EP1576269A1

EP1576269A1 - Catalyst temperature modelling during exothermic operation

Info

Publication number: EP1576269A1
Application number: EP03813071A
Authority: EP
Inventors: Matthias Mansbart
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2002-12-13
Filing date: 2003-07-25
Publication date: 2005-09-21
Also published as: DE10258278A1; WO2004055346A1; US20050228572A1; JP2006509947A

Abstract

A method and a calculating device for modelling the temperature (T_kat) of a catalyst (34) in the exhaust of an internal combustion engine (10) are disclosed. The heat input into the catalyst (34) from exothermic reactions is considered. The method is characterised in that a first correction value (delta_Tl) and a second correction value (delta_T2) are generated, which each concern heat input into the catalyst (34) from exothermic reactions, whereby (delta_Tl) is dependent on the relationship (AF) of the amount of fuel (S) to the air mass, which is burnt in the internal combustion engine (10), together with said air mass and (delta_T2) is dependent on a heat input resulting from an exothermic reaction of a second fuel mass which is dosed for the regeneration of the catalyst (34), as a supplement to the fuel proportion dosed and burnt as a fuel/air mixture in the internal combustion engine (10).

Description

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Catalyst temperature modeling be e .-. Ut, herm ^ rπ E-

State of the art

The invention relates to a method for calculating the temperature of a catalytic converter in the exhaust gas of an internal combustion engine, comprising the steps:

Forming a base value for the Ternpe ra u L of the catalyst,

Calculate a correction size delta_T that takes into account the heat input into the catalytic converter due to exothermic reactions in the catalytic converter and the ratio of the ei burned in the combustion, t ι simultaneously with an air mass Fuel mass and depends on the exhaust gas temperature,

Filtering a catalyst temperature-correlated value with low-pass filtering and forming a new value for the temperature of the catalyst, taking into account the base t- ¹ to and the result of the low-pass filtering. The invention is also directed to a

Calculating device for calculating the temperature of a catalyst in the exhaust gas of an internal combustion engine, which carries out the above-mentioned steps.

Such a procedure and one

Calculation devices are known from US 4,656,829. According to this document, the temperature of a catalytic converter in the exhaust gas stream of an internal combustion engine is calculated on the basis of the air mass drawn in by the internal combustion engine and the fuel / air ratio of the mixture burned in the internal combustion engine. Thereby, temperature contributions are used which have been empirically determined for steady-state conditions of internal combustion engine operation at certain values of the air mass flow rate and the fuel / air ratio. The steady state values are subjected to first order delay time filtering based on the air mass flow through the internal combustion engine and representing the response of the catalyst temperature to transient operating conditions of the internal combustion engine.

With today's favorite concepts for

Exhaust gas aftertreatment systems of internal combustion engines use catalysts that work on the storage principle and / or regeneration principle. For example, NOx storage catalytic converters are used in exhaust systems for internal combustion engines with gasoline direct injection. Operating an internal combustion engine with excess air produces comparatively high NOx emissions. A large part of the nitrogen oxide emissions can be absorbed by a NOx storage catalytic converter. However, the absorption capacity of storage catalytic converters is limited, so these storage catalytic converters are regular must be regenerated in order to be able to absorb nitrogen oxides again. Such regeneration can take place, for example, by generating excess fuel in the exhaust gas of the internal combustion engine in certain regions of the catalyst temperature.

In connection with the operation of diesel internal combustion engines, it is also known to use particle filters in the exhaust gas in order to reduce the emission of such particles. These particle filters also have a limited absorption capacity and must also be regenerated regularly. This can also be done by generating excess fuel in the exhaust gas upstream of the particle filter in connection with compliance with certain conditions for the particle filter temperature.

Since the regeneration of both NOx storage catalytic converters and particle filters only takes place satisfactorily if certain conditions for the exhaust gas temperature are met, it is very important to know the current exhaust gas temperature and the temperature of exhaust gas-carrying components as precisely as possible for the control of the internal combustion engine and the control of the above Regeneration processes in connection with the operation of the internal combustion engine. These temperatures must therefore be measured or modeled. It is also known to use oxidation catalysts for exhaust gas purification. Oxidation catalysts are operated either by lean engine operation or by additional air injection with excess air in order to oxidize CO and HC. In oxidation catalysts, exothermic reactions take place at almost every operating point due to the oxidation of unburned HC, NO, etc.

Generally, exhaust aftertreatment systems require in certain operating points, for example when operating with a low air mass throughput and thus comparatively low exhaust gas heat generation, additional measures to raise the exhaust gas temperature. Modern injection systems enable fuel to be injected late. A late injection is an injection that takes place so late, relative to the start of combustion, that large parts of the injected fuel quantity are not burned in the combustion chamber. The unburned parts of the injected fuel quantity are transported with the exhaust gas into the oxidation catalytic converter and are catalytically oxidized there, which can lead to a significant increase in temperature if, in particular, the temperature conditions for the onset of the catalytic reaction are met.

In particular, a minimum temperature must have been exceeded for the catalytic reaction to start. On the other hand, exothermic reactions in the catalytic converter can release amounts of heat that could lead to overheating of the catalytic converter. It is therefore desirable to know the temperature of catalysts in general, and NOx storage catalysts, particle filters and oxidation catalysts in particular, not only in steady-state operating states and during transitions from a first stationary operating state to a second stationary operating state, but also when one is regenerating Catalyst with the help of controlled triggered exothermic reactions in the catalyst to have knowledge of the resulting catalyst temperature.

Against this background, the object of the invention is a method and an apparatus for calculation specify the catalyst temperature, each of which enables a calculation of the catalyst temperature in normal operation without exothermic regeneration and also in operation with exothermic regeneration of the catalyst.

This object is achieved in a method of the type mentioned at the outset by forming a first correction variable delta_Tl and a second correction variable delta_T2 for the calculation of delta_T, delta_Tl depending on the ratio of the first fuel mass burned in the internal combustion engine with an air mass and a base value for the exhaust gas temperature is formed and delta_T2 is formed as a function of the base value for the exhaust gas temperature and a heat input into the exhaust gas which results from an exothermic reaction of at least part of a second fuel mass which, in addition to the fuel fraction of the fuel burned in the internal combustion engine, regenerates the catalyst / Air mixture was dosed.

This object is also achieved by a calculation device of the type mentioned at the outset, which carries out the above-mentioned steps in the formation of the first correction variable delta_Tl and second correction variable delta T2.

Advantages of the invention

The invention advantageously allows the catalyst or particle filter temperature to be taken into account when controlling the internal combustion engine in connection with regeneration of the catalyst or particle filter. This can in particular prevent the internal combustion engine for example, if the exhaust gas temperature is insufficient, it is operated with excess fuel in order to trigger regeneration. If the exhaust gas temperature was too low, the excess fuel would at least not fully react in the catalytic converter or the particle filter, so that the desired temperature increase and regeneration did not take place. In addition, unburned hydrocarbons were also emitted into the environment.

If, on the other hand, an exothermic regeneration exceeds a permitted maximum value for the temperature of the exhaust gas aftertreatment system, countermeasures can be drawn. For example, the exothermic regeneration can be stopped entirely or it can be interrupted in order to be triggered again after the temperature drops below a critical temperature.

As a result, both undesirable HC emissions and undesirable high thermal loads on the exhaust gas aftertreatment system can be avoided. These advantages are achieved within the scope of the invention presented here by a calculation based on operating parameters that are present in a control unit anyway. An expensive temperature sensor, which would have to be arranged in such a way that it detects the temperature at the location of a possible exothermic reaction, that is to say in the catalytic converter itself, can therefore be dispensed with.

It is preferred that the first correction variable delta_Tl is determined from a map in which influences of the temperature-dependent specific heat capacity of the exhaust gas are taken into account.

The first correction-sized delta__Tl is a measure of Temperature contributions that occur regardless of regeneration measures through chemical reactions in the exhaust gas aftertreatment system. The decisive factor for these contributions is the exhaust gas temperature and

Oxygen concentration in the exhaust gas. It is therefore possible to determine a temperature increase delta_Tl from a map directly as a function of the exhaust gas temperature upstream of the exhaust gas aftertreatment system and the prevailing oxygen concentration, since this increase in the exhaust gas temperature is independent of the exhaust gas mass flow. The influences of the exhaust gas temperature-specific heat capacity of the exhaust gas can be taken into account directly in the map. The exhaust gas temperature in front of the exhaust gas aftertreatment system can either be measured or modeled. Both measurements and modeling are assumed to be known. To distinguish these from the models that are assumed to be known, it should be noted once again that the aim of the invention is to calculate the influence of exothermic reactions in the exhaust gas aftertreatment system on the exhaust gas temperature or on the exhaust gas aftertreatment system.

It is further preferred that the second correction variable delta_T2 is formed as a function of a value which is read out as a function of the base value for the exhaust gas temperature from a characteristic diagram for the catalyst sorter activity.

This refinement advantageously takes into account that the catalyst activity and thus the extent of the heat generated in the catalytic converter in an exothermic reaction that is generated depends on the temperature of the catalytic converter or of the exhaust gas aftertreatment system. The result of taking this influence into account is the accuracy of the modeling of the temperature increased.

It is further preferred that the sum of the base value for the temperature of the catalyst, the first correction variable delta_T1 and the second correction variable delta_T2 is formed as the catalyst temperature-correlated value.

It has been shown that the low-pass filtering of this sum describes the actual temperature profile in the catalytic converter in an exothermic reaction.

It is further preferred that the heat input into the exhaust gas, which results from an exothermic reaction of at least part of the second fuel mass, is formed by multiplying this part of the second fuel mass by the specific calorific value of the fuel used.

Here, too, it has been shown that good results are achieved if the heat input into the exhaust gas is formed in the manner described.

It is further preferred that the part of the second fuel mass by a minimum selection between the value of the second fuel mass and the result of a maximum selection between the value zero and the value of a difference in a fuel mass that can be stoichiometrically combusted with the air mass enclosed in the internal combustion engine for combustion , and the first fuel mass actually involved in the combustion is determined.

This embodiment advantageously takes into account that the catalyst is free in the event of an exothermic reaction heat is not only dependent on the amount of fuel available for such an exothermic reaction, but also on the amount of oxygen available in the exhaust gas. In addition, this configuration specifies how the amount of oxygen available can be formed from operating parameters already present in the control unit of the internal combustion engine. In this way, the heat released during an exothermic reaction and the associated temperature increase are precisely determined even when the amount of air available for the reaction is not sufficient to utilize the entire second fuel mass available for the reaction. In this case, for example, and in addition to the advantages already described, the control device can ensure that the second fuel mass is reduced in subsequent injections in order to prevent or at least reduce the release of HC emissions in the environment.

It is further preferred that the low-pass filtering is a PTI filtering, the time constant of which is dependent on the operating parameters of the internal combustion engine.

It has been shown that with such a time constant which is dependent on the operating parameters of the internal combustion engine, particularly good, i.e. results corresponding to the actual conditions can be achieved when modeling the exhaust gas temperature and / or temperature of the exhaust gas aftertreatment system.

It is further preferred that the time constant of the PT1 filtering is dependent on the exhaust gas mass flow.

It is also preferred that the time constant from the reciprocal of the exhaust gas mass flow and the quotient specific heat capacities of the catalytic converter and the exhaust gas.

It has been shown that precisely these variables result in a time constant curve which leads to good results of the temperature modeling in the case of the PTl filtering.

Further advantages result from the description and the attached figures.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own without departing from the scope of the present invention.

drawing

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the description below. Show it:

FIG. 1 shows the technical environment in which the invention is effective,

Figure 2 shows a link in one

Data available to the calculation device and sensor signals supplied to the calculation device for input variables for calculating the temperature of the catalytic converter,

Figure 3 shows a combination of such input variables for calculating the temperature of the catalyst.

Description of the exemplary embodiments The number 10 in FIG. 1 denotes an internal combustion engine with a combustion chamber 12 in which a mixture of fuel and air is burned. Air is supplied to the combustion chamber 12 via a suction air duct 14, the air supply being controlled by at least one inlet valve 16. The mass of the air drawn in by the internal combustion engine 10 is recorded by an air mass meter 18, which transmits an air mass signal to a calculation device 20, for example an electronic control unit. The calculation device 20 is supplied with signals from further sensors, of which FIG. 1 shows an example of a speed sensor 22, an accelerator pedal sensor 24 and an exhaust gas sensor 26.

It goes without saying that the calculation device 20 can also be supplied with signals from further transmitters, for example via temperatures in the area of the internal combustion engine or via the transmission stage of a downstream torque converter and the like. The speed sensor 22 shown in FIG. 1 can be an inductive sensor, for example, which inductively scans ferromagnetic markings 28 on a sensor wheel 30. The accelerator pedal sensor 24 can have a potentiometer, by means of which the angle of the accelerator pedal and thus the driver's torque request can be detected.

The exhaust gas sensor 26 can be an oxygen concentration sensor, as is widely used in today's motor vehicles. As is known, the oxygen concentration sensor 26 can not only provide a signal about the oxygen concentration in the exhaust gas, but it can also provide information about the temperature of the exhaust gas sensor 26 and thus about the temperature from its signal of the exhaust gas are kept at the installation location of the exhaust gas sensor 26. For example, the internal resistance of a sensor ceramic that is conductive for oxygen ions and / or the electrical resistance of an electrical exhaust gas probe heater or the like can be used to determine the temperature.

Exhaust gas sensors 26 are not only suitable oxygen concentration sensors, but sensitive sensors such as NOx sensors, CO sensors and / or HC sensors can also be used for other exhaust gas components. Of course, the exhaust gas and / or catalyst inlet temperature can also be detected by a separate temperature sensor, for example a thermocouple, and transferred to the calculation device 20.

Using the data from the sensors mentioned, the calculation device 20 calculates signals for controlling actuators for controlling the internal combustion engine 10 using data stored in characteristic curves and / or characteristic diagrams. For example, the calculation device 20 calculates a fuel metering signal, for example one

Injection pulse width with which a fuel metering unit 28, for example an injection valve, is controlled. In the illustration in FIG. 1, the injection valve 28 is arranged such that the fuel is metered directly into the combustion chamber 12 of the internal combustion engine 10. This corresponds to direct fuel injection, as is used today in both diesel internal combustion engines and gasoline internal combustion engines. Of course, the invention is not limited to internal combustion engines with direct injection. It can also be used in Otto combustion engines with intake manifold injection become. After combustion of the fuel / air mixture enclosed in the combustion chamber 12, which, depending on the working principle of the internal combustion engine 10, can be triggered by self-ignition or by spark ignition of the compressed mixture, the exhaust gases are discharged via an exhaust valve 30 and an exhaust gas guide 32, for example a composite exhaust manifold and exhaust pipes, to a catalyst 34 in which undesirable exhaust gas components such as CO, HC and NOx are catalytically oxidized, stored or reduced.

The catalyst 34 can be either an oxidation catalyst or a reduction catalyst or a 3-way catalyst. In addition, it can be a NOx storage catalytic converter or a particle filter. The catalytic converter 34 can therefore also be referred to more generally as an exhaust gas aftertreatment device 34. In connection with the invention presented here, it is essential that the exhaust gas aftertreatment device 34 can be operated at least temporarily exothermally, the temperature change occurring due to the exothermic reaction of both the

Exhaust gas aftertreatment device 34 itself and also the exhaust gas flowing through the exhaust gas aftertreatment device 34 can be calculated by the calculation device 20 using a calculation model.

FIG. 2 shows how, in the context of such a calculation model, input variables for the calculation are initially formed from data available in the calculation device 20 and from sensor signals transmitted to the calculation device 20.

Field 36 represents the exhaust gas mass flow, that is to say the mass of that emitted by the internal combustion engine 10 per unit of time Exhaust gas. It can be calculated in the control unit 20 from the fuel mass metered in via injection valves 12 and the air mass sucked in via the air mass meter 18. The exhaust gas mass flow is also referred to below as m_abg. Field 38 denotes the catalyst inlet temperature T_in. T_in can initially be a plausible base value, for example a fixed value for an average bypass temperature, when starting the internal combustion engine 10, or T_in can be obtained by a separate sensor or by evaluating the signal of the exhaust gas sensor 26, as described above.

Field 40 represents the signal of the exhaust gas sensor 26, here an oxygen concentration sensor, which provides a measure of the value lambda, which indicates whether the combustion in the combustion chamber 12 was carried out with excess air or excess fuel. Field 42 represents the air mass m_l sucked in per time unit, as it is supplied by the air mass meter 18 to the control unit 20. Field 44 corresponds to a first fuel mass (fuel mass_l) per unit of time, which is supplied to combustion chambers 12 by regular main injections for the most complete possible combustion in combustion chamber 12. Field 46 represents a fuel mass_2 per unit of time which is supplied to combustion chambers 12 by late injections and which at least does not react completely with the air present in combustion chamber 12.

In branch 48, the thermal energy H is calculated from the air mass, the fuel mass_l and the fuel mass_2, which in a subsequent reaction in the

Exhaust aftertreatment device 34 can be released. First, an equivalent fuel mass is calculated from the air mass in block 52 by division by the value 14.5 (block 50), that with the air mass could be burned stoichiometrically. In block 54, the fuel mass_l is subtracted from this theoretical fuel mass. The value output by block 54 therefore corresponds to that fuel mass which can be stoichiometrically combusted with the oxygen remaining after the combustion of fuel mass 1. This value can be less than zero, zero or greater than zero.

The maximum of this value and the value zero is selected in block 56, so that the value output by block 56 is either zero or greater than zero. This value indicates the fuel mass which, if it is available, can react exothermically in the exhaust gas aftertreatment device 34 with the remaining oxygen.

In block 58, the minimum is selected from this value and the value of fuel mass_2. The value obtained in this way corresponds to the fuel mass that is actually available to in the

Exhaust aftertreatment device 34 to react exothermically with the remaining oxygen. This fuel mass is multiplied in block 60 by the calorific value H_U of the type of fuel used, so that the product delivers the amount of heat H, which in the

Exhaust aftertreatment device 34 can be released by exothermic reaction. It does not matter for the understanding of the invention whether the value H was calculated as an absolute heat quantity or as a heat quantity per unit of time.

An average catalyst temperature T_mean is also formed as a further input variable. For this purpose, the catalyst temperature T kat calculated by the model becomes recursive linked in block 62 to the value of the catalyst inlet temperature T_in from field 38 and in block 64 the result is subjected to averaging. The mean value obtained in this way represents the further input variable T_mittel for the subsequent calculation of T_kat. The average also serves

Catalyst temperature T_mittel together with the lambda value from the field 40 for addressing a map 66 stored in the control unit 20, which provides the specific heat capacity cp_abg of the exhaust gas as a function of the input variables mentioned. Block 68 represents the property of the real exhaust gas conversion device 34 under the influence of the input variables m_abg, T_mittel, cp_abg, T_in, Lambda and H to assume the temperature T_kat at the output of the exhaust gas aftertreatment device 34.

In addition, the speed m of the internal combustion engine is also taken into account, in particular to standardize the intake air mass flow to individual combustion chamber fillings.

In other words, the heat flow is determined in the branch 48, which is supplied to the exhaust gas aftertreatment device 34 by the fuel mass_2 not burning in the combustion chamber. First, an equivalent amount of fuel is determined from the air mass flow using the stoichiometric ratio. The fuel mass_l is subtracted from this equivalent quantity of fuel. The resulting difference describes the mass of fuel that can still react to the maximum with the residual oxygen in the exhaust gas. If the difference is less than or equal to zero, it can be assumed that there is no longer any oxygen in the exhaust gas and the fuel mass flow 2 or the fuel mass 2 cannot react. Is the On the other hand, a difference greater than zero may react to some or all of the fuel mass flow_2 (fuel mass_2).

FIG. 3 illustrates an embodiment of the method for calculating the temperature of a catalytic converter from the input variables mentioned above. First, the provision of the value T_in in field 38 corresponds to the step of forming a basic value for the temperature of the catalyst. To form a first correction variable deltaTl, a map 74 is addressed with the average temperature Tjnittel represented by field 72 and the lambda value represented by field 40, from which the first correction variable deltaTl can be read out depending on the input variables mentioned. The first correction variable deltaTl takes into account the chemical reactions occurring in the exhaust gas aftertreatment device 34 regardless of regeneration measures. The exhaust gas temperature and exhaust gas composition are decisive for these reactions. Correspondingly, a temperature increase delta_Tl is determined directly from the characteristic diagram 74 as a function of lambda and temperature, since this temperature increase is independent of the exhaust gas mass flow. The influences of the temperature-dependent specific heat capacity of the exhaust gas can be taken into account directly in the map 74.

To form the correction variable delta_T2, the exhaust gas mass m_abg provided in field 76 is first multiplied in block 78 by the specific heat capacity cp_abg provided by 80 of the exhaust gas. The result represents an amount of heat related to the temperature unit or a heat flow related to the temperature unit. In other words, the result indicates the amount of heat that is necessary to make a temperature difference of one Degrees. In block 80, the amount of heat H provided by field 82 is divided by the value output by block 78. The result represents the maximum energy flow that can be released by the catalytic reaction of the late injected fuel mass 2 with the oxygen still remaining in the combustion chamber after the combustion of the fuel mass 1. A certain part of this maximum value is actually released, which is dependent on the catalytic activity of the exhaust gas aftertreatment device 34. This dependence is taken into account by multiplying the output of block 80 by the value of the catalytic activity read out from a characteristic curve (block 82) in block 84. Block 82 is addressed with the average catalyst temperature T_mittel from field 72, since the catalytic activity is temperature-dependent. The result of the link in block 84 thus represents the value of the second correction variable deltaT2, which describes a heat input into the exhaust gas, which results from an exothermic reaction of at least part of a second fuel mass, which, in addition to the fuel content of the internal combustion engine, regenerates the catalyst burned fuel / air mixture was dosed.

The first correction variable delta__Tl, the second correction variable delta_T2 and the base value for the catalyst temperature T_in provided in field 38 are additively linked in block 86 and subjected to a low-pass filtering in block 88, which preferably has a PT1 characteristic. The time constant of the low-pass filtering is dependent on the reciprocal of the exhaust gas mass flow m_abg and the quotient of specific heat capacities of the catalytic converter (c_kat) provided by field 90 and the exhaust gas. In block 92, c_kat is the one Division represents, linked to the exhaust gas mass m_abg and the heat capacity of the exhaust gas cp_abg.

The temperature calculation presented takes into account that the reactions and thus also the temperature increases take place inside the catalytic converter or the exhaust gas aftertreatment device 34. To simplify matters, a corrected inlet temperature, which is composed, is first determined in the model formation presented here

Catalyst inlet temperature T_in, temperature increase delta_Tl through normal, i.e. even without regeneration, exothermic reactions take place in the catalytic converter, and temperature increase delta_T2 through fuel, which was specifically dosed as fuel mass 2 for regeneration purposes. Due to the design of the catalytic converter, it can be considered as a good heat exchanger.

It follows that the catalytic converter temperature T_kat and exhaust gas temperature at the outlet of the catalyst 34 and the exhaust gas aftertreatment device 34 can be regarded as identical at all times. This assumption leads to a differential equation, which can be read mathematically on a PTI filtering with the variable time constant of the product from the reciprocal of the exhaust gas mass flow and the quotient from specific heat capacities of the catalytic converter and the exhaust gas. For this reason, the current catalyst temperature at the outlet of the catalyst 34 can be modeled by the PT1 filtering of the corrected inlet temperature.

Claims

Expectations

1. Method for calculating the temperature (T_kat) of a catalytic converter (34) in the exhaust gas of an internal combustion engine (10) with the steps:

Forming a base value (T_in) for the temperature (T_kat) of the catalyst (34),

- Calculating a correction quantity delta_T, which takes into account the heat input into the catalytic converter (34) due to exothermic reactions in the catalytic converter (34) and the ratio of a first fuel mass S to the air mass and from in the internal combustion engine (10; burned simultaneously with an air mass) is dependent on the exhaust gas temperature,

Formation of a catalyst temperature-correlated value as a function of the base value and the cor ιe t r g .o.ic,

- Forming a value for the temperature (T_kat; of the catalytic converter (34) by filtering the catalyzed temperature-correlated value with low-pass filtering (59 ,,

characterized in that a first correction variable delta_Tl and a second correction variable delta_T2 are formed, each taking into account a heat input into the catalytic converter (34) due to exothermic reactions in the catalytic converter (34), delta_Tl depending on the ratio (AF) of that in the internal combustion engine (10) simultaneously with one Air mass burned first fuel mass S to the air mass and a base value (T_in) for the temperature of the catalyst (34) is formed, and delta_T2 is formed depending on the base value (T_in) for the temperature of the catalyst (34) and a heat input into the exhaust gas , which results from an exothermic reaction of at least part of a second fuel mass, which was metered for regeneration of the catalyst (34) in addition to the fuel portion of the fuel / air mixture burned in the internal combustion engine (10).

2. The method according to claim 1, characterized in that the first correction size delta_Tl is determined from a characteristic diagram (74) in which influences of the temperature-dependent specific heat capacity of the exhaust gas are taken into account.

3. The method according to claim 1 or 2, characterized in that the second correction variable delta_T2 is formed as a function of a value which is read out as a function of the base value for the exhaust gas temperature from a characteristic diagram (82) for the catalyst activity.

4. The method according to any one of claims 1-3, characterized in that the sum of the base value (T_ιn) for the temperature of the catalyst (34), the first correction size delta_Tl and the second correction size delta_T2 is formed as the catalyst temperature-correlated value. 2?

5. The method according to any one of claims 1-4, characterized in that the heat input into the exhaust gas, which results from an exothermic reaction of at least part of the second fuel mass, is formed by multiplying this part of the second fuel mass by the specific calorific value of the fuel used becomes.

6. The method according to any one of claims 1-5, characterized in that the part of the second fuel mass by a minimum selection (58) between the value of the second fuel mass and the result of a maximum selection (56) between the value zero and the value of a difference one Fuel mass which can be stoichiometrically combusted with the air mass enclosed in the internal combustion engine for combustion, and the first fuel mass actually involved in the combustion is determined.

7. The method according to any one of the preceding claims, characterized in that the low-pass filtering (88) is a PTI filtering (88) with a time constant dependent on operating parameters of the internal combustion engine.

8. The method according to claim 1, characterized in that the time constant of the PTI filtering (88) is dependent on the exhaust gas mass flow (m_abg).

9. The method according to claim 8, characterized in that the time constant of the PTI filtering (88) is dependent on the reciprocal of the exhaust gas mass flow (m_abg) and the quotient of specific heat capacities of the catalyst (c_kat) and the exhaust gas (c_abg).

10. Calculation device (20) for calculating the temperature (T_kat) of a catalyst (34) in the exhaust gas of an internal combustion engine (10) with the steps: Forming a base value (T_in) for the temperature (T_kat) of the catalyst (34),

Calculating a correction variable delta_T which takes into account the heat input into the catalytic converter (34) due to exothermic reactions in the catalytic converter (34) and which is dependent on the ratio of the fuel mass burned simultaneously with an air mass in the internal combustion engine and on the exhaust gas temperature,

- Forming a catalyst temperature-correlated value as a function of the base value (T_in) and the correction variable, and

Formation of a value (T_kat) for the temperature of the catalyst (34) by filtering the catalyst temperature-correlated value with low-pass filtering (88),

characterized in that

a first correction variable delta_Tl and a second correction variable delta_T2 are formed, each taking into account heat input into the catalytic converter (34) due to exothermic reactions in the catalytic converter (34), delta_Tl depending on the ratio of the first burned with an air mass in the internal combustion engine (10) Fuel mass and a base value (T_in) for the temperature of the catalyst (34) is formed and delta_T2 depending on the base value (T__in) for the temperature of the catalyst (34) and a heat input into the exhaust gas, which is formed from an exothermic reaction of at least results in part of a second fuel mass, which was metered for regeneration of the catalyst (34) in addition to the fuel portion of the fuel / air mixture (AF) burned in the internal combustion engine (10).