Title of Invention

METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE IN PARTICULAR OF A MOTOR VEHICLE

Abstract

A method for operating an internal combustion engine, in particular of a motor vehicle, in which fuel is injected into a combustion chamber in a lean operating mode and in a rich operating mode, and in which the engine is switched between the two operating modes, characterized in that an air mass and an injection quantity for the lean-burn mode are continually determined, in that a lambda for the lean-burn mode is continually determined from the air mass and the injection quantity, in that a lambda for the rich operating mode and for the transitions to it, the said lambda differing from the lambda for the lean-burn mode, is predetermined, and in that a desired air mass for the rich operating mode and for the transitions to it is determined from the lambda for the lean-burn mode and from the lambda for the rich operating mode and for the transitions to it.

Full Text

The invention is based on a method for operating an internal combustion engine in particular of a motor vehicle, in which fuel is injected into a combustion chamber in a lean-burn operating mode and in a rich-burn operating mode, and in which the engine is switched between the two operating modes. The invention also relates to a corresponding internal combustion engine and to a control unit for an internal combustion engine of this type. In diesel and gasoline internal combustion engines, it is known to use a NOx storage catalytic converter in order to reduce the emissions of pollutants. For operation of the NOx storage catalytic converter, it is necessary for the internal combustion engine to be switched from the lean-burn operating mode to the rich-burn operating mode. The NOx storage catalytic converter is regenerated in this rich-burn operating mode. After the regeneration has been carried out, the internal combustion engine is switched back to the lean-burn operating mode. When switching between the lean-burn operating mode and the rich-burn operating mode, it must be ensured that, in particular, there is no jolting changeover or the like. Therefore, when switching between the two operating modes, the air mass which is fed to the internal combustion engine and also the quantity of fuel injected into the internal combustion engine have to be influenced in such a way that, in particular, the torque which is generated by the internal combustion engine does not have any peaks or sudden jumps or the like. Object and advantages of the invention It is an object of the invention to provide a method for operation of an internal combustion engine, in particular of a motor vehicle, in which it is possible to switch between the rich-burn operating mode and the lean-burn operating mode without any changeover pressure or the like. According to the invention, in a method of the type described in the introduction this object is achieved by the fact that an air mass and an injection quantity for the lean-burn operation are continually determined, that a lambda for the lean-burn operation is continually determined from the air mass and from the injection quantity, that a lambda, which differs from the lambda for the lean-burn operation, is predetermined for the rich-burn operating mode and for the transitions to this operating mode, and that a desired air mass for the rich-burn operating mode and for the transitions to this operating mode is determined from the lambda for the lean-burn operation and from the lambda for the rich-burn operating mode and for the transitions to this operating mode. Therefore, control of the internal combustion engine during the transition from the lean-burn operating mode to the rich-burn operating mode, and also in the rich-burn operating mode itself, is based on the injection quantity and on the air mass which are inherently provided for the lean-burn operating mode. A lambda for the lean-burn operating mode is calculated from this air mass and injection quantity for the lean-burn operation. This lambda is linked to a lambda which represents the desired lambda” for the transition to the rich-burn operating mode or for the rich-burn operating mode itself. Then, the desired air mass in which the internal combustion engine is supplied during transition to the rich-burn operating mode or during the rich-burn operating mode itself is determined from this linking of the calculated lambda for the lean-burn operating mode and the desired lambda for the rich-burn operating mode or for the transition to this operating mode. It will be understood that further operating variables of the internal combustion engine may also play a role in determining the desired air mass. Overall, the control arrangement according to the invention represents an air-governed system. The desired air mass which is to be fed to the internal combustion engine is calculated on the basis of the lambda for the lean-burn operation as a function of the desired lambda for the rich-burn operating mode or for the transition to this operating mode. Therefore, in the first step the internal combustion engine is directed toward the rich-burn operating mode with the aid of a change in the air mass. It will be understood that corresponding statements also apply when the internal combustion engine is switched from the rich-burn operating mode to the lean-burn operating mode. An essential factor in the control arrangement according to the invention is that a sudden jump in the desired air mass still does not cause any damage. The actual air mass and therefore also the desired injection quantity and the torque generated by the internal combustion engine remain free from sudden jumps. Any peaks or sudden jumps in the torque generated by the internal combustion engine are reliably avoided in this way. It is particularly advantageous if the lambda for the lean-burn operation is converted into an efficiency for the lean-burn operation, and the lambda for the rich-burn operating mode is converted into an efficiency for the rich-burn operating mode if the efficiency for the lean-burn operation is multiplied by the air mass for the lean-burn operation and if the result of the multiplication is divided by the efficiency for the rich-burn operating mode. This represents a particularly simple and effective way of enabling the lambda for the lean-burn operation to be linked to the predetermined lambda for the rich-burn operating mode and for the transitions to this operating mode. In this context, it is essential for both lambdas to each be converted into an efficiency. This conversion allows simple linking of the respective variables and calculation of the desired air mass according to the invention therefrom. In an advantageous refinement of the invention, in which an actual air mass is measured or simulated or modeled, a desired value for the lambda in the rich-burn operating mode and for the transitions to this operating mode is determined as a function of the air mass and the injection quantity for the lean-burn operation, and a desired injection quantity for the rich-burn operating mode and for the transitions to this operating mode is determined from the actual air mass and the desired value for the lambda. As has already been mentioned, the control arrangement according to the invention represents an air-governed system. According to the invention, the desired air mass is determined as a function of the lambda which is desired in each case. In the above refinement of the invention, the actual air mass, i.e. the mass of air which is actually supplied to the internal combustion engine, is measured. It is also possible for the actual air mass to be simulated or modeled from other operating variables of the internal combustion engine. This actual air mass changes according to the changes in the desired air mass. According to the invention, a change in the actual air mass leads to a change in the desired injection quantity. This means that the desired injection quantity is ultimately matched to the desired air mass. Overall, therefore, a desired air mass and a desired injection quantity, which on the one hand are dependent on the desired lambda and on the other hand are always adapted to one another, are always generated. Therefore, the air-governed system according to the invention is completed by the change in the desired injection quantity as a function of the actual air mass and therefore as a function of the desired air mass. Since the desired injection quantity and the actual air mass are always adapted to one another, it is ensured that there can be no sudden jumps or peaks or the like in the torque which is generated by the internal combustion engine. It is particularly advantageous if the desired value for the lambda in the rich-burn operating mode and for the transitions to this operating mode is determined from a desired efficiency for the rich-burn operating mode and for the transitions to this operating mode and if the desired efficiency is determined by dividing the actual air mass by the abovementioned multiplication result. This represents a particularly simple and effective way of enabling the desired injection quantity to be calculated. Once again, it is an essential factor that a conversion from an efficiency to a lambda is carried out. Furthermore, in this context it is of importance that the multiplication result which results from the air mass and the injection quantity for the lean-burn operation is likewise used according to the invention in the determination of the desired injection quantity. In this way, even with the desired injection quantity it is ensured that there is no sudden jump in the desired injection quantity when switching between the operating modes. In an advantageous configuration of the invention, the conversion of a lambda into an associated efficiency or vice versa is carried out by means of a characteristic reference curve and by means of additive and/or multiplicative corrections. This ensures, firstly, that the conversion between a lambda and an efficiency or vice versa can be carried out with the minimum possible difficulty of calculation. Secondly, this ensures that changes in the internal combustion engine can be corrected with the aid of the additive and/or multiplicative adaptation. In a further advantageous configuration of the invention, in which the fuel which is to be injected into the combustion chamber with one injection is injected in two or more partial injections, the start of injection or the start of actuation and/or the duration of injection or the duration of actuation of the partial injections is determined differently as a function of the operating mode and/or as a function of operating variables of the internal combustion engine. In this context, it is particularly advantageous if a hysteresis is taken into account for the start of injection and/or the duration of injection when switching between the operating modes. These measures make it particularly easy to apply the method according to the invention for the operation of an internal combustion engine to engines which carry out two or more partial injections for each injection of fuel. This is the case in particular for diesel internal combustion engines. This principle can also be applied in particular to internal combustion engines with direct ignition. It is particularly important to realize the method according to the invention in the form of a computer program which is provided for a control unit of the internal combustion engine. The computer program can be run on a computer of the control unit and is suitable for carrying out the method according to the invention. In this case, therefore, the invention is realized by the computer program, so that this computer program represents the invention in the same way as the method which the computer program is able to execute. The computer program may preferably be stored on a flash memory. The computer provided may be a microprocessor. The control unit in which the computer program is contained is provided in particular for the purpose of controlling a plurality of operating variables of the internal combustion engine. Further features, possible applications and advantages of the invention will emerge from the following description of exemplary embodiments of the invention, which are illustrated in the figures of the drawing, in which all the features described or illustrated, on their own or in any desired combination, form the subject matter of the invention, irrespective of the way in which they are put together in the patent claims or the way in which these claims refer back, and irrespective of their wording or illustration in the description or in the drawing. Exemplary embodiments of the invention Figure 1 shows a schematic circuit diagram of an exemplary embodiment of a method according to the invention for operating an internal combustion engine in particular of a motor vehicle. Figures 2a and 2b show schematic circuit diagrams of exemplary embodiments for converting an efficiency to lambda and vice versa, Figure 3 shows a schematic circuit diagram of an exemplary embodiment for using various characteristic diagrams for the actuation duration of a main injection, Figure 4 shows a schematic circuit diagram of an exemplary embodiment for taking account of a hysteresis for the injection of the fuel into the internal combustion engine, and Figure 5 shows a schematic diagram illustrating the relationship between an efficiency and lambda when using a hysteresis. The following method for controlling an internal combustion engine is described on the basis of a diesel internal combustion engine. However, it should be noted that the method described can also be used, in suitably adapted form, for a gasoline internal combustion engine. In particular, it is possible for the method described to be used in an internal combustion engine with direct injection. To reduce the emissions of pollutants from a diesel internal combustion engine, an NOx storage catalytic converter is provided. In this NOx storage catalytic converter, the internal combustion engine is alternately operated in a lean-burn operating mode and a rich-burn operating mode. The nitrogen oxides which are formed in the lean-burn operating mode are taken up by the NOx storage catalytic converter and temporarily stored. The NOx storage catalytic converter is laden with the nitrogen oxides. Before the NOx storage catalytic converter is completely laden with the nitrogen oxides, the internal combustion engine is switched over to a rich-burn operating mode. In this rich-burn operating mode, unburnt hydrocarbons and carbon monoxide and hydrogen pass to the NOx storage catalytic converter. The nitrogen oxides which are stored in the NOx storage catalytic converter then react with the hydrocarbons, the carbon monoxide and the hydrogen and can then be released to atmosphere, inter alia as carbon dioxide and water. The rich-burn operating mode of the internal combustion engine is maintained until the nitrogen oxides have been removed as completely as possible from the NOx storage catalytic converter. This removal of nitrogen oxides is also known as regeneration of the NOx storage catalytic converter. Therefore, for the above-described operation of the internal combustion engine, it is necessary to switch repeatedly between a lean-burn operating mode and a rich-burn operating mode. During these switching operations there must in particular be no sudden jump in torque. Figure 1 shows a control system which allows the engine to be switched between a lean-burn operating mode and a rich-burn operating mode without there being any sudden jump in torque. The starting point for the control system shown in Figure 1 is a predetermined injection quantity ME.iean fo^ lean-burn operation and a predetermined air mass ML, lean likewise for lean-burn operation. These two variables ME.iean and ML,iean sre provided by a general control unit of the internal combustion engine. If the internal combustion engine has, for example, exhaust gas recirculation, said variable ML,iean is usually generated by a control unit for this exhaust gas recirculation. The variable ME.iean usually corresponds to the driver"s desired thrust or the torque which is to be generated. In Figure 1, as a further input variable there is an actual air mass ML,actual/ which is measured with the aid of an air mass sensor. It is in this case possible for the signal of the air mass sensor to be corrected by means of further measured variables. Switching between the lean-burn operating mode and the rich-burn operating mode takes place with the aid of a predeterminable lambda value •intermediate/ which - as has been explained - can be changed to a rich lambda value or a lean lambda value in particular as a function of the loading of the NOx storage catalytic converter. In the case of diesel fuel, the injection quantity ME, lean is multiplied by a fixed factor 14.5 before then being divided by the air mass ML,iean- The result of this division is then a lambda value "lean for the lean-burn operation. This lambda value "lean is permanently generated from the two variables Mg^iean and ML,iean/ irrespective of whether the internal combustion engine is in a lean-burn operating mode or a rich-burn operating mode. As has been explained with reference to Figures 2a and 2b, the lambda value "lean is converted, in a block 10, into an efficiency •lean for the lean-burn operation. This efficiency "lean is then linked by multiplication to the air mass ML,iean- The result of this multiplication is indicated by reference symbol A in Figure 1. The predeterminable lambda value •intermediate is converted into an efficiency •intermediate by a block 11. This conversion is explained in more detail in connection with Figures 2a and 2b. The above multiplication result A is divided by the efficiency "intermediate- The result of this division represents a desired air mass ML,des- This desired air mass ML.des is an output signal from the control arrangement shown in Figure 1. The desired air mass ML.des can be used, for example, to influence the opening angle of a throttle valve by means of which the air which is fed to the internal combustion engine, for example via an intake pipe, can be varied. The desired air mass ML,des represents the desired value, i.e. the mass of air which it is desired to feed to the internal combustion engine. As has already been mentioned, the air mass which is actually supplied to the internal combustion engine is measured with the aid of an air mass sensor. The measurement signal is then -as has already been explained - the actual air mass ML,actual• According to Figure 1, the abovementioned multiplication result A is divided by the actual air mass ML,actual- The result of the division represents a desired efficiency des • This desired efficiency des is converted into a lambda desired value des by a block 12. This conversion is explained in more detail with reference to Figures 2a and 2b. In the case of diesel fuel, the lambda desired value des is multiplied by a fixed factor 14.5. Then, the actual air mass ML,actual is divided by the lambda desired value des which has been multiplied by 14.5. The result of the division is a desired injection quantity ME,des- The desired injection quantity ME,des represents an output signal from the control arrangement shown in Figure 1. The desired injection quantity ME,des can be used, for example, to actuate an injection valve of the internal combustion engine, which is used to inject the desired injection quantity ME,des into the combustion chamber of the internal combustion engine. The control arrangement which is illustrated in Figure 1 and has been explained above is air-governed. This means that first of all the desired air mass ML,des is calculated from the input variables of the control arrangement. As has been explained, this desired air mass ML,des leads to the actual air mass ML,actual- Then, the desired injection quantity ME,des is calculated from this measured actual air mass ML,actual- If the internal combustion engine is in the lean-burn operating mode, the lambda value "intermediate corresponds to the lambda val ue "lean for the lean-burn operation. This means that the desired air mass ML,des is equal to the air mass ML,lean for lean-burn operation. Likewise, the desired injection quantity ME,des is equal to the injection quantity ME, lean for the lean-burn operation. Therefore, in this lean-burn operating mode, the control arrangement shown in Figure 1 does not lead to any change in the two input variables ME,lean and ML,lean- If it is now desired to switch over to a rich-burn operating mode in order for the NOx storage catalytic converter to be regenerated, the lambda value •intermediaLe is changed toward a rich lambda value. Therefore, the lambda value •intennediate is, for example, reduced toward 0.95. This means that, via the intervention of the efficiency •intermediate/ the desired air mass ML,des changes. The desired air mass ML,des is reduced on account of the desired rich-burn operating mode. This leads to the actual air mass ML,actual also being reduced. According to the control arrangement shown in Figure 1, this then also leads to the desired injection quantity ME,des being increased. The overall result is that the air/fuel ratio shifts toward a rich-burn operating mode, i.e. toward excess fuel. Once the regeneration of the NOx storage catalytic converter is concluded, it is possible to move back to the lean-burn operating mode of the internal combustion engine. This is achieved by increasing the lambda value •intermediate again toward the lambda value "lean for lean-burn operation. This then leads to the desired air mass ML,des becoming greater and, at the same time, to the desired injection quantity ME,des becoming smaller. The air/fuel ratio in the internal combustion engine is therefore shifted toward a lean-burn operating mode. As soon as the lambda value •intermediate has returned to the lambda value "lean for the lean-burn operation, the equilibrium which has been explained above is established again, according to which the desired air mass ML,des corresponds to the air mass ML,iean for lean-burn operation and the desired injection quantity ME,des corresponds to the injection quantity ME,lean for lean-burn operation. In the control arrangement shown in Figure 1, a lambda value is converted into an efficiency in blocks 10 and 11. Conversely, in block 12 an efficiency is converted into a lambda value. Figures 2a and 2b show how these conversions can be carried out. In Figure 2a, an efficiency • is present as an input variable and a lambda value • is present as an output variable. Furthermore, the rotational speed n of the internal combustion engine and the injection quantity ME, lean ^OT the lean-burn operation of the internal combustion engine are predetermined. The two latter operating variables of the internal combustion engine are fed to a total of four characteristic diagrams. The values yoff, Ymui / y^ott and Xmui SLTG generated by the four characteristic diagrams as a function of these operating variables. The value yoff is subtracted from the efficiency •. The difference which is formed is divided by the value ymu: • The result of the division is fed to a characteristic reference curve 24 for converting the efficiency into the lambda value. The value Xoff is subtracted from the output signal of the characteristic reference curve 24. The result of the subtraction is divided by the value x^ui. The lambda value • is then available as the result of the division. Therefore, with the aid of the characteristic diagrams 20, 21, 22, 23 it is possible to correct the characteristic reference curve 24. The characteristic diagrams 20, 22 are in each case used for additive correction, while the characteristic diagrams 21, 23 effect a multiplicative correction. In Figure 2b, a lambda value • is converted into an efficiency • in a corresponding but reverse manner. Once again, there are four characteristic diagrams 25, 26, 27, 28, with which a characteristic reference curve 29 for converting a lambda value into an efficiency can be corrected. Once again, the characteristic reference curve 29 can be corrected in an additive and multiplicative manner. The characteristic diagram 25 is identical to the characteristic diagram 23. The same applies to the remaining characteristic diagrams 26, 27, 28 and 22, 21, 20. The characteristic curve 29 is the inverse function of the characteristic curve 24. As has already been explained, the desired injection quantity Ms.des from Figure 1 can be used to actuate an injection valve of the internal combustion engine. This injection valve is then used to inject said desired injection quantity Mg^des into the combustion chamber of the internal combustion engine. In the case of diesel internal combustion engines, it is advantageous for the injection of the fuel into the combustion chamber of the internal combustion engine to be divided into two partial injections. For example, a preinjection quantity ME.VE is injected into the combustion chamber of the internal combustion engine as part of a preinjection, and a main injection quantity ME,HE is injected into the combustion chamber of the internal combustion engine as part of a main injection. The preinjection quantity ME.VE and the main injection quantity ME,HE together result in the desired injection quantity ME,des- To define the abovementioned preinjection and main injection, the respective start of actuation or start of injection and the respective duration of actuation or duration of injection are of decisive importance. The way in which the desired injection quantity ME,des is divided into the preinjection and the main injection, and the way in which the respective start of actuation and the respective duration of actuation of the preinjection and of the main injection are fixed, are dependent on a plurality of operating variables of the internal combustion engines. Under certain circumstances, for example during a lean-burn operating mode of the internal combustion engine, it is possible for there to be no longer any preinjection at all. It is also possible, for example during a rich-burn operating mode of the internal combustion engine, for the time interval between the preinjection and the main injection to be significantly increased. One reason for these measures is the fact that, in the case of internal combustion engines with a pressure store, the rail pressure Praii at which the fuel is fed to the injection valves is influenced by the successive preinjection and main injection. In particular, it is possible for the preinjection to cause a vibration in the pressure chamber in which the fuel is made available for injection via the injection valves. The main injection is then dependent on this fluctuation in the rail pressure praii to the extent that a time shift in the main injection in relation to the preinjection leads directly to a change in the rail pressure Praii which is present during the main injection. Figure 3 illustrates, by way of example, one possible way of allowing the duration of actuation ADHE for the main injection to be determined as a function of the operating state of the internal combustion engine. For this determination of the duration of actuation ADHE for the main injection, the injection quantity ME,HE for the main injection and the rail pressure Praii are predetermined as input variables. These input variables are fed to three characteristic diagrams 30, 31, 32. The characteristic diagram 30 is used to deliver a duration of actuation ADHE for the main injection in which there is no preinjection. The characteristic diagram 31 is used to deliver a duration of actuation ADHE for the main injection where there is a preinjection. And finally, the characteristic diagram 32 is used to deliver a duration of actuation ADHE for the main injection which is provided for the rich-burn operating mode of the internal combustion engine. One of the three characteristic diagrams 30, 31, 32 is selected with the aid of a switch 33 as a function of a signal B. Then, the switch 33 is used to transmit the respective output signal of the selected characteristic diagram 30, 31, 32 as duration of actuation ADHE- The signal B is a status symbol which is predetermined, for example, as a function of the operating mode of the internal combustion engine. The signal B may also be predetermined as a function of further operating variables of the internal combustion engine. The possibility of switching between different characteristic diagrams which is described by way of example in Figure 3 with reference to the duration of actuation ADHE for the main injection can also be applied in a corresponding way to the start of actuation for the main injection, the duration of actuation for the preinjection and to the start of actuation for the preinjection. As a further measure, it is possible to perform the transition between the lean-burn operating mode and the rich-burn operating mode and, conversely, the transition between the rich-burn operating mode and the lean-burn operating mode with the aid of a hysteresis. Figure 4 shows, by way of example with reference to the start of actuation ABVE of the preinjection, a possible way allowing a hysteresis of this type to be implemented. For example, a characteristic diagram 40 is provided, which is fed as input signals with the rotational speed n of the internal combustion engine and the injection quantity ME,lean for lean-burn operation of the internal combustion engine. As the output signal, the characteristic diagram 40 generates a delta value -ABVE for the start of actuation of the preinjection. Furthermore, the lambda desired value "aes is fed to a characteristic hysteresis curve 41. If the lambda desired value is in a rich-burn range, the characteristic hysteresis curve 41 generates the value 1 as output signal. On the other hand, if the lambda desired value "des is in a lean-burn range, the output value of the characteristic hysteresis curve 41 is equal to 0. This output value of the characteristic hysteresis curve 41 is linked by multiplication to the delta value •ABvE fo3f the start of actuation of the preinjection. This means that this delta value "ABVE in a rich-burn range of the internal combustion engine is completely transmitted, but in a lean-burn range of the internal combustion engine is completely suppressed. Then, the multiplication result generated in the manner described is combined by addition with the start of actuation ABVE, lean fo^^ the preinjection in a lean-burn operating mode. The result of this addition is then the start of actuation ABVE for the preinjection, which ultimately defines the time at which the injection valve is opened for the purposes of preinjection. Overall, therefore, in Figure 4 in a lean-burn operating mode the predetermined start of actuation ABVE,lean is not changed, since the output signal of the characteristic hysteresis curve 41 is equal to 0. By contrast, in a rich-burn operating mode of the internal combustion engine, the start of actuation ABVE, lean is changed by the delta value "ABVE- This means that the start of actuation of the preinjection within said rich-burn operating mode of the internal combustion engine is changed to an earlier time. The above-described influencing of the start of actuation ABVE of the preinjection can also be applied in a corresponding way to the start of actuation of the main injection and to the duration of actuation of the preinjection and/or of the main injection. If a hysteresis is used, as explained by way of example in connection with Figure 4, it may be advantageous or even necessary for a hysteresis also to be employed in the conversions carried out in blocks 10, 11 and 12 from Figure 1. A hysteresis of this type is illustrated by way of example in Figure 5 . If the hysteresis shown in Figure 5 is used in blocks 10, 11, 12 in Figure 1, it is expedient or even necessary for the additive and multiplicative corrections of the characteristic reference curves 24 and 29 shown in Figures 2a and 2b to be carried out in sections, specifically in each case separately for the two branches of the hysteresis illustrated in Figure 5. WE CLAIM : 1. A method for operating an internal combustion engine, in particular of a motor vehicle, in which fuel is injected into a combustion chamber in a lean operating mode and in a rich operating mode, and in which the engine is switched between the two operating modes, characterized in that an air mass (ML,iean)and an injection quantity (ME,]ean) for the lean-bum mode are continually determined, in that a lambda (X. ean) for the lean-burn mode is continually determined from the air mass and the injection quantity, in that a lambda (‘’inter) for the rich operating mode and for the transitions to it, the said lambda differing from the lambda for the lean-burn mode, is predetermined, and in that a desired air mass (ML,des) for the rich operating mode and for the transitions to it is determined from the lambda for the lean-burn mode and from the lambda for the rich operating mode and for the transitions to it. 2. The method according to Claim 1, wherein the lambda for the lean-burn mode is converted into an efficiency for the lean-burn mode, and the lambda for the rich operating mode and for the transitions to it is converted into an efficiency for the rich operating mode and the transitions to it, in that the efficiency for the lean-burn mode is multiplied by the air mass for the lean-burn mode, and in that the multiplication result is divided by the efficiency for the rich operating mode and for the transitions to it. 3. The method according to Claim 1 or 2, wherein an actual air mass is measured or simulated or modeled, a desired value for the lambda in the rich operating mode and for the transitions to it is determined as a function of the actual air mass and the injection quantity for the lean-burn mode, and in that a desired injection quantity for the rich operating mode and for the transitions to it is determined from the actual air mass and the desired value for the lambda. 4. The method according to Claims 2 and 3, wherein the desired value for the lambda in the rich operating mode and for the transitions to it is determined from a desired efficiency for the rich operating mode and for the transitions to it, and in that the desired efficiency is determined by dividing the actual air mass by the said multiplication result 5. The method according to any one of the preceding claims, wherein the conversion of a lambda into an associated efficiency or vice versa is carried out by means of a reference characteristic curve and by means of additive or multiplicative corrections. 6. The method according to any one of the preceding claims, in which the fuel which is to be injected into the combustion chamber by an injection is injected in two or more sub-injections, wherein the start of actuation or the duration of actuation of the sub-injections is determined differently as a function of the operating mode or as a function of operating variables of the internal combustion engine. 7. The method according to Claim 6, wherein a hysteretic is taken into account for the start of actuation or the duration of actuation when switching between the operating modes

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