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 ride quality, detailing a vibration recorder, its calibration, and comparative test results from various 1920-1924 car models.
| Identifier | ExFiles\Box 43\3\ Scan019 | |
| Date | 28th September 1923 guessed | |
| PAGE 12 AIR-SPRINGS AND RIDING-QUALITY the number of vibrations in excess of a certain acceleration that the instrument is set for. As the tape may slip because it is friction-fed, a positive mechanical counter is used to check-up the tape length. This counting attachment records the radial movement of the friction drum in degrees and is used in connection with an individual counter that registers each complete rotation of the drum. This counting attachment gives a quick answer and an accurate indication of the results that are to be expected on the tape. The instrument is set to record each and every vibration exceeding an acceleration greater than 10 ft. per sec. per sec. and its approximate limit is an acceleration of 40 ft. per sec. per sec. The larger vibrations are thus recorded as they occur, because the throw of the weight is governed by the force of the shock. The record on the tape, therefore, shows the total number of vibrations exceeding an acceleration of 10 ft. per sec. per sec. and also the accumulated intensity of all the vibrations that exceed the acceleration just stated. It is necessary to consider both of these factors, as it is possible to reduce the accumulated accelerations at the expense of increasing the total number of vibrations. In other words, the intensity of a certain vibration will be partly damped out but will result in additional forced vibrations in the car itself. The introduction of any damping device, positively connected between the main body and the spring, will always limit the movement, but it will likewise increase the forced oscillations in the structure as a whole. ACCELERATION AND FREQUENCY Acceleration and frequency are unquestionably the factors we have to measure to classify riding-quality. Just what combination of acceleration and frequency is objectionable and destructive is a question that has been asked many times and as yet not answered. We have assumed an acceleration of 10 ft. per sec. per sec. to be objectionable and have also considered that the more frequently an acceleration exceeding the above figure occurs, the more objectionable the results will be. In saying “assumed,” we mean it; we have no data or experiments to fall back on to prove the assumption. The instrument is 3 3/8 in. deep, 8 3/8 in. long and 12 in. high; it weighs 15 1/2 lb.; and is made entirely of aluminum except for the weight element, including its springs and screws. The front and the two sides of the housing are open at all times to inspection, as non-breakable glass windows are used to protect the mechanism from dust and dirt. The front window is removable and slides out of the way when adjustments or a new roll of tape are required. The sensitiveness of the weight is governed by rotating the spiral-spring cap, which is locked in place by two set-screws. An ordinary phonograph-needle is used in the weight element as the perforating pin and is easily replaceable. The instrument can be considered dead-beat for practical purposes, as we have succeeded after considerable trouble and experimentation in eliminating any rebound or recording action of the weight on its return stroke when it perforates the paper, irrespectively of the throw of the weight, which, of course, is governed by the tensity of the acceleration registered. To do this we had to use a low-period flat spiral-spring in connection with the radius-arm, which is really a lever that multiplies the static deflection of this spiral spring. The friction drum is a hollow aluminum casting made particularly light to eliminate the trouble we had experienced from the inertia of this part. The stop for the weight itself is located off the center of gravity at a slight angle, to neutralize the natural rebound action. FRICTION Friction is eliminated as much as possible in both the upward and the downward movements of the weight. The only resistance to the upward motion is that of the pawl, which engages the friction drum, rotates it and moves the tape. On the down motion the pawl is inoperative. FIG. 20—GRAPHIC CHART SHOWING THE COMPARISON OF ACTUAL TAPE-RECORDS AS MADE ON THE VIBRATION RECORDER. The Upper Record Was Made Without Air-Springs and the Lower One With. The Difference in Vibration Is Shown Graphically by the Intensity Charts Under Each Tape. The Only Similar Feature That May Be Recognized in Both Tapes Is the Break That Ocurred at Sections 8 and 10 on Both. These Vibrations Are Marked S on the Intensity Charts for Identification Purposes. They Were Caused by an Extra Large Chuck-Hole That No One Would Drive Through under Ordinary Conditions PAGE 13 AIR-SPRINGS AND RIDING-QUALITY FIG. 21—TRACING OF TEST TAPE SHOWING HOW THE INSTRUMENT RECORDED THE DECREASING AMPLITUDE AND ACCELERATION WHEN SET VIBRATING ON COIL SPRINGS. The Initial Deflection or Amplitude Was 4 1/8 In. and the Period of Vibration Equaled 90. The Tape Movement for Certain Accelerations Is Indicated by the Spacing between the Dots and Is Given in the Table Table Data from Fig. 21: Period: 90, 90, 90, 90, 90 Amplitude In.: 1 27/64, 2 1/64, 2 45/64, 3 1/8, 4 1/8 Acceleration ft. per Sec. per Sec.: 10.00, 15.00, 20.00, 25.00, 32.39 Drum Rotation Deg.: ..., 6, 25, 44, 56 Tape Movement, In.: 0.042, 0.250, 1 3/64, 1 57/64, 2 19/64 The flat cantilever spring just above the weight is placed there only to take care of violent throws that occur occasionally on very hard-riding light-trucks in bad country. The ordinary passenger-car rarely throws the weight against this stop. Even on an acceleration that will deflect the cantilever spring that has been mentioned 1/2 in. or more we have been unable to detect a rebound that will register or move the tape. When one considers that the tape record of some cars will at times show perforations that are so close together that it is hard to distinguish the separate perforations, one will realize that the instrument does not skip. TABLE 5—COMPARATIVE READINGS ON TEST RUNS MADE OVER THE 1-MILE FACTORY COURSE¹ Test No. | Make of Car | Type | Model of | Snubber or Shock-Absorber | Tape Record (Average Length, In.) | Perforations (Average Number) 22, 23 | Overland | Touring | 1920 | None | 106 3/4 | 495 29, 30, 31, 32, 33 | Lincoln | Sedan | 1924 | Device No. 6 | 36 1/2 | 203 34, 35, 36 | Maxwell | Sedan | 1924 | None | 79 1/8 | 324 46, 47, 48, 49, 50 | Ford | Touring | 1920 | New Rear Steel Springs/Snubber No.3 | ... | 391 55, 56, 57, 58, 59, 60, 61 | Pierce-Arrow | Sedan | 1923 | None, Snubber No.7, Device No. 6 | 46 5/8, ..., 28 7/8 | 287, ..., 197 62, 63, 64, 65 | Essex | Coach | 1924 | None, Device No. 4 | 99 7/8, ..., 61 1/8 | 310, ..., 233 89, 90, 91, 92, 93, 94 | Paige | Coupe-Sedan | 1922 | None, Snubber No.2, Device No. 5 | 68 1/2, ..., 61 1/8, ..., 43 7/8 | 356, ..., 393, ..., 321 ¹ All of these tests were made at a speed of 15 m.p.h. with a load of two passengers. | ||