TECHNICAL FIELD
[0001] This application is a divisional of Indian Patent application number 201641022474 filed on June 30th 2016.
[0002] The present subject matter relates generally to an internal combustion 5 engine. More particularly, the present subject matter relates to a forced air cooling system employed to cool the internal combustion engine.
BACKGROUND
[0003] An internal combustion (IC) engine converts thermal energy obtained from burning of a fuel with air into mechanical energy, which can be employed to 10 do a wide variety of mechanical work. It is used to provide motive force for movement of an automobile. The main parts of the IC engine include a cylinder head, a reciprocating piston on a cylinder block and a connecting rod which connects the piston to the reciprocating crankshaft. During operation of the IC engine, the burning of fuel and oxidizer occurs in a combustion chamber 15 ■ interposed between the cylinder head and cylinder block and transfers mechanical energy to the reciprocating piston. This operation generates lot. of thermal energy in and around the cylinder head and cylinder block. This thermal energy increases the temperature around cylinder head and cylinder block and the atmospheric air surrounding it. Hence, it is necessary to cool the cylinder head, cylinder block, its 20 associated components and the surrounding air. In automobiles such as a two wheeled vehicle wherein the IC engine is swingably supported towards the rearward direction of the vehicle and permitting a step-through structure in the front, a body surrounds the IC engine, and the IC engine is completely enclosed within the body parts and vehicular components. Hence, for such two wheeled 25 vehicles, it is necessary to employ additional forced air cooling system for cooling the IC engine. Normally, such forced cooling system comprises a cooling fan which is integrally connected to the crankshaft, and the cooling fan forces air flow through a shroud surrounding the IC engine. IC engine layout is very critical for locating and mounting of the cooling fan. Conventionally in such two wheeled 30 vehicles, since a transmission system is located towards left side of the vehicle

direction, the cooling fan can be integrally connected to the crankshaft on the right side. But due to additional engine components, layout constraints, accommodating transmission related elements and IC engine design requirements, it always not possible to mount the cooling fan on the right side of the vehicle. The present 5 subject matter proposes to mount the cooling fan in a direction opposite to that of the hot zones in the IC engine (such as to cool a spark plug). This additionally requires innovative design to streamline the cooling system to ensure efficient cooling. Hence, effective shroud design is also desirable. Thus to provide effective cooling and address above discussed problems, a modified and efficient 10 forced air cooling system is proposed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The detailed description is described with reference to the accompanying figures. The same numbers are used throughout the drawings to reference like features and components.
15 [0005] Fig. 1. illustrates the side view, of a two wheeled vehicle employing an embodiment of the present subject matter
[0006] Fig. 2a. illustrates the side view of the internal combustion (IC) engine employing the forced air cooling system according to the embodiment of the present subject matter.
20 [0007] Fig. 2b. illustrates the isometric rearward view of the IC engine and the according to the embodiment of the present subject matter.
[0008] Fig. 3. illustrates an exploded view of the forced air cooling system mounted on the IC engine according to the embodiment of the present subject matter.
25 [0009] Fig. 4a. illustrates the cross-sectional view of the IC engine showing the cooling fan and shroud assembly and the attachment of the cooling fan according to the embodiment of the present subject matter.

[00010] Fig. 4b. illustrates the cross-sectional view (Y-Y) of the cylinder block and cylinder head of the IC engine along with the shroud assembly according to the embodiment of the present subject matter.
[00011] Fig. 5a. illustrates the cross-sectional view (Y-Y) of the cylinder block 5 and cylinder head of the IC engine along with the forced air cooling system and the air flow within the forced air cooling system according to the embodiment of the present subject matter.
[00012] Fig. 5b. illustrates the cross-sectional view (Z-Z) of the cylinder head and cylinder block enclosed by the forced air cooling system along with the air flow 10 according to the embodiment of the present subject matter.
DETAILED DESCRIPTION [00013] Various features and embodiments of the present subject matter here will be discernible from the following further description thereof, set out hereunder. According to an embodiment, an internal combustion engine (IC) described here
15 operates in four cycles. Such an IC engine is installed in a step through- type two wheeled vehicle. It is contemplated that the concepts of the present invention may be applied to other types of vehicles such as a three-wheeled vehicle wherein the IC engine is enclosed within the spirit and scope of this invention. Further "front" and "rear", and "left" and "right" referred to in the ensuing description of the
20 illustrated embodiment refer to front and rear, and left and right directions as seen from a rear portion of the IC engine and looking forward. The detailed explanation of the constitution of parts other than the present subject matter which constitutes an essential part has been omitted at suitable places.
[00014] The IC engine comprises of a cylinder head, a reciprocating piston inside 25 a cylinder block located below the cylinder head, a rotatable crankshaft to transfer mechanical energy to the transmission system and a connecting rod transferring energy imparted to the reciprocating piston to the rotatable crankshaft. During operation of the IC engine, the burning of air fuel mixture occurs in a combustion chamber interposed between the cylinder head and cylinder block. This operation

generates lot of thermal energy in and around the cylinder head and cylinder block. This thermal energy increases the temperature of the-cylinder block, the cylinder head and the atmospheric air surrounding it. If this thermal energy is not dissipated, it may result in cylinder block and cylinder head failure. Additionally, 5 due to high temperatures, the film of the lubricating oil inside the cylinder block may get oxidized, thus producing carbon deposits on the internal surface of the cylinder block. This may result in seizure of the reciprocating piston. Also, large temperature differences may lead to a distortion of the IC engine components due to the thermal stresses which are set up. It is also seen that higher temperatures 10 results in lower volumetric efficiency of the IC engine. Hence, it is necessary to cool the cylinder block, the cylinder head, its associated components and the surrounding air through a cooling system.
[00015] Cylinder head and cylinder block has critical heat zones where the temperature around these zones is greater than its surrounding areas. Such critical
15 heat zone areas include zone around the spark plug and around the exhaust pipe connection. Most of the thermal energy generated in the combustion chamber is expelled in the form of hot exhaust gases. The exhaust gases are expelled through the exhaust pipe, hence the zone around exhaust gas pipe connection has greater temperatures and this thermal energy should be removed efficiently. It is also seen
20 that, part of the thermal energy generated in the combustion chamber is radiated away through the spark plug. Hence, the zone around the area of the cylinder head where spark plug is connected also has substantially greater temperature than the rest of the heat zones around the cylinder head. It is important that the zone around the exhaust gas exit is cooled effectively as it may result in melting the
25 connections and lead to distortion. Additionally the temperature at the tip of the spark plug is a very important parameter to measure the life of the spark plug and control of ignition inside the combustion chamber. Increased temperatures affects the fouling characteristics on the spark plug tip, and also cause pre-ignition or engine knocking. Even if, the spark plug is replaced by fuel injector, proper and
30 efficient cooling of fuel injector is required as increased temperatures can

suppress generating of the vapor lock in the fuel supplied to the fuel injector, which decreases combustion efficiency.
[00016] Generally a forced air cooling system is used to perform engine cooling. In forced air cooling systems, atmospheric air is drawn inside the cooling system 5 from the outer atmosphere through an inlet by using a cooling fan. The rotation of the cooling fan is integrated to the rotation of the crankshaft. A shroud surrounding the cylinder head, cylinder block and the IC engine to enable atmospheric air circulation, and thereby cooling the all the components. Hence, the heat generated due to combustion will be conducted to the fins and when the
10 air flows over the fins, heat will be dissipated to air. Shroud design is critical as they not only create an air path to guide the air flow while cooling, but also help in efficient performance of cooling system through suitable shroud shape and design. Shroud geometry design is critical to getting better guidance over its inner surfaces and one can enhance the design to obtain maximum utilization of cooling
15 capacity of flowing air. The shroud design also enables variation of parameters of air flow rate and air velocity as extreme care must be taken to ensure the IC engine is cooled at all conditions of operations.
[00017] Typically in some two wheeled vehicles, such as a straddle-type vehicle (also called motorcycle) the IC engine is mounted forwardly and is exposed to the
20 outside atmospheric air. In such an IC engine arrangement, the IC engine is at least partially cooled by adopting natural air cooling systems. Since the IC engine in the straddle type vehicle is mounted forwardly, it typically has some end-transmission means such as a chain drive and sprocket to transfer the driving force of the IC engine to the rear wheel of the two wheeled vehicle. Hence, such IC
25 engines usually have a stepped transmission system such as that of constant mesh gear transmission system having plurality of gear shifts to change speed ratios based on power and torque requirements. The gear shifts are either manually shifted by the rider or automatically shifted as in an automated manual transmission (AMT) system. Such straddle type vehicles have advantages of
30 increased power output, greater mechanical efficiency and improved fuel

efficiency. In other types of two wheeled vehicles, such as a step-through type vehicle (also called a scooter) the IC engine is usually located towards the-rearward portion of the vehicle below the seat assembly and is swingably supported by rear suspension system and geared to the rear wheel of the two 5 wheeled vehicle. The IC engine usually has an automatic continuously variable transmission (CVT) system located leftward of the two wheeled vehicle which can continuously change the gear ratios to offer a continuous range of torque and power outputs. But CVT systems have a disadvantage of lower efficiency compared to gear shift mechanism, frequent servicing and shorter life of CVT
10 components and lesser mileage. The step-through type vehicle also generally have two side body covers placed on either side of the frame surrounding the IC engine to make the vehicle more attractive. However, such body covers may have a detrimental effect on cooling air. flow, both to the IC engine and to other . . components. The area around the cylinder head and cylinder block of such IC
15 engines are enclosed and are heated up during their operation. Since, proper air circulation is lacking around the enclosed cylinder block, such IC engines are typically cooled by employing forced air cooling system covering the IC engine.
[00018] Step-through vehicles provides various advantages over straddle-type vehicles such as easier to balance and good control with better operability in
20 heavy, stop and go driving in congested areas. The IC engine in step-through vehicle is disposed low and towards the rear of the "two wheeled vehicle and provides a lower center of gravity making it easier to balance and control giving it better rurnability and maneuverability. Such step-through type vehicles are also lighter in weight as compared to corresponding straddle-type vehicles. They also
25 have built-in storage below the seat assembly and on the floorboard between and front of the legs. The rider can just place their feet on the floorboard and sit upright avoiding the need to sit astride the vehicle. Hence, it is desirable to accommodate the IC engine used in the straddle-type vehicle in the step-through type vehicle with an AMT system instead a CVT system. This would provide the
30 combined advantages of IC engine used in straddle type vehicle such as increased

power output, greater mechanical efficiency and improved fuel efficiency with the advantages of the step-through type vehicle highlighted above.
[00019] In IC engine of such a two wheeled vehicle as described above, the layout of the engine is a very important criterion as space availability to accommodate
5 various elements is constrained due to the small size of the IC engine. There are various sub systems which form a part of the overall working of the IC engine. Such systems include transmission system, lubrication system, electrically operated actuators and sensors etc. To accommodate all these systems inside the IC engine layout is difficult and there may arise situations where the
10 accommodating the cooling system becomes challenging when the other system are disposed within. Since, cooling fan needs to be integrally attached to the crankshaft and needs to draw cooling air inside the shroud surrounding the IC engine, the design of such a cooling system is important as it can be accommodated on IC engines having specific engine layouts.
15 [00020] In the IC engine layout for the above two wheeled vehicle, the gear transmission system such as clutch system and gear shift mechanism is mounted rightward of the crankshaft and located right of the crankcase and a magneto assembly is mounted leftward of the crankshaft arid located left of the crankcase. The clutch system and gear shift mechanism control are accompanied by ancillary
20 mechanisms to operate the clutch engagement/ disengagement and plurality of gear shifts to control the torque at the output which are also disposed on the right side of the crankcase. The gear transmission system can also be an AMT system, wherein the AMT system performs manual gear shifts automatically. This system eliminates the need of mechanical actuation of a clutch lever by the driver and
25 eliminating the need to shift the gears manually. It uses various sensors, actuators, motors and a controller unit to continuously control the operation of the clutch and manual gear based on various inputs received such as engine speed, gear position, clutch position, throttle position and vehicle speed. These actuators and motors also need to be accommodated on the right side as the clutch system and
30 gear shift mechanism control is located on the right side. Hence, such an engine

layout prevents additional components being accommodated on the right side of the crankcase such as the cooling fan and shroud assembly for the forced air cooling system required for the step-through type vehicle.
[00021] Other essential components are disposed inside the engine thus defining
5 the engine layout wherein, the starter motor is operably coupled to the rightward side of the crankshaft. A sprocket integrally attached to the gear transmission system of the IC engine is disposed leftward of the crankcase through which power output is transmitted to the rear wheel by means of a chain drive. A kick-starter mechanism is also operably connected to the gear transmission system and
10 disposed below the sprocket on the left side of the crankcase. In such an IC engine layout, the spark plug is constrained to be located on the right side of the cylinder head surface. It is difficult to accommodate the spark plug in any other location in the cylinder block as, the cam chain and a hollow chamber inside on which the cam chain is disposed is located on the left side of the cylinder block.
15 Additionally the layout of the camshaft, valves and rocker arm needs to be changed inside the cylinder head and the combustion chamber redesigned if the spark plug position were to be accommodated in any other location. Since, spark plug zone and exhaust exit are critical heat zones that need to be cooled efficiently, the forced air cooling system is required that can be mounted within
20 such an IC engine layout as described above and cool the spark plug and exhaust exit zone effectively. Such forced air cooling system essentially requires innovative design of shroud assembly to facilitate collection and guiding of atmospheric air flowing in the interior portions of the shroud assembly.
[00022] Due to the above problems in using the forced air cooling system to cool 25 the cylinder block and cylinder head in such IC engine layout, the present subject matter aims to address the above drawbacks by providing a cooling system wherein the cooling fan is fixedly mounted on the crankshaft of the internal combustion engine in a layout where magneto is located on the left side and spark plug to be cooled is provided on the right side. To achieve this aim, the solution 30 proposed is simple in construction, reliable and effective in operation.

[00023] Further, the present subject matter aims to improve cooling system effectiveness by directing air towards critical cooling zones (spark plug zone and exhaust pipe zone) in the cylinder head and cylinder block by proposing a new innovative shroud assembly to direct air to the critical hot zones. A new shroud 5 assembly is designed to ensure effective and streamlined flow of air circulating around the IC engine and guide air to critical hot zones and increase the flow rate around the critical hot zones with least changes in shroud dimensions.
[00024] With the above design changes, the following advantages can be obtained such as simple in construction, improved air circulation in shroud, avoiding use of 10 additional elements such as deflectors, avoid use of additional brackets, and easy to remove and mount giving rise to improved serviceability.
[00025] According to the present subject matter to attain the above mentioned objectives, a first characteristic of the present invention is a two wheeled vehicle comprising: a frame assembly, extending from a front portion to a rear portion
15 along a longitudinal axis; an IC engine swingably connected to the rear portion of the frame assembly, said IC engine comprising: a crankcase extending rightward and leftward in a lateral direction of the longitudinal axis; a transmission assembly disposed on the rightward side of the crankcase; a cylinder block attached to the crankcase, and said cylinder block having a cylinder head disposed above it, said
20 assembly of cylinder block and cylinder head forming a cylinder unit; said cylinder unit comprising a first face facing the rightward side of the crankcase, a second face adjacent to the first face and facing a upward side of the crankcase, a third face adjacent to the second face and facing the leftward side of the crankcase, and a fourth face adjacent to the third face and facing a bottom side of
25 the crankcase; a spark plug mounted on the first face of the cylinder unit; an intake manifold attached to the second face of the cylinder unit; wherein, a cooling fan is operably attached to the crankcase , and said cooling fan disposed on the leftward side of the crankcase; a shroud assembly is disposed on the IC engine to cover at least a portion of said IC engine, the cooling fan and the
30 cylinder unit including the spark plug , and said shroud assembly comprising: a

cylinder unit shroud part disposed to cover at least a portion of the cylinder unit to form an first air path between the cylinder unit and the cylinder unit shroud part, and said first air path capable of capable of directing air to the spark plug disposed on the first face, and an air introduction part enclosing the cooling fan 5 and capable of directing air to the cylinder unit shroud part.
[00026] A second characteristic of the present invention is a two wheeled vehicle characterized in that, said first air path comprising: a collection portion configured to have a gradually increasing cross sectional profile as viewed from the top view of the cylinder unit; a curved portion disposed downstream of the collection 10 . portion, said curved portion configured to have a cross sectional profile to follow a circular trajectory towards the spark plug as viewed from the top view of the cylinder unit; and a constricted portion disposed downstream of the curved portion, said constricted portion configured to have a cross sectional profile sharply curved inwards as viewed from the top view of the cylinder unit.
15 [00027] In addition to the first characteristic, a third characteristic of the present invention is a two wheeled vehicle wherein, the air introduction part comprises: an inner fan shroud connected to the crankcase disposed on the leftward portion of the crankcase extending till the cylinder unit shroud part; an outer fan shroud having a matching profile as the inner fan shroud, and configured to mate
20 perfectly with the inner fan shroud to form a space therein, said outer fan shroud comprising a grill portion to permit access to said space; said cooling fan enclosed in the space formed between the inner fan shroud and outer fan shroud and capable of drawing air through the grill portion on operation of said IC engine; and a second air path formed in the first space between the inner fan shroud and
25 outer fan shroud to direct the air towards the cylinder unit shroud part.
[00028] In addition to the first characteristic, a fourth characteristic of the present invention is a two wheeled vehicle wherein, the cylinder unit shroud part further comprising: a front shroud arranged to cover the second face of the cylinder unit, and said front shroud comprising a mouth to receive the air from the air 30 introduction part; a right-hand shroud arranged to cover the first face of the

cylinder unit including the spark plug such that the junction of attachment of the front shroud to the right-hand shroud forms the intake manifold opening and the spark-plug opening is disposed on the right-hand shroud; and a left-hand shroud arranged to cover the third face of the cylinder unit such that the junction of the 5 attachment of the right-hand shroud to the left-hand shroud forms the exhaust opening.
[00029] In addition to the first characteristic, a fifth characteristic of the present invention is a two wheeled vehicle wherein, the left-hand shroud comprises an hot-air exit, said hot-air exit configured to direct the air to exit in a direction 10 perpendicular to the third face of the cylinder unit and below the IC engine.
[00030] In addition to the second characteristic, a sixth characteristic of the present invention is a two wheeled vehicle wherein, the collection portion comprises a mouth to receive the air from the air introduction part, said collection portion is disposed over the second face of the cylinder unit, and having the 15 gradually increasing cross sectional profile extending from the mouth to the intake manifold..
[00031] In addition to the second characteristic, a sixth characteristic of the present invention is a two wheeled vehicle wherein, the curved portion is disposed over the second face of the cylinder unit and downstream of the collection portion,
20 said curved portion having the cross sectional profile to follow a circular trajectory extending till the edge of the junction between the second face and first face, and the said cross sectional profile having the circular trajectory so shaped to have the cylinder unit shroud part at the beginning of the curved portion to be greater than the clearance between the surface of the cylinder unit and the cylinder
25 unit shroud part at the end of the curved portion as viewed from the top view of the cylinder unit.
[00032] In addition to the second characteristic, a seventh characteristic of the present invention is a two wheeled vehicle wherein, the constricted portion is disposed over the first face and downstream of the curved portion to direct air to 30 the spark plug mounted on the first face of the cylinder unit.

[00033] In addition to the second characteristic, a eighth characteristic of the present invention, is a two wheeled vehicle wherein, the first air path further comprises a narrow portion disposed downstream of the constricted portion beyond the spark plug and disposed over the first face, said narrow portion 5 having a cross sectional profile gently curved inwards to have the clearance between the first face of the cylinder unit and the cylinder unit shroud part at the lowest point to be lesser than the width of the mouth of the collection portion as viewed from the top view of the cylinder unit.
[00034] In addition to the second characteristic, a sixth characteristic of the 10 present invention is a two wheeled vehicle wherein, the lower part of the cylinder unit shroud part has a profile directed inwards as compared to the upper part of the cylinder unit shroud part to have the clearance between the second face of the cylinder unit in the upper part to be greater than the lower part as viewed from a front view of the second face of the cylinder unit.
15 [00035] The present subject matter along with all the accompanying embodiments and their other advantages would be described in greater detail in conjunction with the figures in the following paragraphs.
[00036] Fig. 1 illustrates a two wheeled vehicle, having an IC engine (101) having an AMT system according to one embodiment of the present subject matter. The
20 two wheeled vehicle is a step through vehicle with an IC engine (101) connected below a frame assembly (150). The frame assembly (150) comprises of a head tube (102), a down tube (107), a step-through through structure (117), a pair of side frame tubes (109) (only one shown), and a swing arm assembly. The head tube (102) supports a steering shaft (122) with two brackets - upper bracket (not
25 shown) and lower bracket (not shown) at each end. Two telescopic front suspension (121) is attached to the lower bracket (not shown) on which is supported the front wheel (119). The upper portion of the front wheel (119) is covered by a front fender (103) mounted to the lower portion of the steering shaft (122). A handlebar assembly (124) is fixed to steering shaft (122) on the upper
30 portion of the upper bracket (not shown) and can rotate to both sides. The

handlebar assembly (124) comprises of a visor assembly which encloses the handlebar (106), mirror assembly (105), instrument cluster (not shown) and a headlight (104). The down tube (107) extends downwardly from an upper portion of me head pipe (102) and joins the step-through structure (117). The pair of side
5 frame tubes (109) (only one shown) extends upwardly and rearwardly forming a
substantially horizontal direction from the step-through structure (117) as seen
from the side view of the two wheeled vehicle. A plurality of cross brackets (not
shown) is secured in between the pair of side-tubes (109) to support vehicular
attachments including a utility box (not shown), a seat (108), a pillion hand-rest
10 (118) and a fuel tank assembly (not shown). A left and right rear swing arm
bracket (not shown) is pivoted on the frame assembly (150) at the rear of the step-
through structure (117), and supports a swing arm assembly. The swing arm
assembly comprises of the left and right swing arms (115) (only one.shown)
pivoted to the left and right rear swing arm brackets (not shown), and is capable of
15 swinging vertically about the pivot and supported through two rear wheel |
suspensions (111) arranged of the rear of the swing arm assembly. The IC engine j
(101) is mounted between a front engine mounting cross tube (not shown) and a j
rear engine mounting cross tube (125) such that the IC engine (101) is swingably |
supported on the swing arm assembly. The rear wheel (113) is connected to rear j
20 end of the swing arm assembly and configured to rotate by the driving force of the |
IC engine (101) transmitted through a chain drive (not shown) from the IC engine j
(101). A rear fender (110) is covering at least a portion of the rear wheel (113)
and it is positioned below the fuel tank (not shown). ;
[00037] Fig. 2a illustrates the side view of the IC engine (101). The IC engine
25 (101) is made up of a cylinder head (201), cylinder block (202) and crankcase (203). The cylinder head (201) and the cylinder block (202) when assembled form an cylinder unit (220) comprising four faces around which the forced air cooling system is enclosed. The four faces of the cylinder unit (220) are the first face (220c) facing rightward, second face (220d) facing upward, third face (220b)
30 facing leftward, and the forth face (220e) facing downward of the IC engine riOll. The crankcase is made up of left-hand crankcase (203a) (hereafter LH

crankcase) and right-hand crankcase (203b) (hereafter RH crankcase). The IC engine (101) also comprises of an magneto assembly (401) which functions as a magneto coil assembly during operation to recharge a battery. The IC engine (101) also has a sprocket (204) disposed outside of the LH crankcase (203a) and 5 is fixed to an output shaft (not shown) inside and capable of rotation when the IC engine (101) is in operation. The IC engine (101) also comprises a kick-starter system which when actuated by the kick-lever (205) helps in cranking the IC engine (101) during start. The forced air cooling system is disposed on the LH crankcase (203a) located next to the sprocket (204) and is capable of drawing air 10 inside A part of the forced air cooling system (the grill cover 304a) is also exposed to the atmosphere as seen from the two wheeled vehicle side view (see Fig. 1) to permit effective entry of atmospheric air.
[00038] Fig. 2b. illustrates the isometric rearward view of the IC engine (101) and the forced air cooling system. The forced air cooling system according to the 15 embodiment of the present subject matter is shown, arranged to cover a part of the IC engine (101). One embodiment the IC engine (101) uses a transmission assembly (250) such as an AMT system. The IC engine (101) having transmission assembly (250) comprises of a clutch actuation system (209), a gear actuation system (209), a clutch sensor (210), a magneto sensor pulsar coil (211), a gear 20 sensor (not shown), a throttle sensor (not shown) located on the throttle body (not
shown) and a vehicle speed measuring sensor (212). The clutch actuation system , (208) is operably connected such that, when it is powered, it engages or disengages a clutch (not shown). The clutch sensor (210) comprises of a sensor that detects the instantaneous clutch position and sends a signal to a controller unit 25 (not shown). The controller unit (not shown) in turn based on such input from the
clutch sensor (210) controls the clutch actuation motor (not shown). Additionally, there is a mechanically operated clutch lever (not shown) which is provided for safety, which can be operated by the driver incase the clutch actuation system (208) fails. The gear actuation system also comprises of a gear actuation motor 30 (209), which is connected to a gear-shifting cam (not shown). The gear sensor (not shown) comprises of a sensor that detects the instantaneous gear position and

sends a signal to a controller unit (not shown). The controller unit (not shown) in turn based on such input from the gear sensor (not shown) controls the gear actuation motor (209) and hence real time gear shifts take place in the transmission system. The AMT system used is a synchronous constant mesh 5-5 speed gear box.
[00039] Fig. 3 illustrates the exploded view of the forced air cooling system and a cooling fan (306) mounted on the IC engine (101). In this embodiment the forced air. cooling system comprises of an air introduction part (420) and a cylinder unit shroud part (410). The air introduction part (420) encloses the cooling fan (306)
10 and draws air from the atmosphere and introduces it to the cylinder unit shroud part (410) which circulates the air around the spark plug (404) and exhaust pipe zone (202a). The air introduction part (420) comprises an inner fan shroud (305), and an outer fan shroud (304). The cylinder unit shroud part, (410) comprises a front shroud (302), a left-hand shroud (hereafter LH shroud) (303) and a right-
15 hand shroud (hereafter RH shroud) (301) covering the cylinder unit (220) forming a first air path (430) between the cylinder unit (220) faces. The inner fan shroud' (305) is mounted on the IC engine (101) through fasteners mounted through bosses present on the LH crankcase 203a and inner fan shroud 305 (see 305a, 305b and 305c). The inner fan shroud (305) acts as a cover over the internal
20 components of the IC engine (101) supported by the LH crankcase (203a). The inner fan shroud (305) has a large central opening (see 305d) towards its base to accommodate the outer rotor of a magneto assembly (401) inside the central opening. The assembly is configured such that, when the inner fan shroud (305) is mounted on the LH crankcase (203a), the flat radial surface of the outer rotor of
25 the magneto assembly (401) is just exposed outside the inner fan shroud (305). During assembly of the IC engine (101), the inner fan shroud (305) is mounted on the LH crankcase (203a) which acts as a cover to other parts of IC engine (101) and encloses them leaving a small part of the crankshaft (not shown) exposed. The magneto assembly (401) is subsequently mounted on the crankshaft (not shown)
30 through the large central opening (305d). The outer rotor of the magneto assembly

(401) comprises plurality of holes with internally tapped threads (see 401a) which are used to mount the cooling fan (306) on it.
[00040] The outer fan shroud (301) has a profile being a mirror image of the inner fan shroud (305) and configxired to cover the inner fan shroud (305) so that they
5 mate perfectly. This connection is achieved by bringing together both and securing the outer fan shroud (304) by fasteners near its base and by providing snap-fit connection towards the upper portions of the outer fan shroud (301) and inner fan shroud (305). The outer fan shroud (301) at its lower portion is modified to have a circular raised projected area with a grill cover (304a) and a plurality of
10 boss portions (304b) disposed around its outer periphery. The circular raised projected area (304a) has a space formed on its inner periphery so as to accommodate the cooling fan (306) completely enclosing it. The plurality of boss portions (see 304b and 304c) which are distributed equidistant to each other match exactly with the corresponding boss portions (see 305a and 305b) on the
15 inner fan shroud (305). Hence, the outer fan shroud (304) and inner fan shroud (305) abut perfectly and can be attached using fastening means such as fasteners. When covered, me space between me outer fan shroud (304) and the inner fan
shroud (305) provide a second air path (304d) to guide the atmospheric air towards the upper portions of the shroud assembly near the cylinder block (202) 20 and cylinder head (201). The gentle curved shape of the second air path (see 304d) ensures smooth and turbulent free air flow (402) towards the upper portions of the shroud assembly and directs the air flow without any loss in velocity; the ' air path (304d) ensures air recirculation and prevents air stagnation. The grill cover (304a) provides a passage to draw the atmospheric air inside when the 25 cooling fan (306) is in operation. The grill cover (304a) also acts as a protective cover, preventing atmospheric contaminants such as water, mud, stones and other particles from entering the interior portions of the forced cooling system and cause damage to the components within it. Additionally, the opening has an outer strip of cone (304e) projecting radially throughout the outer circumferential edge 30 of the opening which further aids in prevention of entry of water, mud, and stones. As seen in Fig. 1, The IC engine (101) is disposed rearward of the two wheeled

vehicle such that, the opening with the part of the grill cover (304a) of the outer fan shroud (304) is exposed to outside atmosphere to permit intake of atmospheric • air inside the air introduction part (420).
[00041] In one embodiment, the cooling fan (306) is designed to be of centrifugal 5 type and comprises a central hub (306b), plurality of twisted vanes (306a) and a back-plate (306c) on which the central hub (306b) and plurality of twisted guide vanes (306a) are attached. The central hub (306b) has plurality of holes disposed on its rear end which is used to mount the cooling fan (306) on the outer rotor of the magneto assembly (401) by using fastening means like fasteners (see 401a). 10 The back-plate (306c) also forms part of the rear end of the cooling fan (306) to which the central hub (306b) is attached. The plurality of twisted guide vanes (306a) is disposed radially and equidistant around the outer portion of the back-plate (306c). The guide vanes (306a) are twisted such that, atmospheric air is drawn in due to pressure difference near the central hub (306b) and due to 15 centrifugal force is pushed towards the outer parts of the cooling fan (306) which is received by the twisted guide vanes (306a). The guide vanes (306a) then direct the air towards the cylinder unit shroud part (410) by joining the air path. [00042] Fig. 4a illustrates the cross-sectional view of the IC engine (101) showing the air introduction part (420), the cylinder unit shroud part (410) and the 20 attachment of the cooling fan (306) to the magneto assembly (401). The air flow (402) from the air path enters the cylinder unit shroud part (410) and is received by the front shroud (302). As highlighted in the preceding paragraphs, the air flow (402) is directed tangentially to the front shroud (302) due to the gentle curved shape of air path (see 304d). The point at which the air path (see 304d) meets the 25 front shroud (302) is located substantially adjacent to the second face (220d) of the cylinder unit (220) (see Fig. 4b). This design is essential to enable free entry of atmospheric air with no restriction. If the location is disposed towards the cylinder head (201), the restriction due to a intake manifold (212) would disrupt the air flow will not be able to obtain a proper turbulent free air flow.

[00043] The front shroud (302) is disposed to cover the second face (220d) of the
cylinder unit (220) and has a mouth (302a) to receive the air flow (402) from the
air introduction part (420) to enter the first air path (430). The front shroud (302)
after receiving the air flow (402) directs it towards the RH shroud (301). The front
5 shroud (302) having the first air path (430) covering the second face (220d) has a
profile slant and angularly oriented (see 302b) from the mouth (302a) to the
intake pipe (212). The profile is having the gradually increasing cross sectional
. profile (302b) such that the clearance between the second face (220d) of the
cylinder unit (220) and the front shroud (302) to be greater than the width (e) of
10 the mouth (302a) as viewed from the top view of the cylinder unit (220). Hence,
when the narrow mouth (302a) is connected to the broader end (b greater than e) a j
slanting oriented profile (302b) is formed. This profile is designed to collect air and streamline flow so that there is increased flow rate of air when it flows over the spark plug heat zone. Fig. 5a illustrates a collection portion (see 601) within 15 the front shroud (302) formed by this profile. As it can be seen in Fig 3, the junction of front shroud (302) covering the cylinder head (201) is restricted by the presence of intake pipe (212), hence the broader portion at the end is positioned such that, the collection portion (601) formed by the profile causes a reliving flow and permits more air to enter the system (see Fig. 5a). Further, the front shroud 20 (302) performs two other functions, to permit ease of assembly during manufacturing connecting the air introduction part (420) with the RH shroud (301) by having a transit part between them. The second function of the front shroud (302) is to prevent the entry of air flow into the LH shroud (303) (i.e. from flowing over the third face 220b) by having a restriction (405) (see Fig. 4b) 25 positioned in close proximity to the entry to LH shroud (303). This is essential as the primary objective of the forced air cooling system is to extract thermal energy from high heat zones like spark plug zone (404) and exhaust pipe zone (202a). Any deviation of the straight air flow towards the third face (220b) at the entry of air flow near the mouth (302a) would decrease the volume and velocity of air 30 flowing over the spark plug zone (404) and exhaust pipe zone (202a), which is undesirable. Additionally, the third face (220b) comprises a cam chain chamber

and lubrication oil circuit path which enhances heat dissipation. Hence, the restriction (405) prevents the air flow from entering the LH shroud (303) and almost the entire air flow proceeds towards the RH shroud (301).
[00044] The front shroud (302) is connected to the RH shroud (301) by 5 connecting the bosses disposed on both the front shroud (302) and the RH shroud (301). By joining the bosses a intake manifold opening (410a) is provided to accommodate the inlet manifold (212) coming from a throttle body (not shown). The intake manifold opening (410a) has a circumferential profile is so shaped to match perfectly with the contours of the inlet manifold (212) and prevent any 10 escape of air outside this opening. Further, a rubber gasket can be placed to prevent air escape. The RH shroud (301) covers the remaining portion of the second face (220b) and the third face (220d) of the cylinder unit (220). The corner of the RH shroud (301) is made substantially curved (see 301c) to follow a circular trajectory such that the profile is designed to provide smooth and 15 turbulent free air path and directed towards the first face (220c) and towards the spark plug (404). The circular trajectory of RH shroud (301c) is such that, the RH shroud (301) at the beginning of the curved portion (b) is greater than the clearance between the surface of the cylinder unit (220) and the RH shioud (301) at the end of the curved portion (c) as viewed from the top view of the cylinder 20 unit (220). This forms an exterior protruding bulged portion which is prominently bulged on the upper areas of the RH shroud (301). Fig. 5b illustrates the bulged portion (301c). This bulged portion having the circular trajectory provides increased flow rate of air as it flows over the spark plug area (see 608). The spark plug (404) is located on the first face (220c) between the air flow (402) directed 25 by the RH shroud (301). On the right portion of the cylinder head (201) close to the left edge (see 202c), the RH shroud (301) comprises a constricted portion (see 301d), and having a sharply curved profile which is curving inwards, said constricted portion (301d) so curved so as to deflect and direct air flow (402) towards the spark plug zone (404). This design overcomes a significant drawback JO in prior arts by permitting cost saving, and reduced number of components. In prior arts the shroud design involves use of separate deflectors or baffle plates, but

the present invention utilizes a constriction portion (301d). Further, the narrow constriction between the RH shroud and first face (220c) located just after the constricted portion permits throttling of air (see 603a) to increase air velocity as it flows over the spark plug (404).
5 [00045] Fig. 5a illustrates the cross-sectional view (Y-Y) of the cylinder unit (220) along with the cylinder unit shroud part (410) and the air flow within the cylinder unit shroud part (410) when in operation. With the combination of air collection due to profile of the front shroud (see 601), increased flow rate of air in the bulged portion (see 608), deflection by the constricted portion (see 603) and
10 throttling of air (see 603a) in the area after the constricted portion (301d), effective cooling of spark plug zone (404) can be achieved even when the cooling fan (306) is located in a direction opposite to that of spark plug (404). The RH
shroud (301) has two openings namely, the spark plug opening (301a) which
provides accessibility to the spark plug (404) in case of removal and replacement,
15 and SAI opening (301b) which provides access to insert secondary air injection (SAI) tube (not shown) to the exhaust side of the cylinder head (201).
[00046] Fig. 5b illustrates a cross-sectional view (Z-Z) of the cylinder unit (220) enclosed by the cylinder unit shroud part (410) as viewed from the front towards the third face (220b) of the cylinder unit (220). The curved portion (301c) of the
20 RH shroud (301) is illustrated figuratively along with the air flow. The curved portion of the RH shroud (301c) permits increased flow rate of air (see 608) resulting in circulation of more air towards cylinder block-cylinder head junction. As the cylinder unit shroud part (410) extends to cover the cylinder unit (220), the curved portion (301c) is located predominantly in the cylinder block-cylinder
25 head junction as viewed from the front towards the third face (220b) of the cylinder unit (220) and has a profile which narrows towards bottom of the cylinder unit (see 301e). The profile is such that, the clearance between the second face (220d) of the cylinder unit (220) in the upper part (f) to be greater than the lower part (g) as viewed from a front view of the second face (220d) of the
50 cylinder unit (220). This design is advantageous over cylinder unit shroud part

(410) as increased flow rates can be obtained close to the cylinder head-cylinder block junction (see 608) and lesser flow rates is sufficient to circulate along the bottom of the cylinder block (see 609). In prior arts as in conventional shroud systems, uniform flow throughout the shroud assembly is seen and results in air 5 circulation in zones wherein high air flow rates are not required. Consequently, the zone near the cylinder block-cylinder head junction wherein more flow is required, the desired flow is not obtained. Since, the temperature gradient is higher at the centre as compared to the bottom portions, the bulge permits increased air flow towards the critical zones in the centre such as the spark plug 10 zone and the exhaust pipe zone. Hence, designing the shroud assembly to ensure less flow rate of air at the bottom (see 609) compared to central portion (that is, the cylinder block-cylinder head junction), we can provide targeted cooling towards critical zones.
[00047] The LH shroud (303) covers substantially the front and left-hand portion 15 of the cylinder block (202). The LH shroud (303) and RH shroud (301) is connected at the exhaust pipe zone (see 202a) to form an exhaust opening (410b). The connection is achieved by connecting plurality of large projecting arms (see 301d and 303d) by fasteners such that the exhaust opening (410b) between the arms is formed to permit the exhaust pipe connection. The exhaust opening
20 (410b) also serves additional function of removing excess "hot air accumulated by incoming cold air flow (402). The LH shroud (303) also comprises the hot air exit (303a) which.is a long extended vent opening projected perpendicularly outward from the surface of the LH shroud (303) towards the vehicle bottom. The hot air exit (303a) is sufficiently long to vent out the hot air outside the atmosphere and
25 prevent any hot air from re-circulating back inside the forced air cooling system and also heat the cabin parts of the two wheeled vehicle. One side of the hot air exit (303a) wall is conjoined with the large opening covering the exhaust pipe zone (202a). Additionally a stopper maybe provided projecting outward from the LH shroud (303) to restrict the intake of this hot air back to be re-circulated. Fig.
30 5a and Fig. 5b illustrate the air flow around the zone (see 202a) where the exhaust pipe (206) is connected to the cylinder block (202). The design of the hot air exit

(303a) is substantially below the two wheeled vehicle and helps change the direction of air exiting the cylinder unit shroud part (410). The hot air exit (303a) is also maintained flat to vent out more hot air towards the bottom. This avoids hot air flow towards the cabin area heating up the utility box (not shown).
5 [00048] The RH shroud (301) further downstream beyond the spark plug zone (404) has a narrow portion (604a) whose profile is curved or bulged inwards (see 301f) and forms a continuation of the already narrow profile formed before the spark plug zone (404). It is further curved to reduce the distance between the inner surface of the RH shroud (301) and the first face (220c) to make it narrow and
10 throttle the air flow and increase its velocity before the air flow passes through the exhaust pipe zone 202a (see 604a). This resultant increase in velocity increases the ability to extract heat from the exhaust pipe zone (202a). Further, the portion of air flow which flows through the pathway around the cylinder head (see 610) exits through the left side of the cylinder head (see 606) and flows again through
15 the exhaust pipe zone (see 604b). The narrow pathways provided through the cylinder head (201) further throttles the air flow (see 606). Further, as seen from the front cross sectional view in Fig. 5b, it is seen that, due to the crurved portion (301c),. the resultant air flow has increased velocity at the exhaust pipe zone 202a (see 604c and 604d). The resultant air flows (604a, 604b, 604c and 604d) results
20 in adequate circulation of air around the exhaust pipe zone (202a) to enable improved heat extraction.
[00049] From the foregoing description, it will be appreciated that the present subject matter offers many advantages including those described above. In the forced air cooling system, atmospheric air is drawn in by the cooling fan located
25 on one side of the IC engine and made to cool critical hot zones of the IC engine located opposite sides of the IC engine. The shroud assembly is designed to collect air, throttle air, divert air and increase the flow rate of air to bring the cooling characteristics of the forced air cooling system equal to that of cooling obtained when fan is located in the same side of the IC engine as the critical parts
30 to be cooled. The above forced air cooling system has the advantage of providing

space on that side of the IC engine wherein critical zones of IC engine is located, to accommodate other critical components such as transmission system.
[00050] Many modifications and variations of the present subject matter are possible in the light of above disclosure. Therefore, within the scope of claims of 5 the present subject matter, the present disclosure may be practiced other than as specifically described.

We Claim:
1. A two wheeled vehicle (100) comprising:
a frame assembly (150), extending from a front portion (F) to a rear portion (R) along a longitudinal axis (F-R);
an internal combustion (IC) engine (101) swingably connected to the rear portion (R) of the frame assembly (150), said IC engine (101) comprising:
a crankcase (203) extending rightward and leftward in a lateral direction of the longitudinal axis (F-R);
a transmission assembly (250) disposed on the rightward side of the crankcase (203);
a cylinder block (202) attached to the crankcase (203), and said cylinder block (202) having a cylinder head (201) disposed above it, said assembly of cylinder block (202) and cylinder head (201) forming a cylinder unit (220);
said cylinder unit (220) comprising a first face (220c) facing the rightward side of the crankcase (203), a second face (220d) adjacent to the first face (220c) and facing a upward side of the crankcase (203), a third face (220b) adjacent to the second face (220d) and facing the leftward side of the crankcase (203), and a fourth face (220e) adjacent to the third face (220b) and facing a bottom side of the crankcase (203);
a spark plug (404) mounted on the first face (220c) of the cylinder unit (220); . an intake manifold (212) attached to the second face (220d) of the cylinder unit (220);
a cooling fan (306) is operably attached to the crankcase (203), and said cooling fan (306) disposed on the leftward side of the crankcase (203); and a shroud assembly (300) disposed on the IC engine (101) to cover at least a portion of said IC engine (101), the cooling fan (306) and the cylinder unit (220) including the spark plug (404), and said shroud assembly (220) comprising:

a cylinder unit shroud part (410) disposed to cover at least a portion of the cylinder unit (220) to form an first air path (430) between the cylinder unit (220) and "the cylinder unit shroud part (410), and said first air path (430) capable of capable of directing air to the spark plug (404) disposed on the first face (220c), and an air introduction part (420) enclosing the cooling fan (306) and capable of directing air to the cylinder unit shroud part (410); characterized in that,
said first air path (430) comprising:
a collection portion (601) configured to have a gradually increasing cross sectional profile (302b) as viewed from the top view of the cylinder unit (220);
a curved portion (602) disposed downstream of the collection portion (601), said curved portion (602) configured to have a cross sectional profile to follow a circular trajectory (301c) towards the spark plug (404) as viewed from the top view of the cylinder unit (220); and
a constricted portion (603a) disposed downstream of the curved portion (602), said constricted portion configured to have a cross sectional profile sharply curved inwards (30Id) as viewed from the top view of the cylinder unit (220).
2. A two wheeled vehicle (100) as claimed in claim 1 wherein, the collection portion (601) comprises a mouth (302a) to receive the air from the air introduction part (420), said collection portion (601) is disposed over the second face (220d) of the cylinder unit (220), and having the gradually increasing cross sectional profile (302b) extending from the mouth (302a) to the intake manifold (212).
3. A two wheeled vehicle (100) as claimed in claim 1 wherein, the curved portion (602) is disposed over the second face (220d) of the cylinder unit (220) and downstream of the collection portion (601), said curved portion

(602) having the cross sectional profile to follow a circular trajectory (301c) extending till the edge of the junction between the second face (220d) and first face (220c), and the said cross sectional profile having the circular trajectory (301c) so shaped to have the cylinder unit shroud part (410) at the beginning of the curved portion (b) to be greater than the clearance between the surface of the cylinder unit (220) and the cylinder unit shroud part (410) at the end of the curved portion (c) as viewed from the top view of the cylinder unit (220).
4. A two wheeled vehicle (100) as claimed in claim 1 wherein, the constricted
portion (603) is disposed over the first face (220c) and downstream of the
curved portion to direct air to the spark plug (404) mounted on the first face
(220c) of the cylinder unit (220).
5. A two wheeled vehicle (100) as claimed in claim 1 wherein, the first air path
. (430) further comprises a narrow portion (604a) disposed downstream of the
constricted portion (603) beyond the spark plug (404) and disposed over the first face (220c), said narrow portion (604a) having a cross sectional profile gently curved inwards. (301f) to have the clearance between the first face. (220c) of the cylinder unit (220) and the cylinder unit shroud part (410) at the lowest point (d) to be lesser than the width (e) of the mouth (302a) of the collection portion (601) as viewed from the top view of the cylinder unit (220).
6. A two wheeled vehicle (100) as claimed in claim 1 wherein, the lower part of
the cylinder unit shroud part (410) has a profile directed inwards (301e) as
compared to the upper part of the cylinder unit shroud part (301c) to have the
clearance between the second face (220d) of the cylinder unit (220) in the
upper part (f) to be greater than the lower part (g) as viewed from a front view
of the second face (220d) of the cylinder unit (220). /~