DE102004051747A1 - Internal-combustion engine operation comprises determining nitrogen oxide concentration, fill level, and operating temperature of the nitrogen oxide accumulator catalyst and correcting a signal off set - Google Patents

Abstract

The increased gradient of the NOx sensor (16) signals is corrected, which is conducted in operating condition of the engine (10). Exhaust gas recycling is switched off and intake of air stream of the engine is throttled and/or air number of lambda of the engine supplied air-force material mixture is increased to a value greater than 1. An INDEPNDENT CLAIM is also included for a device carried out by using the above operation.

Description

The Invention is based on a method for operating an internal combustion engine, in the exhaust gas an NOx storage catalytic converter and downstream the NOx storage catalyst NOx sensor are arranged, and a device for carrying out the Method according to the preamble of the independent claims.

In the DE 198 43 879 A1 an operating method of an internal combustion engine is described, in the exhaust gas region of a NOx storage catalyst is arranged. In a first operating phase, in which the internal combustion engine is operated lean within the scope of a stratified cylinder charge, the NOx emission of the internal combustion engine is stored in the NOx storage catalytic converter.

In a second operating phase in which the internal combustion engine in Frame of a homogeneous cylinder filling stoichiometric or operated fat, there is a regeneration of the NOx storage catalyst.

One downstream detected after the NOx storage catalytic converter arranged NOx sensor an increasing NOx concentration in the exhaust gas during the storage phase. The signal increase results from the fact that the NOx breakthrough with decreasing storage capacity of the NOx storage catalyst increases.

One Change to the regeneration phase is initiated as soon as the NOx concentration exceeds a predetermined threshold. In other embodiments A change takes place from the storage phase to the regeneration phase when the NOx mass flow or the integral of the NOx mass flow in the storage phase behind the NOx storage catalyst a exceeds the given threshold.

Of the NOx mass flow downstream after the NOx storage catalyst can from the NOx sensor signal, the Exhaust gas mass flow, for example, determined from the measured intake air mass flow can be, and a constant factor that represents the molecular weight, to be obtained.

In the DE 100 36 453 A1 is described an operating method of an internal combustion engine, in the exhaust gas also a NOx storage catalyst is arranged. The changeover from the storage phase to the regeneration phase takes place as a function of the NOx mass stored in the NOx storage catalytic converter. The NOx mass flow occurring after the NOx storage catalytic converter is calculated both on the basis of a model of the NOx storage catalytic converter and determined from the NOx sensor signal. By comparing the two mass flows, the model of the NOx storage catalyst is corrected.

Currently known NOx sensors can In particular, have a signal offset, the operating conditions the NOx sensor and those of the internal combustion engine depends. Farther can they NOx sensors have a pitch and / or linearity error. One with Faulty NOx sensor signal can cause the NOx storage catalytic converter either unnecessary often or no longer regenerates. Furthermore, the reliability a condition diagnosis of the NOx storage catalyst is no longer guaranteed.

Of the Invention is based on the object, a method for operating an internal combustion engine and an apparatus for carrying out the Specify a method that provides high reliability and a correction option of the NOx sensor signal provided by a NOx sensor.

The The object is achieved by those specified in the independent claims Features each solved.

Advantages of invention

The inventive method provides that in an operating state of the NOx storage catalyst, in which the NOx storage catalyst has no or only a low NOx storage capacity, a comparison of a measure for the NOx concentration upstream is performed before the NOx storage catalyst with the NOx sensor signal provided by the NOx sensor and that in dependence made a correction of the NOx sensor signal from the comparison result becomes.

The inventive approach based on the fact that with a low NOx storage capacity of the downstream The NOx mass flow occurring at least approximately to the NOx storage catalyst equal to the upstream in front of the NOx storage catalytic converter occurring NOx mass flow. The invention uses the fact from that with a low NOx storage capacity only a small in the NO x storage flowing NO x mass flow is branched from the flowing through the NOx storage catalyst NOx mass flow, so that a high NOx breakthrough occurs.

One first advantage of the procedure according to the invention This is because the comparison result under normal operating conditions of the NOx sensor during the operation of the internal combustion engine is obtained. It results a high accuracy in the correction of the NOx sensor signal.

Farther is advantageous that the aging of the NOx storage catalyst no influence on the comparison result and thus on the correction of the NOx sensor signal has. This advantage is obtained by that the comparison result only in an operating state of the NOx storage catalyst is obtained in which the NOx storage catalyst no or only a low NOx storage capacity having. An aged NOx storage catalyst already has the limited NOx storage capability to be specified.

advantageous Further developments and refinements of the procedure according to the invention arise from dependent Claims.

suitable operating conditions of the NOx storage catalyst, in which the NOx storage catalyst no or only one NOX storage capacity has, for example, at a high NOx level or within certain temperature ranges.

The Measure of the NOx concentration upstream before the NOx storage catalyst, for example as NOx mass flow can be stated, corresponds to the raw NOx emission of the internal combustion engine, if no other catalyst in the exhaust area upstream the NOx storage catalyst is arranged or if the operating conditions such a catalyst for a NOx conversion to other substances are unfavorable. Preferably the NOx raw emission of the internal combustion engine based on a model calculated. Optionally, to detect the measure of the NOx concentration upstream before the NOx storage catalytic converter used another NOx sensor become.

One Another significant advantage results from the fact that during the inventive approach not just a low NOx mass flow to determine the signal offset can be specified, but that the NOx mass flow largely can be set arbitrarily. Thus, the comparison can also be at least one higher one Signal level, preferably several higher signal levels of the NOx sensor signal be performed. As a result, both a comparatively simple correction of a Gradient error as well as a more complex correction of a linearity error of NOx sensor signal possible.

The inventive device for operating an internal combustion engine initially applies Controller, that to carry out of the method is prepared.

The control unit contains in particular an operating state determination for the operating state of the NOx storage catalytic converter, a first signal correction for correcting the signal offset and / or a second signal correction to correct the slope and / or the linearity of the NOx sensor provided by the NOx sensor signal and a Level detection for the NOx level in the NOx storage catalytic converter and / or a temperature determination for the operating temperature of the NOx storage catalyst. The control unit preferably contains at least an electrical storage in which the process steps as a computer program are stored.

advantageous Further developments and refinements of the procedure according to the invention arise from other dependent Claims and from the description below.

drawing

1 shows a technical environment in which a method according to the invention runs, 2 shows waveforms as a function of time and 3 shows a NOx storage capability of a NOx catalyst as a function of the temperature.

1 shows an internal combustion engine 10 , in their intake area 11 an air sensor 12 and in their exhaust area 13 a NOx storage catalyst 14 , a lambda sensor 15 , a first NOx sensor 16 , an exhaust gas temperature sensor 17 and a second NOx sensor 18 are arranged.

The air sensor 12 gives to a control unit 20 an air signal msL, the internal combustion engine 10 a speed signal n, the lambda sensor 15 a lambda signal lam, the first NOx sensor 16 a first NOx sensor signal NOxSvK, the exhaust gas temperature sensor 17 an exhaust gas temperature signal Tabg and the second NOx sensor from a second NOx sensor signal NOxSnK from.

The control unit 20 represents the internal combustion engine 10 an ignition signal Zü, one of the internal combustion engine 10 associated fuel metering device 22 a fuel signal mK and exhaust gas recirculation 23 an exhaust gas recirculation signal agr available.

Downstream of the internal combustion engine 10 enters a NOx raw emission msNOxvK the internal combustion engine 10 on.

The control unit 20 contains a catalyst state determination 30 , which is the exhaust gas temperature signal Tabg and one of a NOx level detection 31 provided level signal 32 to provide. The catalyst state determination 30 gives a first enable signal 32 to an AND link 33 starting, which continues to receive a second enable signal 34 is supplied, that of an engine condition determination 35 provided. The engine condition determination 35 becomes the speed signal n, the fuel signal mK and a cold start signal 36 made available.

The AND link 33 gives a third release signal 37 to a comparator 38 Next, an adder 39 containing the second NOx sensor signal NOxSnK and one of a NOx model 50 determined measure NOxvK for the NOx concentration upstream of the NOx storage catalytic converter 14 the NOx level detection continues 31 is made available.

The NOx model 50 the speed signal n, the fuel signal mK, the air signal msL, the exhaust gas recirculation signal agr and the ignition signal Zü are provided.

The comparator 38 represents a comparison result 40 a signal offset determination 41 and a signal slope determination 42 to disposal. The second NOx sensor signal NOxSnK becomes both the signal offset detection 41 as well as the signal slope determination 42 made available. The signal offset determination 41 gives a first correction signal 43 to a first signal correction 44 and the signal slope detection 42 a second correction signal 45 to a second signal correction 46 from.

The second signal correction 46 provides a corrected NOx sensor signal NOxSnKkorr, that of the NOx level detection 31 is made available.

2 shows the time course of the measure NOxvK for the NOx concentration upstream of the NOx storage catalyst 14 , a first course 60 of the second NOx sensor signal NOxSnK, which is entered in dashed lines, and a second course 61 of the second NOx sensor signal NOxSnK, which is entered in dash-dotted lines.

The measure NOxvK for the NOx concentration upstream of the NOx storage catalyst 14 has a zero level from a start time t0. From a first time t1 is a first setpoint 62 and from a second time t2 a second setpoint 63 in front. The first waveform 60 has a first signal offset OF1 and the second signal waveform 61 a second signal offset OF2.

3 shows a NOx storage capability as a function of the temperature of the NOx storage catalyst 14 , Shown is a first storage capability history 70 , which is for a new NOx storage catalyst 14 and a second storage capability history 71 , which is an aged NOx storage catalyst 14 applies.

The method according to the invention works as follows:
An object of the method according to the invention is the correction of the second NOx sensor 18 provided second NOx sensor signal NOxSnK, which is hereinafter referred to as NOx sensor signal NOxSnK. The NOx sensor signal NOxSnK may include a signal offset and / or a slope error. Any linearity error that may be present is regarded as a pitch error. Different forms of offset error and pitch error are calculated using the in 2 illustrated waveforms illustrated.

The NOx sensor signal NOxSnK can have, for example, the first signal offset OF1 or, for example, the second signal offset OF2. Irrespective of this, a pitch error can occur. Although the NOx sensor signal NOxSnK from the first setpoint 62 to the second setpoint 63 If, for example, the NOx sensor signal NOxSnK associated with the first signal offset OF1 increases according to the first profile 60 to a higher value, while the NOx sensor signal NOxSnK associated with the second signal offset OF2 according to the second course 61 only reached a lower value.

The correction of the signal offset OF1, OF2 takes place in the first signal correction 44 including an adder, which receives the first correction signal from the NOx sensor signal NOxSnK 43 subtracted. The correction of the slope takes place in the second signal correction 46 showing the slope multiplicatively in response to the second correction signal 45 corrected. If an optionally existing pitch error at more than two different signal levels is determined, is in the second signal correction 46 It is also possible to eliminate an optional non-linearity in the NOx sensor signal NOxSnK.

The method according to the invention is based on a comparison of the NOx sensor signal NOxSnK with the measure NOxvK for the NOx concentration upstream of the NOx storage catalytic converter 14 , The comparator 38 The comparison can be based on mass flows or concentrations or of perform other comparable sizes. That of the comparator 38 provided comparison result 40 reflects a deviation between that from the second NOx sensor 18 detected NOx sensor signal NOxSnK and the measure NOxvK again, wherein a faultless NOx sensor 16 . 18 regardless of the signal level has no deviation from the measure NOxvK. The deviations that may be present are compared to the result of the comparison 40 the signal offset determination 41 and the signal slope detection 42 provided the correction signals 43 . 45 determine.

The comparator 38 may suitably perform a comparison only if the NOx storage catalyst 14 the measure NOxvK for the NOx concentration upstream of the NOx storage catalyst 14 not or only slightly influenced. The presence of this requirement can be determined by the catalyst state determination 30 be ensured that the first enable signal 32 provides. According to one embodiment, the first enable signal 32 be fed directly to the comparator. The catalyst state determination 30 preferably determines the NOx storage capability of the NOx storage catalyst 14 ,

The provision of the comparison result 40 from the comparator 38 is only in an operating state of the NOx storage catalytic converter 40 possible, in which the NOx storage catalyst 14 has no or only a low NOx storage capacity. With a low NOx storage capacity is the through the NOx storage catalyst 14 flowing NOx mass flow influenced only slightly. This condition corresponds to NOx breakthrough.

The NOx storage capacity decreases with increasing NOx level. The NOx level is determined by the NOx level detection 31 for example, as a function of the measure NOxvK for the NOx concentration upstream of the NOx storage catalytic converter 14 or as a function of the corrected NOx sensor signal NOxSnKkorr or preferably determined from the NOx mass flow. In one case, the NOx level detection is based on a model and in the other case on a measurement. In both cases, the NOx level is calculated by integration and with the NOx level signal 32 the catalyst state determination 30 provided that compares the NOx level, for example, with a predetermined threshold and in response to the comparison result, the first enable signal 32 provides. When comparing, if appropriate, the aging state of the NOx storage catalyst 14 be taken into account.

Furthermore, the NOx storage capability depends, for example, on the operating temperature of the NOx storage catalytic converter 14 from. The context is schematic in 3 shown. From the in 3 reproduced two temperature curves 70 . 71 It can be seen that the NOx storage capability is low below a lower temperature limit of, for example, 200 ° C and above an upper temperature limit of, for example, 600 ° C.

The operating temperature can be calculated, for example, based on a temperature model. An alternative embodiment provides for the use of a temperature sensor in or on the NOx storage catalytic converter 14 is arranged. In the illustrated embodiment according to 1 is the exhaust temperature sensor 17 provided downstream of the NOx storage catalyst 14 is arranged. If the exhaust gas temperature sensor 17 in close proximity to the NOx storage catalyst 14 is arranged, the exhaust gas temperature signal Tabg reflects at least approximately the operating temperature of the NOx storage catalyst 14 contrary.

The catalyst state determination 30 represents the first enable signal 32 ready if the temperature is below the lower temperature limit or above the upper temperature limit. In comparison, the aging state of the NOx storage catalyst is preferably 14 considered. With increasing age, the NOx storage capacity decreases according to the second temperature profile 71 , This fact can be used to shift the temperature thresholds.

According to an advantageous embodiment, it is provided that the comparison result 40 depending on the state of the internal combustion engine 10 provided. The condition becomes in the engine condition determination 35 detected the second enable signal 34 preferably with the first enable signal 32 AND-linked. The engine condition determination 35 preferably takes into account the speed signal n and / or the load of the internal combustion engine 10 , which is reflected for example in the fuel signal mK, and / or a cold start of the internal combustion engine 10 the cold start signal 36 symbolizes.

Preferably, the second enable signal 34 provided in response to the presence of the engine idling. At idle, a low NOx raw mass flow msNOxvK occurs at which, in particular, the signal offset OF1, OF2 can be determined. Furthermore, the second enable signal 34 preferably when the cold-start signal occurs 36 provided. The cold start signal 36 can be provided, for example, based on the temperature of a coolant or the oil temperature. A cold start is usually the temperature of the NOx storage catalyst 14 low, so according to 3 a low NOx storage capacity is present.

For the comparison, a measure NOxvK is for the NOx concentration upstream of the NOx storage catalyst 14 required. If the first NOx sensor 16 is provided, which provides the first, the NOx raw mass flow msNOxvK corresponding NOx signal NOxSnK, the measure of the NOx concentration upstream of the NOx storage catalyst 14 immediately available.

Preferably, the measure NOxVK becomes the NOx concentration of the NOx model 50 determined. If upstream upstream of the NOx storage catalytic converter 14 other catalysts or components, the NOx mass flow in the exhaust gas area 13 affect, can exist, the NOx model 50 be adjusted to calculate the measure NOxvK The determination of the measure NOxvK is preferably carried out at least on the basis of that of the internal combustion engine 10 provided speed signal n and a measure of the load of the internal combustion engine 10 which, for example, reflects the fuel signal mK. An increase in accuracy results from the consideration of the air signal msL, which is the air sensor 12 provides. If the exhaust gas recirculation 23 is present, can be taken into account with the consideration of the exhaust gas recirculation signal agr a significant influence on the NOx raw mass flow msNOxvK and thus on the measure NOxvK. If it is the internal combustion engine 10 is an externally ignited internal combustion engine, a further refinement of the result can be obtained by taking into account the ignition signal Zü. In particular, the ignition timing plays a role.

For the diagnosis of the slope is a higher NOx concentration than in the normal idling of the internal combustion engine 10 required. In order to still be able to carry out the diagnosis at idle, for example, the possibly existing exhaust gas recirculation 23 switched off and / or an intake air flow of the internal combustion engine 10 with a 1 not shown in detail reduced throttle and / or the air ratio lambda of the internal combustion engine 10 supplied air-fuel mixture can be influenced. The change in the air ratio lambda can be carried out, for example, by influencing the air supply and / or by influencing the fuel signal mK.

One embodiment provides that before the determination of the comparison result 40 a regeneration of the NOx storage catalyst 14 is carried out. This measure can ensure that the NOx level detection 31 provided NOx level signal 32 due to the NOx level detection 31 existing integrator has a high reliability. An alternative embodiment provides that before the determination of the comparison result 40 at an insufficient NOx level, the NOx level of the NOx storage catalyst 14 is specifically increased to a comparison result 40 to obtain.

Claims (13)

Method for operating an internal combustion engine ( 10 ), in the exhaust area ( 13 ) a NOx storage catalyst ( 14 ) and downstream of the NOx storage catalyst ( 14 ) a NOx sensor ( 18 ) are arranged, characterized in that in an operating state of the NOx storage catalyst ( 14 ), in which the NOx storage catalyst ( 14 ) has no or only a low NOx storage capacity, a comparison of a measure (NOxvK) for the NOx concentration (NOxvK) upstream of the NOx storage catalytic converter ( 14 ) with the downstream of the NOx storage catalyst ( 14 ) arranged NOx sensor ( 18 ) NOx sensor signal (NOxSnK) is performed and that, depending on the comparison result ( 40 ) a correction of the NOx sensor signal (NOxSnK) is made. A method according to claim 1, characterized in that the operating state of the NOx level of the NOx storage catalyst ( 14 ) is used. A method according to claim 1, characterized in that at a low NOx level of the NOx level of the storage catalyst ( 14 ) is specifically increased before the comparison. Method according to Claim 1, characterized in that the operating temperature of the NOx storage catalytic converter ( 14 ) is used. Method according to claim 1, characterized in that the signal offset (OF1, OF2) of the NOx sensor signal (NOxSnK) is corrected. Method according to claim 1, characterized in that that the slope of the NOx sensor signal (NOxSnK) is corrected. A method according to claim 1, characterized in that the correction of the NOx sensor signal (NOxSnK) in a predetermined operating state of the internal combustion engine ( 10 ) is made. Method according to Claim 7, characterized in that the correction during idling of the internal combustion engine ( 10 ) is made. A method according to claim 7, characterized gekenn records that the correction after a cold start of the internal combustion engine ( 10 ) is made. A method according to claim 7, characterized in that an exhaust gas recirculation ( 23 ) is switched off and / or the intake air flow of the internal combustion engine ( 10 ) is throttled and / or the air ratio lambda of the internal combustion engine ( 10 ) is increased to a value greater than 1) supplied air-fuel mixture. A method according to claim 1, characterized in that the measure (NOxvK) for the NOx concentration upstream of the NOx storage catalyst ( 14 ) based on a NOx model ( 50 ) is determined. Device for operating an internal combustion engine, characterized in that at least one prepared for carrying out the method according to one of the preceding claims control device ( 20 ) is provided. Apparatus according to claim 13, characterized in that the control unit ( 20 ) an operating state determination ( 30 ) for the operating state of the NOx storage catalytic converter ( 14 ), a first signal correction ( 44 ) for the correction of the signal offset (OF1, OF2) and / or a second signal correction ( 46 ) for correcting the slope of the NOx sensor ( 18 ) provided NOx sensor signal (NOxSnK) and a NOx level detection ( 31 ) for the NOx level in the NOx storage catalyst ( 14 ) and / or a temperature determination for the operating temperature of the NOx storage catalyst ( 14 ) contains.