Electronically controlled ignition system

Claim 1

An electronically controlled ignition system comprising an ignition coil having a primary winding, means for supplying primary current to said primary winding at a timing which is controlled in accordance with speed, said primary current only reaching the value required for ignition shortly before the moment of ignition, means for determining immediately before the moment of ignition whether said primary current has reached said value required for ignition, said determining means comprising means for deriving a test pulse dependent on the duration for which said primary current is at said value required for ignition, said test pulse switching off the electronic control for a fixed period when there is no primary current or insufficient primary current to prevent misfiring, and an ignition pulse generator producing a control signal the timing of said primary current being derived directly from said control signal, wherein the system further comprises an integrating stage, said integrating stage extending said test pulse by a predetermined period of time to produce an extended pulse, a logic circuit having first and second inputs, said extended pulse being fed to said first input and means for deriving a trigger pulse for the trailing flank of said control signal, said trigger pulse being supplied to said second input, said logic circuit producing an output pulse for switching off the electronic control only if said integrating stage does not produce a said extended pulse during the said trigger pulse.