TRANSMISSION SYSTEM FOR A TWO WHEELED VEHICLE
FIELD OF THE INVENTION
The present invention relates to 'Transmission system for a two wheeled vehicle and more particularly to an air inlet structure and an air outlet structure in the cooling arrangement for a V-belt drive continuously variable transmission in a two-wheeled vehicle.
BACKGROUND OF THE INVENTION
In vehicles with V-belt Continuously Variable Transmission (CVT), frictional heat is generated by frictional contact between the V-belt and the pulleys, namely the driven pulley and the driven pulley. Due to generation of this frictional heat, temperature inside the transmission system increases which leads to expansion of the V-belt, which further leads to the desired gear change ratio not being obtained. Frictional heat also leads to deterioration of the V-belt. Therefore effective cooling of a V-Belt CVT is necessary to obtain the desired gear ratio as well as to improve the durability of parts of the CVT especially the V-belt.
Cooling arrangement for CVT known in the art generally has its air inlet at the side of the transmission case, towards the engine, near the cooling cowl of the engine. In such an arrangement, due to heat radiated from the engine, the cooling air entering the inlet of the CVT cooling arrangement gets heated up leading to reduction in cooling efficiency. Further, the air outlet in a conventional CVT cooling arrangement is generally located at the bottom side of the transmission case towards the rear wheel of the vehicle. Such an arrangement makes exit of hot air from the CVT cooling arrangement difficult. Further, in such an arrangement, dust and muddy water raised by the rear wheel can easily enter the air outlet. Therefore to obviate defects in the prior art, there is a requirement for a CVT cooling arrangement that provides enhanced

cooling efficiency of the CVT system and prevents entry of dust and muddy water into the air outlet structure, and this forms the main objective of the present invention.
SUMMARY OF THE INVENTION
A conventional scooter type vehicle has a body frame; the body frame is constituted of a head pipe positioned at the front of the body frame 36, and a down tube extending from a rear lower portion of the head pipe towards a rear downward portion, extending in a substantially horizontal direction towards a rear portion from an intermediate portion thereof. A pair of side frames arranged side by side extending in the rearward direction and then extending obliquely upward. A handle bar is attached to the head pipe. The lower end of handle bar is attached to a front fork, and a front wheel 31 is movably supported by the lower end of the front fork.
Furthermore, a handle bar cover is attached for covering the handle bar, and a headlamp is attached to the handle bar cover. A front fender is arranged in such a manner that it covers the upper portion of the front wheel. The suspension 37 acts as shock absorber for the front wheel of the vehicle. A rear wheel 35 is attached to the rear end of the body frame and a rear fender is attached in a way that it covers the upper portion of the rear wheel.
Floor board upper portion also called as step floor 32 is used for resting the foot of the rider with floor board lower portion 33 for blocking the road dust. Further, a driver seat commonly serving as a lid for the storage box is placed above the box in a manner to be freely opened and closed, and a fuel tank is arranged in a rear portion of the storage box. A swinging engine unit 34 is arranged in substantially central lower portion of the side frames. A V-belt drive CVT is arranged in the lower part of the engine unit towards the rear wheel. The V-belt drive CVT is housed between a transmission case and the crankcase. The cooling arrangement as per the present invention is provided on the transmission case.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig.l shows a typical structure of a two wheeler.
Fig. 2 shows the kick starter assembly and air entry in transmission cover.
Fig. 3 shows the inlet and outlet for CVT cooling.
Fig. 4 shows the cut section of CVT cooling inlet.
Fig. 5 shows the flow of air inside the transmission case for CVT cooling.
Fig. 6 shows the transmission cover air exit.
Fig. 7 shows the outlet for CVT cooling.

DETAILED DESCRIPTION OF THE INVENTION
A two wheeled vehicle with the engine has been shown in Fig.l. A swinging engine unit 34 is arranged in substantially central lower portion of the side frames. A V-belt drive CVT is arranged in the lower part of the engine unit towards the rear wheel. The V-belt drive CVT is housed between a transmission case and the crankcase. The cooling arrangement as per the present invention is provided on the transmission case.
By arranging a cushion between the engine unit and the rear part of the body frame, rear suspension is provided for the scooter. A pillion handle is attached to the rear end of side frames. Furthermore, a tail lamp is arranged below the pillion handle. A portion between the seat and the head pipe is provided with a low step floor on which a rider puts both feet is arranged in a bottom portion thereof. Also the step floor is arranged so as to cover a horizontal portion of the down tube from the above and is fixed to the down tube. A side stand is a provided upright and inclined slightly leftward.
Figure 2 shows the kick starter assembly with the transmission cover having air intake 10. Air intake entry is just above the lever kick starter 16.
Figure 3 shows both the air intake inlet 1 for CVT cooling, cover variator 3 and air outlet 11 of CVT through the holes 13 and 14.
Fig. 4 shows the CVT air entry l's cross sectional view. It comprises of air entry from passage 2, an air filter 10 for filtering the dusty air. Air enters into the transmission cover from the passage 2. The filtered air from filter 10 passes through the fan 5 fixed on the fixed drive.
The V belt drive CVT is structured such that a V belt is put on a drive pulley mounted to the crankshaft and a driven pulley arranged at the rear end of the transmission case. The drive pulley includes a cylindrical drive shaft member spline connected to the crankshaft so as to be rotated therewith. The driven pulley includes a cylindrical driven shaft member rotatably mounted to a rotating shaft rotatably supported by the

transmission case. The drive pulley is provided with a fixed pulley half fixed to the crankshaft and a movable pulley half that can approach the fixed pulley half and can be separated from the fixed pulley half. Power for driving the movable pulley half axially to vary the width of a belt groove formed between the fixed pulley half and the movable pulley half for winding the V belt, is transmitted to the movable pulley half from an electric motor attached to the transmission case.
The driven pulley is provided with an inner cylinder coaxially encircling the output shaft so that the output shaft can be relatively rotated, an outer cylinder with which the inner cylinder is slid ably engaged so that relative turning around the axis and axial relative movement is possible. The driven pulley is also provided with a fixed pulley half fixed to the inner cylinder, a movable pulley half fixed to the outer cylinder opposite to the fixed pulley half. The V belt is wound onto a belt groove formed between the fixed pulley half and a movable pulley half of both the pulleys. The distance between the centers of the pulleys to where the belt makes contact in the groove is known as the pitch radius.
When the pulleys are far apart, the belt rides lower and the pitch radius decreases. When the pulleys are close together, the belt rides higher and the pitch radius increases. The ratio of the pitch radius on the driving pulley to the pitch radius on the driven pulley determines the gear. When one pulley increases its radius, the other decreases its radius to keep the belt tight. As the two pulleys change their radii relative to one another, they create an infinite number of gear ratios, from low to high and everything in between. For example, when the pitch radius is small on the driving pulley and large on the driven pulley, the rotational speed of the driven pulley decreases, resulting in a lower gear. When the pitch radius is large on the driving pulley and small on the driven pulley, then the rotational speed of the driven pulley increases, resulting in a higher gear.
The cooling arrangement for V-belt drive CVT'for a two-wheeled vehicle as per the present invention is characterized in Fig. 4 by an air inlet 2 formed between an air inlet cover 1 and the transmission case 3. The air inlet 2 through which cooling air

enters the CVT system is located at a position towards the upper end of the transmission case 3 and above a cooling fan top opening 6,which is formed on the transmission case 3. An air inlet passage which extends from the cooling air inlet 2 to the cooling fan top opening 6 is formed such that the cooling air is taken in through the air inlet 2 and flows obliquely downwards towards the cooling fan top opening 6. The air outlet 8 of the CVT cooling arrangement as per the present invention is between the transmission case 3 and an outlet cover 11. The air outlet 11 through which hot air exits is formed at a position on the transmission case 3 beside the clutch housing casing area.
As shown in Fig. 7, the outlet cover 11 comprises of atleast two outlet holes 13 on its sidewall and atleast one outlet hole 14 on its bottom portion. The arrangement as per the present invention provides better cooling efficiency since the location of the air inlet 1 is away from the cooling cowl of the engine and therefore cooling air entering the CVT is not heated by the heat radiating from the engine. Further, the location of the air outlet 11 towards the upper end of the transmission case 3 near the clutch housing casing area allows hot air to exit easily. Due to the outlet cover 13, the outflow passage for the exiting hot air is made in such a manner that dust or muddy water raised by the rear wheel is prevented from entering the outlet structure. This is because the outflow passage is so formed that dust or muddy water entering will have to move against gravity. Hence the cooling arrangement as per the present invention apart from providing enhanced cooling efficiency for the CVT system, also prevents entry of dust and muddy water, thereby leading to better durability of the CVT system parts especially the V-belt and therefore results in reduced running costs.
Fig. 5 shows the flow path for cooling air to cool down the CVT V belt and the clutch assembly.
Fig. 6 shows the air exit 13 in the transmission cover. It comprises of plurality of
openings for the hot air exit. ~~ "

WE CLAIM:
1. A method for cooling continuous variable transmission system of a
vehicle comprising of:
a cooling air inlet, through which atmospheric air is taken inside the continuous variable transmission system, wherein the said cooling air inlet is formed on an upper end of the transmission case such that the fan is inside the transmission case and the air inlet is on the transmission case;
2. A cooling air intake structure as claimed in claim 1, wherein the cooling air
inlet comprises of an air filter which is disposed on the transmission case.
3. The continuous variable transmission cooling system as claimed in claim 1,
wherein the air inlet guides the inlet air to the centre of the fan and the fan spreads the incoming air in peripheral direction.
4. A hot air outlet structure for a V-Belt drive continuously variable
transmission for a vehicle wherein the hot air outlet structure has a curved surface with plurality of holes for guiding the coming cooling air from the air inlet to the outer atmosphere.