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).
Visit to Vauxhall regarding their experience with tank clutches.
| Identifier | ExFiles\Box 127\4\ scan0257 | |
| Date | 17th December 1940 | |
| To Hm.{Capt. W. Hallam - Head Repairs} from Rm{William Robotham - Chief Engineer}/GB. Copy to Ev.{Ivan Evernden - coachwork} & FJH.{Fred J. Hardy - Chief Dev. Engineer} VISIT TO VAUXHALL - 11/12-12-40 A number of subjects were discussed at this visit: TANK CLUTCHES - Vauxhall's own experience is as follows: 1. Under persuasion Borg & Beck supplied the 18" single disc clutch for a torque of 840 lb/ft. They would not recommend it for more than 750. 2. The Vauxhall engine developed 960 lb/ft torque when it left the bed. It is now thought to be nearer to 1000 lb/ft., due to freeing off with use. 3. The liners were half worn away after 150 miles; i.e. liner life is 300 miles. This makes our own case look rather hopeless, but it should not be, for the following reasons: Track resistance is so high that the change from 1st to 2nd is impossible, and from 2nd to 3rd very difficult (They had no figure for track resistance). The usual practice is therefore to start off in the gear one intends to run in or at speed, whichever is the lower. This practice is hard on the clutch. Another point which should not be forgotten is that engine speed cannot be judged by ear in a tank. It was stated that the µ for the Vauxhall clutch was .3. Their spring load (200 lb. each spring) makes it .24. Possibly .3 is the working coefficient at the end of the liner life. The spring load is not enough to pull the engine speed down quickly and Borg & Beck are to supply some 210 lb. springs. Vauxhall are to try VG9T liners as these have a µ which rises with temperature. For clutches where the revolving speeds were high Dartmouth iron castings were recommended. The iron used in these castings had an ultimate strength of 18 tons sq.in. and this strength was not lost in the casting operation. | ||