JP7581777B2 - Vehicle underbody structure - Google Patents

Description

The present invention relates to a vehicle undercarriage structure.

Vehicles such as automobiles are equipped with a vehicle underbody structure that connects a front member, which is made up of various components located at the front of the vehicle, to a rear member, which is made up of various components located at the rear of the vehicle, with side members that are located below the side sills and floor panel. With this type of vehicle underbody structure, the entire frame of the vehicle bears the load in the fore-and-aft direction of the vehicle.

In the vehicle structure described in Patent Document 1, a side member 3 extending to the rear bumper is disposed between rocker portions 15 that correspond to side sills. The side member 3 has, as a portion located on the underside of the floor portion 11, an inwardly inclined portion 33 that inclines inward in the vehicle width direction, a straight portion 34 that extends straight rearward from the rear portion of the inwardly inclined portion 33, and a widening inclined portion 35 that inclines from the rear end of the straight portion 34 toward the rocker portion 15. Furthermore, the upper surfaces of the inwardly inclined portion 33, the straight portion 34, and the widening inclined portion 35 of the side member 3 are welded to the underside of the floor portion 11. In this way, the vehicle structure of Patent Document 1 improves the impact absorption performance during a frontal collision of the vehicle.

JP 2020-97281 A

In the vehicle structure of Patent Document 1, the floor section 11 is divided in the vehicle width direction with the side members 3 as boundaries. The straight sections 34 of the side members 3 are positioned closer to the tunnel section 12 side in the vehicle width direction than the rocker sections 15. As a result, in the floor section 11, the dimensions of the floor surface on the outer side in the vehicle width direction are larger at the straight sections 34 as boundaries, which may make floor vibrations (particularly surface vibrations) more likely to occur.

Furthermore, in the side member 3, the rear end position of the widening inclined portion 35 is offset in the vehicle width direction by a larger amount than the rear end position of the straight portion 34. As a result, in the floor portion 11, the dimensions in the vehicle width direction of the floor surface between the widening inclined portion 35 and the tunnel portion 51 and between the widening inclined portions 35 become larger, which may make floor vibration more likely to occur.

In view of these problems, the present invention aims to provide a vehicle undercarriage structure that can suppress floor vibrations using floor side members.

In order to solve the above problems, a representative configuration of the vehicle underbody structure according to the present invention is a vehicle underbody structure that includes a floor panel that forms the floor surface of the vehicle, the vehicle underbody structure further includes a side sill extending in the vehicle longitudinal direction along the edge of the floor panel, a center tunnel that extends in the vehicle longitudinal direction at the center of the floor panel in the vehicle width direction, a rear side member that extends from the rear end of the vehicle to the front of the vehicle between the side sill and the center tunnel, and a floor side member that connects the rear side member and a front side member located at the front of the vehicle under the floor panel, the floor side member having a front inclined portion that inclines inward in the vehicle width direction toward the rear of the vehicle, a straight portion that extends straight from the rear end of the front inclined portion to the rear of the vehicle, and a rear inclined portion that inclines outward in the vehicle width direction from the rear end of the straight portion toward the rear of the vehicle.

The present invention provides a vehicle undercarriage structure that can suppress floor vibrations using floor side members.

1 is a bottom view showing a vehicle underbody structure according to an embodiment of the present invention. FIG. 2 is a diagram showing a part of the vehicle undercarriage and various suspensions of FIG. 1. 3A is a diagram showing a cross section taken along line DD of the vehicle underbody structure of FIG. 2A and a comparative example. FIG. 2A and 2B are diagrams showing a part of the vehicle underbody structure of FIG. 1 and a modified example thereof; 4( a )的车辆下结构的状态图。 FIG. 4 ( a ) vehicle underbody structure seen from another direction. 2 is a diagram showing a part of the vehicle underbody structure of FIG. 1 as viewed from the front of the vehicle. FIG. FIG. 2 is a detailed view of a modified example of the vehicle underbody structure of FIG. 1 . 8 is a diagram showing the vehicle underbody structure of FIG. 7 as viewed from another direction. FIG. FIG. 2 is a diagram illustrating another modified example of the vehicle underbody structure of FIG. 1 . FIG. 2 is a diagram showing still another modified example of the vehicle underbody structure of FIG. 1 .

A typical configuration of a vehicle underbody structure according to one embodiment of the present invention is a vehicle underbody structure including a floor panel that forms the floor surface of the vehicle, the vehicle underbody structure further including a side sill extending in the vehicle longitudinal direction along the edge of the floor panel, a center tunnel that extends in the vehicle longitudinal direction at the center of the floor panel in the vehicle width direction, a rear side member that extends from the rear end of the vehicle to the front of the vehicle between the side sill and the center tunnel, and a floor side member that connects the rear side member and a front side member located at the front of the vehicle under the floor panel, the floor side member having a front inclined portion that inclines inward in the vehicle width direction toward the rear of the vehicle, a straight portion that extends straight from the rear end of the front inclined portion toward the rear of the vehicle, and a rear inclined portion that inclines outward in the vehicle width direction from the rear end of the straight portion toward the rear of the vehicle.

In the above configuration, the floor side member connects the front side member and rear side member, which are located at the front and rear of the vehicle. The rear side member is also located between the side sill and the center tunnel. For this reason, the floor side member is arranged between the side sill and the center tunnel. The floor panel is therefore divided in the vehicle width direction with the floor side member as a boundary. Here, floor vibration can be suppressed by arranging the floor side member at the midpoint of the floor vibration surface of the floor panel. The midpoint of the floor vibration surface is the position where, in the horizontal plane of the floor panel, the dimension between the center tunnel and the floor side member is approximately the same as the dimension between the side sill and the floor side member.

In addition, in the above configuration, the floor side member has a front inclined portion and a rear inclined portion. As a result, even if the connection position of the floor side member to the front side member or the rear side member located at the front and rear of the vehicle is away from the center position of the floor vibration surface, the straight portion located between the two inclined portions can be moved closer to the center position of the floor vibration surface by adjusting the inclination degree and length of the two inclined portions. Therefore, according to the above configuration, floor vibration can be suppressed by moving the straight portion of the floor side member closer to the center position of the floor vibration surface.

In order to solve the above problems, another representative configuration of the vehicle understructure according to the present invention is a vehicle understructure having a floor panel that forms the floor surface of the vehicle, the vehicle understructure further comprising a side sill extending in the vehicle longitudinal direction along the edge of the floor panel, a center tunnel extending in the vehicle longitudinal direction at the center of the floor panel in the vehicle width direction, a rear side member extending from the rear end of the vehicle to the front of the vehicle between the side sill and the center tunnel, and a floor side member connecting the rear side member and a front side member located at the front of the vehicle under the floor panel, the floor side member having a front inclined portion that inclines outward in the vehicle width direction as it approaches the rear of the vehicle, a straight portion that extends straight from the rear end of the front inclined portion to the rear of the vehicle, and a rear inclined portion that inclines outward in the vehicle width direction as it approaches the rear of the vehicle from the rear end of the straight portion.

In the above configuration, a floor side member is disposed between the side sill and the center tunnel. Therefore, the floor panel is divided in the vehicle width direction with the floor side member as a boundary. In the above configuration, a front inclined portion and a rear inclined portion are set in the floor side member. As a result, even if the connection position of the floor side member to the front side member or the rear side member located at the front and rear of the vehicle is located away from the center position of the floor vibration plane, the straight portion located between the two inclined portions can be moved closer to the center position of the floor vibration plane by adjusting the inclination degree and length of the two inclined portions. Therefore, according to the above configuration, floor vibration can be suppressed by moving the straight portion of the floor side member closer to the center position of the floor vibration plane.

The straight portion of the floor side member may be located in the floor panel at a midpoint between the side sill and the center tunnel.

In this way, the front inclined portion and rear inclined portion of the floor side member allow the straight portion to be close to the midpoint between the side sill and the center tunnel, i.e., the midpoint in the vehicle width direction of the horizontal floor vibration surface located between the side sill and the center tunnel. In the above configuration, the straight portion of the floor side member is overlapped at the midpoint, so the dimensional difference between one side and the other side of the floor vibration surface with the straight portion of the floor side member as the boundary is small, and floor vibration can be suppressed.

The floor side member may have a suspension connection portion to which the front suspension frame is connected.

As a result, the floor side member is supported by the highly rigid front suspension frame via the suspension connection. This makes it possible to suppress vibrations in the floor side member itself, and therefore floor vibrations in the floor panel connected to the floor side member can also be suppressed.

The above-mentioned suspension connection portion preferably extends in a straight line from the front end of the front inclined portion toward the front of the vehicle.

In this way, in the floor side member, the susflex connection portion, which is a separate part from the front inclined portion, extends in a straight line from the front end of the front inclined portion toward the front of the vehicle. This makes it easier to position the rear fixing point of the front suspension frame, which is connected to the susflex connection portion, on the outside in the vehicle width direction, compared to when a connection portion with the front suspension frame is provided on the front inclined portion itself. As a result, when a load in the vehicle width direction acts on the floor side member, the load can be easily dispersed and released from the rear fixing point of the susflex connection portion to the front fixing point of the front suspension frame, which is connected to the front side member, etc. This makes it possible to suppress vibration of the front side member itself and thereby suppress floor vibration.

In addition, even if the front fixed point of the front suspension frame, which is set on the front side member, or the torque rod connected to the front suspension frame receives a load in the vehicle width direction, this load can be easily distributed to the floor side member and released. This suppresses vibration of the front suspension frame, improving stability during steering.

In addition, because the suspension connection portion extends in a straight line from the front end of the front inclined portion toward the front of the vehicle, when the front inclined portion receives a load from the front, the front inclined portion deforms in the vehicle width direction, preventing front members such as the dash cross member and the front suspension frame from moving backward.

The vehicle undercarriage structure further includes a rear cross member extending in the vehicle width direction and connected to the rear inclined portion of the floor side member, the rear inclined portion having a first rear inclined portion located forward of the connection position where the rear cross member is connected and a second rear inclined portion located rearward of the connection position, and the first rear inclined portion preferably has a gentler inclination outward in the vehicle width direction than the inclination of the second rear inclined portion.

In this way, the first rear inclined portion of the floor side member, which is forward of the connection position of the rear cross member, has a gentler inclination than the second rear inclined portion, which is rear of the connection position. This makes it less likely for stress to concentrate locally on the floor side member when it receives a load from the front, and makes it possible to suppress deformation in the vehicle width direction due to this load.

In addition, because the inclination of the first rear inclined portion is gentler than that of the second rear inclined portion, the degree of change in the dimensional difference in the vehicle width direction between one side and the other side of the floor vibration surface bounded by the first rear inclined portion also becomes gentler, which makes it possible to suppress floor vibration.

If the inclination of not only the first rear inclined portion but also the second rear inclined portion were made gentler, the dimension of the rear inclined portion in the vehicle's fore-aft direction would become large, and the dimension of the straight portion in the vehicle's fore-aft direction would be limited. Therefore, in the above configuration, the inclination of the second rear inclined portion is made steeper than that of the first rear inclined portion, thereby preventing the overall dimension of the rear inclined portion in the vehicle's fore-aft direction from becoming large, and space is secured for arranging the straight portion extending in the vehicle's fore-aft direction.

Furthermore, if the inclination degree of the second rear inclined portion is increased, stress tends to concentrate locally on the second rear inclined portion when a load is applied from the front, making the second rear inclined portion more likely to deform in the vehicle width direction. Therefore, in the above configuration, by setting the connection position with the rear cross member in front of the second rear inclined portion, the rear cross member can suppress deformation of the second rear inclined portion in the vehicle width direction.

The vehicle undercarriage structure may further include a rear cross member extending in the vehicle width direction and connected to the side sill, the rear side member, and the rear inclined portion of the floor side member, the rear inclined portion having a bulge portion that bulges upward, and the rear cross member may be connected to the upper surface of the bulge portion and at least one of the front surface and the rear surface of the bulge portion.

Here, when the side sill, rear side member, and rear inclined portion are connected by a rear cross member, if the rear inclined portion does not have a bulge portion as configured above, the rear cross member would be connected to the upper surface of the rear inclined portion. In such a configuration, the connection area between the rear inclined portion and the rear cross member cannot be secured, making it difficult to suppress deformation of the rear inclined portion in the vehicle width direction. Therefore, in the above configuration, a bulge portion that bulges upward is provided on the rear inclined portion, increasing the connection area between the rear cross member and the rear inclined portion and increasing the connection rigidity. Therefore, with the above configuration, deformation and vibration of the floor side member can be suppressed, and floor vibration can also be suppressed.

The rear end of the floor side member is connected to the rear side member, and the floor side member, together with the rear side member and the rear cross member, preferably forms a closed cross section.

This allows the rigidity of the floor side member, rear side member and rear cross member as a whole to be increased by the closed cross section, thereby increasing the support rigidity of the rear side member and the connection rigidity of the floor side member. As a result, vibration of the floor side member can be suppressed, and floor vibration caused by this vibration can be reduced. Furthermore, because one of the components of the closed cross section is the floor side member extending toward the front of the vehicle, it is easy to make adjustments such as distributing the load to the floor side member side to avoid stress concentration.

The preferred embodiment of the present invention will be described in detail below with reference to the attached drawings. The dimensions, materials, and other specific values shown in the embodiment are merely examples to facilitate understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same function and configuration are given the same reference numerals to avoid repeated explanation, and elements that are not directly related to the present invention are not shown. In this embodiment, connection includes various forms such as joining that joins separate members, abutment that brings separate members into contact, and integration that makes each member the same member.

Figure 1 is a bottom view showing a vehicle underbody structure 100 according to an embodiment of the present invention. The figure shows the vehicle underbody structure 100 as seen from below the vehicle. In each of the following figures, the front-to-rear direction of the vehicle is indicated by arrows Front and Back, the left and right directions of the vehicle width are indicated by arrows Left and Right, and the top-to-bottom direction of the vehicle are indicated by arrows Up and Down.

The vehicle undercarriage structure 100 includes a floor panel 102 that forms the floor surface of the vehicle, a pair of side sills 104, 106, and a center tunnel 108. The pair of side sills 104, 106 are spaced apart in the vehicle width direction and extend in the vehicle front-rear direction along edges 110, 112 of the floor panel 102. The center tunnel 108 extends in the vehicle front-rear direction at the center of the floor panel 102 in the vehicle width direction. The floor panel 102 includes a floor horizontal surface 114 surrounded by dotted line A in the figure, and upwardly inclined portions 116, 118 surrounded by dotted lines B, C in the figure, which are respectively disposed on the vehicle width outer sides of the floor horizontal surface 114.

The vehicle underbody structure 100 further includes a pair of suspension fixing parts 120, 122, a pair of rear side members 124, 126, and a pair of floor side members 128, 130. As the vehicle underbody structure 100 has a symmetrical structure as shown in FIG. 1, only the structure on the right side in the vehicle width direction will be described below unless otherwise necessary.

Figure 2 shows a part of the vehicle undercarriage 100 in Figure 1 and various suspensions 132, 134. Figure 2(a) shows an enlarged view of the suspension fixing part 120 and its surrounding structure. Figures 2(b) and 2(c) show the schematic configuration of general suspensions 132, 134 with different pivot axis directions (pivot axis directions).

The suspension fixing part 120 is a portion to which a swingable suspension 132 for a rear wheel 136 shown in Fig. 2(b) is fixed. The suspension 132 has a so-called semi-independent axle structure, and has a trailing link 138, a coupling profile 140 extending in the vehicle width direction, and a shock absorber 142. The suspension 132 has a swing axis Sb in the vehicle width direction that passes through a front end 144 of the trailing link 138.

The front end 144 of the trailing link 138 in FIG. 2(b) is fixed to the suspension fixing part 120. The suspension fixing part 120 is also connected to the inclined part 146 of the rear side member 124 as shown in FIG. 1.

The rear side member 124 is a member located below the floor panel 102 and extending from the rear end 148 of the vehicle forward between the side sill 104 and the center tunnel 108, and extends to the rear of the vehicle beyond the side sill 104, for example, on the inner side of the side sill 104 in the vehicle width direction. Note that the rear side member 124 is not limited to being located on the inner side of the side sill 104 in the vehicle width direction, and may be located on the rear side of the vehicle.

The inclined portion 146 of the rear side member 124 is a portion that inclines outward in the vehicle width direction as it approaches the front of the vehicle, as shown in FIG. 1. Because the suspension fixing portion 120 is connected to the inclined portion 146 of the rear side member 124, the pivot axis Sa passing through the suspension fixing portion 120 in FIG. 2(a) in the vehicle undercarriage structure 100 is inclined toward the front of the vehicle as it approaches the inside of the vehicle width direction, perpendicular to the inclined portion 146.

The suspension 134 shown in FIG. 2(c) is a so-called spring strut independent suspension, and has a wheel carrier 150, a tie rod 152, a lower A-arm link 154, and a shock absorber 156. The suspension 134 has a swing axis Sc in the vehicle's fore-and-aft direction that passes through the front end 158 and rear end 160 of the lower A-arm link 154.

By applying the suspensions 132, 134 to the suspension fixing portion 120, the vehicle underside structure 100 is not limited to the swing axis Sa whose swing axis direction is inclined toward the front of the vehicle as it moves inward in the vehicle width direction, but has swing axes Sb, Sc whose swing axis direction is in the vehicle width direction or the vehicle front-rear direction. Note that, unlike the swing axes Sa, Sb, Sc, although not shown in the figure, the vehicle underside structure 100 can also be applied to a suspension having a swing axis whose swing axis direction is inclined toward the rear of the vehicle as it moves inward in the vehicle width direction.

For this reason, the rear side member 124 connected to the suspension fixing part 120 receives a load in the swing axis direction from the suspension 132 via the suspension fixing part 120 while the vehicle is traveling, for example. Furthermore, when the vehicle undercarriage structure 100 is applied to the suspension 134, the rear side member 124 receives a load as a vibration component in the vehicle width direction due to vibrations while the vehicle is traveling, even if a swing axis Sc is set with the swing axis direction being the vehicle fore-and-aft direction. In other words, the rear side member 124 receives a load in the swing axis direction or the vehicle width direction via the suspension fixing part 120.

The floor side member 128 connects the rear side member 124 to the front member 162 or front side member 164 located at the front of the vehicle below the floor panel 102 shown in FIG. 1. The front member 162 includes a dash cross member 166 that extends in the vehicle width direction and is located between the side sills 104, 106, and a front suspension frame 168. In the figure, the outline of the front suspension frame 168 is shown by a chain line, and various members that overlap with the front suspension frame 168 are shown transparently. In addition, braces 169a, 169b that are inclined outward in the vehicle width direction toward the rear of the vehicle are arranged on the outer side of the dash cross member 166 in the vehicle width direction, and connect the dash cross member 166 to the side sills 104, 106.

A front side extension 170 is disposed on the vehicle front side of the side sill 104. A front suspension 172 is located between the front side member 164 and the front side extension 170. On the left side of the vehicle width direction in the vehicle undercarriage structure 100, as shown in FIG. 1, a front side extension 174 located on the vehicle front side of the side sill 106, a front side member 176, and a front suspension 178 are disposed.

The front suspension frame 168 also has rear fixing points 180, 182 with the floor side members 128, 130, and intermediate fixing points 184, 186 with the front side members 164, 176. The front suspension frame 168 also has forward fixing points 188, 190 with other members located further forward of the intermediate fixing points 184, 186. Note that the front side members 164, 176 and the floor side members 128, 130 are separate members, but this is not limiting and they may be of an integrated structure.

As described above, the rear side member 124 receives a load in the swing axis direction or vehicle width direction via the suspension fixing part 120. Therefore, in order to suppress vibration of the rear side member 124 in the swing axis direction or vehicle width direction, the vehicle undercarriage structure 100 employs a configuration in which the floor side member 128 and the suspension fixing part 120 are connected to adjacent areas of the rear side member 124 (see FIG. 3(a)) or opposing areas (see FIG. 9(a) and FIG. 9(b)).

Figure 3 shows a cross section taken along line D-D of the vehicle underbody structure 100 in Figure 2(a) and a comparative example. As shown in the cross section taken along line D-D in Figure 3(a), the rear side member 124 has the suspension fixing part 120 connected to its underside 192. In addition, the rear end part 194 of the floor side member 128 shown in Figure 2(a) has a bulging part 196. The bulging part 196 is a part that bulges out towards the rear side member 124 as shown by the dotted line E.

Furthermore, as shown in FIG. 3(a), the bulge portion 196 is connected to a side surface 198 on the inner side in the vehicle width direction adjacent to the lower surface 192 of the rear side member 124 to which the suspension fixing portion 120 is connected. In this way, the side member 128 and the suspension fixing portion 120 are connected to adjacent regions of the rear side member 124, i.e., the side surface 198 and the lower surface 192 on the inner side in the vehicle width direction, respectively. Furthermore, the side surface 198 of the rear side member 124 is a side surface that is approximately perpendicular to the oscillating axis direction of the oscillating axis Sa (see FIG. 2(a)), which is formed by inclining the oscillating axis Sb of the suspension 132.

The vehicle underbody structure 100A of the comparative example shown in FIG. 3(b) differs from the vehicle underbody structure 100 in that it does not have a floor side member 128. As a result, in the vehicle underbody structure 100A, the rear side member 124 swings in the swing axis direction or vehicle width direction indicated by arrow F due to the load transmitted from the suspension 132 via the suspension fixing part 120 while the vehicle is traveling, and vibrates out of position as indicated by dotted line G.

In contrast, in the vehicle underbody structure 100 of FIG. 2(a), the load transmitted from the suspension fixing part 120 to the rear side member 124 can be dispersed and released to the front member 162 or front side member 164 via the floor side member 128 in the periphery 200 of the suspension fixing part 120 of the rear side member 124, i.e., on the upstream side of the load transmission path where the load is transmitted from the suspension fixing part 120.

As shown in FIG. 2(a), the rear end 194 of the floor side member 128 has a bulge 196 that is connected to the side surface 198 of the rear side member 124, so that the connection area of the floor side member 128 to the rear side member 124 can be increased. This increases the connection rigidity of the floor side member 128 to the rear side member 124, making it easier for the floor side member 128 to receive a load from the rear side member 124. Furthermore, because the side surface 198 of the rear side member 124 is a side surface that is nearly perpendicular to the swing axis direction of the swing shaft Sa, the load received by the rear side member 124 can be efficiently received by the highly rigid floor side member 128, distributed, and released.

As a result, vibrations of the rear side member 124 in the swing axis direction or vehicle width direction, particularly vibrations in the load transfer path downstream of the connection position of the rear side member 124 with the floor side member 128, are suppressed. Therefore, the vehicle underbody structure 100 can reduce torsional vibrations of the vehicle body and floor vibrations of the floor panel 102 caused by vibrations of the rear side member 124.

As shown in FIG. 2(a), in the vehicle underbody structure 100, the bulging portion 196 of the floor side member 128 bulges toward the rear side member 124, so there is no need to incline or curve the rear end 194 of the floor side member 128 to approach the rear side member 124 by the amount of this bulging. This makes it possible to suppress deformation such as shrinking in the vehicle's fore-and-aft direction when the floor side member 128 receives a load from the vehicle's fore-and-aft direction.

The vehicle undercarriage 100 further includes a first rear cross member 202 and a second rear cross member 204 spaced apart in the vehicle longitudinal direction as shown in FIG. 1. The first rear cross member 202 extends in the vehicle width direction and is connected to the rear ends 194, 206 of the floor side members 128, 130 and the rear side members 124, 126. The second rear cross member 204 extends in the vehicle width direction and is connected to the front ends 208, 210 of the rear side members 124, 126 and the floor side members 128, 130.

This allows the load transmitted to the rear side member 124 via the suspension fixing portion 120 to be dispersed and released from the rear side member 124 to the floor side member 128, the first rear cross member 202, and the second rear cross member 204. In addition, even if the floor side member 128 receives a load from the rear side member 124, the first rear cross member 202 and the second rear cross member 204 can suppress vibration of the floor side member 128 in the swing axis direction or the vehicle width direction.

Furthermore, since the load transmitted to the rear side member 124 can be dissipated to the floor side member 128, which is stiffer or heavier than the first rear cross member 202 and the second rear cross member 204, vibration of the rear side member 124 can be suppressed while suppressing an increase in stiffness or thickness of the first rear cross member 202 and the second rear cross member 204.

As shown in FIG. 2A, since the first rear cross member 202 is connected to the rear end 194 of the floor side member 128, the rear end 194 of the floor side member 128 is supported by the rear side member 124 and the first rear cross member 202, and the load transmitted from the rear side member 124 to the rear end 194 of the floor side member 128 is easily released to the first rear cross member 202 side, so that the vibration of the floor side member 128 can be suppressed. Furthermore, since the vibration is easily transmitted between the rear side member 124 and the first rear cross member 202 via the rear end 194 of the floor side member 128, the vibration of the rear side member 124 and the first rear cross member 202 can also be suppressed. Furthermore, since the floor side member 128 is connected overlapping the connection surface between the first rear cross member 202 and the rear side member 124, the connection rigidity of the first rear cross member 202 and the rear side member 124 can be increased. In addition, the floor side member 128 supports the rear side member 124 and is further connected to the first rear cross member 202 and the second rear cross member 204. This increases the support rigidity of the floor side member 128, making it possible to suppress vibration of the rear side member 124 in the swing axis direction or the vehicle width direction.

As shown in FIG. 1, in the vehicle undercarriage structure 100, a frame structure is formed by the floor side members 128, 130, the first rear cross member 202, and the second rear cross member 204, and a frame structure is further formed by the rear side members 124, 126, the first rear cross member 202, and the second rear cross member 204. This increases the overall rigidity of the members that make up this frame structure, thereby increasing the support rigidity of the rear side members 124, 126 and the floor side members 128, 130.

In the vehicle underbody structure 100 of FIG. 2(a), it is assumed that the transmission path of the load transmitted to the rear side member 124 via the suspension fixing part 120 branches in a direction intersecting the swing axis direction of the swing axis Sa, for example, toward the front or rear of the vehicle. In such a case, in the vehicle underbody structure 100, as shown in FIG. 2(a), the first rear cross member 202 and the second rear cross member 204, which are spaced apart in the vehicle longitudinal direction, are disposed at positions sandwiching the swing axis Sa. Therefore, in the vehicle underbody structure 100, the loads transmitted downstream of the branch point of the load transmission path can be transmitted to the first rear cross member 202 or the second rear cross member 204. As a result, the vibration of the rear side member 124 in the swing axis direction or vehicle width direction can be suppressed, and the torsional vibration and floor vibration caused by this vibration can be reduced.

The rear side member 124 is sandwiched between the side sill 104 and the floor side member 128 in the pivot axis direction or vehicle width direction as shown in FIG. 2(a). This allows the load transmitted to the rear side member 124 via the suspension fixing part 120 to be transmitted and dispersed to the highly rigid floor side member 128 and side sill 104. The floor side member 128 is connected upstream of the second rear cross member 204 in the load transmission path that does not pass through the side sill 104.

Furthermore, the floor side member 128, together with the rear side member 124 and the second rear cross member 204, forms a closed cross section 212 of a triangular truss structure as a frame structure surrounded by a chain line H in FIG. 2(a). As a result, the rigidity of the entire floor side member 128, the rear side member 124 and the second rear cross member 204 can be increased by the closed cross section 212, so that the support rigidity of the rear side member 124 can be increased. As a result, the vibration of the rear side member 124 in the swing axis direction or the vehicle width direction is suppressed, and further, the vibration of the floor side member 128 is also suppressed, so that the torsional vibration and floor vibration caused by these vibrations can be reduced. Moreover, since one of the components of the closed cross section 212 is the floor side member 128 extending forward of the vehicle, it is easy to make adjustments such as distributing the load to the floor side member 128 side to avoid stress concentration.

In addition, in the vehicle undercarriage structure 100, the rear side member 124 has an inclined portion 146 as shown in FIG. 1, and the side surface 198 of the rear side member 124 that is connected to the rear end portion 194 of the floor side member 128 is formed on this inclined portion 146. Therefore, even if the rear end portion 194 of the floor side member 128 is not significantly inclined so as to approach the rear side member 124, the connection area between the floor side member 128 and the rear side member 124 can be increased. This makes it possible to increase the connection rigidity between the floor side member 128 and the rear side member 124.

Therefore, according to the vehicle underbody structure 100, even if the floor side member 128 receives a load from the vehicle longitudinal direction, it is possible to suppress deformation such that it shrinks in the vehicle longitudinal direction, while suppressing vibration of the rear side member 124 in the swing axis direction or vehicle width direction, thereby reducing torsional vibration and floor vibration caused by this vibration. In addition, in the vehicle underbody structure 100, the rear side member 124 connected to the suspension fixing part 120 to which the suspension 132 is fixed is sandwiched between the second rear cross member 204 and the side sill 104, so that vibration of the suspension 132 can also be suppressed.

The floor side member 128 also has a recess 214 recessed inward in the vehicle width direction between the rear side member 124 and the front member 162 shown in FIG. 1, and is connected to the side surface 198 of the rear side member 124 (see FIG. 2(a)) at the recess 214. This allows the recess 214, which is part of the floor side member 128, to be positioned inward in the vehicle width direction, thereby suppressing surface vibration of the floor panel 102 (described later). In addition, because the floor side member 128 is connected to the side surface 198 of the rear side member 124 at the recess 214, the connection area between the two is increased, thereby increasing the connection rigidity.

Here, in the vehicle undercarriage structure 100, floor side members 128, 130 are disposed between the side sills 104, 106 and the center tunnel 108, as shown in FIG. 1. Therefore, the floor panel 102 is divided in the vehicle width direction with the floor side members 128, 130 as boundaries.

Therefore, in order to suppress floor vibration, the vehicle underbody structure 100 adopts a configuration in which the floor side members 128, 130 are arranged close to the intermediate positions 216, 218 of the floor vibration surface of the floor panel 102. The intermediate position 216 of the floor vibration surface is the position on the horizontal surface 114 of the floor panel 102 where the dimension La between the center tunnel 108 and the floor side member 128 and the dimension Lb between the side sill 104 and the floor side member 128 are approximately the same.

Figure 4 shows a part of the vehicle undercarriage structure 100 of Figure 1 and a modified example. As shown in Figure 4 (a), the floor side member 128 has a front inclined portion 220, a straight portion 222, and a rear inclined portion 224. The front inclined portion 220 is a portion that inclines inward in the vehicle width direction toward the rear of the vehicle. The straight portion 222 is a portion that extends straight from the rear end 226 of the front inclined portion 220 toward the rear of the vehicle. The rear inclined portion 224 is a portion that inclines outward in the vehicle width direction from the rear end 228 of the straight portion 222 toward the rear of the vehicle.

In this way, in the vehicle underbody structure 100, two inclined portions, namely the front inclined portion 220 and the rear inclined portion 224, are set in the floor side member 128. As a result, even if the connection position between the front member 162 or the front side member 164 located at the front and rear of the vehicle of the floor side member 128 and the rear side member 124 is located away from the intermediate position 216 of the floor vibration surface, the straight portion 222 located between the two inclined portions can be brought closer to the intermediate position 216 of the floor vibration surface by adjusting the inclination degree and length of the two inclined portions. Therefore, according to the vehicle underbody structure 100, floor vibration can be suppressed by bringing the straight portion 222 of the floor side member 128 closer to the intermediate position 216 of the floor vibration surface.

In other words, in the floor side member 128, the front inclined portion 220 and the rear inclined portion 224 allow the straight portion 222 to be positioned close to and at the midpoint between the side sill 104 and the center tunnel 108, i.e., the midpoint 216 in the vehicle width direction of the horizontal floor vibration surface located between the side sill 104 and the center tunnel 108.

In this way, in the vehicle undercarriage structure 100, the straight portion 222 of the floor side member 128 is arranged overlapping at the intermediate position 216 as shown in FIG. 1, so that the dimensional difference between one side and the other side of the floor vibration surface of the floor panel 102 with the straight portion 222 as the boundary is small, i.e., the dimensions La and Lb approach the same dimension, thereby suppressing floor vibration.

As shown in FIG. 4(a), the floor side member 128 further has a suspension connection portion 230. The suspension connection portion 230 extends linearly from the front end 232 of the front inclined portion 220 toward the front of the vehicle, and is connected to the front suspension frame 168 at the rear fixing point 180 (see FIG. 1). The front end 232 of the front inclined portion 220 is positioned so as to overlap in the vehicle width direction with the inclined surfaces of the braces 169a, 169b shown in FIG. 1.

As a result, the floor side member 128 is supported by the highly rigid front suspension frame 168 via the suspension connection portion 230. This makes it possible to suppress vibrations in the floor side member 128 itself, and therefore floor vibrations in the floor panel 102 connected to the floor side member 128 can also be suppressed.

As shown in FIG. 4(a), in the floor side member 128, the suspension connection part 230, which is a part different from the front inclined part 220, extends in a straight line from the front end 232 of the front inclined part 220 toward the front of the vehicle. Therefore, in the vehicle undercarriage structure 100, it is easier to position the rear fixed point 180 with the front suspension frame 168, which is connected to the suspension connection part 230, on the outer side in the vehicle width direction, compared to a case in which a connection part with the front suspension frame 168 is provided on the front inclined part 220 itself.

As a result, when a load in the vehicle width direction acts on the floor side member 128 , the load can be easily dispersed and released from the rear fixing point 180 of the suspensory connection part 230 to the front fixing point 188 (see FIG. 1) of the front suspension frame 168 which is connected to the front side member 176 on the left side in the vehicle width direction. Therefore, vibration of the front side member 176 itself can be suppressed, and floor vibration can be suppressed.

In addition, even if the front fixed points 188, 190 of the front suspension frame 168 set on the front side members 164, 176 in FIG. 1, or the torque rod (not shown) connected to the front suspension frame 168, receive a load in the vehicle width direction, this load can be easily dispersed to the floor side members 128, 130 and released. This suppresses vibration of the front suspension frame 168, improving stability during steering.

As shown in FIG. 4(a), the suspension connection portion 230 extends in a straight line from the front end 232 of the front inclined portion 220 toward the front of the vehicle. When the front inclined portion 220 receives a load from the front, the front inclined portion 220 deforms in the vehicle width direction, preventing the front member 162, such as the dash cross member 166 and the front suspension frame 168 shown in FIG. 1, from moving rearward.

The suspension connection part 230 is the front end part of the floor side member 124 as shown in FIG. 1, and is connected to the upper surface and rear surface of the dash cross member 166. Furthermore, the front suspension frame 168 is connected to the upper part of the suspension connection part 230. In other words, the floor side member 124 is sandwiched in the vertical direction between the dash cross member 166 and the front suspension frame 168.

As shown in FIG. 4A, the second rear cross member 204 is connected to the rear inclined portion 224 of the floor side member 128. The rear inclined portion 224 has a first rear inclined portion 234 and a second rear inclined portion 236. The first rear inclined portion 234 is located forward of a connection position 238 where the second rear cross member 204 is connected. The second rear inclined portion 236 is located rearward of the connection position 238. The first rear inclined portion 234 inclines outward in the vehicle width direction at a gentler rate than the second rear inclined portion 236. Therefore, when the floor side member 128 receives a load from the front, stress is less likely to be concentrated locally, and deformation in the vehicle width direction due to this load can be suppressed.

As shown in FIG. 4(a), the inclination of the first rear inclined portion 234 is gentler than that of the second rear inclined portion 236, so the degree of change in the dimensional difference in the vehicle width direction between one side and the other side of the floor vibration surface bounded by the first rear inclined portion 234 is also gentler, so floor vibration can be suppressed. If the inclination of not only the first rear inclined portion 234 but also the second rear inclined portion 236 were made gentler, the dimension of the rear inclined portion 224 in the vehicle fore-aft direction would become larger, and the dimension of the straight portion 222 in the vehicle fore-aft direction would be limited.

Therefore, in the vehicle undercarriage structure 100, the inclination degree of the second rear inclined portion 236 of the rear inclined portion 224 is made steeper than the inclination degree of the first rear inclined portion 234, thereby preventing the overall fore-aft dimension of the rear inclined portion 224 from becoming larger, and ensuring space for arranging the straight portion 222 extending in the fore-aft direction of the vehicle.

In addition, if the inclination degree of the second rear inclined portion 236 is increased, stress tends to concentrate locally on the second rear inclined portion 236 when a load is applied from the front, making the second rear inclined portion 236 more likely to deform in the vehicle width direction. Therefore, in the vehicle undercarriage structure 100, by setting a connection position 238 with the second rear cross member 204 in front of the second rear inclined portion 236, the deformation of the second rear inclined portion 236 in the vehicle width direction can be suppressed by the second rear cross member 204.

In addition, in the vehicle underbody structure 100, the vibration surface of the floor panel 102 shown in Fig. 1 is divided by the upward inclined portions 116, 118 between the floor horizontal surface 114 and the floor, so that the surface vibration can be suppressed. Furthermore, since the upward inclined portions 116, 118 are provided on the outer side of the floor horizontal surface 114 in the vehicle width direction, the floor side members 128, 130 can be easily arranged toward the center in the vehicle width direction, and can be easily bent toward the rear side members 124, 126 in order to connect them to the rear side members 124, 126. In the vehicle underbody structure 100, the floor side members 128, 130 are arranged at the intermediate positions 216, 218 of the floor vibration surface, so that the vibration surface of the floor horizontal surface 114 of the floor panel 102 is divided into four substantially equal portions in the vehicle width direction.

Figure 5 shows the vehicle underbody structure 100 of Figure 4(a) as viewed from another direction. Figures 5(a) and 5(b) show the floor side members 128, 130 as viewed diagonally below and diagonally above, respectively.

The second rear inclined portion 236 has a side surface 240 shown in Fig. 4(a), Fig. 5(a) and Fig. 5(b). In Fig. 4(a), only the portion showing the side surface 240 is a side view, and the remaining portion is a top view. An upwardly bulging portion 242 is formed on the side surface 240 of the second rear inclined portion 236. As shown in Fig . 4(a), the second rear cross member 204 is connected to an upper surface 244 (see Fig. 5(a)) and a front surface 246 of the upwardly bulging portion 242. In order to increase the connection area with the second rear cross member 204, the front end 248 of the upper bulging portion 242 shown in Fig. 4(a) is inclined or arc-shaped in a side view. In accordance with the shape of the front end 248 of the upper bulging portion 242, the rear end 250 of the second rear cross member 204 shown in Fig. 5(b) is also inclined. Furthermore, an upper end 252 of the second rear cross member 204 extends rearward and abuts against an upper surface 244 of the upward bulge 242, thereby increasing the connection area therebetween.

Here, if the rear inclined portion 224 of the side sill 104, rear side member 124, and floor side member 128 is connected by the second rear cross member 204, if the rear inclined portion 224 does not have an upward bulge 242, the second rear cross member 204 will be connected to the upper surface of the rear inclined portion 224. In such a configuration, the connection area between the rear inclined portion 224 and the second rear cross member 204 cannot be secured, making it difficult to suppress deformation of the rear inclined portion 224 in the vehicle width direction.

Therefore, in the vehicle underbody structure 100, by providing an upward bulge 242 on the second rear inclined portion 236 of the rear inclined portion 224, the connection area between the second rear cross member 204 and the rear inclined portion 224 is increased, and the connection rigidity is improved, thereby suppressing deformation and vibration of the floor side member 128 and also suppressing floor vibration.

Figures 4(b) and 4(c) are both examples of the present invention, and are schematic diagrams of a floor side member 128 and a modified floor side member 128A. Note that dashed lines I and J in the figures indicate the state of floor side members 128 and 128A during a frontal collision.

The floor side member 128A of the modified example shown in FIG. 4(c) differs from the floor side member 128 in that the rear inclined portion 224A is inclined from the rear end 228 of the straight portion 222 outward in the vehicle width direction at a constant inclination. In the floor side member 128A, depending on the inclination degree of the rear inclined portion 224A, there is a risk that the rear end 228 of the straight portion 222 will be significantly deformed inward in the vehicle width direction during a frontal collision, as shown by the dashed line J in FIG. 4(c).

In contrast, the floor side member 128 in FIG. 4(b) has a rear inclined portion 224 formed by a first rear inclined portion 234 and a second rear inclined portion 236, which have different inclination degrees. As a result, the floor side member 128 can suppress deformation of the rear end 228 of the straight portion 222 inward in the vehicle width direction during a frontal collision, as shown by the dashed line I in FIG. 4(b).

The vehicle undercarriage structure 100 further includes a connecting member 254 that extends along the vehicle front side of the second rear cross member 204 as shown in FIG. 4(a), and brackets 256, 258 located on the vehicle widthwise outer side of the connecting member 254. The connecting member 254 connects the upper bulge 242 to the bracket 256 by joining to the upper surface 244 and the front surface 246 of the upper bulge 242. The bracket 256 holds the rear side frame 124 shown in FIG. 1 together with the second rear cross member 204 from above and below, and is also connected to the side sill 104 (see FIG. 6).

In the vehicle underbody structure 100, as shown in FIG. 5A, the connecting member 254 is connected so as to be sandwiched in the vehicle width direction by the upper part of the floor side members 128, 130. This configuration increases the connection surface between the second rear cross member 204 and the floor side members 128, 130, thereby increasing the connection rigidity. Furthermore, as shown in FIG. 5B, a bracket fixing portion 259 for fixing a rear seat mounting bracket (not shown) is provided in an area spanning the rear end portion 250 and the upper end portion 152 of the second rear cross member 204. The bracket fixing portion 259 and the upper bulging portion 242 of the floor side member 128 are arranged to overlap in the vertical direction, thereby suppressing the rear seat (not shown) from vibrating in the vertical direction.

Figure 6 is a diagram showing a portion of the vehicle underbody structure 100 in Figure 1 as viewed from the front of the vehicle. As shown in Figure 6, the vehicle underbody structure 100 sandwiches the rear side frame 124 and the side sill 104 between the underside surface 260 of the outer end of the second rear cross member 204 and the upper surface 262 of the outer end of the bracket 256.

Figure 7 is a detailed view of a portion of a modified vehicle underbody structure 100 of Figure 1. Figure 7(a) is a bottom view of a portion of the modified vehicle underbody structure 100A. Figure 7(b) shows the vehicle underbody structure 100A of Figure 7(a) as viewed from diagonally below. Figure 8 shows the vehicle underbody structure 100A of Figure 7 as viewed from another direction.

The modified vehicle underbody structure 100A differs from the above vehicle underbody structure 100 in that, instead of the second rear cross member 204, it is equipped with a second rear cross member 204A that includes a connecting member 254 and brackets 256 and 258.

As shown in FIG. 7(a), in the vehicle undercarriage structure 100A, the second rear cross member 204A is joined to the side sill 104 and the rear side member 124, and the side sill 104 is joined to the rear side member 124. In other words, the side sill 104 and the rear side member 124 joined to the second rear cross member 204A are joined to each other.

As a result, in the vehicle substructure 100A, the rigidity of the members supporting the second rear cross member 204A, i.e., the supporting rigidity of the second rear cross member 204A, can be increased while dispersing and dissipating the load and vibration transmitted to the second rear cross member 204A to the side sill 104 and the rear side member 124. Therefore, vibration of the second rear cross member 204A can be suppressed.

The second rear cross member 204A has a first joint 264 shown in Figures 7(a) and 7(b) and a second joint 266 shown in Figure 7(b). The first joint 264 is the area surrounded by dotted line K in the figure, where the lower flange 268 of the second rear cross member 204A, the side sill 104, and the rear side member 124 overlap in the vertical direction.

The second joint 266 is the area surrounded by dotted line L in FIG. 7(b), where the side flange 270 of the second rear cross member 204A, the inner side surface 272 of the side sill 104, and the side flange (not shown) of the rear side member 124 overlap in the vertical direction.

This allows the three-piece joint area of the second rear cross member 204A, the side sill 104 and the rear side member 124 to be increased, while these members are firmly joined in the vertical and transverse directions by the first joint 264 and the second joint 266. Therefore, in the vehicle lower structure 100A, the connection rigidity of the second rear cross member 204A to the side sill 104 and the rear side member 124 can be increased, and vibrations, particularly torsional vibrations, of the second rear cross member 204A can be suppressed.

The lower end 274 of the second rear cross member 204A is formed with a widened portion 276 that is widened in the vehicle front-rear direction. The widened portion 276 is formed with a first joint 264 and a second joint 266, and further with a third joint 278. The third joint 278 is the area surrounded by dotted line M in Figures 7(a) and 7(b), does not overlap with the side sill 104, and is where the lower flange 268 of the second rear cross member 204A and the lower surface 280 of the rear side member 124 are joined together.

In this way, the widened portion 276 of the second rear cross member 204A is formed with a third joint 278 that is joined together with the rear side member 124, and a first joint 264 and a second joint 266 that are joined together with the side sill 104 and the rear side member 124. This increases the connection area of the second rear cross member 204A to the rear side member 124, thereby increasing the connection rigidity of the second rear cross member 204A.

In addition, in the second rear cross member 204A, the vibration and load of the rear side member 124 can be easily dispersed and released from the third joint 278 to the first joint 264 and the second joint 266 via the widened portion 276. As a result, the vibration of the rear side member 124 is transmitted to the side sill 104, thereby suppressing the vibration of the second rear cross member 204A.

Furthermore, as shown in FIG. 8, a fourth joint 282 and a fifth joint 284 are formed in the widened portion 276 of the second rear cross member 204A. The fourth joint 282 is the area surrounded by dotted line N in the figure, and is joined to and overlaps in the vertical direction with the upper flange 288 of the second rear cross member 204A, the upper surface 286 of the side sill 104, and the floor panel 102 (not shown here).

The fifth joint 284 is the area surrounded by the dotted line O in the figure, adjacent to the fourth joint 282, does not overlap the floor panel 102, and is joined to the upper flange 288 of the second rear cross member 204A and the upper surface 286 of the side sill 104 by overlapping them in the vertical direction. Note that the fifth joint 284 is not limited to this, and may be joined in three pieces so as to overlap the floor panel 102. Alternatively, as a modified example, the fifth joint 284 may function as another first joint formed on the upper surface 286 of the side sill 104 by extending the rear side member 124 so as to overlap between the upper flange 288 of the second rear cross member 204A and the upper surface 286 of the side sill 104, and joining the three pieces.

In addition, when four or more plates are spot welded, the stability of the welding process is reduced, and the joining cost and joining time increase. Therefore, instead of joining four plates, the second rear cross member 204A is divided into a portion where the three plates are joined to the side sill 104 and a portion where the three plates are joined to the floor panel 102, thereby shortening the welding work and welding time compared to the case where the four plates are joined, that is, the second rear cross member 204A, the side sill 104, the rear side member 124, and the floor panel 102. Moreover, by arranging the fourth joint 282 as a three-piece joint joined to the floor panel 102 and the other first joint as a three-piece joint which is a modified example of the fifth joint 284 joined to the side sill 104 adjacent to each other, it is possible to disperse the vibration of the floor panel 102 from the other first joint to the adjacent fourth joint 282 and make it easier to escape. Therefore, the vibration of the floor panel 102 is transmitted to the side sill 102 and the second rear cross member 204A, and the vibration of the floor panel 102 can be suppressed. If the joining costs and joining time are acceptable, the second rear cross member 204A, the side sill 104, the rear side member 124, and the floor panel 102 may be joined together in four pieces.

The vehicle lower structure 100A also has other joints 290, 292. The joint 290 is the area surrounded by dotted line P in FIG. 8, and is joined to the floor panel 102, the rear side member 124, and the second rear cross member 204A, overlapping in the vertical direction to form three pieces. The joint 292 is joined to the side sill 104 and the rear side member 124, overlapping in the vertical direction, as shown in FIG. 7(a) and FIG. 7(b). However, the joint 292 is not limited to this, and the second rear cross member 204A may be extended to join the three pieces together with the side sill 104 and the rear side member 124.

The rear side member 124 shown in FIG. 7(b) has an inner side surface 296 adjacent to the side surface flange 294 of the second rear cross member 204A, an upper surface flange 298 continuing with the inner side surface 296, a side surface flange 300 continuing with the lower surface 280, and a lower flange 302 continuing with the side surface flange 300. Here, the rear side member 124 forms a closed cross section with the upper surface flange 298, the lower surface 280, the inner side surface 296, and the inner side surface 272 of the side sill 104. The outer side surface is also used as the inner side surface 272 of the side sill 104. Since the rear side member 124 is cantilevered, the side surface flange 300 and the lower flange 302 are provided on the lower surface 280 to increase the joint area with the side sill 104.

In the vehicle substructure 100A, the second rear cross member 204A is joined to the side sill 104 and the rear side member 124 so as to overlap the joint surface between the side sill 104 and the rear side member 124, i.e., the first joint 264 and the second joint 266 where the three pieces are joined.

This allows the joint surfaces of the side sill 104 and the rear side member 124, the joint surfaces of the second rear cross member 204A and the side sill 104, and the joint surfaces of the second rear cross member 204A and the rear side member 124 to be close to or overlap each other. This increases the support rigidity of the second rear cross member 204A. In addition, by joining the second rear cross member 204A to the joint surface of the side sill 104 and the rear side member 124, which has increased support rigidity, the connection rigidity of the second rear cross member 204A to the side sill 104 and the rear side member 124 can be increased. This allows the vibration of the second rear cross member 204A to be more sufficiently suppressed.

At point Q of the vehicle undercarriage structure 100 shown in FIG. 2(a), the rear side member 124 is connected to the first rear cross member 202 and the floor side member 128, so the support rigidity of the second rear cross member 204A can be increased. At point Q, the floor side member 128, the first rear cross member 202, and the rear side member 124 are joined in three pieces, overlapping each other in the vertical direction. Adjacent to the area including point Q where the three pieces are joined, there is an area where the rear side member 124 and the floor side member 128 are joined in two pieces, an area where the floor panel 102 is also joined in three pieces, and an area where the first rear cross member 202 and the floor side member 128 are joined in two pieces. This allows the support rigidity of the second rear cross member 204A to be increased more sufficiently.

The dotted line R in the vehicle undercarriage structure 100 shown in FIG. 2(a) indicates the joining area between the side sill 104 and the rear side member 124. In this joining area, a recess 304 is provided behind the rear of the side sill 104, and a protrusion 306 of the rear side member 124 is joined to this recess 304. This allows the rear side member 124 and the side sill 104 to be joined in the vehicle fore-and-aft direction and in the vehicle width direction, thereby increasing the support rigidity of the second rear cross member 204A.

2A of the second rear cross member 204A, the rear portion 307 of the widening portion 276 shown in FIG. 2A extends in a direction substantially perpendicular to the inner side surface 296 of the rear side member 124 (see FIG. 7B). The rear portion 307 of the widening portion 276 further has an inner portion 307a and an outer portion 307b. The inner portion 307a is continuous with the outer portion 307b and is located on the inner side of the outer portion 307b in the vehicle width direction. As shown in FIG. 2A, the inner portion 307a has a greater degree of inclination than the outer portion 307b, and is inclined to follow the rear inclined portion 224 of the floor side member 128 (see FIG. 4A). This configuration increases the joint area between the widening portion 276 and the front end portion 208 of the rear side member 124, while making it easier to transmit vibrations transmitted to the widening portion 276 to the front side of the floor side member 128. Furthermore, if the inner portion 307a of the rear portion 307 of the widened portion 276 is inclined along the pivot axis Sa passing through the suspension fixing portion 120, vibrations transmitted from the suspension fixing portion 120 to the rear side member 124 are easily transmitted to the floor side member 128. The suspension fixing portion 120 may also be joined to the side sill 104 by a bracket (not shown).

In the vehicle underbody structure 100, the front side member 164, floor side member 128, and rear side member 124 are each separate, but this is not limited thereto and they may be of an integrated structure. In this specification, the term "side member" is a concept that includes the front side member 164, floor side member 128, and rear side member 124.

Figure 9 is a schematic diagram showing another modified example of the vehicle underbody structure 100 of Figure 1. In the vehicle underbody structures 100B and 100C shown in Figure 9(a), when the swing axes Ta and Tb are in the vehicle width direction and the vehicle front-rear direction, the floor side member 128 and the suspension fixing part 120 are connected to the areas of the rear side member 124 that face each other in the vehicle width direction, i.e., the side surfaces 308 and 310, respectively. Even with such vehicle underbody structures 100B and 100C, it is possible to suppress vibration of the rear side member 124 in the swing axis direction or the vehicle width direction.

In the vehicle underbody structures 100D and 100E shown in FIG. 9(b), when the swing axes Ta and Tb are in the vehicle width direction and the vehicle front-rear direction, the floor side member 128 and the suspension fixing part 120 are connected to the areas of the rear side member 124 that face each other in the vertical direction, i.e., the upper surface 312 and the lower surface 314, respectively. Even with such vehicle underbody structures 100D and 100E, it is possible to suppress vibration of the rear side member 124 in the swing axis direction or the vehicle width direction.

In the vehicle undercarriage structures 100, 100B to 100E, the floor side member 128 and the suspension fixing part 120 are connected to adjacent or opposing areas of the rear side member 124, respectively, but this is not limited to the above. As an example, when the shock absorber 142 (see FIG. 2(a)) of the suspension 132 is fixed to the suspension fixing part 120, the floor side member 128 and the shock absorber 142 may be connected to adjacent or opposing areas of the rear side member 124, respectively. The width dimension of the shock absorber 142 in the vehicle fore-and-aft direction is smaller than the width dimension of the suspension fixing part 120 in the vehicle fore-and-aft direction.

In the vehicle underbody structures 100F, 100G shown in FIG. 9(c), when the swing axes Ta, Tb are in the vehicle width direction and the vehicle front-rear direction, the floor side member 128 and the rear side member 124 are arranged to face each other in the vehicle width direction via the suspension fixing part 120, and are each connected to the suspension fixing part 120. Even with such vehicle underbody structures 100F, 100G, it is possible to suppress vibration of the rear side member 124 in the swing axis direction or the vehicle width direction.

Figure 10 shows yet another modified example of the vehicle underbody structure 100 of Figure 1. Figure 10(a) shows modified floor side members 128B, 130A. As shown in the figure, floor side members 128B, 130A have a symmetrical structure, so here, the structure of floor side member 128B will be described.

The floor side member 128B differs from the above-described floor side member 128 in that it has a front inclined portion 220A that inclines outward in the vehicle width direction toward the rear of the vehicle instead of the front inclined portion 220. In the floor side member 128B, a straight portion 222 extends straight from a rear end 226A of the front inclined portion 220A toward the rear of the vehicle, and a suspension connection portion 230 extends straight from a front end 232A of the front inclined portion 220A toward the front of the vehicle.

Therefore, even if the connection position between the front member 162 or front side member 164 shown in FIG. 1, which is located at the front or rear of the vehicle of the floor side member 128B, and the rear side member 124 is located away from the intermediate position 216 (see FIG. 1) of the floor vibration surface, by adjusting the inclination degree and length of the two inclined portions, i.e., the front inclined portion 220A and the rear inclined portion 224, the straight portion 222 located between the two inclined portions can be moved closer to the intermediate position 216 of the floor vibration surface, thereby suppressing floor vibration.

As shown in FIG. 1, in the vehicle undercarriage structure 100, the front end position of the floor side member 128, i.e., the connection position between the front side member 164 and the floor side member 128, and the rear end position of the floor side member 128, i.e., the connection position between the floor side member 128 and the rear side member 124 or the side sill 104, are located outside the vehicle width direction of the intermediate position 216 of the floor vibration surface. On the other hand, when the modified floor side member 128B is applied, the front end position of the floor side member 128B is located inside the vehicle width direction of the intermediate position 216, and the rear end position is located outside the vehicle width direction of the intermediate position 216.

However, without being limited to the modified example shown in FIG. 10(a), one of the front end position and the rear end position of the floor side member may be located outside the intermediate position 216 in the vehicle width direction (not shown). Also, one of the front end position and the rear end position of the floor side member may be located at the intermediate position 216. When the front end position of the floor side member is at the intermediate position 216, for example, the front side member 164 is connected to the front end of the straight portion 222. When the rear end position of the floor side member is at the intermediate position 216, for example, the rear side member 124 is connected to the rear end of the straight portion 222.

In the vehicle lower structure 100H shown in FIG. 10(b), the rear side member 124A is joined to the underside of the floor panel 102A, while the side surface 316 of the floor panel 102A, the side sill 104A, and the side surface 318 of the rear side member 124A are joined together in the vehicle width direction. The inside of the floor panel 102A in the vehicle width direction is joined to the center tunnel 108A and the reinforcing member 320. Note that a cross member 322 is disposed between the side sill 104A and the center tunnel 108A, extending in the vehicle width direction above the floor panel 102A.

In this vehicle underbody structure 100H, the load and vibration transmitted to the cross member 322 can be dispersed and released to the side sill 104A and rear side member 124A via the three-piece joint. This makes it possible to suppress vibration of the cross member 322. Furthermore, since vibration of the floor panel 102A can be dispersed and released to the side sill 104A, rear side member 124A, and cross member 322, vibration of the floor panel 102A can be suppressed.

In the vehicle undercarriage structure 100I shown in FIG. 10(c), a rear side member 124B is disposed on the vehicle rear side of the side sill 104B, and the side sill 104B and the rear side member 124B, which are joined to the second rear cross member 204B, are joined to each other. As shown in the figure, the joint surface 324 between the side sill 104B and the rear side member 124B, the joint surface 326 between the second rear cross member 204B and the side sill 104B, and the joint surface 328 between the second rear cross member 204B and the rear side member 124B are brought into close proximity.

As a result, the vehicle substructure 100I can increase the support rigidity of the second rear cross member 204B while dispersing and dissipating the load and vibration transmitted to the second rear cross member 204B to the side sill 104B and the rear side member 124B. This makes it possible to suppress vibration of the second rear cross member 204B.

The vehicle underbody structure 100 may have multiple suspension fixing parts corresponding to multiple swing axes. In such a case, the suspension fixing part 120 and floor side member 128 corresponding to any one of the swing axes may be connected to adjacent or opposing areas of the rear side member 124. This makes it possible to suppress vibration of the rear side member 124 in the swing axis direction or vehicle width direction.

The above describes preferred embodiments of the present invention with reference to the attached drawings, but it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modified or revised examples within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

The present invention can be used in vehicle undercarriage structures.

100, 100B to 100I... Vehicle underbody structure 102, 102A... Floor panel 104, 104A, 104B, 106... Side sill 108, 108A... Center tunnel 110, 112... Edge of floor panel 114... Floor horizontal surface 116, 118... Upward inclined portion 120, 122... Suspension fixing portion 124, 124A, 124B, 126... Rear side member 128, 128A, 128B, 130, 131 30A...floor side members 132, 134...suspension 136...right rear wheel 138...trailing link 140...coupling profiles 142, 156...shock absorber 144...front end of trailing link 146...inclined portion of rear side member 148...rear end of vehicle 150...wheel carrier 152...tie rod 154...lower A-arm link 158...front end of lower A-arm link 160 ...rear end portion 162 of lower A-arm link...front member 164, 176...front side member 166...dash cross member 168...front suspension frame 169a, 169b...brace 170, 174...front side extension 172, 178...front suspension 180, 182...rear fixing point 184, 186...intermediate fixing point 188, 190...front fixing point 192, 280, 314...lower surface 194, 206 of rear side member...rear end portion 196 of floor side member...bulge portion 198...side surface 200 of rear side member...periphery 202 of suspension...first rear cross member 204, 204A, 204B...second rear cross member 208, 210...front end portion 212 of rear side member...closed cross section 214...recess 216, 218 of floor side member...middle position 220, 2 20A...Front inclined portion 222...Straight portion 224, 224A...Rear inclined portion 226, 226A...Rear end 228 of front inclined portion...Rear end 230 of straight portion...Suspension connection portion 232, 232A...Front end 234 of front inclined portion...First rear inclined portion 236...Second rear inclined portion 238...Connection position 240 of second rear cross member...Side surface 242 of second rear inclined portion...Upward bulge portion 244...Top surface 246 of upper bulge portion...Upward bulge portion Front surface 248...front end 250 of upward bulge portion...rear end 252 of second rear cross member...upper end 254 of second rear cross member...connecting member 256, 258...bracket 259...bracket fixing portion 260...lower surface 262 of outer end of second rear cross member...upper surface 264 of outer end of bracket...first joint portion 266...second joint portion 268...lower flange 270, 294 of second rear cross member...second rear cross member [0033] A side flange 272 of the rear cross member... An inner side surface 274 of the side sill... A lower end portion 276 of the second rear cross member... An expanded portion 278... A third joint portion 282... A fourth joint portion 284... A fifth joint portion 286... An upper surface 288 of the side sill... An upper flange 290, 292 of the second rear cross member... An other joint portion 296... An inner side surface 298 of the rear side member... An upper surface 300 of the rear side member... A side flange 302 of the rear side member... A lower flange 304 of the rear side member... A recess 306 of the side sill... A protrusion 307 of the rear side member... A rear portion 307a of the expanded portion... An inner portion 307b of the expanded portion... An outer portion 308, 310 of the expanded portion... A side surface 312 of the rear side member... An upper surface 316 of the rear side member... A side surface 318 of the floor panel... A side surface 320 of the rear side member... A reinforcing member 322... A cross member 324, 326, 328... A joint surface

Claims (7)

A floor panel that forms a floor surface of the vehicle;
a side sill extending in a vehicle front-rear direction along an edge of the floor panel;
a center tunnel extending in a vehicle front-rear direction at a center of the floor panel in a vehicle width direction;
a rear side member extending from a rear end of the vehicle forward between the side sill and the center tunnel;
a floor side member that connects the rear side member and a front side member located at a front part of the vehicle below the floor panel,
The floor side member is
A front inclined portion that inclines inward in the vehicle width direction toward the rear of the vehicle;
a straight portion extending straight from a rear end of the front inclined portion toward the rear of the vehicle;
a rear inclined portion inclined outward in a vehicle width direction from a rear end of the straight portion toward the rear of the vehicle ,
A vehicle undercarriage structure characterized in that the straight portion of the floor side member is located at a middle position in the vehicle width direction of a floor vibration surface of the floor panel that is located between the side sill and the center tunnel . A floor panel that forms a floor surface of the vehicle;
a side sill extending in a vehicle front-rear direction along an edge of the floor panel;
a center tunnel extending in a vehicle front-rear direction at a center of the floor panel in a vehicle width direction;
a rear side member extending from a rear end of the vehicle forward between the side sill and the center tunnel;
a floor side member that connects the rear side member and a front side member located at a front part of the vehicle below the floor panel,
The floor side member is
A front inclined portion that inclines outward in a vehicle width direction toward the rear of the vehicle;
a straight portion extending straight from a rear end of the front inclined portion toward the rear of the vehicle;
a rear inclined portion inclined outward in a vehicle width direction from a rear end of the straight portion toward the rear of the vehicle. 3. The vehicle underbody structure according to claim 1, wherein the floor side member has a suspension connection portion to which a front suspension frame is connected. 4. The vehicle underbody structure according to claim 3 , wherein the suspension connection portion extends linearly from a front end of the front inclined portion toward the front of the vehicle. The vehicle underbody structure further includes a rear cross member extending in a vehicle width direction and connected to the rear inclined portion of the floor side member,
The rear inclined portion is
a first rear inclined portion located forward of a connection position where the rear cross member is connected;
a second rear inclined portion located rearward of the connection position,
5. The vehicle underbody structure according to claim 1, wherein the first rear inclined portion is inclined outward in a vehicle width direction at a more gentle angle than the second rear inclined portion. The vehicle underbody structure further includes a rear cross member extending in a vehicle width direction and connected to the side sill, the rear side member, and the rear inclined portion of the floor side member,
The rear inclined portion has a bulging portion that bulges upward,
5. The vehicle underbody structure according to claim 1, wherein the rear cross member is connected to an upper surface of the bulge and at least one of a front surface and a rear surface of the bulge. A rear end portion of the floor side member is connected to the rear side member,
7. The vehicle underbody structure according to claim 5 , wherein the floor side member, the rear side member and the rear cross member form a closed cross section.

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