GB1382175A - Circuit to ascertain discharge phenomena at sparking plugs - Google Patents

Abstract

1382175 Testing ignition circuits VOLKSWAGENWERK AG 1 Sept 1972 [4 Sept 1971] 40624/72 Heading G1U An I.C. engine ignition circuit is characterized in that a relay contact 13a is provided in the lead to a sparking plug 1 and in that means are provided to open the contact 13a (and simultaneously to short the ht supply direct to earth via a contact 18a) for a pre-set number of cycles of the engine during which the degree of ionization existing in the plug can be determined by an appropriate device 35, which device produces a potential representing the resistance of the discharge path on a first output lead 36, and a pulse if the discharge current rises above a pre-set level, of e.g. 5 microamperes, on a second lead 37. As described ignition pulses 3 are shaped 4 and divided 5 by the number of cylinders in the engine to apply to gates 19, 29 one pulse for each cycle of the engine. In a "single shot" mode of operation, for which a mode switch 6 is set as shown, depression of a start key 7 causes a trigger 8 to apply a pulse to a control trigger 2. Control trigger 2 therefore reverses its state, relays 13 and 18 are energized via amplifiers 12 and 17 to open and close contacts 13a and 18a respectively and the test begins. Control trigger 2 also opens gate 19 which passes pulses, one per engine cycle, to a pre-set counter 22, 23, 24, 25, which after receipt of the pre-set number, resets both itself and the control trigger 2, so that the test ends. In the "repeat mode" of operation, with the position of switch 6 reversed, the control trigger 2 is repeatedly set to start a test by pulses received from a second pre-set counter 10, which receives its pulses via the gate 29, the first test period in a repeat mode commencing immediately switch 6 is changed over.