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 memo comparing the effect of brake torque on the front suspension of the Bentley III and Packard models.
| Identifier | ExFiles\Box 100\1\ scan0154 | |
| Date | 27th May 1938 | |
| 446 also 1086 To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale} c. Da.{Bernard Day - Chassis Design} c. Da{Bernard Day - Chassis Design}/Iv. BENTLEY III FRONT SUSPENSION. EFFECT OF BRAKE TORQUE ON B.III & PACKARD. As stated in our Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale}2/MH.{M. Huckerby}9.5.38, we have measured the effect of brake torque on B.III and Packard front suspension. We find that under the same brake torque the Packard suspension is only half as flexible as the B.III and under maximum brake torque the upper yoke bearing only moves about half its possible travel, whereas the B.III bush moves to the limit of its travel and allows metal to metal contact. This appears to be due to an increase of bending moment in the yoke, which gives an increase of deflection of 41% at the upper bearing, and to a lower bearing very much weaker than the Packard since the bending moment in it is only half. With reference to the attached report, the major deflexions take place in the yoke and lower bearing. Again, we cannot easily stiffen the lower bearing but we are stiffening the yoke and if we can make it as stiff as the Packard we should reduce our deflexion by 28% which is a big improvement. We can, of course, weaken the upper triangle and so reduce the movement of the rubber bush, but as the former is already 54% weaker than the latter this does not appear desirable in view of the weakness of the lower bearing. It should be remembered that in expecting the lower bearing to take nearly all the brake torque we are not being unreasonable as the bearing is the same size as the steering pivot bearing which has the same torque to carry. Experience on the road indicates that although the suspension is flexible there is no reason to suppose it will inevitably fail, as brake applications are relatively infrequent. Practical tests show that with the rear brakes working normally the upper bearing only deflects .040" under heavy braking on a smooth road, but that on a rough road bumps may cause metal to metal contact. If the front brakes are made to lock the rubber bush can move .158". | ||