| 摘要 |
PURPOSE:To produce optimum ON/OFF frequency even if motion characteristics of an engine is changed, by a method wherein ON/OFF frequency of a gas injector is changed until the injection duty amplitude value of the gas injector and the rich/lean period of an oxygen sensor stay at a set value. CONSTITUTION:A CPU 13 drives a gas injector 8 in response to an oxygen signal from an oxygen sensor 10. The gas injector 8 repeats injection and stop at a specified ON/OFF frequency to control an additional amount of gas. The CPU 13 determines ON/OFF frequency from an injection duty amplitude value serving as a substitution value of puring performance of a three-dimentional catalyst 9 or determines ON/OFF frequency from the rich/lean period of the oxygen sensor 10. This enables production of optimum ON/OFF frequency even if motion characteristics of an engine is changed due to a change with time.
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