DE102016219781A1 - Method and control unit for balancing and diagnosing an exhaust gas recirculation mass flow meter - Google Patents

Abstract

A method for determining a value for the influence of a deviation of the signals of an exhaust gas recirculation mass flow meter (48) of an internal combustion engine (10) from a correct value of the signals to a determination of the exhaust gas recirculation mass flow in a normal operation of the internal combustion engine (10) is presented. The method is characterized in that it is carried out with the internal combustion engine (10) with closed throttle valve (28) and opened exhaust gas recirculation valve (40) and that in determining the value of the influence, a first value of the recirculated exhaust gas recirculation mass flow is used depending on is determined by a prevailing before the intake valves of the internal combustion engine (10) temperature (T_34), prevailing before the inlet valves pressure and the present speed (p_36).

Description

State of the art

The present invention relates to a method according to the preamble of claim 1 and a control device according to the independent device claim. Such a method and such a controller are assumed to be known per se.

The method is used in the operation of an internal combustion engine having an exhaust gas recirculation line, a controllable exhaust gas recirculation valve arranged in the exhaust gas recirculation line and an exhaust gas recirculation mass flow meter arranged in the exhaust gas recirculation line and a throttle valve. In this environment, the method relates to the determination of at least one value for the influence of a deviation of signals of the exhaust gas recirculation mass flow meter from a correct value of these signals to a determination of a value of the exhaust gas recirculation mass flow, which takes place in a normal operation of the internal combustion engine with fully or partially opened throttle. The control unit is set up to carry out the method.

In an internal combustion engine, for example the internal combustion engine of a vehicle, part of the exhaust gas produced during the combustion of cylinder fillings of the internal combustion engine is returned to subsequent cylinder fillings. A distinction is made between internal exhaust gas recirculation, in which the exhaust gas either remains after combustion in the cylinder or is sucked back through the exhaust valve from the exhaust pipe, and external exhaust gas recirculation, in which the exhaust gas is passed through an exhaust gas recirculation line in the air supply line of the internal combustion engine. The exhaust gas recirculation line may include a radiator and a radiator bypass. It opens at a supply point in the air supply line, so that the recirculated exhaust gas is there mixed with the fresh air. The invention relates to an external exhaust gas recirculation.

The external exhaust gas recirculation is a widely used especially in diesel engines technology, which there serves primarily to reduce the emission of harmful exhaust gas components, in particular nitrogen oxides (NOx). The exhaust gas recirculation changes the chemical composition and thus the heat capacity of the gas mixture; as a result, the peak temperature in the combustion is lower, whereby less NOx is formed. In addition, the gas temperature before and - after dropping the peak temperature - even after combustion higher than without exhaust gas recirculation. Due to the higher gas temperature in the exhaust pipe, the exhaust aftertreatment catalysts can be operated at a more favorable operating point, which improves their NOx conversion.

The mass flow of the recirculated exhaust gas is determined by the pressure gradient between the discharge from the exhaust pipe and the supply in the air supply line, the temperature of the exhaust gas and the cross section of the exhaust gas recirculation line. It is influenced by the positions of different actuators in the engine. These actuators can include an exhaust gas recirculation valve arranged in the exhaust gas recirculation line, a throttle valve arranged in the air supply line, and turbochargers in turbocharged engines, for example an actuator for adjusting a variable turbine geometry (VTG) or a wastegate of an exhaust gas turbocharger or an electrically operated compressor. In modern internal combustion engines, these actuators are connected to a control unit and are controlled by the control unit so that the exhaust gas recirculation mass flow corresponds to a setpoint determined in the control unit.

Since the exact setting of the exhaust gas recirculation mass flow has a high importance for the reduction of pollutant emissions and engine performance, equipped with external exhaust gas recirculation internal combustion engine in a modern vehicle usually has a device connected to the engine control unit for measuring the exhaust gas recirculation mass flow. The measured value obtained by the measurement serves as an input variable for a control that takes place by the control unit.

Accurate adjustment of exhaust gas recirculation mass flow may also be important for the protection of engine components. Excessive or too low exhaust gas recirculation mass flow can in fact lead to damage of engine components, for example to the mechanical damage of an exhaust gas turbocharger due to an excessively low exhaust gas recirculation mass flow, which causes too high fresh air mass flow, or to thermal damage of engine components due to an excessive exhaust gas recirculation mass flow, which too high a temperature of the gas downstream of the supply point and / or can cause an excessively high exhaust gas temperature.

In addition to the aforementioned prior art, in which an exhaust gas recirculation mass meter installed in the exhaust gas recirculation line is used, a device for determining the exhaust gas recirculation mass flow is also known, in which the exhaust gas recirculation mass flow is not measured directly, but is calculated by subtracting the fresh air mass flow from the total mass flow into the cylinders , The fresh air mass flow is through a in the air supply line upstream of the supply point and thus measured in the flow direction of the air upstream of the supply point mass flow meter.

The total mass flow into the cylinders is calculated from the gas pressure upstream of the intake valves, the gas temperature upstream of the intake valves, the engine speed, the cylinder displacement, the number of cylinders, and the volumetric efficiency of the cylinders determined during development.

The mass flow meters used in motor vehicles usually have a certain degree of inaccuracy. Often the inaccuracy can be approximated sufficiently well by a first order function, i. by the sum of an additive error - an offset error and a slope error. The inaccuracy of the mass flow meter may change over its lifetime.

Causes are, for example, manufacturing tolerances, wear or contamination.

It is therefore advantageous to balance the mass flow meter during operation. One known method is to match the mass flow reading to zero while the engine is stopped. By this method one can determine a parameter of inaccuracy, namely the offset at mass flow equal to zero.

For mass flow meters, which are installed in the air supply line upstream of the exhaust gas recirculation feed line, it is also known to adjust the mass flow at further operating points at which the exhaust gas recirculation valve is closed. It makes use of the fact that when the exhaust gas recirculation valve is closed, the fresh air mass flow is equal to the total mass flow into the cylinder and the total mass flow into the cylinder from the gas pressure before the intake valves, the gas temperature before the intake valves, the engine speed, the cylinder displacement, the number of cylinders and the evolution of cylinder volumetric efficiency can be calculated.

By balancing at other operating points, the inaccuracy of the mass flow meter can be compensated much more accurately than by offset compensation alone. In particular, a pitch error can already be determined by the adjustment at only one further operating point. With knowledge of the offset and the pitch error, the inaccuracy of the mass flow meter can be compensated in the approximation of the first order, which experience has shown that a fairly good accuracy of the mass flow measurement is already achieved.

Deviating from this technical environment, the present invention relates to a technical environment in which a built-in exhaust gas recirculation line mass flow meter is used. Such an environment will be in the US 7,946,117 B2 discloses, but does not contain any information on the need for an adjustment or to verify the accuracy of the output signal of such a mass flow meter.

Disclosure of the invention

From the above-mentioned prior art, the present invention differs in its method aspects by the characterizing features of claim 1 and in their device aspects by the characterizing features of the independent device claim.

Characterized in that the method is performed with the internal combustion engine with the throttle closed and the exhaust gas recirculation valve open and that in the determination of the value of the influence, a first value of the recirculated exhaust gas recirculation mass flow is used, which is dependent on a prevailing in the implementation of the method before intake valves of the internal combustion engine temperature , is determined before the inlet valves prevailing pressure and the present speed, the inaccuracy of the mass flow meter can be compensated much more accurate than by offset compensation alone.

It is essential that the method works with a non-zero exhaust gas recirculation mass flow. The advantage over the prior art is that the adjustment can be done more accurately by the determination of the offset at zero mass flow alone. The invention allows a compensation of the inaccuracy in a variety of operating points, which has a high accuracy of the compensation result, which has an overall positive effect on the pollutant emissions, the engine performance and possibly also on the component protection.

In addition, a higher reliability of a check of the functionality of the exhaust gas recirculation mass flow meter is achieved, so that the probability is lower that a defective exhaust gas recirculation mass flow meter is not recognized or a non-defective exhaust gas recirculation mass flow meter is erroneously displayed as defective. Experience has shown that the authorities responsible for vehicle certification often require the on-board diagnosis of an emission-relevant sensor to be carried out at at least two operating points.

It is further preferred that correction values for one or more operating points are determined and a correction value function is formed therefrom.

A further preferred embodiment is characterized in that the at least one correction value is determined as the value of a deviation of the first value of the exhaust gas recirculation mass flow, which is determined as a function of the temperature prevailing in front of the intake valves, the pressure prevailing in front of the intake valves and the present rotational speed, from a second value of the exhaust gas recirculation mass flow, which is determined from the signal of the exhaust gas recirculation mass flow meter, and that certain correction values for different operating points of the internal combustion engine are stored via raw values of the signal of the exhaust gas recirculation mass flow meter.

It is also preferred that the correction value is determined as the value of a deviation of a substitute signal of a sensor signal provided by the exhaust gas recirculation mass flow meter from that sensor signal, the substitute signal being determined as a function of a temperature prevailing in front of the intake valves, a pressure prevailing in front of the intake valves and the present rotational speed and that for various operating points of the internal combustion engine, certain correction values are stored via raw values of the sensor signal of the exhaust gas recirculation mass flow meter.

It is also preferred that the measured with the exhaust gas recirculation mass flow meter and correlated with the exhaust gas recirculation mass flow signal is a differential pressure signal.

It is further preferred that the correction value determination be carried out in the overrun mode.

It is also preferable that the determination takes place at a target position of the throttle valve and the exhaust gas recirculation valve provided for determining the correction value.

It is further preferred that the throttle valve and the exhaust gas recirculation valve when triggering the correction value determination in overrun not abruptly, but gradually adjusted to the intended for the determination of the correction value target position, first the exhaust gas recirculation valve is opened and only then the throttle is closed.

A further preferred refinement is characterized in that triggering of the correction value determination takes place as a function of release conditions, wherein the release conditions depend on specific operating parameters and threshold values for these operating parameters.

It is also preferable that the operating parameters include the rotational speed and / or a pressure upstream of the intake valves.

Furthermore, it is preferred that triggering of the correction value determination takes place as a function of release conditions, which include data of a route prediction.

It is also preferred that triggering of the correction value determination takes place as a function of release conditions, which include a value for the reliability of previously determined correction values.

A further preferred embodiment is characterized in that the correction value determination and the closing of the throttle valve are terminated when a certain speed is exceeded and / or a certain maximum duration of closing the throttle valve is exceeded and / or on the basis of data of the route prediction a short predicted end of the shift operation is predicted.

It is also preferable that the value for the influence for checking the operability of the exhaust gas recirculation mass flow meter is compared with an upper and / or a lower threshold and that the exhaust gas recirculation mass flow meter is judged to be faulty if the upper threshold exceeded by a predetermined minimum frequency or the lower threshold falls below a predetermined minimum frequency.

A further preferred embodiment is characterized in that the lower threshold and / or the upper threshold is determined as a function of the not yet corrected value of a value of the exhaust gas recirculation mass flow, which is determined from the signal of the exhaust gas recirculation mass flow meter.

It is also preferable that the at least one value for the influence in a normal operation of the internal combustion engine, in which the open-throttle internal combustion engine is operated in the non-towed state, be used for controlling the exhaust gas recirculation valve. With regard to the device aspects, it is preferred that the controller is adapted to perform a method according to any of the above-enumerated preferred embodiments.

Further advantages will be apparent from the dependent claims, the description and the attached figures.

It is understood that the abovementioned and those still to be explained below Characteristics can be used not only in the specified combination, but also in other combinations or in isolation, without departing from the scope of the present invention.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. In this case, the same reference numerals in different figures denote the same or at least functionally comparable elements. In each case, in schematic form:

1 the technical environment; and

2 a flowchart as an embodiment of a method according to the invention.

In detail, the shows 1 the technical environment of the invention in the form of an internal combustion engine 10 with an air supply system 12 , an exhaust system 14 and a controller 16 , Into the air supply system 12 of the internal combustion engine 10 incoming air passes through an air filter 18 and is powered by a compressor 20 an exhaust gas turbocharger 22 compacted. The compressed air is through an optional intercooler 24 cooled. The temperature of the cooled air is provided by an optional supply air temperature sensor 26 captured and the control unit 16 fed. Downstream of the supply air temperature sensor 26 is one from the control unit 16 controllable throttle 28 in the air supply system 12 , with which the mass flow of the internal combustion engine 10 supplied air can be varied.

Downstream of the throttle 28 there is an exhaust gas supply point 30 at which an exhaust gas recirculation line 32 into the air supply system 12 opens. Between the exhaust gas supply point 30 and the intake valves of the internal combustion engine 10 are a feed gas temperature sensor 34 that is the temperature T_34 of the internal combustion engine 10 supplied feed gas, which usually contains fresh air and recirculated exhaust gas, and a supply gas pressure sensor measures 36 arranged, the the absolute pressure p_36 of the internal combustion engine 10 supplied feed gas measures. The measured values T_34, p_36 of the feed gas temperature sensor 34 and the feed gas pressure sensor 36 be the controller 16 fed. The control unit 16 From these two values, it is possible to calculate the density ρ of the exhaust gas which prevails at this location of the measurements.

In the exhaust system 14 of the internal combustion engine 10 is a turbine 38 the exhaust gas turbocharger 22 arranged, which is driven by the exhaust gas. Between the exhaust valves of the internal combustion engine 10 and the turbine 38 is the exhaust gas recirculation line 32 to the exhaust system 14 connected, so that part of the exhaust gas of the internal combustion engine 10 as exhaust gas recirculation mass flow into the air supply system 12 can be directed. In the exhaust gas recirculation line 32 is located one of the controller 16 controllable exhaust gas recirculation valve 40 ,

Next to the exhaust gas recirculation valve 40 and the throttle 28 controls the controller 10 if necessary, a fault lamp 42 indicating an error of the exhaust gas recirculation system. At the control unit 16 it is preferably the engine control unit, including the metering of fuel for the internal combustion engine 10 controls.

Optionally located between the port 44 the exhaust gas recirculation line 32 to the exhaust system 14 and the exhaust gas recirculation valve 40 an exhaust gas recirculation mass flow cooler through which the exhaust gas recirculation mass flow flows 46 , A speed sensor 49 detects the speed n of the internal combustion engine 10 and passes the acquired values to the controller 16 ,

Between the exhaust gas recirculation valve 40 and the exhaust gas supply point 30 is a traversed by the exhaust gas recirculation mass flow exhaust gas recirculation mass flow meter 48 in the exhaust gas recirculation line 32 arranged. The exhaust gas recirculation mass flow meter 48 works on the Venturi principle. In this case, the exhaust gas flows through a Venturi nozzle 48.1 , wherein the differential pressure between two points with different line cross-section through a differential pressure sensor 48.2 is measured. The measured differential pressure is the control unit 16 fed. Furthermore, in front of or behind the Venturi nozzle 48.1 the exhaust absolute pressure pabs with an exhaust gas absolute pressure sensor 48.3 and the exhaust gas temperature with an exhaust gas temperature sensor 48.4 measured. The measured exhaust gas temperature and the measured exhaust absolute pressure pabs are the control unit 16 fed. The control unit 16 From these two values, it is possible to calculate the density ρ of the exhaust gas which prevails at this location of the measurements.

der Abgasrückführmassenstrom bestimmen. Dabei bedeuten:

ms_AGR

Abgasrückführmassenstrom

A1

Leitungsquerschnitt am ersten Punkt der Differenzdruckmessung

A2

Leitungsquerschnitt am zweiten Punkt der Differenzdruckmessung

∆p

Differenzdruck, p1–p2; wobei

p1

Druck am ersten Punkt der Differenzdruckmessung

p2

Druck am zweiten Punkt der Differenzdruckmessung

ρ

Dichte des Abgases

From these quantities can be calculated according to the equation (1)

determine the exhaust gas recirculation mass flow. Where:

ms_AGR

Exhaust gas recirculation mass flow

A1

Conductor cross section at the first point of the differential pressure measurement

A2

Conductor cross section at the second point of the differential pressure measurement

Ap

Differential pressure, p1-p2; in which

p1

Pressure at the first point of the differential pressure measurement

p2

Pressure at the second point of the differential pressure measurement

ρ

Density of the exhaust gas

The core of the procedure is, with towed internal combustion engine 10 , also referred to in the vehicle technology as a shift operation, the exhaust gas recirculation valve 40 to open the throttle 28 close and the reading of the exhaust gas recirculation mass flow meter 48 (or from its output signals for temperature, absolute pressure and differential pressure from the controller 10 measured value formed) with a determined from other signals total mass flow into the cylinder. Since fresh air is not supplied when the throttle valve is closed, the exhaust gas recirculation mass flow is equal to the total mass flow into the cylinders.

Under towing or pushing operation means a state in which the engine is not burned, but is driven by the rotation of the coupled drive train. This distinction is the fired operation in which combustion chamber fillings are burned. On vehicles, coasting often occurs during braking or when driving on downhill stretches. The method is also possible when decoupling the engine from the driveline and then turning it out due to the inertia of the engine, which is also referred to as free fall. The following description applies to both sliding and free fall operation.

2 shows a flowchart as an embodiment of a method according to the invention. From a main program used to control the internal combustion engine 50 becomes with the internal combustion engine in one step 52 checks whether predetermined release conditions are met for carrying out the method according to the invention. Examples of release conditions will be discussed in detail below.

If no release condition is met, the program returns to the main program 50 , When a release condition is satisfied, a determination of a value K of the influence of a deviation of the signals of one in an exhaust gas recirculation passage of a throttle valve becomes 28 and an exhaust gas recirculation valve 40 having the internal combustion engine 10 arranged Abgasrückführmassenstrommessers 48 from a correct value of the signals to one in a normal operation of the internal combustion engine 10 with fully or partially opened throttle 28 determining a value of the exhaust gas recirculation mass flow triggered. In a first embodiment, the value K for the influence of the deviation is a correction value which compensates for this influence and, in normal operation, forms the actuating signals for the exhaust gas recirculation valve 40 is used.

In another embodiment, the value for the influence is a correlated with the exhaust gas mass flow sensor reading of the exhaust gas recirculation mass flow meter 48 , for example, the differential pressure. In the following, the method will be described with a focus on the first embodiment.

When the release conditions are present, first in one step 54 the exhaust gas recirculation valve 40 open. Only after a certain time after closing the exhaust gas recirculation valve 40 will the throttle 28 in one step 56 closed. Closing the throttle 28 possibly not abruptly but over a period of the order of one second. This can pump the turbocharger 22 be reduced. Otherwise, it could lead to increased wear or even destruction of the turbocharger bearings.

Subsequently, in one step 58 a first value of the recirculated exhaust gas recirculation mass flow as a function of a in the implementation of the method before intake valves of the internal combustion engine 10 prevailing temperature T_34, prevailing before the inlet valves pressure and the present speed p_36 determined. This is preferably done with the following equation (2) ms_total = iN_ZylV_ZylW p_36 / RT_34n (2)

ms_gesamt

gesamter Massenstrom in die Zylinder

i

gleich 1 für Zweitaktmotoren, gleich ½ für Viertaktmotoren

N_Zyl

Anzahl der Zylinder

V_Zyl

Hubvolumen eines Zylinders

W

volumetrischer Wirkungsgrad der Zylinder

R

spezifische Gaskonstante des Gases

p_36

Druck des Gases in der Luftzufuhrleitung vor den Einlassventilen

T_34

Temperatur des Gases in der Luftzufuhrleitung vor den Einlassventilen

n

Motordrehzahl

Where:

ms_gesamt

total mass flow into the cylinders

i

equal to 1 for two-stroke engines, equal to ½ for four-stroke engines

N_Zyl

Number of cylinders

V_Zyl

Stroke volume of a cylinder

W

volumetric efficiency of the cylinders

R

specific gas constant of the gas

p_36

Pressure of the gas in the air supply line in front of the intake valves

T_34

Temperature of the gas in the air supply line before the inlet valves

n

Engine speed

The physical quantities used in this formula are according to the 1 in the control unit 16 available. The pressure p_36 and the temperature T_34 are detected by the sensors installed in the air supply line upstream of the intake valves 36 . 34 measured or calculated by means of models from other sensor signals, in particular from the signals of pressure and temperature sensors, which are installed farther in the air supply line.

At this step 58 closes a step 60 in which a second value ms_AGR of the exhaust gas mass flow with the exhaust gas recirculation mass flow meter is determined according to equation (1) given above.

In the subsequent step 62 is a correction value K as a value of a deviation of the prevailing in front of the intake valves T_34 and the pressure prevailing before the intake valves pressure and the present speed p_36 determined first value of the exhaust gas recirculation mass flow of a second value of the exhaust gas recirculation mass flow, which is derived from the signal of Abgasrückführmassenstrommessers 48 results, determined.

Preferably, not only a single value K for the deviation is determined. Instead, the control unit detects after opening the exhaust gas recirculation valve 40 and then closing the throttle 28 and lapse of a time required for stabilizing the operating point for predetermined time intervals or predetermined portions of the engine speed respectively the measured value of the exhaust gas recirculation mass flow meter 48 and the total mass flow into the cylinders, calculated according to equation (2). This is done by repeating the steps 58 to 64 , where in step 64 one assignment each in step 62 certain correction value to its associated time interval or speed interval takes place.

In the already mentioned step 62 Both mass flow values are optionally freed of noise by suitable filter algorithms. From these values, in step 62 For each interval, a correction value is calculated according to equation (3). K = ms_AGR_roh - ms_total (3)

K

Berechneter Korrekturwert

ms_AGR_roh

Rohwert des AGR-Massenstroms

ms_gesamt

siehe Gleichung (2)

Where:

K

Calculated correction value

ms_AGR_roh

Raw value of the EGR mass flow

ms_gesamt

see equation (2)

The raw value of the EGR mass flow ms_AGR_roh is the value in the control unit 16 from the various output signals of the exhaust gas recirculation mass flow meter 48 calculated according to equation 1 exhaust gas mass flow before application of the calibration method described below.

It may be the case directly from the raw signal of the exhaust gas recirculation mass flow meter 48 calculated mass flow or by a value that is already the result of prior art correction algorithms for the respective sensor type, these correction algorithms are not the subject of this invention. An example is correction algorithms as a function of a sensor temperature.

The correction values K calculated according to equation (3) are determined in step 66 in a memory of the control unit 16 stored and assigned to the associated raw values ms_AGR_roh the exhaust gas recirculation mass flow. The assignment can be solved by software, for example, such that two arrays are stored, the raw values of the exhaust gas recirculation mass flow being stored in the first array and the associated correction values K in the second array. In this way, a further correction value at mass flow 0 (offset) can be stored, which is determined according to the previously known method according to the prior art.

Subsequently, a return to the main program 50 in which the internal combustion engine 10 is controlled so that it generates, for example, a required torque.

In a partial step 50.1 of the main program calculates the controller 16 from those in the step 66 stored values a correction function, FKorr (ms_AGR_roh) (4) which is defined for all values of ms_AGR_roh. This can be done, for example, by linear interpolation between the stored correction values K via ms_AGR_roh, beyond the highest stored value of ms_AGR_ohigh value by constant continuation or linear extrapolation. Alternatively, the determination of a regression function for minimizing a (for example quadratic) error or a more complex data-based method using, for example, a neural network or a Gaussian process model is possible.

In the other to the main program 50 counting step 50.2 the value of the influence is used to correct the influence of the deviation of the signals of the exhaust gas recirculation mass flow meter on the determination of the value of the exhaust gas recirculation mass flow to compensate for this influence. For this purpose, the control unit calculates the exhaust gas recirculation mass flow with the aid of the correction function according to equation (5). ms_AGR = ms_AGR_roh - FKorr (ms_AGR_Roh) (5) where ms_AGR is the exhaust gas recirculation mass flow calculated by the controller according to equation (3), and wherein Fkorr (ms_AGR_roh) is calculated according to equation (4).

Because of the high importance of exhaust gas recirculation mass flow measurement for the reduction of pollutant emissions must be an exhaust gas recirculation mass flow meter 48 in a road vehicle in many countries due to legal regulations are monitored by an on-board diagnostic (OBD) procedure. This must be in the engine control unit 16 Algorithms may be implemented based on sensor signals that detect when the exhaust gas recirculation mass flow meter 48 no longer works according to its specification. Will be a faulty exhaust gas recirculation mass flow meter 48 detected, an error code is set, which can be read by a diagnostic tool and the driver is activated by the activation of a fault lamp 42 warned and asked to visit a workshop for repair.

In addition to the OBD regulations, the desire to avoid engine damage may also be an implementation of diagnostic methods of the exhaust gas recirculation mass flow meter 48 in the control unit 16 As described above, the precise adjustment of the exhaust gas recirculation mass flow may also be important for the protection of engine components. Therefore, such a method is also interesting for engines that are still not subject to OBD regulations, such as engines of agricultural or construction machinery.

In the same to the main program 50 counting step 50.3 a comparison of the value K for the influence takes place with an upper and / or a lower threshold and in the step 50.4 the exhaust gas recirculation is judged to be faulty if the upper threshold exceeded by a predetermined minimum frequency or falls below the lower threshold with a predetermined minimum frequency. In a preferred embodiment, the lower threshold Kmin = F_Kmin (ms_AGR_roh) and / or the upper threshold Kmax = F_Kmax (ms_AGR_roh) of the not yet corrected value ms_AGR_roh a value of the exhaust gas recirculation mass flow, which from the signal of Abgasrückführmassenstrommessers 48 is determined, dependent. In terms of software, this can be done, for example, by a via ms_AGR_roh in the control unit 16 stored characteristic can be realized.

In a further embodiment, the assessment of Abgasrückführmassenstrommessers 48 is not calculated as faulty or functional on the basis of a single correction value K calculated according to equation (3). Instead, in order to improve the diagnostic robustness, a value calculated from a plurality of correction values K calculated in accordance with equation (3) and standardized, independent of ms_AGR_roh is calculated. This value is preferably compared to error thresholds only when a characteristic value indicates that the value was determined with the required reliability or accuracy. The normalized value can be, for example, the slope of a regression line determined from the correction values, and the characteristic value for the reliability can in the simplest case be the number of already performed adjustment processes in the current drive cycle. If the controller 16 the exhaust gas recirculation mass flow meter 48 judged as faulty, it outputs an error signal, for example, the error lamp 42 is turned on. The error signal is alternatively or additionally in a readable error memory of the control unit 16 stored.

The verification procedure may also be performed independently of the matching procedure. This makes sense, for example, if the inaccuracy of the correction value determined by equation (3) is higher than the expected tolerance of a faultless exhaust gas recirculation mass flow meter 48 which may be the case, for example, because of tolerances of the measured quantities entering the equation (2), but is sufficiently small to be error-free from a defective exhaust gas recirculation mass flow meter 48 to distinguish.

In this embodiment, the values K are determined as in equation (3) and possibly a function Fkorr as in equation (4) and only for checking the operability of the exhaust gas recirculation mass flow meter 48 but not used to correct its reading.

Alternatively, the adjustment and / or a check of the functionality of the exhaust gas recirculation mass flow meter 48 on the basis of a correlation with the exhaust gas mass flow sensor reading, for example, the differential pressure. The prerequisite for this is that a reference value for this sensor measured value can be calculated from the total mass flow into the cylinders determined according to equation (2). Conveniently, this alternative method is applied to the measured value which, according to experience, has the greatest influence on the calculated exhaust gas mass flow value. Is it the exhaust gas recirculation mass flow meter 48 For example, to the above-described, operating according to the Venturi principle type, so the largest error influence is based on the differential pressure measurement. During coasting, the differential pressure can be calculated by equation (6) obtained by inserting ms_total for ms_AGR in (2) and resolution after Δp:

The density ρ is determined with the aid of the measured values for absolute pressure and temperature of the exhaust gas in front of or behind the Venturi nozzle. By comparing the measured value of the differential pressure sensor 48.2 With the differential pressure Δp calculated according to equation (6), correction values for the differential pressure sensor can be calculated analogously to the correction value for the exhaust gas mass flow determined according to equation (3) and stored above a raw value for the differential pressure Δp. The further adjustment method and the method for checking the functionality of the differential pressure sensor 48.2 arise in analogy to the methods described above.

In particular, correction values corresponding to differential pressures are determined, and these correction values are determined in a step 66 comparable step in their assignment to the exhaust gas recirculation mass flow meter 48 stored differential pressures stored. In the untraced operation of the internal combustion engine 10 are then the raw values of the exhaust gas recirculation mass flow meter 48 detected differential pressure with these correction values, and the exhaust gas recirculation mass flow is determined on the basis of the thus adjusted differential pressure values.

By using the value for ms_gesamt determined according to equation (2), the correction value is calculated as the value of a deviation of a differential pressure signal Δ calculated depending on a temperature prevailing in front of the inlet valves, a pressure prevailing in front of the inlet valves and the present speed according to equation (6) p from one of the exhaust gas recirculation mass flow meter 48 formed measured differential pressure signal.

Embodiments of the above release conditions will be disclosed below. In one embodiment, the closing of the throttle valve is provided 28 and to make the adjustment or the diagnostic measurement of certain operating parameters dependent and / or time-limited. In particular, it may be provided, the throttle valve 28 only in a certain speed range, only close above a minimum pressure before the intake valves and / or no longer than a certain time.

If the engine speed is too low, it is likely that the engine will be restarted soon, so the throttle valve should be activated 28 already be prepared to be reopened. If the speed is already low at the beginning of the shift operation, then it is to be expected that the length of the shift operation will not be sufficient for a precise adjustment. Furthermore, above a certain speed, an impermissibly low pressure may occur in front of the inlet valves, which must be prevented for reasons of component protection. Setting a maximum time for the closure of the throttle 28 may be required to prevent an upstream of the throttle 28 built-in exhaust gas turbocharger 22 comes to a standstill or reverses the direction of rotation. This could be the exhaust gas turbocharger 22 damage and negatively affect the behavior of resuming the burns. The determination of the appropriate speed range and the maximum time for the closure of the throttle valve is within the scope of development.

In a further modification is provided, the closing of the throttle valve 28 and trigger the comparison or the functional check only if data of the route prediction can be expected that the shift operation lasts sufficiently long. Data of the route prediction are, for example, data of a driving profile predicted for the near future (eg with the ehorizon technology), the length of a downhill track determined from the data of the navigation device of the motor vehicle, that of the data of the navigation device and / or data of a short range recognition / data connection detected impending change in a speed limit, a determined from the proximity detection distance to the preceding vehicles, their speeds, their brake lights, traffic lights, etc., and other data that is also used for autonomous driving.

In a further modification is provided, the closing of the throttle valve 28 and terminate the alignment or function check when a near-end of the coasting operation is predicted based on the route prediction data.

In a further embodiment, the closing of the throttle valve is provided 28 and to trigger the adjustment or the functional check only if a characteristic value for the reliability or the accuracy of the adjustment value indicates that the adjustment has not yet taken place with the required reliability or accuracy. In the simplest embodiment, this may for example depend on how many adjustments have already taken place in the drive cycle. It can thus be provided that no more than a certain number of adjustments are triggered per drive cycle. Also, the entire operating range, parameterized by the raw value of the exhaust gas recirculation mass flow ms_AGR_roh, can be subdivided into subregions, and it can be provided that no more than a specific number of trims are triggered in each subarea. Also, the triggering of a characteristic for the already achieved Accuracy depend, for example, is calculated from the residue of a regression function.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• US 7946117 B2 [0015]

Claims (18)

Method for determining at least one value for the influence of a deviation of the signals of one in an exhaust gas recirculation line ( 32 ) a throttle valve ( 28 ) and an exhaust gas recirculation valve ( 40 ) having an internal combustion engine ( 10 ) arranged exhaust gas recirculation mass flow meter ( 48 ) from a correct value of the signals to one in a normal operation of the internal combustion engine ( 10 ) with fully or partially opened throttle ( 28 ) determination of a value of the exhaust gas recirculation mass flow, characterized in that the method with the internal combustion engine ( 10 ) with closed throttle ( 28 ) and opened exhaust gas recirculation valve ( 40 ) and that in determining the at least one value of the influence, a first value of the recirculated exhaust gas recirculation mass flow is used, which is dependent on a in the implementation of the method before intake valves of the internal combustion engine ( 10 ) prevailing temperature (T_34), a prevailing before the intake valves pressure and the present speed (p_36) is determined. A method according to claim 1, characterized in that correction values for one or more operating points are determined and from this a correction value function is formed. A method according to claim 2, characterized in that the at least one correction value is determined as the value of a deviation of the first value of the exhaust gas mass flow, which is determined in dependence on the temperature prevailing in front of the intake valves and the pressure prevailing before the intake valves and the present rotational speed of a second value of the exhaust gas recirculation mass flow, which is determined from the signal of the exhaust gas recirculation mass flow meter, and that for one or more operating points of the internal combustion engine certain correction values are stored via raw values of the signal of the exhaust gas recirculation mass flow meter. A method according to claim 2, characterized in that the correction value as the value of a deviation of a substitute signal of one of the exhaust gas recirculation mass flow meter ( 48 ) is determined by that sensor signal, the substitute signal being calculated as a function of a temperature prevailing in front of the inlet valves, a pressure prevailing in front of the inlet valves and the present speed, and for one or more operating points of the internal combustion engine ( 10 ) certain correction values over raw values of the sensor signal of the exhaust gas recirculation mass flow meter ( 48 ) are stored. A method according to claim 4, characterized in that the with the exhaust gas recirculation mass flow meter ( 48 ) and correlated with the exhaust gas recirculation mass flow signal is a differential pressure signal. Method according to one of the preceding claims, characterized in that the correction value determination is carried out in the overrun mode. A method according to claim 6, characterized in that the determination takes place at an intended for the determination of the correction value target position of the throttle valve and the exhaust gas recirculation valve. Method according to claim 7, characterized in that the throttle valve ( 28 ) and the exhaust gas recirculation valve ( 40 ) when triggering the correction value determination in the overrun mode is not abruptly, but gradually adjusted to the intended for the determination of the correction value target position, first the exhaust gas recirculation valve ( 40 ) and only then the throttle ( 28 ) is closed. Method according to one of the preceding claims, characterized in that triggering of the correction value determination takes place as a function of release conditions, wherein the release conditions depend on specific operating parameters and threshold values for these operating parameters. A method according to claim 9, characterized in that the operating parameters include the speed and / or pressure upstream of the intake valves. Method according to one of the preceding claims, characterized in that a triggering of the correction value determination takes place as a function of release conditions, which include data of a route prediction. Method according to one of the preceding claims, characterized in that triggering of the correction value determination takes place as a function of release conditions, which include a value for the reliability of previously determined correction values. Method according to one of the preceding claims, characterized in that the correction value determination and the closing of the throttle valve are terminated when a certain speed is exceeded and / or a certain maximum duration of the closing of the throttle valve is exceeded and / or on the basis of data of Route prediction is predicted an imminent end of the shift operation. Use of a method according to one of the preceding claims for checking the operability of the exhaust gas recirculation mass flow meter ( 48 ), characterized in that the value for the influence is compared with an upper and / or a lower threshold and that the exhaust gas recirculation mass flow meter is judged to be faulty if the upper threshold exceeded by a predetermined minimum frequency or the lower threshold is exceeded by a predetermined minimum frequency , Use according to claim 14, characterized in that the lower threshold and / or the upper threshold is determined as a function of the not yet corrected value of a value of the exhaust gas recirculation mass flow, which from the signal of the exhaust gas recirculation mass flow meter ( 48 ) is determined. Use of a method according to one of claims 1 to 15, characterized in that the at least one value for the influence in a normal operation of the internal combustion engine ( 10 ), in which the internal combustion engine ( 10 ) is operated with the throttle open in the unthreaded state, for controlling the exhaust gas recirculation valve ( 40 ) is used. To control a throttle ( 28 ) and an exhaust gas recirculation valve ( 40 ) having the internal combustion engine equipped control unit ( 16 ), which is set up, at least one value for the influence of a deviation of the signals of one in an exhaust gas recirculation line ( 32 ) of the internal combustion engine ( 10 ) arranged exhaust gas recirculation mass flow meter ( 48 ) from a correct value of the signals to one in a normal operation of the internal combustion engine ( 10 ) with fully or partially opened throttle ( 28 ) determination of a value of the exhaust gas recirculation mass flow, characterized in that the control device ( 16 ) is adapted to the at least one value for the influence of the internal combustion engine ( 10 ) with closed throttle ( 28 ) and opened exhaust gas recirculation valve ( 40 ) and thereby determine a value of the recirculated exhaust gas recirculation mass flow as a function of one before intake valves of the internal combustion engine ( 10 ) prevailing temperature (T_34), prevailing before the intake valves pressure and the present speed (p_36) and to be used in the determination of the influence of the deviation on the value of the recirculated exhaust gas recirculation mass flow. Control unit ( 16 ) according to claim 11, characterized in that it is adapted to a method according to one of claims 2 to 8 for checking the operability of the exhaust gas recirculation mass flow meter ( 48 ).

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