Exhaust pipe supporting structure

An exhaust pipe supporting structure (10) comprising an anti-vibratory member (14) reduced in spring coefficient, gradually along the length from one part (14a, 8b) thereof connected at the side of a vehicle body (6, 8) to another part (14b, 13) thereof connected at the side of an exhaust pipe (2, 3, 11, 12, 13) drawn out from an engine (1) mounted at the vehicle body side. In a view from a point off in a direction in which a torque roll axis (Tro) of the engine (1) or a principal axis (Io) of inertia extending in the same direction as the torque roll axis (Tro) extends, the aforesaid one part (14a, 8b) of the elastic member (14) and the aforesaid another part (14b, 13) thereof are found on a single tangent line (L.sub.1) to an imaginary arc (22) of a predetermined radius that has the torque roll axis (Tro) or the principal axis (Io) of inertia as a center axis thereof.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to a supporting structure for 
exhaust pipes. More particularly, the invention relates to a supporting 
structure for exhaust pipes such as in a vehicle, of the type with which 
an exhaust pipe drawn out from an engine is supported at the side of a 
vehicle body through an elastic member. 
2. Description of Relevant Art 
In general, the exhaust pipe, which is drawn out from an engine installed 
in a vehicle, is supported at the side of a body of the vehicle through an 
elastic member. 
In the accompanying drawings, FIG. 5 is a schematic side view exemplarily 
showing such supporting structure for exhaust pipes. 
In this exhaust pipe supporting structure, a flexible tube 56, which 
constitutes a substantially intermediate part of an exhaust pipe 52 drawn 
out from an engine 51 mounted at the side of a body (not shown) of a 
vehicle, is supported at the side of a frame 54 of the vehicle body 
through an elastic member 53 as an anti-vibratory member, with an 
intention to thereby prevent the transmission of vibrations from the 
exhaust pipe 52 to the side of the vehicle body, while restricting the 
displacement of the exhaust pipe 52. 
The engine 51 is of a horizontal type disposed in the front part of the 
vehicle, and the exhaust pipe 52 is extended therefrom once downwardly and 
then substantially horizontally in the longitudinal direction of the 
vehicle. 
Detailed description will now be made of this exhaust pipe supporting 
structure. 
The elastic member 53 is of a circular form elongated in the vertical 
direction in side view, and has a uniform thickness t (see FIG. 6) in the 
transverse direction of the vehicle. 
At the upper part of the elastic member 53, there is inserted therethrough 
an extension 55a as a bent part of a stay 55 which is fixed to the body 
frame 54 and extended in the rearward direction of the vehicle, whereby 
the elastic member 53 is supported at the vehicle body side. 
Further, from a flange 57 at the rear end of the flexible tube 56 is 
standing a bracket 58 in the frontward direction of the vehicle. The 
bracket 58 has at the front end thereof a pin 58a projected therefrom in 
the transverse direction of the vehicle. The pin 58a is inserted into the 
lower part of the elastic member 53, whereby the exhaust pipe 52 is 
supported at the vehicle body side through the member 53. 
Incidentally, in FIG. 5, designated at reference numeral 60 is a slot 
punched to be opened, in the form of a letter "H" in side view, through 
the vertically central part of the elastic member 53, in the thickness 
direction thereof. 
Moreover, as shown in FIG. 5, a line segment L.sub.6 passing a connection 
point 55a at the vehicle body side of the elastic member 53 and the pin 
58a as another connection point thereof at the side of the exhaust pipe 52 
is set to be substantially vertical, in side view. 
On the elastic member 53 arranged like this, there are acting, as shown in 
FIG. 6 which is a sectional view along line VI--VI of FIG. 5, forces 
(collectively designated by reference character F.sub.1 ') in the 
tension/compression direction of the member 53 as well as forces (likewise 
designated by reference character F.sub.2 ') in the shearing direction 
thereof. Further, in cases where the forces F.sub.1 ', F.sub.2 ' are 
caused to concurrently act on the elastic member 53, there are resulted 
such forces (likewise designated by reference character F.sub.3 ') that 
act on the member 53 with a tendency to rotate the elastic member in 
either direction of rotation about the connection point 55a as a 
supporting point thereof at the vehicle body side. 
In this concern, in FIGS. 4A and 4B, designated at C.sub.6, C.sub.7 are 
characteristic curves showing, for a case where the thickness t of the 
elastic member 53 is relatively small, those relations to be observed, in 
the tension/compression direction and the shearing direction of the member 
53, respectively, between various values, in terms of kg, of the forces 
F.sub.1 ', F.sub.2 ' acting on the member 53 and displacements D, in terms 
of mm, by corresponding deformations of the member 53. 
As will be comprehended, the elastic member 53 is not well adapted for 
effective exhibition of restraint against the respective external forces 
F.sub.1 ', F.sub.2 '. 
In view of such characteristic of the elastic member 53, the restraint by 
the member 53 against the force F.sub.1 ' in the tension/compression 
direction thereof might well be raised by employing such an elastic member 
as one higher in spring coefficient or spring rate than the member 53 but 
similar thereto in configuration and size, including thickness. But, in 
this case, it would be hardly possible to raise the restraint against the 
force F.sub.2 ' in the shearing direction of the elastic member 53. 
On the other hand, by way of such a modification that the thickness t of 
the elastic member 53 be increased, the restraint against the force 
F.sub.2 ' in the shearing direction of the member 53 might well be raised 
as shown by curve C.sub.9 of FIG. 4B. In this case, however, the restraint 
against the force F.sub.1 ' in the tension/compression direction of the 
elastic member 53 would be excessively raised as shown by curve C.sub.8 of 
FIG. 4A, in addition to corresponding increase in the quantity of rubber 
to be used as such elastic member, as well as in cost. 
In this respect, in Japanese Utility Model Lay-Open Print No. 55-94225 laid 
open on June 30, 1980, there is disclosed a different type of elastic 
member as an anti-vibratory member to be used in an exhaust pipe 
supporting structure for vehicles. 
In the accompanying drawings, FIGS. 7 and 8 are a side and a sectional 
views of an elastic member 100 of the disclosed type. 
The elastic member 100 is gradually enlarged in thickness along its length 
from the upper part to the lower part thereof, with an intention to 
thereby make uniform the respective deformations at various points along 
the length of the member 100, when it is subjected to forces acting in the 
tension/compression direction and the shearing direction thereof. 
However, the restraint by the elastic member 100 is not yet sufficiently 
effective against such forces that act on the member 100, in the rotating 
direction, like the force F.sub.3 ' acting on the member 53. 
Referring again to FIG. 5, designated at reference character Tr is a torque 
roll axis adapted to serve as a center axis of vibrations of the engine 51 
when the vehicle is accelerated or decelerated. In accordance with 
horizontal arrangement of the engine 51, the torque roll axis Tr is set so 
as to extend in the transverse direction of the vehicle. 
The vertical line segment L.sub.6, on which the connection points 55a, 58a 
of the elastic member 53 are located as described, is designed so as to 
cross, in side view, an imaginary arc 64 as a part of such a circle about 
the torque roll axis Tr that passes the center of gravity of the member 
53. 
In other words, the two connecting points 55a, 58a of the elastic member 53 
will not be both found on any imaginary arc of an arbitrary radius that 
has the center thereof on the torque roll axis Tr. 
Accordingly, no vibrating forces on the exhaust pipe 52 due to engine 
vibrations about the torque roll axis Tr will substantially act as a force 
on the elastic member 53 in the tension/compression direction thereof. 
Against such engine vibrations, therefore, the restraint by the elastic 
member 53 is low, thus resulting in the difficulty of effectively reducing 
the engine vibration by use of the afore-mentioned exhaust pipe supporting 
structure. Besides, if managed to be adapted for such reduction, this 
supporting structure would be complicated in constitution and would be 
expensive. 
Incidentally, the above comments on the torque roll axis Tr applies also to 
one I of the principal axes of inertia of the engine 51 that extends in 
the same direction as the torque roll axis Tr and functions as a principal 
center axis of vibrations of the engine 51 while the vehicle is not 
accelerated or decelerated. Though, generally, depending on the engine 
structure, the principal axis I and the torque roll axis Tr are coincident 
with each other in the example shown. 
Such problems in conventional exhaust pipe supporting structures of the 
type described are particularly remarkable in an FF (front-engine, 
front-drive) type vehicle with an engine arranged horizontal, in which, in 
plan view, an exhaust pipe is rearwardly directed to be perpendicular to a 
torque roll axis of the engine or to such principal axis of inertia 
thereof as extending in the same direction as the torque roll axis, so 
that an exhaust system is greatly affected by engine vibrations about the 
torque roll axis or the principal axis of inertia. 
The present invention has been achieved to effectively solve such problems 
in conventional exhaust pipe supporting structures of the type described. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide an exhaust 
pipe supporting structure permitting effective restriction of those forces 
which act on an elastic member that interconnects an exhaust pipe with the 
side of a vehicle body, in the tension/compression direction and the 
shearing direction of the elastic member, as well as in the rotating 
direction thereof. 
Another object of the present invention is to provide, in the exhaust pipe 
supporting structure, such adaptation that those vibratory forces of the 
exhaust pipe which are due to vibrations of an engine about a torque roll 
axis of the engine or about one of the principal axes of inertia of the 
engine that extends in the same direction as the torque roll axis are made 
to act, against the elastic member, as forces in such a direction as to be 
coincident with the tension/compression direction of the elastic member, 
to thereby effectively reduce the engine vibrations. 
To achieve the afore-mentioned object, the present invention provides an 
exhaust pipe supporting structure comprising an anti-vibratory member 
connected at one part thereof to the side of a vehicle body and at another 
part thereof to the side of an exhaust pipe drawn out from an engine 
mounted at the vehicle body side, wherein the anti-vibratory member is 
gradually reduced in spring coefficient or spring rate along the length 
from the aforesaid one part thereof to the aforesaid another part thereof. 
Advantageously, in a view from a point off in a direction in which a torque 
roll axis of the engine is extended, the anti-vibratory member is disposed 
such that the aforesaid one part thereof and the aforesaid another part 
thereof are found on a single tangent line to an imaginary arc of a 
predetermined radius that has the torque roll axis as a center axis 
thereof so that those vibratory forces of the exhaust pipe which are due 
to vibrations of the engine about the torque roll axis are made to act, 
with respect to the anti-vibratory member, as a force in a 
tension/compression direction. 
More preferably, in a view from a point off in a direction in which a 
principal axis of inertia extending in the same direction as a torque roll 
axis of the engine extends, the anti-vibratory member is disposed such 
that the aforesaid one part thereof and the aforesaid another part thereof 
are found on a single tangent line to an imaginary arc of a predetermined 
radius that has the principal axis of inertia as a center axis thereof so 
that those vibratory forces of the exhaust pipe which are due to 
vibrations of the engine about the principal axis of inertia are made to 
act, with respect to the anti-vibratory member, as a force in a 
tension/compression direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, designated at reference numeral 10 is an exhaust 
pipe supporting structure according to a preferred embodiment of the 
present invention. The supporting structure 10 comprises an elastic member 
14 as an anti-vibratory member interposed between an exhaust pipe 2 drawn 
out from a horizontal engine 1 of an FF type vehicle (not shown) and 
extended once rearwardly-inclinedly downwardly and then rearwardly 
horizontally of the vehicle and a rear beam 6 connected to the side of a 
body (not shown) of the vehicle. 
The elastic member 14 is of an elongated circular form in side view, and 
reduced, in thickness in the transverse direction of the vehicle that is 
perpendicular to the longitudinal direction of the exhaust pipe 2, 
gradually along the length from the upper part to the lower part thereof, 
as will be described later. 
As shown also in FIGS. 2 and 3, the elastic member 14 has inserted through 
an upper portion 14a thereof, in the thickness direction of the member 14, 
an extension 8b as a bent part of a stay 8 which is fixed to the rear beam 
6 and extended in the rearward direction of the vehicle, whereby the 
elastic member 14 is supported at the side of the vehicle body. 
Incidentally, in FIG. 3, designated at reference character 8a is a bent 
end part of the stay 8. 
Further, from a flange 11 at the rear end of a flexible tube 3 there 
extends a bracket 12 in the frontward direction of the vehicle. The 
bracket 12 has at the front end thereof a pin 13 projected therefrom in 
the transverse direction of the vehicle. The pin 13 is inserted in the 
thickness direction of the elastic member 14 to a lower portion 14b of the 
member 14, whereby the exhaust pipe 2 is supported at the vehicle body 
side through the elastic member 14. 
Incidentally, in FIG. 3, designated at reference character 13a is a bent 
end part of the pin 13, and 25 is a slot punched to be opened, in the form 
of a letter "H" in side view, through a longitudinally central part of the 
elastic member 14, in the thickness direction thereof. 
In the engine 1, which is of a horizontal type, there is provided a torque 
roll axis Tro extending substantially in the transverse direction of the 
vehicle. On the other hand, in side view, a line segment L.sub.1 passing a 
connection point 8b to the vehicle body side of the elastic member 14 and 
the pin 13 as another connection point thereof at the side of the exhaust 
pipe 2 is set tangential to an imaginary arc 22 as a part of such a circle 
about the torque roll axis Tro that passes the center of the elastic 
member 14, in side view. 
In this respect, the engine 1, as it is inclusive of integral members such 
as a transmission (not shown), has three principal axes of inertia 
extending substantially in the longitudinal, transverse, and vertical 
directions of the vehicle, respectively, among which the transverse 
principal axis Io is substantially coincident with the torque roll shaft 
Tro. It thus so follows that the imaginary arc 22 has the center thereof 
on the principal axis Io of inertia or, in other words, the line segment 
L.sub.1 is tangential to the imaginary arc 22, as it has the center 
thereof on the principal axis Io, and hence the aforesaid connection 
points 8b, 13 on the line segment L.sub.1 are located both on a single 
tangent line of the imaginary arc 22. 
As shown in FIG. 3, the elastic member 14 is tapered in longitudinal 
section such that, letting the thickness at the upper and lower portions 
14a, 14b thereof to be t.sub.1 and t.sub.2, respectively, the transition 
part therebetween is gradually reduced in thickness from t.sub.1 to 
t.sub.2. 
In this concern, the elastic member 14 is made of a uniform rubber, and 
therefore the spring coefficient or spring rate with respect to forces 
acting in the tension/compression direction of the member 14, as well as 
in the shearing direction thereof, is rendered maximum at the upper 
portion 14a of the member 14 and gradually made smaller with transition 
along the length from the upper portion 14a to the lower portion 14b 
thereof, thus becoming minimum at the lower portion 14b. 
On the elastic member 14 configured like this and arranged as described, 
there are acting those forces (collectively designated by reference 
character F.sub.1) which have their lines of action in the 
tension/compression direction of the member 14 and those forces (likewise 
designated by reference character F.sub.2) which have their lines of 
action in the shearing direction of the member 14 and, besides, under the 
condition that the forces F.sub.1, F.sub.2 are concurrently appearing, 
such forces (likewise designated by reference character F.sub.3) that have 
their lines of action in either direction of rotation about the extension 
8b as a supporting part at the vehicle body side. 
In this respect, in FIGS. 4A and 4B, represented by characteristic curves 
C.sub.1, C.sub.2 are relations between various values, in terms of kg, of 
the forces F.sub.1, F.sub.2 acting on the elastic member 14, respectively, 
and associated displacements, in terms of mm, of the entirety of the 
member 14. 
As will be comprehended, the elastic member 14 has exhibited, against both 
of the forces F.sub.1, F.sub.2 in the tension/compression direction and 
the shearing direction, such spring coefficients as adequate, as a whole, 
to perform effective restriction. 
In other words, notwithstanding relatively large spring coefficients shown 
against forces F.sub.2 in the shearing direction of the elastic member 14, 
the spring coefficient against the force F.sub.1 in the 
tension/compression direction of the member 14 is kept from becoming 
excessively large. 
Moreover, the elastic member 14, the thickness of which is rendered maximum 
t.sub.1 at the upper portion 14a that functions as a center of rotation of 
the member 14 in cases where the force F.sub.3 in the rotating direction 
is acting, is adapted to exhibit effective restriction against the force 
F.sub.3 as well. 
Incidentally, for comparison purpose, it is supposed that the thickness of 
the elastic member 14 be equal, at the upper portion 14a t.sub.1 thick, to 
the uniform thickness of that elastic member in the relevant art which has 
such characteristics as shown by the curves C.sub.8, C.sub.9 of FIGS. 4A, 
4B and, at the lower portion 14b t.sub.2 thick, to the uniform thickness 
of that elastic member in the relevant art which has such characteristics 
as shown by the curves C.sub.6, C.sub.7 of FIGS. 4A, 4B. 
Accordingly, the elastic member 14 has a smaller volume than the elastic 
member of the uniform thickness t.sub.1 that has the characteristic curves 
C.sub.8, C.sub.9, so that cost reduction is possible for the member 14. 
Further, on account of distinct orientation of the line segment L.sub.1 
passing the connection point 8b at the vehicle body side of the elastic 
member 14 and the connection point 13 at the exhaust pipe side thereof, 
which segment L.sub.1 is tangential to the imaginary arc 22 having the 
torque roll axis Tro as the center axis thereof in the side view or in a 
view from a point off in a direction in which the axis Tro extends, those 
vibratory forces of the exhaust pipe 2 which are due to vibrations of the 
engine 1 about the torque roll axis Tro are made to act, against the 
elastic member 14, as a force or forces having a line or lines of action 
in such direction as to be coincident with the tension/compression 
direction of the member 14, thereby assuring effective exhibition of 
restraint by the member 14 against vibrations of exhaust system due to 
such engine vibration. As a result, the engine vibration about the torque 
roll axis Tro is effectively reduced by the elastic member 14. 
Furthermore, since the principal axis Io of inertia extending in the 
transverse direction of the vehicle is substantially coincident with the 
torque roll axis Tro, the elastic member 14 is adapted for effective 
exhibition of restraint also against those vibrations of exhaust system 
which are due to engine vibrations about the principal axis Io of inertia 
of the engine 1 while the vehicle is not accelerated or decelerated. 
Incidentally, in the exhaust pipe supporting structure 10 according to the 
present embodiment, the elastic member 14 made of a uniform rubber is 
reduced in thickness and hence in cross sectional area, gradually along 
the length from the upper portion 14a acting as a connecting part at the 
vehicle body side to the lower portion 14b acting as a connecting part at 
the exhaust pipe side, to thereby gradually change the spring coefficient 
of the member 14. In this respect, however, a similar effect may 
preferably be achieved by employment of an elastic member of which the 
rubber material or mechanical property is continuously or stepwise changed 
along its length, while having a uniform sectional area. 
Moreover, in the exhaust pipe supporting structure 10, the elastic member 
14 is connect at two points 8b, 13 to the side of the vehicle body and the 
side of the exhaust pipe 2, respectively, to thereby render the line 
segment L.sub.1 passing the two points 8b, 13 tangential to the imaginary 
arc 22. In this respect, however, there may preferably employed an 
arrangement in which an elastic member is connected exemplarily at one 
point thereon to the vehicle body side and at two points thereon to the 
exhaust pipe side in such a manner that, while the three points above are 
cooperating together to have three interconnection line segments 
thereamong constituting a substantially isosceles triangle, a bisector of 
the angle between two equal sides of the triangle is made tangential to an 
imaginary arc of a predetermined radius that has the center axis thereof 
on a torque roll axis of an engine. 
Further, according to the present embodimemt, the elastic member 14 is 
utilized so as to suspend the exhaust pipe 2 from the vehicle body side. 
In this respect, the present invention may be advantegeously applied to an 
exhaust pipe supporting structure in which an exhaust pipe is borne to be 
supported on the vehicle body side through an elastic member. 
Furthermore, in the embodiment described, the structure 10 is employed for 
supporting the exhaust pipe 2 which is drawn out from the horizontal type 
engine 1 in the FF type vehicle. In this respect, it will be easily 
comprehended that the present invention may be advantageously applied also 
to a supporting structure for exhaust pipes in other engine arrangements, 
exemplarily of a vertical engine in an FR (front-engine, rear-drive) type 
vehicle. 
Although there has been described what is at present considered to be the 
preferred embodiment of the invention, it will be understood that the 
present invention may be embodied in other specific forms without 
departing from the spirit or essential characteristics thereof. The 
present embodiment is therefore to be considered in all respects as 
illustrative and not restrictive. The scope of the invention is indicated 
by the appended claims rather than by the foregoing description.