Patent GB-1483611-A (GB)
Title: Ignition systems for internal combustion engines
IPC: F02P5/152
Filed: 1974-05-07
Abstract: 1483611 Ignition systems; timing ignition LUMENITION Ltd 7 May 1975 [7 May 1974] 20148/74 Heading F1B An electronic ignition system for an I.C. engine includes means for advancing or retarding the ignition to ensure that commencement of the second stage of the combustion process, (as hereinafter defined), in a cylinder of the engine during each firing cycle, takes place at a predetermined crank-shaft angle. Commencement of the second stage of the combustion process is marked by a sudden rise in both the pressure and temperature within the cylinder at some point in time after ignition and slow propagation of the flame through the cylinder. As shown, a disc 3 having four apertures 9 and sixty-eight slots 10 is rotated by the crank-shaft between a pair of infra red sources 5, 6, e.g. gallium arsenide lamps and a pair of phototransistors 7, 8 connected to respective inverse fast switching triggers 11, 12 as in Specification 1410782. The output from the trigger 11 is fed to a power stage 18 and to an AND gate 19, the  second input of which is connected to a trigger 13  receiving an output from a Piezo-electric sensor 16 when the pressure in the engine cylinder exceeds a predetermined value, to signify commencement of the second stage of combustion. The AND gate feeds an output signal to a frequency divider 14, which counts the pulses from the second trigger 12 according to the number set therein and, when the count down is completed, the power stage 18 switches off the current to the ignition coil to produce a spark. At the predetermined crank-shaft angle, the first trigger reverts to its low level to extinguish the spark and reset the frequency divider 14. If the leading edge of the pulse from the trigger 13 occurs before the predetermined crank-shaft angle, no coincidence is detected at AND gate 19 and counter 14 is reduced by one step at a time until coincidence is detected. Similarly, if coincidence is detected, the counter is increased by one step at a time until coincidence is no longer detected. Again, Fig. 10, (not shown), the AND gate may be eliminated and an output transistor (70) of trigger 11 connected in parallel with an output transistor (72) of trigger 13. Alternatively, Figs. 4 and 5, (not shown), the AND gate is replaced by a comparator (17), and a differentiating circuit (21), limiter (22) and inverter (24) are connected in series between trigger 11 and the comparator. A frequency divider circuit (25) is provided between the inverter and comparator to divide by four if only one cylinder of a four cylinder engine has a detection device. The divider circuit is synchronized from trigger 13. Commencement of the second stage of combustion may alternatively be detected by a second spark-plug (44), Fig. 6, (not shown), across which a low voltage is maintained so that when the gap becomes fully ionized by the passage of the wave front thereacross, current will flow in a resistor in series with the gap. Again, Fig. 8, (not shown), a quartz glass window (54) is provided in the cylinder wall, and a fibre-optic cable (56) extends therefrom to a photo-transistor. In an alternative embodiment, Figs. 11 to 13, (not shown), the required advance and retard are determined electro-mechanically rather than electronically, the trigger 12 and frequency divider 14 being omitted. Instead, inlet manifold depression is utilized to position a forked rod (92) carrying the infra red radiation sources 5 and detectors 7 of the first trigger 11 with respect to an engine-driven disc having four apertures (102). One edge of each aperture extends radially but the other is inclined with respect to the radius to vary the crank-shaft angle at which to coil is switched off, according to the distance of the source 5 and detector 7 from the centre of the disc.