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).
Article discussing cylinder bore wear and an analysis of new steel piston ring designs.
| Identifier | ExFiles\Box 132\5\ scan0081 | |
| Date | 1st March 1939 | |
| 90 THE AUTOMOBILE ENGINEER MARCH, 1939 Cylinder Bore Wear—contd. designed to have the correct initial radial pressure. Ring wear has been suggested as a possible handicap for high-tension rings. If too dry they will, undoubtedly, wear, but when normally used they prove themselves by their service. Reference has been made to tests conducted by the Atlantic Refining Company in America on six American cars. The ring wear in these engines averaged 0·002in. per side for each, for 100,000 miles. Now, assuming that the test was not a good bore wear test due to continuous driving, at least it must be admitted that the rings which were of the high-tension high-point type and individually cast, would have worn themselves by the scrubbing action alone during this mileage if tension was the factor that promoted wear. Fig. 19. Bleed type of thermostat. (Image labels: VALVE, BYPASS PIPE, BELLOWS) Blow-by is the enemy of rings, and if not controlled will be taken as an excuse to introduce new metals. The extreme pressure in aviation engines may require better ring material than is now used in motor cars, but if blow-by control is really studied for this type of engine, the more expensive materials will be worth while. In conclusion, it may be pointed out that the practical illustrations which are given in this paper can be repeated in many thousands of trucks and cars on the highways of the world. It is the author's opinion that good practice leading to a better result or more favourable cost is worthy of consideration, regardless of the origin of the idea. Opposition should be based upon other grounds than scepticism or a desire to be different regardless of cost. STEEL PISTON RINGS Some Notes on the New Designs At the Paris Show there were a number of steel piston rings. Despite the exceptional wearing properties of cast iron, steel has a definite vogue. The original Cord steel piston ring consists of pairs of thin pointed arch rings of the section shown in Fig. 1. Fundamentally the idea is, of course, that these units of two pairs of rings have a spring capacity in both the radial and axial directions. They therefore conform, as shown in Fig. 3, to the contour of the cylinder, even after excessive cylinder wear. Further, if the groove is worn it will fit tightly. Fig. 1. “Cord” steel piston ring. Fig. 2. “Steelcraft” piston ring. Fig. 6. “Ondulex” oil control ring. A piston ring marketed under the name “Steelcraft” (Fig. 2) is of the same design. The Steelcraft rings have a width of only 1/32in., or 0·7935 mm., and are of special steel, heat-treated so that they have a heat resistance of 800 deg. C. The design of the Champion rings is based on the same principle as the rings of a pointed arch section but with variations. That known as Champion Double Spiral W is a design with two coils similar to the Clupet rings. In the case of the Champion Lock, this ring has on one face a wave to prevent the movement of the ring elements. This wavy section does not appear to be an improvement, as it makes the ring stiffer at this point and seems detrimental to the uniformity of the radial pressure. Fig. 4 shows the application with four and five rings. It is evident that the elements may be varied in number and combination. They are manufactured in steel, or in bronze for use in hardened liners. Ondulex rings (Fig. 5) consist of several thin, flat steel rings which are fitted in one groove so that an undulated ring is sandwiched between the ring and exerts axial pressure. At the same time this undulated ring forms an efficient oil groove as shown in Fig. 6. In this design the number of plates can be varied to fit suitably in the groove. The Dran-Bac ring (Etablissements Jaques Floquet) is a combination of a cast iron ground ring and several thin steel rings as illustrated in Fig. 7. Radial pressure is exerted by an expander which is so shaped that the passage of oil is not checked. All these rings are more or less designed to avoid the expense of reboring worn cylinders, or they can be fitted in oversized piston grooves. The true value of steel rings of this kind cannot be decided by theory alone. It is a question of thorough tests and practical experience. It is possible that in many cases good results may be obtained, as the manufacturers of such rings claim. It seems, however, that experience with this material is at present not wide enough to enable users to reach a definite decision. Fig. 3. “Steelcraft” piston ring in normal cylinder (right) and oval cylinder (left). Fig. 4. “Champion” multiple piston rings. Fig. 5. “Ondulex” multiple piston rings. In the piston assembly drawings it may be significant that the first ring on the top, i.e., the compression ring, and sometimes the second as well, are of the cast iron type. If the heat resisting and all the other properties of the steel rings are as good as claimed by the manufacturers, why are they not good enough for use as compression rings? It is here that the need exists for improvements, while new designs of oil rings are probably not so important. It is interesting, however, to study these new developments. Fig. 7. “Dran-Bac” oil control ring. | ||