Spring devices – Fibrous – Glass fiber
Patent
1990-02-01
1991-11-19
Butler, Douglas C.
Spring devices
Fibrous
Glass fiber
267153, 267158, 267165, F16F 136
Patent
active
050659880
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a spring for compression and tension, mainly in axial direction, which spring is made of a material having a Young's modulus of elasticity E, which is at least 39 GPa, such as metal, steel, glass, plastic or reinforced plastic, the spring being rotation symmetrical around a symmetry axis and in the form of a tube or a ring, the material thickness of the spring wall between the end sections of the spring being practically constant. The spring, in its length direction, comprises at least two mutually integrated spring parts, in radial direction oppositely directed, and in cross section half-wave or U-shaped.
A U-shaped spring is known from German published patent application DE-AS 35 36 661, where FIG. 10 shows a rotation symmetrical U-shaped spring, where the wall of the spring has a practically constant thickness of material. The axial ends of this spring loosely abut a cylindrical ring, and consequently there must be radial exterior or interior guiding surfaces to keep the spring in position. Such an interior or exterior guiding surface gives a friction, when the spring moves, and consequently a certain hysteresis loop.
Known are also springs shaped like bellows, which tightfitting confine a temperature expanding medium or a movement suppressing medium, and a common purpose for these types of springs are to obtain a flexibility as large as possible with a spring resistance as small as possible, since the compressive force mainly has to be generated by the medium confined in the spring.
SUMMARY OF THE INVENTION
The spring according to the present invention is characterized in that each end section of the spring comprises an annular axial rigid projection extending between the diameters of the wave crests of the two nearest half wave formed spring parts, through which projection a neutral surface of the spring is passing. By that means it has appeared that a spring may be obtained with a hysteresis loop substantially smaller than the hysteresis loop of U-shaped springs made of the same material and having the same thickness of material. Presumably this is due to the line of the centres of gravity of the axial cross sections of the spring passing through or very close to the axial end projections of the spring, and thereby simultaneously the neutral surface of the spring is passing through or close to the axial end projections of the spring. The neutral surface of the spring is an imaginary surface and may be defined as a stress neutral or stress balanced surface, in relation to which the bending stresses occurring radially outside the surface are equal to and opposite directed to the bending stresses occurring radially inside the surface during the increasing, decreasing or stationary load of the spring. This neutral surface of the spring may be a cylinder surface, a cone surface, an hour-glass shaped surface or a vase shaped surface depending on the performance of the spring. Compression or tension stresses are of course not zero in the neutral surface. Due to the fact that the spring transfers its compressive or tensile force at its ends via the axial projections, which are situated close to the said neutral surfaces, a spring is obtained, which is substantially more uniformly balanced than the said known U-shaped spring of DE 35 36 661, and therefore the spring according to the invention shows a hysteresis smaller than the hysteresis of the known spring. Therefore springs according to the invention will be suitable in many more applications than the known similar springs, particularly where precision springs are needed in measuring instruments, where an extremely small hysteresis is important.
BRIEF DESCRIPTION OF DRAWINGS
The invention will now be described by way of example with reference to the accompanying drawings, of which:
FIG. 1 shows a spring composed of two spring parts and a cylinder shaped projection at each end, the two spring parts in cross section being half wave or U-shaped in opposite directions,
FIG. 2 shows a spring correspond
REFERENCES:
patent: 3036180 (1962-05-01), Greenwood
patent: 3272491 (1966-09-01), Knittel
patent: 3444962 (1969-05-01), Lech
patent: 3989232 (1976-11-01), Steinbach et al.
patent: 4235427 (1980-11-01), Bialobrzeski
patent: 4512209 (1985-04-01), Linnemeier
patent: 4815663 (1989-03-01), Tada
patent: 4832320 (1989-05-01), Scowen et al.
patent: 4905972 (1990-03-01), Scowen
patent: 4927124 (1990-05-01), Spedding et al.
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