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 vehicle harshness and structural rigidity, illustrated with diagrams of torsional deflection twist tests.
| Identifier | ExFiles\Box 154a\2\ scan0004 | |
| Date | 1st January 1939 guessed | |
| 4 S. A.{Mr Adams} E.{Mr Elliott - Chief Engineer} JOURNAL (Transactions) Vol. 44, No. 1 [Diagram: Fig. 2] Text within diagram: COMPLETE CAR - PROOF LOAD DIAGRAM of TORSIONAL DEFLECTION OVERALL LENGTH 166 IN. (A-O) STATIONS SPACED AT 12 IN. ORIGINAL POSITION _______ DEFLECTED POSITION ---- CAR AT ROAD WEIGHT PLUS PASSENGERS CAR SUPPORTED ON DIAGONALLY OPPOSITE WHEELS - RIGHT FRONT WHEEL HANGING FREE Station Deflection Values: O': 0.10", N': 0.18", M': 0.15", L': 0.12", K': 0.15", J': 0.12", H: 0.0", G: 0.15", F: 0.18", E: 0.29", D: 0.39", C: 0.48", B: 1.10", A: 1.21" TOTAL TWIST - 1.31" [Caption for Fig. 2] Fig. 2 - The deflection characteristics of the complete car shown were obtained by means of the twist test indicated [Main Text] stiff springs and the less-rigid structure. The riveted joints of the frame tended to loosen after continued reversals. Different sprung parts of the car indulged in considerable motion relative to one another because the structure was not stiff enough to hold them in their proper relationship. Excitation of the natural frequencies of some parts of the structure sometimes resulted in car door, seat, floor, steering-wheel and windshield amplitudes of motion even greater than those of the exciting forces. The result was a most disagreeable roughness and harshness. Certain characteristics of a car, even though not classified as harsh in nature, may contribute greatly to the apparent roughness. One is familiar with the close association of the senses of hearing, feeling, and seeing. In a ride over a rough railroad crossing the roughness that is felt is augmented greatly if accompanied by numerous noises and rattles from structure and units having flexible supports. The fact that the early car structure was characterized by looseness and flexibility prevented further manifestation of harshness as the energy of the vibration was dissipated or lost in the structure, or in producing noise, before reaching the passengers. With increased rigidity the present-day car is not free from harshness. In making the car rigid the structure was welded, the load-carrying members made direct, and the thin sheet metal of the body stressed. A rigid structure is an excellent conductor of vibrations. Tests have shown that an increased frequency of vibration in the shake range greatly increases its perceptibility. By making the structure more rigid, the natural resonance frequency of the structure was increased, often making the structure more susceptible to harshness. The modern trend in other fields is also toward greater rigidity; this statement is true in practically all branches of engineering, especially in automotive, marine, and structural branches. However, with increase in rigidity has come an increase in harshness. As an example, the early steamships constructed of wood with looseness in the joints had a low-frequency vibration whose energy was dissipated quickly in the discontinuous structure. However, a modern steamship built as a rigid structure and with stressed shell is vibrated easily by a poorly balanced engine or propeller. Also, vibration in old and loosely constructed buildings is not transmitted readily and is not troublesome as it is lost in the structural looseness. The modern structurally rigid building presents a real problem in vibration study as the vibration is transmitted readily through the entire structure. These two examples present parallel cases of what, to a certain extent, has been experienced in the development of the automobile structure from a shake or harshness standpoint. Harshness and Structural Rigidity In the modern automobile the car body is an important part of the primary structure. The common idea that the frame [Diagram: Fig. 4] Text within diagram: Graph lines labeled: FRAME ONLY, COMPLETE CAR, BODY LENGTH Table: | | FRAME ONLY | COMPLETE CAR | |---|---|---| | OVERALL (A-O) | 7.28" 100% | 1.31" 20.3% | | BODY LENGTH (D-O) | 5.67" 100% | 0.94" 13.4% | | RATIO BODY LENGTH TO OVERALL | 73.0% | 48.3% | [Caption for Fig. 4] Fig. 4 - This elevation diagram illustrates graphically how much stiffer the complete car is than its frame in the twist test | ||