GB987833A - Improvements in or relating to electronic ignition systems - Google Patents

Abstract

987,833. Ignition systems. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Sept. 5, 1963 [Sept. 8, 1962] No. 35114/63. Heading FIB. An ignition system for an internal-combustion engine comprises a transistor, a source of power therefor, a transformer having primary and secondary windings, means connecting the primary winding of the transformer in the emitter-collector circuit of the transistor, means normally applying a bias voltage between the emitter and base electrodes of such a magnitude as to preclude the flow of current in the emittercollector circuit and means for suddenly reducing the bias voltage to switch the emittercollector circuit to a low impedance condition so as to apply substantially the full potential of the source of power to the primary winding to produce a high voltage pulse in the secondary winding of the transformer the means for suddenly reducing the bias voltage comprising a triggered pulse producing circuit controlled by an ignition timing mechanism and the timing mechanism comprising a bridge network incorporating in two arms thereof Hall effect semi-conductors the semi-conductors being adjacent each other and subjected sequentially to a moving magnetic field which alternatively unbalances the bridge in one direction and then the other to produce a voltage change initiating operation of the means for suddenly reducing the bias voltage. Transistor 11 produces oscillations which are rectified by the diodes 9, 10 to produce a voltage of for instance 50 volts across the capacitor 12. Transistor 20 is provided with an emitter voltage somewhat negative with respect to the positive terminal of the supply the actual voltage thereof being determined by the setting of the variable resistor 13 controlled by the accelerator pedal. The base electrode bias of the transistor 20 is initially determined by resistors 15, 36, 38 and Hall effect semi-conductors 33, 37 and is such that the transistor is normally cut off when no magnetic bias is applied to the semiconductor elements 33, 37 a rotating disc 34 is provided with permanent magnet members 35 which when the disc rotates each successively applies a moving field to the element 33 and then to the element 37 so that the base electrode voltage of the transistor 20 first is moved positive due to the increased resistance of the element 33 and then negative due to the subsequent increase of the resistance of the element 37 the resistance of element 33 having returned to normal. Although the schematic diagram shows elements 33, 37 as being spaced apart in practice they will be immediately adjacent to each other. The increase of the resistance of element 37 is designed to be sufficient to reduce the base bias of transistor 20 to the point where regenerative current conduction will take place due to the voltage feedback supplied by transformer 19. The regeneratively produced collector current which flows in the transistor 20 produces a voltage pulse in the transformer 25 which is supplied as a negative pulse to the base electrode of normally cut off power transistor 26 to suddenly render it heavily conducting. A stepped up voltage of for instance 200 volts appears between terminals 31, 32 and is applied to the primary of the ignition coil. The upper part of coil 30 may be the ignition coil primary itself. If desired a bi-stable transistorised multivibrator circuit or other suitable pulse producing source may replace the monostable oscillator comprising transistor 20. U.S.A. Specifications 2,898,392 and 2,966,615 are referred to.