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 description of an engine's crankshaft, connecting rods, and supercharger components.
| Identifier | ExFiles\Box 148\2\ scan0096 | |
| Date | 28th November 1938 | |
| -3- (b) CRACKSHAFT, CONNECTING RODS ETC. The crankshaft is an unmachined steel forging. It is counter-balanced, and as mentioned above, has two crankpins with a 15° phase angle between them. This angle gives the exhaust piston a lead which aids scavenging of the combustion space and idling. Two main bearings are used. The particular phase angle used is experimental and no doubt tests have been conducted by this time using different angles. The connecting rods are unmachined steel forgings and are of orthodox H section design. The big end bearings are made of a lead bronze alloy material. No Master connecting rod is employed, each bearing using 25% of the journal area. (c) Super charger. The engine is fitted with a medium pressure Roots type supercharger. As in normal practice this is mounted between the carburetter and engine. It was designed to give a maximum boost of 13 inches of mercury - about 6.5 lbs.sq.in. running at 3500 r.p.m. The rotors used are the three lobe type and on each rotor there is in addition a 30° twist. This was done to reduce noise and to even out the impulses when running slowly. There is a by-pass connecting intake and exhaust ports. This comes into operation by means of a spring loaded butterfly valve when a certain predetermined pressure is exceeded (13" Hg. in this case). It also serves as a pressure release valve in the event of the engine spitting and producing abnormally high pressures on the blower casing and rotors. The rotors are made of machined cast steel and the casing is a heavily ribbed aluminium casting. Experiments are being made with pressed steel rotors - pressed in two halves and electrically butt welded together. The degree of accuracy necessary in a Roots type rotor appeared to be within the capabilities of the dies and the only machining or grinding operation necessary was that of removing the surplus weld metal. | ||