Claims:I/We claim:
1. An engine assembly (110) for a saddle-type vehicle (100), said engine assembly (110) comprising:
a drive shaft (202) functionally connected to a driven wheel (106) of said saddle-type vehicle (100);
a drive sprocket (201) rotatably and circumferentially supported on said drive shaft (202) and a driven sprocket (203) rotatably attached on a portion of said driven wheel (106);
a transmission member (111) rotatably supported between said drive sprocket (201) and said driven sprocket (203),
wherein, said drive sprocket (201) includes an inner face (207i) and an outer face (207o), a stepped projected portion (201e) is formed on said inner face (207i) of said drive sprocket (201).
2. The engine assembly (110) for a saddle-type vehicle (100) as claimed in claim 1, wherein said stepped projected portion (201e) is configured to extend laterally away from said inner face (207i).
3. The engine assembly (110) for a saddle-type vehicle (100) as claimed in claim 1, wherein said drive shaft (202) includes a first end (202OE) configured to receive said drive sprocket (201) and a second end (202ce) disposed opposite to said first end (202OE), said stepped projected portion (201e) is configured to extend away from said first end (202OE) and towards said second end (202ce) in assembled condition.
4. The engine assembly (110) for a saddle-type vehicle (100) as claimed in claim 1, wherein an inner diametrical portion (201ID) of said drive sprocket (201) includes plurality of integrally formed splined structures (201s), said plurality of splined structures (201s) are configured to include drive sprocket chamfering (201c).
5. The engine assembly (110) for a saddle-type vehicle (100) as claimed in claim 1, wherein said drive sprocket (201) includes an outer diametrical portion (201a) comprising plurality of teeth (201t).
6. The engine assembly (110) for a saddle-type vehicle (100) as claimed in claim 1, wherein said inner face (207i) includes an outer diametrical surface (201a) shaped into plurality of teeth (201t).
7. The engine assembly (110) for a saddle-type vehicle (100) as claimed in claim 1, wherein said outer face (207o) is configured to abut against a retainer member (204) disposed on said drive shaft (202).
8. The engine assembly (110) for a saddle-type vehicle (100) as claimed in claim 1, wherein said drive shaft (202) includes a grove (202a), said grove (202a) is disposed at first end (202OE) of said drive shaft (202), said grove is configured to accommodate a retainer member (204).
9. The engine assembly (110) for a saddle-type vehicle (100) as claimed in claim 8, wherein said first end (202OE) is configured with plurality of drive extensions (202b), the plurality of drive extensions (202b) are configured to mate with a plurality of extensions (204a) of said retainer member (204).
10. The engine assembly (110) for a saddle-type vehicle (100) as claimed in claim 1, wherein said drive shaft (202) includes a first end (202OE), said first end includes one or more projections (202d), said one or more projections are configured with drive shaft chamfering (202c).
11. A drive sprocket (201) for an engine assembly (110), said drive sprocket (201) comprising:
an inner face (207i);
an outer face (207o);
an outer diametrical portion (201a), said outer diametrical portion (201a) shaped into outwardly projecting plurality of teeth (201t);
a stepped projected portion (201e) formed on said inner face (207i), said stepped projected portion (201e) is situated at a center portion (SC) of said drive sprocket (201),
said stepped projected portion (201e) includes an inner diametrical surface (201ID), said inner diametrical surface (201ID) is configured to include integrally formed plurality of splined structures (201s).
12. The drive sprocket (201) for an engine assembly (110) as claimed in claim 11, wherein said plurality of splined structures (201s) are projecting inwardly and include drive sprocket chamfering (201c).
13. The drive sprocket (201) for an engine assembly (110) as claimed in claim 11, wherein said stepped projected portion (201e) includes two or more holes (201h) configured to receive two or more mounting members (201m), said two or more holes (201h) include a body diameter D1 mm and an end diameter D2 mm, wherein D1>D2.
14. The drive sprocket (201) for an engine assembly (110) as claimed in claim 13, wherein said end diameter D2 mm is for an end portion (208) of said two or more holes (201h), said end portion (208) is disposed away from a inner face (207i). , Description:TECHNICAL FIELD
[0001] The present subject matter relates generally to an engine assembly of a saddle-type vehicle and more particularly but not exclusively, to a secondary drive for the engine assembly of the saddle type vehicle.
BACKGROUND
[0002] A saddle-type vehicle is powered by an internal combustion engine comprising a crankshaft assembly rotatably supported by a crankcase assembly. Generally, an internal combustion engine for a saddle-type vehicle, for example, a two-wheeled vehicle includes a crankcase assembly divided into two crankcase halves, a crank chamber being defined and formed by the crankcase halves, a crankshaft housed in the crank chamber and a cylinder block connected to the crankcase. A crankshaft is rotatably attached on a crankcase through a pair of rotary bearings each disposed on a left-hand side crankcase and a right-hand side crankcase, a piston slidable in a cylinder bore is connected to a crank pin of the crankshaft through a connecting rod. The crankcase houses the crankshaft assembly, clutch assembly, starter assembly and gearbox assembly and other ancillary systems, which include lubrication system, cooling system and exhaust system, all housed in the main engine body. The crankcase is made of know metals like aluminium.

BRIEF DESCRIPTION OF THE DRAWINGS
[0003] The detailed description of an engine assembly of the present subject matter is described with reference to the accompanying figures. Same numbers are used throughout the drawings to reference like features and components.
[0004] Figure 1 depicts an exemplary left side view of a two-wheeled vehicle, in accordance with an embodiment of the present subject matter.
[0005] Figure 2 illustrates an assembly of a secondary reduction in the transmission system.
[0006] Figure 3 illustrates an exploded view of a drive shaft assembly according to an embodiment of the present invention.
[0007] Figure 4 illustrates a sectional view of the drive shaft assembly taken along a shaft axis MM` as shown in the Figure 2 according to an embodiment of the present invention.
[0008] Figure 5a illustrates a perspective side view of a drive sprocket according to an embodiment of the present invention.
[0009] Figure 5b illustrates a sectional side view of a drive sprocket according to an embodiment of the present invention.
[00010] Figure 5c illustrates an aspect of a hole in the drive shaft for receiving the mounting member.
[00011] Figure 6 illustrates a graphical representation of a comparative study of the pressure stress at the contact area according to the thickness of the drive sprocket.
DETAILED DESCRIPTION
[00012] Generally, a conventional two wheeled vehicle is powered by an internal combustion engine disposed at a lower half of the vehicle. The engine converts chemical energy into mechanical energy by combustion of air-fuel mixture within a combustion chamber of the engine. The engine, among other components, has a cylinder comprising a cylinder head atop or in front of the cylinder and receiving a reciprocating piston from the bottom or the rear. On combustion of the air-fuel mixture, the piston transfers the energy generated during combustion to a crankshaft through a connecting rod thereby driving the crankshaft. In this way, the reciprocatory motion of the piston is converted to rotatory motion of the crankshaft. The crankshaft is housed inside a crankcase beneath or behind the cylinder block. In order to set the vehicle into motion, the power supplied to the crankshaft of the internal combustion engine is carried to a driven wheel of the vehicle, in a controllable way, through a transmission system. The transmission system in the conventional vehicle employs a clutch and a gearbox with plurality of gears, wherein gear shift is achieved manually which enables gears to be selected only in an ascending or descending sequence.
[00013] An engine sprocket is a connecting component between the engine assembly and the driven wheel. It is the final reduction area for torque produced by the engine assembly. Normally, in the two-wheeled vehicle, this arrangement is referred to as secondary drive. The torque produced by the engine is being transmitted to the driven wheel. The torque produced by the engine assembly is multiplied by a gear box. The gear box is connected between a torque generating member and a drive shaft of the engine assembly. The two main components involved in the end to end transmission between the engine assembly and the rear wheel are the engine sprocket and a driven sprocket. Both engine sprocket and the driven sprocket are rotating members. A transmission member is connected between the engine sprocket and the driven sprocket. The secondary reduction is through the engine sprocket, which is functional before the torque is being passed on to the driven wheel.
[00014] Conventionally, drive sprocket also called as the engine sprocket, is mounted using fasteners on the drive shaft. The drive sprocket includes plurality of splined structures. The plurality of splined structures includes an inner diametrical surface of a specific inner diameter, an outer circumferential surface of a specific outer diameter and a particular width. These inner diametrical surfaces and the outer diametrical surface are referred to as female and male portions respectively. Correspondingly, the drive shaft includes male and female portions of plurality of spline respectively, to align with that of the drive sprocket.
[00015] The thickness of the drive sprocket varies for variety of vehicles, depending upon the layout constraints.
[00016] For example, for vehicles producing higher torque output, a drive sprocket of higher thickness is required. In this case, the contact area between the drive sprocket and the drive shaft is subjected to higher load. Therefore, it is desirable to have an improved contact area between the drive sprocket and the drive shaft to minimize the stress on the parts at the interface.
[00017] The torque generated by the engine assembly is transmitted to the driven wheel. The transmission of the torque generated thereto, occurs only when the transmission member is engaged to plurality of teeth on an outer diametrical surface of the drive sprocket. A smooth rotational movement between the transmission member and the plurality of teeth is obtained as a result of the engagement of sprocket with transmission member. Further, the plurality of splined structures present at the centre of the drive sprocket are in contact with the drive shaft. The drive sprocket with higher thickness may put an additional pressure stress on the drive shaft, that may eventually lead to failure of the drive shaft.
[00018] Further, the drive sprocket with higher thickness is not desirable, due to layout constraints in the vehicle. The drive sprocket with higher thickness requires corresponding transmission member with increased thickness, for example, the transmission member may be a chain member. In the two-wheeled vehicles, the transmission member with higher thickness leads to undesirable trade-off if it has to be packaged within in the limited space available in between other neighbouring components. The transmission member with increased thickness as said above is not preferred due to packaging constraints.
[00019] In particular, over a period of time, after the vehicle has reached certain mileage, the plurality of spline on the drive shaft tend to wear out. However, the wear out of the spline on the drive shaft is not a phenomenon that occurs suddenly, the wear out occurs gradually over a period of time, which is typically noticed only when failure of the drive shaft occurs. The failure of the drive shaft is detrimental to the other driving parts of the engine assembly, which in turn affects the overall reliability of the engine assembly.
[00020] To further understand the above stated problem, the vehicle including a clutch system is explained herewith. The clutch is a member that connects/disconnects the transmission with the engine assembly. During vehicle running condition, a clutch lever remains de activated. The deactivated clutch means clutch is not engaged and thereby the drive shaft is engaged with a gear box. The drive shaft is configured to receive power from a particular gear ratio of the gear box and transmit that particular power/torque to the driven wheel. The driven wheel is configured to enable motion of the vehicle.
[00021] Further, whenever a change in the gear ratio is required, for example, change from a lower gear ratio to a higher ratio, the clutch is actuated. The engagement of the clutch through actuation of a clutch lever or the like provides disconnection between the gear box and the engine assembly for a moment. The engine assembly that is disconnected from the gear box has a particular rotational movement of a particular rotation per minute (rpm). The gear box that is disconnected from the engine assembly typically operates at another rpm. The rpm of the gear box is often lesser than the engine rpm. The rotating parts like the engine assembly and the gear box rotate at a certain rpm irrespective of connection between them. In particular, the drive sprocket and the drive shaft of the engine assembly rotate at a particular rpm.
[00022] The clutch once enabled leads to disengagement of the engine assembly with the gear box. The vehicle continues to be in the running state due to particular inertia from the driven wheel of the vehicle. The disconnection of the gear box from the engine assembly does not stop the rotation of the sprocket. The sprocket continues to be in a rotational movement due to the inertia of the rotation of the driven wheel.
[00023] Further, again, in a connected state between the gear box and the engine assembly, after the shift in the gear ratio has been completed, the sprocket has a rotational movement of a higher rpm. The higher rpm of the sprocket is due to the shift in the gear from a lower gear ratio to a higher gear ratio.
[00024] Accordingly, the sprocket includes a continuous rotational movement either at a higher rpm or lower rpm. The sprocket will continue to rotate at X rpm according to the gear ratio received. The rpm of the sprocket may reduce slightly whenever the clutch is activated. After attaining a particular gear ratio by actuation of the clutch, the drive sprocket rotates at an rpm of Y. The Y rpm may be lesser than or greater than X rpm depending upon the gear shift chosen. The sprocket rotates at a zero rpm only when a brake of the vehicle is completely actuated. The direction of rotation of the drive sprocket remains same throughout the operation of the secondary drive.
[00025] As explained above, whenever the gear box is connected, a functional connection exists between the engine assembly, the gear box, the secondary drive and the driven wheel. Further, whenever the clutch is disengaged, the functional connection is completely decoupled. The driven wheel includes a particular rpm and the engine assembly includes a different rpm. The engagement of the driven wheel with the engine assembly, each rotating at different rpms, provides a jerk or an impact load on the drive shaft and particularly at the contact area between the plurality of splined structures of the drive sprocket and the plurality of spine of the drive shaft. The sudden change in the speed of the rotational movement of the rotating parts results in wear out of the plurality of splined structure of the drive sprocket and also results in digging mark on the drive shaft at the contact area.
[00026] Over a period of time, due to wear out of the plurality of spline on the drive shaft, the drive sprocket gets displaced or misaligned from its assembled position on the drive shaft. In a typical layout, the drive sprocket runs over the drive shaft along the axial direction of the drive shaft. The misalignment occurs between the drive sprocket and the driven sprocket and resulting in wobbling of the transmission member takes place. As a result, failure of entire secondary reduction occurs. The vehicle remains completely disconnected from the engine assembly. Such a failure may be detrimental to the rider.
[00027] The wear out of the plurality of splined structures in the drive sprocket and the plurality of spline on the drive shaft results in clearance therebetween. The rotating parts including the drive sprocket and the drive shaft are allowed to rotate in the increased clearance owing to the wear and tear. The rotational movement therebetween results in undesirable noise.
[00028] However, the problem is being perceived as an undesired noise occurred due to rotation of the drive sprocket and the drive shaft in the increased clearance therebetween. The occurring of undesired noise takes place at early stages of wear out of the spline on both the drive shaft and the drive sprocket. A minimum amount of undesired clearance would have already been formed by then. However, the wear out of the drive sprocket and the drive shaft is not noticed until the failure of the rotating parts occur.
[00029] To address the above said problem, the hardness of the drive sprocket may be increased to prevent the wear out of the plurality of splined structures. However, the hardness of the drive sprocket is not desired to be greater than hardness of the drive shaft. The same is not desired to protect the drive shaft from being affected by the drive sprocket. This stems from the fact that the serviceability of the drive sprocket is possible with relative ease, however, the service of the drive shaft is an impossible task or highly cumbersome. The service of the drive shaft involves dismantling of the entire engine assembly. The dismantling of the entire engine assembly is a time consuming and complicated task and adds to cost of service.
[00030] Several attempts have been made in the past to address the aforementioned problem relating to wear out of the drive shaft. One of the attempts involves providing an intermediate member between the drive sprocket and the drive shaft. However, the same is not desired due to increase in cost, complications in assembly and increase in number of parts. Further, such an intermediate member may undergo displacement from its assembled conditions over a period of time.
[00031] Therefore, to address the above explained problems and other problems of known art, an improved drive sprocket is provided according to the present subject-matter.
[00032] An improved drive sprocket includes selectively localized increased thickness as compared to the conventional sprocket. By improving localized thickness of the drive sprocket, the requirement of overall change in the thickness of the transmission member, the chain member is not required. This is because, the thickness of the drive sprocket is not increased uniformly all over the surface of the drive sprocket. Therefore, the portion of the drive sprocket, in particular, an outer diametrical surface which is configured to include plurality of teeth remains same and can receive the transmission member without need for any changes. Therefore, vehicle layout constraints do not hamper or compel any trade-off on the performance and weight of the vehicle. However, the thickness of the drive sprocket is increased at the centre, in particular at and around the contact portion with the drive shaft. This way, the stress level that used to occur at a spot on the drive shaft is being distributed over an increased surface caused by the increased contact area between the drive sprocket and the drive shaft.
[00033] Further, the plurality of splined structures is provided at the centre of the drive sprocket. This plurality of splined structures is chamfered. The chamfering of the plurality of splined structures enable ease of assembly of the drive sprocket and the drive shaft. In an embodiment, the drive shaft includes corresponding chamfer. The chamfering on both the drive sprocket and the drive shaft provides ease of alignment of the plurality of splined structure on the drive sprocket with that of the plurality of spline on the drive shaft. This way, smooth rotation of the drive sprocket and the drive shaft is achieved. Further, due to increased contact surface area, the wear out of the drive shaft is reduced.
[00034] According to an embodiment of the present invention, the drive sprocket is inserted on to the drive shaft with the help of a retainer member. The retainer member is received by a grove created on the drive shaft. The retainer member is configured to include plurality of projections on an inner diametrical surface. These plurality of projections mate with plurality of counterpart projections when the retainer member is being inserted on the drive shaft, during assembly. Further, after rotation of the retainer member on the groove, the retainer member is locked in the groove. When rotating, the plurality of projections in the retainer member are no more aligned with the counterpart projections on the drive shaft. Therefore, the retainer member cannot slip out of the drive shaft after being locked in the groove. The drive sprocket is inserted into the drive shaft prior to insertion of the retainer member. The retainer member includes two or more holes and similar holes are present in the drive sprocket as well. The retainer member is locked to the drive sprocket through two or more mounting members.
[00035] According to an embodiment of the present invention, the one or more holes present in the drive sprocket include different diameters. A portion of the one or more holes configured to receive the one or more mounting members include a predetermined diameter. Whereas, an end portion towards the stepped portion of the drive sprocket includes reduced diameter. This configuration is carried out to provide ‘mistake-proofing’ during assembling. For instance, if the assembly of the drive sprocket is carried out in a random manner, for example, the stepped portion of the drive sprocket is facing the open end of the drive shaft, then the one or more mounting members will never be able to enter the drive sprocket due to presence of the reduced diameter on that side. This way, it is ensured that the drive sprocket is always assembled as desired.
[00036] A butting surface between the retainer member and the drive sprocket defines a sprocket-centre line. It is desirable to always have the sprocket centre line running centrally and longitudinally through the centre of the transmission member. This is achieved to have alignment of the drive sprocket with the driven sprocket. So that, the transmission member rotates along a straight line without any wobbling or inclination. This ensures effective transmission from the secondary reduction.
[00037] The thickness of the drive sprocket at the centre cannot be increased on both sides. If so, the chain contact area, according to the sprocket centre line will undergo shift and accommodating the same in the compact layout of the vehicle becomes difficult.
[00038] The improper rotation of the transmission member may lead to failure of the transmission member.
[00039] The improved drive sprocket according to the present subject matter prevent wear out of the drive shaft and enables ease of assembly of the drive sprocket on the drive shaft along with being able to maintain alignment with the driven sprocket.
[00040] According to an embodiment of the present subject matter, the localized increment in thickness of the drive sprocket is carried out at the centre on one side of the sprocket only. Preferably, the increment in the thickness of the sprocket is carried out on the side facing a closed end of the drive shaft. The closed end of the drive shaft is an end opposite to an open end that is configured to receive the drive sprocket.
[00041] These and other advantages of the present subject matter would be described in greater detail in conjunction with the figures in the following description. The present subject matter is further described with reference to accompanying figures. It should be noted that the description and figures merely illustrate principles of the present subject matter. Various arrangements may be devised that, although not explicitly described or shown herein, encompass the principles of the present subject matter. Moreover, all statements herein reciting principles, aspects, and examples of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof
[00042] Figure 1 depicts an exemplary left side view of a two wheeled vehicle, in accordance with an embodiment of the present subject matter. The vehicle 100 comprises a vehicle frame assembly (not shown) supporting a front wheel 105 and a driven wheel 106. The front wheel 105 and the driven wheel 106 are rotatably supported by a front suspension assembly 108 and a rear suspension assembly 109, respectively. In one embodiment, the driven wheel 106 may be additionally supported by a swing arm 107. Further, the front wheel 105 is steerable by a handle bar assembly 114, which is functionally connected to the front wheel 105 for maneuvering the vehicle. The handlebar assembly 114 is configured to support at least one headlamp assembly 103.
[00043] In the present embodiment, an engine assembly 110 which is basically a power unit of the vehicle is mounted to a front lower portion of the frame structure by means of two or more engine mounting brackets (not shown). The engine assembly 110 is connected to a muffler (not shown in figure) being part of an exhaust system (not shown), which is capable of attenuating noise and treating harmful exhaust gases before emitting the exhaust gases to the atmosphere. The muffler assembly extends rearwards to the right side of the driven wheel 106. The engine assembly 110 is coupled to a transmission system 115 for transferring power to the driven wheel 106. Further, the swing arm 107 extending rearwards is swingably connected to a lower rear portion of the frame structure. A transmission case 112 is attached to the swing arm 107 assembly and helps in covering a transmission member 111 during vehicle functioning.
[00044] In a front portion of the vehicle, a fuel tank assembly 102 is arranged immediately behind the handlebar assembly 114 and is disposed over the engine assembly 110. The handle bar assembly 114 supports an instrument cluster, vehicle controls including throttle, clutch, or electrical switches. An upper portion of the front wheel 108 and the driven wheel 106 are covered by a fender assembly 116 in order to prevent mud and water getting deflected towards the vehicle 100 and entering the steering shaft or the engine assembly 100 and an exhaust system.
[00045] Further, a seat assembly 104 is mounted to the vehicle frame assembly and disposed rearward of the fuel tank assembly 102. The rider can operate the vehicle 100 in a seated position on the seat assembly 104. Further, to improve the overall aesthetics of the vehicle, a plurality of panel covers 113 are provided mounted to the frame member and covering the frame member and/or parts of the vehicle 100. Also, the vehicle 100 may be provided with plurality of mechanical, electronic, and electromechanical system (not shown in figure) and may include an anti-lock braking system, a vehicle safety system, or an electronic control system.
[00046] Figure 2 illustrates an assembly of a secondary reduction in the transmission system. The secondary reduction 200 includes a drive sprocket 201 which is rotatably and circumferentially supported on an end portion of a drive shaft 202. The drive shaft 202 is functionally connected to a driven wheel 106. On the other end, a driven wheel 106 is disposed. The driven wheel 106 is provided with required torque through a transmission member 111. The transmission member 111 is rotatably supported between the drive sprocket 201 at the drive shaft end 202 and a driven sprocket 203 at the other end. The driven sprocket 203 is rotatably supported by the driven wheel 106. The drive shaft 202, the drive sprocket 201, and the driven sprocket 203 are designed such that the drive sprocket 201 and the driven sprocket 203 are always in alignment in a plane. This alignment facilitates rotating of the transmission member 111 along a vehicle longitudinal direction LM in a straight line.
[00047] Any kind of misalignment between the drive sprocket 201 and the driven sprocket 203 will not facilitate proper rotation of the transmission member 111 as desired. As a result, the required torque that has to be transmitted to the driven wheel 106 is affected. Any misalignment could also lead to failure of the transmission member 111.
[00048] Figure 3 illustrates an exploded view of a drive shaft assembly according to an embodiment of the present invention. The drive shaft assembly 300 includes a drive shaft 202, a drive sprocket 201. The drive shaft 202 is configured to rotate about a shaft axis XY`. The drive shaft includes a first end 202OE and a second end 202ce disposed opposite to said first end 202OE. The first end 202OE is an open-ended portion, whereas the second end 202ce is connected to a gear box (not shown). The first end 202OE includes one or more projections 202d. The drive first end 202OE includes a groove 202a. The groove 202a is configured to receive a retainer member 204. The drive sprocket 201 is accommodated on the drive shaft 202 along with the retainer member 204. The drive sprocket 201 includes an outer diametrical portion 201a. The outer diametrical portion 201a of the drive sprocket 201 includes outwardly projecting plurality of teeth 201t. The drive sprocket 201 includes an inner diametrical portion 201ID that includes plurality of splined structures 201s that are projecting inwardly towards a centre of the drive sprocket 201.
[00049] According to an embodiment of the present invention, the plurality of projections 202d are configured to mate with the plurality of splined structures 201s of the inner diametrical portion 201ID in assembled condition.
[00050] According to another embodiment of the present invention, the plurality of splined structures 201s and the plurality of projections 202d are chamfered. A drive sprocket chamfering 201c and a drive shaft chamfering 202c are carried out for ease of assembly during assembly procedure. The drive sprocket chamfering 201c and a drive shaft chamfering 202c allow smooth entry and smooth contact between the drive shaft 202 and the drive sprocket 201.
[00051] According to an embodiment of the present invention, the drive sprocket 201 includes a stepped projected portion 201e. This way, the thickness of the drive sprocket 201 at the centre is greater compared to other portions of the drive sprocket 201. The stepped projected portion 201e is extending away from an inner face 207i (not shown). The inner face 207i is a surface other than the stepped projected portion 201e and the centre of the drive sprocket 201. The inner face 207i (not shown) is extending laterally away from the centre of the drive sprocket 201 and away from the stepped projected portion 201e.
[00052] During assembly, the drive sprocket 201 is first inserted into the drive shaft 202. The plurality of projections 202d are aligned to be in between the plurality of splined structures 201s. After inserting the drive sprocket 201, the retainer member 204 is inserted into the grove 202a. The outer face 201o (not shown) of the drive sprocket 201 is configured to abut against the retainer member 204. The retainer member 204 is configured to include plurality of extensions 204a. The plurality of extensions 204a are configured to enter in between and through the plurality of drive extensions 202b. The drive extensions 202b are present at an end portion of a first end 202OE. After the retainer member 204 has entered the end portion, then the retainer member 204 is inserted in the grove 202a. After which, the retainer member is slightly rotated in the groove 202a. Now, due to rotation, misalignment between plurality of extensions 204a and plurality of drive extensions 202b occurs, because of which, the retainer member 204 remains locked in the groove 202a.
[00053] According to an embodiment of the present invention, the retainer member 204 and the drive sprocket 201 include two or more holes 204h and 201h respectively. The plurality of holes 204h and 201h are configured to receive two or more mounting members 201m. The retainer member 204 and the drive sprocket 201 are locked to each other.
[00054] Figure 4 illustrates a sectional view of the drive shaft assembly taken along a shaft axis XY as shown in the Figure 2 according to an embodiment of the present invention. The drive sprocket 201 includes an inner face 207i, an outer face 207o and a stepped face 201s (not shown). The stepped face is on the stepped projected portion 201e at the centre of the drive sprocket 201. The stepped projected portion 201e is formed on the inner face 207i of the drive sprocket 201. The drive sprocket 201 includes one or more contact portions 201cp configured to be in direct contact with the drive shaft 202. The one or more contact portions 201cp are disposed around the drive shaft 202 in assembled condition. The one or more contact portions 201cp are at the centre of the drive sprocket 201. The one or more contact portions 201cp at the centre are configured to include the stepped projected portion 201e. The stepped projected portion 201e is provided only on one side of the drive sprocket 201. The stepped projected portion 201e is configured to extend towards the second end 202ce of the drive shaft 202. In assembled condition, the retainer member 204 is locked to the drive sprocket 201. The locking is carried out through two or more mounting members 201m received by two or more holes 201h. The two or more holes 201h are threaded. There exists a butting surface 205 between the retainer member 204 and the drive sprocket 201. The butting surface 205 decides the sprocket centre line CP. The sprocket centre line CP is required to be substantially in the lateral centre of the drive sprocket 202 as illustrated in the figure. The sprocket centre line CP as illustrated, enables alignment of the drive sprocket 201 with the driven sprocket (not shown). Therefore, the stepped projected portion 201e cannot exist on the other side of the drive sprocket 201 towards the retainer member 204. If so, then, the sprocket centre line CL shifts accordingly towards the open end 202OE of the drive shaft 202 and there could be misalignment with the driven sprocket (not shown). As a result of which, the transmission member (not shown) cannot rotate along straight longitudinal axis of the vehicle and instead wobbling of the transmission member occurs.
[00055] Figure 5a illustrates a perspective side view of a drive sprocket according to an embodiment of the present invention. The stepped projected portion 201e is configured to extend laterally away from the inner face 207i. The stepped projected portion 201e includes a stepped face 207s. The stepped face 207s is disposed away from the inner face 207i. According to an aspect of the present invention, the stepped projected portion 201e is formed on the inner face 207i, the stepped portion 201e is situated at a canter portion SC of said drive sprocket 201.
[00056] Figure 5b illustrates a sectional side view of a drive sprocket according to an embodiment of the present invention. The figure represents varying thickness of the drive sprocket that is achieved according to the present subject matter. The drive sprocket includes the sprocket surface 207 including a first predetermined thickness of T1. The first predetermined thickness of T1mm is sufficient for the plurality of teeth (201t not shown) to receive the transmission member (not shown) without any requirement of changes in the layout of the two-wheeled vehicle.
[00057] Further, the thickness of the drive sprocket 201 is increased to a second predetermined thickness T2mm. The second predetermined thickness T2 mm provides improved interface with the drive shaft (not shown). The second predetermined thickness T2 mm includes the stepped projected thickness T4mm and a third predetermined thickness T3mm. The third predetermined thickness T3mm includes the thickness of the stepped projected portion 201e, which is extended beyond stepped projected thickness T4mm. The third predetermined thickness T3mm is provided for chamfering. Therefore, the second predetermined thickness T2mm includes the first predetermined thickness T1mm, the stepped projected thickness T4mm and the third predetermined thickness T4mm (T2mm= T1mm + (T1mm-T4mm) +T3mm).
[00058] Further, the thickness is increased for T4mm. The increased thickness, amounts to increased contact area between the plurality of splined structures (not shown) in the drive sprocket 201 and the plurality of projections (not shown) in the drive shaft 202. The increased contact area reduces the pressure stress that was being exerted on a single spot or narrow area on the drive shaft 202. Now, due to the improved contact area therebetween, the pressure exerted is distributed all over the contact area and the drive shaft 202 is not adversely affected by the pressure exerted during operation of the engine. Therefore, the failure of the drive shaft 202 is prevented to a greater extent.
[00059] According to another embodiment of the present invention, the thickness of the drive sprocket 201 is further increased above T4 mm to achieve chamfering of the plurality of splined structures. The chamfering 201c is provided to achieve ease of assembly of the drive sprocket 201 into the drive shaft (202 not shown).
[00060] Figure 5c illustrates an aspect of a hole in the drive shaft for receiving the mounting member. According to an embodiment of the present invention, the two or more holes 201h are configured to receive two or more mounting members 201m. The two or more holes include a body diameter of D1mm. The body diameter is a portion that is configured to accommodate the two or more mounting members 201m. Further, the two or more holes 201h includes an end portion 208 comprising an end diameter D2mm. The end portion 208 is disposed away and at the end of the body portion. The body diameter D1 is greater than the end diameter D2.
[00061] The end portion includes reduced diameter D2mm as compared to the body diameter D1mm for not allowing the two or more mounting members 201m to pass through during the assembly. In other words, the mistake proofing during assembly of the drive sprocket 201 is prevented by the feature of the reduced diameter D2mm.
[00062] For example, during assembly of the drive sprocket, the stepped projected portion 201e should be facing away from the retainer member (not shown). However, if the drive sprocket 201 is inserted otherwise, that is, the stepped portion is facing the retainer member. Then the two or more mounting members cannot enter the two or more holes 201h due to reduced diameter D2mm that cannot receive the two or more mounting members of D1mm. This way fool proof assembly is provided according to the present invention.
[00063] Figure 6 illustrates a graphical representation of a comparative study of the pressure stress at the contact area according to the thickness of the drive sprocket. The x axis represents the varying thickness of the drive sprocket 201. The Y-axis represents the pressure stress experienced by the plurality of splined structures in the drive sprocket and the plurality of projections in the drive shaft. It can be observed that as the thickness of the drive sprocket is increasing along the X-axis, the pressure-stress experienced by the contact surface area is reduced. This is depicted by a falling curve 401 as illustrated in the graphical representation. Therefore, according to the present subject matter, the increased thickness of the sprocket as per the present invention provides for an increased contact area between the mating parts and the stress experienced by them is reduced. This will reduce the wear out, due to which the noise emanated if there was clearance created is eliminated. As a result, the rider is not subjected to any discomfort and surprise failure of the engine assembly is prevented.
[00064] Althcough the subject matter has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. It is to be understood that the aspects of the embodiments are not necessarily limited to the features described herein.