GB1359055A - Ignition systems - Google Patents

Abstract

1359055 Ignition system ROBERT BOSCH GmbH 24 Sept 1971 [28 Sept 1970] 44611/71 Heading F1B In an ignition system for an internal combustion engine comprising an ignition coil 14 with primary 14a and secondary 14b windings, spark plug 16 and a triggering device for supplying signals to a switching device 12 to periodically open and close the primary circuit, a monitoring device 9 also responds to the triggering signals and includes a timing circuit 23 for opening the primary circuit when a signal is not applied to the switching device 12 during period which exceeds the longest period between consecutive triggering signals when the engine is running. The timing circuit comprises a capacitor connected in series with a charging resistor across a D.C. voltage source and the monitoring device includes a discharge device triggered by the triggering signals for discharging the capacitor and means responsive to the charge on the capacitor exceeding a predetermined value for opening the switching device in the primary circuit. Thus currents flowing in the primary circuit during standstill of the engine, while the ignition switch 10 is closed, are prevented. During running of the engine capacitor 17 charges but is periodically discharged through element 19 when the latter is triggered by switching element 12 which also opens and closes the primary circuit. If the engine is stopped, switch 10 remaining closed, the switching device 12 ceases to operate so that capacitor 17 is no longer discharged and after a time, e.g. 1 second, device 23 passes a signal to the switching device 12 to open the ignition circuit. Two transistorized circuits are described one depending upon a cam operated mechanical switch and the other a magnetic pulse generator 70, Fig. 3, for the triggering signals. As shown in Fig. 3, in a monitoring device 113 capacitor 114 charges through resistor 115 but is periodically discharged due to transistor 118 being rendered conductive by a pulse derived from the pulse generator 70. When the engine is stopped the pulse generator no longer triggers and capacitor 114 is no longer discharged and hence after a time reaches the breakdown voltage of Zener 123 to thereby turn on transistor 124 and cut off transistors 91, 101, 103 and power transistor 106 to open the ignition circuit.