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

Abstract

Sensor arrangement (10) for determining at least one parameter of a fluid medium flowing through a channel structure (22), in particular an intake air mass flow of an internal combustion engine, wherein the sensor arrangement (10) comprises a sensor housing (12), in particular a plug-in sensor inserted or insertable into a flow tube, in which the channel structure (22) is formed, and at least one sensor chip (42) arranged in the channel structure (22) for determining the parameter of the fluid medium, wherein the sensor housing (12) has an inlet (34) into the channel structure (22), which points against a main flow direction (36) of the fluid medium, and an outlet (82) from the channel structure (22), wherein the channel structure (22) is bounded by channel walls (94, 96), wherein the channel structure (22) comprises a main channel (24) and a measuring channel (28), wherein the measuring channel (28) is separated from the main channel (24). branches off,wherein the sensor chip (42) is arranged in the measuring channel (28), wherein the main channel (24) and the measuring channel (28) are joined in a junction section (88) which adjoins an outlet section (92) with the outlet (82) from the channel structure (22), wherein at least one channel wall (94) of the channel walls (94, 96) in the outlet section (92) has curved wall sections (98, 100, 102), wherein the curved wall sections (98, 100, 102) are configured such that a tangent (104) at a transition (106) between two curved wall sections (98, 100, 102) extends in the direction of the measuring channel (28), characterized in that the sensor housing (12) defines a longitudinal extension direction (120) which is perpendicular to an end face (30) of the sensor housing (12), wherein the outlet (82) is inclined relative to the longitudinal direction (120) in the main flow direction (36) and the curved wall sections (98, 100,102) are arranged on a channel wall (94) facing away from the measuring channel (28) in the outlet section (92).

Description

State of the art

[0001] Numerous methods and devices for determining the flow properties of fluid media, i.e., liquids and / or gases, are known from the prior art. These flow properties can be any physically and / or chemically measurable properties that qualify or quantify the flow of the fluid medium. In particular, they can be flow velocity and / or mass flow rate and / or volume flow rate.

[0002] The invention is described below in particular with reference to so-called hot-film air mass meters, as described, for example, in 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, with a sensor membrane as the measuring surface or sensor area, which is permeable to the flowing fluid medium. 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. An asymmetry in the temperature profile detected by the temperature sensors, which is influenced by the flow of the fluid medium, allows conclusions to be drawn about the mass flow and / or volume flow of the fluid medium.Hot-film air mass meters are typically designed as plug-in sensors that can be permanently or interchangeably inserted into a flow pipe. This flow pipe could, for example, be the intake manifold of an internal combustion engine.

[0003] In this system, a partial flow of the medium passes through at least one main channel provided in the hot-film air mass meter. A bypass channel is formed between the inlet and outlet of the main channel. Specifically, 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. This curved section then transitions into a section in which the sensor chip is located. This latter section constitutes the actual measuring channel in which the sensor chip is positioned. A flow guide is provided in the bypass channel to direct the flow and prevent the flow of the partial medium stream from separating from the channel walls of the measuring channel.Furthermore, the inlet area of ​​the main channel, in the region of its opening which faces the opposite direction of flow, is provided with inclined or curved surfaces designed in such a way that the medium flowing into the inlet area is deflected away from the part of the main channel leading to the sensor chip. This prevents liquid or solid particles contained in the medium from reaching the sensor chip and contaminating it due to their inertia.

[0004] In practice, such hot-film air mass meters must meet a multitude of requirements and boundary conditions. Besides the goal of reducing the overall pressure drop across the hot-film air mass meter through suitable flow-optimized designs, one of the main challenges is to further improve the signal quality and the robustness of such devices against contamination by oil and water droplets, as well as soot, dust, and other solid particles. This signal quality relates, for example, to the mass flow rate of the medium through the measuring channel leading to the sensor chip, and, where applicable, to the reduction of signal drift and the improvement of the signal-to-noise ratio.Signal drift refers to the deviation, for example, of the medium's mass flow rate, in the sense of a change in the characteristic curve relationship between the actual mass flow rate and the signal determined during calibration in manufacturing. When determining the signal-to-noise ratio, the sensor signals output in rapid succession are considered, whereas characteristic curve or signal drift refers to a change in the mean value.

[0005] In typical hot-film air mass meters of the type described, a sensor carrier with a sensor chip attached to or embedded in it usually protrudes into the measuring channel. For example, the sensor chip can be glued into or onto the sensor carrier. The sensor carrier can form a single unit with a metal base plate, to which electronics, such as a control and evaluation circuit in the form of a printed circuit board, may also be glued. Alternatively, 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, for example, by bonding. The resulting electronic module can then be glued into a sensor housing, and the entire sensor assembly can be sealed with a cover.

[0006] From EP 1 091 195 A1 a generic sensor arrangement for determining at least one parameter of a fluid medium flowing through a channel structure is known.

[0007] Further sensor arrangements are known from US 2002 / 0023485 A1 and from DE 10 2008 052 393 B3.

[0008] Despite the improvements brought about by this sensor arrangement, there is still potential for improvement regarding signal acquisition accuracy.

[0009] For the hot-film air mass meter to deliver the most accurate air mass signal possible, a uniform flow to the sensor and through the measuring channel within it, and especially across the measuring surface of the sensor chip, is crucial. A gap exists between one end face of the sensor carrier and the wall of the measuring channel; its width is subject to manufacturing variations. In the area of ​​the sensor carrier, the fluid flowing in the measuring channel splits into three partial mass flows. A first partial mass flow flows over the sensor carrier and the sensor chip, a second partial mass flow flows under the sensor carrier, and a third partial mass flow flows through the gap. After the flow has passed around the sensor carrier, an unstable wake forms with fluctuating flow velocities and pressures.This leads to fluctuating flow rates upstream, especially in the area of ​​the sensor chip, which result in fluctuations in the measurement signal, particularly with oscillation modes typical for the dimensions of the sensor carrier and the flow velocity. Disclosure of the invention

[0010] Therefore, a sensor arrangement is proposed for determining at least one parameter of a fluid medium flowing through a channel structure, which can largely avoid the disadvantages of known methods and strategies and in which, in particular, a reduction of mass flow fluctuations in the channel structure, signal noise and flow sensitivity can be reduced and the adjustability is improved.

[0011] The sensor arrangement for determining at least one parameter of a fluid medium flowing through a channel structure, in particular an intake air mass flow of an internal combustion engine, comprises a sensor housing, in particular a plug-in sensor inserted or insertable into a flow tube, in which the channel structure is formed, and at least one sensor chip arranged in the channel structure for determining the parameter of the fluid medium. The sensor housing has an inlet into the channel structure, which points against a main flow direction of the fluid medium, and an outlet from the channel structure. The channel structure is bounded by channel walls. The channel structure comprises a main channel and a measuring channel, the measuring channel branching off from the main channel, and the sensor chip being arranged in the measuring channel.The main channel and the measuring channel are joined in a junction section, which adjoins an outlet section with the channel structure's exit. At least one channel wall in the outlet section has curved wall sections. The curved wall sections are designed such that a tangent at a transition between two curved wall sections extends towards the measuring channel. According to the invention, the sensor housing defines a longitudinal direction perpendicular to the end face, with the outlet inclined relative to the longitudinal direction in the main flow direction. The curved wall sections are arranged on a channel wall facing away from the measuring channel in the outlet section.

[0012] The radii of curvature of the curved wall sections can differ from one another. The channel wall in the outlet section can have at least one first curved wall section, one second curved wall section, and one third curved wall section. The first curved wall section and / or the third curved wall section can be curved in the opposite direction to the second curved wall section. The third curved wall section can be adjacent to the outlet, and the second curved wall section can be located between the first and third curved wall sections. The first curved wall section can have a larger radius of curvature than the second curved wall section. The tangent can be located at a transition between the third and second curved wall sections.A tangent can extend at a transition between the first curved wall section and the second curved wall section in the direction of the outlet. The tangent can also extend at the transition between the first curved wall section and the second curved wall section in the direction of a wall section facing away from the measuring channel, which defines the outlet.

[0013] Within the scope of the present invention, the main flow direction is understood to be the local flow direction of the fluid medium at the location of the sensor or sensor arrangement, whereby, for example, local irregularities such as turbulence can be disregarded. In particular, the main flow direction can thus be understood as the locally averaged transport direction of the flowing fluid medium. The main flow direction can therefore refer either to the flow direction at the location of the sensor arrangement itself or to the flow direction in the channel within the sensor housing, such as at the location of the sensor carrier or the sensor chip, whereby these two main flow directions may differ. Within the scope of the present invention, it is therefore always specified to which location the main flow direction refers.Unless otherwise specified, the main flow direction refers to the location of the sensor arrangement.

[0014] In the context of the present invention, a downstream arrangement is understood to mean the arrangement of a component at a point which the fluid medium reaches later in time than a reference point when flowing in the main flow direction.

[0015] Similarly, 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 which the fluid medium flowing in the main flow direction reaches earlier in time than a reference point.

[0016] Within the scope of the present invention, the sensor carrier can be configured wholly or partially as a circuit carrier, in particular as a printed circuit board, or can be part of a circuit carrier, in particular a printed circuit board. For example, the circuit carrier, in particular the printed circuit board, can have a projection which forms the sensor carrier and which projects into the channel, for example the measuring channel of a hot-film air mass meter. The remaining part of the circuit carrier, in particular the printed circuit board, can be housed, for example, in an electronics compartment, in a housing of the sensor arrangement, or in a plug-in probe of the sensor arrangement.

[0017] In the context of the present invention, a printed circuit board (PCB) is generally understood to be a substantially plate-shaped element that can also be used as a carrier for electronic structures, such as conductive traces, terminal contacts, or the like, and preferably also has one or more such structures. In principle, at least slight deviations from the plate shape are also conceivable and are included in the definition. The PCB can, for example, be made of a plastic material and / or a ceramic material, such as an epoxy resin, in particular a fiber-reinforced epoxy resin. In particular, the PCB can, for example, be designed as a printed circuit board (PCB) with conductive traces, in particular printed conductive traces.

[0018] In this way, the electronics module of the sensor assembly can be greatly simplified, eliminating the need for a base plate and a separate sensor carrier, for example. The base plate and sensor carrier can be replaced by a single circuit board, which can also house, in whole or in part, the control and evaluation circuitry for the sensor assembly. This control and evaluation circuitry is used to control the at least one sensor chip and / or to evaluate the signals generated by this sensor chip. By combining these elements, the manufacturing effort for the sensor assembly can be significantly reduced, and the space required for the electronics module can be greatly minimized.

[0019] The sensor arrangement can, in particular, comprise at least one housing, wherein the channel is formed within the housing. For example, the channel can include a main channel and a bypass or measuring channel, wherein the sensor carrier and the sensor chip can, for example, be arranged in the bypass or measuring channel. Furthermore, the housing can have an electronics compartment separate from the bypass channel, wherein the electronic module or the printed circuit board is essentially housed in the electronics compartment. The sensor carrier can then be designed as an extension of the printed circuit board projecting into the channel. This arrangement is technically comparatively simple to implement, in contrast to the complex electronic modules known from the prior art.

[0020] Particularly when a printed circuit board is used as a sensor substrate, but also in other cases and / or when using other media as sensor substrates, the sensor substrate can be designed, at least partially, as a multilayer sensor substrate. Thus, the sensor substrate can be designed using a so-called multilayer technique and have two or more interconnected substrate layers. For example, these substrate layers can be made of a metal, a plastic, a ceramic material, or a composite material and be bonded together using bonding techniques such as adhesive bonding.

[0021] In this case, where a multilayer technique is used with several sensor layers of the sensor carrier, the leading edge can be at least partially stepped by varying the dimensions of the carrier layers, oriented against the main flow direction of the fluid medium. In this way, the profiles can be approximated, at least in a stepped manner. For example, rectangular profiles, or—approximated by a stepped design—at least approximately round, rounded, or wedge-shaped profiles, can be formed in a cross-sectional plane perpendicular to the plane of extension of the sensor carrier. The sensor chip can be arranged on or in the sensor carrier such that it is oriented perpendicular to the local main flow direction.For example, the sensor chip can be rectangular in shape, with one side of this rectangle arranged perpendicular or substantially perpendicular, for example with an orientation that deviates from the vertical by no more than 10 degrees, to the local main flow direction.

[0022] The sensor chip can be electrically contacted via at least one electrical connection. For example, the sensor carrier, in particular a printed circuit board forming the sensor carrier or an extension of this printed circuit board, can have one or more conductive traces and / or contact pads which are connected to corresponding contacts on the sensor chip, for example by a bonding process. In this case, the electrical connection can be protected by at least one cover and separated from the fluid medium. This cover can be designed, in particular, as a so-called glob top, for example as a drop of plastic and / or adhesive, which covers the electrical connection, for example the bond wires. In this way, influences on the flow caused by the electrical connection can also be reduced, since the glob top has a smooth surface.

[0023] Furthermore, the sensor chip can have at least one sensor area. This sensor area can be, for example, a sensor surface made of a porous ceramic material and / or, in particular, a sensor membrane. The sensor membrane, as the measuring surface or sensor area, can be permeable to the flowing fluid medium. The sensor chip comprises, for example, 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 located upstream of the heating element and the other temperature sensor located downstream of the heating element. An asymmetry in the temperature profile detected by the temperature sensors, which is influenced by the flow of the fluid medium, can be used to infer the mass flow rate and / or volume flow rate of the fluid medium.

[0024] A key concept of the present invention is the elimination of the conventional main channel outlet and the merging of the main channel with the measuring channel, as well as the displacement of the common outlet in an upstream direction. Furthermore, the contour of the channel wall is modified between the common outlet and the merging zone of the main channel and measuring channel in forward flow, or the separation zone in reverse flow, such that it causes a deflection of the mass flow, resulting in a proportionally higher mass flow returning to the measuring channel than to the main channel. This allows the relevant section to be reduced in relation to pressure fluctuations in a specific case of turbocharger pressure fluctuations, thereby reducing the registered pressure difference and consequently decreasing the mass flow fluctuation in the channel structure. This, in turn, leads to a lower absolute value for the mass flow under-indicated reading.By eliminating the lateral main channel outlet and creating a common outlet, pressure differences between the main channel outlet and the measuring channel outlet are eliminated, resulting in reduced signal noise, lower inflow sensitivity, and improved adjustability.

[0025] In the case of pulsations with backflow in the flow tube, the backflow in the measuring channel and across the micromechanical sensor membrane increases, thus changing the pulsation error from a significantly positive false reading to a smaller positive false reading, ultimately resulting in a correct mass flow reading. Conversely, with the same amount of backflow into the outlet, a reduction in the backflow in the main channel indirectly increases the backflow in the measuring channel and across the micromechanical sensor membrane, thus changing the pulsation error during backflow in the flow tube from a significantly positive false reading to a smaller positive false reading, ultimately resulting in a correct mass flow reading.

[0026] Furthermore, a neutral behavior results in forward flow, particularly with regard to characteristic curve stability, adjustability and signal noise. Brief description of the drawings

[0027] Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are shown schematically in the figures.

[0028] They show: Fig. 1. Perspective view of a sensor array, Fig. 2 an enlarged view of an electronic module of the sensor assembly, Fig. 3 a top view of the measuring channel cover with the measuring channel and the sensor carrier, Fig. 4 a rear view of the sensor arrangement and Fig. 5 a perspective view of a sensor arrangement according to the present invention. Detailed description of the embodiments of the invention

[0029] Fig. Figure 1 shows a perspective view of a sensor arrangement 10 for determining a parameter of a fluid medium. The sensor arrangement 10 is designed as a hot-film air mass meter and comprises a sensor housing 12 designed as a plug-in sensor, which can be inserted, for example, into a flow pipe, in particular an intake manifold of an internal combustion engine. The sensor housing 12 has a housing body 14, a measuring channel cover 16, an electronics compartment 18, and an electronics compartment cover 20 for closing the electronics compartment 18. A channel structure 22 is formed in the measuring channel cover 16. The channel structure 22 has a main channel 24, which terminates in a main channel outlet 25 ( Fig. 5) on subpage 26 relating to the representation in Fig. The sensor housing 12 has a main channel 1, as well as a bypass or measuring channel 28 branching off from the main channel 24, which opens into a bypass or measuring channel outlet 32 ​​located on an end face 30 of the sensor housing 12. A representative quantity of the fluid medium can flow through the channel structure 22 via an inlet opening 34, which, in the installed state, points against a main flow direction 36 of the fluid medium at the location of the sensor housing 12.

[0030] Fig. Figure 2 shows an enlarged view of an electronic module 38 of the sensor arrangement 10. In the installed state of the electronic module 38, a sensor carrier 40 in the form of a wing projects into the measuring channel 28. A sensor chip 42 is embedded in this sensor carrier 40 such that a micromechanical sensor membrane 44, designed as the sensor area of ​​the sensor chip 42, is permeable to the fluid medium. The sensor carrier 42 and the sensor chip 42 are components of the electronic module 38. The electronic module 38 further comprises a curved base plate 46 and a printed circuit board 48, for example glued to it, with a control and evaluation circuit 50. The sensor chip 42 is electrically connected to the control and evaluation circuit 50 via electrical connections 52, which are implemented here as wire bonds.The resulting electronic module 38 is inserted into the electronics compartment 18 within the housing body 14 of the sensor housing 12, for example by gluing. The sensor carrier 40 projects into the channel structure 22. The electronics compartment 18 is then closed by the electronics compartment cover 20.

[0031] Fig. Figure 3 shows a top view of the channel structure 22 in the measuring channel cover 16. A centrifugal force deflection 54 is arranged in the measuring channel cover 16. Opposite the centrifugal force deflection 54, a counter contour 55 with a tear-off edge is arranged. The measuring channel cover 16 is further designed such that a measuring channel ramp 56 is formed in the measuring channel 28. Furthermore, the following is made of Fig. 3. The arrangement of the sensor carrier 40 can be seen. In its inserted state, the sensor carrier 40 protrudes into the measuring channel 28. Viewing the Fig. Figure 3 shows the sensor carrier 40 with its rear or underside 58. The rear or underside 58 is the side of the sensor carrier 40 opposite the sensor membrane 44. The sensor carrier 40 further has a leading edge 62, which may be rounded and which points against the main flow direction 60 of the fluid medium in the measuring channel 28, and a trailing edge 64 downstream of the leading edge 62. The measuring channel ramp 56 extends in the area between the centrifugal deflection 54 and the trailing edge 64 of the sensor carrier 40. The measuring channel 28 is bounded, at least in the area of ​​the sensor chip 42, by the housing body 14, the measuring channel cover 16, a wall section 66 facing the electronics compartment, and a wall section 68 facing away from the electronics compartment.Furthermore, the measuring channel cover 16 has a recess 70 as a positioning contour for a pin of the sensor housing 12 (not shown) and a wall or tongue 72 of a tongue-and-groove system for bonding the measuring channel cover 16 to the sensor housing 12. A reliable, low-tolerance setting and bonding process must be ensured, particularly in the area of ​​the sensor carrier 40. However, the geometric tolerances during the setting and bonding of the measuring channel cover 16 also lead to deviations in static and dynamic mass flow signals, including in the area of ​​the main channel outlet 25, because the channel ramp 56 in the measuring channel 28 is aligned with the window contour of the sensor housing 12 there.

[0032] Fig. Figure 4 shows a rear view of sensor array 10. Fig. Figure 4 shows the pressure conditions at the inlet opening 34, at the main channel outlet 25, and at the measuring channel outlet 32 ​​of the flow-guiding channel structure 22. At the inlet opening 34, the pressure is higher than the static pressure of the environment (74), at the measuring channel outlet 32, the pressure is lower (76), and at the main channel outlet 25, the pressure is on the order of the static pressure of the environment (78). These pressure conditions cause the flow through the channel structure 22 in the sensor housing 12 when flowing forward.Since the pressures 76, 78 at the measuring channel outlet 32 ​​and at the main channel outlet 25 can vary considerably in magnitude and ratio compared to ideal flow, and since pressure increases at one outlet and simultaneous pressure decreases at the other outlet can occur in opposite phases, the topology of two outlets in conjunction with one inlet causes mass flow fluctuations at the sensor chip 42. These topology-induced mass flow fluctuations are to be reduced by the inventive embodiment of the sensor arrangement 10.

[0033] The pressure conditions during reverse flow are not easy to determine, either experimentally or by simulation. Due to the geometric design of the channel structure 22, pulsations with reverse flow in the flow tube can result in only a relatively small mass flow rate developing in the measuring channel 28. Consequently, the reverse flow over the micromechanical sensor membrane 44 is also weak. This leads to false positive mass flow readings from the sensor arrangement 10. The geometric design according to the invention, described in detail below, aims to convey a larger mass flow rate backwards into the measuring channel 28 and over the micromechanical sensor membrane 44 in order to reduce the false mass flow readings during pulsations with reverse flow in the flow tube.

[0034] Fig. Figure 5 shows a perspective view of a sensor arrangement 10 according to the present invention. The differences from the conventional sensor arrangement described above are particularly highlighted. The channel structure 22 is designed such that the measuring channel 28 branches off from the main channel 24 at the junction 80. However, the main channel 24 and the measuring channel 28 both open into an outlet 82 located in the end face 30. The main channel outlet 25 is therefore omitted. Due to the special design of the channel structure 22, the main channel 24 has at least a first main channel section 84, in which the measuring channel 28 branches off, and a second main channel section 86. The second main channel section 86 adjoins a junction section 88 of the channel structure 22, in which the measuring channel 28 and the main channel 24 are joined.The main channel 24 also has at least one curved main channel section 90, which connects the first main channel section 84 and the second main channel section 86.

[0035] Channel structure 22 further comprises a discharge section 92 with the outlet 82 from channel structure 22. Discharge section 92 adjoins junction section 88. Discharge section 92 is bounded by channel walls 94 and 96. A channel wall 94 of the channel walls 94 and 96 in discharge section 92 has curved wall sections 98, 100, and 102. The curved wall sections 98, 100, and 102 are arranged on a channel wall 94 in discharge section 92 facing away from measuring channel 28. For example, a first curved wall section 98, a second curved wall section 100, and a third curved wall section 102 are provided in channel wall 94, arranged in this order from the main channel 24 and in the direction of outlet 82.In other words, the third curved wall section 102 adjoins the outlet 82, and the second curved wall section 100 is located between the first curved wall section 98 and the third curved wall section 102. The curved wall sections 98, 100, 102 are configured such that a first tangent 104 at a transition 106 between two curved wall sections 98, 100 extends in the direction of the measuring channel 28. For example, the first tangent 104 at a transition 106 between the third curved wall section 102 and the second curved wall section 100 extends in the direction of the measuring channel 28. The first curved wall section 98 and the third curved wall section 102 are curved in the opposite direction to the second curved wall section 100.

[0036] The curved wall sections 98, 100, 102 have radii of curvature 108, 110, 112. The radii of curvature 108, 110, 112 of the curved wall sections 98, 100, 102 differ from each other. The first curved wall section 98 has a larger radius of curvature 108 than the second curved wall section 100.

[0037] A second tangent 114 at a transition 116 between the first curved wall section 98 and the second curved wall section 102 extends towards the outlet 82. More precisely, the second tangent 114 at the transition 116 between the first curved wall section 98 and the second curved wall section 100 extends towards a wall section 118 facing away from the measuring channel 28, which delimits the outlet 82. The sensor housing 12 defines a longitudinal direction 120 that is perpendicular to the end face 30. The outlet 82 is inclined relative to the longitudinal direction 120 in the main flow direction 36. This divides the outlet 82 into a main flow pulse zone 122 and a measuring channel pulse zone 124. (Referring to the representation of the) Fig. In section 5, the main flow pulse zone 122 is located on the left side of the outlet 82, and the measurement channel pulse zone 124 is located on the right side of the outlet 82. The measurement channel pulse zone 124 has a smaller area than the main flow pulse zone 122. The measurement channel pulse zone 124 comprises 20% to 40%, and preferably 25% to 33%, of the total area of ​​the outlet 82, for example, 28%.

[0038] The following describes the fluid-mechanical characteristics resulting from the inventive design of the channel structure 22. According to the invention, the curved wall sections 98, 100, 102, which form a backflow contour, are located between the outlet 82 and the junction section 88 of the main channel and measuring channel 28 in the case of forward flow, or between the separation zone in the case of reverse flow. This arrangement of the curved wall sections 98, 100, 102 in the form of a wave causes a deflection of the mass flow in the case of reverse flow, i.e., flow entering through the outlet 82, so that proportionally more mass flow returns to the measuring channel 28 than to the main channel 24. Fig. The first tangent 104 drawn in figure 5 to the crucial wall area of ​​the wave is intended to illustrate this.

[0039] For the forward flow present across a wide operating range of typical passenger car combustion engines, the geometry developed for pulsating backflow presents no or only extremely minor disadvantages. This includes the fact that the wave-shaped backflow contour in the area of ​​the Fig. The third radius of curvature 112, as depicted in Figure 5, creates a flow situation which, in the case of forward flow, causes no disadvantages with regard to characteristic curve stability, adjustability, and signal noise. In the case of forward flow, a receding wall forms in the region of the third radius of curvature 112. Such a configuration leads to flow separation, the extent of which is subject to temporal and spatial fluctuations. This can result in a change in the ratio of main channel flow to measurement channel flow, which in turn can have disadvantages with regard to the criteria mentioned above. Therefore, the backflow contour, in the form of the wave with radii of curvature 108, 110, and 112, is designed to achieve both the positive effect described for backflow and a high degree of neutrality with regard to the forward flow criteria mentioned above.

[0040] A shaft that is relatively neutral with respect to the above criteria is therefore designed according to the invention as follows. The first radius of curvature 108 is relatively large, for example 2 mm to 7 mm, particularly preferably 3.5 mm, so that, in conjunction with the second radius of curvature 110, the second tangent 114 to the shaft is formed, which points towards the wedge-shaped wall section 118 at the outlet 82, facing away from the measuring channel 28. The second radius of curvature 110 is relatively small, for example 0.2 mm to 2 mm, particularly preferably 1 mm, so that, in the case of forward flow, a geometry-induced and thus spatially and temporally relatively stable separation occurs in the area of ​​the receding third curved wall section 102 with the third radius of curvature 112.The third radius of curvature 112, for example 1 mm to 5 mm, particularly preferably 1.5 mm, is designed such that, in the event of backflow, in conjunction with the second radius of curvature 110, a deflection of the mass flow into the measuring channel 28 is achieved, as indicated by the first tangent 104 in the direction of the measuring channel 28. The mass flow of the main flow channel 24 is thus deflected by means of the first radius of curvature 108 and the second radius of curvature 110 in the direction of the... Fig. 5 main current pulse zone 122 of the outlet 82 is shown.

Claims

[1] Sensor arrangement (10) for determining at least one parameter of a fluid medium flowing through a channel structure (22), in particular an intake air mass flow of an internal combustion engine, wherein the sensor arrangement (10) comprises a sensor housing (12), in particular a plug-in sensor inserted or insertable into a flow tube, in which the channel structure (22) is formed, and at least one sensor chip (42) arranged in the channel structure (22) for determining the parameter of the fluid medium, wherein the sensor housing (12) has an inlet (34) into the channel structure (22), which points against a main flow direction (36) of the fluid medium, and an outlet (82) from the channel structure (22), wherein the channel structure (22) is bounded by channel walls (94, 96), wherein the channel structure (22) comprises a main channel (24) and a measuring channel (28), wherein the measuring channel (28) is separated from the main channel (24) branches off,wherein the sensor chip (42) is arranged in the measuring channel (28), wherein the main channel (24) and the measuring channel (28) are joined in a junction section (88) which adjoins an outlet section (92) with the outlet (82) from the channel structure (22), wherein at least one channel wall (94) of the channel walls (94, 96) in the outlet section (92) has curved wall sections (98, 100, 102), wherein the curved wall sections (98, 100, 102) are configured such that a tangent (104) at a transition (106) between two curved wall sections (98, 100, 102) extends in the direction of the measuring channel (28), , characterized by, that the sensor housing (12) defines a longitudinal extension direction (120) which is perpendicular to an end face (30) of the sensor housing (12), wherein the outlet (82) is inclined relative to the longitudinal extension direction (120) in the main flow direction (36) and the curved wall sections (98, 100, 102) are arranged on a channel wall (94) facing away from the measuring channel (28) in the outlet section (92). [2] Sensor arrangement (10) according to the preceding claim, wherein the radii of curvature (108, 110, 112) of the curved wall sections (98, 100, 102) differ from each other. [3] Sensor arrangement (10) according to one of the preceding claims, wherein the channel wall (94) in the outlet section (92) has at least a first curved wall section (98), a second curved wall section (100) and a third curved wall section (102), wherein the first curved wall section (98) and / or the third curved wall section (102) is curved opposite to the second curved wall section (100). [4] Sensor arrangement (10) according to the preceding claim, wherein the third curved wall section (102) adjoins the outlet (82) and the second curved wall section (100) is arranged between the first curved wall section (98) and the third curved wall section (102). [5] Sensor arrangement (10) according to the preceding claim, wherein the first curved wall section (98) has a larger radius of curvature (108) than the second curved wall section (100). [6] Sensor arrangement (10) according to one of the three preceding claims, wherein the tangent (104) is arranged at a transition (106) between the third curved wall section (102) and the second curved wall section (100). [7] Sensor arrangement (10) according to one of the four preceding claims, wherein a second tangent (114) extends at a transition (116) between the first curved wall section (98) and the second curved wall section (100) in the direction of the outlet (82). [8] Sensor arrangement (10) according to the preceding claim, wherein the second tangent (114) at the transition (116) between the first curved wall section (98) and the second curved wall section (100) extends in the direction of a wall section (118) facing away from the measuring channel (28) and which limits the outlet (82).

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