Measuring and testing – Engine detonation – Specific type of detonation sensor
Patent
1997-10-03
2000-02-01
McCall, Eric S.
Measuring and testing
Engine detonation
Specific type of detonation sensor
324399, G01M 1500
Patent
active
06018986&
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for carrying out an ionic current measurement in an internal combustion engine using a lean fuel mixture and, owing to that, requiring an increased burning duration for the ignition spark.
PRIOR ART
At present, the motor car industry is working on the object to use as lean fuel mixtures as possible, by that means decreasing noxious outlets of exhausts. (By the expression lean fuel mixtures is meant fuel mixtures with an increased air supply.) This requires a high quality of the ignition sparks in the ignition plugs. The lean fuel mixtures require an increased burning duration of the ignition spark involving an increased ignition plug wear. The wear becomes so great that the ignition plugs must be replaced at short intervals which is inconvenient and leads to increased costs. The increased burning duration has the further result that conventional ionic current measurement cannot be used.
Our SE-A-9501259-7 indicates a method and a device for increasing the burning duration of an ignition spark with a minimum of ignition plug wear in an ignition system for an internal combustion engine by initially supplying a short high tension pulse to give a short high-energy ignition spark, which spark then can be extended by supplying a potential having a lower level.
For being able to optimize the proportion fuel/air in the mixture in the device mentioned above, in relation to an increased burning duration for the ignition spark and a minimum of the wear of the ignition plug, and also for the measurement of other combustion related characteristics, the ionic current in the combustion chamber is measured.
One problem in that connection is that the ionic current measurement cannot be carried out during the period when a spark is oscillating in the spark gap. An ignition system according to what is indicated above, usually has an oscillating spark, i.e. the spark is obtained by an alternating current. The fact is that a `direct current spark` only includes half the energy compared with a corresponding `alternating current spark`.
There is the following explanation to the fact that an ionic current measurement cannot be carried out in the course of a spark oscillating in the spark gap. Since a spark current has the magnitude of 0.5 A and the ionic current about 0.01 mA, the spark current is about 50 000 times greater than the ionic current. A small extension of the burning duration of the spark current involves that 1/50 000 of the decaying spark current still can exist when the ionic current signal is initiated, i.e. the magnitude of the remaining spark current affects the ionic current.
At a motor speed of 6000 r.p.m., 200 .mu.s is equivalent to about 7.degree.. This short extension of the spark current is required for lean fuel mixtures. The spark current decays but a current of at least the magnitude of the ionic current is left during about 30.degree. having an influence on the said ionic current. In real difficult conditions, i.e. with lean fuel mixtures, and in order to decrease the emissions of exhausts, a burning duration of 1-2 ms is required, during which period the ionic current "is drowned" by the spark current, especially at high speed. Accordingly, a measurement of the ionic current cannot be carried out until the ignition spark is cut off.
SUMMARY OF THE INVENTION AND ITS ADVANTAGES
The invention solves the object to carry out the ionic current measurement in an internal combustion engine using such a lean fuel mixture as possible and by that means an increased burning duration of the ignition spark. The invention is characterized in that the start of the combustion of the fuel mixture is detected, after which the ignition spark generating the combustion is cut off, after which the measurement of the ionic current can be done.
DESCRIPTION OF AN EMBODIMENT
An ionic current measurement is used for detecting if a motor `is knocking`, which fuel/air mixture that exists, if the combustion does not occur and other characteristics which are import
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Bengtsson Jorgen
Ottosson Lars-Olof
McCall Eric S.
SEM AB
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