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Engine comprising a catalytic converter with failsafe operationEngine comprising a catalytic converter with failsafe operation description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20090158708, Engine comprising a catalytic converter with failsafe operation. Brief Patent Description - Full Patent Description - Patent Application Claims
The invention relates to a method of monitoring the effectiveness of a catalytic converter installed in an exhaust line of an internal combustion engine, particularly a diesel engine. The catalytic converters at which the invention is aimed are, in particular, the converters designed to trap the oxides of nitrogen NOx present in the gases. It is known that internal combustion engines produce exhaust gases which contain pollutants such as the aforementioned oxides of nitrogen NOx, unburnt hydrocarbons HC and also carbon monoxide CO. These pollutants have to be treated so that their emissions meet the criteria dictated by standards such as European standards for example. To do this, one known technique used for reducing these emissions is to incorporate a catalytic converter into the engine exhaust line. This converter is able, on the one hand, to store the NOx and then, during a particular phase of operation known as “purging the catalyst”, to reduce these NOx to release them into the atmosphere in the form of nitrogen N2 and carbon dioxide CO2. On the other hand, this catalytic converter has a function of oxidizing the reducing species such as carbon monoxide CO and unburnt hydrocarbons HC. In order to obtain such results, a catalytic converter that traps NOx comprises, as is known per se, a catalytic phase in the cells of a monolith that are in contact with the gases. The catalytic phase typically consists of platinum, of palladium, of rhodium, and/or of alkaline earth metals. One of the problems with catalytic converters is that the catalytic phase loses effectiveness as it ages. In particular, aging of this phase often results in a reduction in the number of NOx storage sites and therefore in a drop in the effectiveness with which NOx, HC and co can be stored and treated. There are other factors that lead to the drop in converter performance as the converters age but in any event, particularly given the pollution levels dictated by the standards, use of a catalytic converter with a trap for nitrogen oxides usually entails monitoring the operation of such a converter in order to avoid troublesome deviations. Monitoring systems have already been proposed. In general, their function is to detect failure of a component of a piece of pollution-reducing equipment installed in a vehicle and to alert a driver to any failure that will cause the aforementioned emission levels to be exceeded, so that repairs can be carried out promptly. Thus, document FR 2 866 926 discloses a monitoring system in which use is made of a mixture richness lambda probe installed downstream of a catalytic converter to measure the richness of the exhaust gases at this point and from this make a diagnosis regarding the operating status of the converter. More specifically, the diagnosis is based on measuring the effective time taken to reduce the stored NOx, this time being a function of a voltage supplied by the lambda probe. Also, document U.S. Pat. No. 5,228,335 discloses a system for detecting failure of a catalytic converter on the basis of the use of two proportional mixture richness probes (the voltage supplied by the probe is proportional to the richness) installed one upstream and one downstream of the converter. More specifically, that system makes a diagnosis on the basis of integrating, with respect to time, the difference between the signals supplied by each of the two probes. This diagnosis therefore relies on calculating an area which is a function of the measurement signals from the probes, and this area is then compared against a threshold value in order to evaluate the operating status (or, which amounts to the same, the degree of aging) of the converter. Although they have proved most useful, such systems are, however, relatively expensive and tricky to implement. It is therefore an object of the invention to provide a method and a system for robustly and reliably monitoring the operating status of a catalytic converter, doing so at a lower cost. To this end, the invention proposes an engine comprising a catalytic converter, a first probe capable of delivering a first signal proportional to an oxygen content in an exhaust gas and installed upstream of the converter, a second oxygen probe downstream of the converter and capable of supplying a second signal, and means for making a diagnosis regarding an operating status of the converter, characterized in that: Continue reading about Engine comprising a catalytic converter with failsafe operation... 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