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).
Lever specifications and stress failure analysis for a front axle control damper.
| Identifier | ExFiles\Box 12\1\ 01-page118 | |
| Date | 7th December 1928 | |
| c. BY/HEB.{H. Biraben} c. Hs.{Lord Ernest Hives - Chair} Y7420 BY7/G.7.12.28. FRONT AXLE CONTROL DAMPER. Referring to DA{Bernard Day - Chassis Design}1/M1.12.28. the facts of the case are as follows :- 1/- On the present standard Phantom the length of the external lever is 12.500", the inside lever 2.625". 2/- S.S. External lever 11.625" length, 2.500" inside lever. 3/- G.2B. Rear Damper - External lever 13.00" length, inside lever 1.750". As the standard lever is 12.500" we propose to strengthen up the SS.{S. Smith} lever as you suggest, that is the boss will be increased to standard diameter and the radii between the shank and the boss increased. At present we do not propose to strengthen up the standard lever. In regard to the last paragraph of your memo, we agree that the limits are wider than necessary, but as the internal square is made with a broach nothing like the limit quoted should have been given, as a matter of fact the fine limit being actually used. I have examined the levers in the Works, and find that the maximum slack is between .002" and .003 of an inch. We have corrected our limits on both the standard car and the SS.{S. Smith} We are inclined to think that the cause of the failure of the internal lever is that there is a concentration of stress on the centre line of the boss owing to the draw allowed on the forging producing an increased diameter at this point, with the result that with the forces imposed by the tightening up of the bolt, and those which are the result of stress along the lever, give a high concentrated stress at the point in question. We therefore have suggested milling the lever, so as to make a parallel cylinder, and converting the lever to a 'H' section, widening the metal on the two legs of the 'H' section to the width of the boss, thereby spreading out the stress across the whole area of the material and preventing the concentration in question. At the same time we consider it desirable to move the projection, locking the head of the bolt to the side of the bolt remote from the boss. | ||