Vehicular front pillar

Abstract

To provide a vehicular front pillar which can be suppressed from deforming at the time of a collision of a vehicle and which can be further reduced in weight.SOLUTION: In a vehicular front pillar, when a longitudinal direction is defined as an x-axis, a direction that is orthogonal to the x-axis, in which an angle difference between the direction and a vehicle width direction is smallest is defined as a y-axis, a direction that is orthogonal to the x-axis, in which an angle difference between the direction and a vehicle height direction is smallest is defined as a z-axis, full plastic moment of a yz cross section of the front pillar is defined as Mp, and bending moment at the time when the front pillar receives a load from an x-axis direction is defined as M, a relational expression of Mp>|M| is satisfied on the whole of the yz cross section in the front pillar.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vehicle front pillar, and more particularly to a vehicle front pillar that can suppress deformation during a frontal collision of the vehicle and can also be made lighter. [Background technology]

[0002] Vehicle front pillars are made primarily from steel plates and are one of the automotive frame components that are positioned along the left and right edges of the vehicle windshield. In recent years, automotive frame components have been required to further improve safety from the perspective of passenger protection, while also being required to be lighter in weight in order to comply with fuel economy regulations and achieve carbon neutrality.

[0003] In particular, front pillars are required to protect the passenger space and deflect the impact to the rear of the vehicle body when another vehicle collides with them from the front.

[0004] For example, front pillars play a role in preventing impact on occupants by directing the impact of deformation to the rear of the vehicle. For this reason, front pillars are required to have high strength and rigidity to prevent deformation in the event of a frontal collision.

[0005] Specifically, when measuring the displacement in the longitudinal direction of the vehicle due to deformation of the front pillar and the load received by the front pillar during a frontal collision, the load increases as the displacement increases as the collision progresses, and eventually, in front pillars with low strength or low rigidity structures, the load begins to decrease at a certain point, while in front pillars with high strength and rigidity structures, the load does not decrease.

[0006] To maximize the weight of front pillars while still meeting collision safety standards, it is necessary to optimize the strength and thickness of the steel plates used, the shape of the front pillar, and the longitudinal boundaries of the front pillar where the strength and thickness change, among other factors, during the design stage of the front pillar.

[0007] As guidelines for optimizing components, Patent Document 1 proposes a cross-sectional shape for a simple hat shape. Patent Document 2 proposes a cross-sectional shape for a closed cross-section front pillar. Patent Document 3 proposes a structure in which weak parts are provided at the upper and lower ends of the front pillar. Patent Document 4 proposes an optimal design for a cross-sectional shape based on the second moment of area. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2022 / 080172 [Patent Document 2] International Publication No. 2021 / 010389 [Patent Document 3] Japanese Patent Application Publication No. 2020-050169 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-214212 Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, various methods for optimizing components have been studied up to now. However, the methods in Patent Documents 1 and 2 do not provide quantitative guidelines for the shape of the cross section perpendicular to the longitudinal direction, which is an important factor for resisting moments around the vehicle width direction.

[0010] Furthermore, the method of Patent Document 3 attempts to induce deformation at the upper or lower end, and does not propose a method for suppressing deformation of the front pillar itself.The method of Patent Document 4 is a design guideline based on the second moment of area, and does not optimize the strength of the steel plate or take into account the plastic deformation of the steel plate, leaving room for improvement.

[0011] Furthermore, in any of these methods, the optimization policy has the above-mentioned problems, and there is a problem that the weight of the front pillar cannot be reduced to the maximum extent.

[0012] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a vehicle front pillar that can suppress deformation during a frontal collision of the vehicle and can also be made lighter. [Means for solving the problem]

[0013] (1) A vehicle front pillar according to one aspect of the present invention comprises: The longitudinal direction of the vehicle front pillar is defined as an x-axis, The direction perpendicular to the x-axis and having the smallest angle difference with the vehicle width direction is defined as the y-axis, The direction perpendicular to the x-axis and having the smallest angle difference with the vehicle height direction is defined as the z-axis, The yield strength of the yz cross section perpendicular to the x axis is YP, The total plastic moment around the y-axis in the y-z cross section is defined as Mp shown in the following formula 1: When the vehicle front pillar receives a load in the x-axis direction, When the bending moment around the y-axis input to the vehicle front pillar is M, Mp>|M| is satisfied at all yz cross sections in the vehicle front pillar. Mp=∫ S z p YP p dS...(Formula 1) where: S: The yz cross section (cut surface of the front pillar) z p : The distance from the neutral axis of the infinitesimal element dS in the yz section YP p : Yield strength of the infinitesimal element dS of the yz cross section Neutral axis: The axis where compressive stress and tensile stress switch over in the yz cross section relative to M, and where the strain in the x-axis direction in the yz cross section is zero (2) In the vehicle front pillar described in (1) above, The yield moment around the y-axis in the y-z cross section is defined as My as shown in the following formula 2: When the vehicle front pillar receives the load in the x-axis direction, The elapsed time when the load is applied is defined as t, When the relationship between My and M is defined as N shown in the following formula 3, With the elapsed time t, My<|M| and d 2 N / dx 2 At the part where ≦0 d / dt(|dN / dx|)≦0 may be satisfied. My=YP y I y / z y ...(Formula 2) N=|M| / My (Equation 3) where: I y : Moment of inertia about the y-axis in the yz section z y : The distance from the neutral axis to the point where the material yields earliest due to the bending moment M, which is constantly increasing, in the yz plane at coordinate x. YP y : The strength of the part that yields earliest due to the bending moment M that increases from moment to moment in the yz plane at coordinate x dN / dx: First derivative of N in the x-axis direction d 2 N / dx 2 : The second derivative of N in the x-axis direction d / dt(|dN / dx|): Time derivative of the absolute value of dN / dx (3) In the vehicle front pillar described in (1) or (2) above, the total plastic moment Mp may vary discontinuously along the x-axis. (4) In the vehicle front pillar described in any one of (1) to (3) above, the position where the full plastic moment Mp changes discontinuously along the x-axis may be a laser welding position of the steel plate. (5) In the vehicle front pillar according to any one of (1) to (4) above, the total plastic moment Mp may vary continuously along the x-axis. (6) In the vehicle front pillar according to any one of (1) to (5) above, the yield moment My may vary discontinuously along the x-axis. (7) In the vehicle front pillar described in any one of (1) to (6) above, the position at which the yield moment My changes discontinuously along the x-axis may be a laser welding position of the steel plate. (8) In the vehicle front pillar according to any one of (1) to (7) above, the total plastic moment Mp may vary discontinuously along the x-axis. (9) In the vehicle front pillar described in any one of (1) to (8) above, the position where the full plastic moment Mp changes discontinuously along the x-axis may be a laser welding position of the steel plate. (10) In the vehicle front pillar according to any one of (1) to (9) above, the yield moment My may vary continuously along the x-axis. (11) In the vehicle front pillar according to any one of (1) to (10) above, the total plastic moment Mp may vary continuously along the x-axis. (12) In the vehicle front pillar according to any one of (1) to (11), Even when the bending moment M, which increases with the elapsed time t, reaches its maximum, the bending moment M is Mp>|M| may be satisfied. (13) In the vehicle front pillar according to any one of (1) to (12) above, Even at the time when the bending moment M, which increases with the elapsed time t, reaches a maximum, My<|M| and d 2 N / dx 2 At the part where ≦0 d / dt(|dN / dx|)≦0 may be satisfied. [Effects of the Invention]

[0014] According to the above-described aspects of the present invention, it is possible to provide a vehicle front pillar that can suppress deformation during a frontal collision of the vehicle and that can also be made lighter. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram illustrating a vehicle front pillar according to an embodiment of the present invention, showing the distribution of the total plastic moment Mp and the yield moment My that change discontinuously. FIG. [Figure 2] 1 is a diagram illustrating a vehicle front pillar according to the present embodiment, and is a diagram illustrating the distribution of index N in the front pillar. FIG. [Figure 3] FIG. 1 is a diagram illustrating a conventional vehicle front pillar, showing the distribution of index N in the front pillar. [Figure 4] 1 is a diagram illustrating a vehicle front pillar according to the present embodiment, and is a diagram illustrating the distribution of continuously changing full plastic moment Mp and yield moment My. FIG. [Figure 5] 1 is a schematic cross-sectional view showing an example of a vehicle front pillar according to an embodiment of the present invention. [Figure 6] FIG. 2 is a schematic diagram of a vehicle front pillar used in the analysis. [Figure 7] FIG. 1 is a diagram showing the analysis results of Example No. 1. [Figure 8] FIG. 10 is a diagram showing the analysis results of Examples No. 2 and No. 3. [Figure 9] FIG. 10 is a diagram showing the analysis results of Examples Nos. 4 to 6. [Figure 10] FIG. 10 is a diagram showing the analysis results of Examples No. 7 and No. 8. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention are described in detail below. However, the present invention is not limited to the configurations disclosed in the present embodiments, and various modifications are possible without departing from the spirit of the present invention. Furthermore, the drawings used in the following description may clearly show the features of the present embodiments, and the dimensional ratios of each component may not be the same as the actual ones. Furthermore, the numerical ranges described below include the lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" do not include the numerical range. "%" regarding the content of each element means "mass %."

[0017] The inventors of the present invention conducted extensive research into the strength and thickness arrangement of each part of the front pillar, as well as the state of deformation of the front pillar when hit by a frontal collision of the vehicle, with the aim of obtaining a vehicle front pillar that can suppress deformation during a frontal collision of the vehicle and also enable weight reduction. As a result, they discovered that the desired front pillar can be obtained by suitably controlling the full plastic moment Mp at each part along the longitudinal direction (x-axis) of the front pillar in accordance with the bending moment M (moment M) about the y-axis (the direction perpendicular to the x-axis and with the smallest angle with the vehicle width direction) that is input during a frontal collision of the vehicle.

[0018] Specifically, the vehicle front pillar according to this embodiment is The longitudinal direction of the vehicle front pillar is defined as the x-axis, The direction perpendicular to the x-axis and having the smallest angle difference with the vehicle width direction is defined as the y-axis, The direction perpendicular to the x-axis and having the smallest angle difference with the vehicle height direction is defined as the z-axis, Let YP be the strength of the yz section perpendicular to the x axis. The total plastic moment around the y-axis in the yz cross section is defined as Mp as shown in the following formula 1: When the vehicle front pillar receives a load in the x-axis direction, When the bending moment around the y-axis input to the vehicle front pillar is M, Mp>|M| is satisfied at all yz cross sections in the vehicle front pillar. Mp=∫ S z p YP p dS...(Formula 1) where: S: Above yz cross section (cut surface of the front pillar) z p : Distance from the neutral axis of the infinitesimal element dS in the above yz section YP p : Yield strength of the small element dS in the above yz cross section Neutral axis: The axis where compressive stress and tensile stress change over in the yz section relative to the above M, and where the strain in the x-axis direction in the yz section is zero.

[0019] Fig. 1 shows an example of a vehicle front pillar according to this embodiment in which the full plastic moment Mp is controlled in accordance with the bending moment M about the y-axis input during a collision. Fig. 1 shows, as an example, a distribution in which the full plastic moment Mp changes discontinuously.

[0020] In Fig. 1, the horizontal axis represents the longitudinal distance of the front pillar, and the vertical axis represents the magnitude of the moment. Fig. 1 also shows an example of the bending moment M about the y-axis (the direction perpendicular to the x-axis and with the smallest angle with the vehicle width direction) that is input when the vehicle is hit from the front. Note that this bending moment M is a value that varies depending on the vehicle body structure and collision conditions. Details of the bending moment M will be described later.

[0021] In the vehicle front pillar according to this embodiment, the total plastic moment Mp is increased at every location relative to the expected bending moment M. Specifically, as shown in FIG. 1, the vehicle front pillar according to this embodiment is controlled so that Mp > |M| at every location from the lower end to the upper end in the longitudinal direction of the front pillar.

[0022] In areas of the front pillar where Mp > |M|, local deformation such as buckling deformation is unlikely to occur during a collision from the front of the vehicle. However, the vehicle front pillar of this embodiment controls Mp > |M| at all areas in the longitudinal direction of the front pillar, thereby protecting the occupant space during a collision and deflecting the impact to the rear of the vehicle body.

[0023] In addition, in parts of a component where Mp<|M|, localized deformation such as buckling deformation is likely to occur in the event of a frontal collision of the vehicle. For example, components that undergo buckling deformation can be used as impact absorbing components because they can absorb the impact of a collision. However, front pillars are used as deformation suppression components to protect the passenger space in the event of a collision. For this reason, in the vehicle front pillar according to this embodiment, Mp>|M| is controlled at all longitudinal portions of the front pillar as described above.

[0024] Furthermore, in the vehicle front pillar according to this embodiment, the thickness of the steel plate can be optimized according to the location, assuming that Mp > |M| is controlled for each location, which makes it possible to reduce the overall weight of the front pillar.

[0025] Furthermore, in the vehicle front pillar according to this embodiment, the yield moment My at each portion may be preferably controlled relative to the expected bending moment M at any portion.

[0026] Specifically, the vehicle front pillar according to this embodiment is The yield moment around the y-axis in the above yz cross section is defined as My as shown in the following formula 2: When the vehicle front pillar receives the load in the x-axis direction, The elapsed time when the above load is applied is defined as t. When the relationship between the above My and the above M is defined as N shown in the following formula 3, With the elapsed time t, My<|M| and d 2 N / dx 2 At the part where ≦0 d / dt(|dN / dx|)≦0 may be satisfied. My=YP y I y / z y ...(Formula 2) N=|M| / My (Equation 3) where: I y : Moment of inertia about the y-axis in the above yz section z y : The distance from the neutral axis to the point that yields earliest due to the bending moment M that increases from moment to moment in the yz plane at coordinate x (the distance from the neutral axis to the point that yields earliest in the yz cross section according to the above t) YP y : The strength of the part that yields earliest due to the ever-increasing bending moment M in the yz plane at coordinate x (the strength of the part that yields earliest in the yz cross section according to the above t) dN / dx: First derivative of N in the x-axis direction d 2 N / dx 2 : The second derivative of N in the x-axis direction d / dt(|dN / dx|): Time derivative of the absolute value of the above dN / dx

[0027] Figure 1 shows an example in which the yield moment My is controlled in addition to the full plastic moment Mp. Figure 1 also shows a distribution in which the yield moment My changes discontinuously.

[0028] The vehicle front pillar according to this embodiment may preferably control the total plastic moment Mp and yield moment My at each portion with respect to the expected bending moment M. For example, in Fig. 1, the total plastic moment Mp and yield moment My are increased in two stages from the lower end to the upper end in the longitudinal direction of the front pillar.

[0029] To maximize the weight reduction of a front pillar, the bending moment M can be made smaller so that it exceeds the yield moment My, thereby causing the material to plastically deform. However, in a shape where My is small, Mp also becomes small, making it more likely that the bending moment M will reach the full plastic moment Mp, resulting in localized deformation.

[0030] The vehicle front pillar according to this embodiment may suppress M from reaching Mp by dispersing deformation at the portion where My<|M| is satisfied. Specifically, in the front pillar according to this embodiment, at the portion where My<|M| is satisfied and d 2 N / dx 2 ≦0, control may be performed so that d / dt(|dN / dx|)≦0 is satisfied. If d / dt(|dN / dx|)≦0, deformation is dispersed, and even if collision deformation progresses, the bending moment M is preferably prevented from reaching the full plastic moment Mp. As a result, the front pillar can protect the passenger space while diverting the impact to the rear of the vehicle body. The above-mentioned parameters will be described in detail later.

[0031] In the vehicle front pillar according to this embodiment, the above-mentioned My<|M| and d 2 N / dx 2 Similarly, the thickness of the steel plate can be optimized so that My ≧ |M| in a range other than My < |M|. As a result, it is possible to reduce the weight of the front pillar as a whole.

[0032] The vehicle front pillar according to this embodiment will be described in detail below.

[0033] The technical concept that led to the creation of the vehicle front pillar according to this embodiment will be outlined below.

[0034] (1) Of the loads and bending moments input to the front pillar during a frontal collision, the main factor in buckling of the front pillar is the bending moment M (moment M about the y axis) about the y axis (the direction perpendicular to the longitudinal direction of the front pillar and with the smallest angle difference with the vehicle width direction). By increasing the total plastic moment Mp, which is determined by the shape and material of the component, at all longitudinal parts of the front pillar rather than this moment M about the y axis, buckling during a collision becomes less likely to occur.

[0035] (2) At the same time, to maximize the weight reduction of the front pillar, the bending moment M can be plastically deformed by appropriately reducing My so that it exceeds the yield moment My. However, in a shape where the yield moment My is small, the full plastic moment Mp also becomes small, making it easier for the bending moment M to reach the full plastic moment Mp. Therefore, at the position where the bending moment M exceeds the yield moment My, the relationship between M, My, and Mp must be optimally controlled, including the full plastic moment Mp in addition to M and My.

[0036] The following describes specific features of the front pillar that satisfy the above technical concept.

[0037] < Mp=∫ S z p YP p dS > Mp represents the total plastic moment of a vehicle front pillar. In a vehicle front pillar, the longitudinal direction of the front pillar is defined as the x-axis, the direction perpendicular to the x-axis and at the smallest angle with the vehicle width direction is defined as the y-axis, and the direction perpendicular to the x-axis and at the smallest angle with the vehicle height direction is defined as the z-axis. The following equation 1 is used to calculate the total plastic moment Mp, and specifically, it is used to calculate the value of the bending moment required for the entire surface of any yz cross section (cross section perpendicular to the longitudinal direction of the front pillar) in the longitudinal direction of the front pillar to reach a plastic deformation state due to bending moment M about the y-axis, which is the main input during a frontal collision of the vehicle. Mp=∫ S zp YP p dS...(Formula 1) where: S: A cross section of the front pillar appearing on the yz plane at coordinate x, z p : the distance from the neutral axis of the infinitesimal element dS in the surface S, YP p : Yield strength of the small element dS in the above yz cross section is. The neutral axis indicates the axis along which compressive stress and tensile stress switch in the yz cross section during bending deformation, and is the axis along which the strain in the direction perpendicular to the yz plane is zero.

[0038] < Mp>|M| > In a frontal collision of a front pillar, if the front pillar buckles due to the input bending moment M, there is a risk that the front pillar may come into contact with the driver or passenger seat occupants, and the front pillar will not be able to deflect the load from the front direction to the rear. Therefore, it is important for the front pillar to have the ability to withstand the input bending moment M without deformation.

[0039] If Mp>|M| is satisfied at any position x0 in the longitudinal direction of the front pillar, and if this holds true for all positions x0 in the x-axis direction of the front pillar, then the front pillar will be less likely to buckle under bending moment M.

[0040] < My=YP y I y / z y > My represents the yield moment of a vehicle front pillar. The x-axis, y-axis, and z-axis are the same as above. Equation 2 below is a formula for calculating the yield moment My, specifically, the value of the bending moment required to reach a plastic deformation state in part of the yz cross section (cross section perpendicular to the longitudinal direction) of the front pillar due to the bending moment M about the y-axis, which is the main input during a frontal collision of the vehicle. My=YP y I y / z y ...(Formula 2) where: YP y : The strength of the part that yields earliest due to the bending moment M that increases from moment to moment in the yz plane at coordinate x I y : Moment of inertia about the y-axis in the yz-plane at coordinate x z y : The z-coordinate (distance from the neutral axis) of the position at which the specimen will yield earliest due to an increasing bending moment M in the y-z plane at coordinate x. is. The neutral axis indicates the axis along which compressive stress and tensile stress switch in the yz cross section during bending deformation, and is the axis along which the strain in the direction perpendicular to the yz plane is zero.

[0041] < N=|M| / My > N is an index for controlling the relationship between the yield moment My of a vehicle front pillar and the bending moment M input to the front pillar during a collision, and represents the ratio of the bending moment M to the yield moment My. The following equation 3 is a formula for calculating the index N, and is a formula for evaluating whether M is likely to reach Mp as collision deformation progresses. N=|M| / My (Equation 3)

[0042] < My<|M| > My<|M| indicates that the bending moment M around the y-axis input to the front pillar during a frontal collision of the vehicle is greater than the yield moment My of the vehicle's front pillar. In areas of the front pillar where My<|M|, there is a higher possibility that deformation will be concentrated locally during a collision, but the existence of areas in the front pillar where My<|M| leads to a reduction in the weight of the front pillar. On the other hand, the weight of the portion of the front pillar where My≧|M| is excessively greater than that of the portion where My<|M|.

[0043] < d 2 N / dx 2 <=0 > d 2 N / dx 2 indicates that the index N is second-order differentiated with respect to the x-axis direction, and represents the distribution pattern of the index N in the x-axis direction. As will be described later, the vehicle front pillar according to this embodiment may control d / dt(|dN / dx|). This d / dt(|dN / dx|) represents the time change in the rate of change (|dN / dx|) of the index N with respect to the position x. However, when the position x and the index N are a cubic or higher function, d 2 N / dx 2 At the inflection point where d = 0, the tendency of the change rate of index N relative to position x (|dN / dx|) changes. Therefore, in order to correctly control d / dt (|dN / dx|), 2 N / dx 2 Evaluation must be performed under conditions where ≤0.

[0044] The part where My<|M| and d 2 N / dx 2 At the location in the front pillar where x is less than or equal to 0, the function of position x and index N forms an upward convex graph that includes an inflection point. At this location, the value of N gradually increases toward the maximum point on the graph. On the other hand, d 2 N / dx 2 For the area in the front pillar where N is >0, the value of N gradually decreases as it moves away from the maximum point.

[0045] In the above, as an example, the case where the position x and the index N are a function of degree 3 or higher has been described, but in this embodiment, the position x and the index N may be a function of degree 2 or lower. For example, when the position x and the index N are a quadratic function, d 2 N / dx 2 is a negative constant, and when the position x and the index N are linear functions, d 2 N / dx 2 The value of should be zero.

[0046] < d / dt(|dN / dx|)≦0 > d / dt(|dN / dx|) represents the time derivative of the absolute value of the first-order derivative dN / dx of the index N in the x-axis direction. In other words, d / dt(|dN / dx|) represents the situation in which the rate of change (|dN / dx|) of the index N relative to the position x changes over time when the front pillar is subjected to a load due to a collision.

[0047] In the vehicle front pillar according to this embodiment, d / dt(|dN / dx|) may be controlled to be equal to or less than 0. In this case, even in a portion of the front pillar where My<|M|, the collision deformation is dispersed rather than concentrated locally, and even if the collision deformation progresses, the bending moment M is prevented from reaching the full plastic moment Mp. Note that, taking into consideration the measurement accuracy of the component dimensions, the value of d / dt(|dN / dx|) can be determined to be d / dt(|dN / dx|)≦0 when d / dt(|dN / dx|)<0.00005.

[0048] Fig. 2 shows an example of the distribution of the index N in the vehicle front pillar according to this embodiment, and Fig. 3 shows an example of the distribution of the index N in the vehicle front pillar according to the prior art.

[0049] 2 and 3, the horizontal axis represents the longitudinal distance of the front pillar, and the vertical axis represents the size of the index N. Also, in FIG. 2 and FIG. 3, d 2 N / dx 2 2 and 3, the dashed line represents the distribution of the index N at elapsed time t1, and the solid line represents the distribution of the index N at elapsed time t2. <t2である。

[0050] As shown in FIG. 2, the rate of change (|dN / dx|) of index N at the same location at t1 and t2 is exemplified; if d / dt(|dN / dx|)<0, |dN / dx| decreases with time. On the other hand, as shown in FIG. 3, the rate of change (|dN / dx|) of index N at the same location at t1 and t2 is exemplified; if d / dt(|dN / dx|)>0, |dN / dx| increases with time. Note that the case where d / dt(|dN / dx|)=0 is not shown, but in this case, |dN / dx| does not change with time.

[0051] d 2 N / dx 2 ≦0 and d / dt(|dN / dx|)>0, the rate of change of the index N (|dN / dx|) increases over time. In other words, in the front pillar, the area where |M|>My and the value of N is larger than the surrounding area is d 2 N / dx 2 If d / dt(|dN / dx|) is less than or equal to 0 and d / dt(|dN / dx|) is greater than 0, the value of N continues to increase over time. An increase in the value of index N corresponds to the bending moment M input to the front pillar approaching the collapse moment, so in this case, collision deformation tends to be concentrated in a localized area, making it difficult for the front pillar to protect the passenger space and to deflect the impact.

[0052] On the other hand, d 2 N / dx 2 ≦0 and d / dt(|dN / dx|)≦0, the rate of change of the index N (|dN / dx|) decreases or remains unchanged over time. In other words, even in the front pillar where |M|>My and the value of N is larger than the surrounding area, d 2 N / dx 2 When d / dt(|dN / dx|)≦0 and d / dt(|dN / dx|)≦0, the increase in the value of N at the maximum point is suppressed over time. In this case, the collision deformation is dispersed rather than concentrated in a specific area, allowing the front pillar to absorb the impact of the collision while protecting the passenger space.

[0053] The bending moment M about the y-axis, which is the main input when a vehicle is hit from the front, is a value that changes with the time t that has elapsed since the front pillar received the load. Therefore, the index N also changes from moment to moment during a collision from the front of the vehicle. In the vehicle front pillar according to this embodiment, it is preferable that Mp>|M| be satisfied at all yz cross sections in the front pillar even at the time when the bending moment M, which increases with the time t, reaches its maximum. Furthermore, in the vehicle front pillar, My<|M| and d 2 N / dx 2 It is preferable that d / dt(|dN / dx|)≦0 is satisfied at the site where d / dt(|dN / dx|)≦0.

[0054] For example, when a collision occurs from the front of the vehicle, the initial velocity of the colliding body at the time of collision decreases with elapsed time t as energy is absorbed by the collision, but the bending moment M increases with elapsed time t. In the vehicle front pillar according to this embodiment, it is preferable to satisfy the above condition Mp > |M|, and it is further preferable to satisfy the above condition d / dt(|dN / dx|)≦0, even when the velocity of the colliding body approaches zero and the value of the bending moment M reaches a maximum.

[0055] < Bending moment M around the y-axis input during a frontal collision > The bending moment M around the y-axis input to the front pillar during a frontal collision varies depending on the collision safety standard evaluation and the overall vehicle structure that defines the constraint conditions for the front pillar.

[0056] In the vehicle front pillar according to this embodiment, this bending moment M is not particularly limited, and can be controlled so that Mp>|M| holds true at all longitudinal portions of the front pillar based on the bending moment M determined, for example, according to the vehicle body structure into which the front pillar is incorporated and the collision safety standards required for that vehicle body.

[0057] The following conditions may be used as an example of a method for determining the bending moment M about the y-axis. For example, calculation may be performed using a full-car crash analysis. Specifically, a test may be performed using the finite element method, in which a vehicle equipped with a front pillar is crashed at an initial velocity of 64.4 km / h against a rigid wall installed on the driver's side that is 25% of the vehicle width. Furthermore, if a full-car crash analysis is difficult to perform because the overall vehicle structure is unknown, a partial structural crash analysis may be performed. Specifically, a test may be performed using the finite element method, in which the front pillar is fixed and pin-supported, with its upper and lower ends allowed to rotate about the y-axis, subjected to forced displacement in the x-axis, and unable to rotate about the x-axis or z-axis or move in the y-axis or z-axis directions. As an example of the plastic work during a front pillar collision, the finite element method may be used to simulate this test. From the results of these crash analyses, the bending moment M can be calculated by calculating the constantly changing bending moment around the y-axis at any cross section within the front pillar normalized to the x-axis, and performing this calculation at multiple cross sections. This calculation should be performed at positions that divide the distance from x=0 to the total length L into at least 100 equal parts. The shape of the front pillar can be measured using a 3D measuring device or similar and converted into electronic data. Information necessary for performing the finite element method, such as mechanical properties, can also be obtained from each part of the front pillar, and then the analysis can be performed as described above. The analysis results can be output at intervals of Δt=0.005 seconds.

[0058] < Mp or My changes discontinuously along the x-axis > In the vehicle front pillar according to this embodiment, a point may be provided where the total plastic moment Mp or the yield moment My changes discontinuously along the x-axis.

[0059] The arrangement of the total plastic moment Mp and the yield moment My in the front pillar may be set in any manner. For example, if the bending moment M is controlled to be as small as possible while satisfying Mp>|M|, the weight of the part can be reduced. One method for setting such a total plastic moment Mp is to vary the total plastic moment Mp discontinuously along the x-axis. Furthermore, for example, in a region where the bending moment M satisfies Mp>|M| and My<|M|, and 2 N / dx 2 If My is controlled so that d / dt(|dN / dx|)≦0 is satisfied in the areas where d / dt≦0, the product can be made even lighter.

[0060] In Figure 1, the point at which the values ​​of the full plastic moment Mp and the yield moment My suddenly change at the midpoint in the longitudinal direction of the front pillar corresponds to the point at which the full plastic moment Mp and the yield moment My change discontinuously. Methods for creating the point at which the full plastic moment Mp and the yield moment My change discontinuously include changing the thickness, material properties, cross-sectional shape, etc. of the adjacent steel plates.

[0061] <The point where Mp or My changes discontinuously along the x-axis is the laser welding position of the steel plate> In the vehicle front pillar according to this embodiment, the point at which the full plastic moment Mp or the yield moment My changes discontinuously along the x-axis may be the laser welding position of the steel plate.

[0062] The following method may be used as a method for providing a point where the full plastic moment Mp or the yield moment My changes discontinuously along the x-axis, and as a method for preferably reducing the weight of the front pillar. For example, a tailored blank may be used, in which blanks of multiple materials that will become the raw materials for the front pillar are trimmed from a coil, joined by laser welding, and then pressed.

[0063] Here, by arranging adjacent steel plates having different plate thicknesses and material properties, the full plastic moment Mp and the yield moment My can be discontinuously changed in a desirable manner. Furthermore, with the tailored blank, adjacent steel plates are seamlessly connected by laser welding at the points where Mp or My change discontinuously, which makes it easier to effectively transfer the impact caused by deformation to the rear of the vehicle body.

[0064] < Mp or My changes continuously along the axis > < Mp or My changes continuously along the x-axis > In the vehicle front pillar according to this embodiment, the total plastic moment Mp or the yield moment My may change continuously along the x-axis.

[0065] The arrangement of the total plastic moment Mp and the yield moment My in the front pillar may be set by any method. For example, if the bending moment M is controlled to be as small as possible while satisfying Mp>|M|, the weight of the part can be reduced. One method for setting such a total plastic moment Mp is to continuously change the total plastic moment Mp. Furthermore, for example, in a region where the bending moment M satisfies Mp>|M| and My<|M|, and d 2 N / dx 2 If My is controlled so that d / dt(|dN / dx|)≦0 is satisfied in the areas where d / dt≦0, the product can be made even lighter.

[0066] Fig. 4 shows the distribution of continuously changing full plastic moment Mp and yield moment My for a vehicle front pillar according to this embodiment. In Fig. 4, as in Fig. 1, the horizontal axis represents the distance in the longitudinal direction of the front pillar, and the vertical axis represents the magnitude of the moment, showing an example of bending moment M about the y-axis (the direction perpendicular to the longitudinal direction of the front pillar and with the smallest angle with the vehicle width direction) input during a collision from the front of the vehicle.

[0067] In Figure 4, the full plastic moment Mp and yield moment My are continuously controlled from the bottom to the top of the front pillar in the longitudinal direction. Furthermore, Mp > |M| is satisfied at all points in the front pillar in the longitudinal direction.

[0068] One method for providing a point at which the full plastic moment Mp and the yield moment My change continuously is to provide a material in which the hardness of the component changes gradually before and after the point at which the full plastic moment Mp and the yield moment My change.

[0069] Furthermore, as a method for continuously varying the total plastic moment Mp and the yield moment My along the x-axis, for example, in a hot stamp forming process for manufacturing a vehicle front pillar, the heating conditions may be changed depending on the location when heating the workpiece, the cooling conditions may be changed depending on the location when cooling the workpiece after hot stamping, or the tempering conditions may be changed depending on the location when tempering the workpiece after hot stamping.

[0070] <Other features>

[0071] Furthermore, in the vehicle front pillar according to this embodiment, the structural structure of the steel is not particularly limited, as long as the steel structure of the vehicle front pillar according to this embodiment includes martensite, tempered martensite, bainite, retained austenite, ferrite, pearlite, and the like.

[0072] However, since the vehicle front pillar according to this embodiment is premised on having high strength (hardness), it is preferable that the steel structure in each portion in the longitudinal direction of the front pillar is a structure mainly composed of martensite.

[0073] Furthermore, the vehicle front pillar according to this embodiment is intended to be a component that receives a load in the component longitudinal direction, and therefore, in order to suppress material fracture, it is preferable that the ultimate deformability is high. If the steel structure contains a small number of microvoids that serve as fracture initiation points, the ultimate deformability is increased, which is preferable. Furthermore, if the steel structure does not contain ferrite or pearlite, the concentration of plastic deformation at one location is suppressed, and the ultimate deformability is increased, which is preferable.

[0074] Furthermore, in the vehicle front pillar according to this embodiment, the chemical composition of the steel is not particularly limited. For example, the vehicle front pillar according to this embodiment may have a steel composition, in mass %, of: C: 0.08~0.70%, Si: 0.100 to 3.000%, Mn: 0.100~3.000%, P: 0.1000% or less, S: 0.0100% or less, N: 0.0200% or less, O: 0.1000% or less, Al: 3.0000% or less, B: 0.0005~0.0200%, Nb: 0 to 0.200%, Ti: 0 to 0.200% Cr: 0~1.00%, Mo: 0-1.00%, Co: 0-5.00%, Ni: 0-3.00% Cu: 0-3.00% V: 0~3.00%, W: 0~3.00%, Ca: 0 to 1.0000%, Mg: 0 to 1.0000%, REM: 0 to 1.0000%, Sb: 0 to 1.00% Zr: 0 to 1.00%, Sn: 0 to 1.00% As: 0 to 1.0000%, and the remainder is Fe and impurities.

[0075] Furthermore, the shape of the component of the vehicle front pillar according to this embodiment is not particularly limited. It may have any shape according to the design of the automobile. For example, the vehicle front pillar according to this embodiment may have a cross-sectional shape of a component that is a single hat shape or a double hat shape when viewed from the longitudinal direction. FIG. 5(a) shows, as an example, a cross-sectional schematic diagram of a front pillar whose cross-sectional shape, normal to the longitudinal direction, is a single hat shape, and FIG. 5(b) shows a cross-sectional schematic diagram of a front pillar whose cross-sectional shape, normal to the longitudinal direction, is a double hat shape.

[0076] Next, a method for measuring the characteristics of the vehicle front pillar according to this embodiment will be described.

[0077] The above-mentioned full plastic moment Mp can be calculated using commercially available CAD (computer-aided design) software, by calculating ∫ S z p YP p dS can be calculated at multiple cross sections, at least at positions that divide the distance from x=0 to the total length L into at least 100 equal parts. Specifically, the shape of the front pillar can be measured using a 3D measuring device or the like and converted into electronic data, and information necessary to calculate the full plastic moment Mp, such as proof stress, can be obtained from the yz cross section of the front pillar, after which the full plastic moment Mp can be calculated using CAD as described above.

[0078] The yield moment My mentioned above can also be calculated using commercially available CAD (computer-aided design) software, using the formula My = YP y I y / z yis calculated for multiple cross sections. This calculation should be performed at positions that divide the distance from x=0 to the total length L into at least 100 equal parts. Specifically, the shape of the front pillar is measured using a 3D measuring device or the like and converted into electronic data, and the information necessary to calculate the yield moment My, such as the strength, is obtained from the yz cross section of the front pillar, and then the yield moment My is calculated using CAD as described above.

[0079] Under the above analysis conditions, the indices N, Mp, and My are values ​​at discrete cross sections obtained by dividing the front pillar into 100 equal parts from x=0 to L (i.e., the distance Δx between adjacent cross sections is Δx=L / 100), and the above N is a value at a discrete time output every time Δt=0.0005 seconds. Therefore, from the difference values ​​of the indices N, Mp, and My between adjacent cross sections and between times, d 2 N / dx 2 and d / dt(|dN / dx|) may be calculated.

[0080] For example, for a cross section at position x among 100 cross sections obtained by dividing the front pillar into equal parts from x=0 to L, the values ​​of the indices N, Mp, and My at an arbitrary time t0 are defined as N(x, t0), Mp(x), and My(x), respectively. At this time, at position x and time t0, d 2 N / dx 2 ={N(x+Δx, t0)+N(x-Δx, t0)−2N(x, t0)} / (Δx) 2 d / dt(|dN / dx|)=(1 / Δt)(1 / Δx){|N(x+Δx, t0+Δt)―N(x, t0+Δt)|―|N(x+Δx, t0)―N(x, t0)|} Based on d 2 N / dx 2 and d / dt(|dN / dx|) may be calculated.

[0081] In addition, when the full plastic moment Mp or the yield moment My changes discontinuously along the x-axis of the front pillar, the d calculated by the above method is used at the location where the discontinuous change occurs. 2N / dx 2 In calculations, the values ​​of d and d / dt (|dN / dx|) may deviate significantly from the surroundings locally. However, the deviation of the above values ​​at the location where there is discontinuous change is a local phenomenon and does not affect the behavior of N, which changes from moment to moment. Therefore, at the local location where Mp and My change discontinuously along the x-axis of the front pillar, d 2 N / dx 2 It is not necessary to consider the judgment of d / dt(|dN / dx|).

[0082] Specifically, d at each cross section 2 N / dx 2 When determining the value of d or d / dt (|dN / dx|), if the results of the determination match three or more consecutive sections between adjacent sections, the determination result is adopted. If the results of the determination match two or less consecutive sections between adjacent sections, the results of the determination of these sections do not have to be adopted. For example, d 2 N / dx 2 When there are three or more consecutive sections where ≦0, these sections are 2 N / dx 2 Similarly, when there are three or more consecutive cross sections where d / dt(|dN / dx|)≦0, it is judged that these cross sections are d / dt(|dN / dx|)≦0. 2 N / dx 2 When there are two or fewer consecutive sections where d is ≦0, these values ​​are considered to be singular values, and the d 2 N / dx 2 Similarly, when there are two or fewer consecutive sections where d / dt(|dN / dx|)≦0, these values ​​are considered to be singular values, and the judgments of d / dt(|dN / dx|) of these sections can be replaced with the judgment results that are acceptable adjacent to these sections. 2 N / dx 2 >0 and d / dt(|dN / dx|)>0 can be determined in the same manner as above.

[0083] The length L of the front pillar in the longitudinal direction can be determined by measuring the maximum length of the front pillar in the longitudinal direction.

[0084] In the vehicle front pillar according to this embodiment, when measuring each feature, the units of each value may be as follows. Yield strength YP, YP y , Y.P. p :MPa Yield moment My: N m Fully plastic moment Mp: N m Bending moment M: N m Moment of inertia I y :mm 4 Elapsed time t: seconds distance x, z y , z p :mm yz cross section S:mm 2 Total length L:mm

[0085] The structural structure of the steel described above may be observed by the following method. The observation surface is a cross section perpendicular to the longitudinal direction, and this observation surface is polished and immersed in an acetylacetone-based electrolyte, electrolytically etched, and then observed at a magnification of 5000 times (for example, at least 625 μm) using a field emission scanning electron microscope equipped with a secondary electron detector. 2 By observing the secondary electron image in a field of view (field of view), it is possible to distinguish between ferrite and pearlite and structures other than ferrite and pearlite. A structure consisting of massive crystal grains that does not contain a substructure such as lath within the structure is considered to be ferrite. A structure consisting of layered plate-like ferrite and Fe-based carbides is considered to be pearlite.

[0086] Also, at the same observation point as above, a magnification of 10,000 times (for example, at least 150 μm 2Tempered martensite and bainite can be distinguished by observing a secondary electron image in a field of view (field of view). A structure that is an aggregation of lath-shaped crystal grains and contains Fe-based carbides with a major axis of 20 nm or more and elongated in different directions is considered to be tempered martensite. A structure that is an aggregation of lath-shaped crystal grains and does not contain Fe-based carbides with a major axis of 20 nm or more within the structure, in which Fe-based carbides have precipitated between the laths, and a structure in which Fe-based carbides have precipitated within the laths and the Fe-based carbides are elongated in the same direction is considered to be bainite.

[0087] In addition, at the same observation location as above, the observation surface is re-polished to a mirror finish, strain is removed, and crystal orientation information can be obtained by electron backscatter diffraction at measurement intervals of 0.4 μm. Regions with an fcc crystal structure are considered to be retained austenite.

[0088] Furthermore, the region other than ferrite, pearlite, tempered martensite, bainite, and retained austenite obtained by the above-mentioned method is considered to be martensite.

[0089] The chemical composition of the steel may be measured by a general steel analysis method. For example, the chemical composition may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). C and S may be measured using the combustion-infrared absorption method, N may be measured using the inert gas fusion-thermal conductivity method, and O may be measured using the inert gas fusion-non-dispersive infrared absorption method. [Example]

[0090] The effects of one aspect of the present invention will be explained in more detail using examples. However, the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved. The present invention will be explained in more detail below by illustrating examples and comparative examples.

[0091] The steel composition, in mass%, is: C: 0.08-0.70%, Si: 0.100-3.000%, Mn: 0.100-3.000%, P: 0.1000% or less, S: 0.0100% or less, N: 0.0200% or less, O: 0.1000% or less, Al: 3.0000% or less, B: 0.0005-0.0200%, Nb: 0-0.200%, Ti: 0-0.200%, Cr: 0-1.00%, Mo: 0-1.00%, Co: 0-5.00%, Ni: 0-3.00%, Cu: 0- The deformation state of a vehicle front pillar made of steel plate containing the following elements was analyzed using the finite element method (FEM): Fe: 3.00%, V: 0-3.00%, W: 0-3.00%, Ca: 0-1.0000%, Mg: 0-1.0000%, REM: 0-1.0000%, Sb: 0-1.00%, Zr: 0-1.00%, Sn: 0-1.00%, As: 0-1.0000%, with the remainder being Fe and impurities. The deformation state of a vehicle front pillar when subjected to a load in the longitudinal direction (x-axis) was analyzed using the finite element method (FEM).

[0092] Figure 6 shows the shape of a vehicle front pillar 1 used in the analysis. The bending moment M around the y-axis input to the front pillar during a collision was calculated using the finite element method under the conditions that the front pillar was joined to jigs C and D, which were joined to jigs A and B, respectively, and jigs A and B were free to rotate around the y-axis, and jig A was forced to displace in the x-axis direction at an initial velocity of 1000 mm / s. In the finite element method analysis, the elements were 2 mm square shells, and the R part of the member was divided into seven elements. The analysis results were output at intervals of Δt = 0.00005 seconds. The x-axis velocity of jig A was controlled with a uniform deceleration so that it reached 0 at 0.005 seconds (displacement of 5 mm).

[0093] Additionally, the total plastic moment Mp and yield moment My of the vehicle's front pillar were controlled by laser welding materials with different material properties together and then pressing, or by partially tempering the front pillar after pressing. These total plastic moments Mp and yield moments My were calculated using CAD (computer-aided design) software. In the CAD calculations, the front pillar was divided into 100 equal parts from x = 0 to the total length L, and Mp and My were calculated for each yz cross section.

[0094] The above analysis results are summarized in Table 1. Table 1 also shows the analysis results 0.0005 seconds before the time when the velocity of jig A in the x-axis direction became 0 (elapsed time t4, described later). In Table 1, "Condition a" indicates whether Mp>|M| is satisfied in all yz cross sections in the front pillar, and "Condition b1" indicates whether My<|M| and d 2 N / dx 2 ≦0, and "Condition b2" indicates whether My<|M| and d 2 N / dx 2 "Condition c" indicates whether d / dt(|dN / dx|) ≦ 0 is satisfied at the point where d / dt ≦ 0 is satisfied. "Condition c" indicates whether the full plastic moment Mp and the yield moment My change continuously, discontinuously, or mixed (continuous + discontinuous) along the x-axis of the front pillar. In Table 1, "Crash Performance" indicates whether excessive deformation at the point where early buckling occurs during a frontal collision is suppressed. The table shows "Excellent (EX.)," "Good," "Fair," and "Bad" in order of superiority. A score of "Fair" or better indicates that deformation during a frontal collision is suppressed. In Table 1, "Lightweight" indicates whether optimization of the steel plate thickness enabled weight reduction for the entire front pillar. The table shows "Excellent (EX.)," "Good," "Fair," and "Bad" in order of superiority. A score of "Fair" or better indicates that weight reduction for the entire front pillar is possible.

[0095] The above-mentioned "crash performance" and "weight reduction" were evaluated as follows. For example, the "crash performance" was evaluated as follows. When the load in the x-axis direction received by jig A is measured over time, the load gradually increases as the collision progresses, protecting the passenger space during the collision and diverting the impact to the rear of the vehicle. On the other hand, if localized deformation such as buckling is likely to occur during the collision, the load decreases at a certain point, making it difficult to protect the passenger space and to divert the impact to the rear of the vehicle. If the maximum load (hereafter referred to as Fmax) during the movement of jig A is small, it can be said that collision deformation is likely to be concentrated in a localized area. Specifically, when Fmax < 75kN, the "crash performance" was judged to be "Bad." When 75 ≦ Fmax < 100kN, the "crash performance" was judged to be "Fair." When 100 ≦ Fmax < 135kN, the "crash performance" was judged to be "Good." When 135kN ≦ Fmax, the "crash performance" was judged to be "Excellent (EX.)." Additionally, "weight reduction" was evaluated based on the weight of the front pillar (hereafter referred to as m) shown in Figure 6, which was used in the analysis. When m<2.5 kg, "weight reduction" was judged to be "Excellent (EX.)". When 2.5≦m<3.5 kg, "weight reduction" was judged to be "Good". When 3.5≦m<4.5 kg, "weight reduction" was judged to be "Fair". When 4.5 kg≦m, "weight reduction" was judged to be "Bad".

[0096] Note that under the above analysis conditions, the above Mp, My, and N are values ​​at discrete cross sections obtained by dividing the front pillar into 100 equal parts from x=0 to L (i.e., the distance Δx between adjacent cross sections is Δx=L / 100), and the above N is also a value at a discrete time output every time Δt=0.0005 seconds. Therefore, it was evaluated whether the above conditions a, b1, and b2 were satisfied from the difference values ​​of Mp, My, and N between adjacent cross sections and between times.

[0097] Specifically, for a cross section at position x among 100 cross sections obtained by dividing the front pillar into equal parts from x=0 to x=L, the values ​​of Mp, My, and N at any time t0 may be defined as Mp(x), My(x), and N(x, t0), respectively. At this time, at position x and time t0, d 2 N / dx 2 ={N(x+Δx, t0)+N(x-Δx, t0)−2N(x, t0)} / (Δx) 2 d / dt(|dN / dx|)=(1 / Δt)(1 / Δx){|N(x+Δx, t0+Δt)―N(x, t0+Δt)|―|N(x+Δx, t0)―N(x, t0)|} It is required as follows. In addition, d 2 N / dx 2 The value of and the value of d / dt(|dN / dx|) may be determined based on the above-mentioned method.

[0098] As mentioned above, under the above analysis conditions, the values ​​of Mp and My are values ​​at discrete cross sections. It is also possible to evaluate whether or not these Mp and My satisfy condition c by increasing the number of cross sections into which the front pillar is divided and minimizing the value of the distance Δx between the cross sections. However, condition c shown in Table 1 shows the results of evaluation based on the manufacturing method of the component. In other words, the changes in Mp and My were considered "discontinuous" at the boundary between sections where materials with different material properties were joined by laser welding and then press-processed. Furthermore, the changes in Mp and My were considered "continuous" at the boundary between sections that were partially tempered after press-processing and sections that were not tempered.

[0099] [Table 1]

[0100] The analysis results of Test No. 1 shown in Table 1 are shown in Figures 7(a) to 7(d). In Figures 7(a) to 7(d), the horizontal axis indicates the position in the longitudinal direction (x-axis direction) of the front pillar, the vertical axis indicates the magnitude of the moment, and the diagrams show the bending moment M about the y-axis, which changes with elapsed time (t1 to t4). As shown in Figures 7(a) to 7(d), the bending moment M increases with elapsed time. As shown in Figure 7(d), in Test No. 1, Mp<|M| became true at elapsed time t4. Therefore, deformation during a collision could not be suppressed favorably.

[0101] The analysis results for Test No. 2, listed in Table 1, are shown in Figure 8(a), and the analysis results for Test No. 3 are shown in Figure 8(b). In Figures 8(a) and (b), the horizontal axis indicates the longitudinal position of the front pillar (x-axis direction), and the vertical axis indicates the magnitude of the moment. As shown in Figures 8(a) and (b), Test No. 2 and Test No. 3 satisfied the condition Mp > |M| even at elapsed time t4. Therefore, deformation during a collision was suppressed. Weight reduction was also satisfactory.

[0102] The analysis results of Test No. 4 shown in Table 1 are shown in Figure 9(a), the analysis results of Test No. 5 are shown in Figure 9(b), and the analysis results of Test No. 6 are shown in Figure 9(c). In Figures 9(a) to 9(c), the horizontal axis indicates the position in the longitudinal direction (x-axis direction) of the front pillar, and the vertical axis indicates the magnitude of the moment. As shown in Figures 9(a) to 9(c), Tests No. 4 to No. 6 satisfied Mp > |M| even at elapsed time t4. Therefore, deformation during a collision was suppressed. Weight reduction was also satisfactory. Although not shown in the figures, Tests No. 5 and No. 6 not only satisfied Mp > |M|, but also contained My < |M| and d 2 N / dx 2 ≦0, and My<|M| and d 2 N / dx 2 The condition d / dt(|dN / dx|)≦0 was satisfied in the areas where d / dt(|dN / dx|)≦0 was satisfied. Therefore, deformation during a collision was preferably suppressed. Weight reduction was also preferably satisfied.

[0103] The analysis results of Test No. 7 shown in Table 1 are shown in Figure 10(a), and the analysis results of Test No. 8 are shown in Figure 10(b). In Figures 10(a) and 10(b), the horizontal axis indicates the position in the longitudinal direction (x-axis direction) of the front pillar, and the vertical axis indicates the magnitude of the moment. As shown in Figures 10(a) and 10(b), Test No. 7 and Test No. 8 satisfied Mp > |M| even at elapsed time t4. Although not shown in the figures, Test No. 7 and Test No. 8 also satisfied the condition My < |M| and d 2 N / dx 2 ≦0, and My<|M| and d 2 N / dx 2 The condition d / dt(|dN / dx|)≦0 was satisfied in the areas where d / dt(|dN / dx|)≦0 was satisfied. Therefore, deformation during a collision was preferably suppressed. Weight reduction was also preferably satisfied.

[0104] Although the analysis results of Test Nos. 9 to 13 shown in Table 1 are not shown, these Test Nos. 9 to 13 satisfied Mp>|M|. Therefore, deformation during a collision could be suppressed. Weight reduction was also satisfactory. In addition, among the tests No. 9 to 13, No. 9 and No. 10 are further tested for My<|M| and d 2 N / dx 2 The condition d / dt(|dN / dx|)≦0 was satisfied in the areas where d / dt(|dN / dx|)≦0 was satisfied. Therefore, deformation during a collision was preferably suppressed. Weight reduction was also preferably satisfied. [Industrial Applicability]

[0105] According to the above aspects of the present invention, it is possible to provide a vehicle front pillar that can suppress deformation during a frontal collision of the vehicle and can also be made lighter, thereby having high industrial applicability. [Explanation of symbols]

[0106] 1. Front pillar for vehicle Mp Full plastic moment Mp My Surrender Moment M is the bending moment around the y-axis (the direction perpendicular to the longitudinal direction of the front pillar and with the smallest angle with the vehicle width direction) input during a frontal collision.

Claims

1. In front pillars for vehicles The longitudinal direction of the vehicle front pillar is defined as an x-axis, The direction perpendicular to the x-axis and having the smallest angle difference with the vehicle width direction is defined as the y-axis, The direction perpendicular to the x-axis and having the smallest angle difference with the vehicle height direction is defined as the z-axis, The yield strength of the yz cross section perpendicular to the x axis is YP, The total plastic moment around the y-axis in the y-z cross section is defined as Mp shown in the following formula 1: When the vehicle front pillar receives a load in the x-axis direction, When the bending moment around the y-axis input to the vehicle front pillar is M, Mp>|M| is satisfied in all yz cross sections in the vehicle front pillar, A front pillar for a vehicle. Mp=∫ Ｓ z ｐ •YP ｐ dS ・・・(Formula 1) where: S: the yz cross section (cut surface of the front pillar) z ｐ : Distance from the neutral axis of the infinitesimal element dS in the yz section YP ｐ : proof stress at the infinitesimal element dS of the yz cross section Neutral axis: An axis along which compressive stress and tensile stress switch in the yz cross section relative to M, and on which the strain in the x-axis direction becomes zero in the yz cross section

2. In the vehicle front pillar, The yield moment around the y-axis in the y-z cross section is My shown in the following formula 2: When the vehicle front pillar receives the load in the x-axis direction, The elapsed time when the load is applied is defined as t, When the relationship between My and M is defined as N shown in the following formula 3, With the elapsed time t, My<|M| and d ２ N / dx ２ At the part where ≦0 d / dt(|dN / dx|)≦0 fulfill, 2. The front pillar for a vehicle according to claim 1. My = YP ｙ ・I ｙ / z ｙ ・・・(Equation 2) N=|M| / My...(Formula 3) where: I ｙ : second moment of area around the y-axis in the y-z cross section z ｙ : The distance from the neutral axis to the point at which the bending moment M increases most rapidly in the yz plane at coordinate x. YP ｙ : The strength of the part that will yield earliest due to the ever-increasing bending moment M in the yz plane at coordinate x dN / dx: first derivative of N in the x-axis direction d ２ N / dx ２ : second derivative of N in the x-axis direction d / dt(|dN / dx|): time derivative of the absolute value of dN / dx

3. 2. The vehicle front pillar according to claim 1, wherein the total plastic moment Mp varies discontinuously along the x-axis.

4. 4. The vehicle front pillar according to claim 3, wherein the position where the total plastic moment Mp changes discontinuously along the x-axis is a laser welding position of the steel plate.

5. 2. The vehicle front pillar according to claim 1, wherein the total plastic moment Mp varies continuously along the x-axis.

6. 3. The vehicle front pillar according to claim 2, wherein the yield moment My varies discontinuously along the x-axis.

7. 7. The vehicle front pillar according to claim 6, wherein the position at which the yield moment My changes discontinuously along the x-axis is a laser welding position of the steel plate.

8. 7. The vehicle front pillar according to claim 6, wherein the total plastic moment Mp varies discontinuously along the x-axis.

9. 9. The front pillar for a vehicle according to claim 8, wherein the position where the total plastic moment Mp changes discontinuously along the x-axis is a laser welding position of the steel plate.

10. 3. The vehicle front pillar according to claim 2, wherein the yield moment My varies continuously along the x-axis.

11. 11. The vehicle front pillar according to claim 10, wherein the total plastic moment Mp varies continuously along the x-axis.

12. Even when the bending moment M, which increases with the elapsed time t, reaches a maximum, the bending moment M is Mp>|M| fulfill, 12. The front pillar for a vehicle according to claim 1.

13. Even at the time when the bending moment M, which increases with the elapsed time t, reaches a maximum, My<|M| and d ２ N / dx ２ At the part where ≦0 d / dt(|dN / dx|)≦0 fulfill, 13. The front pillar for a vehicle according to claim 12.

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