DE102018219729A1 - Device for determining at least one parameter of a fluid medium flowing in a flow tube - Google Patents

Abstract

The proposal relates to a device for determining at least one parameter of a fluid medium flowing in a flow tube, in particular an air mass in an intake line of an internal combustion engine, the device (10) having a sensor housing (12) which is designed as a plug-in sensor which can be inserted or inserted into the flow tube A channel structure (14) is formed in the sensor housing (12), which has a measuring channel (24) and at least one sensor chip (34) arranged in the measuring channel (24) for determining the parameter of the fluid medium, the sensor housing ( 12) an inlet (16) into the channel structure (14), which faces a main flow direction (18) of the fluid medium flowing in the flow tube, and has at least one outlet (28) from the channel structure (14), the channel structure (14) is limited by wall sections (50). It is proposed that at least one wall section (51) of the channel structure (14) be provided with at least one sound absorber (60) designed as a resonator.

Description

State of the art

Devices for determining at least one flow property of fluid media, that is to say liquids and / or gases, are known from the prior art. The flow properties as a possible parameter can be physical and / or chemical measurable properties which qualify or quantify a flow of the fluid medium. In particular, it can be a flow velocity and / or a mass flow of the flowing medium.

The invention is described below in particular with reference to so-called hot film air mass meters, as are known, for example, from Konrad Reif (ed.): Sensors in a Motor Vehicle, 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, 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, one temperature sensor being arranged upstream of the heating element and another temperature sensor being arranged downstream of the heating element. A mass flow and / or volume flow of the fluid medium can be concluded from an asymmetry of the temperature profile detected by the temperature sensors, which is influenced by the flow of the fluid medium.

The sensor housing of the hot film air mass meter is usually designed as a plug-in sensor, which can be inserted into a flow tube in a fixed or exchangeable manner.

For example, this flow tube can be an intake line of an internal combustion engine.

Channel structure can be formed in the sensor housing, which has a measuring channel and at least one sensor chip arranged in the measuring channel for determining the parameter of the fluid medium. The sensor housing has an inlet into the channel structure, which in the installed state of the sensor housing in the suction line points against a main direction of flow of the fluid medium in the suction line, and at least one outlet.

A partial flow of the medium flowing in the flow tube passes through the inlet into a bypass channel of the channel structure. Between the inlet and the outlet of the bypass channel, the bypass channel has a branch point at which a measuring channel branches off from the bypass channel. The measuring channel has a curved section for deflecting the media flow that has entered, the curved section subsequently merging into a section in which the sensor chip is arranged. Finally, the measuring channel opens into the bypass channel or into a separate outlet provided on the sensor housing.

Such hot film air mass meters must meet a variety of requirements. In addition to the goal of reducing the pressure drop across the hot film air mass meter as a whole by means of suitable fluidic designs, the main challenge is to further improve the signal quality and the robustness of the devices against contamination by oil and water pots as well as soot, dust and other solid particles. In the operation of such a device, a high-frequency acoustic disturbance may also occur in the intake line, which may originate, for example, in an exhaust gas turbocharger connected to the intake line. The high-frequency pressure pulsation of the intake line can interact with the air in the channel structure of the device for determining the at least one parameter and cause an adverse resonance oscillation there. The resonance vibration is dependent on the geometry of the channel structure of the sensor housing and can occur in such devices in a frequency range in the kilohertz range. The resonance oscillation can cause large fluctuations in the speed of the air flowing in the measuring channel, which overall can lead to the device not being able to correctly record the measured value due to its thermal inertia.

Disclosure of the invention

The device according to the invention for determining at least one parameter of a fluid medium flowing in a flow tube, in particular an air mass in an intake line of an internal combustion engine, has a sensor housing which is designed as a plug-in sensor which can be inserted or inserted into a flow tube. A channel structure is formed in the sensor housing, which has a measuring channel and at least one sensor chip arranged in the measuring channel for determining the parameter of the fluid medium, the sensor housing having an inlet into the channel structure which points against a main direction of flow of the fluid medium, and at least one outlet from the channel structure, the channel structure being delimited by wall sections. According to the invention, at least one wall section of the channel structure is provided with at least one sound absorber designed as a resonator.

Advantages of the invention

A high-frequency fluctuation in the speed of the air flowing in the duct structure can advantageously be weakened or avoided entirely by the at least one sound absorber designed as a resonator. In this way, a faulty measurement signal can be avoided more reliably and the robustness of the performance compared to high-frequency pressure pulsations is increased.

Advantageous refinements and developments of the invention are made possible by the features contained in the dependent claims.

The sound absorber can be designed, for example, as a Helmholtz resonator, as a Herschel-Quincke resonator or as a simple lambda / 4 tube. The latter two cases use destructive wave interference to absorb sound.

However, training as a Helmholtz resonator is particularly advantageous. The at least one sound absorber can be designed in a simple and cost-saving manner through a cavity in the sensor housing, the cavity surrounding an air volume and being connected to the channel structure only via a connecting channel which is formed in the at least one wall section. With such a design of the sound absorber as a Helmholz resonator, the mass of the air contained in the connecting duct forms, with the elasticity of the air volume contained in the cavity, quasi an oscillatory mass-spring system which has at least one natural frequency which is the natural frequency of the at least one sound absorber is.

This at least one natural frequency of the sound absorber is particularly advantageously adapted to a resonance frequency of the oscillation of the air flow occurring in operation in the channel structure or to the resonance frequency of the pressure pulsation, so that the oscillation of the air flow oscillating in the channel structure with the resonance frequency is damped by the sound absorber. This is advantageously brought about by the fact that the energy contained in the oscillation is used according to the principle of a Helmholtz resonator to excite the sound absorber at the natural frequency. As a result, this energy is ultimately converted into heat in the sound absorber and thereby absorbed. It is sufficient for this that the resonance frequency of the oscillation lies approximately in the range of the natural frequency of the sound absorber. Ideally, the at least one natural frequency of the sound absorber corresponds to the resonance frequency of the oscillation of the air flow occurring in operation in the channel structure, or it comes as close as possible to this.

Such a sound absorber can be used particularly advantageously in connection with a device which has a channel structure with a bypass channel and a measuring channel branching off from the bypass channel at a branching point. In such devices, a partial flow of the medium first passes through the inlet into the bypass channel of the channel structure and through the bypass channel to an outlet from the channel structure. The air that has entered the bypass duct is partially branched off at a branching point and enters the actual measuring duct there. The branching point is designed in such a way that large centrifugal forces act on the branched-off air flow, so that relatively heavy particles, such as impurities, are transported further to the outlet due to the inertia while maintaining their trajectory in the bypass channel, while the relatively light air molecules are redirected and redirected Measurement channel are fed. The air in the measuring duct is therefore cleaner than in the bypass duct. The arrangement of the sound absorber in the measuring channel advantageously ensures that the connecting channel of the sound absorber is protected from contamination, so that the reliability of the mode of operation of the sound absorber during operation is increased.

The at least one sound absorber can be formed in a simple manner in a wall section of the measuring channel. Since the sensor housing is often made of plastic, it is relatively easy to provide an additional cavity in this plastic, which is in fluid communication with the measuring channel via a defined connecting channel.

The at least one sound absorber is advantageously integrated into the sensor housing downstream of the sensor chip and upstream of the outlet, since in this section there is enough space for the integration of the sound absorber into the sensor housing and critical resonance vibrations can preferably occur at this point.

In one embodiment, several sound absorbers can be provided in the channel structure. These can be dimensioned differently, that is to say they can be designed with different geometric dimensions of the cavity and / or the length and the diameter of the connecting channel. From the different dimensions result in different natural frequencies, so that high-frequency fluctuations, which can have several different resonance frequencies, are absorbed in the channel structure.

Figure list

• 1 1 shows a perspective view of a front side of a device for determining at least one parameter of a fluid medium flowing through a measuring channel, the device being designed as a plug-in sensor which can be inserted or inserted into a flow tube,
• 2nd shows a view of the same front of the device 1 with the electronics compartment cover removed and without the measuring duct cover,
• 3rd shows a perspective partial view of a section of a sensor housing for a plug-in sensor designed according to the invention with a channel structure in which at least one sound absorber designed as a Helmholtz resonator is provided.

Embodiments of the invention

1 shows a schematic perspective view of a device 10th for determining a parameter of a fluid medium flowing through a flow tube, not shown. The device 10th is designed in this exemplary embodiment as a hot film air mass meter and can in particular detect an intake air mass flow of an internal combustion engine. In this embodiment, the device 10th formed as a plug-in sensor, which can be inserted into a flow tube, in particular an intake tract of the internal combustion engine.

The device 10th has a sensor housing 12 on. In the sensor housing 12 is a channel structure 14 formed through which via an inlet opening or an inlet 16 which in the inserted state of a main flow direction 18th of the fluid medium, a subset of the fluid medium in the channel structure 14 can reach. The channel structure 14 points downstream of the inlet 16 a bypass channel 20th on which in a separate channel outlet 21st ( 2nd ) on a front 22 of the sensor housing 12 can open, as well as one of the bypass channel 20th branching measuring channel 24th which is in an outlet 28 the channel structure 14 flows, which can also be the exit of the bypass channel. The outlet 28 can be on the front or a side wall of the plug-in sensor 12 can be arranged, such as on the front 30th or a backside facing away from it 22 .

2nd shows a perspective view of the sensor arrangement 10th in an unlocked state. In the measuring channel 24th protrudes like a conventional hot film air mass meter a sensor carrier 32 . In or on the sensor carrier 32 is a sensor chip 34 arranged such that one as the sensor area of the sensor chip 34 trained sensor membrane is flowed over by the fluid medium flowing in the measuring channel. The sensor carrier 32 is with the sensor chip 34 Part of an electronics module 36 , which is a curved base plate as a sensor carrier 32 as well as a printed circuit board attached to it, for example 38 with a control and evaluation circuit 40 can have. The sensor carrier 32 can, for example, be molded onto the floor panel as a plastic component. The sensor chip 34 can with the control and evaluation circuit 40 via electrical connections 42 , for example wire bond connections, be electrically connected. The electronics module 36 is in an electronics room 44 of the sensor housing 12 introduced, for example glued. This can be done in such a way that the sensor carrier 32 doing so in the channel structure 14 protrudes. Then the electronics room 44 from an electronics compartment cover 46 ( 1 ) locked. The channel structure 14 can in a measuring channel cover 48 be formed, the part of the sensor housing 12 is and to the front 30th of the sensor housing 12 is put on.

3rd shows a perspective view of the measuring channel cover 48 according to an embodiment of the invention. The channel structure 14 is in the measuring channel cover in this exemplary embodiment 48 educated. 3rd shows a possible variant of the channel structure 14 where the bypass channel 20th and the measurement channel 24th together in the outlet 28 on one face 26 the device 10th flow out. How out 3rd can be seen, the channel structure 14 of wall sections 50 limited. The wall sections 50 thus give the shape of the channel structure 14 in front. The channel structure 14 is at least on three sides of the wall sections 50 inside the measuring channel cover 48 limited. The fourth side of the boundary can be, for example, a wall section on a rear side 22 of the sensor housing 12 be realized.

The wall sections 50 can at least partially from the material of the measuring channel cover 48 are formed, for example from a plastic. As in 3rd is recognizable is, for example, a wall section 51 the channel structure 14 with a sound absorber 60 provided, which is preferably designed in this exemplary embodiment as a Helmholtz resonator.

wobei

• L die Länge des Verbindungskanals,
• Ao die Querschnittsfläche des Verbindungskanals und
• po die Dichte der Luft ist.

A Helmholtz resonator consists of an air volume of any shape, which is provided with an opening to the outside via a connecting channel. The inertial mass of the air in the connecting duct is: $$m={\rho }_0\cdot L\cdot A_0$$

in which

• L the length of the connecting channel,
• Ao the cross-sectional area of the connecting channel and
• po is the density of the air.

The inertial mass m of the air contained in the connecting channel forms, with the elasticity of the air volume contained in the cavity, a quasi oscillatory mass-spring system which has at least one natural frequency.

mit $$\mathrm{\Delta }L\approx \frac{\pi }{4}R$$

wobei

• V das umschlossene Luftvolumen in der Kavität ist,
• c die Schallgeschwindigkeit des Mediums und
• R der Radius des Verbindungskanals ist.

If the connecting channel is approximately cylindrical, for example, such a system has a natural frequency fo, for which the following applies: $$f_0=\frac{c}{\mathrm{2nd}\pi }\sqrt{\frac{A_0}{V\left(L+\mathrm{2nd}\mathrm{\Delta }L\right)}}$$

With $$\mathrm{\Delta }L\approx \frac{\pi }{\mathrm{4th}}R$$

in which

• V is the enclosed volume of air in the cavity,
• c the speed of sound of the medium and
• R is the radius of the connecting channel.

The at least one sound absorber can be designed in a simple and cost-saving manner by a cavity in the sensor housing surrounding an air volume V, the cavity being connected to the channel structure only via a single connecting channel which is formed in the at least one wall section. In 3rd is recognizable that the sound absorber 60 a cavity 61 has a small connecting channel 62 with the measuring channel 24th the channel structure 14 connected is.

The natural frequency of the sound absorber 60 is at an expected resonance frequency in the channel structure 14 Adjusted the oscillation of the air flow during operation. This resonance frequency can easily be determined in tests in a flow channel. By a suitable choice of the volume V and the geometrical dimensions R and L of the connecting channel, the sound absorber can be designed in a simple manner, for example in accordance with the physical relationships described above, in such a way that the natural frequency of the sound absorber is adapted to the resonance frequency. As a result, the oscillation occurring in the resonance case becomes that in the channel structure 14 with the resonance frequency oscillating air flow through the sound absorber 60 at least subdued or completely absorbed. The energy contained in the oscillation is used according to the principle of a Helmholtz resonator to excite the sound absorber 60 spent in natural frequency and thus absorbed. It is sufficient if the resonance frequency of the oscillation is approximately in the range of the natural frequency of the sound absorber. In the ideal case, however, the natural frequency of the sound absorber corresponds to the resonance frequency of the oscillation of the air flow occurring in operation in the duct structure.

The sound absorber is preferred 60 as shown downstream of the sensor chip 34 and upstream of the outlet 28 arranged. Deviating from this, it is also possible to use the sound absorber 60 elsewhere in the channel structure 14 in another wall section 50 to provide.

Furthermore, in a further embodiment it is also possible to have several sound absorbers at different points in the channel structure 14 to provide. It is particularly possible, but not necessary, to dimension the sound absorbers differently, that is to say to provide them with different geometric dimensions, so that different sound absorbers have different natural frequencies.

It is also possible, but not necessary, to design at least one sound absorber in other embodiments, for example according to the operating principle of lambda / 4 tubes or Herschel-Quincke resonators. Both embodiments are based on the principle of destructive wave interference.

Claims (11)

Device for determining at least one parameter of a fluid medium flowing in a flow tube, in particular an air mass in an intake line of an internal combustion engine, the device (10) having a sensor housing (12) which is designed as a plug-in sensor which can be inserted or inserted into the flow tube, wherein A channel structure (14) is formed in the sensor housing (12), which has a measuring channel (24) and at least one sensor chip (34) arranged in the measuring channel (24) for determining the parameter of the fluid medium, the sensor housing (12) having a Inlet (16) in the channel structure (14), the one main flow direction (18) of the fluid medium flowing in the flow tube and has at least one outlet (28) from the channel structure (14), the channel structure (14) being delimited by wall sections (50), characterized in that at least one wall section (51 ) of the channel structure (14) is provided with at least one sound absorber (60) designed as a resonator. Device after Claim 1 , characterized in that the sound absorber (60) is designed as a Helmholtz resonator. Device after Claim 1 or 2nd , characterized in that the at least one sound absorber (60) is formed by a cavity (60) in the sensor housing (12) surrounding an air volume, which cavity is connected to the channel structure (14) via a connecting channel (62) in the at least one wall section (51) ) is connected. Device after Claim 3 , characterized in that the mass of the air contained in the connecting channel (62) with the elasticity of the air volume contained in the cavity (61) forms an oscillatory mass-spring system which has at least one natural frequency which is a natural frequency of the at least one sound absorber (60) is. Device after Claim 4 , characterized in that the at least one natural frequency of the sound absorber (60) is matched to a resonance frequency of an oscillation of the air flow occurring in operation in the duct structure (14) such that the oscillation of the air flow oscillating in the duct structure (14) with the resonance frequency results from the sound absorber (60) is damped. Device after Claim 4 , characterized in that the at least one natural frequency of the sound absorber (60) corresponds to the resonance frequency of the oscillation of the air flow occurring in operation in the channel structure (14). Device according to one of the preceding claims, characterized in that the channel structure (14) has a bypass channel (20) and has a measuring channel (24) branching off from the bypass channel at a branching point (52). Device after Claim 7 , characterized in that the at least one sound absorber (60) is formed in a wall section (51) of the measuring channel (24). Device according to one of the preceding claims, characterized in that the at least one sound absorber (60) is arranged downstream of the sensor chip (34) and upstream (28) from the outlet (28). Device according to one of the preceding claims, characterized in that a plurality of sound absorbers (60) are provided. Device after Claim 10 , characterized in that the sound absorbers (60) are dimensioned differently and have different natural frequencies resulting from their different dimensions.

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