Cooling structure of belt transmission for vehicle

A cooling structure of a belt transmission for vehicles which limits the consumed power for cooling to a minimum and does not deteriorate cooling performance of the transmission. A drive pulley having a variable pitch diameter and a driven pulley which is driven through a drive belt and has a variable pitch diameter is housed in a substantially elliptical housing. An intake port formed in the vicinity of a suction part of the cooling fan formed on the drive pulley in the housing to forcedly introduce air from the outside and exhaust air to the outside. An exhaust port on the housing in a normal direction of the driven pulley at the rearward of a center of rotation of the driven pulley as seen from a side.

FIELD OF THE INVENTION 
The present invention relates to a cooling structure of a belt transmission 
mounted as a transmission on vehicles such as two-wheelers, three- or 
four-wheeled working vehicles, three- or four-wheeled leisure vehicles, or 
snow mobiles. 
BACKGROUND OF THE RELATED ART 
Conventionally, a belt transmission has been employed as a transmission for 
vehicles such as two-wheelers, three- or four-wheeled working vehicles, 
three- or four-wheeled leisure vehicles, or snow mobiles because the 
structure is simple, a gear-change is unnecessary and shock is not caused 
when changing the gear. 
The belt transmission has a structure in which a whole belt transmission 
mechanism comprising a variable pitch diameter type drive pulley driven by 
a drive shaft of an engine and a variable pitch diameter type driven 
pulley driven by the drive pulley through a drive belt is isolated from 
the environment by a housing in such a manner that sand, dust and the like 
do not get into the contact faces of the drive belt and the pulleys. 
Air is sucked into the housing through an intake duct, and is exhausted 
from an exhaust duct provided at a position on the housing apart from the 
intake duct so that the inside of the housing is forcedly cooled by the 
air. Thus, friction heat and other heat generated between the drive belt 
and the pulleys are exhausted to the outside. 
In order to efficiently cool the inside of the housing by the air, a 
cooling fan is integrally provided on the drive pulley to forcedly suck 
the air from the intake duct, and the cooling fan is also provided on the 
driven pulley to forcedly exhaust the air in the housing to the outside. 
In the belt transmission, it is necessary to efficiently cool the inside 
of the housing by the air under low speed/high load conditions such as 
hilly terrains or the case where heavy packages are loaded as well as high 
speed conditions. In order to efficiently perform air-cooling under the 
low speed conditions as well as the high speed conditions, accordingly, 
the cooling fan is provided on the drive pulley and the driven pulley as 
described above in such a manner that the air is forcedly sucked and 
exhausted. The prior art of this kind has been disclosed in Japanese 
Unexamined Utility Model Publication No. 58-96157. 
However, if the cooling fan is provided on the driven pulley as described 
above, a certain amount of power of the engine is consumed for the cooling 
fan. Consequently, the engine power applied to drive a vehicle is reduced. 
More specifically, in case of a leisure vehicle on which an engine of 
about 20 horsepower is mounted and which runs at a maximum speed of about 
40 to 60 km/h, about 3 to 4 horsepower is sometimes consumed by the 
cooling fan of the driven pulley. In other words, runability is 
deteriorated for the power consumed by the cooling fan of the driven 
pulley. 
SUMMARY OF THE INVENTION 
In consideration of the foregoing, it is an object of the present invention 
to provide a cooling structure of a belt transmission for vehicles which 
controls a consumed horsepower for cooling to a minimum and does not 
deteriorate cooling performance in the transmission. 
A first aspect of the present invention is directed to a cooling structure 
of a belt transmission for vehicles comprising a belt transmission 
mechanism including a drive pulley which is driven by a drive shaft of an 
engine and has a variable pitch diameter, and a driven pulley which is 
driven by the drive pulley through a drive belt and has a variable pitch 
diameter, an almost elliptic housing for housing the belt transmission 
mechanism as seen from a side surrounding the drive pulley and the driven 
pulley, a cooling fan formed on the drive pulley, an intake port formed in 
the vicinity of a suction part of the cooling fan of the housing for 
forcedly introducing air from an outside environment into the housing, and 
an exhaust port formed in the vicinity of the driven pulley of the housing 
for exhausting the air cooling the inside of the housing to the outside, 
wherein the exhaust port is provided on the housing in a normal direction 
of the driven pulley at the rearward of a center of rotation of the driven 
pulley as seen from a side. 
According to the cooling structure of a belt transmission for vehicles 
having such a structure that the exhaust port is provided on the housing 
in a normal direction of the driven pulley at the rearward of a center of 
rotation of the driven pulley, a very smooth cooling air flow path is 
formed from the intake port to the exhaust port provided in the rear 
position thereof on the housing. Therefore, the cooling air in the housing 
flows with a very small pressure loss and less turbulence, and a great air 
flow for cooling is formed. Consequently, necessary cooling performance 
can be obtained even if the cooling fan is not provided on the driven 
pulley unlike a conventional cooling structure. 
A second aspect of the present invention is directed to the cooling 
structure of a belt transmission for vehicles as defined in the first 
aspect of the present invention, wherein the driven pulley is provided in 
such a manner that a center of the exhaust port is almost coincident with 
a center of a V-tapered trench of the pulley in a state in which a movable 
sheave and a fixed sheave of the driven pulley are the closest to each 
other as seen in a plane. Consequently, during high speed running which 
requires the greatest cooling, the movable sheave of the driven pulley 
separates from the fixed sheave thereof most greatly so that a large space 
is formed therebetween. In other words, the state in which both sheaves 
are not positioned in front of the exhaust port is obtained (see a 
two-dotted line in FIG. 1). As a result, a straight path is formed toward 
the exhaust port in the housing. Consequently, very efficient cooling can 
be obtained. More specifically, the cooling air which is forcedly 
introduced from the intake port cools the drive pulley, the drive belt, 
the driven pulley and the like, and flows almost like a laminar flow at a 
high speed through the large space formed between the movable sheave and 
the fixed sheave of the driven pulley. As a result, a large amount of 
cooling air sucked during high speed running can pass almost like the 
laminar flow in the housing at a high speed, can effectively absorb heat 
of each pulley and the drive belt, a casing or the like and can be 
exhausted to the outside of the housing. 
A third aspect of the present invention is directed to the cooling 
structure of a belt transmission for vehicles as defined in the first or 
second aspect of the present invention, wherein the exhaust port is 
substantially provided on the housing on the extended line rearward 
through the center of rotation of the driven pulley as seen from a side. 
Consequently, a cooling flow path having a very small pressure loss is 
formed from the intake port to the exhaust port. The cooling air which is 
forcedly sucked by the cooling fan of the drive pulley can 
hydrodynamically be guided very smoothly to the exhaust port on the basis 
of a relationship with a shape of the housing, and can be exhausted from 
the exhaust port to the outside of the housing. 
A fourth aspect of the present invention is directed to the cooling 
structure of a belt transmission for vehicles as defined in any of the 
first to third aspects of the present invention, wherein a rear portion of 
the housing is formed so as to be gradually reduced toward the exhaust 
port. Consequently, the cooling air flow can smoothly be guided almost 
like a laminar flow to the exhaust port more efficiently. 
A fifth aspect of the present invention is directed to the cooling 
structure of a belt transmission for vehicles as defined in any of the 
first to fourth aspects of the present invention, wherein a guide portion 
for guiding, to the exhaust port, a mainstream of cooling air which is 
forcedly supplied into the housing by the cooling fan and flows toward the 
exhaust port is formed in succession to the exhaust port. By guiding 
function of the guide portion, the cooling air can be guided to the 
exhaust port more efficiently. 
A sixth aspect of the present invention is directed to a cooling structure 
of a belt transmission for vehicles comprising a belt transmission 
mechanism including a drive pulley which is driven by a drive shaft of an 
engine and has a variable pitch diameter, and a driven pulley which is 
driven by the drive pulley through a drive belt and has a variable pitch 
diameter, an almost elliptic housing for housing the belt transmission 
mechanism as seen from a side surrounding the drive pulley and the driven 
pulley, a cooling fan formed on a side of the drive pulley, an intake port 
formed in the vicinity of a suction part of the cooling fan of the housing 
for forcedly introducing air from an environment outside into the housing, 
an exhaust port formed in the vicinity of the driven pulley of the housing 
for exhausting the air cooling an inside of the housing to the outside, 
and a second exhaust port provided in the vicinity of the driven pulley of 
the housing. 
According to the cooling structure of a belt transmission for vehicles 
having such a structure, the total sectional area of the exhaust port is 
increased by adding the second exhaust port. Consequently, even if the 
driven pulley has no cooling fan itself, the cooling air flow in the 
housing is increased so that a consumed power for cooling can be 
controlled to a minimum and cooling performance of the transmission can be 
maintained. 
A seventh aspect of the present invention is directed to the cooling 
structure of a belt transmission for vehicles as defined in the sixth 
aspect of the present invention, wherein a movable sheave of the driven 
pulley is positioned in an inner part (engine side) of the housing with 
respect to a fixed sheave, and the second exhaust port is provided in a 
side portion of the housing positioned on an inner part (engine side) of 
the movable sheave of the driven pulley. Consequently, when the vehicle 
runs at a low speed with a high load in which an amount of sucked cooling 
air is decreased, the movable sheave of the driven pulley separates from 
the second exhaust port so that a cooling air path is enlarged. Thus, the 
cooling air can be exhausted from the second exhaust port more 
effectively. With a structure in which even if the second exhaust port is 
blocked to some extent when the vehicle runs at a high speed, a large 
space is formed between both sheaves of the driven pulley as defined in 
the second aspect of the present invention, the cooling air path is 
sufficiently kept. In addition, the revolution speed of the drive pulley 
including the cooling fan is high. Consequently, a large amount of cooling 
air can be sucked and can be exhausted from the exhaust port. Thus, the 
inside of the housing of the transmission can be cooled sufficiently. 
Furthermore, because the second exhaust port is provided on the side part 
of the movable sheave of the driven pulley in the housing, the second 
exhaust port does not protrude onto the outside of the housing. 
Consequently, this structure is excellent in that protrusion onto the 
outside of the vehicle can be eliminated when mounting the transmission on 
the vehicle. 
According to the cooling structure of a belt transmission for vehicles of 
the present invention, the pressure loss of the air flowing in the housing 
is reduced and the cooling performance of the transmission is not 
deteriorated.

DETAILED DESCRIPTION OF THE INVENTION 
A cooling structure of a belt transmission for vehicles according to an 
embodiment of the present invention will be described below with reference 
to the drawings. 
By way of example, the case where the cooling structure of a belt 
transmission for vehicles is mounted on a four-wheeled leisure vehicle 
will be described in the present embodiment. 
FIG. 1 is a sectional plan view showing the cooling structure of a belt 
transmission for vehicles according to the embodiment of the present 
invention, which is taken along sectional lines I--I in FIG. 2, and FIG. 2 
is a side view of the transmission showing a shape of a housing and its 
internal structure (seen from reference lines II--II in FIG. 1). 
In FIGS. 1 and 2, a housing H houses a transmission mechanism which 
comprises a drive pulley 1 and a driven pulley 2. A drive belt B is wound 
on the drive pulley 1 and the driven pulley 2. 
The drive pulley 1 is provided on a tip of an input shaft 3 (the right side 
in FIG. 1) in such a manner that it rotates integrally with the input 
shaft 3. The input shaft 3 is integrally engaged with a crankshaft C 
extended from an engine E provided on the left side in FIG. 1 (an engine 
itself is not shown). The drive pulley 1 includes a fixed sheave 1A and a 
movable sheave 1B in pairs. The movable sheave 1B is formed so as to 
approach or separate from the fixed sheave 1A provided on the engine E 
side on the input shaft 3. More specifically, a centrifugal movable device 
D is built in the movable sheave 1B side. The centrifugal movable device 
D.sub.1 has a structure in which the movable sheave 1B is drawn to 
approach the fixed sheave 1A side as the revolution speed of the input 
shaft 3 is increased, and the movable sheave 1B is pushed to separate from 
the fixed sheave 1A side as the revolution speed of the input shaft 3 is 
decreased. 
A plurality of fins 4 are provided on a back face (a left face in FIG. 1) 
1a of the fixed sheave 1A so that a centrifugal cooling fan is formed. 
As shown in FIG. 1, the driven pulley 2 is provided on an output shaft 8 of 
the transmission so as to rotate integrally. The driven pulley 2 includes 
a fixed sheave 2A and a movable sheave 2B in pairs. The movable sheave 2B 
is formed so as to approach or separate from the fixed sheave 2A provided 
on an opposite side of the engine E over the output shaft 8 corresponding 
to operation of the drive pulley 1. More specifically, a movable device 
D.sub.2 is built in the driven pulley 2. The movable device D.sub.2 serves 
to cause the movable sheave 2B to separate from the fixed sheave 2A side 
during high speed driving and to approach the fixed sheave 2A side during 
low speed driving, for example, under high load conditions. 
The movable devices D.sub.1 and D.sub.2 of the drive pulley 1 and the 
driven pulley 2 operate synchronously. When the movable device D.sub.1 on 
the drive pulley 1 side causes the movable sheave 1B to operate so as to 
approach the fixed sheave 1A side, the movable device D.sub.2 on the 
driven pulley 2 side causes the movable sheave 2B to operate synchronously 
so as to separate from the fixed sheave 2A side, and when the movable 
device D.sub.1 on the drive pulley 1 side causes the movable sheave 1B to 
operate so as to separate from the fixed sheave 1A side, the movable 
device D.sub.2 on the driven pulley 2 side causes the movable sheave 2B to 
operate synchronously so as to approach the fixed sheave 2A side. 
The movable devices D.sub.1 and D.sub.2 themselves have well-known 
structures. 
The housing H includes a wall H.sub.1 of the engine E (the left side in 
FIG. 1) and a cover H.sub.2 positioned on the outside of a transmission 
mechanism interposed therebetween (on the right side in FIG. 1) for 
covering the transmission mechanism. The cover H.sub.2 has an almost 
elliptic shape so as to surround the drive pulley 1 and the driven pulley 
2 shown in FIG. 2 as seen from a side. At least the wall surrounding the 
drive pulley 1 and the driven pulley 2 is substantially ellipticly shaped. 
As shown in FIG. 1, an intake port 5 is formed on the wall H.sub.1 of the 
housing H on the engine side (the left side in FIG. 1) corresponding to a 
suction port 1a formed on the center of the fin 4 provided on a back face 
of the fixed sheave 1A in the housing H. 
The intake port 5 is extended up to a space S provided below a bonnet Q on 
a front of the vehicle through an intake path 6 and an intake duct 7 as 
shown in FIGS. 2, 3 and 4. The space S is opened toward a front of the 
vehicle. The other peripheral faces of the space are generally insulated 
from the outside. The intake duct 7 is connected to an opening formed on 
the insulated rear face. 
An exhaust port 9 is formed preferably on a rear end of the housing H. In 
the present embodiment, as shown in FIG. 2, the exhaust port 9 is located 
on the housing H on a normal line extended rearward through a center 
O.sub.3 of rotation of the driven pulley 2, and is directed roughly toward 
the normal line (i.e. air flow outwardly at the exhaust port 9 is roughly 
directed along the extended normal line). In more detail, the exhaust port 
9 is located on the housing on a horizontal line extended rearward through 
the center O.sub.3 of rotation of the driven pulley 2 and is directed 
approximately toward the center O.sub.3 of rotation of the driven pulley 
2. As shown in FIGS. 1 and 2, the housing H is formed so as to be 
gradually reduced toward the exhaust port 9 as seen in a plane and from a 
side. In other words, as shown in FIG. 1, the housing H is formed in such 
a manner that a side wall ha of the cover H.sub.2 is gradually reduced 
from a central portion of the driven pulley 2 toward the exhaust port 9 as 
seen in a plane and a peripheral wall ha of the cover H.sub.2 is gradually 
reduced toward the exhaust port 9 so as to surround a periphery of the 
driven pulley 2 from the central portion of the driven pulley 2 toward the 
exhaust port 9 as seen from a side. The cover H.sub.2 is formed of plastic 
such that a light weight and a smooth surface can be obtained. 
As shown in FIG. 2, a guide portion 10 is formed on a connecting portion of 
the exhaust port 9 of the housing H having the exhaust port 9 formed 
thereon such that a cooling air W.sub.1 flowing along the bottom wall of 
the housing H is guided to the outside of the exhaust port 9. In the 
present embodiment, the guide portion 10 includes a weir portion 10a to 
change direction of the cooling air W.sub.1 and conduct it to the exhaust 
port 9, and a guide wall portion 10b to conduct the cooling air W.sub.1 to 
the weir portion 10a as shown in FIG. 2. In the present embodiment, the 
drive pulley 1 rotates clockwise in FIG. 2, and the amount of the cooling 
air W.sub.1 flowing along the bottom wall of the housing H shown in FIG. 2 
from the intake port 5 toward the exhaust port 9 is high (this flow is a 
mainstream). Consequently, the guide wall portion 10b is formed along an 
internal wall of the housing H in a direction of a tangent from a slightly 
low portion on a lower end 9a of an inlet end of the exhaust port 9. In 
addition, the weir portion 10a is formed on an upper end 9b of the inlet 
end of the exhaust port 9 in succession to a terminal end of the guide 
wall portion 10b and meet the to main stream of cooling air at an upward 
position of the upper part of the exhaust port 9. The weir portion 10a is 
constructed with a wall with an angle .theta. of about 90 degrees to the 
guide wall portion 10b. An angle .alpha. formed by the guide wall portion 
10b and a center line of the exhaust port 9 has an intersection angle of 
about 80 degrees. The guide wall portion 10b is connected to the weir 
portion 10a by a smooth curve such that the cooling air W.sub.1 is turned 
smoothly. As described above, the cooling air W.sub.1 flowing along the 
bottom of the housing H is caused to flow along the guide wall portion 10b 
in the direction of the tangent from slightly below the lower end 9a of 
the inlet end of the exhaust port 9, and is caused to closely come in 
contact with the weir portion 10a and to be turned toward the inside of 
the exhaust port 9 and guided to the outside of the housing H. 
While the angle .theta. formed with respect to the guide wall portion 10b 
is set to about 90 degrees in the present embodiment, it may be set to an 
optimal value in consideration of a strength of the cooling air, the 
intersection angle .alpha. formed by the guide wall portion and the center 
line of the exhaust port and the like. Furthermore, the angle .alpha. 
formed by the guide wall portion 10b and the center line of the exhaust 
port 9 is not restricted to about 80 degrees. The weir portion 10a, which 
is not always located at an upward position of the upper part of the 
exhaust port 9, may be located in line with the upper end 9c of the 
exhaust port 9. 
In the above embodiment the guide wall portion 10b is formed in a direction 
of a tangent from a slightly low portion on a lower end 9a of an inlet end 
of the exhaust port 9. However the present invention is not limited to the 
above embodiment if the guide wall portion 10b may introduce a cooling air 
into the exhaust port in cooperation with the weir portion 10a. 
As shown in FIG. 1, the exhaust port 9 is arranged such that a center line 
O.sub.2 of the movable sheave 2B and the fixed sheave 2A of the driven 
pulley 2 is almost coincident with a center line O.sub.9 of the exhaust 
port 9 when the movable sheave 2B is the closest to the fixed sheave 2A as 
seen in a plane. 
As shown in FIG. 3, the exhaust port 9 is connected to a space formed below 
a seat R of the vehicle through a flexible exhaust duct 14 (which can bend 
freely) so as to exhaust the cooling air toward the engine E side 
positioned ahead thereof. During backward movement of the vehicle, mud, 
water, dust and the like can be prevented from getting into the exhaust 
port 9 from the back. 
A second exhaust port 11 is provided on the wall H.sub.1 of the housing H 
on the engine E side of the movable sheave 2B of the driven pulley 2 in 
parallel with the output shaft 8, that is, in parallel with a direction of 
movement of the movable sheave 2B. The second exhaust port 11 is 
positioned near a bottom portion of the housing H and near a peripheral 
portion of the movable sheave 2B as seen from a side shown in FIG. 2. And 
as seen in a plane shown in FIG. 1, the second exhaust port 11 is provided 
on the wall H.sub.1 on the engine E side faced to the backside of the 
movable sheave 2B. Accordingly, when the movable sheave 2B is the closest 
to the fixed sheave 2A, the movable sheave 2B separates from the inlet end 
of the second exhaust port 11 so that a large space is formed. 
In the state in which the belt transmission for vehicle is mounted on the 
vehicle, the side wall ha of the housing H opposite to the wall H.sub.1 is 
positioned on the outside of the vehicle as shown in FIG. 1 (see FIG. 5). 
The second exhaust port 11 is provided on the wall H.sub.1 of the housing 
H on the engine E side. Accordingly, the exhaust duct 12 originating and 
extending from the second exhaust port 11 does not protrude onto the 
outside of the vehicle. 
The second exhaust port 11 is connected to a space below the seat R, 
communicating with the outside through the exhaust duct 12 as shown in 
FIGS. 4 to 6. The exhaust duct 12 is provided so as not to interfere with 
the exhaust duct 14 and a suspension 15 of a rear wheel of the vehicle. 
The exhaust duct 12 and the exhaust duct 14 are provided on both sides with 
the suspension 15 interposed therebetween in such a manner that the 
exhaust duct 12 and the exhaust duct 14 do not interfere with each other 
as seen in a plane shown in FIG. 5 and as seen from the rear shown in FIG. 
6. 
In the present embodiment, the wall H.sub.1 of the housing H on the engine 
side is an outer wall of a crankcase of the engine E such that a dimension 
of the transmission in a direction of a width is reduced as much as 
possible. In other words, an outer wall of an aluminum die casting 
crankcase of the engine E is used as the wall H.sub.1 of the housing H on 
the engine side. 
The belt transmission for vehicles having the above-mentioned structure has 
the following functions for cooling the inside of the housing thereof as 
well as usual speed changing functions. 
When the vehicle runs at a high speed, the input shaft 3 rotates at a high 
speed so that a large amount of cooling air is forcedly sucked from the 
intake port 5 into the housing H by the fin 4 provided on the fixed sheave 
1A of the drive pulley 1. 
In this case, the driven pulley 2 is brought into the state in which the 
movable sheave 2B separates from the fixed sheave 2A most greatly and the 
drive belt B is moved nearest to the center of the pulley. Consequently, a 
large path (space) for the cooling air is formed between the fixed sheave 
2A and the movable sheave 2B as seen in a plane shown by a two-dotted line 
in FIG. 1, and a large amount of air passes through the path and is 
exhausted from the exhaust port 9 to the outside through the exhaust duct 
14. In this case, as the large path is formed as described above, a 
pressure loss is reduced as much as possible. Accordingly, a large amount 
of air sucked from the intake port 5 can pass through the housing H, can 
absorb heat in the housing H and can effectively be exhausted to the 
outside. The drive pulley 1 rotates clockwise as seen from a side shown in 
FIG. 2. For this reason, the air sucked into the housing H generates a 
flow of a large amount of cooling air (mainstream) in a direction shown by 
an arrow W.sub.1. The cooling air W.sub.1 flows toward the exhaust port 9 
along the bottom portion of the housing H. Since the housing H (the cover 
H.sub.2 of the housing H) is formed so as to be gradually reduced toward 
the exhaust port 9 and the guide portion 10 is formed on the exhaust port 
9, the cooling air W.sub.1 is effectively gathered in the exhaust port 9 
and is exhausted to the outside. In this case, furthermore, a cooling air 
W.sub.2 is also generated. The cooling air W.sub.2 helps the cooling air 
W.sub.1 being turned in the weir portion 10a. 
As a matter of course, also in this case the air cooling the back face (the 
left face in FIG. 1) of the movable sheave 2B of the driven pulley 2 and 
the like is also exhausted from the second exhaust port 11. 
As stated above, when the vehicle runs at a high speed, a large amount of 
air is sucked by high speed rotation of the drive pulley 1 and is 
exhausted from the exhaust port 9 with a very small pressure loss, that 
is, due to a large space formed between sheaves of the driven pulley 2, 
and the air cooling the back face of the movable sheave 2B is also 
exhausted from the second exhaust port 11. As a result, the inside of the 
housing H can be cooled effectively. 
When the vehicle runs under low speed/high load conditions, the driven 
pulley 2 is kept in a state in which the movable sheave 2B is close to the 
fixed sheave 2A as shown by a solid line in FIG. 1. For this reason, a 
space (path) which is formed ahead of the exhaust port 9 is not larger 
than a space formed during high speed running. However, the housing H is 
formed so as to be gradually reduced toward the exhaust port 9, and the 
guide portion 10 is formed on the exhaust port 9. Consequently, the air 
flowing in the housing H is effectively exhausted from the exhaust port 9. 
In addition, since the movable sheave 2B is moved to the fixed sheave 2A 
side (see the flexible sheave 2B shown by a solid line in FIG. 1), there 
is no obstacle ahead of the second exhaust port 11. Consequently, the air 
sucked from the intake port 5 is effectively exhausted from the second 
exhaust port 11 as well as the exhaust port 9. Accordingly, the inside of 
the housing H is effectively cooled under the low speed/high load 
conditions of the vehicle. 
In the belt transmission for vehicles, an exhaust fin is not provided on 
the driven pulley 2. For this reason, the power of an engine is not 
consumed unnecessarily so that high runability performance can be 
obtained. 
As described above, the second exhaust port 11 and the exhaust duct 12 are 
formed on the engine side of the housing H and do not protrude onto the 
outside of the vehicle (see FIG. 5). In addition, because the outer wall 
of the engine is the wall H.sub.1 of the housing H on the engine side, the 
dimensions of the engine and the transmission in the direction of the 
width can be reduced as much as possible. As a result, a driver who rides 
on the vehicle can get a good driving position. 
In the present embodiment, the exhaust port 9 is provided in a position of 
the housing H on the extended line in the direction of the normal through 
the center O.sub.2 of rotation of the driven pulley 2 backward as shown in 
FIG. 2. If some reduction in a smooth cooling air flow is permitted, the 
exhaust port may be turned obliquely upward or downward from the same 
arrangement, that is, it may be provided in the position of the housing on 
the extended line in the direction of the normal of the driven pulley at 
the back of the center of rotation of the driven pulley as seen from a 
side. 
Although the present invention has fully been described by way of example 
with reference to the accompanying drawings, it is to be understood that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless otherwise such changes and modifications depart 
from the scope of the invention, they should be construed as being 
included therein.