Ignition systems for internal combustion engines

Abstract

The advance and retard of the spark ignition in an ignition system of an internal combustion engine is achieved electronically by generating two series of pulses in synchronism with the engine using one series as a reference for maximum advance and the other series to operate a counter to count down the requisite number of pulses beyond the maximum advance point before the spark is initiated, the count of the counter being varied from a computer in accordance with speed and/or load on the engine.

What I claim and desire to secure by Letters Patent is: 
     
       1. An electronic device for controlling the advance and retard of the ignition timing of an internal combustion engine in accordance with engine requirements, including means for generating a first series of square-wave voltage pulses in synchronism with the engine revolutions to provide a series of alternate first and second voltage levels; means for generating a second series of square-wave voltage pulses also in synchronism with the engine revolutions and at a fixed multiple of the first series of square-wave voltage pulses, so that the frequency of the second series of voltage pulses is greatly in excess of the frequency of the first series of voltage pulses; means for counting a .Iadd.predetermined .Iaddend.number of the second series of voltage pulses from a .[.predetermined.]. point .[.in relation to the first series of voltage pulses,.]. .Iadd.at which the logic level of the first series of pulses changes to the first voltage level.Iaddend., the number of said pulses counted depending on the engine requirements; means for producing an output at the first voltage level from said counting means after said count has been completed; means for detecting the presence of both an output at the first voltage level from the first pulse generating means.[.,.]. and an output at the first level from the counting means .[.in order to initiate.]. .Iadd.and, upon such occurrence, initiating .Iaddend.the production of a spark .Iadd.and causing spark duration to begin .Iaddend.for the combustion of the fuel, .Iadd.the outputs from both the counting means and the first pulse generating means remaining at the first voltage level until the logic level of the first pulse generating means changes to a second voltage level at a given engine crankshaft position and causes termination of spark duration.Iaddend.; and means for continuously varying the count of the counting means, so as to advance and retard the ignition timing in accordance with the requirements of the engine. 
     
     
       2. An electronic device according to claim 1, including an ignition coil having primary and secondary windings, wherein the counting means starts to count from a position equivalent to the maximum advance for any given running condition of the engine, a high voltage level output from the first pulse generating means, representing said first voltage level, initiating the start of the count, the counting means then counting down the predetermined number set therein before giving a high voltage level output, which together with the high voltage level output of the first pulse generating means, causes the de-energization of the primary winding of the ignition coil in order to induce a voltage in the secondary winding of the ignition coil sufficient to produce a spark. 
     
     
       3. An electronic device according to claim 1, wherein the counting means is a frequency divider. 
     
     
       4. An electronic device according to claim 3, wherein the means for varying the count of the frequency divider is a computer whose digital output is modified in accordance with digital information fed thereto as regards the speed and load conditions on the engine. 
     
     
       5. An electronic device according to claim 1, wherein the first and second series of generated pulses are each applied to respective trigger circuits, each trigger circuit comprising a plurality of cascaded transistors arranged to switch in inverse relation to one another so that at any one time one transistor is fully saturated while the immediately neighboring transistors are fully cut off. 
     
     
       6. An electronic device according to claim 1, including a power transistor stage; and a pre-amplifier stage the pre-amplifier stage being arranged to be turned on only in the presence of both a high voltage level pulse from the first pulse generating means and a high voltage level pulse from the counting means, the transistors of the pre-amplifier stage and the power transistor stage switching in inverse relation to one another. 
     
     
       7. An electronic device according to claim 6, wherein the power transistor stage comprises a darlington pair having a commoned collector electrode, a zener diode and series resistor being connected between the commoned collectors and the base electrode of the first transistor of the pair, the collector electrode of the transistor of the pre-amplifier stage being connected to the base electrode of the first transistor of the darlington pair by way of a diode. 
     
     
       8. An electronic device according to claim 1, including: an opaque disc driven in synchronism with the engine; 68 equi-spaced slits around the disc near the periphery thereof; n equi-spaced apertures near the center of the disc, where n is related to the number of cylinders in the engine; a pair of infra-red sources positioned on one side of the disc, in line with the slits and apertures; a pair of infra-red detectors positioned on the other side of the disc for generating said first and second square-wave voltage pulses as "high" and "lows" representing the first and second voltage levels respectively, the count of the counting means commencing at the instant that the infra-red radiation is cut off from the first detector. 
     
     
       9. An electronic device for controlling the advance and retard of the ignition timing of an n cylinder internal combustion engine, having an ignition coil with primary and secondary windings, said device including an opaque disc driven in synchronism with the engine; a series of equi-spaced slits around the disc; n equi-spaced apertures in the disc; a pair of infra-red radiation sources and a pair of infra-red radiation detectors arranged on opposite sides of the disc, .[.the.]. .Iadd.a .Iaddend.first element of each pair being arranged to cooperate with said n apertures and .[.the.]. .Iadd.a .Iaddend.second element of each pair .Iadd. being arranged to cooperate .Iaddend.with the slits, .[.one.]. .Iadd.a first one of said .Iaddend.infra-red .[.detector.]. .Iadd.detectors .Iaddend.generating a first series of square-wave voltage pulses in synchronism with the engine revolutions, to provide a series of alternate first and second voltage levels; .[.the other.]. .Iadd.a second one of said .Iaddend.infra-red  .[.detector.]. .Iadd.detectors .Iaddend.generating a second series of square-wave voltage pulses also in synchronism with the engine revolutions, and at a fixed multiple of the first series of square-wave voltage pulses, so that the frequency of the second series of voltage pulses is greatly in excess of the first series; a .[.frequency divider circuit.]. .Iadd.counter .Iaddend.for counting .[.the pulses generated from the second infra-red detector at a starting point determined when said respective first series of pulses change from the second to the first voltage level.]. .Iadd.a predetermined number of the second series of voltage pulses from a point at which the logic level .Iadd.of the first series of voltage pulses changes to the first voltage level, the number of said pulses counted depending on engine requirements; means for producing an output at the first voltage level from said counter after said count has been completed.Iaddend.; a computer connected to receive .[.analogue.]. .Iadd.analog .Iaddend.information from a pair of inputs regarding the requirements of the engine, and providing a corresponding digital output, in accordance with that information for changing the count of the .[.frequency divider, the frequency divider producing an output after the predetermined count.]. .Iadd.counter; logic circuitry for detecting the presence of both an output at the first voltage level from the first detector and an output at the first voltage level from said counter.Iaddend.; a transistorized power stage in series with the primary winding of the ignition coil, the power stage being rendered non-conductive .[.at the instant when there is a first voltage level output from the frequency divider and the first detector thereby initiating the spark for ignition, the advance and retard of the ignition timing being continuously adjusted in accordance with engine requirements.]. .Iadd.in response to the logic circuitry detecting the presence of both outputs and thereby initiating the production of a spark and causing spark duration to begin for the combustion of the fuel, the outputs from both said counter and the first detector remaining at the first voltage level until the logic level of the first detector changes to a second voltage level at a given engine crankshaft position.Iaddend.. 
     
     
       10. An electronic device according to claim 9, wherein the computer has four outputs which are connected to four inputs of the frequency divider circuit, the outputs from the computer representing either a 1 or a 0, whereby a digital count of sixteen can be fed into the frequency divider, in accordance with binary notation, said computer providing a digital output to the frequency divider in accordance with information fed thereto regarding the engine requirements, and digital output being continuously modified as these engine conditions change, so that the ignition timing is appropriately controlled in sixteen steps between maximum and minimum advance requirements.