Patent ID: 7261084

Claim:
An arrangement for controlling a combustion engine wherein the combustion engine comprises a combustion chamber, a movable piston in the combustion chamber and the piston being movable to compress a fuel mixture in the combustion chamber so that self-ignition of the fuel mixture takes place, a crankshaft connected to and driven by movements of the piston; an inlet valve to the combustion chamber and an exhaust valve from the combustion chamber; a control unit operable for controlling the self-ignition of the fuel mixture to an optimum crankshaft angle (cad iopt ) of the crankshaft within a load range (L tot ), wherein the load range (L tot ) is divided into at least two subranges (L II , L III ) and the control unit is operable for controlling the self-ignition of the fuel mixture towards the optimum crankshaft angle (cad iopt ) of the crankshaft within a first one of the subranges (L II ) by a strategy (II) of varying the effective compression ratio (c) in the cylinder within a range bounded downwards by a lowest acceptable compression ratio c min ), and within a second one of the subranges (L III ) by a strategy (III) which entails leading cooled exhaust gases (ceg) to the combustion chamber in a quantity also enabling within the second subrange (L III ) control of the self-ignition of the fuel mixture towards the optimum crankshaft angle (cad iopt ) of the crankshaft by variation of the effective compression ratio (c) within the range bounded downwards by the lowest acceptable compression ratio (C min ).