GB959882A - Improvements in or relating to ignition systems - Google Patents

Abstract

959,882. Ignition systems. FORD MOTOR CO. Ltd. Jan, 7, 1963 [Jan. 31, 1962], No. 727/63. Heading F1B. In a transistorized ignition system -electromagnetic means operable by interruption of current in the input circuit of the transistor applies a reverse bias to the input terminals of the transistor. In the start position of the ignition switch 43 the movable arms 45 and 46 are in engagement with contacts 53 and 56. After the engine has started the switch is moved to the "on" position in which the movable arms 45 and 46 are positioned in engagement with the contacts 52 and 55 when the breaker points 66 are opened the current through the first input winding 17 is interrupted or substantially reduced to zero during normal operating conditions. The transistor 10 will therefore tend to be turned to its non-conducting state. It has however a large inductive element, primary winding 71 of ignition coil 72, connected in series with it. Current will continue to flow therefore through the transistor 10 for a short interval of time. This current also traverses the second input winding 25 and since it has a magnitude of approximately 12 amperes it will switch the core from its negative state of saturation to its positive state of saturation in a very rapid switching action. As a result of the switching of the core a voltage is induced in the output winding 31. This voltage is of a polarity to cause a reverse current to flow in the base emitter circuit of the transistor. The voltage is sufficient to cause a breakdown in the base to emitter junction of the transistor 10 and to cause a pulse of current through the base emitter circuit including the winding 31 and resistor 34 of a peak magnitude of approximately one ampere. This reverse current very rapidly switches the transistor 10 from its conducting to its non-conducting state since this current is reached in approximately 1/10 of a microsecond It has been determined that the transistor can be turned off in the range of from 3 to 6 microseconds. This will provide high output voltages from the secondary winding 74 of the ignition coil 72. Fig. 2 shows a modification in which current continuously flows through the second input winding 25. Thus the core 16 is continuously biased towards a direction of positive magnetization. The transistor may be of the pnp or npn type. Other means for interrupting the base current may be employed. For example a magnetic device that includes a winding positioned in series with the base circuit and a multi pole permanent magnet driven by the distributer and placed adjacent the winding may be employed.