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).
Big end bearings, fatigue tests, and automatic car transmissions.
| Identifier | ExFiles\Box 178\2\ img051 | |
| Date | 26th March 1940 | |
| Hm.{Capt. W. Hallam - Head Repairs} - page 2 Serial No. 53 CY 13/D/Mar.26.40 stay with 12 cylinders in Vee or flat formation and "blow up" the cylinder bores. Big Ends In connection with this, he has done intensive work on big end bearings. Finds that these fail in shear-fatigue on modern high power work. Has demonstrated this tendency with pyroxylin models and polarized light. The shear planes are normal to crankpin centerline and highest stresses are at about 30 - 45 degrees either side of longitudinal center plane of rod. Did not say what he had done to benefit or rectify this condition. In view of enormous loadings used on radial engines, the line engine makers should not be in trouble with T.V. loadings 80% as high. In other words, line engine makers are under-loading the big ends, which is additional argument for larger bores. Fatigue Tests W.R.C. said he could show me scores of tests on big end bearings and numerous other similarly high loaded parts showing that in this range of stresses, the fatigue life varied inversely as something over the cube of the stress. For example, big ends good for 3000-4000 miles at 90 m.p.h., would run 45,000 miles at half the stress, or approximately 60 m.p.h. I did not like any such assumption as compared with developing proper fatigue lines for the material, but had to admit that life was too short to develop such fatigue charts for most applications. Car Transmission Packard working on automatic transmission with fluid flywheel. W.R.C. has developed one in 90 days and has it running, using temporarily a Chrysler fluid flywheel. This confirms recent conversations in which Clyde Pattion - Chief engineer of Packard - said they only found one serious trouble with the Olds Hydramatic (of which they have two) i.e. the tendency for car to creep when started in zero weather. Had no criticism whatever of shifting smoothness, which they consider better than any other type. Griswold has tested Cotal box in Packard. Finds incurably harsh shift, and gets some report from men who have tried it in France. The box will not shift under power without hard "clunk". Magnetic clutches reluctant to release because of residual magnetism. When power shifting is attempted, the clutch faces score. Consequently, only method on Cotal is to use hand shift and "luff up" on accelerator to make the shift. W.R.C. considers that really automatic shifting is essential, and the luffing up method will not satisfy the public. | ||