DE102011016533B4 - Method for operating a catalyst - Google Patents

Abstract

Process for operating a catalytic converter to which exhaust gas from an internal combustion engine is applied, with the process continuously updating a variable indicating the aging of the catalytic converter while the catalytic converter is in use and, under a predetermined condition, the catalytic converter depending on the final value for this variable is heated, characterized in that the variable is or comprises the integral of the product of the catalyst temperature minus a temperature limit value on the one hand and exhaust gas mass flow of the exhaust gas from the internal combustion engine on the other hand for catalyst temperatures above the temperature limit value over the operating time of the catalyst.

Description

The invention relates to a method for operating a catalytic converter, which is acted upon in particular in a motor vehicle with exhaust gas from an internal combustion engine in order to convert pollutants still contained in the exhaust gas.

It is known that such a catalyst works optimally only if it has a certain temperature. For this purpose, the catalyst is heated, typically by exhaust gas itself, which is supplied to it. For this u. a. the efficiency of the internal combustion engine deliberately deteriorates, so that more heat energy is available.

It is also known that with increasing aging of the catalyst must be heated longer or more intense than necessary for a new catalyst. In this context, the DE 101 54 041 A1 a method and a device for reducing a pollutant emission, in which, depending on an aging of a catalyst, a lower temperature threshold for a temperature of this catalyst or the exhaust gas is determined. This temperature threshold determines from which temperature a measure for increasing an exhaust gas and / or catalyst temperature is carried out. In the method according to the DE 101 54 041 A1 Measured values from sensors are used to deduce the aging of the catalyst system.

The relationship between such measurements and catalyst aging is very complex and not always clear.

The DE 10 2007 031 768 A1 describes a method for controlling the heating of a catalyst in the exhaust gas of an internal combustion engine after a start. In this case, a first quantity of heat flowing into the catalyst and / or a second quantity of heat released in the catalyst by exothermic reactions are influenced in such a way that at least one measure is activated in a new catalyst, with which the first and / or the second amount of heat is reduced.

From the US 5 191 763 A For example, a device for controlling the heating of a catalyst is known. The device comprises a corresponding heating element with which the heat which is transferred to the catalyst is adjusted as a function of the operating time of the catalyst.

The DE 43 23 243 A1 describes a demand-oriented heating method for a catalyst in the exhaust system of an internal combustion engine, wherein from at least two measured values, a signal with respect to the conversion capacity of the catalyst is determined and the catalyst can be heated depending on the conversion capacity.

It is an object of the present invention to improve the heating of a catalyst such that carbon dioxide is emitted to a reduced extent.

The object is achieved by a method having the features according to claim 1.

According to the invention, during the use of the catalyst, a variable indicating the aging of the catalyst is continuously updated, i. H. the size is re-determined each time, with the new value for the size taking the previous value for the size. In the method, the catalyst is then heated under a predetermined condition as a function of the last valid value (ie the current value) for this variable.

The invention is based on the recognition that the aging of the catalyst can most likely be fixed to a permanently updated variable; then it is not necessary to establish complex relationships between the actual measured values that have been recorded for the catalyst and its performance itself and the aging of the catalyst. A continuously updated variable indicates directly the aging of the catalyst, corresponding correlations are thus easy to represent.

By setting the type or extent of heating depending on the latest value for this quantity, the aging of the catalyst during heating is immediately taken into account. Determining the extent of heating involves determining the heating intensity, that is, by how many degrees Celsius the catalyst temperature is raised above the given temperature.

The continuously updated quantity is to be particularly accurately associated with aging when determining the total heat generated during the service life of the catalyst. Aging causes the heat above a temperature limit. The harmful heat can thus be determined as the integral of the product of catalyst temperature minus the temperature limit and exhaust gas mass flow of the exhaust gas from the internal combustion engine over the operating time of the catalyst. The catalyst temperature and the exhaust gas mass flow are in this case time-dependent variables, over which is integrated, in the integral only contributions from times are received, in which the catalyst temperature is above the temperature limit, ie it will only positive Values of the named product are taken into account. If such an integral is used, its updating is also easy to accomplish, because then only summed summaries are added in a numerical calculation to a calculated sum.

What exactly is specified here can be different: In one aspect, the heating time is determined as a function of the last value for the size. The heating time is the easiest to detect. Likewise, the idling speed of the internal combustion engine can be set depending on the last value for the size. In particular, when it is heated at idle, the exhaust gas mass flow is determined as a function of the last value for the size. If the idling speed increases with increasing aging, this means that more fuel is being used during idling. Likewise, the duration of the addition of non-internal combustion engine secondary air to the exhaust gas may be set depending on the latest value for the quantity. The duration of the addition of secondary air and thus oxygen directly determines how excess fuel contained in the exhaust gas is burned and thus can heat the catalyst. Finally, the heating intensity depends substantially on the efficiency of the internal combustion engine. The further this deviates from the optimum efficiency, the more energy is converted into heat, which is desirable for heating. In particular, an ignition angle (which indicates the angular position of a camshaft at which the ignition of the combustion mixture takes place) is suitable for determining the engine efficiency. In the present case, therefore, this firing angle can be set absolutely, or it can be specified a Zündwinkelversatz with respect to the ignition angle at which the efficiency is optimal.

Alternatively, especially if the heat integral is not available for any reason, the size used may be the mileage driven by the motor vehicle or the operating time of the motor vehicle. In particular, the availability or plausibility of the integral can first be checked, and only such a different size can be used as a substitute.

In a preferred embodiment of the invention, the predetermined condition includes that the oxygen storage capability of the catalyst correlates to size according to a predetermined prescription. Here it can be considered that the aging shows at least approximately at a lower oxygen storage capacity. The predetermined condition may also include failure of catalyst-damaging dropouts during operation of the internal combustion engine not more than a predetermined number of times. Here it can be taken into account that the aging occurred excessively in a quantity not resulting from the heat equivalent. Likewise, it can be considered if predetermined errors of predetermined components of the motor vehicle occurred, then the predetermined condition can be regarded as not given. In particular, in the case of hardware errors in the motor vehicle, calculations can no longer be valid or the validity of such calculations can no longer be valid.

Preferably, if the predetermined condition is not met, the catalyst is heated as much as possible. Here, the fact is taken into account that possibly the oxygen storage capacity is too low and therefore more must be heated than from the heat equivalent closable, that the catalyst is damaged by said dropouts and must be heated particularly strongly, or that should be heated for safety, because the functioning of certain components is not guaranteed.

Hereinafter, a preferred embodiment of the invention will be described with reference to the drawing, in which the single figure is a flow chart for explaining an embodiment of the method according to the invention.

In a motor vehicle, an internal combustion engine is followed by a catalytic converter, which is intended to convert pollutants from the exhaust gas. In the present case, it is assumed that an aging state of the catalyst can be specified by the parameter "heat equivalent", namely the integral of the product of catalyst temperature and exhaust gas mass flow of the exhaust gas from the internal combustion engine over the operating time of the catalyst. This heat equivalent is continuously calculated in the context of the invention, ie the integral is in each case supplemented by further integral parts or summands.

The process begins with a need for catalyst heating. In the first step S10 it is now checked whether the parameter "heat equivalent" is actually available or an available value is plausible. While this is usually the case, values may be reset because of the change of a component such as a controller. Therefore, if the parameter "heat equivalent" is not plausible, it is checked in step S12 whether a replacement parameter is available, for. If the replacement parameter is not available, somewhat because the kilometer gauge has been reset, a maximum catalyst heating takes place in step S14, ie, the catalyst is heated as much as possible to convert as efficiently as possible. The heating takes place by charging the catalyst with rich exhaust gas and at the same time supplying air. The rich exhaust gas is supplied in particular during idling of the internal combustion engine. The ignition timing is shifted so that the efficiency of the internal combustion engine deteriorates.

If either the parameter is available or the substitute parameter is available, it is now checked in step S16 whether the oxygen storage capacity (OSC) corresponds to the available parameter according to a predetermined assignment specification. For example, it may be associated with a particular heat equivalent that the oxygen storage capacity has decreased to a certain extent. A threshold value can then be specified, below which the test question is to be answered with "No" in step S16. In this case, the catalyst is also maximally heated according to step S14 '.

If the oxygen capability corresponds to the parameter, then it is checked in step S18 whether the engine control unit stores misfires more than n times. If this is the case, then the catalyst could be damaged more severely than can be concluded from the heat equivalent or the replacement parameter, and according to step S14 ", a maximum heating of the catalyst takes place again.

If the test question was answered in step S18 with "No", it is checked in step S20, whether a hardware fault in the vehicle is present, ie whether an error of a component of the motor vehicle is registered in a corresponding control unit. If so, the catalyst may also be excessively damaged, and maximum catalyst heating will occur according to step S14 '' '.

If the test question is answered "NO" in step S20, then there are predetermined conditions, namely the parameter is available, the oxygen storage capacity corresponds to the parameter, and there are no special reasons why an excessive aging of the catalyst can be deduced. Then, in step S20, a determination of the catalyst heating time as a different quantity, the idling speed of the internal combustion engine as a different size, the duty ratio for secondary air as another size, and the engine efficiency with z is set in accordance with a map relating the parameter to other quantities. B. the ignition angle or time as a different size. If these variables are determined as a function of the parameter, the appropriate selection of the characteristic diagram ensures that the catalyst is optimally heated so that it converts sufficiently well, but on the other hand, not excess energy is used for the heating and therefore by the heating even excessive carbon dioxide is produced.

Claims (8)

A method of operating a catalyst to which exhaust gas is applied from an internal combustion engine, wherein the method continuously updates a catalyst aging amount during use of the catalyst, and under a predetermined condition, updates the catalyst as a function of the ultimate value for that size is heated, characterized in that the size is the integral of the product of catalyst temperature minus a temperature limit on the one hand and exhaust gas mass flow of the exhaust gas from the internal combustion engine on the other hand for catalyst temperatures above the temperature limit over the operating time of the catalyst or comprises. A method according to claim 1, characterized in that a heating period is determined in dependence on the last valid value for the size. A method according to claim 1 or 2, characterized in that an idling speed of the internal combustion engine is determined in dependence on the last valid value for the size. Method according to one of Claims 1 to 3, characterized in that the duration of the addition of secondary air not originating from the internal combustion engine to the exhaust gas is determined as a function of the last valid value for the variable. Method according to one of claims 1 to 4, characterized in that the efficiency of the internal combustion engine is determined as a function of the last valid value for the size, in particular by establishing an ignition angle. Method according to one of claims 1 to 5, characterized in that the size, in particular as an alternative, is the one driven by the internal combustion engine and the catalytic converter motor vehicle mileage or the operating time of this motor vehicle or includes. Method according to one of the preceding claims, characterized in that the predetermined condition includes that the oxygen storage capacity of the catalyst correlates with the size and / or no more than for a predetermined number of times catalyst-damaging dropouts during operation of the internal combustion engine made and / or predetermined errors of predetermined components of the motor vehicle did not occur. Method according to one of the preceding claims, characterized in that when not given the predetermined condition, the catalyst is maximally heated.

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