Patent GB-1154270-A (GB)
Title: Improvements relating to Fuel Injection Systems
IPC: F02D41/30
Filed: 1967-11-14
Abstract: 1,154,270. Electric control of fuel injection. ROBERT BOSCH G.m.b.H. Nov. 14, 1967 [Nov. 25, 1966], No.51660/67. Heading G1N. [Also in Division H3] In a fuel injection control system for an I. C. engine in a vehicle, the injection period T Fig. 2 is varied automatically in dependence on a plurality of engine operating parameters and variations of battery voltage. The control system comprises a multi-vibrator 32 Fig. 1 which produces pulses, the duration T 1  of which is dependent on engine speed (cam-shaft operated switch 55) and inlet manifold pressure (core 68 of transformer 58 movable by pressure sensor 72, the pressure changing when accelerator pedal 75 is pressed to operate butterfly valve 73); and a timing device including a pulse prolonging device or multivibrator 35 and timing circuit 39, the commencement of and duration of pulses T 2  from which device are controlled by the multi-vibrator 32; and an OR gate circuit 28 for applying both the pulses T 1  and T 2  to power transistors 22 or 23 controlling electromagnetic injection valves 13 on the engine. The injection period T = T 1  + T 2 , and T 2  is related to T 1  as follows:- T 2  = b T 1  - a where a is a function of battery voltage and b is a function of engine temperature. Circuit Operation Each time switch 55 closes a negative pulse U, Figs. 1 and 2 is applied to junction 45 and blocks a diode 43 and a transistor 33 for a period T 1 , so that transistor 34 conducts and permits exponentially increasing current to flow through primary 66 of the transformer and an exponentially declining voltage from secondary 57 maintains 33 base at earth potential for a period depending on the Primary inductance, after which 33 conducts and blocks 34. Thus positive pulses U 2 , synchronized with engine speed, appear at transistor 33 collector, having a duration T 1  dependent on the position of the transformer core 68. The pulses U 2  are fed via R107 to the OR gate 28 and transistor 29 thereof becomes conductive for the period of each pulse U 2 . Thus depending on the position of a cam-shaft operated switch 27, transistor 22, or 23 becomes conductive and a pair of fuel injection valves 13 are opened - Also the timing circuit transistor 40 is maintained conductive via R119 C118 for the duration of pulse U 2 . During a period when transistor 40 is cut-off a positive voltage U 5  appears at its collector and capacitor 77 is caused to discharge more rapidly via transistor 37. At each positive pulse U 2 , transistor 36 receives a base potential midway between that of positive and negative leads and a substantially constant collector current charging a capacitor 77 flows in 36 for the duration T 1  of pulse U 2  so that its voltage increases linearly with time U 3  in fig. 2. At the end of pulse U 2  transistor 33 is conductive again and the base and collector of 36 becomes more negative. The jump in collector potential is transmitted by C77 via diode 78 to block a transistor 38. A positive potential then appears at 38 collector and is transmitted to the base of gate transistor 29 via R106 and maintains 29 conductive so that the pair of valves remain open and the injection period is extended beyond period T 1 . C77 now discharges through R82 and transistors 33, 36, 37, and when discharged sufficiently the base of transistor 38 becomes positive again after the period T 2 . Transistor 38 conducts so that its collector becomes negative thus blocking the OR gate transistor 29 and the injection period T is terminated. The timing circuit 39 co-operates to control the discharge rate of C77 by controlling the emitter collector current of transistor 37 through which C77 discharges and causes the period T 2  to increase more than proportionally as T 1  is increased. Correction for engine temperature. An NTC resistor 96 in heat conductive relationship to the engine is utilized to cause a greater quantity of fuel when the engine is cold. When R96 is high, diode 94 conducts and the base potential of transistor 37 becomes more positive, so that the resistance of 37 increases thereby increasing the discharge time of C77 and the duration T 2 . At engine operating temp. e.g. 80‹C., R94 no longer influences T 2 . Correction during cold starting When starter switch 104 is closed junction 93 is made more positive via R103 and diode 94, and the discharge time of C77 and duration of T 2  is increased as described above, and a very rich fuelair, mixture is injected provided the resistance of NTC resistor 96 is not sufficiently low to block diode 94. Correction for fluctuations in battery voltages Arrangements are described with reference to Fig. 1, Figs. 3 and 4 (not shown) whereby increase in the battery voltage U B  results in a reduction in the duration of T 2  by an amount #T, a portion of C77 discharging current flowing through a Zener diode 86 which current increases more than proportionally as the battery voltage increases.