Method for adjusting an increased exhaust gas temperature in an exhaust pipe connected to a motor vehicle internal combustion engine

Abstract

Method for adjusting an increased exhaust gas temperature in an exhaust pipe (6) connected to a motor vehicle internal combustion engine, in which a quantity of post-injection of fuel required to adjust the increased exhaust gas temperature is calculated, wherein the post-injection of fuel is designed as a co-combustible post-injection of fuel which is injected into the combustion chamber (8) during an expansion stroke of the internal combustion engine, characterized in that the quantity of post-injection of fuel is calculated from a first temperature (T3, T3 v ) is determined, which is calculated for the exhaust gas of the internal combustion engine at the inlet of a turbine (11) of an exhaust gas turbocharger of the internal combustion engine and the first temperature (T3, T3 v ) from a second temperature (T AV , T vAV) is calculated, which is determined for a combustion gas enclosed in the combustion chamber (8) of the internal combustion engine during the expansion stroke immediately before opening an exhaust valve (10) closing the combustion chamber (8) and the second temperature (T AV , T vAV ) from an instantaneous pressure (p i , p iv ) and / or a pressure profile (p i (t), p iv (t)) of the combustion gas in the combustion chamber (8) is determined.

Description

[0001] The invention relates to a method for adjusting an increased exhaust gas temperature in an exhaust pipe connected to a motor vehicle internal combustion engine according to the preamble of claim 1.

[0002] Particularly for carrying out regeneration processes for exhaust gas purification components located in the exhaust system of motor vehicle internal combustion engines, such as particulate filters or nitrogen oxide storage catalysts, elevated exhaust gas temperatures of approximately 600 °C or above are required. These temperatures are rarely reached during normal vehicle operation and therefore often have to be deliberately induced by modifying the fuel combustion process of the internal combustion engine. This modification of the fuel combustion process includes, in particular, post-combustion fuel injection. For example, it is known from DE 100 33 159 A1 to measure an exhaust gas temperature upstream of a particulate filter and to adjust the timing and / or quantity of post-combustion fuel injection based on its deviation from a target temperature.Due to the unavoidable inertia of temperature measurement, post-injection control based on the exhaust gas temperature determined by a temperature sensor often cannot be as fast as desired. On the other hand, low-inertia temperature sensors are very sensitive and have a short lifespan.

[0003] DE 60 2004 011 048 T2 discloses a method for adjusting an increased exhaust gas temperature in an exhaust pipe connected to a motor vehicle internal combustion engine, in which the quantity of post-injection required to adjust the increased exhaust gas temperature is calculated. The post-injection is designed as a co-combustion post-injection, which is injected into the combustion chamber during an expansion stroke of the internal combustion engine. The quantity of post-injection is determined from a first temperature measured for the exhaust gas of the internal combustion engine at the inlet of a turbine of an exhaust gas turbocharger of the internal combustion engine.

[0004] DE 10 2006 021 303 A1 discloses a post-injection of additional fuel into a combustion chamber, wherein the post-injected fuel is already ignited in the combustion chamber, which can occur due to the end of the main combustion or the high temperatures present in the combustion chamber towards the end of the combustion, so that the exhaust gas temperature of the exhaust gases pushed into the exhaust tract is increased within the engine.

[0005] The object of the invention is therefore to provide a method which, while avoiding the aforementioned disadvantages, enables a rapid adjustment or regulation of an increased exhaust gas temperature.

[0006] This problem is solved by a method having the features of claim 1.

[0007] In the inventive method for adjusting an increased exhaust gas temperature in an exhaust line connected to a motor vehicle internal combustion engine, the quantity of post-injection required to adjust the increased exhaust gas temperature is calculated. This post-injection is to be injected into a combustion chamber of the internal combustion engine after a main fuel injection. The post-injection is designed as a co-combustible post-injection, which is injected into the combustion chamber during an expansion stroke of the internal combustion engine. According to the invention, the quantity of post-injection is determined from a first temperature calculated for the exhaust gas of the internal combustion engine at the inlet of a turbine of an exhaust gas turbocharger of the internal combustion engine.

[0008] Fuel injection with combustion is defined as fuel injection that occurs during a specific time or crankshaft angle range in the expansion stroke of an internal combustion engine, preferably operating on a four-stroke principle, during which the injected fuel participates in the combustion process taking place in the combustion chamber. In particular, combustion is predominantly or nearly complete. This fuel injection with combustion is torque-effective, thus contributing to the generation of torque delivered by the internal combustion engine. The exhaust gas exiting the combustion chamber(s) into the exhaust manifold after fuel injection and opening of the exhaust valve has an elevated temperature due to the injection, which is primarily determined by the amount of fuel injected.The increased exhaust gas temperature is present very quickly after the exhaust gas exits the inlet side, i.e., a few centimeters or less upstream of the turbine. Therefore, measuring the exhaust gas temperature at the turbine inlet has the advantage of a minimal time delay between the post-injection setting and its activation.

[0009] Furthermore, thermal overload of the turbine can be reliably avoided if the exhaust gas temperature present at the turbine inlet is used for the controlled adjustment of the post-injection quantity. The exhaust gas temperature can be very reliably set to temperatures below a permissible, predefined maximum temperature. Rapid adjustment of the post-injection quantity based on a calculated temperature at the turbine inlet also has the advantage of avoiding the inertia of a temperature sensor. Due to the rapid execution of computational algorithms available today, a quick and precise adjustment of the post-injection quantity is therefore possible to achieve a desired increase in exhaust gas temperature or to set a higher exhaust gas target temperature.

[0010] The first temperature is calculated from a second temperature, which is determined for combustion gas trapped in the combustion chamber of the internal combustion engine during the expansion stroke immediately before the opening of an exhaust valve that closes the combustion chamber. "Immediately before the opening of the exhaust valve" is understood to mean a crank angle range of less than 5°, preferably less than 2°, before the exhaust valve lifts and thus releases the exhaust valve opening, most preferably practically simultaneously with the lifting of the exhaust valve. The second temperature is therefore a temperature of the combustion gas trapped in the combustion chamber with the intake and exhaust valves closed. The second temperature corresponds at least approximately to the temperature of the exhaust gas as it exits the combustion chamber of the internal combustion engine through the exhaust valve opening. Preferably, heat loss can be determined using a heat loss model.Temperature losses of the exhaust gas on its way to the turbine of the exhaust gas turbocharger can be calculated. In this way, it is possible to calculate an accurate value for the initial temperature of the exhaust gas at the inlet side of the exhaust gas turbocharger turbine.

[0011] The second temperature is determined from the instantaneous pressure and / or pressure profile of the combustion gas in the combustion chamber. A pressure sensor is preferably used for this purpose, which can detect the internal combustion chamber pressure and transmit it to a processing unit for evaluation. Since the use of such sensors in modern internal combustion engines is not uncommon, the pressure profile in one or all combustion chambers of the engine can be monitored in real time without additional effort, which makes the adjustment of the increased exhaust gas temperature according to the invention extremely fast. The detected internal combustion chamber pressure can simultaneously be evaluated in relation to other operating parameters of the internal combustion engine that need to be set or monitored.

[0012] In an embodiment of the invention, a first temperature value and a second temperature value are determined for the first temperature, wherein the first temperature value corresponds to the exhaust gas temperature when post-injection of fuel is performed with a predefinable quantity, and the second temperature value corresponds to the exhaust gas temperature without post-injection. Thus, the influence of a currently performed post-injection on the first temperature, i.e., on the exhaust gas temperature at the turbine inlet, can be continuously monitored and, in particular, at least approximately in real time, determined or calculated. This allows for a very rapid response to the influence of disturbances, such as a change in one or more internal combustion engine operating parameters.

[0013] It is particularly advantageous if, in a further embodiment of the invention, a correlation between post-injection of fuel and the first temperature is determined from the difference between the first and second temperature values ​​and used to determine the quantity of post-injection of fuel. In the simplest case, especially with small deviations of the first temperature value from a target value for the exhaust gas temperature at the turbine inlet, a linear correlation or a directly proportional relationship can be used.

[0014] In a further embodiment of the invention, the torque contribution of post-injection to the torque delivered by the internal combustion engine is calculated, and the amount of the main fuel injection is varied depending on the determined torque contribution of the post-injection such that a target torque to be delivered by the internal combustion engine is at least approximately achieved. In this way, the torque-effective post-injection remains at least almost imperceptible to the driver of the respective vehicle. This enables the regeneration of, for example, a particulate filter with a high level of driving comfort. It is preferably provided that the torque contribution of the post-injection to the torque delivered by the internal combustion engine is calculated from the pressure profile of the combustion gas in the combustion chamber.

[0015] Advantageous embodiments of the invention are illustrated in the drawings and described below. The features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the present invention.

[0016] This shows: Fig. 1 a schematic partial representation of a motor vehicle internal combustion engine with connected exhaust system, Fig. 2 a diagram showing the combustion chamber pressure as a function of the crankshaft angle, Fig. 3 a diagram which consists of the pressure profiles according to Fig. 2 calculated temperature profiles depending on the crank angle and Fig. 4 a diagram showing calculated temperature profiles for exhaust gas escaping from the combustion chamber of the internal combustion engine.

[0017] In Fig. Figure 1 is a schematic and partial representation of an internal combustion engine of a motor vehicle with an attached exhaust system. Only one cylinder 1 of the typically multi-cylinder engine is shown. In this case, the engine is a compression-ignition diesel engine. A piston 2 can oscillate up and down in cylinder 1 between top dead center and bottom dead center. Mechanically, the piston 2 is connected via a connecting rod 3 to a crankshaft 4, which can transmit torque generated by the engine to the vehicle's drive wheels (not shown). An air intake 5 and an exhaust 6 are connected to cylinder 1. Combustion air for the combustion of fuel can be supplied to cylinder 1 via the air intake 5. The fuel can be injected into a combustion chamber 8 of cylinder 1 by means of a fuel injector 7.Fuel burned in combustion chamber 8 can be discharged from cylinder 1 via exhaust pipe 6. The intake of combustion air and the discharge of exhaust gas are enabled by actuating an intake valve 9 and an exhaust valve 10, respectively. In the illustrated state, intake valve 9 and exhaust valve 10 are closed, thus sealing combustion chamber 8. Exhaust gas exiting combustion chamber 8 with exhaust valve 10 open, due to overpressure and / or expelled as a result of the upward movement of piston 2, passes through exhaust pipe 6 to an intake side 12 of a turbine 11 of an exhaust gas turbocharger associated with the internal combustion engine. The turbine 11 is connected via a turbocharger shaft 14 to a compressor of the exhaust gas turbocharger located in the air intake pipe 5, which can compress the combustion air (not shown in detail). Exhaust gas exiting turbine 11 via a turbine outlet 13 is fed to an exhaust gas cleaning unit 15.Preferably, the exhaust gas purification unit 15 is arranged close to the internal combustion engine, i.e., in the so-called engine compartment of the motor vehicle. Without limiting the generality of the information, it is assumed below that the exhaust gas purification unit 15 is designed as a particulate reduction unit, which preferably comprises an oxidation catalyst and a particulate filter arranged a short distance downstream of it, although this is not shown in detail.

[0018] A pressure sensor 16 is provided to detect the pressure of the gas located in the combustion chamber 8 of cylinder 1, hereinafter referred to as combustion gas. The pressure sensor 16 can transmit its generated signal, which correlates with the detected pressure, to an electronic control unit 17 via a signal line 18. The fuel injector 7 is connected to the control unit 17 via a further signal line 19. The control unit 17 is connected to sensors and actuators (not shown) via further signal lines 20 in order to monitor and control the operation of the internal combustion engine and exhaust system. For this purpose, the control unit 17 preferably has a processing unit for evaluating the received signals and calculating the control signals, as well as a storage unit in which executable programs, characteristic curves, and maps are stored.

[0019] The exhaust gas purification unit 15, located in the exhaust gas line 6 and designed here as a particle reduction unit, is subject to recurring regeneration processes. These processes require an increased exhaust gas temperature of approximately 650 °C or more to burn off soot accumulated in the particle filter of the particle reduction unit. Since such high exhaust gas temperatures are not achieved during normal operation of the internal combustion engine, special measures are necessary.

[0020] A preferred method for adjusting an increased exhaust gas temperature within the scope of the invention is explained in more detail below. In particular, this method relates to adjusting an increased exhaust gas temperature, hereinafter referred to as T3, at the inlet side 12 of the turbine 11 to a target temperature T3. soll from, for example, 600 °C to 750 °C. Raising the exhaust gas temperature T3 to the target temperature T3 sollThis is primarily achieved by a torque-effective post-injection of fuel into the combustion chamber 8 by means of the fuel injector 7. The post-injection preferably begins at a predefinable time or crank angle, which is particularly dependent on the crankshaft speed. This time is preferably immediately or shortly after the completion of a main fuel injection. A so-called activation start, at which the fuel injector 7 is activated by the control unit 17 to deliver the post-injection, can, for example, occur at approximately 50° of crank angle after the top dead center of the piston 2 during the compression stroke. The duration of the post-injection, in conjunction with the post-injection pressure of fuel in the injector supply, primarily determines the post-injection quantity m. NE of the respective post-injection process. The post-injection quantity m NEThis in turn significantly determines the exhaust gas temperature T3 at the inlet side of turbine 11. Therefore, the post-injection quantity m NE can be considered as a control variable in the control process for adjusting the increased exhaust gas temperature T3.

[0021] The setting of a temperature T3 that is at least approximately the target temperature soll corresponding increased exhaust gas temperature T3 at the inlet side 12 of the turbine 11 requires post-injection quantity m NE,soll The pressure for each working cycle of cylinder 1 is preferably calculated using the pressure values ​​provided continuously or at a high frequency of 10 kHz or more by the pressure sensor 16.

[0022] For further explanation, reference is made to Fig. 2 taken, in which, for example, a determined combustion chamber internal pressure p iThe curve is shown as a function of the crank angle φ. The solid curve marked 21 represents the combustion chamber internal pressure p measured by the pressure sensor 16. i when performing a post-injection of fuel with a predetermined quantity m NE1 The post-injection of fuel occurred at a time detached from the main fuel injection, which took place shortly after top dead center at φ = 0 °KWnOT. The start of the post-injection of fuel is at the point indicated in Fig. 2 shows a fairly typical example with a crank angle φ = φ ABNE of approximately 52°. In this diagram of Fig. 2 Crank angle φ marked by a vertical line 23 ABNEAt the start of the control cycle, the fuel injector 7 is activated by the control unit 17 to open the injector or injector openings. Combustion of the post-injected fuel is indicated by a temporary flattening of the curve 21 for the combustion chamber internal pressure p, which occurs shortly thereafter. i The point in time or crank angle at which the closed combustion chamber 8 is opened by lifting the exhaust valve 10 is marked by a vertical line 24. In this case, this occurs at a typical crank angle of φ = 135 °KWnOT. This point in time or crank angle is subsequently denoted by φ AV designated.

[0023] In addition to the combustion chamber internal pressure p shown by curve 21, which was determined using measurement technology, i is in Fig. 2 A dashed line represents a curve 22. This curve begins at the crank angle φ. ABNEThe curve branch 22, which follows curve 21, represents a calculated profile of the combustion chamber internal pressure in the crankshaft angle range with φ Σ φ ABNE This shows how it would behave under the same operating conditions without post-injection. This calculated combustion chamber pressure is subsequently referred to as the virtual combustion chamber pressure with p. iv This refers to the calculation of the virtual combustion chamber internal pressure p. iv preferably based on the assumption of a polytropic expansion of the combustion gas in the combustion chamber 8 during downward movement of the piston 2 according to the following formula: piv(φ)=pABNE*[VABNE / V(φ)]n

[0024] This includes p ABNE the value of the measured combustion chamber internal pressure p i at crank angle φ ABNE , with V ABNE the combustion chamber volume at the crank angle φ ABNE, where V(φ) denotes the combustion chamber volume dependent on the crank angle φ, and n denotes the polytropic exponent of the combustion gas.

[0025] Based on the measured or calculated values ​​p i (φ) or p iv (φ) for the combustion chamber internal pressure or virtual combustion chamber internal pressure are a temperature T of the combustion gas in the combustion chamber during post-injection or a virtual temperature T v The temperature of the combustion gas in the combustion chamber can be determined without post-injection. Here, the temperature T of the combustion gas in the combustion chamber is calculated based on the ideal gas law. pi(φ)*V(φ)=m*R*T piv(φ)*V(φ)=m*R*Tv

[0026] Here, m denotes the mass of the combustion gas, which can be determined from the known cylinder filling. R denotes a gas constant specific to the combustion gas.

[0027] Based on the in Fig. The temperature profiles obtained from the two pressure curves shown are in a Fig. The diagram shown in section 3 illustrates this. Curve 25 represents a curve derived from curve 21 for the measured combustion chamber internal pressure p. i (φ) of Fig. Figure 2 shows the resulting curve for the temperature T of the combustion gas in combustion chamber 8 after post-injection. Similarly, the dashed curve 26 represents a curve derived from curve 21 for the virtual combustion chamber internal pressure p. iv (φ) of Fig. 2 resulting course for the virtual temperature T v for the combustion gas in combustion chamber 8 without carrying out a post-injection.

[0028] According to the invention, the calculation of the exhaust gas temperature T3 at the inlet 12 of the turbine 11 with post-injection is now carried out from a temperature value T. AVfor the temperature of the combustion gas in the combustion chamber 8, as it is according to the procedure explained above immediately before opening the exhaust valve 10 at crank angle φ AV This is preferably achieved by a computational heat loss model, which takes into account heat or temperature losses of the exhaust gas on its way from the combustion chamber 8 opened by the exhaust valve 10 to the inlet side 12 of the turbine 11.

[0029] The present model uses a heat loss model in which a sum of mixed products of relevant internal combustion engine operating parameters x i = x i (t) is formed. The internal combustion engine operating parameters x i These are preferably those that are available in control unit 17 due to metrological acquisition or calculation. In general form, this model can be represented formulaically as follows. y=a0+a1x1+…anxn+an+1x1x2+…amxn−2xn+am+1x1x2x3+… +akxn−2xn−1xn+ak+1x1x2x3x4+…aixn−3xn−2xn−1xn+ai+1Πi=1i=nxi

[0030] The constants are a i in particular by empirical determination, for example based on test bench measurements, specified or predeterminable.

[0031] In the purely exemplary, concrete case of five internal combustion engine operating sizes, the calculation model is as follows. T3=a0+a1x1+a2x2+a3x3+a4x4+a5x5+a6x1x2+a7x1x3+a8x1x4+a9x1x5+a10x2x3+a1 1x2x4+a12x2x5+a13x3x4+a14x3x5+a15x4x5+a16x1x2x3+a17x1x2x4+a18x1x2x5+a1 9x1x3x5+a20x1x4x5+a21x1x3x4a22x2x3x4+a23x2x3x5+a24x2x4x5+a25x3x4x5+a26 x1x2x3x4+a27x1x2x3x5+a28x1x2x4x5+a29x1x3x4x5+a30x2x3x4x5+a31x1x2x3x4x5

[0032] In addition to the internal combustion engine operating size x1 = T, which is used in every case AV for the temperature of the combustion gas in the combustion chamber 8 immediately before opening the exhaust valve 10 at crank angle φAV The crankshaft speed, the combustion air-fuel ratio, and preferably a pressure in the air intake line 5, and optionally an internal combustion engine coolant temperature, especially at a coolant temperature of less than 70 °C, are preferably taken into account as further operating parameters of the internal combustion engine.

[0033] In a completely analogous manner, another temperature value T3 is calculated. v calculated, which, starting from a virtual temperature T vAv for the combustion gas in the combustion chamber 8 immediately before opening the exhaust valve 10 at crank angle φ AV , specifies a virtual temperature of the exhaust gas at the inlet side 12 of the turbine 11 without performing a post-injection.

[0034] An example calculation result is shown in a Fig. The diagram shown in section 4 illustrates this. The dotted curve 27 represents the time course of the exhaust gas temperature T during post-injection in the time range t > t. AV , i.e., after the lifting of the exhaust valve 10 at time t AV corresponding to the crank angle φ AV Similarly, the dotted curve 28 shows a time course of the virtual temperature T. v of the exhaust gas without post-injection in this time range. Curve 27 begins at time t AV of the lifting of the exhaust valve 10, which corresponds to the crank angle φ AV corresponds to the temperature value T AV, which corresponds to the temperature T of the combustion gas at this time or crank angle. The curve 27 ends at a time marked by a vertical line 29, at which the exhaust gas has reached the inlet side 12 of the turbine 11. During this time, the exhaust gas temperature continuously decreases due to heat losses through wall contacts and the like, to the temperature T3, which the exhaust gas has immediately before entering the turbine 11. Similarly, the curve 28 begins for the virtual temperature T. v of the exhaust gas at temperature T vAv and ends at the comparatively lower temperature T3 v .

[0035] From the calculated exhaust gas temperature T3 for an internal combustion engine operation with post-injection, the post-injection quantity m, specified for example by a pilot control system, can be determined. NE1 , and the exhaust gas temperature T3 vWithout post-injection, a clear correlation emerges between the post-injection quantity m NE1 and the resulting temperature increase ΔT3 ≈ (T3 - T3 v ) = f (m NE1 ) or a clear correlation between a desired temperature increase to achieve the target temperature T3 soll and the required post-injection quantity m NE Preferably, this correlation is implemented in a controller, which thus has a control over the quantity m, which is considered the manipulated variable. NE The post-injection increases the temperature T3 of the exhaust gas at the inlet side 12 of the turbine 11 to the target value T3. soll regulates.

[0036] Since the fuel post-injection according to the invention is designed as a comparatively early, torque-effective post-injection, it is particularly preferred to determine its contribution to the torque M delivered by the internal combustion engine and to adjust the quantity of the main fuel injection so that torque neutrality is achieved, or a torque M specified according to the driver's request. soll is submitted. To explain the preferred procedure for this, reference is again made to the section in Fig. 2. Diagram showing the curves of the measured combustion chamber internal pressure p i with the execution of a post-injection and the calculated virtual combustion chamber internal pressure p iv Reference is made without post-injection.

[0037] In determining the torque component of the post-injection, it is assumed that the torque M delivered by the internal combustion engine is directly proportional to the so-called indicated mean effective pressure p. mi The corresponding relationship can be expressed by the formula pmi=4*π*M / VH be reproduced, with V H This represents the displacement volume of the internal combustion engine. Since p mi On the other hand, it can be represented as an integral of the combustion chamber pressure profile over a working cycle, giving the curve enclosed by curves 21 and 22, in Fig. 2. Area marked by dashed lines 30 represents the torque contribution caused by the post-injection. Since a correlation M = f (m HE ) between main injection quantity m HE and the resulting torque M is known and stored, for example, as a characteristic curve or table, the main injection quantity m can be determined. HEWhen performing a post-injection, the torque component is corrected or reduced in such a way that it is used to achieve the target temperature T3. soll set post-injection quantity m NE is compensated.

[0038] Overall, the inventive method thus enables extremely rapid adjustment to a predefinable target temperature T3. soll at the inlet 12 of the turbine 11 while simultaneously enabling high driving comfort. Reference symbol list 1 cylinder 2 pistons 3 connecting rods 4 Crankshaft 5 Air intake pipe 6 Exhaust pipe 7 Fuel injector 8 Combustion chamber 9 Inlet valve 10 Exhaust valve 11 Turbine 12 Turbine inlet side 13 Turbine outlet 14 Turbocharger shaft 15 Exhaust gas purification unit 16 Pressure sensor 17 Control unit 18 Signal line 19 Signal line 20 additional signal lines 21 Curve for combustion chamber internal pressure 22 Curve for virtual combustion chamber internal pressure 23 Line for the crank angle of the start of the control 24 Line for the crank angle of the exhaust valve lifting 25 Curve for the temperature of the combustion gas in the combustion chamber 26 Curve for the virtual temperature of the combustion gas in the combustion chamber 27 Curve showing the time course of the exhaust gas temperature 28 Curve for a time course of the virtual temperature of the exhaust gas Line 29 represents the time at which the exhaust gas reached the inlet side of the turbine. T3 Exhaust gas temperature at turbine inlet side T3 v virtual exhaust gas temperature at turbine inlet side p i internal combustion chamber pressure p ivvirtual combustion chamber internal pressure φ Crank angle φ AV Crank angle when the exhaust valve lifts t AV Time of lifting of the exhaust valve T Temperature of the combustion gas / exhaust gas T v virtual temperature of the combustion gas / exhaust gas T AV Temperature of the combustion gas immediately before opening the exhaust valve T vAV virtual temperature of the combustion gas immediately before the exhaust valve opens

Claims

[1] Method for adjusting an increased exhaust gas temperature in an exhaust line (6) connected to a motor vehicle internal combustion engine, in which a quantity of post-injection of fuel to be injected into a combustion chamber (8) of the internal combustion engine after a main fuel injection is calculated to adjust the increased exhaust gas temperature, wherein the post-injection of fuel is designed as a co-combustible post-injection of fuel which is injected into the combustion chamber (8) during an expansion stroke of the internal combustion engine, characterized by , that the amount of post-injection fuel from a first temperature (T3, T3 v ) is determined, which is calculated for the exhaust gas of the internal combustion engine at the inlet of a turbine (11) of an exhaust gas turbocharger of the internal combustion engine and the first temperature (T3, T3 v ) from a second temperature (T AV , T vAV) is calculated, which is determined for a combustion gas enclosed in the combustion chamber (8) of the internal combustion engine during the expansion stroke immediately before opening an exhaust valve (10) closing the combustion chamber (8) and the second temperature (T AV , T vAV ) from an instantaneous pressure (p i , p iv ) and / or a pressure profile (p i (t), p iv (t)) of the combustion gas in the combustion chamber (8) is determined. [2] Method according to claim 1, characterized by , that for the first temperature (T3, T3 v ) a first temperature value (T3) and a second temperature value (T3 v ) are determined, where the first temperature value (T3) corresponds to a temperature of the exhaust gas with fuel post-injection with a predefinable quantity and the second temperature value (T3 v ) corresponds to an exhaust gas temperature without fuel post-injection. [3] Method according to claim 2, characterized by , that from the difference between first temperature value (T3) and second temperature value (T3 v ) a correlation between post-injection of fuel and first temperature (T3) is determined and used to determine the amount of post-injection of fuel. [4] Method according to any one of claims 1 to 3, characterized by , that a torque contribution caused by the post-injection of fuel is calculated in relation to a torque delivered by the internal combustion engine, and a quantity of the main fuel injection is changed depending on the determined torque contribution of the post-injection of fuel in such a way that a target torque to be delivered by the internal combustion engine is at least approximately achieved. [5] Method according to claim 4, characterized by, that the torque contribution caused by the post-injection to the torque delivered by the internal combustion engine results from a pressure profile (p i (t), p iv (t)) of the combustion gas in the combustion chamber (8) is calculated.

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