Patent GB-1245648-A (GB)
Title: Method of regulation of the duration of a repeated rectangular electric control signal and device for carrying out this method
IPC: H03K7/08
Filed: 1968-09-06
Abstract: 1,245,648. Pulse duration control circuits. SOC. DES PROCEDES MODERNES D'INJECTION SOPROMI. 6 Sept., 1968 [26 Sept., 1967], No. 42600/68. Heading H3T. [Also in Division G3] The duration of pulses is regulated in dependence upon their repetition frequency (e.g. to reduce the duration with increasing frequency) by producing a regulating voltage which starts to increase a predetermined time after an input pulse, terminating the increase by a succeeding input pulse and using the amplitude of the regulating voltage to control the timing of the trailing edge of a following output pulse. The invention as described controls the width of fuel injection pulses of an engine to maintain the speed constant by reducing the pulse width if the speed exceeds the desired value. In Fig. 2, pulses A from the engine trigger a variable duration monostable circuit producing injection pulses . Ti, they also trigger a reference period producing monostable circuit providing pulses To. The end of this pulse (c) initiates the charging of a capacitor and this charging is terminated either by it reaching a limiting value Vm or, if this occurs first, at V R , the value when the next engine pulse occurs. The amplitude of this voltage is used to control the unstable period of the monostable circuit producing the injection pulses. Thus if the engine is going too slowly the regulation voltage reaches its maximum value and maximum length injection pulses are provided. If the engine is running too fast the gap between the end of the reference pulse and the beginning of the next input pulse is reduced and the amplitude of the regulating signal is reduced, this correspondingly reducing the length of the injection pulses. The circuit may be arranged such that if the engine speed is much too slow the injection pulses are reduced in length (Fig. 9, not shown). In Fig. 4, a negative pulse at E1 triggers a complementary type monostable circuit T1, T2, U1, timed by a capacitor C1 and a unijunction transistor U1. The output of this at S1 operates the injection circuit. The leading edge of the injection pulse triggers a similar complementary type monostable circuit T3, T4, U 2  producing the reference pulse. The trailing edge of this pulse switches off a transistor T6 so that a capacitor C3 charges through R21 and an adjustable resistor P4 and this produces a corresponding regulating voltage in a capacitor C4 where the voltage is stored. This voltage is applied to a base of the unijunction transistor U1 to control the timing circuit of the injection pulse monostable circuit T1, T2 so as to control the trailing edge of the next pulse produced by that circuit, the higher the regulating voltage the longer the pulse. If the engine is running too slowly the capacitor C3 and C4 have time to charge to their maximum value and accordingly the next injection pulse is of maximum length. If the engine is running too fast, i.e. if the next pulse occurs too soon after the end of the pulse from the monostable circuit T3, T4 the charge across C3 and C4 does not reach its maximum value, the regulting voltage is diminished and the injection pulse is correspondingly shorter. At the end of each injection pulse a voltage from T2 through T8 is momentarily applied to a transistor T9 which discharges C3 ready for the next charging cycle. Capacitor C4 discharges slowly through the unijunction diode of U1 until clamped by diode D7 and potentiometer P3. The timing capacitor C2 of the reference pulse generator T3, T4 is discharged at the instant of triggering by a transistor T5 which is rendered momentarily conducting by the leading edge of the triggering pulse applied through D3 and C7. This ensures correct operation if the resistor P2 is adjusted suddenly. The circuit may be adapted to operate on every nth pulse, where n is greater than 1, in which case some modification of the triggering and regulating voltage holding capacitor circuit is necessary (Figs. 5 to 7, not shown). The length of the injection pulse may also be made to decrease if the engine speed is too slow and thus the repetition frequency of the input voltages too low. This is effected (Figs. 8 to 11, not shown) by a further monostable circuit (C) which is triggered by the trailing edge of the reference pulse generator (D). If the engine speed is below a predetermined level the spacing between the engine pulses would exceed the sum of the reference pulse and the further pulse in which case a discharging circuit (D) causes the regulation voltage to decrease (E, e-f), this decrease being terminated either by the next input pulse or, if it exceeds a predetermined duration, by the operation of a circuit (D) which relaxes after a given interval and prevents further discharge.