Engine with modified cam profiles for internal EGR control

This invention relates to valve trains for internal combustion engines and more particularly to modified cam overlap profiles for control of internal exhaust gas recirculation or retention (EGR). An engine includes cams for actuating intake and exhaust valves controlling transport of air and combustion products to and from a combustion chamber of the engine. The cams have valve opening and closing curves capable of being timed so that the intake valve opening curve partially overlaps the exhaust valve closing curve, allowing retention of some combustion products in the combustion chamber with an incoming air charge. At least one of the cams has variable timing to vary the valve overlap for controlling the amount of exhaust gas retention or recirculation (EGR). The overlapping portions of the cam opening and closing curves are extended to provide a relatively linear variation in valve overlap area over the range of cam variable timing. Thus, variation of exhaust gas retention in the combustion chamber becomes a relatively constant function of the duration of valve overlap in each engine cycle and control of the amount of EGR is improved.