Subframe structure for automobile and reinforcement member for

Abstract

A subframe structure (1) for an automobile according to the present invention is provided with: a pair of left and right side members (3) having a hollow member having a substantially rectangular cross-section extending in the front-rear direction of the vehicle, and provided with a suspension arm connection section (11); and at least one cross member (5) having a hollow member having a substantially rectangular cross-section extending in the left-right direction of the vehicle and connected to the side member (3), the side member (3) and the cross member (5) being connected via a bent portion (7), the cross member (5) being provided with a reinforcing member (9). The reinforcing component integrally covers and reinforces the suspension arm connecting part (11a) in the side beam (3) and the bent ridge line part (7a) in the bent part (7) from the suspension arm connecting part (11a) to the cross beam (5).

Description

Technical Field

[0001] The present invention relates to a sub-frame structure of an automobile with improved rigidity and a reinforcing member for the sub-frame structure of an automobile. Background Art

[0002] In an automobile body, there is a structure in which a sub-frame that couples a suspension arm and an automotive body is provided. For the sub-frame, generally, the left and right ends of a cross member extending in the left-right direction of the vehicle are connected to a pair of left and right side members extending in the front-rear direction of the vehicle. Moreover, in the sub-frame, there are a sub-frame having a pair of front and rear cross members and having a well shape in a plan view, and a sub-frame having one cross member provided on the rear side of the vehicle and having an H shape in a plan view. In addition, the side member and the cross member are not limited to being different components and being connected by another component, and there is also a structure in which the side member and the cross member are integrated.

[0003] The sub-frame is deformed due to the load input from the suspension arm during vehicle travel, and thus high stiffness is required. The high stiffness of the sub-frame improves ride comfort and increases the value of the automobile. On the other hand, from the viewpoint of the energy efficiency of the automobile, the sub-frame is also required to be lightweight.

[0004] For weight reduction of the sub-frame, when the automotive part constituting the sub-frame is manufactured by press forming a metal sheet of a metal material, it is effective to reduce the sheet thickness. However, if the sheet thickness is reduced, the rigidity generally decreases, so there is a trade-off relationship between high rigidity and lightweight of the sub-frame.

[0005] In addition, as the vehicle body performance that decreases when the sheet thickness of the metal sheet is reduced, there are crashworthiness, deformation strength when a primary load is input, fatigue strength, etc. These vehicle body performances can be ensured by applying a metal sheet with high strength. However, even if a general metal sheet is made to have high strength, the elastic coefficient hardly changes, so high rigidity of the sub-frame due to high strength of the metal sheet cannot be expected. Therefore, several techniques for achieving high rigidity of the sub-frame regardless of the strength of the metal sheet have been proposed so far.

[0006] For example, the following technologies are proposed in Patent Document 1 and Patent Document 2: In a sub-frame structure of an automobile formed by side beams and cross beams in a grid pattern, the rigidity is improved by providing a new member inside the connection portion between the side beam and the cross beam. Further, according to Patent Document 1, by providing tubular members that connect the upper surface side and the lower surface side inside the side beam and the cross beam at the connection portion between the side beam and the cross beam, the rigidity can be improved. Additionally, according to Patent Document 2, by filling or providing a resin (resin) stiffening member (stiffing member) having a columnar portion that connects the upper surface side and the lower surface side inside the side beam and the cross beam at the connection portion between the side beam and the cross beam, the rigidity can be improved.

[0007] Moreover, Patent Document 3 discloses a sub-frame for the front body or rear body of an automobile, which has a reinforcing structure configured to be able to assemble a charging module and is used to improve torsional stiffness (torsional stiffness). Further, according to Patent Document 3, the charging module assembled to the reinforcing structure is a component of the reinforcing structure, and it contributes to the reinforcement of the sub-frame by itself.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2020-083018

[0011] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2020-075656

[0012] Patent Document 3: Japanese Patent No. 5822896 Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] The technologies disclosed in Patent Document 1 and Patent Document 2 add or fill new members (reinforcing components) to improve the rigidity of the sub-frame structure. Therefore, the number of components increases, resulting in an increase in manufacturing cost and a decrease in productivity.

[0015] In addition, although the technology disclosed in Patent Document 3 can improve the torsional rigidity of the sub-frame by providing a reinforcing structure with shear strength (shearstrength), the vehicle body weight will increase.

[0016] The present invention has been completed to solve the above problems, and an object thereof is to provide a sub-frame structure for an automobile and a reinforcing component for the sub-frame structure of an automobile that improve rigidity without increasing the number of components and suppress the increase in weight to a minimum.

[0017] Means for Solving the Problem

[0018] The sub-frame structure of an automobile according to the present invention includes: a pair of left and right vehicle front-rear direction extending portions, which are hollow members having a substantially rectangular cross-section extending in the vehicle front-rear direction, and are provided with suspension arm connecting portions; and at least one vehicle left-right direction extending portion, which is a hollow member having a substantially rectangular cross-section extending in the vehicle left-right direction. The vehicle front-rear direction extending portion and the vehicle left-right direction extending portion are connected via a bent portion. Among them, the sub-frame structure of the automobile is provided with a reinforcing member that integrally covers and reinforces the bent ridgeline portion in the suspension arm connecting portion and the bent portion from the suspension arm connecting portion to the vehicle left-right direction extending portion.

[0019] The sub-frame structure of an automobile according to the present invention is based on the above invention, wherein the reinforcing member also covers the ridgeline portion on the vehicle outer side of the vehicle front-rear direction extending portion in the suspension arm connecting portion.

[0020] The sub-frame structure of an automobile according to the present invention is based on the above invention, wherein the vehicle front-rear direction extending portion and the vehicle left-right direction extending portion are made of a steel sheet with a tensile strength of 590 MPa grade or more.

[0021] The reinforcing member of the sub-frame structure of an automobile according to the present invention reinforces the sub-frame structure of the automobile. The sub-frame structure of the automobile includes: a pair of left and right vehicle front-rear direction extending portions, which are hollow members having a substantially rectangular cross-section extending in the vehicle front-rear direction, and are provided with suspension arm connecting portions; and at least one vehicle left-right direction extending portion, which is a hollow member having a substantially rectangular cross-section extending in the vehicle left-right direction. The vehicle front-rear direction extending portion and the vehicle left-right direction extending portion are connected via a bent portion. Among them, the reinforcing member of the sub-frame structure of the automobile is integrally formed with a local reinforcing portion and a global reinforcing portion. The local reinforcing portion covers the suspension arm connecting portion and locally reinforces the suspension arm connecting portion. The global reinforcing portion extends from the local reinforcing portion along the bent ridgeline portion in the bent portion to the vehicle left-right direction extending portion to cover the bent ridgeline portion and globally reinforces the sub-frame structure.

[0022] The reinforcing member of the sub-frame structure of an automobile according to the present invention is based on the above invention, wherein the local reinforcing portion also covers the ridgeline portion on the vehicle outer side of the vehicle front-rear direction extending portion in the suspension arm connecting portion.

[0023] Advantages of the Invention

[0024] In the present invention, a reinforcing member is provided, and the reinforcing member integrally covers the suspension arm connecting portion and the bending ridge line portion in the bent portion formed by connecting the vehicle front-rear direction extending portion and the vehicle left-right direction extending portion extending from the suspension arm connecting portion, thereby strengthening. As a result, it is possible to suppress deformation at the bent portion without increasing the number of components and without reducing productivity, and to improve the rigidity of the entire subframe structure. In addition, according to the present invention, it is also possible to expect an improvement in collision strength, deformation strength when a primary load is input, and fatigue strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 FIG. is a view showing a subframe structure of an automobile according to an embodiment of the present invention.

[0026] Figure 2 FIG. is an enlarged view showing a reinforcing member provided at a portion where a side beam as a vehicle front-rear direction extending portion is connected to a cross beam as a vehicle left-right direction extending portion in the subframe structure of an automobile according to an embodiment of the present invention.

[0027] Figure 3 FIG. is a view showing a reinforcing member of the present invention which is an object of investigation of rigidity in Example 1 and a subframe structure to which the reinforcing member is applied.

[0028] Figure 4 FIG. is a view showing an existing reinforcing member which is an object of investigation of rigidity in Example 2 and a subframe structure to which the reinforcing member is applied.

[0029] Figure 5 FIG. is a view showing conditions in an analysis based on the finite element method for calculating the rigidity of the subframe structure in Example 1 ((a) torsion condition, (b) bending condition).

[0030] Figure 6 FIG. is a view showing conditions in a collision analysis for calculating the collision characteristics of the subframe structure in Example 1.

[0031] Figure 7 FIG. is a view illustrating the structure of an existing subframe structure of an automobile. DETAILED DESCRIPTION OF THE INVENTION

[0032] <Background of the Invention>

[0033] Before describing the embodiments of the present invention, as an example, based on Figure 7 the subframe structure 41 of the automobile shown, the background of the present invention will be described. Hereinafter, the subframe structure 41 will be simply referred to as "subframe structure 41".

[0034] Figure 7The shown sub-frame structure 41 includes a pair of left and right side beams 3 and a pair of front and rear cross beams 5 (5A, 5B).

[0035] The side beam 3 has a hollow member with a substantially rectangular cross-section extending in the vehicle front-rear direction, and there are two suspension arm connection portions 11a, 11b for connecting the suspension arms provided in the vehicle front-rear direction.

[0036] The cross beam 5 has a hollow member with a substantially rectangular cross-section extending in the vehicle left-right direction, and is disposed between the pair of left and right side beams 3.

[0037] In the sub-frame structure 41, the side beam 3 and the rear cross beam 5B on the vehicle side are connected via a bent portion 7. The bent portion 7 is formed by bending the inner surface of the vehicle, and has a bent ridge line portion 7a connecting the inner ridge line portion 3a of the side beam 3 and the front ridge line portion 5a of the cross beam 5. Figure 7 The shown sub-frame structure 41 is manufactured by integrating a pair of left and right side beams 3 and a pair of front and rear cross beams 5, and the bent portion 7 is formed on the side beam 3.

[0038] The inventor has conducted in-depth research on effective strengthening parts in order to improve the rigidity of the sub-frame structure 41. As a result, it has been found that by strengthening the inner bent ridge line portion 7a of the bent portion 7 formed in an L shape connecting the side beam 3 and the cross beam 5B, the rigidity of the sub-frame structure 1 can be effectively improved.

[0039] In addition, conventionally, at the suspension arm connection portion 11a on the front side of the vehicle of the side beam 3, in order to prevent local deformation when connecting the suspension arm, a strengthening member 43 covering the suspension arm connection portion 11a is used. Therefore, the inventor thought of extending the strengthening member 43 toward the bent ridge line portion 7a side to integrally cover the suspension arm connection portion 11a and the bent ridge line portion 7a from the suspension arm connection portion 11a to the cross beam 5B. And it has been found that by integrally covering the suspension arm connection portion 11a and the bent ridge line portion 7a for strengthening, the rigidity of the sub-frame structure can be improved without increasing the number of parts.

[0040] The present invention has been completed based on such research. Hereinafter, its specific structure will be described.

[0041] <Automobile sub-frame structure>

[0042] Hereinafter, the sub-frame structure of an automobile according to an embodiment of the present invention will be described.

[0043] Figure 1FIG. 0 shows an overall view of the subframe structure 1 as seen from above the vehicle. The subframe structure 1 includes a pair of left and right side beams 3 and a pair of front and rear cross beams 5 (front side of the vehicle: 5A, rear side of the vehicle: 5B). The side beam 3 is connected to the rear cross beam 5B on the vehicle side via a bent portion 7. The subframe structure 1 is formed by a pair of left and right side beams 3 and a pair of front and rear cross beams 5 to form a grid shape in a plan view. Moreover, as Figure 1 shown, the subframe structure 1 is provided with a reinforcing member 9.

[0044] "Vehicle longitudinal extension part"

[0045] The side beam 3 is a vehicle longitudinal extension part, which is a hollow member having a substantially rectangular cross section extending in the vehicle longitudinal direction, and is provided with a suspension arm connection part 11 for connecting a suspension arm. In addition, the side beam 3 has ridge line portions 3a and 3b that form corners of a substantially rectangular cross section on the inner side and the outer side in the vehicle width direction, respectively. Further, in each side beam 3, as the suspension arm connection part 11, suspension arm connection parts 11a and 11b are provided at two locations in the front and rear on the vehicle rear side.

[0046] "Vehicle lateral extension part"

[0047] The cross beam 5 is a vehicle lateral extension part, which is a hollow member having a substantially rectangular cross section extending in the vehicle lateral direction. In addition, a front cross beam 5A on the vehicle side and a rear cross beam 5B on the vehicle side are disposed between the pair of left and right side beams 3. And, the rear cross beam 5B on the vehicle side has a ridge line portion 5a that forms a corner of a substantially rectangular cross section on the vehicle front side.

[0048] "Bent portion"

[0049] The bent portion 7 is a portion that bends inward from the side beam 3 to the cross beam 5B near the suspension arm connection part 11. The cross beam 5B near the suspension arm connection part 11 refers to the rear cross beam on the vehicle side in the case of the subframe structure 1 as shown in Figure 1 shown. This is because the suspension arm connection part 11 is provided on the vehicle rear side of the side beam 3.

[0050] Moreover, the bent portion 7 has a bent ridge line portion 7a that connects the inner ridge line portion 3a in the side beam 3 and the front ridge line portion 5a in the cross beam 5B.

[0051] In the subframe structure 1, the bent portion 7 is formed in the side beam 3.

[0052] "Reinforcing member"

[0053] The reinforcing member 9 integrally covers the suspension arm connection part 11a and the bent ridge line portion 7a in the bent portion 7 from the suspension arm connection part 11a to the cross beam 5B to perform reinforcement.

[0054] In the present embodiment, as Figure 1 shown, the reinforcing member 9 has a local reinforcing portion 9a and a global reinforcing portion 9b.

[0055] The local reinforcing portion 9a covers the suspension arm connecting portion 11a and locally reinforces the suspension arm connecting portion 11a.

[0056] The global reinforcing portion 9b extends from the local reinforcing portion 9a along the bending ridge line portion 7a in the bending portion 7 to the cross member 5B to cover the bending ridge line portion 7a, and globally reinforces the sub-frame structure 1.

[0057] The reason for the increase in rigidity in the sub-frame structure 1 of the vehicle in the present embodiment will be described below.

[0058] In the sub-frame structure 1, the bending portion 7 connecting the side beam 3 and the cross member 5 is a portion where the shape changes in the same shape in the vehicle front-rear direction or the vehicle left-right direction (hereinafter referred to as "shape change portion").

[0059] When a load is input to such a sub-frame structure 1 from the suspension arm connecting portion 11, compared with the portion having the same shape, the stress distribution is disturbed in the shape change portion, and the stress is locally increased and stress concentration is likely to occur. Therefore, in the shape change portion, the deformation is concentrated along with the stress concentration, which becomes the cause of the reduction in rigidity of the sub-frame structure 1.

[0060] In addition, since both the side beam 3 and the cross member 5 are formed of hollow members having a substantially rectangular cross section, when a bending or torsional load is applied to the sub-frame structure 1, stress concentration occurs at the ridge line portion that becomes the corner of the substantially rectangular cross section. Therefore, as a portion for strengthening the bending portion 7, it is important to strengthen the ridge line portion in the shape change portion, that is, the bending ridge line portion 7a in the bending portion 7.

[0061] Therefore, in the sub-frame structure 1 of the present embodiment, similar to the reinforcing member 43 provided in the existing sub-frame structure 41 ( Figure 7 ), the local reinforcing portion 9a of the reinforcing member 9 covers the suspension arm connecting portion 11 along the upper surface of the side beam 3. Thereby, the plate thickness of the appearance of the suspension arm connecting portion 11 can be increased, and the local rigidity can be improved.

[0062] Moreover, the global reinforcing portion 9b of the reinforcing member 9 covers the bending ridge line portion 7a in the bending portion 7 from the suspension arm connecting portion 11a to the cross member 5B. Thereby, the deformation of the bending portion 7 can be suppressed, and the rigidity of the entire sub-frame structure 1 can be improved.

[0063] Thus, a reinforcing member 9 is provided in the sub-frame structure 1, and the reinforcing member 9 integrally covers and reinforces the suspension arm connecting portion 11a and the bent ridgeline portion 7a in the bent portion 7 from the suspension arm connecting portion 11a to the cross member 5. Thereby, it is possible to suppress the deformation of the bent portion 7 where stress concentration is likely to occur when the side beam 3 is connected to the cross member 5, without increasing the number of components. In addition, the deformation at the bent portion is suppressed without reducing the productivity, and the rigidity of the entire sub-frame structure 1 is improved.

[0064] In addition, according to the sub-frame structure 1 of the present embodiment, it is also possible to expect an improvement in collision strength, deformation strength when a primary load is input, and fatigue strength.

[0065] Moreover, in the present invention, for the reinforcing member 9, it is more preferable to be provided so as to also cover the ridgeline portion 3b on the vehicle outer side of the side beam 3, like the local reinforcing portion 9a as Figure 1 shown. Thus, it becomes a structure in which the ridgeline portion 3b on the vehicle outer side covered by the local reinforcing portion 9a is connected to the bent ridgeline portion 7a covered by the global reinforcing portion 9b to transmit the load, and the reinforcing performance of the reinforcing member 9 can be improved.

[0066] In the present embodiment, since the reinforcing member 9 is used to improve the rigidity of the sub-frame structure 1, it is not necessary to apply a high-strength metal plate to the reinforcing member 9, and a metal plate having a tensile strength of 270 MPa or more is sufficient.

[0067] In contrast, by providing the reinforcing member 9, the rigidity of the entire sub-frame structure 1 can be improved. Therefore, for components other than the reinforcing member 9 (the side beam 3 and the cross member 5), from the viewpoint of the rigidity of the entire sub-frame structure 1, it is possible to achieve thinning of the metal plate.

[0068] Therefore, in order to maintain the strength of the sub-frame structure 1 and achieve weight reduction, a steel plate having a tensile strength of 590 MPa or more can be applied to portions other than the reinforcing member 9 in the sub-frame structure 1.

[0069] In the above description, the global reinforcing portion 9b of the reinforcing member 9 covers the bent ridgeline portion 7a on the vehicle upper side in the bent portion 7. The bent portion 7 is a portion where the side beam 3 formed of a hollow member having a substantially rectangular cross-sectional shape is connected to the cross member 5 formed of a hollow member having a substantially rectangular cross-sectional shape. Therefore, in addition to the bent ridgeline portion 7a on the vehicle upper side, the bent portion 7 sometimes has a bent ridgeline portion on the vehicle lower side that connects the ridgeline portion on the vehicle inner side in the side beam 3 and the ridgeline portion on the vehicle front side in the cross member 5.

[0070] In such a case, the global reinforcement portion of the reinforcement member can also extend from the local reinforcement portion so as to cover the bent ridge line portion on the vehicle lower side in the bent portion. That is, the sub-frame structure of the present invention does not limit the bent ridge line portion reinforced by the global reinforcement portion of the reinforcement member, and it is only necessary to reinforce the bent ridge line portion that is easily covered by the global reinforcement portion.

[0071] In addition, Figure 1 The reinforcement member 9 shown is provided on the outer surface side of the side beam 3, the cross beam 5, and the bent portion 7 that constitute the sub-frame structure 1, but it may also be provided on their inner surface side.

[0072] Figure 1 The sub-frame structure 1 shown is a structure in which a suspension arm is connected to a suspension arm connecting portion 11 provided on the outer surface (the surface on the vehicle upper side on the vehicle outer side) of the side beam 3. However, the sub-frame structure of the present invention may also be a structure in which an opening is provided on the side surface on the vehicle outer side of the side beam, the suspension arm is inserted into the opening, and fastened to the side beam with bolts or the like. Even in this case, by providing a reinforcement member having a local reinforcement portion covering the suspension arm connecting portion and a global reinforcement portion extending from the suspension arm connecting portion and covering the bent ridge line portion, deformation of the bent portion can be suppressed and rigidity can be improved.

[0073] The sub-frame structure 1 of the present embodiment is manufactured by integrating the side beam 3 and the cross beam 5, but the present invention is not limited to integrating the side beam and the cross beam.

[0074] In addition, in the sub-frame structure 1, the bent portion 7 is formed on the side beam 3, but a bent portion may also be formed on the cross beam.

[0075] Moreover, as Figure 1 shown, the above description is about the sub-frame structure 1 in which a pair of left and right side beams 3 and a pair of front and rear cross beams 5 are connected via a bent portion 7 to form a grid shape. However, as Figure 2 shown, the present invention may also be a sub-frame structure 21 in which a pair of left and right side beams 23 and a single cross beam 25 are connected via a bent portion 27 to form an H shape.

[0076] In the H-shaped sub-frame structure 21, on the side beam 23, as suspension arm connecting portions 31, suspension arm connecting portions 31a and 31b are provided at two places in the front and rear directions in the vehicle longitudinal direction. In addition, the cross beam 25 is disposed near the suspension arm connecting portion 31 where the suspension arm 33 is connected in the side beam 23.

[0077] And, in the H-shaped sub-frame structure 21, when a load is input from the suspension arm connecting portion 31, stress concentration also occurs in the bent portion 27 that connects the side beam 23 and the cross beam 25.

[0078] Therefore, in the H-shaped sub-frame structure 21, a reinforcing member 29 is provided that integrally covers the suspension arm connection portion 31a and the bent ridge line portion 27a in the bent portion 27 from the suspension arm connection portion 31 to the cross member 25.

[0079] Thereby, when a load is input to the sub-frame structure 21, deformation at the bent portion 27 can be suppressed, and the rigidity of the sub-frame structure 21 can be improved.

[0080] <Reinforcing Member of Automobile Sub-Frame Structure>

[0081] The above description relates to the sub-frame structure 1 provided with the reinforcing member 9, but as another aspect of the present embodiment, it may also be configured as a reinforcing member 9 for reinforcing the sub-frame structure 1.

[0082] That is, as shown in the above-mentioned Figure 1 The reinforcing member 9 of the automobile sub-frame structure reinforces the sub-frame structure 1 having the side beam 3 and the cross member 5, and the side beam 3 and the cross member 5B are connected via the bent portion 7. Moreover, the reinforcing member 9 is integrally formed with a local reinforcing portion 9a and a global reinforcing portion 9b.

[0083] The local reinforcing portion 9a covers the suspension arm connection portion 11a and locally reinforces the suspension arm connection portion 11a.

[0084] The global reinforcing portion 9b extends from the local reinforcing portion 9a along the bent ridge line portion 7a in the bent portion 7 to the cross member 5 to cover the bent ridge line portion 7a, and globally reinforces the sub-frame structure 1.

[0085] According to the reinforcing member 9, deformation at the bent portion 7 where stress concentration is likely to occur when a load is input to the sub-frame structure 1 can be suppressed, and the overall rigidity of the sub-frame structure 1 can be improved.

[0086] As described above, it is more preferable that the local reinforcing portion 9a of the reinforcing member 9 also covers the outer ridge line portion 3b of the side beam 3. Thereby, a structure can be formed in which the outer ridge line portion 3b covered by the local reinforcing portion 9a is connected to the bent ridge line portion 7a covered by the global reinforcing portion 9b to transmit the load, and the reinforcing performance of the reinforcing member 9 is further improved.

[0087] [Example 1]

[0088] Since an investigation for verifying the effect of the sub-frame structure of the automobile of the present invention has been conducted, the following description will be given.

[0089] In Example 1, the rigidity of the sub-frame structure of the automobile of the present invention was investigated.

[0090] As in the above-described embodiment Figure 1As shown, the sub-frame structure 1 to be investigated has a pair of left and right side beams 3 and a pair of front and rear cross beams 5. The side beam 3 and the cross beam 5B are connected via a bent portion 7. And, as Figure 1 and Figure 3 shown, the sub-frame structure 1 is provided with a reinforcing member 9 (Inventive Example 1). In Figure 3 , the X-axis direction is the right direction of the vehicle, the Y-axis direction is the front direction of the vehicle, and the Z-axis direction is the upward direction of the vehicle (the same applies to Figure 4 described later).

[0091] As Figure 1 shown, the reinforcing member 9 integrally covers and strengthens the suspension arm connecting portion 11a provided on the side beam 3 and the bent ridge line portion 7a in the bent portion 7 from the suspension arm connecting portion 11a to the cross beam 5B. And, as Figure 1 and Figure 3 of (a) shows, the reinforcing member 9 has a local reinforcing portion 9a and a global reinforcing portion 9b.

[0092] In Example 1, as Figure 1 and Figure 3 of (b) shows, the local reinforcing portion 9a covers the suspension arm connecting portion 11a and the ridge line portion on the vehicle outer side of the side beam 3 at the suspension arm connecting portion 11a.

[0093] On the other hand, as Figure 1 and Figure 3 of (b) shows, the global reinforcing portion 9b extends from the local reinforcing portion 9a along the bent ridge line portion 7a of the bent portion 7 to the cross beam 5B to cover the bent ridge line portion 7a.

[0094] In the sub-frame structure 1, the side beam 3 and the cross beam 5 are integrally manufactured using a steel plate with a thickness of 2.0 mm and a tensile strength of 440 MPa grade.

[0095] The reinforcing member 9 is manufactured using a steel plate with a thickness of 2.0 mm and a tensile strength of 270 MPa grade. Moreover, the reinforcing member 9 is joined to the sub-frame structure 1 by welding.

[0096] In Example 1, for comparison, as Figure 4 shown, the rigidity of the sub-frame structure 41 provided with the existing reinforcing member 43 that strengthens the suspension arm connecting portion 11 was also investigated (Existing Example). As Figure 4 of (a) shows, the reinforcing member 43 does not have the global reinforcing portion 9b of the reinforcing member 9 of Inventive Example 1, and is formed in a shape corresponding to the local reinforcing portion 9a.

[0097] Further, in the sub-frame structure 41 of the existing example, the side beams 3 and the cross beam 5 are manufactured using steel plates with a thickness of 2.0 mm and a tensile strength of 270 MPa, just as in Invention Example 1.

[0098] For the reinforcing member 43, as in Invention Example 1, it is manufactured using a steel plate with a thickness of 2.0 mm and a tensile strength of 270 MPa, and is joined to the sub-frame structure 41 by welding.

[0099] In Example 1, for the sub-frame structure 1 of Invention Example 1 and the sub-frame structure 41 of the existing example, analyses based on the finite element method for the specified load of the load are respectively performed, the displacements of the load input points with respect to the unit load are obtained, and the reciprocals thereof are obtained as the rigidity. Then, the rigidity improvement rate in Invention Example 1 with respect to the rigidity in the existing example is calculated.

[0100] The analysis based on the finite element method is carried out for Figure 5 the "torsion condition" shown in (a) of Figure 5 and the "bending condition" shown in (b) of

[0101] Figure 5 The "torsion condition" shown in (a) of

[0102] is a condition in which the left and right ends of the cross beam 5B, i.e., the rear bush 15, are constrained, and upward and downward loads (1 kN) in the vehicle up and down direction are respectively applied to the left and right ends of the cross beam 5A, i.e., the front bush 13. Figure 5 And, with the torsion condition shown in (a) of

[0103] as the analysis condition, for the sub-frame structure 1 of Invention Example 1 and the sub-frame structure 41 of the existing example, the displacement amounts in the vehicle up and down direction per unit load in the front bush 13 of the cross beam 5A are respectively obtained as the torsion rigidity.

[0104] The torsion rigidity improvement rate [%] = (torsion rigidity of Invention Example 1 - torsion rigidity of the existing example) / (torsion rigidity of the existing example) × 100

[0105] The torsion rigidity improvement rate of Invention Example 1 is 6.2%, indicating an improvement in torsion rigidity compared to the sub-frame structure 41 of the existing example.

[0106] Figure 5The "bending condition" shown in (b) is a condition that restrains the left and right end portions of the cross member 5B, i.e., the rear bushings 15, and applies a rightward load (1 kN) in the vehicle's left-right direction to the left and right end portions of the cross member 5A, i.e., the front bushings 13.

[0107] And, Figure 5 Based on the bending condition shown in (b), for the sub-frame structure 1 of Invention Example 1 and the sub-frame structure 41 of the Existing Example, the displacement amount in the vehicle's left-right direction per unit load in the front bushing 13 of the cross member 5A is obtained as the bending stiffness, respectively.

[0108] Based on the bending stiffness obtained for Invention Example 1 and the Existing Example respectively, the bending stiffness improvement rate of the sub-frame structure 1 of Invention Example 1 is calculated. The bending stiffness improvement rate is the improvement rate of the bending stiffness of Invention Example 1 based on the bending stiffness of the Existing Example, and is calculated by the following formula.

[0109] Bending stiffness improvement rate [%] = (Bending stiffness of Invention Example 1 - Bending stiffness of Existing Example) / (Bending stiffness of Existing Example) × 100

[0110] The bending stiffness improvement rate of Invention Example 1 is 4.9%, indicating an improvement in bending stiffness compared to the sub-frame structure 41 of the Existing Example.

[0111] [Example 2]

[0112] In Example 2, the relationship between the improvement in rigidity and the increase in weight in the sub-frame structure of the vehicle of the present invention was investigated. In addition, the crash worthiness of the sub-frame structure of the vehicle of the present invention was also investigated.

[0113] In Example 2, the same sub-frame structure 1 as in Example 1 ( Figure 3 ) was used as the object of investigation.

[0114] In the sub-frame structure 1, the plate thickness of the steel plates used for the side beams 3 and the cross member 5 was changed from 2.0 mm to 1.8 mm so that its rigidity was the same as that of the sub-frame structure 41 ( Figure 4 ) provided with the above-mentioned existing reinforcing member 43. Moreover, in the sub-frame structure 1, the tensile strength of the steel plates used for the side beams 3 and the cross member 5 was set to 590 MPa grade (Invention Example 2).

[0115] In Example 2, first, for the sub-frame structure 1 of Invention Example 2, in the same manner as in Example 1 described above, Figure 5 Based on the "torsion condition" and "bending condition" shown, an analysis based on the finite element method was performed to obtain the torsion stiffness and the bending stiffness, respectively.

[0116] Table 1 shows the rigidity (torsional rigidity and flexural rigidity) and weight of the sub-frame structure 1 of Invention Example 2, along with the rigidity and weight results of Invention Example 1 of the aforementioned Example 1 and the prior art example.

[0117] [Table 1]

[0118]

[0119] As shown in Table 1, the improvement rates of torsional rigidity and flexural rigidity of Invention Example 2 based on the prior art example are both ±0%, and the rigidity of the sub-frame structure 1 of Invention Example 2 is the same as that of the sub-frame structure 41 of the prior art example.

[0120] The sub-frame structure 1 of Invention Example 1 with the same plate thickness of the side beam 3 and the cross beam 5 as the prior art example uses the reinforcing member 9 having the global reinforcing portion 9b, and the weight increases by 1.2% compared with the sub-frame structure 41 of the prior art example.

[0121] In contrast, the sub-frame structure 1 of Invention Example 2 with the reduced plate thickness of the side beam 3 and the cross beam 5 uses the same reinforcing member 9 as Invention Example 1, but the weight is reduced by 8.5% compared with the sub-frame structure 41 of the prior art example. From this, it can be seen that in the sub-frame structure 1 of Invention Example 2, weight reduction is achieved while maintaining the same rigidity as the sub-frame structure 41 of the prior art example.

[0122] Next, a crashworthiness analysis was performed on the sub-frame structures 1 of Invention Example 1 and Invention Example 2 and the sub-frame structure 41 of the prior art example.

[0123] The crashworthiness analysis was carried out as Figure 6 shown, causing the rigid body wall 51 to collide from the front side of the vehicle. And the following constraint conditions were given: full degrees of freedom were constrained for the rear bushings 15 at the left and right ends of the cross beam 5B, and translational degrees of freedom in the Z-axis direction (the upward direction of the vehicle) were constrained for the front bushings 13 at the left and right ends of the cross beam 5A.

[0124] Through the crashworthiness analysis, for the sub-frame structures 1 of Invention Example 1 and 2 and the sub-frame structure 41 of the prior art example, the maximum load generated during the collision of the rigid body wall 51 and the absorbed energy during the collision process were respectively calculated. Then, for the calculated maximum load and absorbed energy, the change rates based on the maximum load or absorbed energy in the prior art example were respectively obtained.

[0125] In Table 1 above, the maximum load and absorbed energy obtained by collision analysis for Invention Example 1, Invention Example 2, and the existing example are shown respectively.

[0126] As shown in Table 1, for the maximum load generated in the sub-frame structure during collision based on collision analysis, when taking the existing example as a reference, Invention Example 1 is +0.6% and Invention Example 2 is +2.8%, both higher than the existing example. In addition, for the collision absorbed energy, compared with the existing example, Invention Example 1 is +1.5% and Invention Example 2 is +4.6%, both higher than the existing example.

[0127] As described above, it is confirmed that in the sub-frame structure of the present invention, by thinning the plate thickness of the steel plate in a manner that makes it have the same rigidity as the existing sub-frame structure and using high-strength steel plates, it is possible to achieve weight reduction and improvement of collision characteristics while maintaining rigidity.

[0128] [Industrial Applicability]

[0129] According to the present invention, since there is a reinforcing member that integrally covers and reinforces the bending ridge line portion in the suspension arm connecting portion and the bending portion, it is possible to suppress deformation in the bending portion without increasing the number of components and without reducing productivity. As a result, the rigidity of the entire sub-frame structure is improved. In addition, according to the present invention, it is possible to improve the collision strength, the deformation strength when inputting a primary load, and the fatigue strength.

[0130] Explanation of Reference Numerals

[0131] 1 Sub-frame structure

[0132] 3 Side beam

[0133] 3a Ridge line portion

[0134] 3b Ridge line portion

[0135] 5 Cross beam

[0136] 5A Cross beam

[0137] 5B Cross beam

[0138] 5a Ridge line portion

[0139] 7 Bending portion

[0140] 7a Bending ridge line portion

[0141] 9 Reinforcing member

[0142] 9a Local reinforcing portion

[0143] 9b Global reinforcing portion

[0144] 11 Suspension arm connecting portion

[0145] 11a Suspension arm connection part

[0146] 11b Suspension arm connection part

[0147] 13 Front bushing

[0148] 15 Rear bushing

[0149] 21 Sub-frame structure

[0150] 23 Side beam

[0151] 25 Cross beam

[0152] 27 Bending part

[0153] 27a Bending ridge line part

[0154] 29 Reinforcing member

[0155] 29a Local reinforcing part

[0156] 29b Global reinforcing part

[0157] 31 Suspension arm connection part

[0158] 31a Suspension arm connection part

[0159] 31b Suspension arm connection part

[0160] 33 Suspension arm

[0161] 41 Sub-frame structure

[0162] 43 Reinforcing member

[0163] 51 Rigid wall.

Claims

1. A sub-frame structure of an automobile, comprising: a pair of left and right vehicle front-rear direction extending portions, which are hollow members having a substantially rectangular cross-section extending in the vehicle front-rear direction, and are provided with suspension arm connection portions; and at least one vehicle left-right direction extending portion, which is a hollow member having a substantially rectangular cross-section extending in the vehicle left-right direction, wherein the vehicle front-rear direction extending portion and the vehicle left-right direction extending portion are connected via a bent portion. The sub-frame structure of the automobile is provided with a reinforcing member that integrally covers and reinforces the bending ridge line portion in the suspension arm connection portion and the bent portion from the suspension arm connection portion to the vehicle left-right direction extending portion.

2. The sub-frame structure of the automobile according to claim 1, wherein the reinforcing member also covers the ridge line portion on the vehicle outer side of the vehicle front-rear direction extending portion in the suspension arm connection portion.

3. The sub-frame structure of the automobile according to claim 1 or 2, wherein the vehicle front-rear direction extending portion and the vehicle left-right direction extending portion are made of a steel plate with a tensile strength of 590 MPa or more.

4. A reinforcing member for a sub-frame structure of an automobile, which reinforces the sub-frame structure of the automobile. The sub-frame structure of the automobile comprises: a pair of left and right vehicle front-rear direction extending portions, which are hollow members having a substantially rectangular cross-section extending in the vehicle front-rear direction, and are provided with suspension arm connection portions; and at least one vehicle left-right direction extending portion, which is a hollow member having a substantially rectangular cross-section extending in the vehicle left-right direction, wherein the vehicle front-rear direction extending portion and the vehicle left-right direction extending portion are connected via a bent portion. The reinforcing member for the sub-frame structure of the automobile is integrally formed with a local reinforcing portion and a global reinforcing portion. The local reinforcing portion covers the suspension arm connection portion and locally reinforces the suspension arm connection portion. The global reinforcing portion extends from the local reinforcing portion along the bending ridge line portion in the bent portion to the vehicle left-right direction extending portion to cover the bending ridge line portion and globally reinforces the sub-frame structure.

5. The reinforcing member for the sub-frame structure of the automobile according to claim 4, wherein the local reinforcing portion also covers the ridge line portion on the vehicle outer side of the vehicle front-rear direction extending portion in the suspension arm connection portion.

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