WO2014063888A1

WO2014063888A1 - Method for operating an air flow meter

Info

Publication number: WO2014063888A1
Application number: PCT/EP2013/069845
Authority: WO
Inventors: Stephan Schürer; Stephen Setescak; Thorsten Knittel
Original assignee: Continental Automotive Gmbh
Priority date: 2012-10-23
Filing date: 2013-09-24
Publication date: 2014-05-01
Also published as: DE102012219290A1

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. 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: Determining a first measurement value of the air flow meter by means of the sensor element in the case of a zero mass flow, B: Storing the first measurement value 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: Determining a second measurement value of the air flow meter after operating the internal combustion engine in the case of a zero mass flow, E: Comparing the first measurement value to the second measurement value, 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

description

Method for operating an air mass meter

The invention relates to a method for operating an air mass meter for determining an air mass supplied to an internal combustion engine, wherein the air mass meter has a trained in micro-electro-mechanical design sensor element ^¬ .

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 then optimized ^¬ a way that an exactly to the air mass coordinated quantity of fuel to the respective combustion chambers supplied ^¬ leads is. As a result, thereby a better energy ^¬ utilization is achieved with reduced pollutant emissions.

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.

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. In the development of modern air mass sensors, which work on the basis of sensor elements, which are designed as microelectromechanical systems (MEMS), it has been found that the measurement results of the sensor elements are particularly adversely affected by contamination. As a result of contamination 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.

This object is solved by the features of the independent claim. Advantageous embodiments are the subject of the dependent claims.

According to the invention, the following method steps are carried out to solve the problem:

A: determination of a first measured value of the air mass meter with the sensor element at a zero mass flow,

B: storing the first measured value of the air mass meter in an electronic memory,

C: operating the internal combustion engine and determining the air mass flow supplied to the internal combustion engine with the air mass meter,

D: determination of a second measured value of the air mass meter after the operation of the internal combustion engine at a zero mass flow,

E: comparing the first measured value with the second measured value, 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 first measured value of the air mass meter with the sensor element at a zero mass flow, a reliable reference value is obtained with which it is possible to detect contamination-induced signal drift. This measured value is stored in an electronic memory. The electronic memory may be a component of the air mass ^¬ knife itself or be formed in an external control device. When the internal combustion engine is operated and the air mass flow supplied to the internal combustion engine with the air mass meter is determined, contamination can occur on the sensor element, which leads to signal drift. With the signal drift distort the measured values, which are determined by the air ^¬ mass meter for the internal combustion engine supplied air mass flow. To detect this, the determination of a second measured value of the air mass meter with the possibly polluted in the operation of the internal combustion engine sensor element at a zero mass flow. By comparing the first measured value with the second measured value, a contamination-related signal drift of the sensor element can be detected. When determining a deviation between the first measured value and the second measured value, a correction of the offset of the characteristic curve of the sensor element takes place. In this way, a pollution-induced offset drift of trained in microelectromechanical sensor design can constantly correct element, resulting in highly accurate measurement resulting ^¬ nissen MAF over its entire lifetime.

In one embodiment of the inventive method, the zero mass flow is determined when the internal combustion engine for

Standstill has come. In this situation, no air mass promoted to the internal combustion engine, which are well reproducible conditions to measure the zero mass flow.

In a further development of the invention, the zero mass flow is determined when the internal combustion engine is cooled. This ensures that chimney effects that can result even when switched off the engine when hot combustion ^¬ combustion engines in the intake air flows to be excluded.

In one embodiment of the invention, the stoppage of the internal combustion engine is detected by the air mass meter itself. This can be done by an electronic circuit which is arranged in the air mass meter and recognizes independently based on parameters, whether the internal combustion engine has come to a standstill.

Such a parameter may be the pulsation of the air mass flow. The air mass meter detects the stoppage of the internal combustion engine when there is no pulsation in the measuring signal of the air mass flow sensor. Pulsations are cyclic He ^¬ increases and reductions in the air mass flow in the intake of the engine. The reductions may go as far as reversing the air mass flow at which the air mass moves away from the engine. Pulsations of the air mass occur particularly pronounced in internal combustion engines with four cylinders. The trained in microelectromechanical design sensor element can pulsations particularly well he ^¬ know because it can react very quickly to changes in the air mass flow.

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: 1 shows an air mass meter,

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,

Figure 4 shows a situation in which the air mass flow through the

Inlet port flows in the auxiliary tube of the mass air flow sensor, Figure 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, Figure 6, the sensor element with the first temperature sensor element and the second temperature sensor element,

Figure 7 is a flowchart. 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. For the efficient combustion of the fuel into the cylinders of an internal combustion engine, it is necessary to get an accurate In ^¬ formation 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 on ^¬ . As a rule, the temperature sensor elements 7, 8 are formed from resistors or thermopiles which assume different resistance values in accordance with the temperature prevailing at the temperature sensor element. 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 through the inlet opening 4 in the housing 3 of the air ^¬ mass meter 2 via first flows the first Tem ^¬ peratursensorelement 7, and then the heater 12, after which the air mass flow 10 reaches the second temperature sensor element 8 and along the auxiliary pipe 5 to the outlet opening 6 of the air mass meter 2 is passed. The air mass flow 10 reaches the first temperature sensor element 7 at a certain temperature. This temperature is detected by the first temperature sensor element 7. 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 present temperature of the air mass flow 10 with the second temperature sensor element 8 is determined. From the difference between the temperature measured by the first temperature sensor element 7 and 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 contain an evaluation unit 13, which evaluates the measurement signals of the first temperature sensor element 7 and the second temperature sensor element 8. The information obtained about the air mass flow 10 is forwarded to a not shown motor control wei ^¬.

It should be noted that the invention is described by way of example with reference to an air mass meter, but this is not

Limitation of the method for operating a mass flow sensor on the measurement of air mass flows means. With the 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 designed 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. For this purpose, a first temperature sensor element 7 and a second temperature sensor element 8 are formed on a thin membrane 17. 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 built on ^¬ Sensor element 15 also a transmitter 13 is integrated, which evaluate the measurement signals of the temperature sensor elements 7, 8 immediately and can convert a signal that is proportional to the air mass flow 10. However, the transmitter 13 may just as well be integrated in a downstream electronic device. The information about the air mass flow 10 are then forwarded via connection pads 19 and connecting wires 18 to a subsequent electronic engine control, not shown here.

FIG. 3 shows a sensor element 15 designed as a microelectromechanical system (MEMS) for an air mass meter 2, which is formed on a single substrate, the substrate being arranged in an auxiliary tube 5 of the air mass meter 2. 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 state is referred to as zero mass flow in the context of the present disclosure. When the heating element 12 is supplied with electrical energy on the sensor element 15, the symmetrical temperature distribution 20 shown here is produced around the heating element 12. Thus, the first temperature sensor element 7 and the second temperature measuring element _n

tursensorelement 8 the same temperature and after Dif ^¬ ference of the temperature measurement 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. Thus, the second temperature ^¬ sensor element 8 measures a significantly higher temperature than the first temperature sensor element 7. By determining the Diffe ^¬ temperature of the two temperature sensor elements 7, 8 with the transmitter 13 can now determine the mass air 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

Now calculate the differential temperature signal with the

Summentemperatursignal, can on the changed thermal Conductivity and / or the changed heat capacity of the passing air mass are closed.

FIG. 5 shows the sensor element 15 of the air mass meter 2, 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

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 soiling on the sensor element 15, this is also referred to as a single drift of the air mass meter 2. This signal drift is undesirable and should be suppressed and / or compensated.

Figure 6 shows the sensor element 15 with the first temperature ^¬ tursensorelement 7 and the second temperature sensor element 8 and the disposed 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. This is located in the Flow direction of the air mass flow 10, the first Tempe ^¬ temperature sensor element 7 in front of the heating element 12 and the second Tem ^¬ temperature sensor element 8 behind the heating element 12. Both the first temperature sensor element 7 and the second temperature ture sensorelement 8 set 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.

Furthermore, 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 15. 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 resistors, which are 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, which ultimately leads to the falsification of the measured values for the air mass flow 10 detected by the sensor element 15. In addition, the deposition of the contaminants preferably takes place in the edge region of the membrane 17. The asymmetrical deposition of the oil droplets 11 has physical reasons which originate in particular in the higher temperature in the region of the second sensor element 8 and in the temperature gradient in the edge region of the membrane 17. FIG. 7 shows a flow diagram which represents the invention

A method for operating an air mass meter is closer. 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 this microelectromechanical

Systems against contamination and the resulting signal drift of these sensor elements has already been mentioned above explained. He ^¬ the mediation of a measured value of the air-mass meter with the Sen ^¬ sorelement takes place to avoid the signal drift and to compensate for these signal drift in a first step A, at a zero mass flow. This measured value determined with a zero mass flow represents a reference value which is stored in an electronic memory in a step B. The stored in the electronic memory first measured value is maintained at least as long in the electronic memory until after operation of the internal combustion engine and the determination of the added of the engine air mass flow with the mass air flow meter, a determination of a second measured value of the air mass meter, which measured also at a Nullmas ^¬ senstrom is, however, after a certain period of operation of the sensor element and the associated possible contamination of the sensor element by z. B. oil droplets. For this purpose, the internal combustion engine can be parked, for example. The first measured value for the zero mass flow is then compared with the second measured value for the zero mass flow in method step E, and it is determined in method step F whether there is a deviation between the first measured value and the second measured value. If there is no deviation between the first measured value and the second measured value, the method can be restarted at step A, wherein the determination of a further first measured value of the air mass meter with the sensor element takes place at a zero mass flow. However, there is a deviation between the first measurement value and the second measured value of the air flow meter at zero mass flow rates, then a correction of the offset of the characteristic curve of the sensor element ^¬. In this case, this offset correction of the sensor characteristic curve does not have to be completed in order For example, in the case of faulty first and second measured values for a zero mass flow, the result is not an excessive incorrect correction of the offset of the characteristic curve. It is conceivable in the case of a deviation between the first measured value and the second measured value of the air mass meter for a zero mass flow to initiate only a small offset correction of the characteristic curve of the sensor element and then to restart the method according to the invention at point A in order to interact with the caused by the pollution caused offset drift of the sensor ^¬ element and gradually correct this in several rounds of the process.

Claims

A method of operating an air mass meter (2) for determining a an internal combustion engine supplied air mass flow (10), wherein the air mass meter (2) has a hole formed in micro-electro-mechanical construction sensor element (15), with the following method ^¬ steps of:

A: determination of a first measured value of the air mass meter (2) with the sensor element (15) at a zero mass flow,

B: storing the first measured value of the air mass meter (2) in an electronic memory (13),

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: determination of a second measured value of the air mass meter (2) after operation of the internal combustion engine at a zero mass flow,

E: comparing the first measured value with the second measured value,

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.

Method for operating an air mass meter (2) according to claim 1, characterized in that the zero mass flow is determined when the internal combustion engine has come to a standstill. Method for operating an air mass meter (2) according to claim 1 or 2, characterized in that the zero mass flow is determined when the internal combustion engine is cooled down.

Method for operating an air mass meter (2) according to claim 2, characterized in that the stoppage of the internal combustion engine from the Luftmas ^¬ senmesser (2) itself is detected.

5. A method for operating an air mass meter (2) according to claim 4, characterized in that the air mass meter (2) detects the stoppage of the internal combustion engine when no pulsation in the measurement signal of the air mass meter (2) is present.