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).
Investigation into a steering problem on the Wraith model, specifically concerning friction in the pivot pins.
| Identifier | ExFiles\Box 9\7\ 07-page108 | |
| Date | 10th January 1938 | |
| 650 To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} c. Da.{Bernard Day - Chassis Design} c. EV.{Ivan Evernden - coachwork} WRAITH STEERING. The steering of 27.G.Vl.{V. Lewis / Mr Valentine} recently tightened up to such an extent that all self-centring was lost and the car was almost undrivable. It subsequently became more free but remained unpleasantly tacky. Judged by feel, the friction appeared to be at the road wheel end of the sponge, i.e. in the pivot pins. This trouble has occurred to a less extent several times previously on Wraith chassis but has cured itself before the cause could be investigated. The pivot pins of 27.G.Vl.{V. Lewis / Mr Valentine} were dismantled and found to have picked up on the journal bearing at the lower end. This bearing consists of a hardened steel pin in a hardened steel bush. A further pivot pin which had run in another Wraith chassis also shows slight signs of picking up. As an experiment we have had the pins of 27.G.Vl.{V. Lewis / Mr Valentine} copper plated and fitted in cast iron bushes. This combination of materials has been very successful for not sticking or picking up on the hydraulic tappet eccentrics on Ph.III, where the same conditions of high loads and small movements occur. We have calculated the journal and thrust loads due to the weight of the car and corresponding friction torques on the pins of our various chassis. The results are shown on the attached table. We have neglected the friction of the upper bearing as this is of the roller type and have assumed /u to be 0.25. As will be seen the journal load on Wraith is twice that on either 25/30 or Bentley Il. and is even greater than on Ph.III. The friction torque is correspondingly higher. We attribute the tendency to picking up to the high journal loading. So far as we can see it is not easy to fit a roller journal bearing at the lower end of the pin so experimentally we are trying to find a combination of materials which will not pick up. It remains to be seen whether we still have more friction than is required with the reduced castor angle recently adopted. continued. | ||