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).
Design of cams, springs, and valves for an engine.
| Identifier | ExFiles\Box 43\3\ Scan101 | |
| Date | 29th December 1926 | |
| L4003 To E.{Mr Elliott - Chief Engineer} from R.{Sir Henry Royce} c. to BJ. Wor.{Arthur Wormald - General Works Manager} RG.{Mr Rowledge} c. to Hs.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} R1/M29.12.26. RR.F.10. CAMS AND SPRINGS, INLET AND EXHAUST VALVES. X.3822 X.4003 X.4011 There is tremendous latitude, and pitfalls in arranging the acceleration diagram. I have made certain suggestions which may be imperfect and incomplete: trust you will find out the good. Since we have now a spring of different characteristics we must get the acceleration when we can. Supposing we say the air passing the valve only causes definite pressure during the closing period, it seems sound to take more time closing the inlet valve than opening it. Probably at the worst period the spring is discounted by 20%. Now assuming this, can we arrange the pressure between cam and roller to be the same during the whole of the time the contact depends upon the action of the spring? Supposing the cam is kept open xx say at half lift long enough for efficiency, then the sharp deceleration period would be shorter and the max. speed of the closing valve (i.e. max. velocity) would be less during the closing period. If however it was found absolutely necessary to close the valve as quickly as possible, then the spring must be capable of, and allowed to get the valve moving quickly while the spring is giving its max. pressure, (i.e. first period of closing half). This may suggest a cam thus, with full open dwell, as we find on Curtiss and Mercedes. However my views are that since the spring is discounted we must have more time for closing, and since spring can give maximum acceleration when fully compressed, we must allow it to do so, otherwise the valve will be moving too slowly, and the force of our spring pressure be kept uniform for our max. engine speed, there cannot be anything wrong between cam shape and spring pressure. One thinks the double spring shewn is the more practical. Have we decided on heavy exhaust valves with larger stems? If so, I cannot see what use is the triple spring, as we must use one type for both valves. R.{Sir Henry Royce} | ||