Power plants – Internal combustion engine with treatment or handling of... – Methods
Patent
1994-06-22
1996-01-30
Hart, Douglas
Power plants
Internal combustion engine with treatment or handling of...
Methods
60276, 60277, 60285, F01N 320
Patent
active
054872693
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for monitoring the efficiency of a catalytic converter for treating exhaust gases from an internal combustion engine equipped with a device for regulating the engine inlet air/fuel mixture and with at least one fuel injector whose opening time is controlled by this device.
Today motor vehicles propelled by an internal combustion engine are currently equipped with a device for regulating the composition of the engine inlet air/fuel mixture and with a catalytic converter arranged in the pipe of the exhaust gases of the engine in order to reduce or oxidise certain components of the latter into less noxious chemical species. The catalytic converter is said to be "three-way" when it oxidises carbon monoxide and unburnt hydrocarbons as well as reducing nitrogen oxides, produced by the combustion of the air/fuel mixture. To this end, the converter comprises, on a matrix made, for example, from ceramic, shaped in such a manner as to establish a maximum exchange surface with the exhaust gases, a coating comprising an oxidation catalyst metal such as platinum for example, a reduction catalyst metal such as rhodium for example and an oxygen storage metal such as cerium.
This coating degrades with time under the effect of "poisons" or attack such as for example the combustion of unburnt hydrocarbons in the catalytic converter following engine misfires. The active surface of the coating thus diminishes thereby lowering the overall efficiency of the catalytic converter.
Increasingly stricter anti-pollution standards now stipulate that motor vehicles are to be equipped with installed means for permanently monitoring the efficiency of the catalytic converter, so that degradation of this efficiency is detectable and so that a remedy is sought before this efficiency drops below a minimum admissible level.
Measuring the efficiency of a catalytic converter by its ability to store oxygen is known. In fact, it has been observed that the degradation of the oxygen-storage metal follows that of the other metals used in the catalytic converter. In order to measure the capacity of the converter to store oxygen, it has been proposed to arrange an oxygen probe downstream of the converter and to determine, from the signal supplied by this probe, the capacity of the converter to "smooth" the fluctuations in the oxygen concentration of the exhaust gases by absorption/resorption of oxygen.
To this end a method is known from the document U.S. Pat. No. 3,969,932 for monitoring the activity of a catalytic converter for treating the exhaust gases of an internal combustion engine equipped with a device for regulating the composition of the air/fuel mixture of the engine, which consists in arranging an oxygen probe at the inlet to the converter and another such probe at the outlet of the converter, in giving rise to a switching of the output signals of the oxygen probes by switching over the fuel richness of the air/fuel mixture inlet to the engine, from a high level to a low level, and in measuring the time offset between the switchings of the two probes, this offset being proportional to the quantity of oxygen that the catalytic converter is capable of storing. In fact, when the mixture is rich in fuel there is desaturation of the oxygen storer. When the mixture is then regulated to a "lean" level there is resaturation of the oxygen storer, the duration of this resaturation being proportional to the quantity of oxygen which the oxygen storer is capable of absorbing. By comparing the time offset in switchings of the two probes to a predetermined threshold, a correct state of the converter can thus be diagnosed if the offset is greater than the threshold, and an incorrect state in the opposite case.
The monitoring method described hereinabove suffers, however, two drawbacks. On the one hand, the measurement of the offset value is rendered inaccurate by the fact that the transition instants to be observed on the output signals of the oxygen probes are difficult to determine accurately. Moreover, the high
REFERENCES:
patent: 4622809 (1986-11-01), Abthoff et al.
patent: 5077970 (1992-01-01), Hamburg
Atanasyan Alain A.
Tarroux Francis
Greenberg Laurence A.
Hart Douglas
Lerner Herbert L.
Siemens Automotive S.A.
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