Automotive exterior panel

Provided is a configuration that makes up for a lack of tensile rigidity and a lack of collision properties at the same time. [Solution] An automotive exterior panel according to the present invention: an exterior material 110; and a reinforcing member 120 that is in contact along an automobile inside surface of the exterior material 110 and of which a second moment of area in a direction orthogonal to the exterior material is less than or equal to 15,000 mm4 in a cross section orthogonal to a longitudinal direction of the 10 reinforcing member. By this configuration, the second moment of area in a direction orthogonal to the longitudinal direction of the reinforcing member 120 is made less than or equal to 15,000 mm4, and hence a lack of tensile rigidity can be made up for at the same time.

TECHNICAL FIELD

The present invention relates to an automotive exterior panel.

BACKGROUND ART

Thus far, Patent Literature 1 below has described a technology that assumes the provision of a reinforcing member of an outer sheet of an automotive body that can achieve a weight reduction of the component itself and has a high effect of improvement in the surface rigidity of the outer sheet of the car body, for example.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

These days, an exterior material used for an automotive exterior panel or the like tends to be reduced in wall thickness in response to requests of weight reduction etc.; however, the reduction in wall thickness causes a problem that tensile rigidity is reduced. Consequently, there is a problem that, when a door panel or the like is pushed by a hand, the exterior material deforms easily, for example.

A more detailed description is as follows: for tensile rigidity in a conventional exterior panel, necessary properties have been satisfied by using the sheet thickness, the shape (regarding curvature etc.), and character lines of the exterior material, and the installation of a conventional reinforcing component in a part with the weakest tensile rigidity (for example, the center of the panel). On the other hand, if a reduction in the wall thickness of an exterior material for the purpose of weight reduction is made, such measures other than the sheet thickness by themselves have difficulty in making up for a lack of tensile rigidity.

In this regard, there is a technology that attempts to improve a conventional reinforcing component from the viewpoint of improvement in tensile rigidity, like in Patent Literature 1 above, for example; however, if the degree of wall thickness reduction is increased like, for example, a wall thickness reduction from 0.7 mm to less than or equal to 0.5 mm in terms of the original thickness of the exterior material, there is a problem that, if it is attempted to make up for a lack of tensile rigidity by the entire exterior panel of the object, the number of necessary reinforcing components is increased, and the weight reduction effect is reduced to some extent. Further, the increase in the number of necessary reinforcing components may lead to even a weight increase on the contrary.

As above, it is difficult for the structure of a conventional exterior panel to make up for a lack of tensile rigidity when the exterior material is reduced in wall thickness and at the same time to obtain a weight reduction effect, which is an original object of the wall thickness reduction of the exterior material.

Thus, the present invention has been made in view of the problem mentioned above, and an object of the present invention is to provide an automotive exterior panel capable of making up for a lack of tensile rigidity.

Solution to Problem

To solve the problem described above, according to an aspect of the present invention, there is provided an automotive exterior panel including: an exterior material; and a reinforcing member that is in contact along an automobile inside surface of the exterior material and of which a second moment of area in a direction orthogonal to the exterior material is less than or equal to 15,000 mm4in a cross section orthogonal to a longitudinal direction of the reinforcing member.

A yield stress of the reinforcing member may be more than or equal to 500 MPa.

In addition, a cross portion may be provided in the reinforcing member, and the second moment of area in the direction orthogonal to the exterior material may be less than or equal to 15,000 mm4in the cross section orthogonal to the longitudinal direction of the reinforcing member extending from the cross portion.

In addition, two or more cross portions may be provided.

In addition, the reinforcing member may be stuck to the exterior material in a region of more than or equal to ⅓ of a total length of the reinforcing member.

In addition, the exterior material may have a concave curved portion that is curved concavely as viewed from an outside of an automobile, and the reinforcing member overlapping with the concave curved portion may be stuck to the exterior material.

In addition, the reinforcing member may go across the exterior material.

In addition, the reinforcing member may be joined to the exterior material.

In addition, the reinforcing member may pass through an inside of a circle in which, among three line segments obtained by trisecting a longest line segment among line segments each connecting any two points on an outline of the exterior material, a line segment located in a center is taken as a diameter.

In addition, a plurality of the reinforcing members may be arranged between a first side and a second side of the exterior material that face each other, at least one of the reinforcing members may be placed more on a side of the first side than an intermediate line between the first side and the second side, at least one of the reinforcing members may be placed more on a side of the second side than the intermediate line, an extending direction of each of the reinforcing members may be a direction along a nearer one of the first side and the second side, and a first distance between adjacent two of the reinforcing members may be shorter than a second distance from the first side or the second side to a nearest one of the reinforcing members.

In addition, an angle between the reinforcing member and one side near to the reinforcing member out of the first side and the second side may be within 30°.

In addition, the first distance may be a distance between two points at which adjacent two of the reinforcing members and a line segment connecting a midpoint of the first side and a midpoint of the second side cross.

In addition, the second distance may be a distance between the midpoint of the first side and a point at which the reinforcing member nearest to the first side and the line segment connecting the midpoint of the first side and the midpoint of the second side cross.

In addition, the second distance may be a distance between the midpoint of the second side and a point at which the reinforcing member nearest to the second side and the line segment connecting the midpoint of the first side and the midpoint of the second side cross.

Advantageous Effects of Invention

As described above, according to the present invention, a lack of tensile rigidity can be made up for.

DESCRIPTION OF EMBODIMENTS

First, a configuration of an automotive exterior panel according to an embodiment of the present invention is described with reference toFIG. 1.FIG. 1is a schematic diagram showing a state where an automotive exterior panel100according to the present embodiment is viewed from the back side (the inside of the automobile). Herein, a door panel is shown as an example of the exterior panel100, but the exterior panel100may be a panel of another part of the automobile, such as a fender, a hood, or a roof.

As shown inFIG. 1, the exterior panel100is composed of an exterior material110and reinforcing members120. The exterior material110is formed of a steel sheet with a thickness of approximately 0.4 mm, as an example. The exterior material110is curved such that the front side forms a convex surface. The curvature of the curve runs along the vehicle height direction of the automobile (the up and down direction).

The reinforcing members120include first reinforcing members122arranged in the up and down direction and second reinforcing members124arranged in the vehicle length direction of the automobile (the horizontal direction). The first reinforcing member122is curved to follow the curvature of the exterior material110. The second reinforcing member124extends almost in a straight line; however, in the case where the exterior material110is curved, the second reinforcing member124has a shape following the curve. Both the first reinforcing member122and the second reinforcing member124are stuck to the exterior material110, and are preferably joined (adhered) to the exterior material110.

FIG. 2is a schematic diagram showing a conventional structure for comparison. InFIG. 2, a door impact bar300and a reinforce310are arranged on the inside of the exterior material110.FIG. 3toFIG. 7are diagrams showing, as the exterior panel100, automotive door panels according to the present embodiment.FIG. 3toFIG. 7are schematic diagrams showing variations of the arrangement of reinforcing members120. The example shown inFIG. 3shows an example in which only first reinforcing members122arranged in the up and down direction are provided in the exterior panel100.

Further, the example shown inFIG. 4shows an example in which only second reinforcing members124arranged in the front and rear direction are provided in the exterior panel100. The example shown inFIG. 5shows an example in which first reinforcing members122arranged in the up and down direction and second reinforcing members124arranged in the front and rear direction are provided in the exterior panel100. The example shown inFIG. 6shows an example in which reinforcing members120are arranged radially in the exterior panel100. The example shown inFIG. 7shows an example in which reinforcing members120are arranged to cross obliquely in the exterior panel100.

FIG. 8is a perspective view showing a configuration of the reinforcing member120. The basic configurations of the first reinforcing member122and the second reinforcing member124may be the same.FIG. 8shows also a cross-sectional configuration orthogonal to the longitudinal direction of the reinforcing member120. The reinforcing member120has a rectangular cross section. The reinforcing member120is produced by bending a sheet material130. In the example shown inFIG. 8, the reinforcing member120has a cross-sectional shape of a square, with one side of approximately 6 mm to 10 mm. The sheet thickness of the sheet material130forming the reinforcing member120is approximately 0.8 mm, as an example. A steel sheet may be used as the sheet material130.

As shown inFIG. 8, a prescribed gap is provided between end130aand end130bof the bent sheet material130. On the other hand, end130aand end130bmay be stuck together. Further, end130aand end130bmay be joined together by welding, adhesion, or the like. The reinforcing member120is preferably placed such that the surface on the opposite side to the surface on which ends130aand130bare located is stuck to the exterior material110. Thereby, when the reinforcing member120is curved by being pushed from the outside of the exterior panel100in the configuration in which ends130aand130bare not joined together, an event in which the cross section opens from ends130aand130band the cross-sectional shape collapses can be prevented; thus, the rigidity of the exterior panel100can be enhanced more. When being joined together, the reinforcing member120and the exterior material110may also be arranged such that the surface on which ends130aand130bof the reinforcing member120are located is joined to the exterior material110. This is because an event in which the cross section opens from ends130aand130band the cross-sectional shape collapses can be prevented by joining ends130aand130bto the exterior material110. The cross-sectional configuration of the reinforcing member120is not limited to a configuration of a closed cross section like that ofFIG. 8, and may be a gutter-like (channel) shape with a cross section in which the surface on the opposite side to the exterior material110is opened, or the hat shape shown inFIG. 20, for example.

As above, in the present embodiment, the first and second reinforcing members122and124are in contact with the exterior material110. Thereby, the area of each of the regions surrounded by the first and second reinforcing members122and124and the outline of the exterior material110is smaller than the area of the entire exterior material110; therefore, it is likely that tension will occur earlier when external force acts on the exterior material110, and hence the tensile rigidity of the exterior material110can be enhanced. It is more preferable that the exterior material110and the reinforcing member120be joined together; thus, when the exterior material110deforms, tension occurs still earlier in the exterior material110in a region between adjacent reinforcing members120, and tensile rigidity can be improved even more.

In the reinforcing member120, the second moment of area in a direction orthogonal to the longitudinal direction is set to less than or equal to 15,000 mm4, and is preferably set to less than or equal to 12,000 mm4. The material quality, the sheet thickness, and the cross-sectional shape of the sheet material130of the reinforcing member120are set so as to satisfy this condition, as appropriate. By satisfying this condition, the reinforcing member120is allowed to have a small cross-sectional shape; thus, even when a plurality of first and second reinforcing members122and124are arranged in order to enhance tensile rigidity, a large weight increase is not caused, and tensile rigidity can be improved efficiently. When the second moment of area in a direction orthogonal to the longitudinal direction of the reinforcing member120is smaller, the cross-sectional shape can be smaller, and the weight per reinforcing member120can be lighter; hence, the flexibility of the number and arrangement of reinforcing members120for tensile rigidity improvement is improved, and tensile rigidity can be improved more efficiently; however, in view of fabrication ability at the time of fixing the reinforcing member120to the exterior panel100, the second moment of area mentioned above may be set to more than or equal to 10 mm4.

The yield stress of the reinforcing member120is set to more than or equal to 500 MPa. Thereby, even when external force acts on the reinforcing member120, the occurrence of plastic deformation can be prevented; thus, tensile rigidity can be ensured effectively, and a weight reduction can be achieved.

A certain length or more of the reinforcing member120is placed along the exterior material110. Specifically, the reinforcing member120is stuck to the exterior material110in a region of more than or equal to ⅓ of the total length of the reinforcing member120. By placing the reinforcing member120such that it is stuck to the exterior material110, the tensile rigidity of the exterior panel100can be improved even when the degree of wall thickness reduction of the exterior material110is increased (for example, a wall thickness reduction from 0.7 mm to less than or equal to 0.5 mm in terms of the original thickness). The reinforcing member120and the exterior material110are more preferably stuck and joined together, and thereby the tensile rigidity of the exterior panel100can be enhanced more by causing tension to act on the exterior material110during the deformation of the exterior material110.

In particular, the first reinforcing member122is placed in the up and down direction along the direction of the curvature of the exterior material110. Thereby, the tensile rigidity of a convex curved portion that is curved so as to protrude toward the outside of the automobile can be improved. Further, the exterior material110has a concave curved portion that is curved so as to protrude toward the inside as viewed from the outside of the automobile, and the reinforcing member120overlapping with the concave curved portion is stuck to the exterior material110. The concave curved portion is inferior to the convex curved portion in tensile rigidity against a load from the outside of the automobile; thus, the tensile rigidity of the entire exterior panel can be improved effectively by placing the reinforcing member120such that it is stuck to the concave curved portion.

The reinforcing member120goes across (traverses) the exterior material110. In the present embodiment, the second moment of area of the reinforcing member120is small, and the yield stress is high (the elastic deformation region is large). Hence, in order to improve tensile rigidity as the whole of the exterior panel100, the reinforcing member120is preferably made as long as possible.

In the example shown inFIG. 5, a cross portion where the first reinforcing member122and the second reinforcing member124cross is provided. The second moment of area in a direction orthogonal to the longitudinal direction of the reinforcing member120extending from the cross portion is set to less than or equal to 15,000 mm4. When there is a cross portion, the area of a region of the exterior material sandwiched by reinforcing members120extending from the cross portion is smaller than the area of the entire surface of the exterior panel, and the ratio of the sheet thickness to the area sandwiched by reinforcing members120is relatively increased; therefore, tensile rigidity can be improved more. Thus, tensile rigidity can be improved effectively by providing a cross portion.

Further, by providing two or more cross portions, the individual region sandwiched by adjacent reinforcing members120of the exterior material110is made still smaller, and the ratio of the sheet thickness to the area of the individual region is relatively increased; therefore, tensile rigidity can be further improved. Thus, tensile rigidity can be improved effectively.

In the cross portion, concave portions122aand124aare provided in the first and second reinforcing members122and124, respectively, as described later; thereby, the thickness of each of the first reinforcing member122and the second reinforcing member124in the direction orthogonal to the exterior material110is reduced. Thereby, the first and second reinforcing members122and124and the exterior material110can be stuck and joined together also in a neighboring region including the cross portion, and tensile rigidity can be improved effectively.

Next, preferred arrangements of reinforcing members120for improving the tensile rigidity of the exterior material110are described. The periphery of the exterior material110has a relatively high tensile rigidity because another member is linked to the periphery or the periphery is supported by another member. On the other hand, a central portion of the exterior material110has a low tensile rigidity unless supported by another member. Therefore, it is mainly in a central portion of the exterior material110that the ensuring of tensile rigidity is important.FIG. 17is a schematic diagram showing arrangement positions when reinforcing members120are arranged in order to ensure tensile rigidity in the case where a door panel of an automobile is used as the exterior panel100like inFIG. 3toFIG. 7.

As shown inFIG. 17, an imaginary circle C through which reinforcing members120pass is set in the center of the exterior material110of the exterior panel100. The imaginary circle C is a circle in which, among three line segments obtained by trisecting line segment L with a length of D shown inFIG. 17, the line segment located in the center is taken as the diameter (=D/3). Line segment L is the longest line segment among the line segments each obtained by connecting any two points that are set on the outline (the edge of the outer periphery) of the exterior material110. In the case where the exterior panel100is a door panel, line segment L is a diagonal line connecting opposite angles of the door panel, as shown inFIG. 17.

After an imaginary circle C like the above is set, the reinforcing member120according to the present embodiment is placed so as to pass through the inside of the imaginary circle C. By placing the reinforcing member120such that it passes through the imaginary circle C, the reinforcing member120passes through the neighborhood of the center of the exterior material110whatever panel the exterior panel100is, such as a fender (the front portion or the rear portion), a hood, a door panel, a roof, or a trunk. Therefore, tensile rigidity can be enhanced in the neighborhood of the center of the exterior material110.

Also in the case where a plurality of reinforcing members120are arranged, at least one reinforcing member120is placed so as to pass through the inside of the imaginary circle C. Further, by arranging two or more reinforcing members120such that they pass through the inside of the imaginary circle C, tensile rigidity in the neighborhood of the center of the exterior material110can be enhanced more.

FIG. 18is a schematic diagram showing another example of positions where reinforcing members120are arranged in order to ensure tensile rigidity in the case where a door panel of an automobile is used as the exterior panel100.

In the example shown inFIG. 18, a plurality of reinforcing members120are arranged between two facing sides112and114of the exterior material110. Although inFIG. 18two reinforcing members120are arranged between two sides112and114, three or more reinforcing members120may be arranged. Further, although inFIG. 18the two facing sides112and114of the exterior material110are sides in the vehicle length direction of the door panel, they may be sides in the vehicle height direction. At least one reinforcing member120is placed more on the side112side than an intermediate line L0located in the middle between side112and side114. Further, at least one reinforcing member120is placed more on the side114side than the intermediate line L0. The direction in which each of the reinforcing members120extends is a direction along the nearer one of side112and side114.

In the present embodiment, in the arrangement of reinforcing members120shown inFIG. 18, the distance D1between adjacent two reinforcing members120is shorter than the distance D2from side112to the nearest reinforcing member120. Further, the distance D1between adjacent two reinforcing members120is shorter than the distance D3from side114to the nearest reinforcing member120.

In general, the exterior panel100is linked to another member or supported by another member on the outline of the exterior panel100. Hence, a region relatively near from the outline of the exterior material110is held by another member, and has a relatively high tensile rigidity. Therefore, the tensile rigidity of a region along side112can be ensured even when the distance D2from side112to the nearest reinforcing member120is set relatively long. Similarly, the tensile rigidity of a region along side114can be ensured even when the distance D3from side114to the nearest reinforcing member120is set relatively long.

On the other hand, the neighborhood of the intermediate line L0in the center of the exterior material110is far from side112or side114, and therefore the tensile rigidity in this portion is more likely to be reduced than in a region along side112or side114. Thus, the distance D1between adjacent two reinforcing members120is set shorter than the distance D2from side112to the nearest reinforcing member120, and thereby tensile rigidity can be enhanced in the neighborhood of the intermediate line L0in the center of the exterior material110. Similarly, the distance D1between adjacent two reinforcing members120is set shorter than the distance D3from side114to the nearest reinforcing member120, and thereby tensile rigidity can be enhanced in the neighborhood of the intermediate line L0in the center of the exterior material110.

InFIG. 18, in the case where side112and side114are not parallel, it is envisaged that the values of distances D1, D2, and D3are different in accordance with the measured positions. Hence, a line segment LP1-P2connecting the midpoint P1of side112and the midpoint P2of side114is set, and points P3and P4at which the line segment LP1-P2connecting P1and P2and reinforcing members120cross are found; D1is defined as the distance between P3and P4, D2is defined as the distance between P1and P3, and D3is defined as the distance between P4and P2.

AlthoughFIG. 18shows a case where reinforcing members120are arranged substantially parallel to side112and side114, the reinforcing member120may not be parallel to side112or114. In the present embodiment, the angle between a reinforcing member120near to side112and side112is within 30°. Further, the angle between a reinforcing member120near to side114and side114is within 30°. By thus setting the angle between a reinforcing member120and the side near to the reinforcing member120out of side112and side114within 30°, tensile rigidity in the vicinity of side112or side114can be enhanced.

FIG. 19is a schematic diagram showing arrangement positions when reinforcing members120are arranged in order to ensure tensile rigidity in the case where a roof of an automobile is used as the exterior panel100. In the case of a panel placed on an upper surface of an automobile such as a roof, the vehicle height direction does not exist in the panel. The vehicle height direction of a panel placed on a side surface of an automobile such as a door panel (the up and down direction) corresponds to the vehicle width direction of a panel placed on an upper surface of an automobile such as a roof (the left and right direction). In the example shown inFIG. 19, like inFIG. 18, three reinforcing members120are arranged between two facing sides112and114of the exterior material110. At least one reinforcing member120is placed more on the side112side than an intermediate line L0located in the middle between side112and side114. Further, at least one reinforcing member120is placed more on the side114side than the intermediate line L0. The direction in which each of the reinforcing members120extends is a direction along the nearer one of side112and side114.

Like inFIG. 18, also in the arrangement of reinforcing members120shown inFIG. 19, each of the distances D6and D7between adjacent two reinforcing members120is shorter than the distance D8from side112to the nearest reinforcing member120. Further, each of the distances D6and D7between adjacent two reinforcing members120is shorter than the distance D9from side114to the nearest reinforcing member120.

Also inFIG. 19, a region relatively near from the outline of the exterior material110is held by another member that is linked to the outline or supports the outline, and has a relatively high tensile rigidity. Therefore, the tensile rigidity of a region along side112can be ensured even when the distance D8from side112to the nearest reinforcing member120is set relatively long. Similarly, the tensile rigidity of a region along side114can be ensured even when the distance D9from side114to the nearest reinforcing member120is set relatively long.

On the other hand, the neighborhood of the intermediate line L0in the center of the exterior material110is far from side112or side114, and therefore the tensile rigidity in this portion is more likely to be reduced than in a region along side112or side114. Thus, each of the distances D6and D7between adjacent two reinforcing members120is set shorter than the distance D8from side112to the nearest reinforcing member120, and thereby tensile rigidity can be enhanced in the neighborhood of the intermediate line L0in the center of the exterior material110. Similarly, each of the distances D6and D7between adjacent two reinforcing members120is set shorter than the distance D9from side114to the nearest reinforcing member120, and thereby tensile rigidity can be enhanced in the neighborhood of the intermediate line L0in the center of the exterior material110.

Also inFIG. 19, a line segment LP1-P2connecting the midpoint P1of side112and the midpoint P2of side114is set, and points P4, P5, and P6at which the line segment LP1-P2connecting P1and P2and reinforcing members120cross are found. Then, D6is defined as the distance between P4and P5, D7is defined as the distance between P5and P6, D8is defined as the distance between P1and P4, and D9is defined as the distance between P6and P2.

Also inFIG. 19, the angle between side112or114near to a reinforcing member120and the reinforcing member120is set within 30°, and thereby tensile rigidity in the vicinity of side112or side114can be enhanced.

FIG. 13is a schematic diagram showing a cross-sectional configuration in a direction orthogonal to the longitudinal direction of each of the first and second reinforcing members122and124. As shown inFIG. 13, each of the first and second reinforcing members122and124has a cross-sectional shape of a rectangle, with a size of approximately 16 mm vertically and approximately 10 mm horizontally, as an example. Like inFIG. 8, each of the first and second reinforcing members122and124is formed by bending a sheet material130, and end130aand end130bface each other. The first and second reinforcing members122and124may not necessarily have the same cross-sectional shape (that is, the same second moment of area); and one reinforcing member may have a cross-sectional shape of a rectangle like that shown inFIG. 13, and the other reinforcing member may have a cross-sectional shape of a square like that shown inFIG. 8, for example. Further, in the case where a plurality of first reinforcing members122and a plurality of second reinforcing members124are arranged, the first reinforcing members122may not necessarily have the same cross-sectional shape either; similarly, the second reinforcing members124may not necessarily have the same cross-sectional shape either. This is because the effect of improvement in the tensile rigidity of the exterior panel100and the effect of weight reduction can be obtained with better efficiency.

In the configuration shown inFIG. 13, the side of the short side of the cross-sectional shape of a rectangle is stuck to the exterior material110. Thereby, a reinforcing member120having a cross-sectional shape with the best efficiency can be formed in order to ensure a desired second moment of area.

FIG. 20is a schematic diagram showing an example in which each of end130aand end130bof a sheet material130is bent on the opposite side to the bending side of the configuration shown inFIG. 13. The shape ofFIG. 20is referred to as a hat shape.

Also in the configuration shown inFIG. 20, the side of the short side of the cross-sectional shape of a rectangle is stuck to the exterior material110. Thereby, a reinforcing member120having a cross-sectional shape with the best efficiency can be formed in order to ensure a desired second moment of area.

FIG. 14is a characteristic diagram showing, in the configuration example ofFIG. 9andFIG. 10, relationships between the application load of an indenter140and the amount of displacement, obtained by a simulation in order to evaluate tensile rigidity.FIG. 9is a schematic diagram showing an exterior panel100(a door panel) in which first reinforcing members122are arranged in the up and down direction of the exterior material110and second reinforcing member124are arranged in the front and rear direction of the exterior material110, and shows the configuration ofFIG. 5in detail.FIG. 10is a schematic diagram showing a state viewed from the direction of arrow A ofFIG. 9.FIG. 9shows a state where the exterior panel100is viewed from the front side (from the outside of the automobile), and shows first reinforcing members122and second reinforcing members124in a state where the exterior material110is seen through. The indenter140shown inFIG. 9is a member that presses the exterior panel100in the simulation shown inFIG. 14. The simulation result shown inFIG. 14shows a case where the thickness of the exterior material110is 0.4 mm and neither the first reinforcing member122nor the second reinforcing member124is joined to the exterior material110(Invention Example 1, the characteristics shown by the solid line) and a case where the thickness of the exterior material110is 0.4 mm and the first reinforcing member122and the second reinforcing member124are joined to the exterior material110(Invention Example 2, the characteristics shown by the alternate long and two short dashes line). The simulation result shown inFIG. 14shows, for comparison, also characteristics in a case where the thickness of the exterior material110is 0.7 mm and there is no reinforcing member (the alternate long and short dash line) and characteristics in a case where the thickness of the exterior material110is 0.4 mm and there is no reinforcing member (the broken line).

The thickness of a common automotive exterior panel in current use is approximately 0.7 mm, and is equivalent to the characteristics of the alternate long and short dash line. As shown inFIG. 14, Invention Example 2 (the alternate long and two short dashes line) in which the first reinforcing member122and the second reinforcing member124are joined to the exterior material110has obtained a result in which the amount of displacement with respect to the application load is equal to or more than that in the characteristics in the case where the thickness of the exterior material110is 0.7 mm and there is no reinforcing member (the alternate long and short dash line). In particular, in Invention Example 2, when the load is more than 80 [N], the amount of displacement with respect to the application load is lower than that in the characteristics of the alternate long and short dash line. Further, in the characteristics of Invention Example 1 (the solid line) in which neither the first reinforcing member122nor the second reinforcing member124was joined to the exterior material110, the amount of displacement with respect to the application load was slightly larger than that in the characteristics of the alternate long and short dash line, but was equal to that in the characteristics of the alternate long and short dash line when the application load was approximately 200 [N]. Therefore, according to the present embodiment, a reduction in tensile rigidity can be prevented even when the thickness of the exterior material110is set to 0.4 mm, which is much thinner than at present. Thus, the thickness of the exterior material110can be reduced to, for example, approximately 0.4 mm, and the exterior panel100can be reduced in weight.

As shown by the characteristics of the broken line inFIG. 14, in the characteristics in the case where the thickness of the exterior material110is 0.4 mm and there is no reinforcing member, the amount of displacement with respect to the application load is much larger than those in the other characteristics. This shows that the exterior material110deforms largely when the exterior panel is pushed. Therefore, in the case where the thickness is 0.4 mm and there is no reinforcing member, the exterior material is difficult to use as an automotive exterior panel.

As described hereinabove, by the reinforcing member120of the present embodiment, the tensile rigidity of the exterior material110can be improved with reliability. Further, by the reinforcing member120of the present embodiment, also impact resistance properties at the time of a collision can be improved. In the following, improvement in collision resistance properties by the reinforcing member120of the present embodiment is described.

As described above, in the reinforcing member120, the second moment of area in a direction orthogonal to the longitudinal direction is set to less than or equal to 15,000 mm4, and is preferably set to less than or equal to 12,000 mm4. The material quality, the sheet thickness, and the cross-sectional shape of the sheet material130of the reinforcing member120are set so as to satisfy this condition, as appropriate. When this condition is satisfied, there is a case where not only an effect regarding improvement in tensile rigidity like that described above but also an effect regarding improvement in collision resistance properties is obtained. That is, by satisfying the condition of the second moment of area described above, the plastic buckling limit of the reinforcing member120can be increased; hence, upon reception of the input of a collision load, plastic buckling is less likely to be caused; thus, reaction force based on elastic deformation can be utilized effectively for collision resistance properties. Reaction force based on elastic deformation provides a relatively large amount of increase in reaction force against deformation, and plastic deformation has a small amount of increase in reaction force against deformation. Therefore, reaction force based on elastic deformation can be utilized effectively as collision resistance properties. If the second moment of area is set large, even small bending is likely to cause plastic buckling. In a conventional structure, the second moment of area of a door impact bar300is set to approximately 18,000 mm4, and it is assumed that collision resistance properties by plastic deformation are brought out. On the other hand, in the present embodiment, the upper limit value of the second moment of area is set as above; as a result, upon reception of the input of a collision load, the plastic buckling of the reinforcing member120is suppressed, and a collision resistance function can be brought out by elastic deformation.

Further, the yield stress of the reinforcing member120is set to more than or equal to 500 MPa. Thereby, the plastic buckling limit of the reinforcing member120can be increased, and reaction force based on elastic deformation can be utilized more effectively; thus, collision resistance properties can be improved effectively.

Further, even when the reinforcing member120is formed of a fine member, reinforcing members120serve as practical impact absorption members by crossing them. If the number of door impact bars300is only one like in a conventional structure, a hitting failure may occur depending on the position where a collision load is applied. If a plurality of door impact bars300are installed as a measure against hitting failure, a great weight increase is caused. According to the present embodiment, reinforcing members120having lighter weights than in the past can be arranged largely on the entire surface of the exterior panel100, and therefore a hitting failure can be avoided while a weight increase is suppressed. Further, since the first and second reinforcing members122and124are connected together as the reinforcing members120, a collision load applied to one reinforcing member propagates also through the other reinforcing member, and both members can absorb the impact together.

Further, in the case where the exterior material110and the reinforcing member120are joined together, the falling-in (rotation) of the reinforcing member120when the deformation of the reinforcing member120is large during collision deformation can be suppressed, and collision resistance properties can be further improved. Further, also a feature in which, during collision deformation, tension occurs in the exterior material in a region between adjacent reinforcing members120is effective. When the exterior material110is made thin, rigidity is lost, and the exterior material110becomes dented (warped) easily and is not useful for impact absorption; however, by joining the exterior material110and the reinforcing member120together to restrain the exterior material110, when the reinforcing member120deforms, the exterior material110around the deformed place is pulled in the in-plane direction. Even though the exterior material110does not have rigidity in the thickness direction, it has tensile strength in the in-plane direction, and can therefore resist tensile deformation; thus, the properties of the impact absorption member can be improved.

From the foregoing, the exterior panel100according to the present embodiment can improve not only tensile rigidity but also collision resistance properties. Thus, the effect of further weight reduction can be obtained by the simplification or omission of conventional collision resistance components. In the case where conventional collision resistance components are used, the exterior panel100according to the present embodiment can contribute to further improvement in collision safety properties.

Further, by being placed in the up and down direction along the direction of the curvature of the exterior material110, the first reinforcing member122can improve the collision resistance function of a convex curved portion that is curved so as to protrude toward the outside of the automobile.

Further, the reinforcing member120goes across (traverses) the exterior material110. In the present embodiment, the second moment of area of the reinforcing member120is small, and the yield stress is high (the elastic deformation region is large). Hence, the load and the impact at the time of a collision of the exterior panel100are caught by the entire member; thus, the reinforcing member120is preferably made as long as possible. Further, by the reinforcing member120going across the exterior material110, the setting flexibility of a support point with which the reinforcing member120that has received a collision load obtains reaction force (a contact point with another conventional component) can be enhanced. Further, by making the reinforcing member120as long as possible, the area where an impact is caught at the time of a collision can be enlarged, and collision resistance properties can be improved.

In the following, improvement in the collision resistance function of the exterior panel100by providing the reinforcing member120is described.FIG. 9is a schematic diagram showing an exterior panel100(a door panel) in which arrangement is made such that, as described above, the longitudinal direction of the first reinforcing member122is the up and down direction of the exterior material110and the longitudinal direction of the second reinforcing member124is the horizontal direction of the exterior material110, and shows the configuration ofFIG. 5in detail.

InFIG. 9, the first reinforcing member122is supported by support units220arranged at both ends in the up and down direction of the exterior panel100. Further, the second reinforcing member124is supported by support units230arranged at both ends in the up and down direction of the exterior panel100. More specifically, both ends of the first reinforcing member122are sandwiched and supported by the exterior material110and the support units220. Similarly, both ends of the second reinforcing member124are sandwiched and supported by the exterior material110and the support units230. InFIG. 9, the distance between a cross portion on the outside in the up and down direction of the vehicle or on the outside in the front and rear direction among the cross portions between the first reinforcing members122and the second reinforcing members124and a supported portion of the first reinforcing member122or the second reinforcing member124supported by the support unit220or the support unit230is within ⅓ of the length of the first reinforcing member122or the second reinforcing member124, respectively. Thereby, when a load caused by a collision is applied to reinforcing members120, the load caused by the collision can be caught by elastic deformation with good efficiency because, for example, the load applied to second reinforcing members124is applied to first reinforcing members122via cross portions and the distance from a cross portion to the supported portion of the first reinforcing member122supported by the support unit220is short.

FIG. 9shows an example in which concave portions122aand124aare provided and crossed in a cross portion between the first reinforcing member122and the second reinforcing member124and thereby the first reinforcing member122and the second reinforcing member124are arranged in the same plane. InFIG. 9, first reinforcing members122and second reinforcing members124are arranged in an interknitted manner, and the vertical arrangement of the first reinforcing member122and the second reinforcing member124is made different between adjacent cross portions.

When the first and second reinforcing members122and124are arranged in an interknitted manner, the efficiency of load transfer between the first reinforcing member122and the second reinforcing member124is improved. Thereby, at the time of a collision, an impact absorption function can be ensured effectively by the first and second reinforcing members122and124.

FIG. 11andFIG. 12are perspective views showing cross portions between the first reinforcing member122and the second reinforcing member124inFIG. 9in detail.FIG. 11corresponds to cross portion C1shown inFIG. 9, andFIG. 12corresponds to cross portion C2shown inFIG. 9. In cross portion C1, the second reinforcing member124is located more on the outside of the vehicle (on the exterior material110side) than the first reinforcing member122. Thus, the first and second reinforcing members122and124can be arranged in an interknitted manner. By concave portion122abeing provided in the first reinforcing member122and concave portion124abeing provided in the second reinforcing member124, the first reinforcing member122and the second reinforcing member124are arranged in the same plane. In cross portion C2, the first reinforcing member122is located more on the outside of the vehicle than the second reinforcing member124. Also in cross portion C2, by concave portion122abeing provided in the first reinforcing member122and concave portion124abeing provided in the second reinforcing member124, the first reinforcing member122and the second reinforcing member124are arranged in the same plane.

Although illustration is omitted, the first and second reinforcing members122and124do not necessarily need to be arranged in an interknitted manner; for a reason regarding fabrication at the time of fixing to the exterior panel100or the like, all first reinforcing members122may be arranged more on the exterior panel side than all second reinforcing members124, or conversely all second reinforcing members124may be arranged more on the exterior panel side than all first reinforcing members122.

As described above, the second moment of area in a direction orthogonal to the longitudinal direction of the reinforcing member120extending from a cross portion is less than or equal to 15,000 mm4. By providing a cross portion, the distance between a support point of bending deformation that is given to the reinforcing member120at the time of the input of a collision load and the point of application can be shortened, and therefore the amount of increase in reaction force against deformation can be further increased. Thus, collision properties can be improved effectively by providing a cross portion.

Further, by providing two or more cross portions, the distance between a support point of bending deformation that is given to the reinforcing member120at the time of the input of a collision load and the point of application can be further shortened, and therefore the amount of increase in reaction force against deformation can be increased even more. Further, an impact load can be propagated through and caught by a plurality of other reinforcing members120, and therefore still higher reaction force can be obtained. Thereby, collision properties are improved even more.

Further, by providing concave portions122aand124ain the first and second reinforcing members122and124in a cross portion, the thickness of each of the first reinforcing member122and the second reinforcing member124in the direction orthogonal to the exterior material110is reduced. Thereby, the first and second reinforcing members122and124and the exterior material110can be stuck and joined together also in a neighboring region including the cross portion, and collision properties are improved.

Further, by providing a cross portion, the first reinforcing member122and the second reinforcing member124are restrained to each other in the cross portion. Thereby, for example, in the case where the reinforcing member120has a cross section of a rectangle and the side of the short side is stuck to the exterior material110, an event in which, upon reception of a collision, the reinforcing member120experiences falling-down and the side of the long side comes close to the exterior material110can be prevented. Further, by arranging first and second reinforcing members122and124in an interknitted manner, an event in which, upon reception of a collision, the reinforcing member120experiences falling-down and the side of the long side comes close to the exterior material110can be prevented. When the spacing between cross portions is shortened, the restraint of rotation prevention is made at a short spacing, and therefore the first and second reinforcing members122and124are less likely to fall down. Thereby, a reduction in the second moment of area due to the falling-down of the reinforcing member120can be prevented, and a reduction in collision resistance properties can be prevented.

The impact absorption member needs to be supported by something and catch an impact load so that the impact absorption member does not make rigid-body movement with respect to the direction of load input. Since a load is inputted from the exterior material110, support units220and230that catch an impact load are provided on the opposite side of reinforcing members120from the exterior material110. At this time, when the point of load input to the reinforcing member120(a cross portion) and the support unit220or230are nearer, higher reaction force can be obtained with smaller deformation. In the case where the exterior panel100is a door panel, a part in contact with a door inner panel, a front pillar, a center pillar, a side sill, or the like falls under the support unit220or230. In the case of an exterior panel100other than a door, the exterior panel100may be supported by keeping support units220and230in contact with other body structure materials. For example, in the case of a panel of a roof, a part in contact with a roof side rail, a front roof rail, a rear roof rail, or the like corresponds to the support unit220or230. The support units220and230may be brought into contact with these body structure materials via other support components additionally provided, and may be supported.

In the reinforcing member120, the supported portion supported by the support unit220or230is an end portion of the reinforcing member120. Thus, by supporting end portions of the reinforcing member120, the entire reinforcing member120can be utilized for impact absorption. Further, by joining the supported portion to some other component than the exterior material, the supported portion can be restrained also in a direction other than the direction of load input; thus, collision properties can be improved, and contributions to the prevention of the falling-in of the reinforcing member120etc. can be made. The supported portion may be provided in a place other than an end portion of the reinforcing member120.

Next, the result of evaluation of the bending strength of the exterior panel100according to the present embodiment with consideration of the occasion of a collision is described on the basis ofFIG. 15andFIG. 16.FIG. 15is a schematic diagram showing a state where, in the configuration ofFIG. 9, a collision of a side surface of an automobile (a side collision) is envisaged and an application load is applied to the exterior panel100by a load application member300.

FIG. 16is a characteristic diagram showing, in the configuration ofFIG. 9, relationships between the stroke and the load when a load is applied by the load application member300.FIG. 16shows a case where a load larger than the load ofFIG. 14is applied and a stroke equivalent to the occasion of a collision is made in order to evaluate the collision resistance function. InFIG. 16, the characteristics shown by the broken line show characteristics in a case where the conventional structure shown inFIG. 2is evaluated under the same conditions for comparison. Further, the characteristics shown by the solid line correspond to Invention Example 1 in which neither the first reinforcing member122nor the second reinforcing member124is joined to the exterior material110, and the characteristics shown by the alternate long and two short dashes line correspond to Invention Example 2 in which the first reinforcing member122and the second reinforcing member124are joined to the exterior material110.

As shown inFIG. 16, in the configuration of Invention Example 1, the load is higher than the load in the conventional structure particularly when the stroke is more than or equal to 50 mm, and impact absorption properties higher than those of the conventional structure have been obtained. In the configuration of Invention Example 2, the load is higher than the load in the conventional structure in almost the entire region of the stroke, and impact absorption properties still higher than those of Invention Example 1 have been obtained. As described above, in the conventional structure, it is assumed that an impact resistance member such as a door impact bar300is caused to undergo plastic deformation; therefore, as the stroke becomes larger, plastic deformation becomes more likely to occur; thus, the rate of increase of the load due to the increase of the stroke is lower than in Invention Example 1 and Invention Example 2. On the other hand, in Invention Example 1 and Invention Example 2 according to the present embodiment, impact absorption is made in the range of elastic deformation, and therefore the rate of increase of the load due to the increase of the stroke is larger than in the conventional structure. Thus, by the configuration example ofFIG. 9, sufficient impact absorption properties can be obtained even when, for example, a side collision of a pole in which a utility pole or the like collides with the door panel occurs.

The simulation result shows that, in the configuration ofFIG. 9, plastic buckling did not occur even at strokes up to approximately 75 mm in both Invention Example 1 and Invention Example 2. Thus, according to the present embodiment, the impact of a collision can be absorbed by using the reinforcing member120as an elastic member. In Invention Example 1, the load has dropped temporarily at a stroke of approximately 65 mm; this is because part of the reinforcing member120experienced falling-down due to the fact that the reinforcing member120was not joined to the exterior material110. However, such falling-down of the reinforcing member120can be suppressed by joining the reinforcing member120and the exterior material110together like in Invention Example 2, providing a cross portion in the reinforcing member120as described above, or arranging reinforcing members120in different directions in an interknitted manner.

The first reinforcing member122and the second reinforcing member124may not be separate members, and the first and second reinforcing members122and124may be formed as one body by, for example, processing one steel sheet into a press molded body in a lattice configuration having a thin cross section. In this case, a branched place serves as a cross portion.

The exterior material110and the reinforcing member120are not limited to a steel material, and may be formed of a nonferrous metal such as aluminum, or the like, for example. Further, for example, the exterior material110may be formed of a CFRP, and ribs corresponding to first and second reinforcing members122and124may be arranged on the back side of the exterior material110. In this case, the ribs corresponding to the first and second reinforcing members122and124may be molded integrally. In this case, a branched place (a cruciform place) is regarded as a cross portion. Further, the ribs corresponding to the first and second reinforcing members122and124may be molded integrally with the exterior material110; in this case, the ribs corresponding to the first and second reinforcing members122and124are regarded as being joined to the exterior material110.

As described hereinabove, according to the present embodiment, reinforcing members120are arranged on and stuck to an exterior material110formed of an approximately 0.4-mm thin sheet, and thereby tensile rigidity can be enhanced significantly. Thus, the deformation of the exterior panel100can be prevented even when a user touches an exterior panel100formed of a thin sheet or a user pushes the exterior panel100.

As necessary, a plurality of first reinforcing members122and a plurality of second reinforcing members124may be arranged in a lattice configuration and stuck to the exterior material110, and a collision load may be caused to be absorbed principally by elastic deformation; thereby, collision resistance properties can be improved. Thus, an automotive exterior panel in which a weight reduction is achieved, tensile rigidity is improved, and collision resistance properties are excellent can be provided.

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