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).
Journal page discussing automotive ride harshness and its measurement, with a cutaway diagram of a car's body and chassis construction.
| Identifier | ExFiles\Box 154a\2\ scan0002 | |
| Date | 1st January 1939 | |
| 2 S. A.{Mr Adams} E.{Mr Elliott - Chief Engineer} JOURNAL (Transactions) Vol. 44, No. 1 DIAGRAM LABELS: ALL STEEL BODY STEEL BODY TOP BODY TRANSVERSE BRACING BOXED MEMBERS ROUNDED CORNERS DIAGONAL BRACES - STRAIGHT MEMBERS X BRACE TYPE FRAME BOXED FRAME RAILS BOXED FRAME CROSS MEMBERS Fig. 1—The present trend toward greater rigidity has resulted in reduced shake and better driving feel high enough to be at present annoying. Occasionally, however, the reverse is true and some road obstructions result in a jolt or series of jolts which are really harsh to the car and its occupants. These jolts are harsh because the accelerations are high. Harshness can occur with lesser accelerations when the frequencies are higher. This point is clearly shown by the work of Prof. H.{Arthur M. Hanbury - Head Complaints} M.{Mr Moon / Mr Moore} Jacklin in his study of “Human Reactions to Vibration.”¹ His riding-comfort factor depends entirely upon the acceleration of the motion and its frequency. He has shown, for instance, that an acceleration of 4 ft. per sec. per sec. at a frequency of 6 cycles per sec. is fully as disturbing as an acceleration half as high with a frequency of 11 cycles per sec. To establish a line of demarcation between motions which are harsh and those which are not, we will say that motions become harsh when they become decidedly disturbing to the sensibilities of the car passenger. This differentiation fixes no definite numerical values, but it is a satisfactory definition as far as the present discussion is concerned. Measuring Harshness It might be well, at this point, to consider some of the methods of measuring or rating car harshness. They are usually quite rudimentary. In the laboratory, the general subject of vibration has been attacked by setting up a body-and-frame assembly and vibrating it by means of an eccentric weight driven by a motor. The supporting method has been chosen to duplicate actual conditions as nearly as possible. Such studies lead to valuable information. Witnessing the vibration by means of a stroboscope may help to locate weak parts of a construction. But, as yet, no tie-up between such investigations and the harshness problem has been made. On the other hand, wheel fight has been investigated with considerable success and saving of time. For this work, the car front wheels are run on rolls to which cleats have been attached, thus simulating the road obstacle. By measuring the travel of the steering-wheel rim with a suitable recording device, studies and comparisons can be made easily and quickly. Instruments for comparing car rides have been given considerable attention, and the S.A.E. has had occasion to investigate and report on the various accelerometers and ride meters on the market. Accelerometers should have considerable application in harshness studies. For ourselves, we can say that we have had little or no success with their use for this work. This is due to the many complications introduced into the curve traced by the instrument because of the complex motion of the car over the roads used for test. There is a little instrument which we have used on the road and which has furnished some very satisfactory results. It is adapted to problems concerned with shake. By any comparison with the elaborate instruments which are termed accelerometers, it would be considered crude. The instrument is a simple pedometer. For longitudinal and transverse vibrations, the balancing spring is removed so that the instrument consists of a pendulum, freely suspended and geared to a recording hand. The pendulum operates between stops. Any swing of the pendulum caused by movement of the instrument advances the pointer around the dial. It should be noted that this device is not a counter. It records in proportion to the amount of swing by integrating the pendulum motions which evaluate the severity of displacements. The gearing is such that one revolution of the pointer represents about 1500 swings of the pendulum between stops, or an increased number of movements when the pendulum swings through only part of its full travel. For vertical vibrations, the instrument is used as received, with the pendulum balanced in a horizontal position. Runs are made over a sufficient length of rough road to give readings large enough to be considered suitable for comparison purposes. With these instruments, the entire car can be explored – from the ornament on the grille to the rear body bolt and from the floor to the roof of the car. The nodes and anti-nodes of the car shake become plainly evident when readings taken at various points along the span are plotted; roll or torsional shake is shown by the larger readings near the roof as compared to lesser readings at the floor. But here, again, it must be admitted that a direct measurement of harshness is not obtained. However, since a vibration consists of an amplitude, a frequency, and an associated acceleration the results of pedometer tests do afford a rough comparison of cars from the harshness standpoint. In the last analysis, observer opinion delivers the final verdict in the rating of cars for harshness. There are som ¹ See S.A.E. TRANSACTIONS, Vol. 39, October, 1936, pp. 401-408: “Human Reactions to Vibration,” by H.{Arthur M. Hanbury - Head Complaints} M.{Mr Moon / Mr Moore} Jacklin. | ||