Engine spark timing system and method with supplementary retard in normal and starting modes

A spark timing control for a spark ignited, internal combustion engine having a rotating crankshaft characterized by a range of normal rotational speeds during engine operation other than engine starting, cranking means actuatable to rotate the crankshaft for engine starting at a cranking speed less than any of the normal rotational speeds and means for generating fuel ignition sparks in response to spark timing pulses, the spark timing control comprising, in combination:

• first means driven by the crankshaft and effective to generate normal spark timing pulses at predetermined angles of crankshaft rotation;
• a first capacitor;
• second means effective at the time of each normal spark firing pulse to commence a progressively varying voltage in a first direction across the first capacitor at a first substantially constant rate and, when the voltage across the capacitor reaches a reference, to generate a retarded spark timing pulse;
• third means effective at the time of each retarded spark timing pulse to commence a progressively varying voltage across the first capacitor in a direction opposite the first direction at a second substantially constant rate slower than the first substantially constant rate and continuing until the next following normal spark timing pulse;
• first switch means responsive to a first predetermined set of engine conditions to connect the first means to the spark generating means and thereby generate ignition sparks at times determined by the normal spark timing pulses and further responsive to actuation of one of a) the cranking means and b) a second predetermined set of engine operating conditions to connect the second means to the spark generating means and thereby generate fuel ignition sparks at times determined by the retarded spark timing pulses;
• a second capacitor;
• second switch means responsive to actuation of the cranking means to connect the second capacitor in parallel with the first capacitor during engine starting, whereby the first and second substantially constant rates of the progressively varying voltage are reduced in the same proportion to prevent clipping of the progressively varying voltage at the cranking speed and thus maintain the desired timing of the retarded spark timing pulses during engine starting.

A method of controlling the spark timing of a spark-ignited combustion engine having a crankshaft characterized by a range of normal rotational speeds in engine operation other than during engine starting and further having cranking means actuatable to rotate the crankshaft during engine starting at a cranking speed less than any of the normal rotational speeds, the method comprising:

• generating normal spark timing signals at predetermined times as the crankshaft rotates;
• generating a bidirectional ramp voltage across capacitor means normally having a first capacitance in a first direction at a first time rate and a second direction, opposite the first direction, at a second time rate;
• changing the direction of the ramp voltage from the second to the first direction at the time of each normal spark timing signal;
• changing the direction of the ramp voltage from the first to the second direction each time the ramp voltage equals a predetermined reference voltage;
• generating, each time the ramp voltage equals the predetermined reference voltage, a retarded spark timing signal corresponding to, but retarded in crankshaft angle with respect to, a normal spark timing signal;
• selecting, in response to at least one engine operating condition, one of each normal and corresponding retarded spark timing signals during normal engine operation;
• selecting, during actuation of the cranking means, the retarded spark timing pulses;
• increasing the capacitance of the capacitor means to a second capacitance during actuation of the cranking means, whereby the first and second time rates are slowed proportionally to prevent clipping of the bidirectional ramp voltage at cranking speed.