[0001]The present invention relates to a lower vehicle body structure.
Priority is claimed on Japanese Patent Application No. 2019-042634 filed in
Japan on March 8, 2019, the content of which is incorporated herein by reference.
[Background Art]
10 [0002]
Automobiles include a lower vehicle body structure for supporting suspension
components such as arm components and a steering mechanism at a lower portion of the
vehicle body of the automobile. A subframe as exemplified, for example, in Patent
Document 1 cited below is provided in the lower vehicle body structure. A subframe
15 requires stiffness as a design requirement. Specifically, in addition to stiffness to
support a weight of each component such as a rack gear, a sufficient stiffness that also
can withstand a lateral force applied from arm components during cornering of the
automobile and a longitudinal force applied from the arm components when the
automobile accelerates or decelerates is required.
20 [0003]
It is also conceivable to simply increase a sheet thickness of a subframe to
increase the stiffness, but in that case, there is a concern that a weight of the subframe
itself will increase and fuel efficiency will deteriorate. Generally, since improvement in
mechanical strength and weight reduction are in a contradictory relationship,
25 compatibility of these is not easy.
1
For example, Patent Document 2 discloses a front vehicle body structure
including a pair of left and right lower arms that support front wheels, a first transverse
member that connects between support parts on a rear side of the left and right lower
arms in the vehicle body, a second transverse member that connects between portions on
5 a front end side of a pair of left and right rockers, and a coupling structure that integrally
couples the first transverse member and the second transverse member.
10
According to this front vehicle body structure, a strength against a collision load
that is input backward via the front wheels at the time of a fine lap collision can be
secured while curbing increase in mass of the vehicle body.
In addition, Patent Document 3 to 6 also disclose lower vehicle body structures
of various types.
[Citation List]
[Patent Document]
[0004]
15 [Patent Document 1]
20
Japanese Unexamined Patent Application, First Publication No. 2010-100275
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. 2014-94588
[Patent Document 3]
Japanese Unexamined Patent Application, First Publication No. 2013-159223
[Patent Document 4]
PCT International Publication No. WO 20131145549
[Patent Document 5]
Japanese Unexamined Patent Application, First Publication No. 2009-61879
25 [Patent Document 6]
2
5
PCT International Publication No. WO 2018/016051
[Summary of the Invention]
[Problems to be Solved by the Invention]
[0005]
However, the front vehicle body structure described in Patent Document 2 has a
structure in which a longitudinal force generated in accordance with a behavior of the
automobile is received by a joint part on an upper surface of a front cross (cross member).
That is, a brace that transmits a longitudinal force is joined to the upper surface of the
front cross, and a point of application of the longitudinal force due to the brace is
10 significant! y deviated in a vertical direction with respect to a central axis of the front
15
cross. Since this large deviation causes a bending moment that twists the front cross
that receives a longitudinal force around a central axis thereof, there is a high likelihood
of adversely affecting a load transmission efficiency when an input is transmitted to the
front cross.
On the other hand, in a case of Patent Document 1 cited above, at the time of a
head-on collision of the vehicle, a mount bolt may come off from a second hole of the
frame structure so that a reinforcing effect of the vehicle body structure of the frame
structure is lost and thereby deceleration of the vehicle body is reduced. That is, the
purpose is to actively lose the reinforcing effect at the time of a head-on collision and
20 improvement in stiffness is not intended.
[0006]
Also, in the lower vehicle body structure of Patent Document 3, a configuration
in which a bent part of a brace member is connected to a center cross member is
employed. However, there is still room for improvement in stiffness of the connection
25 structure between the center cross member and the brace member such as the connection
3
position in a plan view being far away from an axis of the center cross member.
The front subframe structure of Patent Document 4, the vehicle body suspension
device of Patent Document 5, and the vehicle body frame described in Patent Document
6 still have problems from the perspective of improving stiffness for the same reason as
5 in Patent Document 3 described above.
[0007]
The present invention has been made in view of the above circumstances, and an
objective thereof is to provide a lower vehicle body structure that is lightweight and has
high stiffness and a high load transmission efficiency.
10 [Means for Solving the Problem]
[0008]
In order to solve the above-described problems and achieve the objective, the
present invention employs the following measures.
(1) A lower vehicle body structure according to one aspect of the present
15 invention includes: suspension components; a cross member including a pair of part cross
members connected to the suspension components and a reinforcing part coaxially
connected between the pair of part cross members; a plurality of body mounts; and a
plurality of connection members directly connecting each of the plurality of body mounts
and the reinforcing part, wherein a minimum sheet thickness of the reinforcing part at
20 connection positions with respect to the pair of part cross members is 1.6 times or more
an average sheet thickness at connection ends of the pair of part cross members with
respect to the reinforcing part.
[0009]
According to the lower vehicle body structure of the above-described (1), a
25 lateral force in a longitudinal direction of the cross member and a longitudinal force
4
perpendicular to the longitudinal direction are applied to the cross member from the
suspension components. Of these, the cross member receives the lateral force as a
compressive axial force or a tensile axial force in a direction in which the cross member
extends. Therefore, higher stiffness can be secured than that when the lateral force is
5 received by bending of the cross member. In addition, the cross member is supported
by the plurality of body mounts via the plurality of connection members. Therefore, the
longitudinal force applied to the cross member can be transmitted to the plurality of body
mounts with a high load transmission efficiency.
Here, since the minimum sheet thickness of the reinforcing part is set to 1.6
10 times or more the average sheet thickness at the connection ends of the part cross
members, a bending stiffness of a wall portion of the reinforcing part at the connection
positions with respect to the part cross members can be increased to four times or more a
bending stiffness of the part cross members. Since the lateral force and the longitudinal
force applied to the cross member are transmitted to the body mounts by interposing the
15 reinforcing part having such high bending stiffness, a high load transmission efficiency
can be obtained. Moreover, stiffness at portions joining to the connection members can
be particular! y increased in the entire cross member. Therefore, lightness in weight is
achieved compared to a case in which a sheet thickness and a cross-sectional dimension
are increased over the entire length of the cross member to increase stiffness.
20 [0010]
(2) In the case of the above-described ( 1 ), the following configuration may be
employed: the connection end at one of the pair of part cross members is abutted and
connected to a first wall surface of the reinforcing part; the connection end at the other of
the pair of part cross members is abutted and connected to a second wall surface of the
25 reinforcing part; and one of the part cross members, the first wall surface, the second wall
5
surface, and the other of the part cross members are coaxially aligned in that order in a
longitudinal direction of the cross member.
According to the lower vehicle body structure of the above-described (2), a
lateral force applied to one of the part cross members from the suspension component
5 can be efficiently received as an axial force toward the other of the part cross members
via the reinforcing part. Similarly, a lateral force applied to the other of the part cross
members from the suspension component can also be efficiently received as an axial
force toward one of the part cross members via the reinforcing part.
10
[0011]
(3) In the case of the above-described (1) or (2), the following configuration
may be employed: the plurality of connection members include a first connection
member and a second connection member; and, in a longitudinal section perpendicular to
the longitudinal direction of the cross member, which includes a position where an
extended line of a first axis passing through a centroid of an outer shape at any position
15 in a longitudinal direction of the first connection member in a cross section perpendicular
20
25
to the longitudinal direction, and an extended line of a second axis passing through a
centroid of an outer shape at any position in a longitudinal direction of the second
connection member intersect in a plan view, both the extended line of the first axis and
the extended line of the second axis are inside the reinforcing part.
According to the lower vehicle body structure of the above-described (3), the
cross member is supported by the plurality of body mounts via the appropriately disposed
first connection member and second connection member. Therefore, a longitudinal
force applied to the cross member can be transmitted to the plurality of body mounts with
a high load transmission efficiency.
Further, the above-described "inside the reinforcing part" refers to the inside of a
6
range defined by outer shape lines when the reinforcing part is viewed in a longitudinal
section. However, the above-described outer shape lines include not only a case in
which all of them are connected to form a closed cross section but also a case in which
some of them are not connected to form an open cross section. In a case of an open
5 cross section, when end portions of outer shape lines positioned on both sides of a
missing outer shape line are connected to each other with a virtual straight line to form a
closed outer shape, this closed outer shape can be referred to as the "inside the
reinforcing part."
10
[0012]
( 4) In the case of the above-described (3 ), the extended line of the first axis and
the extended line of the second axis may coincide with each other at one point in the
reinforcing part in a view of the longitudinal section.
In the case of the above-described ( 4 ), a longitudinal force applied to the cross
member can be transmitted to the body mounts with a higher load transmission
15 efficiency.
[0013]
(5) In the lower vehicle body structure according to the above-described (4),
both the extended line of the first axis and the extended line of the second axis may be
inside a projected outer shape of the connection end of each of the pair of part cross
20 members in a view of the longitudinal section.
25
In the case of the above-described (5), a longitudinal force applied to the cross
member can be transmitted to the plurality of body mounts with a higher load
transmission efficiency.
[0014]
(6) In the lower vehicle body structure according to any one of the
7
above-described (3) to (5), the first connection member may be joined to one of the body
mounts via a first extension piece extending from an end portion of the first connection
member.
In the case of the above-described (6), since surface-joining is performed via the
5 first extension piece, a higher joining strength can be obtained than that when
abutting-joining is simply performed.
[0015]
(7) In the lower vehicle body structure according to any one of the
above-described (3) to (6), the second connection member may be joined to another of
10 the body mounts via a second extension piece extending from an end portion of the
second connection member.
In the case of the above-described (7), since surface-joining is performed via the
second extension piece, a higher joining strength can be obtained than that when
abutting-joining is simply performed.
15 [0016]
20
(8) In the lower vehicle body structure according to any one of the
above-described (1) to (7), the reinforcing part may be a rack gear mount, another body
mount, a differential gear mount, a motor mount, a battery mount, or any combination
thereof.
In the case of the above-described (8), the reinforcing part can be formed
without using an additional component.
[0017]
(9) In the lower vehicle body structure according to any one of the
above-described (1) to (8), the following configuration may be employed: the reinforcing
25 part is any one of the rack gear mount, the body mount, the differential gear mount, the
8
motor mount, and the battery mount, each of which having a cylindrical shape; and the
pair of part cross members and the plurality of connection members are abutted and
connected to an outer circumferential surface of the reinforcing part.
In the case of the above-described (9), the reinforcing part has a cylindrical
5 shape having a high mechanical strength, and since an outer circumferential surface
thereof receives an external force from the part cross members and the connection
members, a higher load transmission efficiency can be obtained.
[0018]
(1 0) In the lower vehicle body structure according to any one of the
10 above-described (1) to (9), a virtual straight line connecting centroids of outer shapes in a
cross section perpendicular to the longitudinal direction of the cross member at positions
of both ends of the cross member may pass through the inside of the cross member at any
position in the longitudinal direction of the cross member.
In the case of the above-described (1 0), since a degree of linearity of the cross
15 member is increased, the stiffness against a lateral force is higher than that in a case of a
shape having a large curvature. Further, the outer shape at each position of both ends of
the cross member is not limited only to a case of an outer shape closed by connecting all
the outer shape lines but also includes a case of an outer shape that is open without some
of the outer shape lines (for example, U-shape or the like). In a case of the open outer
20 shape, it is preferable to connect end portions of outer shape lines positioned on both
sides of a missing outer shape line to each other with a virtual straight line to form a
closed outer shape, and then obtain a centroid on the basis of this closed outer shape.
[Effects of the Invention]
[0019]
25 According to the above-described aspects, a lower vehicle body structure that is
9
5
lightweight and has high stiffness and a high load transmission efficiency can be
provided.
[Brief Description of Drawings]
[0020]
FIG. 1 is a perspective view of a front subframe provided in a lower vehicle
body structure according to one embodiment of the present invention.
FIG. 2 is an exploded perspective view of the front subframe.
FIG. 3 is a plan view of the front subframe.
FIG. 4 is a perspective view illustrating a connection relationship of a front cross
10 member with a first connection member and a second connection member in the front
15
20
subframe.
FIG. 5 is a perspective view illustrating a connection relationship of the front
cross member with the first connection member and the second connection member in
the front subframe when viewed from a direction A of FIG. 4.
FIG. 6 is a perspective view illustrating joining of the first connection member
and the second connection member to a first body mount collar in the front subframe and
is an enlarged view of a portion B1 or a portion B2 of FIG. 5. Further, part numbers in
parentheses indicate part numbers of B2.
FIG. 7 is a perspective view illustrating a rear member of the front subframe.
FIG. 8 is a view illustrating a joined state between members of the front
subframe and is an enlarged perspective view of a portion C in FIG. 3.
FIG. 9 is a view illustrating a joined state between members of the front
subframe and is an enlarged perspective view from a back surface side of FIG. 8.
FIGS. 1 O(a) and 1 O(b) are views illustrating a main part of the front subframe, in
25 which FIG. 10(a) is an enlarged view of a portion Din FIG. 3, and FIG. 10(b) is a
10
longitudinal sectional view along line E-E of FIG. 10(a).
FIG. 11 is a view illustrating the main part of the front subframe and is a
longitudinal sectional view illustrating a case in which an extended line b 1 of a first axis
b and an extended line c 1 of a second axis c are deviated from each other in the same
5 cross section as FIG. 10(b).
FIG. 12 is a perspective view illustrating a front subframe of comparative
example 1.
FIG. 13 is a diagram showing a first example of the present invention and is a
bar graph obtained by comparing a weight efficiency of stiffness with respect to an
10 external force received from each direction between invention example 1 and
15
comparative example 1.
FIG. 14A is a plan view of a front subframe according to invention example 2.
FIG. 14B is a plan view illustrating comparative example 2 of a front subframe.
FIG. 14C is a plan view illustrating comparative example 3 of a front subframe.
FIG. 14D is a plan view illustrating comparative example 4 of a front subframe.
FIG. 15 is a bar graph comparing stiffness of each front subframe illustrated in
invention example 2 and comparative examples 2 to 4 when an inward lateral force is
applied.
FIG. 16 is a bar graph comparing stiffness of each front subframe illustrated in
20 invention example 2 and comparative examples 2 to 4 when a lateral force in one
direction is applied.
FIG. 17 A is a diagram showing a third example of the present invention, and is a
graph showing change in weight efficiency of stiffness when a sheet thickness ratio
obtained by dividing a minimum sheet thickness of an engine mount 13 by an average
25 sheet thickness of a front cross member 10 of the front subframe illustrated in FIG. 1 was
11
changed.
FIG. 17B is a graph showing change in slope of "stiffness/mass KIM" in FIG.
17 A according to the sheet thickness ratio.
FIG. 18 is a view illustrating a fourth example of the present invention and is a
5 partial perspective view illustrating a case in which a box-shaped reinforcing part 113 is
used instead of the engine mount 13 in the front subframe illustrated in FIG. 1.
FIG. 19A is a graph showing change in weight efficiency of stiffness when a
sheet thickness ratio obtained by dividing a minimum sheet thickness of the reinforcing
part 113 by an average sheet thickness of the front cross member 10 of the front sub frame
10 illustrated in FIG. 18 was changed.
15
FIG. 19B is a graph showing change in slope of "stiffness/mass KIM" in FIG.
19A according to the sheet thickness ratio.
[Embodiment for implementing the Invention]
[0021]
One embodiment of a lower vehicle body structure of the present invention will
be described below.
The lower vehicle body structure of the present embodiment includes a pair of
lower arms (suspension components) and a sub frame that supports these lower arms at a
lower portion of a vehicle body of an automobile. In the following description, a front
20 subframe disposed on a front side of a lower portion of the vehicle body will be
exemplified as the subframe. Also, in the following description, a front side in a
traveling direction of the vehicle body is referred to as a forward side, a back side is
referred to as a rearward side, and a vehicle width direction is referred to as a left-right
direction in some cases. Also, in the drawings, a forward side as viewed from the
25 vehicle body is indicated by an arrow F, a rearward side is indicated by an arrow B, a left
12
direction is indicated by an arrow L, and a right side is indicated by an arrow R in some
cases.
[0022]
As illustrated in FIGS. 1 to 3, a front subframe of the present embodiment
5 includes a front cross member 10 having both ends connected to the lower arms (not
illustrated), a pair of rear body mounts (body mounts) 20 disposed to be spaced apart
from each other in a left-right direction at positions on a rearward side relative to the
front cross member 10, a pair of connection members (a first connection member and a
second connection member) 30 and 40 connecting the front cross member 10 and each of
10 the rear body mounts 20, a rectangular rear member 50 that holds the rear body mounts
20 and is joined to both ends of the front cross member 10, and a pair of front body
mounts 60 joined to both the front cross member 10 and the rear member 50. Here, the
lower arms are an example of suspension components. As suspension components
connected to the front subframe, arm components such as upper arms, link components,
15 or the like can be exemplified.
[0023]
As illustrated in FIGS. 4 and 5, the front cross member 10 (cross member) is a
skeleton member extending in the left-right direction. The front cross member 10
includes a first part member (part cross member) 11 positioned on one side (left side) in
20 an extending direction of the front cross member 10, a second part member 12 positioned
on the other side (right side), and an engine mount 13 coaxially connecting the first part
member 11 and the second part member (part cross member) 12. As described above,
the front cross member 10 includes the first part member 11 and the second part member
12 which are coaxially disposed with the engine mount 13 sandwiched therebetween.
25 [0024]
13
The first part member 11 is a tube member. As illustrated in FIG. 5, the first
part member 11 includes a left end 11 a whose cross-sectional shape is constant in the
above-described extending direction, a tapered part 11 b that is continuous with the left
end 11a and in which the cross-sectional shape described above gradually decreases in
5 size in a direction away from the left end 11 a, and a straight part 11 c that is continuous
with the tapered part 11 b and in which the cross-sectional shape described above is
constant in the above-described extending direction. As illustrated in FIG. 2, a
cross-sectional shape perpendicular to the extending direction of the first part member 11
is substantially rectangular, but such a cross-sectional shape is not limited to a rectangle,
10 and may be, for example, circular, elliptical, or polygonal. Furthermore, when it is
polygonal, a corner portion thereof may either have a ridge line or have an arc-shaped
surface. Also, the first part member 11 may not have a tapered shape as illustrated in
FIG. 5 and may be formed by a tube member whose cross-sectional shape at any position
in the extending direction is substantially constant. That is, a shape of the first part
15 member 11 is not particularly limited.
[0025]
The second part member 12 is a tube member whose cross-sectional shape
perpendicular to an extending direction thereof is substantially rectangular. As
illustrated in FIG. 5, the second part member 12 includes a right end 12a in which the
20 above-described cross-sectional shape is constant in the above-described extending
direction, a tapered part 12b that is continuous with the right end 12a and in which the
above-described cross-sectional shape gradually decreases in size in a direction away
from the right end 12a, and a straight part 12c that is continuous with the tapered part 12b
and in which the above-described cross-sectional shape is constant in the
25 above-described extending direction. As illustrated in FIG. 2, a cross-sectional shape
14
perpendicular to an extending direction of the second part member 12 is substantially a
rectangular shape, but such a cross-sectional shape is not limited only to a rectangular
shape, and may be, for example, a circular shape, an elliptical shape, or a polygonal
shape. Furthermore, in a case of a polygonal shape, a corner portion thereof may either
5 have a ridge line or have an arc-shaped surface. Also, the second part member 12 may
not have a tapered shape as illustrated in FIG. 5 and may be formed by a tube member
whose cross-sectional shape at any position in the extending direction is substantially
constant. That is, a shape of the second part member 12 is not particularly limited.
10
[0026]
The engine mount 13 is a component that supports an engine mounted on the
vehicle body. The engine mount 13 is a cylinder having an axis in a vertical direction,
and a cross-sectional shape thereof perpendicular to the axis is the same at any position in
the axis. That is, the engine mount 13 has substantially the same outer diameter
dimensions, inner diameter dimensions, and sheet thickness at any position in the axial
15 direction thereof. The engine mount 13 is coaxially connected to an intermediate
position of the front cross member 10 in the longitudinal direction.
As illustrated in FIGS. 2 and 5, the straight part (connection end) 11c of the first
part member 11 is welded and fixed to a first wall surface 13a1 of an entire outer
circumferential surface 13a of the engine mount 13 in a state in which it is abutted
20 against the first wall surface 13al. Similarly, the straight part (connection end) 12c of
the second part member 12 is also welded and fixed in a state in which it is abutted
against a second wall surface 13a2 of the entire outer circumferential surface 13a of the
engine mount 13.
As illustrated in FIG. 2, the first wall surface 13a1 and the second wall surface
25 13a2 are outer circumferential surfaces of a pair of curved wall portions which are on
15
5
opposite sides with the central axis of the engine mount 13 sandwiched therebetween.
Then, the first part member 11, the first wall surface 13a1, the second wall surface 13a2,
and the second part member 12 are coaxially disposed in that order in the longitudinal
direction of the front cross member 10.
The first part member 11 and the second part member 12 are coaxial with each
other, and the central axis of the engine mount 13 perpendicular! y intersects central axes
of them.
[0027]
As illustrated in FIG. 5, extension pieces 11a1, 11a2, and 11a3 are formed at the
10 left end 11a of the first part member 11. Of these, the extension pieces 11a1 and 11a2
face each other and protrude reward. On the other hand, the extension piece 11 a3
positioned between the extension pieces 11a1 and 11a2 protrudes toward the left side.
Also, a hole 11a4 for connecting a left lower arm (not illustrated) is formed at the left end
11 a of the first part member 11.
15 Extension pieces 12a1, 12a2, and 12a3 are also formed at the right end 12a of
the second part member 12. Of these, the extension pieces 12a1 and 12a2 face each
other and protrude rearward. On the other hand, the extension piece 12a3 positioned
between the extension pieces 12a1 and 12a2 protrudes toward the right side. Also, a
hole 12a4 for connecting a right lower arm (not illustrated) is formed at the right end 12a
20 of the second part member 12.
[0028]
25
In the front cross member 10 constituted by the constituent elements described
above, sheet thicknesses of the tapered part 11 b, the straight part 11 c, the tapered part
12b, and the straight part 12c are all the same.
On the other hand, the engine mount 13 has a larger sheet thickness than the
16
tapered part 11b, the straight part 11c, the tapered part 12b, and the straight part 12c.
That is, when a stiffness distribution is viewed in the longitudinal direction of the front
cross member 10, a part at the position of the engine mount 13 in the middle in the
longitudinal direction has high stiffness. The engine mount 13 serves as a reinforcing
5 part in which a minimum sheet thickness at connection positions thereof with respect to
the straight parts 11 c and 12c is 1.6 times or more an average sheet thickness of the
straight parts (connection ends) 11 c and 12c joined to both sides of the engine mount 13.
When the minimum sheet thickness is set to 1.6 times or more the average sheet
thickness, an effect of increase in weight due to increase in the sheet thickness can be
10 kept low while dramatically improving the stiffness of the front subframe. Further, the
minimum sheet thickness is more preferably 2.0 times or more the average sheet
thickness. Also, the minimum sheet thickness is preferably 10.0 times or less the
average sheet thickness from the perspective of suppressing increase in weight.
Furthermore, the minimum sheet thickness is more preferably 8.0 times or less the
15 average sheet thickness.
[0029]
Further, the left end 11 a and the right end 12a of the front cross member 10 may
have a larger sheet thickness than other portions of the front cross member 10. Since
the end portions of the front cross member 10 are each a connection point with the lower
20 arm, stress concentration occurs at the connection point due to an input from the lower
arm, and local deformation is likely to occur. Therefore, when a sheet thickness in the
vicinity of the connecting point is made larger than sheet thicknesses of other portions,
decrease in stiffness due to the local deformation can be reduced.
[0030]
25 The pair of rear body mounts 20 (body mounts) illustrated in FIGS. 4 to 6 are
17
5
each a component fixed to a lower portion of the vehicle body (not illustrated). The rear
body mounts 20 each have, for example, a cylindrical shape having an axis in the vertical
direction. The pair of rear body mounts 20 are disposed to be aligned on the left and
right sides with a space therebetween.
An enlarged diameter part 21 having a large outer diameter is formed on an
upper portion of each of the rear body mounts 20. Since a longitudinal force or the like
from the vehicle body is directly applied to the pair of rear body mounts 20, sheet
thicknesses of these, even at a thinnest portion, are configured to be thicker than a sheet
thickness of each portion of the front cross member 10. Further, the structure of the rear
10 body mount 20 illustrated in each figure is not limited only to such an example, and
structures of general body mounts can be employed.
[0031]
The connection member 30 (first connection member) is, for example, a skeleton
member made of a linear pipe material and directly connects the engine mount 13 and
15 one of the pair of rear body mounts 20. Specifically, one end side of the connection
member 30 is welded and fixed in a state in which it is abutted against the outer
circumferential surface 13a of the engine mount 13. Also, the other end side of the
connection member 30 is welded and fixed at a pair of extension pieces (first extension
pieces) 32 in a state in which it is abutted against an outer circumferential surface 20a of
20 one of the rear body mounts 20. An axis of the connection member 30 is substantially
perpendicular to the axis of the engine mount 13. Also, the axis of the connection
member 30 is also substantially perpendicular to an axis of one of the rear body mounts
20. Further, a female screw may be formed on a side surface of the engine mount 13, a
male screw may be formed on one end side of the connection member 30, and the male
25 screw may be screwed into the female screw to fix them. Conversely, a male screw
18
may be formed on the engine mount 13 and a female screw may be formed on the
connection member 30 side, and the male screw may be screwed into the female screw to
fix them. Also, a protruding part that protrudes from the engine mount 13 to the
connection member 30 may be formed to join the connection member 30 to the
5 protruding part.
[0032]
As illustrated in FIG. 6, on the other end side of the connection member 30, a
recessed portion 31 cut out to match an outer circumferential surface of the rear body
mount 20, and the pair of extension pieces 32 sandwiching the recessed portion 31
10 therebetween are formed. The pair of extension pieces 32 protrude outward from the
end of the connection member 30. The recessed portion 31 is joined to the outer
circumferential surface 20a of the rear body mount 20, and inner surfaces of the pair of
extension pieces 32 are also joined to the outer circumferential surface 20a of the rear
body mount 20. Further, the above-described one end side of the connection member
15 30 may also be joined to the outer circumferential surface 13a of the engine mount 13 via
a pair of extension pieces (not illustrated).
[0033]
Also, a cross-sectional shape of the connection member 30 is not particularly
limited. For example, the connection member 30 may be formed by a tube member
20 whose cross section has a polygonal shape, a circular shape, an elliptical shape, or the
like. Furthermore, in a case of a polygonal shape, a corner portion thereof may either
have a ridge line or have an arc-shaped surface. Also, a cross-sectional outer shape at
any position in a longitudinal direction of the connection member 30 may be constant in
the longitudinal direction or may change from an intermediate position in the
25 longitudinal direction.
19
[0034]
The connection member 40 (second connection member) is, for example, a
skeleton member made of a linear pipe material and directly connects the engine mount
13 and the other of the pair of rear body mounts 20. Specifically, one end side of the
5 connection member 40 is welded and fixed in a state in which it is abutted against the
outer circumferential surface 13a of the engine mount 13. Also, the other end side of
the connection member 40 is welded and fixed at a pair of extension pieces (second
extension pieces) 42 in a state in which it is abutted against an outer circumferential
surface 20a of the other rear body mount 20. An axis of the connection member 40 is
10 substantially perpendicular to the axis of the engine mount 13. Also, the axis of the
connection member 40 is also substantially perpendicular to an axis of the other rear
body mount 20. Further, a female screw may be formed on a side surface of the engine
mount 13, a male screw may be formed on one end side of the connection member 40,
and then the male screw may be screwed into the female screw to fix them. Converse! y,
15 a male screw may be formed on the engine mount 13 and a female screw may be formed
on the connection member 40 side, and the male screw may be screwed into the female
screw to fix them. Also, a protruding part that protrudes from the engine mount 13 to
the connection member 40 may be formed to join the connection member 40 to the
protruding part.
20 [0035]
The other end of the connection member 40 includes a recessed portion 41 and
the pair of extension pieces 42 similarly to the above-described recessed portion 31 and
the pair of extension pieces 32 formed on the other end side of the connection member 30.
The recessed portion 41 is joined to the outer circumferential surface 20a of the other rear
25 body mount 20, and inner surfaces of the pair of extension pieces 42 are also joined to
20
the outer circumferential surface 20a of the other rear body mount 20. Further, the
above-described one end side of the connection member 40 may also be joined to the
outer circumferential surface 13a of the engine mount 13 via a pair of extension pieces
(not illustrated).
5 [0036]
Also, a cross-sectional shape of the connection member 40 is not particularly
limited. For example, the connection member 40 may be formed by a tube member
whose cross section has a polygonal shape, a circular shape, an elliptical shape, or the
like. Furthermore, in a case of a polygonal shape, a corner portion thereof may either
10 have a ridge line or have an arc-shaped surface. Also, a cross-sectional outer shape at
any position in a longitudinal direction of the connection member 40 may be constant in
the longitudinal direction or may change from an intermediate position in the
longitudinal direction.
15
[0037]
Further, the connection member 30 and the connection member 40 illustrated in
FIG. 1 or the like are formed by straight pipes, but shapes of the connection member 30
and the connection member 40 are not limited only to such an example. For example,
the connection member 30 and the connection member 40 may be formed by a pipe
material having an enlarged diameter or reduced diameter at an end portion or a pipe
20 material that is partially bent. Also, the connection member 30 may be formed so that a
25
virtual straight line connecting centroids of outer shapes at both end positions of the
connection member 30 in a cross section perpendicular to the extending direction is
inside the connection member 30. The same applies to the connection member 40.
[0038]
The rear member 50 illustrated in FIG. 7 is a skeleton member having
21
substantially aU-shape in a plan view and includes a pair of upper plate 51 and lower
plate 52, and a side plate 53 connecting the upper plate 51 and the lower plate 52.
The upper plate 51 includes a central part 51 a extending linearly in the left-right
direction in a plan view, a left corner part 51 b which is continuous with a left side of the
5 central part 51 a and in which a through hole 51b1 for holding the rear body mount 20 is
formed, a left arm part 51 c which is continuous to the front from the left corner part 51 b,
a right corner part 51 d which is continuous with a right side of the central part 51 a and in
which a through hole 51d1 for holding the rear body mount 20 is formed, and a right arm
part 51e which is continuous to the front from the right corner part 51d.
10 A direction in which the central part 51 a extends and a direction in which the left
corner part 51 b and the left arm part 51 c are aligned are substantially perpendicular to
each other. A direction in which the central part 51 a extends and a direction in which
the right corner part 51d and the right arm part 51e are aligned are also substantially
perpendicular to each other.
15 [0039]
The lower plate 52 has the same shape as the upper plate 51 in a plan view.
That is, the lower plate 52 includes a central part 52a extending linearly in the left-right
direction in a plan view, a left corner part 52b which is continuous with a left side of the
central part 52a and in which a through hole 52b 1 for holding the rear body mount 20 is
20 formed, a left arm part 52c which is continuous to the front from the left corner part 52b,
a right corner part 52d which is continuous with a right side of the central part 52a and in
which a through hole 52d1 for holding the rear body mount 20 is formed, and a right arm
part 52e which is continuous to the front from the right corner part 52d.
A direction in which the central part 52a extends and a direction in which the left
25 corner part 52b and the left arm part 52c are aligned are substantially perpendicular to
22
5
each other. A direction in which the central part 52a extends and a direction in which
the right corner part 52d and the right arm part 52e are aligned are also substantially
perpendicular to each other.
[0040]
The side plate 53 includes a central part 53a that connects both front side edges
of the central part 51 a and the central part 52a in the vertical direction, a left corner part
53b that connects both inner side edges of the left corner part 51 b and the left corner part
52b in the vertical direction, a left arm part 53c that connects both inner side edges of the
left arm part 51c and the left arm part 52c in the vertical direction, a right corner part 53d
10 that connects both inner side edges of the right corner part 51 d and the right corner part
52d in the vertical direction, and a right arm part 53e that connects both inner side edges
of the right arm part 51e and the right arm part 52e in the vertical direction.
The left corner part 53b and the left arm part 53c are continuous to be integrated
with each other. The right corner part 53d and the right arm part 53e are also
15 continuous to be integrated with each other. Also, a through hole 53h1 for inserting the
connection member 30 is formed between the central part 53a and the left corner part 53b.
Similarly, a through hole 53h2 for inserting the connection member 40 is formed between
the central part 53a and the right corner part 53d.
20
[0041]
Further, the side plate 53 includes a central part 53f that connects both rear side
edges of the central part 51 a and the central part 52a in the vertical direction, a left corner
part 53 g that connects both outer side edges of the left corner part 51 b and the left corner
part 52b in the vertical direction, a left arm part 53h that connects both outer side edges
of the left arm part 51c and the left arm part 52c in the vertical direction, a right corner
25 part 53i that connects both outer side edges of the right corner part 51d and the right
23
corner part 52d in the vertical direction, and a right arm part 53j that connects both outer
side edges of the right arm part 51e and the right arm part 52e in the vertical direction.
The central part 53a, the left corner part 53g, and the right corner part 53i are continuous
to be integrated with each other.
5 [0042]
10
Holes 51 b2 and 52b2 for connecting the left lower arm (not illustrated) are
formed in the left corner part 51 b and the left corner part 52b of the rear member 50.
Similarly, holes 51d2 and 52d2 for connecting the right lower arm (not illustrated) are
formed in the right corner part 51d and the right corner part 52d of the rear member 50.
In the left arm part 51 c of the rear member 50, an extension piece 51 c 1 is
formed to protrude toward the front. Similarly, also in the left arm part 52c, an
extension piece 52c1 is formed to protrude toward the front. Further, also in the left
arm part 53b, an extension piece 53c1 is formed to protrude to the right.
In the right arm part 51e of the rear member 50, an extension piece 51e1 is
15 formed to protrude toward the front. Similarly, also in the right arm part 52e, an
extension piece 52e1 is formed to protrude toward the front. Further, also in the right
arm part 53e, an extension piece 53e1 is formed to protrude to the left.
[0043]
As illustrated in FIGS. 8 and 9, the extension piece 51 c 1, the extension piece
20 52c1, and the extension piece 53c1 are joined to a connection portion between the left
end 11a and the tapered part 11b of the front cross member 10. Specifically, the
above-described connection portion is sandwiched between a pair of extension piece
51c1 and extension piece 52c1, and the extension piece 53c1 is joined to a side surface of
the tapered part 11 b.
25 Similarly, the extension piece 51e1, the extension piece 52e1, and the extension
24
piece 53e1 are joined to a connection portion between the right end 12a and the tapered
part 12b of the front cross member 10. Specifically, the above-described connection
portion is sandwiched between a pair of extension piece 51e1 and extension piece 52e1,
and the extension piece 53e1 is joined to a side surface of the tapered part 12b.
5 [0044]
The front body mounts 60 illustrated in FIG. 1 are components fixed to the
lower portion of the vehicle body and include a left body mount 61 disposed on the left
side and a right body mount 62 disposed on the right side.
The left body mount 61 includes a standing part 61a provided to stand obliquely
10 upward to the left from a position on a rear side of the left end 11 a of the front cross
member 10 and on a leftward side of the rear member 50, and a collar 61 b fixed to an
upper portion of the standing part 61 a.
The collar 61 b is a component fixed to the lower portion of the vehicle body and
has a cylindrical shape having an axis in the vertical direction. An enlarged diameter
15 part having a large outer diameter is formed on an upper portion of the collar 61b.
[0045]
The standing part 61a is joined so that a lower end portion thereof is sandwiched
between a pair of extension pieces 11a1 and 11a2 described above. In addition, the
extension piece 11a3 is also joined to a side surface of the above-described lower end
20 portion.
Also, a pair of extension pieces 61 a 1 protruding leftward are formed on the
upper portion of the standing part 61a. Then, the collar 61b is joined to be sandwiched
between the pair of extension pieces 61 a 1.
Also, a hole 61 a2 for connecting the left lower arm is formed on a surface of the
25 standing part 61a on a side facing the front cross member 10.
25
[0046]
The right body mount 62 includes a standing part 62a provided to stand
obliquely upward to the right from a position on a rear side of the right end 12a of the
front cross member 10 and on a rightward side of the rear member 50, and a collar 62b
5 fixed to an upper portion of the standing part 62a.
The collar 62b is a component fixed to the lower portion of the vehicle body
together with the above-described collar 61b and has a cylindrical shape having an axis
in the vertical direction. An enlarged diameter part having a large outer diameter is
formed on an upper portion of the collar 62b.
10 [0047]
15
20
The standing part 62a is joined so that a lower end portion thereof is sandwiched
between a pair of extension pieces 12a1 and 12a2 described above. In addition, the
extension piece 12a3 is also joined to a side surface of the above-described lower end
portion.
Also, a pair of extension pieces 62a 1 protruding rightward are formed on the
upper portion of the standing part 62a. Then, the collar 62b is joined to be sandwiched
between the pair of extension pieces 62a1.
Also, a hole 62a2 for connecting the left lower arm is formed on a surface of the
standing part 62a on a side facing the front cross member 10.
Further, the structure of the front body mounts 60 illustrated in each figure is not
limited only to such an example, and structures of general body mounts can be employed.
[0048]
The front subframe having the above-described configuration is fixed to the
lower portion of the vehicle body at four places including the collars 61 b and 62b and the
25 pair of rear body mounts 20. Also, the left lower arm (not illustrated) is connected to
26
the left end 11a, and the right lower arm (not illustrated) is connected to the right end
12a.
During cornering of the vehicle body, a lateral force with respect to the front
cross member 10 in an axial direction thereof is applied from the left or right lower arm
5 (not illustrated). Also, when the vehicle body accelerates or decelerates, a longitudinal
force is applied to the front cross member 10 from the left and right lower arms. The
front subframe according to the present embodiment is lightweight, has high stiffness,
and has a high load transmission efficiency. A specific structure for that will be
described below.
10 [0049]
The left lower arm (not illustrated) is connected to the hole 11 a4 of the left end
11 a in the front cross member 10, the hole 61 a2 of the standing part 61 a, and the hole
51 b2 of the left corner part 51 b and the hole 52b2 of the left corner part 52b in the rear
member 50 illustrated in FIG. 1. Also, the right lower arm (not illustrated) is connected
15 to the hole 12a4 of the right end 12a in the front cross member 10, the hole 62a2 of the
standing part 62a, and the hole 51d2 of the right corner part 51d and the hole 52d2 of the
right corner part 52d in the rear member 50.
[0050]
Further, although a shape of the front cross member 10 is not particularly limited,
20 for example, in the plan view illustrated in FIG. 3, the front cross member 10 may be
formed so that a virtual straight line EL connecting a centroid of an outer shape in a cross
section perpendicular to the extending direction of the first part member 11 at a left end
edge LE and a centroid of an outer shape in a cross section perpendicular to the
extending direction of the second part member 12 at a right end edge RE is present inside
25 the first part member 11, the second part member 12, and the engine mount 13.
27
Specifically, the virtual straight line EL is preferably present within a range of an outer
shape defined by front surfaces ff, rear surfaces rf, top surfaces tf, and lower surfaces bf
of the first part member 11 and the second part member 12 and within a range of an outer
shape defined by a front surface 13f, a rear surface 13r, a top surface 13t, and a lower
5 surface 13b of the engine mount 13 illustrated in FIG. 10. According to the
above-described configuration, regardless of whether a lateral force L1 is applied from
the left lower arm or the right lower arm, the front cross member 10 can receive the
lateral force L 1 as an axial force in a longitudinal direction thereof. Therefore, higher
stiffness can be exhibited compared to a structure in which the lateral force L1 is
10 received by bending or twisting of the front cross member 10. Such a front cross
member 10 may have, for example, substantially a straight shape or the like as illustrated
in FIG. 1.
[0051]
Further, the connection members 30 and 40 are connected to the front cross
15 member 10 having the above-described shape with a relative positional relationship as
illustrated in FIG. 10.
That is, as illustrated in FIG. 10(a), an extended line b1 of a first axis b passing
through a centroid of an outer shape at any position in a longitudinal direction of the
connection member 30 in a cross section perpendicular to the longitudinal direction and
20 an extended line c1 of a second axis c passing through a centroid of an outer shape at any
position in a longitudinal direction of the connection member 40 in a cross section
perpendicular to the longitudinal direction intersect (match) at a position of an
intersection point P in the engine mount 13 of the front cross member 10 in a plan view.
This intersection point Pis positioned between the front surface 13f and the rear surface
25 13r of the engine mount 13 when viewed in a front-rear direction.
28
[0052]
Further, as illustrated in FIG. 10(b), when the intersection point Pis viewed in a
longitudinal section perpendicular to the longitudinal direction of the front cross member
10 including the position of the intersection point P, the extended line b 1 and the
5 extended line c 1 are positioned inside the engine mount 13 of the front cross member 10.
More specifically, the extended line b1 and the extended line c1 are each present as a
"point" in the longitudinal section of FIG. 1 O(b ), but positions of these "points" are
within the range of the outer shape defined by the front surface 13f, the rear surface 13r,
the top surface 13t, and the lower surface 13b of the engine mount 13. Further, the top
10 surface 13t and the lower surface 13b of the engine mount 13 open upward and
downward, but in this case, when a square frame is formed by connecting upper edges
and lower edges of the front surface 13f and the lower surface 13r to each other, it is
regarded as the above-described outer shape of the engine mount 13.
15
[0053]
Even when another component (for example, a rack gear mount, a body mount,
a differential gear mount, a motor mount, a battery mount, or the like) is employed as the
reinforcing part instead of the engine mount 13, in a longitudinal sectional view at the
position of the intersection point P, both the extended line b 1 and the extended line c 1 are
configured to be positioned in a closed cross section in which all outer shape lines
20 forming an outer shape thereof are connected or in an open cross section in which some
25
of the outer shape lines are not present. In this case also, the extended line b 1 and the
extended line c 1 may match or be separated from each other in the above-described
longitudinal section.
[0054]
In the case of the present embodiment, as illustrated in FIG. 1 O(b ), even in the
29
range of the above-described outer shape in the longitudinal section, both the extended
line b 1 and the extended line c 1 are preferably positioned particular! y within a range
illustrated by hatching. In this case also, the extended line b 1 and the extended line c 1
may match or be separated from each other in the longitudinal section. The range
5 illustrated by hatching is a range of outer shape lines of the straight part 11 c of the first
part member 11 and the straight part 12c of the second part member 12 at both side
positions Uoining positions) of the engine mount 13 defined by the front surface ff, the
rear surface rf, the top surface tf and the lower surface bf. As illustrated in FIG. 10(b),
outer shapes of the first part member 11 and the second part member 12 are closer to a
10 centroid of the front cross member 10 than an outer shape of the engine mount 13 is.
15
Therefore, when both the extended line b 1 and the extended line c 1 are positioned within
the range illustrated by the hatching, a load transmission efficiency can be further
improved.
[0055]
Further, the extended line b 1 of the first axis b and the extended line c 1 of the
second axis c need only intersect in a plan view. That is, in the longitudinal sectional
view, the extended line b 1 of the first axis b and the extended line c 1 of the second axis c
do not necessarily have to intersect. For example, as illustrated in FIG. 11, the
connection member 30 and the connection member 40 need only be provided so that the
20 extended line b 1 of the first axis b and the extended line c 1 of the second axis c pass
25
through the inside of the front cross member 10. Further, in FIG. 11, the extended line
b 1 of the first axis b and the extended line c 1 of the second axis c intersect at a position
on a vertical line VL in a plan view.
[0056]
As illustrated in FIG. 1 O(b ), in the present embodiment, at the position of the
30
intersection point P at which the extended line b 1 of the first axis b and the extended line
c1 of the second axis c intersect when viewed from a normal direction n (a direction
corresponding to a vehicle vertical direction in the present embodiment) of the extended
line of the first axis b in a cross section perpendicular to the longitudinal direction of the
5 front cross member 10, the extended line b 1 of the first axis b and the extended line c 1 of
the second axis c are positioned inside the front cross member 10, and the extended line
b 1 of the first axis b and the extended line c 1 of the second axis c are inside the front
cross member 10 in a cross-sectional view perpendicular to the longitudinal direction of
the front cross member 10.
10 [0057]
Also, as illustrated in FIG. 3, when the entire length from the left end edge LE to
the right end edge RE of the front cross member 10 is L (mm), joining positions of the
connection members 30 and 40 to the front cross member 10 are preferably adjusted so
that a distance Lx (mm) from the left end LE to the intersection point P is within a range
15 of 0.20xL (mm) or more and 0.80xL (mm) or less. Further, the distance Lx (mm) is
more preferably 0.35xL (mm) or more and 0.65xL (mm) or less.
[0058]
According to the above-described configuration, since the front cross member
10 that has received the lateral force L1 is supported by the pair of rear body mounts 20
20 via the connection members 30 and 40, relative displacement thereof with respect to the
rear member 50 can be prevented. That is, since deformation of the rectangular frame
constituting the front subframe can be prevented, it is possible to increase stiffness of not
only the front cross member 10 alone but also the front subframe as a whole. Moreover,
since the stiffness can be increased without increasing a sheet thickness and a
25 cross-sectional dimension, a front subframe having high stiffness while being lightweight
31
can be obtained.
[0059]
The present invention is not limited only to the configuration described in the
above-described embodiment and various modifications can be made within the scope
5 not departing from the gist of the present invention.
For example, a shape of the engine mount 13 is a cylindrical shape in the
above-described embodiment, but the present invention is not limited only to the shape.
As the engine mount 13, since a recess for receiving an arm (not illustrated above) that
supports rocking of the engine need only be formed in addition to the partial
10 reinforcement of the front cross member 10, a polygonal cylindrical shape such as a
quadrangular cylindrical shape may also be employed instead. Furthermore, in a case of
a polygonal shape, a corner portion thereof may either have a ridge line or have an
arc-shaped surface.
In cases of any shape, it is preferable to employ the engine mount 13 having an
15 external dimension in the front-rear direction larger than those of the first part member 11
and the second part member 12. When the connection members 30 and 40 are joined to
such an engine mount 13, joining positions of the connection members 30 and 40 can be
separated from the intersection point P. Thereby, the joining position of the connection
member 30 and the joining position of the connection member 40 can be separated from
20 each other. As a result, since the connection members 30 and 40 can be joined with a
spatial room, reliability of a joining strength can be further improved.
[0060]
Also, in the above-described embodiment, the structure has been configured
such that stiffness at the joint portion of the front cross member 10 with respect to the
25 connection members 30 and 40 is partially increased by causing the engine mount 13
32
having a larger sheet thickness than the first part member 11 and the second part member
12 to be interposed therebetween, but the present invention is not limited to the structure.
For example, the front cross member 10 may be formed as a single component by
omitting the engine mount 13 from between the first part member 11 and the second part
5 member 12. Then, reinforcing plates (not illustrated) may be joined to positions of the
joint portions of the front cross member 10 with respect to the connection members 30
and 40 in the longitudinal direction to partially increase a sheet thickness thereof by
welding or the like in advance. In this case, when viewed in a cross section
perpendicular to the longitudinal direction of the front cross member 10, of the four side
10 surfaces, the reinforcing plate may be provided only on one side surface to which the
connection members 30 and 40 are joined, but the reinforcing plate is preferably
provided on all the four side surfaces to increase the sheet thickness. Also, a total
thickness of the portion reinforced by the reinforcing plate is preferably 1.6 times or
more and 10.0 times or less an average sheet thickness on both sides thereof to which the
15 reinforcing plate is not provided, even at the thinnest portion.
[0061]
Further, as a material of each constituent element constituting the front subframe,
it is most preferable to use steel (particularly a cold-rolled steel sheet made of
high-tensile steel), but other materials may also be used. For example, acrylic fibers,
20 carbon fibers, carbon fiber-reinforced resin (CFRP) using reinforced plastic, glass
fiber-reinforced resin (GFRP), or the like may be used. In this case, joining between the
constituent elements may be performed by joining methods of various types such as an
adhesive or bolt fastening. Light metals such as aluminum or magnesium may also be
employed.
25 Joining methods of various types such as an adhesive, arc welding, spot welding,
33
laser welding, bolt fastening, or screwing can be applied to the joining between the
constituent elements.
Forming of each constituent element may be any of press forming, casting, and
forging.
5 [0062]
Also, in the above-described embodiment, a configuration in which a length of
the first part member 11 is smaller than that of the second part member 12, and a position
of the engine mount 13 is deviated to the left side away from a central position in the
left-right direction has been employed. The reason for this is that the engine (not
10 illustrated) disposed to be displaced to the left side is supported by the engine mount 13
that is also disposed to be displaced to the left side. However, the position of the engine
mount 13 is not limited only to the configuration in which the engine mount 13 is
displaced to the left side. Conversely, a configuration in which a length of the second
part member 12 is smaller than that of the first part member 11, and a position of the
15 engine mount 13 is deviated to the right side away from the central position in the
left-right direction may also be employed. Alternatively, a configuration in which
lengths of the first part member 11 and the second part member 12 are equal, and a
position of the engine mount 13 is at the central position in the left-right direction may
also be employed.
20 [0063]
Also, in the above-described embodiment, an example in which the first part
member 11 and the second part member 12 are formed by a square hollow member has
been described, but a shape of the front cross member 10 formed by these is not
particularly limited. For example, the front cross member 10 may be formed by a tube
25 member whose cross section has a polygonal shape, a circular shape, an elliptical shape,
34
or the like. Furthermore, in a case of a polygonal shape, a corner portion thereof may
either have a ridge line or have an arc-shaped surface.
Also, a cross-sectional outer shape of the front cross member 10 at any position
in the longitudinal direction may be constant in the longitudinal direction or may change
5 from an intermediate position in the longitudinal direction.
[0064]
Also, in the above-described embodiment, a case in which the present invention
is applied to the front subframe disposed at a front position of the vehicle body has been
described, but the present invention may also be applied to a rear subframe disposed at a
10 rear position of the vehicle body. Furthermore, the present invention may be applied to
both the front subframe and the rear subframe. When the present invention is applied to
both the front subframe and the rear subframe, a configuration in which the engine mount
13 is provided on a side at which the engine is disposed, and the reinforcing plate, instead
of the engine mount 13, is provided on a side at which the engine is not disposed may be
15 used. When the present invention is applied to a rear subframe of a rear-wheel drive
vehicle or a four-wheel drive vehicle, a collar of a differential gear mount may be used as
the reinforcing part. Also, for example, when the vehicle body is for an electric vehicle,
since there is a less need to provide an engine mount, the engine mount 13 may not be
provided. In a case of an electric vehicle, a mount part of the motor or battery may be
20 used as the reinforcing part.
[0065]
Also, in the above-described embodiment, a case in which the connection
members 30 and 40 are connected between the front cross member 10 and each of the
pair of rear body mounts 20 has been described, but the number of the rear body mounts
25 20 may also be three or more. In this case, the number of connection members
35
extending from the rear body mounts 20 to the front cross member 10 may be two or
more. Also, of the plurality of connection members extending from the rear body
mounts 20, at least two connection members may be joined to the front cross member 10
as described above.
5 [0066]
Also, in the above-described embodiment, an example in which the pair of rear
body mounts 20 and the connection members 30 and 40 are connected has been
described, but the technology according to the present disclosure is not limited to such an
example. For example, a front-rear positional relationship between the cross member of
10 the sub frame and the body mounts may be reversed. That is, when the cross member of
the subframe is provided on a vehicle rear side with respect to a frame member including
the body mounts, the body mounts and the cross member may be joined by the
connection members as described above.
15
[0067]
Also, in the above-described embodiment, an example in which the technology
of the present disclosure is applied to a structure of the subframe has been described as
an example of the lower vehicle body structure, but the technology according to the
present disclosure is not limited to such an example. For example, the technology
according to the present disclosure is not limited to the structure of the subframe and can
20 be applied to suspension structures of various types.
[0068]
The gist of the lower vehicle body structure according to the above-described
embodiment will be summarized below.
(1) A lower vehicle body structure according to the present embodiment
25 includes: the lower arms (suspension components); the front cross member (cross
36
member) 10 having the first part member 11 and the second part member 12 which are a
pair of part cross members connected to the lower arm, and the engine mount
(reinforcing part) 13 coaxially connected between the first part member 11 and the
second part member 12; the plurality of rear body mounts (body mounts) 20; and the
5 connection members 30 and 40 directly connecting between each of the rear body mounts
20 and the engine mount 13. Then, a minimum sheet thickness of the engine mount 13
at connection positions with respect to the first part member 11 and the second part
member 12 is 1. 6 times or more an average sheet thickness at connection ends of the first
part member 11 and the second part member 12 with respect to the engine mount 13.
10 [0069]
According to the lower vehicle body structure of the above-described (1), a
lateral force in a longitudinal direction of the front cross member 10 and a longitudinal
force perpendicular to the longitudinal direction are applied to the front cross member 10
from the lower arms. Of these, the front cross member 10 receives the lateral force as a
15 compressive axial force or a tensile axial force in a direction in which the front cross
member 10 extends. Therefore, higher stiffness can be secured than that when the
lateral force is received by bending of the front cross member 10.
[0070]
In addition, the front cross member 10 is supported by the plurality of rear body
20 mounts 20 via the connection members 30 and 40. Therefore, the longitudinal force
applied to the front cross member 10 can be transmitted to the plurality of rear body
mounts 20 with a high load transmission efficiency.
Here, since a minimum sheet thickness of the engine mount 13 is set to 1. 6 times
or more an average sheet thickness at the connection ends of the first part member 11 and
25 the second part member 12 with respect to the engine mount 13, a bending stiffness of a
37
wall portion of the engine mount 13 at connection positions of the first part member 11
and the second part member 12 with respect to the engine mount 13 can be increased to
four times or more a bending stiffness of each of the connection ends. Since the lateral
force and the longitudinal force applied to the front cross member 10 are transmitted via
5 the engine mount 13 having such high bending stiffness, a load transmission efficiency
can be improved. Moreover, the stiffness of the front cross member 10 particular! y at
the joining portion to the connection members 30 and 40 can be increased. Therefore, a
weight can be reduced compared to a case in which a sheet thickness and a
cross-sectional dimension are increased over the entire length of the front cross member
10 10 to increase stiffness.
[0071]
(2) In the above-described (1), the following configuration may also be
employed.
That is, the straight part (the connection end) 11c of the first part member (one
15 of the part cross members) 11 is abutted and connected to the first wall surface 13a1 of
the engine mount 13, and the straight part (the connection end) 12c of the second part
member (the other of the part cross members) 12 is abutted and connected to the second
wall surface 13a2 of the engine mount 13. Then, the first part member 11, the first wall
surface 13a1, the second wall surface 13a2, and the second part member 12 are coaxially
20 disposed in that order in the longitudinal direction of the front cross member 10.
[0072]
(3) In the case of the above-described (1) or (2), the following configuration
may also be employed.
That is, the plurality of connection members include the connection member
25 (first connection member) 30 and the connection member (second connection member)
38
40. Further, in a longitudinal section perpendicular to the longitudinal direction of the
cross member 10, which includes a position of the intersection point P where the
extended line b1 of the first axis b passing through a centroid of an outer shape at any
position in the longitudinal direction of the connection member 30 in a cross section
5 perpendicular to the longitudinal direction and the extended line c 1 of the second axis c
passing through a centroid of an outer shape at any position in the longitudinal direction
of the connection member 40 in a cross section perpendicular to the longitudinal
direction intersect in a plan view, the extended line b 1 of the first axis b and the extended
line c 1 of the second axis c are inside the engine mount 13.
10 [0073]
According to the lower vehicle body structure of the above-described (3), the
front cross member 10 is supported by the plurality of rear body mounts (body mounts)
20 via the appropriately disposed connection members 30 and 40. Therefore, a
longitudinal force applied to the front cross member 10 can be transmitted to the plurality
15 of rear body mounts 20 with a higher load transmission efficiency.
Further, the above-described "inside the engine mount 13" refers to the inside of
a range defined by outer shape lines when the engine mount 13 is viewed in a
longitudinal section including a central axis thereof. However, the above-described
outer shape lines include not only a case in which all of them are connected to form a
20 closed cross section but also a case in which some of them are not connected to form an
open cross section. In a case of the open cross section, when end portions of outer
shape lines positioned on both sides of a missing outer shape line are connected to each
other with a virtual straight line to form a closed outer shape, this closed outer shape can
be referred to as the "inside the engine mount 13."
25 [0074]
39
( 4) In the case of the above-described (3 ), the extended line b 1 of the first axis b
and the extended line c 1 of the second axis c may coincide with each other at one point
(intersection point P) in the engine mount 13 when viewed in the longitudinal section.
In the case of the above-described ( 4 ), a longitudinal force applied to the front
5 cross member 10 can be transmitted to the rear body mounts 20 with a higher load
transmission efficiency.
[0075]
(5) In the lower vehicle body structure according to the above-described (4),
both the extended line b 1 of the first axis b and the extended line c 1 of the second axis c
10 may be inside a projected outer shape of the straight part 11 c of the first part member 11
and the straight part 12c of the second part member 12 when viewed in the longitudinal
section. More specifically, when outer shape lines of the connection end of the straight
part 11 c with respect to the engine mount 13 and outer shape lines of the connection end
of the straight part 12c with respect to the engine mount 13 are projected onto the
15 longitudinal section, both the extended line b 1 and the extended line c 1 may be
positioned inside these two projected outer shapes.
In the case of the above-described (5), a longitudinal force applied to the front
cross member 10 can be transmitted to the plurality of rear body mounts 20 with a higher
load transmission efficiency.
20 [0076]
25
(6) In the lower vehicle body structure according to any one of the
above-described (3) to (5), the connection member 30 may be joined to one of the pair of
rear body mounts 20 via the pair of extension pieces (first extension pieces) 32 facing
each other.
In the case of the above-described (6), since surface-joining is performed via the
40
extension pieces 32, a higher joining strength can be obtained than that when
abutting-joining is simply performed.
[0077]
(7) In the lower vehicle body structure according to any one of the
5 above-described (3) to (6), the connection members 40 may also be joined to the other of
the pair of rear body mounts 20 via a pair of extension pieces (second extension pieces)
42 facing each other.
In the case of the above-described (7), since surface-joining is performed via the
extension pieces 32, a higher joining strength can be obtained than that when
10 abutting-joining is simply performed.
[0078]
15
20
(8) In the lower vehicle body structure according to any one of the
above-described (1) to (7), the engine mount 13 has been exemplified as a bush collar
forming a reinforcing part.
In the case of the above-described (8), reinforcement can be made without using
an additional component.
Further, not being limited only to the engine mount 13, a rack gear mount,
another body mount, a differential gear mount, a motor mount, or a battery mount may be
employed as the reinforcing part.
That is, a rack gear mount illustrated in FIG. 18A may be coaxially connected
between the first part member 11 and the second part member 12, and in this case, a sheet
thickness within a range indicated by reference symbol R is used for a minimum sheet
thickness of the rack gear mount.
Also, when a body mount illustrated in FIG. 18B is coaxially connected between
25 the first part member 11 and the second part member 12, a sheet thickness within a range
41
indicated by reference symbol R is used for a minimum sheet thickness of the body
mount.
Also, when a differential gear mount illustrated in FIG. 18C is coaxially
connected between the first part member 11 and the second part member 12, a sheet
5 thickness within a range indicated by reference symbol R is used for a minimum sheet
thickness of the differential gear mount.
Also, when a motor mount illustrated in FIG. 18D is coaxially connected
between the first part member 11 and the second part member 12, a sheet thickness
within a range indicated by reference symbol R is used for a minimum sheet thickness of
10 the motor mount.
Also, when a battery mount illustrated in FIG. 18E is coaxially connected
between the first part member 11 and the second part member 12, a sheet thickness
within a range indicated by reference symbol R is used for a minimum sheet thickness of
the battery mount.
15 [0079]
(9) In the lower vehicle body structure according to any one of above-described
(1) to (8), the following configuration may also be employed.
The reinforcing part is the engine mount 13, or any one of the rack gear mount,
the body mount, the differential gear mount, the motor mount, and the battery mount
20 having a cylindrical shape; and the first part member 11, the second part member 12, and
the connection members 30 and 40 are abutted and connected to an outer circumferential
surface of the reinforcing part.
In the case of the above-described (9), the reinforcing part has a cylindrical
shape having a high mechanical strength, and since an outer circumferential surface
25 thereof receives an external force from the first part member 11, the second part member
42
12, and the connection members 30 and 40, a higher load transmission efficiency can be
obtained.
[0080]
(1 0) In the lower vehicle body structure according to any one of the
5 above-described (1) to (9), as illustrated in FIG. 3, a virtual straight line EL connecting
centroids of outer shapes in a cross section perpendicular to the longitudinal direction at
positions of both ends of the front cross member 10 may pass through the inside of the
front cross member 10 at any position in the longitudinal direction of the front cross
member 10.
10 According to this configuration, since a degree of linearity of the front cross
member 10 is increased, the stiffness against a lateral force is higher than that in a case of
a shape with a large curvature. Further, the outer shape at each position of both ends of
the front cross member 10 is not limited only to a case of an outer shape closed by
connecting all the outer shape lines but also includes a case of an outer shape that is open
15 without some of the outer shape lines (for example, U-shape or the like) as illustrated in
FIG. 5. In a case of the open outer shape, it is preferable to connect end portions of
outer shape lines positioned on both sides of a missing outer shape line to each other with
a virtual straight line to form a closed outer shape, and then obtain a centroid on the basis
of this closed outer shape. When it is described with reference to FIG. 4, a substantially
20 quadrangular closed space is formed by providing the virtual straight line EL after
removing the extension pieces 11a1 and 11a2 from the left end of the first part member
11. Then, a centroid of this closed space is obtained.
[Examples]
[0081]
25 [Example 1]
43
5
In order to confirm effects of the present invention, weight and stiffness of the
sub frame according to the above-described embodiment (invention example 1) and those
of a subframe according to comparative example 1 were compared by a numerical
calculation.
Invention example 1 has the structure illustrated in FIG. 1. That is, in
invention example 1, in a longitudinal section perpendicular to the longitudinal direction
of the cross member 10, which includes a position of the intersection point P at which the
extended line b 1 of the first axis b passing through a centroid at any position in the
longitudinal direction of the connection member 30 and the extended line c 1 of the
10 second axis c passing through a centroid at any position in the longitudinal direction of
the connection member 40 intersect in a plan view, the extended line b 1 of the first axis b
and the extended line c 1 of the second axis c are inside the front cross member 10. Also,
when viewed also in the longitudinal section, the extended line b 1 of the first axis b and
the extended line c 1 of the second axis c coincide with each other at the intersection point
15 P which is one point in the front cross member 10. The engine mount 13 is connected at
the position of the intersection point P.
[0082]
Comparative example 1 has a structure illustrated in FIG. 12. That is, a
subframe of comparative example 1 includes a substantially rectangular frame X in
20 which an upper component XI and a lower component X2 are overlapped and joined to
each other, a collar X3 fixed to the frame X, a pair of rear body mounts X4, and a pair of
front body mounts X5. In the frame X, a front cross member part X6 is formed at a
position between the pair of front body mounts X5. The collar X3 is disposed at an
intermediate position in a longitudinal direction of the front cross member part X6.
25 Then, one connection part X7 connecting the collar X3 and one of the rear body mounts
44
X4 is formed in the frame X.
As illustrated in FIG. 12, in comparative example 1, a central portion of the front
cross member part X6 in the longitudinal direction is largely curved to be convex toward
the rear. Therefore, a virtual straight line Lx connecting centroids at positions of both
5 ends of the front cross member part X6 in the longitudinal direction is outside the front
cross member part X6 at a central portion of the front cross member part X6 in the
longitudinal direction. Also, since there is only one connection part X7, an extended
line of an axis passing through a centroid at any position in a longitudinal direction
thereof does not form an intersection point inside the front cross member part X6.
10 [0083]
As a condition at the time of a numerical calculation for each of invention
example 1 and comparative example 1, first, four body mounts of both the subframes
were completely fixed to the vehicle body. Then, an external force (1 kN) was applied
to both ends of the front cross member to which a lower arm is connected and a support
15 point of an engine, and an amount of displacement of an input point of the external force
was obtained. Then, a value obtained by dividing the external force applied to the input
point by the amount of displacement of the input point was obtained, and this was used
as a stiffness evaluation value. Further, the stiffness evaluation value of invention
example 1 was divided by the stiffness evaluation value of comparative example 1 to
20 make it dimensionless. Finally, a weight efficiency of stiffness was obtained by
dividing the stiffness evaluation value that has been made dimensionless in this way by a
ratio by weight (constant value) of invention example 1 to comparative example 1. The
results are shown in FIG. 13.
Further, a fastening point of the body mount, a fastening point of the lower arm,
25 and a position of the engine mount, which were other boundary conditions at the time of
45
the numerical calculation, were set as conditions common to invention example 1 and
comparative example 1.
[0084]
In FIG. 13, numbers 1 to 4 on the horizontal axis indicate a stiffness ratio of
5 invention example 1 to comparative example 1. Specifically, number 1 on the
horizontal axis indicates an analysis result when a lateral force acted on both ends of the
front cross member in an inward direction in which a pair of lower arms come close to
each other. Also, number 2 on the horizontal axis indicates an analysis result when the
lateral force acted on both ends of the front cross member in one direction from one end
10 to the other end of both ends. Also, number 3 on the horizontal axis indicates an
analysis result when a longitudinal force toward the rear side of the vehicle body acted on
both ends of the front cross member. Also, number 4 on the horizontal axis indicates an
analysis result when the longitudinal force toward the rear side of the vehicle body acted
on a center of the collar disposed in the front cross member.
15 [0085]
As illustrated in FIG. 13, it was shown that the weight efficiency of stiffness of
invention example 1 was higher than that of comparative example 1 by more than 1.0 in
any of numbers 1 to 4 on the horizontal axis.
In invention example 1, since the structure receives a load not as a bending load
20 of the skeleton member but as a tensile load or a compressive load, decrease in stiffness
is suppressed even when the skeleton member is made thinner. Therefore, the weight
efficiency of stiffness is higher than that of comparative example 1 that is made of a thick
member.
As described above, it was confirmed that weight reduction was achieved while
25 securing stiffness in invention example 1.
46
[0086]
[Example 2]
Next, in order to confirm effects on a stiffness of a support structure by the
connection members 30 and 40 of invention example 2 (FIG. 14A), calculation models
5 illustrated in FIGS. 14B to 14D were also prepared, and stiffness strength when a
common external force was applied to each of them were compared.
First, as a description for each calculation model, FIG. 14A is a plan view of a
front subframe according to invention example 2 described above. Invention example 2
has the same configuration as the front subframe illustrated in FIG. 1.
10 [0087]
FIG. 14B is comparative example 2 in which connection members 30A and 40A
are employed instead of the connection members 30 and 40 illustrated in FIG. 14A.
These connection members 30A and 40A have the same outer diameter dimension and
inner diameter dimension as the connection members 30 and 40, but they are joined to a
15 rear side surface of the front cross member 10 in a state of being spaced apart from each
other in the left-right direction. Therefore, in comparative example 2, a first axis bA
passing through a centroid at any position in a longitudinal direction of the connection
member 30A and a second axis cA passing through a centroid at any position in a
longitudinal direction of the connection member 40A do not intersect to form an
20 intersection point P within a range between the front surface ff and the rear surface rf of
the front cross member 10 in a plan view.
[0088]
FIG. 14C employs an inverted Y-shaped connection member 30B instead of the
connection members 30 and 40 illustrated in FIG. 14A. The connection member 30B
25 includes a first member 30B 1, a second member 30B2, and a third member 30B3 having
47
the same outer diameter dimension and inner diameter dimension as the connection
members 30 and 40. One end side of the first member 30B 1 and the second member
30B2 are joined to the rear body mounts 20, and the other ends thereof are joined to each
other at an intersection point PB. Further, the third member 30B3 connects the
5 intersection point PB and the rear side surface of the front cross member 10. Therefore,
in comparative example 3, the intersection point PB of the first member 30B 1 and the
second member 30B2 is not within a range between the front surface ff and the rear
surface rf of the front cross member 10 in a plan view.
10
[0089]
FIG. 14D employs connection members 30C and 40C instead of the connection
members 30 and 40 illustrated in FIG. 14A. One end side of the connection members
30C and 40C are joined to the rear body mounts 20, and the other ends thereof are joined
not to the rear side surface of the front cross member 10 but to the top surface tf. Then,
a first axis bC passing through a centroid at any position in the longitudinal direction of
15 the connection member 30C and a second axis cC passing through a centroid at any
position in the longitudinal direction of the connection member 40C intersect at an
intersection point PC within a range between the front surface ff and the rear surface rf of
the front cross member 10 in a plan view. However, the intersection point PC is not
within a range between the top surface tf and the lower surface bf of the front cross
20 member 10 in a side view (longitudinal sectional view).
25
[0090]
Stiffness when an external force was applied to each of invention example 2 and
comparative examples 2 to 4 having the above-described configurations was evaluated by
a numerical calculation.
As a condition at the time of the numerical calculation, first, the four body
48
mounts (the rear body mounts 20 and the front body mounts 60) of each subframe were
completely fixed to the vehicle body. Then, an external force (1 kN) acting as a lateral
force was applied to both ends of the front cross member 10 to which lower arms are
connected, and an amount of displacement of an input point of the external force was
5 obtained. Then, a value obtained by dividing the external force applied to the input
point by the amount of displacement of the input point was obtained, and this was used
as a stiffness evaluation value. Further, each stiffness evaluation value of invention
example 2 and comparative examples 2 to 4 was divided by the stiffness evaluation value
of invention example 2 to make it dimensionless. The results obtained in this way are
10 shown in FIGS. 15 and 16.
15
20
Further, a fastening point of the body mount and a fastening point of the lower
arm, which were other conditions at the time of the numerical calculation, were set as
conditions common to invention example 2 and comparative examples 2 to 4.
[0091]
FIG. 15 shows an analysis result when a lateral force acted on both ends of the
front cross member 10 in an inward direction in which a pair of lower arms come close to
each other. As can be found from this analysis result, it was confirmed that the stiffness
of invention example 2 was more than twice as high as the stiffness in comparative
examples 2 to 4.
FIG. 16 shows an analysis result when a lateral force acted on both ends of the
front cross member 10 in one direction from one end to the other end of both ends. As
can be found from this analysis result, it was confirmed that the stiffness of invention
example 2 was higher than that of any of comparative examples 2 to 4.
Further, a case in which a longitudinal force was applied to the front cross
25 member 10 instead of the lateral force was also evaluated, but there was no difference
49
between invention example 2 and comparative examples 2 to 4. Therefore, it was
confirmed that a position of the intersection point P was extremely important for
increasing stiffness against a lateral force.
[0092]
5 [Example 3]
In the front sub frame illustrated in FIG. 1, the stiffness of the front cross
member 10 tends to improve when a sheet thickness of the engine mount 13 is increased.
On the other hand, when the sheet thickness is increased too much, the weight of the
engine mount 13 increases, and as a result, a weight efficiency of stiffness tends to
10 decrease. Therefore, there is a preferable sheet thickness ratio from the perspective of
the weight efficiency of stiffness.
[0093]
Therefore, in the front subframe illustrated in FIG. 1, a ratio of a minimum sheet
thickness tp (mm) of the engine mount 13 to an average sheet thickness tc (mm) of the
15 straight parts 11c and 12c was set to tc/tp, and how the weight efficiency of stiffness was
displaced was obtained by a numerical calculation.
As a condition at the time of the numerical calculation, first, the front subframe
illustrated in FIG. 1 was fixed to the vehicle body at four points including the pair of rear
body mounts 20 and the pair of front body mounts 60. Then, the ratio tc/tp was changed
20 between 1 and 10, and a stiffness value and a mass were obtained for each ratio tc/tp.
Then, a relationship between the ratio tc/tp and the weight efficiency of stiffness
(stiffness/mass KIM) was summarized in the graph shown in FIG. 17 A. Also, a slope of
the weight efficiency (stiffness/mass KIM) of stiffness of the curve in FIG. 17 A at each
ratio tc/tp was obtained and summarized in FIG. 17B.
25 [0094]
50
As is apparent from FIG. 17B, the slope rises sharply in accordance with
increase in the ratio tc/tp, reaches a maximum value when the ratio tc/tp reaches 1.6, and
then gradually decreases.
From this, it has been found that 1.6 or more is preferably employed as the ratio
5 tc/tp at which the slope is maximum in the curve shown in FIG. 17 A. More desirably,
the ratio tc/tp is preferably 3 or more in which 80% or more of the maximum value of the
weight efficiency can be achieved. On the other hand, as an upper limit of the ratio tc/tp,
it is more preferable to employ 8.0 at which the weight efficiency has the maximum
10
value in FIG. 17 A.
From the above-described results, it has been ascertained that the minimum
sheet thickness of the engine mount 13 at the connection positions with respect to the part
members 11 and 12 is preferably 1.6 times or more the average sheet thickness at the
connection ends of the part members 11 and 12 with respect to the engine mount 13.
[0095]
15 [Example 4]
In example 3, a case in which the reinforcing part (engine mount 13) has a
cylindrical shape has been described, but the same tendency as in example 3 can be
obtained even when a reinforcing part having a shape other than the cylindrical shape is
employed. In regard to this, a box -shaped reinforcing part 113 illustrated in FIG. 18
20 will be described as an example.
[0096]
The box-shaped reinforcing part 113 has substantially a cubic shape, and only a
front surface of six surfaces is open. Then, the part member 11 is abutted and connected
to one of a pair of side walls on both sides of the opening. Also, the part member 12 is
25 abutted and connected to the other of the pair of side walls. Further, the connection
51
members 30 and 40 are abutted and connected to a back surface of the reinforcing part
113 facing the opening. A relative positional relationship between the part members 11
and 12 and the connection members 30 and 40 with the reinforcing part 113 as a center is
the same as the relative positional relationship between the part members 11 and 12 and
5 the connection members 30 and 40 with the engine mount 13 described with reference to
FIG. 1 as a center. Also, the other configurations are the same as those of the subframe
illustrated in FIG. 1.
A minimum sheet thickness of the reinforcing part 113 at a connection position
113a1 with respect to the part member 11 is 1.6 times or more an average sheet thickness
10 of the part member 11 joined thereto. Similarly, a minimum sheet thickness of the
reinforcing part 113 at a connection position with respect to the part member 12 is also
1.6 times or more an average sheet thickness of the part member 12 joined thereto.
[0097]
Also in the front subframe illustrated in FIG. 18, the stiffness of the front cross
15 member 10 tends to improve when the sheet thickness of the reinforcing part 113 is
increased. On the other hand, when the sheet thickness is increased too much, the
weight of the reinforcing part 113 increases, and as a result, the weight efficiency of the
stiffness tends to decrease. Therefore, there is a preferable sheet thickness ratio from
the perspective of a weight efficiency of stiffness.
20 [0098]
25
Therefore, in the front subframe illustrated in FIG. 18, a ratio of a minimum
sheet thickness tp (mm) of the reinforcing part 113 to an average sheet thickness tc (mm)
of the straight parts 11 c and 12c was set to tc/tp, and how the weight efficiency of
stiffness was displaced was obtained by a numerical calculation.
As a condition at the time of the numerical calculation, first, the front subframe
52
illustrated in FIG. 18 was fixed to the vehicle body at four points including the pair of
rear body mounts 20 and the pair of front body mounts 60 illustrated in FIG. 1. Then,
the ratio tc/tp was changed between 1 and 10, and a stiffness value and a mass were
obtained for each ratio tc/tp. Then, a relationship between the ratio tc/tp and the weight
5 efficiency of stiffness (stiffness/mass KIM) was summarized in the graph shown in FIG.
19A. Also, a slope of the weight efficiency (stiffness/mass KIM) of stiffness of the
curve in FIG. 19A at each ratio tc/tp was obtained and summarized in FIG. 19B.
[0099]
As is apparent from FIG. 19B, the slope is maximum when the ratio tc/tp is 2.5
10 after passing 1.6, reaches a maximum value when the ratio tc/tp reaches 8.0, and
gradually decreases thereafter.
From this, it has been found that 1.6 or more is preferably employed and 2.5 or
more is more preferably employed as the ratio tc/tp at which the slope is maximum in the
curve shown in FIG. 19A. On the other hand, as an upper limit of the ratio tc/tp, it is
15 more preferable to employ 8.0 at which the weight efficiency has the maximum value in
FIG. 19A.
From the above-described results, it has been ascertained that the minimum
sheet thickness of the box -shaped reinforcing part 113 at the connection positions with
respect to the part members 11 and 12 is preferably 1.6 times or more and more
20 preferably 2.5 times more the average sheet thickness at the connection ends of the part
members 11 and 12 with respect to the reinforcing part 113.
25
[0100]
Although one embodiment and examples of the present invention have been
described above, the content of the present invention is not limited only thereto.
For example, in the above-described embodiment illustrated in FIG. 1, a case in
53
which the engine mount 13 (bush collar) is used as the reinforcing part has been
described as an example, but instead of the engine mount 13, any of a rack gear mount, a
body mount, a differential gear mount, a motor mount, and a battery mount may be
employed. Also in these cases, a sheet thickness of each of the above-described mounts
5 is preferably 1.6 times or more an average sheet thickness at a connection end of a part
member.
[Industrial Applicability]
[0101]
According to the present invention, a lower vehicle body structure that is
10 lightweight and has high stiffness and a high load transmission efficiency can be
provided. Therefore, industrial applicability is high.
15
20
25
[Brief Description of the Reference Symbols]
[0102]
10 Front cross member (cross member)
11 First part member (part cross member)
11a Left end (both end)
11c, 12c Straight part (connection end)
12 Second part member (part cross member)
12a Right end (both end)
13 Engine mount (reinforcing part)
13a1 First wall surface
13a2 Second wall surface
20 Rear body mount (body mount)
30 Connection member (first connection member)
32 Extension piece (first extension piece)
54
5
40 Connection member (second connection member)
42 Extension piece (second extension piece)
b First axis
b 1 Extended line
c Second axis
c 1 Extended line
EX Virtual straight line
P Intersection point (intersecting position)

WE CLAIMS

A lower vehicle body structure comprising:
suspension components;
a cross member including a pair of part cross members connected to the
suspension components and a reinforcing part coaxially connected between the pair of
part cross members;
a plurality of body mounts; and
a plurality of connection members directly connecting each of the plurality of
10 body mounts and the reinforcing part, wherein
15
20
25
a minimum sheet thickness of the reinforcing part at connection positions with
respect to the pair of part cross members is 1.6 times or more an average sheet thickness
at connection ends of the pair of part cross members with respect to the reinforcing part.
[Claim 2]
The lower vehicle body structure according to claim 1, wherein:
the connection end at one of the pair of part cross members is abutted and
connected to a first wall surface of the reinforcing part;
the connection end at the other of the pair of part cross members is abutted and
connected to a second wall surface of the reinforcing part; and
one of the part cross members, the first wall surface, the second wall surface,
and the other of the part cross members are coaxially aligned in that order in a
longitudinal direction of the cross member.
[Claim 3]
The lower vehicle body structure according to claim 1 or 2, wherein:
the plurality of connection members include a first connection member and a
56
second connection member; and,
in a longitudinal section perpendicular to the longitudinal direction of the cross
member, which includes a position where
an extended line of a first axis passing through a centroid of an outer
5 shape at any position in a longitudinal direction of the first connection member in a cross
section perpendicular to the longitudinal direction, and
10
an extended line of a second axis passing through a centroid of an outer
shape at any position in a longitudinal direction of the second connection member
intersect in a plan view,
both the extended line of the first axis and the extended line of the second axis
are inside the reinforcing part.
[Claim 4]
The lower vehicle body structure according to claim 3, wherein
the extended line of the first axis and the extended line of the second axis
15 coincide with each other at one point in the reinforcing part in a view of the longitudinal
section.
[Claim 5]
The lower vehicle body structure according to claim 4, wherein
both the extended line of the first axis and the extended line of the second axis
20 are inside a projected outer shape of the connection end of each of the pair of part cross
members in a view of the longitudinal section.
[Claim 6]
The lower vehicle body structure according to any one of claims 3 to 5, wherein
the first connection member is joined to one of the body mounts via a first
25 extension piece extending from an end portion of the first connection member.
57
[Claim 7]
The lower vehicle body structure according to any one of claims 3 to 6, wherein
the second connection member is joined to another of the body mounts via a
second extension piece extending from an end portion of the second connection member.
5 [Claim 8]
10
The lower vehicle body structure according to any one of claims 1 to 7, wherein
the reinforcing part is a rack gear mount, another body mount, a differential gear
mount, a motor mount, a battery mount, or any combination thereof.
[Claim 9]
The lower vehicle body structure according to any one of claims 1 to 8, wherein:
the reinforcing part is any one of the rack gear mount, the body mount, the
differential gear mount, the motor mount, and the battery mount, each of which having a
cylindrical shape; and
the pair of part cross members and the plurality of connection members are
15 abutted and connected to an outer circumferential surface of the reinforcing part.
[Claim 10]
The lower vehicle body structure according to any one of claims 1 to 9, wherein
a virtual straight line connecting centroids of outer shapes in a cross section
perpendicular to the longitudinal direction of the cross member at positions of both ends
20 of the cross member passes through the inside of the cross member at any position in the
longitudinal direction of the cross member.