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).
Improvements to the Bentley and IN CIRG type fan-ventilated dynamo.
| Identifier | ExFiles\Box 168a\3\ img208 | |
| Date | 3rd July 1935 | |
| Ha'/Jat.6/JA.3.7.35. BENTLEY AND IN CIRG TYPE FAN VENTILATED DYNAMO. During the last few months a considerable improvement has been achieved in dynamo output and performance by altering the dynamo poles, reducing the dynamo armature diameter and providing a fan for direct cooling. In our efforts to improve the standard larger dynamo, the first essential was to reduce the amount of sparking at the bushes, in order to make any increase in output a safe proposition. With this in view special poles were developed, having a larger polar arc, (85° as compared with 69°) a smaller normal air gap (.015" as compared with .020") and a chamfer on each tip increasing the air gap from .015" to .10" over a range of 15°. The success with these poles makes possible the safe use of a fan. The advantage of the fan could be used in the direction of rapidly removing the extra heat, generated, either entirely by an increased output, or, by the use of a larger number of small gauge conductors, for the purpose of obtaining an earlier cutting in. In the machine we are putting forward for standardisation a compromise has been made between output and cutting in; the use of the fan being manifest in a lower cutting in speed, as well as in an increased output. By using 4 turns per coil of 16 S.W.G. wire on the armature, as compared with 3 turns per coil of 16 S.W.G. at present used, it was possible to reduce the diameter of the armature, and, correspondingly, increase the radial length of the pole core. We were thus able to accomodate a larger field coil which, together with the larger polar arc, and smaller normal air gap, resulted in the cutting-in speed being lowered from 800 R.P.M. (standard) to 650 R.P.M. At the same time, the output was increased from 16 amperes (std) to 20.5 amperes. | ||