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).
Patent specification for an improved laminated spring design by removing material from the compression surface.
| Identifier | ExFiles\Box 154a\2\ scan0352 | |
| Date | 28th June 1940 | |
| 2 532,698 described and ascertained in and by the following statement:— This invention relates to laminated springs. When a load is applied to a laminated spring fibre stresses are induced in each leaf varying from maximum compressive stress at one side of the leaf to zero at the neutral axis and increasing from the neutral axis to maximum tensile stress at the opposite side of the leaf. It is therefore apparent that the material at the core in the region of the neutral axis of the leaf is comparatively idle, that is to say subjected to only very small stresses, and that the only material which is used efficiently is that remote from the neutral axis on each side thereof. It has already been proposed to use leaves and also to use leaves each of which has grooves on the compression side so as to take advantage of the known greater fatigue resistance which spring steel possesses when in compression than when it is in tension. It has furthermore been proposed to use for such leaves a section having a single central or median groove on the compression side of a depth extending beyond the neutral axis. According to the present invention we remove material from the compression surface of one or more of the leaves of a laminated spring by forming a groove or grooves in the compression surface having a depth extending beyond the neutral axis and into the tension zone of the leaf and the width or widths of which amounts to, or together amount to, approximately half the total width of the leaf. Thereby we avoid having relatively idle material in the core of the section of a leaf and full advantage is taken of the greater compressional fatigue resistance of spring steel as mentioned above. As used herein in reference to spring leaves the term “ neutral axis ” denotes the hypothetical surface separating the compression zone from the tension zone when the leaf is loaded; this plane passes through the centre of gravity of the leaf (after removal of the material from the compression zone thereof as already set forth). The aforesaid groove or grooves are accordingly of such depth that they extend from the compression surface of the leaf beyond this hypothetical surface. The depth is preferably approximately two-thirds of the total depth of the section of the leaf. If a leaf is provided with a single groove extending across half the sectional width and to two-thirds of the sectional depth, then the longitudinal shear stresses in the material in the reduced depth become appreciable and may even cause failure of the spring. For this reason we preferably provide in the compression side of a leaf two or more grooves each having a depth equal to approximately two-thirds of the section the added widths of the grooves being approximately one-half of the section width. Where an even number of grooves may be provided these grooves may be arranged symmetrically across the width so as to leave the median portion ungrooved and when this is done locating depressions or dimples may be provided in said ungrooved portion in the well known manner for the purpose of fixing the relative positions of the leaves of the spring, and our improved spring leaves will thus be interchangeable with those of present known designs. In the accompanying drawings three particular forms of leaf for laminated springs according to the invention are shown in cross-section. The neutral axis of the leaf is indicated in each of the figures by the line N—A.{Mr Adams} The leaf shown in Figure 1 is formed with two grooves 4 and 5 having a depth of approximately two-thirds the total depth t of the section of the leaf, that is to say the depth of the grooves extends beyond the neutral axis N—A and into the tension zone of the leaf. The widths of the grooves 4 and 5 are such that together they amount to approximately one-half the total width of the leaf and with such a width, or rather combined widths, of groove with the aforesaid depth of groove, i.e. .666 t, the neutral axis lies at a distance .583 t from the compression surface of the leaf. The leaf shown in Figure 2 is formed with three grooves 6, 7 and 8 arranged symmetrically across the width of the leaf. In this case also the depth of the grooves is .666 t and their combined widths is the same as the combined widths of the grooves 4 and 5 in the leaf shown in Figure 1. Thus the neutral axis N—A lies in this case also at a distance .583 t from the compression surface of the leaf. The combined widths of the grooves 4 and 5 in Figure 1 and 6, 7 and 8 in Figure 2 are, as shown, almost exactly one-half the total width of the leaf, but as stated this proportion need be only approximately one-half, say between 45% and 55%. The leaf shown in Figure 3 is similar to that of Figure 1 as regards the number and dimensions of the grooves but is formed with a depression or dimple 9 for the purpose already mentioned. It will be understood that this dimple is formed more or less at a point and is not a depression extending along the length of the leaf. Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:— 1. A laminated spring comprising a leaf or leaves having material removed from the compression surface thereof by forming a groove or grooves in the compression surface having a depth extending beyond the neutral axis and into the tension zone of the leaf and the width or widths of which amounts to, or together amount to, approximately half the total width of the leaf. 2. A leaf for a laminated spring according to claim 1, wherein the depth of the groove or grooves is approximately two-thirds of the total depth of the section of the leaf. 3. A laminated spring comprising a leaf or leaves having material removed from the compression surface thereof by forming in the leaf or leaves two or more grooves each having a depth equal to approximately two-thirds of the section and a width such that the added widths of the grooves is approximately one-half of the section width. 4. A laminated spring according to claim 3, wherein the compression surface or surfaces of the leaf or leaves of the spring is or are provided with an even number of grooves arranged symmetrically across the width so as to leave the median portion ungrooved. 5. A laminated spring according to claim 4, wherein the ungrooved median portion of each leaf is provided with depressions or dimples as and for the purpose specified. 6. A method of manufacturing a laminated spring which comprises removing material from the compression surface of a leaf or leaves thereof by forming a groove or grooves each having a depth extending beyond the neutral axis and into the tension zone of the leaf and a width which amounts to, or together amount to, approximately one-half of the width of the leaf. 7. A method of manufacturing a laminated spring which comprises removing material from the compression surface of a leaf or leaves thereof substantially as herein described. 8. Laminated springs having a leaf or leaves constructed substantially as herein described with reference to the accompanying drawings. Dated this 28th day of June, 1940. A.{Mr Adams} A.{Mr Adams} THORNTON, Chartered Patent Agents, 7, Essex Street, Strand, London, W.C.2. For the Applicants. Leamington Spa: Printed for His Majesty’s Stationery Office, by the Courier Press.—1941. | ||