GB1420814A - Ignition timing for internal combustion engines - Google Patents

Abstract

1420814 Ignition systems; timing ignition LUMENITION Ltd 1 April 1974 [6 April 1973] 16680/73 Heading FIB In an electronic ignition system for an internal combustion engine each spark at a spark plug is extinguished at a predetermined crank shaft angle irrespective of the crank shaft angle at which this spark is initiated. As the disc 3 is rotated at crank shaft speed of the engine the infrared radiation from lamps 5 and 6 impinges on respective phototransistors 7 and 8 through the apertures 9 and slits 10. Accordingly the photo-transistor 7 produces four current pulses per revolution of the disc 3 whilst the photo-transistor 8 produces a large number of pulses per revolution. The two triggers comprising transistors 30a, 32a and 30b, 32b fast switch and amplify these pulses. During the time that the photo-transistor 7 is energized the transistors 30a and 32a are respectively OFF and ON. When the infrared radiation is cut off the output of the first trigger becomes high. This output is applied to both a frequency divider 14 and a transistor 50. The frequency divider 14 now counts the pulses from the second trigger 30b, 32b according to the number set into it from a computer 16. The output of the frequency divider 14 is at a low level unless the computer calls for maximum advance. Therefore when the first trigger 30a, 32a produces a high level output the power transistors 54, 56 are not switched because of the continued presence of a low level output from the frequency divider 14. In the example illustrated the frequency divider is set to count down a total of six pulses before the output switches to the high level. When the count of six has been completed the output becomes high at the seventh pulse and the transistor 50 switches on. This in turn switches the power transistor Darlington pair 54, 56 off to switch off the flow of current in the primary winding of the ignition coil 26 and thus initiate a spark at a plug 72. After a predetermined time the output of the first trigger reverts to a low level thus extinguishing the spark and resetting the frequency divider which also reverts to a low level, these events both happening when the photo transistor 7 is again energized by infrared radiation. The computer 16 receives at two inputs 24a, 24b information concerning the speed and load of the engine and the computer calculates the count down necessary to obtain the correct advance or retard of the ignition timing.