Vehicle frame

Abstract

This vehicle frame comprises: a pair of rear-side member assemblies that extend along the front-rear direction with a space in the width direction; and a rear suspension cross that includes a first rear cross member having both ends connected to the pair of rear-side member assemblies, and a second rear cross member having both ends connected to the pair of rear-side member assemblies forward of the first rear cross member. Defining a bending moment generated when the entire cross section of a rear-side member assembly in the front-rear direction of the vehicle is plastically deformed as a full plastic moment of the rear-side member assembly, the pair of rear-side member assemblies are each configured such that the full plastic moment of a second portion extending rearward from a connection position with the first rear cross member is smaller than the full plastic moment of a first portion extending between the connection position with the first rear cross member and a connection position with the second rear cross member.

Description

Vehicle frame

[0001] The present disclosure relates to a vehicle frame.

[0002] Conventionally, vehicles equipped with a motor and a battery for supplying electric power to the motor (for example, electric vehicles and hybrid vehicles) are known. For example, Patent Document 1 describes a vehicle in which a motor is mounted on the front portion of the vehicle, and a battery pack (battery) is mounted below a floor panel.

[0003] Incidentally, when a vehicle collides with another vehicle or the like, there is a risk that the motor and the battery may be damaged. Therefore, it is conceivable to absorb collision energy by the vehicle frame so that an excessive load is not applied to the motor or the battery. Patent Document 1 describes a technique in which deformation of a rear side member (a part of a frame) when receiving an impact from the rear of the vehicle allows the rear side member to absorb collision energy and protect the battery pack.

[0004] Japanese Unexamined Patent Publication No. 2019-156028

[0005] However, even if the motor is attached to the rear suspension cross member of a vehicle with a high ground clearance, when a vehicle with a low ground clearance collides with the high-ground-clearance vehicle, the low-ground-clearance vehicle collides by slipping under the rear side member of the high-ground-clearance vehicle, so the rear side member cannot effectively absorb the collision energy, and an excessive load is applied to the motor, which may result in damage to the motor.

[0006] In view of the above circumstances, at least some embodiments of the present invention aim to provide a vehicle frame capable of effectively absorbing collision energy even when a vehicle with a low ground clearance collides by slipping under the rear side member of a vehicle with a high ground clearance.

[0007] A vehicle frame according to at least some embodiments of the present invention is a vehicle frame on which a motor is mounted. The vehicle frame comprises a pair of rear side member assemblies spaced apart in the width direction of the vehicle and extending along the longitudinal direction of the vehicle; a first rear cross member whose ends are connected to each of the pair of rear side member assemblies; a second rear cross member whose ends are connected to each of the pair of rear side member assemblies further forward than the first cross member in the longitudinal direction of the vehicle; and a rear suspension cross including a connecting portion that connects the first rear cross member and the second rear cross member in the longitudinal direction of the vehicle, wherein a motor is mounted further forward than the first rear cross member in the longitudinal direction of the vehicle. The bending moment is the product of the yield stress of the material constituting the rear side member assembly and the section modulus of the rear side member assembly in the longitudinal direction of the vehicle. When the bending moment when the entire cross section of the rear side member assembly in the longitudinal direction of the vehicle undergoes plastic deformation is defined as the full plastic moment, each of the pair of rear side member assemblies is configured such that the second full plastic moment, which is the full plastic moment of the second portion extending towards the rear of the vehicle from the connection point with the first rear cross member, is smaller than the first full plastic moment, which is the full plastic moment of the first portion extending between the connection point with the first rear cross member and the connection point with the second rear cross member.

[0008] According to at least some embodiments of the present invention, since the full plastic moment of the second portion of each of the pair of rear side member assemblies is smaller than the full plastic moment of the first portion, when a bending moment acts on the rear side member assembly, the second portion deforms plastically before the first portion. Therefore, the second portion of the rear side member assembly can effectively absorb the collision energy before the first portion begins to deform plastically. In other words, according to at least some embodiments of the present invention, it is possible to provide a vehicle frame that can effectively absorb the collision energy even if a low-riding vehicle collides with a high-riding vehicle in a way that causes it to slide under the rear side member.

[0009] Figure 1 is a schematic cross-sectional view of the frame of a vehicle according to one embodiment, viewed from the width direction of the vehicle. This figure illustrates the moment acting on the rear side member assembly of the frame when a vehicle with a lower ride height than the vehicle shown in Figure 1 collides with it. This is a schematic diagram of the frame of a vehicle according to one embodiment, viewed from above the vehicle. This is a schematic cross-sectional view of the rear side member assembly according to one embodiment, viewed from the width direction of the vehicle, showing a cross-section of the main body member of the rear side member assembly. This is a schematic cross-sectional view of the main body of the rear side member assembly shown in Figure 4, viewed from the rear of the vehicle. This is a schematic cross-sectional view of the rear side member assembly according to another embodiment, viewed from the width direction of the vehicle, showing a cross-section of the main body member of the rear side member assembly. This is a schematic diagram of the rear side member assembly according to yet another embodiment, viewed from above. This is a schematic cross-sectional view of the rear side member assembly according to one embodiment, viewed from the width direction of the vehicle, showing cross-sections of the main body member and reinforcing member of the rear side member assembly. This is a schematic cross-sectional view of the main body member and reinforcing member of the rear side member assembly shown in Figure 8, viewed from the rear of the vehicle. This is a schematic cross-sectional view of a rear side member assembly according to another embodiment, viewed from the width direction of the vehicle, showing the cross-sections of the main body member and reinforcing member of the rear side member assembly. This is a schematic diagram of a rear side member assembly according to yet another embodiment, viewed from above. This is a schematic cross-sectional view of a rear side member assembly according to yet another embodiment, viewed from the width direction of the vehicle, showing the cross-sections of the main body member and reinforcing member of the rear side member assembly.

[0010] Hereinafter, several embodiments of the present invention will be described with reference to the attached drawings. However, the dimensions, materials, shapes, relative arrangements, etc., of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples.

[0011] Figure 1 is a schematic cross-sectional view of the frame of a vehicle according to one embodiment, viewed from the width direction of the vehicle. Figure 2 is a diagram illustrating the moment acting on the rear side member assembly of the frame when a vehicle with a lower ride height than the vehicle shown in Figure 1 collides with it. Figure 3 is a schematic diagram of the frame of a vehicle according to one embodiment, viewed from above the vehicle. In the following, the vehicle frame may be abbreviated as "frame".

[0012] As shown in Figure 1, the frame 10 of the vehicle 1 according to several embodiments constitutes a part of the vehicle's skeleton. The vehicle 1 is a vehicle whose wheels 110 are driven by a motor 100. The vehicle 1 is, for example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle.

[0013] In some embodiments, as shown in Figures 1 and 3, the frame 10 includes a pair of rear side member assemblies 20 and a rear suspension cross 60. The pair of rear side member assemblies 20 extend along the longitudinal direction X2 of the vehicle 1, spaced apart in the width direction X1. The rear suspension cross 60 includes a first rear cross member 62, a second rear cross member 64, and a connecting portion 66. The first rear cross member 62 has ends 62A, 62B that connect to each of the pair of rear side member assemblies 20. Similarly, the second rear cross member 64 has ends 64A, 64B that connect to each of the pair of rear side member assemblies 20. The second rear cross member 64 also connects to the pair of rear side member assemblies 20 in the longitudinal direction X2 of the vehicle 1, forward F from the first rear cross member 62. The connecting portion 66 connects the first rear cross member 62 and the second rear cross member 64 in the longitudinal direction X2. The motor 100 is mounted on the rear suspension cross 60 at a point F in front of the first rear cross member 62 in the longitudinal direction X2 of the vehicle 1. The motor 100 is also mounted on the rear suspension cross 60 at a point R in the longitudinal direction X2 of the vehicle 1 behind the second rear cross member 64. The motor 100 may also be mounted on a mounting portion 68 connected to a connection portion 66 of the rear suspension cross 60.

[0014] Each of the pair of rear side member assemblies 20 includes a first portion 22 extending between a connection point P1 with the first rear cross member 62 and a connection point P2 with the second rear cross member 64. Each of the pair of rear side member assemblies 20 also includes a second portion 24 extending from the connection point P1 with the first rear cross member 62 toward the rear R of the vehicle 1. That is, the second portion 24 extends between the connection point P1 with the first rear cross member 62 and the rear end position P3 of the rear side member assembly 20.

[0015] Furthermore, each of the pair of rear side member assemblies 20 is configured such that the full plastic moment M_y of the second portion 24 is smaller than the full plastic moment M_y of the first portion 22. Specifically, the second full plastic moment M_y2, which is the full plastic moment M_y of the second portion 24 of the rear side member assembly 20, is smaller than the first full plastic moment M_y1, which is the full plastic moment M_y of the first portion 22. The full plastic moment M_y of the rear side member assembly 20 is a bending moment that corresponds to the product of the yield stress of the material constituting the rear side member assembly 20 and the section modulus of the rear side member assembly 20 in the longitudinal direction X2 of the vehicle 1. In other words, the full plastic moment M_y is the bending moment when the entire cross-section of the rear side member assembly 20 undergoes plastic deformation in the longitudinal direction X2 of the vehicle 1. The yield stress is determined by performing a tensile test on the material constituting the rear side member assembly 20 in accordance with the Japanese Industrial Standard JIS Z 2241 "Tensile Test Method for Metallic Materials".

[0016] As shown in Figure 2, when a lower vehicle 3 collides with a higher vehicle 1, vehicle 3 may slide under the rear side member assembly 20 of vehicle 1. At this time, as shown in Figure 2, a bending moment M acts on the rear side member assembly 20 in a direction that lifts the rear side member assembly 20 upward. The region of the rear side member assembly 20 in which the stress generated by the bending moment M reaches the yield stress of the material constituting the rear side member assembly 20 undergoes plastic deformation. As the bending moment M increases, the region of plastic deformation of the rear side member assembly 20 increases. When the bending moment M reaches the full plastic moment M_y, the entire cross-section of vehicle 1 in the longitudinal direction X2 undergoes plastic deformation. According to the above configuration, since the second full plastic moment M_y2 of the second part 24 of the rear side member assembly 20 is smaller than the first full plastic moment M_y1 of the first part 22, the second part 24 undergoes plastic deformation before the first part 22. Therefore, the second portion 24 of the rear side member assembly 20 can effectively absorb the collision energy before the first portion 22 undergoes plastic deformation. In other words, even if a low-riding vehicle 3 collides with a high-riding vehicle 1 in a way that it slips under the pair of rear side member assemblies 20 of the vehicle 1, the frame 10 of vehicle 1 can effectively absorb the collision energy. Consequently, the frame 10 of vehicle 1 can effectively protect the motor 100.

[0017] In the embodiments shown in Figures 1 and 3, each of the pair of rear side member assemblies 20 may further include a crash box 26 connected to the rear end 24D of the second portion 24. That is, the crash box 26 is located rearward R from the rear end position P3 of the rear side member assembly 20. Furthermore, the crash box 26 is configured such that its total plastic moment M_y is lower than the second total plastic moment M_y2 of the second portion 24 of the rear side member assembly 20.

[0018] As described above with reference to Figure 2, when vehicle 3 collides with vehicle 1 such that it penetrates below the rear side member assembly 20 of vehicle 1, a bending moment M acts on the rear side member assembly 20. According to the above configuration, this bending moment M also acts on the crash box 26. Since the full plastic moment M_y of the crash box 26 is lower than the second full plastic moment M_y2 of the second part 24, the crash box 26 deforms plastically before the second part 24 deforms plastically. Therefore, the collision energy can be absorbed more effectively by the plastic deformation of the second part 24 and the crash box 26 before the first part 22 deforms plastically, thus protecting the motor 100 more effectively.

[0019] Furthermore, in the embodiments shown in Figures 1 and 3, the frame 10 may further include a third rear cross member 70, the ends of which are connected to each of the rear ends 24D of the second portion 24 of a pair of rear side member assemblies 20. That is, the third rear cross member 70 has ends 70A, 70B that are connected to the pair of rear side member assemblies 20.

[0020] According to the above configuration, the rear end portion 24D of each second portion 24 of the pair of rear side member assemblies 20 is less likely to spread outward in the width direction X1 of the vehicle 1. Therefore, the second portion 24 is more likely to bend and deform upward toward the vehicle 1, with the connection position P1 with the first rear cross member 62 as the fixed end. Thus, the collision energy between vehicle 1 and vehicle 3 can be absorbed more effectively.

[0021] Next, with reference to Figures 4 to 12, several embodiments for realizing the rear side member assembly 20 including the first part 22 and the second part 24 will be described. Figure 4 is a schematic cross-sectional view of a rear side member assembly according to one embodiment, viewed from the width direction of the vehicle, and shows a cross-section of the main body member of the rear side member assembly. Figure 5 is a schematic cross-sectional view of the main body of the rear side member assembly shown in Figure 4, viewed from the rear of the vehicle. Figure 6 is a schematic cross-sectional view of a rear side member assembly according to another embodiment, viewed from the width direction of the vehicle, and shows a cross-section of the main body member of the rear side member assembly. Figure 7 is a schematic schematic diagram of a rear side member assembly according to yet another embodiment, viewed from above. Figure 8 is a schematic cross-sectional view of a rear side member assembly according to one embodiment, viewed from the width direction of the vehicle, and shows cross-sections of the main body member and reinforcing member of the rear side member assembly. Figure 9 is a schematic cross-sectional view of the main body member and reinforcing member of the rear side member assembly shown in Figure 8, viewed from the rear of the vehicle. Figures 10 and 12 are schematic cross-sectional views of a rear side member assembly according to another embodiment, viewed from the width direction of the vehicle, and show cross-sections of the main body member and reinforcing member of the rear side member assembly. Figure 11 is a schematic diagram of a rear side member assembly according to yet another embodiment, viewed from above. For the sake of explanation, Figures 4, 6 to 8 and 10 to 12 only show the range of the rear side member assembly 20 between the connection position P2 with the second rear cross member 64 and the rear end position P3 of the second portion 24.

[0022] As shown in Figures 4 to 12, in some embodiments, each of the pair of rear side member assemblies 20 includes a main body member 30 connected to the end 62A (62B) in the width direction X1 of the first rear cross member 62 and the end 64A (64B) in the width direction X1 of the second rear cross member 64. The main body member 30 is configured such that the full plastic moment M_y in the second portion 24 is smaller than the full plastic moment M_y in the first portion 22.

[0023] In one embodiment, as shown in Figures 4 to 6, the main body member 30 is configured such that the height H12 of the second part 24 is lower than the height H11 of the first part 22. In other words, the section modulus of the main body member 30 of the second part 24 is smaller than the section modulus of the main body member 30 of the first part 22. Therefore, if the material constituting the main body member 30 is the same for the first part 22 and the second part 24, the full plastic moment M_y of the main body member 30 of the second part 24 will be smaller than the full plastic moment M_y of the main body member 30 of the first part 22.

[0024] In the embodiment shown in Figure 6, the main body member 30 is configured such that the height H12 of the main body member 30 of the second portion 24 decreases as it moves from the connection position P1 with the first rear cross member 62 toward the rear R of the vehicle 1. In other words, the main body member 30 of the second portion 24 is configured such that the cross-sectional area viewed from the front-rear direction X2 of the vehicle 1 decreases toward the rear R of the vehicle 1. With this configuration, the section modulus of the main body member 30 of the second portion 24 decreases toward the rear R of the vehicle 1, so the full plastic moment M_y becomes smaller towards the rear end of the main body member 30 of the second portion 24. Therefore, the main body member 30 of the second portion 24 becomes easier to plastically deform sequentially from the rear end 24D of the second portion 24 toward the front F of the vehicle 1, so that it can absorb collision energy more effectively. Note that the main body member 30 of the second portion 24 may be configured such that the height H12 decreases at a constant rate toward the rear R of the vehicle 1, or it may be configured such that the amount of decrease in height H12 increases toward the rear R of the vehicle 1.

[0025] In other embodiments, as shown in Figures 4 to 7, the main body member 30 is configured such that the thickness t12 of the main body member 30 in the second part 24 is thinner than the thickness t11 of the main body member 30 in the first part 22. In other words, the section modulus of the main body member 30 in the second part 24 is smaller than the section modulus of the main body member 30 in the first part 22. Therefore, if the material constituting the main body member 30 is the same in the first part 22 and the second part 24, the full plastic moment M_y of the main body member 30 in the second part 24 will be smaller than the full plastic moment M_y of the main body member 30 in the first part 22.

[0026] In the embodiment shown in Figure 6, the main body member 30 is configured such that the thickness t12 of the main body member 30 of the second portion 24 decreases as it moves from the connection position P1 with the first rear cross member 62 toward the rear R of the vehicle 1. In other words, the main body member 30 of the second portion 24 is configured such that the cross-sectional area viewed from the longitudinal direction X2 of the vehicle 1 decreases toward the rear R of the vehicle 1. With this configuration, the section modulus of the main body member 30 of the second portion 24 decreases toward the rear R of the vehicle 1, so the full plastic moment M_y becomes smaller towards the rear end of the main body member 30 of the second portion 24. Therefore, collision energy can be absorbed more effectively. Note that the main body member 30 of the second portion 24 may be configured such that the thickness t12 decreases at a constant rate toward the rear R of the vehicle 1, or it may be configured such that the amount of decrease in thickness t12 increases toward the rear R of the vehicle 1.

[0027] In yet another embodiment, as shown in Figure 6, the main body member 30 is composed of different materials for the main body member 30 of the second part 24 and the main body member 30 of the first part 22. Specifically, the main body member 30 of the second part 24 is made of a material with a lower yield strength than the main body member 30 of the first part 22. In other words, the yield strength of the material constituting the main body member 30 of the second part 24 is lower than the yield strength of the material constituting the first part 22. Therefore, if the section modulus of the main body member 30 of the first part 22 and the section modulus of the main body member 30 of the second part 24 are the same, the full plastic moment M_y of the main body member 30 of the second part 24 will be smaller than the full plastic moment M_y of the main body member 30 of the first part 22.

[0028] In yet another embodiment, as shown in Figures 4 to 12, the main body member 30 is configured such that the cross-sectional shape of the main body member 30 of the second portion 24, as viewed from the front-rear direction X2 of the vehicle 1, opens upward toward the vehicle 1. In this case, the main body member 30 of the second portion 24 includes a bottom portion 36 extending along the width direction X1 of the vehicle 1, and lateral portions 38 (38A, 38B) extending upward toward the vehicle 1 from the ends 36A, 36B of the bottom portion 36 in the width direction X1, respectively. In other words, the main body member 30 of the second portion 24 forms an opening 39 between the lateral portions 38A, 38B. According to the above configuration, the section modulus of the main body member 30 of the second portion 24 is smaller on the side of the opening 39 formed in the main body member 30 than on the side of the bottom portion 36. Therefore, the main body member 30 of the second portion 24 is more easily bent upward toward the vehicle 1, with the connection position P1 with the first rear cross member 62 as the fixed end. Therefore, the energy from the collision can be absorbed more effectively by the bending deformation of the second portion 24. In addition, the main body member 30 of the first portion 22 may form an opening 39 between the lateral portions 38A and 38B, together with the main body member 30 of the second portion 24.

[0029] In the embodiment shown in Figure 7, the lateral portions 38 (38A, 38B) of the main body member 30 of the second portion 24 are configured such that the thickness t12 of the lateral portions 38 (38A, 38B) decreases as you move from the connection position P1 with the first rear cross member 62 toward the rear R of the vehicle 1. In other words, the main body member 30 of the second portion 24 is configured such that the cross-sectional area viewed from the front-rear direction X2 of the vehicle 1 decreases toward the rear R of the vehicle 1. To put it another way, the lateral portions 38 (38A, 38B) of the main body member 30 of the second portion 24 are configured such that the opening 39 formed between each of the lateral portions 38 (38A, 38B) widens toward the rear R of the vehicle 1. Furthermore, each of the lateral portions 38 (38A, 38B) of the main body member 30 of the second portion 24 may be configured such that the thickness t12 decreases at a constant rate as it moves toward the rear R of the vehicle 1, or it may be configured such that the amount of decrease in thickness t12 increases as it moves toward the rear R of the vehicle 1.

[0030] In some embodiments, as shown in Figures 8 to 12, each of the pair of rear side member assemblies 20 includes a main body member 30 and a reinforcing member 40. As described above, the main body member 30 is connected to the end 62A (62B) in the width direction X1 of the first rear cross member 62 and the end 64A (64B) in the width direction X1 of the second rear cross member 64. The reinforcing member 40 is a member housed inside the main body member 30. The reinforcing member 40 is configured such that the full plastic moment M_y of the portion 44 housed in the main body member 30 of the second portion 24 is smaller than the full plastic moment M_y of the portion 42 housed in the main body member 30 of the first portion 22. The main body member 30 may also be configured such that the full plastic moment M_y of the main body member 30 of the second portion 24 is smaller than the full plastic moment M_y of the main body member 30 of the first portion 22. Furthermore, as shown in Figures 8 to 12, the main body member 30 may be configured such that the full plastic moment M_y of the main body member 30 of the first portion 22 is the same as the full plastic moment M_y of the main body member 30 of the second portion 24.

[0031] According to the above configuration, by housing the reinforcing member 40 in the main body member 30, the second full plastic moment M_y2 of the second portion 24 of the rear side member assembly 20 can be made smaller than the first full plastic moment M_y1 of the first portion 22. Therefore, even if the main body member 30 is not configured such that the full plastic moment M_y of the main body member 30 of the second portion 24 is smaller than the full plastic moment M_y of the main body member 30 of the first portion 22, a frame 10 that can effectively absorb the energy of a collision between a low-riding vehicle 3 and a high-riding vehicle 1 can be provided.

[0032] In one embodiment, as shown in Figures 8 to 10, the reinforcing member 40 is configured such that the height H22 of the portion 44 housed in the main body member 30 of the second portion 24 is lower than the height H21 of the portion 42 housed in the main body member 30 of the first portion 22. In other words, the section modulus of portion 44 of the reinforcing member 40 is smaller than the section modulus of portion 42 of the reinforcing member 40. Therefore, if the material constituting the reinforcing member 40 is the same for the portion 42 housed in the main body member 30 of the first portion 22 and the portion 44 housed in the main body member 30 of the second portion 24, the full plastic moment M_y of portion 42 of the reinforcing member 40 will be smaller than the full plastic moment M_y of portion 44 of the reinforcing member 40.

[0033] In the embodiment shown in Figure 10, the reinforcing member 40 is configured such that the height H22 of the portion 44 housed in the main body member 30 of the second portion 24 decreases as it approaches the rear R of the vehicle 1. In other words, the portion 44 of the reinforcing member 40 is configured such that the cross-sectional area viewed from the longitudinal direction X2 of the vehicle 1 decreases as it approaches the rear R of the vehicle 1. With this configuration, the section modulus of the portion 44 of the reinforcing member 40 decreases as it approaches the rear R of the vehicle 1, so the total plastic moment M_y becomes smaller towards the rear end of the portion 44 of the reinforcing member 40. Therefore, the portion 44 of the reinforcing member 40 becomes easier to plastically deform sequentially from the rear end toward the front F of the vehicle 1, and thus can absorb collision energy more effectively. Note that the portion 44 of the reinforcing member 40 may be configured such that the height H22 decreases at a constant rate as it approaches the rear R of the vehicle 1, or it may be configured such that the amount of decrease in height H22 increases as it approaches the rear R of the vehicle 1.

[0034] In other embodiments, as shown in Figures 8 to 11, the reinforcing member 40 is configured such that the thickness t22 of the portion 44 housed in the main body member 30 of the second portion 24 is thinner than the thickness t21 of the portion 42 housed in the main body member 30 of the first portion 22. In other words, the section modulus of portion 44 of the reinforcing member 40 is smaller than the section modulus of portion 42 of the reinforcing member 40. If the same is true for the portion 42 housed in the main body member 30 of the first portion 22 and the portion 44 housed in the main body member 30 of the second portion 24, the full plastic moment M_y of portion 42 of the reinforcing member 40 is smaller than the full plastic moment M_y of portion 44 of the reinforcing member 40.

[0035] In the embodiment shown in Figure 10, the reinforcing member 40 is configured such that the thickness t22 of the portion 44 housed in the main body member 30 of the second portion 24 becomes thinner as it approaches the rear R of the vehicle 1. In other words, the portion 44 of the reinforcing member 40 is configured such that the cross-sectional area viewed from the longitudinal direction X2 of the vehicle 1 decreases as it approaches the rear R of the vehicle 1. With this configuration, the section modulus of the portion 44 of the reinforcing member 40 decreases as it approaches the rear R of the vehicle 1, so the full plastic moment M_y becomes smaller towards the rear end of the portion 44 of the reinforcing member 40. Therefore, collision energy can be absorbed more effectively. Note that the portion 44 of the reinforcing member 40 may be configured such that the thickness t22 decreases at a constant rate as it approaches the rear R of the vehicle 1, or it may be configured such that the amount of decrease in thickness t22 increases as it approaches the rear R of the vehicle 1.

[0036] In yet another embodiment, as shown in Figure 10, the reinforcing member 40 is composed of different materials for the portion 44 housed in the main body member 30 of the second portion 24 and the portion 42 housed in the main body member 30 of the first portion 22. Specifically, portion 44 of the reinforcing member 40 is made of a material with a lower yield stress than portion 42 of the reinforcing member 40. In other words, the yield stress of the material constituting the reinforcing member 40 housed in the main body member 30 of the second portion 24 is lower than the yield stress of the material constituting the reinforcing member 40 housed in the main body member 30 of the first portion 22. Therefore, if the section modulus of portion 42 of the reinforcing member 40 and the section modulus of portion 44 are the same, the full plastic moment M_y of portion 44 of the reinforcing member 40 will be smaller than the full plastic moment M_y of portion 42 of the reinforcing member 40.

[0037] In yet another embodiment, as shown in Figures 8 to 12, the reinforcing member 40 is configured such that the cross-sectional shape of the portion 44 housed in the main body member 30 of the second portion 24, as viewed from the front-rear direction X2 of the vehicle 1, opens upward toward the vehicle 1. In this case, the reinforcing member 40 housed in the main body member 30 of the second portion 24 includes a bottom portion 46 extending along the width direction of the vehicle 1, and lateral portions 48 (48A, 48B) extending upward toward the vehicle 1 from the ends 46A, 46B of the bottom portion 46 in the width direction X1, respectively. In other words, the portion 44 of the reinforcing member 40 forms an opening 50 between the lateral portions 48A, 48B. According to the above configuration, the section modulus of the portion 44 of the reinforcing member 40 is smaller on the side of the opening 50 formed in the reinforcing member 40 than on the side of the bottom portion 46 of the portion 44 of the reinforcing member 40. Therefore, portion 44 of the reinforcing member 40 becomes more easily bent and deformed upward toward the vehicle 1, with the connection position P1 with the first rear cross member 62 as the fixed end. Thus, the energy from the collision can be absorbed more effectively by the bending deformation of the second portion 24. In addition, portion 42 of the reinforcing member 40 may form an opening 50 between the lateral portions 48A and 48B, along with portion 44 of the reinforcing member 40.

[0038] In the embodiment shown in Figure 11, the lateral portions 48 (48A, 48B) of the portion 44 of the reinforcing member 40 are configured such that the thickness t22 of the lateral portions 48 (48A, 48B) decreases as they move toward the rear R of the vehicle 1. In other words, the portion 44 of the reinforcing member 40 is configured such that the cross-sectional area viewed from the front-rear direction X2 of the vehicle 1 decreases as it moves toward the rear R of the vehicle 1. To put it another way, the lateral portions 48 (48A, 48B) of the portion 44 of the reinforcing member 40 are configured such that the opening 50 formed between each of the lateral portions 48 (48A, 48B) widens as it moves toward the rear R of the vehicle 1. Note that each of the lateral portions 48 (48A, 48B) of the portion 44 of the reinforcing member 40 may be configured such that the thickness t22 decreases at a constant rate as it moves toward the rear R of the vehicle 1, or it may be configured such that the amount of decrease in thickness t22 increases as it moves toward the rear R of the vehicle 1.

[0039] In the embodiment shown in Figure 12, the reinforcing member 40 housed in the main body member 30 of the second portion 24 includes the aforementioned lateral portions 48 (48A, 48B), and the lateral portions 48 (48A, 48B) have notches 52 configured to open upward toward the vehicle 1. With the above configuration, portion 44 of the reinforcing member 40 becomes more easily bent and deformed at the notches 52. Therefore, portion 44 of the reinforcing member 40 can be deformed more reliably, and impact energy can be absorbed more effectively. The number of notches 52 formed in portion 44 of the reinforcing member 40 is not particularly limited.

[0040] In the embodiment shown in Figure 12, the reinforcing member 40 housed in the main body member 30 of the second portion 24 has a bellows structure. That is, the reinforcing member 40 has a plurality of recesses 54 that are recessed from the outer surface 44a of the portion 44 of the reinforcing member 40. The plurality of recesses 54 are recesses provided in a plurality along the longitudinal direction X2 of the vehicle 1. With the above configuration, the reinforcing member 40 housed in the main body member 30 of the second portion 24 becomes more easily bent and deformed, so that collision energy can be absorbed more effectively.

[0041] 1: Vehicle 3: Vehicle 10: Frame 20: Rear side member assembly 22: First part 24: Second part 24D: Rear end 26: Crash box 30: Main body member 36: Bottom 36A, 36B: End 38 (38A, 38B): Side part 39: Opening 40: Reinforcement member 46: Bottom 46A, 46B: End 48 (48A, 48B): Side part 50: Opening 52: Notch 60: Rear suspension cross 62: First rear cross member 64: Second rear cross member 66: Connection part 70: Third rear cross member 100: Motor H11, H12, H21, H22: Height M: Bending moment M_y : Full plastic moment M_y1: First full plastic moment M_y2: Second full plastic moment P1, P2: Connection position X1: Width direction X2: Front-to-back direction t11, t12, t21, t22: Wall thickness

Claims

1. A frame for a vehicle on which a motor is mounted, comprising: a pair of rear side member assemblies spaced apart in the width direction of the vehicle and extending along the longitudinal direction of the vehicle; a first rear cross member whose ends are connected to each of the pair of rear side member assemblies; a second rear cross member whose ends are connected to each of the pair of rear side member assemblies in front of the first rear cross member in the longitudinal direction of the vehicle; and a rear suspension cross including a connecting portion that connects the first rear cross member and the second rear cross member in the longitudinal direction of the vehicle, wherein the motor is mounted in front of the first rear cross member in the longitudinal direction of the vehicle, wherein the bending moment is the product of the yield stress of the material constituting the rear side member assembly and the section modulus of the rear side member assembly in the longitudinal direction of the vehicle, and the total plastic moment of the rear side member assembly is defined as the bending moment when the entire cross section of the rear side member assembly in the longitudinal direction of the vehicle undergoes plastic deformation, A vehicle frame in which each of the pair of rear side member assemblies is configured such that the second full plastic moment, which is the full plastic moment of the second portion extending toward the rear of the vehicle from the connection point with the first rear cross member, is smaller than the first full plastic moment, which is the full plastic moment of the first portion extending between the connection point with the first rear cross member and the connection point with the second rear cross member.

2. The frame of a vehicle according to claim 1, wherein each of the pair of rear side member assemblies includes a main body member connected to the widthwise end of the first rear cross member and the widthwise end of the second rear cross member, and a reinforcing member housed inside the main body member, wherein the reinforcing member is configured such that the full plastic moment in the portion of the second portion housed in the main body member is smaller than the full plastic moment in the portion of the first portion housed in the main body member.

3. The frame of a vehicle according to claim 2, wherein the reinforcing member is configured such that the height of the portion of the second part housed in the main body member is lower than the height of the portion of the first part housed in the main body member.

4. The frame of a vehicle according to claim 2, wherein the reinforcing member is configured such that the thickness of the portion of the second part housed in the main body member is thinner than the thickness of the portion of the first part housed in the main body member.

5. The vehicle frame according to claim 2, wherein the yield stress of the material constituting the reinforcing member housed in the second part of the main body member is lower than the yield stress of the material constituting the reinforcing member housed in the first part of the main body member.

6. The frame of a vehicle according to any one of claims 2 to 5, wherein the reinforcing member is configured such that the portion of the second part housed in the main body member has a cross-sectional shape that opens upward toward the vehicle when viewed from the front-rear direction of the vehicle.

7. The frame of a vehicle according to any one of claims 2 to 5, wherein the reinforcing member housed in the main body member of the second portion includes a bottom portion extending along the width direction of the vehicle and lateral portions extending upward from each end of the bottom portion in the width direction toward the vehicle, the lateral portions having notches configured to open toward the vehicle toward the vehicle toward the vehicle.

8. The frame of a vehicle according to any one of claims 2 to 5, wherein the reinforcing member housed in the main body member of the second part has a bellows structure.

9. The frame of a vehicle according to claim 1, wherein each of the pair of rear side member assemblies includes a main body member connected to the widthwise end of the first rear cross member and the widthwise end of the second rear cross member, the main body member being configured such that the full plastic moment in the second portion is smaller than the full plastic moment in the first portion.

10. The frame of a vehicle according to claim 9, wherein the main body member is configured such that the height of the second part of the main body member is lower than the height of the first part of the main body member.

11. The frame of a vehicle according to claim 9, wherein the main body member is configured such that the thickness of the second part of the main body member is thinner than the thickness of the first part of the main body member.

12. The vehicle frame according to claim 9, wherein the yield stress of the material constituting the main body member of the second part is lower than the yield stress of the material constituting the main body member of the first part.

13. The frame of a vehicle according to any one of claims 9 to 12, wherein the main body member is configured such that the cross-sectional shape of the second portion of the main body member, when viewed from the front-rear direction of the vehicle, opens upward toward the vehicle.

14. The frame of a vehicle according to claim 3 or 10, wherein the main body member is configured such that the height of the second portion of the main body member decreases as it moves from the connection point with the first rear cross member toward the rear of the vehicle.

15. The frame of a vehicle according to claim 3, wherein the reinforcing member is configured such that the height of the portion of the second part housed in the main body member decreases as it moves toward the rear of the vehicle.

16. The frame of a vehicle according to claim 4 or 11, wherein the main body member is configured such that the thickness of the second portion of the main body member decreases as it moves from the connection position with the first rear cross member toward the rear of the vehicle.

17. The frame of a vehicle according to claim 4, wherein the reinforcing member is configured such that the thickness of the portion of the second part housed in the main body member decreases as it moves toward the rear of the vehicle.

18. The frame of a vehicle according to claim 13, wherein the main body member includes a bottom portion extending along the width direction of the vehicle and lateral portions extending upward from each end of the bottom portion in the width direction toward the upper part of the vehicle, the lateral portions being configured such that the thickness of the lateral portions decreases as they move toward the rear of the vehicle from the connection position with the first rear cross member.

19. The frame of a vehicle according to claim 6, wherein the reinforcing member housed in the main body member of the second part includes a bottom portion extending along the width direction of the vehicle and lateral portions extending upward from each end of the bottom portion in the width direction toward the vehicle, wherein the thickness of the lateral portions decreases toward the rear of the vehicle.

20. A frame for a vehicle according to any one of claims 1 to 5 and 9 to 12, wherein each of the pair of rear side member assemblies further comprises a crash box connected to the rear end of the second portion of the pair of side member assemblies, configured such that its full plastic moment is lower than the second full plastic moment of the second portion.

21. A vehicle frame according to any one of claims 1 to 5 and 9 to 12, further comprising a third rear cross member, the ends of which are connected to each of the rear ends of the second portion of the pair of side member assemblies.

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