From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Oscillograph work and measurements comparing the ignition systems of the Wraith and Delco-Remy distributors.
| Identifier | ExFiles\Box 168\3\ img149 | |
| Date | 19th April 1939 | |
| Lr{Mr Ellor}/HWS/SGL.7/WJ.19.4.39. OSCILLOGRAPH WORK ON 'WRAITH' IGNITION. Oscillograph records have been taken of the primary and secondary voltages and currents in a Wraith ignition coil. The measurements were taken to give a comparison between the Rolls-Royce and Delco-Remy distributors. An ignition rig in the electrical Laboratory was used. Oscillograms of the primary current through the coil, show an exponential rise of current at the make, a sharp drop at the break followed by a series of oscillations at a frequency of about 2000 cycles per second. These low frequency oscillations are totally different from the high frequency oscillations which cause radio interference. The frequency and degree of damping of these oscillations is about the same for both distributors. Owing to the Delco Remy having a slightly higher make-break ratio, the current goes on rising for a slightly longer period than with the R.R. distributor. The Rolls-Royce distributor shows signs of an irregular break on one of the photographs, at 650 RPM. The circuit is made again for an infinitesimal fraction of a second just after the break. This bad break probably only occurs occasionally, as it was not visible in the image on the oscillograph screen which gives a mean picture of several cycles, while a photograph gives a single cycle only. A bad break of this sort would cause a seriously reduced spark energy and would probably cause a misfire. Oscillograms of the voltage across the primary of the coil show a potential difference of 12 volts falling to about 10 as the current rises. At the break there is a sharp negative voltage peak of about 160 volts followed by an exponentially decaying oscillation of the same type as that observed in the primary current curve. There is very little difference in the primary voltage curves for the two distributors. Two sets of curves were taken of the secondary voltage across a sparking plug in a compressed air chamber. One was with the pressure at 68 and the other with it at about 50 to 55 lbs. per sq.in. At 68 lbs the spark did not pass. | ||