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).
Study on air-springs and riding quality, analyzing static friction and axle movements.
| Identifier | ExFiles\Box 43\3\ Scan016 | |
| Date | 1st September 1924 guessed | |
| PAGE 6 AIR-SPRINGS AND RIDING-QUALITY cal{Mr Calvert} friction of the moving element and that due to the lubricant used. It is not my intention to go into this particular phase of air-spring design, but simply to call attention to the improvements that are possible by research and refinement of design. Fig. 7 shows the difference in static friction in different types of cup leather. Starting at the top, it is noted that two rubber packings having a total expander spring tension of 27 1/2 lb. present a serious friction problem. Comparing this curve with two leathers having a total spring-tension of 14 lb. at the bottom of Fig. 7, we can appreciate readily that this friction factor is highly important. All these tests were made on the same air-spring under nearly identical conditions, the only difference being the material used in the cups and the strength of the expander spring. The curves in Fig. 7 represent the total static friction, including that of the cup washers and the oil and the mechanical bearing-friction. The last two factors are small in quantity in the type of spring that these tests were made on, as is indicated clearly by the difference in friction between the different kinds of cup leather alone. Fig. 8 illustrates the difference in friction due to the oil factor. In all tests we have made in comparing different kinds of oil, we have found that a lower temperature will show considerably less friction. Fig. 9 shows the increase in friction due to increase in temperature with our No. 4 oil. However, it seems that the viscosity of the oil has considerable to do with the friction and, if it were possible to obtain a zero cold-test oil that had a flat curve when its viscosity was plotted against temperature, and yet was of sufficient FIG. 7—CURVES SHOWING THE DIFFERENCE IN THE STATIC FRICTION WITH VARIOUS TYPES OF CUP PACKING Included in This is the Friction of the Cup Washers, the Mechanical Bearing-Friction and That of the Oil. The Marked Difference between the Two Rubber Packings at the Top Having a Total Spring-Tension of 27 1/2 Lb. and the Two Leathers Treated by the W.A.S. Process Having a Total Spring Tension of 14 Lb. Should Be Noted as Indicating the Importance of the Friction Factor. (Graph Labels on Fig. 7: Energy, lb.; Air Pressure, lb. per sq. in.; Two Rubber-Total Spring Tension 27 1/2 lb.; Top Leather-Bottom Rubber-Total Spring Tension 14 lb.; One Rubber-Bottom Rubber-Total Spring Tension 14 lb.; Two Leathers-W.A.S. Treated No.1-Total Spring Tension 14 lb.; Two Leathers-Total Spring Tension 46 lb.) FIG. 8—CURVES SHOWING STATIC FRICTION DEVELOPED WITH DIFFERENT OILS The Increase in Friction Due to Temperature Increase is Very Marked with the Two Different Kinds of Oil Tested. This Is the Biggest Contrast Found in Over 300 Different Tests of Various Oils and Different Conditions of Test, All Measurements of the Static Friction, Including That of the Cup Leather, Is in the Curve. The Viscosity of the Two Oils Tested at Different Temperatures Is Given in the Following Table (Graph Labels on Fig. 8: Energy, lb.; Air Pressure, lb. per sq. in.; Tests at 70 Deg. Fahr.; Sample No. 20; Westinghouse No. 4 Oil; Sample No. 20; Tests at Zero Deg. Fahr.; Westinghouse No. 4 Oil) Oil No. 4 Viscosity at 32 Deg. Fahr., Saybolt sec. 11,731 Viscosity at 65 Deg. Fahr., Saybolt sec. 2,230 Viscosity at 100 Deg. Fahr., Saybolt sec. 600 Oil No. 20 Viscosity at 32 Deg. Fahr., Saybolt sec. 4,313 Viscosity at 65 Deg. Fahr., Saybolt sec. 791 Viscosity at 100 Deg. Fahr., Saybolt sec. 221 FIG. 9—CURVE SHOWING STATIC FRICTION INCREASE DUE TO TEMPERATURE RISE All These Tests are Made with the 14-lb. Best Periods between Readings, So That the Cup Leather Will Set Tightly against the Cylinder-Wall, Thus the Worst Case of Friction Will Be Found in the Air-Spring. (Graph Labels on Fig. 9: Energy, lb.; Temperature, deg. fahr.) PAGE 7 AIR-SPRINGS AND RIDING-QUALITY density to maintain a flexible film of lubricant around the moving element, one of the minor difficulties experienced in air-spring operation would be overcome. The subject of air-spring friction should be treated seriously. FRONT-AXLE MOVEMENTS WITH AND WITHOUT AIR-SPRINGS In the field tests a record of the movement was obtained by mounting a motor-driven recording paper-roll on the chassis, the recording pen being connected directly to the axle. A series of tests was made at various speeds over two different sizes of obstacles. The results always showed the same characteristic difference with and without air-springs. The single-bump curves mentioned for Fig. 10 were all taken at a car speed of 15 m.p.h. and show the axle movement as the car passes over a 2 3/4-in. high by 5 1/2-in. wide plank laid on a cement road. Fig. 10 shows the curves obtained in these tests. The curves were superimposed to show the comparison. FIG. 10—TRACING OF AN ACTUAL RECORD OF THE AXLE MOVEMENT IN PASSING OVER A SINGLE OBSTACLE AT A SPEED OF 15 M.P.H. The Solid Line Is the Movement of the Axle Relative to the Chassis with Air-Springs. The Dotted Line Is the Same Movement without Air-Springs. The Small Irregularity Marked X on the Right Side Is a Wide Crack or Joint in the Concrete, the Curves Being Superimposed and Lined-Up from This Point To Show the Relative Difference in Axle Movement. (Graph Labels on Fig. 10: Without Air-Springs; With Air-Springs; 1/5 SEC.) FIG. 11—HOW THE AIR-SPRING INCREASES THE AMPLITUDE OF DEFLECTION The Record Was Obtained with the Same Car Passing over the Same Obstruction as in Fig. 10. In This Case the Car Was Completely Equipped with Air-springs. As the Paper on Which the Record Was Traced Was Traveling at a Faster Speed, the Record Is Spread Out More than in Fig. 10 (Graph Labels on Fig. 11: 1/5 SEC.) FIG. 12—RECORD OF FRONT-AXLE MOVEMENT IN PASSING OVER THE SAME OBSTRUCTION In This Particular Test the Car Was Equipped with Air-Springs on the Rear Axle Only (Graph Labels on Fig. 12: 1/5 SEC.) FIG. 13—ANOTHER RECORD OF FRONT-AXLE MOVEMENT In This Case the Car Had No Air-Springs, Merely Being Equipped with the Original Steel Springs. The Curves Represented in Figs. 10, 11, 12 and 13 Were All Obtained at the Same Car-Speed, 15 M.P.H., and Care Was Taken To Have All the Other Conditions as Nearly Identical as Possible (Graph Labels on Fig. 13: 1/5 SEC.) | ||