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In a method for the operation of a four-stroke reciprocating piston internal combustion engine with alternating compression. ignition and spark ignition, fuel is injected directly, fresh charge is delivered and combustion exhaust gas is led off. At low and medium partial load a partially homogenized

In a method for the operation of a four-stroke reciprocating piston internal combustion engine with alternating compression. ignition and spark ignition, fuel is injected directly, fresh charge is delivered and combustion exhaust gas is led off. At low and medium partial load a partially homogenized, lean basic mixture of air, fuel and retained exhaust gas is formed for the compression ignition, and at higher partial load and at full load a homogeneous, stoichiometric mixture is formed for the spark ignition. Further features include exhaust gas retention, a build-up of exhaust gas and activation injection into the retained exhaust gas. For a smooth transition between the two operating modes, in addition to the co-ordinated interaction of exhaust gas retention, build up of exhaust gas, restriction of the fresh charge, and of the ignition advance angle in spark ignition, together with the quantity and the timing of the fuel injection, use is also made of exhaust gas recirculation.

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1. A method for operating a four-stroke reciprocating piston internal combustion engine with alternating compression ignition and spark ignition, comprising the steps of: directly injecting fuel into at least one combustion chamber, a volume of which varies cyclically; delivering fresh charge ai

1. A method for operating a four-stroke reciprocating piston internal combustion engine with alternating compression ignition and spark ignition, comprising the steps of: directly injecting fuel into at least one combustion chamber, a volume of which varies cyclically; delivering fresh charge air through at least one inlet element; leading off combustion exhaust gas through at least one exhaust element; forming a partially homogenized lean basic mixture of air, fuel and retained exhaust gas at a low and medium partial load; performing compression ignition at partial load; forming a homogeneous stoichiometric mixture at higher partial load and at full load; performing spark ignition at full load; performing exhaust gas retention due to controllable valve interval and build-up of exhaust gas; performing activation injection into the retained exhaust gas; forming a signal for a change of operating mode in accordance with exhaust gas retention of the exhaust gas build-up, restriction of the fresh charge, ignition advance angle in spark ignition, quantity and timing of fuel injection and exhaust gas recirculation; changing-over between compression ignition and spark ignition by synchronous actuation of a throttle valve, an exhaust sensor flap and an exhaust gas recirculation valve; and controlling a connecting line by the exhaust gas recirculation valve, the connecting line arranged between an exhaust pipe upstream of the exhaust gas sensor flap and an intake line downstream of the throttle valve. 2. The method according to claim 1, wherein the changing-over step includes the substep of changing between valve interval and valve overlap in accordance with a displacement of a camshaft. 3. The method according to claim 1, wherein the changing-over step is performed over more than one operating cycle. 4. The method according to claim 3, further comprising the steps of: shutting off the fuel injection during the changing-over step; and restarting the fuel injection in a new operating mode. 5. The method according to claim 3, further comprising the step of compensating for a fall in speed during the changing-over step by a load pulse. 6. The method according to claim 5, wherein the compensating step is performed after the changing-over step. 7. The method according to claim 2, further comprising the step of gradually closing a throttle valve and gradually opening an exhaust gas sensor flap and the exhaust gas recirculation valve when changing over from compression ignition to spark ignition after shifting the camshaft to valve overlap. 8. The method according to claim 7, further comprising the step of stoichiometrically adjusting the fuel injection quantity and adjusting an ignition advance angle to stabilize a torque after changing over from compression ignition to spark ignition. 9. The method according to claim 1, further comprising the step of gradually opening the throttle valve, gradually closing the exhaust gas sensor flap and maintaining the exhaust gas recirculation valve open, at least until spark ignition is switched off, when changing over from spark ignition to compression ignition after shifting a camshaft to valve interval.