GB1335893A - Fuel injection systems for internal combustion engines - Google Patents

Abstract

1335893 Electronic fuel injection Systems ROBERT BOSCH GmbH 13 July 1971 [14 July 1970] 32691/71 Heading G1N In an I. C. engine electronic fuel injection system of the type having a monostable multivibrator to provide injection valve opening pulses in synchronism with engine rotation a first electronic device is provided to operate, when the butterfly valve of the engine is closed, to prevent the opening pulses being effective when the engine speed exceeds an upper limit and to allow the pulses to be effective again when the engine speed falls to a lower limit above the idling speed, and a second electronic device is provided to operate, in any operating position of the butterfly valve, to prevent the opening pulses being effective when the maximum engine speed is exceeded, the pulses being restored below this speed. As shown, in normal operation, the multivibrator 16 provides pulses to block a transistor 48 which in turn causes energisation of the valve solenoids 13 via transistor 11. The output of the multi-vibrator 16 is also applied to two passive networks 30, 30', whose outputs are in turn applied to respective bistable circuits 45, 46 having a common transistor formed by transistor 48. When the butterfly valve is closed, a switch 39 in the network 30 is closed and if the engine speed exceeds the upper limit, the network 30 switches the bistable circuit 45 and prevents transistor 48 from becoming blocked to provide the opening pulses. A resistor 53 provides the hysteresis whereby the engine speed must fall to the lower limit before the opening pulses can be restored. Network 30' operates in a similar manner for maximum engine speed cut-off, switch 39 and resistor 53 being, however, omitted. In a modification, Fig. 2 (not shown), the two electronic inhibiting devices are applied to a two group injection system utilising a bistable circuit to trigger the monostable multivibrator 16 and AND gates to select the group of injectors for immediate energisation. In further modifications, the lower limiting speed to which the network 30 is responsive may be engine temperature dependent by replacing the resistor 35 with a temperature dependent voltage divider. Further, to avoid the effect of intake manifold pressure on the mark-to -space ratio of the pulses which are applied to the network 30', the input of the network 30' can be connected to a constant mark-to-space ratio pulse generator, e.g. the bistable trigger in Fig. 2 (not shown), or a further multivibrator triggered by the multivibrator 16.