Internal-combustion engines – Charge forming device – Including cylinder pressure or temperature responsive means
Patent
1998-11-12
2000-03-07
Wolfe, Willis R.
Internal-combustion engines
Charge forming device
Including cylinder pressure or temperature responsive means
12340626, F02D 4140
Patent
active
060326506
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for closed-loop control of injection timing in combustion engines, based upon analysis of the characteristics of the ionisation current as detected via a measuring gap arranged within the combustion chamber.
Lambda sensors are often used in order to obtain closed loop control of stochiometric combustion in combustion engines. A stochiometric combustion is the ideal operation mode for a conventional three-way catalytic converter. The type of lambda sensors used in mass-produced cars have been a so-called narrow-banded lambda sensor, which type of sensors exhibit a distinct transition as of its output signal at a lambda value just below 1.0. This type of narrow-banded lambda sensor is used in order to control the combustion, wherein the control is operated such that the output signal of the lambda sensor switches between a low or high output signal.
An alternative to the narrow-banded lambda sensors is the linear type of lambda sensors, but these sensors are very expensive, at least 10-fold, and could therefore in terms of cost not justify an introduction in mass-produced cars. The linear type of lambda sensors emits an output signal proportional to the present air/fuel ratio. By using lambda sensor of the kind mentioned above, the amount of fuel being supplied could be controlled, in order to maintain a defined air/fuel ratio, i.e. A/F-ratio (Air/Fuel).
An alternative to lambda sensors is shown in U.S. Pat. No. 4,535,740 having an ion current sensor in the combustion chamber where the spark gap of the conventional spark plug is used as measuring gap enabling detection of the burn duration within the combustion chamber. A parameter representative of the burn duration, and thus the air/fuel ratio, is detected by measuring the length of time the ion current signal is above a predetermined threshold value. At certain operating ranges where the ion current signal exhibit a low accuracy, the closed loop control is based upon the termination of the burn duration. The characteristics of the burn duration vary considerably at different operating cases, i.e. load and rpm's, and for that reason alone there is a need for a number of different threshold values to be used for the detection of burn duration, or alternatively of using different weight factors for different load cases.
In U.S. Pat. No. 5,425,339 another closed-loop system is shown, wherein information from the ionisation current is used in order to control ignition timing and the amount of fuel being supplied, i.e. the present A/F ratio. In this implementation the product of the duration of the ionisation signal and the peak value is maximised, during variation of the fuel amount being supplied or alternatively during variation of the ignition timing. By duration of the ionisation signal is meant the time the ionisation current exceeds a predefined threshold level. In an alternative embodiment the integrated value of the ionisation current signal could be maximised during variation of either the fuel amount or the ignition timing.
In U.S. Pat. No. 5,425,339 is also shown (FIG. 5) a previously known system configuration, wherein also the injection timing could be controlled in a conventional manner. This conventional manner uses a feed-forward model, using empirically determined matrices for the injection timing, wherein the dominating parameters such as rpm, load and temperature all determine the present injection timing. Nothing in U.S. Pat. No. 5,425,339 suggests that the injection timing should be controlled in a closed-loop manner dependent on the ionisation current signal.
In SE,C, 503900 is shown an alternative for detecting the present A/F-ratio. Instead of using the duration of the ionisation current signal in order to determine the A/F ratio, as shown in U.S. Pat. No. 4,535,740, it is suggested in SE,C,503900 that a parameter extracted from the ionisation current signal and typical for a basic frequency content instead be used for this A/F detection. As an alternative the deriva
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Mecel AB
Vo Hieu T.
Wolfe Willis R.
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