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).
Analysis of the causes, effects, and methods for reducing harshness in the ride of an automobile.
| Identifier | ExFiles\Box 154a\2\ scan0001 | |
| Date | 1st January 1939 | |
| File for Rm{William Robotham - Chief Engineer} 1305 Harshness in the Automobile By H.{Arthur M. Hanbury - Head Complaints} A.{Mr Adams} Hicks and G.{Mr Griffiths - Chief Accountant / Mr Gnapp} H.{Arthur M. Hanbury - Head Complaints} Parker Chrysler Corp. Abstract: HARSHNESS in the ride of an automobile is felt as a disagreeable tremor or shock, sudden in nature as distinguished from the opposite sensation which could be described as slow, soft, and mellow, the authors state. They add that it is in the nature of a tremor having a frequency in the higher shake range and approaching the threshold of audibility. This paper is limited to analysis of the harsh vibrations which emanate from tire contact with the road, excluding the effects of the tires themselves. The authors describe methods of measuring harshness both in the laboratory and on the road, discuss car harshness in its relation to rigidity, and touch upon its relation to suspension. It is pointed out that there has been a decided trend toward more rigid construction and that, in general, harshness has increased as rigidity has been obtained. It is also noted that fore-and-aft shocks are more pronounced with independent suspension than when leaf springs are used. Two methods of reducing harshness are explained, although the authors state that there are probably many ways of solving the problem. Main Text: FROM the standpoint of comfortable transportation, the ideal car should rapidly traverse an ordinary road in such a manner that the only indication of motion would be sight of the passing landscape. Under such conditions, no shakes or jolts would be felt, no car noises heard, no offensive odors smelled. Human faculties would be unhindered and would remain unimpaired for the complete enjoyment of a journey. We probably shall never realize a complete attainment of this ideal, but progress in its direction has been steady. There is no reason why it should not continue. There are many kinds of car harshness which affect human sensibilities. Harsh noises assail the ears. Wheel fight and wheel shake feel harsh to the driver. Body jitters and shudders are unpleasant to all of the car occupants. Harsh vibrations which affect our sense of feeling may emanate from the powerplant and the tire contact with the road. However, this discussion will be limited to harshness from the tire road contact, excluding, of course, the effects of the tires themselves. Vibration is the general name for both shake and noise. When the frequency of the vibration is below, approximately, 30 per sec., it is manifested as shake. When it is above this figure, it is heard as a noise. Harshness is felt as a disagreeable tremor or shock, sudden in nature as distinguished from the opposite sensation which could be described as slow, soft, and mellow. Harshness is in the nature of a tremor having a frequency in the higher shake range and approaching the threshold of audibility. On smooth pavement, harshness from the road does not exist as there is no exciting force to cause the vibration. It produces its most noticeable and disagreeable effect when a car is driven on rough roads. Certain speeds, and not necessarily high speeds, produce the worst condition for any particular car. To some the term “harshness” may appear as an intangible, abstract characteristic having no commercial application. This condition may be because the harsh automobile does not always get into production. It often happens that a car is designed and the structure tested in the laboratory and found to be considerably superior to current production. The first trip on a rough road, however, may show up a very severe condition of harshness. As the wheels of the car encounter bumps or pot-holes in the road, sudden shocks or tremors occur throughout the entire structure, starting at the suspension attachment to the frame, passing up through the frame and body, up through the roof-rail to be transmitted to the reaction points at the opposite end of the car. In its effect on the car driver, harshness increases nervous tension and hastens fatigue. It often may be responsible for driving mistakes and carelessness which result in accidents. Let us now consider harshness from a physical standpoint. Human sensibilities cannot detect velocity. If you are moving in a straight line, at a uniform rate, regardless of how rapid it may be, you cannot feel that motion. You can, however, feel accelerations – somewhat in proportion to their magnitudes. A single ride on a fast elevator is all that is needed to convince one of the truth of both of the foregoing statements. The unpleasantness occurs at the starting and the stopping. During the constant-speed part of the ride, no unusual sensation can be noticed. The acceleration of the elevator can be small or slow enough so that little discomfort is felt, or it can be so rapid that a decidedly unpleasant feeling results. The same is true for the automobile. We are not concerned, of course, with the accelerations associated with an increase in speed or with slowing down, but only with those accelerations induced by an irregular road surface or by other vibration sources. Car suspensions and car structures have been improved to the point where many road shocks do not result in accelerations [This paper was presented at the Semi-Annual Meeting of the Society, White Sulphur Springs, West Va., June 14, 1938.] January, 1939 1 | ||