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).
The development and testing of a new air piston for a B.11 semi-expanding carburettor.
| Identifier | ExFiles\Box 13\3\ 03-page409 | |
| Date | 5th April 1932 | |
| 87080 To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Lsv. c. to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. to Rg.{Mr Rowledge} E.{Mr Elliott - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} Da.{Bernard Day - Chassis Design} Hs{Lord Ernest Hives - Chair}/Lsv.2/MJ.5.4.32. B.11 SEMI-EXPANDING CARBURETTER. We have tested out the new air piston shown in R.2/M.9.3.32 (Lec.3029 Sch.1) in which the suction in the dash pot is delayed by transferring it past the annular clearance between the piston and the dashpot. On test this scheme appears very promising and is effective in giving the delayed movement of the piston required for good snap acceleration. We have been experimenting with various degrees of clearance round the air piston and found with the initial clearance of .0005 the lift was too delayed and on shutting the throttle the fall of the piston was far too slow. The annular clearance has been increased by stages up to .003 at which clearance the snap acceleration is very good and the rate of fall is sufficiently rapid. We have now tried two schemes which have given satisfactory results - First the 45º seat piston with large suction holes in the seat which are closed when the valve is at rest. The initial delayed lift being obtained by means of a small suction hole in the side of the piston. Second this latter scheme Lec.3029 Sch.1. We favour this latter scheme, which has given us :- (1) Sufficient delay action for snap acceleration. (2) Sufficiently rapid fall. (3) Full lift at 3000 R.P.M. A central guide we consider is very desirable and a feature which is too good to leave out of the present design. It avoids the stacking up trouble we frequently get and have always bad on the standard type air valve. Having shewn that the delay action when snap accelerating depends upon the annular clearance round the piston, the central guide would avoid wear at this point and so tend to maintain consistent operation. We are, at the moment, establishing the limits of clearance between which it will be necessary to work in order to maintain the desired characteristics. The general metering of the carburetter is good but we are still working on the jet needle tapers to get some of the fine points right. We are arranging to fit up our test model carburetter | ||