FR2825412A1 - Process for desulfurizing a nitrogen oxide storage catalyst in a diesel engine comprises heating the catalyst above a determined lowest desulfurization temperature, and operating the engine in a lean-rich alternating method - Google Patents

Abstract

Process for desulfurizing a nitrogen oxide storage catalyst arranged with a particle filter in the exhaust gas purification device of a diesel engine comprises heating the catalyst above a determined lowest desulfurization temperature; and operating the engine in a lean-rich alternating method. The heating is carried out up to a time when the sulfur charge of the catalyst has exceeded a lowest value and regeneration of the filter has started. The engine is operated in a lean-rich alternating method when prescribed desulfurizing releasing conditions determined by the engine are fulfilled. Preferred Features: The lean-rich alternating method is produced using alternating lean and rich phases for 3-20 seconds. Heating of the catalyst is carried out using a lean engine operation and with a subsequent post-injection of fuel into the combustion chamber of the engine following the main injection of fuel. After desulfurization, the particle filter is regenerated when the particle charge has exceeded a predetermined threshold value.

Description

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 The invention relates to a process for the desulphating of a nitric oxide storage catalyst disposed in the exhaust gas purification system of an internal combustion engine, in particular in a diesel engine used in automobiles, by heating the nitric oxide storage catalyst at a temperature above a predetermined minimum desulfation temperature and subsequently performing a lean-fat alternating regime on the internal combustion engine.

 Publication DE 198 50 757 A1 describes a process for the desulphating of a nitric oxide storage catalyst, in which the temperature necessary to carry out the desulfating operation is generated at least partially by the regeneration of a filter. particles disposed upstream of the nitric oxide storage catalyst, in the exhaust system.

 Exhaust gas cleaning systems incorporating nitric oxide storage catalysts are used in various ways to remove the nitric oxides contained in the exhaust gases of internal combustion engines, operated primarily in a lean regime. For this purpose, in the lean regime of the internal combustion engine, the barium carbonate, contained for example in the accumulation component of the catalyst material extracted from nitric oxide (NOx) exhaust gases which are then oxidizing, by forming barium nitrate in solid form. Due to the depletion of material related to this operation, a regeneration of the NOx storage catalyst is required from time to time. The so-called nitrate regeneration is carried out in that the internal combustion engine is operated in a fat regime over a period of time. For this purpose, the unstable barium nitrate contained in the resulting exhaust gas containing reduction products decomposes to form barium carbonate again and release NOx. On the precious metal component applied to the accumulator catalyst

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 of NOx, the latter is then reduced mainly to non-harmful nitrogen (N2) by the reduction products then contained in the exhaust gases (H2, CO and HC).

 If a sulfurous fuel is used, the exhaust gases contain sulfur oxides which are collected by the accumulation component, with formation of stable sulfates, resulting in a continuous pollution of the nitric oxide storage catalyst. A regeneration procedure referred to as desulfation regenerates a nitric oxide storage catalyst of this type. Most of the time, the desulfation is caused when the sulfur load has exceeded a maximum value which is no longer tolerable to ensure the efficiency of the nitric oxide storage catalyst. However, as a general rule, the desulphating requires a heating of the nitric oxide storage catalyst or of the exhaust gases, to a value greater than a minimum desulfation temperature of 550 ° C. for example and a setting at least temporary to obtain a overall reducing composition of the exhaust gas. The heating and adjustment to obtain a reducing composition of the exhaust gas supposes an overconsumption of fuel which must be maintained at a minimum value.

 Especially on diesel engines, in addition to the elimination of nitric oxides, the elimination of the particles contained in the exhaust gas is also significant. For this purpose, there are different ways of particulate filters in the exhaust gas purification system. These particulate filters need to be regenerated from time to time, to release them from the particles that are deposited there in the usual manner in the form of soot particles. To regenerate the particulate filters, it is also necessary to bring the exhaust gas or the particle filter to a high temperature, for example exceeding 450 ° C. If the exhaust gases are oxidizing, the soot deposits are then consumed. , which allows to regenerate the particle filter.

 If the exhaust gas cleaning system of the corresponding internal combustion engine contains both a catalytic converter

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 a nitric oxide accumulator and a particulate filter, the fuel consumption during the regeneration of the constituent elements mentioned can be reduced for example in that the temperature required to carry out the desulfation of the nitric oxide storage catalyst is generated at less partially by the regeneration of the particulate filter. It should however be noted that, on the one hand, the corresponding regeneration operations, in particular desulphating, can not be carried out as problematically in all the operating regimes of the respective internal combustion engine and that, on the other hand, they should not be done more often than necessary. In addition, the overconsumption of fuel generated by regeneration should be kept as low as possible.

 The object of the invention is to indicate a process for improving the regeneration operations of nitric oxide storage catalysts or particulate filters and in particular the desulfation of the nitric oxide storage catalyst.

 This object is achieved according to the invention by a process of the aforementioned type in which the heating takes place at the latest at times when the sulfur load of the nitric oxide storage catalyst has exceeded a minimum value Smin and where a regeneration of the Particle filter has been started and a lean-fat alternating regime of the internal combustion engine is realized, when predefined conditions for validation of the desulfation, determined by the speed of the internal combustion engine are met.

 The process according to the invention is based on the observation that the desulphating of a conventional nitric oxide storage catalyst requires to bring it to a high minimum desulfation temperature of approximately 550 ° C. and to make a subsequent adjustment of the exhaust gases, so that they have at least a temporarily reducing effect. A lean-fat alternating diet has been found to be particularly advantageous for carrying out an effective desulfurization operation. This term refers to a repeatedly repetitive passage of an oxidizing composition to a reducing composition of the exhaust gas. For this purpose, targeted heating of the catalyst and

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 transition from the lean regime to the fat diet are generated by the electronic control device of the engine, preferably by a corresponding modification of the fuel injection conditions. Other additional support measures, such as a throttling of the internal combustion engine are also possible to cause the rise in temperature.

 According to the invention, the heating of the nitric oxide storage catalyst for desulfating purposes does not take place only when the sulfur load has reached a maximum value which is no longer tolerable to guarantee the efficiency of the catalyst, but advantageously, also and as soon as the sulfurous charge of the nitric oxide storage catalyst has exceeded a certain minimum value S min and a regeneration of the particle filters has been started simultaneously. The sulfur charge is determined by the engine control device, for example from the accumulated fuel consumption or the path traveled by the vehicle, correlated with the sulfur content in the fuel. Moreover, methods which are based on the reduction of the efficiency of the accumulator catalyst due to sulfur pollution are also conceivable.

 The need for regeneration of the particulate filter is also typically determined by the engine controller, by evaluation of corresponding signals, such as a high differential pressure, found above the particulate filter. However, the evaluation of the path taken by the vehicle can also be used as a criterion for determining the need for regeneration of the particulate filter.

 Since the regeneration operation of the particulate filter also requires higher temperatures in the exhaust gas or in the particulate filter, the heating process carried out for the regeneration of the particulate filter can advantageously be optimally used. for subsequent desulphating of the nitric oxide storage catalyst.

 In particular on diesel engines, the adjustment of the fat regime or the adjustment of the reducing exhaust gases is linked to

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 particular problems with the combustion technique. Moreover, the driving comfort or the silence of operation of the vehicle can suffer undesirably, especially during a transition from lean diet to fat. Therefore, according to the invention, after corresponding heating, the adjustment of the lean-fat alternating regime finally causing the desulphating takes place once the prescribed conditions for validation of desulphating, which are defined by the exploitation of the internal combustion engine are fulfilled.

These validation conditions may be related for example to the presence of a certain operating speed or a certain load range of the internal combustion engine. If they are recognized by the engine control device as being satisfied, the lean-fat alternate diet will be realized. This advantageously makes it possible to use the heating operation economically and also to perform the generally difficult operation of desulfating the nitric oxide storage catalyst at a more favorable moment for this purpose. The desulfation operation is generally improved, and particularly with regard to the operation of the internal combustion engine.

 The measures mentioned below offer possibilities for improvement and improvement of the process according to the invention indicated above.

 In the improved method according to a first arrangement, the conditions of validation of the desulfation or lean-fat alternating operation operation include the condition of a temporary constant mechanical power restored by the internal combustion engine. The respect of this condition makes it possible to safely avoid undesirably impairing driving comfort during desulfating. For this purpose, the temporary constancy of the mechanical power restored by the internal combustion engine can be determined for example by the detection of the movements of the accelerator. In addition, the desulfation validation conditions may be related to other values influencing the operation of the internal combustion engine during driving, such as the

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 presence of a temporarily constant vehicle driving speed or the presence of a certain engine load range.

 In the improved method according to a second arrangement, the lean-fat alternating regime of the internal combustion engine is achieved by lean phases and consecutive and alternating fatty phases, the lean phases and the fatty phases respectively extending over a period of time between 3 seconds and 20 seconds. In the fatty phases, the lubrication is preferably performed at a lambda value, ie an air-fuel ratio in a range of 0.7 to 0.99. To reduce the release of hydrogen from sulfur, it is advantageous to modify this lambda value during the fatty phases. Preferably, the fatty phase must begin with a very large lubrication, that is to say a lambda value of about 0.7 and this lubrication must be restricted continuously or in stages until a lambda value of 0.99 about. During desulphating, the sulfur load of the nitric oxide storage catalyst decreases and therefore the amount of volatile sulfur compounds released also decreases. This can advantageously be exploited by the fact that, in the fatty phases, the curve of the lambda values changes during desulfation. A variable duration of the fatty phases, which preferably decreases during desulfation or a variable ratio of the duration of the fatty phases relative to the duration of the lean phases are particularly advantageous. It has been found that, on the one hand, and on the basis of the sulfur charge, on the one hand a particularly effective desulphation is obtained and on the other hand the release of hydrogen from sulfur as an undesirable product of the operation. desulphating can be avoided.

 According to a third provision, the heating of the nitric oxide storage catalyst, that is to say the heating of the exhaust gas to the temperature necessary for the regeneration of the particulate filter or, if appropriate, at a higher temperature , is achieved by operating the internal combustion engine at lean regime and by post-fuel injection following the main injection of fuel into the combustion chamber of the internal combustion engine. The post-injection allows to obtain that the exhaust

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 contain a residual content of unburned fuel. If one is in parallel in the presence of an excess of oxygen, one attends in these conditions of exhaust gas remaining overall lean, with a heating by exothermic oxidation of the exhaust gases and constitutive elements crossed by the gases of d 'exhaust. By adjusting the motor controller with the amount of fuel injected, it is possible to control the amount and speed of the rise in temperature. The rise in temperature generated by an exothermic oxidation of unburned fuel in the nitric oxide storage catalyst can be further promoted by adjusting the injection conditions for a relatively late combustion situation, which already generates a heating of the gases. exhaust on the engine side. By a corresponding control of the post-injection, it is also possible to create exhaust gases having overall reducing conditions, which are necessary for the realization of the fatty phases, during the desulfation operation.

The creation of high temperature reducing exhaust gas for unchanged torque and a favorable combustion curve can be particularly generated by multi-stage injection or multi-stage combustion. For this purpose, the injection is distributed for example in a pre-injection, a main injection and a post-injection. In this way, it is possible to achieve both a heating of the aftertreatment components of the exhaust gas disposed in the exhaust circuit and a lean-fat alternating regime.

 According to a fourth provision, when carrying out the desulfation operation by adjusting the lean-fat alternating regime, the charge of the nitric oxide storage catalyst is counted at least during the fatty phases. This phenomenon is preferably achieved in the electronic control device of the internal combustion engine, which also drives the lambda value of the fat regime. This makes it easy to use the amount of oxidizing product made available in the exhaust gas during the fat phases to calculate the amount of sulphate of sulphate converted reductively. According to this

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 fourth provision, the desulfation terminates when through desulphating, the sulfur load falls below a predefined minimum value or if the validation conditions of the desulfating operation are no longer given. The first phenomenon is typically reached after about ten lean-fat changes, the last phenomenon may be caused by the fact that the mechanical power restored by the internal combustion engine changes according to the power demanded by the driver.

 According to a fifth provision, the presence of a sufficiently good degree of desulfation can also be ascertained by determination and comparison of the lambda values of the exhaust gas on the inlet side and the outlet side of the nitric oxide storage catalyst. Usually, the lambda value here designates the air-fuel ratio, with which the internal combustion engine should be operated to provide exhaust gases having corresponding fractions of reducing components and oxidizing components. As in the case of desulphating, the chemical reduction of sulphate of sulphate generates a consumption of the reduction product present in the exhaust gas, at least at the beginning of desulfation, the content of reduction product in the exhaust gas is higher than the inlet side of the nitric oxide storage catalyst than the outlet side of the nitric oxide storage catalyst. As a result, the lambda values in the inlet and outlet side exhaust gases of the nitric oxide storage catalyst typically compensate for during desulfation. According to this fifth provision, the desulphating operation is terminated because the desulphation validation conditions are no longer given or if the fuzz ratio of the lambda values of the exhaust gases AI and "A2 measured on the inlet side and on the outlet side of the accumulator catalyst. nitric oxide has reached a predefined value between 0.8 and 1.25.

 A particularly advantageous improvement of the process according to the invention results from a sixth arrangement according to which, at the end of the desulfation operation, the regeneration of the particulate filter is carried out when the particulate load of the particulate filter has exceeded a

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 certain predefined threshold value. These measurements make it possible advantageously to exploit the high temperature still present at the end of the desulphating operation.

 The invention is explained in the following description, with the aid of the drawing and on the basis of a concrete embodiment.

The figures show:
Figure 1: a schematic block diagram of an internal combustion engine, with a corresponding exhaust gas purification system,
FIG. 2: a functional diagram for carrying out by way of example the process according to the invention,
Figure 3: another functional diagram for the flow as an example of the method according to the invention.

 Figure 1 is a schematic representation of an internal combustion engine with a corresponding exhaust gas purification system and a corresponding engine control device. For this purpose, non-determining constitutive elements for the invention, such as the exhaust gas turbocharger, the fuel supply, the injection valves and the like are not shown in the figure, to give a better view overall.

 According to Figure 1, the exhaust gas of an internal combustion engine which is designed as a diesel engine are fed into an exhaust pipe 2 in which are preferably arranged near the engine and short distance one behind the other a nitric oxide storage catalyst 3 and a particulate filter 4 which are traversed by the exhaust gas. With the aid of temperature sensors 9 and 10, the temperature of the exhaust gas can be measured at the inlet of the nitric oxide storage catalyst 3 and at the inlet of the particulate filter 4. Lambda sensors 5 and 6 are used to measure the lambda value of the exhaust gas at the inlet and the outlet of the nitric oxide storage catalyst 3. At the inlet and outlet side of the particulate filter 4, pressure sensors 7 and 8 are accommodated by elsewhere in the exhaust duct and are used to measure pressure drops above the particulate filter. Through

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 signal lines 11, the sensors 5,6, 7,8, 9,10 are connected to the electronic control device of the motor 12 which evaluates the corresponding signals. Furthermore, the motor control device 12 is preferably connected to the diesel engine 1, via a signal line 13 which is preferably designed for bidirectional data transfer. This data line makes it possible, on the one hand, to transmit to the engine control device 12 information that characterizes the engine speed, such as, for example, the engine speed. information includes engine load, engine rotation speed, driving speed, throttle position and throttle movements. On the other hand, the motor control device 12 transmits to the motor or to the control members inherent to the motor signals that influence the speed of the motor. In particular, these are signals that influence fuel injection, fresh air supply, or exhaust rate. The control device of the motor 12 also contains a computer which is not the object of a detailed representation, intended to process the signals received or to determine the signals to be transmitted. A memory which is not integrated in the drawing and which is located in the control device of the motor 12 serves to receive identification fields. Thanks to the possibilities mentioned, the state of the nitric oxide storage catalyst 3, the state of the particulate filter and the temperature, as well as the fuel-air ratio in the exhaust gases can be continuously recorded or determined and it is possible to react, if necessary, with appropriate actions for the regeneration of the particulate filter 4 and the nitric oxide storage catalyst 3, depending on the driving conditions. For a further improvement of the recording of the state of all the constituent elements and of the exhaust gases, it is of course possible to provide additional or alternative sensors, for example sensors for measuring the concentration of nitric oxide or the CO concentration in the exhaust gas.

 To explain the progress of the method according to the invention, reference is first made to the functional diagram reproduced in FIG.

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 The functional diagram designated by A describes an interrogation loop in the control device 12 which is continuously traversed in the event of normal operation of the diesel engine 1 or the automobile. The term normal speed means here that the engine 1 is not operated in the low partial load regime range, as the case occurs for example at idle speed or a low driving speed. In the interrogation loop A, a continuous interrogation is carried out to determine whether the sulfur content S of the nitric oxide storage catalyst 3 has exceeded a predefined maximum value C max or if the charge C of the particulate filter 4 has exceeded a value maximum also predefinable. For this purpose, the value of the sulfur content of the nitric oxide storage catalyst 3 is determined by the engine control device 12, for example by means of a model based on fuel consumption or on the basis of a noted deterioration of the capacity of the nitric oxide storage catalyst 3 to accumulate nitric oxide. For this purpose, the curve of the signals restored in the lambda sensors 5 and 6 during the nitrate regeneration can be particularly evaluated.

 For the definition of the particulate filter load, the motor controller 12 preferably evaluates the information provided by the pressure sensors 7 and 8 and the pressure drop above the particle filter 4 and the load of the filter. particles is also determined via the templates or identification fields stored in the engine controller 12.

Of course, it is also possible to determine the particle filter load using the path taken by the automobile, given driving regimes that appear during the journey.

 If within the functional diagram A, the interrogation concerning the exceeding of the maximum permissible sulfur charge Smax of the nitric oxide storage catalyst 3, the control device of the engine 12 answers with a yes, the routine C (see Figure 3) whose functions are described below is introduced.

 If within the functional diagram A, the query concerning the exceeding of the maximum permissible load Cmax for

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température p ! us étevée DPF-régén. suffisamment é ! evée pour procéder à l'opération de régénération du filtre à particules, et la routine B est introduite. L'échauffement est généré de préférence par injection tardive ou par post-injection de carburant dans la chambre de combustion du moteur à combustion interne 1. Ce carburant post-injecté ne participe pas ou participe pour une faible part à la combustion propre du moteur, mais il s'oxyde plutôt sous l'effet des gaz d'échappement contenant de l'oxygène, soit dans le conduit des gaz d'échappement 2, soit dans le catalyseur accumulateur d'oxyde nitrique 3 ou dans le filtre à particules 4. La chaleur réactive qui est alors libérée provoque l'échauffement des gaz d'échappement ou du filtre à particules 4. A cet effet, la quantité de carburant post-injecté est dimensionnée de manière à permettre une montée à une température supérieure à 450 C, de préférence de l'ordre de 550 C, mesurée en amont du filtre à particules 4. the particulate filter, the engine control device 12 responds with yes, triggering corresponding heating actions, the exhaust gas or the particulate filter 4 are brought to a

temperature p! us off DPF-regenerate. enough! evoked to proceed with the regeneration operation of the particulate filter, and the routine B is introduced. The heating is preferably generated by late injection or by fuel injection in the combustion chamber of the internal combustion engine 1. This post-injected fuel does not participate or contributes to a small part to the clean combustion of the engine, but it is oxidized rather under the effect of oxygen-containing exhaust gases, either in the exhaust gas duct 2, or in the nitric oxide storage catalyst 3 or in the particulate filter 4. The reactive heat which is then released causes the heating of the exhaust gas or the particulate filter 4. For this purpose, the amount of post-injected fuel is dimensioned so as to allow a rise to a temperature above 450 C, preferably of the order of 550 ° C., measured upstream of the particulate filter 4.

 In routine B, the flow of the process for carrying out the regeneration of the particulate filter is shown by way of example. For this purpose, an external interrogation loop is first initiated. In the latter, there is an interrogation, to know if a minimum predefinable value Cmin for the charge of the particle filter 4 is exceeded. For this purpose, the charge of the particulate filter is determined by the engine controller as described above. If the minimum load Cmin is not exceeded, we return to routine A of the normal diet and the warming actions are completed. If the question about exceeding the minimum charge of the particulate filter Cmin obtains the answer yes, a time counter Z1 is first loaded with a predefinable value, which is preferably derived from the charge of the particulate filter 4 which has was determined by the engine control device 12. Then, inside an internal interrogation loop, the regeneration mode of the particulate filter is set or maintained, which means that, by the continuation of the actions of heating by a controlled post-injection

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 as needed, the required temperature for the regeneration of the particulate filter is maintained. For this purpose, during the passage of the internal interrogation loop, the time counter Z1 is continuously decremented, as is the charge of the particle filter. For decrementing the charge of the particulate filter, a model stored in the engine control device 12 is preferably used, which preferably takes into account the dependence of the soot burning speed on the temperature and on the flow rate of the gases. exhaust. However, the decrementation of the particulate filter load can also be determined on the basis of the decrease of the pressure drop which is measured continuously above the particle filter 4. The passage of the internal interrogation loop with decrementing the charge of the particle filter and decrementing the time counter Z1 lasts until the predefined regeneration period set by the interrogation frequency and by the value appearing at the time counter Z1 has elapsed. Depending on the charge value of the particulate filter, with which the internal interrogation loop has been penetrated, the regeneration mode of the particulate filter is maintained in this manner for a period of about 30 seconds to about 3 minutes. After expiration of the regeneration time of the particulate filter! Are you interrogating Zl = 0? so get the answer yes. According to the invention, at this time, therefore, in correlation with the carrying out of a regeneration of the particulate filter, there is an interrogation concerning the presence of a predefined minimum sulfur load Smin of the oxide storage catalyst. nitric 3 (interrogation S> min?). If this interrogation obtains the no answer, it returns again at the beginning of routine B with the interrogation concerning the presence of a minimum load Cmin of the particle filter. But if within the routine B for performing the regeneration of the particulate filter, the exceeding of a minimum predefinable sulfur load S min is detected by the engine control device 12, during the corresponding interrogation, the unwinding routine C is introduced.

 When introducing the unwinding routine C (see FIG. 3), a desulfation requirement for the nitric oxide accumulator catalyst

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 3 is given and heating actions are engaged to raise the temperature of the exhaust gas or the nitric oxide storage catalyst 3 to the minimum temperature T. desulf. min required for the desulphating operation. Typically, this minimum desulfation temperature is greater than 550 ° C, for the usual nitric oxide storage catalysts 3, it is preferably between 600 C and 650 C. The corresponding heating actions are substantially the same as for heating for performing the regeneration of the particulate filter (see above).

 If the unwinding routine C is introduced from the unwinding routine B for the regeneration of the particulate filter, the advantage of the method according to the invention is highlighted at this time. As in this case, the exhaust gas is already at a high temperature, only a relatively low energy or fuel expenditure is required for subsequent heating to the minimum temperature T. desulf. min required for carrying out the desulphating and the necessary temperature is reached quickly. According to the invention, the actual desulphating procedure is not started immediately, for example by the temporary adjustment of reducing conditions in the exhaust gas. But a certain waiting state is set by starting a timer Z2. During this waiting period, on the one hand, the heating actions are continued to the extent necessary to maintain the minimum temperature of desulfation T. desulf. min. On the other hand, an interrogation loop in which the time counter Z2 is decremented and where a continuous interrogation takes place according to the invention, to find out if validation conditions are fulfilled (interrogation: validation?) Is crossed. After which, preferably, in parallel with the criterion which is part of the validation conditions, the interrogation also relates to a mechanical restitution power which is constant in time. Obviously, along with the interrogation of the validation conditions, it is also possible to identify other criteria, for example the criterion of a constant driving speed. This interrogation according to the invention of predefinable validation conditions, determined by the engine speed, makes it possible to guarantee

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 advantageously, the desulphating is carried out only at the moment when this operation does not generate non-tolerable disadvantages in terms of engine speed, conductivity or driving comfort.

 Thanks to a continuous decrementation and to a continuous interrogation (Z = 0?) Of the time counter Z2 in the waiting loop, it is avoided to keep the heating actions very greedy for too long if all the conditions of validation are inadequate. are not fulfilled. In this case routine C is dropped and routine B is introduced. Preferably, the maximum waiting time in the interrogation loop is limited by the start of the timer Z2 as needed, ie a particular urgency of a desulfating operation will be taken in consideration in that at the entry in the routine C, the time counter Z2 is set to a relatively large value. If, upon entering routine C, the sulfur load of the nitric oxide storage catalyst 3 is low, the time counter Z2 is only adjusted to a relatively low value. For the time counter, values limiting the maximum waiting time in the interrogation loop to a value between about 2 minutes and 10 are typical. If during this waiting period, the interrogation concerning the presence of the validation conditions obtains the answer yes, we immediately go into desulphating mode itself. According to the invention, the latter is characterized in that the engine control device 12 passes the engine 1 in alternating lean-fat mode, consisting of lean phases and consecutive and alternating fatty phases, the lean phases and the fatty phases. extending over a respective period of time between about 3 seconds and 20 seconds. Particularly in the fatty phases, the sulfur stored as sulphates in the nitric oxide storage catalyst 3 is reduced and discharged as a gas simultaneously with the exhaust gas. This fact is taken into account by the calculated decrementation of the value relating to the sulfur charge which is stored in the engine control device 12.

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 Especially in the case of too much or too long lubrication, a reduction of sulfur in sulfur hydrogen can take place in the fatty phases, which is not desirable of course, because of the odors released. In the process according to the invention, this disadvantage can be overcome in that, depending on the sulfur load of the nitric oxide storage catalyst 3 determined by the engine control device 12, the duration of the fatty phase and / or or the greasing power are adapted accordingly. During the desulphating operation, the interrogation concerning the presence of the validation conditions or the exceeding of the minimum sulfur contents S min in the nitric oxide storage catalyst 3 is continuously continued in an interrogation loop. As long as both queries get the answer yes, the lean-fat alternating diet is kept on the internal combustion engine and the desulphating continues.

 If the validation conditions are no longer given, the interrogation loop of the waiting state and the decrementation of the counter Z2 continue, starting from the last state of said counter.

 As during the possible waiting period, until the presence of the validation conditions or during the lean-fat alternating regime some soot burning also takes place in the particulate filter 4 and that, as a result, the filter load with particles decreases, when the minimum sulfur content Smin is exceeded, the routine B for the regeneration of the particulate filter is not introduced. On the contrary, a term is put to the warm-up actions and we go into main routine A.

 The undershoot of the minimum sulfur content Smin is preferably achieved by a model-based decrementation performed in the engine control device 12. For this purpose, the calculation model stored in the engine control system is preferably designed in such a way that the importance of decrementing the sulfur content depends on the duration and the importance of the lubrication. Typically, there is a change from a lean to a fat diet ten times.

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 Another advantageous method for determining whether the desulphation is sufficient is based on the comparison of the lambda value of the exhaust gas, measured on the inlet side and the outlet side of the nitric oxide storage catalyst 3, using the lambda 5 sensors and 6.

As during desulphating, the chemical reduction of sulphate of sulphate causes a consumption of reducing product, as long as this case arises, the lambda value in the exhaust gas measured at the exit side of the nitric oxide accumulator catalyst 3 is greater than the lambda value in the exhaust gases measured at the inlet side of the nitric oxide storage catalyst 3. With increasing desulphating, the consumption of reducing product is weakened, which is why the lambda values measured in the exhaust gases on the input side and the outlet side of the nitric oxide storage catalyst 3 are approximately identical. A particularly important index for the integrity of the desulfation is the ability of the nitric oxide storage catalyst 3 to catalyze the reaction of the gas with water. During this reaction, carbon monoxide and water are converted to carbon dioxide and hydrogen under reducing conditions. The enrichment of the hydrogen exhaust gases caused by this reaction is reflected in the signal of the lambda probe 6 at the outlet side of the nitric oxide storage catalyst 3, by a decrease in the lambda value measured in the exhaust gas. . By comparison between the measured lambda value in the exhaust gas on the inlet side and the outlet side of the nitric oxide storage catalyst 3, using the sensors of lambda 5 and 6, it is possible to advantageously assess the advancement of the desulphating operation. In the case of continuous desulphating, the query concerning the undershoot of the minimum sulfur load Smin thus obtains the answer yes, if the Al: A2 ratio of the lambda values measured in the exhaust gas at the inlet and the outlet side of the catalyst. Nitric oxide accumulator 3 has reached a predefined value between 0.8 and 1.25. The determining value depends in the first line on the nature of the catalyst or the nature of the lambda 5.6 probes used.

Claims (7)

A process for the desulfation of a nitric oxide storage catalyst, disposed in association with a particulate filter in the gas cleaning system of an internal combustion engine, in particular a diesel engine used in motor vehicles, by heating the nitric oxide storage catalyst at a temperature above a predetermined minimum temperature of desulphating and by consecutive production of a lean-fat alternating regime on the internal combustion engine, the heating being carried out at the latest at times when the sulfur load of the nitric oxide storage catalyst has exceeded a minimum value Smin and where regeneration of the particulate filter has been initiated and a lean-fat alternating regime of the internal combustion engine is achieved, when conditions predefined validation of the desulfation, determined by the speed of the internal combustion engine are met.  2. Method according to claim 1, characterized in that the validation conditions include a temporarily constant mechanical power restored by the internal combustion engine.  3. Method according to any one of claims 1 or 2, characterized in that the lean-fat alternating regime of the internal combustion engine is achieved by lean phases and consecutive and alternating fatty phases, the lean phases and the fatty phases. extending over a respective duration between 3 seconds and 20 seconds.  4. Method according to any one of claims 1 to 3, characterized in that the heating of the nitric oxide storage catalyst is achieved by a lean regime of the internal combustion engine and by a fuel injection post-injection into the chamber combustion of <Desc / Clms Page number 19>  internal combustion engine, following the main fuel injection.  5. Method according to any one of claims 1 to 4, characterized in that at least during the fatty phases of the lean-fat alternating regime of the internal combustion engine, the sulfur load of the nitric oxide accumulator catalyst is and that the desulphation is completed when the desulfation validation conditions are no longer met or when the sulfur load has reached a value below the minimum value Smin.  6. Method according to any one of claims 1 to 4, characterized in that the desulphalation is completed, when the desulfation validation conditions are no longer met or when the U: A2 ratio of the lambda values B1 and A2 measured in the exhaust gas on the inlet side and outlet side of the nitric oxide storage catalyst has reached a predefined value of between 0.8 and 1.25.  7. Method according to any one of claims 5 or 6, characterized in that, after the desulphating, the regeneration of the particulate filter is performed, when the particulate load of the particulate filter has exceeded a predefined threshold value .