METHOD FOR HEATING AN EXHAUST AFTERTREATMENT COMPONENT IN THE EXHAUST SYSTEM OF AN EXTERNALLY IGNITED INTERNAL COMBUSTION ENGINE

Description

[0001] The invention relates to a method for heating an exhaust aftertreatment component in the exhaust system of a spark-ignition combustion engine, as well as a control unit and a combustion engine for carrying out such a method according to the preamble of the independent claims.

[0002] With a view to further tightening of emissions standards, for example with the introduction of the EU7 standard, it is necessary to significantly reduce cold-start emissions, which account for a large proportion of total emissions. During cold starts, i.e., immediately after the combustion engine starts, the exhaust aftertreatment components are generally not yet sufficiently warmed up to enable the conversion of the raw emissions generated during fuel combustion. This leads to increased exhaust emissions, particularly during the cold-start phase, which, even if the raw emissions are completely converted after the cold start phase, result in the emission limits for total emissions accumulated during a test cycle no longer being met.To avoid this, for combustion engines with exhaust aftertreatment systems known from the state of the art, customer restrictions such as a driving ban or a limitation of power immediately after the combustion engine starts would be necessary to ensure compliance with the EU7 emission limits under all required boundary conditions.

[0003] To meet the EU7 emissions standard for gasoline engines, exhaust aftertreatment systems have become widespread, comprising one or more three-way catalytic converters and a particulate filter. A three-way catalytic converter is a vehicle catalyst for the exhaust aftertreatment of internal combustion engines, in which carbon monoxide (CO), nitrogen oxides (NOx), and unburned hydrocarbons (HC) are converted into carbon dioxide (CO2), molecular nitrogen (N2), and water vapor (H2O). The name of the catalyst derives from the simultaneous conversion of these three air pollutants. In-engine heating measures are known for heating the exhaust aftertreatment components of the internal combustion engine. These measures include retarding the ignition timing, meaning significantly after the piston's top dead center in the ignition cycle. This reduces the thermal efficiency of the internal combustion engine and increases the exhaust gas enthalpy.The achievable reduction in efficiency is limited by the maximum retarded ignition angle due to the engine's smooth running, as the retarded combustion is associated with poorer ignition and combustion boundary conditions. The known method is therefore unsatisfactory because it leads to a deterioration of ignition conditions due to the retarded ignition timing. Furthermore, it is known to heat the three-way catalytic converter using an external heating medium, such as an electric heating element or an exhaust gas burner, so that the catalytic converter reaches its light-off temperature more quickly and is available sooner after a cold start for the effective conversion of limited emissions.

[0004] A disadvantage of existing exhaust aftertreatment systems is that the known in-engine heating measures are likely insufficient to meet the requirements of the EU7 emissions standard under all operating conditions. Even with external heating elements, there is a brief period during which the exhaust aftertreatment components have not yet reached their light-off temperature, and raw emissions are released into the environment untreated. Furthermore, external heating elements significantly increase the cost of the exhaust aftertreatment system and require additional design effort, which can lead to space constraints and packaging challenges, particularly in compact engine compartments.

[0005] German patent application DE 100 02 483 A1 discloses a method for rapidly heating exhaust aftertreatment components on an internal combustion engine with valve control. In this method, the combustion chamber of the engine has at least one exhaust valve. During the compression phase of the engine, the exhaust valves are briefly opened to introduce secondary air or a fuel-air mixture for afterburning. DE 100 02 483 A1 further discloses an internal combustion engine for carrying out this method with a fully variable hydraulic, pneumatic, and / or electric valve control system, wherein the valve control is actuated by an electronic control unit.

[0006] From DE 103 48 774 A1, a method for air injection for thermal aftertreatment of exhaust gases in the exhaust tract of an internal combustion engine is known. The air injection is achieved with minimal effort by controlling individual cylinders during a warm-up phase in such a way that they take on the function of an air pump for injecting air into the exhaust tract.

[0007] US Patent 10,954,869 B1 discloses an internal combustion engine with variable valve timing and a method for opening and closing exhaust valves in such an internal combustion engine. In one embodiment, the exhaust valves are opened twice during a charge cycle by means of two different cams on a camshaft, so that at least some of the unburned hydrocarbons remain in the cylinder and are not expelled into the exhaust system.

[0008] From DE 103 51 375 B4, a method for controlling an internal combustion engine is known which, in a four-stroke operation, cyclically goes through an intake, compression, power, and exhaust stroke. The internal combustion engine is equipped with a variable valve timing system, wherein the operation of the internal combustion engine is temporarily such that at least the intake valve is opened while the piston moves downwards in the cylinder during the power stroke, so that the intake air is supplied from the intake system into the cylinder.

[0009] From US patent 2014 / 0014066A1, a system for a four-stroke internal combustion engine is disclosed, the system comprising: at least two cylinders; a fuel direct injection device; a variable valve timing system; an engine control unit for controlling spark ignition and valve timing; wherein, below a lower load threshold, a first cylinder is deactivated, fuel is injected into a combustion chamber of the first cylinder, and an exhaust valve of the first cylinder is open during a compression stroke.

[0010] DE 10 2019 204 091 A1 describes a method for starting an internal combustion engine with an adjustable valve train, wherein the internal combustion engine is accelerated by means of an electric drive. The valve train of the internal combustion engine is switched to a starter mode before and / or at the beginning of the acceleration of the internal combustion engine by allowing gas to flow into a cylinder and / or gas to flow out of a cylinder through an open valve during at least part of the power stroke and / or compression stroke, and the internal combustion engine is initially accelerated in this starter mode before the valve train is switched to an operating mode intended for the operation of the internal combustion engine.

[0011] Furthermore, DE 10 2019 113 738 A1 discloses a valve actuation device for an internal combustion engine, comprising an intake camshaft and an exhaust camshaft. This valve actuation device combines switchable rocker arms and multiple and single cams, which are partially actuated by an intake sliding sleeve that is axially displaceable on a base shaft of the intake camshaft and / or an exhaust sliding sleeve that is axially displaceable on a base shaft of the exhaust camshaft. Such a valve actuation device enables, in the simplest possible design, normal operation of the internal combustion engine, partial operation in which at least one second combustion chamber of the internal combustion engine is deactivated, and a heating operation in which relatively hot exhaust gas is expelled from the second combustion chamber. Furthermore, such a valve train allows for decompression of the combustion chambers during a starting process.

[0012] JP 2016 011 589 A describes an engine valve train control unit. The engine valve train control unit is designed to improve the response to changes in the internal EGR rate and, consequently, the response to changes in engine operating conditions.

[0013] The invention is based on the objective of improving the heating of an exhaust aftertreatment component, in particular a three-way catalytic converter, in the exhaust system of a spark-ignition combustion engine.

[0014] The problem is solved by a method for heating an exhaust aftertreatment component in the exhaust system of an internal combustion engine with at least one combustion chamber, preferably several combustion chambers. The combustion chamber is delimited by a movable piston and has an inlet opening which is connected to an intake manifold of the internal combustion engine and can be closed by an inlet valve. The combustion chamber also has an outlet opening which is connected to an exhaust system and can be closed by an outlet valve. A fuel injector for injecting fuel is arranged on the combustion chamber and / or on the intake manifold. Furthermore, a spark plug is arranged on the combustion chamber, which is configured to ignite a combustible fuel-air mixture in the combustion chamber.The internal combustion engine features a valve lift curve switching mechanism that allows for a shift and / or change in the opening times of the exhaust valve and a shift and / or change in the opening times of the intake valve. The process comprises the following steps: Opening of the intake valve, whereby fresh air flows into the combustion chamber to produce an ignitable fuel-air mixture; closing of the intake valve, whereby an ignitable fuel-air mixture is produced in the combustion chamber; ignition of the ignitable fuel-air mixture in a power stroke of the combustion chamber, whereby the piston moves from top dead center towards bottom dead center; opening of the exhaust valve, whereby the exhaust gases produced during combustion flow at least partially into the exhaust system; closing of the exhaust valve and reopening of the intake valve when the piston is in a downward movement after ignition of the ignitable fuel-air mixture, thereby drawing additional fresh air into the combustion chamber; and closing of the intake valve and reopening of the exhaust valve.the fresh air drawn into the combustion chamber when the intake valve reopens is introduced into the exhaust system as secondary air.

[0015] Thus, two valve lift curves each are provided for the intake and exhaust valves, between which switching is possible – one valve lift curve for normal operation and one valve lift curve for catalyst heating operation. Catalyst heating operation constitutes the core of the process described here.

[0016] The method according to the invention makes it possible to significantly increase the exhaust gas enthalpy of the spark-ignition combustion engine by introducing secondary air and additional fuel. This involves increasing both the exhaust gas mass flow and the exhaust gas temperature. To maximize the exhaust gas enthalpy, the valve opening times are modified, in particular by advancing the exhaust gas opening compared to conventional catalyst heating methods. This results in a reduction in the efficiency of the combustion engine, so that the exothermic conversion of the fuel occurs at least partially in the exhaust system, thus maximizing the heat input into the exhaust aftertreatment component. Since the combustion engine is used as a piston pump for secondary air supply, it has a delivery characteristic that differs fundamentally from that of conventional secondary air blowers.These are often designed as turbomachines similar to radial blowers and therefore, by their very nature, exhibit a high sensitivity to exhaust backpressure of the conveyed airflow. This disadvantage is significantly reduced in piston pumps and thus represents a decisive advantage of the method described here with regard to its robust tuning.

[0017] The method according to the invention utilizes a significant advancement of the exhaust valve opening time to shorten the expansion phase effectively usable for torque generation. In the method according to the invention, the exhaust phase is also shortened so that a portion of the expansion phase remains available after the exhaust valves close. This portion of the expansion phase is used by closing the exhaust valves and reopening the intake valves to draw in additional fresh air into the combustion chamber and, in a subsequent compression phase, expel this fresh air as secondary air into the exhaust system. During this process, the remaining unburned exhaust gas components in the combustion chamber, as well as any additional fuel injected into the combustion chamber, react exothermically with the secondary air in the exhaust system, thus heating the exhaust aftertreatment component, in particular a three-way catalytic converter.

[0018] According to the invention, additional fuel is introduced into the combustion chamber during or after the intake valve reopens. This fuel, together with the secondary air, undergoes an exothermic reaction in the exhaust system after the intake valve closes and the exhaust valve reopens. This exothermic reaction of the additional fuel with the secondary air further increases the exhaust gas enthalpy. As a result, the exhaust aftertreatment component can be heated even more efficiently to its light-off temperature.

[0019] The features listed in the dependent claims enable advantageous further developments and improvements of the method for heating the exhaust aftertreatment component listed in the independent claim.

[0020] According to a preferred embodiment of the method, ignition of the ignitable fuel-air mixture occurs within a range of 20° crank angle before top dead center (TDC) to 10° crank angle after TDC. The crank angle (CA) describes the angle of the crankshaft relative to the piston's top dead center (TDC). Since the piston traverses a crank angle of 720° during a combustion cycle and thus reaches top dead center twice, a distinction is made between the ignition top dead center (TDC) and the top dead center during the charge exchange. By igniting within the range of 20° CA before TDC to 10° CA after TDC, the ignition timing, compared to a retarded ignition timing known from the prior art, lies within a range of increased pressure and temperature. This results in a comparatively favorable thermodynamic condition for ignition, thereby improving ignition and smooth running, and benefiting ignition systems such as...Pre-chamber spark plugs can be used, which are otherwise unsuitable for this operating state of the combustion engine due to their increased requirements regarding the thermodynamic boundary conditions. Increased heat input into the exhaust system results from two main factors: firstly, the earlier opening of the exhaust valves compared to conventional heating methods, which leads to a reduction in efficiency; and secondly, the increased exhaust enthalpy due to the additional conversion of secondary air and fuel, which do not contribute significantly to the combustion engine's torque generation. This results in more waste heat being introduced into the exhaust system, causing the exhaust aftertreatment component to heat up more quickly.

[0021] In an advantageous embodiment of the method, the exhaust valve is opened within a range of 30° crank angle after top dead center (TDC) to 50° crank angle after TDC. By opening the exhaust valves early, a portion of the energy that would otherwise act on the piston during the expansion stroke is transferred to the exhaust system, with at least a fraction of unburned exhaust gas components remaining in the combustion chamber of the internal combustion engine. This fraction can then subsequently react exothermically with the secondary air, further heating the exhaust aftertreatment component.

[0022] Furthermore, in an advantageous embodiment of the method, the exhaust valve is closed in a range of 80° crank angle to 100° crank angle after top dead center (TDC), and the intake valve is reopened in a range of 90° crank angle to 110° crank angle after TDC. By closing the exhaust valves early and reopening the intake valves, the further downward movement of the piston during the expansion stroke can be used to draw in fresh air again and subsequently expel it as secondary air into the exhaust system during a compression phase.

[0023] In an advantageous embodiment of the method, the intake valve closes again after reopening in the range of 170° to 190° crank angle after top dead center (TDC). This allows the downward piston movement to be used optimally to maximize the intake air mass. It is advantageous to close the intake valves in the region of TDC to prevent the expulsion of fresh air and exhaust gases remaining in the combustion chamber into the intake manifold during a subsequent compression phase.

[0024] Furthermore, shortly after bottom dead center, no more fresh air flows into the combustion chamber, so keeping the intake valves open any longer would be counterproductive. This allows the piston movement to be used optimally to maximize the intake air mass.

[0025] Furthermore, in an advantageous embodiment of the method, the exhaust valve is reopened within a range of 180° crank angle after bottom dead center (BDC) and 220° crank angle after BDC. Opening the exhaust valves after bottom dead center introduces secondary air, exhaust gas remaining in the combustion chamber, and any additional fuel injected into the combustion chamber into the exhaust system, where the secondary air reacts exothermically with the unburned exhaust gas or fuel components. This enables particularly efficient heating of the exhaust aftertreatment component.

[0026] In an advantageous embodiment of the method, the exhaust valve closes in the range of 340° crank angle to 380° crank angle after top dead center (TDC). At the top dead center of the charge exchange, i.e., 360° crank angle after TDC, the exhaust gases in the combustion chamber are almost completely expelled into the exhaust system. Therefore, it is advantageous to close the exhaust valves at this point in time to achieve the most complete charge exchange possible in the combustion chamber.

[0027] In an advantageous embodiment of the method, the inlet valve opens approximately 360° crank angle after top dead center (TDC), i.e., at approximately top dead center of the charge exchange. "Approximately" in this context refers to a deviation of a maximum of 15° crank angle, preferably a maximum of 10° crank angle, and particularly preferably a maximum of 5° crank angle. This allows the full expansion stroke in the charge exchange phase to be utilized to draw fresh air into the combustion chamber.

[0028] In an advantageous embodiment of the process, the intake valve closes approximately 540° crank angle after top dead center (TDC). Beyond this crank angle, no significant further filling of the combustion chamber with fresh air is achieved. Rather, a substantial extension of the opening time beyond 540° crank angle would result in the fresh air being pushed back into the intake manifold. Shortening the intake phase would lead to a Miller effect, which would be associated with a reduction in the volumetric efficiency and thus a minimization of the airflow and exhaust gas enthalpy.

[0029] In a further advantageous embodiment of the method, the internal combustion engine is designed as a direct-injection engine, in which a first quantity of fuel is injected into the combustion chamber after the intake valve closes and a second quantity of fuel is injected after the intake valve reopens. This allows for particularly precise control of the amount of fuel introduced into the combustion chamber and the exhaust system. In particular, the second quantity of fuel, which, together with the secondary air, is essentially converted exothermically in the exhaust system to heat the exhaust aftertreatment components, can be precisely controlled, resulting in particularly efficient heating of the exhaust gas.

[0030] However, the invention is not limited to direct-injection gasoline engines, but can also be implemented in spark-ignition engines where the fuel is injected into the intake manifold.

[0031] In an advantageous embodiment of the method, the temperature of the exhaust aftertreatment component is determined, and the method is initiated when the determined temperature of the exhaust aftertreatment component falls below a first threshold temperature. The first threshold temperature preferably corresponds to the light-off temperature of the exhaust aftertreatment component. The temperature of the exhaust aftertreatment component can be determined, in particular, by a temperature sensor on the exhaust aftertreatment component or by a computational model in the control unit of the combustion engine. By determining the temperature of the exhaust aftertreatment component, it can be easily determined whether additional heating of the exhaust aftertreatment component is necessary during the combustion engine start-up process.This is advantageous because it avoids unnecessary heating phases, which are associated with increased fuel consumption.

[0032] Another aspect of the invention relates to an internal combustion engine with at least one combustion chamber, preferably with at least three combustion chambers. Each combustion chamber is delimited by a movable piston. Each combustion chamber has at least one inlet port and at least one outlet port, which connect the combustion chamber to an intake manifold and an exhaust system of the internal combustion engine, respectively. Each inlet port can be closed by an inlet valve and each outlet port by an outlet valve. A fuel injector for injecting fuel and a spark plug for igniting an ignitable fuel-air mixture are arranged in each combustion chamber or in the intake manifold. The internal combustion engine also has a valve lift curve switching mechanism, which allows for a shift and / or extension of the opening times of the exhaust valve. An exhaust aftertreatment component is arranged in the exhaust system.The combustion engine is operatively connected to a control unit which is configured to carry out a method according to the invention for heating the exhaust aftertreatment component when a machine-readable program code stored in a storage unit of the control unit is executed by a computing unit of the control unit.

[0033] Such an internal combustion engine makes it possible to raise the temperature of an exhaust aftertreatment component to a temperature within a short time interval that allows for efficient conversion of pollutants in the exhaust stream of the internal combustion engine, even without external heating measures such as an exhaust gas burner or an electrically heated catalyst.

[0034] In a preferred embodiment of the invention, the internal combustion engine is designed as a direct-injection gasoline engine turbocharged by means of an exhaust gas turbocharger. Due to their high thermal efficiency, direct-injection gasoline engines are particularly critical when it comes to rapidly heating the exhaust aftertreatment component. This challenge is further exacerbated in turbocharged direct-injection gasoline engines, since the turbocharger turbine must first be heated before the exhaust aftertreatment component can be heated. The proposed method for heating an exhaust aftertreatment component is therefore particularly advantageous in a turbocharged direct-injection gasoline engine, as it allows for a temporary, significant reduction in thermal efficiency and enables the introduction of a corresponding amount of heat into the exhaust system in the shortest possible time.

[0035] According to an advantageous embodiment of the internal combustion engine, the spark plug is designed as a hook spark plug. Hook spark plugs are simpler in design and less expensive to manufacture than pre-chamber spark plugs. However, pre-chamber spark plugs offer an advantage in defining a small ignition chamber and in the propagation of the flame front within the combustion chamber. The method according to the invention is designed such that a simple hook spark plug can reliably ignite the fuel-air mixture in the combustion chamber and ensures maximum heat input into the exhaust system for heating the exhaust aftertreatment component. Due to the higher pressure and temperature levels at the ignition point compared to conventional catalytic converter heating methods, improved ignition conditions result, which enable the use of a passive pre-chamber spark plug.

[0036] In an advantageous embodiment, the exhaust aftertreatment component is a three-way or four-way catalytic converter. The conversion of pollutants in a direct-injection gasoline engine is generally carried out by one or more three-way catalytic converters and a particulate filter downstream of the three-way catalytic converter. To comply with the emission limits, it is necessary to heat at least one three-way catalytic converter to its light-off temperature as quickly as possible.

[0037] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0038] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show: Figure 1 shows a schematic representation of an internal combustion engine with an exhaust system for carrying out a method according to the invention for heating a catalyst; Figure 2 shows a further schematic representation of an internal combustion engine for carrying out a method according to the invention for heating a catalyst; Figure 3 shows a schematic representation of a pressure-volume diagram (pV diagram) during the execution of an ideal Otto cycle; Figure 4 shows a simplified representation of a combustion chamber of an internal combustion engine for carrying out such a method for heating a catalyst; Figure 5 shows a curve of combustion chamber pressure and valve lift of the intake and exhaust valves in a known method for heating the exhaust system by retarding the ignition timing;and Figure 6 shows the combustion chamber pressure and valve lift of the inlet and outlet valves during the execution of a method according to the invention for heating an exhaust aftertreatment component.

[0039] Figure 1 shows an internal combustion engine 10 with at least one combustion chamber 12, preferably as in Figure 1The combustion engine 10 is designed as a direct-injection gasoline engine, depicted with at least three combustion chambers 12. Each combustion chamber 12 is equipped with a spark plug 14 for igniting an ignitable fuel-air mixture and a fuel injector 30 for injecting fuel into the respective combustion chamber 12. Each combustion chamber 12 is connected to an intake manifold 34 via at least one inlet opening 16 and to an exhaust system 40 via at least one outlet opening 18. A fluidic connection from the intake manifold 34 to the combustion chamber 12 can be closed by an inlet valve 20. A fluidic connection from the combustion chamber 12 to the exhaust system 40 can be closed by an outlet valve 22.

[0040] The exhaust system 40 comprises an exhaust duct 42 in which, in the direction of flow of an exhaust gas stream from the internal combustion engine 10 through the exhaust system 40, a turbine 46 of an exhaust gas turbocharger 44 and, downstream of the turbine 46, at least one exhaust gas aftertreatment component 48 are arranged. Preferably, as in Figure 1A first three-way catalyst 50 is shown downstream of the turbine 46, and at least one further exhaust aftertreatment component 52, in particular a second three-way catalyst 54, an oxidation catalyst 58, and / or a particulate filter 56, is arranged downstream of the first three-way catalyst 50. The second three-way catalyst 54 and the particulate filter 56 can also be combined in a single component as a so-called four-way catalyst. Furthermore, one or more exhaust gas sensors 60 can be arranged in the exhaust system 40 to monitor the functionality of the exhaust aftertreatment component 48, 52. Preferably, a first lambda sensor 64 is arranged upstream of the first three-way catalytic converter 50 in the exhaust system 40, and a second lambda sensor 66, a temperature sensor 62 and optionally a pollutant sensor 68 are arranged downstream of the first three-way catalytic converter 50.

[0041] The internal combustion engine 10 is operatively connected to a control unit 80, which comprises a storage unit 82 and a processing unit 84. The storage unit 82 contains one or more machine-readable program codes 86 for controlling the internal combustion engine 10, in particular for controlling the ignition timing of the spark plug 14, the injection quantity and injection timing of the fuel injector 30, and for controlling the opening times of the valves 20, 22.

[0042] In Figure 2The internal combustion engine 10 is shown in a further schematic representation. The opening times of the intake valves 20 are controlled by an intake camshaft 24. The opening times of the exhaust valves 22 are controlled by an exhaust camshaft 26. A valve lift curve switching mechanism 38 is provided on both the intake camshaft 24 and the exhaust camshaft 26, by which a switchable cam profile 28, 29, which can be activated by a switching mechanism 36, can switch between a first opening curve of the intake valves 20 or the exhaust valves 22 and a second opening curve of the intake valves 20 or the exhaust valves 22.

[0043] Figure 3 schematically shows an ideal Otto cycle process, which provides a theoretical basis for the method according to the invention and Figure 4Figure 1 schematically shows a combustion chamber 12 of an internal combustion engine 10 with a piston 70, which is connected via a connecting rod 74 to a crankshaft 76 to carry out such a cycle. The combustion chamber 12 is sealed by piston rings 72, which seal a gap between the piston and a cylinder wall of the combustion chamber 12 and bear against the cylinder wall. Furthermore, in Figure 3 The compression volume VK and the stroke volume VH are shown. In such an ideal process, no dissipation losses, mechanical friction losses, or the like are considered. Furthermore, the working gas has the same properties throughout the entire cycle, and flow losses are not taken into account. Additionally, no mixing of the charge mixture with exhaust gas is assumed.

[0044] The invention preferably relates to a method for a direct-injection four-stroke gasoline engine turbocharged by means of an exhaust gas turbocharger 44. Each stroke consists of one piston stroke of the piston 70 or half a crankshaft revolution. In the four-stroke gasoline engine, the changes of state can be assigned to the power strokes. This will be shown below with reference to the Figure 3 and 4 described: The first stroke, the intake stroke, includes the intake, in which the piston 70 moves downwards and the combustion chamber 12 fills with fresh air ( Figure 4 This corresponds to the diagram in Figure 3 the connecting line between points 0 and 1.

[0045] The second stroke, the compression stroke, involves compressing the combustion chamber charge, with the piston moving 70 degrees into Figure 4 moved to the left. This corresponds to the diagram in Figure 3the isentropic connecting line between points 1 and 2 and the isochoric heat input qZU is achieved by igniting and burning the gas charge, which corresponds to the connecting line between points 2 and 3 (constant volume combustion).

[0046] The third stroke, the expansion or power stroke, comprises the isentropic expansion, during which the piston moves 70 degrees into Figure 4 as a result of the exothermic combustion, it is moved downwards again. This corresponds to the diagram in Figure 3 the connecting line between points 3 and 4.

[0047] The fourth stroke is also called the exhaust stroke (heat dissipation), in which Figure 4 The piston 70 moves back to the left and, through the opening of the exhaust valve 22, the exhaust gases expand outwards at bottom dead center without any further work being done (connecting line between points 4 and 1 in Figure 3) and the remainder of the exhaust gas is pushed outwards by the piston stroke (connecting line between points 1 and 0). In doing so, the heat q contained in the exhaust gas is released to the environment. The ideal process does not take into account that the remaining quantity in the compression chamber does not reach ambient temperature.

[0048] In Figure 5Figure 1 describes a method known from the prior art for increasing the exhaust gas enthalpy in an exhaust system 40 of an internal combustion engine 10. The method for a four-stroke gasoline engine comprises a power cycle I and a charge exchange cycle II that alternates with power cycle I. In power cycle I, the ignition timing is retarded, for example, to the range of 20°CA to 30°CA after top dead center (TDC). This reduces the thermal efficiency of the internal combustion engine 10, so that a smaller proportion of the energy contained in the fuel is used to generate torque, and hotter exhaust gas is expelled into the exhaust system 40. The exhaust valve 22 of the combustion chamber 12 opens to initiate charge exchange cycle II at approximately 150°CA after TDC. The hot exhaust gas flows into the exhaust system 40 and heats the exhaust aftertreatment component 48.The exhaust valve 22 closes approximately 360° crank angle after top dead center (TDC), i.e., at the top dead center of the charge exchange, while the intake valve 20 opens at approximately the same time. In the subsequent expansion phase, fresh air is drawn into the combustion chamber 12. The intake valve 20 closes at the end of the charge exchange cycle, approximately at bottom dead center, i.e., about 540° crank angle after TDC.

[0049] In Figure 6Figure 1 illustrates a method according to the invention for heating an exhaust aftertreatment component 48, in particular a three-way catalyst 50, in the exhaust system 40 of an internal combustion engine 10. In the method according to the invention, during a working cycle I, an ignitable fuel-air mixture is ignited in the combustion chamber 12 near top dead center (TDC) in a range from 20° crank angle before TDC to 10° crank angle after TDC. After ignition, the exhaust valve 22 opens early in the range of approximately 40° crank angle after TDC. The exhaust valve 22 is closed again at approximately 90° crank angle after TDC, and the intake valve 20 opens at approximately 100° crank angle after TDC, so that the remaining downward movement of the piston 70 can be used to draw fresh air into the combustion chamber 12. The opening of the intake valve 20 initiates secondary air operation III of the internal combustion engine 10.In this secondary air operation III, a second quantity of fuel can be injected into the combustion chamber 12 and / or the intake manifold 34, which then enters the combustion chamber 12 together with the fresh air. The intake valve 20 closes approximately 180° crank angle after top dead center (TDC), i.e., at approximately bottom dead center of the piston 70. Approximately 200° crank angle after TDC, i.e., at the beginning of the upward movement of the piston 70, the exhaust valve 22 opens again, whereby the secondary air, together with the combustible exhaust gas and fuel components still present in the combustion chamber 12, is reacted exothermically in the exhaust system 40, thus heating the exhaust aftertreatment component 48. The exhaust valve 22 closes approximately 360° crank angle after TDC, i.e., at approximately charge exchange TDC. The closing of the exhaust valve 22 ends secondary air operation III.The inlet valve 20 is opened at approximately TDC of the charge exchange, i.e., about 360° crank angle after TDC, to draw fresh air into the combustion chamber 12 of the internal combustion engine 10 for the next working cycle I.

[0050] In summary, the present invention utilizes a significant advance in the opening time of the exhaust valve 22 to shorten the expansion phase of the combustion chamber 12 that is effectively usable for torque generation. During this exhaust process, a large mass of exhaust gas is expelled into the exhaust system 40 in a very short period. By closing the exhaust valve 22 after this short period, a considerable portion of the expansion stroke remains available. In the present invention, this remaining portion of the expansion stroke is used by further opening the intake valve 20 to draw additional fresh air into the combustion chamber 12.The subsequent upward movement of piston 70 is not used in this case to expel the exhaust gases from the combustion, but essentially to expel the previously drawn-in additional fresh air, and thus corresponds in its effect to the injection of secondary air into the exhaust system 40. The subsequent downward movement of piston 70, as in a conventional four-stroke process, is used to draw in fresh air for a subsequent working cycle I, which, after injection of fuel, is compressed and converted exothermically in the combustion chamber 12 to generate a driving torque. Reference symbol list

[0051] 10 Internal combustion engine 12 Combustion chamber 14 Spark plug 16 Intake port 18 Exhaust port 20 Intake valve 22 Exhaust valve 24 Intake camshaft 26 Exhaust camshaft 28 Switchable cam exhaust camshaft 29 Switchable cam intake camshaft 30 Fuel injector 32 Camshaft adjuster 34 Intake manifold 36 Switching mechanism for selectable cam 38 Valve lift curve switching mechanism 40 Exhaust system 42 Exhaust duct 44 Exhaust turbocharger 46 Turbine 48 Exhaust aftertreatment component 50 Three-way catalytic converter 52 Further exhaust aftertreatment component 54 Second three-way catalytic converter 56 Particulate filter 58 Oxidation catalyst 60 Exhaust gas sensor 62 Temperature sensor 64 First lambda sensor 66 Second lambda sensor 68 Pollutant sensor 70 Piston 72 Piston rings 74 Connecting rod 76 Crankshaft 80 Control unit 82 Storage unit 84 Computing unit 86 Machine-readable program code HHub KW crank angle pPressure VK Compression volume VH Stroke volume q to isochoric heat input q off Heat contained in exhaust gas I. Working cycle II. Charging cycle III. Secondary air operation

Claims

1. Method for heating an exhaust gas post-treatment component (48) in an exhaust system (40) of an internal combustion engine (10) having at least one combustion chamber (12), wherein the combustion chamber (12) is delimited by a movable piston (70) and has an inlet (16) which is connected to an intake tract (34) of the internal combustion engine (10) and can be closed by an inlet valve (20), and an outlet (18) which is connected to an exhaust system (40) and can be closed by an outlet valve (22), wherein a fuel injector (30) for injecting a fuel is arranged on the combustion chamber (12) and / or on the intake tract (34), and having a spark plug (14) which is designed to ignite a combustible fuel-air mixture in the combustion chamber (12), and having a valve lift curve switching mechanism (38) which allows the opening times of the outlet valve (22) to be shifted and / or changed and allows the opening times of the inlet valve (20) to be shifted and / or changed, the method comprising the following steps: - opening the inlet valve (20), wherein fresh air flows into the combustion chamber (12) in order to produce a combustible fuel-air mixture, - closing the inlet valve (20), wherein a combustible fuel-air mixture is produced in the combustion chamber (12), - igniting the combustible fuel-air mixture in a firing stroke of the combustion chamber (12), causing the piston (70) to move from a top dead center in the direction of a bottom dead center, - opening the outlet valve (22), wherein the exhaust gases produced during combustion flow at least partially into the exhaust system (40), - closing the outlet valve (22) and reopening the inlet valve (20) when the piston (70) is in a downward movement after the ignition of the combustible fuel-air mixture, causing additional fresh air to be drawn into the combustion chamber (12), and - closing the inlet valve (20) and reopening the outlet valve (22), wherein the fresh air drawn into the combustion chamber (12) when the inlet valve (20) is reopened is introduced into the exhaust system (40) as secondary air, characterized in that during or after reopening of the inlet valve (20), additional fuel is introduced into the combustion chamber (12), which fuel, together with the secondary air, undergoes an exothermic reaction in the exhaust system (40) after the inlet valve (20) has been closed and the outlet valve (22) has been reopened.

2. Method according to claim 1, wherein the combustible fuel-air mixture is ignited in a range from 20° KW before TDC to 10° KW after TDC.

3. Method according to either of claims 1 to 2, wherein the outlet valve is opened (22) in a range from 30° KW after TDC to 50° KW after TDC.

4. Method according to any of claims 1 to 3, wherein the outlet valve (22) is closed in a range from 80° KW after TDC to 100° KW after TDC, and the inlet valve (20) is reopened in a range from 90° KW after TDC to 110° KW after TDC.

5. Method according to any of claims 1 to 4, wherein the outlet valve (22) is reopened in a range from 180° KW after TDC and 220° KW after TDC.

6. Method according to any of claims 1 to 5, wherein the internal combustion engine (10) is designed as a direct injection internal combustion engine (10) and a first quantity of fuel is injected into the combustion chamber (12) after the inlet valve (20) has been closed, and a second quantity of fuel is injected into the combustion chamber after the inlet valve (20) has been reopened.

7. Internal combustion engine (10) comprising: - at least one combustion chamber (12), wherein the combustion chamber (12) is delimited by a movable piston (70) and has an inlet (16) which is connected to an intake tract (34) of the internal combustion engine (10) and can be closed by an inlet valve (20), and an outlet (18) which is connected to the exhaust system (40) and can be closed by an outlet valve (22), and a fuel injector (30) for injecting a fuel into the combustion chamber (12) is arranged on the combustion chamber (12) and / or on the intake tract (34), - a spark plug (14) which is designed to ignite a combustible fuel-air mixture in the combustion chamber (12), and - a valve lift curve switching mechanism (38) which allows the opening times of the outlet valve (22) and the inlet valve (20) to be shifted and / or changed, - an exhaust gas post-treatment component (48) arranged in the exhaust system (40), and - a control unit (80) which is designed to carry out a method according to any of claims 1 to 6 when a machine-readable program code (86) stored in a memory unit (82) of the control unit (80) is executed by a computing unit (84) of the control unit (80).

8. Internal combustion engine (10) according to claim 7, wherein the valve lift switching mechanism (38) has switchable cams (28, 29) by means of which the opening times of the outlet valve (22) and the inlet valve (20), in a first switching state of the valve lift curve switching mechanism (38), enable early opening and closing of the outlet valve (22) in order to heat the exhaust gas post-treatment component (48) and, in a second switching state, enable late opening of the outlet valve (22) with the aim of efficiency-optimized combustion in the combustion chamber (12).

9. Internal combustion engine (10) according to claim 7 or 8, wherein the exhaust gas post-treatment component (48) is a three-way catalytic converter (50) or a four-way catalytic converter.