Pulse controlled spark advance unit for an internal combustion engine

Abstract

A power unit (79) includes a spark advance unit (80) connected to a solid state ignition system (81) for selectively supplying ignition sparks to operate an internal combustion engine (83). A pulse generator (107) responds to a series of negative polarity half-cycle alternations (96) provided by an alternator winding (20') to provide a first pulse output (110) of a first frequency. A pulse counter (119) counts the pulses of the first pulse output (110) to provide a second pulse output (120) having a second frequency which is an exact fraction of the frequency of the first pulse output (110). A pair of counters (162, 141) selectively accumulate constant frequency pulses from an independent oscillator (127), as selectively controlled by the first and second pulse outputs (110, 120), to establish high and low speed advance points which are inter-related by a fixed numerical ratio. A pair of latch circuits (170, 149) are respectively connected to respond to one of the first and second pulse outputs (110, 120) and to the count status of one of the counters (162, 141) to selectively operate a modifying circuit (203, 180) to provide control signals to the ignition system (81) to provide a rapid spark angle advance at preselected speeds.