Patent GB-744790-A (GB)
Title: Distributor testing instrument
IPC: F02P17/00
Filed: 1953-07-08
Abstract: 744,790. Testing ignition distributers for internal-combustion engines. BRITISH PETROLEUM CO., Ltd., [formerly ANGLO-IRANIAN OIL CO., Ltd.], WITHERS, J. G., HULF, H. J., and HATHAWAY, R. W. June 23, 1954 [July 8, 1953], No. 18906/53. Class 37. [Also in Group XXXVIII] Apparatus for testing ignition distributers for internalcombustion engines comprises a bi-stable multivibrator responsive to spark and reference signals and having a pulseaveraging output meter indicating spark occurrence-time. The spark signals are derived from a spark-gap connected to a resistance and the reference signals produced at a frequency dependent on the test speed of the distributer may operate an electronic tachometer. The distributer under test is driven by a variablespeed motor which may also drive electromagnetic pick-up devices producing the reference signals. The apparatus (by appropriate switch selection) provides for spark-timing for individual plugs or average timing for all plugs and in effect measures the phase-difference or interval between the two signals as this varies with distributer speed. Circuit details; spark timing.-The individual reference pulses taken from selected pick-ups PU1-PU10 and amplified/inverted by pentode V1 actuate a single shot multivibrator V2/V3 and the resulting V3 signal is differentiated and flashes a thyratron V4 whereby condenser C10 re-charging voltage after differentiation triggers V5 of bi-stable multivibrator V5/V6. The spark signals are taken from G1/R41 and rectified at V7 (in the screened filter box shown) are amplified/inverted by pentode V8 and then after differentiation are delivered into single shot multivibrator V9/V10 whose V10 signal is differentiated and then flashes thyratron V11 whereby associated condenser C26 on recharging produces a voltage which after differentiation triggers V6 of multivibrator V5/V6. The cyclical repetition of reference and spark signals when the distributer arm is rotating causes a train of rectangular current pulses to pass through the milliammeter M1 (moving coil galvanometer) in the anode circuit of V6 and the pointer of M1 takes up a position equivalent to the mean value of the pulse train which is directly proportional to the angular relation or interval between the spark occurrence and the reference signal pick-up position or occurrence. The test signals from the spark-gap/resistance combination G1/R41 are converted into highly damped pulses by oscillation of distributer input lead capacitance SC1, condenser C16 and inductance L1 and in the operation of V9/V10 the V9 signal is fed back to the suppressor grid of pentode V8 so that V8 is cut-off and blanks out the diminishing pulses in the highly damped pulse train. Similarly in the operation of V2/V3 the V2 signal is fed back to V1 to momentarily block V1 and blank out interference signals. A high-frequency filter R3/C9 is also used to attenuate interference signals. Electronic tachometer.-The repetition rate of the square shape pulses produced at the anode of V2 of single shot multivibrator V2/V3 is directly proportional to distributer speed so that a milliammeter M2 in the anode circuit of V2 indicates mean current and thus distributer speed. Reference signal electromagnetic pick-up arrangements.-The motor driving the distributer may also drive (i) a rotor comprising pointers which co-operate with a single fixed pick-up; or (ii) a rotor comprising a single pointer cooperating with a plurality of fixed pick-ups; or (iii) a drum rotor W, Fig. 6, comprising magnetic material in peripheral slots Q which cooperates with pick-up units N. Miscellaneous details.-The Specification gives full instructions concerning switch selection &c. for calibrating M1 for the range of distributer degrees desired and adapting M1 for different cam lobes on test distributers. Details for calibrating distributer-speed indicator M2 are included. Diagrams, Fig. 2 (not shown), illustrating the waveforms at different stages in the circuit of Fig. 1 are also provided. The test equipment (including clamping of the test distributer &c.) (Fig. 5, not shown), is generally similar to the disclosure in Specification 715,898. A source of variable sub-atmospheric pressure may be provided.