Patent ID: 7080613

Claim:
A method for controlling the air-fuel ratio in a four-stroke direct injection engine operable with controlled auto-ignition combustion and having at least one cylinder containing a piston reciprocably connected with a crank and defining a variable volume combustion chamber including at least one intake valve controlling communication with an air intake and at least one exhaust valve controlling communication with an exhaust outlet, the method comprising: operating the engine with controlled auto-ignition combustion involving homogeneous charge compression ignition with or without spark ignition assistance, the engine performing two sequential pairs of expansion and contraction strokes during two revolutions of the crank, said two revolutions of the crank defining a combustion cycle; employing a variable valve actuating system operated with one of an exhaust re-compression valve strategy and an exhaust re-breathing valve strategy controlling cylinder charge ignition temperatures within a self ignition range at ignition of each charge; and adjusting the flow of air and burned gases entering the combustion chamber to obtain a desired air-fuel ratio for each operating speed and load condition within the self ignition range.