ADVENT of engines operating at higher compression and higher speed than engines used a few years ago in automotive vehicles has necessitated refinement of all engine accessories, including the ignition equipment. It is necessary that the ignition units give unfailing performance at top speed of the engine without sacrifice of long life of the units. Storage-battery ignition, with a generator as a source of energy, is used almost universally in this Country today, and is asserted to be the cheapest, simplest, easiest to service and most reliable system known for vehicles in which a storage battery is required for starting, lighting and other purposes.
The electrical circuit used in the ignition system of automobiles today is almost identical with that designed for the 1912-model Cadillac, which was equipped with the Delco electrical engine-starter, except for refinements and greater reliability. Development has been carried on to adapt the system to the more exacting requirements imposed by the high-compression ratios and at the same time to improve its performance at top speed of the high-speed engine.
Essential parts of the battery ignition-system are listed and the required mechanical and electrical properties of a system that will operate satisfactorily on present high-speed high-compression engines are described.
The author discusses the exactions imposed on the distributor by engine torsional vibration, the need of an automatic spark-advance mechanism in the distributor, the peculiar conditions in some engines caused by non-homogeneous mixture surrounding the spark-plugs, the difficulties arising from shrinkage of materials used for coil tops, rotors, and distributor caps during their manufacture, the characteristics of the primary and secondary currents, the influence of the high-compression engine on design of the distributor cam and circuit-breaker lever, construction of the ignition coil and the advantage of the high-inductance coil, and other related matters.
No attempt is made to predict the future trend in ignition, but belief is expressed that a device that will automatically advance the spark above full-throttle position when operating at low load with partly closed throttle would make possible a better carbureter-setting on part throttle and result in better fuel economy at car speeds between 15 and 50 m.p.h.