Method for determining the operating state of a burner

Abstract

The invention relates to a method (500) for determining an operating state (Z) of a burner (110), in particular an exhaust gas burner in an exhaust system (100) of an internal combustion engine (120), wherein air is supplied to the burner (110) by means of a secondary air system (101) and fuel is supplied by means of a fuel system, and wherein exhaust gas generated in the burner (110) is expelled into an exhaust system (100), in particular the exhaust system (100) of the internal combustion engine (120), wherein the method (500) comprises: acquiring a sensor signal (p) from at least one pressure sensor arranged in an air path upstream (132, 134, 136) and / or downstream (138) of the burner (110), and determining (510) an amplitude (512, 514, 522) of at least one periodic partial signal contained in the sensor signal with a predetermined frequency (f1, f2), and determining (540, 550, 560, 570) the operating state (Z) of the burner (110) as a function of the determined amplitude (512,514, 522). Furthermore, a computing unit (140), an exhaust system (100) and a computer program for carrying out such a procedure are proposed.

Description

[0001] The present invention relates to a method for determining an operating state of a burner as well as a computing unit and a computer program for carrying out the method and a corresponding exhaust gas system. Background of the invention

[0002] To achieve legally prescribed emission limits, three-way catalysts (TWC) can be used, which convert the relevant gaseous pollutants NO x , HC, and CO into harmless products such as N2, H2O, and CO2. For these catalytic reactions to proceed as intended, the temperatures in the catalyst must generally exceed the so-called light-off temperature of typically 300-400°C. Once this temperature is reached or exceeded, the catalyst converts the relevant pollutants almost completely (the so-called catalyst window).

[0003] To achieve this state as quickly as possible, so-called in-engine catalyst heating can be used. This reduces the efficiency of the gasoline engine by retarding the ignition angle, thus increasing the exhaust gas temperature and the enthalpy input into the catalyst. At the same time, combustion stability can be ensured through adapted injection strategies (e.g., multiple injections).

[0004] In addition to these internal catalyst heating measures, external catalyst heating measures can also be used, for example, using electrically heated catalysts or exhaust gas burners. Such external heating measures are described, for example, in DE 41 32 814 A1 and DE 195 04 208 A1.

[0005] To further reduce emissions compared to conventional operation with internal engine heating measures, especially during cold starts, i.e. high loads on the internal combustion engine in a cold state without an idling phase, so-called catalytic converter burners have proven to be an extremely effective measure for accelerating the TWC light-off. Disclosure of the invention

[0006] According to the invention, a method for determining the operating state of a burner, as well as a computing unit and a computer program for implementing the method, and a corresponding exhaust gas system with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0007] The invention uses a pressure sensor to assess the operating state of a burner, in particular an exhaust gas burner in an exhaust system of an internal combustion engine. The sensor is arranged in an air path upstream and / or downstream of the burner. Combustion taking place in the burner causes pressure fluctuations upstream and downstream of the burner, which can be evaluated to draw conclusions about the operating state of the burner. In particular, a partial signal can be extracted from the pressure sensor signal that fluctuates periodically with the injection frequency of the fuel metering to the burner. The amplitude of such a partial signal can be used to determine particularly reliably whether combustion in the burner is functioning or whether the flame has extinguished. In embodiments of the invention, partial signals with a different frequency, in particular multiples of the injection frequency, can also be used alternatively or additionally.

[0008] Specifically, air is supplied to the burner by means of a secondary air system and fuel by means of a fuel system, and an exhaust gas generated in the burner is expelled into an exhaust system, in particular the exhaust system of the internal combustion engine. The method comprises detecting a sensor signal from at least one pressure sensor arranged in an air path upstream and / or downstream of the burner, determining an amplitude of at least one periodic partial signal contained in the sensor signal with a predeterminable frequency, and determining the operating state of the burner as a function of the determined amplitude.

[0009] In at least one embodiment, the method further comprises comparing the determined amplitude with a predeterminable threshold value and determining the operating state as heating (ie combustion in the burner is active) if the determined amplitude is greater than the threshold value and determining the operating state as non-heating (ie combustion in the burner is inactive or not sufficiently stable) if the determined amplitude is less than or equal to the threshold value.

[0010] The threshold value can be selected, in particular, depending on a previously determined operating state, in particular wherein the threshold value is increased if the previously determined operating state is a non-heating operating state, and / or wherein the threshold value is lowered if the previously determined operating state is a heating operating state. The amplitude of the pressure signal is particularly high at the beginning of combustion, since in this state the burner is still cold and therefore each flame burst is accompanied by a greater volume expansion (and thus pressure surge) than is the case when the burner is already hot.

[0011] In embodiments of the invention, the predeterminable frequency of the at least one partial signal can be equal to an injection frequency during the supply of fuel to the burner and / or equal to a multiple of the injection frequency. As already mentioned at the beginning, this can be used to determine particularly reliably whether combustion in the burner is taking place in a stable manner.

[0012] In particular, when controlling the burner within the scope of embodiments of the invention, the injection frequency of the burner and / or its multiple is selected to be different from a rotation frequency of the internal combustion engine and its multiple. Thus, the partial signal generated by the combustion in the burner can be easily distinguished from the pressure fluctuations in the exhaust system generated by the internal combustion engine.

[0013] In at least one embodiment, the amplitude of the at least one periodic partial signal is determined using a Fourier transform of the sensor signal. This is a particularly simple way to extract periodic or at least partially periodic partial signals from a combined signal.

[0014] In at least one embodiment, the determination of the operating state is repeated more than one, two, three, five, ten, or more than twenty times per second. This allows for essentially continuous monitoring of the burner, so that in the event of an (unintentional) extinction, a rapid response can be made to improve the emissions behavior of the burner or the internal combustion engine as a whole.

[0015] Alternatively or additionally, in embodiments of the invention, the determination of the operating state can be completed for the first time at the latest 1 s, 0.5 s, 0.3 s, 0.1 s or at the latest 0.05 s after the start of the supply of fuel to the burner. This means that the burner's operation can be monitored immediately after it has started, which is generally not possible with other sensor technologies. For example, a temperature sensor is generally capable of reliably detecting a burner operating state. The temperatures measured at the burner outlet are directly related to the combustion in the burner's combustion chamber. However, the temperature sensor is only able to reliably indicate the burner's operating state significantly later than the pressure sensor used according to the invention, since the thermal behavior of the exhaust system is significantly slower than the pressure behavior.The situation is similar with chemical sensors, such as a lambda sensor, which must first be heated to a minimum operating temperature before it is ready for use. This means that a lambda sensor is also only ready for use well after the burner has started operating. The higher the number of unburned injections, the higher the burner's raw emissions. In particular, the resulting hydrocarbon emissions can, in individual cases, exceed legally stipulated limits (e.g., in the case of vehicle emissions standards). Rapid combustion detection is therefore a basic prerequisite for safe and robust burner operation. The aforementioned sensors for temperature or air-fuel ratio are therefore less suitable for monitoring burner start-up.

[0016] In at least one embodiment, the method comprises carrying out a measure depending on the determined operating state, wherein the measure comprises in particular issuing a warning message and / or switching off the fuel system and / or switching off the secondary air system and / or blocking the internal combustion engine and / or activating an ignition of the burner.

[0017] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0018] An exhaust system according to the invention for an internal combustion engine comprises at least one burner configured to heat at least one component of the exhaust system, in particular a catalytic converter, at least one pressure sensor in an air path upstream and / or downstream of the burner, and a computing unit according to the invention, wherein the at least one sensor is connected to the computing unit in a signal-conducting manner. The exhaust system thus benefits correspondingly from the advantages already explained with regard to the method.

[0019] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g. via a WLAN network, a 3G, 4G, 5G or 6G connection, etc.).

[0020] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0021] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing. Short description of the drawings Fig. 1 shows schematically an embodiment of an exhaust system according to the invention. Fig. 2 shows sensor signals as they can be obtained in embodiments of the invention. Fig. 3 illustrates how a sensor signal can be used within the scope of embodiments of the invention. Fig. 4 shows a partial signal of a sensor signal that can be used within the scope of embodiments of the invention. Fig. 5 shows schematically an embodiment of a method according to the invention. Fig. 6 shows an example of the effect of an embodiment of the invention, in particular of the method from Fig. 5. Embodiment(s) of the invention

[0022] In Fig. 1 shows an embodiment of an exhaust system according to the invention, for example, an exhaust system of a vehicle, schematically illustrated using a block diagram and designated overall by 100. The exhaust system 100 comprises a secondary air system 101 with a burner 110 and an exhaust aftertreatment system 150, which is arranged downstream of the burner 110 and downstream of an internal combustion engine 120 and here has, for example, three components 152, 154, 156 (e.g., catalysts, particulate filters, or the like).

[0023] The secondary air system 101 upstream of the burner 110 comprises an air filter 102, a secondary air pump 106, and an air valve 108. The burner 110 comprises a fuel metering device, in particular an injection device 112, and an ignition device 114. At least one pressure sensor is provided in the air path upstream and / or downstream of the burner 110, i.e., within the secondary air system 101. An absolute pressure sensor or a differential pressure sensor can be used as the pressure sensor. Fig. 1, possible installation positions in this regard are designated 132, 134, 136, and 138, respectively. However, for the invention, a single pressure sensor at one of these possible installation positions 132, 134, 136, and 138 is sufficient. Typically, a sensor is installed in installation position 132 anyway, in particular an air mass sensor, which optionally includes further sensors, for example, temperature sensors or the like. A chemical sensor for monitoring the exhaust gas composition of the burner 110, for example, a lambda sensor, can be provided at installation position 138. In at least one embodiment of the invention, the pressure sensor can be integrated into such an already present sensor (e.g., in installation position 132 or 138).

[0024] The sensor(s) (132, 134, 136, 138) are connected in a signal-conducting manner to a processing unit 140, for example, a control unit of the burner 110. The signal line can be partially or completely wireless or wired. In the example shown here, the processing unit 140 is configured to control the burner 110 and, for this purpose, is connected in a signal-conducting manner to the secondary air pump 106, the air valve 108, the injection device 112, and the ignition device 114. Furthermore, the processing unit 140 can be communicatively connected to a controller 160 of the internal combustion engine 120.

[0025] In Fig. 2, sensor signals, such as can be obtained in embodiments of the invention, are shown using diagrams 210, 220 over a common time axis t. In diagram 210, a signal p of the pressure sensor is plotted over time t, and in diagram 220, a signal from a tachometer, which detects the rotational speed w of the internal combustion engine 120, is plotted over time t. A time t0 denotes the start of the burner 110, a time t1 the start of the internal combustion engine 120. T2 marks the end of operation of the burner 110. It can be seen from diagram 210 that the pressure fluctuations in the secondary air system increase as burner operation begins. The internal combustion engine 120 also has a significant influence on these fluctuations in the pressure signal.However, it is also clearly evident that a clear identification of the operating state of the burner 110 is not reliably possible from the raw signal alone, as shown in diagram 210, since an increase in the fluctuation amplitude can indicate both combustion in the burner 110 (t0) and extinguishing of the burner (t2).

[0026] In Fig. 3 illustrates how, within the scope of embodiments of the invention, the Fig. 2 shown pressure sensor signal (diagram 210) can be used. In Fig. 5 shows a corresponding embodiment of a method according to the invention and is designated overall by 500. The method 500 can be used in particular in conjunction with the method shown in Fig. 1, but is in no way limited to this specific exhaust system 100. If reference is made below to device components, these references may in particular refer to the exhaust system 100. However, the method 500 can also be used with other suitable exhaust systems, so that such references are merely illustrative and are not to be understood as requiring the exact design of the exhaust system 100 for certain method steps. Within the scope of the method 500, in particular the pressure sensor signal p(t), as shown in diagram 210 in Fig. 2. Within the scope of the method 500, the sensor signal p(t) is evaluated for several consecutive time steps. Fig. 3, a first diagram 310 and a second diagram 320 depict two consecutive observation steps, with the time intervals examined (i.e., sections of the respective diagrams 310, 320) labeled Δt1 and Δt2, respectively. In the example shown, the time intervals Δt1 and Δt2 are of equal length but begin at different times. For example, the starting times of two immediately consecutive observation periods can be separated by less than 100 ms.

[0027] Within the scope of the invention, at least one periodic partial signal is determined from the pressure signal p(t) for each such observation period Δt1, Δt2. Fig. 4, several such partial signals are shown in the form of a diagram I(f), where I stands for the signal amplitude and f for the frequency of the respective partial signal. Such an I(f) diagram can be determined for each time step Δt1, Δt2. For this purpose, in a step 510 of the method 500, a Fourier transformation, in particular in the form of a fast Fourier transformation (FFT) or a discrete Fourier transformation, is carried out. It is particularly advantageous to only use partial signals of very narrow frequency bands, in particular in the range of the Fig. 4 shown injection frequency f1 and / or its multiples f2, f3. In Fig. The additional frequencies with high signal amplitude shown in Figure 4 (frequency bands n1, n2, n3, n4) are frequencies at which the exhaust system 100 or the secondary air system 101 is excited to resonant vibrations. These depend in particular on operating parameters of the exhaust system, e.g., absolute pressure, temperature, geometry, and the like, and are therefore generally variable, whereas the maxima at f1, f2, f3 are immobile in the frequency domain at a constant injection frequency. Optionally, such sound pressure maxima determined by the hardware can also be included.For step 510, in addition to the pressure signal over the respective observation interval Δt1, Δt2, further input variables 505, such as exhaust gas temperature, temperature of one or more components of the exhaust system 100, ambient pressure, natural frequencies of the exhaust system, injection frequency of the burner 110 and / or the internal combustion engine 120, lambda signal from downstream of the burner 110 and / or downstream of the internal combustion engine 120 and the like, can be used, in particular in order to select one or more suitable frequencies for the evaluation at which the pressure signal is influenced as little as possible by other factors.

[0028] In principle, it is sufficient to analyze just a single suitable frequency, for example the injection frequency of the burner 110, for monitoring. To ensure robust evaluation, however, it is advisable to analyze additional frequencies as redundancy. In the method used, this can also be represented with little computing power on the control unit. From the evaluation 510 of the selected frequency bands (here two, e.g. f1, f2), amplitudes 512, 514, in particular integrals over a narrow frequency band around the selected frequency f1, f2, are output. These are calculated in a step 520 to form a combustion indicator value 522. For example, the calculation 520 can comprise applying one or more mathematical operations, for example summation, division, multiplication, averaging, or the like, to the amplitudes 512, 514.

[0029] Based on the indicator value 522, an operating state of the burner 110 is subsequently determined. For this purpose, the operating state determined in a previous run of the method 500 is first determined in a step 530. If combustion was previously determined to be active, the method 500 continues with a step 540, in which the indicator value 522 is compared with a first threshold value. If the indicator value 522 is below the first threshold value, the method 500 determines in a step 570 that the combustion in the burner 110 has been extinguished or is unstable and, if necessary, implements one or more countermeasures, for example by activating the ignition device 114, adjusting the injection quantity of the injection device 112, deactivating the burner 110, blocking the start of the internal combustion engine 120, issuing a warning message, or the like.In some embodiments, the selection of the specific measure to be implemented can be dependent on other influencing variables, such as the exhaust lambda value, the temperature of one or more components of the exhaust system 100, or the like. The method can return from step 570 to step 510 to further monitor combustion or determine whether any initiated measures are successful.

[0030] If, however, it is determined in step 540 that the indicator value 522 is above or at the first threshold value, it is determined in a step 560 that the combustion in the burner 110 is stable or active, and the method 500 can return to step 510 to monitor the further course of the burner operation.

[0031] If it was determined in step 530 that combustion in burner 110 was previously inactive or unstable, the method continues with step 550, in which indicator value 522 is compared with a second threshold value, which may in particular have a greater value than the first threshold value. Analogous to step 540 already explained above, depending on the result of this comparison, method 500 continues with steps 570 (indicator value 522 less than the second threshold value) or 560 (indicator value 522 greater than or equal to the second threshold value) and then returns to step 510 if necessary. The result of method 500, i.e., step 560 or 570, is in each case returned to step 530 of the subsequent method run in order to be able to carry out the corresponding sequence of steps (or the corresponding selection between the first and second threshold values).

[0032] In Fig. 6 is an example of the effect of an embodiment of the invention, in particular of the method 500, as described in Fig. 5. Three diagrams 610, 620, 630 are shown, which share a common time axis t. Diagram 610 represents the sensor signal p(t), diagram 620 a signal amplitude I(f1) of a partial signal with the frequency f1 or the values ​​with respect to Fig. 5 already explained indicator value 522 and diagram 630 show the result of the determination of the operating state Z of the burner 110, where a high signal level represents active or stable combustion and a low signal level represents inactive or unstable combustion in the burner 110.

[0033] Diagrams 610, 620, 630 were recorded for demonstration purposes. The internal combustion engine 120 was started at a time t1, while the burner 110 (in contrast to the Fig.2) was only started thereafter at a time t0. At times t3 and t4, the injection device 112 of the burner 110 was deactivated briefly, so that at these times the combustion in the burner became unstable or extinguished. At time t2, the burner 110 was deactivated.

[0034] As can be clearly seen, the operation of the internal combustion engine 120 generates a pressure signal that exhibits significant fluctuations (period between t1 and t0 in diagram 610). However, only a very low signal can be seen in diagram 620 during this period, since these pressure fluctuations do not lie within the frequency band under consideration, so that the amplitude I(f1) of the partial signal under consideration is low during this period and, in particular, lies below a threshold value 622. Immediately after the activation of the burner 110 (t0), however, this amplitude I(f1) increases sharply and remains high essentially throughout the entire burner operation. At times t3, t4, at which the burner operation was intentionally interrupted briefly, this amplitude suddenly drops again to almost zero.Accordingly, as illustrated in diagram 630, the operating state Z of burner 110 is determined as heating (active), with the exception of the intentional interruptions in operation (t3, t4), while the operating state Z is also determined as non-heating (inactive) at precisely the times at which operation was actually interrupted. Although the raw signal p, as depicted in diagram 610, also exhibits increased fluctuations at these times, these fluctuations cannot be readily assigned to a specific operating state of burner 110 or internal combustion engine 120. However, as the evaluation of the frequency-specific signal analysis (diagram 620) shows, this assignment is reliably possible using the invention. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] DE 41 32 814 A1

[0004] DE 195 04 208 A1

[0004]

Claims

[1] Method (500) for determining an operating state (Z) of a burner (110), in particular an exhaust gas burner in an exhaust gas system (100) of an internal combustion engine (120), wherein air is supplied to the burner (110) by means of a secondary air system (101) and fuel is supplied by means of a fuel system, and wherein an exhaust gas generated in the burner (110) is expelled into an exhaust gas system (100), in particular the exhaust gas system (100) of the internal combustion engine (120), the method (500) comprising: detecting a sensor signal (p) of at least one pressure sensor arranged in an air path upstream (132, 134, 136) and / or downstream (138) of the burner (110), Determining (510) an amplitude (512, 514, 522) of at least one periodic partial signal contained in the sensor signal with a predeterminable frequency (f1, f2), and Determining (540, 550, 560, 570) the operating state (Z) of the burner (110) as a function of the determined amplitude (512, 514, 522). [2] Method (500) according to claim 1, comprising comparing (540, 550) the determined amplitude (512, 514, 522) with a predeterminable threshold value (622) and determining the operating state (Z) as heating (560) if the determined amplitude (512, 514, 522) is greater than the threshold value (622), and determining the operating state as non-heating (570) if the determined amplitude (512, 514, 522) is less than or equal to the threshold value (622). [3] Method (500) according to claim 1 or 2, wherein the threshold value (622) is selected as a function of a previously determined operating state (Z), in particular wherein the threshold value (622) is increased if the previously determined operating state (Z) is not heating (570), and / or wherein the threshold value (622) is lowered if the previously determined operating state (Z) is heating (560). [4] Method (500) according to one of the preceding claims, wherein the predeterminable frequency (f1, f2) of the at least one partial signal is equal to an injection frequency in the context of supplying (112) fuel to the burner (110) and / or equal to a multiple of the injection frequency. [5] Method (500) according to claim 4, wherein the injection frequency of the burner (110) and / or a multiple thereof is selected to be different from a rotation frequency of the internal combustion engine (120) and a multiple thereof. [6] Method (500) according to one of the preceding claims, wherein the amplitude (512, 514, 522) of the at least one periodic partial signal is determined using a Fourier transformation of the sensor signal (p). [7] Method (500) according to one of the preceding claims, wherein the determination of the operating state (Z) is repeated more than one, two, three, five, ten or more than twenty times per second. [8] Method (500) according to one of the preceding claims, wherein the determination of the operating state (Z) is completed for the first time at the latest 1 s, 0.5 s, 0.3 s, 0.1 s or at the latest 0.05 s after a start of the supply (112) of fuel to the burner (110). [9] Method (500) according to one of the preceding claims, comprising carrying out a measure depending on the determined operating state (Z), wherein the measure comprises in particular issuing a warning message and / or switching off the fuel system (112) and / or switching off the secondary air system (101) and / or blocking the internal combustion engine (120) and / or activating an ignition (114) of the burner (110) if the operating state (Z) was determined to be non-heating (570). [10] Computing unit (140) which is configured to carry out all method steps of a method (500) according to one of the preceding claims. [11] Exhaust system (100) for an internal combustion engine (120) with at least one burner (110) which is designed to heat at least one component (152, 154, 156) of the exhaust system (100), in particular a catalyst, at least one pressure sensor in an air path upstream (132, 134, 136) and / or downstream (138) of the burner (110) and a computing unit (140) according to claim 10, wherein the at least one sensor is connected to the computing unit (140) in a signal-conducting manner. [12] Computer program which causes a computing unit (140) to carry out all method steps of a method (500) according to one of claims 1 to 9 when it is executed on the computing unit (140). [13] A machine-readable storage medium having stored thereon a computer program according to claim 12.

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