PURPOSE: To lower the specific fuel consumption of an engine and to reduce the amount of noxious gas exhausted from the same, by enabling the engine to operate at a low speed at the time of its no-load operation by varying engine variables such as the ignition timing, the injection quantity of fuel and the quantity of by-pass intake air by a test signal, and correcting the variables according to the detected conditions for generating fluctuation of rotation.
CONSTITUTION: At the time of no-load operation of an engine, the ignition timing θ of engine variables is varied an infinitesimal quantity δθ from that of the no-load operation by a test signal for a short while (t) in a stepwise manner, and the speed N of rotation of a crankshaft is varied in a wave form. Then, a first maximum value NH1, a first minimum value NL1 and a second maximum value NH2 of the wave form of said speed N are measured and the degree Rm of stability is detected from the above extreme values. In case that it is detected that the degree Rm of stability is high and the engine operation is instable, the quantity of by-pass intake air of the engine variables is corrected according to the degree Rm of stability to render the engine operation stable so that the tendency to cause fluctuation of rotation is made low, whereby it is enabled to prevent generation of fluctuation of rotation. In case that the engine operation is instable so that the tendency of causing fluctuation of rotation is high, on the other hand, the variables are corrected according to the degree of fluctuation causing tendency, so that there is no possibility of causing excessive correction.
BAN HITOSHI
MIYASHITA MASANORI
NISHIMURA YOSHIHIRO
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