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).
Experiments with direct braking on four-wheel Bentley vehicles.
| Identifier | ExFiles\Box 84\2\ scan0190 | |
| Date | 29th October 1934 | |
| To E.{Mr Elliott - Chief Engineer} c. to SG.{Arthur F. Sidgreaves - MD} c. to WGR. c. to DA.{Bernard Day - Chassis Design} c. to Ev.{Ivan Evernden - coachwork} c. to Hdy.{William Hardy} c. to Bn.{W.O. Bentley / Mr Barrington} Hs{Lord Ernest Hives - Chair}/Cry.2/KM.29.10.34. Direct Braking to Four Wheels - Bentley. We have been experimenting with this type of layout on 3-B-IV and have obtained a satisfactory scheme. Our difficulties have been lost pedal movement due to sponge and drum expansion, the pedal effort required to stop the car while shunting without servo assistance, and Variations in the ratio of front to rear braking caused by changes that take place in the coefficient of friction of the linings after being raised to high temperatures. Taking these in turn :- (1) (a) Lost Movement due to Sponge. Sponge had been measured of a considerable magnitude due to bending of the brake pedal, twist of the front axle torsion shafts, deflection of the front drums, deflection of the brake shoes, and a backward movement of the front axle buckling the rear half of the springs. These points have been corrected or reduced by R.Sch.4011, Sch.4005, Ex.16384, Bn.{W.O. Bentley / Mr Barrington}1518, and shackling the springs at the rear, respectively. On 3-B-IV the last item is further improved by the method of axle control to R.Sch.4178, in which the axle is shackled both ends and located by a radius rod and torque arm. (b) Lost Movement due to Drum Expansion. Large variations in shoe clearance had been noted when running aluminium shoes against cast iron drums. Immediately after a stop from high speeds the clearances were greatly increased. After a few less violent applications the drum had cooled and the shoes become hotter, resulting in a diminution of clearance, nearly .020 initial clearance being required at the shoe centre to prevent seizure. Steel shoes prevented the latter effect but aggravated the former. An increase of clearance of 3 half turns adjustment all round was found after one descent of Porlock hill. We therefore suggested steel shoes in conjunction with flush brass rivets running against the drum. This has been very successful. | ||