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).
Paper about using an electric telemeter to investigate valve-spring surge.
| Identifier | ExFiles\Box 56\2\ Scan085 | |
| Date | 15th January 1929 | |
| To Mr Robotham P. H.{Arthur M. Hanbury - Head Complaints} Futter PREPRINT—Paper to be presented at the Annual Meeting of the Society of Automotive Engineers, Detroit, Jan. 15-18, 1929. Subject to revision. This preprint is issued primarily to stimulate written and oral discussion. The paper shall not be published in full prior to Jan. 17. Electric Telemeter and Valve-Spring Surge By W. T. DONKIN¹ and H.{Arthur M. Hanbury - Head Complaints} H.{Arthur M. Hanbury - Head Complaints} CLARK² ANNUAL MEETING PAPER Illustrated with PHOTOGRAPHS, DIAGRAMS AND CHARTS THE electric telemeter presents an excellent means for investigating the phenomenon of valve-spring surge. Basically, the telemeter is composed of two differentially connected stacks of thin carbon discs so arranged that, when the apparatus is subjected to strain, the pressure is increased on one stack and decreased on the other. Each stack forms one arm of a Wheatstone's bridge, and the resistances of the stacks vary with the pressure on them, thus slightly upsetting the balance of the bridge. If an oscillograph galvanometer-element be substituted for the usual bridging instrument, the arrangement will be found suitable for making photographic records. To study valve-spring surge, the telemeter is connected across the points of a stiff C-spring, one end of which is held against the valve-spring in such a way that vibrations of the spring are transferred to the C-spring and thence to the telemeter. This equipment has made it possible to identify the cause of valve-spring surge as a resonant condition at certain speeds. Except at low engine-speeds, the stress conditions of a spring having resonant points are much worse than is indicated by the conventional stress-formula, both as to degree and as to the rapidity of the stress cycle. Surge and stress conditions are improved by designing the springs for high frequency, and by making the pitch variable so that the frequency is variable as the valve lifts, thus eliminating resonance. IT has been recognized for some time that valve-springs for poppet-valve engines come into resonance and vibrate freely in their natural periods at certain speeds within their operating range. This vibrational phenomenon has been designated as “surge.” Surge points can be detected visually, as the vibrating spring has a fuzzy or blurred appearance, and audibly, because the vibrating spring emits a tone. However, it is all but impossible to evaluate the magnitude of the surge by simple visual and audible detection, and to determine what happens when the spring seems not to be surging. To be of real value, a surge investigation should include some concrete record and should indicate what effect the surge has upon the stress conditions in the spring. In this paper is presented the electric telemeter, with its auxiliary apparatus, as a means for making a thorough study of the operation of valve-springs, together with the results of some investigations made with it. By means of the telemeter, we obtain an oscillographic record of the operation of the valve-spring throughout its entire speed-range. Such an oscillogram consists of a series of valve-lift curves upon which are superimposed the wave-form of the free vibrations of the spring. Fig. 1, in the form in which it is used for the testing of valve-springs. Essentially, the telemeter consists of two differentially connected stacks of thin carbon discs so mounted in a frame that any displacement caused by vibration will increase the pressure on one stack and decrease the FIG. 1—ELECTRIC TELEMETER APPLIED TO SPRING-TESTING MACHINE CONSTRUCTION OF THE TELEMETER The electric telemeter was developed at the Bureau of Standards by Burton McCollum and O.{Mr Oldham} S. Peters³. It has been improved and refined⁴ and has had its field widened until it is now readily adaptable to all kinds of dynamic testing. The instrument can be seen in ¹ A.S.A.E.—Engineer, Cleveland Wire Spring Co., Cleveland. ² Engineer, Cleveland Wire Spring Co., Cleveland. ³ See Technologic Papers of the Bureau of Standards, No. 247. ⁴ See Proceedings of American Society for Testing Materials, vol. 25, part II, 1925, p. 522. 1 | ||