structure 14. The channel structure 14 has a main channel 20, which leads into a main channel outlet 22 on a bottom side 24 of the plug-in sensor 12, as shown in Fig. 1, as well as a bypass or measuring channel 26 branching off from the main channel 20, which ends in a on the surface 28, which in this embodiment is the front side or front face related to the illustration in the Fig. 1 of the plug-in sensor 12, arranged outlet 30 of the bypass or measuring channel 26. However, it is explicitly emphasized that the outlet 30 can also be arranged in another surface of the plug-in sensor 12, such as in the underside 24 or a top side.

[0029] As with conventional hot-film air mass meters, a sensor carrier (not shown) in the shape of a wing protrudes into the measuring channel 26. A sensor chip is embedded in this sensor carrier in such a way that a sensor membrane designed as the sensor region of the sensor chip is overflowed by the fluid medium. The sensor carrier, together with the sensor chip, is part of an electronic module which has a curved base plate as the sensor carrier and a printed circuit board attached thereto, for example glued, with a control and evaluation circuit. The sensor carrier can be injection-molded onto the base plate, for example as a plastic component. The sensor carrier, which can be injection-molded onto the base plate, for example as an injection-molded component or can be formed integrally with the base plate of the printed circuit board, is provided with a leading edge, which can be rounded.

[0030] The sensor chip is electrically connected to the control and evaluation circuitry via electrical connections, which can be implemented here as wire bonding. The resulting electronic module is inserted, such as glued, into an electronics compartment 32 of a sensor housing 34 of the plug-in sensor 12, in which the channel structure 14 is also formed. This can be done in such a way that the sensor carrier protrudes into the channel structure 14. The electronics compartment and the channel structure 14 are then closed by covers 36, 38.

[0031] Out of Fig. 1 that the end face 28 has a downstream step 40, i.e. a step downstream of the outlet 30, and an upstream step 42, i.e. a step upstream of the outlet 30. The downstream step 40 and the upstream step 42 border the outlet 30. In particular, the downstream step 40 and the upstream step 42 extend at least partially perpendicular to the main flow direction 18. The downstream step 40 and the upstream step 42 each have a separation edge 44, 46. The downstream step 40 and the upstream step 42 border the outlet 30 on all sides, as in Fig. 1. The outlet 30 has, for example, a rectangular opening cross-section. The downstream step 40 and / or the upstream step 42 protrude perpendicularly from the end face 28. The downstream step 40 and the upstream step 42 thereby form a chimney-like projection 48 from the end face 28. For example, the downstream step 40 and / or the upstream step 42 can protrude from the end face 28 by 0.5 mm to 5 mm, preferably by 0.75 mm to 3 mm, and even more preferably by 1.2 mm to 2.2 mm, for example 1.5 mm. The separation edge 44 of the downstream step 40 and / or the separation edge 46 of the upstream step 42 has a dimension in the main flow direction 18 of 0.2 mm to 0.4 mm and preferably of 0.25 mm to 0.35 mm, for example 0.3 mm.

[0032] Fig. Figure 2 schematically shows a top view of the plug-in sensor 12 in the region of the outlet 30. In particular, the flow through the bypass channel 26 is indicated by an arrow 50. In particular, normal operation, i.e., a pulsation-free flow of the fluid medium, is shown in the main flow direction 18.

[0033] In a conventional design of the outlet 30, in which the outlet 30 is flush with the end face 28, a stagnation point of the flowing fluid medium forms in a transition region from a side surface 52 facing opposite the main flow direction 18, in which the inlet 16 is also formed, into the end face 28. In the immediate vicinity of the stagnation point, the formation of a laminar boundary layer begins. With increasing length along the transition region and the end face 28 towards the outlet 30, the boundary layer becomes thicker. Initially, the boundary layer is laminar up to immediately upstream of the outlet 30. From a critical boundary layer thickness, disturbances in the boundary layer are no longer sufficiently dampened, so that it becomes turbulent.The turbulent flow can arise depending on flow-influencing parameters, such as wall friction, flow impulses, flow velocity and the like, at the level of the outlet 30, ie in a common plane perpendicular to the main flow direction 18, or its downstream end or downstream of the outlet 30.

[0034] The transition between the laminar and turbulent boundary layer occurs in a transition region upstream of outlet 30, at the latest in the area of ​​the outlet, i.e., at the level of outlet 30. This transition region is characterized by poor reproducibility, as it reacts very sensitively to the various boundary conditions. For example, the transition region lies in the area of ​​outlet 30. The conventional hot-film air mass meter will be difficult to calibrate in this velocity range due to the poor reproducibility of the transition region.

[0035] Since the position of the transition region changes with the air flow velocity, an operating state can arise in which the outlet 30 is temporarily located just within the transition region during operation. If a slight change in the pulsation amplitude or the average flow velocity results in the bypass channel 26 no longer being swept by the transition region, this can have a nonlinear effect on the average air mass flow in the bypass channel 26, from which the sensor chip generates the measurement signal. This also makes the pulsation behavior of the hot-film air mass meter nonlinear, which complicates application in the vehicle.

[0036] The sensor arrangement 10 according to the invention avoids this problem in that the outlet 30 is not flush with the end face 28, but has the aforementioned shape. As mentioned above, according to the invention, the outlet 30 is formed as a chimney-like projection 48 from the end face 28. The outlet 30 is extended in such a chimney-like manner that the steps 40, 42 force the formation of a turbulent boundary layer. Accordingly, the outlet 30 is located at a position on the end face 28 where the flow is turbulent. Fig. Figure 2 illustrates this behavior in more detail using an exemplary flow line 54. Downstream of the transition from the side surface 52, facing the main flow direction 18, to the front surface 28, the flow is transitional from a position 56 onward. From a position 58, which is at the level of the upstream step 42, a turbulent boundary layer is newly formed. Thus, the transition region is always outside or upstream of the outlet 30. In particular, the transition region lies only between positions 56 and 58.

[0037] In order to force the re-formation of a turbulent boundary layer even at higher air mass flows, without extending the chimney-like projection 48 from the end face 28 in a manner deviating from the above-mentioned dimensions, the present invention provides that the surface 28, as seen in the main flow direction 18, has a plurality of depressions 60 upstream of the outlet 30. The depressions 60 are spaced apart from one another. As can be seen from Fig.1, the depressions are formed as grooves 62. The grooves 62 are formed in particular perpendicular to the main flow direction 18. The grooves 62 also extend perpendicular to a direction of extension of the plug-in sensor 12. For example, the grooves 62 extend from the top side towards the bottom side 24 of the sensor housing 34 or vice versa. The depressions 60 can have a section-wise cross-section. In other words, the depressions can be formed concavely in the plug-in sensor 12 and have a cross-section in the shape of a circular section. The depressions 60 are arranged in the plug-in sensor 12 such that the centers of their section-wise circular shape all lie on a common circular path. The circular path has, for example, a radius of 10.3 mm. On this circular path, the centers of the section-wise circular shape of the depressions are spaced from one another by 15°.In other words, the distance between two adjacent centers on the circular path is 15°. The recesses 60 can have a depth of 0.4 mm to 0.8 mm, for example, 0.6 mm.

[0038] By reforming the boundary layer from position 58 onwards, interactions between the boundary layer at the outlet 30 and any transition region present upstream thereof are also minimized. This allows the sensor arrangement 10 to be well calibrated even at flow velocities that would generate a transition region on a continuous wall contour in a conventional hot-film air mass meter. If the position of the outlet 30 is shifted as part of adjusting the pulsation behavior, the basic pulsation behavior will change significantly less than in designs according to the prior art, since the influence of the transition region has been minimized. Thus, based on a good initial configuration, variants of the sensor arrangement 10 according to the invention can be quickly created that are similar in basic behavior but adapted to specific customer requirements.

[0039] Since the requirement for a longer chimney-like projection 48 contradicts customer requirements for the shortest possible overall length of the sensor housing 34, an extension of the chimney-like projection 48 from the end face 28 to compensate for higher air mass flows is only possible to a certain extent. According to the invention, this problem is solved, as described above, in that the recesses 60, which can be designed as grooves 62, are provided in the end face 28 in the otherwise smooth wall contour of the end face 28. The recesses 60 repeatedly force subcritical separations, which lead to a reattachment of the flow. Thus, with the chimney-like projection 48 of the same height, a new formation of the boundary layer can be forced from position 58 even at high flow velocities.

[0040] This effect is comparable to the effect of nubs on a golf ball, which delay the flow separation, so that the golf ball flies farther than a smooth ball, which creates greater separation and is thus decelerated more severely. However, since the sensor housing 34 is subjected to a known flow with a clear preferred direction, i.e., the main flow direction 18, grooves 62 are more effective and, in terms of tooling, require no additional expenditure and are therefore easier to manufacture than nubs. Grooves 62 can be manufactured by injection molding, whereas nubs would require an additional slider in the injection mold, which would increase manufacturing costs.

Claims

[1] Sensor arrangement (10) for determining at least one parameter of a fluid medium flowing through a channel (26), in particular an intake air mass flow of an internal combustion engine, wherein the sensor arrangement (10) has a sensor housing (34), in particular a plug-in sensor (12) which is introduced or can be introduced into a flow tube and in which the channel (26) is formed, and at least one sensor chip arranged in the channel (26) for determining the parameter of the fluid medium, wherein the sensor housing (34) has an inlet (16) into the channel (26) which faces the main flow direction (18) of the fluid medium, and at least one outlet (30) from the channel (26) in a surface (28) of the sensor housing (34), wherein the surface (28) of the sensor housing (34) has a plurality of recesses (60) upstream of the outlet (30) as seen in the main flow direction (18), characterized byin that the surface (28) of the sensor housing (34), as seen in the main flow direction (18), downstream of the outlet (30) has a downstream step (40) adjacent to the outlet (30) with a separation edge (44) and upstream of the outlet (30) has an upstream step (42) adjacent to the outlet (30) with a separation edge (46), wherein the downstream step (40) and the upstream step (42) form a chimney-like projection (48) from the surface (28) and the downstream step (40) and the upstream step (42) delimit the outlet (30) on all sides. [2] Sensor arrangement (10) according to the preceding claim, wherein the recesses (60) are spaced apart from one another. [3] Sensor arrangement (10) according to one of the preceding claims, wherein the recesses (60) are formed as grooves (62). [4] Sensor arrangement (10) according to one of the preceding claims, wherein the recesses (60) are formed perpendicular to the main flow direction (18). [5] Sensor arrangement (10) according to claim 1, wherein the downstream step (40) and / or the upstream step (42) protrude perpendicularly from the surface (28). [6] Sensor arrangement (10) according to claim 1 or 5, wherein the downstream stage (40) and / or the upstream stage (42) extend at least partially perpendicular to the main flow direction (18).

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