| 摘要 |
In an intake system for a multicylinder engine, discrete intake passage portions immediately connected to the respective cylinders are divided into two groups so that intake timings of the discrete intake passage portions in each group are not immediately successive, and the discrete intake passage portions in each group are concentrated to form a concentrated portion. Branch intake passage portions extend upstream from the concentrated portions for the both groups and are integrated with each other to form a main intake passage portion. Bypass air for adjusting the engine rpm during idling, blowby gas from the crankcase, fuel vapors trapped by the canister, exhaust from the exhaust system and the like are introduced into the concentrated portions of the discrete intake passage portions or the branch intake passage portions by way of a fluid introduction passage comprising a pair of branch introduction passage portions which are connected to the respective concentrated portions at one end and to a downstream end of a main introduction passage portion at the other end. The main introduction passage portion is connected to sources of the fluids described above at the upstream end portion. The average length l and the diameter d of the branch introduction passage portions are selected to satisfy the condition d/ 2ROOT l<D/ 2ROOT L, wherein D and L respectively represent the diameter and the average length of the branch intake passage portions. Flow control valves for controlling the amount of the fluids described above to be introduced into the branch intake passage portions or the concentrated portions are provided in the fluid introduction passage upstream of the junction of the branch introduction passage portions to the main introduction passage portion.
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