Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-09-18
2002-06-11
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S274000, C060S276000, C060S297000
Reexamination Certificate
active
06401453
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method and an apparatus for monitoring the functional ability of a catalyst disposed in the exhaust duct of an internal combustion engine.
Nowadays, aftertreatment of the exhaust gas of internal combustion engines is generally performed by one or more catalysts in an exhaust system of the internal combustion engine. Strict emission limits for pollutant emissions of internal combustion engines, particularly vehicles, make it necessary that the catalyst used should be monitored reliably. It is required of such diagnostic methods that they should allow continuous checking of the catalyst in operation, also referred to as On-Board-Diagnosis.
A catalyst-monitoring method known for spark-ignition engines is based on evaluating the relationship between the oxygen storage capacity and degree of conversion of a three-way catalyst. A method of this kind is known, for example, from Published, Non-Prosecuted German Patent Application DE 195 36 252 A1; here, two oxygen or lambda probes are used, one upstream and one downstream of the catalyst. This method can only be used when the lambda control system is active and the catalyst has reached its operating temperature. Evaluating the lambda-probe signals allows only indirect monitoring of the catalyst, and the correlation between the oxygen storage capacity and the degree of conversion of the catalyst is not very good. This method, like that known from Published, Non-Prosecuted German Patent Application DE 24 44 334 A1, is therefore restricted to the diagnosis of relatively large differences in the degree of conversion, as a result of which it is possible to diagnose only a severe deterioration of the catalyst. These methods are not suitable for diagnosing a slight deterioration of the catalyst, as required by strict emission limits.
A method known from Published, Non-Prosecuted German Patent Application DE 40 39 429 A1 adopts a different approach to the checking of a catalyst. It provides a carbon-monoxide and/or hydrogen-concentration pick-up downstream of the catalyst. When a specified limiting value of the carbon-monoxide and/or hydrogen content is exceeded, a defective catalyst is recognized. The measurements are taken in defined steady-state operating conditions of the internal combustion engine, i.e. when the catalyst is at its maximum degree of conversion.
Published, Non-Prosecuted German Patent Application DE 195 37 778 A1 has disclosed a method for monitoring the operation of a NO
x
-reducing catalyst of a diesel internal combustion engine, in which fuel is metered in upstream of the catalyst as a reducing agent. Here, a sensor for the concentration of hydrocarbons in the exhaust gas is provided downstream of the NO
X
-catalyst for the purpose of monitoring the catalyst so as to be able to recognize lessening of the catalytic reduction from increased hydrocarbon concentrations in the exhaust gas. In normal operation, i.e. after the operating temperature has been reached, precise control of an internal combustion engine with catalysts in the exhaust duct allows very high degrees of conversion, e.g. over 95%. Strict emission limits allow only slight deviations from this almost complete conversion, for which reason the on-board diagnostic (OBD) system must be capable of detecting even slight deviations.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and device for monitoring the functional ability of a catalyst of an internal combustion engine which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, in which even a slight deterioration in the degree of conversion due to aging can be detected very accurately.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for monitoring a functional ability of a catalyst disposed in an exhaust duct of an internal combustion engine. The method includes the steps of: determining by continuous measurements during a heating-up phase of the catalyst, a first variable that is characteristic of a temperature of the catalyst; determining by continuous measurements during the heating-up phase of the catalyst, a second variable that is characteristic of a degree of conversion of the catalyst and is dependent on the first variable; and using a change in a dependency of the second variable on the first variable caused by aging of the catalyst to monitor the functional ability of the catalyst.
According to the invention, the functional ability of the catalyst is checked during the warm-up phase of the internal combustion engine. Since the largest proportion of pollutants emitted is emitted during the warm-up phase of the internal combustion engine, checking the functioning of the catalyst is particularly important during this period. On the other hand, it is easier to diagnose changes in the functional ability of the catalyst owing to the higher concentration of pollutants in the exhaust gas downstream of the catalyst during the warm-up phase.
The basic idea of the method according to the invention and of the device according to the invention is based on the relationship between the degree of conversion and the level of emission of an exhaust-gas component downstream of the catalyst to be monitored and the thermal properties, i.e. the temperature, of the catalyst. The degree of conversion of the catalyst depends directly on its temperature. This dependency changes with the aging of the catalyst. The degree of conversion becomes poorer as the age of the catalyst increases. This change in the dependency of the degree of conversion of the catalyst on its temperature with aging thus offers a way of monitoring the functional ability of the catalyst.
The thermal property of the catalyst can be expressed by the body temperature of the catalyst itself or by the heat fed to the catalyst. The latter can be accomplished by determining the exhaust-gas temperature upstream of the catalyst and determining the volume flow fed to the catalyst and subsequently calculating the heat fed to the catalyst from the exhaust-gas temperature, the volume of flow and the heat capacity of the exhaust gas. Energy supplied by any catalyst heating system present must, of course, likewise be taken into account. The exhaust-gas temperature upstream of the catalyst can preferably be calculated by a model and on operating parameters of the internal combustion engine. The heat fed to the catalyst is furthermore preferably determined only when no more latent heat is being absorbed by the evaporation of condensates in the catalyst after the starting of the internal combustion engine.
In the invention, the catalyst is preferably monitored using measurements of one pollutant component, in particular carbon monoxide (CO), hydrocarbon (HC) or nitrogen oxides NO
X
. However, it is also possible for a plurality of these pollutant components to be taken into account.
In one embodiment of the invention, the concentration of a pollutant component in the exhaust gas is measured upstream and downstream of the catalyst. The degree of conversion of the catalyst is calculated from these measured values. In one embodiment of the method according to the invention, inadequate functioning of the catalyst is detected when the catalyst temperature is above a threshold value at a given degree of conversion. As an alternative, this is also possible if a minimum degree of conversion is not reached at a given catalyst temperature. If the heat fed to the catalyst is used as a measure of the temperature of the catalyst, a non-functional catalyst can be detected by determining the energy required to increase the degree of conversion of the catalyst from an initial value &eegr;
i
, e.g. 20%, to a final value &eegr;
j
, e.g. 60%. The energy required to achieve the increase in the degree of conversion &eegr;
f
−&eegr;
i
, which has to be fed to the catalyst in the form of heat, is higher in the case of an aged, non-functional catalyst than in the c
Denion Thomas
Greenberg Laurence A.
Mayback Gregory L.
Siemens Aktiengesellschaft
Stemer Werner H.
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