Patent GB-1397827-A (GB)
Title: Arrangement for limiting the speed of an internal combustion engine
IPC: F02P9/00
Filed: 1972-11-03
Abstract: 1397827 Regulating I C engines; indicating working conditions; ignition systems ROBERT BOSCH GmbH 3 Nov 1972 [6 Nov 1971]  50714/72 Heading F1B Pulses produced by a pulse generator driven by an I.C. engine, or pulses derived from them, are fed to the first input of an AND gate and are also fed to the trigger input of a monostable multivibrator, the monostable multi-vibrator being triggerable by the pulses to apply to the second input of the AND gate further pulses of a phase relate to the pulses applied to the first input and of a period such that coincidence of pulses at the inputs of the AND gate occurs only when a predetermined engine speed is exceeded, the AND gate being operable in response to the coincidence to inhibit ignition and thereby prevent further rise of speed. Broad pulses at A generated by a contact breaker 3 (or other type, e.g., electromagnetic, Piezo-electric or optical, of enginedriven signal generator) are shaped into narrow pulses at C by means of a differentiator 6 and a Schmitt trigger or other level detector 7, these narrow pulses being fed to one input of an AND gate 8 which comprises diodes 40, 41 and a resistor 42. After being inverted in an inverter stage 9, the narrow pulses are fed via a further inverter stage 49 as triggering pulses via a differentiator 77, 78, 85 to the discharging thyristor 68 of a capacitor discharge ignition system 14 and are also fed to a differentiator 10. The positive-going spikes produced in the differentiator 10 by the trailing edges of the inverted narrow pulses are fed as triggering pulses to a monostable multi-vibrator 11 to produce broad pulses which are fed to the other input of the AND gate 8. Since these broad pulses are non-coincident with the narrow pulses, there is normally no output from the AND gate. If, however, the engine speed rises above the permissible limit, each narrow pulse occurs before the termination of the broad pulse derived from the previous narrow pulse, whereby the AND gate 8 produces an output pulse at G. This output pulse is applied to a thyristor switch circuit 13 to short a point 64 to earth, thereby disabling the charging circuit which charges the capacitor 67 of the capacitor discharge ignition system and so preventing further ignition. The pulse fed from the inverter stage 49 to trigger the thyristor 68 to discharge the capacitor 67 and thereby produce ignition is also applied to the base of a transistor 86 to recharge the capacitor 67. The pulse switches on the transistor 86, and positive feedback via the primary winding 102 of a transformer 103, a secondary winding 104 and a diode 105 maintains the transistor 86 in a conductive state after the pulse has ended, until the total voltage across the winding 104 and a further secondary winding 107 has increased to a value at which it acts, via a voltage divider 95, 96, to trigger a thyristor 94 into conductance, thereby shortcircuiting the secondary windings to cause the transistor 86 to be abruptly switched off. The resultant pulse generated in the secondary winding 89 of a transformer 87 charges the capacitor 67 via a rectifier 98. Fig.4 shows an indicator circuit in which the AND circuit 110, 111, 112 is the AND circuit 8 of Fig.3, its output being connected via a Zener diode 114 and an integrator 115, 116 to the control gate of a thyristor 117 whereby a flasher unit 119 is switched on if the engine speed is excessive.