HK1213962B - Method for reducing the particle emissions of an internal combustion engine and engine controller - Google Patents

Description

Method and motor controller for reducing particle emissions from an internal combustion engine

Technical Field

The invention relates to a method for reducing particle emissions of an internal combustion engine over its service life and to an engine controller.

Background Art

A common problem in internal combustion engines is that higher particulate emissions occur with increasing engine operating time, that is, with increasing engine aging. This is at least partially due to the cylinder filling with a smaller amount of combustion air during the intake stroke due to aging phenomena, such as carbon deposits. It is known to reduce particulate emissions in internal combustion engines by performing post-injection, in which an additional fuel injector is inserted into the cylinder during its ignition stroke after or during the actual, torque-generating combustion. According to a first, though controversial, theory, this post-injection causes soot particles present in the cylinder's combustion chamber and ejected into the exhaust pipe to burn into ash. According to a second theory, post-injection increases the exhaust gas temperature, which leads to a more effective reduction in particulate matter during additional exhaust gas aftertreatment.

A disadvantage here is that post-injections, which are carried out permanently over the entire service life of the internal combustion engine, lead to increased wear of the fuel injectors, thus necessitating premature replacement of the fuel injectors or shortening the service life of the engine overall.

Summary of the Invention

The object of the present invention is therefore to provide a method which makes it possible to reduce the particle emissions which increase during the service life of an internal combustion engine and at the same time keep injector wear as low as possible. It is also an object of the present invention to provide an engine controller which is suitable for carrying out such a method.

This object is achieved by providing a method characterized by gradually increasing the number of cylinders of an internal combustion engine that perform post-injection over the life of the internal combustion engine. Preferably, this number is gradually increased based on at least one parameter. The idea is based on the fact that particulate emissions typically increase continuously over the life of the engine and therefore do not necessarily need to be constant at the beginning of the life. In other words, in the new state of the engine, maximum consumption is activated to reduce particulate emissions. Furthermore, it is apparent that the consumption activated for particulate emissions can be gradually adjusted to the typically increasing particulate emissions over the life of the engine. Thus, by gradually increasing the number of cylinders performing post-injection (referred to as cylinders that perform post-injection or cylinders with post-injection), long-term post-injection is avoided in all cylinders over the total life of the internal combustion engine. This protects the injectors of cylinders that do not perform post-injection from excessive wear. Accordingly, preferably, as few injectors as possible are always subjected to post-injection loads, while still achieving at least an adequate reduction in particulate emissions. At the same time, the number of cylinders that are post-injected is adjusted to the service life of the internal combustion engine and thus preferably also to the rising particle emissions, which are reduced as required.

It is thus shown that the particle emissions which increase with age can be partially or completely compensated by selectively activating the post-injection for specific cylinders.

In this context, the life phase, in particular from the first commissioning of the internal combustion engine to its final shutdown, corresponds to the service life of the motor to a certain extent.

A preferred method is characterized in that no post-injection is performed in any cylinder in the new state of the internal combustion engine. The idea is based on this step so that the internal combustion engine has only relatively low particle emissions in its supply or new state, which do not need to be reduced by post-injection. This makes it possible to protect the injectors from the additional load caused by post-injection in the new state of the internal combustion engine. In an alternative embodiment of the method, it is possible to perform post-injection in at least one cylinder in the new state. This can reduce particle emissions in the new state or bring about at least one other effect, especially in terms of exhaust gas aftertreatment. In particular, it is possible to provide a certain degree of regular post-injection of at least one cylinder, as is generally known. Starting with the number of cylinders that perform post-injection in the new state, this number can then be gradually increased over the service life of the internal combustion engine.

A method is also preferred, characterized in that the number of cylinders active for post-injection is gradually increased based on operation or operating time, preferably measured in operating hours, in particular based on a specific value of the operating time of at least one motor assembly, based on distance data, and/or based on a particle concentration value in the exhaust gas. It is possible to consider the operating time, preferably measured in operating hours, or the distance data of the internal combustion engine itself as at least one parameter, thereby gradually increasing the number of cylinders active for post-injection. Alternatively or additionally, it is possible to consider the operating time of at least one motor assembly as at least one parameter. For example, the operating time, preferably measured in operating hours, of at least one injector can be observed. It is possible to consider the operating times of multiple motor assemblies as a parameter, particularly preferably considering the operating times of all injectors of the internal combustion engine. Distance data of the internal combustion engine is preferably considered as a parameter when the internal combustion engine is used to drive a vehicle, so that it is useful to consider the distance covered by the vehicle as a criterion for the aging of the internal combustion engine. The distance data can be specified (preferably in kilometers). Alternatively or additionally, it is possible to consider the load distribution of the internal combustion engine as a parameter. The term load distribution here particularly corresponds to the total power output by the internal combustion engine during its operation up to the present operating time (up to the currently observed time point), or the total power integrated over time, thus the total energy output by the internal combustion engine up to that time, preferably measured in kWh. When using an internal combustion engine in practical situations (which includes a meter for detecting the output power in kWh), it is particularly preferred to consider the load distribution. The concept of faster onset of aging phenomena in an internal combustion engine corresponds to considering the load distribution as a parameter: when the internal combustion engine continuously outputs more power or is subjected to a greater load than when it continuously outputs less power or is operated at a lower load point. Alternatively or additionally, it is possible to consider a value for the particle concentration in the exhaust gas as at least one parameter measured at least at time intervals, particularly preferably at predetermined time intervals. In a preferred embodiment of the method, the value for the particle concentration is continuously measured. This value is preferably measured using a measuring device, such as a detector or a scattered light-based measuring device.

This shows that for gradually increasing the number of cylinders with post-injection, time relationships must not necessarily be taken into account during the service life of the internal combustion engine. Furthermore, it is possible to use a number of other parameters for the method that do not describe time per se but are indirectly related to the operating time of the internal combustion engine or to the operating time of components of the internal combustion engine.

The number of cylinders active for post-injection is preferably increased when a predetermined threshold value of the observed variable or at least one parameter is reached or exceeded. For this purpose, the at least one parameter is preferably detected continuously or at preferably regular time intervals and compared with the threshold value. Thus, it is possible to increase the number of cylinders active for post-injection when the operating time, preferably measured in operating hours, of at least one engine assembly, preferably the internal combustion engine itself, reaches or exceeds a predetermined threshold value, in particular a predetermined number of operating hours. It is also possible to take into account threshold values for distance data, load distribution, and/or particle concentration.

Shown here, the cylinder quantity that plays the effect of post-injection preferably is not once but increases many times during the service life of internal combustion engine.Therefore preferably set a plurality of predetermined threshold values, when reaching or exceeding its situation, further increase the cylinder quantity that plays the effect of post-injection.

Typically, it is possible to increase the number of cylinders active for post-injection by one cylinder. Alternatively, it is possible to increase the number of cylinders active for post-injection by two or more cylinders. There is no mandatory requirement that this number be increased by the same number of cylinders in each increase step. This makes it possible, for example, to initially set post-injection in a single cylinder starting from a new state of the internal combustion engine without post-injection when a predetermined threshold value is reached or exceeded. If the next threshold value is reached or exceeded, it is possible, for example, to activate post-injection in two additional cylinders. Other sequences of increase steps are also possible as required and, in particular, calibrated to the typical increase in particle emissions for a specific internal combustion engine. Preferably, only as few injectors as possible are always subjected to the post-injection load, thus keeping the number of cylinders active for post-injection as small as possible. Therefore, it is particularly preferred not to overcompensate for the rising particle emissions.

A method is also preferred, characterized in that the cylinders performing post-injection, that is, the cylinders contributing to post-injection, are selected so as to be evenly distributed in the overall firing order of all cylinders. The cylinders of the internal combustion engine have a defined firing order, in which they are ignited sequentially from the first to the last cylinder. The first cylinder is then ignited after the last cylinder. If the cylinders contributing to post-injection are not evenly distributed in the firing order, this can lead to noticeable noise generation and rotational vibrations, as the torque generated during the working stroke of the cylinders contributing to post-injection differs from the torque generated during the working stroke of the cylinders not contributing to post-injection. Therefore, the cylinders contributing to post-injection are preferably evenly distributed in the firing order so that the same number of cylinders not contributing to post-injection are provided in the firing order between all pairs of sequentially ignited cylinders contributing to post-injection.

For example, if a twelve-cylinder internal combustion engine is operated so that post-injection is performed in two cylinders, the post-injection is evenly distributed in the overall firing order so that the cylinder with post-injection is followed by five cylinders without post-injection. For example, post-injection is performed in the first and seventh cylinders in the firing order, while post-injection is not performed in the second to sixth and eighth to twelfth cylinders. If, in the example of a twelve-cylinder internal combustion engine, post-injection is performed in four cylinders, then preferably two cylinders without post-injection are arranged in the firing order between the two cylinders with post-injection. For example, the cylinders with post-injection are then in the firing order of the first, fourth, seventh, and tenth cylinders.

A method is also preferred, characterized in that, for a first cylinder performing post-injection, post-injection is terminated after a predetermined, preferably adjustable, time interval. Simultaneously, post-injection is activated for a second cylinder that previously did not perform post-injection. After the predetermined time interval, the cylinder performing post-injection is correspondingly replaced; thus, the cylinder performing post-injection is replaced. This allows the additional load on the injector caused by post-injection to be distributed across more than one cylinder, with post-injection not being permanently performed in one and the same cylinder, so that the same injector is not permanently loaded. Preferably, the cylinder directly following or preceding the first cylinder in the firing order is selected as the second cylinder. This results in a position shift in the execution of post-injection (as viewed in the firing order). Particularly preferably, this replacement is performed again after each subsequent predetermined time interval. This allows all cylinders to be replaced as evenly as possible with respect to post-injection, thus distributing the additional injector wear caused thereby evenly across the entire internal combustion engine.

In this context, a method is also preferred, characterized in that all cylinders active for post-injection are replaced after a predetermined time interval, thus being replaced by cylinders that did not previously perform post-injection. In this case, a successor that is directly adjacent in the firing order is preferably determined for each cylinder active for post-injection. The number of cylinders active for post-injection is maintained. Replacing cylinders active for post-injection therefore does not serve to increase the number of cylinders active for post-injection, but rather to evenly distribute injector wear.

In the example of an internal combustion engine with twelve cylinders, where, for example, the first and seventh cylinders are initially selected as cylinders active for post-injection, the first and seventh cylinders are preferably replaced by the second and eighth cylinders in the firing order after a predetermined time interval. After another predetermined time interval, the second and eighth cylinders are then preferably replaced by the third and ninth cylinders in the firing order. The third and ninth cylinders are then preferably replaced by the fourth and tenth cylinders after a predetermined time interval, and the fourth and tenth cylinders are then replaced by the fifth and eleventh cylinders after a predetermined time interval. Finally, after a predetermined time interval in which post-injection is activated in the fifth and eleventh cylinders, post-injection is simultaneously activated in the sixth and twelfth cylinders. After a further predetermined time interval, post-injection is then deactivated in the sixth and twelfth cylinders, with post-injection being simultaneously reactivated in the first and seventh cylinders.

Overall, it is shown that in this way a switching post-injection is achieved, wherein the cylinder responsible for post-injection is continuously replaced, so that injector wear is evenly distributed over the entire internal combustion engine, thereby increasing the service life of the injector and thus the internal combustion engine as a whole.

A predetermined, preferably adjustable, time interval is preferably selected identically for each replacement. In a preferred embodiment of the method, this time interval is at least 0.25 to a maximum of 2 minutes, preferably at least 0.5 seconds to a maximum of 1 minute. The cylinders responsible for post-injection are therefore not replaced after each injector event, but rather after predetermined time intervals that are measured such that they preferably encompass multiple injector events or revolutions or working cycles of the internal combustion engine.

The increase in the number of cylinders active for post-injection can be time-planned so that it occurs simultaneously with the replacement of the cylinder active for post-injection. If a threshold value is reached or exceeded, it can be provided that, starting at this point in time, a waiting period is maintained until a predetermined time interval has elapsed and the cylinder active for post-injection is replaced. The number of cylinders active for post-injection can then be increased simultaneously. Alternatively, it is possible to shorten or extend the predetermined time interval when the threshold value is reached or exceeded, in particular to immediately carry out the replacement, including the increase in the number of cylinders active for post-injection. Alternatively, it is possible to increase the number of cylinders active for post-injection independently of the replacement of the cylinder active for post-injection.

A method is also preferred, characterized in that the efficiency of the internal combustion engine is calculated based on the number of cylinders that are post-injected. A performance map is used for engine control, which depends on the currently available efficiency. This map shows that the efficiency of the internal combustion engine decreases once post-injection is performed in a cylinder. It is important to note that the fuel quantity supplied to the cylinder per working cycle is taken into account in determining the efficiency, in terms of the torque generated in the cylinder or the power output by the cylinder. Because post-injection occurs at a time measured in crankshaft degrees, and the combustion of the post-injected fuel can only achieve a torque effect or no torque effect, the efficiency of the post-injected cylinders and, therefore, the overall efficiency of the internal combustion engine is reduced. Therefore, to maintain the power of the internal combustion engine when post-injection is activated, at least all cylinders that are post-injected must be supplied with an increased fuel quantity.

The fuel quantity supplied to the cylinders per working cycle is therefore adjusted depending on the current efficiency, in particular the performance map assigned to this efficiency. It is possible to adjust the fuel quantity only for the cylinders that are post-injected. Alternatively, it is preferably provided that the fuel quantity for all cylinders is adjusted. The efficiency loss of the internal combustion engine caused by post-injection can be divided by the total number of cylinders, with each cylinder (irrespective of whether it is a post-injection cylinder or a non-post-injection cylinder) being supplied with a correspondingly increased fuel quantity. This makes it possible to compensate for the efficiency loss by increasing the fuel quantity in a homogeneous and evenly distributed manner across the entire internal combustion engine.

For proper operation of an internal combustion engine, it is essential to select a performance map for engine control that corresponds to the actually existing efficiency at each operating point. In particular, the internal power, or the torque detected by the engine controller, must correspond to the actual output power. Furthermore, in speed-controlled internal combustion engines, an incorrect performance map can change other operating parameters, such as injector start or injector pressure, so that the engine can still maintain the set target speed but no longer maintain the specified exhaust gas values. Using a correct performance map that corresponds to the actual, current efficiency, it is possible, in particular, to adjust the fuel quantity supplied to the cylinders per working cycle so that changes in other operating parameters are preferably avoided at the same load point. This allows, in particular, the engine speed to be regulated to the target value while maintaining the specified exhaust gas values despite changes in efficiency.

In this context, preference is also given to a method which is characterized in that the efficiency is calculated according to the following formula:

η=a(1-K)+bK (1)

Here, n is described as the current efficiency of the internal combustion engine, taking into account the current number of cylinders that are post-injected. Parameter a indicates the efficiency of the internal combustion engine in a state in which no post-injection is performed in a cylinder, and parameter b indicates the efficiency of the internal combustion engine in an operating state in which post-injection is performed in all cylinders. Parameter K describes the quotient of the number of cylinders that are post-injected divided by the total number of cylinders in the internal combustion engine.

It is easy to see that when post-injection is not being performed in any cylinder (particularly in the new state of the internal combustion engine), the parameter K=0. In this case, the current efficiency η corresponds to the parameter a. If, on the other hand, post-injection is activated in all cylinders of the internal combustion engine, the value of the quotient K=1. In this case, the current efficiency η corresponds to the parameter b. The calculation is based on the assumption that there is a linear relationship between the number of cylinders affected by post-injection and the efficiency of the internal combustion engine.

The performance map of the internal combustion engine is selected according to the efficiency calculated with the aid of formula (1).

A method is also preferred, characterized in that different performance maps for the internal combustion engine are applied depending on the number and/or type of activated turbochargers. Depending on the number and/or type of activated turbochargers, and therefore the turbocharger state, the values of parameter a and, consequently, parameter b, are selected differently, i.e., the efficiency of the internal combustion engine in an operating state without post-injection in any cylinder and in an operating state with post-injection in all cylinders. The efficiency of the internal combustion engine is significantly dependent on the turbocharger state, i.e., how many and/or which turbochargers are activated, for example, a high-pressure or low-pressure turbocharger in the case of two-stage or multi-stage supercharging. The position of a valve that allows for a recirculation flow from the high-pressure turbocharger to the low-pressure turbocharger, thus enabling a so-called bypass or high-pressure turbine bypass, can also be considered. Therefore, preferably, a separate efficiency and, therefore, a separate performance map is used for engine control or regulation for each turbocharger state.

Finally, the object is also achieved by providing an engine controller for an internal combustion engine. This is characterized in that the engine controller is configured to execute a method according to any of the previously described embodiments. This achieves the advantages already explained in relation to the method with respect to the engine controller.

In particular, the method and the engine controller make it possible to maintain the internal combustion engine within permissible limit values for particle emissions in future-proof, downstream stages without having to provide a particle filter or an additional or larger particle filter overall.

BRIEF DESCRIPTION OF THE DRAWINGS

Next, the present invention will be explained in detail with reference to the accompanying drawings, wherein:

FIG1 shows a schematic, graphical representation depicting particle emissions versus motor operating time with and without the implementation of the method, and

FIG. 2 shows a schematic diagram of the calculation of the efficiency of an internal combustion engine as a function of the number of cylinders that are post-injected.

DETAILED DESCRIPTION

FIG1 shows a schematic, graphical representation of the particle emissions PE of an internal combustion engine versus the engine's operating time τm. The drawn straight line 1 illustrates the development of particle emissions due to aging of the internal combustion engine, without taking any reduction measures, in particular without implementing the method proposed herein. Starting from the particle emissions in the new state of the internal combustion engine, which are at the intersection of the ordinate and the abscissa of the illustrated coordinate system, the particle emissions rise continuously, in this case substantially linearly, with operating time.

The operating time τm of the internal combustion engine is divided into operating time segments delimited from one another by predetermined threshold values σ. FIG1 shows threshold values σ1, σ2, and σ3, by which four segments of the operating time τm are delimited from one another.

From the new state of the internal combustion engine until the time at which the operating time τm reaches or exceeds a first predetermined threshold value σ1, in the preferred embodiment of the method shown in FIG1 , no post-injection is performed in any cylinder. Accordingly, the number n of post-injection-enabled cylinders of the internal combustion engine is equal to zero. The efficiency of the internal combustion engine corresponds to the parameter a, the specific value of which in turn depends on the turbocharger state, in particular the number and/or type of active turbochargers.

After reaching or exceeding the first threshold value σ1, in the illustrated embodiment of the method, the number is increased to two, so that post-injections are performed in two cylinders of the internal combustion engine. These post-injections are preferably evenly distributed over the overall firing order of all cylinders. In particular, the cylinders in which the post-injections are performed are preferably changed at predetermined time intervals, i.e., a switching post-injection is performed.

The particle emissions drop suddenly due to the post-injection at time σ1, and then increase continuously, preferably substantially linearly, due to overall aging of the internal combustion engine. The course of the particle emissions when executing the method proposed here is illustrated in FIG. 1 by the dot-dash line 3 .

If post-injection is carried out in both cylinders, the internal combustion engine has an efficiency η2, the specific value of which in turn depends on the turbocharger state.

If the lifespan τm of the internal combustion engine reaches or exceeds the second threshold value σ2, in the illustrated exemplary embodiment, the number n of cylinders subject to post-injection is increased by one, so that n now amounts to three. Accordingly, at time σ2, particle emissions then decrease suddenly, with particle emissions subsequently increasing continuously, here essentially linearly, due to aging. If post-injection is performed in three cylinders, the internal combustion engine has an efficiency η3, the specific value of which then depends on the turbocharger state.

If the operating time τm of the internal combustion engine reaches or exceeds the third threshold value σ3, in the illustrated exemplary embodiment, the number n is increased by two cylinders, so that it now amounts to five. At time σ3, the particle emissions then drop suddenly, so that they subsequently increase continuously, in this case, substantially linearly, due to aging. An internal combustion engine with five cylinders that are post-injected has an efficiency η5, the specific value of which depends on the turbocharger state.

The method can be continued in this way, either until a predetermined, maximum operating time of the internal combustion engine is reached, or until post-injection is performed in all cylinders of the internal combustion engine. If this operating state is reached, it is of course no longer possible to further increase the number n to be equal to N of cylinders performing post-injection.

As is clear from FIG. 1 , the increment in the number n does not necessarily have to be the same when a predetermined threshold value is reached or exceeded. However, embodiments of the method are conceivable in which the increments are the same, or in which increments different from those shown here are selected. It is important to gradually increase the number of cylinders that are post-injected during the operating time of the internal combustion engine, thereby reducing particle emissions that increase with operating time τm, preferably so that as few injectors as possible are exposed to the post-injection load.

It is also important to change the cylinder responsible for post-injection after a predetermined time interval has elapsed, so that a post-injection switchover is achieved to a certain extent and the additional load on the injector due to the post-injection event is evenly distributed over the entire internal combustion engine.

In the method shown in FIG. 1 , the number n is increased solely based on the operating time, which can be measured in operating hours or as distance data. Alternatively or additionally, the number n can be determined based on the particle concentration in the exhaust gas, at least at preferably predetermined time intervals, particularly preferably by continuously measuring the value of this number. It is also possible to define a predetermined threshold value, and when the predetermined threshold value is reached or exceeded, the number n is increased by a predetermined increment or a value based on the particle concentration. Furthermore, it is possible to increase the number n based on the operating time of at least one motor component, preferably at least one injector, based on distance data, and/or based on the load distribution. In all embodiments, it is preferably provided that a predetermined threshold value is defined, and when the threshold value is reached or exceeded, the number n is increased.

FIG2 shows a graphical representation of the calculation of the temporary efficiency of an internal combustion engine as a function of a number n. First, the efficiency η[n=0] of the internal combustion engine for an operating state in which no cylinders are performing post-injection is calculated (depending on the turbocharger state). The value of this efficiency is preferably equal to or proportional to the value of parameter a, which serves as the basis for further calculations. Accordingly, a value for parameter b is determined that is equal to or proportional to the efficiency η[n=N] for an operating state in which post-injection is performed in all cylinders (of which N represents the total number of cylinders). Parameter b is also considered in the following calculations. For the temporarily existing operating state, a quotient K is calculated, which is obtained by dividing the number n of cylinders performing post-injection by the total number N of all cylinders of the internal combustion engine.

According to the formula a(1-K)+bK, the efficiency of the currently existing operating state with the number n of post-injection cylinders is thus calculated according to the formula (1) described above. Therefore, starting from this, there is a linear relationship between the efficiency ηn and the number n of post-injection cylinders.

It is also clear from the relationships described here that the efficiency ηn depends on the turbocharger state of the internal combustion engine. This is taken into account by selecting the values of the parameters a and b depending on the number and/or type of activated turbochargers.

Overall, it is possible to associate a performance map with each operating state of the internal combustion engine, which is based on the efficiency currently present in the internal combustion engine. In this way, the fuel quantity supplied to the cylinders per working cycle can be adjusted based on the current efficiency ηn so that changes in other operating parameters, such as injector start or injector pressure, are avoided at the same load point. This makes it possible to achieve consistently identical, predefined exhaust gas values at the same load point despite changes in the number n and/or changes in the turbocharger state of the internal combustion engine.

Overall, it has been shown that the method makes it possible to reduce the aging-related particle emissions of an internal combustion engine while largely avoiding injector wear. It is also possible to maintain the next-highest permissible particle emission value applicable in the future in the internal combustion engine without having to provide a particle filter or an additional, larger particle filter overall.

Claims (13)

1. A method for reducing particle emissions of an internal combustion engine over its service life, characterized in that the number of cylinders of the internal combustion engine that perform post-injection is gradually increased over the service life of the internal combustion engine. 2. The method according to claim 1 , characterized in that the number of cylinders with post-injection is gradually increased as a function of the operating time of the internal combustion engine itself, distance data, load distribution and/or particle concentration values in the exhaust gas, wherein the particle concentration values are measured at least in part of the time interval. 3 . The method according to claim 2 , wherein the particle concentration value is measured continuously at least during a portion of the time interval. 4 . The method according to claim 2 , wherein the number of cylinders that are post-injected is increased when a predetermined threshold value of the observed variable is reached or exceeded. 5 . The method according to claim 1 , wherein the cylinders performing the post-injection are selected in such a manner that they are evenly distributed in the overall firing order of all cylinders. 6 . The method according to claim 1 , wherein for a first cylinder that performs post-injection, post-injection is terminated after a predetermined time interval, while for a second cylinder that previously did not perform post-injection, post-injection is activated. 7 . The method of claim 6 , wherein a cylinder that directly follows or precedes the first cylinder in the firing order is selected as the second cylinder. 8 . The method according to claim 6 , wherein after a predetermined time interval, all cylinders performing post-injection are replaced by cylinders that did not previously perform post-injection, wherein the number of cylinders contributing to post-injection remains unchanged. 9. The method according to claim 1, wherein the current efficiency of the internal combustion engine is calculated as a function of the number of cylinders that are post-injected, wherein a characteristic map that depends on the currently existing efficiency is used for engine control. 10. The method according to claim 9, characterized in that the amount of fuel supplied to the cylinder in each working cycle is adjusted according to the current efficiency of the cylinder or all cylinders that play a role in post-injection, thereby avoiding changes in other operating parameters at the same load point. 11. The method according to claim 9 is characterized in that the current efficiency of the internal combustion engine is calculated according to the formula η=a(1-K)+bK, wherein η represents the current efficiency of the internal combustion engine, a represents the efficiency of the internal combustion engine under the condition that post-injection is not performed in any cylinder, b represents the efficiency of the internal combustion engine under the condition that post-injection is performed in all cylinders, and K represents the quotient of the number of cylinders that play a role in post-injection divided by the total number of cylinders of the internal combustion engine. 12. The method according to claim 11, characterized in that, depending on the number and/or type of activated turbochargers, different efficiencies are selected for the internal combustion engine without post-injection in any cylinder and for the internal combustion engine with post-injection in every cylinder. 13 . An engine controller for an internal combustion engine, characterized in that the engine controller is configured to carry out the method according to claim 1 .