Spark ignition circuits

1,111,716. Ignition systems. JOSEPH LUCAS (INDUSTRIES) Ltd. Oct.14, 1965 [Dec. 1964; July 7, 1965], Nos. 48947/64 and 28749/65. Heading F1B. A spark ignition circuit comprises a magnetic pick-up winding 11 associated with the starter gear ring 12, the starter gear ring producing pulses in the magnetic pick-up winding at a frequency proportional to engine speed, a capacitor, an integrating circuit 29, 31, 32 coupling the capacitor 34 to the magnetic pick-up winding, whereby a voltage proportional to engine speed is developed across the capacitor 34 and a control circuit coupling the capacitor to the primary winding 47 of the ignition coil, the control circuit being sensitive to the voltage across the capacitor and stopping current flow in the primary winding when the voltage is above a predetermined value. The control circuit may include a bi-stable circuit 33, 41 which normally occupies a first state but above a predetermined engine speed is driven to a second state in which it stops current flow through the primary winding. Current may flow through the bi-stable circuit when in its second state to energize a relay the contacts of which short circuit the primary winding. The bi-stable circuit may act when in its second state to break the circuit of the primary winding.