Ignition circuit for a combustion engine

An ignition circuit for a combustion engine defining a combustion chamber, said combustion engine including:

• a spark plug arranged in said combustion chamber and a piston delimiting said combustion chamber;
• said piston being movable in a reciprocating manner between top dead center and bottom dead center;
• a crankshaft and a connecting rod connecting said piston to said crankshaft to facilitate rotation of said crankshaft via said connecting rod;
• and,
• an intake channel having a control element for apportioning combustion air for an idle situation and an acceleration situation of said combustion engine;
• said ignition circuit comprising:
• an electronic control circuit configured to trigger an ignition spark at said spark plug in dependence upon a crankshaft angle (°CA) of said crankshaft at an ignition time (IT);
• said control circuit being provided with at least one ignition time point (IT) for said idle situation and at least one ignition time point (ITA) for said acceleration situation;
• said control circuit being configured, in said idle situation, to set the predetermined idle point (IT) for said idle situation;
• said control circuit being further configured, in said idle situation, to monitor the course of a rotational speed (N) of said crankshaft over at least one predetermined crankshaft angle range and, in said idle situation, to detect a drop in rotational speed (Δn), occurring within said at least one predetermined crankshaft angle range, in said rotational speed (N) of said crankshaft as a value, and being configured to compare said value of said detected drop in rotational speed (Δn) with a predetermined value of a drop in rotational speed (ΔnL) and, when said predetermined value (ΔnL) of said drop in rotational speed (Δn) is exceeded, to switch over to said ignition time (ITA) for said acceleration situation;
• and wherein said at least one predetermined crankshaft angle range extends over a crankshaft angle (CA) of up to 300°.

A method for switching over an ignition time in a spark-ignition combustion engine having a spark plug arranged in a combustion chamber of the combustion engine, and a piston which compresses a fuel/air mixture, supplied to the combustion chamber, on its way from bottom dead center to top dead center, wherein the supplied combustion air is apportioned with a control element via an intake channel in dependence on an operating state of the combustion engine, wherein the method comprises the steps of:

• detecting a drop in rotational speed (Δn) occurring during a compression stroke in an idle situation of the combustion engine;
• comparing the detected drop in rotational speed (Δn) to a predetermined drop in rotational speed (ΔnL);
• and,
• making a switch over to an ignition time for an acceleration situation when the detected drop in rotational speed (Δn) exceeds the predetermined drop in rotational speed (ΔnL).