| 摘要 |
PROBLEM TO BE SOLVED: To suppress the fluctuation of engine speed in the fluctuation of air excess rate by providing a memory means preliminarily storing the throttle opening for suppressing the fluctuation of engine speed in the fluctuation of air excess rate, and setting the throttle opening to the preliminarily stored opening in the fluctuation of air excess rate. SOLUTION: An air feed pipe 21 and a fuel gas feed pipe 20 are connected to a mixer 3, and the feed quantity of fuel gas to the mixer 3 is controlled by an air excess rate control valve 7 driven by a step motor 6. The air-fuel mixture obtained in the mixer 3 is supplied to an internal combustion engine 1 through an air-fuel mixture feed pipe 23 having a throttle. 5. The air excess rate control valve 1 is controlled so as to increase its opening by a CPU 10 when it is detected from the output of oxygen sensors 8, 9 that a NOx storage catalyst 14 reaches a storage set value. At this time, the opening of the throttle 5 is read from a map on the basis of the present engine speed and load to control the throttle opening, whereby the fluctuation of the engine speed is suppressed.
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