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).
Technical page from an S.A.E. journal analysing vehicle frame and body deflection with different mounting systems.
| Identifier | ExFiles\Box 154a\2\ scan0006 | |
| Date | 1st January 1939 guessed | |
| S.A.E. JOURNAL (Transactions) Vol. 44, No. 1 REFERENCE POINTS - OVERALL - 156 IN [GRAPH] Y-Axis: DEFLECTION X-Axis Labels: A, B, C, D, E, F, G, H, I, J, K, L, M, N Curve 1: COMPLETE CAR - PRODUCTION Curve 2: DEFLECTION - COMPLETE CAR VS{J. Vickers} FRAME Curve 3: COMPLETE CAR - BODY MOUNTED ON RUBBER GROMMETS- (SEE DETAIL) EXPERIMENTAL Curve 4: FRAME ONLY [DIAGRAMS] SPOOL TYPE INSUL. PRODUCTION Labels: BODY, BODY BOLT, FRAME DETAIL AT BODY BOLT - EXPERIMENTAL Labels: BODY-FLOATS IN RUBBER, RUBBER GROMMETS, BODY BOLT, FRAME [DIAGRAM OF CAR UNDER LOAD] LOADING: EQUIVALENT OF SPRUNG WEIGHT PLUS PASSENGERS - SIMILAR LOAD APPLIED TO FRAME AS TESTED ALONE Weights shown: 200#, 700#, 200#, 450#, 300#, 450#, 600#, 200# Fig. 6 — This chart shows that the deflection of the complete car was doubled when rubber grommets were inserted at each body bolt between the frame and the body when equal wheel loading was applied along the span are applied to the frame alone, and a comparable deflection curve results (Fig. 5). It is shown that the chassis frame contributes as little as 25 per cent to the resistance to deflection of a complete car. The discussion of these tests finds a place in this paper because of the relation that exists between harshness and rigidity. Rigidity has been shown to be desirable, but harshness accompanies rigidity into some of our modern automobiles. If the body were divorced entirely from the frame and no load was transmitted to it, harshness would not exist. Imagine the body as a rigid unit within itself but floating on a thick pad of soft rubber over the frame. Shocks at the road would be softened to negligible magnitude at the passenger. But the frame, to be of adequate strength and sufficiently rigid within itself to be commercial by present standards, would be so large and heavy as to be impractical. Fig. 6 shows the effect of rubber grommets inserted at each body bolt between the frame and body. The deflection of the complete car was doubled. These mountings are not to be confused with the restrained rubber body mountings which are now used in Chrysler products. They will be discussed in a later paragraph. This chart illustrates the part that the body plays in reinforcing the frame. In all of these studies which have been illustrated by charts, it is evident that the greater part of the deflection of our conventional cars today, whether under twist or equal wheel load, occurs ahead of the dash (Fig. 7). Deflection in the body length is negligible. Unit construction — the integral body and frame — has, as one of its basic advantages, rigidity. This rigidity has been accomplished by extending the body forward over a greater part of the complete car length. Because of the knowledge that shallow frame rails extending ahead of the dash account for most of the deflection, the cowl is extended as a deep cantilever or inclined struts are used to brace this part of the car span. But unit construction has been labeled as harsh and, in general, harshness has increased as rigidity has been attained. The possible ways in which stiffness influences harshness can be summarized as follows: 1. Undoubtedly, the increased rigidity has eliminated almost entirely any secondary suspension effect from the structure. If the deflections of the structure itself, in the past, have made up for deficiencies in the suspension then, with unit construction, the suspension must be refined further. The general problem of harshness is a dynamic one rather than a static one. Its solution by structural means is, therefore, difficult. Its elimination by mechanical means should be, in comparison, much easier. 2. Increased rigidity raises the natural frequency of the structural assembly of the car. Harshness has been described in terms of frequency and, in these rigid structures, it is quite [DIAGRAMS - FIG. 7] DEFLECTION (EITHER FOR TWISTING OR NORMAL BEAM LOADS) OCCURS IN THE PART OF THE FRAME NOT SUPPORTED BY THE BODY UNSUPPORTED FRAME RAILS SUPPORTED BY BODY CAR SHAKE IS DEFLECTION RESULTING FROM BEAM SHOCKS Fig. 7 — The greater part of the deflection of a car occurs in the frame ahead of the dash | ||