Patent Application
20170038273
The present invention relates to a device for detecting a parameter of a gas, to a measuring system for determining a parameter of a gas, to a method for operating a device for detecting a parameter of a gas, to a corresponding device and to a corresponding computer program.
Exhaust gas sensors for detecting oxygen or nitrogen oxides are currently produced almost exclusively by ceramic technology, or LTCC (low-temperature cofired ceramics). Active layers, which are used as ion conductors, are in this case usually made of yttrium oxide-stabilized zirconium oxide (YSZ) and are combined with further layers, for example aluminum oxide-based insulation layers or conductive layers, for example of Pt which by means of metal paste printing is structured and burnt in.
There are also concepts for the construction of solid electrolyte-based micromechanical sensors, in which the electrical currents are proportional to the ionic currents through the electrolyte.
Furthermore, pressure sensors are known which can measure small pressure differences, or even absolute pressures, with very high resolution by means of a deformable membrane, a gas-tight cavity with a constant enclosed amount of gas being used for the absolute pressure measurement. Known processes for the production of cavities, which could be suitable inter alia for use in the sensors, are for example an APSM process or processes based on SOI.
DE 102004036032 A1 discloses a method for producing a semiconductor component, in which, by means of a first epitaxy layer which is applied to a semiconductor carrier, a membrane is produced with first doping above a region in the semiconductor carrier, and a structured stabilization element is applied to the semiconductor carrier by means of a second epitaxy layer which is applied to the semiconductor carrier.
Against this background, with the approach proposed here, a device for detecting a parameter of a gas, a measuring system for determining a parameter of a gas, a method for operating a device for detecting a parameter of a gas, as well as a device which uses this method, and lastly a corresponding computer program, according to the main claims are provided. Advantageous configurations may be found in the respective dependent claims and the description below.
A device for detecting a parameter of a gas, having a cavity for receiving the gas, comprises two layers of an electrically conductive material on opposite sides of an ion-conducting membrane covering the cavity, as well as a pressure measuring element arranged on the membrane. In this way, it is possible to produce a combined sensor consisting of a pressure sensor and a gas sensor based on an electrical voltage between the layers of the electrically conductive material.
A sensor device constructed according to the concept proposed here makes it possible to improve the detection of gases that can be measured directly and indirectly by means of ion-conducting materials, i.e. for example oxygen or pollutant gases such as nitrogen oxides, particularly in the exhaust gas of, for example, a vehicle.
In one refinement of the approach proposed here, instead of an instantaneous measurement of small gas concentrations, a measurement mode integrating over time, which requires little outlay, may be carried out. In this way, it is possible to take into account current exhaust gas standards which require integrated values, for example detection over a particular driving distance, instead of detection of instantaneous concentrations. In a sensor device produced according to the concept proposed here, it is also possible to use electrical currents between the electrically conductive layers, which do not necessitate amplification and/or shielding. In this way, the outlay for a downstream measurement can be reduced effectively.
The proposed concept furthermore makes it possible to reduce the power consumption and the heating time of the sensors, for example by bringing only the ion-conducting layers, and not the sensors as a whole, to operating temperature by means of a heater during operation of the device. By virtue of very rapid heating, which is thereby possible, an installation site of the sensors can be selected freely, for example at a large distance from high exhaust gas temperatures of a vehicle engine, which are unfavorable for a housing of the device. As a further advantage, in a refinement of the proposed concept, the use of one of the electrically conductive layers on the ion-conducting element as an electrode and as a heating structure allows significantly simplified construction with lower costs and increased reliability.
A device for detecting a parameter of a gas is provided, the device having the following features:
at least one cavity for receiving the gas from an external space;
at least one membrane for separating the cavity from the external space, a first side of the membrane, facing toward the external space, comprising a first layer of an electrically conductive material, and a second side, facing toward the cavity and lying opposite the first side, of the membrane comprising a second layer of an electrically conductive material, and at least one section of the membrane comprising an ion-conducting material; and
at least one pressure measuring element, arranged on the membrane, for detecting a gas pressure in the cavity.
The device may be a sensor device for determining a gas concentration, for example in the exhaust gas of a vehicle. To this end, one or more parameters of the gas may be detected, for example a value of a pump current required in order to pump the gas into the cavity, and/or a gas pressure of the gas contained in the cavity. The at least one cavity may applied in the form of a trough in a substrate for carrying individual elements of the device, for example by an etching process carried out on a surface of the substrate. The external space may refer to an environment lying outside the cavity. The external space may extend between the membrane and a housing of the device, or beyond the latter. An ambient pressure may prevail in the external space. The membrane may be produced and formed from a material which allows elastic deformation, in order to form a curvature in the direction of the external space in a manner corresponding to a gas pressure inside the cavity. In particular, the membrane may be formed by means of the ion-conducting material in order to allow diffusion of the gas between the external space and the cavity. The first and second layers of an electrically conductive material may be metal layers to which an electrical potential can be applied via electrical contact terminals arranged on them, and/or from which an electrical potential can be tapped via the contact terminals. The pressure measuring element may, for example, be arranged and formed on the side of the membrane facing toward the external space, in order to detect the gas pressure piezoelectrically and/or piezoresistively. For example, the pressure measuring element may be a strain gauge, or the pressure measuring element may comprise a strain gauge.
According to one embodiment of the device, the first layer of an electrically conductive material, the membrane and the second layer of an electrically conductive material may be configured in order to pump the gas through the membrane when an electrical voltage is applied between the first layer and the second layer. As an alternative or in addition, the first layer of an electrically conductive material, the membrane and the second layer of an electrically conductive material may be configured in order to generate an electrical voltage between the first layer and the second layer in the event of diffusion of the gas through the membrane. In this way, by means of detection of a pump current pumping the gas from the external space into the cavity and/or from the cavity into the external space, and as an alternative or in addition by means of tapping an electrical voltage based on diffusion of the gas, it is readily possible to deduce a composition of the gas.
In particular, the first layer of an electrically conductive material and/or the second layer of an electrically conductive material may comprise a gas-permeable noble metal. In this way, gas permeability of the membrane, or of the ion-conducting section of the membrane, can advantageously be maintained.
According to another embodiment, the first layer of an electrically conductive material and/or the second layer of an electrically conductive material may comprise a first electrical contact terminal and a second electrical contact terminal, and be configured accordingly in order to heat at least a section of the membrane on the basis of an electrical current flow between the first electrical contact terminal and the second electrical contact terminal. An amount of heat required for heating the membrane may be generated in a straightforward way by applying different electrical potentials to the first and second electrical contact terminals. Thus, it is possible to omit a heating element in the device and thereby save on cost and installation space.
In particular, the pressure measuring element may be arranged outside the section, to be heated, of the membrane. In this way, it is readily possible to ensure that a measurement functionality of the pressure measuring element cannot be impaired by temperature variations or temperatures that damage the pressure measuring element.
According to one particular embodiment, the first layer of an electrically conductive material and/or the second layer of an electrically conductive material may be arranged in a meandering shape, for example extending in a meandering shape a plane essentially parallel to the first and second sides of the membrane. In particular, the electrically conductive material layer which is used for heating the section of the membrane may have the meandering profile. It is thus possible to provide, in a straightforward and robust way, an extended heating section for optimal heating of the membrane. Furthermore, when a material which is not gas-permeable is used for the layers of an electrically conductive material, exposed regions for passage of gas can be provided.
The device may comprise a stop element for limiting a deflection of the membrane. The stop element may, in particular, be arranged on a bottom of the cavity. With this embodiment, damage to the membrane can be avoided in a straightforward and economical way.
According to another embodiment, the device may comprise at least one second pressure measuring element. The second pressure measuring element may be arranged at a further position, different to a position of the pressure measuring element, on the membrane. In this way, by detecting the gas pressure at different positions of the membrane, it is possible to determine the gas pressure prevailing in the cavity even more accurately. In particular, a detection direction of the pressure measuring element may be different to a detection direction of the further pressure measuring element. The detection direction may be a direction in which the pressure measuring element experiences a physical and/or chemical change during the recording of a measurement quantity. If the pressure measuring element is configured as a strain gauge, for example, the detection direction may correspond to an expansion direction of the strain gauge. This special refinement of this embodiment allows even more accurate determination of the gas pressure.
According to one particular embodiment, the device may comprise at least one further cavity for receiving the gas from the external space, at least one further membrane for separating the further cavity from the external space, and at least one further pressure measuring element, arranged on the membrane, for detecting a gas pressure in the further cavity. In this case, a first side of the further membrane, facing toward the external space, may have a further first layer of an electrically conductive material, and a second side, facing toward the further cavity and lying opposite the first side, of the further membrane may have a further second layer of an electrically conductive material. At least one section of the further membrane may comprise the ion-conducting material. With this embodiment, two or more sensor elements can be integrated on the device. By the sensor elements being usable independently of one another for the measurement process, a function test of the individual sensor elements can be carried out in a straightforward way. In particular, by using temporally offset and/or rotating individual sensor elements, it is possible to produce a mode integrating over time for the detection of the gas.
A measuring system for determining a parameter of a gas is furthermore provided, wherein the measuring system has the following features:
the device as described in one of the above-mentioned embodiments; and
an evaluation instrument, the evaluation instrument being coupled to the first layer and/or the second layer of an electrically conductive material and/or the pressure measuring element, and being configured in order to determine the parameter of the gas on the basis of at least one electrical potential of the first layer and/or of the second layer and/or on the basis of the gas pressure in the cavity, detected by the pressure measuring element.
The evaluation instrument may configured in order to determine the gas alternately or simultaneously on the basis of the electrical potential and on the basis of the gas pressure. In particular, evaluation instrument may be configured in order, for a temporally integrated measurement, to carry out the determination of the gas repeatedly over a predetermined period of time, for example one journey of the vehicle.
Furthermore, a method for operating a device for detecting a parameter of a gas is provided, wherein the device comprises at least one cavity for receiving the gas from an external space, at least one membrane for separating the cavity from the external space, a first side of the membrane, facing toward the external space, comprising a first layer of an electrically conductive material, and a second side, facing toward the cavity and lying opposite the first side, of the membrane comprising a second layer of an electrically conductive material, and at least one section of the membrane comprising an ion-conducting material, and at least one pressure measuring element, arranged on the membrane, for detecting a gas pressure in the cavity, and wherein the method comprises the following steps:
applying an electrical voltage between the first layer and the second layer in order to pump the gas through the membrane from the external space into the cavity; and
detecting an electrical quantity at least at the first layer and/or the second layer and/or at the pressure measuring element, in order to detect the parameter of the gas.
The electrical quantity, if it is detected at the first layer and/or the second layer, may for example be an electrical current strength of a pump current pumping the gas through the membrane. If the electrical quantity is detected the pressure measuring element, it may be an electrical voltage based on an elastic deformation of the pressure measuring element.
According to one embodiment, the method may furthermore comprise a step of reapplying the electrical voltage between the first layer and the second layer in order to pump the gas through the membrane from the cavity into the external space, and correspondingly a step of redetecting the electrical quantity at least at the first layer and/or the second layer and/or at the pressure measuring element, in order to redetect the parameter of the gas. This embodiment allows determination, integrated over time, of the gas or a gas composition in a straightforward, economical and flexible way.
According to another embodiment, the method for operating the device may be carried out as a pulse width modulation method, the step of applying the electrical voltage between the first layer and the second layer being carried out alternately with a step of applying an electrical voltage via the first layer or the second layer in order to heat the section of the membrane. Thus, by means of the method, advantageous combined heating of the membrane and measurement value determination of the gas can be carried out by means of the same device element.
The approach proposed here also provides a device which is configured in order to carry out, or implement, the steps of a variant of a method proposed in corresponding instruments. This alternative embodiment of the invention, in the form of a device, can also achieve the object of the invention rapidly and efficiently.
In the present case, a device may be understood as an electrical apparatus which processes sensor signals and outputs control and/or data signals as a function thereof. The device may comprise an interface, which may be configured as hardware and/or software. In the case of a hardware configuration, the interfaces may for example be part of a so-called system ASIC, which comprises a wide variety of functions of the device. It is, however, also possible for the interfaces to be separate integrated circuits, or to consist at least partially of discrete components. In the case of a software configuration, the interfaces may be software modules, for example existing besides other software modules on a microcontroller.
Advantageously, a computer program product or computer program, having program code which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used in order to carry out, implement and/or control the steps of the method according to one of the embodiments described above, in particular when the program product or program is run on a computer or a device.
The approach proposed here will be explained in more detail below by way of example with the aid of the appended drawings, in which:
In the following description of favorable exemplary embodiments of the present invention, identical or similar references are used for the elements which are represented in the various figures and have identical or similar effects, repeated description of these elements being omitted.
In the exemplary embodiment of the device 100 as shown in
Ideally, the chamber 104 is configured to be as shallow as possible so that, together with a small volume, a large area of the membrane 106 can simultaneously be exposed. In this case, even small amounts of pumped gas can achieve high pressure changes. The height of the chamber wall 126 does, however, have a lower limit since, with too low a distance of the heated membrane 106 from the chamber bottom 124, heat transfer would also occur in this case. Since the surface area to volume ratio of the chamber 106 is determined only by the height of the chamber 104, it is possible to carry out miniaturization of the chamber 104 and adaptation to geometrical requirements of the pressure sensor 118. The minimum size of the chamber or cavity 104 may furthermore be established on the basis of reliability aspects, for example a minimum size required for a pump element in order to ensure a function even in the event of deposits.
The membrane 106 has a rectangular shape corresponding to the bottom 124 of the cavity 104, dimensions of the membrane 106 being greater than the dimensions of the bottom 124 of the cavity 104. As shown by the representation in
In the exemplary embodiment shown in
In the exemplary embodiment of the device 100 as shown in
In the exemplary embodiment of the device 100 as shown in
The exemplary sensor 100 shown in
By means of the ion-conducting element in the form of the membrane 106, the gas or a multiplicity of gases are moved in a defined way from the external space 108 into the internal space or the cavity 104 of the sensor 100, and/or vice versa. This “pumping” of gas leads to pressure differences between the internal space 104 and the external space 108, which are detected by the pressure sensor 118, here in the form of the strain gauge. With detection of the pump current and/or the pressure, the gas concentration can be calculated. If the two parameters are detected simultaneously, the functionality and accuracy of the device 100 can advantageously be increased, or advantageously checked in the scope of an integrated self-test.
In the cross section of an exemplary structure of the sensor 100 as shown in
The pumping of the gas into the closed chamber 104 through the ion-conducting element 106 leads to a pressure increase there, which is measured piezoelectrically or piezoresistively by means of the pressure measuring element 118. With detection of the pump current and the pressure, the gas concentration is measured. In an advantageous operating mode of the sensor 100, the gas is pumped first into the chamber 104 and subsequently out of the chamber 104, and both processes are measured. In this way, the function of the sensor 100 as a whole can be monitored in the scope of a self-test. As an alternative, gas which is present only with a small concentration in the external space 108 may also be pumped over a longer period of time, which is accurately defined temporally or is measured, into the cavity 104 with a small current that can be measured only with difficulty. In this case, the gas accumulates in the chamber 104 until the amount of gas pumped into the chamber 104 can be determined with sufficient accuracy by the pressure sensor 118. Before another measurement process, the gas contained in the internal space 104 is then pumped out again, in which case, with integration of the pump current, i.e. the pump charge that has flowed, this process provides additional information about the amount of gas previously accumulated in the chamber 104.
In the concept of an exhaust gas sensor as proposed herein, only the ion-conducting material needs to be brought to a high temperature. Since the ion-conducting properties are in this case required only on the membrane 106, or parts thereof, heating which is very economical in terms of power can be carried out. For the sensor 100 only partially heated in this way, or the partially heated thin-film membrane 106, the power consumption is in particular drastically lower compared with conventional ceramic exhaust gas sensors. The rest of the sensor element 100 can be operated at ambient temperature or at a temperature which is constant but lies only slightly above the ambient temperature, for example by means of the heat dissipation from the heated membrane 106 or by means of a second heater. By the heating in the membrane 106, it is furthermore possible to determine the presence of gas in the chamber 104, and optionally also, with the aid of differing behavior during temperature changes, the composition thereof. When there is gas present in the chamber 104, during heating, a pressure increase which can be measured by the sensor element 118 takes place because of the membrane 106. By virtue of the heating, it is therefore simultaneously possible to carry out a function check or integrity check of the sensor 100. A defined temperature increase must in this case lead to a defined pressure increase, which is optionally established beforehand by means of calibration.
In the exemplary embodiment of the device 100 as shown in
In the operating mode of heating the membrane 106 by a pulse width modulation method, during the off phase a potential may be applied to the lower electrode 116 or a potential applied to the lower electrode 116 may be measured. Advantageously, all electrodes which are connected to the heated ion-conducting layer 106 are connected with high impedance during the application of voltage to the heater 116, in order to avoid charging or polarization effects due to potential differences from the heater 116.
According to alternative exemplary embodiments, the second electrically conductive layer 116 may be used exclusively as an electrode and a separate heater may be installed for heating the membrane 106.
With the aid of a plan view,
As shown by the representation in
The sensor 100, as shown by way of example in
In order to increase the accuracy and in order to be able to compensate for variations in the pressure of the external space 108, according to exemplary embodiments one of the four sensor elements 200 or a further sensor element may be used as a reference pressure sensor without a pump function. A plurality or all of the sensor elements 200 may also have an identical functionality in time-offset operation, for example with a first of the sensor elements 200 pumping gas into its chamber 104, a second of the sensor elements 200 being pumped empty during this time, and a third of the sensor elements 200 being used as a reference element for the varying pressure in the external space 108. According to other exemplary embodiments, at least the temperature and also an exhaust-gas flow rate may by means of further measuring elements—not shown in the figures—in order to be able to deduce the actual flow rate of the exhaust gas and therefore the gas concentration.
By the combination, proposed by way of example in
Besides the advantage explained above, that the individual elements 200 are operated alternately during normal operation, the exemplary redundant embodiment of the device 100 as proposed in
The vehicle 304 may be a road vehicle such as an automobile or a truck. Via a line system 308 of the vehicle 304, a partial flow of the gas or exhaust gas 306 is diverted and fed to the measuring system 300 in order to expose the sensor 100 to the gas 306. Depending on the configuration of the measuring system 300, the evaluation device 302 is coupled to the first layer of an electrically conductive material and/or to the second layer of an electrically conductive material and/or to the pressure measuring element of the device 100 (this is not shown explicitly in the representation in
The device 100 illustrated in
In a step 402, an electrical voltage is applied between a first layer and a second layer of an electrically conductive material of the sensor, in order to pump gas through an ion-conducting membrane arranged between the first and second layers, from an external space into a cavity of the sensor, arranged below the membrane. In a step 404, an electrical quantity is detected at the first layer and/or the second layer and/or at a pressure measuring element of the sensor, arranged on the membrane, in order to detect the parameter of the gas. In a step 406, the electrical voltage is reapplied between the first layer and the second layer in order to pump the gas through the membrane from the cavity into the external space. A step 408 of redetecting the electrical quantity at the first layer and/or the second layer and/or at the pressure measuring element is carried out in order to redetect the parameter of the gas.
According to one embodiment, the method 400 may be configured as a pulse width modulation method. In this case, the step 402 of applying the electrical voltage, or the step 406 of reapplying the electrical voltage, may be carried out alternately with a step of applying an electrical voltage via the first layer or the second layer, in order to heat the membrane.
A pressure sensor/sensor combination constructed according to the concept proposed here, based on ion-conducting material, is suitable for use as a chemical gas sensor, in particular as an exhaust gas sensor for motor vehicles, and for static applications. One main possible application involves use as a lambda probe, optionally with an alternative structure for also detecting further exhaust gas components, such as nitrogen oxides.
The exemplary embodiments described and shown in the figures are only selected by way of example. Different exemplary embodiments may be combined with one another fully or in relation to individual features. One exemplary embodiment may also be supplemented with the features of another exemplary embodiment.
Furthermore, the method steps proposed here may be carried out repeatedly and in a sequence other than that described.
If an exemplary embodiment comprises an “and/or” conjunction between a first feature and a second feature, this is to be interpreted as meaning that the exemplary embodiment according to one embodiment comprises both the first feature and the second feature, and according to another embodiment either only the first feature or only the second feature.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2014 207 480.0 | Apr 2014 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/057716 | 4/9/2015 | WO | 00 |
