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).
Improving motor brush performance, including experiments with pressure and different material compositions.
| Identifier | ExFiles\Box 35\1\ scan 016 | |
| Date | 22th September 1917 guessed | |
| -2- EFC6/E.{Mr Elliott - Chief Engineer} Contd. Although we have found the brush of present quality C.M. the most satisfactory of the three, we are not altogether satisfied with the operation of these brushes, but we are not quite sure as to whether we have the right conditions for the running of these. We have already increased our brush pressure once and are putting through some still stronger springs to experimentally increase this further; this we may find an improvement. It is also suggested by our Mr. Royce that a brush with a larger percentage of carbon than the C.M. would be more satisfactory, but this we have not found to be the case in our experiments, although wethink it may possibly be the case if we still further increase the brush pressure. We should, therefore, very much like to have the benefit of your experience in this matter. As you probably know, our system is a 12 volt system, the motor is a four pole machine with a two circuit wave winding but with four brushes at 90º. At the instant of starting, each brush has to carry about 120 amperes. When the engine is cold and being normally turned over by the motor, this falls to about 60 amperes. The cross sectional area of each brush we are taking as .4 sq.inch. We have yourlist of principal types of brushes and their application, and we note from this that the C.M. type of brush ought to be the best one for the purpose, as it states that it is suitable when the current density is high and for D.C. machines up to 10 volts. Is there not a grade of brush similar to the C.M. but containing a larger proportion of carbon, but not so great a proportion as the C.M.4 ? The C.M.1 type would appear from its colour to contain some other substance than copper and carbon. We should very much like to know if this is the case. We do not suppose there would be any advantage in trying the C.M.6 or C.M.9 quality, and we should be glad if you would confirm this. Yours faithfully, | ||