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

Abstract

Sensor (10) 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, wherein the sensor (10) comprises a sensor housing (12), in particular a plug-in sensor inserted or insertable into a flow tube, in which the channel (22) is formed, and at least one sensor chip (42) arranged in the channel (22) for determining the parameter of the fluid medium, wherein the sensor chip (42) comprises a frame element (58), wherein the frame element (58) has a first recess (62) and a sensor area (44) at least partially limiting the first recess (62), wherein the frame element (58) has a second recess (64), wherein the sensor chip (42) is electrically connected to a fixed potential (68) in the area of ​​the second recess (64).

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 possible parameters, can be any physical and / or chemical measurable properties that qualify or quantify the flow of the fluid medium. In particular, these 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, 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, 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, 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 recorded 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.

[0003] 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.

[0004] In this process, 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.

[0005] In conventional hot-film air mass meters of the type described, a sensor carrier with a sensor chip attached to or embedded in it typically 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 unit with a metal base plate, onto which electronics, a control and evaluation circuit (e.g., with a circuit board, especially a printed circuit board), can 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 to each other, for example, by bonding. The resulting electronic module can then be glued into a sensor housing, and the entire plug-in sensor can be sealed with covers.

[0006] In practice, such hot-film air mass meters must meet a multitude of requirements. 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 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 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.

[0007] DE 10 2010 020 264 A1 describes an air mass meter whose entire housing is made of plastic and in which part of the flow channel has electrostatically dissipative properties.

[0008] WO 02 / 084226 A1 describes a sensor chip which has at least one potential surface upstream of a sensor area which, through electrical interaction with the contaminants in the flowing medium, prevents deposition in the sensor area.

[0009] WO 02 / 073140 A2 describes a sensor chip with an additional heater that is arranged upstream and at a significant distance from a sensor area.

[0010] From US 2012 / 0197155 A1, a sensor chip for determining a parameter of a flowing fluid medium is known, in which a frame element has a first recess forming a sensor area and a second recess connected to a fixed potential.

[0011] Despite the numerous advantages of known methods for preventing contamination of the sensor element by, for example, dust particles, these methods still offer potential for improvement. For instance, particles carrying an electrical charge that strike the sensor chip are only inadequately prevented from reaching it. Disclosure of the invention

[0012] Therefore, a sensor for determining at least one parameter of a fluid medium flowing through a channel is proposed, which can largely avoid the disadvantages of known methods and strategies and in which improved function can be ensured by shielding electrical interference fields as much as possible, so that acceleration of charged particles in the clean air channel and there in particular in the bypass channel above the sensor chip towards the sensor chip and subsequent adhesion of these particles is avoided.

[0013] A sensor according to the invention 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 inserted or insertable 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 chip has a frame element. The frame element has a first recess and a sensor area that at least partially delimits the recess. The frame element has a second recess, wherein the sensor chip is electrically connected to a fixed potential in the area of ​​the second recess.

[0014] In the context of the present invention, an electrical connection in the region of the second recess is understood to mean an electrical contact with the second recess. This electrical contact is referenced to a fixed electrical potential.

[0015] The second recess can be smaller than the first recess. The sensor chip can be made at least partially of a semiconductor material. The frame element can be formed by a core and at least one layer, wherein the layer can be arranged on the core and can be made of a dielectric material, and wherein the sensor area can be a section of the layer located above the first recess. The sensor chip can be arranged on a sensor carrier, wherein the sensor carrier can have at least partially electrically conductive properties, and wherein the sensor chip is connected to the sensor carrier in the area of ​​the second recess by means of an electrically conductive adhesive. The sensor carrier can be made at least partially of an electrically conductive material.In the context of the present invention, electrically conductive properties mean that the respective component is designed to conduct electrical charges. This can be achieved by arranging electrically conductive components, such as electrical wires, on or within the component. Preferably, the electrical conductivity is achieved through the component's material. For example, the sensor carrier is at least partially made of at least one electrically conductive material. This means that the sensor carrier can be made of a single material or of several materials, which may differ. For example, the sensor carrier is made of an electrically conductive plastic. Alternatively, various materials are conceivable for the sensor carrier. For example, the sensor carrier can be made of one-component or two-component materials.This allows the sensor carrier to be manufactured using an injection molding process. The injection molding process can be designed so that different materials or components, such as conductive and non-conductive components, can be present in different areas of the sensor carrier. In particular, fiber-matrix composites, sphere-matrix composites, or other fiber-reinforced composites can be injection molded using one-component or two-component processes. Sufficient conductivity of the sensor carrier can be achieved, for example, using a plastic injection molding process that incorporates at least 5%, but preferably more, carbon fiber. The electrically conductive plastic can include at least one element selected from the following group: conductive polymers, conductive fibers, conductive carbon black, and conductive coatings. These elements can, for example, be integrated into the plastic.Plastics with conductive components, such as polymers, fibers, and / or conductive carbon black, are cost-effective and easy to integrate. Suitable conductive fibers in plastics include carbon or metal particles.

[0016] The second recess can be produced using a photolithographic process. The second recess can have a cross-sectional area of ​​25 µm². 2 up to 1000 µm 2 exhibit.

[0017] In the context of the present invention, the cross-sectional area of ​​the second recess is understood to be an area of ​​the recess perpendicular to its direction of extension, in which the recess extends into the frame part.

[0018] The fixed potential can be a sensor mass.

[0019] In the context 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 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The sensor can, in particular, have at least one housing, wherein the channel is formed in the housing or in the housing cover. For example, the channel can comprise 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.

[0024] 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 joining techniques such as adhesive bonding.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] A basic idea of ​​the present invention is based on the fact that in known sensor chips, a first recess in the form of a cavern is introduced into the frame part, for example by means of an anisotropic etching process with KOH, and a second recess is provided at another location of the frame part, for example by means of a photolithographic process, wherein the access to the core of the frame part thus created is electrically connected to a fixed potential. Brief description of the drawings

[0029] 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.

[0030] They show: Fig. 1 a perspective view of a sensor, Fig. 2an enlarged view of an electronic module of the sensor and Fig. 3. A cross-sectional view of a sensor chip. Detailed description of the embodiments of the invention

[0031] 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 housing body 16. The channel structure 22 has a main channel 24, which is located in a main flow outlet 26, for example, on the underside 30, as shown in Figure 1. Fig. The sensor housing 12 has a main channel 12, as well as a bypass or measuring channel 30 branching off from the main channel 24, which leads into a bypass or measuring channel outlet 32, which can be separate or integrated. 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 in the opposite direction to the main flow direction 36 of the fluid medium at the location of the sensor housing 12.

[0032] Fig. Figure 2 shows an enlarged view of an electronic module 38 of the sensor arrangement 10. In the inserted state of the electronic module 38, a sensor carrier 40 projects into the measuring channel 30. A sensor chip 42 is embedded in this sensor carrier 40 such that a micromechanical sensor membrane, designed as the sensor area 44 of the sensor chip 42, is permeable to the fluid medium. The sensor carrier 40 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 of the housing body 14 – itself an integral part of the sensor housing 12 – for example, by gluing. The sensor carrier 40 protrudes into the channel structure 22. The electronics compartment 18 is then closed by the electronics compartment cover 20.

[0033] Fig. Figure 3 shows a cross-sectional view of the sensor chip 42. The sensor chip 42 has a frame element 54. The frame element 54 is formed by a core 56 and at least one layer 58, which is arranged on the core 56 and made of a dielectric material, such as silicon dioxide. For example, the layer 58 is arranged on both sides of the core 56. Optionally, the layer 58 can be covered by a protective layer 60. The sensor chip 42 is at least partially made of a semiconductor material. For example, the core 56 is made of silicon.

[0034] The frame element 54 has a first recess 62 in the form of a cavern. The first recess 62 is at least partially bounded by the sensor area 44. The first recess 54 can be introduced into the frame element 54 by means of an anisotropic etching process with KOH. As in Fig. As shown in Figure 3, the sensor area 44 is a section of layer 58 located above the first recess 62. The frame element 54 also has a second recess 64. The second recess 64 is formed next to the first recess 62. The second recess is contactable, in particular electrically contactable. The second recess 64 is smaller than the first recess 62. The second recess 64 has a cross-sectional area 66 of 25 µm². 2 up to 1000 µm 2 for example, no more than 900 µm 2The second recess 64 is produced using a photolithographic process. Therefore, the second recess 64 is not covered by the protective layer 60. Such small openings in the area of ​​layer 58 and the optional protective layer 60 close up during an etching process with KOH and form a conical or pyramidal depression in the core 56.

[0035] In the region of the second recess 64, the sensor chip 42 is electrically connected to a fixed potential 68. Preferably, the fixed potential is a sensor ground. The electrical connection can be realized, for example, as described below. As mentioned above, the sensor chip 42 is arranged on the sensor carrier 40. The sensor carrier 40 has at least partially electrically conductive properties. For example, the sensor carrier 40 is made at least partially of an electrically conductive material. The sensor carrier 40 is, for example, made of an electrically conductive plastic. The sensor chip 42 is bonded to the sensor in the region of the second recess 64 by means of an electrically conductive adhesive 70 ( Fig.2) connected to the sensor carrier 40. The sensor carrier 40 is in turn connected to the base plate 46 as described above, which is in turn connected to a ground pin of the attached circuit board 48 or the control and evaluation circuit 50. If the measuring channel cover 16 or the electronics compartment cover 20 also has electrically conductive properties, comprehensive shielding of the sensor chip 42 from electrical interference fields is achieved, thus improving the function of the sensor chip 42.

Claims

[1] Sensor (10) 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, wherein the sensor (10) comprises a sensor housing (12), in particular a plug-in sensor inserted or insertable into a flow tube, in which the channel (22) is formed, and at least one sensor chip (42) arranged in the channel (22) for determining the parameter of the fluid medium, wherein the sensor chip (42) comprises a frame element (58), wherein the frame element (58) comprises a first recess (62) and a sensor area (44) at least partially delimiting the first recess (62), wherein the frame element (58) comprises a second recess (64), wherein the sensor chip (42) is electrically connected to a fixed potential (68) in the area of ​​the second recess (64). [2] Sensor (10) according to the preceding claim, wherein the area of ​​the second recess (64) is contactable and is not covered by a protective layer. [3] Sensor (10) according to one of the preceding claims, wherein the second recess (64) is smaller than the first recess (62). [4] Sensor (10) according to one of the preceding claims, wherein the sensor chip (42) is at least partially made of a semiconductor material. [5] Sensor (10) according to one of the preceding claims, wherein the frame element (54) is formed by a core (56) and at least one layer (58), wherein the layer (58) is arranged on the core (56) and is made of a dielectric material, wherein the sensor area (44) is a section of the layer (58) which is arranged above the first recess (62). [6] Sensor (10) according to one of the preceding claims, wherein the sensor chip (42) is arranged on a sensor carrier (40), wherein the sensor carrier (40) has at least partially electrically conductive properties, wherein the sensor chip (42) is connected to the sensor carrier (40) in the area of ​​the second recess (64) by means of an electrically conductive adhesive (70). [7] Sensor (10) according to the preceding claim, wherein the sensor carrier (40) is at least partially made of an electrically conductive material. [8] Sensor (10) according to one of the two preceding claims, wherein the sensor carrier (40) is made of an electrically conductive plastic. [9] Sensor (10) according to one of the preceding claims, wherein the second recess (64) is produced by a photolithographic process. [10] Sensor (10) according to one of the preceding claims, wherein the fixed potential (68) is a sensor mass.

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