GB1468834A - Electronic tester for motor vehicles - Google Patents

Abstract

1468834 Ignition system testing DOYCE ELECTRONICS Ltd 18 July 1974 [24 July 1973] 35291/73 Heading G1U An apparatus for testing the electrical system of a I.C. engine is characterized in that it includes a digital display device, a cathode ray tube display, and switch means whereby input signals may be fed to either or both of the display devices. As described leads 14, Fig. 1, are connected across the contact breaker points, leads 22 are connected to the plug of No. 1 cylinder, leads 30 are connected to the output of the ignition coil, and wander leads 10 are connected, by clips, to any point in the engine from which signals may usefully be extracted, or about which impedance measurement may usefully be made. Signals on leads 10 and 14 may be applied via switches and appropriate circuits to a digitizer and digital display device 44, and also via a switch to the y-input of a cathode ray tube 36 having its time base triggered by signals, on leads 22, from the No. 1 cylinder. The following tests may be made. (a) Battery By connecting the leads 10 to the battery the battery voltage may be displayed digitally on the device 44 either with the engine stationary, with the engine being cranked, or with the engine running. (b) Generator The generator output voltage may be displayed, via leads 10, either digitially 44, or on the c.r.t. 36. (c) Ignition coil With the engine stationary the resistances of the coil primary and secondary may be measured, via leads 10, and displayed digitally 44. With the engine running the coil primary and secondary voltages may be displayed, via leads 14 and 30 respectively, on the c.r.t. 36. The c.r.t. display can be controlled so that the secondary voltage is blanked for selected cylinders. (d) Distributer capacitor The capacitance of the distributer capacitor, and any leakage current through it when a high voltage source 80 is connected across it, may be measured and indicated digitally 44, using leads 10. (e) Engine speed The engine speed, in r.p.m. is displayed on a separate indicator 48, so that other tests may be performed at known engine speeds. (f) Power balance With the engine running, the high voltage spark pulses to a selected cylinder can be inhibited, by shunting the contact breaker with a conductive S.C.R. at the time when it opens, and the reduction in engine speed displayed 44. By repeating the operation for all the cylinders, a test engineer can note whether the speed reduction by any one cylinder is significantly less than that for the other cylinders. Basic, and conventional, measuring circuits for the above tests are described.