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(11) | EP 0 898 066 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method of controlling an air-fuel ratio of an engine |
| (57) The elapsed time Ta(i) of a 30° crank angle near top dead center of compression and
the elapsed time Tb(i) of a 30° crank angle near 90° after top dead center of compression
are found. The difference DTa(i) of the elapsed times Ta(i) between 720° crank angle
for a first cylinder and a second cylinder performing combustion after the first cylinder
is found. The assumed elapsed time when assuming that there is no torque fluctuation
is calculated from the difference DTa(i) of the elapsed time of the first cylinder
and the elapsed time of the second cylinder is calculated and the assumed elapsed
time is used to calculate the basic amount of torque fluctuation. A set value is found
based on the engine speed. The set value represents a deviation of the basic amount
of torque fluctuation due to the detection error of the elapsed time, and due to the
torsional vibration of the engine drive system and the torsional vibration of the
crankshaft. The set value is subtracted from the basic amount of torque fluctuation
to calculate the amount of torque fluctuation. The air-fuel ratio is controlled based
on the amount of torque fluctuation. |