Vehicle rear suspension

In a rear suspension comprising left and right wheel supports for supporting left and right rear wheels for rotation, a cross member connected to the wheel supports at opposite ends, left and right trailing arms which are connected to the cross member at the rear ends and to the vehicle body at the front ends by way of elastic members for vertical swinging motion and longitudinal displacement and a lateral rod which is connected to the cross member at one end by way of an elastic member and to the vehicle body at the other end by way of an elastic member, nonlinear toe characteristics of the outer rear wheel are obtained by selecting the positions of the junctions of the trailing arms to the vehicle body and the cross member, the position of the lateral rod, and the elastic characteristics of the elastic members.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a torsion-axle type rear suspension for a 
vehicle. 
2. Description of the Prior Art 
There has been known a torsion-axle type rear suspension as disclosed in, 
for instance, Japanese Unexamined Utility Model publication No. 
58(1983)-58906. As shown in prior art FIGS. 21 and 22 of the present 
application, the torsion-axle type rear suspension generally comprises 
left and right wheel supports 2a and 2b for supporting left and right rear 
wheels 1a and 1b for rotation, a cross member 3 which extends in the 
transverse direction of the vehicle body and is connected to the wheel 
supports 2a and 2b at opposite ends, left and right trailing arms 5a and 
5b which are fixed to the cross member 3 at the rear ends and connected to 
the vehicle body 4 at the front ends by way of elastic members 6a and 6b 
for vertical swinging motion and longitudinal displacement and a lateral 
rod 8 which is connected to the cross member 3 at one end by way of one 
elastic member 7 and to the vehicle body 4 at the other end by way of 
another elastic member 7. The lower ends of shock absorbers 9 which are 
connected to the vehicle body at the upper ends are connected to the 
respective junctions of the trailing arms 5a and 5b to the cross member 3. 
A torsion bar 10 extends inside the cross member 3. 
It is generally preferred in order to improve running performance of the 
vehicle that the toe of the rear wheels in addition to turn of the front 
wheels in response to turn of the steering wheel. For example, when the 
steering wheel is turned by a slight angle while the vehicle runs 
straight, it is preferred that the outer (with respect to the turning 
direction) rear wheel be caused to toe in to generate understeer tendency, 
thereby improving running stability of the vehicle. On the other hand, 
during hard cornering, it is preferred that the outer rear wheel be caused 
to toe out to weaken strong understeer tendency especially in the case of 
a front-engine front-drive type vehicle in which understeer tendency is 
stronger. In another aspect, it is generally preferred that when the 
steering wheel is turned while the vehicle runs at a low speed, the outer 
rear wheel be caused to toe out to improve heading performance of the 
vehicle. On the other hand, during hard cornering or lane change at a high 
speed, it is preferred that the outer rear wheel be caused to toe in to 
ensure running stability. 
Such behavior of the outer rear wheel can be obtained by controlling the 
toe of the rear wheel according to the side force that is generated by 
change of centripetal acceleration and acts on the rear wheel when the 
steering wheel is turned. However, in the case of the conventional 
torsion-axle type rear suspension, when side force acts on the rear wheel, 
the rear wheel is merely caused to toe in or toe out depending on whether 
the lateral rod is mounted on the vehicle body on the front side or the 
rear side of the line of action of the side force. That is, when a side 
force G acts on the rear wheels 1a and 1b in FIG. 22, a rightward rotating 
moment is generated since the lateral rod 8 is mounted on the vehicle body 
4 on the rear side of the line of action of the side force G, and 
accordingly, the right trailing arm 5b is displaced rearward under 
deformation of the elastic member 6b while the left trailing arm 5a is 
displaced forward under deformation of the elastic member 6a, whereby the 
rear wheels 1a and 1b are turned rightward and the left rear wheel 1a toes 
in. Though the elastic members 7 on the ends of the lateral rod 8 are also 
deformed by the side force G, this deformation only displaces the cross 
member in the transverse direction of the vehicle body and does not affect 
the toe of the left rear wheel 1a since the trailing arms 5a and 5b are 
parallel to each other. When the lateral rod 8 is on the front side of the 
line of action of the side force G, the left rear wheel 1a is caused to 
toe out as can be understood from the description above. At any rate, the 
rear wheel only toes out or in when the side force G acts thereon and 
increase of the side force G with increase in the centripetal acceleration 
only increases the degree of the toe-in or toe-out. 
SUMMARY OF THE INVENTION 
In view of the foregoing observations and description, a first object of 
the present invention is to provide a rear suspension in which the outer 
rear wheel can be caused to toe in when the side force that is produced by 
centripetal acceleration and acts thereon is relatively weak and be caused 
to toe out when the side force is relatively strong. 
A second object of the present invention is to provide a rear suspension in 
which the outer rear wheel can be caused to toe out when the side force 
that is produced by centripetal acceleration and acts thereon is 
relatively weak and be caused to toe in when the side force is relatively 
strong. 
This invention is based on the fact that the position of the instantaneous 
center of rotational displacement of the rear wheel generated by the side 
force can be freely controlled by selecting the position of the left and 
right trailing arms, and in accordance with the present invention, 
nonlinear toe characteristics are obtained by a suitable combination of 
toe changes of the rear wheel depending on the position of the trailing 
arms and depending on the position of the lateral rod and the elastic 
characteristics of the elastic members for connecting the lateral rod to 
the vehicle body and the cross member. That is, nonlinear toe 
characteristics of the rear wheel are obtained by selecting the positions 
of the junctions of the trailing arms to the vehicle body and the cross 
member, the position of the lateral rod and the elastic characteristics of 
the elastic members. 
The first object of the present invention is accomplished by a rear 
suspension comprising left and right wheel supports for supporting left 
and right rear wheels for rotation, a cross member connected to the wheel 
supports at opposite ends, left and right trailing arms which are 
connected to the cross member at the rear ends and to the vehicle body at 
the front ends by way of elastic members for vertical swinging motion and 
longitudinal displacement and a lateral rod which is connected to the 
cross member at one end by way of an elastic member and to the vehicle 
body at the other end by way of an elastic member, characterized in that 
the left and right trailing arms are disposed so that the space 
therebetween is larger at the front ends than at the rear ends, the 
lateral rod is connected to the vehicle body on the front side of the line 
joining the wheel centers of the left and right rear wheels, and each of 
the elastic members for connecting the lateral rod to the vehicle body and 
to the cross member has such elastic characteristics as to be soft in a 
small displacement range and to be hard in a large displacement range. 
In accordance with this arrangement, since the rear wheels (a rigid body 
including the rear wheels, the cross member and the wheel supports) are 
supported by the trailing arms disposed so that the space therebetween is 
larger at the front ends than at the rear ends, the instantaneous center 
of the displacement of the rear wheel generated by side force acting 
thereon is on the rear side of the line joining the wheel centers of the 
left and right rear wheels. This means that if the rear wheel is supported 
solely by the trailing arm, the rear wheel is displaced in the direction 
of toe-in. (Since this is based on the concept of the instantaneous 
center, such a displacement occurs only within a small displacement 
range.) On the other hand, since the lateral rod is connected to the 
vehicle body on the front side of the line joining the wheel centers, the 
rear wheel is displaced in the direction of toe-out when the side force 
governed by the lateral rod acts thereon. However, since the elastic 
members connecting the lateral rod to the vehicle body and the cross 
member are soft in the small displacement range and hard in the large 
displacement range, the influence of the lateral rod on the toe of the 
rear wheel is small when the side force acting on the rear wheel is 
relatively weak and is large when the side force is relatively strong. 
Accordingly, the rear wheel is caused to toe in under the influence of the 
trailing arm when the side force is relatively weak, and is caused to toe 
out when the side force is increased and the influence of the lateral rod 
overcomes the influence of the trailing arm. 
The first object can also be accomplished by a rear suspension of the same 
type characterized in that the left and right trailing arms are disposed 
so that the space therebetween is larger at the rear ends than at the 
front ends, the lateral rod is connected to the vehicle body on the rear 
side of the line joining the wheel centers of the left and right rear 
wheels, and each of the elastic members for connecting the lateral rod to 
the vehicle body and to the cross member has such elastic characteristics 
as to be hard in a small displacement range and to be soft in a large 
displacement range. 
In accordance with this arrangement, since the rear wheels (a rigid body 
including the rear wheels, the cross member and the wheel supports) are 
supported by the trailing arms disposed so that the space therebetween is 
larger at the rear ends than at the front ends, the instantaneous center 
of the displacement of the rear wheel generated by side force acting 
thereon is on the front side of the line joining the wheel centers of the 
left and right rear wheels. This means that if the rear wheel is supported 
solely by the trailing arm, the rear wheel is displaced in the direction 
of toe-out. (Since this is based on the concept of the instantaneous 
center, such a displacement occurs only within a small displacement 
range.) On the other hand, since the lateral rod is connected to the 
vehicle body on the rear side of the line joining the wheel centers, the 
rear wheel is displaced in the direction of toe-in when the side force 
governed by the lateral rod acts thereon. However, since the elastic 
members connecting the lateral rod to the vehicle body and the cross 
member are hard in the small displacement range and soft in the large 
displacement range, the influence of the lateral rod on the toe of the 
rear wheel is large when the side force acting on the rear wheel is 
relatively weak and is small when the side force is relatively strong. 
Accordingly, the rear wheel is caused to toe in under the influence of the 
lateral rod when the side force is relatively weak, and is caused to toe 
out when the side force is increased and the influence of the trailing arm 
overcomes the influence of the lateral rod. 
The second object can be accomplished by a rear suspension of the same type 
characterized in that the left and right trailing arms are disposed so 
that the space therebetween is larger at the front ends than at the rear 
ends, the lateral rod is connected to the vehicle body on the front side 
of the line joining the wheel centers of the left and right rear wheels, 
and each of the elastic members for connecting the lateral rod to the 
vehicle body and to the cross member has such elastic characteristics as 
to be hard in a small displacement range and to be soft in a large 
displacement range. 
In accordance with this arrangement, since the rear wheels (a rigid body 
including the rear wheels, the cross member and the wheel supports) are 
supported by the trailing arms disposed so that the space therebetween is 
larger at the front ends than at the rear ends, the instantaneous center 
of the displacement of the rear wheel generated by side force acting 
thereon is on the rear side of the line joining the wheel centers of the 
left and right rear wheels. This means that if the rear wheel is supported 
solely by the trailing arm, the rear wheel is displaced in the direction 
of toe-in. (Since this is based on the concept of the instantaneous 
center, such a displacement occurs only in a small displacement range.) On 
the other hand, since the lateral rod is connected to the vehicle body on 
the front side of the line joining the wheel centers, the rear wheel is 
displaced in the direction of toe-out when the side force governed by the 
lateral rod acts thereon. However, since the elastic members connecting 
the lateral rod to the vehicle body and the cross member are hard in the 
small displacement range and soft in the large displacement range, the 
influence of the lateral rod on the toe of the rear wheel is large when 
the side force acting on the rear wheel is relatively weak and is small 
when the side force is relatively strong. Accordingly, the rear wheel is 
caused to toe out under the influence of the lateral rod when the side 
force is relatively weak, and is caused to toe in when the side force is 
increased and the influence of the trailing arm overcomes the influence of 
the lateral rod. 
The second object can be also accomplished by a rear suspension of the same 
type characterized in that the left and right trailing arms are disposed 
so that the space therebetween is larger at the rear ends than at the 
front ends, the lateral rod is connected to the vehicle body on the rear 
side of the line joining the wheel centers of the left and right rear 
wheels, and each of the elastic members for connecting the lateral rod to 
the vehicle body and to the cross member has such elastic characteristics 
as to be soft in a small displacement range and to be hard in a large 
displacement range. 
In accordance with this arrangement, since the rear wheels (a rigid body 
including the rear wheels, the cross member and the wheel supports) are 
supported by the trailing arms disposed so that the space therebetween is 
larger at the rear ends than at the front ends, the instantaneous center 
of the displacement of the rear wheel generated by side force acting 
thereon is on the front side of the line joining the wheel centers of the 
left and right rear wheels. This means that if the rear wheel is supported 
solely by the trailing arm, the rear wheel is displaced in the direction 
of toe-out. (Since this is based on the concept of the instantaneous 
center, such a displacement occurs only within a small displacement 
range.) On the other hand, since the lateral rod is connected to the 
vehicle body on the rear side of the line joining the wheel centers, the 
rear wheel is displaced in the direction of toe-in when the side force 
governed by the lateral rod acts thereon. However, since the elastic 
members connecting the lateral rod to the vehicle body and the cross 
member are soft in the small displacement range and hard in the large 
displacement range, the influence of the lateral rod on the toe of the 
rear wheel is small when the side force acting on the rear wheel is 
relatively weak and is large when the side force is relatively strong. 
Accordingly, the rear wheel is caused to toe out under the influence of 
the trailing arm when the side force is relatively weak, and is caused to 
toe in when the side force is increased and the influence of the lateral 
rod overcomes the influence of the trailing arm. 
The lateral rod may be connected to the cross member and the vehicle body 
at opposite ends both by way of the elastic members, or may be connected 
to the cross member and the vehicle body at opposite ends one end by way 
of the elastic member the other end without elastic member. 
Further, since the line joining the wheel centers is slightly displaced 
from the line of action of the side force acting on the rear wheel by 
amount of pneumatic trail, the term "the line joining the wheel centers" 
as used in this specification should be interpreted to mean the line of 
action of the side force acting on the rear wheel in the strict sense of 
the term.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, a rear suspension in accordance with a first embodiment of the 
present invention comprises left and right wheel supports 12a and 12b for 
supporting left and right rear wheels 11a and 11b for rotation, a cross 
member 13 which extends in the transverse direction of the vehicle body 
and is connected to the wheel supports 12a and 12b at opposite ends, left 
and right trailing arms 15a and 15b which are fixed to the cross member 13 
at the rear ends and connected to the vehicle body 14 at the front ends by 
way of elastic members 16a and 16b for vertical swinging motion and 
longitudinal displacement and a lateral rod 18 which is connected to the 
cross member 13 at one end by way of one elastic member 17 and to the 
vehicle body 14 at the other end by way of another elastic member 17. 
The trailing arms 15a and 15b diverge away from each other toward the front 
ends thereof at which the trailing arms 15a and 15b are connected to the 
vehicle body 14, and accordingly, the space therebetween is larger at the 
front ends than at the rear ends. The cross member 13 is disposed so that 
the central axis thereof is aligned with the line joining the wheel 
centers of the left and right rear wheels 11a and 11b, and the lateral rod 
18 is connected to the vehicle body 14 on the front side of the cross 
member 13. 
The elastic member 17 for connecting the lateral rod 18 to the vehicle body 
14 comprises, as shown in FIG. 2, a rubber body filling the space between 
an outer tubular member 21 integrally formed on the end of the lateral rod 
18 and an inner tubular member 22 fixed to the vehicle body 14. The elastic 
member 17 is provided with a pair of arcuate through holes 23 extending 
through the rubber body on the left and right side of the inner tubular 
member 22 in parallel to the central axis thereof. By virtue of the 
through holes 23, the relation between the lateral load acting on the 
elastic member 17 and the deformation of the elastic member 17 changes at 
a preset load f.sub.0 as shown in FIG. 3. That is, the elastic member 17 
is soft (spring constant of k1) in the small displacement range and hard 
(spring constant of k2) in the large displacement range. 
The operation of the rear suspension of this embodiment will be described 
with reference to FIGS. 4 and 5, hereinbelow. 
In FIG. 4, it is assumed that side force G1 generated by a relatively small 
centripetal acceleration acts on the rear wheels 11a and 11b due to slight 
rightward turning of the steering wheel during straight forward travel or 
the like. Since the trailing arms 15a and 15b diverge away from each other 
toward the front ends, the instantaneous center of the rotational 
displacement of the cross member 13 and the rear wheels 11a and 11b (These 
may be considered to form a rigid body.) supported by the trailing arms 15a 
and 15b may be considered to be on the intersection P of the rearward 
extensions of the longitudinal axes of the trailing arms. Since the 
elastic member 17 is soft (spring constant of k1) in the range f.sub.1 in 
which a relatively weak side force acts thereon as shown in FIG. 3, the 
lateral rod 18 is immediately displaced in the direction of arrow X1 in 
FIG. 4 and the influence of the lateral rod 18 on the toe of the rear 
wheels 11a and 11b (urging the rear wheels to rotate in the 
counterclockwise direction in FIG. 4, i.e., urging the outer rear wheel 
11a to toe out) is negligible in this situation. Accordingly, the rear 
wheels 11a and 11b are displaced as shown by the broken line in FIG. 4 
under the rotational moment about the instantaneous center P. Thus, the 
outer rear wheel 11a is caused to toe in (.delta..sub.1) with respect to 
the original position. 
In the range f.sub.2 (FIG. 3) in which a stronger side force G2 acts on the 
rear wheels 11a and 11b, the elastic member 17 is hard (spring constant of 
k2), and accordingly, the influence of the lateral rod 18 on the toe of 
the rear wheels 11a and 11b urging the rear wheels 11a and 11b to rotate 
in the counterclockwise direction is enlarged. (The force urging the rear 
wheels 11a and 11b in the counterclockwise direction is due to a 
counterclockwise rotational moment which is generated by virtue of the 
fact that the junction of the lateral rod 18 to the vehicle body 14 is 
forwardly spaced from the line of action of the side force G2 by a 
distance e). Accordingly, the rear wheels 11a and 11b are displaced as 
shown by the broken line in FIG. 5 and thus the outer rear wheel 11a is 
caused to toe out (.delta..sub.2). That is, the outer rear wheel 11a is 
caused to toe out by .delta..sub.2 -.delta..sub.1 with respect to the 
original position shown by the solid line in FIG. 4. 
FIG. 6 shows the toe characteristics of the outer rear wheel 11a with 
respect to the centripetal acceleration or the side force G. 
As shown by the solid line, when a relatively weak side force acts on the 
outer rear wheel 11a due to a small centripetal acceleration generated, 
for instance, when the steering wheel is turned by a small angle during a 
straight travel, the outer rear wheel 11a is caused to toe in, and when a 
relatively strong side force acts on the outer rear wheel 11a due to a 
large centripetal acceleration generated, for instance, during a hard 
cornering, the outer rear wheel 11a is caused to toe out. As described 
above, this effect is obtained by virtue of the characteristics of the 
elastic member 17, the position of the junction of the lateral rod 18 to 
the vehicle body 14, and the positions of the junctions of the trailing 
arms 15a and 15b to the vehicle body 14 and the cross member 13. By 
changing the selection of the these items, various toe characteristics of 
the outer rear wheel 11a can be obtained as shown by the chained lines in 
FIG. 6. 
Now a second embodiment of the present invention will be described with 
reference to FIGS. 7 to 11, hereinbelow. 
In FIGS. 7 to 11, the parts analogous to the parts shown in FIGS. 1 to 6 
are given the same reference numerals and the following description will 
focus mainly on the difference between the first embodiment and the second 
embodiment. In this embodiment, the left and right trailing arms 15a and 
15b diverge away from each other toward the rear ends and the lateral rod 
18 is connected to the vehicle body 14 on the rear side of the cross 
member 13. 
As shown in FIG. 8, a resin plate 24 is press-fit into each through hole 23 
of the rubber body of the elastic member 17. By virtue of the resin plates 
24 inserted into the through holes 23, the relation between the lateral 
load acting on the elastic member 17 and the deformation of the elastic 
member 17 changes at a preset load f.sub.0 ' as shown in FIG. 9. That is, 
the elastic member 17 is hard (spring constant of k1') in the small 
displacement range and soft (spring constant of k2') in the large 
displacement range. 
The operation of the rear suspension of this embodiment will be described 
with reference to FIGS. 10 and 11, hereinbelow. 
In FIG. 10, it is assumed that side force G1 generated by a relatively 
small centripetal acceleration acts on the rear wheels 11a and 11b due to 
slight rightward turning of the steering wheel during straight forward 
travel or the like. Since the elastic member 17 is hard (spring constant 
of k1') in the range f.sub.1 ' in which a relatively weak side force acts 
thereon as shown in FIG. 10, the influence of the lateral rod 18 on the 
toe of the rear wheels 11a and 11b urging the rear wheels 11a and 11b to 
rotate in the clockwise direction is large. (The force urging the rear 
wheels 11a and 11b in the clockwise direction is due to a clockwise 
rotational moment which is generated by virtue of the fact that the 
junction of the lateral rod 18 to the vehicle body 14 is rearwardly spaced 
from the line of action of the side force G1 by a distance e.) Accordingly, 
the rear wheels 11a and 11b are displaced as shown by the broken line in 
FIG. 10 and thus the outer rear wheel 11a is caused to toe 
in(.delta..sub.1). 
In the range f.sub.2 ' (FIG. 9) in which a stronger side force G2 acts on 
the rear wheels 11a and 11b, the elastic member 17 is soft (spring 
constant of k2'), and accordingly, the lateral rod 18 is immediately 
displaced in the direction of arrow X2 in FIG. 11 and the influence of the 
lateral rod 18 on the toe of the rear wheels 11a and 11b (urging the rear 
wheels to rotate in the clockwise direction in FIG. 11, i.e., urging the 
outer rear wheel 11a to toe in) is negligible in this situation. Since the 
trailing arms 15a and 15b diverge away from each other toward the rear 
ends, the instantaneous center of the rotational displacement of the cross 
member 13 and the rear wheels 11a and 11b (These may be considered to form 
a rigid body.) supported by the trailing arms 15a and 15b may be 
considered to be on the intersection P of the forward extensions of the 
longitudinal axes of the trailing arms. Accordingly, the rear wheels 11a 
and 11b are displaced as shown by the broken line in FIG. 11 under the 
counterclockwise rotational moment about the instantaneous center P. Thus, 
the outer rear wheel 11a is caused to toe out (.delta..sub.2). That is, the 
outer rear wheel 11a is caused to toe out by .delta..sub.2 -.delta..sub.1 
with respect to the original position shown by the solid line in FIG. 10. 
Also in this embodiment, the toe characteristics of the outer rear wheel 
11a with respect to the centripetal acceleration or the side force G can 
be as shown in FIG. 6. 
A third embodiment of the present invention will be described with 
reference to FIGS. 12 to 16, hereinbelow. 
FIGS. 12 and 13 are views similar to FIGS. 1 and 2 but showing the third 
embodiment of the present invention. As can be seen from FIGS. 12 and 13, 
in this embodiment, the trailing arms 15a and 15b and the lateral rod 18 
are disposed in the same manner as the first embodiment, and the elastic 
member 17 is of the same structure as the one shown in FIG. 8. Accordingly 
the rear suspension of this embodiment will be described herebelow only 
with respect to its operation. 
In FIG. 14, it is assumed that side force G1 generated by a relatively 
small centripetal acceleration acts on the rear wheels 11a and 11b due to 
rightward turning of the steering wheel during low speed travel or the 
like. Since the elastic member 17 is hard (spring constant of k1') in the 
range f.sub.1 ' in which a relatively weak side force acts thereon as 
shown in FIG. 14, the influence of the lateral rod 18 on the toe of the 
rear wheels 11a and 11b urging the rear wheels 11a and 11b to rotate in 
the counterclockwise direction is large. (The force urging the rear wheels 
11a and 11b in the counterclockwise direction is due to a counterclockwise 
rotational moment which is generated by virtue of the fact that the 
junction of the lateral rod 18 to the vehicle body 14 is forwardly spaced 
from the line of action of the side force G1 by a distance e.) 
Accordingly, the rear wheels 11a and 11b are displaced as shown by the 
broken line in FIG. 14 and thus the outer rear wheel 11a is caused to toe 
out (.delta..sub.1). 
In the range f.sub.2 ' (FIG. 9) in which a stronger side force G2 acts on 
the rear wheels 11a and 11b, the elastic member 17 is soft (spring 
constant of k2'), and accordingly, the lateral rod 18 is immediately 
displaced in the direction of arrow X2 in FIG. 15 and the influence of the 
lateral rod 18 on the toe of the rear wheels 11a and 11b (urging the rear 
wheels to rotate in the counterclockwise direction in FIG. 14, i.e., 
urging the outer rear wheel 11a to toe out) is negligible in this 
situation. Since the trailing arms 15a and 15b diverge away from each 
other toward the front ends, the instantaneous center of the rotational 
displacement of the cross member 13 and the rear wheels 11a and 11b (These 
may be considered to form a rigid body.) supported by the trailing arms 15a 
and 15b may be considered to be on the intersection P of the rearward 
extensions of the longitudinal axes of the trailing arms. Accordingly, the 
rear wheels 11 a and 11b are displaced as shown by the broken line in FIG. 
15 under the clockwise rotational moment about the instantaneous center P. 
Thus, the outer rear wheel 11a is caused to toe in (.delta..sub.2). That 
is, the outer rear wheel 11a is caused to toe in by .delta..sub.2 
-.delta..sub.1 with respect to the original position shown by the solid 
line in FIG. 14. 
FIG. 16 shows the toe characteristics of the outer rear wheel 11a with 
respect to the centripetal acceleration or the side force G in the third 
embodiment. 
As shown by the solid line, when a relatively weak side force acts on the 
outer rear wheel 11a due to a small centripetal acceleration, for 
instance, during cornering at a low to middle speed, the outer rear wheel 
11a is caused to toe out, and when a relatively strong side force acts on 
the outer rear wheel 11a due to a large centripetal acceleration, for 
instance, during lane change at a high speed, the outer rear wheel 11a is 
caused to toe in. As described above, this effect is obtained by virtue of 
the characteristics of the elastic member 17, the position of the junction 
of the lateral rod 18 to the vehicle body 14, and the positions of the 
junctions of the trailing arms 15a and 15b to the vehicle body 14 and the 
cross member 13. By changing the selection of the these items, various toe 
characteristics of the outer rear wheel 11a can be obtained as shown by the 
chained lines in FIG. 16. 
A fourth embodiment of the present invention will be described with 
reference to FIGS. 17 and 18, hereinbelow. 
FIGS. 17 and 18 are views similar to FIGS. 1 and 2 but showing the fourth 
embodiment of the present invention. As can be seen from FIGS. 17 and 18, 
in this embodiment, the trailing arms 15a and 15b, the lateral rod 18 are 
disposed in the same manner as the second embodiment and the elastic 
member 17 is of the same structure as one shown in FIG. 2. Accordingly the 
rear suspension of this embodiment will be described herebelow only with 
respect to its operation. 
In FIG. 19, it is assumed that side force G1 generated by a relatively 
small centripetal acceleration acts on the rear wheels 11a and 11b due to 
rightward turning of the steering wheel during a low speed travel or the 
like. Since the trailing arms 15a and 15b diverge away from each other 
toward the rear ends, the instantaneous center of the rotational 
displacement of the cross member 13 and the rear wheels 11a and 11b (These 
may be considered to form a rigid body.) supported by the trailing arms 
15pi a and 15b may be considered to be on the intersection P of the 
forward extensions of the longitudinal axes of the trailing arms. Since 
the elastic member 17 is soft (spring constant of k1) in the range f.sub.1 
in which a relatively weak side force acts thereon as shown in FIG. 3, the 
lateral rod 18 is immediately displaced in the direction of arrow X1 in 
FIG. 19 and the influence of the lateral rod 18 on the toe of the rear 
wheels 11a and 11b (urging the rear wheels to rotate in the clockwise 
direction in FIG. 19, i.e., urging the outer rear wheel 11a to toe in) is 
negligible in this situation. Accordingly, the rear wheels 11a and 11b are 
displaced as shown by the broken line in FIG. 19 under the rotational 
moment about the instantaneous center P. Thus, the outer rear wheel 11a is 
caused to toe out (.delta..sub.1) with respect to the original position. 
In the range f.sub.2 (FIG. 3) in which a stronger side force G2 acts on the 
rear wheels 11a and 11b, the elastic member 17 is hard (spring constant of 
k2), and accordingly, the influence of the lateral rod 18 on the toe of 
the rear wheels 11a and 11b urging the rear wheels 11a and 11b to rotate 
in the clockwise direction is enlarged. (The force urging the rear wheels 
11a and 11b in the clockwise direction is due to a clockwise rotational 
moment which is generated by virtue of the fact that the junction of the 
lateral rod 18 to the vehicle body 14 is rearwardly spaced from the line 
of action of the side force G2 by a distance e.) Accordingly, the rear 
wheels 11a and 11b are displaced as shown by the broken line in FIG. 20 
and thus the outer rear wheel 11a is caused to toe in (.delta..sub.2). 
That is, the outer rear wheel 11a is caused to toe in by .delta..sub.2 
-.delta..sub.1 with respect to the original position shown by the solid 
line in FIG. 20. 
Also in this embodiment, the toe characteristics of the outer rear wheel 
11a with respect to the centripetal acceleration or the side force G can 
be as shown in FIG. 16. 
Though the operation of each of the first to fourth embodiments has been 
described above on the assumption that only the elastic member 7 
connecting the lateral rod 18 to the vehicle body 14 of the two elastic 
members 7 on opposite ends of the lateral rod 18 is deformed, the same 
operation and effect can be obtained even if both the elastic members 17 
are deformed.