The present invention relates to a method of controlling exhaust-gas recirculation (EGR) particularly for an internal combustion engine having primary and secondary intake passages.
There have been known internal combustion engines which include a primary intake passage for supplying an air-fuel mixture under a full range of loads and a secondary intake passage for supplying an air-fuel mixture under high loads. The primary intake passage has a diameter that is small enough for it to be able to take care of the practical range of engine operation, and the secondary intake passage has a larger diameter such that it will come into operation only when the engine undergoes acceleration or is otherwise put under a higher load. Such a larger ratio between the cross-sectional areas of the primary and secondary intake passages is selected for more effective functioning of the internal combustion engine with primary and secondary intake passages. With the larger cross-sectional ratios of the primary and secondary passages, however, an EGR valve for the engine cannot be effectively actuated only by a vacuum introduced through a vacuum signal port from the primary intake passage, and hence a sufficient amount of EGR which is proportional to engine loads is not available.