FR2833300A1 - Functional process of purification units in a vehicle exhaust system, optimizes emission of pollutants and the functioning of the engine by adjustment of the air/fuel ratio (lambda coefficient) - Google Patents

Abstract

Process of purification system installed in exhaust system of internal combustion engine, in which emission values of at least one specific component or at least two (optimally three) other specific components, in exhaust gases downstream of purification unit, are compared with pre-established values. Resulting from the comparison, the working temperature of the unit is adjusted to optimize its rate of conversion. Working process of a purification system installed in the exhaust system of an internal combustion engine, in which the emission values of at least one of components CO, CO2, H2O, NH3, CH4 or at least two (optimally three) of the components HC, NOx, CO, CO2, H2O, NH3, CH4, O2 and H2, or a pollutant containing S, in the exhaust gases downstream of the purification unit, are compared with pre-established values. Resulting from the comparison, the working temperature of the unit is adjusted to optimize its rate of conversion.

Description

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 The invention relates to a method for operating exhaust gas cleaning devices.

 Because conventional internal combustion engines require an aftertreatment of exhaust gases because of the relatively large gross emissions of pollutants or other undesirable components of these gases, exhaust gas cleaning devices, in particular catalyst devices, are installed jointly with appropriate sensors in the exhaust system of these engines.

To differentiate the perception of pollutant emissions, it is then known to establish separately the emission rates of the various components of the exhaust gas. In this regard, U.S. Patent No. 5,329,764 discloses an engine control system for optimizing the conversion efficiency of a catalyst device installed in the exhaust system of a combustion engine. internal, which has a sensor of nitrogen oxides (NO,) and a sensor of carbon monoxide (CO) and hydrocarbons (HC). Both sensors are installed downstream of the catalyst device. A differential signal that is generated from the signals of both sensors is sent as a feedback variable to a fuel control device to set a desired air / fuel ratio. The differential signal then serves as a corrective signal for adjusting the lambda value of the exhaust gas, in order to achieve a maximum conversion efficiency of the catalyst device. However, the optimization of the emission regime that this known system has to achieve is limited to a single range for a stoichiometric air / fuel ratio, which makes it here also, because of the influence exerted by other quantities such as leaks in the exhaust system, imprecise correction is only possible.

 DE 195 11 548 A1 also discloses a method for reducing the nitrogen content in gases

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 exhaust system of an internal combustion engine, in which the content of this gas in hydrocarbons, carbon monoxide or nitrogen oxides is measured downstream of a nitrogen oxide accumulator, and is carried out switching in each case from a stoichiometric phase or enriched operation to a depletion operating phase as soon as the content of hydrocarbons or carbon monoxide has exceeded a prescribed value or as soon as the oxides content of nitrogen has dropped below a prescribed value.

The transition from a depleted operation phase to a stoichiometric phase or enrichment phase is carried out as soon as the measured nitrogen oxide content rises above a prescribed value.

 German Patent No. 195 432 19 has already disclosed a method of operating a diesel engine whose exhaust pipe is equipped with a storage catalyst in which the nitrogen oxides can be absorbed, desorbed and reduced, and a sensor disposed downstream of the storage catalyst for detecting the NOx concentration in the exhaust gas stream.

When a NOx oxide accumulation threshold that varies as a function of the rotation speed and the load has been reached, this sensor makes it possible to switch an operation with a lambda value greater than 1 to an operation with a lambda value. less than 1. The regeneration control of NOx oxidation catalyst for lambda <1 is carried out by means of an HC sensor. This sensor recognizes the entire regeneration in the operation with lambda <1, since the HC emissions increase strongly in rich service, as soon as the regeneration of the NOx accumulation catalyst is completed. In addition, this document also discloses a structured catalyst system comprising a NOx oxide storage catalyst near the engine and a rocker catalyst, in which the window

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oxydes NOx, les hydrocarbures sont réinjectés conformément à la quantité existante de NOx. Au début de la fenêtre de température efficace pour la désorption et la réduction, la réinjection d'hydrocarbures est utilisée rationnellement pour élever la température et modifier la composition du gaz d'échappement.

the temperature of the two catalysts is adapted to a NOx oxidation and hydrocarbon dosing strategy conducted according to the temperature of the exhaust gas, and the absorption, desorption and reduction of the NOx oxides can thus be carried out and influenced in the catalyst system. In the effective temperature window of the catalyst for accumulation of

NOx oxides, the hydrocarbons are reinjected according to the existing amount of NOx. At the beginning of the effective temperature window for desorption and reduction, hydrocarbon re-injection is used rationally to raise the temperature and change the composition of the exhaust gas.

Also known from European Patent No. 0 899 563, WO 79/47 962, European Patent No. 090 941 and German Patent No. 198 31 424, sensors for determining the concentration of gas constituents. exhaust, in particular to determine the concentration of one or more gases NOx, CO, H2 and preferably unsaturated hydrocarbons. These sensors are used to optimize combustion reactions and to recognize component function faults. Unlike other types of known sensors, in particular sensors called lambda probes for the determination of the value of air on the basis of the Nernst effect, they allow the determination of the absolute values of gas components. exhaust.

 The problem of the processes according to the invention is to allow an optimization of the operation of an exhaust gas cleaning device with the objective of safety of emissions and efficiency, particularly with regard to the duration of exhaust gas purification device life and fuel consumption.

 This problem is solved according to the invention as follows:

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According to the invention, for the purpose of operating an exhaust gas cleaning device installed in the exhaust system of an internal combustion engine, the emission values of at least one exhaust components CO, CO2, H2O, NH3, CH4, H2, or at least two, and optimally at least three of the exhaust components HC, NOx, CO, CO2, H2O, NH3, CH4, O2, H2 or a pollutant containing sulfur in the exhaust gas are measured downstream of the exhaust gas purification device, compared with predetermined setpoints and, depending on the result of the comparison , the operating temperature of the exhaust gas purification device is varied to optimize a conversion rate of this device.

 Since the behavior of the exhaust gas purification device for the exhaust components NOx, CO, HC, NH3, SO2, H2S and COS is a function, in different ways, of the operating temperature of this device, the process according to the invention makes possible a substantially more efficient operation of the exhaust gas purification device. Greater stability of the operation with respect to disturbances is achieved when, according to a preferred embodiment of the invention, the operating temperature of the exhaust gas cleaning device is set to a certain value. predetermined according to the result of the comparison. Since within a pre-established temperature window the conversion rate increases with the operating temperature of the exhaust gas cleaning device, it is provided according to another embodiment. of the invention that the operating temperature of this device is high until the result of the comparison corresponds to the transition to

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 below prescribed emission values of at least one of the components of the exhaust gas.

 According to a preferred embodiment of the method of the invention, the operating temperature varies in the zone of a light-off phase of the exhaust gas purification device, which allows optimization of the operation. of this device taking into account this phase, in particular different conversion rates for different components of the exhaust gas.

 In another embodiment of the process according to the invention, the exhaust gas purification device comprises at least one precatalyst. In this case, a measurement of the emission values is carried out downstream of the precatalyst and optionally upstream of a second catalyst installed in series, preferably a NOx accumulation catalyst, at the same time as the regulation or regulation. the lambda value of the exhaust gas to the precatalyst at a pre-established value. An embodiment is particularly preferred in which, from a lambda value greater than 1 for a comparison result which corresponds to a passage below the preset thresholds of the emission values, the exhaust gases are brought back at a lower lambda value, preferably lambda = 1.

Since in the light-off phase, the conversion rate depends strongly on the lambda value for a given value of the operating temperature, the emission spectrum then undergoes a particularly strong influence.

 Another object of the present invention is to create a method of operating an exhaust gas purification device, wherein the emission of pollutants downstream of this device is used to diagnose the service state of the engine. purification device.

 According to the invention, the operating temperature of the exhaust gas purification device is

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déterminée, les valeurs d'émission d'au moins l'un des composants d'échappement CO, CO2, H2O, NH3, CH4, H2 ou d'au moins deux et, dans le cas optimal, d'au moins trois des composants d'échappement HC, NOx, CO, CO2, H2O, NH3, CH4, Os, H2 ou d'un polluant contenant du soufre sont mesurées en aval du dispositif d'épuration, comparées avec des valeurs de consigne dépendant de la valeur de la température d'exploitation et des déductions en matière de pollution sont tirées de la valeur de comparaison. L'invention part du fait connu que chaque taux de conversion se reflète dans les valeurs d'émission des divers composants des gaz d'échappement pour une température donnée d'exploitation d'un dispositif catalyseur, et que l'altération du catalyseur peut à son tour être estimée à partir de ces valeurs.

determined, the emission values of at least one of the exhaust components CO, CO2, H2O, NH3, CH4, H2 or at least two and, in the optimal case, at least three of the components Exhaust HC, NOx, CO, CO2, H2O, NH3, CH4, Os, H2 or a sulfur-containing pollutant are measured downstream of the purification device, compared with setpoints depending on the value of the operating temperature and deductions for pollution are derived from the comparison value. The invention is based on the fact that each conversion rate is reflected in the emission values of the various components of the exhaust gases for a given operating temperature of a catalyst device, and that the alteration of the catalyst can in turn, be estimated from these values.

 In a preferred form of implementation of the process according to the invention, the emission values of at least two of the mentioned components of the exhaust gas upstream of the purification device of these gases are also measured and compare them with the emission values measured downstream of this device and from this comparison a purification efficiency, in particular a conversion rate of a catalyst device, is established. This way of operating offers a greater precision in the determination of the degree of alteration.

 A method is preferred in which the measurement of the emission values is carried out in the region of a predetermined temperature window of the catalyst device, because it is thus possible to exploit the high efficiency of the catalyst device which differs according to the temperature of the catalyst. exploitation. A method is particularly preferred in which the light-off temperature of the catalyst device is determined from the measured emission values and is compared with a predetermined reference value, depending in particular on the lambda value of the exhaust gas. and we draw from

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 comparison value of the deductions on catalyst deterioration. This allows an extremely accurate diagnosis of an eventual alteration of the catalyst device, since its temperature of light-off is shifted due to aging process.

 For the variation of the operating temperature of the catalyst device, an exhaust gas recirculation rate, a position of the butterfly valve, an ignition time, an injection time, a load pressure, additional fuel supply or a similar parameter.

 In order to improve the exploitation of a NOx accumulation catalyst with regard to the emission of nitrogen oxides as well as carbon dioxide, hydrocarbons and ammonia, an improved method for the regeneration of NOx is proposed. a NOx accumulation catalyst.

According to the invention, the emission values of at least one of the exhaust components CO, COs, H2O, NH3, CH4, H2 or at least two, and in the optimal case of at least three of the exhaust components HC, NOx, CO, CO2, Ho, NH3, CH4, O2, H2 or a sulfur-containing pollutant downstream of the NOx accumulation catalyst, these values are compared with pre-established setpoints and, depending on the result of the comparison, a lambda value of regeneration of the exhaust gas is varied at least during a regeneration phase. This allows optimization of the regeneration of the NOx accumulation catalyst as a function of the measured emission values of the exhaust components of which there are at least two.

 In a preferred embodiment of the invention, the regeneration phase is completed as a function of the time at which the result of the comparison corresponds to a breakthrough of one or more of the exhaust components. This avoids an excessively long regeneration of the NOx accumulation catalyst and

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 the resulting increase in pollutant emissions and fuel consumption.

 An adaptation of the parameters of the regeneration process to the state of the NOx accumulation catalyst, in particular to aging and / or weathering phenomena, can be obtained when the regeneration lambda value during at least one subsequent regeneration phase is of a predetermined quantity, in the case where a breakthrough of one or more components of the exhaust gas occurs earlier than at the prescribed time.

à accumulation de NO,,. Conformément à l'invention, les valeurs d'émission d'au moins l'un des composants d'échappement CO, CO2, H2O, NH3, CH4, H2 ou d'au moins deux, et dans le cas optimal d'au moins trois des composants d'échappement HC, NOx, CO, CO2, H20, NH3, CH4, O2, H2 ou d'un polluant contenant du soufre sont mesurées en amont du catalyseur à accumulation de NOx, comparées à des valeurs de consigne préétablies et un degré de contamination par le soufre du catalyseur à accumulation de NOx est déduit du résultat de la comparaison. L'invention part du fait connu que la contamination par le soufre d'un catalyseur à accumulation de NOx qui a lieu dans le cas de l'utilisation d'un carburant contenant du soufre dépend non seulement des valeurs d'émission des composants contenant du soufre dans les gaz d'échappement, mais aussi des composants Noix, HC, CO et/ou NH3 de ces gaz. It is another object of the present invention to provide a method of operating a NOx accumulation catalyst installed in the exhaust system of an internal combustion engine, wherein the emission values of the engine are used. to diagnose sulfur contamination of the catalyst

with accumulation of NO ,,, According to the invention, the emission values of at least one of the exhaust components CO, CO2, H2O, NH3, CH4, H2 or at least two, and in the optimal case of at least two three of the exhaust components HC, NOx, CO, CO2, H2O, NH3, CH4, O2, H2 or a sulfur-containing pollutant are measured upstream of the NOx accumulation catalyst, compared to predetermined set values and a degree of sulfur contamination of the NOx accumulation catalyst is deduced from the result of the comparison. The invention is based on the fact that the sulfur contamination of a NOx accumulation catalyst which takes place in the case of the use of a sulfur-containing fuel depends not only on the emission values of the components containing the sulfur in the exhaust gases, but also components Nuts, HC, CO and / or NH3 of these gases.

 A method is preferred in which the emission values of at least one sulfur-containing SO 2, H 2 S, COS exhaust component and / or one of the NO x, HC, CO, H 2 or NH 3 components are furthermore measured. downstream from

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 NOx accumulation catalyst and are compared with the emission values measured upstream, a sulfur balance is established from the result of this comparison and a degree of sulfur contamination of the NOx accumulation catalyst is deduced. This way of operating has the advantage that the degree of sulfur contamination can be determined with greater precision.

 In order to eliminate sulfur from a NOx accumulation catalyst placed in the exhaust system of an internal combustion engine, a degree of sulfurization is determined according to one of the processes described above for the diagnosis of contamination. by sulfur. A minimum temperature of the NOx accumulation catalyst and a lambda value of less than 1 of the exhaust gas are then adjusted for a period of desulphurization time and the length of the desulfurization time interval is set according to the determined degree of sulfur contamination. Since the desulphurisation range may be better adapted to the actual degree of sulfur contamination based on such a more precisely determined degree of contamination, a desulfurization time interval that is too long or too short is avoided. .

 Another problem underlying the invention lies in the improvement of a desulfurization process adjusted according to the lambda value, known according to German Patent No. 19 923 483 for a NOx accumulation catalyst installed in the system. exhaust of an internal combustion engine. According to the invention, emission values of hydrogen sulfide and / or at least one of the constituents of hydrogen sulphide are measured downstream of the NOx accumulation catalyst, at least during a period of desulfurization time. hydrocarbon exhaust (HC), carbon monoxide (CO), ammonia (NH3), nitrogen oxides (NOx), hydrogen (H2) or other exhaust component containing sulfur and the lambda value is varied of the

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 exhaust gas according to the result of the comparison. Optimization of the desulphurization can then be carried out to avoid disturbing concentrations of hydrogen sulfide and / or breakthroughs of other components of the exhaust gas.

 Particularly preferred is a form of implementation of the method in which, starting from a lambda value of less than 1, a result of comparison corresponding to an H2S breakthrough is set to a lambda value greater than 1, since Effective and rapid removal of hydrogen sulfide disturbance concentrations in the exhaust gas can then be prevented.

 Greater precision in the implementation of the processes is obtained when the exhaust gas components of the optical sensors, in particular infrared sensors, in particular infrared reflection spectroscopy sensors, are used for measuring the concentration of the components. This allows the measurement of absolute concentrations of components. The measurement possibly made of the oxygen content in the exhaust gas then relates to the effective oxygen content and not to the known measurement of the excess oxygen by oxygen-sensitive measuring devices.

 The invention is illustrated in detail below with reference to the drawings according to an embodiment of which one can deduce other advantages and features of the invention.

 The attached drawings show schematically: FIG. 1, an internal combustion engine to which an exhaust system is attached, FIG. 2, a diagram of the conversion rate of a three-way catalyst for carbon monoxide and hydrocarbons, depending on the temperature of the catalyst; FIG. 3, a diagram of the conversion rate of a three-way catalyst for hydrocarbons based on

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 the operating temperature of the catalyst, in each case for a new catalyst and for an aged catalyst, in each option for two different lambda values; FIGS. 4 to 6 show curves of variation of the lambda value as a function of time for a NOx accumulation catalyst with regeneration and accumulation phases.

 FIG. 1 is a schematic representation of an internal combustion engine 1, for example a spark ignition engine that can operate with a lean mixture or a diesel engine, comprising an exhaust system 2 and an apparatus 3 motor control unit, preferably for the operation of a motor vehicle.

The internal combustion engine 1 has several rows of cylinders 4 (the corresponding components are assigned only one reference sign), each followed by their own escape route 5. An exhaust gas purification device comprising a precatalyst 6 and a main catalyst 7 is installed in the exhaust system 2 for the conversion of harmful or undesirable components of the exhaust gas into other components. The precatalyst 6 is preferably carried out as a three-way catalyst and the main catalyst 7 is carried out as a NOx accumulation catalyst. Downstream of the rows of cylinders 4 are arranged in the exhaust paths 5 of the sensors 8 with which the concentrations of components of the exhaust gas passing through the exhaust system 2 of the internal combustion engine 1 can be measured. For example, it may be HC, NOx, CO, COs, HO, NHs, Lt, Oz, Hz or a sulfur-containing pollutant. Upstream of the precatalyst 6 is further disposed another sensor 8 for measuring the components of the exhaust gas. Another sensor 9 for determining the concentration of pollutants in the exhaust gas is disposed in the zone of the exhaust system 2 between the precatalyst 6 and

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 the main catalyst 7, downstream of the precatalyst 6 and upstream of the main catalyst 7. Another sensor 10 is provided downstream of the main catalyst 7 in the exhaust system 2. It goes without saying that in the case of a device multi-part exhaust gas purification, sensors may be arranged upstream or downstream of the parts concerned.

 With regard to the sensors 8, 8 ', 9 and 10 which are shown only schematically in FIG. 1, they may be multi-component sensors, each of which is capable of picking up more than one component in the exhaust gas, or multiple sensors, collated in the drawings for simplicity, each of which separately measures various components of the exhaust gas.

 Advantageously, multicomponent optical sensors, preferably infrared reflection spectroscopy sensors, are used as sensors 8, 8 ', 9 and / or 10 which can determine the absolute concentration of exhaust gas components by means of a known spectrographic method. Such sensors operate extremely fast, with measurement times less than or equal to 500 microseconds. The shortness of the measurement times allows measurement intervals of, for example, 200 microseconds. In addition, such sensors have a sufficiently high physical and chemical stability, particularly with regard to temperature, fouling and chemical reactions in the exhaust gas. However, next to optical sensors, electrochemical sensors, for example based on zirconium oxide, are also considered with more than one oxygen pump. The sensors used advantageously make it possible, in addition to measuring the concentration of exhaust gas components, also to measure the lambda air / fuel ratio.

 In addition to the mentioned sensors, upstream and downstream of the precatalyst 6 and upstream of the catalyst are provided.

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principal 7 des sondes lambda 11 et 12 de même que des capteurs de température 13, 13'servant à déterminer la température de fonctionnement des dispositifs catalyseurs.

main 7 lambda probes 11 and 12 as well as temperature sensors 13, 13'aservant to determine the operating temperature of the catalyst devices.

Of course, alternatively or in addition, other temperature sensors may be provided for measuring the operating temperature of the exhaust gas cleaning device or parts thereof. For the recirculation of the exhaust gas, the internal combustion engine 1 has a device 14 for recycling the gases provided with an adjustable valve.

 The engine control apparatus 3 captures, in a known manner by means of other non-illustrated sensors, operating parameters of the internal combustion engine 1 such as, for example, the position of the butterfly valve, the recycling speed. Exhaust gas, timing of ignition, timing of injection advance, main injection and injection delay, injection pressure, Tumble valve position , the load pressure, the camshaft phase adjusters, the speed of rotation, the position of the accelerator pedal, the load, the driving speed, etc., and it can possibly influence these parameters by means of adjusting members (not shown), a cable system 14 or a similar system being provided for communication between the motor control apparatus 3 and the sensors or adjusting members.

 The engine control apparatus 3 comprises in particular a lambda control system for regulating the oxygen concentration in the exhaust gas, in other words, the lambda value. Through the lambda value, it is also possible to influence the gross emission of exhaust gas components, in particular HC, CO and NOx.

 In addition, the total emission of pollutants depends decisively on the lambda value, in particular the fact that the purification efficiency, in particular the functions

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 conversion of exhaust gas cleaning devices, in particular catalyst devices, are dependent on the lambda value. A NOx accumulation catalyst 7 usually operates in an accumulation cycle which comprises at least one usually slow absorption mode and a faster regeneration mode. But the accumulation by absorption takes place at a lambda value greater than 1, the withdrawal at a later time for a lambda value less than or equal to 1.

accumulation des gaz NO, accumulation des gaz NOx pour réduire l'émission de ces gaz, toutefois des mesures particulières telles qu'un recyclage important des gaz d'échappement ou l'injection de carburant dans le système d'échappement sont nécessaires pour décharger les catalyseurs d'accumulation et pour convertir les oxydes NOx pour une valeur lambda inférieure à 1. Dans le cas de moteurs à combustion interne à injection directe, il est en outre avantageux, à cause des émissions de particules qui apparaissent, de doter en outre le dispositif d'épuration des gaz d'échappement d'un filtre à particules, d'un dispositif réduisant en continu la Such accumulation catalysts are therefore mainly used in the case of engines operating with a lean mixture. Unlike these storage catalysts, three-way catalysts are exploited as much as possible by accurately maintaining a lambda value equal to 1. They are therefore used mainly for conventional spark-ignition engines or as a precatalyst during a phase. heating, before a NOx oxide storage catalyst has reached the temperature necessary for the accumulation of these oxides, in the case of spark ignition engines operating with a lean mixture. Since internal combustion engines can operate with an excess of air, that is to say with a lambda value greater than 1, it is certainly possible to use catalysts with

accumulation of NO gases, accumulation of NOx gases to reduce the emission of these gases, however special measures such as a significant recycling of exhaust gas or fuel injection into the exhaust system are necessary to unload the storage catalysts and to convert the NOx oxides to a lambda value of less than 1. In the case of internal combustion engines with direct injection, it is furthermore advantageous, because of the emissions of particles that appear, to further provide the device for cleaning the exhaust gases of a particulate filter, a device continuously reducing the

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 proportion of particles or a particulate catalyst, which is however not shown in the drawing.

 Figure 2 is a schematic representation of the conversion rate of a three-way catalyst for CO and HC emissions as a function of the service temperature of the catalyst.

 As can be seen, the conversion rate exceeds a value of 50% only from a minimum temperature, ie the temperature referred to as the "light-off temperature." In addition, it is possible to recognize in FIG. 2 that the light-off temperature of the catalyst is different for the various components of the exhaust gases, which results in a temperature-dependent emission spectrum which is different for the various components of the exhaust gases. Exhaust downstream of the catalyst For the scenario shown in Figure 2, the TCO light-off temperature for the CO component of the exhaust gas is lower than the THC lightoff temperature for the HC component of these gases.

 Fig. 3 shows the HC conversion ratio of fresh and aged three-way catalyst for different lambda values, i.e. lambda = 1 and lambda = 1.05. It can be seen that the light-off temperature for an aged catalyst is higher than for a fresh catalyst. It can also be noted that for a lambda value of 1.05, the temperature of light-off is lower than for lambda = 1. This last remark results from the fact that the oxidation of HC is facilitated by the highest proportion of Bones in poor exhaust for lambda = 1.05. The rise of the light-off temperature for an aged catalyst is the result of deactivation of the noble active metals present in the catalyst, for example by formation of oxide. In addition, aging leads to a maximum conversion rate of less than 100%, for example at a reduced conversion rate of 10%. Temperature offsets of 30 K and

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 70 K shown in the drawings are typical values which may deviate, in a particular case, from the values given here.

 The accumulation and regeneration behavior of NOx accumulation catalysts also depends on the temperature. NOx storage takes place in a lean environment in a temperature range of about 250 to 500 C. The release of NOx and the reduction of NOx in N2 takes place in a lower atmosphere than the stoichiometry. Above a temperature of about 250 C, oxidation of HC occurs in poor or stoichiometric exhaust.

 According to the invention, the emission values, for example, of the HC and CO components of the exhaust gases are measured downstream of the catalyst device and compared with pre-established setpoint values. The operating temperature of the catalysts 6 and 7 is modified according to the result of the comparison in order to optimize the conversion rate. The preset setpoints for the emission values form characteristic diagrams that model the conversion behavior of the NOx accumulation catalyst. The characteristic diagrams are chosen according to parameters such as the catalyst operating temperature and / or the lambda value of the exhaust gases arriving at the NOx accumulation catalyst. The operating temperature of the catalysts 6 and 7 can in particular be adjusted to a preset value depending on the result of the comparison. The operating temperature of the catalysts 6 and 7 can be raised in particular within the limits of a preset temperature window until the result of the comparison corresponds to the passage below predetermined thresholds of the emission values of the at least one of the exhaust components. In particular, the light-off efficiency of the catalyst device can also be improved.

 The variation of the operating temperature of the catalyst device is influenced in a known way

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 by varying the value of a throttle valve position, an exhaust gas recirculation rate, or by adding additional quantities of fuel.

 When the catalyst device comprises a precatalyst 6, preferably a three-way catalyst and a NOx accumulation catalyst 7 as shown in FIG. 1, a measurement of the emission values can be carried out downstream of at least the precatalyst 6 and / or NOx accumulation catalyst 7.

 In addition, in the case where the exhaust gas purification device consists of a precatalyst and a nut storage catalyst, the operating temperatures of the precatalyst and the NOx storage catalyst may vary separately.

 When the exhaust gas purification device comprises at least one precatalyst produced as a three-way catalyst, the exhaust gases arriving at the precatalyst are brought back from a lambda value of greater than 1 to a preset value, preferably lambda = 1, when the result of the comparison corresponds to a lowering below pre-established thresholds of the emission values downstream of the three-way catalyst.

 According to the invention, an alteration of the catalyst is demonstrated according to the conversion behavior as a function of the temperature of the catalyst device. The operating temperature of the precatalyst is then determined and the emission values of at least one of the exhaust components CO, CO2, H2O, NH3, CH H2 or at least two, and optimally at least three of the exhaust components HC, NOx, CO, CO2, H2O, NH3, CH4, O2, H2 or a sulfur-containing pollutant are measured downstream of the precatalyst and compared with set values depending on the value the service temperature. Deductions concerning the alteration of the

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 catalyst are derived from the result of the comparison. This operation is preferably performed in a temperature window ranging from 200 to 600 ° C., in particular from 250 to 400 ° C.

 In general, the light-off temperature is higher for an aged precatalyst than for a fresh precatalyst. In particular, an aged precatalyst must be heated for a longer period of time than a fresh catalyst, to bring it into the light-off temperature range. Therefore, it is in particular the light-off behavior of a precatalyst that is used for the diagnosis of its possible alteration.

 According to a development of the invention, the emission values of at least one exhaust component NOx, CO, HC, NH3, SO2, H2S, COS, CH4, H2, CO2 and H2O are measured upstream of the precatalyst and compared with emission values measured downstream of the precatalyst. A conversion rate of the precatalyst can be deduced and compared with the conversion setpoint values depending on the value of the operating temperature of the precatalyst. The degree of possible alteration of the catalyst is established according to the result of the comparison.

 As already mentioned, the lightoff temperature varies depending on the aging process of the catalyst. Therefore, the alteration of the catalyst can be estimated from the established light-off temperature compared to a pre-set setpoint. The set value of the light-off temperature is preferably determined from the lightoff temperature of a still unused catalyst device, and an individual calibration which takes into account the exemplary dispersions is then possible. Since the temperature of light-off usually depends on the lambda value, the preset setpoints are chosen not only according to the value of the temperature of the lamp.

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 service of the catalyst device, but also of the lambda value of the exhaust gases.

 When an alteration of the catalyst is detected, an indicating device can be activated via the motor control apparatus 3 and / or a fault indication is recorded in a data accumulator.

 The exploitation of the emission values of at least one of the CO, CO2, H2O, NH3, CH4, H2 or at least two exhaust components and, in the optimal case, at least three of the Exhaust components HC, NOx, CO, CO2, Haro, NH3, CH4, Os, H2 or a sulfur-containing pollutant downstream of a NOx accumulation catalyst allows a more efficient regeneration control and presenting better security of emission. For this purpose, according to the invention, the emission values of at least one of the exhaust components CO, CO2, H2O, NH3, CH4, H2 or at least two and, in the optimal case, at least three of the exhaust components HC, NOx, CO, CO2, H2O, NH3, CH4, O2, H2 or a pollutant containing sulfur of the sensor 10 are measured downstream of the NOx accumulation catalyst 7 and compared with predetermined set values.

During the regeneration phase, NOx accumulation catalysts operate mainly with a regeneration lambda value of less than 1, but at most with a lambda value equal to 1.05. Since the proportion of fuel for lambda <1 dominates the proportion of oxygen, reducing agents are formed in relatively large proportions which serve to reduce the nitrogen oxides included. Carbon monoxide is the main regeneration component for these lambda values. According to the invention, the lambda regeneration value of the exhaust gas during the regeneration phase is set according to the measured emissions of at least one exhaust component.

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 The preset setpoints for the emission values form characteristic diagrams that model the regeneration behavior of the NOx accumulation catalyst. The characteristic diagrams are preferably chosen according to parameters such as the catalyst operating temperature and / or the lambda value of the exhaust gases arriving at the NOx accumulation catalyst. A lambda regeneration value is established based on the comparison of the measured emission values of the exhaust components with the setpoints.

 If the measured emission values fall below the pre-established threshold values, the regeneration lambda value can be reduced in accordance with the invention during the regeneration phase to thereby obtain a shorter total regeneration time.

 It is preferably the emission values of the main CO and HC reduction components that are measured and used. In the case of HC components, a differential measurement of components such as CH4 can also be performed. In addition, the component emission values of sulfur-containing and / or NH3-containing exhaust gases can be compared with corresponding magnitudes of the characteristic diagram. The NOx emission values can also be taken into account in the determination of the lambda value in the regeneration phase.

 The proportions of CO, HC, NH3 as well as sulfur-containing exhaust gas components can be lowered by oxidation by raising the lambda value during the regeneration phase. In particular, the regeneration phase can be terminated depending on a time when a breakthrough of one or more of the mentioned exhaust components appears. In this respect, it is considered as a breakthrough the passage over a pre-established threshold value. Moreover, from the beginning of a regeneration phase, the moment when a breakthrough of one or

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 several of the escape components appear.

The corresponding time interval is stored. If a breakthrough occurs at an earlier time in a subsequent regeneration phase, the lambda regeneration value may be raised by a predetermined amount during at least one subsequent regeneration phase.

 FIG. 4 illustrates, for two cases, the pace over time of a lambda regeneration value in a regeneration time interval between T1 and T2. For case A, the lambda value is raised from a lower value and the regeneration lambda value at the time T1, up to the time T2, that is to say the end of the regeneration phase. Curve B in dashed lines has a steeper slope compared to that of curve A. In accordance with the invention, a pace in time is preferably chosen for the regeneration lambda value with a steeper slope when the values of emission of at least one of the mentioned components of the exhaust gas passes above pre-established thresholds.

 FIG. 5 represents the time course of the regeneration lambda value during two time intervals T1, T2 and T1 ', T2'. In this case, T1 represents the beginning and T2 the end of a regeneration phase. The term of regeneration at time T2 can be established according to known criteria. In FIG. 5, TD represents a time within the range T1, T2 for which a breakthrough of one or more components of the exhaust gas has been established. In this case, the lambda regeneration value is recorded in the regeneration interval T1 ', T2' following; the corresponding curve of the lambda value is designated by the letter D in FIG.

 FIG. 6 represents another preferred curve of the regeneration lambda value as a function of time. The regeneration lambda is then raised in the regeneration interval T1, T2 from the time T1 until a time TS.

The time TS is determined by the fact that the lambda of

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 regeneration then reached its threshold value S. In the continuation of the regeneration, the regeneration lambda is maintained at its value S. The initial value of the regeneration lambda can then be determined as much as the threshold S of the lambda value in measured emission values of the exhaust components mentioned.

 In another embodiment of the invention, the mentioned emission values of the exhaust gases are established with the sensor 9 disposed upstream of the NOx accumulation catalyst 7. After comparing the measured emission values with the downstream sensor 10, a reaction balance for the individual exhaust components in the NOx accumulation catalyst 7 can be calculated. For this purpose, the difference between the emission values measured upstream and downstream is established. This reaction balance of several components is compared with pre-established thresholds which generally depend on the lambda value and the temperature and is used to set the lambda regeneration value.

 With a view to establishing a possible sulphurization of the NOx accumulation catalyst 7 in the case of the use of a fuel containing sulfur, the charge of the exhaust gases with at least one sulfur-containing component such as SO 2, H 2 O COS is established according to the invention with the sensor 9 arranged upstream.

 Alternatively, it is also possible to measure the emission values of at least one of the sulfur-containing exhaust components and at least one of the exhaust components NOx, HC, CO and / or NH3. The measured values are compared with setpoints and a degree of sulfur contamination of the NOx accumulation catalyst is established from the result of the comparison. The relationship between the result of the comparison and the degree of sulfur contamination

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 to be determined from a standard calculation and / or experimentally.

 In addition, the exhaust gas charge with S02, H2S, COS components containing sulfur as well as NOx, HC, CO, H2 and / or NH3 exhaust components can be additionally established with the sensor. 10 installed downstream of a NOx accumulation catalyst 7. A comparison with the emission values established by the sensor 9 upstream of the NOx accumulation catalyst 7 allows the calculation of a sulfur balance for the NOx accumulation catalyst 7. The degree of sulfur contamination of the NOx accumulation catalyst 7 is established from the sulfur balance by integration over time.

 Since sulphate formation due to sulfur contamination leads to slow deactivation of NOx accumulation catalysts and sulfur removal is only carried out at temperatures above a catalyst temperature of approx. 6500C because of the higher chemical stability of the sulphates, the introduction of sulfur into a NOx accumulation catalyst must not only be monitored for the sake of sufficient emission safety, but elimination of sulfur. During sulfur removal, the sulphates introduced are reduced to a lambda value below 1 and at elevated temperatures. In accordance with the invention, sulfur removal is carried out as necessary by setting a sulfur removal time interval whose onset and length are determined according to the established degree of sulfur contamination of the catalyst. NOx accumulation. In addition, the sulfur removal temperature and the lambda value are set during sulfur removal as a function of the established degree of sulfur contamination. Sulfur elimination too

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 Frequent and / or too long and the unnecessary overconsumption of fuel related thereto are thus preventable in particular. In addition, high emission safety is therefore also ensured in case of supply with fuels with a high sulfur content exceeding 500 ppm. Active sulfur removal can be stopped immediately for a total measured discharge of sulfur.

 Since hydrogen sulfide is produced in a NOx storage catalyst under the influence of reducing conditions during removal of sulfur in sulfur dioxide, mainly at high catalyst temperatures and at low lambda values, and that this hydrogen sulfide can be discharged into the atmosphere, the appearance of hydrogen sulfide in the exhaust gas is further controlled by means of the sensor 10. When the prescribed values of H2S emission are exceeded the lambda value is changed accordingly, as is the catalyst temperature, if necessary. In particular, the lambda value of the exhaust gas can be increased from a value of less than 1 to a value greater than 1 to achieve the rapid termination of an H2S discharge.

 In addition, the emission values of HC, CO, H2 and / or NH3 can be measured downstream of the NOx accumulation catalyst 7 during the sulfur removal and when breakthroughs of these exhaust components occur, is possible to go from rich exploitation to poor exploitation. In the presence of a minimum sulfur removal temperature, the NOx storage catalyst 7 continues to receive lean exhaust gas until a NOx breakthrough is measured downstream of the catalyst. Then, a return to rich operation switching is possible, until a later moment when high values of HC, CO, H2, NH3 and / or H2S emission are measured. By a change

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 periodic between rich exhaust gas and poor exhaust gas, a total consumption of oxygen stored in the catalyst is then avoided and the formation of H2S is largely controlled. It is therefore equally possible to obtain total sulfur removal as to avoid a significant discharge of H2S.

 In the methods according to the invention, sensors are preferably used for the exhaust components CO, NO, NO 2, NH 3, SO 2, H 2 S, COS, CH 4, H 2 as well as other HC components which are at the same time detectable. separately from each other. The measurement can then be carried out continuously or discontinuously.

 The specific manner in which the sensors assume their function is essentially irrelevant to the invention described above. However, optical sensors, in particular infrared sensors, are preferably used in the optimal case of reflection-infrared spectroscopy sensors, which make it possible in particular to determine the absolute concentration of the components in the exhaust gas. These sensors allow very short measurement times, for example less than 500 microseconds and measurement intervals of, for example, less than 200 microseconds, and a faster and more precise operation of the emission values concerned.

 Finally, a considerable possibility of improvement, with a small additional expense, of the emission behavior of an internal combustion engine is created by the methods according to the invention. A particular advantage lies in the fact that these methods can be used for the most diverse types of internal combustion engines, spark ignition engines of conventional type or operating with a lean mixture, diesel engines or similar engines and association with various catalysts and various devices

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 strategies for reducing exhaust emission values.

composants d'échappement CO, CO2, H2O, NH3, CH4, H2 ou d'au moins deux, de façon optimale d'au moins trois des composants d'échappement HC, NO,, CO, CO2, H20, NH3, CH4, O2, H2 ou d'un polluant contenant du soufre dans les gaz d'échappement en aval d'au moins une partie du dispositif d'épuration des gaz, comparées avec des valeurs de consigne préétablies et, en fonction du résultat de la comparaison, la température d'exploitation du dispositif d'épuration des gaz d'échappement est amenée à varier en vue d'optimiser un taux de conversion de ce dispositif. More generally, it is recalled that the invention relates to a method of operating an exhaust gas cleaning device installed in the exhaust system of an internal combustion engine, characterized in that the emission values of at least one of the

exhaust components CO, CO2, H2O, NH3, CH4, H2 or at least two, optimally at least three of the exhaust components HC, NO ,, CO, CO2, H20, NH3, CH4, O2, H2 or a pollutant containing sulfur in the exhaust gas downstream of at least a part of the gas purification device, compared with preset setpoint values and, depending on the result of the comparison, the operating temperature of the exhaust gas purification device is varied to optimize a conversion rate of this device.

 The invention also proposes a method for the diagnosis of an exhaust gas purification device installed in the exhaust system of an internal combustion engine, characterized in that the operating temperature of a part at least of the exhaust gas purification device is determined, in that the emission values of at least one of the exhaust components CO, CO2, H2O, NH3, CH4, H2 or from at least two, optimally at least three of the exhaust components HC, NO ,, CO, CO2, HsO, NH3, CH4, Os, H2 or a sulfur-containing pollutant are measured downstream of a portion of at least the exhaust gas purification device, compared with the set values depending on the value of the operating temperature and the deductions of the alteration of at least some elements of the gas cleaning device. exhaust are derived from the comparison value.

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moins deux, de façon optimale d'au moins trois des composants d'échappement HC, NOx, CO, C02, H20, NH3, CH4, O2, H2 ou d'un polluant contenant du soufre sont mesurées en amont d'un élément du dispositif d'épuration des gaz d'échappement et comparées avec des valeurs d'émission mesurées en aval d'au moins l'élément en question, un taux de conversion de l'élément ou des éléments est établi et comparé avec des valeurs de consigne de conversion dépendant de la valeur de la température d'exploitation, et en ce que des déductions sur le degré d'altération du ou des éléments sont tirées du résultat de la comparaison. It also relates to a method for the diagnosis of an exhaust gas cleaning device installed in the exhaust system of an internal combustion engine, characterized in that the operating temperature of a part at least the exhaust gas cleaning device is determined, the emission values of at least one of the exhaust components CO, CO2, H2O, NH3, CH4, H2 or from

at least two, optimally at least three of the exhaust components HC, NOx, CO, CO2, H2O, NH3, CH4, O2, H2 or a sulfur-containing pollutant are measured upstream of an element of the exhaust gas purification device and compared with emission values measured downstream of at least the element in question, a conversion rate of the element or elements is established and compared with setpoint values conversion dependent on the value of the operating temperature, and in that deductions on the degree of alteration of the element or elements are derived from the result of the comparison.

 It also proposes a method of operating at least one NOx accumulation catalyst installed in the exhaust system of an internal combustion engine and which can be operated in phases of accumulation and regeneration, characterized in that that emission values of at least one of the exhaust components CO, CO2, H2O, NH3, CH4, H2 or at least two, optimally at least three of the HC exhaust components , NOx, CO, CO2, H2O, NH3, CH4, Os, H2 or a sulfur-containing pollutant (SO2, H2S, COS) are measured downstream of the NOx accumulation catalyst (s), compared with setpoints pre-established and a lambda value of regeneration of the exhaust gas is caused to vary according to the result of the comparison by means of a device for regulating the lambda value at least during a regeneration phase.

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 The invention also relates to a method of operating at least one NOx accumulation catalyst installed in the exhaust system of an internal combustion engine, in which the emission of pollutants from the internal combustion engine is used to diagnose the sulfur contamination of the NOx accumulation catalyst, characterized in that upstream of the NOx accumulation catalyst (s), emission values of at least one of the sulfur-containing components of the exhaust gases (SOs, H28, COS) as well as at least one of the hydrocarbon components (HC), carbon monoxide (CO), ammonia (NH2) or nitrogen oxides (NOx) Exhaust rates are measured, compared with predetermined setpoint values and a degree of sulfur contamination of the NOx accumulation catalyst (s) is determined from the result of the comparison.

 It also relates to a process for removing sulfur from at least one NOx accumulation catalyst installed in the exhaust system of an internal combustion engine, wherein a minimum temperature of the NOx accumulation catalyst (s) and a lambda value less than 1 of the exhaust gas is established for a sulfur elimination time interval, characterized in that a degree of sulfur contamination is established as described above and the length of the time interval Sulfur removal is based on the established degree of sulfur contamination.

 Finally, it proposes a process for removing sulfur from at least one NOx accumulation catalyst installed in the exhaust system of an internal combustion engine, in particular according to the process just described, characterized by the downstream of the NOx storage catalyst (s), at least during a sulfur removal time interval, hydrogen sulphide (H2S) emission values and / or at least one hydrocarbon exhaust (HC) components,

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 carbon monoxide (CO), ammonia (NH3), hydrogen (H, nitrogen oxides (NOx) or other sulfur-containing exhaust component are measured and compared with pre-established setpoints, and the lambda value of the exhaust gas is varied according to the result of the comparison.

Claims (27)

A method of operating an exhaust gas cleaning device installed in the exhaust system of an internal combustion engine, characterized in that the emission values of at least one of the exhaust components CO, CO2, H2O, NH3, CH4, H2 or at least two, optimally at least three of the exhaust components HC, NO ,, CO, CO2, H2O, NH3, CH4, O2, H2 or a pollutant containing sulfur in the exhaust gas downstream of at least a part of the gas purification device, compared with preset setpoint values and, depending on the result of the comparison, the operating temperature of the exhaust gas purification device is varied to optimize a conversion rate of this device.  2. Method according to claim 1, characterized in that the operating temperature of at least a portion of the exhaust gas purification device is set to a preset value according to the result of the comparison.  Method according to Claim 1 or 2, characterized in that the operating temperature of at least a portion of the exhaust gas cleaning device is high within a pre-set temperature range up to the result of the comparison corresponds to a passage of the emission values of at least one exhaust component below the preset thresholds.  4. Method according to at least one of the preceding claims, characterized in that the operating temperature is varied during a light-off phase of the relevant part of the exhaust gas cleaning device.  5. Method according to any one of the preceding claims, characterized in that the exhaust gas purification device comprises at least one <Desc / Clms Page number 31>  catalyst and in that under the action of a device for adjusting or regulating the lambda values from an exhaust gas lambda value greater than 1, for a comparison performance which corresponds to a passage below the preset thresholds of the emission values downstream of the three-way catalyst, the lambda value is reduced to a preset value, preferably lambda = 1.  6. Process according to any one of the preceding claims, characterized in that the exhaust gas purification device comprises at least one precatalyst preferably produced as a three-way catalyst, preferably a three-way catalyst, and at least one NO. accumulation catalyst, installed downstream of the precatalyst, and in that the measurement of the emission values is carried out downstream of the precatalyst (s) and / or the NOx accumulation catalyst (s).  7. Method according to any one of the preceding claims, characterized in that in the presence of an exhaust gas purification device comprising at least two elements, the operating temperature of the individual elements is varied. separately.  8. A method for the diagnosis of an exhaust gas cleaning device installed in the exhaust system of an internal combustion engine, characterized in that the operating temperature of at least a part of the device exhaust gas purification is determined, in that the emission values of at least

 one of the exhaust components CO, COs, H20, NH3, CH4, H2 or at least two, optimally at least three of the exhaust components HC, NOx, CO, CO2, H20, NH3 , CH4, 02, H2 or a sulfur-containing pollutant are measured downstream of at least a portion of the exhaust gas purification device, compared with the set values depending on the temperature value of the exhaust gas. exploitation, and <Desc / Clms Page number 32>  deductions from the alteration of at least some elements of the exhaust gas cleaning device are derived from the comparison value.  9. A method for the diagnosis of an exhaust gas cleaning device installed in the exhaust system of an internal combustion engine, characterized in that the operating temperature of at least a part of the device of the exhaust gases is determined, in that the emission values of at least one of the exhaust components CO, COs, H2O, NH3, CH4, H2 or at least two, of at least three of the exhaust components HC, Nitrogen, CO, CO2, H2O, NH3, CH4, O21 H2 or a sulfur-containing pollutant are measured upstream of an element of the water purification device. exhaust gas and compared with emission values measured downstream of at least the element in question, a conversion rate of the element or elements is established and compared with conversion dependent setpoint values of the value of the operating temperature, and in that deductions on the degree of alteration element (s) are derived from the result of the comparison.  Method according to one of Claims 8 and 9, characterized in that the emission value measurement is carried out in the range of a pre-established temperature window of at least one element of the gas cleaning device. 'exhaust.  11. A method according to any one of claims 8 to 10, characterized in that a light-off temperature of at least one element of the exhaust gas purification device is determined from the emission values. measured and compared with a predetermined set value, depending in particular on the lambda value of the exhaust gases, and in that deductions on the deterioration of the element in question are taken from the result of the comparison. <Desc / Clms Page number 33>  12. Process according to any one of Claims 8 to 11, characterized in that the exhaust gas purification device comprises at least one precatalyst preferably produced as a three-way catalyst and / or at least one catalyst for accumulation. of NOx installed downstream of the precatalyst.  13. The method of claim 12, characterized in that the diagnosis for each element of the exhaust gas purification device is performed separately.  14. A method according to one of claims 8 to 13, characterized in that the set value of the light-off temperature is determined from the light-off temperature of elements that have not yet been used. an exhaust gas purification device.  15. A method according to one of claims 8 to 14, characterized in that in the presence of an alteration of at least one element of the exhaust gas purification device, an indicator device is activated and / or a disturbance message is logged in a data memory.  Method according to one of the preceding claims, characterized in that the value of a throttle valve position, an exhaust gas recirculation rate, an ignition timing, a several times of injection of a charge movement valve, a charge pressure and / or an additional quantity of fuel is modified with a view to varying the operating temperature of the catalyst device.  17. A method of operating at least one NOx accumulation catalyst installed in the exhaust system of an internal combustion engine and operable in accumulation and regeneration phases, characterized in that for emitting at least one of the exhaust components CO, CO2, H2O, NH3, CH4, H2 or at least two, optimally at least three of the exhaust components HC, NOx, CO, CO2, H2O, NH3, CH4, O2, <Desc / Clms Page number 34>  H2 or a sulfur-containing pollutant (SOs, HsS, COS) are measured downstream of the NOx accumulation catalyst (s), compared with pre-established setpoint values and a lambda value for regeneration of the exhaust gas is brought to vary according to the result of the comparison by means of a device for regulating the lambda value at least during a regeneration phase.  18. A method according to claim 17, characterized in that the regeneration phase is terminated depending on the time at which the result of the comparison corresponds to a breakthrough of one or more of the relevant components of the exhaust gas.  19. A method according to claim 17 or 18, characterized in that the lambda regeneration value is high by a pre-established amount depending on the moment of a breakthrough of one or more of the relevant components of the exhaust gas, during at least one subsequent regeneration phase.  20. Process according to one of Claims 17 to 19, characterized in that the regeneration lambda value is raised from a pre-established starting value during a regeneration phase until a pre-established stopping value has been reached.  A method of operating at least one NOx storage catalyst installed in the exhaust system of an internal combustion engine, wherein pollutant emission from the internal combustion engine is used to diagnose the contamination by sulfur of the NOx accumulation catalyst, characterized in that upstream of the NOx accumulation catalyst (s), emission values of at least one of the sulfur-containing components of the exhaust gases (SOz , H2S, COS) as well as at least one of the hydrocarbon (HC), carbon monoxide (CO), ammonia (NH2) or nitrogen oxide (NOx) components of the exhaust gas are measured, compared with pre-established setpoints, and a degree of contamination by the <Desc / Clms Page number 35>  The sulfur of the NOx accumulation catalyst (s) is determined from the result of the comparison.  22. Process according to Claim 21, characterized in that downstream of the accumulation catalyst (s)

 of NOx, emission values of at least one of the sulfur-containing components (SO2, H2S, COS) of the exhaust gas and / or at least one of the hydrocarbon (HC), monoxide components carbon (CO), hydrogen (H2), ammonia (NH3) or nitrogen oxide (NOx) exhaust gases are measured and compared with emission values measured upstream, and in that a balance of sulfur is established from the result of the comparison and a degree of sulfur contamination of the NOx accumulation catalyst (s) is deduced from this balance.  23. A method for removing sulfur from at least one NOx storage catalyst installed in the exhaust system of an internal combustion engine, wherein a minimum temperature of the NOx storage catalyst (s) and a lower lambda value to 1 of the exhaust gases are established for a sulfur removal time interval, characterized in that a degree of sulfur contamination is established according to one of claims 21 and 22 and the length of the gap Sulfur removal time is set based on the established degree of sulfur contamination.  24. Process for the removal of sulfur from at least one NOx accumulation catalyst installed in the exhaust system of an internal combustion engine, in particular according to claim 23, characterized in that downstream from or NOx accumulation catalysts, at least during a sulfur removal time interval, hydrogen sulfide (H2S) emission values and / or at least one of the hydrocarbon exhaust components ( HC), carbon monoxide (CO), ammonia (NH3), hydrogen (H2), nitrogen oxide (NOx) or other sulfur-containing exhaust component are <Desc / Clms Page number 36>  measured and compared with predefined setpoint values, and in that the lambda value of the exhaust gas is varied according to the result of the comparison.  25. A method according to claim 24, characterized in that a lambda value greater than 1 is set from a lambda value less than 1 of the exhaust gas for a comparison result which corresponds to a breakthrough of the sulfide of hydrogen.  26. A method according to any one of the preceding claims, characterized in that the exhaust gas purification device comprises a particle filter, a particle catalyst or a continuous reducing device attenuating the particles.  Method according to one of the preceding claims, characterized in that the measurement of the exhaust gas component (s) is carried out by means of an optical sensor, in particular an infrared sensor, optimally by means of of a reflection infrared spectroscopy sensor.