FR2873756A1 - Catalyst temperature maintaining method for control device, involves making air supply throttling leader zone of engine in conversion zone, increasing exhaust gas reintroduction coefficient and/or shifting center of gravity of combustion - Google Patents

Abstract

The method involves activating a heating unit if a catalytic activity of a catalyst (34) is found in predefined sub-optimal conversion zones. An air supply throttling leader zone of an internal combustion engine (10) is made in a partial zone of the conversion zones. An exhaust gas reintroduction coefficient is increased and/or the center of gravity of the combustion is shifted in another partial zone. An independent claim is also included for a control device applied to an internal combustion engine.

Description

Field of the invention

  The present invention relates to a method for maintaining a catalyst temperature in the exhaust gas of an internal combustion engine according to which: - the catalytic activity of the catalyst is determined, - the catalytic activity is monitored in a predefined range of suboptimal conversion and a heating means is triggered if the catalytic activity is in the predefined range.

  The invention also relates to a control apparatus for implementing such a method.

  STATE OF THE ART There is known such a method and such a control apparatus according to DE 100 43 366 A1.

  For optimum conversion of the exhaust gases into the catalysts, the catalyst must be at a minimum temperature. For this reason, appropriate measures are taken after a cold start to achieve this minimum temperature as quickly as possible by increasing the temperature of the exhaust gas. The main heating means used now are the timing of the ignition angle in the direction of the delay, the raising of the idle engine speed and the use of a secondary air pump.

  The optimization of the combustion process in the case of internal combustion engines with direct injection leads to better engine efficiency and thus to a reduction in the temperature of the exhaust gas. This effect is accentuated by a mass flow of fresh air, important when the engine is in non-throttled mode (stratified mode) so that the catalyst temperature in stratified mode and for low doses injected (partial or low load range ) for which the motor is virtually unshrinked, fall below this minimum temperature.

  In existing internal combustion engines, the exhaust gas temperature even when the engine is operating in non-throttled mode, operates in extended operating ranges to maintain the catalyst temperature. These operating ranges decrease, however, as the combustion processes are optimized, in particular in guided jet processes, because this further optimization leads to a decrease in the temperature of the exhaust gases. At exhaust gas temperatures that are too low, switching between stratified mode and homogeneous mode is frequently effected; in the latter mode the motor runs in a strangled manner. The benefit of stratified mode consumption disappears in this case.

  As an alternative to the switching of the homogeneous mode, in the case of the non-choked laminate mode, catalyst heating means are used. This achieves exhaust gas temperatures sufficient for the catalyst to ensure the conversion of pollutants. In non-choked laminate mode, the heating means are more economical from the point of view of consumption than the homogeneous mode of operation.

  According to the document DE 100 43 366 A1 mentioned above, in the case of a direct injection internal combustion engine gasoline for several modes of operation, one chooses an optimal heating strategy for each mode of operation. As heating means this document provides a deterioration of the thermodynamic efficiency by changing the ignition angle, a post-injection after combustion in the combustion chamber of the internal combustion engine, the restriction of the amount of air sucked by the internal combustion engine and homogeneous mode switching of the laminate mode. The control apparatus presented in this document must also control other functions to achieve a more efficient combustion of the charge of the combustion chamber. As an example in this context it is envisaged a reintroduction of exhaust gas and ventilation of the tank without these means to maintain the catalyst temperature.

  However, the means for maintaining a catalyst temperature result in an increase in fuel consumption even in stratified mode.

  OBJECT OF THE INVENTION In this context, the object of the present invention is to develop a catalyst that can maintain its temperature with a lower fuel consumption.

  DISCLOSURE AND ADVANTAGE OF THE INVENTION For this purpose the invention relates to a method of the type defined above, characterized in that at least in a partial range of the predefined range is carried out a start of strangulation of the feed in air of the internal combustion engine, and in another partial range of the predefined range, in addition to the throttling primer increases the coefficient of reintroduction of exhaust gas and / or displaces the center of gravity of combustion .

  In the case of a control apparatus of the type defined above, this problem is solved in that this control apparatus implements the method defined generally above.

  The combustion plant or the center of gravity of combustion according to the usual definition of engine technology, is characterized by the point of the piston cycle in the combustion chamber for which 50% of the combustion chamber charge has been converted into energy.

  It has been found that even a throttling primer can already result in an increase in the temperature of the exhaust gas. This heating means or measure consumes very little additional fuel compared to other heating means. It has furthermore been found that an increase in the rate of re-introduction of the exhaust gas without throttling only resulted in a negligible heating effect, but in connection with a throttling primer this resulted in a significant increase in temperature. The same applies for a displacement of the center of gravity of combustion. Compared to other heating means or measures, both the increase in the rate of reintroduction of the exhaust gases and also the shift in the center of gravity of the combustion resulted in a smaller increase in combustion than the means recommended by DE 100 43 366 A1, so that the surprising effect of the combination of a throttling primer and an increase in the rate of reintroduction of the exhaust gas and / or an offset The center of gravity of the combustion system generally resulted in a reduction in fuel consumption when the heating means were used for the catalyst.

  It is advantageous to define as a simulation quantity of the activity of the catalyst, the actual temperature of the catalyst.

  The catalyst temperature is simply defined.

  Since the temperature of the catalyst is correlated with the activity of the catalyst, this development results in a relatively simple input quantity to be obtained for controlling the catalyst heating means. Alternatively, the catalyst activity can be determined for example by comparing the signals provided by an exhaust gas sensor installed upstream of the catalyst and another exhaust gas sensor installed downstream of the catalyst.

  It is also advantageous to use as a measure of catalyst activity a length of a catalyst partial zone defined in that in this zone the catalyst temperature exceeds a threshold.

  For the conversion of pollutants, the catalyst is the place of exothermic reaction that heats the catalyst. At low exhaust temperatures, for example, it may occur that warmer partial zones of the catalyst convert pollutants and are thus active while cooler zones are at a temperature already insufficient to ensure conversion. The overall efficiency of the conversion and thus the overall activity of the catalysts depends on the length of the active zone so that this length can also serve as a measure or magnitude of simulation or substitution of the catalyst activity.

  It is further advantageous to measure the temperature of the catalyst. Alternatively, it is particularly advantageous to determine the catalyst temperature from operating parameters of the internal combustion engine.

  This embodiment has the advantage of requiring no particular measurement sensor to capture the catalyst temperature which results in a corresponding saving.

  It is also advantageous to use the speed of the vehicle driven by the internal combustion engine as an operating parameter or a characteristic quantity of operation of the internal combustion engine.

  This embodiment makes it possible to take into account the cooling of the catalyst also by external air streams in the modeling of the temperature of the catalyst.

  Another preferential development is characterized in that the calorific demand of the catalyst is determined and compared with a threshold.

  The amount of heat released is different for the different heating means. Thus, this development makes it possible to choose appropriate heating means according to the calorific demand of the catalyst.

  It is also advantageous that if the heat demand is greater than the threshold, postinjection is triggered in at least one combustion chamber of the internal combustion engine.

  Post-injections release a particularly large amount of heat. This is why we can provide a significant heat flow in the operating ranges in which a throttling primer more advantageous from the point of view of consumption is no longer sufficient to meet the demand. Postinjections have the advantage of being in the stratified mode which remains advantageous from the point of view of consumption.

  In the case of an internal combustion engine operating with direct fuel injection, if the activity of the catalyst is in stratified mode below the predefined range, it is advantageous to then switch to homogeneous mode.

  In homogeneous mode, particularly important heat flows are released.

  Another preferred development provides that, in addition to the throttling, at least one of the following measures is taken: anticipated opening of the exhaust valves of the internal combustion engine; raising the temperature of the cooling water; raising the temperature of the supplied air; increase of exhaust gas counterpressure; raising the engine load by activating a generator and opening an exhaust door or a turbocharger bypass.

  All these measures have the advantage of increasing the heat flow supplying the catalyst in a manner that is economical from the point of view of consumption.

  In order to provide the control apparatus, it is advantageous for the control unit to control the operation of at least one of the above-mentioned characteristics of the process.

  Drawings The present invention will be described in more detail below with the aid of exemplary embodiments shown in the accompanying drawings, in which: FIG. 1 shows the technical environment of the invention, FIG. structures of a signal processing in a control apparatus which executes the process of a process according to the invention; - Figure 3 shows the different partial ranges in a plane subtended by the activity of the catalyst KA and the demand. Figure 4 shows a flowchart as an embodiment of a method according to the invention.

  FIG. 5 shows the relationship between the temperature of the catalyst and the pressure in the intake duct; FIG. 6 shows the relationship between the catalyst temperature and the rate of reintroduction of the exhaust gases; FIG. the relationship between the catalyst temperature and the position of the combustion.

  DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION FIG. 1 shows an internal combustion engine 10 having at least one combustion chamber 12 closed by a mobile piston 14. The combustion chamber 12 is charged with air by a combustion system. The burnt load of the combustion chamber is exhausted by an exhaust system 18. The exchange of the charge of the combustion chamber is controlled by an intake valve 20 and an exhaust valve 22 actuated by an intake valve actuator 24 and an exhaust valve actuator 26. An injector 28 doses an appropriate amount of fuel into the air charge of the combustion chamber 12.

  The resulting fuel / air mixture in the combustion chamber 12 is ignited by an ignition device 30 if the internal combustion engine 10 is a gasoline engine.

  However, the invention is not limited to gasoline engines and can also be applied to diesel engines. In this case there is no ignition device 30. The throttle flap 32 of the intake system 16 strangles the air stream supplying the combustion chamber 12. throttle flap 32 can also be used variable valve control by changing the opening curve of the inlet valve 20 to achieve a throttling effect.

  The exhaust gas that arrives in the exhaust system 18 when the exhaust valve 22 is open is cleaned in a catalyst 34. The kinetic energy of the exhaust gas can be used to drive the turbine 36. a possible exhaust gas turbocharger 38, the compressor 40 of which is installed in the intake system 16 and delivers the air towards the combustion chambers 12. A bypass 42 makes it possible to bypass the turbine 36 of the gas turbocharger. 38 and in this case the bypass 42 may comprise a controlled valve 44. A valve for reintroduction of the exhaust gas 46 allows to take the exhaust gas exhaust system 18 to reintroduce into the intake system 16. An exhaust gas flap 48 provided as an option allows the dynamic pressure in the exhaust system 18 to be changed.

  The combustion of the charge of the combustion chamber 12 releases heat collected in part in the cooling system 50 and discharged to the environment by a heat exchanger (radiator) 52. The control of the power of a cooling is optionally provided by a valve or valve in the connection between the internal combustion engine 10 and the heat exchanger 52. The internal combustion engine 10 drives for example a generator 58 via a V-belt 56. When the switch 60 is closed, the generator charges a battery 62. The internal combustion engine 10 is controlled by a control device 64. For this the control unit 64 receives the signals from the sensors concerning the operating parameters of the engine to internal combustion 10 and / or the exhaust system 18.

  As an example of such sensors, FIG. 1 shows an air mass flowmeter 66, an aspirated air temperature sensor 68, a cooling water temperature sensor 70, a tachometer 72, a gas temperature sensor. exhaust 74, a displacement speed sensor 76, a driver demand sensor 78 and exhaust gas sensors 80, 82 respectively installed upstream and downstream of the catalyst 34. In addition, the control apparatus 64 can detect the state of charge of the battery 62 via a link 84.

  From the signals supplied by the sensors indicated above, the control device 64 generates adjustment variables for controlling the actuating members shown in FIG. 1. These actuating members comprise, if appropriate, the actuator of FIG. intake valve 24, the exhaust valve actuator 26, the injector 28, the igniter 30, a throttle valve actuator 84 controlling the angular position of the throttle valve 32 installed in the intake system 16, the controlled valve 44 of the bypass 42, the exhaust reintroduction valve 46, the controlled valve or valve 54 of the cooling system 50, the switch 60 controlling the charge of the battery 62 by the generator 58 and an exhaust flap actuator 86 controlling the angular position of the exhaust flap 48.

  Figure 1 thus gives an overview of the technical environment of the invention. It should be noted that to achieve the invention, it is not necessary to have all the sensors and actuators described above. It is particularly important for the realization of the invention to have sensors which allow the air supplied to the combustion chambers 12 of the internal combustion engine 10 to be throttled and actuators which make it possible to influence the quantity of gas. reintroduced exhaust or also the position of the operating point. The quantity of exhaust gas reintroduced is regulated in the context of an external reintroduction of the exhaust gases by the exhaust gas return valve 46; it can also be done by an internal reintroduction of the exhaust gases by simultaneously opening the intake valve 20 and the exhaust valve 22. The throttling is done by the throttle flap 32 and / or influencing the curve opening of the intake valve 20.

  FIG. 2 shows extracts of a program structure of the control device 64. The control program of the control device 64 comprises in particular a block 88 which coordinates the various heating means or measurements for To this end, the block 88 is provided as an essential influence quantity, a measure of the activity of the catalyst 34. Since the activity of the catalyst 34 is strongly dependent on the temperature, it is possible to use for this purpose the signal provided by the exhaust gas temperature sensor 74.

  Alternatively or in addition, the activity of the catalyst 34 can also be determined by a catalyst model 90 using the operating parameters of the internal combustion engine 10 and / or the exhaust system 18. In the case of such a model of catalyst, the speed of rotation (speed) of the internal combustion engine 10 provided by the rotational speed sensor 72, the mass flow rate of air supplied by the mass air flow meter 66, the ambient temperature captured by the intake temperature sensor 68, the temperature of the cooling water of the internal combustion engine 10, supplied by the cooling water temperature sensor 70, the vehicle speed delivered by the sensor of the displacement velocity 76 and the signals provided by the exhaust gas sensors 80, 82. The above list is not limiting and a temperature modeling can be based on a larger number or less important operating parameters to the required accuracy.

  Finally, the block 90 forms the temperature of the catalyst from the quantities in memory relative to the heat capacity of the catalyst 34 and the heat flux in the catalyst 34 defined by the amount of heat released in the combustion chambers 12 and the influence of the cooling this is deduced from the signal of the sensor of the suction air temperature 68 and the displacement speed sensor 76.

  Block 88 forms the control variables for triggering the heating means from the activity of the catalyst KA transmitted by the block 90 or the temperature sensor 74 and from the signals of other operating parameters provided by the sensors 72. , 66, 68, 70, 78, 62 and 76. These control variables control the actuating members 32, 46, 24, 26, 60, 28 and 30. It should be noted that for the block 88, the list of input signals of the actuating members is not limiting and it can optionally handle a larger or smaller number of operating parameters.

  Similarly, the embodiment of the invention also does not mean the processing of all the input signals presented and the control of all the actuating members shown.

  Figure 3 shows the function of block 88 by indicating different ranges in a plane subtended by the values of KA catalyst activity and the heat flow demand Q required to have some catalyst activity. The heat flow demand Q depends for example on the mass flow of exhaust gas; the high flow of exhaust gas results in a lower residence time of the exhaust gas in the catalyst and thus requires a higher catalyst activity; for low catalyst activity, a large heat flux is required to allow sufficient conversion of pollutants. The same applies for a high speed of exhaust gas, a speed which is defined in known manner by the standard mass flow of the exhaust gas flowing through a volume of catalyst. The KA activity of the catalyst depends, for example, very significantly on the temperature of the catalyst. To select suitable heating means or measures, the plane subtended by the Q and KA values comprises at least one predefined zone 92, 94 in which the air supply of the internal combustion engine 10 is throttled to increase the activity. KA of the catalyst. The S3 threshold on the KA axis separates a range 100 with sufficient catalyst activity from a range 92 in which the activity of the catalyst is slightly reduced.

  If the activity of the catalyst is within the predefined range 92, the throttling of the air supply of the internal combustion engine 10 is taken as the means for heating or maintaining the temperature of the catalyst 10. If the activity the catalyst is even lower and is in the partial range 94 among the predefined ranges 92, 94, then in addition to the beginning of throttling the rate of reintroduction of the exhaust gases and / or the center of gravity is increased of combustion. The range 94 is characterized by values of the activity of the catalyst between the thresholds S1 and S2 and at the same time by a relatively low demand for heat fluxes. If the KA activity of the catalyst is between the values S1 and S2 and if at the same time there is a high heat demand, greater than a threshold SQ, it is necessary either in alternative or in complement of the means used in the beach 94 also a post-injection in laminate mode. In the Q-KA plane of FIG. 3, this range is characterized by the reference 96. When the activity of the catalyst is greatly reduced and is below the threshold S1, the laminate mode is switched to the homogeneous mode. This range corresponds in the plane Q-KA of Figure 3 to the range bearing the reference 98.

  FIG. 4 gives an exemplary embodiment of a program part of the motor control by which the block 88 selects the different measurements in the different ranges 92, 94, 96, 98. For this, in step 102 that the The catalyst KA activity is firstly defined by a control program of the internal combustion engine 10, and then the KA activity is compared in step 104. S1 threshold catalyst. In the following, it is first assumed that the KA activity of the catalyst is greater than the threshold S3. In this case, the response of step 104 is negative and proceed to step 106. In this one compares the KA activity of the catalyst at threshold S2. The condition is that the activity KA is greater than S3 and thus greater than S2 so that the interrogation of step 106 receives a negative response. Step 106 is followed by step 108 in which the KA activity of the catalyst at threshold S3 is compared. Since the activity KA must be greater than the threshold S3, the interrogation asking whether the activity KA is below the threshold S3 receives a negative response and the block 88 finds that the activity of the catalyst is in the range 100.degree. Figure 3 in which there is no need to take measures to maintain the temperature of the catalyst 34. Therefore, starting from step 108 we go to step 110 which comes back to the subordinate control program of the engine without triggering a heating measurement.

  If, on the other hand, the activity of the catalyst 34 is slightly reduced and the threshold S 2 is no longer exceeded, the interrogation in step 108 proceeds to step 112; in this one initiates a start of throttling of the air supply of the internal combustion engine 10.

  If the KA activity of the catalyst is even smaller and the S2 threshold is no longer exceeded, the program goes from step 106 to step 114. In this, the demand for heat flux Q is defined. to achieve a certain activity of the catalyst. In step 116, the heat flow demand thus defined is compared with a threshold SQ. If the heat flow demand is below the threshold SQ which corresponds to the range 94 of FIG. 3, step 118 is carried out; in this one triggers the beginning of throttling of the air supply. In addition, in step 120 the rate of reintroduction of the exhaust gases is increased or the center of gravity of the combustion is displaced. Alternatively or additionally, in step 120 it is also possible to increase the temperature of the engine by controlling the closing of the control valve 54, by increasing the backpressure of the exhaust gases by the control of the shutter closure. the throttle 48, by increasing the throttle by the opening of the control valve 44 in the branch 42 of the turbine 36 of the exhaust gas turbocharger to trigger an anticipated opening of the exhaust valve 22.

  Alternatively or in addition to the opening of the exhaust gas return valve 46 can also control the inlet valve 20 and the exhaust valve 22 of the combustion chambers 12 of the internal combustion engine 10 to increase the interval during which both valves are simultaneously open. This increases the internal reintroduction of the exhaust gases.

  If, on the other hand, in step 116 it is found that the thermal flow demand exceeds the threshold SQ which characterizes the range 96 of FIG. 3, then step 116 is moved to step 122 in which the trip is triggered. the post-injections in the combustion chambers 12 of the internal combustion engine 10 with an excess of air, that is to say preferentially in stratified mode. This means makes it possible to generate a particularly important heat flow for the catalyst 34. If the activity of the catalyst 34 is very greatly reduced and if one goes below the threshold S1 according to FIG. 3, this corresponds to the step 104 of FIG. FIG. 4 is a flowchart. In this case, it goes from step 104 to step 124 in which the laminate mode is switched, if appropriate, to the homogeneous mode of the internal combustion engine 10. The coordination block 88 thus selects according to the demands of

  temperature and heat flow, the necessary heating means and implements them. The homogeneous mode which is the least advantageous from the point of view of consumption will be selected only if the activity of the catalyst is very greatly reduced. In the other ranges, the mass flow of air can be throttled and, if necessary, other measures can be taken to heat the catalyst 34 advantageously in terms of consumption.

  The increase in throttling losses, that is to say the reduction of the pressure in the inlet pipe downstream of the throttle flap 32 as well as the corresponding reduction in the mass flow of fresh air to the chambers of combustion 12 of the internal combustion engine 10, results in a reduction in the mass flow of the exhaust gas and an increase in the temperature of the exhaust gas. This is shown in FIG. 5 which shows an increase in the temperature of the exhaust gas as a function of the decrease in the pressure p_s of the intake pipe.

  Figure 6 shows the effect on the temperature of the exhaust gases, the replacement of fresh air by the reintroduction of exhaust gas. the curve 126 corresponds to a high pressure in the intake duct and the curve 128 to a reduced pressure in the intake duct, that is to say for a beginning of throttling. Comparison of the curves 126 and 128 shows that the only increase in the rate of reintroduction of the exhaust gases, that is to say without the throttling start as for the curve 126, is practically useless as a means. of heating. On the other hand, at reduced pressure in the intake pipe, there is an increase in the temperature D of the exhaust gases as the rate of reintroduction of the exhaust gas increases as shown by the plot of the curve 128.

  Figure 7 gives similar plots for a shift of the combustion position VL for different pressures in the intake duct. Curve 130 represents the temperature of the exhaust gas with a very flat pattern in the case of a shift of the combustion position. This curve 130 corresponds to operation with a high pressure in the intake duct, that is to say without additional throttling. On the other hand, in the event of a shift of the combustion position combined with a reduction of the pressure in the intake duct as shown in FIG. 132, the temperature is increased as a function of the offset of the combustion position. .

  Figures 6 and 7 demonstrate that precisely the combination of a throttling primer and an increase in the coefficient of reintroduction of the exhaust gas or a shift of the combustion position is an effective way to maintain the Catalyst temperature 34. In other words, in case of operation without any throttling for the internal combustion engine 10 that is to say for high pressures in the intake pipe, these measures as sole heating means are not enough given the high mass flow, dominating fresh air. In combination with a throttling, however, such measures are advantageous in terms of combustion and very effective. Thanks to an anticipated opening, if necessary alternatively or in a complementary manner to the inlet valve 22, the reduced energy exchange with the piston 14 causes the residual heat energy to be higher and can be used for heating. catalyst 34.

  The technical teaching presented herein provides a means for determining the activity of the catalyst in the control apparatus 64.

  This means can be based on a measured or modeled temperature of the catalyst 34. By way of example, a temperature in the catalyst 34 can be compared to a threshold. Alternatively one can take into account that part of the catalyst length above which is a temperature threshold. The coordination block 88 determines, depending on the activity of the catalyst, whether heating measurements are necessary and the means to be taken if necessary. For a simply reduced activity, a throttling primer is chosen and for very low activity it is possible to switch to homogeneous mode. For the rest, the coordination block 88 chooses a throttling primer combined with an offset in the direction of the retardation of combustion and / or an anticipated opening of the intake valves and / or an increase in the temperature of the water cooling and / or an increase in the temperature of the air supplied and / or an increase in the exhaust gas back pressure and / or an increase in the engine load by activating a generator 58 and / or opening an exhaust door or a bypass 42 of the turbocharger.

Claims (12)

  1) Process for maintaining a catalyst (34) in temperature in the exhaust gas of an internal combustion engine (10) in which: the catalytic activity of the catalyst (34) is determined; catalytic activity is within a predefined range (92, 94) of suboptimal conversion and a heating means is initiated if the catalytic activity is in the predefined range (92, 94), characterized in that at least a partial range (92) of the predefined range (92, 94) is made a throttling start of the air supply of the internal combustion engine (10), and in another partial range (94) of the predefined range (92, 94), in addition to the throttling primer, the exhaust gas recoil coefficient is increased and / or the center of gravity of the combustion is displaced.   2) Process according to claim 1, characterized in that the substitution temperature of the catalytic activity is the temperature of the catalyst.   3) Process according to claim 1, characterized in that as a measure of the activity of the catalyst takes a length of a partial region of the catalyst (34) in which the temperature of the catalyst exceeds a threshold.   4) Process according to claim 1, characterized in that one measures the temperature of the catalyst.   5) Process according to claim 1, characterized in that the temperature of the catalyst is determined from operating parameters of the internal combustion engine (10).   6) Process according to claim 5, characterized in that the speed of the vehicle driven by the internal combustion engine (10) is taken as operating parameter of the internal combustion engine (10).   7) Process according to claim 1, characterized in that one determines the heat flow demand of the catalyst (34) and this demand is compared to a threshold.   8) A method according to claim 7, characterized in that the calorific flow demand is determined as a function of the space velocity of the exhaust gas.   9) A method according to claim 7, characterized in that if the heat flow demand exceeds the threshold, is triggered post-injections in at least one combustion chamber (12) of the internal combustion engine (10).   10) Process according to claim 1, characterized in that if for an internal combustion engine (10) with direct fuel injection operating in stratified mode the catalyst activity is less than a predefined range, it is switched to the homogeneous mode.   11) A method according to claim 1, characterized in that in addition to the throttling primer at least one of the following measures is taken: - anticipated opening of the exhaust valves, increase of the temperature of the water cooling, - increasing the temperature of the supplied air, - increasing the exhaust gas counterpressure, - increasing the engine load by activating a generator (58), - opening an exhaust door or a turbo-compressor bypass (42).   12) Control apparatus (64) applied to an internal combustion engine (10), characterized in that it controls the unwinding of at least one of the processes according to any one of claims 1 to 10 io