DE10153901A1 - Process for desulfurizing NOx accumulation catalyst placed downstream of diesel engine by altering amount of fuel injected into working cycle of cylinder(s) of engine - Google Patents

Abstract

Control of the exhaust gas lambda during the alternation phase is by altering the amount of fuel injected into the working cycle of at least one cylinder of the engine The catalyst is heated to a desulfurization temperature during a heating phase (TH) and is supplied with exhaust gas during a consecutive oscillation phase (TW) alternating between a dense lambda ( lambda <= 1) and a weak lambda ( lambda \>1) around a predetermined mean lambda. The amount of fuel injected is influenced by the duration of injection into the cylinder's working cycle, particularly the duration of a main injection starting before top dead center of the cylinder or by the post-injection duration starting at top dead center to establish the mean value of lambda for the exhaust gases including the main injection and possibly a pre-injection. During the alternation phase, the function parameters such as rate of introduction of exhaust gas, position of the butterfly throttle, inlet pressure, fuel injection system pressure, start-up of pre-injection, main injection and post-injection and duration of injection not influenced by control of lambda are held at least approximately constant., taken from the prior reheating phase. The engine torque is held constant during the alternation phase by adapting the exhaust reintroduction

Description

The invention relates to processes for the desulfurization of a NO _x storage catalytic converter connected downstream of a diesel engine with the features mentioned in the preamble of independent claims 1 and 11 and to an apparatus for carrying out the process according to the preamble of claim 18.

In the course of ever stricter legal exhaust gas limit values for internal combustion engines of motor vehicles, the development of increasingly effective methods for exhaust gas aftertreatment is necessary. In the case of self-igniting internal combustion engines (diesel engines), the focus of the developments is on the reduction of particle and nitrogen oxide emissions. Particle emissions can already be reduced effectively today by using regenerable particle filters. It is also known to reduce a raw emission of nitrogen oxides NO _x , the catalytic conversion of which causes problems particularly in lean-burn internal combustion engines, by means of exhaust gas recirculation measures. Part of an exhaust gas flow is removed from the internal combustion engine and fed to the combustion chamber, as a result of which a combustion temperature is lowered and the formation of nitrogen oxides is thus reduced. However, since exhaust gas recirculation in turn causes an increase in particle emissions, there are limits to their application.

To reduce the final NO _x emissions, the use of NO _x storage catalytic converters is therefore known, in particular in the case of spark-ignition internal combustion engines (gasoline engines). According to the present state of the art include a NO _x storage catalytic converters is usually based on a barium salt NO _x storage component, and a 3-way catalytic component, for the conversion of unburned hydrocarbons HC, carbon monoxide CO and NO _X. The catalyst component usually consists of platinum, rhodium and / or palladium. In a lean operating mode of the internal combustion engine, in which a complete 3-way catalytic conversion of nitrogen oxides is not possible due to the excess of oxygen in the exhaust gas, NO _x in the form of nitrate is absorbed by the storage component. In exhausted storage capacity of the NO _x -storage device in periodically performed regeneration phases denitrification of the NO _x -storage device is carried out, wherein the _NOx - storage catalyst for a short time, typically for about 5 seconds, with a rich exhaust gas atmosphere in a preferred temperature range of 200 to 350 ° C is applied (NO _X regeneration). Under these conditions, NO _{x is desorbed} from the storage and the catalyst component is reduced to nitrogen.

A sulfur content contained in today's fuels is a problem for NO _x storage catalysts, since the sulfur, which is mainly present as SO ₂ in the exhaust gas, also competes with NO _x in the NO _x storage component in the sulfate farm. The storage spaces occupied by the sulfur are then no longer available for NO _x absorption, so that there is a decrease in the NO _x storage capacity and the NO _x conversion rate. The sulfur storage is not reversible under the conditions of NO _x regeneration. Rather, the desorption of sulfur requires significantly higher catalyst temperatures, usually above 600 ° C, and significantly longer phases of the rich exhaust gas application, for example, over 240 s. For this reason, it is known to carry out a desulfurization under the above-mentioned conditions in the case of sulfur poisoning, which is recognized on the basis of a decreasing NO _x conversion rate. For this purpose, the NO _x storage catalytic converter is first heated to a temperature which corresponds at least approximately to a catalytic converter-specific minimum desulfurization temperature in a heating phase by means of suitable engine measures. The actual desulfurization then takes place by exposing the NO _x storage catalytic converter to a stoichiometric or rich exhaust gas atmosphere.

Furthermore, it is known, for example from DE 198 35 808, to apply grease to the NO _x storage catalytic converter during desulfurization in a so-called wobble mode, in which the internal combustion engine changes rapidly by an average lambda value of λ = 1 is operated. Due to the short lean phases that occur, oxygen is stored in the NO _x storage catalytic converter, whereby an evolution of hydrogen sulfide H ₂ S can be effectively countered in favor of the formation of sulfur dioxide SO ₂ .

In practice, the use of NO _x storage catalytic converters for diesel engines has not yet been realized. This is due in particular to the fact that, due to their heterogeneous mixture formation, diesel engines are not readily operable under the rich operating conditions necessary for the desulfurization of the NO _x storage catalytic converter. In particular, a reliable ignition cannot be guaranteed with a substoichiometric mixture composition and disadvantageous torque fluctuations must be expected.

The invention is therefore based on the object of providing a process for the desulfurization of a NO _x storage catalytic converter in diesel engines, in which an emission of hydrogen sulfide H ₂ S, carbon oxide sulfide COS and carbon disulfide CS _{2 is} largely suppressed and at the same time reliable ignition and high torque neutrality guaranteed. In particular, the method is intended to ensure quick and accurate lambda control. In addition, a device is to be provided; with which the method can be carried out.

This object is achieved by methods having the features mentioned in independent claims 1 and 11 and by an apparatus according to claim 18. Both methods can be combined particularly advantageously. According to the first method according to the invention, the exhaust gas lambda is regulated during the alternating exhaust gas treatment of the NO _x storage catalytic converter by influencing an injected fuel quantity of at least one injection of a working cycle of at least one cylinder of the diesel engine. According to the invention, the injected fuel quantity is thus used as the actual manipulated variable for regulating the air-fuel ratio during the wobble phase. Compared to the lambda control, which is usually air-side in gasoline engines, the fuel-side control offers the advantage of being able to set the desired air conditions very quickly, at the engine's operating cycle speed, and with high precision. It has proven to be particularly advantageous to influence the amount of fuel injected over a control period of the at least one injection taking place in the working cycle. In standard operation, diesel engines are usually operated with two fuel injections, one pre-injection and one main injection. The activation duration of the main injection for lambda control can preferably be varied here. A lambda reduction (enrichment) required for desulfurization of the NO _x storage catalytic converter is particularly advantageously realized by an additional post-injection carried out after top dead center. In this case, it is particularly advantageously provided to influence the amount of fuel over the activation period of the post-injection.

With the exception of the control duration of the relevant one used for lambda control All other parameters relevant to combustion during the wobble Operation kept at least approximately constant, with a map-dependent Control is provided. The parameters include in particular an exhaust gas recirculation rate, an intake manifold throttle valve position, a boost pressure, a rail pressure Fuel injection system, especially a high pressure injection system, Activation starts of pre, main and post injection as well as the activation duration of the respective injections not influenced for lambda control. In doing so preferably by regulation or during the previous heating phase Pre-control set operating parameters adopted.

The average exhaust lambda in wobble mode is in particular 0.97 to 1.03, preferably 0.99 to 1.01 and particularly advantageously exactly 1.00.

According to a particularly advantageous embodiment of the method, an engine torque delivered by the diesel engine to a transmission is kept constant with respect to an engine torque delivered before wobble operation during the alternating exhaust gas application of the NO _x storage catalytic converter. This is preferably done by adapting the exhaust gas recirculation rate as a function of a deviation of the amount of fuel injected before wobble operation from an average amount of fuel injected during wobble operation.

According to the second method according to the invention, the exhaust gas lambda is regulated during a heating phase of the NO _x storage catalytic converter preceding the wobble phase by influencing an exhaust gas recirculation rate (manipulated variable), with all of the above-mentioned combustion-relevant operating parameters, such as intake manifold throttle valve position, boost pressure, rail pressure, activation start and activation duration from before -, main and post-injection, can be pilot-controlled depending on the map. The advantage of lambda control over the exhaust gas recirculation rate over control over fuel quantity is a lower sensitivity to control deviations.

The present object is further achieved by a device which is characterized by means with which a control of the exhaust gas lambda during the heating-up phase of the NO _x storage catalytic converter can be carried out by influencing an exhaust gas recirculation rate of an exhaust gas recirculation assigned to the diesel engine and / or with which a control of the exhaust gas lambda during the alternating exhaust gas application of the NO _x storage catalytic converter (wobble phase) by influencing an injected fuel quantity at least one injection of a work cycle of at least one cylinder of the diesel engine.

The means preferably comprise an algorithm for performing the regulation of the exhaust gas lambda during the heating phase and / or during the alternating exhaust gas application of the NO _x storage catalytic converter in digital form. The algorithm can be integrated in a control unit, in particular in a conventional engine control unit.

Further preferred refinements of the invention result from the others in the Characteristics mentioned subclaims.

The invention is described in an exemplary embodiment based on the associated Drawings explained in more detail. Show it:

Figure 1 shows schematically a diesel engine with a downstream exhaust system.

FIG. 2 shows time profiles of vehicle speed, exhaust gas lambda and activation times of pre-injection, main injection and post-injection during desulfurization of a NO _x storage catalytic converter according to FIG. 1;

FIG. 3 is time profiles of control start of pilot, main and post injection during the desulphurization;

Fig. 4 temporal courses of throttle valve position, exhaust gas recirculation rate, boost pressure and rail pressure during desulfurization and

Fig. 5 time courses of temperatures at different locations of the diesel engine and the exhaust system during desulfurization.

A diesel engine 10 shown in FIG. 1 comprises, for example, four cylinders 12 , into which direct fuel injection takes place with the aid of a high-pressure injection system 14 , also indicated. Air is supplied to the cylinders 12 of the diesel engine 10 via an air intake pipe 16 , in which a throttle valve 18 for regulating an intake air mass is arranged via a throttle valve actuator, not shown here. An exhaust gas turbocharger, also not shown, can also be provided for compressing the air mass supplied to the cylinders 12 .

The diesel engine 12 is also equipped with an exhaust gas recirculation device 20 . This comprises an exhaust gas recirculation line 22 , via which an exhaust gas partial flow from an exhaust gas duct 24 connected downstream of the diesel engine 10 is removed and supplied to the air mass sucked in and thus combustion chambers of the cylinders 12 . An exhaust gas recirculation rate (EGR rate) can be variably set with the aid of an EGR valve 26 arranged in the exhaust gas recirculation line 22 by means of an EGR actuator (not shown). The measure of exhaust gas recirculation lowers the combustion temperature in the cylinders 12 . Due to a pronounced temperature sensitivity of the nitrogen oxide formation of the combustion process, a reduction in the raw NO _x emission of the diesel engine 10 is achieved by the exhaust gas recirculation. Because of an increased tendency to particle formation with increasing EGR rates, exhaust gas recirculation is limited.

All combustion-relevant parameters are controlled or regulated by an engine control unit 28, depending in part on stored engine speed and engine load-dependent maps. In particular, the EGR rate is predetermined and controlled by the engine control unit 28 by controlling the EGR valve 26 , the air mass supplied to the diesel engine 10 by controlling the position of the throttle valve 18 and a boost pressure of the turbocharger (not shown). The engine control unit 28 also specifies all injection parameters of the high-pressure injection system 14 . These are, in particular, a rail pressure with which the fuel is injected into the combustion chamber, the number of injections during a working cycle of a cylinder 12, and the activation starts and activation durations of the various injections.

An exhaust gas generated by the diesel engine 10 is aftertreated in an exhaust gas system designated by 30 in order to reduce the pollutant emissions. The exhaust system 30 comprises a catalyst system 32 , 34 arranged in the exhaust duct 24 and a number of different sensors 36 , 38 , 40 , 42 . In an advantageous embodiment, the catalytic converter system contains a small-volume oxidation pre-catalytic converter 32 arranged close to the engine, which mainly supports the conversion of unburned hydrocarbons HC and carbon monoxide CO and nitrogen monoxide NO to nitrogen dioxide NO ₂ . A large-volume, downstream NO _x storage catalytic converter 34 absorbs 10 nitrogen oxides NO _{x from} the exhaust gas in lean operating phases of the diesel engine and releases them again in short interposed rich regeneration phases and reduces them to nitrogen.

The air / fuel mixture of the diesel engine 10 is monitored and regulated by measuring the exhaust gas lambda with an oxygen-sensitive measuring device 36 , which is in particular a lambda probe, preferably a broadband lambda probe. Monitoring of the NO _x conversion activity of the storage catalytic converter 34 is advantageously carried out with a NO _x sensor 38 connected downstream thereof, which measures a concentration of nitrogen oxides in the exhaust gas. Optionally, upstream and / or downstream of the storage catalytic converter 34, temperature sensors 40 , 42 are arranged, which detect an exhaust gas temperature and allow the determination of the catalytic converter temperature of the storage catalytic converter 34 . All signals provided by sensors 36 , 38 , 40 , 42 are transmitted to engine control unit 28 and processed further. The engine control unit 28 controls the various operating parameters of the diesel engine 10 as a function of these signals. For example, when the conversion rate of the NO _x storage catalytic converter 34 is detected by the NO _x sensor 38 , the diesel engine 10 is briefly tuned to a rich mixture in order to bring about a regeneration of the storage catalytic converter 34 . In particular, engine control unit 28 also includes an algorithm 44 for performing desulfurization of NO _x storage catalytic converter 34 in accordance with the present invention.

The procedure according to the invention for the desulfurization of the NO _x storage catalytic converter 34 will be explained with reference to FIGS. 2 to 5. These figures show the time profiles of different operating parameters of the diesel engine 10 as well as different control, manipulating and regulating variables during the execution of a desulfurization according to an advantageous embodiment of the method according to the invention. The starting point of the method is the determination of sulfurization of the NO _x storage catalytic converter 34 . The monitoring can be of Verschwefelungsgrades of the NO _x storing catalyst 34 by the downstream _NOx sensor 38, the example of the storage catalyst 34, a critical breakthrough NO _x detected in the lean operation performed despite a NO _X regeneration. Alternatively, the degree of sulfurization can also be mathematically modeled by the engine control unit 28 as a function of suitable operating parameters of the diesel engine 10 , such as engine speed, engine load and / or vehicle speed.

If a desulfurization requirement has been determined, it is first checked whether there is an operating point of the engine 10 that is favorable for desulfurization. For example, a vehicle speed (curve 50 , FIGS. 2 to 5) of between 50 and 160 km / h, in particular between 70 and 141) km / h, should be present for carrying out the desulfurization. Desulphurization can be carried out particularly advantageously at a speed of between 90 and 100 km / h, since relatively high exhaust gas temperatures are already present in this area and torque compensation is possible over a wide range.

If the above conditions are met, a heating phase TH is first initiated in order to heat the NO _x storage catalytic converter 34 at least approximately to the required minimum desulfurization temperature. This is dependent on the nature of the catalyst and is approximately 550 ° C. in the present example. The catalyst 34 is heated by lowering the initially lean air-fuel mixture to an essentially stoichiometric ratio with λ = 1. Shown in FIGS. 2 to 5 is the exhaust gas lambda measured with the broadband lambda probe 36 (curve 52 ). Deviatingly, a slightly lean lambda in the range from 1 to 1.3 can be set during the heating phase, with a final switchover to λ = 1 at the end of the heating phase TH.

According to the preferred embodiment shown, the necessary enrichment takes place by post-injection of fuel into at least one cylinder 12 after top dead center. In the present example, the post-injection takes place with an activation start at 33 ° KWnOT (curve 54 in FIG. 3). The start of pilot injection (curve 56 ) and main injection (curve 58 ) are slightly advanced compared to the lean operation of the diesel engine 10 , here to 35 and 10 ° KWvOT. The fuel injected only partially participates in the combustion. In order to compensate for the portion participating in the combustion and the torque generated thereby, the activation duration of the main injection is reduced (curve 60 in FIG. 2). The activation duration according to the example shown during the heating phase TH is 180 microseconds for the pre-injection (curve 62 ), 320 microseconds for the main injection (curve 60 ) and 500 microseconds for the post-injection (curve 64 ). Monkey values given here for the various parameters are predefined as a function of a current operating point of diesel engine 10 , in particular engine speed and load, and can therefore differ considerably in individual cases from the values mentioned here as examples.

Just like the control periods mentioned (curves 60 , 62 , 64 in FIG. 2) and start of control (curves 54 , 56 , 58 in FIG. 3) of the various injections, the other combustion-relevant parameters - with the exception of the exhaust gas recirculation rate - also become during the heating phase TH piloted to largely constant map-dependent specifications. As can be seen in FIG. 4, these are, in particular, the position of the throttle valve 18 , which is represented by the size of the duty cycle of the throttle valve actuator (curve 66 ), the boost pressure represented by the boost pressure actuator of the exhaust gas turbocharger (curve 68 ) and the rail pressure ( Curve 70 ), which in the illustration in FIG. 4 (lying at 820 bar) is essentially covered by the course of the exhaust gas lambda 52 .

In the heating phase TH, the exhaust gas lambda (curve 52 ) measured by the broadband lambda probe 36 is regulated by influencing the exhaust gas recirculation rate to the desired target from here λ = 1. The required control interventions therefore lead to fluctuations in the duty cycle of the EGR actuator during the heating phase TH (curve 72 ).

By lowering the lambda from the original lean lambda to λ = 1 in the heating phase TH, an increase in the combustion temperature and thus the catalyst temperatures is achieved on the one hand. This is particularly evident from the course of the exhaust gas temperature upstream of the oxidation catalytic converter 32 (curve 74 ) shown in FIG. 5, which shows a sharp increase immediately after the post-injection has started. A further heating effect is achieved by the fuel not participating in the combustion of the fuel quantity supplied by the post-injection. The post-injected fuel leads to an increase in unburned hydrocarbons HC and carbon monoxide CO in the exhaust gas, which are mainly converted (afterburning) on the oxidation catalytic converter 32 . The exothermic nature of the catalytic afterburning leads to heating of the oxidation catalytic converter 32 and the exhaust gas temperature downstream of the oxidation catalytic converter 32 (curve 76 ). Storage catalyst 34 observed only with some time delay, an increase in exhaust gas temperature as well as certain heat losses (curve 78) - due to an exhaust gas transit time between oxidation catalyst 32 and NO _X storage catalyst 34 is upstream of the NO _X. As the course of the exhaust gas temperature behind the NO _x storage catalytic converter 34 (curve 80 ) illustrates, heating of the storage catalytic converter 34 again takes place with a considerable time delay, which is mainly due to the thermal inertia of the relatively large catalyst mass. Furthermore, 5 are shown in Fig. With the curves 82 and 84 upstream of the curves of the exhaust gas temperatures or downstream of the turbocharger shown, which also reflect the heating of the exhaust gas.

As soon as the NO _x storage catalyst 34 has a minimum desulfurization temperature, the actual sulfur discharge from the NO _x storage catalyst 34 begins by thermal dissociation of the embedded sulfate in SO ₃ and subsequent reduction on the catalyst component. It is known that at a constant loading of the catalyst 34 with a rich exhaust gas atmosphere due to the substantial absence of oxygen in the exhaust gas, and an oxygen storage of the NO _X - storage catalytic converter 34 the sulfur for the most part in the form of hydrogen sulfide H ₂ S, carbonyl sulfide COS and Carbon disulfide CS _{2 is} discharged. However, these compounds are odorous and / or toxic, which is why their formation should be largely suppressed. A so-called wobble phase TW suggests storage catalytic converter 34 is introduced, during the fast in one of the NO _X storing catalyst 34 - Therefore, when using the temperature sensors 40, 42 a temperature is detected, to a predeterminable desulphurization of the NO _X Change with a rich and lean exhaust gas lambda is applied. The short lean phases partially fill the oxygen store of the NO _x storage catalytic converter 34 , as a result of which the released SO ₃ in the fat phases is reduced and discharged only up to the oxidation level of the SO ₂ . According to the present invention, the "wobbling" around an average exhaust gas lambda of λ = 1 is preferably carried out, which was already regulated at least at the end of the preceding heating phase TH. The lean specification of the wobble phase TW is advantageously set to a maximum of 1.10, preferably to 1.05, and the fat specification to a minimum of 0.90, preferably to 0.95.

According to the invention, the exhaust gas lambda is regulated during the wobble phase TW by influencing the fuel quantity, in particular that of the post-injection. This is preferably carried out by changing the control duration of the post-injection ( FIG. 2, curve 64 ), which permits particularly rapid and precise control. The fastest possible lambda controller should be used for this.

The control parameters for the control periods of pre and main injection, the start of pilot, main and post injection, throttle valve position, boost pressure and rail pressure are also pre-controlled during the wobble phase TW, whereby the specifications of the heating phase TH are adopted. Furthermore, the duty cycle of the TCS adjuster present at the end of the heating phase TH is "frozen" and initially also adopted ( FIG. 4, curve 72 ).

In order to ensure the highest possible torque neutrality during the wobble phase TW, the amount of fuel injected in the wobble phase TW is adjusted to the amount of fuel injected in the heating phase TH. For this purpose, a temporal mean value of the fuel quantity or the activation duration of the injection that is used for the lambda control, in the present case the post-injection, is determined during the alternating loading of the NO _x storage catalytic converter 34 . This mean value is then compared with the fuel quantity or the activation duration of the relevant injection during the heating phase TH. If a deviation between the average fuel quantity / activation duration is found before and during wobble operation, the exhaust gas recirculation rate is corrected.

This change in the EGR rate takes place - depending on a sign of the Deviation - towards a higher or lower EGR rate and will preferably by gradually adjusting the duty cycle of the EGR actuator carried out.

Various strategies are conceivable for determining the step size. First of all, one fixed increments that are used so often until practically none Deviation from the mean is more detected. In another possibility, the Step size depending on the amount of the deviation of the mean value below Application of a stored characteristic curve determined. Finally, the increment is conceivable depending on the level of the mean deviation and the initial value of the first frozen duty cycle of the EGR controller using an appropriate Map.

Thus, while the lambda control over the activation duration of the post-injection (curve 64 ) is still active while maintaining the rich and lean lambda specifications, the described EGR correction automatically reduces the deviation of the average activation duration of the post-injection from that pre-controlled before wobble operation Activation duration of the post-injection. As soon as the control periods are equalized, the duty cycle of the EGR controller or the EGR rate is frozen again.

It can also be advantageously provided to monitor the exhaust gas temperature during the desulfurization by means of the temperature sensor 42 connected downstream of the NO _x storage catalytic converter 34 in order to detect temperature peaks caused by the exothermic combustion of HC. If a critical temperature which damages the NO _x storage catalytic converter 34 is detected in this way, the desulfurization is first interrupted until sufficient cooling is found, and then initiated again (as described) and carried out to the end.

After the desulfurization has ended, all parameters relevant to combustion or the corresponding steeper are reset to their initial state. REFERENCE SIGN LIST 10 Diesel engine
12 cylinders
14 high pressure injection system
16 air intake pipe
18 throttle valve
20 exhaust gas recirculation device
22 Exhaust gas recirculation line
24 exhaust duct
26 Exhaust gas recirculation valve
28 Engine control unit
30 exhaust system
32 Oxidation catalyst
34 NO _x storage catalytic converter
36 Broadband lambda sensor
38 NO _X sensor
40 temperature sensor
42 temperature sensor
50 vehicle speed
52 Lambda
54 Start of post-injection control
56 Start of pilot injection
58 Start of main injection control
60 Activation period for main injection
62 Pre-injection activation duration
64 Post injection duration
66 Throttle actuator duty cycle
68 Duty cycle charge pressure switch
70 rail pressure
72 Duty cycle EGR actuator
74 Exhaust gas temperature upstream of the oxidation catalytic converter
76 Exhaust gas temperature after oxidation catalytic converter
78 Exhaust gas temperature before NO _x storage catalytic converter
80 Exhaust gas temperature after NO _x storage catalytic converter
82 Exhaust gas temperature before turbocharger
84 Exhaust gas temperature after exhaust gas turbocharger
TH heating phase
TW wobble phase

Claims (20)

1. A process for desulfurization of a diesel engine (10) downstream NO _X - storage catalyst (34), wherein the NO _x storage catalyst is heated (34) during a heating phase (TH) at least approximately to a desulfurization temperature, and in a subsequent wobble phase ( TW) is alternately acted upon by a rich exhaust gas lambda with λ <1 and a lean exhaust gas lambda with λ> 1 in the case of a predeterminable mean exhaust gas lambda, characterized in that regulation of the exhaust gas lambda during the alternating exhaust gas application (TW) of the NO _x storage catalytic converter ( 34 ) by influencing an injected fuel quantity of at least one injection of a working cycle of at least one cylinder ( 12 ) of the diesel engine ( 10 ). 2. The method according to claim 1, characterized in that during the alternating exhaust gas application (TW) of the NO _x storage catalytic converter ( 34 ), the injected fuel quantity is influenced over a control period of the at least one injection of the working cycle of the cylinder ( 12 ). 3. The method according to claim 2, characterized in that the amount of fuel injected is influenced over the activation period of a main injection beginning before an upper dead center of the at least one cylinder ( 12 ). 4. The method according to claim 2, characterized in that the injected Fuel quantity over the activation period of one for the production of the middle one Exhaust Lambda in addition to the main and / or a pre-injection and post-injection beginning after top dead center is influenced. 5. The method according to any one of the preceding claims, characterized in that the operating parameters exhaust gas recirculation rate, intake manifold throttle valve position, boost pressure, rail pressure of a fuel injection system ( 14 ), start of actuation of pre, main during the alternating exhaust gas (TW) of the NO _x storage catalyst ( 34 ) and post-injection and control duration of the injection not influenced for lambda control are controlled at least approximately constant. 6. The method according to claim 7, characterized in that during the alternating exhaust gas (TW) of the NO _x storage catalyst ( 34 ), the operating parameters of the previous heating phase (TH) are adopted at least initially. 7. The method according to any one of the preceding claims, characterized in that during the alternating exhaust gas application (TW) of the NO _x storage catalytic converter ( 34 ), an engine torque of the diesel engine ( 10 ) with respect to an engine torque output before the alternating exhaust gas application is at least largely constant by adjusting the exhaust gas recirculation rate is held. 8. The method according to claim 7, characterized in that a change in Engine torque during alternating exhaust gas exposure (TW) Comparison of an average amount of fuel during the alternating Exhaust gas exposure (TW) for lambda control compared to injection the amount of fuel injected before the alternating exhaust gas supply Injection is determined. 9. The method according to any one of the preceding claims, characterized in that during the alternating exhaust gas application (TW) of the NO _x storage catalytic converter ( 34 ), the average exhaust gas lambda is 0.97 to 1.03, in particular 0.99 to 1.01. 10. The method according to any one of the preceding claims, characterized in that the rich exhaust gas lambda ≥ 0.90, in particular 0.95, and the lean exhaust gas lambda ≤ 1.10 during the alternating exhaust gas application (TW) of the NO _x storage catalyst ( 34 ) , in particular 1.05. 11. A process for the desulfurization of a diesel engine (10) downstream NO _X - storage catalyst (34), wherein the NO _x storage catalyst is heated (34) during a heating phase (TH) at least approximately to a desulfurization temperature, and in a subsequent wobble phase ( TW) is alternately acted upon by a rich exhaust gas lambda with λ <1 and a lean exhaust gas lambda with λ> 1 in the case of a predeterminable mean exhaust gas lambda, characterized in that the exhaust gas lambda is regulated during the heating phase (TH) of the NO _x storage catalytic converter ( 34 ) An exhaust gas recirculation rate of an exhaust gas recirculation device ( 26 ) assigned to the diesel engine is influenced. 12. The method according to claim 11, characterized in that during the heating phase (TH) of the NO _x storage catalytic converter ( 34 ), the operating parameters intake manifold throttle valve position, boost pressure, rail pressure of a fuel injection system, start of pre-injection, main injection and post-injection and activation duration of pre-injection, Main and post-injection can be pilot-controlled depending on the map. 13. The method according to claim 11 or 12, characterized in that during the Heating phase (TH) the mean exhaust gas lambda to λ ≥ 1, in particular to 1 to 1.3, is regulated. 14. The method according to any one of the preceding claims, characterized in that the desulfurization at a speed of a vehicle driven by the diesel engine ( 10 ) between 50 and 160 km / h, in particular between 70 and 140 km / h, in particular between 90 and 100 km / h, is carried out. 15. The method according to any one of the preceding claims, characterized in that a degree of sulfurization of the NO _x storage catalyst ( 34 ) on the basis of a NO _x storage catalyst ( 34 ) downstream NO _x sensor ( 38 ) or depending on the operating parameters of the diesel engine ( 10 ) is determined by calculation. 16. The method according to any one of the preceding claims, characterized in that the exhaust gas lambda is measured via an oxygen-sensitive measuring device ( 36 ), in particular a lambda probe, in particular a broadband lambda probe. 17. The method according to any one of the preceding claims, characterized in that the catalyst temperature of the NO _x storage catalytic converter ( 34 ) is determined using an exhaust gas temperature measured upstream and / or downstream of the NO _x storage catalytic converter ( 34 ) with a temperature sensor ( 40 , 42 ) and / or is mathematically modeled. 18. A device for the desulfurization of a diesel engine (10) downstream NO _X - storage catalyst (34), wherein the NO _x storage catalyst is heated (34) during a heating phase (TH) at least approximately to a desulfurization temperature, and in a subsequent wobble phase ( TW) is alternately acted upon by a rich exhaust gas lambda with λ <1 and a lean exhaust gas lambda with λ> 1 at a predeterminable mean exhaust gas lambda, characterized by means with which the exhaust gas lambda is regulated during the heating phase (TH) of the NO _x storage catalytic converter ( 34 ) can be carried out by influencing an exhaust gas recirculation rate of an exhaust gas recirculation device ( 22 ) assigned to the diesel engine and / or with which the exhaust gas lambda can be regulated during the alternating exhaust gas application (TW) of the NO _x storage catalytic converter ( 34 ) by influencing an injected fuel quantity of at least one injection of a work cycle at least at least one cylinder ( 12 ) of the diesel engine ( 10 ) can be carried out. 19. The apparatus according to claim 18, characterized in that the means an algorithm ( 44 ) in digital form for performing the control of the exhaust gas lambda during the heating phase (TH) of the NO _x storage catalyst ( 34 ) and / or during the alternating exhaust gas application (TW ) of the NO _x storage catalyst ( 34 ). 20. The apparatus according to claim 19, characterized in that the algorithm ( 44 ) is integrated in a control unit, in particular in an engine control unit ( 28 ).