Patent GB-1296091-A (GB)
IPC: F02D41/14
Filed: 1970-02-12
Abstract: 1296091 Regulating I.C. engines ROBERT BOSCH G.m.b.H. 12 Feb 1970 [12 Feb 1969] 6759/70 Heading F1B [Also in Division H2] A device for limiting the maximum speed of an I.C. engine having a pulse generator for supplying triggering pulses having a magnitude dependent upon engine speed to a spark ignition system and/  or an electrically operated fuel injection system comprises a monostable multi-vibrator having an input connectible to the pulse generator and capable of being triggered by a pulse from the pulse generator exceeding a predetermined limit, and an electronic switching path which is operative to inhibit the triggering pulses from acting on the ignition system and/or the fuel injection system during the period that the monostable multivibrator is in its unstable state. The pulse generator comprises an A.C. generator 30 driven by the engine B, the positive half-waves 34 being applied via a monostable multi-vibrator 24 to trigger a transistorized ignition system 19,21, 23 or a transistorized fuel injection system, Fig.3 (not shown). Alternatively a capacitor discharge ignition system may be used. The negative halfwaves 33 are applied to a point P via a Zener diode 47 (and/or a conventional diode 48) which does not conduct until the voltage generated by the generator 30 reaches a valve corresponding to the maximum permissible engine speed. As shown, series-connected Zener diodes 47, 47', 47" or series-connected diodes 48, 48', 48" may be used. The value of the maximum permissible engine speed may be varied in accordance with engine temperature by means of a temperaturedependent resistor 55. It may also be varied in accordance with the gear ratio selected by the gear lever 51, a switch 49 linked with the gear lever selecting various Zener diodes 47, 47a, 47b. The gear lever may also be linked to an adjustable resistor 53 for this purpose. The control voltage appearing at the point P when the maximum permissible engine speed is reached is passed on to the input F of a monostable multi-vibrator M, preferably via a pulse-shaper circuit T which converts the voltage to a square-wave pulse, and a differentiator D. The monostable multi-vibrator M is triggered into its unstable state by the positive peak at the trailing edge of the differentiated pulse and switches on a transistor 91 which then shortcircuits the positive half-waves of the generator 30, whereby ignition or fuel injection is inhibited and further increase of engine speed is thereby prevented. The negative peak at the leading edge of the next pulse returns the multi-vibrator M to its stable state if it has not already returned, in readiness for triggering by the positive peak of the trailing edge. The generator 30 may be such that alternate cycles of its output voltage are of different values, whereby inhibition of ignition or fuel injection when the maximum permissible engine speed is reached occurs initially only at alternate cycles and does not occur at every cycle until this speed is exceeded by a large margin. If the engine has two ignition systems, each with its own pulse generator 30,a single control circuit for limiting the maximum speed is connected to both systems, the single control circuit being connected to one only of the pulse generators.