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).
Cause of a broken stub axle pivot and proposed design modifications.
| Identifier | ExFiles\Box 2\12\ B002_X168-page016 | |
| Date | 1st July 1932 | |
| M.S. 129A (D & D) (7/32). S.L.100 G & S COPY. R10/B4313. From F.H.R. Copies sent to: Mr. Johnson. Mr. Wormald. Mr. Nadin. X 168 Re the Broken Stub axle pivot. At first I thought that the broken stub axle was caused by combined bending and torsion, but as the breakage seems to commence from the very bottom corner it looks as though it were caused by torsion almost entirely. Moreover the piece also seems to be subject to a reverse stress. It is difficult to imagine how the stress can be reversed from road shocks. It would, therefore, seem as though it came from the steering gear in somewhat the same way as it would occur if the steering gear were held rigidly and the front springs incorrectly arranged as was the case with some of the cars about three years ago. This, together with a slack cross-tube or slack bearings of the road wheels might be the cause of the reverse stress. To avoid the harsh knocks that would be caused by the road surface I propose the use of a spring of a special type fitted to the ball in the cross tube. If, however, the trouble arises from knocking both backwards and forwards, the system suggested - which is, in my opinion very practical - is scarcely complete, as the elasticity should in both directions for which it is much more difficult to arrange. I think that experiments ought to be put in hand to re-produce this break both by the Revolving test and also by tests on the chassis. It will be remembered that a sphere has been broken off at the neck in a mysterious manner. To improve matters generally I propose the following modifications in design. (a) That we should remove the aluminium packing behind the rubber buffer and bend the front horn down less far by this amount making the rear shackle of the Front spring suitable so that the spring is normally level. These alterations will bring the axle up by approximately 1/4" and since the inclination of the transmission has come about the axle should clear the engine quite well. This will admit of the stub axle being 1/8" lower down the pivot joint and will result in less bending stress on the lower half of the stub axle forging. It will result in less torsion in the front horn and also in the axle. Should such a stub axle be fitted to the existing cars it will be the means of lifting them slightly and slightly increasing the road clearance without any apparent disadvantage. In fact in the standard cars being made there is no objection to the front end of the car being 1/8" higher if it would have helped matters. Most makers through trouble with designs have their cross steering tubes bent downwards to clear the engine. This may | ||