Indian Patents. 253502:A STRADDLE -TYPE VEHICLE WITH CATALYST

Title of Invention	A STRADDLE -TYPE VEHICLE WITH CATALYST
Abstract	A front catalyst is disposed below a crankcase of an engine. The front catalyst is formed to be low-profile, that is, the size of the catalyst in height is less than that in width. Bottom surfaces of third and fourth pipes of an exhaust conduit positioned below the crankcase extend along the same plane as a bottom surface of the front catalyst.

Full Text	STRADDLE TYPE VEHICLE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a straddle type vehicle such as, for example, a motorcycle. 2. Description of the Related Art Normally, exhaust gases from an engine are released to the atmosphere. It is desired to purify the exhaust gases as clean as possible before the release of the exhaust gases. Therefore, a catalyst (catalyzer) has been disposed midway of an exhaust conduit through which the exhaust gases flow so that the exhaust gases are purified by the catalyst (for example, see JP-B-3026684). However, because the related art employs a structure in which the catalyst is disposed midway of the exhaust conduit extending in a fore to aft direction below a crankcase of the engine, the catalyst protrudes downward greatly beyond the crankcase. It is, therefore, difficult to keep the minimum height of the vehicle body from the ground. Thus, there arises a problem that a layout design of the catalyst is difficult. SUMMARY OF THE INVENTION The present invention is made under the circumstances and relates to a straddle type vehicle that can easily keep the 1 minimum height of the vehicle body from the ground and can make a layout design of a catalyst be simple although the catalyst is disposed below the crankcase. A straddle type vehicle configured in accordance with the present invention and for resolving the problem of the related art includes: an engine including a crankcase and a cylinder block disposed thereon; an exhaust conduit which has an upstream end coupled with the cylinder block and extends downward in front of the engine from the upstream end and further rearward below the crankcase; and a catalyst disposed midway of the exhaust conduit and below the crankcase for purifying exhaust gases flowing through the exhaust conduit. The catalyst is formed to be low-profile, in which the size of the catalyst in width is greater than that in height. According to the present invention as constructed in the manner described, the cross sectional shape of the catalyst can be low-profile, where the size in width is greater than the size in height. Therefore, to the extent that the cross sectional shape of the catalyst is made small in height, the minimum height of the vehicle body including the catalyst and the exhaust conduit from the ground can be easily ensured. In one mode of the present invention, the size of the catalyst in height can be generally equal to the outer diameter of the exhaust conduit. According to this construction, because the size of the catalyst in height can be generally 2 equal to the outer diameter of the exhaust conduit, the catalyst does not protrude below the exhaust conduit, and the minimum height of the vehicle body including the catalyst and the exhaust conduit from the ground can be more easily ensured. In another mode of the present invention, the catalyst can be disposed between right and left frames to which the engine is fixed. According to this construction, because the catalyst can be positioned in a space defined between the right and left frames, the layout design of the catalyst can be easily made. Also, because the catalyst is disposed between the right and left frames, the right and left frames can protect the catalyst from external shocks. In a further mode of the present invention, another catalyst can be disposed midway of the exhaust conduit to be positioned downstream of the catalyst. According to this construction, the exhaust gases discharged from the exhaust conduit can be more efficiently purified using those two catalysts. In a further mode of the present invention, a secondary air introducing conduit can be connected to the exhaust conduit at a location between the catalyst and the another catalyst. According to this construction, because the secondary air can be introduced into the exhaust conduit through the secondary air introducing conduit, the exhaust gases can be more efficiently purified. 3 In a further mode of the present invention, the bottom line of a portion of the exhaust conduit extending below the crankcase in the side view and the bottom line of the catalyst in the side view can be positioned generally on the same straight line. According to this construction, the catalyst can be surely prevented from protruding downward from the exhaust conduit disposed below the crankcase, and the minimum height of the vehicle body from the ground can be more easily ensured. In a further mode of the present invention, the center line of a portion of the exhaust conduit coupled with the exhaust gas inlet port of the catalyst through which the exhaust gases enter the catalyst from the portion of the exhaust conduit and the center line of another portion of the exhaust conduit coupled with the exhaust gas outlet port of the catalyst through which the exhaust gases go out from the catalyst to the another portion of the exhaust conduit can be set off from each other, and the another portion of the exhaust conduit coupled with the exhaust gas outlet port can be deflected to one side of a vehicle body in the width direction thereof. According to this construction, because, in a situation that a muffler placed at a location on the outlet port side is deflected to the one side of the vehicle body in the width direction thereof, the center line of the exhaust conduit coupled with the exhaust gas outlet port of the catalyst is 4 deflected to the one side of the vehicle body in the width direction relative to the center line of the exhaust conduit coupled with the exhaust gas inlet port, the muffler and the exhaust gas outlet port can be easily coupled with each other through a portion of the exhaust conduit. The layout design of the exhaust conduit including the muffler can be easily made. According to the straddle type vehicle of the present invention, because the cross sectional shape of the catalyst can be formed to be low-profile, that is, the size of the catalyst in width is greater than the size of the catalyst in height, the minimum height of the vehicle body from the ground can be easily ensured and the layout design of the catalyst can be easily made, although the catalyst is disposed below the crankcase. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view, showing a motorcycle configured in accordance with an embodiment of the present invention; FIG. 2 is an enlarged view, showing a frame, an exhaust conduit, a front catalyst, a rear catalyst, etc. of FIG. 1; FIG. 3 is a front elevational view, showing the frame, the exhaust conduit, the front catalyst, etc. of FIG. 2; FIG. 4 is a bottom plan view, showing the frame, the exhaust conduit, the front catalyst, the rear catalyst, etc. of FIG. 5 2; FIG. 5 is a side elevational view, showing the exhaust conduit, the front catalyst and the rear catalyst of FIG. 1 solely in an enlarging manner; FIG. 6 is a top plan view, showing the exhaust conduit, the front catalyst and the rear catalyst of FIG. 1 solely in the enlarging manner; FIG. 7 is an enlarged perspective view, showing the front catalyst of FIG. 6 solely; FIG. 8 is a cross sectional view, showing the front catalyst, etc. of FIG. 6 in the enlarging manner; and FIG. 9 is a cross sectional view of the front catalyst, taken along the line VIII-VIII of FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGs. 1 to 7, an embodiment will be described, exemplifying a case that a straddle type vehicle of the embodiment according to the present invention is applied to a motorcycle. A motorcycle 1 of the embodiment of the present invention is structured to include a frame 10, an engine 20, an exhaust conduit 30, a front catalyst 40 and a rear catalyst 50. The frame 10 has a head pipe 11, a left frame 12 formed with a framework which generally has a parallelogram shape, and a right frame 13 formed with another framework shaped as 6 a parallelogram, similarly to the left frame 12. As shown in FIG. 2, the left frame 12 is structured to include: a first frame section 12A, whose front end is coupled with the top end of a head pipe 11, extending obliquely downward rearward from the front end; a second frame section 12B curvedly extending in a dog-leg shape from the rear end of the first frame section 12A to extend obliquely downward rearward, and having a lower end portion which curvedly extends obliquely downward forward; a third frame section 12C curvedly extending forward in a generally horizontal direction from the lower end portion of the second frame section 12B; and a fourth frame section 12D whose top end is coupled with the bottom end of the head pipe 11. The left frame 12 has a seat rail 12E, whose front end is coupled with the boundary portion between the first frame section 12A and the second frame section 12B, extending rearward generally in the horizontal direction from the front end; and a back stay 12F whose front end is coupled with a middle portion of the second frame section 12B in a longitudinal direction, extending obliquely upward rearward. The rear end of the seat rail 12E is coupled with a mid portion of the back stay 12F. As shown in FIGs. 3 and 4, the right frame 13 has a first frame section 13A, a second frame section 13B, a third frame section 13C, a fourth frame section 13D, a seat rail 13E and 7 a back stay 13F, similarly to the left frame 12. As shown in FIG. 1, a pivot shaft (not shown) attached to handlebars 14 is inserted into the head pipe 11 for pivotal movement. The pivot shaft of the handlebars 14 is fixed to respective central portions of an upper bracket 15 and an lower bracket 16 each extending in width direction. Respective top end portions of right and left front forks 17 (only one of them is shown) are inserted into right and left ends of the brackets 15, 16 and fixed thereto. A front wheel 60 is coupled with the bottom end portions of the respective front forks 17 for rotation. The front ends of a swing arm 18 are coupled with the second frame section 12B of the left frame 12 and the second frame section 13B of the right frame 13 to be supported for swing movement. A rear wheel 70 is coupled with the rear ends of the swing arm 18 for rotation. Additionally, an air cleaner 19 is disposed between the seat rails 12E and the back stays 12F of the frame 10. The engine 20 is disposed in an inside space defined by the left frame 12 and the right frame 13 each generally formed with a framework having a rectangular shape (see FIG. 2) . The engine 20 is mounted on the frames 12, 13 by being suspended. As shown in FIGs. 1 and 2, the engine 20 is structured to include a crankcase 21 and a cylinder block 22 positioned on the crankcase 21. 8 As shown in FIG. 2 through FIG. 6, the exhaust conduit 30 has a first pipe 31 arcuately extending forward from the cylinder block 22 of the engine 20, a second pipe 32 extending obliquely downward rearward from the first pipe 31 and partially overlapping with the fourth frame section 12D (13D) of the frame 10 in a side view, a third pipe 33 extending rearward from the second pipe generally in the horizontal direction to be connected to the front catalyst 40 and partially overlapping with the third frame section 12C (13C) of the frame 10 in the side view, a fourth pipe 34 extending rearward from the front catalyst generally in the horizontal direction, a fifth pipe 35 curvedly extending obliquely upward rearward, and a muffler 36 connected to the fifth pipe 35. The exhaust conduit 30 is to discharge exhaust gases externally from the through the front catalyst 40, the rear catalyst 50 and the muffler 36. The front catalyst 40 is positioned below the crankcase 21 and between the third pipe 33 and the fourth pipe 34 of the exhaust pipe 30. As shown in FIGs. 8 and 9, the front catalyst 40 includes a tubular casing 41, whose cross section has an elliptic shape (ellipse configuration), extending in the fore to aft direction; and a catalyst body 42 contained in the casing 41. The casing 41 has an exhaust gas inlet port 43 which is a tubular body tapered forward from the upstream portion of 9 the casing 41 and extending rearward to be unitarily formed with the casing 41. Exhaust gases from the third pipe 33 of the exhaust conduit 30 flow into the exhaust gas inlet port 43. Also, the casing 41 has an exhaust gas outlet port 44 unitarily formed with the casing 41 and extending rearward as a tubular body from a downstream portion of the casing 41 through a sloped portion 44A. The exhaust gas outlet port 44 is to let the exhaust gases which have flowed through the catalyst 40 go out to the fourth pipe 34 of the exhaust conduit 30. In this regard, as shown in FIG. 8, the center line LI of the third pipe 33 of the exhaust conduit 30 connected to the exhaust gas inlet port 43 and the center line L2 of the fourth pipe 34 of the exhaust conduit 30 connected to the exhaust gas outlet port 44 are set off from each other by a distance 5 in the right and left direction. The fourth pipe 34 of the exhaust conduit 30 is deflected to one side (left side) in the width direction (right and left direction) of the vehicle body. As shown in FIG. 3, the front catalyst 40 is positioned between the third frame section 12C of the left frame 12 and the third frame section 13C of the right frame 13. As shown in FIG. 2, the top portion of the front catalyst 40 overlaps with the third frame section 12C (13C) in the side view. In this regard, as shown in FIGs. 7 and 9, the front catalyst 40 is formed to have a low-profile shape whose width W is greater 10 than the height H. As shown in FIG. 3, the height H of the front catalyst 40 is generally equal to the outer diameter D of the third pipe 33 and to the outer diameter (not shown) of the fourth pipe 34 of the exhaust conduit 30. The bottom lines 33A, 34A of the third pipe 33 and the fourth pipe 34 of the exhaust conduit 33 extending below the crankcase 21 in the side view and the bottom line 40A of the catalyst 40 in the side view are positioned generally on the same straight line. The rear catalyst 50 is disposed in the muffler 36 of the exhaust conduit 30 positioned downstream of the front catalyst 40 . As shown in FIGs . 5 and 6, the downstream end of a secondary air introducing conduit 2 is connected to the exhaust gas outlet port 44 of the exhaust conduit 30 positioned between the front catalyst 40 and the rear catalyst 50. The upstream end of the secondary air introducing conduit 2 is connected to the air cleaner 19 (see FIG. 2). The secondary air introducing conduit 2 introduces external air passing through the air cleaner 19 to the rear catalyst 50 through the fourth pipe 34 to enhance the burning efficiency of the exhaust gases in the rear catalyst 50. Additionally, a downstream portion of the secondary air introducing conduit 2 is provided with a stay 100 whereby the downstream portion is supported by the front catalyst 40. The front catalyst 40 and the rear catalyst 50 both burn harmful components (HC, NOx, etc.) contained in the exhaust gases 11 released from the engine 20 to purify the exhaust gases. In the embodiment as thus constructed, the front catalyst 40 is positioned below the crankcase 21 of the engine 20 and the front catalyst 40 is formed to have a low-profile shape whose height h is less than the width W thereof. Therefore, the front catalyst 40 can be prevented from protruding downward beyond the third pipe 33 and the fourth pipe 34 of the exhaust conduit 30 extending below the crankcase 21 in the horizontal direction, and the minimum height H (see FIG. 1) of the vehicle body from the ground can be easily ensured. Also, the layout design of the front catalyst 40 can be made easily. Additionally, in the embodiment, the motorcycle 1 is described as an example of the straddle type vehicle. The present invention, however, is not limited to the motorcycle and can be applied to other straddle type vehicles such as, for example, a three-wheeled vehicle and a sand buggy. 12 WE CLAIM: 1. A straddle type vehicle comprising: an engine including a crankcase and a cylinder block disposed thereon; an exhaust conduit which has an upstream end coupled with the cylinder block and extends downward in front of the engine from the upstream end and further rearward below the crankcase; and a catalyst disposed midway of the exhaust conduit and below the crankcase for purifying exhaust gases flowing through the exhaust conduit, wherein the catalyst is formed to be low-profile, a size of the catalyst in width being greater than that in height. 2. The straddle type vehicle as claimed in Claim 1, wherein the size of the catalyst in height is generally equal to an outer diameter of the exhaust conduit. 3. The straddle type vehicle as claimed in Claim 1, wherein the catalyst is disposed between right and left frames to which the engine is fixed. 4. The straddle type vehicle as claimed in Claim 1, wherein another catalyst is disposed midway of the exhaust conduit to be positioned downstream of the catalyst. 13 5. The straddle type vehicle as claimed in Claim 1, wherein a secondary air introducing conduit is connected to the exhaust conduit at a location between the catalyst and the another catalyst. 6. The straddle type vehicle as claimed in Claim 1, wherein a bottom line of a portion of the exhaust conduit extending below the crankcase in a side view and a bottom line of the catalyst in the side view are positioned generally on the same straight line. 7. The straddle type vehicle as claimed in Claim 1, wherein a center line of a portion of the exhaust conduit coupled with an exhaust gas inlet port of the catalyst through which the exhaust gases enter the catalyst from the portion of the exhaust conduit and a center line of another portion of the exhaust conduit coupled with an exhaust gas outlet port of the catalyst through which the exhaust gases go out from the catalyst to the another portion of the exhaust conduit are set off from each other, and the another portion of the exhaust conduit coupled with the exhaust gas outlet port is deflected to one side of a vehicle body in a width direction thereof. 14 A front catalyst is disposed below a crankcase of an engine. The front catalyst is formed to be low-profile, that is, the size of the catalyst in height is less than that in width. Bottom surfaces of third and fourth pipes of an exhaust conduit positioned below the crankcase extend along the same plane as a bottom surface of the front catalyst.

Full Text

STRADDLE TYPE VEHICLE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a straddle type vehicle
such as, for example, a motorcycle.
2. Description of the Related Art
Normally, exhaust gases from an engine are released to the
atmosphere. It is desired to purify the exhaust gases as clean
as possible before the release of the exhaust gases. Therefore,
a catalyst (catalyzer) has been disposed midway of an exhaust
conduit through which the exhaust gases flow so that the exhaust
gases are purified by the catalyst (for example, see
JP-B-3026684).
However, because the related art employs a structure in
which the catalyst is disposed midway of the exhaust conduit
extending in a fore to aft direction below a crankcase of the
engine, the catalyst protrudes downward greatly beyond the
crankcase. It is, therefore, difficult to keep the minimum
height of the vehicle body from the ground. Thus, there arises
a problem that a layout design of the catalyst is difficult.
SUMMARY OF THE INVENTION
The present invention is made under the circumstances and
relates to a straddle type vehicle that can easily keep the
1

minimum height of the vehicle body from the ground and can make
a layout design of a catalyst be simple although the catalyst
is disposed below the crankcase.
A straddle type vehicle configured in accordance with the
present invention and for resolving the problem of the related
art includes: an engine including a crankcase and a cylinder
block disposed thereon; an exhaust conduit which has an
upstream end coupled with the cylinder block and extends
downward in front of the engine from the upstream end and
further rearward below the crankcase; and a catalyst disposed
midway of the exhaust conduit and below the crankcase for
purifying exhaust gases flowing through the exhaust conduit.
The catalyst is formed to be low-profile, in which the size
of the catalyst in width is greater than that in height.
According to the present invention as constructed in the
manner described, the cross sectional shape of the catalyst
can be low-profile, where the size in width is greater than
the size in height. Therefore, to the extent that the cross
sectional shape of the catalyst is made small in height, the
minimum height of the vehicle body including the catalyst and
the exhaust conduit from the ground can be easily ensured.
In one mode of the present invention, the size of the
catalyst in height can be generally equal to the outer diameter
of the exhaust conduit. According to this construction,
because the size of the catalyst in height can be generally
2

equal to the outer diameter of the exhaust conduit, the catalyst
does not protrude below the exhaust conduit, and the minimum
height of the vehicle body including the catalyst and the
exhaust conduit from the ground can be more easily ensured.
In another mode of the present invention, the catalyst can
be disposed between right and left frames to which the engine
is fixed. According to this construction, because the
catalyst can be positioned in a space defined between the right
and left frames, the layout design of the catalyst can be easily
made. Also, because the catalyst is disposed between the right
and left frames, the right and left frames can protect the
catalyst from external shocks.
In a further mode of the present invention, another
catalyst can be disposed midway of the exhaust conduit to be
positioned downstream of the catalyst. According to this
construction, the exhaust gases discharged from the exhaust
conduit can be more efficiently purified using those two
catalysts.
In a further mode of the present invention, a secondary
air introducing conduit can be connected to the exhaust conduit
at a location between the catalyst and the another catalyst.
According to this construction, because the secondary air can
be introduced into the exhaust conduit through the secondary
air introducing conduit, the exhaust gases can be more
efficiently purified.
3

In a further mode of the present invention, the bottom line
of a portion of the exhaust conduit extending below the
crankcase in the side view and the bottom line of the catalyst
in the side view can be positioned generally on the same
straight line. According to this construction, the catalyst
can be surely prevented from protruding downward from the
exhaust conduit disposed below the crankcase, and the minimum
height of the vehicle body from the ground can be more easily
ensured.
In a further mode of the present invention, the center line
of a portion of the exhaust conduit coupled with the exhaust
gas inlet port of the catalyst through which the exhaust gases
enter the catalyst from the portion of the exhaust conduit and
the center line of another portion of the exhaust conduit
coupled with the exhaust gas outlet port of the catalyst through
which the exhaust gases go out from the catalyst to the another
portion of the exhaust conduit can be set off from each other,
and the another portion of the exhaust conduit coupled with
the exhaust gas outlet port can be deflected to one side of
a vehicle body in the width direction thereof.
According to this construction, because, in a situation
that a muffler placed at a location on the outlet port side
is deflected to the one side of the vehicle body in the width
direction thereof, the center line of the exhaust conduit
coupled with the exhaust gas outlet port of the catalyst is
4

deflected to the one side of the vehicle body in the width
direction relative to the center line of the exhaust conduit
coupled with the exhaust gas inlet port, the muffler and the
exhaust gas outlet port can be easily coupled with each other
through a portion of the exhaust conduit. The layout design
of the exhaust conduit including the muffler can be easily made.
According to the straddle type vehicle of the present
invention, because the cross sectional shape of the catalyst
can be formed to be low-profile, that is, the size of the
catalyst in width is greater than the size of the catalyst in
height, the minimum height of the vehicle body from the ground
can be easily ensured and the layout design of the catalyst
can be easily made, although the catalyst is disposed below
the crankcase.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view, showing a motorcycle
configured in accordance with an embodiment of the present
invention;
FIG. 2 is an enlarged view, showing a frame, an exhaust
conduit, a front catalyst, a rear catalyst, etc. of FIG. 1;
FIG. 3 is a front elevational view, showing the frame, the
exhaust conduit, the front catalyst, etc. of FIG. 2;
FIG. 4 is a bottom plan view, showing the frame, the exhaust
conduit, the front catalyst, the rear catalyst, etc. of FIG.
5

2;
FIG. 5 is a side elevational view, showing the exhaust
conduit, the front catalyst and the rear catalyst of FIG. 1
solely in an enlarging manner;
FIG. 6 is a top plan view, showing the exhaust conduit,
the front catalyst and the rear catalyst of FIG. 1 solely in
the enlarging manner;
FIG. 7 is an enlarged perspective view, showing the front
catalyst of FIG. 6 solely;
FIG. 8 is a cross sectional view, showing the front catalyst,
etc. of FIG. 6 in the enlarging manner; and
FIG. 9 is a cross sectional view of the front catalyst,
taken along the line VIII-VIII of FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIGs. 1 to 7, an embodiment will be
described, exemplifying a case that a straddle type vehicle
of the embodiment according to the present invention is applied
to a motorcycle. A motorcycle 1 of the embodiment of the
present invention is structured to include a frame 10, an engine
20, an exhaust conduit 30, a front catalyst 40 and a rear
catalyst 50.
The frame 10 has a head pipe 11, a left frame 12 formed
with a framework which generally has a parallelogram shape,
and a right frame 13 formed with another framework shaped as
6

a parallelogram, similarly to the left frame 12.
As shown in FIG. 2, the left frame 12 is structured to
include: a first frame section 12A, whose front end is coupled
with the top end of a head pipe 11, extending obliquely downward
rearward from the front end; a second frame section 12B curvedly
extending in a dog-leg shape from the rear end of the first
frame section 12A to extend obliquely downward rearward, and
having a lower end portion which curvedly extends obliquely
downward forward; a third frame section 12C curvedly extending
forward in a generally horizontal direction from the lower end
portion of the second frame section 12B; and a fourth frame
section 12D whose top end is coupled with the bottom end of
the head pipe 11.
The left frame 12 has a seat rail 12E, whose front end is
coupled with the boundary portion between the first frame
section 12A and the second frame section 12B, extending
rearward generally in the horizontal direction from the front
end; and a back stay 12F whose front end is coupled with a middle
portion of the second frame section 12B in a longitudinal
direction, extending obliquely upward rearward. The rear end
of the seat rail 12E is coupled with a mid portion of the back
stay 12F.
As shown in FIGs. 3 and 4, the right frame 13 has a first
frame section 13A, a second frame section 13B, a third frame
section 13C, a fourth frame section 13D, a seat rail 13E and
7

a back stay 13F, similarly to the left frame 12.
As shown in FIG. 1, a pivot shaft (not shown) attached to
handlebars 14 is inserted into the head pipe 11 for pivotal
movement. The pivot shaft of the handlebars 14 is fixed to
respective central portions of an upper bracket 15 and an lower
bracket 16 each extending in width direction. Respective top
end portions of right and left front forks 17 (only one of them
is shown) are inserted into right and left ends of the brackets
15, 16 and fixed thereto. A front wheel 60 is coupled with
the bottom end portions of the respective front forks 17 for
rotation.
The front ends of a swing arm 18 are coupled with the second
frame section 12B of the left frame 12 and the second frame
section 13B of the right frame 13 to be supported for swing
movement. A rear wheel 70 is coupled with the rear ends of
the swing arm 18 for rotation. Additionally, an air cleaner
19 is disposed between the seat rails 12E and the back stays
12F of the frame 10.
The engine 20 is disposed in an inside space defined by
the left frame 12 and the right frame 13 each generally formed
with a framework having a rectangular shape (see FIG. 2) . The
engine 20 is mounted on the frames 12, 13 by being suspended.
As shown in FIGs. 1 and 2, the engine 20 is structured to include
a crankcase 21 and a cylinder block 22 positioned on the
crankcase 21.
8

As shown in FIG. 2 through FIG. 6, the exhaust conduit 30
has a first pipe 31 arcuately extending forward from the
cylinder block 22 of the engine 20, a second pipe 32 extending
obliquely downward rearward from the first pipe 31 and
partially overlapping with the fourth frame section 12D (13D)
of the frame 10 in a side view, a third pipe 33 extending rearward
from the second pipe generally in the horizontal direction to
be connected to the front catalyst 40 and partially overlapping
with the third frame section 12C (13C) of the frame 10 in the
side view, a fourth pipe 34 extending rearward from the front
catalyst generally in the horizontal direction, a fifth pipe
35 curvedly extending obliquely upward rearward, and a muffler
36 connected to the fifth pipe 35.
The exhaust conduit 30 is to discharge exhaust gases
externally from the through the front catalyst 40, the rear
catalyst 50 and the muffler 36.
The front catalyst 40 is positioned below the crankcase
21 and between the third pipe 33 and the fourth pipe 34 of the
exhaust pipe 30. As shown in FIGs. 8 and 9, the front catalyst
40 includes a tubular casing 41, whose cross section has an
elliptic shape (ellipse configuration), extending in the fore
to aft direction; and a catalyst body 42 contained in the casing
41.
The casing 41 has an exhaust gas inlet port 43 which is
a tubular body tapered forward from the upstream portion of
9

the casing 41 and extending rearward to be unitarily formed
with the casing 41. Exhaust gases from the third pipe 33 of
the exhaust conduit 30 flow into the exhaust gas inlet port
43. Also, the casing 41 has an exhaust gas outlet port 44
unitarily formed with the casing 41 and extending rearward as
a tubular body from a downstream portion of the casing 41
through a sloped portion 44A. The exhaust gas outlet port 44
is to let the exhaust gases which have flowed through the
catalyst 40 go out to the fourth pipe 34 of the exhaust conduit
30.
In this regard, as shown in FIG. 8, the center line LI of
the third pipe 33 of the exhaust conduit 30 connected to the
exhaust gas inlet port 43 and the center line L2 of the fourth
pipe 34 of the exhaust conduit 30 connected to the exhaust gas
outlet port 44 are set off from each other by a distance 5 in
the right and left direction. The fourth pipe 34 of the exhaust
conduit 30 is deflected to one side (left side) in the width
direction (right and left direction) of the vehicle body.
As shown in FIG. 3, the front catalyst 40 is positioned
between the third frame section 12C of the left frame 12 and
the third frame section 13C of the right frame 13. As shown
in FIG. 2, the top portion of the front catalyst 40 overlaps
with the third frame section 12C (13C) in the side view.
In this regard, as shown in FIGs. 7 and 9, the front catalyst
40 is formed to have a low-profile shape whose width W is greater
10

than the height H. As shown in FIG. 3, the height H of the
front catalyst 40 is generally equal to the outer diameter D
of the third pipe 33 and to the outer diameter (not shown) of
the fourth pipe 34 of the exhaust conduit 30.
The bottom lines 33A, 34A of the third pipe 33 and the fourth
pipe 34 of the exhaust conduit 33 extending below the crankcase
21 in the side view and the bottom line 40A of the catalyst
40 in the side view are positioned generally on the same
straight line.
The rear catalyst 50 is disposed in the muffler 36 of the
exhaust conduit 30 positioned downstream of the front catalyst
40 . As shown in FIGs . 5 and 6, the downstream end of a secondary
air introducing conduit 2 is connected to the exhaust gas outlet
port 44 of the exhaust conduit 30 positioned between the front
catalyst 40 and the rear catalyst 50. The upstream end of the
secondary air introducing conduit 2 is connected to the air
cleaner 19 (see FIG. 2). The secondary air introducing conduit
2 introduces external air passing through the air cleaner 19
to the rear catalyst 50 through the fourth pipe 34 to enhance
the burning efficiency of the exhaust gases in the rear catalyst
50. Additionally, a downstream portion of the secondary air
introducing conduit 2 is provided with a stay 100 whereby the
downstream portion is supported by the front catalyst 40. The
front catalyst 40 and the rear catalyst 50 both burn harmful
components (HC, NOx, etc.) contained in the exhaust gases
11

released from the engine 20 to purify the exhaust gases.
In the embodiment as thus constructed, the front catalyst
40 is positioned below the crankcase 21 of the engine 20 and
the front catalyst 40 is formed to have a low-profile shape
whose height h is less than the width W thereof. Therefore,
the front catalyst 40 can be prevented from protruding downward
beyond the third pipe 33 and the fourth pipe 34 of the exhaust
conduit 30 extending below the crankcase 21 in the horizontal
direction, and the minimum height H (see FIG. 1) of the vehicle
body from the ground can be easily ensured. Also, the layout
design of the front catalyst 40 can be made easily.
Additionally, in the embodiment, the motorcycle 1 is
described as an example of the straddle type vehicle. The
present invention, however, is not limited to the motorcycle
and can be applied to other straddle type vehicles such as,
for example, a three-wheeled vehicle and a sand buggy.
12

WE CLAIM:
1. A straddle type vehicle comprising:
an engine including a crankcase and a cylinder block
disposed thereon;
an exhaust conduit which has an upstream end coupled with
the cylinder block and extends downward in front of the engine
from the upstream end and further rearward below the crankcase;
and
a catalyst disposed midway of the exhaust conduit and below
the crankcase for purifying exhaust gases flowing through the
exhaust conduit,
wherein the catalyst is formed to be low-profile, a size
of the catalyst in width being greater than that in height.
2. The straddle type vehicle as claimed in Claim 1,
wherein the size of the catalyst in height is generally equal
to an outer diameter of the exhaust conduit.
3. The straddle type vehicle as claimed in Claim 1,
wherein the catalyst is disposed between right and left frames
to which the engine is fixed.
4. The straddle type vehicle as claimed in Claim 1,
wherein another catalyst is disposed midway of the exhaust
conduit to be positioned downstream of the catalyst.
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5. The straddle type vehicle as claimed in Claim 1,
wherein a secondary air introducing conduit is connected to
the exhaust conduit at a location between the catalyst and the
another catalyst.
6. The straddle type vehicle as claimed in Claim 1,
wherein a bottom line of a portion of the exhaust conduit
extending below the crankcase in a side view and a bottom line
of the catalyst in the side view are positioned generally on
the same straight line.
7. The straddle type vehicle as claimed in Claim 1,
wherein a center line of a portion of the exhaust conduit
coupled with an exhaust gas inlet port of the catalyst through
which the exhaust gases enter the catalyst from the portion
of the exhaust conduit and a center line of another portion
of the exhaust conduit coupled with an exhaust gas outlet port
of the catalyst through which the exhaust gases go out from
the catalyst to the another portion of the exhaust conduit are
set off from each other, and the another portion of the exhaust
conduit coupled with the exhaust gas outlet port is deflected
to one side of a vehicle body in a width direction thereof.

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A front catalyst is disposed below a crankcase of an engine.
The front catalyst is formed to be low-profile, that is, the
size of the catalyst in height is less than that in width.
Bottom surfaces of third and fourth pipes of an exhaust conduit
positioned below the crankcase extend along the same plane as
a bottom surface of the front catalyst.

A STRADDLE -TYPE VEHICLE WITH CATALYST

Documents:

Inventors:

PCT Conventions: