Digital timing system for spark advance

Means to set spark advance timing in accordance with engine speed, comprising:

• a source of engine speed reference pulses having a period corresponding with the period between ignitions in a cylinder at whatever speed the engine is running,
• a clock source of high-frequency clock pulses and sub-multiple frequency clock pulses,
• a counter receptive to said high-frequency clock pulses during the period between two engine speed reference pulses to provide an engine reference period number, the value of which represents the time period between said ignitions,
• a read-only memory having successive memory locations each storing an addend quantity and a repeats number,
• an adder unit, including an accumulator, operative during the period between two successive engine speed reference pulses to access the first and following memory locations, and with each access to add, at the sub-multiple clock rate, the addend quantity to the contents of the accumulator repeatedly a number of times equal to the repeats number, said addend quantities having values comparable to the ratio of said high-frequency to said sub-multiple-frequency clock pulses, and
• a comparator producing an ignition firing pulse when the contents of said accumulator corresponds with the value of the reference period number provided by said counter,
• said addend quantities and repeats numbers stored in said memory being such that the contents of the accumulator reaches a value corresponding with the value reached in said counter at a time providing the spark advance desired at the existing engine speed.

Means to set ignition spark timing in accordance with engine speed, comprising in combination:

• a source of engine speed reference pulses having a period corresponding with the speed at which the engine is running;
• a source of clock pulses;
• means responsive to said clock pulses during the period between two engine speed reference pulses to provide an engine reference period number, the value of which represents the time period between ignitions;
• a memory having successive memory locations each storing an addend quantity and a repeats number;
• means for accessing said memory location in an ordered sequence beginning at a starting location following the generation of said engine period number for providing said addend quantities and repeats number in succession therefrom;
• and
• means coupled to said memory for accumulating at a rate determined solely by the rate of said clock pulses the addend quantity at said starting location a number of times equal to its associated repeats number, then accumulating the addend quantity at the next location a number of times equal to its associated repeats number, etc. until the total accumulated sum corresponds with said engine reference period number and in response to said correspondence, producing a spark timing pulse.