Patent GB-1166233-A (GB)
Title: Engine Analyzer.
IPC: F02P17/00
Filed: 1968-01-05
Abstract: 1,166,233. Analyzer for internal combustion engine; measuring speed electrically. MARQUETTE CORP. Jan.5, 1968 [Jan.6, 1967], No.865/68. Headings G1N and G1U. An analyzer for measuring the ignition voltage and contact-breaker dwell-time of a multi-cylinder internal combustion engine comprises a testing circuit adapted for connection to a selected output terminal of a cylinder-identifying circuit which has as many outputs as there are cylinders and that one of the outputs which is energized at any given time identifies that one of the cylinders whose sparking plug is being fired at the time concerned. The cylinder-identifying circuit comprises a ring counter 35. The ignition system comprises coils 11, 12, cam 19, contact breaker 16, 17 and distributer 20, and a switch 105 inter-connects the various parts of the testing circuit according to the different tests carried out, the tests being the measurement of the voltage across individual sparking plugs, the average voltage across several or all plugs, the dwelltime of the contact breaker 16, 17 when any individual plug is fired and the average dwell-times when all of the plugs are fired in succession. Any given plug may be short-circuited by connecting the corresponding ring counter output to a Schmitt trigger circuit so that a normally conducting transistor 128 is switched off, another transistor 134 starts to conduct and the voltage developed across a resistor 136 switches on an SCR 140, thus effectively short circuiting the plug concerned. Several plugs may be short-circuited simultaneously, the effect of such short-circuiting being observed on a tachogenerator 150. In measuring the average voltage across all of the plugs the switch 105 is turned to the appropriate position and the voltage pulses from the ignition coil secondary 12 are fed through an amplifier and integrator 231 to a meter 163. In measuring the voltage across any individual plug the switch 105 acts to connect a normally conductive field-effect transistor 250 into the circuit so that it shunts the amplifier 231 input, but on closing the corresponding one of the switches 66-73 at the ring counter outputs the transistor 250 is cut off and the amplifier and meter 163 measure the corresponding ignition coil secondary voltage. In measuring the average dwell-time, the voltage across contacts 16, 17 when these are open switches on a normally non-conductive transistor 170 and so lowers the voltage across a capacitor 180, the resultant voltage across the capacitor as read by the meter 163 when all the sparking plugs have fired indicating the average time for which the contacts 16, 17 are closed relative to the time for which they are open. In measuring the individual dwell-time the normally high voltage across a resistance 127 is fed to the base of transistor 170 so that the latter conducts continuously except when the corresponding ring counter output is fed to the Schmitt trigger 125, 128 and the voltage drop across resistance 127 fed to the base of transistor 170 is of such magnitude that the transistor becomes responsive to the voltage across the contacts 16, 17 at the time concerned, so that the voltage across the capacitor 180 is a measure of the time for which the contacts 16, 17 are closed during the firing cycle of the particular sparking plug selected, relative to the time for which they are open. To compensate for the low frequency of the voltage pulses fed to the capacitor 180, compensating resistors 200, 201, 202, for a four, six and eight cylinder engine respectively, are connected in parallel with a resistance 178 in the potential divider 178, 179 feeding the capacitor 180, so that a larger portion of the potential divider voltage is supplied to the capacitor. Calibration of the meter 163 when measuring average dwell-time for four and six cylinder engines is effected by adjusting a resistor 182 until the reading on meter 163 coincides with that on a standard meter. For eight cylinder engines a resistor 184 is connected in parallel with resistance 179 and is adjusted until meter 163 indicates the correct dwell-time. Calibration when measuring individual dwell-time is effected by adjusting resistors 200, 201, 202 (for four, six and eight cylinders respectively) until meter 163 gives the same indication as a reference meter. The speed of the engine is measured by applying the squarewave pulses from the generator 60, which produces an output pulse each time the ignition circuit produces a firing pulse, to an RC circuit including a diode 155 so that the average voltage across a resistor 154 as measured by a meter 150 is dependent on the frequency of the pulses and hence on the speed of the engine. Capacitor 151 is used for low engine speeds and has a higher capacitance than capacitor 152 which is used for measuring high speeds.