GB720534A - Improvements in or relating to ignition systems for reciprocating internal combustionengines - Google Patents

Abstract

720,534. Ignition systems ; sparking plugs. ROLLS-ROYCE, Ltd. April 28, 1952 [Jan. 30, 1951], No. 2376/51. Class 7 (4). Ignition circuit. In an ignition system comprising an engine-driven peaked-voltagewave generator 10, Fig. 1, a condenser 12 which is permanently .connected through a high resistance or inductive choke 13 to the generator to be charged thereby, a plurality of low-voltage sparking plugs 14 and distributer means 15 driven in timed relation to the generator through which the condenser is connected to the plugs 14, the distributer means 15 is arranged to have a " make " period which is sufficiently long to permit substantially complete discharge of the condenser directly through the distributer means and a sparking plug. The engine-driven A.C. or D.C. generator is connected to a circuit comprising the resistance 13 (e.g. 33,000 ohms) and the condenser 12, one plate of which latter is earthed whilst the other is connected to the rotor arm 15a of a jump-spark distributer 15. The low-tension sparking plugs 14 are each shunted by a resistance 17 (e.g. 0.5 megohm) and in the twelve cylinder engine illustrated the distributer is in the " make " and " break " condition for about 16 degrees and 14 degrees, respectively, during each revolution of the rotor arm. Sparking plugs. The insulator 22, Fig. 2, which fills the space between the centre and earthed electrodes 20, 21 and covers the protruding end of the centre electrode has the outer surface 23 of the exposed part treated so as to be semi-conductive and to have a negative temperature coefficient of resistance. When the plug is energized the current passes through a small part of surface 23 which heats up and its resistance progressively falls until a sparking condition prevails.