WO2012001932A1

WO2012001932A1 - Lower body structure of vehicle

Info

Publication number: WO2012001932A1
Application number: PCT/JP2011/003631
Authority: WO
Inventors: Katsumi Ejima; Keizo Kawasaki
Original assignee: Mazda Motor Corporation
Priority date: 2010-06-30
Filing date: 2011-06-24
Publication date: 2012-01-05
Also published as: DE212011100114U1; CN203255264U

Abstract

An object of the present invention is to provide a lower body structure of a vehicle that can be easily adapted to changes in conditions such as vehicle model, class, and size and can increase production efficiency of the vehicle. A rear side frame 20 extending in the front-rear direction of the vehicle in the rear portion of the vehicle includes a first frame portion 21 provided with a trailing arm bracket 30 that swingably supports a trailing arm 80 of a suspension, a second frame portion 22 that is connected to the first frame portion 21 on the rear side of the vehicle and has a suspension cross member 50 mounted thereon, and a third frame portion 23 connected to the second frame portion 22 on the rear side of the vehicle.

Description

LOWER BODY STRUCTURE OF VEHICLE

The present invention relates to a lower body structure of a vehicle having a rear side frame that extends in the front-rear direction of the vehicle in the rear portion of the vehicle and is provided with a support portion that swingably supports the trailing arm of a suspension.

The rear portion of conventional vehicles has been provided with a rear side frame extending in the front-rear direction of the vehicle and serving as a frame member, for example, as disclosed in PTL 1 listed below.

A support portion that swingably supports the trailing arm of the rear wheel suspension is typically provided in the front portion of the rear side frame, and a suspension cross member for supporting the rear wheel suspension is provided behind the support portion.

Further, the rear side frame has a function of absorbing impact energy by collapsing and deforming in the front-rear direction of the vehicle in the event of rear end collision of the vehicle.

Japanese Patent Application Laid-open No. 2005-247178

The conventional rear side frame is most often configured by a single frame member extending in the front-rear direction of the vehicle, as disclosed in PTL 1 listed above.

However, a great variety of vehicle models, classes, and sizes have been used in recent years and the specifications of the rear side frame also differ depending on these conditions. Therefore, it is necessary to provide vehicle production plants with several production lines for rear side frames, the number of the production lines corresponding to the variations in vehicle models, classes, and sizes.

For example, where the conditions such as vehicle model, class, and size change, the capacity of the fuel tank installed below the rear portion of the vehicle and the wheel base length also change. In this case, the front-rear length of the front portion of the rear side frame that supports the trailing arm should be changed according to the conditions. Further, where the conditions such as vehicle model, class, and size change, the rear overhang length also changes. In this case, the front-rear length of the rear portion of the rear side frame that collapses and deforms in the front-rear direction of the vehicle in the event of rear collision of the vehicle should be changed according to the conditions.

The object of the invention is to provide a lower body structure of a vehicle that can be easily adapted to changes in conditions such as vehicle model, class, and size and can increase production efficiency of the vehicle.

In the lower body structure of a vehicle in accordance with the present invention, rear side frames extending in a front-rear direction of the vehicle in a rear portion of the vehicle include a first frame portion provided with a support portion that swingably supports a trailing arm of a suspension; a second frame portion that is connected to the first frame portion on the rear side of the vehicle and has a suspension cross member mounted thereon, and a third frame portion connected to the second frame portion on the rear side of the vehicle.

The mounting structure of the suspension cross member is substantially common to rear side frames, regardless of the vehicle model, class, and size. Therefore, specifications (shape, dimensions, etc.) of the parts for mounting the suspension cross member are also common to rear side frames. By contrast, specifications of the abovementioned front portions differ according to the capacity of fuel tank and wheel base length, and specifications of the abovementioned rear portions differ according to the overhang length. Therefore, specifications of the front portion where the trailing arm is supported and specifications of the rear portion differ according to the vehicle model, class, and size.

With such a configuration, by configuring the second frame portion from the members separate from those of the first and third frame portions, it is possible to use the second frame portion commonly, regardless of the vehicle model, class, and size, to select, as appropriate, the first and third frame portions corresponding to the capacity of fuel tank, wheel base length, and overhang length and combine the selected first and third frame portions with the second frame portion. Therefore, it is possible to adapt easily to changes in conditions such as vehicle model, class, and size and increase the production efficiency of vehicles.

Fig. 1 is a bottom view of the lower body structure of a vehicle according of an embodiment of the present invention. Fig. 2 is an enlarged bottom view illustrating the rear portion of the lower part of the vehicle. Fig. 3 is a perspective view of the rear side frame. Fig. 4 is a perspective view illustrating, from below, the periphery of a swinging support point of the trailing arm. Fig. 5 is a cross-sectional view taken along the A-A line in Fig. 4. Fig. 6 is a cross-sectional view taken along the B-B line in Fig. 5. Fig. 7 is an explanatory drawing illustrating the operation effect of the present invention; Fig. 7(a) is a side view illustrating the rear side frame structure in the case in which the present invention is used in a sedan-type vehicle; Fig. 7(b) is a view illustrating the rear side frame structure in the case in which the present invention is used in a minivan-type vehicle; and Fig 7(c) is a view illustrating the rear side frame structure in the case in which the present invention is used in a SUV-type vehicle.

DESCRIPTION OF EMBODIMENT

Embodiments of the present invention will be described below with reference to the appended drawings.

Fig. 1 is a bottom view illustrating the lower body structure of a vehicle V according to an embodiment of the invention. The vehicle V according to the present invention is provided with a dash panel 1 partitioning an engine room E and a vehicle cabin (not shown in the figure) in the front portion of the vehicle and a floor panel 2 forming the bottom surface of the vehicle cabin. The dash panel 1 is provided so as to rise from the floor panel 2. The vehicle V is also provided with a pair of side seals 3 extending in the front-rear direction of the vehicle on the left and right side of the floor panel 2. In the figure, the arrow (F) denotes the front side of the vehicle body and the arrow (R) denotes the rear side of the vehicle body.

A tunnel portion 4 is provided in the center, in the width direction of the vehicle, of the dash panel 1 and the floor panel 2 in the lower portion of the vehicle V. The tunnel portion is connected by the front end portion to the dash panel 1 and protrudes from the floor panel 2 into the vehicle cabin on the inner side of the vehicle body.

A pair of left and right floor frames 5 extending in the front-rear direction of the vehicle are provided between the side seal 3 and the tunnel portion 4 in the floor panel 2. The front end portions of the floor frames are connected to the rear end portions of a pair of left and right front side frames (front frames) 6 extending in the front-rear direction of the vehicle in the engine room E.

In the lower portion of the vehicle V, a suspension cross member 7 for supporting a suspension (not shown in the figure) for the front wheels is provided in a position corresponding to the engine room E on the front side of the vehicle. The suspension cross member 7 has a pair of left and right longitudinal members 7a extending mainly in the front-rear direction of the vehicle and a transverse member 7b that extends in the width direction of the vehicle and connects the longitudinal members 7a to each other.

A reinforcement 8 is provided between the tunnel portion 4 and the floor frame 5 in a connection portion X of the rear end portion of the dash panel 1 and the front end portion of the floor panel 2. Further, a torque box 9 is provided between the floor frame 5 and the side seal 3 in the connection portion X.

In the tunnel portion 4, three

gussets

10, 11, 12 are provided so as follow the shape of the tunnel portion 4 on the outside of the vehicle body.

A flat plate member 13 is provided between the front gusset 10 and the intermediate gusset 11, from among the gussets 10 to 12, so as to close the front portion of the tunnel portion 4. Both end portions, in the width direction of the vehicle, of the plate member 13 are joined to the lower portions of the tunnel portion 4 and connect the lower portions of the tunnel portion 4 to each other in a substantially linear fashion.

An auxiliary member 14 extending in the width direction of the vehicle and connecting the lower portions of the tunnel portion 4 to each other is provided in a front end portion of the plate member 13, that is, at a position corresponding to the connection portion X in the front-rear direction of the vehicle and also at a position corresponding to the front gusset 10. The rear end portion of a guide member 15 is joined to the front portion of the auxiliary member 14. The guide member 15 has a substantially flat shape and the front end portion thereof is joined to the transverse member 7b constituting the suspension cross member 7. The guide member 15 together with the plate member 13 form a substantially continuous plane, and when the vehicle travels, the travel wind is guided by the guide member 15 and the plate member 13 to flow substantially directly below the vehicle from the front side to the rear side of the vehicle.

The hot air with a low flow velocity that has flown from the engine room E into the tunnel portion 4 is prevented by the guide member 15 and the plate member 13 from flowing downward outside of the tunnel portion 4 in the front portion thereof. As a result, interference of the travel wind that has a high flow velocity and the hot air having a low flow velocity is inhibited and aerodynamic performance of the vehicle V can be increased.

A flat plane member 16 is provided below the rear gusset 12 correspondingly to the position thereof in the front-rear direction of the vehicle and connects the lower ends of the tunnel portion 4 to each other.

In the present embodiment, the left and right floor frames 5 connected by the front end portions to the front side frames 6 are provided so as to expand outward in the width direction of the vehicle with a transition toward the rear side of the vehicle. The rear end portions of the floor frames 5 are directly connected to the front end portions of a pair of left and right rear side frames 20 extending in the front-rear direction of the vehicle in the rear portion of the vehicle V. With such a configuration, in the present embodiment, the front side frame 6 and the rear side frame 20 are connected together by the floor frame 5.

A trailing arm bracket 30 (referred to hereinbelow simply as "bracket 30") serving as the below-described trailing arm support portion is provided at the front portion of the rear side frame 20 connected to the floor frame 5.

A cross member 40 extending in the width direction of the vehicle is provided at a position corresponding, in the front-rear direction of the vehicle, to the connection portion in which the floor frame 5 is connected to the rear side frame 20.

Fig. 2 is an enlarged bottom view of the rear portion in the lower part of the vehicle V. As shown in Fig. 1 and Fig. 2, a rear floor panel 41 is provided in the rear portion of the cross member 40, and a cross member 42 connecting the left and right rear side frames 20 extending in the width direction of the vehicle and a cargo room floor 43 forming a bottom surface of the cargo room formed in the rear portion of the vehicle cabin. A region compartmentalized by the left and right rear side frame 20 and

cross members

40, 42 is formed below the rear floor panel 41, and a fuel tank FT is provided in this region as shown by a two-dot-dash line in the figure.

A third cross member 44 extending in the width direction of the vehicle and connecting the left and right rear side frames 20 as shown in Fig. 2 is provided outside the cargo room floor 43 on the outside of the vehicle body, that is, in the bottom surface portion. Wheel houses 45 for rear wheels are provided on the outside, in the vehicle width direction, of the rear side frame 20 at positions corresponding to the

cross members

42, 44.

Further, tubular crush boxes 46 are provided, as shown by respective two-dot-dash lines in Fig. 2, at the rear end portions of the rear side frames 20. The left and right crush boxes 46 are connected by a bumper beam 47 extending in the width direction of the vehicle as shown by a two-dot-dash line in Fig. 2.

The structure of the rear side frame 20 will be explained below in greater detail with reference to Figs. 3 to 6. In the figures, the arrow (IN) denotes the direction inward of the vehicle and the arrow (OUT) denotes the direction outward of the vehicle.

The rear side frame 20 is constituted by a first frame portion 21 provided with the trailing arm bracket 30, a second frame portion 22 connected to the first frame portion 21 on the rear side of the vehicle and having mounted thereon a suspension cross member 50 (see Fig. 2) for supporting a suspension (not shown in the figure) for rear wheels, and a third frame portion 23 connected to the second frame portion 22 on the rear side of the vehicle and having the crush box 46 mounted on the rear end portion thereof.

Among the aforementioned components, the second frame portion 22 is provided with suspension cross

member mounting portions

22a, 22b for mounting the suspension cross member 50 on the vehicle body on the bottom surface of the front-rear end portion of the second frame portion, and

bolts

60, 61 are provided vertically in the suspension cross

member mounting portions

22a, 22b. Further, a reinforcing plate 62 is joined correspondingly to the position of the bolt 60 to the second frame portion 22, thereby increasing the mounting rigidity of the bolt 60 on the front side.

In the present embodiment, the suspension cross member 50 has a pair of left and right longitudinal members 50a extending in the front-rear direction of the vehicle as shown by two-dot-dash lines in Fig. 2 and

transverse members

50b, 50c extending in the width direction of the vehicle and connecting the front and rear sections of the longitudinal members 50a. In the suspension cross member 50, the front-rear end portions of the longitudinal members 50a are mounted on the vehicle body (suspension cross

member mounting portions

22a, 22b of the second frame portion 22), with rubber bushing mounts 51 being interposed therebetween, thereby elastically supporting the suspension cross member 50 on the vehicle body.

The

bolts

60, 61 of the second frame portion 22 are provided correspondingly to the position of the bush mount 51 when the suspension cross member 50 is installed in a predetermined position, and the front-rear end portions of the longitudinal member 50a and the bushing mount 51 are tightened and fixed at the suspension cross

member mounting portions

22a, 22b by tightening members such as the

bolts

60, 61 and nuts.

In the present embodiment, the

cross members

42, 44 are provided in the proximity of the suspension cross

member mounting portions

22a, 22b of the second frame portion 22, the proximal portions of the left and right front suspension cross member mounting portions 22a are connected to each other in the width direction of the vehicle by the cross member 42, and the proximal portions of the left and right rear suspension cross member mounting portions 22b are connected to each other in the width direction of the vehicle by the cross member 44. The "proximal portions" as referred to herein mean portions that are proximal to a degree such that the suspension cross member mounting portion 22a overlaps part of the cross member 42 in the side view of the vehicle and, likewise, proximal to a degree such that the suspension cross member mounting portion 22b overlaps part of the cross member 44. In other words, the suspension cross member mounting portions and the cross members are arranged relative to each other so that at least parts thereof overlap.

A plate-shaped box mounting portion 70 is mounted on the rear end portion of the third frame portion 23, and the front end portion of the crush box 46 (see Fig. 2) is connected by the box mounting portion 70.

In the above-described configuration, the third frame portion 23 is made thinner than the first and

second frame portions

21, 22. As a result, in the event of rear collision of the vehicle, the crush box 46 collapses and deforms in the front-rear direction of the vehicle under the impact load, thereby making it possible to absorb the impact energy. After the collapse deformation of the crush box 46, the third frame portion 23 that is shaped to have a small thickness is caused to collapse and deform in the front-rear direction of the vehicle, thereby making it possible to absorb with the third frame portion 23 the impact energy that has not been absorbed by the crush box 46. As a result, deformation of the second frame portion 22 is inhibited, and the penetration of the collision load into the vehicle cabin can be restricted to a minimum. The sheet thickness of steel in the

frame portions

21, 22, 23 can be set for example as follows: 1.8 mm in the first frame portion 21, 1.8 mm in the second frame portion 22, and 1.6 mm in the third frame portion 23, but these values are not limiting.

However, with a rear suspension having a trailing arm, setting a swinging pivotal point of the front end portion of the trailing arm to as high a position as possible has been conventionally considered to be advantageous from the standpoint of traveling feel and safety of occupants, and setting this point at a position higher than that of the wheel center of rear wheels has been assumed to be even more advantageous.

Accordingly, in the present embodiment, an opening 21a is formed in the bottom surface of the first frame portion 21, and as shown in Figs. 4 to 6, the front end portion of the trailing arm 80 of the rear wheel suspension is provided inside a closed cross section 21A (closed cross section formed by the left and right side surfaces of the first frame portion 21, rear floor panel 41, and lower end surface of the first frame 21 in the cross-sectional view that is taken from the front side of the vehicle as shown in Fig. 5) of the first frame portion 21 through the opening 21a. Further, the swinging pivotal point P of the front end portion of the trailing arm 80 is positioned within the closed cross section 21A above the bottom surface portion of the first frame portion 21 by means of support of the below-described bracket 30. As a result, the swinging pivotal point P can be set at a position higher than the wheel center position of rear wheels.

The trailing arm 80 is connected at the front end thereof to the bracket 30 of the first frame portion 21 and supported at the connection portion as a swinging pivotal point P so as to enable swinging together with the rear wheels in the vertical direction.

As shown in Figs. 4 to 6, an annular portion 81 and a tightening piece 83 that is fixed to the annular portion 81, with a rubber bushing 82 being interposed therebetween, are provided at the front end of the trailing arm 80. Among these components, the tightening piece 83 is tightened to the bracket 30 installed inside the closed cross section 21A of the first frame portion 21 by a tightening member 90 such as a bolt and a nut.

The upper open portion of the first frame portion 21 is covered by and joined to the rear floor panel 41, and the outer side of the first frame portion in the width direction of the vehicle is joined to the inner panel 3a constituting the side seal 3 on the inner side of the vehicle body, as shown in Fig. 5. In the present embodiment, the closed cross section 21A is constituted by the bottom surface of the first frame portion 21, side surface thereof on the inner side in the width direction of the vehicle, the rear floor panel 41, and the inner panel 3a of the side seal 3, and the bracket 30 is installed inside the closed cross section 21A.

As shown in Figs. 3 to 6, the bracket 30 is constituted by the first panel 31 extending in the substantially up-down direction on the front side and the second panel 32 having the below-described tightening seat surface portion 32a and has a substantially L-shaped form, in the side view thereof, obtained by joining these first and

second panels

31, 32 together.

As shown in Figs. 4 and 6, the first panel 31 has

flange portions

31a, 31b, 31c at the lower end portion and both sides in the width direction of the vehicle, and these flange portions are respectively joined to the bottom surface of the first frame portion 21, the side surface portion on the inner side in the width direction of the vehicle, and the inner panel 3a of the side seal 3.

As shown in Figs. 4 to 6, the second panel 32 has

flanges

32b, 32c, 32d at the rear end portion and both sides in the width direction of the vehicle, and these flange portions are respectively joined to the bottom surface of the first frame portion 21 and side surface portions at both sides in the width direction of the vehicle.

As shown in Figs. 3 to 6, the tightening seat surface portion 32a extending substantially horizontally in the second panel 32 is formed at the bracket 30, and a front end accommodation portion 32a1 protruding upward and serving to arrange the front end of the trailing arm 80 further upward is formed at the tightening seat surface portion 32a.

The tightening seat surface portion 32a also has mounting holes 32a2 (see Fig. 5) for inserting the tightening members 90 at both sides of the front end accommodation portion 32a1 on both sides in the width direction of the vehicle, and the tightening piece 83 is tightened to the tightening seat surface portion 32a by the tightening members 90 at the positions of mounting holes 32a2.

Thus, in the present embodiment, the bracket 30 is installed so that the swinging pivotal point P of the trailing arm 80 is positioned within the closed cross section 21A.

In the present embodiment, a large load is assumed to be applied to the swinging pivotal point P of the trailing arm 80, and the thickness of the second panel 32 is set to be larger than the thickness of the first panel 31 in order to ensure the support rigidity in the swinging pivotal point P. Further, as shown in Fig. 5, reinforcing plates 91 are disposed in the tightening sites where bolts 90 are located, and the tightening is performed in a state in which the three components, namely, the tightening piece 83, second panel 32, and reinforcing plate 91, are stacked.

Thus, in the present embodiment, the front end portion of the rear side frame 20 and the rear end portion of the front side frame 6 are connected together by the floor frame 5. As a result, in the event of front collision of the vehicle, the impact load inputted from the front side of the vehicle can be effectively and directly transmitted to the rear side frame 20 by the front side frame 6 and the floor frame 5. In the event of rear collision of the vehicle, the impact load inputted from the rear side of the vehicle can be effectively and directly transmitted to the front side frame 6 by the rear side frame 20 and the floor frame 5. Essentially, in the event of front collision of the vehicle or rear collision of the vehicle, the impact load inputted from one frame in the front-rear direction of the vehicle (here, either of the front side frame 6 and the rear side frame 20), can be effectively and directly transmitted to the other frame in the front-rear direction of the vehicle, by the floor frame 5, and the impact load can be dispersed smoother.

Further, in the case in which the bracket 30 serving as a support portion of the trailing arm 80 is provided at the front portion of the rear side frame 20, as in the present embodiment, by directly connecting the front end portion of the rear side frame 20 to the floor frame 5, it is possible to increase the support rigidity of the front portion of the rear side frame 20, that is, the trailing arm 80 in the first frame portion 21 by using a simple configuration.

By disposing the bracket 30 so that the opening 21a is formed in the bottom surface of the first frame portion 21 and the swinging pivotal point P of the trailing arm 80 is positioned within the closed cross section 21A, it is possible to set the swinging pivotal point P of the trailing arm 80 to a position as high as possible with respect to the wheel center position of rear wheels, and the traveling feel of the occupants and operation stability can be improved.

However, since the opening 21a is formed in the bottom surface of the first frame portion 21, the support rigidity of the trailing arm 80 can be decreased, but this decrease in the support rigidity of the trailing arm 80 can be effectively inhibited with a simple structure by directly connecting the front end portion of the rear side frame 20 to the floor frame 5, as described hereinabove.

Generally, the mounting structure of the suspension cross member 50 is substantially common to the rear side frame 20, regardless of the vehicle model, class, and size. Therefore, specifications (shape, dimensions, etc.) of the parts for mounting the suspension cross member 50 are also substantially common. By contrast, specifications of the front portion where the trailing arm 80 is supported and specifications of the rear portion that collapses and deforms in the event of rear collision of the vehicle differ according to the vehicle model, class, and size because specifications of the front portion differ according to the capacity of the fuel tank FT and wheel base length, and specifications of the rear portion differ according to the overhang length.

Accordingly, in the present embodiment, the rear side frame 20 is constituted by providing the first frame portion 21 where the bracket 30 of the trailing arm 80 is provided, the second frame portion 22 having the suspension cross member 50 mounted thereon, and the third frame portion 23 connected to the rear part of the second frame portion 22.

By so configuring the second frame portion 22 from the members separate from those of the first and

third frame portions

21, 23, it is possible to use the second frame portion 22 commonly, regardless of the vehicle model, class, and size, to select, as appropriate, the first and

third frame portions

21, 23 corresponding to the capacity of the fuel tank FT, wheel base length, and overhang length, combine the selected first and third frame portions with the second frame portion 22, and to adapt easily to changes in conditions such as the vehicle model, class, and size.

Fig. 7(a) is a side view illustrating the structure of the rear side frame 120 in the case in which the present invention is used in a sedan-type vehicle V1. Fig. 7(b) is a view illustrating the structure of the rear side frame 220 in the case in which the present invention is used in a minivan-type vehicle V2. Fig. 7(c) is a view illustrating structure of the rear side frame 320 in the case in which the present invention is used in a SUV-type vehicle V3.

Where the vehicles V1 to V3 are compared, for example, in the vehicles V2 and V3, the wheel base lengths WB2 and WB3 are substantially equal to each other, and the wheel base length WB1 in the vehicle V1 is set shorter than those in the vehicles V2 and V3. Further, the capacity of fuel tank FT (see Figs. 1 and 2) is set to increase in the order of vehicles V1, V2, V3.

In this case, the wheel center of rear wheels shifts rearward with the increase in the wheel base length WB. Therefore, in the rear side frames 220, 320, the front-rear length of the

first frame portions

221, 321 is set larger than that of the first frame portion 121 of the rear side frame 120. Further, since the cross member 40 (see Figs. 1 and 2) is usually disposed further forward to ensure the accommodation space of the fuel tank FT when the capacity thereof increases, the position of the front end of the first frame portion 221 is set further toward the front end of the vehicle than the front end of the first frame portion 121, and the position of the front end of the first frame portion 321 is set even further toward the front end of the vehicle than the front end of the first frame portion 221.

Therefore, the front-rear length of the first frame portion 221 is set larger than that of the first frame portion 121, and the front-rear length of the first frame portion 321 is set larger than that of the first frame portion 221.

The vehicles V1 to V3 have different overhang lengths OH1 to OH3. In this case, the front-rear length of the

third frame portion

123, 223, 323 is set according to the overhang lengths OH1 to OH3.

Referring to Fig. 7, specifications of the

second frame portions

122, 222, 322 are substantially common to the vehicles V1 to V3.

Thus, by configuring the first and third frame portions from separate members, it is possible to use commonly the

second frame portions

122, 222, 322 to select, as appropriate, the

first frame portions

121, 221, 321 and

third frame portions

123, 223, 323 corresponding to the conditions (for example, sedan, minivan, SUV, and the like) such as model, class, and size of the vehicles V1 to V3 and combine the selected frame portions with the

second frame portions

122, 222, 322. Therefore, it is easy to adapt to changes in the aforementioned conditions and the production efficiency of vehicle can be increased.

In the second frame portion 22, by connecting the proximities of the left and right mounting portions of the suspension cross member 50 by

cross members

42, 44 in the width direction of the vehicle, it is possible to increase the mounting rigidity of the suspension cross member 50 in the second frame portion 22 by using a simple configuration.

Further, by connecting the proximities of the mounting portions on the front and rear side of the suspension cross member 50 with

respective cross members

42, 44, it is possible to increase further the effect of increasing the mounting rigidity of the suspension cross member 50.

Further, by setting the thickness of the first and

second frame portions

21, 22 to be higher than the thickness of the third frame portion 23, it is possible to increase the mounting rigidity of the suspension cross member 50 and increase the support rigidity of the trailing arm 80. In addition, since the thickness of the third frame portion is less than that of the first and second frame portions, the vehicle weight can be reduced and the third frame portion formed to a small thickness can be caused to collapse and deform in the front-rear direction of the vehicle in the event of rear collision of the vehicle, thereby making it possible to absorb the impact energy with the third frame portion. As a result, deformation of the second frame portion can be inhibited and the input of impact load to the vehicle cabin can be restricted to a minimum.

The cases in which the present invention is used in vehicles of different classes, such as sedan, minivan, and SUV, are explained with reference to Fig. 7, but the present invention is not limited to such vehicle classes and may be applied, for example, to compact cars and also open cars and large vehicles such as trucks.

Regarding the correspondence between the configuration according to the present invention and the above-described embodiment, the support portion in accordance with the present invention corresponds to the trailing arm bracket 30. Likewise, the cross member corresponds to the

cross members

42, 44. The present invention is not limited to the features of the above-described embodiments and can be carried out in a variety of ways.

The above-described embodiments are summarized below.

The above-described invention of the present application provides a lower body structure of a vehicle in which a pair of left and right rear side frames 20 extending in a front-rear direction of the vehicle are provided in a rear portion of the vehicle, wherein the pair of left and right rear side frames 20 include a first frame portion (21) provided with a support portion (30) that swingably supports a trailing arm (80) of a suspension; a second frame portion (22) that is connected to the first frame portion (21) on the rear side of the vehicle and has a suspension cross member (50) mounted thereon; and a third frame portion (23) connected to the second frame portion (22) on the rear side of the vehicle.

The mounting structure of the suspension cross member is common to rear side frames, regardless of the vehicle model, class, and size. Therefore, specifications (shape, dimensions, etc.) of the parts for mounting the suspension cross member (50) are also common to rear side frames. By contrast, specifications of the abovementioned front portions differ according to the capacity of the fuel tank and wheel base length, and specifications of the abovementioned rear portions differ according to the overhang length. Therefore, specifications of the front portion where the trailing arm (80) is supported and specifications of the rear portion differ according to the vehicle model, class, and size.

Accordingly, with the above-described lower body structure of a vehicle, by configuring the second frame portion 22 from the members separate from those of the first and

third frame portions

21, 23, it is possible to use the second frame portion 22 commonly, regardless of the vehicle model, class, and size, to select, as appropriate, the first and third frame portions corresponding to the capacity of the fuel tank FT, wheel base length, and overhang length, and combine the selected first and third frame portions with the second frame portion. Therefore, it is possible to adapt easily to changes in conditions such as the vehicle model, class, and size and increase the production efficiency of vehicles.

In one embodiment of the present invention, it is preferred that mounting

portions

22a, 22b of the suspension cross member 50 be provided at the front and rear portions, in the front-rear direction of the vehicle, of the second frame portion 22, and

cross members

42, 44 connecting proximal portions of the mounting portions in the width direction of the vehicle are also provided therein. The "proximal portions" as referred to herein mean portions that are proximal to a degree such that the mounting

portions

22a, 22b of the suspension cross member 50 overlap parts of the

cross members

42, 44. In other words, a relative positional relationship is obtained such that at least partial mutual overlapping in the longitudinal direction of the vehicle is realized.

With such features, the mounting rigidity of the suspension cross member 50 in the second frame portion 22 can be increased by means of a simple configuration.

In one embodiment of the present invention, it is preferred that the

cross members

42, 44 be provided respectively in front and rear portions corresponding to the mounting

portions

22a, 22b provided at the front and rear portions of the second frame portion 22.

With such a configuration, the effect of increasing the mounting rigidity of the suspension cross member 50 can be further enhanced.

In one embodiment of the present invention, it is preferred that the first frame portion 21 and the second frame portion 22 be set to have a sheet thickness larger than that of the third frame portion 23.

With such a configuration, the mounting rigidity of the suspension cross member 50 and the support rigidity of the trailing arm 80 can be increased and therefore the mounting rigidity of the suspension can be increased.

Claims

A lower body structure of a vehicle in which a pair of left and right rear side frames (20) extending in a front-rear direction of the vehicle are provided in a rear portion of the vehicle, wherein
the pair of left and right rear side frames (20) include:
a first frame portion (21) provided with a support portion (30) that swingably supports a trailing arm (80) of a suspension;
a second frame portion (22) that is connected to the first frame portion on the rear side of the vehicle and has a suspension cross member (50) mounted thereon; and
a third frame portion (23) connected to the second frame portion on the rear side of the vehicle.
The lower body structure of a vehicle according to claim 1, wherein
mounting portions (22a, 22b) of the suspension cross member (50) are provided at front and rear portions, in the front-rear direction of the vehicle, of the second frame portion (22), and cross members (42, 44) connecting proximal portions of the mounting portions in a width direction of the vehicle are also provided therein.
The lower body structure of a vehicle according to claim 2, wherein
the cross members (42, 44) are provided respectively in front and rear portions corresponding to the mounting portions (22a, 22b) provided at the front and rear portions of the second frame portion (22).
The lower body structure of a vehicle according to any one of claims 1 to 3, wherein
the first frame portion (21) and the second frame portion (22) are set to have a sheet thickness larger than that of the third frame portion (23).