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).
Vehicle air-springs and riding-quality, including a diagram of a vibration recorder.
| Identifier | ExFiles\Box 43\3\ Scan023 | |
| Date | 9th August 1926 guessed | |
| 20 AIR-SPRINGS AND RIDING-QUALITY FIG. 29—SKETCH SHOWING THE METHOD EMPLOYED IN TESTING AND ADJUSTING THE VIBRATION RECORDER In Adjusting or Checking-Up the Instrument the Entire Mass Is Suspended on a Coil Spring Having a Definite Period. With a Given Period and a Certain Amplitude the Whole Mass of the Structure Itself Will Have an Acceleration Equal to Gravity. Using the Well-Known Formula for Acceleration, It is a Simple Matter To Calculate the Amplitude Necessary for Any Given Acceleration. Knowing the Amplitude for That Particular Acceleration, the Jaws of the Spring Instrument Is Set Vibrating and the Adjustment Is Made until the Weight Lifts and Perforates the Tape DIAGRAM TEXT: Coil Spring Period (t = 60/Period) CHECK TEST Electrical Circuit Breaks and Light Flashes when Acceleration Exceeding Gravity is Reached Sliding Hook Allows Instrument Mass to Lift and Break Electric Circuit Small Dry Cell Battery Electric Light Bulb Feeding Roll Weight Spring Adjusting Cap Formula a = (12π²/t²)g a = Amplitude in Feet t = Time in Seconds g = 32.2 MAIN TEXT: QUESTION:—What of the riding-quality produced by a combination of air-springs and balloon tires? MR. McELROY:—We have equipped several cars with air-springs in combination with balloon tires. The results as to riding-quality are very favorable. QUESTION:—How do you determine the base on which to calculate the percentage of improvement in riding-comfort? MR. McELROY:—All our tests are based on comparisons. The instrument shown diagrammatically in Fig. 29 is set to record any vibration exceeding an acceleration of 10 ft. per sec. per sec. In adjusting the instrument or checking it up, we suspend its entire mass on a coil spring having a definite period. With a given period and a certain amplitude, the whole mass of the structure itself will have an acceleration equal to that of gravity. Using the well-known acceleration formula, it is a simple matter to calculate the amplitude necessary for any acceleration, as illustrated in Fig. 29. Knowing the amplitude for that given acceleration, the mass of the spring instrument is set vibrating, and the adjustment is made until the weight lifts and perforates the tape. QUESTION:—Have you ever made comparative tests by designing new steel-springs having the same approximate flexibility as the combination of the former steel-spring with the air-spring? MR. McELROY:—No. I believe that a flexible straight-line-load-curve steel-spring would not be a fair comparison. We have not attempted to build a progressive spring having rising characteristics of the combination load-curve. QUESTION:—Suppose camber blocks were introduced in the case of the steel spring, so that it would produce the same characteristic as that of your air-spring? MR. McELROY:—I presume the camber block is used with a single spring so that, as the load is increased, less of the spring is effective; thus, its stiffness is increased. The Marmon car, I think, has camber blocks between the two cross-springs on the rear. Undoubtedly the load curve of the air-spring and steel-spring combination could be approximated, but the entire deflection would be taken by the free ends of the steel spring, while the combination would have both air-spring and steel-spring deflection, thus giving a counter-spring effect with its subsequent reduction in period and duration of period after absorbing any given shock. It seems to me that the free ends of the camber-block spring would have a higher natural period as the effective length was shortened, even in spite of the fact that the load is increasing. At any rate, I believe that the entire characteristics of an air-spring and steel-spring combination cannot be reproduced with any form of a steel spring alone, whether it be a progressive spring or a camber-block arrangement. It might be done if some form of coil spring were combined with a laminated steel-spring. QUESTION:—In regard to the curve of the air-spring, if the flexure changes as the load is applied, the spring becomes stiffer; then, it would be in the same class as a built-up or step-up spring. If the test covers the vibration of the air-spring up into the higher pressures, I think it would affect the period just as it would in the step-up spring. In other words, is the period reduced as the load is put on? MR. McELROY:—Certainly; it flexes just the same. The period is reduced just as the period of the progressive spring is reduced as the load is put on. Naturally, I meant that the period would be reduced on both of them as the load increased. be available to take care of the larger shocks. Furthermore, the air-spring and steel-spring combination divides the work so that the deflection or bending of the steel spring is materially reduced, thus increasing its efficiency and length of life. QUESTION:—How does the air-spring affect side-sway-ing? MR. McELROY:—A more flexible spring-suspension will give more “lean” to the body. The air-spring will accentuate this condition slightly, but the modern car with its low center of gravity has enabled both the steel-spring and the air-spring manufacturers to use springs of greater flexibility without in any way affecting the roadability of the car. Some years ago when the cars were built very high and we were using our old type of spring, side-sway was a common complaint and it was a just complaint; but plenty of cars are on the road today with the original flexible steel-spring equipment that have more lean or side-sway than has a car equipped with air-springs. QUESTION:—When air-springs on the rear are provided with knuckle-joints to prevent excessive piston and cylinder wear, is not general roadability sacrificed? MR. McELROY:—The air-spring that we discontinued 2 years ago had a ball-and-socket rear-shackle construction that necessitated tapering down the end of the spring to attach the ball. We discontinued it because it was not a good mechanical job; when the wear became excessive, it caused an objectionable roll. We now use a direct-connected shackle, very similar to the car shackle connecting the rear cylinder or the rear moving element directly to the spring-eye. | ||