GB1428171A - Electrically controlled fuel injection system for an internal combustion engine - Google Patents

Abstract

1428171 Electronic fuel injection systems for IC engines ROBERT BOSCH GmbH 8 March 1973 [9 March 1972] 11315/73 Heading G3N [Also in Divisions G4 and H3] In an I.C. engine, electronic fuel injection system, the quantity of fuel injected by at least one electromagnetic injection valve 11 is determined by the volume of intake air, the latter being determined by providing a temperature-dependent resistor 30 in the air intake manifold 25 and maintaining the temperature of resistor 30 constant by a heating current Jh, a voltage dependent upon this current being applied to a squaring circuit 40 whose output voltage, being a linear function of the air intake volume, determines the injection quantity. As shown, the resistor 30 is arranged in a bridge circuit with resistors 33, 34, 35, a regulator R providing the heating current Jh. The voltage Us across resistor 35 is applied to the squaring circuit 40 in which a voltage Uo proportional to the value of the heating current when the engine is inoperative is subtracted from the voltage Us, and the resulting differential voltage Us-Uo is squared. The squared voltage is applied to an integrator 37 to control the charging of a capacitor during each half revolution of the crank-shaft, utilizing a trigger 18 and a bistable circuit 41, the discharge time of the capacitor determining the duration of injection valve opening pulses S. In one embodiment, Figs. 3 and 4 (not shown), the squaring circuit provides constant frequency pulses whose duration and amplitude are determined by the differential voltage Us-Uo, these pulses being applied to an integrator which thus supplies the squared voltage. In a second embodiment, Figs. 5 and 6 (not shown), a sawtooth waveform is provided, both the period and the rate of rise of the sawtooth voltage being determined by the differential voltage Us-Uo. Specifically, the circuit 40 includes a capacitor, which, for a charging period dependent upon the voltage U S -U O , is charged by a current also dependent upon Us-Uo; and which is maintained in the charged state for a short pre-set retention period, and is again recharged after an immediately succeeding pre-set discharge period. A further storage capacitor is provided, the voltage of which is periodically compared, during the retention period, with the voltage of the first capacitor and brought to the same value as the latter. This latter value determines the squared voltage. A further improvement may be achieved by providing a threshold value for the voltage Us-Uo, below which dependence of the squared voltage on the differential voltage is different from that above the threshold value, such dependence being linear, Figs. 7-10 (not shown).