Importance

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Abstract

A premixing apparatus has: a butterfly valve and a changeover valve for changing over, between high and low, a ventilation resistance in an air supply passage and in a gas supply passage, respectively; and an interlocking mechanism to open or close the changeover valve in interlocking with the opening or closing of the butterfly valve. In either of the small-capacity state in which the ventilation resistance in the air supply passage and in the gas supply passage is made high to attain a small-capacity state or in a large-capacity state to attain a large-capacity state, adjustments are arranged to be made to make appropriate the excess air ratio of the air-fuel mixture. An interlocking mechanism is constituted: to maintain the changeover valve in a fully-closed state when the butterfly valve lies in a predetermined first rotation angle range inclusive of the closed posture; and to maintain the changeover valve in a fully-opened state when the butterfly valve lies in a predetermined second rotation angle range inclusive of the opened posture. The rotation angle of the butterfly valve at which the excess air ratio of the air-fuel mixture becomes the predetermined appropriate value within the first rotation angle range is set to a closing-side stop angle of the butterfly valve. The rotation angle of the butterfly valve at which the excess air ratio of the air-fuel mixture becomes the predetermined appropriate value within the second rotation angle range is set to an opening-side stop angle of the butterfly valve.

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First Claim