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WO2014063887A1 - Method for operating an air flow meter - Google Patents

Method for operating an air flow meter Download PDF

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Publication number
WO2014063887A1
WO2014063887A1 PCT/EP2013/069833 EP2013069833W WO2014063887A1 WO 2014063887 A1 WO2014063887 A1 WO 2014063887A1 EP 2013069833 W EP2013069833 W EP 2013069833W WO 2014063887 A1 WO2014063887 A1 WO 2014063887A1
Authority
WO
WIPO (PCT)
Prior art keywords
thermocouple
measured value
absolute temperature
air mass
temperature
Prior art date
Application number
PCT/EP2013/069833
Other languages
German (de)
French (fr)
Inventor
Stephan Schürer
Stephen Setescak
Thorsten Knittel
Original Assignee
Continental Automotive Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Continental Automotive Gmbh filed Critical Continental Automotive Gmbh
Priority to JP2015538353A priority Critical patent/JP6177334B2/en
Priority to EP13766957.8A priority patent/EP2912415A1/en
Priority to KR1020157013349A priority patent/KR20150074129A/en
Priority to CN201380055288.6A priority patent/CN104736978A/en
Publication of WO2014063887A1 publication Critical patent/WO2014063887A1/en

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
    • F02D41/2406—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using essentially read only memories
    • F02D41/2425—Particular ways of programming the data
    • F02D41/2429—Methods of calibrating or learning
    • F02D41/2451—Methods of calibrating or learning characterised by what is learned or calibrated
    • F02D41/2474—Characteristics of sensors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/04—Introducing corrections for particular operating conditions
    • F02D41/042—Introducing corrections for particular operating conditions for stopping the engine
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/696—Circuits therefor, e.g. constant-current flow meters
    • G01F1/6965—Circuits therefor, e.g. constant-current flow meters comprising means to store calibration data for flow signal calculation or correction
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/18—Circuit arrangements for generating control signals by measuring intake air flow
    • F02D41/187—Circuit arrangements for generating control signals by measuring intake air flow using a hot wire flow sensor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/6845—Micromachined devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
    • G01F25/10—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of flowmeters
    • G01F25/15—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of flowmeters specially adapted for gas meters

Definitions

  • the invention relates to a method for operating an air mass meter
  • Air mass meters are used, for example, in motor vehicles for determining the intake of an internal combustion engine air mass.
  • On the basis of the most reliable possible information on an intake air mass combustion by an electronic control of the internal combustion engine can be as ⁇ executed starting optimized so that a precisely to the air mass coordinated quantity of fuel to the respective combustion chambers supplied ⁇ leads is.
  • ⁇ executed starting optimized so that a precisely to the air mass coordinated quantity of fuel to the respective combustion chambers supplied ⁇ leads is.
  • characterized a better energy from ⁇ utilization is achieved at reduced pollutant emissions.
  • an air mass meter which is inserted into an intake passage for determining an air mass, wherein a defined proportion of the total flow passes through the air mass sensor.
  • this is designed as a plug-in duct air mass meter.
  • the air mass meter environmentally summarizes a valve disposed in a measuring channel sensor element, which is arranged in a housing electronics for evaluating and / or acquisition of measured values of the sensor element, and an off ⁇ flow channel beyond the sensor element.
  • the said channels or air guide paths U-, S- or C-shaped so that a total of compact, designed as a plug-in device is formed.
  • sensor elements formed as microelectronic mechanical systems have ⁇ issued ago that the measurement results of the sensor elements be ⁇ Sonders be adversely influenced by dirt. Due to the contamination, which can be caused, for example, by oil droplets in the air mass flow, a signal drift arises in the sensor element over time, which can lead to incorrect measured values for the air mass flow.
  • sensor elements formed as microelectromechanical systems have a number of advantages which are not to be dispensed with, and it is therefore an object of the invention to eliminate or at least keep within narrow limits the falsification of the measurement results due to the contamination of the sensor element.
  • A determination of a first measured value for the absolute temperature of the second thermocouple of the air mass meter
  • an additional determination of a first measured value for the absolute temperature of the first thermocouple takes place in method step A.
  • Method step AI is a formation of the difference between the first measured value of the absolute temperature of the second thermocouple and the first measured value of the absolute temperature of the first thermocouple.
  • the difference between the absolute temperatures can also provide information about the signal drift.
  • process step B in addition to the first measured values for the absolute temperature of the first thermocouple and / or the difference is stored from the first measurement value of the absolute temperature of the second thermocouple and the first measurement value of the absolute ⁇ temperature of the first thermocouple in the electronic memory, are all sorts of comparison values in Memory available to determine a signal drift and the pollution-related place of origin of the signal drift on the sensor element after operation of the internal combustion engine.
  • the differential from the second measured value of the absolute temperature of the second thermocouple and the second measured value of the absolute temperature of the first thermocouple are formed in a method step D1.
  • the signal drift can be detected and in addition statements about the origin of the signal drift can be made. For example, if the second measurement value changes absolute temperature of the first thermocouple significantly, however, the measured values of the second thermocouple stay far ⁇ going the same, there has been contamination of the first thermocouple with high probability.
  • thermocouple This is then in method step E by an additional comparison of the first measured values for the absolute temperature of the first thermocouple and / or the difference between the first measured value of the absolute temperature of the second thermocouple and the first measured value of the absolute temperature of the first thermocouple with the second measured value for the absolute temperature of detected first thermocouple and / or the difference between the second measured value of the absolute temperature of the second thermocouple and the second measured value of the absolute temperature of the first thermocouple.
  • Absolute temperature of the first thermocouple and / or the differential ference is made from the first measurement value of the absolute temperature of the second thermocouple and the first measurement value of the absolute temperature of the first thermocouple of said second measured value for the Abso ⁇ luttemperatur of the first thermocouple element and / or the difference from the second measurement value of the absolute temperature of the second thermocouple and the second measured value the absolute ⁇ temperature of the first thermocouple takes place.
  • Figure 2 is a as a microelectromechanical system (MEMS), from ⁇ formed sensor element
  • Figure 3 is a as a microelectromechanical system (MEMS) from ⁇ formed sensor element which is arranged in an auxiliary tube of the air mass meter,
  • MEMS microelectromechanical system
  • Figure 4 shows a situation in which the air mass flow through the
  • Inlet opening flows into the auxiliary tube of the air mass meter
  • MEMS microelectromechanical system
  • FIG. 6 shows the sensor element with the first temperature sensor element and the second temperature sensor element
  • FIG. 7 shows the sensor element of an air mass meter
  • Figure 8 is a flow diagram according to the invention Ver ⁇ drive for operating an air-mass meter is closer, Figure 9 embodiment of the known method of Figure 8.
  • FIG. 1 shows a mass flow sensor which is designed here as an air mass meter 2.
  • the air mass meter 2 is shown in this example as Einsteckfinger which is inserted into an intake pipe 1 and fixedly connected to the intake pipe 1.
  • the intake pipe 1 carries a mass flow, which here is an air mass flow 10, towards the cylinders of an internal combustion engine.
  • a mass flow which here is an air mass flow 10
  • the air mass meter 2 in Figure 1 shows a first temperature sensor element 7 and a second temperature sensor ⁇ element 8.
  • the first temperature sensor element 7 and the second temperature sensor element 8 are arranged at different locations to ⁇ .
  • the temperature sensor elements 7, 8 are usually formed of resistors or thermopile, also known as thermocouples, which take in accordance with the ⁇ ratursensorelement prevailing at Tempe temperature different resistance values.
  • a heating element 12 is formed between the first temperature sensor element 7 and the second temperature sensor element 8.
  • the air mass flow 10 which enters the housing 3 of the air mass meter 2 through the inlet opening 4, first flows over the first temperature sensor element 7 and then the heating element 12, after which the air mass flow 10 reaches the second temperature sensor element 8 and along the auxiliary tube 5 to the outlet opening 6 of the air mass meter 2 is directed.
  • the air mass flow 10 reaches the first
  • Temperature sensor element 7 with a certain temperature. This temperature is measured by the first temperature sensor element 7 as recorded. Thereafter, the air mass flow 10 passes over the heating element 12, wherein the air mass flow 10 is heated more or less depending on the passing mass. When the heated air mass flow 10 reaches the second temperature sensor element 8, the now existing temperature of the air mass flow 10 with the second temperature sensor element 8 is determined as the absolute temperature. From the difference between the absolute temperature measured by the first temperature sensor element 7 and the absolute temperature measured by the second temperature sensor element 8, the air mass flowed past can be determined.
  • the air mass meter 2 itself may include evaluation electronics 13, which evaluates the measurement signals of the first temperature sensor element 7 and of the second temperature sensor element 8. The information thus obtained about the air mass flow 10 is passed ⁇ to an engine control, not shown here ⁇ .
  • FIG. 2 shows a sensor element 15 for an air mass meter 1.
  • the sensor element 15 is embodied as a microelectromechanical system (MEMS) on a single silicon chip.
  • MEMS microelectromechanical system
  • the sensor element 15 operates on the differential temperature method, whereby the mass of the passing air quantity 10 is determined.
  • a first temperature ⁇ tursensorelement 7 and a second temperature sensor element 8 formed on a thin membrane 17th
  • the first and the second temperature sensor element 7, 8 are located at different locations on the surface 16 of the membrane 17.
  • a heating element 12 is arranged between the first temperature sensor element 7 and the second temperature sensor element 8.
  • a heating element 12 is arranged on the micro-electromechanical system on ⁇ assembled sensor element 15 also has a transmitter 13 integrated, which evaluate the measurement signals of the temperature sensor elements 7, 8 immediately and in a signal that is proportional to the air mass flow 10, can convert.
  • the transmitter 13 may also be integrated in a downstream electronic device. The information about the Lucasmas ⁇ senstrom 10 are then forwarded via terminal pads 19 and leads 18 to a subsequent electronic engine control, not shown here.
  • FIG. 3 a as a microelectromechanical system (MEMS) is formed sensor element 15 shown for an air mass flow sensor 2 which is formed on a single substrate, wherein the substrate is ⁇ arranged in an auxiliary tube 5 of the air flow sensor 2 at.
  • MEMS microelectromechanical system
  • the first temperature sensor element 7 and the second temperature sensor element 8 measures the same absolute temperature and after the subtraction of the measured temperature signals of the temperature sensor elements 7, 8 is detected by the transmitter 13 that no air mass flow 10 is present in the auxiliary tube 5 of the air mass meter 2.
  • this ideal equality of the temperature measurement signals at a zero mass flow can be disturbed, for example, by impurities on the sensor element 15.
  • FIG. 4 shows a situation in which an air mass flow 10 flows through the inlet opening 4 into the auxiliary pipe 5 of the air mass meter 2.
  • the temperature distribution 20 around the heating element 12 is now clearly displaced in the direction of the second temperature sensor element 8.
  • the second temperature sensor element 8 measures a significantly higher temperature than the first temperature sensor element 7.
  • the rence temperature of the two temperature sensor elements 7, 8 in the transmitter 13 can now determine the air mass flow 10.
  • the sum of the temperatures also reacts to the mass flow 10.
  • the sum of the temperatures also reacts to the thermal properties of the air mass, such as the heat capacity and / or the thermal conductivity of the passing air mass flow 10. Increases, for example, at the same air mass flow 10 the thermal conductivity of the air mass, the system cools down and the sum of the temperatures is significantly lower.
  • the differential temperature of the first temperature sensor element 7 and the second temperature sensor element 8 remains unchanged in a first approximation.
  • a change of the thermal properties such as the heat capacity or the thermal conductivity of the air mass can be measured by the sum signal of the first temperature sensor element 7 and the second temperature ⁇ tursensoriatas. 8 If one now calculates the differential temperature signal with the sum temperature signal, it is possible to deduce the changed thermal conductivity and / or the changed heat capacity of the air mass flowing past.
  • FIG. 5 shows the sensor element 15 of the air mass meter, which is designed as a microelectromechanical system (MEMS), in an air mass meter 2, which is integrated as an insertion finger in an intake pipe 1.
  • MEMS microelectromechanical system
  • the air mass flow 10 reaches the inlet opening 4 and enters the auxiliary tube 5.
  • the first temperature sensor element 7 and the second temperature sensor element 8 can be seen.
  • the heating element 12 is arranged.
  • the air mass flow 10 initially reaches the first temperature sensor element 7, then flows over the heating element 12, in order then to reach the second temperature sensor element 8. It can be seen in FIG. 5 that the air mass flow 10 also contains contaminants 9.
  • the air mass flow 10 for example, water droplets 6, oil droplets 11 and / or
  • Figure 6 shows the sensor element 15 with the first temperature ⁇ tursensorelement 7 and the second temperature sensor element 8 and the parent Toggle between the temperature sensing elements 7 and 8 the heating element 12.
  • the direction of the air mass flow 10 is shown.
  • the first temperature ⁇ tursensorelement 7 in front of the heating element 12 and the second Tem ⁇ peratursensorelement 8 12 behind the heating element both the first temperature sensor element 7 and the second temperature ⁇ tursensorelement 8 consist in this example as electrical series circuits of a measuring resistor 22 and at least two comparison resistors 21 together.
  • the measuring resistors 22 are arranged in the inner region of the thin membrane
  • the comparison resistors 21 are arranged in the edge region of the membrane 17.
  • FIG. 6 shows that contaminants 9, and in this case primarily oil droplets 11, are transported to the mass flow 10 to the sensor element 15.
  • the oil droplets ⁇ 11 deposit on the sensor element 15th
  • the deposition of the oil droplets 11 on the sensor element 15 is particularly strong in the region of the second sensor element, which is downstream of the heating element 12 in the flow direction of the air mass flow 10.
  • This asymmetrical deposition of oil droplets 11 on the sensor element 15 leads to a signal drift that ultimately leads to Ver ⁇ falsification of the detected by the sensor element 15 absolute temperature and thus the falsification of the measured value for the air mass flow 10.
  • the deposition of the Ver ⁇ dirt preferably in the edge region of the membrane is carried out 17.
  • FIG. 7 shows the sensor element 15 of a mass air flow sensor 2.
  • the first temperature sensing element 7 and the second Temperatursen ⁇ sorelement 8 of this sensor element 15 are formed as a thermopile 23.
  • Thermopiles 23, also referred to as thermocouples 23, convert heat into electrical energy.
  • Thermocouples 23 are made of two different metals, which are connected together at one end. A temperature difference generates an electrical voltage due to the heat flow in the metal.
  • thermocouple 23 the occurrence of an electrical Po ⁇ tentialdifferenz between two locations at different temperatures of a conductor.
  • the potential difference is approximately proportional to the temperature difference and it depends on the conductor material. If the ends of a single conductor for measurement are at the same temperature, the potential differences always cancel each other out.
  • connecting two different conductor materials together creates a thermocouple 23.
  • many individual thermocouples 23 are usually connected in series. When selecting material pairs for measurement purposes, the highest possible generated thermoelectric voltage should be achieved, together with a high linearity between the temperature change and the voltage change.
  • thermopile 23 shown in Figure 7 consist of a sequence of a respective first metal 24 which is connected at a junction 26 with a second metal 25.
  • the second temperature sensor element 8 which is built from thermocouples 23 to ⁇ , contamination 9 in the form of oil droplets primarily surfaces 11 are deposited. These contaminations 9 lead to a falsification of the absolute temperature measured by the temperature sensor elements 7 and 8.
  • the resulting signal drift has already been mentioned in the description of the aforementioned figures. With the method according to the invention, this signal drift can be compensated, with which the measurement results of the
  • Air flow sensor 2 are very stable over a long time to Ver ⁇ addition.
  • FIG. 8 shows a flowchart which shows in greater detail the method according to the invention for operating an air mass meter.
  • This method according to the invention can be used particularly successfully with air mass meters which have sensor elements that have been manufactured as microelectromechanical systems. The susceptibility of these microelectromechanical systems to contamination and the resulting
  • thermocouple is downstream of the heating element in the flow direction of the air mass flow and particularly affected by contamination by oil contained in the air ⁇ mass flow oil droplets.
  • the first measured value for the absolute temperature of the second thermocouple of the air mass meter is in step B in an electronic
  • step C the internal combustion engine is operated and the air supplied to the internal combustion engine Mass flow is determined with the air mass meter.
  • contaminants are transported with the air mass flow to the sensor element, with oil droplets in particular depositing in the edge region of the second thermal element. This dirt build the thermocouple leads to a signal drift, which is unintentionally and distorted the diameter ⁇ results of MAF.
  • step D a second measured value for the absolute temperature of the second thermocouple of the air mass meter according to the operation of the internal combustion engine.
  • step E then takes place a comparison of the first measured value for the absolute temperature of the second thermocouple with the second measured value for the absolute temperature of the second thermocouple.
  • step F it is determined whether there is a deviation between the first measured value and the second measured value. If a deviation between the measured values is detected, the correction of the offset of the characteristic curve of the sensor element takes place in step F1. If no deviation is detected, the procedure at step A is restarted.
  • the method is restarted at step A after correcting the offset of the characteristic. In this way one achieves a continuous offset correction of the characteristic of the sensor element, whereby high-precision measurement resulting ⁇ nisse MAF are ensured throughout its lifetime.
  • FIG. 9 shows an embodiment of the device known from FIG.
  • step A the determination of a first measured value for the absolute temperature of the second thermocouple of the air mass meter and additional determination of a first measured value for the absolute temperature of the first thermoelement.
  • step AI the difference between the first measured value of the absolute temperature of the second thermoelement and the first measured value of the absolute temperature of the first thermocouple.
  • step B the first measured value for the absolute temperature of the second thermocouple and additionally the first measured value for the absolute temperature of the first thermocouple and / or the difference between the first measured value of the absolute temperature of the second thermocouple and the first measured value of the absolute temperature of the first thermocouple Air mass meter stored in an electronic memory.
  • step C the internal combustion engine is operated and the internal combustion engine supplied shipsmas ⁇ senstromes determined with the air mass meter.
  • the internal combustion engine supplied shipsmas ⁇ senstromes determined with the air mass meter.
  • the internal combustion engine may occur in particular in the edge region of the second thermocouples ⁇ mentes to contamination of the sensor element. These soils, which are mostly caused by oil droplets, distort the measuring signal of the thermocouple, which leads to a so-called signal drift. Then the internal combustion engine can be turned off.
  • step D determines a second measured value for the absolute temperature of the second thermocouple and to ⁇ additional determination of a second measured value for the Abso ⁇ luttemperatur of the first thermocouple of the air mass meter according to the operation of the internal combustion engine. From these measured values, the difference between the second measured value of the absolute temperature of the second thermocouple and the second measured value of the absolute temperature of the first thermocouple then takes place in step D1.
  • the first measured value for the absolute temperature of the second thermocouple is compared with the second measured value for the absolute temperature of the second thermocouple, and additionally the first measured values for the absolute temperature of the first thermocouple and / or the difference from the first measured value of the absolute temperature are compared of the second thermocouple and the first measurement of the Absolute temperature of the first thermocouple with the second measured value for the absolute temperature of the first thermocouple and / or the difference between the second measured value of the absolute temperature of the second thermocouple and the second measured value of the absolute temperature of the first thermocouple.
  • step F If a deviation between the first measured values and the second measured values is determined in step F: a correction of the offset of the characteristic curve of the sensor element takes place in step F1. Then the process can be performed again beginning with step A. If no discrepancy is found between the first readings and the second readings, the procedure may be repeated immediately at step A.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Measuring Volume Flow (AREA)
  • Measuring Temperature Or Quantity Of Heat (AREA)

Abstract

The invention relates to a method for operating an air flow meter for identifying an air mass flow supplied to an internal combustion engine, wherein the air flow meter has a sensor element, having a micro-electromechanical design, which has a heating element, wherein a first thermocouple is arranged upstream on the sensor element, relative to the heating element, and a second thermocouple is arranged downstream, relative to the heating element. In order to resolve, or at least greatly restrict falsification of the measurement results due to contamination of the sensor element, the following method steps are carried out according to the invention: A: Identifying a first measurement value for the absolute temperature of the second thermocouple of the air flow meter, B: Storing the first measurement value for the absolute temperature of the second thermocouple of the air flow meter in an electronic memory, C: Operating of the internal combustion engine and identifying the air mass flow supplied to the internal combustion engine by means of the air flow meter, D: Identifying a second measurement value for the absolute temperature of the second thermocouple of the air flow meter after operating the internal combustion engine, E: Comparing the first measurement value for the absolute temperature of the second thermocouple to the second measurement value for the absolute temperature of the second thermocouple, F: Correcting the offset of the characteristic curve of the sensor element upon determining a deviation between the first measurement value and the second measurement value.

Description

Beschreibung description
Verfahren zum Betreiben eines Luftmassenmessers Method for operating an air mass meter
Die Erfindung betrifft ein Verfahren zum Betreiben eines Luftmassenmessers The invention relates to a method for operating an air mass meter
Luftmassenmesser werden beispielsweise in Kraftfahrzeugen zur Ermittlung der von einer Brennkraftmaschine angesaugten Luftmasse verwendet. Auf der Basis einer möglichst zuverlässigen Information über eine angesaugte Luftmasse kann eine Verbrennung durch eine elektronische Steuerung der Brennkraftmaschine da¬ hingehend optimiert werden, dass eine genau auf die Luftmasse abgestimmte KraftStoffmenge den jeweiligen Brennräumen zuge¬ führt wird. Im Ergebnis wird dadurch eine bessere Energieaus¬ nutzung bei verringertem Schadstoffausstoß erzielt. Air mass meters are used, for example, in motor vehicles for determining the intake of an internal combustion engine air mass. On the basis of the most reliable possible information on an intake air mass combustion by an electronic control of the internal combustion engine can be as ¬ executed starting optimized so that a precisely to the air mass coordinated quantity of fuel to the respective combustion chambers supplied ¬ leads is. As a result, characterized a better energy from ¬ utilization is achieved at reduced pollutant emissions.
Aus der DE 44 07 209 AI ist ein Luftmassenmesser bekannt, der in einen Ansaugkanal zur Bestimmung einer Luftmasse eingesteckt wird, wobei ein definierter Anteil der GesamtStrömung den Luftmassensensor durchströmt. Hierzu ist dieser als Einsteck- kanal-Luftmassenmesser ausgebildet. Der Luftmassenmesser um- fasst ein in einem Messkanal angeordnetes Sensorelement, eine in einem Gehäuse angeordnete Elektronik zur Auswertung und/oder Erfassung der Messwerte des Sensorelementes, sowie einen Aus¬ lasskanal jenseits des Sensorelements. Für eine platzsparende Anordnung werden die genannten Kanäle bzw. Luftführungswege U-, S- oder C-förmig ausgebildet, so dass eine insgesamt kompakte, als Einsteckelement ausgebildete, Vorrichtung gebildet wird. From DE 44 07 209 Al an air mass meter is known, which is inserted into an intake passage for determining an air mass, wherein a defined proportion of the total flow passes through the air mass sensor. For this purpose, this is designed as a plug-in duct air mass meter. The air mass meter environmentally summarizes a valve disposed in a measuring channel sensor element, which is arranged in a housing electronics for evaluating and / or acquisition of measured values of the sensor element, and an off ¬ flow channel beyond the sensor element. For a space-saving arrangement, the said channels or air guide paths U-, S- or C-shaped, so that a total of compact, designed as a plug-in device is formed.
Ein gemäß der Lehre der WO 03/089884 AI ausgebildeter Luftmassenmesser, der als Heißfilmanemometer ausgebildet ist, hat sich prinzipiell bewährt. A trained according to the teaching of WO 03/089884 AI air mass meter, which is designed as a hot-film anemometer, has proven itself in principle.
Bei der Entwicklung moderner Luftmassenmesser, die auf der Grundlage von Sensorelementen arbeiten, die als mikroelektro- mechanische Systeme (MEMS) ausgebildet sind, hat sich her¬ ausgestellt, dass die Messergebnisse der Sensorelemente be¬ sonders von Verschmutzungen nachteilig beeinflusst werden. Durch die Verschmutzung, die zum Beispiel von Öltröpfchen im Luftmassenstrom hervorgerufen werden kann, entsteht im Sensorelement über die Zeit eine Signaldrift, die zu falschen Messwerten für den Luftmassenstrom führen kann. Als mikroelektromechanische Systeme ausgebildete Sensorelemente besitzen jedoch eine Vielzahl von Vorteilen, auf die nicht verzichtet werden soll, und daher ist es eine Aufgabe der Erfindung, die Verfälschung der Messergebnisse durch die Verschmutzung des Sensorelementes zu beseitigen oder zumindest in engen Grenzen zu halten. In the development of modern mass air flow sensors based on sensor elements used as microelectronic mechanical systems (MEMS) are formed, has ¬ issued ago that the measurement results of the sensor elements be ¬ Sonders be adversely influenced by dirt. Due to the contamination, which can be caused, for example, by oil droplets in the air mass flow, a signal drift arises in the sensor element over time, which can lead to incorrect measured values for the air mass flow. However, sensor elements formed as microelectromechanical systems have a number of advantages which are not to be dispensed with, and it is therefore an object of the invention to eliminate or at least keep within narrow limits the falsification of the measurement results due to the contamination of the sensor element.
Diese Aufgabe wird durch die Merkmale des unabhängigen Anspruchs gelöst. Vorteilhafte Ausführungsformen sind Gegenstand der abhängigen Ansprüche. This object is solved by the features of the independent claim. Advantageous embodiments are the subject of the dependent claims.
Erfindungsgemäß werden zur Lösung der Aufgabe die folgenden Verfahrensschritte ausgeführt: According to the invention, the following method steps are carried out to solve the problem:
A: Ermittlung eines ersten Messwertes für die Absoluttemperatur des zweiten Thermoelements des Luftmassenmessers, A: determination of a first measured value for the absolute temperature of the second thermocouple of the air mass meter,
B: Ablegen des ersten Messwertes für die Absoluttemperatur des zweiten Thermoelements des Luftmassenmessers in einem elektronischen Speicher, B: storing the first measured value for the absolute temperature of the second thermocouple of the air mass meter in an electronic memory,
C: Betreiben der Brennkraftmaschine und Ermittlung des der Brennkraftmaschine zugeführten Luftmassenstromes mit dem Luftmassenmesser ,  C: operating the internal combustion engine and determining the air mass flow supplied to the internal combustion engine with the air mass meter,
D: Ermittlung eines zweiten Messwertes für die Absoluttemperatur des zweiten Thermoelements des Luftmassenmessers nach dem Betreiben der Brennkraftmaschine,  D: determination of a second measured value for the absolute temperature of the second thermocouple of the air mass meter after the operation of the internal combustion engine,
E: Vergleichen des ersten Messwertes für die Absoluttemperatur des zweiten Thermoelements mit dem zweiten Messwert für die Absoluttemperatur des zweiten Thermoelements,  E: comparing the first measured value for the absolute temperature of the second thermocouple with the second measured value for the absolute temperature of the second thermocouple,
F: Korrektur des Offsets der Kennlinie des Sensorelementes bei einer Feststellung einer Abweichung zwischen dem ersten Messwert und dem zweiten Messwert. Durch die Ermittlung eines zweiten Messwertes für die Abso¬ luttemperatur des zweiten Thermoelements des Luftmassenmessers nach dem Betreiben der Brennkraftmaschine und den Vergleich des ersten Messwertes für die Absoluttemperatur des zweiten Ther- moelements mit dem zweiten Messwert für die Absoluttemperatur des zweiten Thermoelements, kann eine während des Betriebes der Brennkraftmaschine entstandene Signaldrift erkannt und kor¬ rigiert werden. Dies führt zu einem über lange Zeit hochgenau arbeitenden Sensorelement und somit zu zuverlässigen Messer- gebnissen für den Luftmassenstrom. F: Correction of the offset of the characteristic curve of the sensor element when determining a deviation between the first measured value and the second measured value. By determining a second measured value for the Abso ¬ luttemperatur of the second thermocouple of the air mass meter according to the operation of the internal combustion engine and the comparison of the first measured value for the absolute temperature of the second thermal member with the second measured value for the absolute temperature of the second thermocouple, a can during the Operation of the internal combustion engine resulting signal drift be recognized and corrected kor ¬ . This leads to a long-term highly accurate working sensor element and thus to reliable measurement results for the air mass flow.
Bei einer Ausgestaltung des erfinderischen Verfahrens erfolgt im Verfahrensschritt A eine zusätzliche Ermittlung eines ersten Messwertes für die Absoluttemperatur des ersten Thermoelements. Damit ist die Grundlage zur Erkennung einer Signaldrift vor¬ handen, die von einer Verschmutzung des ersten Sensorelementes hervorgerufen wird. In one embodiment of the inventive method, an additional determination of a first measured value for the absolute temperature of the first thermocouple takes place in method step A. Thus, the basis for the detection of a signal drift before ¬ hands, which is caused by contamination of the first sensor element.
Bei einer Weiterbildung der Erfindung erfolgt nach dem Ver- fahrensschritt A und vor dem Verfahrensschritt B in einemIn a further development of the invention takes place after the procedural step A and before the process step B in a
Verfahrensschritt AI eine Bildung der Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements und dem ersten Messwert der Absoluttemperatur des ersten Thermoelements. Auch die Differenz der Absoluttemperaturen kann Aufschluss über die Signaldrift geben. Method step AI is a formation of the difference between the first measured value of the absolute temperature of the second thermocouple and the first measured value of the absolute temperature of the first thermocouple. The difference between the absolute temperatures can also provide information about the signal drift.
Wenn im Verfahrensschritt B zusätzlich der erste Messwerte für die Absoluttemperatur des ersten Thermoelements und/oder die Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements und dem ersten Messwert der Absolut¬ temperatur des ersten Thermoelements im elektronischen Speicher abgelegt wird, stehen alle möglichen Vergleichswerte im Speicher zur Verfügung, um nach dem Betrieb der Brennkraftmaschine eine Signaldrift und den verschmutzungsbedingten Ursprungsort der Signaldrift auf dem Sensorelement zu ermitteln. Dazu ist es vorteilhaft im Verfahrensschritt D eine zusätzliche Ermittlung eines zweiten Messwertes für die Absoluttemperatur des ersten Thermoelements erfolgt. Diese Ermittlung eines zweiten Messwertes für die Absoluttemperatur erfolgt nachdem die Brennkraftmaschine eine gewisse Zeit betrieben wurde, wobei es eventuell auf dem Sensorelement zur Ablagerungen von Ver¬ schmutzungen gekommen ist. If in process step B, in addition to the first measured values for the absolute temperature of the first thermocouple and / or the difference is stored from the first measurement value of the absolute temperature of the second thermocouple and the first measurement value of the absolute ¬ temperature of the first thermocouple in the electronic memory, are all sorts of comparison values in Memory available to determine a signal drift and the pollution-related place of origin of the signal drift on the sensor element after operation of the internal combustion engine. For this purpose, it is advantageous in method step D to additionally determine a second measured value for the absolute temperature of the first thermocouple. This determination is carried out of a second measured value for the absolute temperature after the internal combustion engine was operated for a certain time, it being possibly come to the sensor element to deposits of dirt ¬ Ver.
Weiterhin ist es Vorteilhaft, wenn nach dem Verfahrensschritt D und vor dem Verfahrensschritt E in einem Verfahrensschritt Dl eine Bildung der Differenz aus dem zweiten Messwert der Absoluttemperatur des zweiten Thermoelements und dem zweiten Messwert der Absoluttemperatur des ersten Thermoelements erfolgt. Mit diesen Messwerten kann die Signaldrift erkannt werden und zusätzlich können Aussagen über den Ursprungsort der Signaldrift getroffen werden. Wenn sich zum Beispiel der zweite Messwert Absoluttemperatur des ersten Thermoelements deutlich ändert, jedoch die Messwerte des zweiten Thermoelements weit¬ gehend gleich bleiben, ist es mit hoher Wahrscheinlichkeit zu einer Verschmutzung des ersten Thermoelements gekommen. Furthermore, it is advantageous if, after method step D and before method step E, the differential from the second measured value of the absolute temperature of the second thermocouple and the second measured value of the absolute temperature of the first thermocouple are formed in a method step D1. With these measured values, the signal drift can be detected and in addition statements about the origin of the signal drift can be made. For example, if the second measurement value changes absolute temperature of the first thermocouple significantly, however, the measured values of the second thermocouple stay far ¬ going the same, there has been contamination of the first thermocouple with high probability.
Dies wird dann im Verfahrensschritt E durch einen zusätzlichen Vergleich des ersten Messwerte für die Absoluttemperatur des ersten Thermoelements und/oder der Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements und dem ersten Messwert der Absoluttemperatur des ersten Thermoelements mit dem zweiten Messwert für die Absoluttemperatur des ersten Thermoelements und/oder der Differenz aus dem zweiten Messwert der Absoluttemperatur des zweiten Thermoelements und dem zweiten Messwert der Absoluttemperatur des ersten Thermoelements erkannt. This is then in method step E by an additional comparison of the first measured values for the absolute temperature of the first thermocouple and / or the difference between the first measured value of the absolute temperature of the second thermocouple and the first measured value of the absolute temperature of the first thermocouple with the second measured value for the absolute temperature of detected first thermocouple and / or the difference between the second measured value of the absolute temperature of the second thermocouple and the second measured value of the absolute temperature of the first thermocouple.
Wonach dann in vorteilhafter Weise im Verfahrensschritt F eine Korrektur des Offsets der Kennlinie des Sensorelementes bei einer Feststellung einer Abweichung des ersten Messwerte für dieThen, in an advantageous manner in method step F, a correction of the offset of the characteristic curve of the sensor element in the case of a determination of a deviation of the first measured values for the sensor
Absoluttemperatur des ersten Thermoelements und/oder der Dif- ferenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements und dem ersten Messwert der Absoluttemperatur des ersten Thermoelements von dem zweiten Messwert für die Abso¬ luttemperatur des ersten Thermoelements erfolgt und/oder der Differenz aus dem zweiten Messwert der Absoluttemperatur des zweiten Thermoelements und dem zweiten Messwert der Absolut¬ temperatur des ersten Thermoelements erfolgt. Absolute temperature of the first thermocouple and / or the differential ference is made from the first measurement value of the absolute temperature of the second thermocouple and the first measurement value of the absolute temperature of the first thermocouple of said second measured value for the Abso ¬ luttemperatur of the first thermocouple element and / or the difference from the second measurement value of the absolute temperature of the second thermocouple and the second measured value the absolute ¬ temperature of the first thermocouple takes place.
Weitere Merkmale und Vorteile der Erfindung werden nachfolgend unter Beschreibung eines Ausführungsbeispiels mit Bezugnahme auf die Abbildungen der Zeichnung angegeben. Über die verschiedenen Abbildungen hinweg werden nachfolgend gleiche Begriffe und Bezugszeichen für gleiche Bauelemente verwendet werden. Dabei zeigt : Further features and advantages of the invention are given below with description of an embodiment with reference to the figures of the drawing. Throughout the various illustrations, the same terms and reference symbols will be used below for identical components. Showing:
Figur 1 einen Luftmassenmesser, 1 shows an air mass meter,
Figur 2 ein als mikroelektromechanisches System (MEMS) aus¬ gebildetes Sensorelement, Figure 2 is a as a microelectromechanical system (MEMS), from ¬ formed sensor element
Figur 3 ein als mikroelektromechanisches System (MEMS) aus¬ gebildetes Sensorelement, das in einem Hilfsrohr des Luftmassenmessers angeordnet ist, Figure 3 is a as a microelectromechanical system (MEMS) from ¬ formed sensor element which is arranged in an auxiliary tube of the air mass meter,
Figur 4 eine Situation, bei der der Luftmassenstrom durch die Figure 4 shows a situation in which the air mass flow through the
Einlassöffnung in das Hilfsrohr des Luftmassenmessers einströmt ,  Inlet opening flows into the auxiliary tube of the air mass meter,
Figur 5 das als mikroelektromechanisches System (MEMS) aus¬ gebildete Sensorelement in einem Luftmassenmesser, der als Einsteckfinger in einem Ansaugrohr integriert ist , 5, the as microelectromechanical system (MEMS) from ¬ formed sensor element in an air-mass meter, which is integrated as an insertion finger in an intake pipe,
Figur 6 das Sensorelement mit dem ersten Temperatursensorelement und dem zweiten Temperatursensorelement, FIG. 6 shows the sensor element with the first temperature sensor element and the second temperature sensor element,
Figur 7 das Sensorelement eines Luftmassenmessers Figur 8 ein Ablaufdiagramm, das das erfindungsgemäße Ver¬ fahren zum Betreiben eines Luftmassenmessers näher darstellt , Figur 9 Ausgestaltung des aus Figur 8 bekannten Verfahrens. FIG. 7 shows the sensor element of an air mass meter Figure 8 is a flow diagram according to the invention Ver ¬ drive for operating an air-mass meter is closer, Figure 9 embodiment of the known method of Figure 8.
Figur 1 zeigt einen Massenstromsensor der hier als Luftmassenmesser 2 ausgebildet ist. Der Luftmassenmesser 2 ist in diesem Beispiel als Einsteckfinger gezeigt, der in ein Ansaugrohr 1 eingesteckt wird und mit dem Ansaugrohr 1 fest verbunden ist. Das Ansaugrohr 1 führt einen Massenstrom, der hier ein Luftmassenstrom 10 ist, hin zu den Zylindern einer Brennkraftmaschine. Zur effizienten Verbrennung des Treibstoffes in den Zylindern einer Brennkraftmaschine ist es notwendig, eine genaue Infor- mation über die zur Verfügung stehende Luftmasse zu erhalten. Anhand der zur Verfügung stehenden Luftmasse kann auf den verfügbaren Sauerstoff geschlossen werden, der zur Verbrennung des in die Zylinder eingespritzten Kraftstoffes notwendig ist. Darüber hinaus zeigt der Luftmassenmesser 2 in Figur 1 ein erstes Temperatursensorelement 7 und ein zweites Temperatursensor¬ element 8. Das erste Temperatursensorelement 7 und das zweite Temperatursensorelement 8 sind an unterschiedlichen Orten an¬ geordnet. Die Temperatursensorelemente 7, 8 werden in der Regel aus Widerständen oder Thermopiles, die auch als Thermoelemente bezeichnet werden, gebildet, die entsprechend der am Tempe¬ ratursensorelement herrschenden Temperatur unterschiedliche Widerstandswerte annehmen. Zwischen dem ersten Temperatursensorelement 7 und dem zweiten Temperatursensorelement 8 ist ein Heizelement 12 ausgebildet. Der Luftmassenstrom 10, der durch die Einlassöffnung 4 in das Gehäuse 3 des Luftmassenmessers 2 eintritt, überströmt zunächst das erste Temperatursensorelement 7 und dann das Heizelement 12, wonach der Luftmassenstrom 10 das zweite Temperatursensorelement 8 erreicht und entlang des Hilfsrohres 5 zur Auslassöffnung 6 des Luftmassenmessers 2 geleitet wird. Der Luftmassenstrom 10 erreicht das ersteFIG. 1 shows a mass flow sensor which is designed here as an air mass meter 2. The air mass meter 2 is shown in this example as Einsteckfinger which is inserted into an intake pipe 1 and fixedly connected to the intake pipe 1. The intake pipe 1 carries a mass flow, which here is an air mass flow 10, towards the cylinders of an internal combustion engine. For efficient combustion of the fuel in the cylinders of an internal combustion engine, it is necessary to obtain accurate information about the available air mass. On the basis of the available air mass can be closed on the available oxygen, which is necessary for the combustion of the injected fuel into the cylinder. In addition, the air mass meter 2 in Figure 1 shows a first temperature sensor element 7 and a second temperature sensor ¬ element 8. The first temperature sensor element 7 and the second temperature sensor element 8 are arranged at different locations to ¬ . The temperature sensor elements 7, 8 are usually formed of resistors or thermopile, also known as thermocouples, which take in accordance with the ¬ ratursensorelement prevailing at Tempe temperature different resistance values. Between the first temperature sensor element 7 and the second temperature sensor element 8, a heating element 12 is formed. The air mass flow 10, which enters the housing 3 of the air mass meter 2 through the inlet opening 4, first flows over the first temperature sensor element 7 and then the heating element 12, after which the air mass flow 10 reaches the second temperature sensor element 8 and along the auxiliary tube 5 to the outlet opening 6 of the air mass meter 2 is directed. The air mass flow 10 reaches the first
Temperatursensorelement 7 mit einer bestimmten Temperatur. Diese Temperatur wird vom ersten Temperatursensorelement 7 als Ab- soluttemperatur erfasst. Danach überstreicht der Luftmassenstrom 10 das Heizelement 12, wobei der Luftmassenstrom 10 je nach vorbeiströmender Masse mehr oder weniger aufgeheizt wird. Wenn der aufgeheizte Luftmassenstrom 10 das zweite Temperatursen- sorelement 8 erreicht, wird die nun vorliegende Temperatur des Luftmassenstroms 10 mit dem zweiten Temperatursensorelement 8 als Absoluttemperatur bestimmt. Aus der Differenz der vom ersten Temperatursensorelement 7 gemessenen Absoluttemperatur und der vom zweiten Temperatursensorelement 8 gemessenen Absoluttem- peratur kann die vorbeigeströmte Luftmasse bestimmt werden. Dazu kann der Luftmassenmesser 2 selber eine Auswerteelektronik 13 enthalten, die die Messsignale des ersten Temperatursensorelementes 7 und des zweiten Temperatursensorelementes 8 aus¬ wertet. Die so gewonnene Information über den Luftmassenstrom 10 wird an eine hier nicht dargestellte Motorsteuerung weiter¬ geleitet . Temperature sensor element 7 with a certain temperature. This temperature is measured by the first temperature sensor element 7 as recorded. Thereafter, the air mass flow 10 passes over the heating element 12, wherein the air mass flow 10 is heated more or less depending on the passing mass. When the heated air mass flow 10 reaches the second temperature sensor element 8, the now existing temperature of the air mass flow 10 with the second temperature sensor element 8 is determined as the absolute temperature. From the difference between the absolute temperature measured by the first temperature sensor element 7 and the absolute temperature measured by the second temperature sensor element 8, the air mass flowed past can be determined. For this purpose, the air mass meter 2 itself may include evaluation electronics 13, which evaluates the measurement signals of the first temperature sensor element 7 and of the second temperature sensor element 8. The information thus obtained about the air mass flow 10 is passed ¬ to an engine control, not shown here ¬ .
Es sei darauf hingewiesen, dass die Erfindung beispielhaft anhand eines Luftmassenmessers beschrieben wird, was jedoch keine Einschränkung des Verfahrens zum Betreiben eines Luftmassenmessers auf die Messung von Luftmassenströmen bedeutet. Mit dem erfindungsgemäßen Verfahren können auch andere Massenströme vorteilhaft erfasst und vermessen werden. Figur 2 zeigt ein Sensorelement 15 für einen Luftmassenmesser 1. Das Sensorelement 15 ist in als mikroelektromechanisches System (MEMS) auf einem einzigen Silizium-Chip ausgebildet. Das Sensorelement 15 arbeitet nach dem Differenztemperaturverfahren, womit die Masse der vorbeiströmenden Luftmenge 10 bestimmt wird. Hierzu sind auf einer dünnen Membran 17 ein erstes Tempera¬ tursensorelement 7 und ein zweites Temperatursensorelement 8 ausgebildet. Das erste und das zweite Temperatursensorelement 7, 8 befinden sich an unterschiedlichen Orten auf der Oberfläche 16 der Membran 17. Zwischen dem ersten Temperatursensorelement 7 und dem zweiten Temperatursensorelement 8 ist ein Heizelement 12 angeordnet. Auf dem als mikroelektromechanisches System auf¬ gebauten Sensorelement 15 ist zudem eine Auswerteelektronik 13 integriert, die die Messsignale der Temperatursensorelemente 7, 8 sofort auswerten und in ein Signal, das proportional zum Luftmassenstrom 10 ist, umwandeln kann. Die Auswerteelektronik 13 kann jedoch auch in einem nachgeschalteten elektronischen Gerät integriert sein. Die Informationen über den Luftmas¬ senstrom 10 werden dann über Anschlusspads 19 und Anschlussdrähte 18 an eine hier nicht dargestellte nachfolgende elektronische Motorsteuerung weitergeleitet. It should be noted that the invention will be described by way of example with reference to an air mass meter, but this does not limit the method for operating an air mass meter to the measurement of air mass flows. With the method according to the invention, other mass flows can be advantageously detected and measured. FIG. 2 shows a sensor element 15 for an air mass meter 1. The sensor element 15 is embodied as a microelectromechanical system (MEMS) on a single silicon chip. The sensor element 15 operates on the differential temperature method, whereby the mass of the passing air quantity 10 is determined. To this end, a first temperature ¬ tursensorelement 7 and a second temperature sensor element 8 formed on a thin membrane 17th The first and the second temperature sensor element 7, 8 are located at different locations on the surface 16 of the membrane 17. Between the first temperature sensor element 7 and the second temperature sensor element 8, a heating element 12 is arranged. On the micro-electromechanical system on ¬ assembled sensor element 15 also has a transmitter 13 integrated, which evaluate the measurement signals of the temperature sensor elements 7, 8 immediately and in a signal that is proportional to the air mass flow 10, can convert. However, the transmitter 13 may also be integrated in a downstream electronic device. The information about the Luftmas ¬ senstrom 10 are then forwarded via terminal pads 19 and leads 18 to a subsequent electronic engine control, not shown here.
In Figur 3 wird ein als mikroelektromechanisches System (MEMS) ausgebildetes Sensorelement 15 für einen Luftmassenmesser 2 gezeigt, das auf einem einzigen Substrat ausgebildet ist, wobei das Substrat in einem Hilfsrohr 5 des Luftmassenmessers 2 an¬ geordnet ist. In Figur 3 strömt durch die Einlassöffnung 4 kein Luftmassenstrom 10, was zum Beispiel bei ausgestellter Brennkraftmaschine der Fall sein wird. Dieser Zustand wird auch als Nullmassenstrom bezeichnet. Wenn das Heizelement 12 auf dem Sensorelement 15 mit elektrischer Energie versorgt wird, ent¬ steht um das Heizelement 12 die hier dargestellte symmetrische Temperaturverteilung 20. Damit misst das erste Temperatursensorelement 7 und das zweite Temperatursensorelement 8 die gleiche Absoluttemperatur und nach der Differenzbildung der Temperaturmesssignale der Temperatursensorelemente 7, 8 wird von der Auswerteelektronik 13 erkannt, dass kein Luftmassenstrom 10 im Hilfsrohr 5 des Luftmassenmessers 2 vorliegt. Diese ideale Gleichheit der Temperaturmesssignale bei einem Nullmassenstrom kann jedoch zum Beispiel durch Verunreinigungen auf dem Sensorelement 15 gestört werden. Figur 4 zeigt eine Situation, bei der ein Luftmassenstrom 10 durch die Einlassöffnung 4 in das Hilfsrohr 5 des Luftmassenmessers 2 einströmt. Die Temperaturverteilung 20 um das Heizelement 12 wird nun deutlich sichtbar in Richtung des zweiten Temperatursensorelementes 8 verschoben. Damit misst das zweite Temperatur- sensorelement 8 eine deutlich höhere Temperatur als das erste Temperatursensorelement 7. Durch die Feststellung der Diffe- renztemperatur der beiden Temperatursensorelemente 7, 8 in der Auswerteelektronik 13 lässt sich nun der Luftmassenstrom 10 bestimmen. Jedoch wären die Einflüsse von Verschmutzungen auf dem Sensorelement nach wie vor wirksam und sie würden die Mess¬ ergebnisse überlagern. Die Summe der Temperaturen reagiert ebenfalls auf den Massenstrom 10. Darüber hinaus reagiert jedoch die Summe der Temperaturen auch auf die thermischen Eigenschaften der Luftmasse, wie zum Beispiel die Wärmekapazität und/oder die thermische Leitfähigkeit des vorbeiströmenden Luftmassenstromes 10. Erhöht sich zum Beispiel bei gleichem Luftmassenstrom 10 die thermische Leitfähigkeit der Luftmasse, so kühlt das System ab und die Summe der Temperaturen wird deutlich geringer. Die Differenztemperatur des ersten Temperatursensorelementes 7 und des zweiten Temperatursensorelementes 8 bleibt jedoch in erster Näherung unverändert. Somit kann durch das Summensignal des ersten Temperatursensorelementes 7 und des zweiten Tempera¬ tursensorelementes 8 eine Änderung der thermischen Eigenschaften, wie zum Beispiel der Wärmekapazität, oder der thermischen Leitfähigkeit der Luftmasse gemessen werden. Verrechnet man nun das Differenztemperatursignal mit dem Summentempera- tursignal, kann auf die veränderte thermische Leitfähigkeit und/oder die veränderte Wärmekapazität der vorbeiströmenden Luftmasse geschlossen werden. In Figure 3 a as a microelectromechanical system (MEMS) is formed sensor element 15 shown for an air mass flow sensor 2 which is formed on a single substrate, wherein the substrate is ¬ arranged in an auxiliary tube 5 of the air flow sensor 2 at. In FIG. 3, no air mass flow 10 flows through the inlet opening 4, which will be the case, for example, when the internal combustion engine is issued. This condition is also called zero mass flow. When the heating element 12 is supplied to the sensor element 15 with electrical energy, ent ¬ is around the heating element 12, shown here symmetrical temperature distribution 20. Thus, the first temperature sensor element 7 and the second temperature sensor element 8 measures the same absolute temperature and after the subtraction of the measured temperature signals of the temperature sensor elements 7, 8 is detected by the transmitter 13 that no air mass flow 10 is present in the auxiliary tube 5 of the air mass meter 2. However, this ideal equality of the temperature measurement signals at a zero mass flow can be disturbed, for example, by impurities on the sensor element 15. FIG. 4 shows a situation in which an air mass flow 10 flows through the inlet opening 4 into the auxiliary pipe 5 of the air mass meter 2. The temperature distribution 20 around the heating element 12 is now clearly displaced in the direction of the second temperature sensor element 8. As a result, the second temperature sensor element 8 measures a significantly higher temperature than the first temperature sensor element 7. rence temperature of the two temperature sensor elements 7, 8 in the transmitter 13 can now determine the air mass flow 10. However, the effects of contamination on the sensor element would still be effective and they would superimpose the measurement ¬ results. The sum of the temperatures also reacts to the mass flow 10. In addition, however, the sum of the temperatures also reacts to the thermal properties of the air mass, such as the heat capacity and / or the thermal conductivity of the passing air mass flow 10. Increases, for example, at the same air mass flow 10 the thermal conductivity of the air mass, the system cools down and the sum of the temperatures is significantly lower. However, the differential temperature of the first temperature sensor element 7 and the second temperature sensor element 8 remains unchanged in a first approximation. Thus, a change of the thermal properties such as the heat capacity or the thermal conductivity of the air mass can be measured by the sum signal of the first temperature sensor element 7 and the second temperature ¬ tursensorelementes. 8 If one now calculates the differential temperature signal with the sum temperature signal, it is possible to deduce the changed thermal conductivity and / or the changed heat capacity of the air mass flowing past.
Figur 5 zeigt das Sensorelement 15 des Luftmassenmessers, das als mikroelektromechanisches System (MEMS) ausgebildet ist, in einem Luftmassenmesser 2, der als Einsteckfinger in einem Ansaugrohr 1 integriert ist. Der Luftmassenstrom 10 erreicht auch hier die Einlassöffnung 4 und tritt in das Hilfsrohr 5 ein. Auf der Oberfläche 16 der Membran 17 sind das erste Temperatursensorelement 7 und das zweite Temperatursensorelement 8 zu erkennen. Zwischen dem ersten Temperatursensorelement 7 und dem zweiten Temperatursensorelement 8 ist das Heizelement 12 angeordnet. Der Luftmassenstrom 10 erreicht zunächst das erste Temperatursensorelement 7, überströmt dann das Heizelement 12, um danach das zweite Temperatursensorelement 8 zu erreichen. In Figur 5 ist zu erkennen, dass der Luftmassenstrom 10 auch Verschmutzungen 9 beinhaltet. Mit dem Luftmassenstrom 10 werden zum Beispiel Wassertröpfchen 6, Öltröpfchen 11 und/oder FIG. 5 shows the sensor element 15 of the air mass meter, which is designed as a microelectromechanical system (MEMS), in an air mass meter 2, which is integrated as an insertion finger in an intake pipe 1. Here too, the air mass flow 10 reaches the inlet opening 4 and enters the auxiliary tube 5. On the surface 16 of the membrane 17, the first temperature sensor element 7 and the second temperature sensor element 8 can be seen. Between the first temperature sensor element 7 and the second temperature sensor element 8, the heating element 12 is arranged. The air mass flow 10 initially reaches the first temperature sensor element 7, then flows over the heating element 12, in order then to reach the second temperature sensor element 8. It can be seen in FIG. 5 that the air mass flow 10 also contains contaminants 9. With the air mass flow 10, for example, water droplets 6, oil droplets 11 and / or
Staubteilchen 14 hin zum Luftmassenmesser 2 transportiert. Diese Verschmutzungen 9 gelangen durch die Einlassöffnung 4 des Luftmassenmessers 2 bis zum Sensorelement 15. Wenn sich die Verschmutzungen 9 im Bereich des ersten Temperatursensorelementes 7 und des zweite Temperatursensorelementes 8 ablagern, kann es mit der Zeit zu einer massiven Verfälschung des Messwertes für den Luftmassenstrom 10 kommen. Da sich diese Verfälschung durch die Akkumulation der Verschmutzung auf dem Sensorelement 15 über einem langen Zeitraum immer weiter aufbaut, spricht man in diesem Zusammenhang auch von einer Signaldrift des Luftmassenmessers 2. Dieser Signaldrift ist unerwünscht und sie sollte unterdrückt und/oder kompensiert werden. Dust particles 14 transported to the air mass meter 2. If the contaminants 9 deposit in the area of the first temperature sensor element 7 and the second temperature sensor element 8, a massive falsification of the measured value for the air mass flow 10 can occur over time , Since this adulteration continues to build up over a long period of time due to the accumulation of the contamination on the sensor element 15, this is also referred to as a signal drift of the air mass meter 2. This signal drift is undesirable and should be suppressed and / or compensated.
Figur 6 zeigt das Sensorelement 15 mit dem ersten Tempera¬ tursensorelement 7 und dem zweiten Temperatursensorelement 8 sowie dem zwischen den Temperatursensorelementen 7 und 8 an- geordneten Heizelement 12. Mit dem Pfeil ist die Richtung des Luftmassenstromes 10 dargestellt. Damit befindet sich in der Strömungsrichtung des Luftmassenstromes 10 das erste Tempera¬ tursensorelement 7 vor dem Heizelement 12 und das zweite Tem¬ peratursensorelement 8 hinter dem Heizelement 12. Sowohl das erste Temperatursensorelement 7 als auch das zweite Tempera¬ tursensorelement 8 setzen sich in diesem Beispiel als elektrische Reihenschaltungen aus einem Messwiderstand 22 und mindestens zwei Vergleichswiderständen 21 zusammen. Es ist zu erkennen, dass die Messwiderstände 22 im inneren Bereich der dünnen Membran angeordnet sind, und die Vergleichswiderstände 21 im Randbereich der Membran 17 angeordnet sind. Figure 6 shows the sensor element 15 with the first temperature ¬ tursensorelement 7 and the second temperature sensor element 8 and the parent Toggle between the temperature sensing elements 7 and 8 the heating element 12. By the arrow, the direction of the air mass flow 10 is shown. Thus located in the flow direction of the air mass flow 10, the first temperature ¬ tursensorelement 7 in front of the heating element 12 and the second Tem ¬ peratursensorelement 8 12 behind the heating element, both the first temperature sensor element 7 and the second temperature ¬ tursensorelement 8 consist in this example as electrical series circuits of a measuring resistor 22 and at least two comparison resistors 21 together. It can be seen that the measuring resistors 22 are arranged in the inner region of the thin membrane, and the comparison resistors 21 are arranged in the edge region of the membrane 17.
Weiterhin zeigt die Figur 6, dass Verschmutzungen 9, und hierbei vornehmlich Öltröpfchen 11, mit dem Massenstrom 10 zu dem Sensorelement 15 transportiert werden. Insbesondere die Öl¬ tröpfchen 11 lagern sich auf dem Sensorelement 15 ab. Es ist deutlich zu erkennen, dass die Ablagerung der Öltröpfchen 11 auf dem Sensorelement 15 besonders stark im Bereich des zweiten Sensorelements erfolgt, welches in Strömungsrichtung des Luftmassenstromes 10 dem Heizelement 12 nachgelagert ist. Diese unsymmetrische Ablagerung von Öltröpfchen 11 auf dem Sensor- element 15 führt zu einer Signaldrift, die letztlich zur Ver¬ fälschung der vom Sensorelement 15 erfassten Absoluttemperatur und damit zur Verfälschung des Messwertes für den Luftmassenstrom 10 führt. Darüber hinaus erfolgt die Ablagerung der Ver¬ schmutzungen bevorzugt im Randbereich der Membran 17. Die un- symmetrische Ablagerung der Öltröpfchen 11 hat physikalische Gründe, die ihren Ursprung insbesondere in der höheren Temperatur im Bereich des zweiten Sensorelementes 8 und im Temperaturgradienten im Randbereich der Membran 17 finden. Figur 7 zeigt das Sensorelement 15 eines Luftmassenmessers 2. Das erste Temperatursensorelement 7 und das zweite Temperatursen¬ sorelement 8 dieses Sensorelementes 15 sind als Thermopiles 23 ausgebildet. Thermopiles 23, die auch als Thermoelemente 23 bezeichnet werden, wandeln Wärme in elektrische Energie um. Thermoelemente 23 bestehen aus zwei unterschiedlichen Metallen, die an einem Ende miteinander verbunden sind. Eine Temperaturdifferenz erzeugt aufgrund des Wärmeflusses im Metall eine elektrische Spannung. Als Seebeck-Effekt wird das Auftreten einer elektrischen Po¬ tentialdifferenz zwischen zwei Stellen unterschiedlicher Temperatur eines Leiters bezeichnet. Die Potentialdifferenz ist annähernd proportional zur Temperaturdifferenz und sie hängt vom Leitermaterial ab. Wenn die Enden eines einzigen Leiters zur Messung auf gleicher Temperatur liegen, heben sich die Potentialdifferenzen stets auf. Verbindet man jedoch zwei unterschiedliche Leitermaterialien miteinander, entsteht ein Thermoelement 23. Bei Messsystemen auf der Basis des Seebeck-Effektes werden in der Regel sehr viele einzelne Thermoelemente 23 in Reihe geschaltet. Bei der Auswahl von Materialpaaren zu Messzwecken sollte eine möglichst hohe erzeugte Thermospannung verbunden mit einer hohen Linearität zwischen Temperaturänderung und Spannungsänderung erreicht werden. Die in Figur 7 gezeigten Thermopiles 23 bestehen aus einer Abfolge eines jeweils ersten Metalls 24, das an einer Verbindungsstelle 26 mit einem zweiten Metall 25 verbunden ist. In Figur 7 ist deutlich zu erkennen, dass im Bereich des zweiten Temperatursensorelementes 8, das aus Thermoelementen 23 auf¬ gebaut ist, Verschmutzungen 9 vornehmlich in Form von Öltröpf- chen 11 abgelagert sind. Diese Verschmutzungen 9 führen zu einer Verfälschung der von den Temperatursensorelementen 7 und 8 gemessenen Absolut-Temperatur . Die hieraus resultierende Signaldrift wurde schon in der Beschreibung der vorgenannten Figuren erwähnt. Mit dem erfindungsgemäßen Verfahren kann diese Sig- naldrift kompensiert werden, womit die Messergebnisse desFurthermore, FIG. 6 shows that contaminants 9, and in this case primarily oil droplets 11, are transported to the mass flow 10 to the sensor element 15. In particular, the oil droplets ¬ 11 deposit on the sensor element 15th It can be clearly seen that the deposition of the oil droplets 11 on the sensor element 15 is particularly strong in the region of the second sensor element, which is downstream of the heating element 12 in the flow direction of the air mass flow 10. This asymmetrical deposition of oil droplets 11 on the sensor element 15 leads to a signal drift that ultimately leads to Ver ¬ falsification of the detected by the sensor element 15 absolute temperature and thus the falsification of the measured value for the air mass flow 10. In addition, the deposition of the Ver ¬ dirt preferably in the edge region of the membrane is carried out 17. The unsymmetrical deposition of the oil droplets 11 has physical reasons that originate in particular in the higher temperature in the range of the second sensor element 8 and the temperature gradient in the edge region of the diaphragm 17 Find. Figure 7 shows the sensor element 15 of a mass air flow sensor 2. The first temperature sensing element 7 and the second Temperatursen ¬ sorelement 8 of this sensor element 15 are formed as a thermopile 23. Thermopiles 23, also referred to as thermocouples 23, convert heat into electrical energy. Thermocouples 23 are made of two different metals, which are connected together at one end. A temperature difference generates an electrical voltage due to the heat flow in the metal. As the Seebeck effect, the occurrence of an electrical Po ¬ tentialdifferenz between two locations at different temperatures of a conductor is referred to. The potential difference is approximately proportional to the temperature difference and it depends on the conductor material. If the ends of a single conductor for measurement are at the same temperature, the potential differences always cancel each other out. However, connecting two different conductor materials together creates a thermocouple 23. In measurement systems based on the Seebeck effect, many individual thermocouples 23 are usually connected in series. When selecting material pairs for measurement purposes, the highest possible generated thermoelectric voltage should be achieved, together with a high linearity between the temperature change and the voltage change. The thermopile 23 shown in Figure 7 consist of a sequence of a respective first metal 24 which is connected at a junction 26 with a second metal 25. In Figure 7 it can be clearly seen that in the region of the second temperature sensor element 8, which is built from thermocouples 23 to ¬, contamination 9 in the form of oil droplets primarily surfaces 11 are deposited. These contaminations 9 lead to a falsification of the absolute temperature measured by the temperature sensor elements 7 and 8. The resulting signal drift has already been mentioned in the description of the aforementioned figures. With the method according to the invention, this signal drift can be compensated, with which the measurement results of the
Luftmassenmessers 2 über eine lange Zeit sehr stabil zur Ver¬ fügung stehen. Air flow sensor 2 are very stable over a long time to Ver ¬ addition.
Figur 8 zeigt ein Ablaufdiagramm, das das erfindungsgemäße Verfahren zum Betreiben eines Luftmassenmessers näher darstellt. Dieses erfindungsgemäße Verfahren kann besonders erfolgreich bei Luftmassenmessers eingesetzt werden, die Sensorelemente auf¬ weisen, die als mikroelektromechanische Systeme gefertigt wurden. Die Anfälligkeit dieser mikroelektromechanischen Sys- teme gegenüber Verschmutzungen und die daraus resultierendeFIG. 8 shows a flowchart which shows in greater detail the method according to the invention for operating an air mass meter. This method according to the invention can be used particularly successfully with air mass meters which have sensor elements that have been manufactured as microelectromechanical systems. The susceptibility of these microelectromechanical systems to contamination and the resulting
Signaldrift dieser Sensorelemente wurde bereits im Vorgenannten erläutert. Zur Vermeidung der Signaldrift bzw. zur Kompensation dieser Signaldrift erfolgt in einem Schritt A die Ermittlung eines ersten Messwertes für die Absoluttemperatur des zweiten Thermoelements des Luftmassenmessers. Das zweite Thermoelement ist dem Heizelement in Strömungsrichtung des Luftmassenstroms nachgelagert und besonders von Verschmutzungen durch im Luft¬ massenstrom enthaltene Öltröpfchen betroffen. Der erste Messwert für die Absoluttemperatur des zweiten Thermoelements des Luftmassenmessers wird im Schritt B in einem elektronischenSignal drift of these sensor elements has already been explained in the aforementioned. In order to avoid the signal drift or to compensate for this signal drift, the determination of a first measured value for the absolute temperature of the second thermocouple of the air mass meter takes place in a step A. The second thermocouple is downstream of the heating element in the flow direction of the air mass flow and particularly affected by contamination by oil contained in the air ¬ mass flow oil droplets. The first measured value for the absolute temperature of the second thermocouple of the air mass meter is in step B in an electronic
Speicher abgelegt. Nun wird in Schritt C die Brennkraftmaschine betrieben und der der Brennkraftmaschine zugeführten Luft- massenstrom wird mit dem Luftmassenmesser ermittelt. Durch den Betrieb der Brennkraftmaschine werden Verschmutzungen mit dem Luftmassenstrom zum Sensorelement transportiert, wobei sich insbesondere Öltröpfchen im Randbereich des zweiten Thermo- elementes ablagern. Diese Verschmut zung des Thermoelements führt zu einer Signaldrift, die ungewollt ist und die die Messer¬ gebnisse des Luftmassenmessers verfälscht. Nun kann die Memory stored. Now, in step C, the internal combustion engine is operated and the air supplied to the internal combustion engine Mass flow is determined with the air mass meter. As a result of the operation of the internal combustion engine, contaminants are transported with the air mass flow to the sensor element, with oil droplets in particular depositing in the edge region of the second thermal element. This dirt build the thermocouple leads to a signal drift, which is unintentionally and distorted the diameter ¬ results of MAF. Now that can
Brennkraftmaschine abgestellt werden. Um die verschmutzungs¬ bedingte Verfälschung der Messwerte des Luftmassenmessers zu Kompensieren wird in einem Schritt D ein zweiter Messwert für die Absoluttemperatur des zweiten Thermoelements des Luftmassenmessers nach dem Betreiben der Brennkraftmaschine ermittelt. Im schritt E erfolgt dann ein Vergleich des ersten Messwertes für die Absoluttemperatur des zweiten Thermoelements mit dem zweiten Messwert für die Absoluttemperatur des zweiten Thermoelements. Im Schritt F wird festgestellt, ob eine Abweichung zwischen dem ersten Messwert und dem zweiten Messwert besteht. Wenn eine Abweichung zwischen den Messwerten festgestellt wird, erfolgt im Schritt Fl die Korrektur des Offsets der Kennlinie des Sen- sorelementes . Falls keine Abweichung festgestellt wird, wird das Verfahren bei Schritt A neu gestartet. Auch wenn eine Abweichung festgestellt wurde, wird das Verfahren, nach erfolgter Korrektur des Offsets der Kennlinie, bei Schritt A neu gestartet. Auf diese Weise erreicht man eine kontinuierliche Offsetkorrektur der Kennlinie des Sensorelementes, wodurch hochgenaue Messergeb¬ nisse des Luftmassenmessers über seine gesamte Lebensdauer sichergestellt sind. Internal combustion engine are turned off. To the pollution caused ¬ falsification of the measured values of the air mass meter to compensate is determined in a step D, a second measured value for the absolute temperature of the second thermocouple of the air mass meter according to the operation of the internal combustion engine. In step E then takes place a comparison of the first measured value for the absolute temperature of the second thermocouple with the second measured value for the absolute temperature of the second thermocouple. In step F it is determined whether there is a deviation between the first measured value and the second measured value. If a deviation between the measured values is detected, the correction of the offset of the characteristic curve of the sensor element takes place in step F1. If no deviation is detected, the procedure at step A is restarted. Even if a deviation has been detected, the method is restarted at step A after correcting the offset of the characteristic. In this way one achieves a continuous offset correction of the characteristic of the sensor element, whereby high-precision measurement resulting ¬ nisse MAF are ensured throughout its lifetime.
Figur 9 zeigt eine Ausgestaltung des aus Figur 8 bekanntenFIG. 9 shows an embodiment of the device known from FIG
Verfahrens. Im Schritt A erfolgt die Ermittlung eines ersten Messwertes für die Absoluttemperatur des zweiten Thermoelements des Luftmassenmessers und zusätzliche die Ermittlung eines ersten Messwertes für die Absoluttemperatur des ersten Ther- moelements. Im folgenden Schritt AI wird die Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoele- ments und dem ersten Messwert der Absoluttemperatur des ersten Thermoelements gebildet. Danach werden im Schritt B: der erste Messwert für die Absoluttemperatur des zweiten Thermoelements und zusätzlich der erste Messwert für die Absoluttemperatur des ersten Thermoelements und/oder die Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements und dem ersten Messwert der Absoluttemperatur des ersten Thermoelements des Luftmassenmessers in einem elektronischen Speicher abgelegt . Process. In step A, the determination of a first measured value for the absolute temperature of the second thermocouple of the air mass meter and additional determination of a first measured value for the absolute temperature of the first thermoelement. In the following step AI, the difference between the first measured value of the absolute temperature of the second thermoelement and the first measured value of the absolute temperature of the first thermocouple. Thereafter, in step B: the first measured value for the absolute temperature of the second thermocouple and additionally the first measured value for the absolute temperature of the first thermocouple and / or the difference between the first measured value of the absolute temperature of the second thermocouple and the first measured value of the absolute temperature of the first thermocouple Air mass meter stored in an electronic memory.
Im nun folgenden Verfahrensschritt C wird die Brennkraftmaschine betrieben und der der Brennkraftmaschine zugeführten Luftmas¬ senstromes mit dem Luftmassenmesser ermittelt. Beim Betreiben der Brennkraftmaschine kann es zu Verschmutzungen des Sensor- elementes, insbesondere im Randbereich des zweiten Thermoele¬ mentes kommen. Diese meist von Öltröpfchen hervorgerufenen Verschmutzungen verfälschen das Messsignal des Thermoelementes, was zu einer sogenannten Signaldrift führt. Dann kann die Brennkraftmaschine abgestellt werden. In the now following method step C, the internal combustion engine is operated and the internal combustion engine supplied Luftmas ¬ senstromes determined with the air mass meter. During operation of the internal combustion engine may occur in particular in the edge region of the second thermocouples ¬ mentes to contamination of the sensor element. These soils, which are mostly caused by oil droplets, distort the measuring signal of the thermocouple, which leads to a so-called signal drift. Then the internal combustion engine can be turned off.
Es folgt im Schritt D die Ermittlung eines zweiten Messwertes für die Absoluttemperatur des zweiten Thermoelements und die zu¬ sätzliche Ermittlung eines zweiten Messwertes für die Abso¬ luttemperatur des ersten Thermoelements des Luftmassenmessers nach dem Betreiben der Brennkraftmaschine. Aus diesen Messwerten erfolgt dann im Schritt Dl die Bildung der Differenz aus dem zweiten Messwert der Absoluttemperatur des zweiten Thermoelements und dem zweiten Messwert der Absoluttemperatur des ersten Thermoelements. This is followed in step D to determine a second measured value for the absolute temperature of the second thermocouple and to ¬ additional determination of a second measured value for the Abso ¬ luttemperatur of the first thermocouple of the air mass meter according to the operation of the internal combustion engine. From these measured values, the difference between the second measured value of the absolute temperature of the second thermocouple and the second measured value of the absolute temperature of the first thermocouple then takes place in step D1.
Im Verfahrensschritt E erfolgt ein Vergleichen des ersten Messwertes für die Absoluttemperatur des zweiten Thermoelements mit dem zweiten Messwert für die Absoluttemperatur des zweiten Thermoelements und zusätzlich erfolgt ein Vergleich des ersten Messwerte für die Absoluttemperatur des ersten Thermoelements und/oder der Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements und dem ersten Messwert der Absoluttemperatur des ersten Thermoelements mit dem zweiten Messwert für die Absoluttemperatur des ersten Thermoelements und/oder der Differenz aus dem zweiten Messwert der Absoluttemperatur des zweiten Thermoelements und dem zweiten Messwert der Absoluttemperatur des ersten Thermoelements. In method step E, the first measured value for the absolute temperature of the second thermocouple is compared with the second measured value for the absolute temperature of the second thermocouple, and additionally the first measured values for the absolute temperature of the first thermocouple and / or the difference from the first measured value of the absolute temperature are compared of the second thermocouple and the first measurement of the Absolute temperature of the first thermocouple with the second measured value for the absolute temperature of the first thermocouple and / or the difference between the second measured value of the absolute temperature of the second thermocouple and the second measured value of the absolute temperature of the first thermocouple.
Wenn im Schritt F: eine Abweichung zwischen den ersten Messwerten und den zweiten Messwerten festgestellt wird, erfolgt im Schritt Fl eine Korrektur des Offsets der Kennlinie des Sensorelementes. Dann kann das Verfahren beginnend mit Schritt A erneut ausgeführt werden. Wenn keine Abweichung zwischen den ersten Messwerten und den zweiten Messwerten festgestellt wird, kann das Verfahren sofort bei Schritt A erneut ausgeführt werden. If a deviation between the first measured values and the second measured values is determined in step F: a correction of the offset of the characteristic curve of the sensor element takes place in step F1. Then the process can be performed again beginning with step A. If no discrepancy is found between the first readings and the second readings, the procedure may be repeated immediately at step A.

Claims

Verfahren zum Betreiben eines Luftmassenmessers zur Ermittlung eines einer Brennkraftmaschine zugeführten Luftmassenstromes (10), wobei der Luftmassenmesser (2) ein in mikroelektromechanischer Bauweise ausgebildetes Sensorelement (15) aufweist, das ein Heizelement (12) auf¬ weist, wobei auf dem Sensorelement (15) ein erstes Ther¬ moelement (7) stromaufwärts bezogen auf das Heizelement (12) angeordnet ist und ein zweites Thermoelement (8) stromabwärts bezogen auf das Heizelement (12) angeordnet ist, mit den folgenden Verfahrensschritten: A method of operating a mass air flow sensor for detecting a supplied to an internal combustion engine air mass flow (10), wherein the air mass meter (2) has a hole formed in micro-electro-mechanical construction sensor element (15) which has a heating element (12) on ¬, wherein on the sensor element (15) a first Ther ¬ moelement (7) upstream of the heating element (12) is arranged and a second thermocouple (8) downstream of the heating element (12) is arranged, with the following method steps:
A: Ermittlung eines ersten Messwertes für die Absolut¬ temperatur des zweiten Thermoelements (8) des Luft¬ massenmessers (2), A: determination of a first measured value for the absolute ¬ temperature of the second thermocouple (8) of the air mass meter ¬ (2),
B: Ablegen des ersten Messwertes für die Absoluttemperatur des zweiten Thermoelements (8) des Luftmassenmessers (2) in einem elektronischen Speicher,  B: storing the first measured value for the absolute temperature of the second thermocouple (8) of the air mass meter (2) in an electronic memory,
C: Betreiben der Brennkraftmaschine und Ermittlung des der Brennkraftmaschine zugeführten Luftmassenstromes (10) mit dem Luftmassenmesser (2),  C: operating the internal combustion engine and determining the air mass flow (10) supplied to the internal combustion engine with the air mass meter (2),
D: Ermittlung eines zweiten Messwertes für die Absolut¬ temperatur des zweiten Thermoelements (8) des Luft¬ massenmessers (2) nach dem Betreiben der Brennkraft¬ maschine, D: determining a second measured value for the absolute ¬ temperature of the second thermocouple (8) of the air mass meter ¬ (2) after operating the internal combustion ¬ machine,
E: Vergleichen des ersten Messwertes für die Absoluttemperatur des zweiten Thermoelements (8) mit dem zweiten Messwert für die Absoluttemperatur des zweiten Thermoelements ( 8 ) ,  E: comparing the first measured value for the absolute temperature of the second thermocouple (8) with the second measured value for the absolute temperature of the second thermocouple (8),
F: Korrektur des Offsets der Kennlinie des Sensorelementes (15) bei einer Feststellung einer Abweichung zwischen dem ersten Messwert und dem zweiten Messwert.  F: Correction of the offset of the characteristic of the sensor element (15) upon detection of a deviation between the first measured value and the second measured value.
2. Verfahren zum Betreiben eines Luftmassenmessers (2) nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , dass im Verfahrensschritt A eine zusätzliche Ermittlung eines ersten Messwertes für die Absoluttemperatur des ersten Thermoelements (7) erfolgt. 2. A method for operating an air mass meter (2) according to claim 1, characterized in that in step A, an additional determination a first measured value for the absolute temperature of the first thermocouple (7).
3. Verfahren zum Betreiben eines Luftmassenmessers (2) nach Anspruch 2, d a d u r c h g e k e n n z e i c h n e t , dass nach dem Verfahrensschritt A und vor dem Verfah¬ rensschritt B in einem Verfahrensschritt AI eine Bildung der Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements (8) und dem ersten Messwert der Absoluttemperatur des ersten Thermoelements (7) erfolgt. 3. A method of operating an air mass meter (2) according to claim 2, characterized in that after step A and before the procedural ¬ rensschritt B in a step AI a formation of the difference from the first measurement value of the absolute temperature of the second thermocouple (8) and the first measured value of the absolute temperature of the first thermocouple (7).
4. Verfahren zum Betreiben eines Luftmassenmessers (2) nach Anspruch 2 oder 3, d a d u r c h g e k e n n z e i c h n e t , dass im Verfahrensschritt B zusätzlich der erste Messwert für die Absoluttemperatur des ersten Thermoelements (7) und/oder die Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements (8) und dem ersten Messwert der Absoluttemperatur des ersten Thermoelements (7) im elektronischen Speicher abgelegt wird. 4. A method for operating an air mass meter (2) according to claim 2 or 3, characterized in that in method step B additionally the first measured value for the absolute temperature of the first thermocouple (7) and / or the difference from the first measured value of the absolute temperature of the second thermocouple ( 8) and the first measured value of the absolute temperature of the first thermocouple (7) is stored in the electronic memory.
5. Verfahren zum Betreiben eines Luftmassenmessers (2) nach Anspruch 3 oder 4, d a d u r c h g e k e n n z e i c h n e t , dass im Verfahrensschritt D eine zusätzliche Ermittlung eines zweiten Messwertes für die Absoluttemperatur des ersten Thermoelements (7) erfolgt. 5. A method for operating an air mass meter (2) according to claim 3 or 4, characterized in that in step D, an additional determination of a second measured value for the absolute temperature of the first thermocouple (7).
6. Verfahren zum Betreiben eines Luftmassenmessers (2) nach Anspruch 4, d a d u r c h g e k e n n z e i c h n e t , dass nach dem Verfahrensschritt D und vor dem Verfah¬ rensschritt E in einem Verfahrensschritt Dl eine Bildung der Differenz aus dem zweiten Messwert der Absoluttemperatur des zweiten Thermoelements (8) und dem zweiten Messwert der Absoluttemperatur des ersten Thermoelements (7) er- folgt. Verfahren zum Betreiben eines Luftmassenmessers (2) nach Anspruch 5 oder 6, d a d u r c h g e k e n n z e i c h n e t , dass im Verfahrensschritt E zusätzlich ein Ver¬ gleich des ersten Messwerte für die Absoluttemperatur des ersten Thermoelements (7) und/oder der Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements (8) und dem ersten Messwert der Absoluttem¬ peratur des ersten Thermoelements (7) mit dem zweiten Messwert für die Absoluttemperatur des ersten Thermoelements (7) erfolgt und/oder der Differenz aus dem zweiten Messwert der Absoluttemperatur des zweiten Thermoelements (8) und dem zweiten Messwert der Absoluttemperatur des ersten Thermoelements (7) erfolgt. 6. A method of operating an air mass meter (2) according to claim 4, characterized in that after step D and before the procedural ¬ rensschritt E in a process step Dl formation of the difference from the second measurement value of the absolute temperature of the second thermocouple (8) and the second measured value of the absolute temperature of the first thermocouple (7) follows. Method for operating an air mass meter (2) according to claim 5 or 6, characterized in that in step E additionally a Ver ¬ equal to the first measured values for the absolute temperature of the first thermocouple (7) and / or the difference from the first measured value of the absolute temperature of the second Thermocouple (8) and the first measured value of the Absoluttem ¬ temperature of the first thermocouple (7) with the second measured value for the absolute temperature of the first thermocouple (7) and / or the difference from the second measured value of the absolute temperature of the second thermocouple (8) and the second measured value of the absolute temperature of the first thermocouple (7).
Verfahren zum Betreiben eines Luftmassenmessers (2) nach Anspruch 7, d a d u r c h g e k e n n z e i c h n e t , dass im Verfahrensschritt F eine Korrektur des Offsets der Kennlinie des Sensorelementes (15) bei einer Feststellung einer Abweichung des ersten Messwerte für die Absoluttemperatur des ersten Thermoelements (7) und/oder der Differenz aus dem ersten Messwert der Absoluttemperatur des zweiten Thermoelements (8) und dem ersten Messwert der Absoluttemperatur des ersten Thermoelements (7) von dem zweiten Messwert für die Absoluttemperatur des ersten Thermoelements (7) erfolgt und/oder der Differenz aus dem zweiten Messwert der Absoluttemperatur des zweiten Thermoelements (8) und dem zweiten Messwert der Absoluttem¬ peratur des ersten Thermoelements (7) erfolgt. Method for operating an air mass meter (2) according to claim 7, characterized in that in step F, a correction of the offset of the characteristic of the sensor element (15) in a determination of a deviation of the first measured values for the absolute temperature of the first thermocouple (7) and / or the Difference from the first measured value of the absolute temperature of the second thermocouple (8) and the first measured value of the absolute temperature of the first thermocouple (7) from the second measured value for the absolute temperature of the first thermocouple (7) and / or the difference from the second measured value of the absolute temperature takes place of the second thermocouple (8) and the second measuring value of the Absoluttem ¬ temperature of the first thermocouple (7).
PCT/EP2013/069833 2012-10-23 2013-09-24 Method for operating an air flow meter WO2014063887A1 (en)

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KR1020157013349A KR20150074129A (en) 2012-10-23 2013-09-24 Method for operating an air flow meter
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