Power plants – Internal combustion engine with treatment or handling of... – Methods
Patent
1995-09-19
1997-07-15
Kwon, John T.
Power plants
Internal combustion engine with treatment or handling of...
Methods
60299, F01N 300
Patent
active
056472056
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method for checking the conversion capability of a catalyzer in accordance with the precharacterizing clause of patent claim 1.
To convert noxious components in exhaust gases of internal combustion engines, use is made of catalyzers which convert the hydrocarbons, carbon monoxide and nitrogen oxide contained in the exhaust gases into compounds which are harmless in terms of their effect on health. In operation, the catalyzers are exposed to severe conditions such as high temperatures and vibration and their life is thus limited. This can lead, during the life of a motor vehicle, to a reduction in the conversion efficiency of the catalyzer, necessitating replacement of the catalyzer.
However, since the legal requirements relating to exhaust gases must be met at all times during the entire period of use, it is necessary to monitor the function of the catalyzer. The monitoring system can here indicate to the driver when the catalyzer is no longer operating satisfactorily by means of an optical or acoustic signal.
German Patent 2,643,739 has disclosed a method for monitoring the activity of catalyzers for exhaust gas purification in which two temperature detectors are provided. One temperature detector is arranged in the catalyzer and the other is arranged just upstream of the catalyzer. This known method exploits the fact that, when the catalyzer is working properly, there is a temperature increase within the system owing to exothermic reactions in the catalyzer and the catalytic effect measured at the catalyzer is a measure of the operation of the catalyzer.
German published, non-prosecuted application 4,100,397 has furthermore disclosed a method and an arrangement for monitoring the conversion efficiency of a catalyzer in which the difference between the temperatures upstream and downstream of the catalyzer which occur in an overrun phase of the internal combustion engine when an ignition failure is produced and a predetermined quantity of fuel/air mixture is supplied is detected and evaluated.
It is the object of the present invention to present a method for checking or monitoring the conversion capability of a catalyzer in which checking or monitoring of the operation of the catalyzer is possible without interfering with the catalyzer.
SUMMARY OF THE INVENTION
This object is achieved according to the invention by means of patent claim 1. Advantageous developments are characterized in the subclaims.
If the exhaust system for an internal combustion engine comprises, for example, a separate precatalyzer and main catalyzer, then to monitor the operating capability of the precatalyzer use can be made of the characteristic that, due to its mass and coating, the precatalyzer is configured in such way that it has a high conversion rate at operating points with low mass flow rates. At these operating points, this leads to a large rise in the temperature characteristic across the catalyzer. If, however, the catalyzer has only an inadequate conversion capability or none at all, the temperature upstream of the catalyzer and that downstream of it are virtually the same, so that it can be concluded that the catalyzer is operating inadequately, if at all.
Owing to the transition from an operating point with a relatively high load and engine speed, via an overrun phase (cooling by oxygen), to an idling phase (an operating point with a low load and engine speed), there is a fundamental drop in the exhaust-gas temperature. The catalyzer has a certain storage effect as regards the temperature and conversion, with the result that this drop in the temperature is measured with a certain time delay downstream of the catalyzer.
The difference in the temperature characteristic of the good catalyzer and a defective catalyzer is only very small. A significant difference can only be detected at the beginning of an idling phase which follows on directly from an overrun phase with the injection switched off, since here there is a strongly exother
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Ketterer Alexander
Treinies Stefan
Wier Manfred
Greenberg Laurence A.
Kwon John T.
Lerner Herbert L.
Siemens Aktiengesellschaft
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