DE19913268C1 - Arrangement for monitoring the efficiency of a catalytic emission reduction device comprises a fuel feed device, flow and temperature sensors and data processing sensors - Google Patents

Abstract

An arrangement for monitoring the efficiency of a catalytic emission reduction device on the exhaust system of an I.C. engine which is operable at stoichiometric or over-stoichiometric conditions, comprises a fuel feed device (4) for dispensing a predetermined quantity of fuel into the exhaust gas stream sent to the catalyst, flow and temperature sensors (7,11,13) for measuring the thermal energy into and out of the catalyst unit, and a data processing unit (9), communicating with the fuel feed device (4) and the temperature sensors. An arrangement for monitoring the efficiency of a catalytic emission reduction device on the exhaust system of an I.C. engine which is operable at stoichiometric or over-stoichiometric conditions comprises a fuel feed device (4) for dispensing a predetermined quantity of fuel into the exhaust gas stream sent to the catalyst to make available an amount of chemical energy Ech, and, dependent on the catalyst efficiency, to provide an amount of thermal energy Eth, flow and temperature sensors (7,11,13) for measuring the thermal energy into and out of the catalyst unit, a data processing unit (9) communicating with the fuel feed device (4) and the temperature sensors, which constructs an energy balance for the catalyst , and hence provides a correlation signal indicating the performance of the catalyst. The system is especially suitable for DENOX catalyst units fitted to diesel engines operated under lean (over-stoichiometric) mixture conditions. The control processor (9) computes the thermal and chemical energies from: Eth = EPSILON mx.Cpx.Tx and Echn =mn.Hu (where, Eth = thermal energy in exhaust gases, Echn = chemical energy content of fuel, x = individual gas components, mx = mass of gas component, Cpx = specific thermal capacity of component x, mn = mass of fuel injected into catalyst feed gas, Hu = lower calorific value for fuel).

Description

Internal combustion engines, especially in motor vehicles, can reduce the emission of environmentally harmful emissions se be equipped with an exhaust gas cleaning system, the egg has a catalyst. The functionality of this Ka talysators is decisive for the pollutant content of the Ab gas emission.

The invention relates to a device by means of which Functionality of a catalytic converter in an internal combustion engine machine can be monitored.

DE 26 43 739 A1 describes a method for monitoring the Activity of a catalyst for exhaust gas purification Motor vehicles known. There is the functionality of the catalyst using two temperature values watches. The exhaust gas temperature is measured with a first temperature sensor temperature preferably in the entrance area of the catalyst telt, while with a second temperature sensor the Abga temperature inside the catalyst is determined. Solan ge the exhaust gas temperature inside the catalyst is higher  than the exhaust gas temperature in the entrance area of the catalyst, it is assumed in the known method that the Kataly sator is fully functional. Such monitoring is however only reliable if it can be ensured that the temperature measurements to monitor the catalyst during stationary operating states of the internal combustion engine be carried out so that the temperature profile the exhaust gas flow through the catalyst is essentially a can set steady state.

DE 40 27 207 A1 describes a method for monitoring the catalytic activity of a catalyst in the exhaust system ei ner internal combustion engine known, also on the Auswer tion of two temperature values of the exhaust gases, preferably on Entry as well as inside the catalyst. From the Signals from the temperature sensors are then a temperature measurement size formed either to form an average taking into account a variety of operating conditions the internal combustion engine over a long period of time observed or taking into account other parameters, the by means of a machine monitoring system and the respective operating state of the internal combustion engine characterize, on one of the respective operating state dependent statement reduced and further with a given one Limit value is compared. Once the tempera so generated tower size is smaller than the aforementioned limit in this known method, it is assumed that the cataly sator is defective.  

DE 41 22 787 A1 describes a device for monitoring the degree of conversion of a catalyst is known. With Hil Fe of a first temperature sensor is there downstream of the Kata analyzer determines the exhaust gas temperature and an evaluation unit supplied with an output of a computer in Ver bond stands. Another temperature sensor determines current on the catalytic converter the prevailing exhaust gas temperature and makes these available to the computer. Also a mas current sensor provided by the through the catalyst flowing air or exhaust gas mass determined and the corresponding forward the measured value to the computer. The difference to the aforementioned surveillance procedures that the convert degree of catalyst based on the difference of two ge determine measured temperatures is preferred here The measuring point downstream of the catalyst is the prevailing Ab gas temperature measured and using the upstream of the Kataly sator measured temperature and with the help of the measured Mass flow taking into account the catalyst geometry a limit temperature calculated, which is in the aforementioned Place of measurement would set if the catalyst without it an exothermic reaction takes place, would be flowed through, d. H. if the catalytic converter were no longer functional. The Dif reference between the measured at this preferred location Temperature and the limit temperature calculated for it here as a measure of the energy converted in the catalytic converter and thus for the degree of conversion of the catalyst.  

The present invention addresses the problem for monitoring the functionality of a catalytic converter tors another option for an internal combustion engine admit.

According to the invention, this problem is solved by a device solved with the features of claim 1.

The invention is based on the general idea of about monitoring the functionality of the catalyst for this to draw up an energy balance in the event that in the Exhaust gas supplied to the catalyst is contained in the fuel. The Invention uses the knowledge that the chemical energy gie is contained in the fuel that the catalyst, in particular by post-injection, is supplied in one fully functional catalyst due to the exothermic reaction completely into thermal energy is converted. When the force applied to the catalyst Amount of substance is known, must be in the fully functional Kata lysator in particular from a thermodynamic view re the measurable thermal energy downstream of the catalyst correspond to a theoretically achievable energy value that resulting from the measurable thermal upstream of the catalyst Energy and composed of the chemical energy that is in the amount of fuel is included, which supplied the catalyst leads, e.g. B. is injected. The further downstream the Catalyst measured thermal energy from this theore achievable energy value deviates, the stronger  the functionality of the monitored catalyst redu graces. Accordingly, the difference between that is theoretical achievable energy value and the ge downstream of the catalyst measured thermal energy a measure of the functional wipes activity of the catalyst.

In a preferred embodiment, the invention is based from that the engine has a fuel injection is available, which makes it possible to move into the Combustion gases a certain, that is known force inject quantity of substance. From the amount of fuel can then that contained in the post-injection quantity, from that used Chemical energy dependent on fuel type determined, in particular which are calculated. To make sure that excl Lich the post-injected fuel to increase the ther mix energy when flowing through the catalyst carries, the device according to the invention sets off at this leadership form at least during the catalyst diagnosis stoichiometric, preferably superstoichiometric operation ahead of the engine. Internal combustion engines the be operated stoichiometrically or superstoichiometrically are generally known.

When the engine is a fuel injector device with the predetermined force for combustion quantities of substance in the combustion chambers of the internal combustion engine bar, the device according to the invention is preferred designed so that the evaluation device with this force  The fuel injector communicates and from this signal receives values with those injected into the combustion chambers Correlate fuel quantity. The energy determination means can then be relatively simple to the Ka Talysator supplied or removed energies voices. For example, a temperature measurement of current is sufficient up and downstream of the catalyst and a measurement of the Amount of air supplied to the catalyst. The evaluation device can then be particularly easily based on the combustion led, known by the fuel injector Fuel quantity and based on the supplied to the catalytic converter fuel quantities known from the fuel supply means ge in connection with a measurement of the incineration amount of air led the energy supplied to the catalyst by measuring the flow temperature upstream of the Kata lysators and the energy given off by the catalyst by egg ne Measurement of the flow temperature downstream of the catalytic converter determine particularly easily.

The device according to the invention or its evaluation device tion provides electricity with regard to the thermal exhaust gas energy up and downstream of the catalyst taking into account the convertible in the catalyst into thermal energy, in after injected fuel contained a chemical energy Energy balance on which they monitor functionality of the catalyst. Since the conversion of the after injected fuel contained chemical energy in the Catalyst in thermal energy runs relatively slowly,  a post-injection or a change in the after affects injection quantity only after a time delay on the downstream measurable thermal energy. In order at the Energiebi to eliminate such delay effects the detection of thermal energy over a sufficient great period. Preferably be used for this purpose for example with a frequency of 10 Hz consecutive Amounts of energy measured and added up or over time in tegrated.

The integration of amounts of energy over time is here preferred, because then the amount of energy depends on time gige sizes of the exhaust gas flow, such as. B. by a be agreed cross section of the exhaust line per unit of time flowing exhaust gas mass (exhaust gas mass flow) can be used can, which are particularly easy to measure.

In a preferred embodiment, the evaluation starts the integration of thermal energies at the start of post-injection. So it can be guaranteed that in the thermal energy of the exhaust gases downstream of the Kataly the chemical energy converted in the catalytic converter after the amount of fuel injected is safely contained. A Integration consumed well before the start of post-injection only storage capacity because of the thermal energies upstream and downstream of the catalyst should be the same size ten. The period during which the integration of energy quantity takes place, is chosen so large that the conversion  the chemical energy of the amount of fuel injected in thermal energy regularly took place completely if the catalytic converter is working properly. If the The catalyst is working properly over that time span integrated thermal energy downstream of the Kataly sators about the same size as the ink that was recorded over this period added thermal energy upstream of the catalyst chemical energy of the injected force amount of substance.

In another embodiment of the invention direction, the evaluation device can integrate perma Do not perform if the internal combustion engine is stoichiome trical or overstoichiometric and with post-injection is driven. As long as the difference in this embodiment between the thermal energy downstream of the catalyst and the thermal energy upstream of the catalyst is about chemical energy of the amount of fuel injected corresponds, the catalytic converter works properly. As soon as however, the aforementioned difference becomes smaller than the chemi cal energy of the post-injected fuel, recognizes the Evaluation device a reduced functionality or malfunction of the catalyst.

In a particularly advantageous embodiment, the Evaluation device for determining the with the functional cloth activity of the catalyst correlated energy value one Carry out post-injection or if there is post-injection  the amount of post-injection varies. With other wor ten, the evaluation device can according to the first Al alternative especially for the monitoring of the functioning speed of the catalyst the post-injection of a certain Introduce the amount of fuel or the second Alternatives for a permanent post-injection the amount of fuel injected for a certain time increase or decrease a certain value. The evaluations establishment can then specifically measure the impact of this post-injection or change in injection quantity on the balance of thermal energies upstream and downstream watch the catalyst.

The device according to the invention is particularly suitable Way for an internal combustion engine designed as a diesel engine ne, the lean, that is operated over stoichiometric and which in particular has a DENOX catalyst. For Improving the efficiency of such a DENOX Post-injection is usually carried out by the catalyst guided. This post-injection can advantageously of the device according to the invention for monitoring the functi efficiency of the catalyst can be used.

Other important advantages and features of the invention Device result from the dependent claims, from the Drawings and from the associated figure description hand of the drawings.  

It is understood that the above and the following standing features to be explained not only in the ever because specified combination, but also in other combinations nations or alone can be used without the To leave the scope of the present invention.

A preferred embodiment of the invention is in the Drawings and is shown in the following Be spelling explained in more detail.

Each shows schematically

Fig. 1 combustion engine, a circuit diagram-like representation of an internal principle, which is equipped with the inventive Vorrich tung,

Fig. 2 is a diagram that shows the thermal energy profile upstream and downstream of a catalyst integrated over time.

According to Fig. 1 is combustion engine in an exhaust system 1 of an internal 2, z. B. a diesel engine, a catalyst 3 , in particular a DENOX catalyst, arranged. The internal combustion engine 2 also includes a Kraftstoffeinspritzein direction 4, are injected with the aid of relatively accurately metered amounts of fuel into the combustion chambers of the engine. 2 The fuel injection device 4 is actuated by an engine control unit 5 via a control line 6 . The engine control unit 5 specifies for the injection, in particular the time of the injection and the amount of fuel that is to be injected into the respective combustion chamber of the internal combustion engine 2 . The internal combustion engine 2 is air-guided, that is to say the regulation of the fuel injection for setting certain operating states of the internal combustion engine 2 takes place with the air supplied to the internal combustion engine 2 as a reference variable. For this purpose, the internal combustion engine 2 has an air mass sensor 7 arranged upstream of the internal combustion engine 2 , which supplies signals correlated with the amount of air supplied to the internal combustion engine 2 to the engine control unit 5 via a corresponding signal line 8 . The air mass sensor 7 can be designed as a hot film measuring device, which is generally known to be.

To monitor the functionality of the catalytic converter 3 , the internal combustion engine 2 is equipped with a monitoring device according to the invention, which has an evaluation device 9 . This evaluation device 9 receives from the engine control unit 5 the values of the air mass measured upstream of the internal combustion engine 2 and the values of the injected fuel quantities. The data stream flowing from the engine control unit 5 to the evaluation device 9 is transmitted via a data or signal line 10 . For example, the data relevant to the injected fuel quantities can be forwarded to the evaluation device 9 . The monitoring device also has a first temperature sensor 11 , which is arranged downstream of the internal combustion engine 2 and upstream of the catalytic converter 3 in the exhaust line 1 and supplies 12 temperature signals to the evaluation device 9 via a corresponding signal line, which prevail in the exhaust gas with the upstream of the catalytic converter 3 Correlate temperature. The monitoring device additionally has a second temperature sensor 13 , which is arranged downstream of the catalytic converter 3 in the exhaust line 1 and via a signal line 14 provides temperature signals of the evaluation device 9 , which prevail with the temperature downstream of the catalytic converter 3 in the exhaust gas correlate.

The evaluation device 9 determines the thermal energy E _thvorKat in the exhaust gas upstream of the catalytic converter 3 in analogy to the following equation:

E _thvorKat = Σ (m _x .c _pmx .T _x )

In this equation:
x = individual exhaust gas component,
m _x = mass of the exhaust gas component x,
c _pmx = specific heat capacity of the exhaust gas component x,
T _x = temperature of the exhaust gas component x.

The sum is formed over x, that is over all exhaust gas components of the exhaust gas. Provided that the temperature T _{x is the} same for all exhaust gas components x and agrees with the temperature measured by the first temperature sensor 11 , the thermal energy E _thvorKat in the exhaust gas upstream of the catalyst 3 can be calculated relatively easily, since the composition of the exhaust gas, that is, the proportions of the individual exhaust gas components in the total mass of the exhaust gases and the individual specific heat capacities c _{pmx are} also known. The mass of the individual exhaust gas components m _x results from the air mass measured upstream of the internal combustion engine 2 and from the known amount of fuel that is supplied to the combustion. From this, the proportionate composition of the exhaust gases after combustion is known.

Likewise, the thermal energy E _thvorKat in the exhaust gas upstream of the catalytic converter 3 can be determined by first calculating or calculating a fuel / air ratio, known as "lambda", from the quantity of air measured with the air mass sensor 7 and the quantity of fuel provided for combustion is measured using a lambda probe, not shown. With this lambda, a value for the heat capacity of the exhaust gases can be assigned from a temperature-dependent map. From this, the thermal energy carried in the exhaust gas can then be determined with the aid of a further characteristic field.

The thermal energy E _thnachKat in the exhaust gas downstream of the catalyst 3 is determined in a corresponding manner analogously to the following equation:

E _thnachKat = Σ (m _x .c _pmx .T _x )

If the effect of fuel post-injection on the thermal energy balance upstream and downstream of the catalyst is to be evaluated, the evaluation device 9 can determine the chemical energy E _chnK contained in the post-injected fuel _quantity in analogy to the following equation:

E _chnK = m _nK .Hu _K

In this equation:
m _nK = mass of the fuel injected,
Hu _K = lower heating value of the fuel.

The type of fuel used by the internal combustion engine 2 , for. B. diesel fuel is usually fixed, so that the lower calorific value Hu _{K of} the fuel is known. From the engine control unit 5 , the evaluation device 9 knows the quantity of fuel injected and can determine the mass m _{nK of} the fuel injected therefrom.

The evaluation device 9 now sets up a number of measurements or calculations which follow one another in time, for example with a frequency of 10 Hz. To monitor the functionality of the catalytic converter 3 , the evaluation device 9 then carries out an integration of the chronologically successive individual measurements over time. This can be done in analogy to the following equation:

∫E.dt

The evaluation device 9 then _draws up an energy balance and observes the difference between the thermal energy E _thnachKat downstream of the catalytic converter 3 and the thermal energy E _thvorKat upstream of the catalytic converter 3 plus the chemical energy E _{chnK of} the quantity of fuel injected afterwards. The invention assumes that the following applies to a fully functional catalyst 3 after a sufficient period of time:

(E _thvorKat + E _chnK ) - E _thnachKat = 0

Here, energy losses, e.g. B. by radiation from the exhaust line 1 into the environment or by storage in the gas line 1 , in particular in the catalyst 3 , z. B. taken into account by appropriate correction factors.

If the evaluation device 9 determines that the above equation is not met, it concludes that the catalytic converter 3 is not fully functional. If the actually determined thermal energy E _thnachKat downstream of the catalytic converter 3 deviates by a predetermined amount from that downstream of the catalytic converter 3 with complete conversion of the chemical energy E _{chnK of} the post-injected fuel quantity theoretically achievable thermal energy, the evaluation device 9 inputs via a line 15 corresponding signal to the engine control unit 5 , which processes this signal in a corresponding manner. For example, when the internal combustion engine 2 is used in a vehicle, the vehicle driver is informed that the exhaust gas cleaning system is malfunctioning. A signal can also be set which only gives the maintenance personnel a corresponding warning during the next maintenance.

In Fig. 2, the time is plotted in the X direction and in the Y direction the course of the energies be considered by the evaluation device 9 as a function of time. A curve I shown with a solid line represents the development over time of the sum of the thermal energy E _thvorKat upstream of the catalytic converter 3 and the chemical energy E _{chnK of} the quantity of fuel injected. An energy curve II shown with a broken line shows the temporal development of the thermal energy E _thnachKat downstream of the catalytic converter 3 . III denotes a time window during which fuel _post- injection takes place, that is to say during which chemical energy E _chnK upstream of the catalytic converter 3 is supplied to the exhaust gas.

In a first time period a, during which no post-injection takes place, the course I corresponds to the thermal energy E _thvorKat upstream of the catalyst 3 and is equal to the course II of the thermal energy E _thnachKat downstream of the catalyst 3 . A post-injection (III) takes place during a time period b, which has a direct effect on the course I of the sum of thermal energy E _thvorKat upstream of catalytic converter 3 and chemical energy E _{chnK of} the quantity of fuel subsequently injected. The conversion of the chemical energy E _{chnK of} the amount of fuel injected into the catalytic converter 3 into additional thermal energy is delayed, so that the thermal energy E _thnachKat downstream of the catalytic converter 3 increases with a corresponding time delay. The energy courses I and II therefore run separately in time period b and in a subsequent time period c. If the catalytic converter 3 functions properly, the energy _profile II, that is to say the thermal energy E _{thnach Kat} downstream of the catalyst 3 , reaches the energy profile I again after a certain time, that is to say the profile of the sum of thermal energy E _thvorKat upstream of the catalyst and che mixer energy E _{chnK of} the amount of fuel injected. In a time period d, the energy profiles I and II again have the same profile.

If the functionality of the catalytic converter 3 is restricted, the energy profile II will no longer reach the energy profile I after the injection process. The distance between the energy profiles I and II after an injection process is then a measure of the functionality or malfunction of the catalytic converter 3 .

In the case of a catalytic converter 3 , which is in any case permanently operated with a post-injection in order to increase its efficiency, according to another embodiment, the course I of the sum of thermal energy E _chvorKat upstream of the catalytic converter 3 and the chemical energy E _{chnK of} the quantity of fuel injected afterwards can be permanently with Course II of the thermal energy E _thnachKat downstream of the catalyst 3 can be compared. As long as the catalytic converter 3 is working properly, the energy profiles I and II lie on one another. As soon as the functionality of the catalytic converter 3 is restricted, the energy profile II moves away from the energy profile I. If the distance between the energy profiles I and II exceeds a predetermined limit value, the evaluation device 9 alerts the engine control unit 5 .

In another embodiment, the evaluation device 9 for the case that the catalytic converter 3 is also permanently operated with a post-injection, the post-injected fuel quantity can vary for a certain period of time, the increase being basically the same as in Fig. 2nd

It is clear that the function of the evaluation device 9 can be integrated into a correspondingly programmable engine control unit 5 .

The integration or summation or generally the observation of the energies can in principle be carried out independently of the respective operating state of the internal combustion engine 2 . However, it is advantageous if before or at which the above equation (E _thvorKat + E _chnK ) - E _thnachKat = 0 is to be fulfilled, there was a stationary or quasi-stationary operating state for a sufficiently long period of time. This period is chosen so that time delays in the flow through the catalyst are taken into account.

In addition, energy "losses" in the catalyst flow are largely taken into account by corrective variables, such as. B. the heat radiated from the catalyst to the outside. These correction values are e.g. B. stored in maps in the evaluation device 9 .

Claims (11)

1. Device for monitoring the operability of a catalyst ( 3 ) in an internal combustion engine ( 2 ) which can be operated stoichiometrically or over-stoichiometrically, with fuel supply means ( 4 ) with which the gas flow supplied to the catalyst ( 3 ) can be set to a certain amount of fuel whose chemical energy (E _ch ) in the catalytic converter ( 3 ) is more or less converted into thermal energy (E _th ) depending on its functionality, with energy determining means ( 7 , 11 , 13 ) which are used to determine the catalytic converter ( 3 ) supplied and discharged energies, and with an evaluation device ( 9 ), which communicates with the fuel supply means ( 4 ) and the energy coordination means ( 7 , 11 , 13 ) and taking into account the amount of fuel supplied to the catalyst ( 3 ) ge an energy balance for the catalyst ( 3 ) and one with the functionality of the catalyst ators ( 3 ) generates a correlated signal value and uses it for evaluation. 2. Device according to claim 1, characterized in that the energy determination means ( 7 , 11 , 13 ) for determining thermal energies (E _th ) in the gas flow upstream and downstream of the catalyst ( 3 ) are formed. 3. Device according to claim 2, characterized in
that the internal combustion engine ( 2 ) has a fuel injection device ( 4 ) with which predetermined amounts of fuel can be injected into the combustion chambers of the internal combustion engine ( 2 ) for combustion,
that the evaluation device ( 9 ) communicates with the fuel injection device ( 4 ) and receives signal values which correlate with the amount of fuel injected into the combustion chambers,
that the energy determination means ( 7 , 11 , 13 ) are designed to determine the temperatures in the gas flow upstream and downstream of the catalyst ( 3 ) and to determine the amount of air supplied to the combustion chambers of the internal combustion engine ( 2 ) for combustion,
that the evaluation device (9) of the fuel injected into the combustion chambers amount of fuel from the determined combustion chambers to guided air amount and from the flow temperature upstream of the catalyst (3), the thermal energy (E _thvorKat) in the exhaust gas upstream of the catalyst (3),
that the evaluation device ( 9 ) determines the chemical energy (E _ch ) from the fuel quantity supplied to the catalyst ( 3 ),
that the evaluation device ( 9 ) from the amount of fuel injected into the combustion chambers, from the amount of air supplied to the combustion chambers, from the amount of fuel supplied to the catalyst ( 3 ) and from the flow temperature downstream of the catalyst ( 3 ) the thermal energy (E _thnachKat ) in the exhaust gas determined downstream of the catalyst ( 3 ),
wherein the thermal exhaust gas energy (E _thvorKat ) upstream of the catalyst ( 3 ) plus the chemical energy (E _ch ) of the amount of fuel supplied to the catalyst ( 3 ) minus the thermal exhaust gas energy (E _thnachKat ) downstream of the catalyst ( 3 ) provides an energy value that correlates with the functionality of the catalyst ( 3 ) and is used by the evaluation device ( 9 ) for evaluation. 4. Device according to one of claims 1 to 3, characterized in
that the fuel supply means are formed by a fuel injection device ( 4 ) of the internal combustion engine ( 2 ), and
that the evaluation device ( 9 ) either actuates the internal combustion engine ( 2 ) to carry out a time-limited sub-stoichiometric operation of the internal combustion engine ( 2 ), in which a certain amount of fuel is supplied with the gas flow from the catalyst ( 3 ), or the fuel injection device ( 4 ) actuated to carry out a fuel post-injection in which a certain amount of fuel is injected into the combustion exhaust gases, or the post-injection amount varies with a time limit if post-injection is present. 5. Device according to one of the preceding claims, characterized in that the evaluation device ( 9 ) for determining the thermal energy (E _th ) in the exhaust gas integrates the thermal energy amounts in the exhaust gas flow over time. 6. The device according to claim 5, characterized in
that the evaluation device ( 9 ) starts the integration approximately at the start of the post-injection or
that the evaluation device ( 9 ) permanently carries out the integration, provided the internal combustion engine ( 2 ) is operated stoichiometrically or over-stoichiometrically and with a fuel supply to the catalytic converter ( 3 ). 7. Device according to one of the preceding claims, characterized in that the means for determining the thermal exhaust gas energy (E _th ) an air mass sensor ( 7 ) which is arranged upstream of the internal combustion engine ( 2 ), a first temperature sensor ( 11 ) which is downstream the internal combustion engine ( 2 ) and upstream of the catalyst ( 3 ) is arranged, and have a second temperature sensor ( 13 ) which is arranged downstream of the catalyst ( 3 ). 8. Device according to one of the preceding claims, characterized in that the catalyst ( 3 ) is designed as a DENOX catalyst. 9. Device according to one of the preceding claims, characterized in that the internal combustion engine ( 2 ) is designed as a diesel engine or as a stoichiometrically operated gasoline engine. 10. Device according to one of the preceding claims, characterized in that the evaluation device ( 9 ) the thermal energy (E _th ) in the exhaust gas in analogy to the equation:
E _th = Σ (m _x .c _pmx .T _x )
calculated where
E _th = thermal energy in the exhaust gas,
x = individual exhaust gas component,
m _x = mass of the exhaust gas component x,
c _pmx = specific heat capacity of the exhaust gas component x,
T _x = temperature of the exhaust gas component x. 11. The device according to one of the preceding claims, characterized in that the evaluation device ( 9 ) the chemical energy (E _chnK ) of the amount of fuel supplied to the catalyst ( 3 ), in particular sprayed afterwards, in analogy to the equation:
E _chnK = m _nK .Hu _K
calculated where
E _chnK = chemical energy of the fuel,
m _nK = mass of the fuel injected,
Hu _K = lower heating value of the fuel.