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).
Technical memorandum discussing the re-design of dynamo brush gear to address issues with brush sparking.
| Identifier | ExFiles\Box 166\1\ img069 | |
| Date | 20th November 1935 | |
| 86093 E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Wst. c. to By.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Wst.2/MA.20.11.35. DYNAMO BRUSH GEAR. We understand By/RD. is now considering the re-design of the brush gear on our dynamos and the following notes, made by Mr.Pignatt when we sent him to Messrs.Morganite's works will prove of interest in this connection :- (1) Brush sparking on our machines is :- (a) Mainly due to under commutation, i.e. commutation taking place in a weak field as the result of armature reaction and consequent field distortion. (b) To a smaller degree due to "jumping" brushes. (c) To a negligible degree due to the lap coil. (2) Since the trouble is mainly due to cause (a), it cannot be cured by merely altering the grade of brush. The only method, lies in altering the design of the machine in the direction of having a larger number of coils on the armature and fewer turns per coil. Also pole modifications such as an increased air gap at the pole tips. (3) Some reduction in sparking could be obtained by giving attention to cause (b). In this connection the Morganite engineers strongly criticised our brush gear as follows :- (a) The surface of the bearing wall of the holder should be machined dead flat. The best broaching is considered not good enough. (b) Brassis preferable for the holder as it provides a harder and smoother surface. (c) Both pressure arms should be so arranged as to be trailing, and consequently in a state of tension, and not in a state of compression, as that on our negative holder. | ||