Exhaust gas recirculation.

摘要

An exhaust gas recirculation system has an EGR valve 18 which is controlled by intake manifold vacuum applied through a pipe 32. In order to prevent the EGR valve being opened wide during gear changes, a bypass passage 48 with a bypass valve 50 is fitted. The bypass valve is set so that it opens and dumps the manifold vacuum when this vacuum exceeds a preset threshold value which lies between the vacuum levels occurring during normal running and the high vacuum occurring at gear changes.