DE102014220522A1 - Determination of a corrected pressure signal - Google Patents

Abstract

Method for determining a corrected pressure value in the exhaust gas line of an internal combustion engine, whereby measured values of pressure, mass flow and local temperature of the exhaust gas are recorded and during the operation of the internal combustion engine correction factors for the measured pressure values are determined and corrected pressure values are determined. Furthermore, a device is provided with which pressure values in the exhaust gas line can be recorded and corrected pressure values determined and output.

Description

The present invention relates to a method for determining a corrected pressure signal with a second degree polynomial fit and a device for outputting a corrected pressure signal.

The precise determination of a local pressure and / or a pressure drop by pressure sensors in various exhaust systems of internal combustion engines, referred to in this application as internal combustion engines or engines, for the calculation of the soot load of a particulate filter, on-board diagnostics, error source analysis or other purposes is essential for the operation of diesel and gasoline engines taking into account the emission standard EURO 6 and other subsequent standards. Unless stated otherwise, sensors in this application are understood to be pressure sensors. The calculation of the relationship between pressure or pressure drop and the load status is positively influenced by a high accuracy of the pressure sensors, the selection of the sensor position and the quality of the signal. Both sensors installed in vehicles and sensors in engine or vehicle test stands have inaccuracies over time and resulting deviations from the actual values. Such deviations are caused by temperature and pressure fluctuations, material behavior and environmental influences. The sensor deviations lead to impossible values, such. B. a value not equal to zero at a flow of exhaust gas equal to zero, d. H. when no mass flow takes place, or a negative pressure or a negative pressure drop when the pressure is more static. Therefore, the pressure sensors must be recalibrated regularly.

There are approaches in the prior art for the determination of sensor deviations, and thus the necessity of recalibrating the sensors, to take into account the arrangement of the sensors ( DE10217728A1 ), approaches that take into account the aging of the sensors ( DE 10 2012 204 353 A1 ), and approaches that take into account external temperature effects, ie whether the temperature is below zero degrees Celsius and the environment of the sensor may be frozen ( DE 10 2004 007 000 ).

However, the recalibration of the sensors can not be performed while a vehicle or engine is in operation. Since it is not possible to recalibrate the sensors during ongoing operation of the engine, it is an object to provide a method with which corrected values are determined and output taking into account the sensor deviation. There is also the task of providing a device with which corrected pressure values can be determined. The first object is achieved according to the features of independent claim 1 and the second object by an apparatus having the features of independent claim 7. Further advantageous embodiments, aspects and details of the invention will become apparent from the independent claim 11, the subclaims, the figures and the description.

• – Messen von Werten eines Druckes, eines Massenstroms und einer lokalen Temperatur eines Abgases durch jeweils mindestens einen Sensor,
• – Übermitteln der gemessenen Werte an eine Speichereinheit,
• – Berechnen eines Volumenstroms Ṽ unter Verwendung der Messwerte und der Gaskonstante R für Abgas durch eine Recheneinheit
• – Erstellen eines Polynom-Fits zweiten Grades aus den erhaltenen Werten durch eine Recheneinheit,
• – Berechnen eines Korrekturfaktors c durch die Recheneinheit,
• – Berechnen eines korrigierten Druckwertes p_korr durch die Recheneinheit und
• – Ausgabe es korrigierten Druckwertes

umfasst.A first aspect of the invention relates to a method for determining a corrected pressure value in the exhaust line of an internal combustion engine, the method comprising the steps

• Measuring values of a pressure, a mass flow and a local temperature of an exhaust gas through in each case at least one sensor,
• Transmitting the measured values to a memory unit,
• - Calculating a volume flow Ṽ using the measured values and the gas constant R for exhaust gas by a computing unit
• Creating a polynomial fit of second degree from the values obtained by a computing unit,
• Calculating a correction factor c by the computing unit,
• - Calculating a corrected pressure value p _corr by the arithmetic unit and
• - Output of corrected pressure value

includes.

The method according to the invention is advantageous, since realistic values of the pressure in the exhaust system can be obtained during operation of a motor vehicle or an internal combustion engine. Accordingly, further parameters, such as the soot loading of the particulate filter, can advantageously be determined. The method according to the invention provides reliable pressure values and at the same time and energy-efficient than conventional methods, since no stopping of the motor for recalibration of the pressure sensors is required. It is therefore particularly preferred if the corrected pressure value is determined during operation of the internal combustion engine.

For the application of the polynomial fit of the second degree, the local volume flow is determined on the basis of the local mass flow, the local pressure and the local temperature as well as the gas constant for exhaust gas of the exhaust gas. The polynomial fit of the second degree corresponds to the square shape of the pressure signals. The polynomial fit of the second degree results from the equation p _r = a ² + b + c (1), where p _{r is} the measured pressure value, Ṽ the volumetric flow and a, b and c are mathematical coefficients of the second degree polynomial fit. The index r in p _r stands for "raw", in German "raw", so that the measured value is also understood as raw value.

Preferably, a corrected pressure value p _{corr is} determined by the correction coefficient c according to the equation p _corr = p _r - c (2) is subtracted from the measured pressure value. The coefficient c is obtained by setting the linear coefficient b equal to zero, and at a theoretical volume flow of zero, the pressure value p _r corresponding to the polynomial fit formula is equal to the coefficient c. The volume flow Ṽ of zero is not determined as in the prior art when the engine is stopped, but advantageously via an extrapolation from the determined curves. The values are extrapolated from the curves of the polynomial fit of the second degree for an assumed volume flow of zero. The obtained value of the point of intersection with the ordinate corresponds to the coefficient c, which thus corresponds to the pressure at a theoretical volume flow of Ṽ = 0.

For this, the motor is advantageously on the one hand in operation for a certain period of time, i. long enough that different values of the individual parameters can be measured and curves can be created. On the other hand, the coefficient c can advantageously be continuously determined from the second-order polynomial fit during ongoing operation of the engine and thus updated, and thus any deviations of the pressure sensors can be compensated for at any time. Thus, corrected and reliable values are output during operation.

The volume flow Ṽ of the exhaust gas is calculated from the measured values of the mass flow ṁ and the local temperature T and the local pressure p in the exhaust gas and the gas constant R for exhaust gas. Alternatively, the mass flow ṁ can be calculated, for example, from the local temperature T and the local pressure p, the mean flow velocity of the exhaust gas and the cross-sectional area of the exhaust gas line at the position of the sensor. The mass flow ṁ is the mass of the exhaust gas, which moves within a period of time through the cross section of an exhaust pipe. The mass flow can be calculated, for example, according to the equation ṁ = dm / dt (3).

The volume flow Ṽ of the exhaust gas results z. From the equation Ṽ = ṁ · R · T / p (4).

A second aspect of the invention relates to an apparatus for carrying out the method described above, comprising a computing unit, a memory unit and a device for outputting a corrected pressure value. The advantages of the device according to the invention correspond to those of the method described above.

In a particularly preferred embodiment, the computing unit of the device is designed to create a polynomial fit of the second degree from the values obtained. Advantageously, the arithmetic unit is also designed to calculate a correction factor c for calculating a corrected pressure value.

The memory of the device stores the measured values of all relevant parameters, that is preferably of pressure p _r , mass flow ṁ and local temperature T. Furthermore, the corrected pressure values p _corr calculated from the respective measured values are stored. The measured pressure values p _r , which deviate from the corrected pressure values p _corr , are stored as empirical values. The advantage is that additional correction _factors can be determined and used for the determination of the corrected pressure values p _corr in comparison with pressure values which were measured under similar conditions. Conditions are the ambient temperature, the mileage of the engine speed or the time since the last regeneration of the particulate filter. Advantageously, thereby the accuracy of the corrected pressure values can be increased even more.

The device for outputting the corrected pressure value p _corr , also referred to as the output unit, is either a direct indicator in the dashboard region of the corresponding motor vehicle or coupled to other devices, so that other values are calculated on the basis of the corrected pressure values p _corr , for example via a Indicated for the soot loading or for the necessary regeneration of the particulate filter in the exhaust system.

A third aspect of the invention relates to a motor vehicle with a device as explained above. In other words, the invention further relates to a motor vehicle having a device comprising a computing unit, a memory unit and an output device for determining and outputting a corrected pressure value P _corr in the exhaust gas tract by means of the method described above. The advantages of the motor vehicle according to the invention correspond to those of the method and the device described above.

The invention will be explained in more detail with reference to FIGS. Show it

1 an exemplary embodiment of the device according to the invention.

2 a flow diagram of an exemplary embodiment of the method according to the invention

3 a diagram for determining a second polynomial fit from the measured raw data.

4 a diagram for the determination of corrected values on the basis of the second degree polynomial fit according to 3 ,

In the in 1 shown exemplary embodiment of the device according to the invention 1 are a pressure sensor 2 , a mass flow sensor 3 and a temperature sensor 4 in the exhaust tract 10 arranged to receive values at various times of operation of the internal combustion engine. The pressure sensor 2 , Mass flow sensor 3 and temperature sensor 4 are exemplary in the flow direction 9 the exhaust stream upstream of a particulate filter 7 arranged. But you can also in the flow direction 9 the exhaust stream behind the particulate filter 7 be arranged. Furthermore, they are with a computing unit 5 and a storage unit 6 connected. The arithmetic unit 5 calculated from the measured pressure values p _r , the measured values for the mass flow ṁ and the local temperature T of the exhaust gas data and the gas constant R for exhaust gas, the volume flow Ṽ and for this volume flow corrected pressure values sent to the output unit 8th be issued. In the storage unit 6 the raw data and the calculated values are stored.

In the in 2 illustrated exemplary embodiment of the method according to the invention are in step S1 at different times of operation of the internal combustion engine by means of the pressure sensor 2 , the mass flow sensor 3 and the temperature sensor 4 in each case a plurality of measured values of the parameters pressure p _r , mass flow of the exhaust gas ṁ, or local temperature of the exhaust gas T are determined. In other words, the measured values are recorded during operation and both to the computing unit 5 transmitted as well as in the storage unit 6 stored. In step S2, by means of the arithmetic unit 5 from the measured pressure values p _r , the data determined from measured values for the mass flow ṁ and the local temperature T of the exhaust gas and the gas constant R for exhaust gas for the volumetric flow Ṽ graphs obtained in a second degree polynomial fit according to the derived equation p _r = aṼ ² + bṼ + c (1) in a coordinate system, like in 3a shown, can be applied. By extrapolating these graphs to the ordinate, as in 3b 1, the coefficient c is determined, which corresponds to a theoretical pressure p _r when the engine is switched off, that is to say a mass flow ṁ = 0. By subtracting the coefficient c from the measured pressure p _r , in step S3, the corrected pressure value p _{corr is} obtained by subtracting the coefficient c from the measured pressure value p _r according to the equation p _corr = p _r - c (2) calculated.

The corrected pressure values determined in this way can also be represented in a second-order polynomial fit ( 4a ). The output values correspond to the corrected signals in 4b ,

In step S4, the corrected pressure value is output, ie eg directly by means of an output unit 8th displayed or transmitted to a facility that the soot loading or the regeneration needs of the particulate filter 7 certainly. The extrapolation of the measured pressure value is carried out continuously while the engine is running, so that the coefficient c is permanently determined and, accordingly, the measured pressure value p _{r is} dynamically transferred to the corrected pressure value p _corr .

For a person skilled in obvious modifications and changes of the invention fall under the protective beginning of the claims.

LIST OF REFERENCE NUMBERS

1

 Apparatus for determining a corrected pressure value

2

 pressure sensor

3

 Mass flow sensor

4

 temperature sensor

5

 computer unit

6

 storage unit

7

 particulate Filter

8th

 output unit

9

 Flow direction of the exhaust stream

10

 exhaust tract

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10217728 A1 [0003]
• DE 102012204353 A1 [0003]
• DE 102004007000 [0003]

Claims (11)

Method for determining a corrected pressure value in the exhaust tract of an internal combustion engine, characterized by the steps: - measuring values of a pressure, a mass flow and a local temperature of an exhaust gas by at least one sensor, - transmitting the measured values to a storage unit, - calculating a volumetric flow Ṽ using the measured values and the gas constant R for exhaust gas by a computing unit - generating a polynomial fit of second degree from the values obtained by a computing unit, - calculating a correction factor c, - calculating a corrected pressure value p _corr , and - output of the corrected pressure value p _corr . The method of claim 1, wherein the corrected pressure value is determined during operation of the internal combustion engine. The method of claim 1 or 2, wherein the second order polynomial fit is from the equation p _r = aṼ ² + bṼ + c where p _{r is} the measured pressure value, Ṽ is the calculated volume flow, and a, b and c are the coefficients of the second degree polynomial. The method of claim 3, wherein the corrected pressure value p _{corr is} determined by the correction coefficient c according to the equation p _corr = pr - c is subtracted from the measured pressure value. A method according to claim 3 or 4, wherein the volume flow Ṽ of the exhaust gas from the measured values of the mass flow ṁ, the pressure p and the local temperature T of the exhaust gas and the gas constant R is calculated for exhaust gas. A method according to claim 4 or 5, wherein the correction coefficient c is determined by the linear coefficient b is set equal to 0 and a zero value of the volume flow Ṽ by extrapolation of the polynomial fit second degree is determined. Contraption ( 1 ) for determining a corrected pressure value in the exhaust gas tract ( 10 ) of an internal combustion engine according to the method of any one of claims 1-6, comprising a computing unit ( 5 ), a storage unit ( 6 ), and a facility ( 8th ) for output of a corrected pressure value. Device according to Claim 7, in which the arithmetic unit ( 5 ) is designed to produce a second degree polynomial fit from the obtained values. Device according to Claim 7 or 8, in which the arithmetic unit ( 5 ) is configured to calculate a correction factor c and to calculate a corrected pressure value. Device according to one of claims 7-9, wherein the memory unit ( 6 ) stores the measured and calculated pressure values. Motor vehicle with a device according to one of claims 7-10.

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