Automotive component design method

Abstract

This method for designing automotive components includes a strength calculation step that calculates the strength of the automotive component using a fiber model, and an energy absorption calculation step that calculates the energy absorption of the automotive component using a spring-mass model.In the strength calculation step, initial conditions are set for the automotive component to calculate the axial force and moment calculated at a cross section at any position of the automotive component, as well as the strength and deformation mode for each cross section.In the energy absorption calculation step, initial conditions are set for a spring-mass model having spring load-compression characteristics determined based on the strength and deformation mode for each cross section, and the relationship between the load and compression of the automotive component, or the relationship between the energy absorption and compression, is determined.

Description

[Technical Field]

[0001] The present invention relates to a method for designing an automobile component. [Background technology]

[0002] 2. Description of the Related Art Automotive structural members (hereinafter, automotive structural members will be simply referred to as automotive members) are required to have excellent crash safety performance, and such automotive members are being developed and designed.

[0003] For example, Patent Document 1 discloses an occupant impact simulation method for a frontal vehicle collision using a dynamic model of a vehicle body and occupants, which includes the steps of: setting the buckling characteristics of the front part of the vehicle body at the time of collision in the dynamic model as a nonlinear spring; and setting the seat belt restraining the occupant to the seat as a linear spring or a nonlinear spring; calculating occupant deceleration while changing the characteristics of the nonlinear spring that represent the buckling characteristics of the front part of the vehicle body as a parameter; and outputting design guideline information for the front part of the vehicle body rigidity based on the ride-down effect from the nonlinear spring characteristics that bring about the minimum value of the occupant deceleration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2005-291841 Summary of the Invention [Problem to be solved by the invention]

[0005] Indicators of the collision safety performance of automotive components include strength, energy absorption-compression, and load-compression characteristics. To achieve the required strength and energy absorption, the design of automotive components is often carried out in the following order: steps (1) to (4). Step (1) Manual calculation of strength and rough cross-sectional shape Step (2) Creating a 3D model of the automotive component Step (3) Creating an FEM (Finite Element Method) model Step (4) Analysis using a CAE (Computer Aided Engineering) model that simulates the actual state of the system installed in a vehicle (full vehicle state) (full vehicle CAE) If the results of the full vehicle CAE do not satisfy the required performance, the above steps (1) to (4) are repeated until the required performance is satisfied.

[0006] In recent years, there has been a demand for shortening development schedules for automotive components, and there is a need to reduce the number of repetitions of steps (1) to (4) as much as possible. To achieve this, computer-based crash simulations are being used to shorten design periods. However, creating FEM models and full vehicle CAE in particular require a large number of man-hours. Therefore, in order to reduce the number of repetitions, it is important to design automotive components with as high precision as possible in steps (1) and (2).

[0007] However, in the manual strength calculation of step (1), it is common to use a full plastic axial force or a full plastic moment, but this method is a strength calculation method that assumes that only one of a compressive axial force or a bending moment is applied to the automobile components. On the other hand, in the event of an automobile collision, a compressive axial force and a bending moment are often input to the automobile components simultaneously, so the above-mentioned manual strength calculation does not match the actual situation and has low accuracy.

[0008] Furthermore, with conventional methods, it is not possible to accurately determine the energy absorption-compression characteristics (i.e., the relationship between energy absorption and compression) and the load-compression characteristics (i.e., the relationship between load and compression) without prior testing or full vehicle CAE. Therefore, in order to obtain accurate performance values, designers must wait for the calculation results and crash test results of step (4), which requires time and effort for design revisions.

[0009] It is possible to easily calculate the energy absorption-compression characteristics and load-compression characteristics using a spring-mass model that simulates an automotive component with multiple springs and mass points. In this case, the spring constant is set based on the designer's experience, crash test results, or FEM analysis results. If the designer has little experience, the spring constant setting accuracy is low, making it difficult to design an automotive component that satisfies the required crash safety performance using calculations using a spring-mass model. Furthermore, when the spring constant is set based on crash test results or FEM analysis results, it takes a lot of time and effort to set the spring constant. Therefore, calculating the energy absorption-compression characteristics and load-compression characteristics using the conventional spring-mass model is not practical.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a method for designing automotive components that can design automotive components that satisfy the required collision safety performance in a short period of time. [Means for solving the problem]

[0011] The inventors came up with the idea of ​​calculating the strength and deformation mode using a fiber model that can input a combination of axial force and moment, and then setting up a spring-mass model with a spring constant calculated based on these, thereby serially calculating the strength, as well as the characteristics of energy absorption-compression and load-compression.

[0012] The gist of the present invention, which was made based on the above findings, is as follows. [1] A design method for an automotive component according to one aspect of the present invention includes a strength calculation step of calculating the strength of the automotive component using a fiber model, and an energy absorption calculation step of calculating the energy absorption of the automotive component using a spring-mass model. In the strength calculation step, the cross-sectional shape, plate thickness, material, and cross-sectional arrangement of the automotive component are set, and the axial force and moment calculated at a cross-section at any position of the automotive component, as well as the strength and deformation mode for each cross-section, are calculated. In the energy absorption calculation step, the spring-mass model is set to have spring load-compression characteristics determined based on the strength and deformation mode for each cross-section, and initial conditions are given to the spring-mass model that limit the initial velocity, the weight of the mass point, and the amount of movement of the mass point, thereby determining the relationship between the load and compression, or the relationship between the energy absorption and compression, of the automotive component. [2] In the method for designing an automobile component described in [1] above, the spring-mass model has one or more springs and a plurality of mass points, the springs are connected in at least one of series and parallel via the mass points, one end of the spring-mass model is a fixed end, the spring load-compression amount characteristic for each spring is a yield strength at the time when deformation of the automobile component starts in each of the cross sections, and the yield strength calculated in the yield strength calculation step is a component yield strength F peak and the energy absorption load F that simulates the energy absorption after the start of the deformation. ea The above spring load-compression characteristic is determined by the compression stop compression amount L that satisfies the following formula (1): stop Compression stop load F stop is set, and the compression amount of the spring is the energy absorption start compression amount L ea If the spring load is less than the member strength F peak and the compression amount is the energy absorption start compression amount L ea The above compression stop compression amount L stop Below this, the spring load is equal to the energy absorption load F ea and the above energy absorption load F ea is a function F of the compression amount L that satisfies the following equation (2). ea (L) may also be used. 0 <L ea <L stop ≦L spring …(1) formula 0 <F ea (L)≦F peak …(2) formula In the above formula (1), L spring is the length of the spring before compression. [3] In the method for designing an automotive component described in [2] above, a weight calculated from the density of the material constituting the automotive component, the cross-sectional area of ​​the automotive component, and the length may be set for the mass point. [4] In the method for designing an automobile component according to the above [2] or [3], in the spring mass model, a mass point having a weight corresponding to the vehicle compartment and arranged at one end opposite to the fixed end, and one or more mass points having a weight corresponding to an internal object of the vehicle body are set, an element is defined that limits the amount of movement of the mass point corresponding to the vehicle compartment and the mass point corresponding to the internal object of the vehicle body, and the distance between the mass point corresponding to the vehicle compartment and the fixed end is defined as L A , the distance between the mass point corresponding to the internal object of the vehicle body and the fixed end is L Bi (i is a natural number), the amount of movement of the mass point corresponding to the above-mentioned compartment is D A , and the amount of movement of the mass point corresponding to the above-mentioned built-in object is D Bi (i is a natural number), the following equations (3) and (4) may be satisfied. 0.3≦D A / L A ≦0.6 …Equation (3) 0.3≦D Bi / L Bi ≦0.7 …(4) formula [5] In the design method for an automobile member according to any one of [2] to [4] above, the function F is different depending on whether the deformation mode is an axial crushing mode in which no tensile stress acts in the cross section or a bending deformation mode in which tensile stress acts in the cross section. ea (L) may be set. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a method for designing an automobile component that can design an automobile component that satisfies the required collision safety performance in a short period of time. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic block diagram showing the functional configuration of a design device for an automobile component; [Figure 2] 1 is a flow diagram of a design method for an automotive component according to an embodiment of the present invention. [Figure 3] FIG. 10 is a flow diagram of a proof stress calculation step in the same embodiment. [Figure 4] FIG. 10 is an explanatory diagram for explaining a proof stress calculation step. [Figure 5] FIG. 10 is an explanatory diagram for explaining a proof stress calculation step. [Figure 6] FIG. 10 is a flow diagram of an energy absorption calculation step. [Figure 7] 1 is a schematic graph of the load-compression amount characteristics of an automobile member in which the deformation mode is an axial crushing mode. [Figure 8] 1 is a schematic graph of the load-compression amount characteristics of an automobile member in which the deformation mode is a bending deformation mode. [Figure 9] FIG. 2 is a schematic diagram illustrating an example of a spring-mass model. [Figure 10] FIG. 10 is a schematic diagram for explaining the correspondence between an automobile member and a spring mass model. [Figure 11] FIG. 10 is another schematic diagram for explaining the correspondence between an automobile member and a spring mass model. [Figure 12] 10 is a schematic graph showing the relationship between spring load and compression amount characteristics for each spring. [Figure 13] FIG. 10 is a schematic diagram for explaining an example of the weight of a mass point to be set. [Figure 14] FIG. 10 is a schematic diagram for explaining another example of the weight of a mass point to be set. [Figure 15] FIG. 15 is a diagram showing a part of the schematic diagram shown in FIG. [Figure 16] FIG. 2 is a schematic diagram illustrating an example of a spring-mass model. [Figure 17] (A) is an example of a graph showing the displacement of a vehicle from the start of a collision when the amount of movement DA of a mass point corresponding to the passenger compartment is set to a predetermined value, (B) is an example of a graph showing the change in the amount of collision energy absorbed by automobile components from the start of the collision, (C) is a graph showing the relationship between the amount of energy absorbed and the amount of compression of automobile components, and (D) is a graph showing the relationship between the load acting on the automobile components and the amount of compression. [Figure 18] 10 is a graph showing a relative comparison of the yield strength of the crushing portion calculated by each calculation method in the examples. [Figure 19] 10 is a graph showing a relative comparison of the yield strength of the bending deformation portion calculated by each calculation method in the examples. [Figure 20] 10 is a graph showing the relationship between the average load calculated by full vehicle CAE in the example and the average load calculated by the energy absorption calculation method in the design method of the embodiment according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] <Design device 1> First, an automotive component design device capable of implementing an automotive component design method according to an embodiment of the present invention will be described. Fig. 1 is a schematic block diagram showing the functional configuration of the automotive component design device 1. The design device 1 includes a control unit 10, an input unit 20, an output unit 30, and a storage unit 40.

[0016] The control unit 10 is configured using a processor such as a CPU (Central Processing Unit) and a memory (main storage device). All or part of the functions of the control unit 10 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0017] The control unit 10 controls various operations of the design device 1. The control unit 10 includes a strength calculation unit 11, an energy absorption amount calculation unit 12, and a determination unit 13.

[0018] The strength calculation unit 11 calculates the strength of the automobile member using the fiber model. In addition, the strength calculation unit 11 calculates the axial force, moment, and axial force / moment ratio of each cross section determined in advance in the automobile member, as well as the strength and deformation mode for each cross section, in order to generate the fiber model.

[0019] The energy absorption calculation unit 12 calculates the energy absorption of the automotive component using a spring-mass model. The energy absorption calculation unit 12 sets a spring-mass model having spring load-compression characteristics based on the yield strength and deformation mode of each cross section. Specifically, the spring load-compression characteristics are set based on the yield strength and deformation mode of each cross section calculated by the yield strength calculation unit 11 and a predefined distance between cross sections. The distance between cross sections corresponds to the length of the spring. The energy absorption calculation unit 12 also calculates the relationship between the load and compression of the automotive component, or the relationship between the energy absorption and compression, based on the initial velocity, mass point weight, and initial conditions that limit the mass point movement, all of which are given to the spring-mass model. The initial velocity, mass point weight, and initial conditions that limit the mass point movement are given by the designer. The initial velocity given to the spring-mass model is the initial velocity of the mass point set to simulate the weight of the vehicle cabin, internal components, or automotive component.

[0020] The determination unit 13 determines whether the overall strength of the automobile component calculated by the strength calculation unit 11 is equal to or greater than the required strength. The determination unit 13 also determines whether the energy absorption amount calculated by the energy absorption amount calculation unit 12 is equal to or greater than the required energy absorption amount.

[0021] The input unit 20 is configured using existing input devices such as a keyboard, a pointing device (mouse, tablet, etc.), buttons, a touch panel, etc. The input unit 20 is operated by a user such as a designer. The designer inputs the member shape, cross-sectional shape, wall thickness, and material via the input unit 20 in the strength calculation step, and inputs the initial conditions that limit the initial velocity, mass point weight, and mass point movement amount in the energy absorption calculation step.

[0022] The output unit 30 is an image display device such as a display or an organic EL (Electro Luminescence) display. The output unit 30 can output various information input by the input unit 20, the calculated axial force, moment, axial force / moment ratio, deformation mode, and yield strength for each cross section, as well as the yield strength of the automobile component. The output unit 30 can also output a spring-mass model and the relationship between load and compression amount of the automobile component, or the relationship between energy absorption amount and compression amount. In addition, the information to be output may be any information related to the design device 1. The output unit 30 may be configured as a touch panel integrated with the input unit 20.

[0023] The storage unit 40 is configured using a storage device such as a magnetic hard disk drive, a semiconductor storage device, etc. The storage unit 14 stores various data used by the control unit 10 and data required when the control unit 10 performs processing.

[0024] <Design method for automotive components> Fig. 2 is a flow diagram of a design method for an automotive component according to one embodiment of the present invention. As shown in Fig. 2, the design method for an automotive component according to this embodiment includes a strength calculation step (step S1) for calculating the strength of the automotive component, a first determination step (step S2), an energy absorption calculation step (step S3) for calculating the energy absorption amount of the automotive component using a spring-mass model, and a second determination step (step S4).

[0025] (Strength calculation step S1) In the strength calculation step S1, the strength calculation unit 11 calculates the strength of the automotive component using a fiber model. In this step, the designer sets the cross-sectional shape, plate thickness, material, and cross-sectional arrangement of the automotive component via the input unit 20. Based on the set information, the strength calculation unit 11 calculates the axial force and moment calculated at a cross section at any position of the component, as well as the strength and deformation mode for each cross section.

[0026] An example of the strength calculation step will be described with reference to Figures 3 to 5. Figure 3 is a flow diagram of the strength calculation step. Figures 4 to 5 are explanatory diagrams for explaining the strength calculation step.

[0027] First, the designer defines the rough shape of the automotive component (step S101). In step S101, the designer sets multiple coordinate points via the input unit 20 for calculating axial forces and moments. If the shape of the automotive component has not been defined, the rough shape of the automotive component is defined by setting coordinate points. In addition, if the thickness and cross-sectional shape at the coordinate points are defined, a cross-sectional layout is performed in which cross-sections of the defined thickness and shape are arranged with the set coordinate points as their centroids. If the shape of the automotive component has already been defined, the centroids of each cross-section are calculated from cross-sections obtained by dividing the automotive component into sections, and the centroids are set as coordinate points to define the rough shape of the automotive component. Next, the designer inputs a load to one end coordinate point (first coordinate point) of the multiple coordinate points via the input unit 20. The strength calculation unit 11 calculates the axial force and moment at an arbitrary position (second coordinate point) of the automotive component, and calculates the axial force / moment ratio from the calculated axial force and moment (step S103). The position where the load is expected to be first applied when a vehicle collides is defined as the load input position (first coordinate point). The magnitude of the load is the magnitude of the load expected to be applied during a collision. The moment (bending moment) is calculated by multiplying the input load by the offset between the load input position (first coordinate point) and the second coordinate point (the component perpendicular to the load direction of the distance between the load input position and the second coordinate point). If the FEM analysis results of the vehicle body that forms the basis of the design have already been obtained, and the axial force and moment at any position (coordinate point) of the vehicle component on that vehicle body are known, the axial force / moment ratio may be calculated based on these.

[0028] Next, for each coordinate point, the designer defines the shape of the cross section including that coordinate point, and the thickness and material of the automobile part (step S105) via the input unit 20. The shape of the cross section including the coordinate point, and the thickness and material of the automobile part are set arbitrarily by the designer so as to satisfy the collision safety performance required of the automobile part.

[0029] The strength calculation unit 11 inputs the axial force and moment calculated in step S103 to each defined cross section (step S107). In detail, the strength calculation unit 11 associates the axial force or the axial force and the moment, and the ratio of the moment to the axial force, with each cross section.

[0030] For each of the cross sections described above, the strength calculation unit 11 generates a fiber model by dividing the cross section into fibers (step S109), and determines the deformation mode for each cross section (step S111). Specifically, the strength calculation unit 11 calculates the strain generated in each fiber when the axial force and moment described above are applied to each cross section, and calculates the stress generated in each fiber based on the strain and the stress-strain diagram of the metal plate constituting the automotive component, thereby obtaining the stress distribution for each cross section. Based on the obtained stress distribution, the strength calculation unit 11 determines the deformation mode of the cross section as an axial crushing mode if no tensile stress is generated in the cross section, and determines the deformation mode of the cross section as a bending deformation mode if tensile stress is generated in the cross section. Whether tensile stress is generated in the cross section is determined by searching the entire cross section for fibers with negative compressive stress values, and if a fiber with a negative compressive stress value is confirmed, it is determined that tensile stress is generated in the cross section. If no fibers with reversed compressive stress are found, it is determined that no tensile stress is occurring within the cross section.

[0031] Next, the strength calculation unit 11 calculates the strength of each cross section (step S113). Specifically, the strength calculation unit 11 calculates the cross-sectional force based on the stress for each cross section, increases the load until full plasticity is achieved, and sets the load at which full plasticity is achieved as the strength of each cross section. Next, the strength calculation unit 11 calculates the sum of the strengths of each cross section and sets this as the strength of the automobile member (step S115).

[0032] In this step S1, the strength calculation unit 11 calculates the axial force / moment ratio at each cross-sectional position, and applies the axial force / moment ratio as an input condition to each cross-section to calculate the stress distribution and cross-sectional forces. Furthermore, since a fiber model in which the cross-section is divided into fibers (rod-shaped elements) is used, the stress distribution within the cross-section can be obtained. Furthermore, the strength calculation unit 11 determines whether the deformation mode is an axial crushing mode or a bending deformation mode, and ultimately determines the load at which full plasticity is reached, thereby enabling the strength of the automotive component to be calculated.

[0033] (First determination step S2) As shown in FIG. 2, in the first determination step S2, the determination unit 13 determines whether the overall yield strength of the automotive component calculated in the yield strength calculation step is equal to or greater than a predetermined value (a value of yield strength necessary to satisfy the required collision safety performance). If the calculated yield strength of the automotive component as a whole is equal to or greater than the predetermined value (step S2 / YES), the energy absorption calculation unit 12 performs the energy absorption calculation step (S3). If the calculated yield strength of the automotive component as a whole is less than the predetermined value (step S2 / NO), the yield strength calculation step S1 is repeated sequentially until the calculated yield strength is equal to or greater than the predetermined value. In S105 of the repeated yield strength calculation step S1, the designer redefines at least one of the cross-sectional shape, size, thickness (plate thickness), material, and cross-sectional layout of the automotive component. That is, in the (n+1)th S105, the designer changes information corresponding to at least one of the cross-sectional shape, size, thickness (plate thickness), and cross-sectional layout of the automotive component to information different from the information defined in the nth S105.

[0034] (Energy absorption calculation step S3) In the energy absorption calculation step S3, the energy absorption calculation unit 12 calculates the energy absorption of the automotive component using a spring-mass model. In this step, the designer defines a spring-mass model having spring load-compression characteristics determined based on the yield strength and deformation mode of each cross section via the input unit 20, and provides the spring-mass model with initial conditions that limit the initial velocity, mass point weight, and mass point movement. The energy absorption calculation unit 12 determines the relationship between the load and compression of the automotive component, or the relationship between the energy absorption and compression. Note that the spring load refers to the load applied to each spring in the spring-mass model. Furthermore, when simply referred to as load, it refers to the load applied to the automotive component.

[0035] An example of the energy absorption amount calculation step will be described with reference to Fig. 6. Fig. 6 is a flow diagram of the energy absorption amount calculation step.

[0036] First, the designer defines a spring-mass model via the input unit 20, whose spring load-compression characteristics are determined based on the yield strength and deformation mode of each cross section (step S301). FIG. 7 shows a schematic graph of the load-compression characteristics of an automobile component whose deformation mode is an axial crush mode, and FIG. 8 shows a schematic graph of the load-compression characteristics of an automobile component whose deformation mode is a bending deformation mode. As shown in FIGS. 7 and 8, the load-compression relationship differs between the axial crush mode and the bending deformation mode. The maximum value of the load acting on a cross section of an automobile component is determined by the yield strength of that cross section, and the compression amount is determined by the distance between the cross sections. Therefore, in this step, a spring-mass model is defined whose spring load-compression characteristics are determined based on the yield strength and deformation mode of each cross section calculated in the yield strength calculation step.

[0037] Next, the designer inputs initial conditions for the set spring-mass model via the input unit 20, limiting the initial velocity, mass point weight, and mass point movement amount, and the energy absorption calculation unit 12 calculates the relationship between the load and compression amount of the automobile components, and the relationship between the energy absorption amount and compression amount (step S303). The relationship between the load and compression amount, and the relationship between the energy absorption amount and compression amount are calculated by analyzing the transient response of the spring-mass model with the given initial conditions. The transient response of the spring-mass model can be analyzed using the dynamic explicit method.

[0038] Conventionally, the relationship between load and compression, the relationship between energy absorption and compression, and the yield strength were calculated independently. However, according to the automotive component design method of this embodiment, the energy absorption-compression characteristics and the load-compression characteristics can be calculated in series based on the yield strength calculation results. Furthermore, conventional manual yield strength calculations were based on the assumption that the automotive component was subjected to only one of a compressive axial force or a bending moment, resulting in poor design accuracy and inappropriate for actual conditions. However, according to this embodiment, the yield strength calculation step assumes that both the axial force and the moment are input simultaneously, allowing for yield strength calculations under conditions closer to actual collision conditions, resulting in highly accurate yield strength calculations. Furthermore, in conventional methods using a spring-mass model, the spring constant is set based on the designer's experience, crash test results, or FEM analysis results. Therefore, if the designer lacks experience, the calculation results using the spring-mass model tend to be less accurate. However, according to this embodiment, the energy absorption-compression characteristics or the load-compression characteristics are calculated using the highly accurate yield strength and stress distribution for each cross section calculated in the yield strength calculation step, resulting in highly accurate results. This allows accurate performance values ​​to be obtained and reduces the number of times that strength and energy absorption calculations need to be performed. As a result, automotive components that meet the required crash safety performance can be designed in a short period of time. In addition, full vehicle CAE can be omitted, reducing the number of man-hours required.

[0039] The energy absorption calculation step will now be described in more detail with examples. Fig. 9 is a schematic diagram showing an example of a spring-mass model. Fig. 10 is a schematic graph showing the relationship between spring load and compression characteristics for each spring.

[0040] A spring-mass model has one or more springs and multiple mass points. One mass point corresponds to one cross section of an automobile component. The springs in the spring-mass model correspond to adjacent cross sections or between a fixed end and a mass point located next to the fixed end. FIG. 9A shows a spring-mass model with one spring S and two mass points m. FIG. 9B shows a spring-mass model in which three springs S are connected in series via mass points m. FIG. 9C shows a spring-mass model in which multiple springs S are connected in series and in parallel via mass points m. As shown in FIGS. 9A to 9C, the mass point located at one end of the spring-mass model is the fixed end. The length of each spring corresponds to the distance between two adjacent cross sections of the automobile component. Therefore, a spring-mass model with one or more springs and multiple mass points corresponds to an automobile component with the same number of coordinate points as the number of mass points. Since the positions of mass points correspond to the cross-sectional positions, the positions and number of mass points match the positions and number of cross-sectional positions. However, as will be described later, if nodes are set in the spring-mass model in addition to the mass points corresponding to the cross-sectional positions, the total number of mass points and nodes will be greater than the number of cross sections.

[0041] FIG. 10 is a schematic diagram for explaining the correspondence between an automobile member and a spring-mass model. As shown in FIG. 10, a plurality of cross sections i (i=1, 2, 3, ...) are set on the automobile member from one end to the other end. In FIG. 10, up to the ninth cross section (cross section 9) are shown. Cross section 1 at one end of the automobile member corresponds to mass point P1 (fixed end) at one end of the spring-mass model, and mass point P i are arranged. Each mass point P i are the weights m i Each mass point P i Weight m iis set by the designer. In the spring-mass model, adjacent masses are connected by springs. Each spring has a length L 1,2 ~L i-1,i and the spring constants are k1~k i-1 is.

[0042] FIG. 11 is another schematic diagram for explaining the correspondence between an automobile member and a spring-mass model. In FIG. 11, similar to FIG. 10, a plurality of cross sections i (i=1, 2, 3, ...) are arranged on the automobile member from one end to the other end. Cross section 1 at one end of the automobile member corresponds to a mass point (fixed end) at one end of the spring-mass model, and mass point P i In the spring-mass model shown in FIG. 11, mass points P1 to P i At the center of each of the spaces, there is a node p 1、2 ~p i-1,i are arranged. Each node p i-1,i are the weights ~m i-1、i The weight of the node m i-1、i is set by the designer. In the spring-mass model shown in Figure 11, adjacent mass points and nodes are connected by springs. Two mass points P i-1 , P i Between the mass P i-1 and node p i-1,i The length of the spring connecting the mass P i and node p i-1,i The length of each spring connecting the i-1,i and the spring constant k i-1 and k i For example, between two mass points P1 and P2, the node p 1、2 are arranged, and mass point P1 and node p 1,2 The length of the spring connecting the mass point P2 and the node p 1,2 The length of each spring connecting the 1,2 On the other hand, one mass point P i The spring constants of the two springs on either side of i Therefore, the mass point P i-1 and mass point P iBetween them, the mass point P i-1 and node p i-1,i is the spring constant k i-1 are connected by springs at node p i-1,i nodes and mass P i is the spring constant k i For example, the spring constant of the two springs on both sides of mass point P2 is k2. Between mass point P1 and mass point P2, mass point P1 and node p 1,2 is connected by a spring with spring constant k1, and the node p 1,2 The node and mass point P2 are connected by a spring with spring constant k2. For the same automobile model, when a spring-mass model with nodes is set up, the spring-mass model is defined with more springs than when a spring-mass model without nodes is set up. Therefore, a spring-mass model with nodes can more precisely represent the load fluctuations when compressed and displaced, making it possible to calculate a load that is closer to the actual load-displacement curve.

[0043] Figure 12 shows an example of the spring load-compression characteristic graph for each spring. As shown in Figure 12, the member yield strength F is the yield strength at which deformation of the automobile component begins in each cross section, and is the yield strength calculated in the yield strength calculation step. peak and the energy absorption load F that simulates the energy absorption after the start of deformation. ea The spring load-compression amount characteristic is determined from the above. The spring load-compression amount characteristic is determined by the compression stop compression amount L that satisfies the following formula (1). stop The compression stop load F stop is set.

[0044] 0 <L ea <L stop ≦L spring …(1) formula (1) In the formula, L spring : Length of spring before compression L ea : Compression amount at which energy absorption begins L stop : Compression stop compression amount is.

[0045] L spring is the length of the spring before compression, and is determined by the distance between the defined cross sections. L ea As shown in Figure 12, after the load F suddenly drops, the load F ea This is the amount of compression when compression begins at a load of (L). stop is the amount of compression that is set so that the spring does not reverse and go from compression to tension. Both of these are defined by the designer before calculation. Compression stop load F stop is the cross-sectional strength F peak It is set to a larger load, e.g., F stop ≧100F peak The strength of the cross section F peak is the strength calculated in the strength calculation step. Therefore, F peak After calculating F stop is defined by the designer. In addition, in the spring load-compression characteristics, the compression amount of the spring is the energy absorption start compression amount L ea Below this, the spring load is peak In addition, the compression amount is the energy absorption start compression amount L ea The above is the compression stop compression amount L stop Below this, the spring load is the energy absorption load F ea This energy absorption load F ea is a function F of the compression amount L, which is set to satisfy the following equation (2): ea (L).

[0046] 0 <F ea (L)≦F peak …(2) formula

[0047] As mentioned above, the load-compression relationship is different between the axial crushing mode and the bending deformation mode. Therefore, when the deformation mode is the axial crushing mode and when the deformation mode is the bending deformation mode, a different function F ea It is preferable to set (L) as the function F eaThe function F (L) can be set based on, for example, the deformation mode, the density of the material constituting the automobile component, the material properties (e.g., stress-strain curve), the cross-sectional area of ​​the automobile component, and the length. ea (L) is an arbitrary function that simulates the load drop during energy absorption.

[0048] By providing initial conditions that limit the initial velocity, mass of the mass, and amount of movement of the mass to a spring-mass model that has spring load-compression characteristics for each mass and spring, it is possible to determine the relationship between load and compression, or the relationship between energy absorption and compression, as an automobile component.

[0049] It is preferable that the mass point is set to a weight calculated from the density, cross-sectional area, and length of the material that constitutes the automobile member.

[0050] 13 is a schematic diagram for explaining an example of the weight of a mass point to be set. i The weight of m i , the cross-sectional area of ​​section i is A i , the length between section i-1 and section i is L i-1,i If the mass density of the material that makes up the automobile parts is ρ, the weight of mass point mi is m i =ρ×A i ×L i-1,i It is expressed as:

[0051] FIG. 14 is another schematic diagram for explaining another example of the weight of the mass point to be set. Also, FIG. 14 shows a spring-mass model in which nodes are defined. FIG. 15 is a diagram showing a part of the schematic diagram shown in FIG. 14. FIG. 15 shows the case in FIG. 14 where the weight is m i Point mass P i The two adjacent nodes p i-1、i , p i、i+1 The weight of the divided part is W i is W i =ρ×A i ×(L i,i+1 +L i-1,i ) / 2. This weight W i is one point mass P iand two nodes p i-1、i , p i、i+1 That is, each mass point and node is divided into ρ×A i ×(L i,i+1 +L i-1,i ) / 6 is distributed. Therefore, the i-th particle P i Weight m i is m i =ρ×A i ×(L i,i+1 +L i-1,i ) / 6. One node p i-1、i If we focus on this, the node in question is the i-2th node p i-2、i-1 The weight of the division between node p is also distributed. i-1、i Weight m i-1、i is m i-1、i =ρ×{A i ×(L i,i+1 +L i-1,i ) / 6+A i-1 ×(L i-1,i +L i,i+1 ) / 6}. However, the node P next to the fixed end 1、2 Weight m (first node) 1、2 is m 1、2 =ρ×{A1×(L i,2 ) / 4+A2×(L 1,2 +L 2,3 ) / 6}.

[0052] As mentioned above, different weights may be set for each mass point depending on the structure of the automobile. For example, an automobile component that absorbs collision energy is a front side member, which is a component that absorbs collision energy when the automobile collides from the front. The front side member is a component that extends in the longitudinal direction of the vehicle at the front end of the side fender that is located on the side of the vehicle. Inside the front side members located on the left and right of the vehicle, internal components of the vehicle (for example, a power train) are located. For example, a spring mass model shown in FIG. 16 can be set for such a front side member. In detail, one end of the spring mass model is provided with a weight M that simulates the passenger compartment. body A point mass P with bodyand the weight M of the assumed vehicle-body built-in object is set at a position corresponding to the position of the vehicle-body built-in object in the longitudinal direction of the vehicle. p A point mass P with p The assumed weight of the vehicle compartment M body is the weight of the part of the body that must be made zero in speed without being crushed by the collision energy absorbing member during a collision. The part that is assumed to be the passenger compartment is the weight of the body excluding the spring mass modeled members (for example, front side members) and the internal components of the body (power train). In Figure 10, mass points P1 to P2 are shown corresponding to the cross sections of the front side members. i is shown. Mass points P1 to P i are the weights m1 to m i In addition, springs S1 to S2 are provided between each cross section, between the vehicle body built-in components and the cross section, and between the cross section and the passenger compartment. i Each spring S1 to S i are lengths L1 to L i and the spring constants are K1 to K i Then, each mass point P2 to P i , P p , P body The initial velocity V0 is input.

[0053] In the event of a frontal collision of the automobile, the above-mentioned built-in components of the automobile body limit the amount of deformation of the portion of the automobile member in front of the built-in components of the automobile body (springs S1 and S2 in FIG. 16). In addition, the vehicle interior limits the amount of deformation of the portion between the built-in components of the automobile body and the vehicle interior (springs S3 to S i ) is limited in deformation. In other words, the amount of movement of the vehicle body's built-in objects and the vehicle interior is limited in the event of a frontal collision. Therefore, the spring mass model includes a mass point P p and the mass point P corresponding to the vehicle compartment body For example, it is preferable to limit the amount of movement of the mass point P corresponding to the vehicle compartment. body The amount of movement that can be made is D A and the mass point P corresponding to the internal object of the car body p The amount of movement that can be made is D B1 In this case, the mass point P corresponding to the vehicle compartment bodyThe total compression of the spring between the fixed end and A and the mass point P corresponding to the internal object of the car body p The total compression of the spring between the fixed end and B1 The mass point P corresponding to this compartment body The amount of movement D A and mass point P corresponding to the internal structure of the vehicle body p The amount of movement D B1 By taking the above into consideration, it is possible to more accurately determine the relationship between the load and the amount of compression of an automobile member, and the relationship between the amount of energy absorption and the amount of compression.

[0054] In the above, the vehicle interior and the vehicle compartment arranged inside the front side member are exemplified as structures that limit the deformation of the front side member. However, if there are other structures that limit the deformation of the front side member, a spring mass model that takes those structures into consideration can be set. The same applies to automobile components other than the front side member. Therefore, in the spring mass model, it is preferable to set a mass point that has a weight corresponding to the vehicle compartment and is arranged at one end opposite the fixed end, and one or more mass points that have a weight corresponding to the vehicle interior, and to define elements that limit the amount of movement of the mass point corresponding to the vehicle compartment and the mass point corresponding to the vehicle interior. Let L be the distance between the mass point corresponding to the vehicle compartment and the fixed end. A , the distance between the mass point corresponding to the internal object of the vehicle body and the fixed end is L Bi (i is a natural number), the amount of movement of the mass point corresponding to the vehicle compartment is D A , and the amount of movement of the mass point corresponding to the built-in object in the vehicle is D Bi (i is a natural number), then D A / L A and D Bi / L Bi are all greater than 0 and less than 1. D A / L A It is preferable that the following formula (3) is satisfied, and D Bi / L Bi It is preferable that the following formula (4) be satisfied.

[0055] 0.3≦D A / L A≦0.6 …(3) formula 0.3≦D Bi / L Bi ≦0.7 …(4) formula

[0056] D A / L A By satisfying equation (3), the spring mass model can more accurately simulate the amount of movement of the vehicle interior during a frontal collision. Bi / L Bi By satisfying equation (4), the spring mass model more accurately simulates the layout of the vehicle's built-in components. As a result, the relationship between the load and the amount of compression, and the relationship between the amount of energy absorption and the amount of compression, of the vehicle components can be determined more accurately.

[0057] Figure 17(A) shows the possible movement of the mass point corresponding to the vehicle compartment, D A 17(A) shows an example of a graph of vehicle displacement from the start of a collision when a predetermined value is set, and FIG. 17(B) shows an example of the change in the amount of collision energy absorbed by an automobile component (front side member) from the start of a collision. FIG. 17(C) shows the relationship between the amount of energy absorbed and the amount of compression of the front side member, and FIG. 17(D) shows the relationship between the load acting on the front side member and the amount of compression. FIGS. 17(A) to 17(D) are graphs obtained by setting the spring mass model shown in FIG. 16. As shown in FIGS. 17(C) and 17(D), by setting a spring mass model having spring load-compression characteristics based on the yield strength, deformation mode, and dimensions, and by providing the spring mass model with initial conditions that limit the initial velocity, mass point weight, and mass point movement, it is possible to obtain the relationship between the load and the amount of compression, and the relationship between the amount of energy absorbed and the amount of compression.

[0058] (Second determination step S4) As shown in Fig. 2, in the second determination step S4, the determination unit 13 determines whether the energy absorption calculated in the energy absorption calculation step is equal to or greater than the required energy absorption. If the calculated energy absorption is equal to or greater than the required energy absorption (step S4 / YES), the design is completed. If the calculated energy absorption is less than the required energy absorption (step S4 / NO), the strength calculation step S1 and subsequent steps are repeated until the calculated energy absorption is equal to or greater than the required energy absorption. The second determination step S4 may be performed by the designer.

[0059] The method for designing an automotive component according to this embodiment has been described above. However, the technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0060] For example, the flow diagram of the strength calculation steps shown in Figure 3 is merely an example, and the order can be changed as appropriate as long as the strength can be calculated. For example, the definition of the shape, thickness, and material for each cross section including each point may be performed before calculating the axial force / moment at each coordinate point.

[0061] Furthermore, in the above-described embodiment, in the spring-mass model in which nodes are provided, one node is set at the center of adjacent mass points, but the number and positions of the nodes are not limited to this. [Example]

[0062] The yield strength of a front impact structural member (front side member) was calculated using three calculation methods: analysis (full-vehicle CAE) using a CAE (Computer Aided Engineering) model simulating the state in which the member is actually installed in a vehicle body (full-vehicle state); manual calculation; and the yield strength calculation method in the design method of this embodiment. Fig. 18 shows a graph relatively comparing the yield strength of the crushed portion calculated by each calculation method, and Fig. 19 shows a graph relatively comparing the yield strength of the bending deformation portion. As shown in Figs. 18 and 19, the yield strength calculation method in the design method of this embodiment was closer to the calculation results using full-vehicle CAE than the manual calculation, and it was found that the yield strength prediction accuracy was improved.

[0063] Next, the energy absorption and deformation of multiple front side members with different shapes, thicknesses, and materials were calculated using two calculation methods: full vehicle CAE and the energy absorption calculation method in the design method of this embodiment. The energy absorption calculated by each calculation method was divided by the deformation to calculate the average load acting on each front side member during a collision. FIG. 20 shows the relationship between the average load calculated by full vehicle CAE and the average load calculated by the energy absorption calculation method in the design method of this embodiment. As shown in FIG. 20, the correlation coefficient between the average load calculated by full vehicle CAE and the average load calculated by the energy absorption calculation method in the design method of this embodiment was 0.95, indicating a high correlation between them. In other words, the design method of this embodiment enables highly accurate calculation of energy absorption without requiring the labor-intensive full vehicle CAE. [Explanation of symbols]

[0064] 1 Design equipment 10 Control Unit 11 Proof strength calculation section 12 Energy absorption calculation section 13 Judgment section 20 Input section 30 Output section 40 Storage section

Claims

1. A method for designing an automobile component, comprising: a yield strength calculation step of calculating a yield strength of the automotive component using a fiber model; an energy absorption amount calculation step of calculating an energy absorption amount of the automobile member using a spring mass model; Including, In the strength calculation step, initial conditions of the cross-sectional shape, plate thickness, material, and cross-sectional arrangement of the automotive member are set, and the axial force and moment calculated at a cross section at an arbitrary position of the automotive member, as well as the strength and deformation mode for each cross section are calculated; In the energy absorption calculation step, the spring mass model is set to have spring load-compression characteristics determined based on the strength and deformation mode for each cross section, and initial conditions are given to the spring mass model to limit the initial velocity, the weight of the mass point, and the amount of movement of the mass point, thereby determining the relationship between the load and compression amount, or the relationship between the energy absorption amount and the compression amount, of the automotive component.

2. the spring-mass model includes one or more springs and a plurality of mass points; the springs are connected in series or in parallel via the mass points; One end of the spring mass model is a fixed end, The spring load-compression characteristic for each spring is the yield strength at the time when deformation of the automobile component begins in each cross section, and is the component yield strength F ｐｅａｋ and an energy absorption load F simulating the energy absorption after the start of the deformation. ｅａ and is determined from The spring load-compression amount characteristic includes a compression stop compression amount L that satisfies the following formula (1): ｓｔｏｐ Compression stop load F ｓｔｏｐ is set, The compression amount of the spring is the energy absorption start compression amount L ｅａ When the spring load is less than the member strength F ｐｅａｋ and The compression amount is the energy absorption start compression amount L ｅａ The compression stop compression amount L ｓｔｏｐ When the spring load is less than the energy absorption load F ｅａ and The energy absorption load F ｅａ is a function F of the compression amount L that satisfies the following equation (2): ｅａ The method for designing an automotive member according to claim 1, wherein the length is (L). 0 < L ｅａ <L ｓｔｏｐ ≦L ｓｐｒｉｎｇ …(1) 0 < F ｅａ (L)≦F ｐｅａｋ …(2) In the formula (1), L ｓｐｒｉｎｇ is the length of the spring before compression.

3. 3. The method for designing an automobile component according to claim 2, wherein a weight calculated from the density of a material constituting the automobile component, the cross-sectional area of ​​the automobile component, and the length of the automobile component is set for the mass point.

4. In the spring-mass model, a mass point having a weight corresponding to the vehicle compartment and disposed at one end opposite to the fixed end, and one or more mass points having weights corresponding to the vehicle body built-in items are set, and an element that limits the amount of movement of the mass point corresponding to the vehicle compartment and the mass point corresponding to the vehicle body built-in item is defined; The distance between the mass point corresponding to the vehicle cabin and the fixed end is L Ａ , the distance between the mass point corresponding to the built-in object and the fixed end is L Ｂｉ (i is a natural number), and the movable amount of the mass point corresponding to the vehicle compartment is D Ａ , and the movable amount of the mass point corresponding to the built-in object of the vehicle body is D Ｂｉ 4. The method for designing an automotive member according to claim 2 or 3, wherein, when i is a natural number, the following formulas (3) and (4) are satisfied: 0.3≦D Ａ / L Ａ ≦0.6 …(3) 0.3≦D Ｂｉ / L Ｂｉ ≦0.7 …(4)

5. The function F differs depending on whether the deformation mode is an axial crushing mode in which no tensile stress acts in the cross section or a bending deformation mode in which tensile stress acts in the cross section. ｅａ The method for designing an automotive member according to claim 2 or 3, further comprising setting (L).

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