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).
The testing and design considerations for the Boshawk battery ignition coil.
| Identifier | ExFiles\Box 45\4\ Scan089 | |
| Date | 18th November 1922 | |
| W.H. 199(SDT) (SD676 19-7-17) MPu8486 X4079 W To R & E.{Mr Elliott - Chief Engineer} from EFC. EFC1/T18.11.22. c. C.J. & I.N. c. Hy.{Tom Haldenby - Plant Engineer} & F.P. c. Eg. & Ds. X.4079 - BOSHAWK BATTERY IGNITION COIL. (1) The coil with rather longer core and four layer primary referred to in our EFC3/T14.11.22 is giving the best results we have had so far from a coil in a bakelite case. This coil has a big air space between the outside of the secondary and the inside of the case. It also has the H.T. terminal covered with a layer of rubber compound before the moulding operation. The results on the standing chassis having been satisfactory, the coil is now undergoing exhaustive trial on the road. (2) The distributor moulding never gets anything like as hot as the coil and for this reason it does not appear that the distributor should be considered definitely wrong. (3) The coil under the exceptional circumstances in which we experiment attains a temperature which we think, for a coil, should be considered excessive. We believe that if the coil is not allowed to attain this temperature by, say, 20° C, i.e. only attain about 70°C, the trouble would not occur. Therefore, is it entirely out of the question moving the coil from its present position right over the engine to another position, but still near to the distributor as previously found to be correct ? Even the stabalite coils in this position, though they do not suffer in the same way, begin to soften and fears are expressed in some quarters that dissatisfaction will occur on this score. (4) In order to prove that no serious proportion of the loss occurs with H.T. terminal insert being in direct contact with the bakelite, we have altered a coil in such a way that provision of a rubber covering on this terminal is the only alteration and a comparative test will be made. (5) The use of paraffin wax as an insulating material in the coil is out of the question so long as the coil is in this position, because it will not stay in position, and dissolves the enamel wire covering when molten. (6) It appears that a definite improvement results in having an air space between the outside of the secondary winding and the inside of the bakelite case and that contrary to what was at first thought, ionization of this air rendering it conductive, does not occur to any extent unless the air space is very narrow. It does not now seem to be any advantage filling up this air space with rubber or rubber base material; what is gained by the deletion of the | ||