inlet during the course of the main lift 42 the reduced lift 48 happens around the mid stroke of the piston and the closure of the valve happens at the bottom dead center bdc of inlet more precisely phase 46 begins between 60 dv and 0 dv before the top dead center whereas the end of phase 46 occurs between 0 dv and 30 dv after the top dead centre of the inlet in the case where the end of the exhaust occurs at the beginning of the admission as is represented on fig7 the phase 46 of low opening of the inlet valve permits the limitation of the quantity of flow back gas exhaust trapped in the cylinder and makes this quantity substantially constant in the diagram represented on fig7 which represents the valve lifts according to the crankshaft degree oe means the opening of the exhaust ce means the closing of the exhaust oa means the opening of the inlet and ca means the closing of the inlet thereby a u201c cross over u201d zone 50 exists during which the inlet valves and the exhaust are simultaneously open the closure 44 of the inlet valve between the pilot lift and the main lift creates a depression in the cylinder when the valves are all closed and when the piston is in a descending phase in these conditions at the start of the main lift.