Joint structure and frame

Abstract

The objective is to provide a highly versatile joining structure that suppresses tempering of hardened areas in the case of welding, and suppresses the reduction of tool life in the case of mechanical fastening. Furthermore, the objective is to provide a frame equipped with this joining structure. [Solution] This joint structure 100 employs a configuration in which both the first member 10 and the second member 20 are provided with an unhardened joint portion 11 at the joint position, and at least one of the first member 10 and the second member 20 is hardened, excluding the unhardened joint portion 11. The frame comprises a metal frame body that partitions a closed space, a metal reinforcing member that is placed in the closed space and reinforces the frame body from the inside, and the joint structure 100, wherein a part of the frame body is the first member 10, the reinforcing member is the second member 20, and the frame body and the reinforcing member are joined at the unhardened joint portion.

Description

Technical Field

[0001] The present invention relates to a joining structure and a frame.

Background Art

[0002] Various mechanical devices are configured by joining a number of members to each other. Among them, an automobile has a strong joining structure to protect passengers from the impact during a collision. For example, Patent Document 1 discloses a joining structure of members in an automobile body. The joining structure of members in this automobile body is "a steel first member having a closed hollow cross-section without an outward flange, extending in one direction, and having a quenched portion with a tensile strength of 1470 MPa or more, a base material portion with a tensile strength of less than 700 MPa, and a transition portion between the quenched portion and the base material portion where the tensile strength gradually changes from the tensile strength of the quenched portion to the tensile strength of the base material portion in the one direction; and a steel second member overlapped with a part of the outer surface of the first member by an overlapping portion, and the first member and the second member are welded at the overlapping portion. In the joining structure of members in an automobile body, the overlapping portion exists across the transition portion from the quenched portion to the base material portion of the first member, and the welded portion formed by the welding exists in the transition portion or the base material portion of the first member" as its configuration. According to this joining structure, "for example, by applying it to the joint between an A-pillar and a side sill, the joint between an A-pillar and a roof rail, or the door beam and its mounting portion, etc., it is possible to suppress a decrease in impact absorption performance due to HAZ softening by welding without reducing the load-bearing performance of the structural member of the automobile body having a quenched portion with a tensile strength of 1470 MPa or more."

Prior Art Documents

Patent Documents

[0003] [Patent Document 1] International Publication No. 2015 / 182549 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Incidentally, in addition to welding, other means of joining components include mechanical fastening such as bolting and self-piercing rivets. The most suitable method for each component is selected depending on its application and intended use. In many cases, the components themselves are heat-treated to ensure their individual mechanical strength. For example, when a hardened component is joined to another component by welding, tempering (second hardening) due to the heat input during welding may occur at the joint. Furthermore, when joining hardened components to other components by mechanical fastening, machining such as drilling holes is performed on the components using tools. However, because the components have already hardened due to the hardening process, there is a problem in that the lifespan of the tools used for cutting them is reduced. Against this backdrop, there is a need for a highly versatile joining structure that does not suffer from the aforementioned problems, whether through welding or mechanical fastening. Furthermore, the application of such a joining structure is also required in applications such as electric vehicle battery frames.

[0005] This invention has been made in view of the above circumstances, and aims to provide a highly versatile joining structure that can suppress tempering of hardened areas in the case of welding and suppress reduction of tool life in the case of mechanical fastening. It also aims to provide a frame equipped with this joining structure. [Means for solving the problem]

[0006] In order to solve the above problems and achieve the above objectives, the present invention employs the following embodiments. (1) A bonding structure according to one aspect of the present invention is: It comprises a first metal member and a second metal member joined to the first member, Both the first member and the second member are provided with an unhardened joint portion at the joining position, At least one of the first member and the second member is quenched, except for the unquenched joint portion. According to the joining structure described in (1) above, when the first and second members are welded together, the welded area is not hardened, thus preventing double hardening that would occur if the entire assembly, including the welded area, were hardened. Furthermore, when the first and second members are joined by mechanical fastening such as bolts or self-piercing rivets, the machining for this purpose is performed on the unhardened, unhardened portion, thus suppressing the problem of reduced tool life.

[0007] (2) The joint structure described in (1) above may be configured as follows: The present invention further comprises an unhardened joint connecting the first member and the second member, The unfired joint portion of the first member and the joint are joined by welding or fastening members. The unfired joint portion of the second member and the joint are joined by welding or fastening members. In the case of the joint structure described in (2) above, since the first member is joined to an unhardened joint at the unhardened joint portion, it is possible to prevent double hardening or to suppress the problem of reduced tool life. Similarly, since the second member is joined to an unhardened joint at the unhardened joint portion, it is possible to prevent double hardening or to suppress the problem of reduced tool life. Alternatively, the first member and the joint may be joined by welding, and the second member and the joint may be joined by mechanical fastening. Conversely, the second member and the joint may be joined by welding, and the first member and the joint may be joined by mechanical fastening.

[0008] (3) In the case of the joint structure described in (2) above, The joint covers both the unfired joint portion of the first member and the unfired joint portion of the second member. You may adopt this configuration. In the case of the joint structure described in (3) above, the entire area of ​​the unfired joint of the first member and the unfired joint of the second member can be reinforced by increasing the plate thickness by overlapping the joints.

[0009] (4) In the case of the joint structure described in (2) or (3) above, it may be configured as follows: The first member has an unheated joint portion and a hardened portion, The Vickers hardness of the unheated joint portion of the first member is Ha1 and the plate thickness is tp1 (mm), and the Vickers hardness of the hardened portion of the first member is Ho1 and the plate thickness is tp1 (mm). The Vickers hardness of the aforementioned joint is Hb and the plate thickness is tb (mm). The following equation 1 is satisfied. Ho1×tp1≦Ha1×tp1+Hb×tb (Formula 1) In the case of the joint structure described in (4) above, by satisfying Equation 1, the sum of the mechanical strength of the unheated joint portion of the first member shown on the right side of Equation 1 and the mechanical strength of the joint is equal to or greater than the mechanical strength of the hardened portion of the first member shown on the left side of Equation 1. Therefore, the mechanical strength of the unheated joint portion of the first member can be reliably compensated for by the mechanical strength of the joint.

[0010] (5) In the case of the joint structure described in (4) above, it may be configured as follows: The second member has the unheated joint portion and the hardened portion, The Vickers hardness of the unheated joint portion of the second member is Ha2 and the plate thickness is tp2 (mm), and the Vickers hardness of the hardened portion of the second member is Ho2 and the plate thickness is tp2 (mm). Furthermore, it satisfies equation 2 below. Ho2×tp2≦Ha2×tp2+Hb×tb (Formula 2) In the case of the joining structure described in (5) above, by satisfying Formula 2, the sum of the mechanical strength at the non-hardened joint portion of the second member shown on the right side of Formula 2 and the mechanical strength of the joint becomes equal to or greater than the mechanical strength of the quenched portion in the second member shown on the left side of Formula 2. Therefore, the mechanical strength of the non-hardened joint portion of the second member can be reliably supplemented by the mechanical strength of the joint. Accordingly, in addition to connecting the first member and the second member by the joint, it is also possible to reinforce the mechanical strength of both non-hardened joint portions.

[0011] (6) The frame according to one aspect of the present invention includes a metal frame body that partitions a closed space, a metal reinforcing member disposed within the closed space to reinforce the frame body from the inside, the joining structure according to any one of (1) to (5) above, and is provided with a part of the frame body is the first member, the reinforcing member is the second member, and the frame body and the reinforcing member are joined at the non-hardened joint portion and adopts such a configuration. According to the frame described in (6) above, since the joining of the reinforcing member to the frame body has the joining structure according to any one of (1) to (5) above, when this joining is welding, tempering can be suppressed, and when it is mechanical fastening, it is possible to suppress a decrease in tool life.

Advantages of the Invention

[0012] According to each of the above aspects of the present invention, it is possible to provide a highly versatile joining structure that suppresses tempering of the quenched portion in the case of joining by welding and suppresses a decrease in tool life in the case of joining by mechanical fastening. It is also possible to provide a frame having this joining structure.

Brief Description of the Drawings

[0013] [Figure 1]This figure shows a first embodiment of the present invention, and is a perspective view of a joining structure in which a second member is joined to a first member via a bracket. In Figure 1, the hatched area indicates the hardened area. [Figure 2] Figure 1 is an exploded perspective view of the joint structure. Note that the hatched areas in Figure 2 indicate the hardened areas. On the other hand, the areas without hatching in the first and second members of Figure 2 indicate the unhardened areas. [Figure 3] This is a plan view showing a battery frame according to a second embodiment of the present invention. [Figure 4] This is a perspective view showing part A in Figure 3. [Figure 5] This is a plan view showing the manufacturing process of a battery frame. [Modes for carrying out the invention]

[0014] Hereinafter, embodiments of the joint structure and the frame equipped with this joint structure of the present invention will be described with reference to the drawings. Specifically, the joint structure, which is the basis of the present invention, will be described as the first embodiment, and thereafter, a battery frame, which is an example of a frame equipped with the same joint structure, will be described as the second embodiment.

[0015] [First Embodiment] The joint structure 100 of this embodiment shown in Figure 1 is configured in which the tip of the second member 20 is perpendicularly abutted against a position midway along the longitudinal direction of the first member 10 and connected by a joint 30. This configuration is applicable, for example, to the joint structure between the side sill and the B-pillar of an automobile.

[0016] As shown in Figure 2, the first member 10 is a hollow steel rectangular tube with a rectangular cross-section (square or rectangle). The first member 10 is not limited to a rectangular tube; for example, circular, elliptical, or other pipe materials with various irregular cross-sectional shapes may be used. Furthermore, if a rectangular tube is used for the first member 10, its cross-sectional shape may be either square or rectangular. Also, while the example shows the first member 10 with a straight pipe axis, it is not limited to a straight line; other pipe materials with a gently arcing pipe axis may be used. Moreover, the material of the first member 10 is a metal whose tensile strength (or Vickers hardness) can be increased by quenching, which involves heating and immediately cooling; specifically, it is steel. Here, "steel" includes not only so-called ordinary steel, but also stainless steel and special steels.

[0017] As shown in Figure 2, the first member 10 is hardened throughout, except for a portion in the longitudinal direction. That is, the first member 10 has an unhardened joint 11 located at an intermediate position in its longitudinal direction, i.e., approximately in the center, away from both the longitudinal end and the other end. With this unhardened joint 11 as the boundary, a hardened portion 12 that is hardened along its entire length is located on one side (left side of the paper), and another hardened portion 12 that is hardened along its entire length is located on the other side (right side of the paper).

[0018] In this embodiment, the unfired joint portion 11 has a long rectangle shape along the pipe axis of the first member 10, with its top, bottom, and both sides being rectangular. However, the shape of the unfired joint portion 11 itself does not affect the joint strength of the joint structure 100, and other shapes may be adopted. That is, the top, bottom, and both sides of the unfired joint portion 11 may be square, or they may be strip-shaped with a length dimension in the direction along the pipe axis shorter than the pipe diameter, or they may be other shapes such as elliptical or circular.

[0019] However, if the joint 30 is joined to the first member 10 by welding, the unfired joint portion 11 must encompass all of the welding locations. That is, for example, if the joint 30 is joined to the first member 10 by spot welding, the dimensions and shape of the unfired joint portion 11 must be set so as to encompass all of the spot welding locations. Furthermore, when the joint 30 is fastened to the first member 10 using mechanical fastening such as bolts or self-piercing rivets, it is necessary to include the entire area in the first member 10 where machining such as drilling is performed. That is, for example, when the joint 30 is bolted to the first member 10, the dimensions and shape of the unfired joint portion 11 must be set so as to include all positions in the first member 10 where female screw holes are formed.

[0020] The second member 20, also shown in Figure 2, is a hollow steel rectangular tube with a rectangular (square or rectangular) cross-section. The second member 20 is not limited to a rectangular tube; for example, other pipe materials with circular, elliptical, or various irregular cross-sectional shapes may be used. Alternatively, the second member 20 may be a press-formed product with a roughly U-shaped cross-section perpendicular to its longitudinal direction, rather than a hollow tube. Here, if a square tube is used as the second member 20, its cross-sectional shape may be either square or rectangular. Also, although the example given for the second member 20 is one in which the tube axis is straight, it is not limited to a straight tube; other tube materials with a gently curved tube axis may also be used. Furthermore, the material of the second member 20 is a metal whose tensile strength (or Vickers hardness) can be increased by quenching, which involves heating and cooling immediately afterward, and specifically steel. The term steel used here includes not only so-called ordinary steel, but also stainless steel and special steels. Furthermore, the cross-sectional shape and material of the second member 20 may be the same as those of the first member 10, or only one of them may be different from each other.

[0021] The second member 20 is not hardened along its entire length. That is, the entire length of the second member 20, including the unhardened joint portion 21 at one end which is the connection point with the joint 30, is unhardened. Although the second member 20 may also be hardened, in that case, the unhardened joint portion 21 must be left unhardened at the end where it is connected to the joint 30. In other words, when the joint 30 is joined to the second member 20 by welding, the range of the unfired joint 21 must be set to encompass all of the welding positions. For example, when the joint 30 is joined to the second member 20 by spot welding, the dimensions and shape of the unfired joint 21 must be set to encompass all of the spot welding positions.

[0022] Furthermore, when the joint 30 is fastened to the second member 20 by mechanical means such as bolting or self-piercing rivets, it is necessary to set the range so as to include the area in the second member 20 where machining such as drilling is performed. That is, for example, when the joint 30 is bolted to the second member 20, it is necessary to set the dimensions and shape of the unfired joint portion 21 so as to include all the positions in the second member 20 where multiple female screw holes are formed.

[0023] Next, the joint 30 shown in Figure 2 comprises a joint body 31 and a fixing means. The fixing means referred to here may be welding such as spot welding sw, or mechanical fastening such as bolting or self-piercing rivets. The joint body 31 has a pair of upper and lower split joints 31a and 31b. These split joints 31a and 31b are T-shaped components in plan view or bottom view, and are manufactured by press working steel plates. When manufacturing each of the split joints 31a and 31b by bending die-cut steel plate components, it is preferable to form a notch c, which is the boundary between the pair of side plates a and b shown in Figure 2, before press working. By forming this notch c in advance, the bending of the side plates a and b becomes extremely easy compared to when there is no notch c.

[0024] Each of the split joints 31a and 31b has a recess that covers the entire surface of the unfired joint portion 11 of the first member 10 and a recess that covers the entire surface of the unfired joint portion 21 at the tip of the second member 20. As for the material of the split joints 31a and 31b, for example, mild steel or low-strength high-tensile steel (preferably with a Vickers hardness of 80 HV to 320 HV, more preferably 135 HV to 200 HV) can be used. Both the split joints 31a and 31b are unhardened. This prevents double hardening during spot welding and reduces the load on the tool during cutting to create bolt holes. These points are the same as those for the unhardened joint 11 of the first member 10 and the unhardened joint 21 of the second member 20.

[0025] Furthermore, the presence or absence of quenching at each position of the first member 10, the second member 20, and the joint body 31 can be determined based on the Vickers hardness measured under a test force of 9.807 N. In the case of steel, it is also possible to determine this by assuming that the Vickers hardness of the quenched portion is 400 HV or higher, and the Vickers hardness of the unquenched portion is 310 HV or lower. Here, Vickers hardness is measured in accordance with JIS Z 2244-1 (2020). Measurements are taken at a measurement position at least 10 mm away from areas where hardness changes locally, such as bent or welded parts of each component. Specifically, a cross-section parallel to the thickness direction is formed at the measurement position, and at the center of the thickness on this cross-section, five Vickers hardness measurements are taken at a measurement interval of 2 mm along a line perpendicular to the thickness direction, using a test force of 9.807 N. The average value of these five points is then taken as the Vickers hardness of that area. Hereafter, Vickers hardness will be obtained according to this measurement method.

[0026] In addition, instead of Vickers hardness, the presence or absence of quenching in each part of the first member 10, the second member 20, and the joint body 31 can also be determined by microstructure analysis. Incidentally, when steel is used as the material, the quenched parts have a martensitic structure as their main structure.

[0027] The joint structure 100 is formed by the combination of the first member 10, the second member 20, and the joint 30 as described above. In other words, as shown in Figure 2, first, the opening of the unfired joint 21 at the tip of the second member 20 is brought into contact with one side surface of the unfired joint 11 of the first member 10, such that the pipe axis is perpendicular to it. In this way, with the second member 20 abutting against the first member 10, a portion of the unburnt joint 11,21 is fitted into the recess of the split joint 31a, and the remaining portion of the unburnt joint 11,21 is fitted into the recess of the split joint 31b. As a result, the entire area of ​​the unburnt joint 11,21 is covered by the split joints 31a,31b, and the plate thickness is increased by the overlapping of the split joints 31a,31b.

[0028] After sandwiching the unburnt joints 11 and 21 between the split joints 31a and 31b in this manner, they are fixed in place by multiple spot welds as shown in Figure 1. Specifically, the upper surface of the unburnt joint 11 and the upper plate of the split joint 31a that overlaps it are joined by multiple spot welds performed at equal intervals. Similarly, the upper surface of the unburnt joint 21 and the upper plate of the split joint 31a that overlaps it are joined by multiple spot welds performed at equal intervals. Similarly, each side surface of the unburnt joint 11 and each side plate of the split joint 31a that overlaps it are joined by multiple spot welds performed at equal intervals. Similarly, each side surface of the unburnt joint 21 and each side plate of the split joint 31a that overlaps it are joined by multiple spot welds performed at equal intervals.

[0029] In the split joint 31b, multiple spot welds are performed in the same manner as in the split joint 31a. That is, the lower surface of the unburnt joint 11 and the bottom plate of the split joint 31b that overlaps it are joined by multiple spot welds sw performed at equal intervals. Similarly, the lower surface of the unburnt joint 21 and the bottom plate of the split joint 31b that overlaps it are joined by multiple spot welds sw performed at equal intervals. Similarly, each side surface of the unburnt joint 11 and each side plate of the split joint 31b that overlaps it are joined by multiple spot welds sw performed at equal intervals. Similarly, each side surface of the unburnt joint 21 and each side plate of the split joint 31b that overlaps it are joined by multiple spot welds sw performed at equal intervals.

[0030] Through the above process, the first member 10 and the joint 30 are joined, and the second member 20 and the joint 30 are joined. As a result, the first member 10 and the second member 20 are joined via the joint 30 in a way that prevents relative movement, and the joint structure 100 shown in Figure 1 is completed. With this joint structure 100, each spot weld sw joins the unhardened, unheated joint portion 11 and the unhardened, divided joints 31a and 31b. Also, each spot weld sw joins the unhardened, unheated joint portion 21 and the unhardened, divided joints 31a and 31b. In this way, all parts where spot welding sw is performed are unhardened, so that the first member 10 does not undergo double hardening. Furthermore, even if the second member 20 is hardened in any part other than the unhardened joint 21, spot welding sw is performed only on the unhardened joint 21, thus preventing the second member 20 from being hardened twice.

[0031] Furthermore, the joint structure 100 shown in Figure 1 has higher mechanical strength than the case where the second member 20 is welded to the first member 10 by butting them together. More specifically, suppose that the Vickers hardness of the unheated joint portion 11 of the first member 10 is Ha1 and the plate thickness is tp1 (mm), and the Vickers hardness of the hardened portion of the first member 10 is Ho1 and the plate thickness is tp1 (mm), and the Vickers hardness of the joint 30 is Hb and the plate thickness is tb (mm). In this case, the joint structure 100 satisfies the following equation 1. Furthermore, as described above, the Vickers hardness measurements for Ho1, Ha1, and Hb are taken at a measurement position at least 10 mm away from areas where hardness changes locally, such as bent or welded sections. Specifically, a cross-section parallel to the plate thickness direction is formed at the measurement position, and at the center of the plate thickness on this cross-section, five Vickers hardness measurements are taken at 2 mm intervals along a line perpendicular to the plate thickness direction, using a test force of 9.807 N. The average of these five Vickers hardness measurements is then taken as the Vickers hardness of that section.

[0032] Ho1×tp1≦Ha1×tp1+Hb×tb (Formula 1)

[0033] Since this joint structure 100 satisfies the above equation 1, the sum of the mechanical strength of the unheated joint portion 11 of the first member 10 shown on the right side of equation 1 and the mechanical strength of the joint 30 is equal to or greater than the mechanical strength of the hardened portion 12 of the first member 10 shown on the left side of equation 1. Therefore, the mechanical strength of the unheated joint portion 11 of the first member 10 can be reliably compensated for by the mechanical strength of the joint 30.

[0034] In addition to the above configuration, if a hardened portion is also formed on the second member, for example, it is possible to configure the structure to satisfy the following Equation 2. That is, the Vickers hardness of the unhardened joint portion 21 of the second member 20 is Ha2 and the plate thickness is tp2 (mm), and the Vickers hardness of the hardened portion (not shown) of the second member 20 is Ho2 and the plate thickness is tp2 (mm). In this case, the joint structure 100 can satisfy the following Equation 2. Furthermore, as described above, the Vickers hardness of each component (Ho2, Ha2, Hb) is measured at a measurement position at least 10 mm away from areas where hardness changes locally, such as bent or welded sections. Specifically, a cross-section parallel to the thickness direction is formed at the measurement position, and five measurement points are taken at a test force of 9.807 N along a line perpendicular to the thickness direction at a measurement interval of 2 mm at the center of the thickness of the cross-section, and the average of these five points is taken as the Vickers hardness.

[0035] Ho2×tp2≦Ha2×tp2+Hb×tb (Formula 2)

[0036] In this case, since the above equation 2 is satisfied, the sum of the mechanical strength of the unheated joint 21 of the second member 20 shown on the right side of equation 2 and the mechanical strength of the joint 30 is equal to or greater than the mechanical strength of the hardened portion of the second member 20 shown on the left side of equation 2. Therefore, the mechanical strength of the unheated joint 21 of the second member 20 can be reliably compensated for by the mechanical strength of the joint 30. Thus, in addition to connecting the first member 10 and the second member 20, the joint 30 can also reinforce the mechanical strength of both unheated joints 11 and 21.

[0037] In the above embodiment, the first member 10 and the second member 20 are joined via a joint 30 by spot welding sw. However, instead of spot welding sw, a configuration that fixes by laser welding, arc welding, or mechanical joining such as bolting or riveting may be adopted. For example, if bolting is used, bolts will be fastened at each position indicated by the reference numeral sw in Figure 1. With this configuration, female screw holes or bolt holes will be formed at each position before bolting, but since machining will be performed on the unhardened, unheated joint portions 11 and 21, the problem of reduced tool life can be suppressed.

[0038] Furthermore, in the above embodiment, an example was given in which the first member 10 is hardened to provide a hardened portion 12, while the second member 20 is left unhardened. Conversely, the first member 10 may be left unhardened along its entire length, while the second member 20 is hardened. In this case, it is necessary to leave only one end of the second member 20, which is the joint position with the joint 30, unhardened. In yet another configuration, the first member 10 may have an unhardened joint portion 11 and a hardened portion 12 as described in the above embodiment, and in addition, the second member 20 may also be hardened. In this case, in the second member 20, only one end portion, which is the joint position with the joint 30, must be left unhardened.

[0039] Although not included in the scope of this embodiment, it is also conceivable that, instead of providing the unhardened joints 11 and 21 described above, both the first member 10 and the second member 20 could be left completely unhardened, then joined together by the joint 30, and finally hardened all the components, including the joint structure. However, in that case, a large-scale hardening device would be required, resulting in inconveniences such as the need for a large space to install the large hardening device. Therefore, adopting the joint structure 100 of this embodiment has advantages from the standpoint of not having to expand the installation space for the processing equipment.

[0040] [Second Embodiment] Next, the battery frame (frame) 200 equipped with the joint structure 100 of the first embodiment described above will be explained below with reference to Figures 3 to 5. This battery frame 200 is a frame that houses the battery installed in an electric vehicle. Since the battery frame 200 is just one example of a frame, the joining structure 100 of the first embodiment may be applied to other frame structures.

[0041] As shown in Figure 3, the battery frame 200 of this embodiment comprises a frame 210 that forms a rectangle in plan view, and a pair of cross members 220 that are reinforcing members arranged within the closed space S partitioned by the frame 210 and reinforcing the frame 210 from the inside. Note that this battery frame 200 is just an example, and the frame 210 may have a shape other than a rectangle. For example, the frame 210 may be a square in plan view, and may be symmetrical or asymmetrical with respect to a center line along the vehicle width direction or vehicle length direction. The number of cross members may also be one or three or more.

[0042] The frame 210 is a component formed by joining a pair of hollow bent parts 211, which form a U-shape in plan view, by butting their ends together and then welding them. Each hollow bent part 211 is manufactured by hot shear bending a straight hollow metal pipe at both ends to create a right-angle bend. Therefore, each hollow bent part 211 is bent at a right angle at two points along its longitudinal direction, and since these bends are all formed by hot shear bending, the radius of curvature on the inside of the bend is extremely small compared to normal hot bending. Specifically, the bending radius is extremely small, ranging from 0.2 to 2 times the cross-sectional width (product width), which is the distance between the outer curve on the inner circumference and the outer curve on the outer circumference of the bend. As a result, it is possible to secure a larger internal volume compared to when the inner corner of the battery frame 200 has a gently curved shape. This makes it possible to increase the installed battery capacity.

[0043] Each hollow bent component 211 is made of a hollow steel square tube with a rectangular cross-section (square or rectangular). However, the hollow bent component 211 is not limited to a square tube; for example, circular, elliptical, or other pipe materials with various irregular cross-sectional shapes may be used. Furthermore, if a square tube is used for the hollow bent component 211, its cross-section may be either square or rectangular. Also, while the example shows the pipe axis of the hollow bent component 211 being straight except for the two bends, it is not limited to a straight line; it may also have a gently arcing pipe axis. Moreover, the material of the hollow bent component 211 is a metal whose tensile strength (or Vickers hardness) can be increased by quenching, which involves heating and immediately cooling; specifically, it is steel. Here, "steel" includes not only so-called ordinary steel, but also stainless steel and special steels.

[0044] As described above, the frame 210 is manufactured by coaxially butting the cut ends of each hollow bent part 211 together and then welding them together. The welded portion of this frame 210 has relatively lower strength than other parts, but it is desirable to set the orientation and position of this joint so that it is not subjected to high external forces when used as a battery frame 200. For example, in Figure 3, if the vertical direction of the paper is the width direction of the vehicle on which this battery frame 200 is mounted, there are no coaxial butt welding structures on either side of the frame 210 in the width direction, so it is possible to exhibit high strength against impacts from the side. Furthermore, if necessary, the welding position can be moved from position w1 to position w2 in Figure 3, thereby shifting the welding position in the vertical direction of Figure 3 between the left and right sides of the paper. In this case, when the manufactured battery frame 200 is placed inside the vehicle so that the horizontal direction of Figure 3 is the vehicle length direction, the two welding positions are different in the vehicle width direction, which allows for higher mechanical strength as a structural component compared to the configuration using position w1.

[0045] Each of the pair of cross members 220 is a hollow metal rectangular tube with a straight tubular axis. Here, rectangular tubes are used as examples for each cross member 220, but other cross-sectional shapes such as circular, elliptical, or other pipe materials with various irregular cross-sectional shapes may also be used. Furthermore, if rectangular tubes are used for the cross members 220, their cross-sectional shape may be either square or rectangular. In addition, the cross members 220 are not limited to hollow tubes, but may also be press-formed products with a roughly U-shaped cross-section perpendicular to the longitudinal direction. Furthermore, the material of the cross member 220 can be the same as that of the hollow bent part 211, for example. More specifically, the material of the hollow bent part 211 is a metal whose tensile strength (or Vickers hardness) can be increased by quenching, which involves heating and cooling immediately afterward, and is specifically steel. Here, steel includes not only so-called ordinary steel, but also stainless steel and special steels.

[0046] Furthermore, the cross members 220 may be made of hardened material, or conversely, unhardened material. However, if hardened material is used for the cross members 220, it is preferable to leave only the connection points unhardened to prevent softening due to heat input during welding with the joints 30. In addition, although the battery frame 200 in this embodiment is reinforced with two cross members 220, it is not limited to two; it may be one or three or more. When changing the number of cross members, since there are two connection points per cross member, twice the number of joints 30 will be required. That is, the required number of joints 30 will be, for example, two if there is one cross member, four if there are two, and six if there are three.

[0047] As shown in Figures 3 and 4, the joining structure 100 described in the first embodiment is applied to the joints between both ends of each cross member 220 and each hollow bent part 211. That is, in this embodiment, the hollow bent part 211 is the first member 10 described in the first embodiment, and the cross member 220 is the second member 20 described in the first embodiment. The hollow bent part 211 and the cross member 220 are joined via the joint 30 described in the first embodiment.

[0048] The joining structure 100 in the battery frame 200 of this embodiment will be explained again using Figure 5 before assembly. As shown in Figure 5, each hollow bent part 211 has two unhardened joints 211a along its longitudinal axis. These unhardened joints 211a have the same configuration as the unhardened joints 11 described in the first embodiment. Each hollow bent part 211 has hardened portions 211b, where the portions other than the unhardened joints 211a are hardened. Therefore, each hollow bent part 211 has three hardened portions 211b and two unhardened joints 211a. The number of unhardened portions 211b2 may be one, two, or four or more.

[0049] Furthermore, each cross member 220 is provided with unhardened, unheated joint portions 221 at both ends. Each cross member 220 is unhardened, even in the portion sandwiched between the pair of unhardened joint portions 221, but the portions excluding these unhardened joint portions 221 may be hardened. Each joint 30 has four connections, corresponding to the number of joints between each cross member 220 and each hollow bent part 211. However, their configuration is the same as that of the joint 30 described in the first embodiment above, and therefore, a redundant explanation is omitted here. The number of joints 30 is as described above.

[0050] To assemble the component shown in Figure 5 into the finished product shown in Figure 3, first, one end and the other end of one of the pair of hollow bent parts 211 are aligned with the other end and then these two points are joined by welding. This assembles a frame 210 that forms a rectangle in plan view, and a closed space S that forms a rectangle in plan view is partitioned inside it.

[0051] Next, the cross members 220 are positioned between one hollow bent part 211 and the other hollow bent part 211 so as to connect the opposing unburnt joint portions 221. As a result, each cross member 220 is positioned so that its respective unburnt joint portion 221 is perpendicularly abutted against the respective unburnt joint portion 211a of each hollow bent part 211. After the unburnt joint portion 221 abuts against all of the unburnt joint portions 211a in this manner, each of these four abutting points is sandwiched between the split joints 31a and 31b. Although four abutting points are shown as an example here, two or an even number of points, such as six or more, may also be used. Next, the gaps between each segmented joint 31a, 31b and the unburnt joints 211a, 221 are fixed by spot welding sw. As a result, as shown in Figure 5, the joint 30 is superimposed and covers the unburnt joints 211a, 221, and the space between the pair of hollow bent parts 211 is reinforced from the inside of the closed space S by the pair of cross members 220. The completed battery frame 200 is shown in Figure 3, and its detailed configuration is as described above.

[0052] With the battery frame 200 having the configuration described above, it is possible to obtain the same effects and advantages as in the first embodiment by including the joining structure 100. For example, in this second embodiment, if the Vickers hardness of the unheated joint portion 211a of the hollow bent part 211 is Ha1 and the plate thickness is tp1 (mm), and the Vickers hardness of the hardened portion 211b of the hollow bent part 211 is Ho1 and the plate thickness is tp1 (mm), and the Vickers hardness of the joint 30 is Hb and the plate thickness is tb (mm), then the joint structure 100 satisfies the following formula 1. Furthermore, as described above, the Vickers hardness values ​​Ho1, Ha1, and Hb are measured at a measurement position at least 10 mm away from areas where hardness changes locally, such as bent or welded sections. Specifically, a cross-section parallel to the plate thickness direction is formed at the measurement position, and five measurement points are obtained at a test force of 9.807 N along a line perpendicular to the plate thickness direction at a measurement interval of 2 mm at the center of the plate thickness on the cross-section, and the average of these five points is taken as the Vickers hardness.

[0053] Ho1×tp1≦Ha1×tp1+Hb×tb (Formula 1)

[0054] In this embodiment as well, since the joint structure 100 satisfies the above equation 1, the sum of the mechanical strength of the unheated joint portion 211a of the hollow bent part 211 shown on the right side of equation 1 and the mechanical strength of the joint 30 is equal to or greater than the mechanical strength of the hardened portion 211b of the hollow bent part 211 shown on the left side of equation 1. Therefore, the mechanical strength of the unheated joint portion 211a of the hollow bent part 211 can be reliably compensated for by the mechanical strength of the joint 30.

[0055] In addition to the above configuration, if a hardened portion is also formed on the cross member 220, for example, it is possible to configure it so as to satisfy the following Equation 2. That is, if the Vickers hardness of the unhardened joint portion 221 of the cross member 220 is Ha2 and the plate thickness is tp2 (mm), and the Vickers hardness of the hardened portion (not shown) of the cross member 220 is Ho2 and the plate thickness is tp2 (mm), then the joint structure 100 can satisfy the following Equation 2. Furthermore, as described above, the Vickers hardness of each component (Ho2, Ha2, Hb) is measured at a measurement position at least 10 mm away from areas where hardness changes locally, such as bent or welded sections. Specifically, a cross-section parallel to the thickness direction is formed at the measurement position, and five measurement points are taken at a test force of 9.807 N along a line perpendicular to the thickness direction at a measurement interval of 2 mm at the center of the thickness of the cross-section, and the average of these five points is taken as the Vickers hardness.

[0056] Ho2×tp2≦Ha2×tp2+Hb×tb (Formula 2)

[0057] In this case, since the above equation 2 is satisfied, the sum of the mechanical strength of the unheated joint 221 of the cross member 220 shown on the right side of equation 2 and the mechanical strength of the joint 30 is equal to or greater than the mechanical strength of the hardened portion of the cross member 220 shown on the left side of equation 2. Therefore, the mechanical strength of the unheated joint 221 of the cross member 220 can be reliably compensated for by the mechanical strength of the joint 30. Thus, in addition to connecting the hollow bent part 211 and the cross member 220, the joint 30 can also reinforce the mechanical strength of both unheated joints 211a and 221. In this embodiment as well, mechanical fastening such as bolting or self-piercing rivets may be used instead of the spot welding sw described above.

[0058] In this embodiment, as shown in Figure 3, a battery frame 200 with a line-symmetric shape is provided as an example, with respect to a center line passing through the center of the paper in the left-right direction. However, the embodiment is not limited to this line-symmetric shape, and a configuration that is asymmetrical on the left and right sides of the paper with respect to the center line may also be adopted. Furthermore, although this embodiment illustrates a joining structure between a first member 10, which is a pipe, and a second member 20, which is also a pipe, it may also be applied to joining materials other than pipes. That is, although not shown in the figures, the above-described joining structure may be applied to joining structures between members such as long angle members or long solid members, where the cross-section perpendicular to the longitudinal direction is an open cross-section rather than a flat cross-section. In that case, an unhardened joint portion is provided at the joining position of both members to be joined, and at least one of the two members is hardened except for the unhardened joint portion.

[0059] The main points of the first and second embodiments described above are summarized below. (1) As shown in Figure 2, the joining structure 100 according to one aspect of the present invention is A first metal member 10 and a second metal member 20 joined to the first metal member 10, Equipped with, Both the first member 10 and the second member 20 are provided with unhardened joint portions 11 and 21 at the joining position, At least one of the first member 10 and the second member 20 is quenched, except for the unquenched joint portions 11 and 21.

[0060] (2) Similarly, as shown in Figure 2, the joint structure 100 described in (1) above may be configured as follows: The system further includes an unhardened joint 30 connecting the first member 10 and the second member 20. The unfired joint portion 11 of the first member 10 and the joint 30 are joined by welding or fastening members. The unfired joint portion 21 of the second member 20 and the joint 30 are joined by welding or fastening members.

[0061] (3) As shown in Figure 1, in the case of the joint structure 100 described in (2) above, The joint 30 covers both the unburnt joint portion 11 of the first member 10 and the unburnt joint portion 21 of the second member 20. You may adopt this configuration.

[0062] (4) Similarly, as shown in Figure 1, in the case of the joint structure described in (2) or (3) above, it may be configured as follows: The first member 10 has an unheated joint portion 11 and a heat-treated portion 12. The Vickers hardness of the unheated joint portion 11 of the first member 10 is Ha1 and the plate thickness is tp1 (mm), and the Vickers hardness of the hardened portion 12 of the first member 10 is Ho1 and the plate thickness is tp1 (mm). The Vickers hardness of joint 30 is Hb and the plate thickness is tb (mm). The following equation 1 is satisfied. Ho1×tp1≦Ha1×tp1+Hb×tb (Formula 1)

[0063] (5) Similarly, as shown in Figure 1, the joint structure described in (4) above may be configured as follows: The second member 20 has an unheated joint portion 21 and a hardened portion (not shown), The Vickers hardness of the unheated joint portion 21 of the second member 20 is Ha2 and the plate thickness is tp2 (mm), and the Vickers hardness of the hardened portion of the second member 20 is Ho2 and the plate thickness is tp2 (mm). Furthermore, it satisfies equation 2 below. Ho2×tp2≦Ha2×tp2+Hb×tb (Formula 2)

[0064] (6) As shown in Figure 3, a battery frame (frame) 200 according to one aspect of the present invention is A metal frame 210 that partitions the enclosed space S, A metal cross member (reinforcement member) 220 is placed within a closed space S and reinforces the frame 210 from the inside, The joining structure 100 described in any one of the above items (1) to (5), Equipped with, A portion of the frame 210 corresponds to the first member 10, and the cross member (reinforcement member) 220 corresponds to the second member 20, with the frame 210 and the cross member (reinforcement member) 220 being joined at the unfired joint portions 211a and 221. It employs a specific configuration. [Explanation of Symbols]

[0065] 10 First Member 11 Unfired joint 12 Hardened section 20 Second Member 21 Unfired joint 30 fittings 31 Fitting body 31a Split joint 31b Split joint 100 joint structure 200 Battery Frame (Frame) 210 Frame 220 Cross member (reinforcement member) S closed space

Claims

1. It comprises a first metal member and a second metal member joined to the first member, Both the first member and the second member are provided with an unhardened joint portion located at the joining position, At least one of the first member and the second member is hardened, except for the unhardened joint portion. A joint structure characterized by the following features.

2. The present invention further comprises an unhardened joint connecting the first member and the second member, The unfired joint portion of the first member and the joint are joined by welding or fastening members. The unfired joint portion of the second member and the joint are joined by welding or a fastening member. The joining structure according to feature 1.

3. The joint covers both the unfired joint portion of the first member and the unfired joint portion of the second member. The joining structure according to feature 2.

4. The first member has an unheated joint portion and a hardened portion, The Vickers hardness of the unheated joint portion of the first member is Ha1 and the plate thickness is tp1 (mm), and the Vickers hardness of the hardened portion of the first member is Ho1 and the plate thickness is tp1 (mm). The Vickers hardness of the aforementioned joint is Hb and the plate thickness is tb (mm). The following equation 1 is satisfied The joining structure according to feature 2. Ho1×tp1≦Ha1×tp1+Hb×tb...(Formula 1)

5. The second member has the unheated joint portion and the hardened portion, The Vickers hardness of the unheated joint portion of the second member is Ha2 and the plate thickness is tp2 (mm), and the Vickers hardness of the hardened portion of the second member is Ho2 and the plate thickness is tp2 (mm). Furthermore, the following equation 2 is satisfied The joining structure according to feature 4. Ho2×tp2≦Ha2×tp2+Hb×tb...(Formula 2)

6. A metal frame that partitions the enclosed space, A metal reinforcing member is placed within the enclosed space and reinforces the frame from the inside, A joining structure according to any one of claims 1 to 5, Equipped with, A portion of the frame is the first member, the reinforcing member is the second member, and the frame and the reinforcing member are joined at the unfired joint. A frame characterized by the following features.

Images