Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1994-05-13
1995-09-26
Dolinar, Andrew M.
Internal-combustion engines
Charge forming device
Fuel injection system
731173, F02D 4122
Patent
active
054526990
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and a device for detecting misfires in an internal combustion engine. More particularly, the present invention also relates to an application of such a method and of such a device to the prevention of degradation of a "catalytic" converter for oxidising the exhaust gases of the engine.
Misfires in an internal combustion engine reveal various disorders which can affect either means dedicated to the igniting of the air/fuel mixture (coils, spark plugs, shortcircuits in the feed lines, etc.) or means for composing the said mixture (carburettor, injector). Means for detecting such misfires are thus useful so as to correct these disorders by cleaning, regulating or replacing the defective components.
Increasingly strict legislation concerning air pollution further leads to considering installing such detection means for other purposes. In fact, the catalytic converters used for oxidising or reducing the exhaust gases of an engine are themselves liable to be degraded by injections of unburnt fuel. In particular, when there is a misfire in one cylinder of the engine, the fuel of the mixture introduced into the cylinder then passes directly into the catalytic converter where it burns by catalysis thereby deteriorating the costly catalyst contained in this converter. Such injections of fuel thus considerably reduce the efficiency of the catalyst in its conversion of the exhaust gases, hydrocarbons, oxides of carbon, oxides of nitrogen, etc. into less pollutant oxides. It is thus appropriate to protect the catalyst from such injections of unburnt fuel, by cutting off, for example, the supply of a fuel injector when misfires have been detected in one cylinder of an engine.
In order to detect such misfires, the document WO 90/02871 proposes the monitoring of the movements of the engine block using an accelerometer sensor for example, sensitive to the oscillations of the oscillatory system composed of the engine and of its elastic means for mounting onto the chassis of a motor vehicle. In the event of missed combustion in one of the cylinders of the engine, the oscillation of the system becomes irregular. A measurement of the phase shift between an acceleration peak and the moment when ignition sparks are emitted enables the cylinders when there has been a misfire to be identified.
The document U.S. Pat. No. 4,930,479 also proposes the monitoring of the variations of the rotational speed of the engine, between predetermined points of the engine cycle, so as to identify possible misfires responsible for abnormal variations of this speed.
The detection methods described in these documents and in other documents of the prior art give satisfactory results under high engine load. In contrast, at low loads, they become sensitive to external disturbances. When the engine is used to propel a motor vehicle, these external disturbances may consist in passing over obstacles on the roadway, such as potholes for example, of changes in speed, etc.
These disturbances apply jolts to the vehicle in general and to the engine in particular. When the detection of misfires is founded upon the detection of jolts, as in the detection methods currently known, the jolts of origin external to the engine may be falsely attributed to misfires and give rise to non-justified cutoffs of the supply of fuel to a cylinder, for example.
The document JP A 63-16153 discloses a system in which the forces transmitted between the engine and the chassis are sensed by two pressure sensors associated with the engine mounts. The difference between the variations of forces measured by the two sensors is used to detect misfires. Said difference is low when the variation of forces is caused by the raggedness of the road surface. However, such a system is not very reliable because false detection of misfires can occur by sudden acceleration changes, caused for example by braking or cornering depending on the position of the engine, and expensive, because of the need of two sensors.
The objective of the present invention ther
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Dolinar Andrew M.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Automotive S.A.
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