Patent GB-1379172-A (GB)
Title: Ignition system for an internal combustion engine
IPC: F02P3/05
Filed: 1972-03-09
Abstract: 1379172 Timing ignition S R FINCH 9 March 1972 [12 March 1971 12 Oct 1971] 11119/72 Heading F1B In an I.C. engine ignition timing system means are provided to detect the speed of the crankshaft and to detect the degree of openness of the throttle, and time delay means are provided to control energization of the ignition means at a selected time in relation to rotation of the crankshaft, the time delay means being controlled by the detecting means to advance the selected time in response to an increase in crank-shaft speed  and to retard the selected time in response to an increase in the degree of openness of the throttle. As shown in Fig.2, the crank-shaft speed is determined by a pair of electromagnetic pick-ups 11,12 respectively providing a pair of pulses 30, 30', Fig.5, and connected to respectively set and reset a flip-flop, Fig.4 (not shown). A pulse 37 is then produced having a leading edge which is delayed by a fixed duration 34 with respect to the set instant of the flip-flop and a trailing edge which is coincident with the reset instant of the flip-flop. For the duration of this pulse, which varies inversely with engine speed, a capacitor C10, varied with the degree of openness of the throttle, Fig.3, is charged, the degree of charge reached at the trailing edge of pulse 37 being inversely related to engine speed. The capacitor is then discharged, the rate of discharge being directly related to the degree of openness of the throttle. The voltage across capacitor C10 is  shown at 42. A pulse 45 is provided for the duration of discharge of the capacitor C10, and during this pulse another capacitor is caused to charge, and thereafter discharge at a constant rate (see voltage curve 47). A pulse 48 is produced whilst the charge on the capacitor is below a threshold 49, the trailing edge of this pulse determining the instant of ignition. In an alternative embodiment, Figs.7-10 (not shown), the degree of openness of the throttle is detected by a variable inductor connected to control the charging rate of a capacitor which is charged from the instant of the pulse from pickup 11, the charging rate also being controlled by the engine speed from the instant of the leading edge of pulse 31. The degree of charge reached at this instant is thereby directly related to throttle opening and inversely related to crank-shaft speed. The capacitor is then discharged at a constant rate, the instant when the charge reaches a certain level determining the instant of ignition. The ignition circuit is shown in Fig. 11. It comprises an ignition coil having a primary winding 10' and a secondary winding 11', a circuit for controlling the voltage across the primary winding and a distributor T. The circuit consists of a transistor Q 1 ' which is a component of the timing circuit, a transistor Q 2 ', resistors R 1 ' and R 2 ' and diodes D 1 ' and D 2 '. When the transistor Q 1 ' is rendered conductive, a high voltage is initially applied to the primary winding 10' in order to rapidly increase the current flow through this winding. When the current reaches the required value, the voltage is reduced due to resistor R 1 ', the current however maintaining its required value. When the transistor Q 1 ' is rendered non-conductive at the  required ignition point, flow of current through winding 10' is interrupted to cause ignition.