Ignition system improvements for internal combustion engines

Abstract

This invention relates to a number of improvements in ignition systems of spark ignition engines. A detector is employed to sense the first or 'breakdown' phase of spark discharge across the spark plug which causes a short duration high current flow across the plug gap. The detection of the breakdown current enables control over a number of ignition system functions. A pulse transformer is used which enables extremely short duration energization of the spark plug at controllable voltages. The existence of end gas auto-ignition is detected by energizing the spark plug during a period of the operating cycle after top dead center of piston travel. Since the threshold voltage necessary to generate spark discharge at the plug differs in conditions where auto-ignition is occurring versus ordinary combustion, sensing of plug breakdown during such energization provides a means of detecting the occurrence of auto-ignition. Further, in accordance with this invention, the spark plug may be caused to multiply discharge within a short duration which has been found to increase the lean burn limit of the engine. The system further enables the duty cycle of the pulse transformer to be reduced thus allowing use of smaller and lighter weight pulse transformers. The ignition system also provides a means of sensing abnormal conditions in the combustion chamber via the spark plug. Pre-ignition occurring at the spark plug electrode gap will result in a very low breakdown voltage which is detected as an indication of an abnormal condition.