GB1233455A - - Google Patents

Abstract

1,233,455. Electric control systems. ROBERT BOSCH G.m.b.H. July 11, 1968 [July 12, 1967], No.33016/68. Heading G1N. [Also in Division F1] In a fuel injection system for an internalcombustion engine comprising a solenoid operated fuel injection valve 3, the open period of which is controlled by the duration of the unstable state of a monostable multi-vibrator C in accordance with the pressure in the intake manifold, opening of the injection valve when the air intake butterfly valve (9) is in its idling position and the engine is running at a speed in excess of its idling speed is prevented by a switching circuit A which interrupts the transmission of triggering pulses to the monostable multi-vibrator C. In operation, pulses generate by a cam operated switch 10 cause momentary blocking of a normally conductive transistor thereby making a normally blocked transistor 50 conductive to trigger the monostable multi-vibrator C. When the butterfly valve (9) is not in the idling position, a switch 38 is open allowing a timing capacitor 31 to discharge rapidly through a transistor 30, diode 36 and resistor 37 so that transistor 40 reverts to its normal conductive state ready for the next pulse from the switch 10. However, when the butterfly valve is in its idling position, the switch 38 is closed thereby blocking diode 36 and retarding the discharge of capacitor 31. If the engine speed is great enough for the next pulse from switch 10 to occur before capacitor 31 has discharged, this pulse is not transmitted to the monostable multivibrator C because transistor 40 is still blocked. The engine speed at which cut-off becomes effective is made temperature dependent by an N. T. C. resistor 20 in thermal contact with the engine. When the engine is cold, diode 32 is conductive thereby increasing the discharge rate of capacitor 31. When the engine is hot, diode 32 is blocked. Hysteresis is introduced by a normally conducting transistor 80 which becomes blocked momentarily each time the multi-vibrator C is triggered thereby making diode 34 momentarily conductive to increase the discharge rate of capacitor 31. When the cut-off is effective, diode 34 is continuously blocked whereby triggering of the monostable multi-vibrator C is only resumed after the engine speed has dropped to a value sufficiently below that at which the cut-off became effective. The duration of the open period of the injection valve is controlled by arranging the position of the core 75 of a transformer in the timing circuit of the multi-vibrator C to be governed by the pressure in the inlet manifold.