Ignition timing measuring apparatus

Apparatus for measuring the ignition timing of a multi-cylinder internal combustion engine having a rotating crankshaft, electrical signal generating means located adjacent a rotating member driven by said crankshaft to indicate when said crankshaft is in a predetermined position subsequent to the top dead center position of the crankshaft, a plurality of igniters, one for each cylinder, and means for periodically and successively energizing said igniters, said apparatus comprising:

• ignition signal means adapted to be connected to that one of said igniters which is energized closest to the time at which said crankshaft is in a top dead center position to produce a first electrical signal when said igniter is energized,
• reference signal means adapted to be connected to said electrical signal generating means to produce a second electrical signal when said crankshaft is in the predetermined position having a fixed relationship subsequent to the top dead center position of the crankshaft,
• means to generate a pulse train having a constant number of pulses per engine revolution,
• a counter connected to said pulse train generating means for counting the pulses produced thereby,
• means connected to said ignition signal means for initiating said counting operation in response to said first electrical signal when said one igniter is energized regardless of whether said igniter is energized prior to or subsequent to said top dead center position,
• means connected to said reference signal means for terminating said counting operation in response to said second electrical signal when said crankshaft is in said predetermined position and for maintaining said counting operation ineffective until said one igniter is again energized,
• compensating means connected to said counter for compensating the operation of said counter in accordance with the reference angle between said predetermined position of the crankshaft and the top dead center position thereof,
• and indicating means connected to said counter for indicating the extent and direction that the position of the crankshaft at which said one igniter is energized differs from the related top dead center position of the crankshaft.