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 review of steering system design, focusing on worm gears, helix angles, and damping friction for Phantom models.
| Identifier | ExFiles\Box 17\3\ Scan211 | |
| Date | 28th March 1928 | |
| DA.{Bernard Day - Chassis Design} Hs.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} c. to BJ. Wor.{Arthur Wormald - General Works Manager} RG.{Mr Rowledge} OY. c. to E.{Mr Elliott - Chief Engineer} CWB. PN.{Mr Northey} Fl. (Handwritten: X7430) R1/M28.3.28. STEERING - PHANTOM ETC. GENERAL REVIEW X. 8430 AND EXP: .900 LARGE WORM. X. 7430 I am not convinced that Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}22.3.28 leaves quite the right impression, because one would conclude that nothing has been done but reduce the speed of the steering, and increase the damping friction on the axle side of the flexibility. (This memo. I think contains an error on page 1., helix angle 14° etc. - both are wrong). That is to say, there is no advantage in reducing the helix angle - i.e. in the larger worm, but in .720 we so put the load up that even with the larger worm we were liable to break down the oil film. Now in .900 we have again increased the worm to give more area, and have also reduced the loading and per unit area very materially, yet the above memo. says no benefit. Perhaps it is not manifest, because increase of area is not now needed with better made .720, and also it has not had quite the same chance because the leverage (speed of steering) is 13/1 instead of our new standard 16/1. Therefore give the new worm a new pendulum lever of 8" instead of 10", and it should be the best you have ever had, and this is what we must try on 'SS{S. Smith}' (EAC.10) If 8" is too short for other reasons, reduce the 7.5 helix angle to 6°. Now as regards damping friction it would seem that this should be on the axle side of the longitudinal flexibility so as to be available for damping out slow speed and high speed wobbles. If it were not needed on this side it would be a greater help towards reducing joggles if it were on the steering box side of the longitudinal flexibility. Try it both ways, and a little on each side. Now what kind of damping friction would be best: (we ought not to have two goes at it as on EAC.7). It must not be of a character to prevent the quickest movement required in manoeuvring suddenly in traffic, or recovery after a corner, and this seems to rule out hydraulic unless it has limit of pressure by ample relief valve action, then I believe it would be ideal (But not dependent on viscosity.) It could be set to give a constant small resistance to movement the same as dry solid friction, and would slightly increase with speed, and could have rather leaky piston effect to fall to nothing at very slow movements. The next best type of friction would be dry solid, in which the resistance at rest would not be contd :- | ||