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 memorandum comparing pneumatic and mechanical servo braking systems.
| Identifier | Morton\M1.A\ img010 | |
| Date | 21th November 1922 | |
| To C.J. from R.{Sir Henry Royce} -2- R12/G22/11/21 Contd. compressed air is not available either forwards or back-wards, and with fairly simple mechanism, much as at present. (4) In addition to this manual operation, I add a compressed air operating cylinder to the brakes for each axle to act instead of, or to arrest the manual operation. (5) The air from the reservoir described in (2) is admitted to the operating cylinders described in (4) in the following way. The usual foot pedal during the first inch of its descent opens a valve between the reservoir and the brake operating cylinders. This pedal is also connected with a piston working in a cylinder, so that the air admitted to the brakes also tends to force the foot pedal up again, and this means the driver feels the air pressure he is admitting to the brake cylinder, and upon relieving the foot pressure on the pedal the piston rises and releases the air and therefore takes off the brakes. (6) It will be noted that the compressed air acts instantaneously and equalises the proportion of braking between the front and back axles, which can be arranged to be in any proportion according to the cylinder sizes and levers used. (7) So that all four brakes are available instantly, independent of the speed and direction that the car is travelling. It can be any reasonable proportion to the foot pedal effort. (8) In case air pressure is not available, reasonable braking can be obtained by the use of the hand and foot operation between all four brakes. (9) The scheme includes a tyre pump and can be applied to an existing chassis by fitting new front axle and the necessary accessories, but without scrapping any further costly parts. The second scheme is entirely mechanical (i.e. not either pneumatic, hydraulic, or electrical) and is more one of the usual servo (relay) systems. (B1) In the usual servo systems trouble occurs owing to the fact that the brakes are ineffective backwards, as the servo tends to take the brake off instead of helping to put it on, hence the brakes are very feeble backwards and recourse has to be taken to the hand brake which usually operates two out of the four brakes. (B2) To avoid this trouble I arranged that the servo drum should be driven from the chassis by two ratchet drives, so geared to run in opposite directions, so that whichever is going in the correct direction carries round the servo drum in the direction of putting on the brakes. This is all right and can be worked out reasonably, but there is the one fault that the free wheel will either make a noise or it will be unreliable. (Contd.) | ||