Patent GB-1191529-A (GB)
Title: Improvements in Fuel Injection Systems
IPC: F02D41/04
Filed: 1967-08-22
Abstract: 1,191,529. Transistor pulse circuits. ROBERT BOSCH G.m.b.H. 22 Aug., 1967 [31 Aug., 1966], No. 38527/67. Heading H3T. [Also in Division G1] A monostable multivibrator, operating for example the fuel injection valves of an internalcombustion engine has transistors 28, 29, 30, Fig. 14, the pulse length of the controlling pulses being variable by means of a differential transformer 34. The differential transformer 34 has two oppositely connected primaries, and a single secondary providing a voltage whose magnitude and polarity depends on the position of the core 38 controlled by the inlet manifold pressure (40). The transistor 29 is normally " off" and transistor 30 " on," and a switch 59 operated by an engine cam (63) twice per revolution, applies the negative line 49 potential to capacitor 58 to turn transistor 29 " on " and 30 " off," The emitter of transistor 30 rises to the potential of positive line 25, the change being conveyed by the transformer 34 to transistor 28 whose collector thus goes negative and holds transistor 29, by means of feedback resistor 57, in the " on " state. The output pulse duration depends on the time taken by capacitor 46 to discharge and restore the circuit to its initial condition, the capacitor being provided with one or more discharge paths. One path consists of resistors 76, 77 and a thermistor 78 sensitive to engine temperature, and a second path comprises a transistor 82 arranged to maintain a constant discharge current and thus to linearize the discharge curve (Fig. 7, not shown). The base of the transistor 82 may be at a fixed potential (Fig. 6, not shown), but preferably is made dependent on engine speed by means of a circuit 90, 91, 92 which provides an output voltage via a resistor 85 to the transistor 82 base. Further discharge circuits disclosed include a diode (71, Fig. 8, not shown) to give a two-part curve approximating to a linear discharge, and simply a resistor (47, Fig. I, not shown). Reduction of battery voltage produces a sluggish operation of the injection valve solenoids with consequent reduction in injection time, and this is compensated by providing a Zener diode 81 by virtue of which the voltage across resistor 54 falls with falling battery voltage, and reduces the negative potential applied to the base of transistor 28, thereby lengthening the discharge time of the circuit (Fig. 13(a) not shown) and increasing the length of the output pulse. The speed dependent circuit 90, 91, 92 comprises a normally " on " transistor 93 which is turned " off " by the trailing edge of the output pulse (u28, Figs. 15, 16, 17, not shown), and a normally " off " transistor 95 which is simultaneously turned " on " to short out a capacitor 109 via a diode 115. Transistors 93, 95 revert after a time determined by a capacitor 96 and resistor 97, and cause transistor 94 to turn " off." This causes capacitors 106, 109 to charge to the negative line potential (u109) for a time determined by capacitor 101 and resistor 104. When the transistor 94 reverts to its " off state capacitors 106, 109 discharge until a new pulse output from the main monostable circuit initiates a new cycle of operation. The portion of the charge and discharge curve (u109) of capacitor 109 which is operative on the base of the " constant current" transistor 82 depends upon the frequency of the speed pulses (u28) relative to the time constants of the circuit 90, 91, 92, and the varying potentials applied to the transistor 82 vary the width of the pulses u28.