Calibration method for calibrating a humidity sensor for detecting at least one humidity parameter of a gas mixture, as well as measuring method and device for detecting at least one humidity parameter of a gas mixture.

Abstract

Calibration method for calibrating a humidity sensor (112) for detecting at least one humidity parameter of a gas mixture, wherein in the calibration method a temperature of the gas mixture is detected, wherein at least one first saturation parameter is inferred from the temperature of the gas mixture, wherein at least one second saturation parameter is detected, wherein the humidity sensor (112) is calibrated by means of a comparison (162) of the first saturation parameter with the second saturation parameter, wherein the calibration method is carried out by at least one control unit (120), characterized in that the humidity sensor (112) comprises at least one sensor element (114) for detecting a proportion of a gas component in the gas mixture, wherein the humidity sensor (112) further comprises at least one pressure sensor (116) for detecting a total pressure of the gas mixture.

Description

State of the art

[0001] Devices comprising at least one humidity sensor, calibration methods for calibrating a humidity sensor, and measurement methods for detecting at least one humidity parameter of a gas mixture are known from the prior art. The invention is described below, without limiting further possible embodiments, essentially with reference to methods and devices which serve for the quantitative and / or qualitative detection of at least one humidity parameter of a gas mixture. For example, the gas mixture can be an exhaust gas from an internal combustion engine and / or an intake air from a fuel cell, particularly in the automotive sector. In technical applications, there can often be a need to measure a humidity parameter, for example a moisture content and / or a vapor pressure and / or a relative air humidity, in particular of a gas mixture, for example of gases.Various technical solutions are known for this purpose from the state of the art, which have different advantages and disadvantages.

[0002] Broadband lambda sensors can be used to measure the oxygen concentration of a gas, as described, for example, in Robert Bosch GmbH: Sensors in Motor Vehicles, first edition 2010, pages 160-165. Using the broadband lambda sensor in combination with a temperature sensor and a pressure sensor, it is also possible to determine the vapor pressure of water and the relative humidity, provided the composition of the dry gas mixture, especially the dry air, is known.

[0003] FR 2 930 842 A1 describes a fuel cell system comprising a cathode-anode fuel cell stack, an upstream collector, and a downstream collector for supplying air to the cells. The system further comprises a water recovery system capable of transferring a quantity of water vapor from the downstream collector to the upstream collector by pervaporation. The system comprises a cell humidity estimation tool and an oxygen estimation probe located above the downstream collector between the cell stacks and the water recovery system. The humidity estimation tool comprises a computer configured to calculate the downstream relative humidity based on the signal received from the downstream oxygen probe.

[0004] A measurement of a moisture parameter, such as humidity, can be used in many different applications. One application example would be the recording of a moisture parameter, such as humidity measurement, in combination with an air mass flow sensor. An air mass flow sensor, such as a hot film air mass meter (HFM), can measure a total mass flow, i.e. the amount of vapor contained is also measured. A deviation between a dry air volume and a moist air volume can cause an error of up to 8% in the determination of the amount of oxygen available for a reaction, depending on the ambient conditions. This error, particularly a deviation, usually leads to a deterioration in exhaust gas quality and performance, for example in combustion engines without air volume compensation.

[0005] The following relationships typically apply to the measurement of humidity parameters, particularly relative humidity, using a broadband lambda sensor. The broadband lambda sensor delivers a current dependent on the oxygen partial pressure of the ambient air.

[0006] The oxygen partial pressure is pO2=p⋅n˙O2n˙air, with air pressure p, oxygen mole flow ṅ O2 and total air mole flow ṅ Luft .

[0007] Similarly, the vapor pressure psteam=p⋅n˙steamn˙air, with ṅ Dampf , the steam mole stream.

[0008] By combining these two formulas we get psteam=pO2⋅n˙steamn˙O2.

[0009] The total air mole flow is approximate, especially neglecting trace gases, although this assumption is rather inconclusive: n˙air=n˙O2+n˙N2+n˙steam.

[0010] An oxygen content x O2 of unused air is usually almost constant and is approximately 0.21, so n˙O2=m˙dry air⋅xO2Mdry air, with ṁ Luft trocken , the mass flow of dry air, and M Luft trocken , the molar mass of dry air.

[0011] Similarly, a nitrogen content x N2 approximately 0.79, so n˙N2=m˙dry air⋅xN2Mdry air By combining the last two formulas we get n˙N2=n˙O2⋅xN2xO2.

[0012] By inserting the last formula and the fourth formula into the third formula, we get pSteam=pO2⋅(n˙air−n˙O2−n˙N2)n˙O2=pO2⋅(n˙O2⋅ppO2−n˙O2−n˙O2⋅xN2xO2)n˙O2=p−pO2⋅(1+xN2xO2).

[0013] A saturation vapor pressure p s, also called vapor saturation pressure, can be calculated according to the state of the art from an air temperature T Luft calculate, i.e. ps=f(Tair).

[0014] A relative humidity Φ Luft is known for ΦAir=pSteamps.

[0015] The relative humidity Φ Luft can thus be calculated from a measured air pressure p, a measured air temperature T Luft and the oxygen partial pressure p O2 , as shown above. For example, a lambda probe, in particular a broadband lambda probe, can be used to measure the oxygen partial pressure p O2 , a pressure sensor, preferably a pressure sensor for detecting the air pressure p, and a temperature sensor, preferably a temperature sensor for detecting the air temperature T Luft, and / or a combined pressure / temperature sensor, the humidity parameter, in particular an absolute vapor partial pressure and / or the relative humidity, air temperature T Luft , can be determined in an evaluation unit.

[0016] There is a known method for adjusting a hygrometer: a small amount of water is poured into a sealable, transparent container. The hygrometer is placed on a small raised surface within the container. The container is then closed and the user waits a few hours until the water condenses on the container walls. Then, quickly remove the hygrometer and set it to 100%. This adjustment procedure is described, for example, in Wikipedia under the keyword "Hygrometer" (http: / / de.wikipedia.org / wiki / Hygrometer).

[0017] WO 94 / 28410 A1 describes a device for calibrating gas sensors, in particular humidity sensors, and a method for calibrating such sensors. In a further aspect, the invention relates to a device for producing a gas mixture comprising a carrier gas and a condensable gas, wherein the condensable gas is at a defined vapor pressure in the carrier gas.

[0018] DE 102 03 637 A1 describes a method for calibrating a humidity sensor, in which a humidity value is recorded with the humidity sensor under first ambient conditions and under second ambient conditions that are different from the first, and in which a correction value for the humidity sensor is determined from the parameters of the ambient conditions and the measured humidity values.

[0019] The known calibration methods, measurement methods, and devices for detecting at least one humidity parameter from the state of the art have several disadvantages. For example, the use of a humidity sensor is useful for adjusting the humidity in fuel cells.

[0020] In "Investigation of water transport through membrane in a PEM fuel cell by water balance experiments," Q. Yan et al., Journal of Power Sources 158 (2006) 316-325, experiments on the transport of water through a membrane of a PEM (polymer electrolyte membrane) fuel cell are described. It has been shown, for example, that humidity, both in the anode and cathode inlet gas, has a significant effect on fuel cell performance. To date, there are no automotive-grade humidity sensors available that cover the entire range of applications of motor vehicles and / or their operating conditions at affordable prices.With knowledge of the air humidity, one can, for example, improve a fuel cell's operating strategy, for example, by regulating a desired inlet humidity or exploiting all potentials to reduce the cathode pressure and the cathode inlet mass flow. In the case of insufficient humidification, for example, at a relative humidity Φ, Kathode= 30%, the ohmic resistance of the fuel cell can be significantly higher than at higher cathode humidities. High ohmic resistances can lead to low efficiencies and / or poor performance and / or high heat generation in a stack, which can potentially lead to stack damage. Sensors are generally prone to error. In particular, inexpensive sensors suitable for automotive applications often have large tolerances. An investigation of a tolerance chain for the detection of a humidity parameter, in particular a humidity measurement, can show that the humidity at the cathode inlet of a fuel cell system can be determined with an accuracy of only approximately 10-20% using the state-of-the-art measuring principle described above.The accuracy of a humidity parameter measurement, particularly a humidity measurement, with a lambda sensor is in the range of + / - 8% to + / - 15% and depends particularly on the humidity level. The tolerance can be smaller at high relative humidities, for example, before entering the cathode of a stack where external humidification is used, than at low relative humidities, such as at the inlet humidity, also known as ambient humidity, which also occurs in air systems. If, in addition to the tolerance of the lambda sensor, tolerances of typical pressure and temperature sensors suitable for automotive applications are taken into account, the tolerances of the humidity measurement at the cathode inlet can increase to a range of approximately + / - 10% to + / - 20%.Such large tolerances in the detection of the humidity parameter, particularly in humidity measurement, are insufficient for a technical application. Therefore, the detection of the humidity parameter, particularly a humidity measurement, with the lambda probe according to the state of the art does not yet represent an adequate substitute for the use of dew point sensors, which in turn are not available in a form suitable for automotive applications and / or are not robust in operation, particularly with regard to the influence of water droplets. A further problem can be sensor aging and the associated change in a sensor value, particularly an aging of the sensor value, over an operating period. In particular, a conflict arises regarding the inaccurate detection of the humidity parameter, particularly a humidity measurement, with the lambda probe and the lack of a dew point sensor suitable for automotive applications.A calibration method, a measuring method and a device for detecting at least one humidity parameter would therefore be desirable, preferably for use in the automotive sector and / or with a small error tolerance and / or with the lowest possible aging effects. Disclosure of the invention

[0021] Accordingly, a calibration method and a measuring method and a device for detecting at least one humidity parameter of a gas mixture are proposed, which at least largely avoid the disadvantages of known calibration methods and / or measuring methods and / or devices.

[0022] The device according to the invention for detecting at least one humidity parameter of a gas mixture comprises at least one humidity sensor. The detection can in principle be quantitative and / or qualitative. The humidity parameter can in principle be any parameter that depends on a liquid content, in particular a water content, in the gas mixture. The humidity parameter can, for example, be a vapor pressure and / or an absolute humidity and / or a relative humidity and / or a dew point temperature and / or a saturation temperature, for example a relative air humidity. The gas mixture can in principle be a mixture of at least one gas component.Particularly preferably, the gas mixture can be air, for example supply air, and / or exhaust air from an internal combustion engine, for example a fuel cell and / or an internal combustion engine. The humidity sensor can in principle be a device which is set up to detect the humidity parameter. The humidity sensor can, for example, be designed in one part or in several parts. For example, the humidity sensor can be at least partially surrounded by at least one housing. For example, the humidity sensor can also consist of several components, for example with several independent housings. The humidity sensor can, for example, be at least one capacitive sensor, in particular at least one capacitive humidity sensor, and / or at least one lambda probe.

[0023] According to the invention, the humidity sensor comprises at least one sensor element for detecting a proportion of a gas component in the gas mixture. The sensor element can in principle be any device designed to detect the proportion of the gas component in the gas mixture. Particularly preferably, the sensor element can be at least one lambda probe. For example, the determination of the humidity parameter, in particular at least one humidity determination, can be carried out at least partially with the lambda probe. The detection of the proportion of the gas component in the gas mixture can in principle be a quantitative and / or qualitative detection. The proportion can, for example, be a percentage and / or a volume fraction and / or a partial pressure and / or an absolute pressure and / or a molar fraction.The gas component can in principle be any gas, for example an atomic gas or a molecular gas. The gas component can particularly preferably be oxygen. For example, the gas component can also be nitrogen and / or at least one nitrogen compound, for example at least one nitrogen oxide. The sensor element can particularly preferably be a lambda probe, for example a broadband lambda probe. The proportion of the gas component in the gas mixture can particularly preferably be an oxygen partial pressure p. O2 act.

[0024] Furthermore, the humidity sensor comprises at least one pressure sensor for detecting a total pressure of the gas mixture. The pressure sensor can, in principle, be any device configured to detect at least one pressure parameter, for example the total pressure of the gas mixture, in particular at at least a portion of the humidity sensor. The detection of the total pressure can, in principle, involve a qualitative and / or quantitative, preferably quantitative, detection of the total pressure of the gas mixture. The total pressure can preferably be an air pressure p.

[0025] The device further comprises at least one temperature sensor for detecting a temperature of the gas mixture. For example, the temperature sensor can also detect multiple temperatures of the gas mixture. The temperature sensor can, in principle, be any device that is configured to detect at least one temperature of the gas mixture. The detection can, in principle, be qualitative and / or quantitative, preferably quantitative. The temperature of the gas mixture can be at least a temperature of a portion of the gas mixture. The temperature of the gas mixture can preferably be an air temperature T Luft act.

[0026] The sensor element and / or the pressure sensor and / or the temperature sensor can be at least partially mechanically and / or electrically connected to one another. For example, they can be at least partially integrated into at least one housing. For example, the pressure sensor and / or the sensor element and / or the temperature sensor can also be designed to be at least partially separate from one another. Particularly preferably, the proportion of the gas component in the gas mixture and / or the total pressure and / or the temperature of the gas mixture can be detected at the same location on the humidity sensor or within the smallest possible area of ​​the humidity sensor. In principle, the proportion of the gas component in the gas mixture and / or the total pressure and / or the temperature of the gas mixture can also be detected at least partially spatially separate from one another.The sensor element can be, for example, a lambda sensor, such as a broadband lambda sensor and / or a step-type sensor, as described, for example, in Robert Bosch GmbH: Sensors in Motor Vehicles, 1st edition 2010, pages 160-165. The sensor element can, in particular, be an electrochemical sensor element. In principle, the sensor element can also be another type of sensor element for detecting a proportion of a gas component. For example, the sensor element can also be an NO. x The sensor element can be a sensor. The sensor element can comprise at least one cell. The cell can, for example, comprise at least two electrodes connected to one another via at least one solid electrolyte. The sensor element can comprise at least one cavity and / or at least one reference gas chamber.

[0027] The pressure sensor can, for example, be a micromechanical pressure sensor. Examples of pressure sensors that can be used within the scope of the present invention are described in Robert Bosch GmbH: Sensors in Motor Vehicles, 1st edition 2010, pages 134-136. The temperature sensor can, for example, be at least one electronic component that can preferably convert a temperature into an electrical and / or electronic quantity. For example, the temperature sensor can be at least one temperature-dependent electrical resistor, for example a resistor with a negative temperature coefficient (NTC). Examples of temperature sensors that can be used within the scope of the present invention are described in Robert Bosch GmbH: Sensors in Motor Vehicles, 1st edition 2010, pages 102-111. In principle, other types of temperature sensors, such as analog thermometers, can also be used.In principle, any temperature sensor can be used. Particularly preferred is a temperature sensor suitable for use in the automotive sector. For example, the temperature sensor can be a temperature sensor that meets standard automotive requirements.

[0028] The device has at least one control. The control is configured to carry out the calibration method according to the invention, as described below, and / or a measuring method according to the invention, as described below. The device and / or the control can have at least one data processing device. For example, the data processing device can be integrated into the control, but for example the data processing device can also be arranged at least partially separately from the control. The control and / or the data processing device can, for example, be and / or be connectable at least partially to the humidity sensor. The control can be understood to mean a device which is configured to support and / or control at least one function of the device, in particular of the humidity sensor.“Connectable” can be understood, for example, as a property by which an electrical connection can be established or already exists. The control can comprise at least one voltage measuring device and / or at least one current measuring device for detecting at least one pump current and / or at least one pump voltage and / or at least one sensor signal, for example a sensor signal of the humidity sensor and / or the pressure sensor and / or the temperature sensor and / or the sensor element, for example alternatively or additionally also for regulating a voltage and / or a current. The control and / or the humidity sensor and / or the sensor element and / or the pressure sensor and / or the temperature sensor can have at least one application device. The application device can in particular comprise at least one voltage source and / or at least one current source.For example, the application device can be configured to apply at least one electrical current, for example a pumping current, and / or at least one electrical voltage, for example a pumping voltage, to the humidity sensor and / or the sensor element and / or the pressure sensor and / or the temperature sensor and / or at least a part of the device.

[0029] A further aspect of the present invention comprises a calibration method for calibrating a humidity sensor for detecting at least one humidity parameter of a gas mixture. The humidity sensor and / or the humidity parameter and / or the gas mixture can be, for example, a humidity sensor and / or a humidity parameter and / or a gas mixture as described above. The humidity sensor comprises at least one sensor element, in particular an oxygen sensor, particularly preferably a lambda probe, for detecting a proportion, for example a percentage proportion and / or a partial pressure, of a gas component, in particular oxygen, in the gas mixture. The sensor element can be, for example, a lambda probe, in particular a broadband lambda probe. The humidity sensor further comprises at least one pressure sensor for detecting a total pressure of the gas mixture.The pressure sensor may be required, for example, especially when using a lambda sensor as a humidity sensor. During the calibration process, at least one temperature of the gas mixture is measured, for example, at the sensor element, in particular at at least one humidity measuring point.

[0030] At least one first saturation parameter is determined from the temperature of the gas mixture. The first saturation parameter can, for example, be any saturation parameter. The saturation parameter can, for example, be a parameter that characterizes a saturation of the gas mixture with a liquid, in particular with water. For example, the saturation parameter can be a dew point temperature and / or a saturation vapor pressure, for example a saturation vapor pressure p s, and / or a saturation temperature and / or a condensation temperature and / or a condensation vapor pressure and / or a vapor saturation pressure. For example, the first saturation parameter can be deduced from the temperature of the gas mixture, in particular by calculating and / or determining the first saturation parameter from the temperature of the gas mixture and a known relationship between the temperature and the saturation parameter, preferably the first saturation parameter. The known relationship can be, for example, the Antoine equation and / or a stored curve and / or a stored table and / or another relationship. The relationship can be, for example, an empirical and / or semi-empirical and / or analytical relationship.The Antoine equation is usually a relationship between temperature and the saturation parameter, for example, a saturation vapor pressure, preferably the first saturation parameter, especially for pure substances. The Antoine equation is derived from the Clausius-Clapeyron equation. The first saturation parameter, especially the saturation vapor pressure p, can be determined from the Antoine equation. s , can be calculated: p1=ps=eA−BC+TAir, where A, B and C are parameters, in particular empirical substance-specific parameters, and T Luft is the temperature of the gas mixture.

[0031] At least one second saturation parameter is detected, wherein the second saturation parameter is detected using the sensor element and / or the pressure sensor. The pressure sensor is particularly necessary when using a lambda probe as a humidity sensor. The second saturation parameter can also be a saturation parameter as described above. For example, the second saturation parameter can be at least one saturation vapor pressure and / or at least one dew point temperature. For example, the second saturation parameter can be determined from a proportion of a gas component of the gas mixture detected by the sensor element, for example an oxygen proportion, preferably the oxygen partial pressure p O2, and from a total pressure measured by the pressure sensor, preferably the air pressure p, calculated and / or determined by a known relationship. The known relationship can be a relationship as described above in the prior art. For example, when using a sensor element as a humidity sensor, particularly preferably when using a lambda probe as a humidity sensor, the second saturation parameter can be p2=ps=p−pO2⋅(1+xN2xO2) act, with p, the total pressure, for example an air pressure, p O2 , the proportion of the gas component in the gas mixture, in particular the oxygen partial pressure, x N2 , a, preferably constant, proportion of nitrogen in the gas mixture and x O2 , a known proportion of oxygen in the gas mixture.

[0032] The humidity sensor is calibrated by comparing the first saturation parameter with the second saturation parameter. The comparison can in principle be a method that determines an equality and / or an inequality and / or at least one commonality and / or at least one difference between the first saturation parameter and the second saturation parameter. The comparison can in particular be carried out by at least one mathematical operation, for example at least one subtraction and / or at least one division. The terms “calibration” and / or “calibration” can in particular be understood to mean an adaptation and / or compensation for aging effects and / or a calibration of the device. Calibration can in particular be understood to mean a method by which the humidity parameter can be determined more precisely, in particular more accurately.

[0033] The calibration method will be explained below primarily based on the detection of the humidity parameter, in particular a humidity measurement, using a lambda sensor, but can also be suitable for other measurement principles. The calibration method according to the invention can, in particular, correct aging of at least a part of the humidity sensor, for example, the lambda sensor, and a related change in the detected humidity parameter and / or a change in a sensor value, for example, of the humidity sensor.

[0034] The calibration method is carried out by at least one controller. The controller can be at least partially part of the humidity sensor and / or the sensor element, but can also be arranged separately from the humidity sensor and / or the sensor element. The controller can, for example, be at least part of an engine control system, which can preferably be arranged separately from the humidity sensor. The expression “carried out by at least one controller” can be understood, for example, to mean that the calibration method is carried out independently, preferably without operation by a user. The calibration method according to the invention and / or the measuring method according to the invention can be at least partially, preferably entirely, an on-board adaptation method.An on-board adaptation method can be understood, for example, as a calibration which is and / or can be carried out independently by the humidity sensor and / or by the control system and / or by the device, in particular without external intervention. The calibration method can, for example, be designed as an online method. The calibration method can preferably be carried out in special operating phases. The calibration method can, for example, be carried out in operating phases during which at least part of the gas mixture and / or the humidity sensor can be cooled and / or during which the gas mixture is ambient air. The calibration method can, for example, be carried out during almost every shutdown process.In particular, the calibration method according to the invention and / or the measuring method according to the invention can be used to correct an aging of the lambda probe and / or an aging of the humidity sensor and an associated change in the humidity parameter and / or a sensor value.

[0035] The second saturation parameter is determined from a total pressure of the gas mixture detected by the pressure sensor and from a proportion of the gas component in the gas mixture detected by the sensor element, in particular when the humidity parameter, for example humidity, is detected using the sensor element, preferably the lambda probe. In principle, the humidity sensor can be any sensor for detecting the humidity parameter. The total pressure can, in particular, be an air pressure. The total pressure can, in particular, be composed of various partial pressures, for example the oxygen partial pressure and / or the nitrogen partial pressure and / or the vapor partial pressure. For example, the total pressure can be calculated by adding various partial pressures detected by the pressure sensor and / or the sensor element.For example, the total pressure can also be detected directly by the pressure sensor. The proportion of the gas component detected by the sensor element can in particular be an oxygen proportion, for example an oxygen partial pressure. The oxygen partial pressure and / or the oxygen proportion can in particular be detected by the lambda probe, for example by a broadband lambda probe. For example, to determine the second saturation parameter, the second saturation parameter can be deduced from the total pressure of the gas mixture and from the proportion of the gas component by using the known relationship mentioned above, for example the Antoine equation. For example, the second saturation parameter can be determined empirically, semi-empirically or analytically and / or calculated and / or stored. From the second saturation parameter, for example, a relative air humidity Φ can be determined. Luftbe determined, in particular by the relationship ΦAir=p2ps=p2p1.

[0036] In the comparison, a difference between the second saturation parameter and the first saturation parameter can be determined. The difference can particularly preferably be the result of a subtraction between the second saturation parameter and the first saturation parameter. For example, before the subtraction, the first saturation parameter and / or the second saturation parameter can be multiplied by at least one pre-factor. For example, the difference can also be multiplied by at least one pre-factor. The pre-factor can be constant, but can also depend, for example, on at least one other parameter, for example at least one temperature. From the difference, at least one correction function can be determined as a function of the temperature of the gas mixture. The correction function can, for example, be at least one correction value and / or at least one correction line.The correction function can, for example, be composed of several correction values, particularly at different temperatures of the gas mixture. The correction function and / or the correction line can be created and / or extended by extrapolation, for example, to temperatures of the gas mixture, particularly high temperatures, which cannot be adjusted during the calibration procedure, at least not in a saturated atmosphere.

[0037] The correction function can be multiplied by at least one factor. For example, the factor can be 1. In principle, the factor can be any number, especially a number < 1. The factor can, for example, be predefined. The factor can be a constant factor, but can also be a factor that depends, for example, on the temperature of the gas mixture. The factor can, for example, be calculated during the calibration process, for example, by the control system.

[0038] The factor can, for example, be multiplied by the correction function by the control. Furthermore, at least one offset can be subtracted from or added to the correction function. A correction value, in particular a correction value of the correction function, can be determined, for example, by calculating an average from various correction values ​​for a gas mixture temperature, for example, also with associated error bars and / or standard deviations.

[0039] At least one temperature sensor can be used to detect the temperature of the gas mixture. The temperature sensor can be a component of the sensor element and / or the humidity sensor and / or the pressure sensor, but can also be designed independently of the humidity sensor and / or the pressure sensor and / or the sensor element. The temperature sensor can also be referred to, for example, as a gas mixture temperature sensor. The temperature sensor can be, for example, at least one temperature measuring resistor, such as a resistor with a negative temperature coefficient (NTC resistor).

[0040] Particularly preferably, the temperature at the humidity sensor and / or at the sensor element can be reduced during calibration. The temperature can be reduced, in particular, by cooling. The cooling can be achieved, for example, by the ambient air, but can alternatively or additionally also be achieved, for example, by active cooling, for example, by at least one Peltier element and / or by connecting, in particular, a measuring section, for example comprising at least the sensor element and / or the humidity sensor, to a cooling circuit. The temperature can be reduced, in particular, starting from an operating temperature of the humidity sensor and / or a highest possible temperature of the humidity sensor, in particular a highest possible temperature of at least part of the device during the detection of the humidity parameter. The temperature can be reduced, in particular, until the temperature reaches and / or falls below the saturation temperature.

[0041] For example, at least a portion of the humidity sensor can be passed through by a gas mixture of known composition before and / or during calibration. For example, at least a portion of the humidity sensor can be passed through by air before and / or during calibration. The air can preferably be ambient air. The air can, in particular, be a gas mixture with a predetermined and / or known composition, in particular with a known oxygen-to-nitrogen ratio.

[0042] The first saturation parameter and / or the second saturation parameter can each be recorded repeatedly over a measurement period. For example, the first saturation parameter and / or the second saturation parameter can be recorded continuously or discontinuously, for example as a function of the respective measurement time over a measurement period and / or as a function of the temperature of the gas mixture. For example, a saturation vapor pressure curve for the first saturation parameter and / or the second saturation parameter can be recorded as a function of time and / or as a function of a dew point temperature. For example, a dew point temperature curve can also be recorded as a function of time for the first saturation parameter and / or for the second saturation parameter.

[0043] The gas mixture and / or the sensor element and / or the humidity sensor can be cooled during the measurement period. The measurement period can in particular be a period of time, for example a period of time of less than 5 hours, in particular of less than 2 hours, particularly preferably of less than 1 hour. The shortest possible period of time can be advantageous. The gas mixture and / or the humidity sensor and / or the sensor element can preferably be cooled at least until at least a saturated atmosphere of the gas mixture is present. Preferably, the gas mixture and / or the sensor element and / or the humidity sensor can be cooled even further. During this cooling, the first saturation parameter and / or the second saturation parameter can preferably be determined several times.

[0044] The first saturation parameter and the second saturation parameter can, for example, be recorded essentially simultaneously. The expression "essentially simultaneously" can be understood to mean that the first saturation parameter and the second saturation parameter are recorded within 10 minutes, preferably within one minute, particularly preferably within 10 seconds. In principle, the first saturation parameter and the second saturation parameter can also be recorded consecutively, for example at an interval of less than 1 hour, preferably less than 30 minutes. Particularly preferably, the first saturation parameter and the second saturation parameter can be recorded simultaneously.

[0045] The cooling of the gas mixture and / or the sensor element and / or the humidity sensor can preferably be carried out continuously, but can also be carried out discontinuously, for example in stages. For example, the cooling can involve a substantially exponential decrease in temperature. The cooling can be carried out, for example, by contact with the ambient air, but can also be carried out by active cooling, for example by at least one cooling device, such as a Peltier element, and / or by connecting, in particular the measuring section, to a cooling circuit.

[0046] The first saturation parameter and / or the second saturation parameter can preferably be detected when the atmosphere of the gas mixture is saturated. The saturated atmosphere of the gas mixture can be a state of the gas mixture in which the liquid and gaseous phases are in equilibrium. For example, the saturated atmosphere of the gas mixture can be a gas mixture at saturation vapor pressure. The saturation vapor pressure can preferably be the pressure of the vapor phase of the gas mixture at which a liquid and a vapor phase are in equilibrium. The saturation vapor pressure can preferably depend solely on the temperature of the gas mixture.

[0047] In the saturated atmosphere of the gas mixture, the evaporation of a liquid can be quantitatively equivalent to the condensation of the gas. For example, the saturated atmosphere of the gas mixture can be a state of the gas mixture at boiling pressure and / or boiling temperature.

[0048] The first saturation parameter and the second saturation parameter can be determined from a minimum measurement time. At the minimum measurement time, a saturated atmosphere is particularly preferably present in the gas mixture. The minimum measurement time can in particular be a time period which characterizes the beginning of the measurement period. The minimum measurement time can in particular be a time at which a saturated atmosphere of the gas mixture, particularly preferably a saturation vapor pressure, is present for the first time in the calibration method and / or during cooling. During the measurement period, in particular after the minimum measurement time, a saturated atmosphere can be present in the gas mixture, preferably continuously.

[0049] Furthermore, at least one ambient temperature of the humidity sensor can be detected by means of at least one ambient temperature sensor. The ambient temperature sensor can in principle be a device which is set up to detect the ambient temperature, in particular a temperature of the environment. The ambient temperature sensor can, for example, be designed like the temperature sensor for detecting the temperature of the gas mixture. For example, the ambient temperature sensor can be an NTC. The ambient temperature can, in particular, be a temperature which has an environment of the humidity sensor, in particular an environment which can cool the humidity sensor and / or the sensor element and / or the gas mixture during the measuring period and / or until the minimum measuring time is reached. For example, the ambient temperature can be a temperature of the ambient air.The ambient temperature can, for example, be an average temperature, for example averaged over different measuring times and / or measuring locations, in particular in the vicinity of the humidity sensor.

[0050] The minimum measurement time can be determined during the calibration method according to the invention. Preferably, the minimum measurement time can be calculated during the calibration method according to the invention. The minimum measurement time can be determined, for example, using the ambient temperature. Particularly preferably, the minimum measurement time can be determined using the ambient temperature and / or at least one vapor pressure and / or the temperature of the gas mixture. The minimum measurement time t MMZPcan be determined, for example, by calculating and / or estimating the time at which cooling has progressed to the point where the gas mixture is saturated, for example, using conventional heat balance relations. The minimum measurement time can be calculated, for example, by: tMMZP=tSD−τ⋅ln[BA−ln pD,SD−C−TAmbTSD−TAmb], with t SD , the time of commencement of the calibration procedure, in particular a shutdown time, τ, a cooling constant typical for the vehicle, the constants A, B and C, the saturation vapor pressure at the shutdown time p D,SD and the temperature of the gas mixture at the start of the calibration procedure, especially during the shutdown, T SD and the ambient temperature T Amb. In general, a shutdown is understood here to mean a process in which a normal operating mode of the device and / or the humidity sensor is stopped. For example, this can be the deactivation of a measuring function and / or a heater and / or the operation of a fuel cell system. Accordingly, a measured variable referred to as a shutdown measured variable refers to the respective measured variable at the time of the shutdown, i.e., at the shutdown time. For example, the shutdown temperature is the temperature at the shutdown time.

[0051] The minimum measurement time can also be determined using at least one initial temperature at the sensor element. The initial temperature can be, in particular, the temperature of the gas mixture at the beginning of the calibration procedure, especially at the beginning of cooling. The initial temperature can, for example, be the shutdown temperature T SDThe initial temperature can, in particular, be the temperature of the gas mixture at the beginning of the calibration. For example, an initial temperature can also be determined at the humidity sensor to determine the minimum measurement time.

[0052] A further aspect of the present invention comprises a measuring method for detecting at least one humidity parameter of a gas mixture. The humidity parameter can be a humidity parameter as described above. The gas mixture can also be a gas mixture as described above. At least one humidity sensor and at least one control are used in the measuring method. The humidity sensor can, for example, have at least one sensor element for detecting a proportion of a gas component in the gas mixture. The humidity sensor and / or the sensor element can be configured as described above. The humidity sensor can optionally have at least one pressure sensor for detecting a total pressure of the gas mixture. The humidity parameter of the gas mixture is determined in at least one normal operating mode.For example, in the normal operating mode, the humidity parameter of the gas mixture can be determined by means of a proportion of the gas components detected by the sensor element and a total pressure of the gas mixture detected by the pressure sensor. The proportion of the gas component can in particular be an oxygen partial pressure. Optionally, the humidity sensor can comprise at least one temperature sensor, wherein the temperature sensor can be configured to determine the temperature of the gas mixture. A relative humidity, preferably a relative air humidity, can be detected from the temperature of the gas mixture and the total pressure and the proportion of the gas component. The calibration method described above can be carried out in at least one calibration mode. The detection of the humidity parameter, in particular during the normal operating mode, can preferably be carried out at a different time than the calibration method.In principle, the recording of the humidity parameter and / or the normal operating mode can also overlap at least partially with the calibration mode.

[0053] In the measuring method, at least one temperature sensor can also be used to detect the temperature of the gas mixture in the normal operating mode. The humidity parameter can be determined using the temperature of the gas mixture in the normal operating mode. The humidity parameter can, in particular when using the temperature sensor, be, for example, a relative humidity and / or other measured variables, such as a proportion of the gas component and / or a total pressure. The relative humidity Φ Luftcan be calculated, in particular using the above formulas, from the total pressure of the gas mixture detected by the pressure sensor, in particular an air pressure p, the proportion of the gas component in the gas mixture detected by the sensor element, preferably an oxygen partial pressure p O2 , and the temperature of the gas mixture T detected by the temperature sensor Luft through: oSteam=p−pO2⋅(1+xN2xO2)and ps=eA−BC+TAirand ΦAir=pSteamps, with xN2xO2, a known ratio of nitrogen to oxygen, preferably 0.79 / 0.21.

[0054] The temperature sensor can be permanently integrated into or on the humidity sensor. Alternatively, the temperature sensor can be removed from the humidity sensor or deactivated at least temporarily during normal operation and / or calibration mode.

[0055] In an embodiment of the measuring method according to the invention without a temperature sensor during normal operation, the humidity parameter can be, for example, the vapor pressure p Dampf In one embodiment of the measuring method according to the invention with a temperature sensor, the humidity parameter can be, for example, the vapor pressure p Dampf and / or the vapor saturation pressure p s and / or the relative humidity Φ Luft be recorded.

[0056] Calibration mode can be performed repeatedly. For example, calibration mode can be performed alternately with normal operation mode. For example, calibration mode can be performed before commissioning the humidity sensor.

[0057] The calibration mode can be repeated at least once after a specific time interval, in particular after the previous calibration mode. The specific time interval can be a predetermined time interval and / or a time interval calculated in the normal operating mode and / or in the calibration mode. The time interval can, for example, be an interval of less than one year, preferably less than one month. The calibration mode can particularly preferably be repeated monthly. The time interval can depend on a particular application. In a vehicle, the time interval could, for example, be shorter than one month. The time interval can, for example, be determined by a tolerable sensor deviation. Small tolerable deviations can, for example, lead to shorter time intervals between the calibration processes.

[0058] The calibration method according to the invention and / or the measuring method according to the invention and / or the device according to the invention can have a multitude of advantages over known calibration methods and / or known measuring methods and / or known devices. The calibration method according to the invention and / or the measuring method according to the invention and / or the device according to the invention improve the accuracy of detecting a humidity parameter of a gas mixture and / or are suitable for automotive applications. The humidity sensor can be calibrated and / or aging of the humidity sensor, for example of at least one lambda probe, and a related change in a sensor value, for example of the humidity parameter, can be corrected. Short description of the drawings

[0059] Embodiments of the invention are illustrated in the following figures and are explained in more detail in the following description.

[0060] They show: Fig. 1 an embodiment of a device according to the invention; Fig. 2A and Fig. 2B shows an embodiment of a calibration method according to the invention; Fig. 3A and Fig. 3B shows a further embodiment of the calibration method according to the invention; Fig. 4 a flowchart of an embodiment of the calibration method according to the invention; Fig. 5 shows an embodiment of a fuel cell system in which an embodiment of the device according to the invention can be used and / or embodiments of the calibration method according to the invention and / or the measuring method according to the invention can be carried out; Fig. 6 Influences of a control of a humidity parameter by means of an embodiment of a device according to the invention; Fig. 7A and Fig. 7B Influences of a control of a humidity parameter by means of an embodiment of the device according to the invention on a fuel cell system; Fig. 8 Tolerance band and tolerance chain of an embodiment of a humidity sensor according to the invention; and Fig. 9A, Fig. 9B, Fig. 9C, Fig. 9D and Fig. 9E Measurement errors and tolerance chains of a humidity sensor according to the invention. Embodiments of the invention

[0061] Fig. 1 shows an embodiment of a device 110 according to the invention for detecting at least one humidity parameter of a gas mixture. The device 110 comprises at least one humidity sensor 112. The humidity sensor 112 comprises at least one sensor element 114 for detecting a proportion of a gas component in the gas mixture. The humidity sensor 112 further comprises at least one pressure sensor 116 for detecting a total pressure of the gas mixture. The device 110 further comprises at least one temperature sensor 118 for detecting the gas mixture. The device 110 has at least one controller 120. The controller 120 is configured to carry out a calibration method according to the invention and / or a measuring method according to the invention. The sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118 and / or the humidity sensor 112 can be connected to the controller 120 via at least one interface 122.The sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118 can be connected to one another, for example mechanically and / or electrically. The humidity sensor 112 and / or the sensor element 114 and / or the pressure sensor 116 can be designed separately from one another, but can also be integrated into the humidity sensor 112. The proportion can be, for example, a concentration and / or a volume fraction and / or a partial pressure, particularly preferably an oxygen partial pressure. The sensor element 114 can preferably be a broadband lambda probe. For example, the sensor element 114 can also be an NO. x-Sensor. The sensor element 114 can preferably be a ceramic sensor element 114, which is based on the use of electrolytic properties of certain solid electrolytes 126, i.e., on the ion-conducting properties of these solids. The sensor element 114 can have at least one pump cell 124 with at least two pump electrodes 128 connected by at least one solid electrolyte 126. The pump cell 124 can in principle be any electrochemical cell comprising at least two electrodes 129, for example pump electrodes 128, and the solid electrolyte 126, wherein the cell is preferably operated in a pumping mode. The solid electrolyte 126 can, in particular, be a ceramic solid. The solid electrolyte 126 can preferably have ion-conducting properties, in particular oxygen ion-conducting properties.Examples of such solid electrolytes 126 are zirconium dioxide-based solid electrolytes 126, such as yttrium-stabilized zirconium dioxide (YSZ) and / or scandium-doped zirconium dioxide (ScSZ). A pump cell 124 can, in particular, be a cell through which an ion current can flow and / or be driven, wherein conversions from an ion current into an electron current can take place at the pump electrodes 128 of the pump cell 124 by oxidation and / or reduction. The pump electrodes 128 can be constructed at least partially from at least one conductive material, for example at least one metallic material. A conversion of an ion current into an electron current can take place on at least one surface of a pump electrode 128.Of the pump electrodes 128, a first pump electrode is exposed to the gas mixture, and a second pump electrode is separated from the gas mixture by at least one porous diffusion barrier 130 and arranged in a cavity 132. The pump electrodes 128 can thus comprise at least one first pump electrode and at least one second pump electrode. The first pump electrode and / or the second pump electrode can, in principle, be configured like a pump electrode 128.

[0062] The terms “first” and “second” serve as a mere designation in the context of the present invention and in particular do not indicate a sequence.

[0063] Furthermore, the designations “first” and “second” do not provide any information as to whether, for example, further pump electrodes or electrodes 129 are included in the pump electrodes 128, for example at least one third pump electrode and / or at least one reference electrode and / or at least one Nernst electrode.

[0064] The device 110 can accordingly comprise, for example, at least one third pump electrode and / or at least one third electrode, for example, at least one reference electrode. Furthermore, the sensor element 114 can comprise at least one Nernst electrode, i.e., an electrode 129, which can detect a Nernst potential, for example in combination with at least one reference electrode. The diffusion barrier 130 can be understood, for example, as a layer made of a material that suppresses a flow of the gas and / or a fluid and / or the gas mixture and / or the gas component, while the layer promotes a diffusion of the gas and / or the fluid and / or the gas mixture and / or the gas component and / or ions.The cavity 132 can be understood as a space within the sensor element 114, which can be supplied with the gas component and / or the gas mixture, for example, via at least one gas access path 140 and / or via the diffusion barrier 130. The cavity 132 can be a chamber, for example. The sensor element 114 can further comprise at least one reference gas space 142 and / or at least one reference gas channel. The device 110 and / or the control 120 can have at least one data processing device 144. For example, the data processing device 144 can be integrated into the control 120, but can also be arranged at least partially separately from the control 120, for example.The controller 120 and / or the data processing device 144 can be connected and / or connectable, for example, to the sensor element 114 and / or to the pressure sensor 116 and / or to the temperature sensor 118 and / or to the humidity sensor 112. The controller 120 can be understood as a device that is configured to support and / or control at least one function of the device 110, for example, of the sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118 and / or the humidity sensor 112. "Connectable" can be understood, for example, as a property in which an electrical connection can be established or already exists.The controller 120 can comprise at least one voltage measuring device and / or at least one current measuring device for detecting at least one electrical current and / or at least one electrical voltage and / or for regulating at least one electrical current and / or for regulating at least one electrical voltage. Alternatively or additionally, the controller 120 and / or the sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118 and / or the humidity sensor 112 can have at least one application device. The application device can in particular comprise at least one voltage source and / or at least one current source. For example, the application device can be configured to apply at least one electrical current and / or at least one electrical voltage to the humidity sensor 112 and / or the sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118.The device 110 can permanently include the temperature sensor 118. For example, the temperature sensor 118 can also be reversibly included in the humidity sensor 112, for example, for a particular operating state of the device 110, for example, during the calibration method according to the invention. During the measurement method according to the invention, the temperature sensor 118 can be at least temporarily removed from the device 110 and / or can be deactivated.

[0065] The device 110 can optionally comprise at least one ambient temperature sensor 146 for determining at least one ambient temperature of an environment of the humidity sensor 112 and / or the device 110 and / or the sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118, in particular to determine a minimum measurement time within the calibration method according to the invention. Other embodiments of the device 110 are possible in principle. <h2 style=";text-align:left;direction:ltr">

[0066] <h2 style=";text-align:left;direction:ltr"> In den<h2 style=";text-align:left;direction:ltr"> Fig. <h2 style=";text-align:left;direction:ltr"> 2A,<h2 style=";text-align:left;direction:ltr"> Fig. <h2 style=";text-align:left;direction:ltr"> 2B,<h2 style=";text-align:left;direction:ltr"> Fig. <h2 style=";text-align:left;direction:ltr"> 3A,<h2 style=";text-align:left;direction:ltr"> Fig. <h2 style=";text-align:left;direction:ltr"> 3B and<h2 style=";text-align:left;direction:ltr"> Fig. 4 shows exemplary embodiments of the calibration method according to the invention for calibrating a humidity sensor 112, as described above, for example, for detecting at least one humidity parameter of a gas mixture. The humidity sensor 112 comprises at least one sensor element 114 for detecting a proportion of a gas component in the gas mixture. The humidity sensor 112 further comprises at least one pressure sensor 116 for detecting a total pressure of the gas mixture. During the calibration method, a temperature of the gas mixture is detected. At least one first saturation parameter is deduced from the temperature of the gas mixture. At least one second saturation parameter is detected. For example, the second saturation parameter can be detected using the sensor element 114 and the pressure sensor 116.The terms "first" and / or "second" are to be understood as mere designations, in particular without reference to a sequence and without reference to whether additional saturation parameters, for example at least a third saturation parameter, can possibly be detected in the calibration method. Humidity sensor 112 is calibrated by comparing 162 the first saturation parameter with the second saturation parameter. The calibration method is carried out by at least one control unit 120. The calibration method according to the invention can, in particular, be an on-board adaptation method.

[0067] The second saturation parameter is determined from a total pressure of the gas mixture detected by pressure sensor 116 and from a proportion of the gas component in the gas mixture detected by sensor element 114, in particular when using sensor element 114, preferably when using the lambda probe. In comparison 162, a difference between the second saturation parameter and the first saturation parameter can be determined, wherein at least one correction function depending on the temperature of the gas mixture can be determined from the difference. The correction function can be multiplied by at least one factor. At least one temperature sensor 118 can be used to detect the temperature of the gas mixture.

[0068] The temperature at the humidity sensor 112 and / or at the sensor element 114 can be reduced during calibration and / or before calibration. At least a portion of the humidity sensor 112 can be passed through by air during calibration and / or before calibration. The first saturation parameter and the second saturation parameter can each be recorded repeatedly over a measurement period. The gas mixture and / or the sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118 and / or the humidity sensor 112 can be at least partially cooled during the measurement period. The first saturation parameter and the second saturation parameter can be recorded in a saturated atmosphere of the gas mixture. The calibration method can also be called a calibration method, for example. After a shutdown, for example a shutdown, of a fuel cell system, in particular a fuel cell system as in Fig. As shown in Figure 5, the fuel cell system and / or the humidity sensor 112 can cool down. At certain locations, for example, between a humidifier outlet and a cathode inlet on a supply air side, condensation can occur even after a slight cooling due to high air humidity. During cooling to condensation, the dew point temperature usually corresponds to the temperature of the gas mixture, in particular the current air temperature. This equality of the temperature of the gas mixture with the dew point temperature during condensation can be used to calibrate the sensor element 114 and / or the humidity sensor 112 and an associated measuring method according to the invention, in particular a humidity measuring method.The calibration method according to the invention can, for example, always be used when, in addition to the humidity sensor 112, comprising, for example, the sensor element 114 and the pressure sensor 116, a temperature sensor, for example the temperature sensor 118, is also present at the corresponding measuring point, for example at least partially at the cavity 132 and / or at the gas access path 140 of the sensor element 114, and condensation is highly likely to occur in certain operating ranges.

[0069] The first saturation parameter and / or the second saturation parameter can preferably be measured from a minimum measurement time t MMZPbe determined. At the minimum measurement time, a saturated atmosphere is preferably present in the gas mixture. At least one ambient temperature of an environment of the humidity sensor 112 can be detected by means of at least one ambient temperature sensor 146. The ambient temperature sensor 146 can be part of the device 110 and / or the humidity sensor 112 and / or the sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118, but can also be arranged and / or configured at least partially separately from the aforementioned elements. The ambient temperature sensor 146 can, for example, be at least partially integrated into the device 110 and / or in the humidity sensor 112 and / or in the sensor element 114 and / or in the pressure sensor 116 and / or in the temperature sensor 118. For example, the ambient temperature sensor 146 can also be configured at least partially separately from the aforementioned elements.The ambient temperature sensor 146 may be at least partially connected to the controller 120, for example via at least one interface 122, as shown in FIG. Fig. 1. The minimum measurement time can be determined using the ambient temperature. The minimum measurement time can also be determined using at least one initial temperature, for example, at the sensor element 114 and / or at the humidity sensor 112. The initial temperature can preferably be detected by the temperature sensor 118.

[0070] In Fig. 2A, temperatures T of the device 110, in particular of an air system 166 of a fuel cell, are plotted over a time t. The temperatures T can be, for example, an air temperature T Luft act. At time t SD In particular, a shutdown can be carried out. At time t SDThis can preferably be the time at which the calibration process begins, in particular a shutdown time. During the shutdown, for example, a normal operating mode of the device 110 and / or the humidity sensor 112 can be stopped. After the shutdown, the device 110, in particular the humidity sensor 112 and / or the air system 166 of the fuel cell, can usually be briefly flowed through with air, preferably without further reactions, for example between oxygen and hydrogen, being able to take place. It can therefore preferably be assumed that a ratio of an oxygen concentration to a nitrogen concentration corresponds to that of the environment and, for example, that no oxygen-depleted air is present in the device 110 and / or in the air system 166 of the fuel cell, also called the system, for example.Thus, a quotient of the nitrogen concentration and the oxygen concentration and / or of a nitrogen fraction and an oxygen fraction can preferably be considered as constant, in particular in order to determine this ratio according to an equation for p. Dampf ; as stated above, to be considered constant. After the shutdown, the device 110 and / or the air system 166 of the fuel cell preferably cools down, which results, for example, in the temperature of the gas mixture, in particular a temperature at a measuring point, in particular at a measuring point of the humidity sensor 112, decreasing, as for example in Fig. 2A in line 148. At the humidity sensor 112, for example at the measuring point, a high relative humidity with a real dew point T TP,real , as in Fig. 2A in line 150. If the temperature falls below the dew point temperature of the gas mixture, especially at the measuring point, condensation may occur preferentially there, whereby the temperature T and the real dew point temperature T TP,real from time t Mess,Start , for example at the minimum measurement time t MMZP are identical. Preferably, at any time, in particular at any time after the minimum measurement time t MMZP , during the calibration method according to the invention, the humidity parameter, in particular a relative humidity, is measured, wherein the calibration method according to the invention also determines the dew point T TP,λ-Sonde , as in line 152 in Fig. 2A, which due to the already discussed sensor inaccuracies of T TP,real This deviation may, as described in Fig. 2B, are plotted against the temperature T and are calibrated as an adaptable correction line and are preferably stored when determining the humidity parameter, in particular a humidity, for example with the sensor element 114, in particular with the lambda probe. This correction line, as shown for example in Fig. 2B, may be temperature dependent. The correction line, as shown for example in Fig. 2B, can be extrapolated, for example, by a line 154. The time t Mess,Start and / or the temperature T(t Mess,Start ) and / or the minimum measurement time t MMZP , from which a calibration and / or an adaptation can preferably take place, can be determined by application in the vehicle and / or in the system, for example from empirical values ​​and / or from calculations and / or from a calculation within the scope of the calibration method according to the invention in the device 110.

[0071] First, calibration and / or correction of the humidity parameter measured by the humidity sensor 112, for example, the humidity measured by the lambda probe, may be possible for temperatures below an operating temperature, in particular of the humidity sensor 112, since cooling is required during calibration and / or adaptation, in particular down to a dew point. Correction of the detected humidity parameter, for example, a correction of the humidity measured by the lambda probe, in particular calibration, is preferably possible for temperatures below an operating temperature, since cooling, preferably down to the onset of condensation, is usually required during adaptation and / or calibration.The correction and / or calibration of the humidity parameter detection, in particular the humidity measurement, may nevertheless be possible at other, particularly higher, operating temperatures, since extrapolation of the correction characteristic and / or the correction value for the dew point typically does not result in excessive errors. For example, sensor-to-sensor deviations, which can also be eliminated with a high degree of probability through extrapolation, can be included in the lambda probe's tolerance. Alternatively or in addition to the extrapolation, calibration and / or adaptation can also be activated only when a highest possible expected operating temperature is reached before shutdown 156.If this should not occur over a longer period of time, a forced increase in the operating temperature for adaptation purposes may be possible, particularly in the calibration method according to the invention, before shutdown, in particular before the shutdown 156. If the system, for example the air system 166 of the fuel cell, is shut down at an elevated operating temperature, the correction and / or calibration, in particular of the humidity measured by the lambda probe, can preferably be carried out at all subsequent operating points in a lower standard temperature range, in particular at lower temperatures, preferably without extrapolation.

[0072] The correction line can be redetermined at specific intervals, for example, monthly. This can be used to correct, for example, an aging effect of the device 110 and / or the humidity sensor 112 and / or the sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118, in particular of a sensor, and, for example, a possibly associated change in a sensor value, for example, of the lambda probe.

[0073] In the Fig. 2A and Fig. 2B shows in particular a reduction of a measurement tolerance through calibration. From the Fig. 2A, for example, the temperature curves shown in Fig. The correction curve shown in Figure 2B can be created. Fig. 2A shows the shutdown of a system, wherein the system preferably comprises the device 110 according to the invention, and / or a cooling down after the shutdown (SD) 156. From t Mess,Startcondenses preferentially water vapor. For t > t Mess,Start applies T TP,real = T. Preferably, the humidity sensor 112, for example the lambda probe, provides a dew point for T TP,min,λ-Sonde <T TP,λ-Sonde <T TP,max,λ-Sonde . From the comparison 162, for example a comparison, between T TP,λ-Sonde and T TP,real a fault of the humidity sensor 112, for example the lambda sensor, ΔT TP,λ-Sonde , especially in Fig. 2B versus temperature T TP,real = T can be plotted, determined and / or corrected.

[0074] By increasing the operating temperature, particularly of the humidity sensor 112, particularly briefly, calibration and / or adjustment can also be performed for a normally lower operating temperature. Condensation in the system, for example, in the device 110, during cooling can be used to calibrate the humidity sensor 112, for example, the lambda sensor. Fig. 2A shows in particular the temperature at the humidity sensor 112 as well as a corresponding vapor pressure, expressed in particular as temperature, plotted over time t.

[0075] Fig. 3A shows a temperature drop after the time of shutdown t SD up to the minimum measurement time t MMZP , where Fig. 3B shows a corresponding curve of the vapor pressure. Fig. Figure 3A shows in particular the temperature T as a function of time t and Fig. 3B shows in particular the vapor pressure p Dampf depending on time t. After the shutdown 156, especially at time t SD , the device 110 and / or the system preferentially cools down, which usually results in the temperature, as in Fig. 3A, in the gas mixture, preferably at the measuring point, decreases, preferably from T SDIn the gas mixture and / or at the measuring point, a high relative humidity is usually present, whereby the gas mixture, for example, the air, is usually unsaturated. The vapor pressure p D,SD is therefore usually lower than the saturation vapor pressure p s at time t SD . Due to the cooling of the device 110 and / or the system, in particular at least a portion of the gas mixture, the humidity measuring point also cools down, in particular such that the saturation vapor pressure approaches the vapor pressure. The minimum measurement time t MMZP is usually achieved when p s and p D,SD are identical, especially if: ps,MMZP=pD,SD, preferably at temperature T MMZP at the minimum measurement time. The saturation vapor pressure can be preferably described by the so-called Antoine equation: ps,MMZP=eA−BC+TMMZP, For example, with the parameters A=11.74, B=3863.84, K and C= -43.7K. Rewriting the last two formulas yields: TMMZP=BA−lnpD,SD−C.

[0076] The cooling behavior can preferably follow an exponential decay, preferably depending on the prevailing temperature during the shutdown T SD and the ambient temperature T AMB : T=TAmb+(TSD−TAmb)⋅etτ.

[0077] To estimate the minimum measurement time, a typical cooling behavior of the device 110 and / or the humidity sensor 112 and / or the sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118 and / or the system and / or the air system 166 and / or the vehicle, generally of a system comprising the humidity sensor 112, can be used as a basis. From the temperature of the gas mixture T SD, in particular the temperature at the humidity measuring point, and the ambient temperature T Amb , at the time of the shutdown 156, in particular the shutdown process, a cooling curve can be calculated and / or simulated and / or simulated. By equating the last two formulas and simplifying, the minimum measurement time is preferably: tMMZP=tSD−τ⋅ln[BA−ln pD,SD−C−TAmbTSD−TAmb].

[0078] This equation can be used to calculate the minimum measurement time, in particular a value for a minimum measurement time, for typical operating conditions. In principle, another equation and / or a table can be used alternatively or additionally. The following values ​​can be used as examples: decay constant τ = 360 min, vapor pressure at the time of shutdown p D,SD = 0.160 bar, corresponding to approximately 50% relative humidity, T SD =70°C and T Amp=10°C. For these exemplary values, the result is t MMZP - t SD = 102 min.

[0079] At this time, preferably at the minimum measuring time, the control 120, for example a control unit of the vehicle, can be awakened and the temperature at the humidity measuring point T MMZP,mess and a vapor pressure p D,MMZP,mess recorded and / or measured. The vapor pressure, in particular a real vapor pressure, is equal to the saturation vapor pressure, especially during the calibration procedure from the minimum measurement time. It can therefore be determined, for example, from the recorded temperature of the gas mixture using the Antoine equation presented above and / or here: pD,MMZP,is=ps,MMZP=eA−BC+TMMZP,mess.

[0080] At P D,MMZP,ist In particular, it can be the first saturation parameter. For p D,MMZP,messIn particular, it can be the second saturation parameter. In the comparison 162 of the first saturation parameter with the second saturation parameter, for example, a sensor error can be calculated. The sensor error can, for example, be Δp D = p D,MMZP,ist - p D,MMZP,mess This sensor error, preferably a deviation, can be included as a correction value in a calculation chain of the humidity sensor 112, for example, as an offset. Preferably, the full correction value is not added, but rather multiplied beforehand by a correction factor, preferably with a correction factor < 1, typically in the range of 0.5. This can serve to increase the robustness of the calibration method, for example, an adaptation, against incorrect measurements.

[0081] In Fig. 4 shows an embodiment of the calibration method according to the invention, for example, at least partially designed as an adaptation algorithm, as a flow chart. Fig. The exemplary embodiment of the calibration method according to the invention, illustrated as a flowchart in Figure 4, begins in particular with the shutdown 156. During the shutdown 156, for example, a normal operating mode, in particular for detecting the humidity parameter, can be set and / or deactivated and / or the device 110 can be purged with air and / or subjected to heating and / or cooling. The shutdown 156 can, for example, be a first step of the calibration method.

[0082] In a further step, a waiting time 158 can be calculated, in particular as the difference between the minimum measurement time and the time of the shutdown t MMZP - t SD from T Amb and T SDbe carried out, for example as described above. In a further step, it can be checked, for example in the form of an algorithm, whether the minimum measurement time has been reached, in particular whether the condition t - t SD > t MMZP is met. If this condition is not met (N), it is preferable to wait, in particular until the condition is met (Y). If the condition is met (Y), the control 120, for example the control unit, is awakened, in particular in an awakening, where, for example, T and p Dampf , preferably T TP,real and P D,MMZP,mess, of the gas mixture, in particular at the humidity measuring point. This step can, for example, involve determining the first saturation parameter and the second saturation parameter 160. In a further step, the comparison 162 can preferably be carried out. In the comparison 162, for example, a calculation of an error of the humidity sensor 112 can be carried out, in particular from the first saturation parameter and the second saturation parameter, for example from the real vapor pressure p D,MMZP,ist , for example calculated from T TP,real , and a measured vapor pressure p D,MMZP,mess , as shown, for example, in the last two formulas. In a further step, for example, the calibration 164 can be carried out, for example as an adaptation of the humidity sensor 112. In the illustrated embodiment of the calibration method according to the invention according to Fig. 4 may in particular be an algorithm for adapting the humidity sensor 112 after the shutdown 156.

[0083] The calibration method according to the invention can generally be carried out in humidity measurements, in particular in the detection of at least one humidity parameter, in which in certain operating states, for example even after switching off the system and / or the device 110 and / or the humidity sensor 112 and / or the sensor element 114 and / or the pressure sensor 116 and / or the temperature sensor 118, condensation can be assumed with a high probability, in particular in the gas mixture, and in which the temperature of the gas mixture can also be determined.

[0084] In the calibration method according to the invention, in particular, the calculation of the minimum measurement time, for example, the time of a control unit (CU) awakening, can be performed. Furthermore, for example, a weakened correction of the humidity sensor tolerances can also be performed, in particular to increase the robustness of the calibration method, including, for example, an adaptation method.

[0085] The measuring method according to the invention for detecting at least one humidity parameter of a gas mixture utilizes at least one humidity sensor 112, in particular the humidity sensor 112 as described above, and at least one controller 120, also as described above. The humidity sensor 112 can, for example, have at least one sensor element 114, for example as described above, for detecting a proportion of a gas component in the gas mixture. The humidity sensor 112 can furthermore have at least one pressure sensor 116, for example as described above, for detecting a total pressure of the gas mixture. The humidity parameter of the gas mixture is determined in at least one normal operating mode.For example, in the normal operating mode, the humidity parameter of the gas mixture can be determined by means of a proportion of the gas component detected by the sensor element 114 and a total pressure of the gas mixture detected by the pressure sensor 116, in particular when using a lambda probe as the sensor element 114. In at least one calibration mode, the calibration method is carried out as described above.

[0086] In the measuring method, at least one temperature sensor 118 can further be used, for example as described above, to detect a temperature of the gas mixture in the normal operating mode. The humidity parameter can be determined using the temperature of the gas mixture in the normal operating mode. The calibration mode can be performed repeatedly in the measuring method. In the measuring method according to the invention, the calibration mode can be repeated at least after a certain time interval, for example, monthly.

[0087] Fig. 5 shows, in particular, an exemplary air system 166 of a fuel cell system, wherein the fuel cell system may comprise an embodiment of a device 110 according to the invention or at least be at least partially regulated by an embodiment of a device 110 according to the invention. The air system 166 of the fuel cell system may, in particular, be a system as already mentioned above. The device 110 may be comprised by the air system 166, but may, in principle, also be configured at least partially separate from the air system 166. In the fuel cell system, oxygen can be supplied to a stack 180, typically through the gas mixture, in particular the medium air. Fig. 5 shows, in particular, a typical air system 166 of a fuel cell system. The air 167 is filtered with at least one air filter 170 before entering a cathode 168 of the stack 180. The pressure can then be increased with at least one fluid energy machine 174 driven by at least one electric motor 172. Finally, the air 167 can be conditioned to the inlet conditions of the cathode inlet of the stack 180 with at least one heat exchanger 176 and at least one humidifier 178. A system pressure can be adjusted independently of the mass flow with at least one throttle valve 182, in particular before an exhaust air outlet 169. If the fluid energy machine 174 is designed as a turbomachine, for example, as a radial compressor, at least one bypass 186 with at least one further throttle valve 184 may be required to protect components, for example, the compressor pumps.The bypass 186 can be used to control humidification at the inlet of the cathode 168.

[0088] In the measuring method according to the invention, the absolute vapor partial pressure and / or the relative air humidity can be determined with a humidity sensor 112, for example comprising at least one sensor element 114, in particular a lambda probe, and / or at least one pressure sensor 116 and / or at least one temperature sensor 118 and / or at least one combined pressure / temperature sensor, in particular with the control 120, for example in an evaluation unit.If the total pressure of the gas mixture, in particular an air pressure, the temperature of the gas mixture, in particular the air temperature, and the proportion of the gas component in the gas mixture, in particular the oxygen partial pressure, are measured, for example, directly upstream of the fuel cell system, in particular the fuel cell, then a controlled variable for reliable operation of the fuel cell system, in particular a fuel cell, is obtained, and the humidity parameter, for example the humidity, can be adjusted depending on the operating strategy. When using alternative sensors, in particular when using alternative sensors to the lambda probe for determining the humidity parameter, for example an absolute vapor pressure and / or the relative humidity, the need to measure the total pressure of the gas mixture can be eliminated, which may be the case, for example, when using the sensor element 114 and / or the lambda probe.Accordingly, for example, in an internal combustion engine, in particular as a system, an oxygen quantity can be corrected. The humidity sensor 112, for example comprising the sensor element 114, in particular the lambda probe, can advantageously be mounted upstream of the cathode 168, in particular upstream of a fuel cell cathode, or in internal combustion engines, for example as a system, upstream of the air filter 170. The detection of the total pressure of the gas mixture, in particular a pressure measurement, and the detection of the temperature of the gas mixture, in particular a temperature measurement, can particularly preferably be carried out upstream of the cathode 168, in particular directly upstream of the fuel cell, and / or upstream of the air filter 170, for example configured as a filter, of an intake tract of an internal combustion engine.

[0089] The influence of various humidity parameters on the performance of fuel cells is described, for example, in Investigation of water transport through membrane in A PEM fuel cell by water balance experiments, Q. Yan et al., Journal of Power Sources 158 (2006) 316-325. Fig. 7A and Fig. 7B shows in particular that in a fuel cell system, especially in fuel cells, a humidity parameter, in particular the humidity of the air, has a decisive influence on the efficiency and on the performance of the stack 180, as for example in Fig. 5 shown. In the Fig. is in particular an ohmic resistance R of the fuel cell in Ohm / cm 2 over a current density j, for example a surface-specific resistance, in mAcm2 for various humidity parameters, especially cathode humidification. In the Fig. 7a and Fig. 7B, lines 188 represent a cathode humidity of 100%, lines 190 represent a cathode humidity of 70%, lines 192 represent a cathode humidity of 50%, and lines 194 represent a cathode humidity of 30%. Fig. 7A anode humidity is 80% and in Fig. 7B, the anode humidity is 100%. The fuel cell has Fig. 7A and Fig. 7B a temperature of approximately 80°C and a stoichiometric ratio of H 2 and air is approximately 2 / 2. In case of insufficient humidification, for example a cathode humidity Φ Kathode= 30%, the ohmic resistance can be significantly higher than at higher cathode humidities. High ohmic resistances can, for example, lead to low efficiencies and / or poorer performance and / or high heat generation of the stack 180, which can potentially lead to stack damage. Determining the humidity parameter by the device 110 according to the invention and the calibration method according to the invention and the measurement method according to the invention are therefore advantageous, for example, for improving the function of a fuel cell system.

[0090] In Fig. the humidity parameter, in particular the relative humidity Φ, is plotted over a time t as a dimensionless quantity. In line 196, in particular, a measured value from a humidity measurement using a conventional, non-automotive humidity sensor Φ(TP meas). Line 198 shows a humidity parameter, in particular the humidity Φ(λ - probe) measured and / or calculated with the device 110 according to the invention, in particular with the lambda probe. Lines 199 show in particular a possible tolerance band of the humidity parameter, in particular the humidity, determined by means of the sensor element 114, wherein only the error ΔΦ(ΔI meas ) with. Line 199 in Fig. 8 shows Φ + ΔΦ(ΔI meas ), where ΔI meas can be a pump current error. In Fig. 8, preferably only tolerances of the sensor element 114, in particular the lambda probe, are taken into account, for example no measurement errors in detecting the temperature and / or detecting the pressure. In Fig. 9A is a tolerance of the humidity measurement ε=|ΔΦΦ| depending on the time t for the measurement Fig. 8. In particular, it can be a function ε(ΔI meas). Fig. 8 and Fig. The dependencies shown in Figure 9A can, in particular, be a situation where ΔT = ±0K and Δp = ±0 mbar, measured at any temperature and any pressure with an ideal, error-free sensor. If, in addition to the tolerance of the lambda sensor, the tolerances of typical automotive-compatible pressure and temperature sensors are taken into account, the tolerances of a humidity measurement, for example, at a cathode inlet, increase to ranges of approximately ±10% to ±20%, as shown in the Fig. 9A, Fig. 9B, Fig. 9C, Fig. 9D and Fig. 9E. The Fig. 9A, Fig. 9B, Fig. 9C, Fig. 9D and Fig. 9E each show a tolerance of the humidity measurement ε=|ΔΦΦ| depending on the time t, in particular functions e(ΔI meas ), for various ΔT and Δp values ​​mentioned in the figures. The Fig. 9A, Fig. 9B, Fig. 9C, Fig. 9D and Fig. 9E preferably also include tolerances of pressure measurements and temperature measurements in addition to the tolerance of the lambda probe. Taking into account a tolerance chain, which includes a tolerance of a temperature determination, a tolerance of a pressure determination, and the tolerance of the sensor element 114, in particular the lambda probe, a humidity measurement with a lambda probe, for example, can determine a cathode humidity to an accuracy of 20%, in particular without applying the calibration method and / or the measuring method according to the invention. The tolerance of the sensor element 114, in particular the lambda probe, can account for a large proportion of the overall tolerance of a humidity measurement, in particular without applying the calibration method and / or the measuring method according to the invention. Fig. 8, Fig. 9A, Fig. 9B, Fig. 9C, Fig. 9D and Fig. 9E show that the tolerances from a tolerance chain of a humidity sensor 112 can be quite high and can therefore be significantly reduced by the calibration method according to the invention and / or the measuring method according to the invention, in particular by at least partially deducting at least part of the deviation ε.

[0091] Fig. 6 shows, for an embodiment of the calibration method and / or the measuring method, in particular for a humidity measurement, in combination with an air mass flow sensor, for example a hot film air mass meter (HFM), a dependence of an error in the determination of an available oxygen quantity ε ṁLuft,ein in percent compared to the ambient temperature T Ambin °C for various humidity parameters. The air mass flow sensor, such as the HFM, can, for example, record a total mass flow, preferably including the vapor content. A deviation between dry and humid air volumes can, for example, result in an error in determining the amount of oxygen available for the reaction, depending on the ambient conditions, of up to 8%, as shown in Fig. 6. This deviation may lead to a deterioration of a

[0092] exhaust gas quality and / or performance, for example in combustion engines without condensation of the air volume. Fig. 6, line 202 shows in particular a curve for a humidity parameter, in particular a humidity, Φ ein = 0.00, line 204 for Φ ein = 0.25, line 206 for Φ ein = 0.50, line 208 for Φ ein = 0.75 and line 210 for Φ ein = 1.00.

Claims

[1] Calibration method for calibrating a humidity sensor (112) for detecting at least one humidity parameter of a gas mixture, wherein in the calibration method a temperature of the gas mixture is detected, wherein at least one first saturation parameter is inferred from the temperature of the gas mixture, wherein at least one second saturation parameter is detected, wherein by means of a comparison (162) of the first saturation parameter with the second saturation parameter the humidity sensor (112) is calibrated, wherein the calibration method is carried out by at least one control (120), characterized by that the humidity sensor (112) comprises at least one sensor element (114) for detecting a proportion of a gas component in the gas mixture, wherein the humidity sensor (112) further comprises at least one pressure sensor (116) for detecting a total pressure of the gas mixture. [2] Calibration method according to the preceding claim, wherein the second saturation parameter is detected using the sensor element (114) and the pressure sensor (116). [3] Calibration method according to one of the two preceding claims, wherein the second saturation parameter is determined from the total pressure of the gas mixture detected by means of the pressure sensor (116) and from the proportion of the gas component in the gas mixture detected by means of the sensor element (114). [4] Calibration method according to one of the preceding claims, wherein in the comparison (162) a difference between the second saturation parameter and the first saturation parameter is determined, wherein from the difference at least one correction function is determined as a function of the temperature of the gas mixture. [5] Calibration method according to the preceding claim, wherein the correction function is multiplied by at least one factor. [6] Calibration method according to one of the preceding claims, wherein at least one temperature sensor (118) is used to detect the temperature of the gas mixture. [7] Calibration method according to one of the preceding claims, wherein at least a part of the humidity sensor (112) is passed through by air before and / or during calibration. [8] Calibration method according to one of the preceding claims, wherein the first saturation parameter and the second saturation parameter are detected in a saturated atmosphere of the gas mixture. [9] Calibration method according to one of the preceding claims, wherein the first saturation parameter and the second saturation parameter are determined from a minimum measurement time, wherein the saturated atmosphere is present in the gas mixture at the minimum measurement time. [10] Calibration method according to one of the preceding claims, wherein at least one ambient temperature of an environment of the humidity sensor (112) is further detected by means of at least one ambient temperature sensor (146). [11] Calibration method according to the preceding claim, wherein the minimum measurement time is determined using the ambient temperature. [12] Measuring method for detecting at least one humidity parameter of a gas mixture, wherein at least one humidity sensor (112) and at least one control (120) are used, wherein the humidity parameter of the gas mixture is determined in at least one normal operating mode, wherein the calibration method according to one of the preceding claims is carried out in at least one calibration mode. [13] Device (110) for detecting at least one humidity parameter of a gas mixture, wherein the device (110) comprises at least one humidity sensor (112), wherein the device (110) further comprises at least one temperature sensor (118) for detecting a temperature of the gas mixture, wherein the device (110) has at least one control (120), wherein the control (120) is set up to carry out a calibration method according to one of the preceding claims relating to a calibration method and / or a measuring method according to the preceding claim.

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