GB1515456A - Apparatus for measuring the dwell of an automotive ignition system - Google Patents

Abstract

1515456 Measuring dwell-ratio of an ignition system for an IC engine SUN ELECTRIC CORP 14 June 1976 [16 June 1975 31 March 1976] 24563/76 Heading G1U In a system for determining the dwell ratio of an ignition system by examining the voltage across the primary winding of the ignition coil, particularly when because of the use of electronic switching the dwell portion B, Fig. 3, of the primary voltage, of which one full cycle A-B is shown, is not absolutely zero (as it is when conventional mechanical points are used for switching) but is merely near zero for a first part (2) to (3) of the dwell portion and then rises (3) to (4) during the latter part of the dwell portion prior to the initiation (1) of the next spark, a first threshold circuit Ql, Fig. 2, monitors the primary voltage from a terminal D7 via a full-wave rectifier IC1, IC2, and allows a capacitor C1 to charge from zero towards +15v, when it is sufficiently small, and a second threshold circuit IC3 which when in its on state (output voltage +15v) monitors the capacitor Cl voltage and switches to its off state (output voltage -15v) when the capacitor Cl voltage exceeds a threshold of about +5v set by a Zener diode D9, and which in its off state monitors the primary voltage directly, via a diode D5, and switches to its on state when the primary voltage becomes sufficiently large as when the next spark (1) is initiated. Thus the off/on ratio of the threshold circuit IC3 corresponds to the dwell ratio B/A, but differs therefrom in that the on time is too long by an amount t, this being the time taken for the capacitor C1 voltage to rise above the turnoff level of threshold IC3. A further pulse train is therefore derived from the output of threshold circuit IC3 in which the on-time is reduced by an amount t. This is achieved by a Schmitt trigger IC4 and a capacitor C2. The resulting waveform which has the required off/on ratio is clipped above and below, IC5, IC6 and smoothed IC7, to provide a d.c. representing the dwell ratio.