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).
The analysis and testing of air-springs and their effect on riding quality and axle-movement.
Identifier | ExFiles\Box 43\3\ Scan017 | |
Date | 28th September 1923 guessed | |
PAGE 8 AIR-SPRINGS AND RIDING-QUALITY TABLE 1—VALUES OF INITIAL, OR MAXIMUM, AXLE-MOVEMENT Equipment | Normal Axle-Line | Total Axle Movement, In. --- | --- | --- | Compression Above, In. | Expansion Below, In. | No Air-Springs | 1 1/8 | 1 3/4 | 2 7/8 Rear Air-Springs Only | 1 3/8 | 2 1/4 | 3 5/8 Air-Springs All Around | 1 5/8 | 2 3/8 | 4 more clearly and were lined-up at the small bump marked X which indicates a joint in the cement. The solid line represents the combined steel-spring and air-spring action at the axle, and the dotted line indicates the steel-spring action at the axle only; in other words, the axle movements with and without air-springs. The maximum movement either above or below the normal line is increased with air-springs and the subsequent rebound shows a considerably more action on the under side of the normal line, the general air-spring tendency being to float the chassis on a slightly higher plane at the time of rebound. In all our tests, a reduction is noticeable in the vibration period and in its duration with an increased axle-travel vertically. FIG. 14—MECHANICAL AXLE-MOVEMENT RECORDER WITH THE OUTSIDE COVER-PLATE REMOVED This Instrument Registers the Total Travel of the Axle in Feet, the Number of Axle Movements, the Number of Times the Axle Passes the Normal Rest Line, the Actual Times in Feet the Axle Is Above the Rest Line and the Corresponding Travel Below. Five Different Phases of Axle Movement Are Automatically Recorded by This Instrument. FIG. 15—THE MECHANICAL AXLE-MOVEMENT RECORDER AS IT IS ATTACHED TO THE FRONT END OF A CAR PREPARATORY TO MAKING A TEST RUN The Connection between the Axle and the Instrument Is Made by an Angle-Iron Extension Projecting from the Front Axle and Connecting to the Moving Rod of the Recorder by a Universal-Joint. This Arrangement Is Not Absolutely Accurate, but the Error Introduced by It Is Practically Negligible. out more due to faster paper-speed. The curve in Fig. 12 shows the same test with rear air-springs only. The curve in Fig. 13 shows the condition with the original steel-spring equipment only. All the curves were taken at the same car-speed, and care was used to make all other conditions as nearly identical as possible. These curves were selected from those for about 50 tests to get the maximum comparison in amplitude, as the total axle movement was the principal factor we desired to determine. Table 1 shows the values of the initial, or maximum, axle-movement in inches. The figures in Table 1 were chosen from curves showing the minimum axle-movement with steel springs only, and maximum with air-springs all around. We have, therefore, a maximum increase in amplitude of 30 per cent on the axle due to the influence of the air-spring. In actual figures this amounts to 3/8 in. more travel upward on the compression or shock stroke, and 5/8 in. more on the downward or rebound stroke. Paper rolls for records that cover a long course are cumbersome to handle and tedious to work with. The records all show the general tendency illustrated in the single-bump curves, but they are far too complicated to analyze. Therefore, we developed an instrument we call an axle-movement recorder. It is shown in Fig. 14 and is an ingenious consolidation of recording dials, so as to act on one rod in the center, this rod being connected to the axle through a bracket and a universal-joint. Thus, all the movements of the axle are transmitted to the instrument, which is designed so that it will record the number of movements irrespective of their amplitude and position in regard to the normal setting of the car. It records also the number of times the axle passes upward above the mean position and, likewise, the number of movements below; further, it gives the total accumulated travel of the axle vertically, up and down, in inches. PAGE 9 AIR-SPRINGS AND RIDING-QUALITY TABLE 2—STUDY OF AVERAGE AXLE-MOVEMENTS WITH AND WITHOUT AIR-SPRINGS† Counter | Description | Without Air-Springs | With Air-Springs | Percentage of Reduction or Increase With Springs --- | --- | --- | --- | --- A | Total Movement Up and Down, ft. | 69.54 | 88.96 | +28 B | Total Movement Above Normal Line, ft. | 20.14 | 14.49 | –29 C | Total Number of Movements | 1,193 | 1,004 | –16 D | Total Movement Below Normal Line, ft. | 14.63 | 29.99 | +105 E | Number of Times Axle Passes Normal Line | 679 | 534 | –21 2B/E | Average Movement of Axle Above Normal Line, in. | 0.690 | 0.650 | ... 2D/E | Average Movement of Axle Below Normal Line, in. | 0.435 | 1.350 | ... | Average Axle Movement, in. | 1.125 | 2.000 | ... | Number of Vibrations Exceeding an Acceleration of 10 Ft. per Sec. per Sec. | 354 | 286 | –19 | Riding-Constant=Number of Vibrations Times the Weight Throw of the Instrument | 72.9 | 49.3 | –32 1/2 †This test of a stripped Lincoln chassis was made over the factory course. The instruments used were the axle-movement recorder and the vibration machine. The instrument is secured to the chassis as is shown in Fig. 15. An angle-iron extension comes out from the axle to extend directly underneath the moving rod and is connected to it by the universal-joint. A slight error is present in this hook-up, but we feel that it is not large enough to be considered. Fig. 16 shows another view of the instrument on the car, and Fig. 17 shows diagrammatically the movements of the axle in relation to the chassis, as well as the readings that are possible with this instrument. All these are made on a picked course. The factory course is an average rough country-road exactly 1 mile in length. The course forms a square; so, the start of the run is also the finish. One-half the distance is level; one-quarter is down-hill and the remaining quarter is up-hill. The last quarter is sandy road “loose” enough to cause the average car to labor in high gear at a speed of 15 m.p.h. Table 2 shows a comparison of axle movements with and without air-springs. The same general increase in amplitude and average axle movements as is shown on the bump curves are again recorded. FIG. 16—ANOTHER VIEW SHOWING THE AXLE-MOVEMENT RECORDER ATTACHED TO THE CAR This Instrument Is Provided with a Universal Bracket That Will Fit Any Standard Car With or Without Air-Spring Equipment. The Front Pan or Apron Must Be Removed During the Test. We have made tests recently on four-wheel-brake cars. The tests were all made on a Belgian-block course 1 mile long, the speed was 15 m.p.h., the same driver and the same load were used on all runs and each run was duplicated to avoid error. Table 4 is a condensed report of the test. The sharp, snubbing action of the snubbing device is brought out clearly by the reduced axle-movements. On this type of road their effectiveness is almost negative; a snubbing device is at its worst on this type of road. We know that the same device on an average country-road will show a riding-quality improvement of from 10 to 15 per cent. The same decrease in free vibrations as was noted in previous tests is again apparent when we consider C showing 1674 vibrations without air-springs and 1386 with them; also the corresponding increase in A, the total amplitude, from 144.37 to 176.34 ft. These comparisons of A and C are for the columns with steel springs alone and air-springs only. The increase in maximum axle-movement is from 2 11/16 in. with snubbers to 3 1/2 in. with air-springs, distributed so that 7/16 in. of the increase is on the compression stroke and 1/2 in. on the rebound stroke. FIG. 17—GRAPHIC REPRESENTATION OF READINGS AS SHOWN ON VIBRATION RECORDER Counter A Records the Total Vertical Movement in Feet in Either Direction, Up or Down. It Is Represented by the Line AD Which Is the Sum of 1, 2, 3 and 4 as Well as 5, 6, 7, 8, etc. Counter B Records the Total Movement in Feet in an Upward Direction Above the Normal Line XY. It Is Represented by the Line AB Which Is the Sum of the Vertical Movements as c, e and g.{Mr Griffiths - Chief Accountant / Mr Gnapp} Counter D Records the Total Upward Axle-Movements Exceeding 3/32 In. Irrespective of Their Position in Relation to the Normal Line. The Points 1, 3, 5, 6 and 8 Are Recorded, but the Points 2, 4, 6 and 8 Are Not Recorded Since They Are at the End of the Downward Path. Counter E Records the Total Movement in Feet in a Downward Direction Below the Normal Line XY. It Is Represented by the Line CD Which Is the Sum of a, b, d and f.{Mr Friese} Counter F Records the Total Movements Exceeding 3/32 in. and Thus Is Just the Reverse of Counter B. Counter G Records the Number of Times the Axle Crosses the Normal Line XY. Thus the Points 4, 6 and 8 Are Recorded when the Normal Center-Line Is Crossed in Either Direction by a Movement Exceeding 1/8 In. The Date That This Instrument Measures Only the Relative Movement between the Frame and the Axle Should Be Borne in Mind. | ||