| 摘要 |
PURPOSE:To prevent exhaust gas from flowing into the downstream side of a shut-off valve which is disposed in an intake-air passage communicated with a high speed intake-air port, upon light load operation, and to carry out internal EGR with the use of exhaust gas downstream the shut-off valve upon low load operation in which a throttle valve alone opens, by connecting the downstream side of the shut-off valve with the direct upstream side of the throttle valve which is fully closed, through a communication pipe. CONSTITUTION:There are provided a low speed intake-air passage 3 and a high speed intake-air passage 4 which are communicated respectively with high and low speed intake-air ports formed in an engine cylinder 7. Further, a throttle valve 15 is disposed in the merging section between both passages, and a shut-off valve 6 is disposed in the high speed intake-air passage 4. The down stream side of the shut-off valve 6 is connected to the direct upstream side of the throttle valve 15 which is fully closed, through a communication pipe 21. During light load operation, both valves 6, 15 are substantially full-closed so that exhaust gas is prevented from remaining in the passage upon overlapping between a high speed intake valve and an exhaust valve, and substantially no intake-air flows through the pipe 21 upon low load operation in which the throttle valve 15 is slightly openedwhile the shut-off valve 6 is closed, so that exhaust gas remains in the intake-air passage 4 to realize internal EGR. |
