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 and development of new experimental 20 HP pistons, including a novel design with an invar ring.
| Identifier | ExFiles\Box 15\3\ Scan015 | |
| Date | 20th July 1928 | |
| Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} from R.{Sir Henry Royce} c. to BJ. Wor.{Arthur Wormald - General Works Manager} +7040 R3/M20.7.28. 20 HP. PISTONS. X.5040 X.7040 X.741 We have already sent you an ordinary type piston strengthened, and we have also sent you a group of designs for experimental rings, some of which may have extremely valuable features. We trust this work will move as rapidly as possible. We expect to send you tomorrow another piston for the 20 HP. of the single bolt pedestal type which is doing so extremely well on 14-EX Phantom, after its long trials, as regards knocks and oil consumption. We have modified this to make it stronger and lighter from the original one designed for the Phantom. We have now added a unique feature of keeping the bottom of the piston to its correct dia. by a steel or invar ring (unsplit). This part of the piston will in this experiment be looked upon as a dia. that does not increase with temp. at a greater rate than the cyl. It has no need therefore to be flexible, and is sprung inwards on to the ring. The upper part of the skirt of this piston is split as usual, and is looked upon as flexible, and suiting itself to changes in temperature. We feel certain that if this piston is rightly fitted it should prove less liable to knocks at low temperature, and possibly may have virtues in keeping down the oil. We hope too that it will prove a light piston, and perhaps more easily got right. In the proportions we have made it the conn. rod must be lengthened 1/8", which is in the right direction for reducing the over-running vibration. We think that with the improved design of this type for the Phantom, and with the improvement in piston rings, and this particular piston, you ought to have material for a definite step forward on pistons, and we believe that it will be most economical to push forward these experiments quickly, with the hope of finding some more permanent cure for the usual troubles with pistons. In the novel piston with invar ring at the bottom (where it is difficult to get the skirt stiff enough) the ring is pushed in tightly, so that by expansion the aluminium never leaves the steel ring. It is ground parallel on the skirt to the cold cyl. ex dia. The upper parts (head) is ground smaller to the correct clearance, slightly tapering upwards, and slightly eccentric. The usual clearance is made at the sides (upper part of skirt). The combination of the upper part of the skirt being compensatingly flexible, and the lower parts being maintained rigidly by the unsplit ring with a correct rate of expansion, is I believe novel, and should have a provisional patent in my name. R.{Sir Henry Royce} | ||