Patent GB-1267742-A (GB)
Title: Improvements in fuel injection systems for internal combustion engines
IPC: F02D41/06
Filed: 1969-05-06
Abstract: 1,267,742. Fuel injection systems. ROBERT BOSCH G. m. b. H. May 6, 1969 [May 6, 1968], No.23006/69. Heading G1N. In an electronically controlled I. C. engine fuel injection system, an excess quantity of fuel, limited by the engine speed, is supplied during cold starting by a device including a first switching device having a switching period decreasing with increasing speed, and a second switching device having a switching period which is independent of the speed and which is shorter than the period of the triggering signals of the generator 18 during starting, but which is longer than the switching period of the first device at the lowest possible idling speed, the shorter switching period of the two switching devices at any given time being used to determine the excess quantity of fuel. As shown, the first switching device consists of a monostable multi-vibrator 61 having a timing capacitor 65, and the second device consists of a monostable device 62 having a storage capacitor 77. In operation, starter switch 80 is closed and we assume that generator switch 40 is about to close and switch 41 is about to open i.e. at time t 1 . These switches are then opened and closed for a period T p . At t 1 , multi-vibrator 61 changes to its unstable state thus allowing capacitor 65 to discharge for a period T o , and capacitor 77 to charge, the period T o  being at least five times the charging time constant of capacitor 77. At the end of period T o , device 61 changes back to its stable state and capacitor 65 charges for the period T n  which is thus dependent upon the engine speed, while capacitor 77 discharges for a period T s  when transistor 75 is blocked. During this period T s , a capacitor 88, which was charged up to the breakdown voltage of a double-base diode 85 at a rate determined by an N. T. C. resistor 90, discharges via path E-B 1  and the negative voltage jump at E is applied to block a transistor 21 in the same manner as the generator switches 40, 41. This occurs a number of times during the period T s  thus producing additional opening pulses J 1 , J 2 , J 3  after the basic opening period T i  of the control multi-vibrator 20. As the engine speed increases, T n  decreases until T p  = T o  + T s  and at higher speed, T n  ends before T s  expires and when T n  ends, transistor 75 returns immediately to its conductive state and short circuits path E-B 1 . When the engine reaches a pre-set temperature, which is set by resistors 96, 98, no additional pulses are applied. A diode 99 protects the circuit against voltage surges from the starter solenoid 81 when starter switch 80 is switched off. In a modification, Fig. 4 (not shown), the switching device 61 is omitted and the 1st switching device is constituted by the generator 18. The switches 40, 41 are connected to capacitor 77 via respective resistors (112), (113) and diodes (115), (116). Device 63 is also omitted, and the output of the second switching device 62 together with the output of the control multi-vibrator 20 is applied to a transistor (105) acting as an OR gate. Switches 40, 41 are closed 180 degrees out of phase with each other for 90 degree periods, the closed period of each switch then constituting the period T n . The potential to which capacitor 77 charges is set by a temperature-dependent voltage divider (120), (121) whose tapping is connected to capacitor 77 via a diode (122). Thus the period T s  is dependent upon engine temperature and thus the quantity of excess fuel injected during starting is so dependent.