GB1403406A - Electrically controlled fuel injection systems for interanl combustion engines - Google Patents

Abstract

1403406 Electrical fuel injection system for I C engines ROBERT BOSCH G.m.b.H. 6 Oct 1972 [8 Oct 1971] 46096/72 Heading G3N In an I.C. engine electrical fuel injection system the injection quantity is controlled in dependence upon air intake quantity determined by a device which includes a temperature dependent resistor 3 located in the air intake manifold 25 and supplied with a heating current having a D.C. portion and a portion of periodically varying magnitude, one of these portions having zero value when the air quantity is zero and being increased by a regulator as the air quantity increases to maintain the temperature of the resistor constant. As shown, in an intermittent fuel injection system, the resistor 30 is arranged in a bridge with resistors 33, 34 and 35, and is supplied with a basic direct heating current which is adjusted by resistance 36 to maintain the temperature of resistor 30 at its desired constant value in the absence of air flow, and an alternating current supplied by a controlled oscillator 38 which is controlled by a differential amplifier 40 connected to a diagonal of the bridge. Thus as the air quantity increases to unbalance the bridge, the amplitude of the alternating current is increased to rebalance the bridge. The A.C. component across resistor 34 is amplified at 45, rectified at 46 and applied to an integrator 47 which receives a signal from a bistable switch 49 triggered in synchronism with engine rotation. During the integrating process a capacitor is charged with a direct current corresponding to the heating current, the discharge time of the capacitor then determining the injection pulse duration. In an alternative, Fig.3 (not shown), the varying magnitude heating current portion is provided by heating current pulses of constant duration and of a frequency adjustable by a regulator connected to a diagonal of the bridge. To control the duration of injection pulses, measurement pulses of constant duration are derived from the heating pulses and the measurement pulses are applied to a modulator which lengthens the pulses or the pulse frequency increases. During the rotation of a predetermined crank-shaft angle a constant current source charges a capacitor during the modulated pulses, the charge on the capacitor being converted by means of a constant current source into an injection pulse. An automatic re-setting device may be provided in which, when the engine ignition is switched off, the bridge and the regulator remain connected for a period of time to the battery of the engine.