Electronic ignition systems for an internal combustion engine

Claim 1

A device for automatic variation of the ignition spark advance angle in an electronic ignition system for an internal combustion engine, of the type comprising an ignition spark discharge control circuit, and a device for varying the instant of discharge of the ignition spark, wherein said device comprises: reference means located on a rotating member of the engine which turns with the crankshaft, said reference means comprising: at least one protuberance phase displaced in advance of a position on said rotating member representing the top dead centre position of said crankshaft of said engine by an angle θ m equal to the maximum spark advance angle required, said protuberance defining a reference position of said crankshaft, and a series of teeth on said rotating member, first pick-up means sensitive to the passage therepast of said teeth on said rotating member and responsive thereto to produce a train of pulses representing the speed of rotation of said rotating member; first counting means for counting said train of pulses from said first pick-up means during each ignition timing cycle of said engine, second pick-up means responsive to the passage therepast of said at least one protuberance to produce a pulse indicating said reference position of said crankshaft, means responsive to the output of said first counting means operating to initiate the ignition spark when said first counting means reach a predetermined count, first logic gating means connected to the output of said first pick-up means, means connecting the output from said first logic gating means to the input of said first counting means, said first logic gating means selectively permitting the passage of pulses fed thereto to said first counting means, second counting means for counting the pulses produced by said first pick-up means from the moment when said protuberance passes said second pick-up means indicating that said crankshaft of said engine is at said reference position, timing circuit means operating to produce a timing signal output a predetermined time T after an input signal has been fed thereto, logic switching circuit means having a control input connected to the output from said second counting means, the output from said switching circuit means being connected to the input of said timing circuit, means connecting the output of said timing circuit, to a second input of said first logic gating means, frequency doubling means connected between said first logic gating means and said first counting means, said frequency doubling means operating to double the frequency of the pulses produced by said first pick-up means in the time interval between the instant when said crankshaft is in said reference position and the instant of discharge of the ignition spark, and if the speed of the engine is lower than a predetermined threshold n 1 , also during said timing interval T or part thereof.

Claim 2

A device for automatic variation of the ignition spark advance angle in an electronic ignition system for an internal combustion engine, of the type comprising an ignition spark discharge control circuit, and a device for varying the instant of discharge of the ignition spark, wherein said device comprises: reference means located on a rotating member of the engine which turns with the crankshaft, said reference means comprising: at least one protuberance phase displaced in advance of a position on said rotating member representing the top dead centre position of said crankshaft of said engine by an angle θ m equal to the maximum spark advance angle required, said protuberance defining a reference position of said crankshaft, and a series of teeth on said rotating member, first pick-up means sensitive to the passage therepast of said teeth on said rotating member and responsive thereto to produce a train of pulses representing the speed of rotation of said rotating member; first counting means for counting said train of pulses from said first pick-up means during each ignition timing cycle of said engine, second pick-up means responsive to the passage therepast of said at least one protuberance to produce a pulse indicating said reference position of said crankshaft, means responsive to the output of said first counting means operating to initiate the ignition spark when said first counting means reach a predetermined count, first logic gating means connected to the output of said first pick-up means, means connecting the output from said first logic gating means to the input of said first counting means, said first logic gating means selectively permitting the passage of pulses fed thereto to said first counting means, second counting means for counting the pulses produced by said first pick-up means from the moment when said protuberance passes said second pick-up means indicating that said crankshaft of said engine is at said reference position, timing circuit means operating to produce a timing signal output a predetermined time T after an input signal has been fed thereto, logic switching circuit means having a control input connected to the output from said second counting means, the output from said switching circuit means being connected to the input of said timing circuit, means connecting the output of said timing circuit, to a second input of said first logic gating means, frequency doubling means connected between said first logic gating means and said first counting means, said frequency doubling means operating to double the frequency of the pulses produced by said first pick-up means in the time interval between the instant when said crankshaft is in said reference position and the instant of discharge of the ignition spark, and if the speed of the engine is lower than a predetermined threshold n 1 , also during said timing interval T or part thereof.