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).
Design decisions for a new servo mechanism, weighing options and detailing improvements over previous models.
| Identifier | ExFiles\Box 179b\1\ img180 | |
| Date | 3rd November 1922 | |
| (2) This, and the reduced speed, may make a considerable difference, but at the same time we ought to increase the area of the surface all that we conveniently can. This I understand will be done. On reviewing the situation it seems that we cannot give - either on Bensport, or Peregrine - both the servo and hydraulic brakes within reasonable cost, or by the time and talent we have available, and as Derby concludes that it is necessary to have the servo, in any case we shall have to be contented with servo and mechanical transmission, and not auto: adjustment for the present. For some time I have been discontented with our present servo, and as on these models it has proved to have too little capacity we have schemed another which I am expecting will give better results. It is like the ordinary brakes of the internal expanding type, and can have cooling ribs on the outside. It can be made in cast iron, or in aluminium lined with a cast iron ring. It will therefore take care of the cooling very much better than the present type. It can have wider friction surfaces so as not to squeeze the material out sideways. For a given external dia. the friction surfaces will be further from the centre, and therefore more efficient. One great point in this type of servo is that it is only about one fifth as exacting for alignment with the worm shaft as the plate type. This reduction brings it much nearer practical possibilities. The reason for this will be seen if we imagine the ball bearing carrying the end of the servo shaft in the same plane as the friction surface. This is not convenient, but it will be so near that the slack and spring of materials will accommodate itself. It will be understood that this comes about by the fact that the servo while in action is always slipping like a brake rather than a clutch. The design that we are getting out works in both directions, and has the usual scissor operating lever. We intend however to put one of these scissor levers direct on the balance lever, the same as the lifting rods, and to make the lifting mechanism much simpler than hitherto. We hope to send a preliminary design of all this by the end of the week. DA.{Bernard Day - Chassis Design} has very definitely helped me to find a suitable mechanism, and a design is developing satisfactorily. F.H.R. R.{Sir Henry Royce} | ||