DE10302700A1 - Process for diagnosing a nitrogen oxides storage catalyst arranged in exhaust gas tract of a lean-burn combustion engine, comprises determining and evaluating a storage value for differential diagnosis during deactivation of the catalyst - Google Patents

Abstract

Process for diagnosing a NOx storage catalyst arranged in the exhaust gas tract of a lean-burn combustion engine comprises determining and evaluating a NOx storage value for differential diagnosis during deactivation of the catalyst based on thermal ageing or sulfurization, and determining a NOx regeneration period. Process for diagnosing a NOx storage catalyst arranged in the exhaust gas tract of a lean-burn combustion engine comprises determining and evaluating a NOx storage value for differential diagnosis during deactivation of the catalyst based on thermal ageing or sulfurization, and determining a NOx regeneration period. Sulfurization is assigned to a NOx storage value with a long NOx regeneration period and a thermal ageing of the NOx storage catalyst is assigned to a short NOx regeneration period. An Independent claim is also included for a device for diagnosing a NOx storage catalyst arranged in the exhaust gas tract of a lean-burn combustion engine.

Description

The invention relates to a method and a device for diagnosing an internal combustion engine capable of running in a lean exhaust gas system arranged NOx storage catalyst according to the preambles of independent Expectations.

For NOx storage catalytic converters and other motor vehicle components, on-board diagnosis is increasingly required by law in order to ensure a sufficiently high emission stability of the vehicle fleets or of the individual vehicles. So is from the published application DE 198 43 859 a method for catalyst diagnosis is known, in which the NOx storage capacity is determined as a function of the oxygen storage capacity of the catalyst. It is already mentioned in this document that today's NOx storage catalytic converters are subject to an at least partially reversible deactivation by sulfur contained in the fuel and a non-reversible deactivation as a result of thermal aging. It is suggested that a sulfur regeneration should be carried out if the total storage capacity has dropped to an unacceptably high level. If the total storage capacity cannot be restored even after repeated attempts at regeneration, irreversible damage must be assumed. Desulphurization that worsens consumption is requested, even if there is an irreversible NOx conversion slump due to aging.

Furthermore, from the US 5,724,808 a method for determining the sulfur poisoning of a three-way catalyst is known, in which a maximum value of an oxygen sensor signal is used. If this maximum value is less than a predetermined value, poisoning of the catalytic converter is assumed. Only after complete desulfation is it examined whether the catalyst has been deactivated by thermal aging.

A method is known from WO 00/77355 is known in which upstream and downstream of a NOx storage catalytic converter from a profile of lambda values a decrease in the absolute NOx storage capacity can be determined, on the one hand due to thermal damage and on the other hand through sulfurization can be caused. There is also a procedure from this document is known in which from the waveform of a downstream of a NOx storage catalyst arranged NOx sensor differentiation of damage as a result of thermal aging and as a result of sulfur poisoning can be made. This procedure requires an accurate one Investigation of damage patterns, i.e. of the signal curve depending by time, but especially after a change of work mode of the internal combustion engine.

Object of the present invention is therefore the creation of a method and a device with more accurate information about the condition of one in one NOx store-in and regeneration cycle operated NOx catalyst can be obtained can, in particular the distinction between deactivation of the NOx catalyst due to sulfurization on the one hand or thermal On the other hand, allow aging.

According to the invention, this object is achieved by Characteristics of the independent Claims resolved.

If, as per the characteristics of the independent Method claim is provided for differential diagnosis between deactivation based on thermal aging or sulfurization of the NOx storage catalytic converter determines a NOx storage value and is assessed, a precise determination of the Deactivation or activation of the NOx storage catalytic converter take place. To differentiate between deactivation due to sulfurization or thermal aging, the invention proceeds from the knowledge from that, if the NOx storage was rated as poor, the NOx regeneration period long for sulfurization and short for thermal aging of the catalyst is. If there is a long NOx regeneration period, sulfurization will occur and with a relatively short NOx regeneration period a thermal aging of the catalyst assigned, if one Deactivation, i.e. NOx storage behavior assessed as poor has been. The NOx regeneration period of the catalyst is used as a parameter of the NOx storage and Regeneration cycle preferably during normal operation of the internal combustion engine determined.

Since the NOx storage depends on an exhaust gas and / or catalyst temperature and an exhaust gas mass flow and / or an engine speed varies, takes place in a preferred embodiment of the invention the evaluation of the NOx storage value only within predetermined limits of exhaust gas and / or catalyst temperature and / or an exhaust gas mass flow and / or an engine speed. Hereby minimal selectivity the diagnosis is guaranteed. Analogously, in a further embodiment of the invention, the NOx regeneration period proceed.

In a preferred embodiment of the invention, in order to increase the selectivity, the evaluation is carried out only for a maximum or a range around this maximum of the NOx storage value. This maximum can be dependent on values of the exhaust gas mass flow and / or the Engine load or from values of a catalytic converter and / or exhaust gas temperature can be determined. In a preferred embodiment of the invention, an optimum of the NOx storage value is determined as a function of the exhaust gas and / or catalyst temperature and the exhaust gas mass flow or the engine load.

It is preferred to determine the NOx storage value the signal of a downstream of the NOx storage catalytic converter arranged NOx sensor used. From this signal can on a simple way to determine a NOx storage load, which in turn characteristic of is the NOx storage behavior of the catalyst.

It is also preferably provided the NOx regeneration period from the signal of at least one downstream of the NOx storage catalytic converter arranged to determine a air ratio of the exhaust gas, since the respective Phase of the NOx storage and regeneration cycle of the catalyst reflects in a particularly simple manner.

With the method according to the invention and the device for execution this procedure it is possible compliance with emissions regulations in a simple manner guarantee and on the other hand unnecessary To avoid desulfation of the NOx storage catalyst and thereby reducing fuel consumption.

The invention is described below Using drawings based on an embodiment explained in more detail which is also independent from their summary in the claims further advantages and features of the invention.

The drawings show in a schematic representation:

1 an internal combustion engine with exhaust system

2 a representation of catalyst states in a differential diagnosis.

1 shows a schematic representation of an internal combustion engine 1 , for example a lean-burn gasoline engine or a diesel combustion engine, with an exhaust tract 2 and an engine control unit 3 , preferably for operating a motor vehicle. The internal combustion engine 1 has a number of cylinders 4 (corresponding components are only provided with a reference symbol), each of which has its own exhaust gas path 5 is connected downstream and can preferably also be operated in a stratified charge mode. In the exhaust system 2 are a three-way catalyst 6 and a NOx storage catalyst 7 arranged. Downstream of the cylinders 4 are in the exhaust gas paths 5 optional sensors 8th arranged with which the concentrations of exhaust gas components through the exhaust tract 2 led exhaust gas of the internal combustion engine 1 can be measured. For example, these can be NOx, SOx, CO, CO2 and HC components. Upstream of the pre-catalyst 6 is also an optional additional sensor 8th' arranged for measuring exhaust gas components. Another optional sensor 9 is in an area of the exhaust system 2 between the pre-catalyst 6 and the NOx storage catalyst 7 downstream of the pre-catalyst 6 and upstream of the NOx storage catalyst 7 arranged. Furthermore, are downstream of the NOx storage catalytic converter 7 a NOx sensor 10 and a measuring device 10 ' arranged to determine an air ratio. The measuring device 10 ' can be a broadband or two-point lambda probe or a NOx sensor with a lambda signal output. The NOx storage catalytic converter 7 is preferably operated in a NOx storage and regeneration cycle. The NOx is stored at a lambda value greater than 1, the NOx regeneration at a later point in time at a lambda value less than / equal to 1 , Storage catalytic converters of this type are therefore predominantly used in engines which are capable of running in a lean condition.

With the sensors 8th . 8th' . 9 and 10 that in the 1 are only shown schematically, it can be multi-component sensors, each capable of sensing more than one pollutant component in the exhaust gas. In addition to the sensors mentioned are upstream and downstream of the pre-catalyst 6 and upstream of the main catalyst 7 lambda probe 11 and to determine the operating temperature of the catalytic converter exhaust gas temperature sensor 13 arranged. There are also optional sensors 12 and 13 ' shown. The internal combustion engine points to exhaust gas recirculation 1 an exhaust gas recirculation device 15 with a controllable valve.

The engine control unit 3 serves to determine the operating states of the internal combustion engine 1 and detects operating parameters such as speed, load, throttle valve position, exhaust gas recirculation rate, ignition timing, injection timing, injection pressure, exhaust gas mass flow and the like in a manner known per se via further sensors, not shown in detail, and can influence these via actuators (not shown), where appropriate, for communication between the control unit 3 and the sensors or actuators a cable system 14 or the like is provided. The engine control unit 3 comprises in particular a lambda control device for regulating the oxygen concentration in the exhaust gas or the lambda value of the exhaust gas, in particular for carrying out the NOx storage and regeneration cycle of the NOx storage catalytic converter 7 , The stratified charging operation takes place in a manner known per se only within a stratified loading window of a load / speed range. About, for example, lambda value, ignition time point and / or exhaust gas recirculation rate can also influence the raw emission of pollutant components, in particular NOx, CO and HC.

To achieve optimal operation of the internal combustion engine with regard to fuel consumption and the emission of pollutants, the engine control unit 3 in addition to engine boundary conditions, emissions of exhaust gas components and the current state of the catalysts 6 . 7 determined. The state of the catalysts is preferably recorded using parameters. Preferred parameters are the upper and lower temperature limits of a conversion window for NOx and / or another exhaust gas component, an HC or CO light-off threshold temperature, an upper limit for raw emissions of exhaust gas components, an upper limit of an exhaust gas mass flow, an upper limit of a NOx - And / or SOx loading of the exhaust gas purification system or one or more of its subsystems. Furthermore, an upper limit for the concentration of a NOx, CO, CO2 or HC exhaust gas component downstream of one or, if appropriate, both catalysts 6 . 7 be used. The values for these parameters are dependent on the operating parameters of the internal combustion engine 1 determined and in a data memory of the engine control unit 3 stored.

According to the invention is an evaluation unit 16 provided that can make a differential diagnosis in the event of thermal aging or sulfurization of the NOx storage catalytic converter. The evaluation unit is preferably 16 as part of the engine control unit 3 educated. The differential diagnosis is based on a determination and evaluation of a NOx storage value of the NOx storage catalytic converter 7 and on a determination of a NOx regeneration period, a sulfurization being assigned a badly evaluated NOx storage value for a long NOx regeneration period and a thermal aging for a short NOx regeneration period. This is based on the knowledge that the NOx storage catalytic converter 7 behaves similarly with regard to NOx storage in a sulphurized and in a thermally aged state, which leads to a similar evaluation of a deactivation caused by sulphurization or thermal aging. In contrast, with the same or similar NOx storage assessment, sulfurization or thermal aging each lead to a different NOx regeneration period. The NOx storage catalytic converter 7 is preferably operated in a NOx storage and regeneration cycle by the engine control unit 3 is regulated. A NOx storage value is formed to characterize the storage behavior of the NOx storage catalytic converter.

It is known that the NOx storage behavior can be modeled as a function of a raw NOx emission, an exhaust gas mass flow and the exhaust gas temperature. To record the storage behavior changed by thermal aging and / or sulfurization, however, the downstream of the NOx storage catalytic converter is preferred 7 arranged NOx sensor 10 used. From the NOx concentration measured with this NOx sensor downstream of the catalytic converter 10 and a corresponding NOx mass flow, a NOx storage value can be determined. For this, preference is given to the raw NOx emission, the measured NOx concentration and the exhaust gas mass flow in the NOx storage catalytic converter 7 stored NOx amount determined. As the NOx concentration downstream of the NOx catalytic converter increases in lean operation with increasing NOx loading 7 increases, the NOx mass can be used as the NOx storage value, which is stored up to an increase in the NOx concentration to a predetermined percentage, for example 50% of the raw NOx emission. The NOx storage value obtained is included in the evaluation unit 16 stored target values are compared and a corresponding evaluation is carried out. In the simplest case, a binary evaluation of a determined stored value is carried out as “good” or “bad”. Since the NOx storage behavior depends on the operating parameters of the internal combustion engine or the driven motor vehicle, the NOx storage value is only evaluated for values of an exhaust gas mass flow, an engine load or the like which are within predetermined limits, such as those determined by the parameters mentioned.

According to the invention, the NOx regeneration period is determined for differential diagnosis in the case of a NOx storage value assessed as poor, compared with a target value and a long NOx regeneration period is assigned a sulfurization and a short NOx regeneration period is assigned a thermal aging of the NOx storage catalytic converter. The regeneration period is preferably determined with a measuring device for an air ratio lambda arranged downstream of the NOx storage catalytic converter. The engine control unit starts the regeneration 3 established. The end time of the regeneration is determined by the fact that the oxygen and the nitrates absorbed in the storage catalytic converter are completely reduced and the lambda value reacts accordingly.

At the in 1 The internal combustion engine shown is at that time from the downstream of the storage catalytic converter 7 arranged measuring device 10 ' a transition from a lambda = 1 value to a lambda value <1 was found. In principle, the determination of the end point of the NOx regeneration is also the determination of an HC and CO breakthrough downstream of the NOx storage catalytic converter 7 possible. As already mentioned, the measuring device 10 ' also a lambda signal output ei be a NOx sensor; in this case there is no distinction between the NOx sensor 10 and the measuring device 10 ' necessary.

The ascertained values of the NOx regeneration duration are included in the evaluation device 16 stored target values compared to make an assignment in a long or short regeneration period.

Because a fresh catalyst has a good storage value and a long NOx regeneration period and a shrunk undamaged Catalyst also a good injection value, but a short one Has regeneration duration, further differentiation between a fresh catalyst and a run-in catalyst without impairment the storage capacity.

In 2 is a summary of the different catalyst states depending on the NOx storage value and the NOx regeneration time.

Since, as is known per se, the NOx storage behavior of the engine load or a correlating exhaust gas mass flow dependent is, it is for high selectivity the diagnostic procedure is favorable, a maximum of the NOx stored value depending on values of an engine load or to determine an exhaust gas mass flow and for the evaluation of the NOx storage value to use only the maximum or an area around the maximum. The selectivity can also be increased, if a maximum of the NOx storage value dependent on determined from values of a catalyst and / or exhaust gas temperature and for them Evaluation of the NOx storage value only the maximum or a range around the maximum. Similarly, for dependency of the NOx storage behavior from the raw NOx emission of the internal combustion engine be moved. Since the NOx storage value depends on various influencing factors, especially as mentioned the catalytic converter and / or exhaust gas temperature, the engine load and / or the exhaust gas mass flow and the raw NOx emission, it is special Cheap, an optimum NOx storage value depending on a combination to choose from two or more of these influencing factors and the evaluation of the NOx storage value only for to make this optimum or an area around this optimum.

The NOx regeneration time also depends from the temperature of the exhaust gas or the catalyst and beyond from the operating point of the internal combustion engine and the air ratio of the in inflowing the catalyst Exhaust gas. Because with increasing temperature the oxygen storage capacity of the catalyst rises, it is advantageous to determine the NOx regeneration time a higher one Temperature than for to set the NOx storage value, to a higher one selectivity the distinction between fresh and aged catalysts to reach. The determination of the NOx storage value and the NOx regeneration period in the same NOx storage and NOx regeneration interval is therefore required a compromise in the choice of the temperature range of exhaust gas and / or catalyst. An increased Total selectivity can can be achieved by evaluating the NOx storage value and the NOx regeneration time separately and under optimal conditions in terms of Temperature, engine load and the like takes place.

To determine intermediate states of deactivation, is it convenient the NOx storage value and to evaluate the NOx regeneration time in a more refined way. At the NOx storage value the rating as good or bad in three or more classes fanned. Likewise, the NOx regeneration period does not become binary, but in three or more classes divided up. The combinations of the ratings of the NOx Einspeicherwerts and the NOx regeneration period then become interpolation values associated with sulfurization and thermal aging.

The assignments of the differential diagnosis obtained according to the invention are preferably further processed for display and / or storage. In the event of sulfurization of the NOx storage catalytic converter, at least one desulphation of the NOx storage catalytic converter must be carried out 7 inexpensive to enable emission-stable operation with low fuel consumption.

Claims (19)

A method of diagnosing arranged in the exhaust system of a lean-executable engine NOx storage catalytic converter, which can be operated in a NOx Injection and NOx regeneration cycle, characterized in that for the differential diagnosis of a based on thermal aging or sulphurisation deactivation of the NOx trap catalyst, a NOx Storage value is determined and evaluated, and a NOx regeneration period is determined, and sulfurization is assigned to a NOx storage value rated as poor in the case of a long NOx regeneration period and thermal aging of the NOx storage catalytic converter in the case of a short NOx regeneration period. A method according to claim 1, characterized in that with a NOx storage value rated as good and one long NOx regeneration period a fresh NOx storage catalytic converter was detected becomes. Method according to at least one of the preceding claims, characterized in that with a NOx storage rated as good value and a short NOx regeneration period, a used, undamaged NOx storage catalytic converter is recognized. Method according to at least one of the preceding Expectations, characterized in that the evaluation of the NOx storage value for values an exhaust gas mass flow, an engine load, a catalyst and / or Exhaust gas temperature is within the specified limits. Method according to at least one of the preceding Expectations, characterized in that a maximum of the NOx storage value dependent on determined from values of an exhaust gas mass flow and / or an engine load and for the evaluation of the NOx storage value only the maximum or an Area around the maximum is used. Method according to at least one of the preceding Expectations, characterized in that a maximum of the NOx storage value dependent on determined from values of a catalyst and / or exhaust gas temperature and for the evaluation of the NOx storage value only the maximum or a range around the maximum. Method according to at least one of the preceding Expectations, characterized in that an optimum of the NOx storage value dependent on values of an exhaust gas mass flow and / or an engine load and a catalyst and / or Exhaust gas temperature determined and for the evaluation of the NOx storage value only the optimum or a Area around the optimum is used. Method according to at least one of the preceding Expectations, characterized in that a maximum of the NOx regeneration period dependent on determined from values of an exhaust gas mass flow and / or an engine load and for the differential diagnosis of the NOx regeneration duration the maximum or an area around the maximum is used. Method according to at least one of the preceding Expectations, characterized in that a maximum of the NOx regeneration period dependent on determined from values of the catalyst and / or exhaust gas temperature and for the Differential diagnosis this maximum or a range around this maximum is pulled around. Method according to at least one of the preceding Expectations, characterized in that the NOx storage value and the NOx regeneration period determined within a NOx storage and regeneration cycle become. Method according to at least one of the preceding Expectations, characterized in that to determine intermediate states of deactivation a lesser or stronger Degree of sulfurization or thermal aging is determined and given conditions is assigned. Method according to at least one of the preceding Expectations, characterized in that to determine the NOx storage value the signal of a downstream of the NOx storage catalyst NOx sensor is used. Method according to at least one of the preceding Expectations, characterized in that to determine the NOx regeneration time Signal from at least one downstream of the NOx storage catalytic converter arranged measuring device for determining an air ratio of an exhaust gas of the internal combustion engine is used. A method according to claim 13, characterized in that the measuring device is a broadband or a two-point lambda probe or is a NOx sensor with at least one lambda signal output. Method according to at least one of the preceding Expectations, characterized in that a display and / or storage from at least one of the assignments of the differential diagnosis. Method according to at least one of the preceding Expectations, characterized in that in the event of sulfurization of the NOx storage catalyst at least one desulfation of the NOx storage catalytic converter is provided is. Device for diagnosing a NOx storage catalytic converter arranged in the exhaust tract of a lean-running internal combustion engine, with at least one measuring device for an air ratio and a NOx sensor arranged downstream of the NOx storage catalytic converter, and with an engine control unit for carrying out NOx storage and regeneration, in which the signals of the The measuring device and the NOx sensor can be processed, characterized in that an evaluation unit is provided which determines and evaluates a NOx storage value, a NOx regeneration duration of the NOx storage catalytic converter, for differential diagnosis when the NOx storage catalytic converter is deactivated due to thermal aging or sulfurization determined and a NOx stored value rated as poor at a long time NOx regeneration time assigns sulfurization and, in the case of short NOx regeneration times, thermal aging. Apparatus according to claim 17, characterized in that the measuring device is a broadband or two-point lambda probe and / or a lambda signal output of a NOx sensor. Device according to claim 17 or 18, characterized in that that at least in the exhaust tract upstream of the NOx storage catalytic converter a pre-catalyst is arranged.