Method for operating a burner in an exhaust tract of an internal combustion engine and motor vehicle

Abstract

The invention relates to a method for operating a burner (18) arranged in an exhaust tract (16) through which exhaust gas from an internal combustion engine (10) can flow and which is designed to heat and / or keep warm at least one component arranged in the exhaust tract (16). The burner has a combustion chamber (24) in which a mixture comprising air and a fuel is to be ignited and thereby burned, and a spark plug (26) by means of which the mixture is to be ignited. At least one variable characterizing sooting of the spark plug (26) is determined by means of an electronic computing device (46). If the variable exceeds a threshold value, the burner (18) is operated in a free-burning mode in which, in order to remove soot from the spark plug (26), the spark plug (26) is operated and / or the mixture is burned in the combustion chamber (24).

Description

[0001] The invention relates to a method for operating a burner in an exhaust tract of an internal combustion engine according to the preamble of patent claim 1. Furthermore, the invention relates to a motor vehicle.

[0002] US 2009 / 0241520 A1 discloses a method for regenerating a diesel particulate filter.

[0003] The object of the present invention is to provide a method for operating a burner in an exhaust tract of an internal combustion engine and a motor vehicle with such a burner, so that a particularly advantageous operation of the burner can be ensured.

[0004] This object is achieved by a method having the features of patent claim 1 and by a motor vehicle having the features of patent claim 10. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0005] A first aspect of the invention relates to a method for operating a burner which is arranged in an exhaust tract of an internal combustion engine, in particular a motor vehicle, through which exhaust gas can flow, and which is designed to heat and / or keep warm at least one component arranged in the exhaust tract and provided in addition to the burner. For example, the component is an exhaust gas aftertreatment component by means of which the exhaust gas can be aftertreated. Very particularly, the component is arranged downstream of the burner in the flow direction of the exhaust gas flowing through the exhaust tract, wherein the component can very preferably be flowed through by the exhaust gas.For example, the component is or comprises at least one catalyst, such as an SCR catalyst and / or a three-way catalyst, and / or the component is or comprises, for example, at least one particulate filter, such as in particular a diesel particulate filter (DPF). Thus, for example, the internal combustion engine, which is designed as a reciprocating piston engine, i.e., a reciprocating piston machine, is designed as a diesel engine. The aforementioned motor vehicle, also simply referred to as a vehicle, can be driven by the internal combustion engine, also referred to as an internal combustion engine or internal combustion engine. The motor vehicle is preferably a commercial vehicle.

[0006] The burner has a combustion chamber in which a mixture can be ignited and thereby burned. The mixture comprises air that is or was introduced into the combustion chamber. The mixture also comprises a fuel. The mixture can be burned in the combustion chamber, whereby the burner can provide an exhaust gas also referred to as burner exhaust gas. For example, the burner exhaust gas can flow out of the combustion chamber in particular and into an exhaust pipe of the exhaust tract through which the exhaust gas can flow, and flow through the exhaust pipe and subsequently the exhaust tract and, for example, also the component, whereby the component can be warmed, i.e. heated up. When the internal combustion engine is in fired operation, combustion processes take place in the internal combustion engine, in particular in at least one combustion chamber of the internal combustion engine.During each combustion process, a fuel-air mixture is burned, resulting in the exhaust gas of the internal combustion engine, also known as engine exhaust. When reference is made above and below to exhaust gas, this refers to the engine exhaust gas of the internal combustion engine, unless otherwise stated. In particular, the burner exhaust gas can be mixed with the engine exhaust gas, which can heat the engine exhaust gas. In other words, the engine exhaust gas and the burner exhaust gas can form an exhaust gas mixture that has a higher temperature than the engine exhaust gas alone. The exhaust gas mixture can, for example, flow through the component, which can heat the component. Thus, by means of the burner, it is possible to heat the component effectively and efficiently and thereby bring it to or above a light-off temperature of the component, which can aftertreat the exhaust gas particularly effectively and efficiently from its light-off temperature.The burner can thus ensure particularly low-emission operation of the vehicle.

[0007] The burner also has a spark plug, by means of which the mixture is to be ignited, particularly in the combustion chamber. The spark plug is designed, for example, to generate an ignition spark, particularly in the combustion chamber, by means of which the mixture, particularly in the combustion chamber, can be ignited and subsequently combusted.

[0008] In order to ensure particularly advantageous, in particular particularly efficient and effective operation of the burner, the invention provides that at least one variable characterizing sooting of the spark plug is determined by means of an electronic computing device, in particular of the motor vehicle. Sooting of the spark plug is to be understood as meaning that, for example, as the running time or operating time of the internal combustion engine progresses, soot originating from the engine exhaust gas can deposit on the spark plug, so that the aforementioned sooting of the spark plug can occur. By means of the electronic computing device, the variable is compared with a predefinable or predetermined threshold value, for example, which is stored, for example, in a data memory, in particular an electronic or electrical one, of the electronic computing device.If it is determined by comparing the variable with the threshold value that the variable exceeds the threshold value, the burner is operated, in particular by means of the electronic computing device, in a free-burning mode. The free-burning mode is provided or designed to at least partially remove the soot from the spark plug, wherein in a first variant it is provided that in the free-burning mode provided and designed to remove the soot from the spark plug, the spark plug is operated, in particular for a predeterminable or predetermined period of time, for example, in particular continuously or continuously, in particular without igniting a mixture in the combustion chamber.In a second variant provided as an alternative or in addition to the first variant, it is provided that in the free-burning mode designed or provided for removing the soot from the spark plug, the mixture is burned, in particular continuously, i.e. without interruption, in the combustion chamber, and thus the burner is operated, in particular continuously, in its burner mode, also referred to as combustion mode, in which the mixture is burned, in particular continuously, i.e. without interruption, in the combustion chamber. In particular, it is provided that the free-burning mode is carried out even though operation of the burner is not necessary, for example because a temperature of the exhaust gas and / or the exhaust tract is sufficiently high and does not or would not need to be increased by means of the burner.Removing soot from the spark plug using the burn-off process is also known as spark plug burn-off. This burn-off process can counteract, prevent, or remove excessive soot buildup on the spark plug. This ensures efficient and effective operation of the burner.

[0009] In a particularly advantageous embodiment of the invention, it is provided that if the variable exceeds the threshold value and the aforementioned temperature of the exhaust gas and / or the exhaust tract is greater than a predetermined or predeterminable limit value, for example, the burner is operated in the free-burning mode by means of the electronic computing device, even though the temperature is greater than the limit value. If the variable is less than or equal to the threshold value and the temperature is greater than or equal to the limit value, the burner is kept deactivated by means of the electronic computing device, thus the burner is deactivated, whereby operation of the spark plug and combustion of a mixture in the combustion chamber are prevented. As a result, the free-burning mode is carried out then and preferably only when this is necessary due to excessive sooting of the spark plug.The background to this embodiment is that if the temperature of the exhaust gas and / or the exhaust tract, for example of the component, is greater than the limit value, neither operation of the spark plug nor operation of the burner as a whole is required, meaning that the burner does not have to be operated to increase the temperature, because the temperature is already sufficiently high that the exhaust gas can already be advantageously aftertreated by means of the component. However, if excessive sooting of the spark plug is determined based on the size, the spark plug or the burner is operated even though the temperature of the exhaust gas and / or the exhaust tract is greater than the limit value, in order to counteract the excessive sooting of the burner. This can ensure efficient and effective operation of the burner.

[0010] In order to avoid unnecessary execution of the free burn operation and thus to ensure efficient and effective operation of the burner, it is provided in a further embodiment of the invention that the size comprises several different sub-sizes.

[0011] A further embodiment is characterized in that the variable comprises a running time of the internal combustion engine since the end of the last operation of the burner. The running time of the internal combustion engine is to be understood in particular as meaning that the internal combustion engine is in its fired mode during the running time. The last operation of the burner is to be understood as the last burner operation of the burner, wherein during the burner operation the mixture in the combustion chamber is or was combusted, in particular to provide the burner exhaust gas. Alternatively or additionally, the variable comprises a mass flow of the exhaust gas that has flowed through at least a partial region of the exhaust tract since the end of a last operation, in particular burner operation, of the burner.Alternatively or additionally, the variable comprises a quantity of soot that has flowed into at least a partial area of ​​the exhaust tract since the end of a last operation, in particular burner operation, of the burner. In particular, the running time and / or the mass flow and / or the quantity can be a respective sub-variable of the variable, wherein by taking the sub-variables into account, the burnout operation can be carried out particularly in line with requirements. In particular, it is thus possible to avoid unnecessary execution of the burnout operation and thus to carry out the burnout operation then and preferably only when this is advantageous due to excessive sooting of the spark plug.

[0012] In order to be able to carry out the free-burning operation in a particularly needs-based manner and thus to avoid unnecessary executions of the free-burning operation, it is provided in a further embodiment of the invention that at least one of the sub-variables is weighted.

[0013] It has proven particularly advantageous if the at least one sub-variable is weighted as a function of at least one environmental condition and / or as a function of an operating point of the internal combustion engine, whereby the free-burning operation can be carried out in a particularly demand-oriented manner.

[0014] A further embodiment is characterized in that the operation of the spark plug in the free-burning mode comprises the spark plug generating the ignition spark several times in succession during a predetermined or predeterminable period of time, without igniting a mixture in the combustion chamber. This means that the spark plug generates the ignition spark, but no burner exhaust gas is generated. This can prevent excessive fuel consumption. Furthermore, this can generate an advantageously high temperature of the spark plug, which can advantageously burn the spark plug free.

[0015] Finally, it has proven particularly advantageous if the free burn operation comprises the mixture being combusted, in particular continuously, in the combustion chamber for a predetermined or predeterminable period of time and the spark plug being operated such that during the period in which the mixture is being combusted, in particular continuously, the spark plug generates the ignition spark several times in succession. During normal, conventional burner operation of the burner, the spark plug generates the ignition spark only once or a few times in succession and in particular only for as long or as often as necessary until the mixture has been ignited and finally burns, in particular by means of the air and the fuel being introduced into the combustion chamber, such that during normal or conventional burner operation, after the mixture has been ignited and while the mixture is being combusted, the spark plug does not generate the ignition spark.In the free-burning mode, however, it is now preferably provided that the spark plug generates the ignition spark several times in succession even after the mixture has been ignited and while the mixture is being burned, in particular continuously. This allows a particularly high temperature of the spark plug to be achieved, which allows the spark plug to be burned free particularly advantageously.

[0016] A second aspect of the invention relates to a motor vehicle, also simply referred to as a vehicle and preferably designed as a commercial vehicle, which is designed to carry out a method according to the first aspect of the invention. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention, and vice versa.

[0017] The invention is based in particular on the following considerations and findings: Combustion engines such as diesel engines require exhaust gas aftertreatment, for example, through catalytic converters and particulate filters, to comply with exhaust gas limits. These catalytic converters, such as SCR catalytic converters for the selective catalytic reduction of nitrogen oxides (NOx), in particular, only exhibit a sufficient conversion rate within a specific temperature range. It is therefore advantageous to bring the catalytic converters into this temperature range as quickly as possible after a cold start and to maintain them there, thus preventing both cooling in a lower temperature range and overheating in a higher temperature range.To achieve particularly low-emission operation of internal combustion engines such as diesel engines, it is advantageous for exhaust gas aftertreatment components, such as catalytic converters, to reach favorable temperatures very quickly after the respective internal combustion engine has been started (also known as engine start), particularly after a cold start. It is also advantageous to prevent the exhaust gas aftertreatment components from cooling down, for example, during extended phases of low engine load or during overrun. Heating elements are suitable for this purpose. These should be placed in the exhaust tract (also known as the exhaust system) at a suitable location, for example downstream of the internal combustion engine or upstream of the components to be heated or kept warm.In principle, electric heaters can be used as such heating elements, but in order to achieve high heating outputs, they require very high electrical outputs, which must be provided by the vehicle's on-board electrical system. Unless there is a particularly high on-board voltage, for example a 48-volt electrical system or even a high-voltage battery as in a plug-in hybrid vehicle, very high electrical currents are required or the achievable heating output remains far below the required level. In this case, burners are more suitable, which can particularly advantageously achieve high heating outputs even with a standard 12-volt on-board electrical system, since they cover their actual energy requirements from the fuel to be burned in the combustion chamber, which is available in sufficient quantities, for example, in the vehicle's fuel tank, and do not have to be drawn from the on-board electrical system.Burners with higher heating output are also possible.

[0018] The combustion of the mixture in the combustion chamber must be initiated by ignition, with this ignition being carried out by the spark plug, in particular by the spark plug generating and thus providing the aforementioned ignition spark. In principle, it would be conceivable to carry out the ignition using a glow plug, although the use of the spark plug would allow for particularly efficient and effective operation.

[0019] If the temperature of the exhaust gas and / or the component designed, for example, as a catalyst or at least comprising a catalyst is sufficiently high, a further heat input to the burner is actually not required or would even be disadvantageous, in particular in high-load engine operation, in which a further heat input could lead to an excessively high temperature of the exhaust gas and / or the component, and the burner is and remains switched off, i.e. deactivated, so that the internal combustion engine runs, in particular in its fired operation, without the burner being operated, i.e. without the burner being in its burner operation, in which the mixture in the combustion chamber is burned and the burner thus provides the burner exhaust gas.

[0020] However, it has been found that during the fired operation of the internal combustion engine with the burner not burning (also known as engine operation), i.e., when the internal combustion engine is operated in its fired mode while the burner is deactivated, sooting can occur on the spark plug due to, for example, engine exhaust containing soot and hydrocarbons flowing back into the combustion chamber, wafting back, diffusing, and / or pulsating. According to previous observations, this appears to occur not only, but particularly during high engine load, and during regeneration of the aforementioned particulate filter.Depending on the operating condition, even a few hours of driving without the burner in operation and with the internal combustion engine running may be enough, unless appropriate countermeasures are taken, to soot the spark plug to such an extent or to such an extent that the next time the burner and thus the spark plug are started up, sliding sparks occur instead of the intended ignition spark, or a short circuit between a center electrode and a ground electrode of the spark plug results in no spark at all, so that the spark plug can either only ignite the mixture poorly or no longer ignites the mixture at all, which can negatively affect the reliable function of the burner. Keeping the burner in continuous operation for this reason in order to avoid a fired operation of the internal combustion engine with the burner not in burner mode and thus excessive sooting of the spark plug is of course out of the question.On the one hand, this would consume unnecessary fuel for the burner, which could lead to high costs and undesirably high emissions. On the other hand, heat input into the exhaust gas by the burner would actually be disadvantageous in some operating situations, for example during high-load engine operation of the internal combustion engine, since in this case the exhaust gas is already very hot without the burner, so that a further increase in the exhaust gas temperature could possibly impair the efficiency of the component and / or lead to other undesirable effects. Continuous burner operation is also not advantageous at present because a secondary air pump for pumping air into the combustion chamber is not sufficient at high engine operating points to promote gas flow through the burner into the exhaust tract against the high exhaust gas backpressure that occurs at these operating points.

[0021] The aforementioned problems and disadvantages can now be avoided by the method according to the invention, so that an incipient sooting of the spark plug is reduced as required, i.e. in good time, before an undesirable impairment of the spark plug occurs, in particular with regard to the ignition or starting ability of the burner.

[0022] The invention is based in particular on the findings that the spark plug has a certain self-cleaning effect when the spark plug is operated, that is to say when the spark plug generates the ignition spark in particular several times in succession, in particular without a mixture being ignited in the combustion chamber, and that it has an even better cleaning effect with regard to removing the soot from the spark plug when the mixture is burned in the combustion chamber and in particular in addition to this, while the mixture is continuously burned in the combustion chamber, the spark plug generates the ignition spark several times in succession, because the temperatures prevailing here, in particular in the burner, allow any soot deposited on the spark plug to advantageously burn off.To ensure that, for example, the spark plug does not become sooted or excessively sooted when the burner is not being used for its actual purpose, i.e. heating up the exhaust tract or preventing it from cooling down, and since it is not activated by an actual burner control or regulation, it is advisable to operate the spark plug at least occasionally or continuously so that it provides the ignition spark several times in succession, or even to run the burner at least occasionally in burner mode without it having to run for its actual purpose, namely heating up the component or preventing the exhaust tract from cooling down. A borderline case of occasional firing or operation of the spark plug is continuous operation for the spark plug, even when the burner is not burning, i.e. when no mixture is being burned in the combustion chamber.

[0023] The method according to the invention makes it possible, on the one hand, to carry out the free-burning operation sufficiently often to avoid excessive sooting of the spark plug or to counteract sooting of the spark plug, but, on the other hand, to avoid excessively frequent carrying out of the free-burning operation so that the spark plug does not accumulate unnecessary operating hours, the burner does not consume excessive fuel and thus there is no excessive wear of the burner.

[0024] For example, the variable is or includes an urgency counter, which is also referred to as a burn-back counter or burn-back urgency counter. One approach to the demand-based burn-back of the spark plug can be to let the urgency counter, also referred to as the spark plug burn-back urgency counter, run, in particular to increment it, while the internal combustion engine is running without a burner. For example, if the urgency counter exceeds the threshold value, the burn-back operation is carried out. The urgency counter, also simply referred to as a counter, is reset, for example, after the burner has been in operation for a sufficiently long time, i.e., it is reset to zero, and then always starts again at zero, for example, when the burner operation is just ending, in particular after a sufficiently long burner duration, i.e., when the soot has completely burned off the spark plug.After only a very short burner operation, the urgency counter, also known simply as the counter, could be reset to zero instead of completely resetting it, i.e., setting it completely to zero, only to reset a certain delta, also known as Δ, which is greater than zero. The Δ corresponds, for example, to the duration of a burner operation that has just ended in relation to the burning time expected for complete cleaning of the spark plug. This would take into account the fact that even a short burner operation already has a certain cleaning effect through burn-off, but due to the brevity of the burner operation, it has not yet been able to completely burn off the soot from the spark plug.

[0025] For example, the urgency counter counts at least or exactly one counter variable suitable for an intended purpose, i.e. a counter variable that provides information about the extent to which the spark plug's sooting has likely built up since the last burner operation of the burner ended. The counter variable can therefore be or include at least one of the sub-variables mentioned. A suitable counter variable or sub-variable of the counter variable is, for example, the running time of the internal combustion engine since the last burner operation of the burner, also known as the engine running time. This follows the basic idea that the longer the internal combustion engine has time to do so, the more sooting can build up on the spark plug, the more it can build up, i.e. the longer the internal combustion engine runs without burner operation and provides the engine exhaust gas that can reach the spark plug, also known as the burner spark plug.However, this approach may not yet take into account that the increase in soot on the spark plug per unit of time may vary depending on the type of engine operation.

[0026] Alternatively or additionally, the sub-quantity, in particular of the counter variable, can be the aforementioned mass flow of exhaust gas that has flowed through at least a portion of the exhaust system, including, for example, a so-called hot end of the exhaust system, since the end of the last burner operation, also referred to as the exhaust gas mass flow or engine exhaust gas mass flow. This follows the basic idea that the greater the supply of soot-containing exhaust gas (engine exhaust gas) that the internal combustion engine, also simply referred to as the engine, provides during its fired operation without burner operation, i.e., without the burner running, and that can reach the spark plug, the more severe the soot buildup.In contrast to engine running time, the engine exhaust mass flow approach already takes into account that the increase in sooting on the spark plug per unit of time can vary. It occurs faster when a large amount of exhaust gas, which is inherently soot-containing, reaches the spark plug and slower when less exhaust gas, which is inherently soot-containing, reaches the spark plug. However, the engine exhaust mass flow approach may not yet take into account that the same exhaust gas mass flow may contain more or less soot mass depending on the operating state of the internal combustion engine, thus leading to a varying rate of increase in sooting on the spark plug.The engine exhaust gas mass flow through the hot end or the partial area of ​​the exhaust tract may not be identical to the exhaust gas mass flow that ultimately exits the exhaust system (exhaust tract), for example, due to a branching of a low-pressure exhaust gas recirculation system that only occurs after the hot end. However, its current level is known to an engine control unit for operating, in particular regulating or controlling, the internal combustion engine, so that the engine exhaust gas mass flow is known by the engine control unit, which may be, for example, the electronic computing device or a component of the electronic computing device.

[0027] Another possible sub-variable of the counter value is, for example, the previously mentioned amount of soot, also referred to as exhaust soot mass, where the exhaust soot mass has flowed at least into the partial area of ​​the exhaust system, at least into the hot end, and thus, for example, to the particulate filter since the end of the last burner operation. This follows the basic idea that the greater the soot mass entrained in the exhaust gas, which the internal combustion engine delivers (i.e., provides) during its fired operation without the burner running and can reach the spark plug, the more severe the soot buildup.This approach therefore not only takes into account that the increase in sooting on the spark plug per unit of time can vary, namely faster when a lot of exhaust gas, which in principle contains soot, reaches the spark plug and slower when less exhaust gas, which in principle contains soot, reaches the spark plug, but also that one and the same exhaust gas mass flow can contain more or less soot mass depending on the operating state of the internal combustion engine, and can therefore lead to a different rate of increase in sooting on the spark plug. However, this approach may not yet take into account that one and the same soot mass flow may still lead to a different rate of increase in sooting on a spark plug depending on the operating state of the internal combustion engine, insofar as the rate of increase can depend on other parameters. This can be taken into account by an additional sub-variable of the numerator.Further sub-variables of the counter variable can be other suitable and, for example, unweighted sub-variables, which can be determined, in particular calculated, by the electronic computing device. For example, the aforementioned sub-variables can be weighted, in particular to different degrees, depending on ambient conditions and / or depending on an operation referred to as engine operation, in particular fired operation, of the internal combustion engine.

[0028] It would also be conceivable to trigger the free-burning operation based on specific indications of an impairment of the spark plug's function (also known as spark plug effect). For example, the electronic computing device, also known as the control unit, can determine, in particular, whether and after how many seconds of spark plug operation (also known as firing or spark plug firing), i.e., after what ignition delay time or after how many ignition attempts, the burner actually started, and thus the mixture was actually ignited.It is therefore possible to evaluate and / or sum up the ignition delay times and / or to count a number of unsuccessful ignition attempts of the spark plug and then, when the threshold value is exceeded, to start the free burn operation or at least to increment the urgency counter in adequately large steps, so that the ignition delay time can be a further sub-quantity of the quantity or the counter quantity.

[0029] If the urgency counter or its value or counter reading exceeds the threshold value, this signals the desire or the need to carry out the free burn operation, also known as cleaning routine or burner cleaning routine, i.e. to start it and subsequently carry it out.

[0030] As previously described, one option may be to fire the spark plug while the burner is not running, i.e., while combustion of a mixture in the combustion chamber, particularly continuously, is not occurring. This allows the spark plug to generate the ignition spark several times in succession while combustion of a mixture in the combustion chamber, particularly continuously, is not occurring, thus preventing excessive soot buildup on the spark plug. This continuous operation, or quasi-continuous operation, of the spark plug represents a borderline case of "occasional firing" for the spark plug when the burner is not burning.

[0031] The following describes the aforementioned weighting of the sub-variables of the urgency counter, also referred to as weighting, wherein the sub-variables are also referred to as input variables, for example by the urgency counter being incremented depending on the input variables. The respective sub-variable can, for example, be suitably weighted depending on ambient conditions and / or an engine operating point of the internal combustion engine. The weighting includes, for example, that the engine running time, the engine exhaust gas mass flow, the exhaust gas soot mass flow and / or another fundamentally suitable sub-variable that is available, in particular calculable, in the electronic computing device and / or the ignition delay time and / or the number of failed ignition attempts are weighted, in particular according to an expected effect on soot build-up on the spark plug.High-load engine operation of the internal combustion engine and regeneration of the particulate filter are conditions that can contribute particularly strongly to sooting of the spark plug. For example, in a regeneration mode intended for regeneration of the particulate filter, the soot on the spark plug grows faster not only with the same operating time, but also with the same exhaust gas mass flow, and even with the same soot mass flow, than in a normal combustion mode in which the internal combustion engine is operated in its fired mode without regeneration mode for regenerating the particulate filter being performed. From a chemical or physical perspective, this may be a consequence of the different exhaust gas temperatures and / or exhaust gas composition during regeneration mode, for example, the higher content of partially burned or unburned hydrocarbons.However, as long as this content cannot be measured using simple methods or modulated sufficiently well, or the mechanism of action is not precisely identified, but the quantitative effect of regeneration mode on the sooting rate can at least be empirically determined, particularly in comparison to normal combustion mode, it would be advantageous, for example, to accelerate the increment or counting of the urgency counter to an appropriate degree when regenerating the particulate filter. For this purpose, the engine running time and / or the engine exhaust gas mass flow and / or the exhaust gas soot mass and / or the other sub-variable can be weighted, in particular with an appropriate weighting factor.

[0032] Something similar is conceivable, of course with a different, specifically designed weighting factor, in the case of high-load engine operation, which can be identified or quantified, for example, using a variable present in the electronic computing device, for example by: - the requested engine power, in particular in kilowatts, whether for a factor activation yes / no measured against a dataable power threshold or for an adjustment of the size of the factor by means of a dataable characteristic curve according to which, for example, the weighting factor is a function of the engine power; - the requested engine torque, in particular Newton metres, whether for factor activation yes / no measured at a dataable torque threshold or for an adjustment of the size of the factor by means of a dataable characteristic curve, according to which, for example, the weighting factor is a function of the engine torque; - the requested fuel injection quantity, in particular in milligrams per working cycle, whether for a factor activation yes / no measured against a dataable injection quantity threshold or for an adjustment of the size of the factor by means of a dataable characteristic curve, according to which, for example, the weighting factor is a function of the injection quantity; - the accelerator pedal position, whether for a factor activation yes / no measured at a dataable accelerator pedal position threshold or for an adjustment of the size of the factor by means of a dataable characteristic curve, according to which, for example, the weighting factor is the function of the accelerator pedal position; - the combustion air ratio λ or its distance to the soot limitation lambda, be it for a factor activation yes / no measured at a dataable absolute lambda threshold or a distance to the soot limitation threshold, or for an adjustment of the size of the factor by means of a dataable characteristic curve, according to which, for example, the weighting factor is a function of λ and / or a function of the distance of the combustion air ratio to the soot limitation lambda.

[0033] Over time, other conditions may prove to be critical for sooting, for example: - Operation in other special combustion processes than just particulate filter regeneration, for example operation in heating combustion processes (due to their increased amount of unburned or partially burned hydrocarbons) or operation in desulfurization and / or denitrification combustion processes in order to regenerate a nitrogen oxide storage catalyst - Operation with delayed post-injection, i.e. not or not completely burning in the combustion chamber - Operation under specific temperature and / or altitude conditions (significant temperatures could be outside, cooling water, oil or exhaust gas temperature, possibly several of these or a combination thereof) - Operation with a low combustion air ratio λ. This occurs not only in the high-load operation mentioned above, but also due to air deficiency, which can occur due to transiently delayed boost pressure buildup of the exhaust turbocharger or at higher altitudes due to lower air density, or during load changes from overrun. Here, for example, one could weight based on lambda or by detecting whether one is at the smoke limit (yes / no) or how close one is (Δ-lambda) to it. - The various special combustion processes, such as heating combustion processes, regeneration modes for regenerating a nitrogen oxide storage catalyst, denitrification mode, and / or desulfurization mode, can be assigned an appropriate weighting factor, similar to the particulate filter regeneration. The other conditions mentioned here can also be identified (yes / no, i.e., factor on / off) or quantified (i.e., adjusting the size of the factor) based on the variables already present in the engine control unit, following a similar pattern as explained above for particulate filter regeneration mode and high-load engine operation: - Quantity (milligrams / cycle) and, if applicable, position / time (degrees of crank angle or microsecond interval) of the late post-injections (i.e. those which only partially burn or do not burn in the combustion chamber), either for the activation (yes / no) of a fixed weighting factor from a threshold which can be set according to the injection quantity and / or position / time or for the adjustment of the size of the factor by means of a dataable characteristic curve, according to which, for example, the weighting factor is a function of the post-injection quantity, or a dataable characteristic map, according to which, for example, the weighting factor is a function of the quantity or position and / or time of the post-injection quantity.

[0034] Conversely, there are also operating conditions without soot buildup in the spark plug, for example, overrun without fuel injection, i.e. without combustion products such as soot in the exhaust gas, and stop phases of a start-stop system. In overrun mode, also simply referred to as overrun, there would be a running time of the internal combustion engine and an exhaust gas mass flow, but incrementing the urgency counter during this time would be disadvantageous, since sooting on the spark plug does not increase during this time. In stop phases of the start-stop system, there would be operating time or engine runtime, but even here incrementing the urgency counter would be disadvantageous, since sooting on the spark plug does not increase when the internal combustion engine is deactivated. In such conditions, it would therefore be sensible to apply a weighting factor of 0.With appropriate weighting according to the above-mentioned approach, dependent on parameters such as the one exemplified above, one could better estimate the significance of the sub-parameters considered for counting with regard to sooting. Depending on the type of burnerless driving operation, one could thus trigger the burnout operation after a shorter or longer period of time as needed, thus avoiding unnecessarily frequent initiation of the burnout operation during low-sooting operation, while still triggering the burnout operation sufficiently frequently during soot-intensive operation. A similar approach, with weighting of suitable indicators, already exists today for the maintenance interval display. This reminds you to change the oil after a shorter period of time during operation with high engine oil load than during operation with low engine oil load.It is reset after an oil change (similar to how the urgency counter should be reset after a burn-off operation has been completed) and when refilling with fresh oil it is reset by a certain Δ (similar to how the urgency counter should only be reset by a certain Δ if the burn-off operation has only been partially completed).

[0035] If the urgency counter or its value, also known as the counter reading, exceeds the threshold value, this signals a desire or a need to initiate, i.e. carry out, the burner cleaning routine.

[0036] The following measures a) and b) are potentially available as cleaning routines for the free burning operation: a) activating the spark plug for a specific period of time with an applicable ignition frequency and ignition energy recognized as optimal for the purpose of burn-off. This ignition frequency and ignition energy used for the self-cleaning mode may deviate from the corresponding values ​​for normal burner operation if, for the cleaning purpose, other values ​​of these applicable parameters prove to be appropriate than those optimal for burner ignition. For example, burn-off with an ignition frequency lower than during burner start-up, in order to save energy and reduce wear. It is therefore conceivable that the spark plug generates, i.e. provides, the ignition spark several times in succession during burn-off operation with an ignition frequency and / or ignition energy lower than during normal burner operation. b) Activating the burner for a specific period of time and thus operating the burner in burner mode, in particular with an applicable power and / or combustion air ratio of the burner recognized as optimal for the purpose of burnout, the combustion air ratio of which is also referred to as burner lambda. The burner power and burner lambda used for the self-cleaning mode can be selected within the adjustable ranges of these parameters for the burner, within which it can be operated stably, in such a way that the optimum is achieved in the tension field between the best possible cleaning effect on the one hand and the lowest possible additional fuel consumption on the other. Compared to measure b), measure a) has a lesser cleaning effect.Compared to measure b), however, measure a) has the advantages that there is no additional fuel consumption and possibly only a slight power consumption from the vehicle electrical system, that measure a) can also be carried out when the engine is at a standstill and, for example, during stop phases of the start-stop system or during a control unit run-on after the end of a journey, and that measure a) can also be carried out at high exhaust gas temperature and / or high exhaust gas back pressure and, for example, close to and at full load or during the regeneration of the particulate filter.

[0037] Measure b) has the advantage over measure a) that it has a higher cleaning effect, since the heat of the burner exhaust gas can burn off the soot on the spark plug at least almost completely, provided that the burner is operated with a suitable burner lambda of, for example, slightly greater than 1, so that on the one hand there is still oxygen available to burn off the soot, and on the other hand the burner exhaust gas is hot enough and a burner flame resulting from the combustion of the mixture is stable.Compared to measure a), measure b) has the disadvantages that additional fuel is consumed, the burner cannot be operated when the engine is at a standstill during stop phases of the start-stop system or during the control unit run-on after the end of a journey, as otherwise local overheating is possible, that the burner cannot be started or operated when the exhaust gas back pressure is high, i.e. at or close to full load, in particular due to the lack of performance of the secondary air pump, and that the burner should not be operated when the exhaust gas temperature is already high, i.e. close to full load or during regeneration of the particulate filter, as the exhaust gas mixture of burner exhaust gas and engine exhaust gas could otherwise become too hot for the component.

[0038] It is therefore advantageous to selectively implement action a) or b), especially depending on the current operating status. For example, intelligent logic is advantageous for selectively implementing action a) or b) in response to the urgency counter, i.e., in response to the urgency counter exceeding the threshold. The following approaches, for example, can be used here: Basically, only measure a) is used, i.e., burn-off via the spark plug, for example because there are hot conditions in which the burner should not be running and / or you want to avoid the small but additional fuel consumption of measure b). In this case, measure a) is either triggered whenever the threshold value is exceeded by the urgency counter (value), or you use the measure at the end of each journey, even before the threshold value is exceeded by the urgency counter, from a certain lower counter reading (which in extreme cases could also be applied to zero), to fire the spark plug for a while during the control unit's run-on time. The need to fire the spark plug for cleaning purposes while the engine is running would then only arise if a journey without burner operation is very long, so that no control unit run-on time occurs for an extended period, for example on a long motorway journey.After completing measure a), the urgency counter is reset to zero or at least reset by a certain Δ, for example to a value greater than zero.

[0039] If the applied spark plug firing duration intended for measure a) is not fully completed but is aborted for whatever reason, for example if the internal combustion engine, also simply referred to as the engine, is switched off exactly when measure a) is carried out, but it would have been decided not to fire the spark plug during the run-on, the urgency counter can be reset by a smaller value corresponding to the proportional time reached up to the abort instead of resetting it completely or by the Δ normally applied for this purpose.If one uses both the firing of the spark plug when the engine is running and the firing of the spark plug after an activation of the internal combustion engine during its run-on period, also known as shutdown, it is also conceivable that the counter is reset by a different Δ for firing when the engine is running than for firing during the run-on period if it turns out that the firing of the spark plug cleans better in one case than in the other.

[0040] The resetting of the urgency counter, also simply referred to as the counter, to zero after the respective measure has been fully run through, i.e., firing the spark plugs for the duration of the cleaning procedure, and the partial resetting if the respective measure has not been fully run through, would be designed, for example, in terms of signal flow logic, similar to that for the burner runtime. Since even with the exclusive use of measure a), i.e., firing the spark plugs when cleaning is required, burner operation, as will continue to occur, also burns off soot from the spark plug as a result of activation for the purpose of heating up or preventing the catalysts from cooling down, the counter would of course also be reset according to the burner duration after such burner operation, which is already taking place.This logic for resetting would therefore be duplicated once again in order to achieve a reset or a reduction of the counter corresponding to the degree of completeness of the burner burnout, both through the burner operation that is already taking place and through the spark plug firing that is triggered purely for cleaning purposes.

[0041] Another approach would be to generally only use measure b), but to delay its activation despite the counter exceeding the threshold in cases where burner operation is not possible, for example, when the engine is not running, at high exhaust backpressures and / or at high engine exhaust temperatures, i.e., when operating at full load or near full load, and / or during particulate filter regeneration. If this delay does not occur or only lasts briefly, the counter is reset to zero after the measure has been fully run through. However, if the delay lasts longer, greater sooting of the spark plug can be expected at the start of the measure, also known as the cleaning procedure, and the level of the urgency counter will then continue to increase beyond the threshold, which is also known as the trigger threshold. Then, one can: - either extend the duration of burner operation for this cleaning procedure accordingly, for example by the ratio of the value of the urgency counter, which has meanwhile continued to run beyond the threshold, to the trigger threshold when the burner actually starts up, and then reset the counter to zero after the end of the cleaning procedure; - or maintain the duration of the measure, simply referred to as a procedure, but then does not reset the value of the urgency counter, which has meanwhile run beyond the threshold value, to zero, but only by a Δ which corresponds exactly to the level of the threshold value, so that after the end of the procedure the counter has the value as the new starting value by which the counter had increased beyond the threshold value due to the delay in the start of the measure.

[0042] Both approaches therefore take into account the fact that operating the burner only burns off the soot on the spark plug at a certain speed, meaning that if a higher amount of soot is to be burned off, it must burn for a correspondingly longer time, or if the burning time is still the same, it will not be able to burn off the higher amount of soot completely, so that part of it remains.

[0043] If the procedure is aborted, for example because during measure b) one of the states already mentioned several times that are prohibited for burner operation is reached, or the internal combustion engine stops because of the start-stop system, the procedure can either simply be interrupted and continued when returning to a state that is permitted for burner operation, or the procedure is not interrupted but aborted, whereby in the latter case the counter reading is not completely reset, but only reset by a Δ, which expresses the part of the procedure that has been completed.If the procedure is aborted very early, it would be advantageous to continue as soon as possible. However, if the procedure is aborted shortly before completion, it would be preferable to forgo the opportunity to continue as soon as possible and instead leave a residual value in the counter, so that the next triggering due to the threshold value or its exceedance will occur somewhat earlier, because it can be assumed that the spark plug may still have residual soot due to the earlier abort of the cleaning procedure. If measure b) is stopped because the internal combustion engine is stopped at the end of the journey, it may be unclear when it could be continued, because it is impossible to predict whether the driver of the vehicle will restart the internal combustion engine shortly thereafter or leave the vehicle stationary for a longer period.In this case, it would be advisable to first reset the counter by a Δ corresponding to the portion of the cleaning procedure completed when the engine is switched off, rather than completely resetting it to zero, and to note in the information in the electronic computer that the procedure was aborted due to the end of the journey. Then, at the beginning of the next journey, one can check how long the internal combustion engine was stationary between the end of the journey that triggered the abort of the procedure and the subsequent start of the current journey. If this is very short, it is advisable to restart or continue the procedure, also known as the cleaning procedure. If, on the other hand, this is a very long pause, it is better not to continue but to restart the cleaning procedure only when the counter exceeds the threshold value again.

[0044] However, since burner operation, for its original purpose, i.e. heating up the component or preventing the exhaust tract from cooling down, causes the spark plug to be cleaned or soot burned off, and therefore the counter is reset even after such burner operation or, if the burner is only operated for a very short time, is at least reduced by a corresponding Δ and is not completely reset to zero, a very long break between two journeys means that the engine is started when the exhaust system (exhaust tract) has cooled down in the meantime, so the burner switches on again when the journey begins anyway, so that in this case the question of whether a cleaning procedure that was interrupted when the engine was last switched off should be continued when the engine is started does not even arise.

[0045] A third approach is that, when the threshold value is exceeded by the urgency counter, measure b) is used preferentially due to its particularly advantageous effectiveness with regard to burning off the soot from the spark plug, but measure a) is used instead if, at that moment, one is in one of the cases in which operating the burner in burner mode is not possible, for example when the internal combustion engine is at a standstill (engine standstill), when there are high exhaust gas back pressures and / or high engine exhaust gas temperatures, i.e. during full-load operation or near-full-load operation and / or during regeneration of the particulate filter.Even if measure b) has started but cannot be completed because one of the cases already mentioned several times occurs during the implementation of measure b), in which the burner operation must not continue, the ongoing cleaning procedure can be continued by changing on the fly from measure b) (burner operation) to or to measure a) (spark plug firing or operation).When resetting the urgency counter, the different effectiveness of measures a) and b) can be taken into account, for example, by resetting the counter completely when measure b) has been fully run through, i.e. resetting it completely to zero, but when measure a) has been fully run through, i.e. if measure b) could not be started due to one of the aforementioned obstacles and measure a) was allowed to run instead, the counter is only reset by a smaller Δ, i.e. not completely reset to zero, whereby the smaller Δ reflects the lower effectiveness of measure a) compared to b).If measure b) was started but had to be switched to measure a) on the fly before it was completed, and this then ran to the end, the counter can be reset by a Δ that lies between the complete reset, as with measure b), and the Δ provided for the complete completion of measure a), in particular according to the proportions of time spent in the respective cleaning procedure. Due to the greater cleaning effect of measure b) compared to measure a), different durations D(a) and D(b) can be specified for the complete completion, i.e., to compensate for the poorer cleaning effect, the duration d(a) for the complete completion of measure a) is longer than the duration D(b) for the complete completion of measure b).Then, in the case of a flying change from measure b) to or to measure a), the following must be taken into account: The remaining duration of measure b), which now has to be replaced by a certain duration of measure a) due to the flying change to measure a), must not be transferred 1:1 to measure a), but converted in the ratio D(a) / D(b), and in particular increased. Finally, for example, after a flying change from measure b) to measure a) has been carried out, there is still the option of switching back from measure a) to measure b) by another flying change when the operating conditions under which burner operation is possible are returned. In this case, the remaining duration would be converted back in accordance with the ratio D(b) / D(a), and in particular shortened.

[0046] A fourth approach involves using both measures a) and b) in a specific cycle. For example, measure a), which is less thorough in cleaning but is possible in almost every operating condition and does not consume additional fuel, is first performed X times, and only then is the more thorough cleaning measure b) performed once. Different strategies can then be pursued with regard to the threshold value (trigger threshold) and the counter reset: - The first X-triggers, i.e., the triggering of action a), could occur at the same counter trigger threshold as the next cleaning request via action b), and the counter would be reset the same in both cases. This would then result in the same intervals between cleanings using action a) as between the Xth cleaning using action a) and the subsequent cleaning using action b). - Alternatively, after each X-cleaning using measure a), the counter could be reset by a smaller Δ than after cleaning using measure b). This way, the less effective cleaning effect of measure a) is taken into account by triggering the next cleaning earlier than after the more thorough cleaning using measure b). - The same effect can be achieved if the counter is completely reset in all cleaning cases a) and b), but a lower trigger threshold is specified for the X cleanings with measure a) than for the subsequent cleaning with measure b). - If the respective measure is not completed in full, the counter is only reset according to the degree of cleaning achieved, similar to an incomplete run for the cases described above. - If measure b) has not been completed, if it was due but had to be aborted, for example due to engine shutdown or operating point-related reasons (exhaust back pressure) or operating mode-related reasons (particle filter regeneration), you can proceed as described above, i.e. either continue as soon as possible or switch to measure a) on the fly. - If, for example, due to the operating point (exhaust back pressure) or operating mode (regeneration of the particulate filter), measure b) cannot be activated, even though it would actually be the next step after X cleaning sequences of measure a), you can proceed as described in the cases mentioned above, i.e. either postpone it for a while or alternatively switch to measure a) again, i.e. change over.

[0047] The following describes the aforementioned continuous operation of the spark plug. Instead of triggering measure a), i.e., firing the spark plug only occasionally when the burner is not lit, for example, according to the criteria suggested in the previous paragraphs, a sensible alternative may be to have the spark plug fire virtually constantly when the burner is not lit. This would then be more of a continuous clean-up mode for the spark plug than a self-cleaning mode. The urgency counter would only be needed in this case if even continuous operation of the spark plug does not keep it sufficiently clean, and therefore, at least occasional burning off of the soot by triggering burner operation, i.e. measure b), is still advantageous or necessary. The advantages and disadvantages of continuous firing compared to only occasional firing of the spark plug, i.e. measure a), would be: - Sooting would probably not form at all. - Cleaning measure b), i.e., the occasional operation of the burner without the need to heat it up or prevent the exhaust system from cooling down, could likely be dispensed with, thus also avoiding excessive fuel consumption. Disadvantages of continuous spark plug operation would be a slightly higher power consumption due to continuous rather than part-time spark plug operation and slightly higher spark plug wear due to increased operating hours. However, the latter disadvantage can be minimized by the following measure: ◯ For the permanent clean-keeping mode, the spark plug could, if necessary, be operated with an ignition frequency and / or ignition energy that differs from its normal operation if other, in particular less wear-intensive, values ​​of these applicable parameters prove to be sufficient for keeping clean than the values ​​recognized as optimal for the purpose of burner or mixture ignition; ◯ If such control of the spark plug with a lower frequency and / or ignition energy is sufficient for the permanent clean mode, the first-mentioned disadvantage is also reduced at the same time, since the electrical power required to be provided by the vehicle electrical system will then be lower. ◯ Even when the burner is not burning, there are operating conditions in which virtually no soot buildup on the spark plug is to be expected. For example, overrun without fuel injection or engine idle during the stop phases of the start-stop system. Such operating conditions can therefore be specifically excluded from the continuous operation of the spark plug, thereby reducing its operating hours and wear without compromising its cleaning effect. ◯ In principle, by selecting suitable spark plug hardware, an appropriate spark plug service life can be achieved even under continuous operation. For example, spark plugs today achieve very high mileage despite being used in high-revving gasoline engines.

[0048] The invention can realize at least the following advantages: Sooting of the burner's spark plug can be prevented or at least kept below a critical level, ensuring reliable burner function at all times, particularly with regard to its ignition and starting capability. Only by ensuring this ignition and starting capability can the burner reliably fulfill its task, namely the rapid heating of the component required to comply with exhaust emission limits and / or the reliable prevention of excessive cooling of the exhaust tract, especially of the component.The inventive use of the variable, i.e. the urgency counter in particular for measures a) and b), ideally in conjunction with the described method of intelligent weighting, advantageously ensures that the free burn operation is triggered and carried out as required, insofar as this always takes place in good time before the ignitability of the burner is impaired and, on the other hand, does not take place unnecessarily often, thus avoiding excessive additional consumption of fuel and / or electrical energy as well as excessive wear of the spark plug.

[0049] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0050] The drawing shows: Fig. 1 a schematic representation of an internal combustion engine in whose exhaust tract a burner is arranged; Fig. 2 is a block diagram illustrating a method for operating the burner; Fig. 3 shows another block diagram illustrating the method; Fig. 4 another diagram illustrating the process; Fig. 5 another diagram illustrating the process; Fig. 6 another diagram illustrating the process; Fig. 7 another diagram illustrating the process; and Fig. 8 shows another diagram to illustrate the procedure.

[0051] In the figures, identical or functionally identical elements are provided with the same reference symbols.

[0052] Fig. 1 shows a schematic representation of an internal combustion engine 10 of a motor vehicle, also simply referred to as a vehicle, which is preferably designed as a commercial vehicle and is drivable by means of the internal combustion engine 10. The internal combustion engine 10 has an engine block 12 with a plurality of cylinders 14, by which a respective combustion chamber is partially defined. During a fired operation of the internal combustion engine 10, also referred to as engine operation, combustion processes take place in the respective combustion chamber, with a respective fuel-air mixture being combusted during the respective combustion process. This results in engine exhaust gas from the internal combustion engine 10, the engine exhaust gas of which is also simply referred to as exhaust gas. The internal combustion engine 10 has an exhaust tract 16 through which the engine exhaust gas flows, which exhaust tract is also referred to as an exhaust system.The internal combustion engine 10 has a burner 18 arranged in the exhaust tract 16, which can be supplied with air and a fuel. The supply of air to the burner 18 is illustrated by an arrow 20, and the supply of fuel to the burner 18 is illustrated by an arrow 22. The air, also referred to as burner air, with which the burner 18 is supplied, is conveyed, for example, by means of a secondary air pump, also simply referred to as an air pump. The burner 18 has a combustion chamber 24 and a spark plug 26. A mixture is formed from the burner air and the fuel, which mixture can be ignited and burned in the combustion chamber 24. This results in a burner exhaust gas from the burner 18. In order to ignite the mixture, in particular in the combustion chamber 24, the spark plug 26 can provide an ignition spark, in particular in the combustion chamber 24.For example, at an inlet point E, the burner exhaust gas from the combustion chamber 24 can flow into an exhaust pipe 28 of the exhaust system through which the engine exhaust gas can flow, so that, for example, at the inlet point E, the burner exhaust gas can mix with the engine exhaust gas. This forms an exhaust gas mixture comprising the burner exhaust gas and the engine exhaust gas, which has a higher temperature than the engine exhaust gas alone.

[0053] In the exhaust system, downstream of the inlet point E, further components 30a-c are arranged in addition to the burner 18, which are designed, for example, as exhaust gas aftertreatment components. The exhaust gas can be aftertreated by means of the exhaust gas aftertreatment components. The exhaust gas aftertreatment components comprise, for example, at least one catalyst, designed in particular as an SCR catalyst, and / or a particulate filter, designed, for example, as a diesel particulate filter. The respective component 30a-c can be heated and thus, in particular, kept warm by means of the burner exhaust gas.

[0054] The internal combustion engine 10 has an intake tract 32 through which air, also referred to as fresh air, flows, and in which a compressor 34 of an exhaust gas turbocharger 36 of the internal combustion engine 10 is arranged. The fresh air can be compressed by means of the compressor 34. Upstream of the combustion chambers and the compressor 34, a charge air cooler 38 is arranged in the intake tract 32, wherein the compressed fresh air is cooled by means of the charge air cooler 38. The compressed fresh air is distributed among the combustion chambers by means of a charge air distribution line 40 of the intake tract 32. The exhaust gas turbocharger 36 also has a turbine 42 arranged in the exhaust tract 16, which turbine can be driven by the engine exhaust gas. The compressor 34 can be driven by the turbine 42, in particular via a shaft.The exhaust tract 16 comprises an exhaust manifold 44, by means of which, for example, the respective exhaust gases from the combustion chambers are combined, in particular to form an exhaust gas mass flow also referred to as the engine exhaust gas mass flow. In particular, the inlet point E is a mixing point at which the burner exhaust gas mixes with the engine exhaust gas, or vice versa. Furthermore, the components 30-c can, for example, have a silencer.

[0055] Based on Fig. 1 to 8, a method for operating the burner 18 is illustrated below. The burner 18 is designed to heat and / or keep the components 30-c warm. This means that the components 30-c can be heated and kept warm by means of the burner 18, thus protecting them from excessive cooling.

[0056] The procedure uses a Fig. 1, the electronic computing device 46, particularly schematically illustrated, determines, in particular calculates, at least one variable that characterizes sooting of the spark plug 26. The variable is or includes, for example, an urgency counter, which is also simply referred to as a counter. If the electronic computing device 46 determines that the variable exceeds a threshold value and thus reaches or exceeds a trigger threshold, the burner 18 is operated by the electronic computing device 46 in a free-burning mode, which is designed to at least partially remove soot from the spark plug 26. In a first variant of the free-burning mode, in order to remove the soot from the spark plug 26, the spark plug is operated, in particular for a period of time and / or continuously, that is to say fired, in particular without a mixture being ignited in the combustion chamber 24.Operating or firing the spark plug 26 means that the spark plug 26 generates the ignition spark several times in succession during the period of time without igniting a mixture in the combustion chamber 24. In particular, there is no mixture of fuel and air in the combustion chamber 24. In the second variant of free-burning operation, the mixture is combusted in the combustion chamber 24, which is provided as an alternative or in addition to the first variant.

[0057] Fig. 2 to 8 show block diagrams to illustrate the method. In Fig. In Figure 2, a block B1 illustrates an integrator, which, for example, is the urgency counter, or the urgency counter is incremented by the integrator depending on an integrator input E1. A block B2 illustrates a selection of the integrator input E1. Arrows P1 indicate input variables, with the respective integrator input E1 being selected from the input variables by block B2, so that the respective input variable can be used as the integrator input E1.A first of the input variables is time, a second of the input variables is the engine exhaust gas mass flow, a third of the input variables is a mass flow of soot contained in the engine exhaust gas, also referred to as soot mass flow, wherein the soot mass flow flows through at least a partial region of the exhaust system, i.e., as a result of the engine exhaust gas flowing through at least the partial region of the exhaust system, a fourth of the input variables is another suitable variable, which is provided, for example, by the electronic computing device 46, and a fifth of the input variables is, for example, an ignition delay time of the burner 18, and a sixth of the input variables is, for example, a number of unsuccessful ignition attempts. The ignition delay time is to be understood as a time that lies between the start of firing of the spark plug 26 and the resulting ignition of the mixture of the burner 18, i.e., the time that elapses.The number of unsuccessful ignition attempts is understood to be the number by which the spark plug 26 has provided the ignition spark without this leading to the ignition of the mixture in the combustion chamber 24. An arrow P2 illustrates an output of block B1, i.e., of the integrator, so that the arrow P2 illustrates, for example, the urgency counter or its value, also referred to as the urgency value.

[0058] In Fig. 3 illustrates that the urgency counter or its urgency value comprises several sub-variables or is formed from several sub-variables, wherein the sub-variables are weighted. The sub-variables are illustrated by arrows P3. One of the sub-variables is, for example, an operating mode, for which an operating mode weighting factor G1 is determined in a block B3, in particular according to a function. Further sub-variables can be an engine power, an engine load, an injection quantity, an accelerator pedal position, a combustion air ratio, and a smoke-limiting combustion air ratio, wherein, for example, a difference between the combustion air ratio and the smoke-limiting combustion air ratio is formed by a block B4.A block B5 selects a sub-variable, for example from the engine power, the engine torque, the injection quantity, the accelerator pedal position, the combustion air ratio, the engine load, and the difference between the combustion air ratio and the smoke-limiting combustion air ratio. This sub-variable is fed to a block B4, according to which an engine load weighting factor G2 is determined for the selected sub-variable, so that, for example, the engine load weighting factor is determined according to a function dependent on the engine load. Furthermore, the sub-variables can include a post-injection quantity, a position of a post-injection, and a time of a post-injection, for which, for example, a post-injection weighting factor G3 is selected in a block B5. Selecting the respective weighting factor means that the respective weighting factor is determined, in particular calculated.The post-injection weighting factor G3 is determined, for example, according to a function that depends on the post-injection quantity, the position after injection, or the time of the post-injection. Furthermore, the sub-variables can include, in particular, a current altitude of the motor vehicle above sea level and / or a current air pressure in the surroundings of the motor vehicle and / or a current outside temperature and / or a cooling water temperature and / or an engine oil temperature and / or an engine exhaust gas temperature, for which a further weighting factor G4, formed, for example, as a temperature and / or altitude weighting factor, is determined in a block B6, in particular according to a function that depends, for example, on the altitude and / or one of the aforementioned temperatures. In a block B6, the weighting factors are multiplied.In block B7, it is determined whether the internal combustion engine 10 is in its fired mode or, for example, is deactivated due to a stop phase of a start-stop system, i.e., is stationary, and in block B8, it is determined whether the internal combustion engine 10 is in its traction mode or in its overrun mode. Depending on a result of block B7, B8, 0 or 1 is selected as the factor, and the factors of blocks B7, B8 are multiplied with one another in block B9, and a result of the multiplication is multiplied by a result of the multiplication of block B6 in block B10, wherein a result of block B10 is multiplied by the input variable selected in block B2 in block B1, B2, wherein a result of the multiplication of block B11 is used as the integrator input E1.

[0059] In Fig. 4, the aforementioned trigger threshold is designated A1. In a block B12, the trigger threshold is compared with the urgency value. If the urgency value is greater than or equal to the trigger threshold, so that the urgency value or the urgency counter exceeds the aforementioned threshold, the free burn operation is carried out, as illustrated by an arrow P4. An arrow P5 illustrates the time, and an arrow P6 illustrates a burner signal, which is, for example, one when the burner 18 is in burner operation, during which the mixture is burned in the combustion chamber 24. The burner signal illustrated by the arrow P6 is zero when the burner 18 is deactivated, i.e., when no mixture is burned in the combustion chamber 24 and thus the burner 18 is not providing its burner exhaust gas. In a block B13, the time (arrow P5) is multiplied by the burner signal (P6).Block B14 represents an integrator, which is a burner burning time counter. Block B15 represents the end of burner operation, at which point the burner signal (P6) drops from one to zero. Arrow P7 indicates that burner operation has just ended. Arrow P8 indicates that the burner burning time counter of block B14 is being reset.

[0060] An arrow P9 illustrates a target combustion duration of the burner 18 for at least complete burnout of the spark plug 26. An arrow P10 illustrates a burnout degree, which is compared to one in a block B15. If the burnout degree is greater than or equal to one, the combustion duration was sufficient to sufficiently remove soot from the spark plug 26, so that, as illustrated by an arrow P11, the urgency counter is reset. An arrow P12 illustrates a burnout degree achieved at the end of burner operation, with the arrow P12 also illustrating a value by which the integrator, and thus the urgency counter of block B1, is reset.

[0061] In Fig. 5, a block B16 illustrates that the value of the urgency counter, whose value is also referred to as the urgency counter value, is greater than the trigger threshold. A block B17 illustrates that the internal combustion engine 10, which is also simply referred to as the engine, is switched off and, for example, the electronic computing device 46 enters its run-on mode, also referred to as control unit run-on mode. A block B18 illustrates a start of firing of the spark plug 26, in particular with frequency and ignition energy advantageous for a self-cleaning purpose or a self-cleaning effect of the spark plug 26. In a block 20, a check is carried out to determine whether a target firing duration for complete cleaning has elapsed. A block B21 illustrates that the firing of the spark plug 26 stopped before the target firing duration for complete cleaning of the spark plug 26 has elapsed.A block B22 illustrates that the urgency counter is only reduced by a portion, expressed, for example, as a percentage, of the Δ provided for the complete sequence, corresponding to the achieved firing duration relative to the target firing duration. For example, if a block B23 determines that the firing of spark plug 26 occurred due to the trigger threshold, a block B24 stops the spark plug firing, and a block B25 resets the urgency counter to zero, or alternatively, the urgency counter is reduced by a Δ provided for this purpose.If it is determined in a block B26 that the firing of the spark plug 26 occurred due to a deactivation of the internal combustion engine 10 and / or due to the control unit run-on, the spark plug firing is stopped in a block B27, and in a block B28 the urgency counter is reset by a Δ provided for this purpose, which is smaller than in the case of firing due to the trigger threshold.

[0062] If in Fig. 6 If a start of the burner 18 is possible in a block B29, the burner operation of the burner 18 is started in a block B30, in particular with an output and combustion air ratio that is advantageous for the cleaning purpose, and in a block B31 the time counter for the burning time of the burner 18 is started.If it is determined in block B32 that the burner start is not possible, for example due to engine shutdown, high exhaust back pressure and / or high engine exhaust temperature, i.e. during full load operation or near full load operation and / or due to regeneration of the particulate filter, so that the urgency counter continues to run, then in block B33, for example, burner 18 or burner operation is started as soon as this is possible again, with burner 18 or burner operation, for example, taking place with an output and combustion air ratio that is advantageous for the cleaning purpose, and in block B34, the time counter for the combustion time of burner 18 is started. In block B35, a check is made to determine whether the target combustion time for complete cleaning has elapsed.If this is the case, burner 18 is stopped in block B36, and the urgency counter is reset to zero in block B37. If it is determined in block B38 that burner operation will stop before the target burning time for complete cleaning has elapsed, then in block B39 the urgency counter is reduced only by a portion, expressed for example as a percentage, of the Δ provided for the complete process, corresponding to the achieved burning time in relation to the target burning time. If it is determined in block B40 that the target burning time for complete cleaning of spark plug 26 has elapsed, then burner 18 is stopped in block B41.If it is determined in block B42 that a burner start delay was less than a limit value or that the urgency counter reading at burner start exceeded the trigger threshold by less than a threshold, the urgency counter is reset to zero in block B43. Or if it is determined in block B44 that the burner start delay was greater than a limit value or that the urgency counter exceeded the trigger threshold by more than a threshold value at burner start, the urgency counter is reduced in block B45 by a Δ equal to the trigger threshold, i.e., not to zero.If it is determined in block B46 that the burner operation stopped before the target burning time for the complete cleaning of the spark plug 26 had elapsed, the urgency counter is reduced in block B47 only by a part, for example as a percentage, of the Δ provided for the complete process, as corresponds to the achieved burning time in relation to the target burning time.

[0063] The block diagram in Fig. 7 basically corresponds to the block diagram in Fig. 6, but with the difference that a block B48 is added, according to which, in block B34, the target burning time is increased in the same ratio as the urgency counter reading at the start of burning compared to the trigger threshold. Thus, block B40 represents the burning time increased by blocks B34 and B48, and block B46 also represents the target burning time increased by blocks B34 and B48. In block B49, the urgency counter is reset to zero, and block B47 represents the target burning time increased by blocks B34 and B48.

[0064] In Fig.8, a block B50 illustrates the start of spark plug firing, particularly with a frequency and energy advantageous for self-cleaning purposes. A block B51 illustrates the start of a time counter for a firing time of the spark plug 26, wherein, according to a block B52, the target firing duration, also designated D(a), will generally be longer than the target burning duration of burner operation, designated D(b). Block B53 checks whether the target firing duration D(a) for complete cleaning has elapsed. If this is the case, a block B54 stops the spark plug firing, and a block B55 resets the urgency counter to zero or reduces the urgency counter by a Δ provided for complete cleaning per spark plug, which may be smaller than the Δ provided for complete cleaning per burner operation.If block B56 determines that burner operation is permitted again before the target combustion time D(a) for complete cleaning has elapsed, block B57 stops the spark plug firing and starts the burner, in particular with a power or combustion air ratio that is advantageous for the cleaning purpose. Block B58 converts the remaining target combustion time D(a) into a remaining target combustion time using a factor D(b) / D(a). Block B59 checks whether the remaining target combustion time for complete cleaning has elapsed. If this is the case, block B60 stops burner operation or burner 18, and block B61 resets the urgency counter to zero.If block B62 determines that burner operation will stop before the remaining target burning time for complete cleaning has elapsed, spark plug firing is restarted at block B63. The remaining target burning time is converted into a remaining firing time of spark plug 26 using a factor D(a) / D(b). This can be performed several times if necessary, possibly with repeated switching between spark plug firing and burner operation, in particular until the target cleaning procedure time is reached. Finally, block B64 stops burner operation or spark plug firing, depending on which was last active, and the urgency counter is reset to zero. Block B65 starts spark plug firing, in particular with a frequency and energy that is advantageous for self-cleaning.In block B66, the remaining target combustion time is converted into a remaining firing time using a factor D(a) / D(b). Block B67 checks whether the remaining target firing time has expired. If so, block B68 stops the spark plug firing, and block B69 resets the urgency counter to zero.If it is determined in block B70 that burner operation is permitted again before the remaining target firing time of the spark plug 26 has elapsed, the spark plug or the spark plug firing is stopped in block B71 and the burner 18 or the burner operation is started again, wherein the remaining target firing time is converted to a remaining target burning time using a factor D(b) / D(a), wherein this is carried out several times if necessary, possibly with several changes between the spark plug firing and the burner operation, in particular until the cleaning procedure time is reached. List of reference symbols 10 Internal combustion engine 12 Engine block 14 cylinders 16 Exhaust system 18 burners 20 Arrow 22 Arrow 24 combustion chamber 26 Spark plug 28 Exhaust pipe 30a-c component 32 Intake tract 34 compressors 36 exhaust gas turbochargers 38 charge coolers 40 charge air distribution line 42 turbines 44 exhaust manifold 46 electronic computing device B1-71 Block E1 integrator input P1-12 Arrow 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] US 2009 / 0241520 A1

[0002]

Claims

[1] Method for operating a burner (18) arranged in an exhaust tract (16) through which exhaust gas of an internal combustion engine (10) can flow and designed to heat and / or keep warm at least one component arranged in the exhaust tract (16), which burner has a combustion chamber (24) in which a mixture comprising air and a fuel is to be ignited and thereby burned, and a spark plug (26) by means of which the mixture is to be ignited, characterized by that by means of an electronic computing device (46): - at least one variable characterising sooting of the spark plug (26) is determined; and - if the size exceeds a threshold value, the burner (18) is operated in a free-burning mode in which, to remove soot from the spark plug (26): ◯ the spark plug (26) is operated; and / or ◯ the mixture is burned in the combustion chamber (24). [2] Method according to claim 1, characterized by , that: - if the value exceeds the threshold value and a temperature of the exhaust gas and / or the exhaust tract (16) is greater than a limit value, the burner (18) is operated in the free-burning mode by means of the electronic computing device (46), even though the temperature is greater than the limit value; and - if the value is less than or equal to the threshold value and the temperature is greater than or equal to the limit value, the burner (18) is kept deactivated by means of the electronic computing device (46), whereby operation of the spark plug (26) and combustion of a mixture in the combustion chamber (24) are prevented. [3] Method according to claim 1 or 2, characterized by that the size includes several different sub-sizes. [4] Method according to one of the preceding claims, characterized by that includes the size: - a running time of the internal combustion engine (10) since the end of a last operation of the burner (18); and / or - a mass flow of the exhaust gas flowing through at least a partial region of the exhaust gas tract (16) since the end of a last operation of the burner (18); and / or - a quantity of soot which has flowed into at least a partial region of the exhaust gas tract (16) since the end of a last operation of the burner (18). [5] Method according to claim 4, characterized by that the running time and / or the mass flow and / or the quantity is a sub-quantity of the quantity. [6] Method according to claim 3 or 5, characterized by that at least one of the sub-variables is weighted. [7] Method according to claim 6, characterized by that the at least one sub-variable is weighted as a function of at least one environmental condition and / or as a function of an operating point of the internal combustion engine (10). [8] Method according to one of the preceding claims, characterized by that the operation of the spark plug (26) in the free-burning mode comprises the spark plug (26) generating the ignition spark several times in succession during a predetermined or predeterminable period of time without a mixture being ignited in the combustion chamber (24). [9] Method according to one of the preceding claims, characterized by that the free-burning operation comprises that during a predetermined or predeterminable period of time in the combustion chamber (24) the mixture is burned and the spark plug (26) is operated, so that during the period of time during which the mixture is burned in the combustion chamber (24), the spark plug (26) generates the ignition spark several times in succession. [10] Motor vehicle which is designed to carry out a method according to one of the preceding claims.

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