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).
Secret internal memo discussing improvements to brake systems, specifically regarding 'jaggers' and backward efficiency.
| Identifier | WestWitteringFiles\L\Jan1924-March1924\ Scan107 | |
| Date | 2nd February 1924 | |
| R.R. 235a (100 T) (S.H. 159 11-8-20) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 2600 ORIGINAL S E C R E T. E.{Mr Elliott - Chief Engineer} A.{Mr Adams} C. TO HS.{Lord Ernest Hives - Chair} RG.{Mr Rowledge} FROM R.{Sir Henry Royce} E.{Mr Elliott - Chief Engineer} DA{Bernard Day - Chassis Design} C. to OJ. BJ. WOR.{Arthur Wormald - General Works Manager} BY.{R.W. Bailey - Chief Engineer} EP.{G. Eric Platford - Chief Quality Engineer} re. BRAKES - JAGGERS AND BACKWARD EFFICIENCY. X9940 Now that we have decided upon slow speed servo which can add to the foot pressure say 3 or 4 times, and this can be divided between the front and back wheels in any desired proportion (say 5 back 3 forward) by making the leverage suitable, we can consider other possibilities, and the following re-suggests itself - Since a long lapping shoe is thought to increase the risk of jaggers (as I thought some time ago if it were not wholly a question of the change of co-efficient) it might be thought advisable to fit short shoes forward and long shoes backwards. The long shoes could be tested stiff, semi-flexible, and jointed (one only of the latter would be quite practical.) My chief object in suggesting this is to increase the backward holding efficiency (this is lost to the greater the added proportion by the servo) so that it makes up for loss of the servo by self servo-ing backwards. (Incidentally it will be found to make a more consistent, better equalised brake less liable to forward jaggers). I am aware it has some disadvantages but anyway it could be tested and also might be adopted in some half way degree with advantage. The want of equal action and varying efficiency is largely due to the variation in bedding by wear on a long forward lapping shoe (and the proportion of pressure between the two shoes) with a shorter shoe this variation should be less and also with a floating fulcrum the pressure should not vary. You will remember that in amongst all the troubles you have so fortunately found us we are still seeking for a more consistent brake, which we fear our present ones are not (and no other designs we know of) from the causes given above or from the varying condition of surface or oiliness. I hope it will be found that with the 4 brakes the heat will be so much less that the wear will be very little indeed, or so they will be more constant for a much longer time and possibly for ever. You will remember that some time ago I asked you to test the difference of the co-efficient of friction at rest and at all speeds up to our probable maximum. I do not remember seeing these figures which should so directly bear upon the phenomenon called jaggers. Naturally the long self lapping shoe will have plenty of weight upon it, because the lapping shoe forward is the one which must wear most. Probably this is the reason why the Hispano arrangement is rather better than anticipated backwards, (but hardly good enough if it is possible to make it better without undue complication.) R.{Sir Henry Royce} | ||