Patent GB-757874-A (GB)
Abstract: 757,874. Ignition systems. GENERAL MOTORS CORPORATION. Dec. 10, 1954 [Jan. 8, 1954; Jan. 8, 1954], No. 35747/54. Class 7(4) [Also in Group XXXV] In a H.F. ignition system comprising a source of A.C., rectifiers 22, Fig. 1, an ignition condenser 34 adapted to be charged by the rectified current and to energize the primary of the ignition coil 38 by periodic discharge under the control of a triggering thyratron 36, and a triggering condenser 44 adapted to be charged by the rectified current and connected by closure of a contact-breaker 54 to the thyratron so as to discharge and render the thyratron conductive, the circuit to the ignition condenser 34 includes a rectifier 30 and an inductor 32. Ignition circuit. The primary winding of an input transformer 20 is supplied with A.C. from a vibrator, not shown, connected to a battery or generator, the transformer secondary feeding a first terminal 28 via the pair of cold-cathode rectifiers 22 and voltage-doubled condensers 24, the terminal 28 having a potential of 600- 1,000 volts and being connected to earth 42 through the cold-cathode rectifier 30, inductor 32, ignition condenser 34 and the primary of the H.F. ignition coil 38. The damped voltage oscillations which would normally occur across the condenser 34 are cut off at the first maximum voltage peak by the rectifier 30, which voltage is twice that at the terminal 28, due to the inductor 32, and is the value to which the condenser is charged. The ignition-coil secondary is in circuit with the sparking plugs 40 through a distributer, not shown. In a modification, the first terminal is connected to a variable-field alternator through bridge-connected rectifiers, the vibrator and associated rectifiers and condensers being dispensed with. In another modification, a winding 130, Fig. 4, is connected in the starter-motor circuit, not shown, so as to be energized therewith whereupon relay contacts 116 and 124 are made and the voltage applied to the rectifiers 22 is that across the ends of the secondary winding 102 of the transformer 20; upon de-energizing winding 130 contacts 122, 124 cooperate and the rectifiers have a reduced voltage from a mid-secondary tapping 104 supplied thereto. A ballast lamp 132 may be located, where shown, or at the point 110 in series with the transformer secondary winding, in order to provide a more constant ignition voltage than would otherwise result. A buffer condenser 136 is shunted across the relay contacts 116 and 122. Triggering circuit. The terminal 28 is connected by a resistance 46 to a second terminal 51 earthed through a main triggering condenser 44 in parallel with a coldcathode regulating valve 50 which conducts and serves as a by-pass whenever the potential of the terminal exceeds a given value, say 300 volts, which is therefore the maximum voltage that can be applied to the condenser 44. When the circuit-breaker contacts 54 are closed an auxiliary triggering condenser 56 is charged from condenser 44 via earth and a cold-cathode thyratron 36 whereby the latter conducts and causes the ignition condenser 34 to energize the primary of the ignition coil 38. Upon opening of the contacts 54 the condenser 56 discharges through resistances 60, 62 and imposes a negative potential on the thyratron grid to remove any possibility of the thyratron conducting. In the Fig. 4 modification, a second thyratron 100 is reversely connected in parallel with the main thyratron 36 so that the small reversed voltage charge which is impressed upon the condenser 34 due to the action of the inductance of primary winding 38, and after the main charge thereof has been dissipated, is used to prolong the duration of the sparking plug breakdown and reduce the power absorbed by the system. Details of the electrical components are given.