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).
Functionality of automatic carburettors and thermostat systems, comparing setups in Bentley, Daimler, and Lanchester vehicles.
| Identifier | ExFiles\Box 126\4\ scan0107 | |
| Date | 4th June 1938 | |
| -2- It must be remembered that this type of automatic carburetter does not give a progressive action; the "starter" is either in or out. There is therefore an intermediate stage which is not catered for. Assuming that the thermostat cuts out at 35°C the following condition arises. The engine is started from cold, and run light for five to ten minutes, and then stopped. After another short interval the complete induction system can be almost cold, while the circulating water may be just about 35°C, thus keeping the "rich" mixture out of action. It is obvious, therefore, that the engine may be difficult to start. This condition is much more likely to occur, where an exhaust heated "hot spot" is used, as is the case of the Daimler '15'. On our proposed scheme for Bentley III the thermostat has been placed in the water hot spot immediately adjacent to the carburetter. We can say, therefore, that the reason for Daimler's decision does not apply to our own case. Considering (b):- S.U. carb. and Smith's thermostat. A normal S.U. carburetter is used, and the usual Mixture control is connected to a Smith's "Automatic Jet Control". This is a strong bellows type of thermostat, the bellows of which connect with the induction pipe to give a compensated action for cold 'get-away'. This system has a distinct advantage over the previous scheme mentioned above, as it is "fully" automatic, being correctly balanced and progressive throughout the speed range, against throttle opening and engine temperature. Mechanically, however, it is doubtful whether we could make this work on Bentley III, because the thermostat is required to do twice as much work in operating two S.U. jets. The set-up on the Lanchester '18' and Daimler light '20' uses one horizontal S.U. carburetter. It is considered, however, that we should obtain the latest model of this type of thermostat from Smiths, and prove this point, and in any case see what we can do about it. The Daimler people had a little trouble with the instrument in the early stages. First, a leak developed by way of the main spindle, through the bellows, into the induction pipe. This was cured by fitting a second smaller bellows of neoprene fastened on by wire. The next stage was, in using wire which was | ||