Exhaust gas temperature dependent regeneration of a particulate filter using a heater

Abstract

Method for operating an internal combustion engine comprising an internal combustion engine (1) and an exhaust system (8) for removing exhaust gas from the internal combustion engine (1), wherein a thermally regenerable exhaust aftertreatment device (10) is integrated into the exhaust system (8), to which an electric heating device (11) is assigned, wherein the exhaust aftertreatment device (10) is heated by means of the heating device (11) in order to reach a temperature sufficient for the regeneration of the exhaust aftertreatment device (10), wherein the heating device (11) is operated when the loading state of the exhaust aftertreatment device (10) is above a first, relatively high loading limit and the internal combustion engine (1) produces exhaust gas with an exhaust gas temperature that lies within a first, relatively low temperature range, and also when the loading state of the exhaust aftertreatment device (10) is above a second,relatively low loading limit and the internal combustion engine (1) produces exhaust gas with an exhaust gas temperature that lies within a second, relatively high temperature range.

Description

[0001] The invention relates to a method for operating an internal combustion engine comprising an internal combustion engine and an exhaust system for removing exhaust gas from the internal combustion engine, wherein an actively thermally regenerated exhaust aftertreatment device is integrated into the exhaust system. The internal combustion engine can, in particular, be part of a motor vehicle.

[0002] Such a thermally regenerated exhaust aftertreatment system can be, in particular, a particulate filter, which serves to reduce particles in exhaust gas produced during combustion processes in an internal combustion engine and which is to be discharged into the environment via the exhaust system. A particulate filter typically needs to be regenerated when a defined loading limit is reached in order to maintain its functionality. For this purpose, it must be temporarily heated to a temperature that is generally between 600°C and 650°C, unless the oxidation temperature of the particles is reduced by the addition of an additive. Utilizing the CRT effect, a corresponding particulate filter must be heated to a temperature of at least 300°C.

[0003] Heating an exhaust aftertreatment system to the temperature required for regeneration is typically achieved by increasing the exhaust gas temperature accordingly, for which various measures, particularly those implemented within the engine itself, are known. Such in-engine measures involve deliberately operating the internal combustion engine at a relatively low efficiency, resulting in a relatively large proportion of the energy supplied to the engine via the fuel being lost as heat energy from the exhaust gas, thus remaining unused for generating drive power. A disadvantage of this approach is therefore the relatively high fuel consumption of the internal combustion engine, which results from the deliberate reduction in efficiency.Furthermore, operating an internal combustion engine with the aim of achieving relatively high exhaust gas temperatures can lead to relatively high pollutant emissions, particularly unburned hydrocarbons (HC) and carbon monoxide (CO), as well as to increased oil dilution, i.e., the introduction of fuel components into the lubricant used to lubricate the engine. Such oil dilution can result in relatively short intervals between lubricant changes, thereby increasing the operating costs of the internal combustion engine.

[0004] To mitigate these disadvantages resulting from the operation of an internal combustion engine, in which relatively hot exhaust gas is deliberately generated, it may be possible to additionally heat the particulate filter of the internal combustion engine electrically for thermal regeneration, so that correspondingly less heat energy has to be provided via the exhaust gas.

[0005] German patent application DE 10 2007 036 257 A1 discloses a particulate filter for a diesel internal combustion engine, wherein the outer area of ​​the particulate filter has an electric heating device. By means of the heating device, the temperature of the exhaust gas flowing through the particulate filter can be selectively increased in an outer area of ​​a filter element of the particulate filter as needed, thereby improving the regeneration of the filter element in this outer area. Simultaneously or shortly after the heating device is activated, the combustion engine of the internal combustion engine can be selectively operated in such a way that it generates relatively hot exhaust gas.

[0006] DE 10 2008 030 307 A1 describes an exhaust system for an internal combustion engine of a motor vehicle, in which two catalyst assemblies are integrated into the exhaust system, each with an associated electric heating device. The first catalyst assembly also includes a particulate filter. The heating device of the first catalyst assembly can be used to heat the exhaust gas flowing through it as needed, which can also be done to regenerate the particulate filter.

[0007] German patent DE 10 2019 204 298 A1 discloses an exhaust gas purification device for an internal combustion engine, comprising a heating catalyst designed to react supplied fuel with exhaust gas. The heating catalyst can also be electrically heated.

[0008] DE 10 2006 033 567 A1 discloses a method for determining the trigger point of a regeneration process for regenerating a particulate filter integrated into the exhaust system of an internal combustion engine, which includes, among other things, the following process steps: determining the current soot loading state of the particulate filter; comparing the determined loading state with a map constructed from data that represents the soot loading necessary for a regeneration process with sufficient regeneration success under different operating conditions of the internal combustion engine; setting a flag "loading state OK" if the currently determined soot loading is greater than or equal to the minimum soot loading required by the map.

[0009] US Patent 2017 / 138235 A1 discloses a method for regenerating a particulate filter, wherein the particulate filter is heated by means of an electric heating device. Regeneration is carried out when the particulate filter has reached a loading limit. Prior to such regeneration, the particulate filter can be heated and slightly regenerated as a test if it has reached a defined, relatively low loading limit. This serves to verify and, if necessary, adjust the particulate filter loading, which is actually calculated, by determining how the temperature of the particulate filter increases due to the test burning of the particles compared to a reference temperature profile.

[0010] The invention was based on the objective of improving the thermal regeneration of an exhaust aftertreatment system and in particular of a particulate filter of an internal combustion engine.

[0011] This problem is solved by carrying out a method according to claim 1. Advantageous embodiments of this method are the subject of further claims and will become apparent from the following description of the invention.

[0012] According to the invention, a method for operating an internal combustion engine is provided, wherein the internal combustion engine comprises at least one combustion engine and an exhaust system for removing exhaust gas from the combustion engine (and for discharging the exhaust gas into the environment), wherein an exhaust aftertreatment device, which can be actively regenerated thermally as needed, is integrated into the exhaust system. The exhaust aftertreatment device can, in particular, be a particulate filter, or it can comprise at least one such particulate filter. An electric heating device is associated with the exhaust aftertreatment device. The heating device is used to heat the exhaust aftertreatment device temporarily and as needed in order to reach a temperature sufficient for the regeneration of the exhaust aftertreatment device.

[0013] Such regeneration is carried out or initiated depending on the soot load, so that the exhaust aftertreatment system is only regenerated when the soot load exceeds a defined limit. The soot load reflects the increasing deterioration in the system's functionality due to previous exhaust aftertreatment. In the case of the particulate filter, which is preferably used as an exhaust aftertreatment system, the soot load therefore increases with the mass of particles that have already been filtered from the exhaust gas and thus stored within it. The higher the soot load, the lower the particulate filter's remaining filtration capacity.Similarly, an increase in the soot load can lead to an undesirable increase in the flow resistance of the exhaust gas passing through the particulate filter. The soot load of such a particulate filter can therefore be determined, for example, by measuring the differential pressure of the exhaust gas across the particulate filter.

[0014] According to the invention, the loading limit at which regeneration of the exhaust aftertreatment system is carried out with the aid of the heating device is adjusted depending on the temperature of the exhaust gas produced by the combustion engine. Specifically, the heating device is operated for regeneration of the exhaust aftertreatment system both when the loading level of the exhaust aftertreatment system is above a first, relatively (compared to a second loading limit) high loading limit and when the combustion engine produces exhaust gas with an exhaust gas temperature that is within a first, relatively (compared to a second temperature range) low temperature range.On the other hand, the heating device for regenerating the exhaust aftertreatment system is also operated when the soot load of the exhaust aftertreatment system is above the second, relatively low load limit and the combustion engine produces exhaust gas with an exhaust gas temperature that lies within the second, relatively high temperature range. The second load limit can preferably correspond to a value between 30% and 50%, particularly 40%, of the first load limit.

[0015] The exhaust gas temperature can be higher the higher the operating load or the combination of operating speed and operating load at which the combustion engine is operated. Therefore, the exhaust gas temperature can be inferred from the operating load or the combination of operating speed and operating load. Alternatively or additionally, the exhaust gas temperature can also be measured directly.

[0016] According to the invention, the exhaust aftertreatment system is regenerated even at a relatively low soot load, when this is not yet functionally necessary but is advantageous due to the current operation of the combustion engine. This is because the relatively hot exhaust gas produced by the combustion engine allows the heating power required by the heating device to be kept low for carrying out or at least initiating the regeneration. This approach minimizes the number of regenerations that would otherwise be necessary when the combustion engine is operating with relatively cold exhaust gas after exceeding the first soot load limit for the exhaust aftertreatment system.This can have an advantageous effect on the overall result, at least with regard to the energy consumption of the heating device and thus with regard to the fuel consumption of the internal combustion engine, which preferably provides the electrical power required for the operation of the heating device directly or indirectly.

[0017] The first temperature range extends from a first lower temperature limit to a first upper temperature limit, and the second temperature range extends from a second lower temperature limit to a second upper temperature limit. The first upper temperature limit is either identical to the second lower temperature limit, meaning the two temperature ranges can merge directly into one another. Alternatively, the first upper temperature limit may be lower than the second lower temperature limit.

[0018] The first lower temperature limit can correspond to a minimum value within the overall temperature range within which the exhaust gas temperature can fall during operation of the combustion engine, with the minimum value being the absolute smallest value within the overall temperature range. Accordingly, regeneration of the exhaust aftertreatment system can be initiated at any exhaust gas temperature, provided the soot load is above the first, relatively high, limit value. However, the first lower temperature limit can also be higher than the minimum value of the overall temperature range, so that regeneration of the exhaust aftertreatment system can be postponed even if the soot load is above the first limit value, until the exhaust gas reaches at least a sufficiently low temperature.

[0019] The second upper temperature limit preferably corresponds to a maximum value of the total temperature range, wherein the maximum value is the absolute largest value of the total temperature range.

[0020] In order to effectively regenerate the exhaust aftertreatment system according to the inventive method even at relatively low loads, it may be advantageous to activate the heating device only when the exhaust aftertreatment system's load is below the first load limit and the combustion engine has already generated exhaust gas with a temperature within the second temperature range for a defined minimum period. This allows for a relatively high probability that the combustion engine will continue operating at a suitable temperature for as much of the period required for regeneration as possible.This helps to avoid, as far as possible, the need to significantly increase the additional heating power provided by the heating device for regeneration during regeneration, because the exhaust gas temperature was only briefly within the second temperature range.

[0021] Furthermore, to avoid unnecessarily high heating output provided by the heating device, it may be stipulated that the operation of the heating device be terminated, and thus, if necessary, the regeneration of the exhaust aftertreatment system also be interrupted, if the combustion engine, after generating exhaust gas with an exhaust gas temperature within the second, relatively high temperature range, generates exhaust gas with an exhaust gas temperature below the second temperature range (and, in particular, within the first temperature range). This may be stipulated at least if the combustion engine generates exhaust gas with an exhaust gas temperature below the second temperature range for a defined minimum period.

[0022] By using a heating device to assist in warming the exhaust aftertreatment system for regeneration, it is possible for the combustion engine to operate, at least temporarily, and preferably always, during the operation of the heating device (for regenerating the exhaust aftertreatment system), without deliberately increasing the exhaust gas temperature of the exhaust gas produced by the combustion engine. This avoids the in-engine measures for increasing exhaust gas temperature that are common in the prior art and are associated with the disadvantages already described.

[0023] In carrying out a method according to the invention, it can be provided that the heating device is supplied, at least temporarily, with the electrical energy required for operation from an electrical energy storage source, for example, a battery. Additionally or alternatively, it can also be provided that the heating device is supplied, at least temporarily, directly (i.e., without the interposition of an electrical energy storage source) by a generator coupled to the internal combustion engine with the electrical energy required for operation. This second possibility has the advantage that the internal combustion engine typically has to be operated at a relatively high load to supply the heating device with electrical energy when the heating device is in operation and regeneration of the exhaust aftertreatment system is required.Due to this relatively high operating load during the operation of the combustion engine, it also generates a relatively high exhaust gas temperature, which in turn means that only relatively little heat energy needs to be provided for regeneration by the heating device.

[0024] For an advantageous implementation of a method according to the invention, it may be beneficial for the heating device to provide at least an electrical heating output of 4 kW, 5 kW, or 6 kW. With such a powerful heating device, it is particularly possible to operate the internal combustion engine during operation of the heating device without a deliberate increase in the exhaust gas temperature, which, as already described, can have a beneficial effect on the fuel consumption of the internal combustion engine.

[0025] In carrying out a method according to the invention, the exhaust gas aftertreatment device can be heated directly by means of the heating device (preferably integrated into the exhaust gas aftertreatment device). Additionally or alternatively, indirect heating via the exhaust gas intended to flow through the exhaust gas aftertreatment device can also be provided. In this case, the exhaust gas is heated by means of the heating device, and then flows through the exhaust gas aftertreatment device, thereby heating it.

[0026] The internal combustion engine of a combustion engine according to the invention can preferably be self-igniting and, in particular, designed as a (self-igniting and quality-controlled) diesel engine, because such an engine generally produces relatively cold exhaust gas, so that thermal regeneration of an associated exhaust aftertreatment system requires, in particular, a targeted increase in exhaust gas temperature. However, it is also possible that the internal combustion engine is a (spark-ignition and quantity-controlled) gasoline engine or a combination of a diesel and gasoline engine, i.e., an internal combustion engine with homogeneous compression ignition. The internal combustion engine can be operated with either liquid fuel (i.e., diesel or gasoline) or a gaseous fuel (in particular, natural gas, LNG, or LPG).

[0027] An internal combustion engine operated according to the invention can, in particular, be part of a motor vehicle, especially a wheeled and non-rail-bound motor vehicle (preferably a passenger car or a truck). The internal combustion engine of the motor vehicle can, in particular, be intended for the (direct or indirect) provision of propulsion power for the motor vehicle.

[0028] The invention is explained in more detail below with reference to an embodiment illustrated in a drawing. The drawing shows: Fig. 1: a simplified representation of an internal combustion engine suitable for carrying out a method according to the invention.

[0029] The one in Fig. 1The internal combustion engine shown comprises a combustion engine 1, which is exemplified as a reciprocating piston engine with four cylinder ports 2 arranged in a row. Each cylinder port 2, together with the reciprocating piston 3 and cylinder head, defines a combustion chamber 4. During operation of the internal combustion engine 1, fresh gas is supplied to these combustion chambers 4 via a fresh gas line 5. The supply of fresh gas is controlled by intake valves 6, which are assigned to the individual combustion chambers 4. The fresh gas consists exclusively or mainly of air drawn in from the environment. Exhaust gas is produced during the combustion of mixtures consisting of the fresh gas and fuel injected directly into the combustion chambers 4 via fuel injectors 7.This exhaust gas is discharged via an exhaust manifold 8 of the internal combustion engine, whereby the discharge of the exhaust gas from the individual combustion chambers 4 is controlled by means of exhaust valves 9.

[0030] The exhaust gas flows through an exhaust aftertreatment device 10 integrated into the exhaust stream 8, which is designed in the form of a particulate filter. An electric heating device 11 is associated with the exhaust aftertreatment device 10 and is integrated directly upstream of the exhaust aftertreatment device 10 into the exhaust stream 8. The heating device 11 can, as needed, heat the exhaust gas flowing around and / or through it until it reaches an exhaust gas temperature that enables regeneration of the exhaust aftertreatment device 10. Specifically, the exhaust gas heated by the heating device 11 heats the exhaust aftertreatment device 10 to a temperature of at least 600°C, thereby causing or initiating the oxidation of (soot) particles that are trapped within the exhaust aftertreatment device 10, which is designed as a particulate filter.Through this oxidation of the particles, they are burned off and the exhaust aftertreatment system 10 is thereby regenerated.

[0031] The energy required to operate the heating device 11 is supplied by a generator 12, which is driven directly by the internal combustion engine 1 or by an output shaft (crankshaft) 13 from it. The corresponding resistance exerted by the generator 12 during operation of the heating device 11 significantly increases the operating load of the internal combustion engine 1. This results in the internal combustion engine 1 producing relatively hot exhaust gas, which is advantageous with regard to the goal of regenerating the exhaust aftertreatment system 10, because only a relatively low heating output from the heating device 11 is required to achieve a sufficiently high exhaust gas temperature for such regeneration.

[0032] Regeneration of the exhaust aftertreatment system 10 is initiated at the latest when it reaches a soot load exceeding a first, relatively high load limit. Regeneration is then initiated even if the combustion engine 1 is operating at a relatively low load and consequently produces exhaust gas at relatively low temperatures. This is intended to ensure the continued functionality of the exhaust aftertreatment system 10. However, a disadvantage is that a relatively high heating output must be provided by the heating device 11. This is particularly true if, as is preferably intended, the combustion engine 1 is to be operated in normal mode even during regeneration of the exhaust aftertreatment system 10.This normal operating mode is also intended when no regeneration of the exhaust aftertreatment system 10 is being carried out, and this system is specifically designed for the highest possible efficiency in operating the combustion engine. It is therefore not intended to deliberately operate the combustion engine 1 at a relatively low efficiency during regeneration of the exhaust aftertreatment system 10 in order to generate relatively hot exhaust gas.

[0033] To minimize the need for regeneration of the exhaust aftertreatment system 10 during operation of the combustion engine 1, which produces relatively cold exhaust gas, it is also provided that the exhaust aftertreatment system 10 is regenerated even when its soot load is still below the first load limit. At the same time, however, the soot load should be above a second, relatively low load limit, which corresponds, for example, to 40% of the first load limit, to ensure that regeneration of the exhaust aftertreatment system 10 also occurs to a relevant extent.Such regeneration of the exhaust aftertreatment system 10 is provided for whenever the soot load of the exhaust aftertreatment system 10 is above this second load limit and the combustion engine 1 generates exhaust gas with relatively high exhaust gas temperatures. According to the invention, the exhaust aftertreatment system 10 is thus regenerated "prematurely" whenever this is worthwhile due to a soot load exceeding the second load limit and when the conditions are advantageous due to the generation of relatively hot exhaust gas by the combustion engine 1, because then the heating device 11 only needs to provide a relatively low heating output to reach the exhaust gas temperature required for regeneration. REFERENCE MARK LIST

[0034] 1 Internal combustion engine 2 Cylinder opening 3 Reciprocating piston 4 Combustion chamber 5 Fresh air system 6 Intake valve 7 Fuel injector 8 Exhaust system 9 Exhaust valve 10 Exhaust aftertreatment system 11 Heating device 12 Generator 13 Output shaft of the internal combustion engine

Claims

1. Method for operating an internal combustion engine comprising a combustion engine (1) and an exhaust system (8) for removing exhaust gas from the combustion engine (1), a thermally regenerative exhaust aftertreatment apparatus (10) with which an electric heating device (11) is associated being integrated into the exhaust system (8), the exhaust aftertreatment apparatus (10) being heated by means of the heating device (11) in order to reach a temperature sufficient for the regeneration of the exhaust aftertreatment apparatus (10), characterized in that the heating device (11) is operated to - initiate a regeneration process of the exhaust aftertreatment apparatus when the loading state of the exhaust aftertreatment apparatus (10) is above a first, relatively high loading limit and the combustion engine (1) produces exhaust gas with an exhaust gas temperature that is within a first, relatively low temperature range and also - initiate a regeneration process of the exhaust aftertreatment apparatus when the loading state of the exhaust aftertreatment apparatus (10) is above a second, relatively low loading limit and the combustion engine (1) produces exhaust gas with an exhaust gas temperature that is within a second, relatively high temperature range, the first temperature range extending from a first lower temperature limit to a first upper temperature limit and the second temperature range extending from a second lower temperature limit to a second upper temperature limit, the first upper temperature limit being identical to or smaller than the second lower temperature limit.

2. Method according to claim 1, characterized in that the exhaust aftertreatment apparatus (10) is a particle filter.

3. Method according to claim 1 or claim 2, characterized in that the second loading limit corresponds to a value between 30% and 50%, and in particular 40%, of the first loading limit.

4. Method according to any of the preceding claims, characterized in that when a loading state of the exhaust aftertreatment apparatus (10) is below the first loading limit, the heating device (11) is put into operation only when the combustion engine (1) has already produced exhaust gas with an exhaust gas temperature within the second temperature range for a defined minimum period of time.

5. Method according to any of the preceding claims, characterized in that the operation of the heating device (11) is terminated when the combustion engine (1), after having produced exhaust gas with an exhaust gas temperature within the second temperature range, produces exhaust gas with an exhaust gas temperature below the second temperature range.

6. Method according to any of the preceding claims, characterized in that the combustion engine (1) is operated during the operation of the heating device (11) without a targeted increase in the exhaust gas temperature.

7. Method according to any of the preceding claims, characterized in that the heating device (11) is supplied with the electrical energy required for operation from an energy storage source.

8. Method according to any of the preceding claims, characterized in that the heating device (11) is supplied with the electrical energy required for operation directly from a generator (12) coupled to the combustion engine (1).

9. Method according to any of the preceding claims, characterized in that the heating device (11) provides an electrical heating output of at least 2 kW or at least 4 kW or at least 6 kW.

10. Method according to any of the preceding claims, characterized in that the combustion engine (1) is self-igniting.

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