INTAKE-AIR DEVICE FOR ENGINE

PURPOSE:To obtain an optional air intake characteristic and to enhance the efficiency of air intake, by providing expansion chambers communicated through shut-off valves with a pipe between an intake-air port and an expansion chamber upstream of an intake-air passage, in the wall of the pipe, and by operating the shut-off valve in accordance with the operating condition of an engine. CONSTITUTION:An intake-air pipe 9 communicated with an intake-air port 6 is communicated with an expansion chamber 4. Shut-off valves 13, 15 are provided in the communicating sections between expansion chambers 10, 11 formed in the wall of the intake- air pipe 9 and the intake-air passage 9, and are opened and closed by means of a control unit 19 which drives actuators 16, 17 in accordance with the rotational speed of the engine 18. When the engine is operated at an extremely low speed, the valves 13, 15 are opened to expand the volume of the intake-air so that the reflecting end of pulsating waves becomes at the B, that is, the effective length of the pipe becomes L. During low speed operation, the valve 13 is closed while the valve 15 is opened so that the volume of the pipe 9 becomes large by an amount corresponding to the volume of the expansion chamber 11 so that the reflecting end of pulsating waves becomes at B. During middle speed operation both valves 13, 15 are closed. During high speed operation the valve 15 is opened while the reflecting end of pulsating becomes at A.