JPH0210293B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention applies to FRP used in vehicle suspension mechanisms, etc.
Regarding leaf springs. [Prior Art] In order to reduce the weight of a leaf spring, it is effective to equalize the stress at each part in the longitudinal direction. Conventionally, from this point of view, a so-called tapered leaf has been considered, in which the plate spring has a large plate thickness at the center and decreases in plate thickness toward the plate ends. However, in forming methods such as filament winding and pull-forming for FRP leaf springs, the content of reinforcing fibers is constant in the longitudinal direction, and it is difficult to use unidirectional continuous reinforcing fibers along the longitudinal direction of the leaf spring. Therefore, the cross-sectional area is constant. For this reason, as an example of a conventional tapered leaf spring made of FRP, the stress at each part in the longitudinal direction is equalized by widening the plate width instead of reducing the plate thickness at the plate end side. [Problems to be solved by the invention] However, the above-mentioned variable plate thickness and variable plate width
When the plate width on the plate end side increases, such as with FRP tapered leaf springs, it may be necessary to use a large bracket at the attachment point to the vehicle body, or it may be difficult to attach a clip to prevent the plate end from shifting laterally. Various problems arise, such as the possibility that the edge of the plate may interfere with the tire side members. For this reason, it is difficult to put tapered leaf springs with variable thickness and width into practical use. On the other hand, by stacking multiple sheets of prepreg with different lengths in the thickness direction, it is possible to maintain a constant board width and variable board thickness.
A method of manufacturing FRP tapered leaf springs is also being considered. However, in this case, as the thickness of the plate ends gradually decreases, the lateral rigidity of the plate ends (rigidity against the load applied in the width direction of the plate spring) is insufficient, and the plate ends do not have enough lateral rigidity to withstand the lateral centrifugal force that occurs when driving around curves. I can't fight it. [Means for Solving the Problems] The present invention consists of reinforcing fibers and matrix resin along the longitudinal direction of the leaf spring, and the thickness of the leaf spring is large at the center and decreases toward the ends. Applicable to FRP tapered leaf springs. In the FRP leaf spring of the present invention, the leaf width is constant over the entire length of the leaf spring, and the number of reinforcing fibers is the same over the entire length of the leaf spring, and
The fiber content on the edge side of the plate is higher than the fiber content on the center side. [Function] In the FRP tapered leaf spring with the above configuration, the number of reinforcing fibers is the same over the entire length of the leaf spring, so
Continuous unidirectional reinforcing fibers can be used and can be formed using filament winding or pull-forming methods. In order to make the fiber content on the edge side of the plate higher than the fiber content on the center side, the amount of resin on the edge side of the plate should be lower than the amount of resin on the center side, without changing the number of reinforcing fibers. A tapered shape is obtained in which the thickness of the plate decreases on the edge side. By adopting such a tapered shape, it is possible to equalize the stress at each part in the length direction compared to conventional FRP leaf springs with the same width and thickness, making it possible to reduce weight. In addition, since the plate width does not widen even at the plate ends, existing mounting tools such as brackets can be used at the attachment point to the vehicle body, clips can be attached in the same way as conventional leaf springs, and the plate ends can be attached to the tire side. There is no interference with other parts. In addition, even though the board thickness is thinner at the edge of the board, the fiber content is higher than that at the center.
Young's modulus is high, and large lateral rigidity can be obtained even at the edge of the plate. Therefore, it is possible to sufficiently resist lateral centrifugal force and the like input to the vehicle body. [Embodiment] In one embodiment illustrated in FIGS. 1 and 2, the leaf spring device includes an FRP leaf spring 1.
This leaf spring 1 is made by hardening unidirectional continuous reinforcing fibers such as glass along its longitudinal direction with a matrix resin such as epoxy resin. The FRP leaf spring 1 has a constant plate width over its entire length, and the number of reinforcing fibers is the same over its entire length. The shape of the leaf spring 1 is tapered such that the thickness is large at the center and decreases toward the ends.
The fiber content on the edge side of the plate is greater than the fiber content on the center side. Furthermore, in this embodiment, eyepiece members 3 are attached to both ends of the leaf spring 1 using seat plates 2, respectively. Further, a center bolt 5 and a nut 6 are provided at a longitudinally intermediate portion of the leaf spring 1 with a center spacer 4 interposed therebetween. The above FRP leaf spring 1 has the following reasons:
The content of the reinforcing fibers is set to be 60% by weight or more and up to about 75% by weight on the center side of the leaf spring 1, and approximately 75% by weight or more and 85% by weight or less on the plate end side. First, the relationship between the fiber volume content V _f and the fiber weight content W _f is given by the following equation. V _f =W _f ·d _n /W _f (d _n −d _f )+d _f In the above formula, d _f represents the specific gravity of the fiber, and d _n represents the specific gravity of the resin at the time of curing. Here, typical values when glass is used as the fiber and epoxy is used as the resin, d _f =2.55g/cm ³ , d _n =1.2
When the relationship between V _f and W _f is expressed in g/cm ³ as a graph, it becomes as shown in Fig. 3. On the other hand, Young's modulus E _n of epoxy resin is 300 to 500
Kg/mm ² , Young's modulus E _f of glass fiber is 7000-7800
Kg/mm ² , so the typical value E _n =300Kg/mm ² ,
If E _f =7400 Kg/mm ² , the Young's modulus E resulting from these combinations is expressed in relation to the fiber volume content V _f as shown in FIG. For example E=3000
When Kgf/mm ² , V _f is 40%, and when E=4500 Kgf/mm ² , V _f is 60%. As described above, the FRP leaf spring 1 of this embodiment has the same number of fibers over the entire length of the leaf spring 1, but the fiber content V f (or W f ) on the leaf end side is different from the fiber content V _f (or W _f ) on the center side. The fiber content is set higher than the fiber content V _f (or W _f ). In other words, although the plate thickness on the plate end side is thinner, the resin content on the plate edge side is reduced by that much to increase the fiber content. As shown in FIG. 4, as the fiber content V _f increases, the Young's modulus E also increases, but this does not increase indefinitely. The maximum weight content W _f of fibers with a circular cross section that can fit into a square cross section is 88%
As long as the cross-sectional shape of the fiber is circular, W _f cannot become larger than this. According to our research, W _f is 88%
When approaching , the degree of contact between the fibers becomes too great, and when durability tests were conducted, it was confirmed that cracks would occur in the longitudinal direction of the leaf spring at an early stage. When the maximum value of W _f was determined on the condition that longitudinal cracks do not occur early, it was found that it can be used up to around W _f = 85% (V _f = 73%). FIG. 5 shows the relationship between the glass fiber content W _f and the strength of an FRP material formed by the filament winding method. From the same figure, W _f =80%
When the tensile strength of FRP material is around 155, which is equivalent to steel
Kg/ ^mm2 . Therefore, in order to use it under the same conditions as steel, it is desirable to keep W _f =80% (V _f =67%). For the above reasons, the fiber content on the plate end side is selected to be at most 85% by weight, preferably 80% by weight or less. On the other hand, since the central portion of the leaf spring 1 is fastened with a U bolt or a center bolt, not only the tensile strength but also the compressive strength is an important factor. As shown in Figure 5, the compressive strength is 75% when the fiber content W _f is 75%.
W f reaches its maximum when it is close to W f , and any further increase in W _f causes a decrease in compressive strength. Moreover, if the fiber content on the center side exceeds W _f =75%, the fiber content on the edge side of the plate will approach the preferred value (W _f =80%) too much, making it impossible to form a sufficient taper shape. It disappears. Therefore, the fiber content on the center side W _f
It is best to keep it up to about 75% (V _f = 60%). V _f
The Young's modulus when = 60% is E = 4500 from Figure 4.
Kg/ ^mm2 . Similarly, on the center side, the fiber content V _f
If it is less than 40%, the resin content is too high, and durability tests have shown that too much stress is placed on the resin, leading to early breakage. Furthermore, as shown in Fig. 4, Young's modulus E is 3000 Kg/mm ² when V _f =40%, but Young's modulus E
and the spring constant k have a proportional relationship, which is expressed as k=6EI/l ³ =6E/l ³ ×bt ² /12=Ebt ³ /2l ³ (I is the second moment of area). Here, if we try to make the spring constant k the same in the case of E=3000Kg/ ^mm2 and the case of E=4500Kgf/ ^mm2 , we can calculate the E
= 3000Kgf/mm ² plate spring plate thickness t is E = 45000Kg
It has to be considerably thicker, 14.5% compared to the plate thickness t of a leaf spring of f/mm ² , which is at the limit of allowable values in terms of installation space and weight. Moreover, V _f
If it is less than 40%, the resin content will be too large and various problems will occur during manufacturing. For the above reasons,
The fiber content in the center of the leaf spring is W _f = 60% or more (V _f
= 40% or more), and W _f = 75% or less (V _f = 60
% or less). As mentioned above, the plate width is constant and the plate thickness is variable.
As shown in FIG. 6, the Young's modulus E _x of the FRP leaf spring increases as the plate thickness reduction rate α increases.
In other words, even if the plate thickness becomes considerably thinner at the edge side,
On the other hand, since E _x becomes higher and the lateral rigidity increases, it is possible to sufficiently resist lateral acceleration that is applied when driving around a curve, for example, and prevent interference between the tires and the vehicle body. The outline of the manufacturing process of the FRP tapered leaf spring according to this example is as follows. First, a reinforcing fiber bundle impregnated with matrix resin is wound around the molding groove of the lower mold (mandrel). Next, an upper mold having a convex portion that fits into the molding groove is pressed onto the lower mold. The thickness of the convex portion gradually increases from the center of the leaf spring toward the ends of the leaf. By heating and curing the upper die while pressing it, a tapered leaf spring having a constant plate width and a plate thickness gradually becoming thinner from the center toward the plate ends can be obtained. In addition, the FRP tapered leaf spring 1 shown in Fig. 7
In the model, the spring constant k is given by the following equation. k _a ＝P _a ／δ _a δ _a ＝∫ ^l ₁₀ P _a x ² ／E ₁ I ₁ dx＋∫ ^l _2l1 P _a x ² ／E _x I _x dx＋∫ ^l _3l2 P _a x ² ／E ₂ I ₂ dx The following table compares the weight of a conventional FRP leaf spring with equal width and thickness and an FRP tapered leaf spring with equal width and variable thickness according to the present invention. As can be seen from the table, by using unidirectional reinforcing fibers and changing the content of matrix resin in any cross section, the same layout (board width/straight span)
Sufficient weight reduction can be achieved under the same spring constant conditions.

〔Effect of the invention〕

According to the present invention, it is lightweight and has high lateral rigidity.
You can get FRP leaf springs.

[Brief explanation of drawings]

FIG. 1 is a front view of an FRP leaf spring showing an embodiment of the present invention, FIG. 2 is a bottom view of the same leaf spring, and FIG. 3 is a diagram showing the relationship between the weight content and volume content of fibers. Figure 4 is a diagram showing the relationship between fiber content and Young's modulus, Figure 5 is a diagram showing the relationship between fiber content and strength, and Figure 6 is a diagram showing the relationship between plate thickness reduction rate and Young's modulus. , FIG. 7 is a schematic diagram of an FRP tapered leaf spring.

Claims (1)

[Claims] 1 In an FRP leaf spring that is made of glass reinforcing fibers and matrix resin that have a circular cross section along the longitudinal direction of the leaf spring, and that is thicker at the center and decreases toward the ends. , the plate width is kept constant over the entire length of the plate spring, the number of reinforcing fibers is the same over the entire length of the plate spring, and the fiber content on the edge side of the plate is larger than the fiber content on the center side. An FRP leaf spring characterized in that the content of each fiber is 60% by weight or more on the center side of the leaf spring and 85% by weight or less on the edge side of the leaf spring.