BAR-SHAPED COMPONENT LOADED IN TORSION

Abstract

A torsion spring may be formed as a bar spring or helical spring comprising a spring wire of fiber composite material. In some examples, the torsion spring comprises a number of layers of fiber reinforcement, which are impregnated with a matrix material. The layers may comprise tensile-loaded fibers and compression-loaded fibers. Groups of layers of the same loading direction may exist and, seen from an inside to an outside, the group stiffness of at least two groups may differ. Likewise, methods for making such torsion springs of fiber composite material are disclosed.

Claims

1.-18. (canceled)

19. A torsion spring configured as a bar spring or a helical spring comprising a spring wire of fiber composite material, the torsion spring comprising a plurality of layers of fiber reinforcement impregnated with a matrix material, wherein each of the plurality of layers comprises only tensile-loaded fibers or only compression-loaded fibers, wherein tensile-loaded groups of layers and compression-loaded groups of layers exist and a group stiffness of at least two groups of layers differs.

20. The torsion spring of claim 19 wherein the group stiffness of groups of layers having a same loading direction differs.

21. The torsion spring of claim 19 wherein the group stiffness of groups of layers having different loading directions differs.

22. The torsion spring of claim 21 wherein the spring wire, without regard to a core mass, has a mass-related fraction of at most 25% in a form of layers classified as non-load-bearing.

23. The torsion spring of claim 19 wherein the group stiffness of the at least two groups of layers differs due to use of different fiber materials.

24. The torsion spring of claim 19 wherein the group stiffness of the at least two groups of layers differs due to use of mixed fibers as fiber materials.

25. The torsion spring of claim 19 wherein the group stiffness of the at least two groups of layers differs due to use of different fiber angles in the at least two groups of layers.

26. The torsion spring of claim 19 wherein the group stiffness decreases from an inside of the torsion spring to an outside of the torsion spring between at least two groups of layers in a set.

27. The torsion spring of claim 19 wherein a mass-related fraction, with respect to the spring wire but disregarding a core mass, of at least 50% in two sets of groups of layers has a group stiffness that decreases or remains constant from an inside of the torsion spring to an outside of the torsion spring.

28. The torsion spring of claim 19 wherein a mass-related fraction, with respect to the spring wire but disregarding a core mass, of at most 50% in two sets of groups of layers has a group stiffness that remains constant from an inside of the torsion spring to an outside of the torsion spring.

29. The torsion spring of claim 19 wherein at least one pair having a group ratio in a range of 0.2 to 5 is formed by two groups of layers.

30. The torsion spring of claim 19 wherein a mass-related fraction, with respect to the spring wire but disregarding a core mass, of at least 50% of groups of layers has formed pairs.

31. The torsion spring of claim 19 wherein for layers with a mixture of base fiber types, each base fiber type is in a mixed fiber layer in a proportion of at least 10% based on mass.

32. The torsion spring of claim 19 wherein the spring wire has a circular, ellipsoidal, or polygonal cross section.

33. The torsion spring of claim 19 wherein a matrix of fiber-reinforced plastic plies consists of a filled or unfilled thermosetting plastic.

34. The torsion spring of claim 19 wherein the spring wire comprises a core that is hollow, comprised of fiber-reinforced material with unidirectional fibers aligned in an axial direction of the spring wire, or comprised of material without fiber reinforcement.

35. A method of making a torsion spring from multi-ply fiber composite material, wherein the torsion spring is configured as a bar spring or as a helical spring, the method comprising: forming groups of fibers from layers of fiber reinforcement having a same loading direction lying one against another; determining a group stiffness for each of the groups of fibers; sorting the groups based on the group stiffnesses into two sets in a sequence from an inside to an outside of the torsion spring such that a tensile set consists of tensile-loaded groups and a compression set consists of compression-loaded groups; adapting the group stiffness within each set such that the group stiffness decreases or remains constant from the inside to the outside; forming pairs from the inside to the outside so that a tensile-loaded group and a compression-loaded group that are radially adjacent always form a pair; determining a group ratio as a quotient of a group extensional stiffnesses of the tensile-loaded and compression-loaded groups of a pair; and minimizing shear stresses between adjacent groups by varying stiffness ratios by at least one of varying layer wall thickness, varying a type of material, or varying fiber angles until the group ratio is in a range of 0.2 to 5.

36. The method of claim 35 further comprising pre-designing the torsion spring.

37. The method of claim 35 further comprising repeating the steps until a desirable load-bearing capacity with a spring stiffness profiled is achieved.

38. The method of claim 35 wherein the adapting the group stiffness comprises at least one of alternating a fiber material, alternating mixtures of different fiber materials, or varying fiber angles.

Description

FIGURES

[0110] The figures FIG. 1a and FIG. 1b schematically show two embodiments of the torsion spring according to the invention. In FIG. 1a, it is represented as a helical spring with a core and in FIG. 1b it is represented as a helical spring without a core.

[0111] FIG. 2 schematically shows the cross section A-A of a spring as shown in FIG. 1a with a solid core (1) and various layers (S.sub.1, to S.sub.J) with the associated layer wall thicknesses and layer materials.

[0112] FIG. 3 schematically shows the cross section A-A of a spring as shown in FIG. 1a with a tubular core (1) and various layers (S.sub.1, to S.sub.J) with the associated layer wall thicknesses and layer materials.

[0113] FIG. 4 schematically shows the cross section B-B of a spring as shown in FIG. 1b without a core and with various layers (S.sub.1, to S.sub.J) with the associated layer wall thicknesses and layer materials.

[0114] FIG. 5 schematically shows the arrangement of the spring construction according to the invention from exemplary embodiment 1 with a braided textile and a core diameter of 4 mm (Tables 1 and 2).

[0115] FIG. 6 schematically shows the arrangement of the spring construction according to the invention from exemplary embodiment 2 with a wound textile (for example on a coiling machine) and a core diameter of 3.5 mm (Tables 3 and 4).

[0116] FIG. 7 schematically shows the arrangement of the spring construction according to the invention from exemplary embodiment 3 with a braided textile, the fourth ply being a UD nonwoven fabric and a homogeneous plastic outer ply lying on the outside of the spring (Tables 5 and 6).

TABLES

[0117] Table 1 shows exemplary embodiment 1 of the design method according to the invention with a braided textile and a core diameter of 4 mm.

[0118] Table 2 shows the fiber materials used for exemplary embodiment 1, with their properties. The properties are known from the prior art and have merely been compiled here.

[0119] Table 3 shows exemplary embodiment 2 of the design method according to the invention with a wound textile (for example on a coiling machine) and a core diameter of 3.5 mm.

[0120] Table 4 shows the fiber materials used for exemplary embodiment 2, with their properties. The properties are known from the prior art and have merely been compiled here.

[0121] Table 5 shows exemplary embodiment 3 of the design method according to the invention with a braided textile, the fourth ply being a UD nonwoven fabric and a homogeneous plastic outer ply being arranged on the outside of the spring.

[0122] Table 6 shows the fiber materials used for exemplary embodiment 3, with their properties. The properties are known from the prior art and have merely been compiled here.

EXEMPLARY EMBODIMENTS

[0123] In all of the exemplary embodiments, the calculation of the cross-sectional area is performed by using the formula for the cross section of an annulus. For the respective exemplary embodiments, the specific situations are described by a sectional representation of the spring wire, a table to describe the spring wire characteristic values and a table to present the assigned material characteristic values.

[0124] Exemplary embodiment 1 (Table 1) shows a simple configuration of the spring according to the invention, which consists of six plies of a braided textile and a hollow core of 4 mm in diameter. The braided fabric plies form the twelve load-bearing layers. According to the convention, a ply is divided into a tensile-loaded layer and a compression-loaded layer, which both have the same layer radius. In FIG. 5, the cross section of the spring wire is schematically represented. For illustrative reasons, in the breakdown the compression-loaded layer is always shown on the inside. The calculation is nevertheless carried out according to the convention (Table 1). Exemplary embodiment 1 only has layers that are classified as load-bearing layers. The textile plies are arranged such that, as broken-down layers, they have a fiber angle of +45 and 45 in relation to the bar axis. The braided fabric plies have from the inside to the outside materials according to Table 2. In this case, the materials are selected such that the material stiffness decreases from the inside to the outside along the fiber. This behavior is also retained after the transformation (in this case without changing the numerical value) in the direction of the layer axis, which is reflected in a reduction in the layer and group stiffnesses from the inside to the outside. The layers are alternately in the compressive direction and tensile direction, which has the consequence that each layer forms an individual group. Once the groups are sorted from the inside to the outside and according to compressive loading and tensile loading, the compression set: (G.sub.1, G.sub.3, G.sub.5, G.sub.7, G.sub.9, G.sub.11) is obtained for the compressive loading and the tensile set (G.sub.2, G.sub.4, G.sub.6, G.sub.8, G.sub.10, G.sub.12) is obtained for the tensile loading. The individual sets have in this case a group stiffness that decreases from the inside to the outside. The pair formation, beginning from the inside, proceeds successfully for all of the groups since the relationships of the group extensional stiffnesses lie within the required ranges. Six pairs are formed, all having the group ratio of 1. In exemplary embodiment 1, 100% of the mass of the spring wire lies in groups with a group stiffness that decreases or remains the same from the inside to the outside. At the same time, all of the groups are assigned to pairs. Consequently, according to the invention, exemplary embodiment 1 is a preferred embodiment with uniform material utilization in terms of loading and a low creep tendency.

[0125] In exemplary embodiment 2 (Tables 3 and 4) there is a spring wire arrangement according to the invention that can be produced for example in a coiling process according to the prior art and has altogether 14 plies. The representation in FIG. 6 corresponds to the basic structure with the wound plies and the hollow core of 3.5 mm in diameter. The first two layers (S.sub.1 and S.sub.2), which also form the first two groups (G.sub.1 and G.sub.2), demonstrate the case that the fiber stiffness is chosen to correspond to the utilization capacity of the fibers in terms of loading. IM carbon fibers with higher compressive strength are used for the compression-loaded layer and UHM carbon fibers are used for the tensile-loaded layer. In order that the two groups exhibit a behavior with as little shear stress as possible in the pair formation, the group extensional stiffnesses of the two groups (G.sub.1 and G.sub.2) are approximated to one another by way of adapting the layer wall thickness, so that their ratio lies within the range of the particularly preferred group ratio. The further outward-lying plies 5, 6 and 7 form two layers. Due to the technically possible deposition of the same fiber material and same fiber angle to the bar axis, the plies 6 and 7 form only one layer (S.sub.6). The layers S.sub.5 and S.sub.6 result in the group G.sub.5, because they are a number of load-bearing layers of one loading direction lying against one another. Group 7 (G.sub.7) shows how the methodology dictates that layers (S.sub.8, S.sub.9 and S.sub.10) in one loading direction are grouped together. These layers have layer stiffnesses differing in their magnitude, which are caused by different fiber materials and different fiber angles. The group stiffness of group 7 is calculated as the area-averaged arithmetic mean of the layers associated with the group. In exemplary embodiment 2, the sets for tensile loading and compressive loading have group stiffnesses decreasing from the inside to the outside, and consequently uniform utilization in terms of loading. The pairs successfully formed on the basis of the group extensional stiffnesses lie within the range of the preferred group ratios.

[0126] In exemplary embodiment 3 (Tables 5 and 6), a more complex construction of the spring according to the invention is represented. The construction corresponds to the representation in FIG. 7. From the inside to the outside, the spring wire is composed of three plies of braided textile (L.sub.1, L.sub.2 and L.sub.3), followed by a wound ply (L.sub.4), followed by two plies of braided textile (L.sub.5 and L.sub.6) and finally followed by an exclusively plastic ply (L.sub.7). For the braided textile plies, the layer and group assignment and the pair formation take place in a way analogous to exemplary embodiment 1. A departure from this is the situation where the material that is used also comprises mixed fibers, of in this case the base fiber types low-alkali glass and HT carbon fibers. These are composed in their mass fractions in such a way as to result in different stiffnesses, in particular in the longitudinal direction of the fibers. Use of the mixed fibers in the braided textiles allow the great differences in stiffness between the glass fiber and the carbon fiber to be compensated better. As a delimitation from exemplary embodiment 1, a further major difference is the plies L.sub.4 and L.sub.7, which are classified as non-load-bearing, and consequently cannot form groups. Ply 4 consists here of a carbon fiber ply with a fiber angle of 0. This is a layer with a fiber angle outside the range of 20 to 70 or the range of 20 to 70, which is therefore classified as non-load-bearing. Such a layer has an advantageous effect on the transverse load insensitivity of the spring wire wound as a helix around the spring axis, and is therefore appropriate to some extent. The ply 7 is similarly a non-load-bearing layer because, as a homogeneous plastic ply, it does not have preferential fiber reinforcement in the tensile-oriented or compression-oriented loading direction. Rather, the ply 7 represents the outward termination of the spring wire in relation to the surroundings. Possible functions here are that of shielding from medial ambient influences, possible impact protection (for example the impact of stones), tribological resistance (for example a friction-resistant protective layer in the spring plates) or the prevention of contact corrosion. The non-load-bearing layers have a mass fraction of 21% with respect to the total mass of the cross section of the spring wire (the mass of a possibly present spring wire core is not taken into consideration for the calculation). Since, in this variant according to the invention, the group stiffnesses decrease from the inside to the outside and the methodology dictates that all of the groups successfully form pairs, the groups represent a mass fraction of more than 75% for both requirements, and consequently this exemplary embodiment 3 is a preferred arrangement.

LIST OF DESIGNATIONS

[0127] L.sub.i Ply i (counting index i on the closed interval of natural numbers [1,I]) [0128] LW.sub.i Ply wall thickness of the ply i [0129] S.sub.j Layer j (counting index j on the closed interval of natural numbers [1,J]) [0130] .sub.j Angular orientation in relation to the bar axis of the layer S.sub.j [0131] Core of the spring wire (optionally present) [0132] M.sub.j Material of the layer S.sub.j [0133] D.sub.j Layer diameter of the layer S.sub.j [0134] W.sub.j Layer wall thickness of the layer S.sub.j [0135] E.sub.S.sub.j Layer stiffness of the layer S.sub.j [0136] E.sub.1 Stiffness longitudinally in relation to the fiber of the material M.sub.j [0137] E.sub.2 Stiffness transversely in relation to the direction of the fibers of the material M.sub.j [0138] G.sub.12 Shear modulus of the material M.sub.j [0139] .sub.12 Large Poisson's ratio of the material M.sub.j [0140] .sub.21 Small Poisson's ratio of the material M.sub.j [0141] G.sub.k Group k (counting index k on the closed interval of natural numbers [1,K]) [0142] A.sub.S.sub.j Cross-sectional area of the layer S.sub.j [0143] E.sub.G.sub.k Group stiffness of the group G.sub.k [0144] F.sub.G.sub.k Group extensional stiffness of the group G.sub.k [0145] P.sub.n Pair n (counting index n on the closed interval of natural numbers [1,N]) [0146] GV.sub.n Group ratio n, calculated from a tensile-loaded group and a compression-loaded group [0147] D.sub.a Spring wire outside diameter [0148] CF Carbon fiber [0149] BF Basalt fiber [0150] GF Glass fiber [0151] S2 Glass fiber with higher stiffness [0152] E Glass fiber with normal stiffness [0153] UHM Carbon fiber with very high stiffness (Ultra High Modulus) [0154] IM Carbon fiber with high stiffness (Intermediate Modulus) [0155] HT Carbon fiber with normal stiffness (High Tenacity)

CITED NON-PATENT LITERATURE

[0156] Helmut Schrmann: Konstruieren mit Faser-Kunststoff-Verbunden [structural design with fiber-plastic composites], first edition, Springer Verlag 2005

TABLE-US-00001 TABLE 1 Layer Ply wall wall Ply Layer Group Pair Orientation Material thickness thickness L.sub.i S.sub.j G.sub.k P.sub.n Classification Loading [degrees] M.sub.j LW.sub.i [mm] W.sub.j [mm] 1 1 1 1 load-bearing compression 45 1 2 1 2 2 load-bearing tensile 45 1 1 2 3 3 2 load-bearing compression 45 2 1.8 0.9 4 4 load-bearing tensile 45 2 0.9 3 5 5 3 load-bearing compression 45 3 1.6 0.8 6 6 load-bearing tensile 45 3 0.8 4 7 7 4 load-bearing compression 45 4 1.4 0.7 8 8 load-bearing tensile 45 4 0.7 5 9 9 5 load-bearing compression 45 5 1.2 0.6 10 10 load-bearing tensile 45 5 0.6 6 11 11 6 load-bearing compression 45 6 1 0.5 12 12 load-bearing tensile 45 6 0.5 Cross- sectional Layer Group Group Layer area stiffness stiffness extensional Group Ply diameter As.sub.j Mass FVC Es.sub.j EG.sub.k stiffness Ratio L.sub.i D.sub.j [mm] [mm.sup.2] [kg/m] [%] [GPa] [GPa] FG.sub.k [kN] GV.sub.n 1 5 7.85 0.012 50% 197 197 1547.2 1.00 5 7.85 0.012 50% 197 197 1547.2 2 6.9 9.75 0.015 50% 147 147 1433.9 1.00 6.9 9.75 0.015 50% 147 147 1433.9 3 8.6 10.81 0.016 50% 116 116 1253.6 1.00 8.6 10.81 0.016 50% 116 116 1253.6 4 10.1 11.11 0.023 50% 49 49 544.2 1.00 10.1 11.11 0.023 50% 49 49 544.2 5 11.4 10.74 0.020 50% 44.7 44.7 480.3 1.00 11.4 10.74 0.020 50% 44.7 44.7 480.3 6 12.5 9.82 0.018 50% 37.9 37.9 372.1 1.00 12.5 9.82 0.018 50% 37.9 37.9 372.1

TABLE-US-00002 TABLE 2 Example configuration [GPa] - 50% FVC Material no. Type Stiffness class Density [kg/m.sup.3] E1 [GPa] E2 [GPa] nu12 nu21 G12 [GPa] 1 CF UHM 1500 197 4.4 0.35 0.008 2.1 2 CF IM 1500 147 5.4 0.28 0.01 2.3 3 CF HT 1500 116 5.4 0.28 0.01 2.3 4 BF 2050 49 6.5 0.29 0.04 2.5 5 GF S2 1870 44.7 6.4 0.29 0.04 2.4 6 GF E 1870 37.9 5.7 0.29 0.04 2.1

TABLE-US-00003 TABLE 3 Layer Ply wall wall Ply Layer Group Pair Orientation Material thickness thickness L.sub.i S.sub.j G.sub.k P.sub.n Classification Loading [degrees] M.sub.j LW.sub.i [mm] W.sub.j [mm] 1 1 1 1 load-bearing compression 45 2 1.5 1.5 2 2 2 load-bearing tensile 45 1 1 1 3 3 3 2 load-bearing compression 45 2 1 1 4 4 4 load-bearing tensile 45 2 1 1 5 5 5 3 load-bearing compression 40 3 1 1 6 6 load-bearing 45 4 1 2 7 load-bearing 45 4 1 1 8 7 6 load-bearing tensile 40 3 1 1 9 8 7 4 load-bearing compression 45 5 1 1 10 9 load-bearing 40 6 1 1 11 10 load-bearing 30 6 1 1 12 11 8 load-bearing tensiile 45 6 1 1 13 12 load-bearing 40 6 1 1 14 13 load-bearing 35 5 1 1 Cross- sectional Layer Group Group Layer area stiffness stiffness extensional Group Ply diameter As.sub.j Mass FVC ES.sub.j EG.sub.k stiffness Ratio L.sub.i D.sub.j [mm] [mm.sup.2] [kg/m] [%] [GPa] [GPa] FG.sub.k [kN] GV.sub.n 1 4.25 10.01 0.016 60% 175.0 175.0 1752.4 1.16 2 5.5 8.64 0.013 60% 235.0 235.0 2030.3 3 6.5 10.21 0.016 60% 175.0 175.0 1786.8 1.15 4 7.5 11.78 0.018 60% 175.0 175.0 2061.7 5 8.5 13.35 0.021 60% 101.4 70.9 3176.2 0.58 6 10 31.42 0.066 60% 58.0 7 60% 8 11.5 18.06 0.028 60% 101.4 101.4 1832.0 9 12.5 19.63 0.038 60% 53.0 40.4 2570.2 1.22 10 13.5 21.21 0.041 60% 47.4 11 14.5 22.78 0.044 60% 23.1 12 15.5 24.35 0.047 60% 44.8 40.3 3130.2 13 16.5 25.92 0.050 60% 40.3 14 17.5 27.49 0.053 60% 36.2

TABLE-US-00004 TABLE 4 Example configuration [GPa] - 60% FVC Material no. Type Stiffness class Density [kg/m.sup.3] E1 [GPa] E2 [GPa] nu12 nu21 G12 [GPa] 1 CF UHM 1550 235 4.6 0.35 0.007 2.4 2 CF IM 1550 175 6.2 0.26 0.01 2.8 3 CF HT 1550 139 6.3 0.26 0.01 2.7 4 BF 2100 58 8 0.28 0.04 3 5 GF S2 1930 53 7.8 0.28 0.04 2.9 6 GF E 1930 44.8 6.9 0.27 0.04 2.6

TABLE-US-00005 TABLE 5 Layer Ply wall wall Ply Layer Group Pair Orientation Material thickness thickness L.sub.i S.sub.j G.sub.k P.sub.n Classification Loading [degrees] M.sub.j LW.sub.i [mm] W.sub.j [mm] 1 1 1 1 load-bearing compression 45 1 2 1 2 2 load-bearing tensile 45 1 1 2 3 3 2 load-bearing compression 45 2 1.8 0.9 4 4 load-bearing tensile 45 2 0.9 3 5 5 load-bearing compression 45 3 1.6 0.8 6 6 3 load-bearing tensile 45 3 0.8 4 7 non-load- 0 1 1.4 1.4 bearing 5 8 7 4 load-bearing compression 45 4 1.2 0.6 9 8 load-bearing tensile 45 4 0.6 6 10 9 5 load-bearing compression 45 5 1 0.5 11 10 load-bearing tensile 45 5 0.5 7 12 non-load- 6 0.5 0.5 bearing Cross- sectional Layer Group Group Layer area stiffness stiffness extensional Group Ply diameter As.sub.j Mass FVC Es.sub.j EG.sub.k stiffness Ratio L.sub.i D.sub.j [mm] [mm.sup.2] [kg/m] [%] [GPa] [GPa] FG.sub.k [kN] GV.sub.n 1 5 7.85 0.012 60% 139 139 1091.7 1.00 5 7.85 0.012 60% 139 139 1091.7 2 6.9 9.75 0.016 60% 122 122 1190.1 1.00 6.9 9.75 0.016 60% 122 122 1190.1 3 8.6 10.81 0.019 60% 96 96 1037.5 1.00 8.6 10.81 0.019 60% 96 96 1037.5 4 10.1 22.21 0.034 60% non- non- non- non- load- load- load- load- bearing bearing bearing bearing 5 11.4 10.74 0.020 60% 70 70 752.1 1.00 11.4 10.74 0.020 60% 70 70 752.1 6 12.5 9.82 0.019 60% 53 53 520.3 1.00 12.5 9.82 0.019 60% 53 53 520.3 7 13.25 10.41 0.012 Plastic non- non- non- non- only load- load- load- load- bearing bearing bearing bearing

TABLE-US-00006 TABLE 6 Example configuration [GPa] - 60% FVC Material no. Type Stiffness class Density [kg/m.sup.3] E1 [GPa] E2 [GPa] nu12 nu21 G12 [GPa] 1 CF HT 1550 139 6.3 0.26 0.01 2.7 2 80% CF + 20% GF 80% HT + 20% S2 1630 122 6.4 0.26 0.01 2.8 3 50% CF + 50% GF 80% HT + 20% S2 1740 96 7.1 0.26 0.3 2.8 4 20% CF + 80% GF 20% HT + 80% S2 1850 70 7.7 0.28 0.04 2.9 5 GF S2 1930 53 7.8 0.28 0.04 2.9 6 Plastic PA6 1140 2.8 2.8 0.3 0.3 1.1