Patent GB-1096163-A (GB)
Title: Ignition testing apparatus
IPC: F02P17/02
Filed: 1965-03-12
Abstract: 1,096,163. Cathode-ray tube circuits; pulse and sawtooth circuits. ROBERT BOSCH G.m.b.H. March 12, 1965 [March 14, 1964], No. 10499/65. Headings H3P and H4T. [Also in Division G1] An apparatus for testing the electrical ignition system of an internal-combustion engine comprises a cathode-ray tube on which is represented the ignition processes, the vertical deflection being dependent upon the ignition voltages, a relaxation oscillator for supplying the horizontal deflection voltages, a pulse shaping stage for shaping pulses derived from the ignition current pulses to derive trigger pulses for the relaxation oscillator independent of the level or shape of the ignition voltage and a delay stage having an adjustable time delay between the pulse shaping stage and the relaxation oscillator. Trigger pulses are derived from a transformer TG connected in the lead to one sparking-plug and passed via a diode D1 to an amplifying stage V1 and thence to a monostable multivibrator including the valves V2 and V3. In the absence of a trigger pulse the valve V2 is non-conducting and V3 conducts. In the anode circuit of V3 a capacitor C11 charges because V3 conducts and then discharges as the neon L2 strikes. This discharge provides a pulse which is differentiated by capacitor C13, resistor R18 which is then applied to the thyratron V4 in the time base circuit, so that a slowly operating time base will always be provided, in the absence of trigger pulses from TG. When, however, such a pulse is applied to the grid of V2, the monostable multivibrator changes its condition for a period determined by the components in the circuit, and then returns to its original state. The capacitor C9 and neon L1 connected to the anode circuit of V1 enable rapid recovery times to be achieved. The voltage change then occurring at the anode of V3 provides the trigger for the thyratron V4. This is connected in a time base circuit which includes a cathode follower V5 supplied from the anode of V4 and with its cathode coupled back to the anode circuit of V5 for linearizing purposes. The sweep voltage derived from the cathode follower resistor R19 is fed via amplifying and inverting stages V6, V7 to the horizontal deflection plates X1, X2 of the cathode-ray tube. The ignition signals to be investigated are derived from a capacitive pick-up SG inserted in the lead between the coil and distributer and supplied by switch S2 to an amplifier V9, and thence over potentiometer P3 to output amplifying and inverting stages V10, V11, from which the signal is supplied to the vertical deflection plates X3, X4. Other inputs may be applied via terminals E3-E5 and amplifier V8. In order to bright up the trace observable on the oscilloscope the signal derived from the pickup SG is also fed to a valve V15 via an arrangement including a diode D5 which eliminates positive going pulses which would blank the trace. In order to provide fly back blanking, the fast falling edge of the time base sweep voltage is differentiated over C28, R52, inverted through V13 and then applied to the grid of a valve V15. The two voltages are added over the common anode load R44. This voltage is fed to the terminal of the cathode-ray tube grid T to provide bright up during signals and blanking during fly back. The input signal may itself be used to trigger the time base; the input signal from the stage V10 is fed via amplifying stage V12 to the valve V1 with the switch S4 in the alternative position to that shown.