Body structure for a motor vehicle

In a body structure for a motor vehicle of a space frame type in which a rear pillar made of an extruded aluminum alloy member and joining a roof side member and a floor side member includes an inwardly curved section to avoid an interference with a rear wheel, a damper mounting base is welded to a part of the rear pillar adjoining the part having the smallest curvature or where the stress tends to concentrate so that the mechanical strength of this part may be reinforced without requiring any special reinforcing member. Thus, both an increase in the rigidity and a reduction in the weight of a vehicle body can be achieved in an efficient manner.

TECHNICAL FIELD 
The present invention relates to a vehicle body structure of a space frame 
type, and in particular to a vehicle body structure including a rear 
pillar which is curved so as to avoid an interference with a rear wheel. 
BACKGROUND OF THE INVENTION 
Elongated hollow members formed by extruding aluminum or other light-weight 
metals into a prescribed cross sectional shape have lately been drawing 
attention as automotive frame members because they can be freely given 
with a desired cross section and may be different in thickness in two 
different directions so that a desired mechanical strength can be achieved 
for each individual part of the vehicle body in a highly efficient manner. 
In a so-called space frame formed by welding metallic tube or other shaped 
members, the rear pillar is sometimes curved in such a manner that an 
intermediate part of the rear pillar bulges out laterally outward to 
maximize the opening of the tail gate and a lower end of the rear pillar 
is curved inward to avoid interference with a rear wheel. 
When a rear pillar given with such a shape is subjected to a bending load 
or a twisting load, a relatively large stress tends to develop in the 
parts having a relatively large curvature while no such large stress tends 
to develop in parts given with a smaller curvature. In particular, the 
mechanical stress tends to concentrate in the part of the rear pillar 
located in an upper part of the bulge for accommodating the rear wheel. 
Therefore, to optimize the overall rigidity of the frame, it was necessary 
to weld reinforcing members to the parts where the stress tends to 
concentrate or to increase the wall thickness of such parts. However, such 
measures inevitably led to an increase in the weight, and compromised the 
advantage of the space frame to allow the weight to be reduced. 
BRIEF SUMMARY OF THE INVENTION 
In view of such problems of the prior art, a primary object of the present 
invention is to provide an improved space frame type vehicle body 
structure which can be made highly rigid without increasing its weight. 
A second object of the present invention is to provide an improved space 
frame type vehicle body structure including a rear pillar which may be 
highly curved while maintaining a sufficient rigidity without using any 
additional reinforcing member. 
A third object of the present invention is to provide an improved space 
frame type vehicle body structure which can maximize the opening area in a 
rear part thereof without compromising the mechanical strength thereof. 
These and other objects of the present invention can be accomplished by 
providing a vehicle body structure including a rear pillar extending 
between a roof member and a floor member, the rear pillar being made of an 
extruded member having a substantially uniform cross section, and having 
an inwardly curved section in a lower part thereof to avoid an 
interference with a rear wheel, comprising: a mounting base for a rear 
suspension component, the mounting base comprising a rear suspension 
component mounting portion for supporting the rear suspension mounting 
component, and a bracket portion for securing the rear suspension 
component mounting portion to a part of the rear pillar adjoining the 
inwardly curved section, the bracket portion having a certain length 
extending along the rear pillar and securely attached to the rear pillar. 
The mechanical stress tends to concentrate in the inwardly curved portion 
particularly when the rear pillar is subjected to a bending load or a 
twisting load, but the bracket portion of the mounting base effectively 
reinforces the rear pillar against such stress concentration. Because the 
bracket portion serves the dual purpose of supporting the rear suspension 
component such as a spring or a damper, it is possible to effectively 
reinforce the rear part of the vehicle body without increasing the weight 
of the vehicle body. 
The curvature of the inwardly curved portion tends to be significant 
particularly when an opening area of a rear opening of the vehicle body is 
desired to be maximized. The rear opening may consist of a normal rear 
window, a tail gate, or a hatch-back rear window. 
According to a preferred embodiment of the present invention, the rear 
pillar consists of an extruded aluminum or aluminum alloy, and the bracket 
portion is welded to a part of the rear pillar having a largest curvature. 
An extruded member may have a desired cross section so that a desired 
rigidity and strength against a bending load in an arbitrary direction can 
be achieved by using a minimum amount of the material. Further, when an 
extruded member is used for forming a vehicle body, the cross section of 
the member may be designed such that the rigidity and strength of the 
member against a twisting load may be optimized. Typically, the rear 
pillar is made of an extruded aluminum or aluminum alloy member, but the 
present invention is equally applicable to frame members made of other 
materials such as plastics and other light weight metals or alloys having 
a substantially uniform cross section. Also, the basic principle of the 
present invention is applicable not only to the rear pillars but also to 
other frame members.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an essential part of a vehicle body frame constructed 
according to the present invention. This vehicle body frame consists of a 
space frame structure formed by combining and welding elongated members 
having a uniform cross section which are made from light metallic material 
such as aluminum or an aluminum alloy by extrusion so as to have a cross 
sectional shape suitable for each particular application. The cross 
sectional shape may be freely selected depending on the need of each 
particular application, and may be hollow or given with other suitable 
shapes. 
A lower end of each of a pair of center pillars 2 is welded to an upper 
surface of a side sill 1 which extends in the fore-and-aft direction. The 
inner side of each of the side sills 1 is welded to a front floor member 3 
which is also made by combining extruded light-weight metallic material, 
and the rear end of the front floor member 3 is welded to a rear floor 
side member 5 via a cross member 4. The rear floor side member 5 and the 
cross member 4 are all made of similar extruded members in this 
embodiment. The rear end of the rear floor side member 5 is welded to the 
lower end of each of a pair of rear pillars 6. Vertically intermediate 
parts of each of the center pillars 2 and the corresponding rear pillar 6 
are joined together by a side beam 7 extending in the fore-and-aft 
direction. 
Each of the rear pillars 6 has a middle part which curves laterally outward 
so as to maximize the opening area of the tail gate. The upper end of each 
of the rear pillars 6 is welded to the rear end of a roof side member 8, 
and the right and left rear pillars 6 are joined together by a roof cross 
member 9 which extends laterally across the vehicle body. The most 
outwardly bulging part of each of the rear pillars 6 is welded to the rear 
end of the side sill 1 which is curved obliquely upward so as to avoid 
interference with the rear wheel. The part of each of the rear pillars 6 
extending from a middle part thereof to a lower end portion thereof is 
curved laterally inward so as to be avoid interference with the rear 
wheel. 
When a rear pillar given with such a shape is subjected to a bending load 
or a twisting load, a relatively large stress tends to develop in the 
parts having a relatively large curvature while no such large stress tends 
to develop in parts given with a small curvature. Therefore, according to 
the present invention, a rear damper base 10 is welded to a part adjoining 
a part 6a of the rear pillar 6 having the smallest curvature, which is 
curved laterally inward to avoid interference with the rear wheel, to 
thereby reinforce this part. Typically, the rear pillar 6 defines a large 
curvature at the upper end of the bulge for accommodating the rear wheel. 
The rear damper base 10 is formed by stamp forming a metallic plate member 
made of a same material as the frame structure members, and comprises a 
cup-shaped damper mounting portion 11 and a bracket portion 12 for 
securing this mounting portion to the rear pillar 6. These two portions 11 
and 12 are formed into a sub-assembly by being welded together in advance. 
By welding this rear damper base 10 to a part of the rear pillar 6 
adjoining the part 6a of the largest curvature or the part of the largest 
curvature itself, it is possible to reinforce the part where the stress 
tends to concentrate without requiring any special reinforcing member. 
Thus, according to the present invention, the damper base is mounted to a 
part of the rear pillar where the stress tends to concentrate so that the 
damper base effectively reinforces the rear pillar, and can increase both 
the bending rigidity and the twisting rigidity of the rear pillar as well 
as the mechanical strength of this part. In particular, because the damper 
base serves also as a reinforcing member, the number of parts can be 
reduced, and the increase in the weight and the manufacturing cost can be 
minimized. 
Although the present invention has been described in terms of preferred 
embodiments thereof, it is obvious to a person skilled in the art that 
various alterations and modifications are possible without departing from 
the scope of the present invention which is set forth in the appended 
claims.