Center pillar for a vehicle

Abstract

Provided is a B-pillar for a vehicle, which includes alternately laminated carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) to reduce the weight of the B-pillar and maintain the strength of the B-pillar. The B-pillar includes a base layer formed of CFRP; and a laminated layer, in which a plurality of CFRP layers and a plurality of GFRP layers are alternately provided on a first surface and a second surface of the base layer, respectively. Accordingly, the CFRP and GFRP laminated on the first surface of the base layer and the CFRP and GFRP laminated on the second surface of the base layer are symmetric with each other with respect to the thickness direction of the B-pillar.

Description

Technical Field

[0001] The present invention relates to a center pillar for a vehicle, and more particularly, to a center pillar for a vehicle having alternately laminated carbon fiber reinforced plastic and glass fiber reinforced plastic to reduce the weight of the center pillar and maintain the strength of the center pillar in consideration of the roof strength and the ability to withstand side impacts. Background Art

[0002] The pillars are part of the vehicle frame and support the roof. These pillars include front pillars, center pillars, and rear pillars starting from the front of the vehicle. The front pillar, center pillar, and rear pillar are also referred to as the A-pillar, B-pillar, and C-pillar, respectively.

[0003] The center pillar is an important structural element that supports the roof of the vehicle, absorbs the impact energy of side impacts, and prevents other vehicles in a collision from entering the passenger compartment. In addition, the center pillar is a structural component of the vehicle for attaching door hinges and attaching seat belts. The center pillar is composed of several elements, most of which are reinforcing materials. To minimize the deformation of the vehicle, high tensile strength steel plates are used as reinforcing plates. Generally, the center pillar is prepared by press-forming a high tensile strength steel plate and attaching the reinforcing plate to the press-formed steel plate by spot welding.

[0004] Therefore, thick high tensile strength steel plates are applied to increase the strength of the center pillar. The thick high strength steel plates are strong, resulting in reduced ductility and increased brittleness. Therefore, the thick high tensile strength steel plates may break due to the impact during a collision.

[0005] In recent years, in order to reduce the weight of the vehicle to improve its fuel efficiency, research has been conducted with the goal of applying fiber reinforced plastics to the center pillar made of high tensile strength steel plates, where the fiber reinforced plastics are lightweight and ensure the strength of the center pillar. For example, a technology has been developed in which a part of the center pillar is made of carbon fiber reinforced plastic (CFRP) instead of high tensile strength steel plates, and the steel and CFRP are combined. However, it is difficult to combine the steel and CFRP according to this technology, and additional fastening components are required for mechanical connection.

[0006] Alternatively, a technology has been developed in which the entire part of the center pillar is made of CFRP instead of high tensile strength steel plates. However, when the center pillar is formed only of CFRP, the manufacturing cost increases. In addition, the use of conductive carbon fibers causes bimetallic corrosion to occur.

[0007] The foregoing is only intended to assist in understanding the background of the present invention and is not intended to mean that the present invention falls within the scope of related art known to those skilled in the art. Summary of the Invention

[0008] The present invention provides a center pillar for a vehicle, which is configured such that carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) are alternately laminated to reduce the weight of the center pillar, maintain the strength of the center pillar in consideration of the roof strength and the ability to withstand side collisions, and minimize an increase in material costs.

[0009] To achieve the above object, the center pillar for a vehicle may include: a base layer formed of carbon fiber reinforced plastic (CFRP); and laminate layers, wherein a plurality of CFRP layers and a plurality of glass fiber reinforced plastic (GFRP) layers are alternately disposed on a first surface and a second surface of the base layer, respectively, in such a manner that the CFRP and GFRP laminated on the first surface of the base layer and the CFRP and GFRP laminated on the second surface of the base layer are symmetric with respect to the thickness direction of the center pillar. The second surface is opposite to the first surface.

[0010] The base layer may be formed of CFRP, wherein the orientation of carbon fibers with respect to the longitudinal direction of the center pillar is 0°. The plurality of CFRP layers forming the laminate layers may be configured such that the orientation of carbon fibers with respect to the longitudinal direction of the center pillar is 0° or ±15°. The plurality of GFRP layers forming the laminate layers may be plain weave fabrics or twill weave fabrics, wherein glass fibers are woven at 0° and 90° with respect to the longitudinal direction of the center pillar.

[0011] The center pillar may be divided into a bottom region, a first transition region, a second transition region, a third transition region, and a top region from its bottom to its top with respect to the longitudinal direction of the center pillar. The bottom region may be provided with a 1-1 zone, wherein CFRP with carbon fibers oriented at ±15° and GFRP formed as a plain weave fabric or a twill weave fabric with glass fibers woven at 0° and 90° are sequentially laminated on opposite surfaces of the base layer. The first transition region may be provided with a 1-1 zone and a 1-2 zone, in the 1-2 zone, CFRP with carbon fibers oriented at ±15°, CFRP with carbon fibers oriented at 0°, and GFRP formed as a plain weave fabric or a twill weave fabric with glass fibers woven at 0° and 90° are sequentially laminated on the 1-1 zone.

[0012] The second transition region may be provided with a 1-1 zone, a 1-2 zone, and a 1-3 zone, in the 1-3 zone, CFRP with carbon fibers oriented at 0° and GFRP formed as a plain weave fabric or a twill weave fabric with glass fibers woven at 0° and 90° are sequentially laminated on the 1-2 zone. Each of the third transition regions may be provided with a 1-1 zone, a 1-2 zone, a 1-3 zone, and a 1-4 zone, in the 1-4 zone, CFRP with carbon fibers oriented at ±15°, CFRP with carbon fibers oriented at 0°, and GFRP formed as a plain weave fabric or a twill weave fabric with glass fibers woven at 0° and 90° are sequentially laminated on the 1-3 zone.

[0013] The center pillar can be configured such that the 1-1 region, 1-2 region, 1-3 region, and 1-4 region are all disposed on the bottom region, the first transition region, the second transition region, the third transition region, and the top region. The center pillar can be divided into a bottom region, a transition region, and a top region with respect to the longitudinal direction of the center pillar from its bottom to its top. The bottom region can be provided with a 2-1 region, where GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90°, CFRP with a carbon fiber orientation of 0°, and GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90° are sequentially laminated on opposite surfaces of a base layer.

[0014] The transition region can be provided with a 2-1 region and a 2-2 region, and in the 2-2 region, CFRP with a carbon fiber orientation of ±15° is laminated on the 2-1 region. The top region can be provided with a 2-1 region, a 2-2 region, and a 2-3 region, and in the 2-3 region, CFRP with a carbon fiber orientation of ±15° is laminated on the 2-2 region. The center pillar can be configured such that the 2-1 region, 2-2 region, and 2-3 region are all disposed on the bottom region, the transition region, and the top region. The CFRP can be approximately 0.16 mm thick, and the GFRP can be approximately 0.5 mm thick.

[0015] According to an exemplary embodiment of the present invention, CFRP and GFRP, which are cheaper compared to CFRP, can be alternately laminated to prepare a center pillar for a vehicle, thereby making it possible to expect weight reduction, strength improvement, and material cost reduction. In addition, since non-conductive GFRP and CFRP can be alternately laminated, it is possible to prevent the center pillar from suffering from bimetallic corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In conjunction with the accompanying drawings, the above and other objects, features, and other advantages of the present invention will be more clearly understood from the following detailed description, in which:

[0017] Figure 1 is an image showing experimental results of roof strength based on the orientation of reinforcing fibers;

[0018] Figure 2 is an image showing experimental results of thickness distribution based on the orientation of reinforcing fibers;

[0019] Figure 3 is a view showing a center pillar for a vehicle according to an exemplary embodiment of the present invention;

[0020] Figure 4 is a view showing according to an exemplary embodiment of the present invention Figure 3 an enlarged view of region A; and

[0021] Figures 5 to 8A table listing the type, orientation, and thickness of the reinforcing fibers for each region, the reinforcing fibers constituting the center pillar according to various exemplary embodiments of the present invention. Detailed Description

[0022] It should be understood that the term "vehicle" or "vehicular" or other similar terms as used herein generally includes motor vehicles, such as passenger vehicles including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, watercraft including various boats and ships, airplanes, etc., and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum).

[0023] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are also intended to include the plural forms. It should also be understood that when the terms "comprises" and / or "comprising" are used in this specification, they specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0024] Unless specifically stated or obvious from the context, as used herein, the term "about" should be understood to be within the normal tolerances in the art, e.g., within 2 standard deviations of the mean. "About" can be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. All numerical values provided herein are modified by the term "about" unless the context clearly indicates otherwise.

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, it should be understood that this specification is not intended to limit the present invention to those exemplary embodiments. On the contrary, the present invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents, and other embodiments that may be included within the spirit and scope of the present invention as defined by the appended claims. In all the drawings, the same reference numerals will refer to the same or similar parts.

[0026] To determine the orientation of carbon fibers (hereinafter referred to as the orientation of carbon fibers) that can be applied to the present invention, among various orientations of carbon fibers, a roof strength test based on the orientation of carbon fibers is conducted, and the optimal orientation of carbon fibers is obtained.

[0027] Figure 1 is an image showing the experimental results of the roof strength based on the orientation of carbon fibers. As Figure 1 shown, a simulation program is used to obtain the thickness of the center pillar that ensures the roof strength required for the center pillar of the vehicle. The orientation of the carbon fibers is set to 0°, 15°, 30°, 45°, 60°, 75°, and 90°, and the results are shown in Figure 1 . As a result, it is confirmed that the feasible thickness distribution is within the orientation range of carbon fibers at 0°, 15°, and 30°, and thus, the desired roof strength level can be obtained within this range. Experiments related to the thickness distribution based on the orientation of carbon fibers are also conducted, and the optimal orientation of carbon fibers is obtained.

[0028] Figure 2 is an image showing the experimental results related to the thickness distribution based on the orientation of carbon fibers. As Figure 2 shown, a simulation program is used to derive the thickness distribution based on the orientation of carbon fibers to ensure the roof strength required for the center pillar of the vehicle. The orientation of the carbon fibers is set to 0°, 15°, 30°, 45°, 60°, 75°, and 90°, and the results are shown in Figure 2 . As a result, it is confirmed that the feasible thickness distribution is within the orientation range of carbon fibers at 0° and 15°, and thus, the desired roof strength level can be obtained within this range.

[0029] When forming the center pillar according to the results shown in Figure 1 and Figure 2 , it has been confirmed that it is advantageous to use a carbon fiber-containing fiber-reinforced plastic with an orientation of 0° or ±15°. It has been confirmed that it is advantageous to form the carbon fiber-containing fiber-reinforced plastic with an orientation of 0° to be about 1.6 mm to 3.0 mm thick, and to form the carbon fiber-containing fiber-reinforced plastic with an orientation of 15° to be about 1.6 mm to about 2.4 mm thick.

[0030] Hereinafter, unless otherwise specified, the angle indicating the orientation of the fiber is based on the longitudinal direction of the center pillar. In particular, the orientation of the fiber being 0° means that the orientation of the fiber is parallel to the longitudinal direction of the center pillar. Various exemplary embodiments of the center pillar implemented by applying the orientation of carbon fibers obtained above will be described.

[0031] Figure 3 is a view showing a center pillar for a vehicle according to an exemplary embodiment of the present invention; and Figure 4 is a view showing Figure 3An enlarged view of region A. As shown in the drawings, a center pillar for a vehicle according to an exemplary embodiment of the present invention may include: a base layer formed of carbon fiber reinforced plastic (CFRP); and a laminated layer, wherein a plurality of CFRP layers and a plurality of glass fiber reinforced plastic (GFRP) layers may be alternately disposed on a first surface and a second surface (e.g., a surface opposite to the first surface) of the base layer. Accordingly, the CFRP and GFRP laminated on the first surface of the base layer and the CFRP and GFRP laminated on the second surface of the base layer may be symmetric with respect to the thickness direction of the center pillar.

[0032] In the present invention, according to the optimal orientation obtained above, CFRP is used, wherein the orientation of the carbon fibers is 0° or ±15°. In particular, the CFRP may be formed into sheets and laminated, wherein in an exemplary embodiment its thickness is about 0.16 mm. Similarly, the GFRP is formed into sheets and laminated, wherein the GFRP may be a plain weave or a twill weave, wherein the glass fibers are woven at 0° and 90°. In this case, sheet-like GFRP with a thickness of about 0.5 mm may be used. Since the glass fibers of the GFRP are woven at 0° and 90°, the thickness of each layer of the glass fiber layers woven at 0° and 90° is about 2.5 mm.

[0033] Particularly advantageously, the base layer is formed of CFRP, wherein the orientation of the carbon fibers is 0°. The laminated layers disposed on the first surface and the second surface of the base layer in a symmetric manner may be formed by alternately laminating CFRP with the orientation of the carbon fibers being 0° or ±15° and GFRP formed as a plain weave or a twill weave with the glass fibers woven at 0° and 90°. Accordingly, for each laminated layer, an odd number or multiple layers of CFRP with the orientation of the carbon fibers being 0° are provided, and an even number of layers of CFRP with the orientation of the carbon fibers being ±15° and an even number of layers of GFRP formed as a plain weave or a twill weave with the glass fibers woven at 0° and 90° are provided.

[0034] The above has been described with reference to Figure 1 and Figure 2 It is advantageous that the fiber reinforced plastic containing carbon fibers with an orientation of 0° is about 1.6 mm to 3.0 mm thick, and the fiber reinforced plastic containing carbon fibers with an orientation of 15° is about 1.6 mm to about 2.4 mm thick. However, it is also advantageous that the total thickness of the fiber reinforced plastic containing carbon fibers with an orientation of 0° is about 1.44 mm to 3.04 mm, and the total thickness of the fiber reinforced plastic containing carbon fibers with an orientation of 15° is about 1.6 mm to 2.56 mm.

[0035] Various exemplary embodiments for implementing the center pillar for a vehicle according to the present invention will be described. As Figure 3 and Figure 4As shown, the middle column can be divided into a bottom region 10, a transition region 20, and a top region 30 relative to the longitudinal direction from bottom to top. In particular, the transition region 20 can be subdivided into a first transition region 21, a second transition region 22, and a third transition region 23 relative to the longitudinal direction from bottom to top. The middle column can include a lower hinge hole 31, and the lower hinge of the rear door is installed in the lower hinge hole 31. The transition region 20 can be provided below the lower hinge hole 31.

[0036] Therefore, the base layer can be provided in the bottom region 10, the first transition region 21, the second transition region 22, the third transition region 23, and the top region 30. Then, for each of the bottom region 10, the first transition region 21, the second transition region 22, the third transition region 23, and the top region 30, the lamination pattern of CFRP and GFRP laminated on the base layer changes. Therefore, its strength can be maintained while minimizing its weight. In addition, the bottom region 10 can be provided with a 1-1 area, where CFRP with a carbon fiber orientation of ±15° and GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90° are laminated on opposite surfaces of the base layer in sequence.

[0037] The first transition region 21 can be provided with a 1-1 area and a 1-2 area. In the 1-2 area, CFRP with a carbon fiber orientation of ±15°, CFRP with a carbon fiber orientation of 0°, and GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90° are laminated on the 1-1 area in sequence. In addition, the second transition region 22 can be provided with a 1-1 area, a 1-2 area, and a 1-3 area. In the 1-3 area, CFRP with a carbon fiber orientation of 0° and GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90° are laminated on the 1-2 area in sequence.

[0038] Each of the third transition region 23 and the top region 30 can be provided with a 1-1 area, a 1-2 area, a 1-3 area, and a 1-4 area. In the 1-4 area, CFRP with a carbon fiber orientation of ±15°, CFRP with a carbon fiber orientation of 0°, and GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90° are laminated on the 1-3 area in sequence. In particular, the CFRP and GFRP forming the 1-1 area provided in the bottom region 10, the first transition region 21, the second transition region 22, the third transition region 23, and the top region 30 can extend over the area.

[0039] The CFRP and GFRP forming the 1-2 zones provided in the first transition region 21, the second transition region 22, the third transition region 23, and the top region 30 can extend over these regions. Additionally, the CFRP and GFRP forming the 1-3 zones provided in the second transition region 22, the third transition region 23, and the top region 30 can extend over these regions. Thus, as Figure 5 shown, the thickness of the middle pillar can gradually increase in the order of the bottom region 10, the first transition region 21, the second transition region 22, the third transition region 23, and the top region 30.

[0040] Figure 5 is a table listing the type, orientation, and thickness of the reinforcing fibers for each region according to the first exemplary embodiment, and shows an example of implementing the first exemplary embodiment. In Figure 5 the table, GFRP in the table indicates GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90°, and the orientations of 0, 15, and -15 in the table indicate CFRP in which carbon fibers are arranged at their respective angles. Hereinafter, these conditions also apply to Figures 6 to 7 . According to the present invention, the middle pillar can be formed such that its thickness does not increase in the order of the bottom region 10, the first transition region 21, the second transition region 22, the third transition region 23, and thus, its thickness and pattern can remain the same over the bottom region 10, the first transition region 21, the second transition region 22, the third transition region 23, and the top region 30.

[0041] Figure 6 is a table listing the type, orientation, and thickness of the reinforcing fibers for each region according to the second exemplary embodiment, and shows an example of implementing the second exemplary embodiment. Each middle pillar according to the above first embodiment and second embodiment can be configured such that GFRP having non-conductive properties is provided on the outermost side to prevent bimetallic corrosion from occurring on the middle pillar. On the other hand, in the case of applying the middle pillar to a vehicle not exposed to bimetallic corrosion, the arrangement of CFRP and GFRP is different from the above exemplary embodiments to maximize strength.

[0042] The middle pillar can be divided into a bottom region 10, a transition region 20, and a top region 30 from the bottom to the top with respect to the longitudinal direction. In particular, the transition region 20 refers to the region including the above first transition region 21, second transition region 22, and third transition region 23. The bottom region 10 can be provided with a 2-1 zone, in which GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90°, CFRP with a carbon fiber orientation of 0°, and GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90° are sequentially laminated on opposite surfaces of the base layer.

[0043] The transition region 20 may be provided with a 2-1 region and a 2-2 region, and in the 2-2 region, a CFRP layer with a carbon fiber orientation of ±15° is laminated on the 2-1 region. Additionally, the top region 30 is provided with a 2-1 region, a 2-2 region, and a 2-3 region, and in the 2-3 region, a CFRP layer with a carbon fiber orientation of ±15° is laminated on the 2-2 region. The CFRP and GFRP forming the 2-1 region provided in the bottom region 10, the transition region 20, and the top region 30 may extend over these regions. The CFRP and GFRP forming the 2-2 region provided in the transition region 20 and the top region 30 may extend over these regions.

[0044] Therefore, as Figure 7 shown, the thickness of the center pillar may gradually increase in the order of the bottom region 10, the transition region 20, and the top region 30. Figure 7 is a table listing the type, orientation, and thickness of the reinforcing fibers for each region according to the third exemplary embodiment, and shows an example of implementing the third exemplary embodiment. According to the present invention, the center pillar may be formed such that its thickness does not increase in the order of the bottom region 10, the transition region 20, and the top region 30, and thus, its thickness and pattern may remain the same over the bottom region 10, the transition region 20, and the top region 30.

[0045] Figure 8 is a table listing the type, orientation, and thickness of the reinforcing fibers for each region according to the fourth exemplary embodiment, and shows an example of implementing the fourth embodiment. Experiments were conducted to analyze the side impact resistance and roof strength of a center pillar made of ordinary steel prepared using a high tensile strength steel plate in the prior art and a center pillar prepared according to the first exemplary embodiment of the present invention. The results are shown in Table 1.

[0046] Table 1

[0047]

[0048] As shown in Table 1, it was confirmed that the center pillar prepared by laminating the composite material according to the exemplary embodiment of the present invention has excellent side impact resistance and excellent roof strength compared to the center pillar made of steel in the prior art.

[0049] Although various exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will understand that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the present invention disclosed in the appended claims.

Claims

1. A center pillar of a vehicle, comprising: a base layer formed of carbon fiber reinforced plastic CFRP; and a laminate layer in which a plurality of CFRP layers and a plurality of glass fiber reinforced plastic GFRP layers are alternately provided on a first surface and a second surface of the base layer respectively, wherein the CFRP and the GFRP laminated on the first surface of the base layer and the CFRP and the GFRP laminated on the second surface of the base layer are symmetric with respect to the thickness direction of the center pillar, wherein the center pillar is divided into a bottom region, a first transition region, a second transition region, a third transition region, and a top region from the bottom to the top with respect to the longitudinal direction of the center pillar, wherein the bottom region is provided with a 1-1 zone, in which CFRP having carbon fibers oriented at ±15° and GFRP formed as a plain weave or twill weave having glass fibers woven at 0° and 90° are sequentially laminated on two opposite surfaces of the base layer, wherein the first transition region is provided with the 1-1 zone and a 1-2 zone, in which CFRP having carbon fibers oriented at ±15°, CFRP having carbon fibers oriented at 0°, and GFRP formed as a plain weave or twill weave having glass fibers woven at 0° and 90° are sequentially laminated on the 1-1 zone, wherein the second transition region is provided with the 1-1 zone, the 1-2 zone, and a 1-3 zone, in which CFRP having carbon fibers oriented at 0° and GFRP formed as a plain weave or twill weave having glass fibers woven at 0° and 90° are sequentially laminated on the 1-2 zone, and wherein each of the third transition region and the top region is provided with the 1-1 zone, the 1-2 zone, the 1-3 zone, and a 1-4 zone, in which CFRP having carbon fibers oriented at ±15°, CFRP having carbon fibers oriented at 0°, and GFRP formed as a plain weave or twill weave having glass fibers woven at 0° and 90° are sequentially laminated on the 1-3 zone.

2. The center pillar according to claim 1, wherein, the base layer is formed of CFRP in which the orientation of carbon fibers with respect to the longitudinal direction of the center pillar is 0°.

3. The center pillar according to claim 1, wherein, the plurality of CFRP layers forming the laminate layer include carbon fibers oriented at 0° or ±15° with respect to the longitudinal direction of the center pillar.

4. The center pillar according to claim 1, wherein, the plurality of GFRP layers forming the laminate layer are plain weave or twill weave, in which glass fibers are woven at 0° and 90° with respect to the longitudinal direction of the center pillar.

5. The center pillar according to claim 1, wherein, the center pillar is formed such that the 1-1 zone, the 1-2 zone, the 1-3 zone, and the 1-4 zone are all provided on the bottom region, the first transition region, the second transition region, the third transition region, and the top region.

6. A center pillar of a vehicle, comprising: A base layer formed of carbon fiber reinforced plastic (CFRP); and a laminated layer, in which a plurality of CFRP layers and a plurality of glass fiber reinforced plastic (GFRP) layers are alternately arranged on the first surface and the second surface of the base layer respectively, wherein the CFRP and the GFRP laminated on the first surface of the base layer and the CFRP and the GFRP laminated on the second surface of the base layer are symmetric with respect to the thickness direction of the middle column, wherein the middle column is divided into a bottom region, a transition region and a top region from the bottom to the top with respect to the longitudinal direction of the middle column, wherein the bottom region has a 2-1 zone, in which a GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90°, a CFRP with carbon fibers oriented at 0°, and a GFRP formed as a plain weave or twill weave of glass fibers woven at 0° and 90° are sequentially laminated on two opposite surfaces of the base layer, wherein the transition region is provided with the 2-1 zone and a 2-2 zone, in which a CFRP layer with carbon fibers oriented at ±15° is laminated on the 2-1 zone, and wherein the top region is provided with the 2-1 zone, the 2-2 zone and a 2-3 zone, in which a CFRP layer with carbon fibers oriented at ±15° is laminated on the 2-2 zone.

7. The middle column according to claim 6, wherein, the middle column is formed such that the 2-1 zone, the 2-2 zone and the 2-3 zone are all provided on the bottom region, the transition region and the top region.

8. The middle column according to claim 1 or 6, wherein, the CFRP is about 0.16 mm thick and the GFRP is about 0.5 mm thick.

9. The middle column according to claim 1 or 6, wherein, the second surface is opposite to the first surface.

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