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).
Valve control mechanisms using bimetallic strips and external pumps with different oil viscosities.
| Identifier | ExFiles\Box 151\2\ scan0383 | |
| Date | 6th February 1939 guessed | |
| -2- cam operated by a spiral bimetallic strip or a strip having a variable rating: it might be possible to obtain this effect from a straight strip by using stops which come into action in succession so that as the temperature is increased the effective length of the bimetal strip is decreased. It will also be seen from these curves that the valve movement required to change from hard to the soft position also varies with temperature: it must however be remembered that this variation will be small compared to the movement of the spring ( of the order of .050") due to the pressure change. Use of external pump. It was suggested that if an external pump with consequently smaller temperature changes were used in conjunction with an oil such as 'Chokol' which has a low viscosity change it might be possible to obviate the need for a bimetal strip control. In order to investigate the possibilities of this idea pressure velocity curves were taken for 'Chokol' at various temperatures using a spring with a low rate to see if the pump would work satisfactorily at low speeds with a low viscosity oil. These curves are shown on Sheet III. It appears that with low viscosity oil and low speeds the pump clearances are too large. So if satisfactory results are to be obtained with 'Chokol' it would be necessary to decrease the pump clearances and/or run the pump at a higher speed. It was found that at speeds below 20 m.p.h. and temps. above 100°C the viscosity of Castrol XL was low in this respect. To conclude it would appear that satisfactory results could be obtained by using a valve with a slightly concave taper operated through a spring having a suitable rate by a cam and spiral bimetallic strip. It would also be advisable to reduce the pump clearances if this could be done without danger of seizure. .......... | ||