TECHNICAL FIELD

[0001] The present subject matter, in general, relates to a power unit for a motor vehicle, and, in particular relates, to a translating member for the power unit.

BACKGROUND

[0002] Generally, a power unit like an internal combustion engine is provided with air-fuel mixture for combustion that creates thermal energy. The thermal energy generated from the combustion process is converted into mechanical energy, which can be used to do some kind of mechanical work. Generally, the combustion process causes a reciprocating member like piston to undergo a reciprocating motion and the reciprocating motion of the reciprocating member is converted into rotational motion by a translational member like a crankshaft. The aforementioned power unit is used in a wide range of applications including providing of motive force for movement of a motor vehicle like two-wheeler or three-wheeler. Thus, the translating member is one of the critical parts of the power unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The detailed description is described with reference to the accompanying figures. In the figures, similar numbers are used throughout the drawings to reference like features and components.

[0004] Fig. 1 depicts a right-side view of an exemplary motor vehicle 100, in accordance with an embodiment of the present subject matter.

[0005] Fig. 2 illustrates a left side view of a power unit, in accordance with an embodiment of the present subject matter.

[0006] Fig. 3 a sectional view of the power unit, in accordance with an embodiment of the present subject matter.

[0007] Fig. 4 depicts a perspective view of a translating member, in accordance with an embodiment of the present subject matter.

[0008] Fig. 5 (a) depicts a partial exploded view of the translating member with selected parts, in accordance with an embodiment of the present subject matter. [0009] Fig. 5 (b) depicts a perspective view of a portion of the translating member, in accordance with an embodiment of the present subject matter. [00010] Fig. 6 depicts a side view of a portion of the translating member, in accordance with an embodiment of the present subject matter.

[00011] Fig. 7 depicts a polar plot depicting unbalanced mass against crank angle for a translating member, in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION

[00012] The translating member is subjected to various loads, for example the force exerted on the reciprocating member during the combustion process is transferred to the translating member. The translating member is made rigid to withstand the various forces acting thereon making it one of the heavier components of the power unit especially in small vehicles like two-wheeler or three-wheeler which typically have a single cylinder.

[00013] Generally, in power unit provided in vehicles like two wheelers or three wheelers, the translating member is formed by two halves. The two halves are connected to the connecting rod at a big end thereof. A crankpin is inserted between the big end of the connecting rod and the halves to form a rotatable connection therebetween. Generally, in two wheelers and three wheelers with single cylinder engine, the aforementioned translating member assembly having split type configuration with the two halves is used. Further, each of these halves that are referred to as counterweights are used to provide required angular momentum to the translational member and also for balancing & providing counter reaction force thereto.

[00014] The power/ torque generated in the power unit is delivered to the wheels through the translating member either through a transmission system or directly, which gets transferred to one or more wheels in case of a two-wheeler or three- wheeler type vehicles. Thus, the translating member must be capable of withstanding various intermittent loads exerted on them, which are subject to change depending on various operating conditions of the power unit like speed of power unit, load on the vehicle, reaction force to the power unit etc. Generally, the translating member is made to be considerably rigid to withstand the aforementioned and other forces, which makes the translating member one of the heavier parts of the power unit. As a result, the inertia of the translating member is typically high, which requires higher force for rotation and which translates into higher fuel consumption. Moreover, mass of the translating member is directly related to the amount of exhaust gases that are generated. Thus, one challenge is to reduce the weight of the translating member to reduce inertia thereby improving the overall efficiency/ fuel economy of the power unit/ vehicle. This has to be attained without compromising on the structural integrity of the translating member.

[00015] Further, in vehicles like two wheelers and three wheelers having a single cylinder type power unit, the translating member is mated with the transmission system. The transmission system is connected to one side of the translating member, which is to one of the halves of the translating member. Thus, one side of the translating member is subjected to higher intermittent forces, which may cause imbalance in the rotation of the translating member. For example, the translating member known in the art is subjected to oil drag due to the oil provided in the power unit. This provides resistance to the rotation of the translating member thereby adding to the inertia of the translating member. Moreover, the translating member is subjected to various intermittent forces/ parameters like varying gear ratio and reaction from the wheel(s) that are being driven onto one side of the translating member etc. The aforementioned and other parameters affect the balance of the translating member. For instance, curve- A (dotted line) depicted in Fig. 7 shows the variation of the unbalanced forces with rotation of the translating member or with respect to crank angle. As shown, the curve- A corresponding to a known translating member is subjected to various unbalanced forces during the rotation thereof. This affects the performance of the power unit as aforementioned, which is undesired.

[00016] Further, imbalance in translating member would affect the travel path (direction or angle) of the translating member and also of the other member connected thereto. This may cause noise in the power unit due to vibration and with time it will affect the clearance between the parts due to aforementioned and other undesired movement of parts affecting clearances therebetween. Further, the vibrations caused by the power unit may creep to the vehicle causing discomfort to the rider. Additionally, this would affect the overall performance and efficiency of the power unit thereby adversely effecting fuel economy.

[00017] Thus, there is a need for a power unit having a translating member that is capable of addressing the aforementioned and other challenges in the known art. Hence, the present subject matter provides a translating member for a power unit, which is capable of offering a balanced operation thereof.

[00018] The present subject matter provides a power unit comprising a reciprocating member within a cylinder block of the power unit. A translating member is at least partially enclosed by and rotatably supported on a crankcase. The reciprocating member is connected to the translating member through a connecting rod or the like. A transmission system is functionally connected to the translating member and the transmission system is disposed towards one of a lateral sides, say a first lateral side of the crankcase.

[00019] The present subject matter provides a translating member, in accordance with an embodiment of the present subject matter which comprises of a first counterweight member disposed on one side of the connecting rod and a second counter weight member disposed towards other side of the connecting rod. The first counterweight member and the second counterweight member are connected to each other through a crankpin. The second counterweight member comprises a second cross-sectional area being smaller than a first cross-sectional area of the first counterweight member. The first counterweight member comprises a cross- sectional area about 1.2 to 1.6 times of the cross-sectional area of the second counterweight member. In one embodiment, the translating member offers asymmetric design due to difference in the cross-section. It is a feature that the second counterweight member with the smaller cross-sectional area is disposed towards the transmission side and is functionally connected thereto. The term ‘functionally connected’ implies that the translating member is either directly connected to the transmission system or through an intermediate system.

[00020] The present subject matter reduces the overall weight of the translating member due to the profile of the first counterweight member and the second counterweight member whereby the inertia thereof is reduced. For example, a first counterweight member gets connected to a transmission system because of which a drag may be experienced on one side of the translating member due to inertia or drag from driving wheel and thus, a smaller cross-sectional area of the first counterweight member (without any compromise on the weight of a web region) of the counterweight member reduces effect of oil drag on the first counterweight member. Whereas, the second counter weight member is provided with a cross- sectional area larger than that of the first counterweight member whereby a drag experienced by the second counterweight member will be larger than the first counterweight member because of a balance of forces is created on the translational member. The translational member would not experience an imbalanced forces acting thereon or would experience a reduces effect of the forces acting thereon resulting in desired rotation of the translational member. Thus, the functional effectiveness and the life of the transitional member and of the associated components is improved. Moreover, a reduction in overall weight and cross-sectional area of the translating member, without compromising on balance of weights of the counterweights, is reflected in the overall weight and performance of the power unit. Due to the reduced oil drag and the weight the efficiency of the power unit is improved.

[00021] The present subject matter, in accordance with one embodiment, comprises an oil sump from lubricating and/or cooling various parts of the power unit. The translating member offers a reduced overall drag due to the smaller cross-section of the second counterweight member yet offers improved balance of mass

[00022] The present subject matter provides, in accordance with one embodiment, a second counterweight member having a first connection portion for the second counterweight member to be secured to the connecting rod through a crank pin or the like, and a first body portion at least partially extending in a radial direction away from the connection portion. The first body portion formed away from the connection portion is towards one side of an axis of rotation of the translating member and the connection portion is formed on the other side of the axis of rotation (considering radial direction or as viewed radially with respect to axis of rotation). [00023] The present subject matter, in accordance with one embodiment, provides the second counterweight member having a non-circular shape when seen in axial direction and the connection portion is disposed at the narrow end of the non circular shape and the first body portion is disposed at broad end of the non circular shape. The first counterweight member is capable of having a cross- sectional area greater than the second counterweight member, wherein in one embodiment, the first counter weight member is circular shape when viewed in axial direction.

[00024] The present subject matter, in accordance with one embodiment, provides the second counterweight member having the first body portion comprises an arc shaped profile. Thus, the first body portion comprises an outer periphery that is partially circular or is arc shaped whereby the contact or drag with the lubrication oil is lesser.

[00025] The present subject matter, in accordance with one embodiment, provides the second counterweight member having a first portion disposed away from a connection portion and a second portion disposed in proximity to the first connection portion, which forms an angular outer periphery of the second counterweight member. The first portion and the second portion are disposed substantially on opposite side (radially) with respect to an axis of rotation of the translating member and the first portion and the second portion are having a width, taken in width wise direction/ axial direction, being substantially greater than a width of rest a first body portion. This helps in providing required momentum as the portion(s) with larger width are provided about certain angular region and the first body portion having a larger angular area/ angular sector is in proximity to the first portion.

[00026] The present subject matter, in accordance with one embodiment, provides a first portion comprises a first peripheral portion covering a first angular area and the second portion having a second peripheral portion covering a second angular area, and wherein the first angular area is substantially greater than the second angular area.

[00027] The present subject matter, in accordance with one embodiment, provides the second counterweight member having a first radial side and a second radial side, wherein the first radial member and said second radial member are having a radial outward end disposed at an acute angle with respect to a radial line passing substantially therealong. This offers the non-circular shaped profile for the second counterweight member.

[00028] The present subject matter, in accordance with one embodiment, provides the second counterweight member having an outward facing axial side therefrom a second arm extending about the axis of rotation, and the outward facing axial side is provided with a second recess portion. This reduces the weight of the second counter weight member as the recess portion reduces the thickness across the member but at the same time retains the structural integrity as the annular periphery comprises a width greater than the thickness at rest of portion of the counter weight member without the annular periphery. Further, second counterweight member provides the counterweight requirements as the body portion with substantial thickness providing mass/weight is provided away from the connection portion.

[00029] The present subject matter, in accordance with one embodiment, provides at least one of a first counterweight member and a second counterweight member comprising a linear arm portion extending between a radial outward end of the radial sides and the linear arm portion is disposed at a radial distance from the axis of rotation of the translating member.

[00030] The present subject matter, in accordance with one embodiment, provides the first counterweight member comprises a first portion disposed away from a connection portion and a second portion disposed in proximity to the connection portion, and a flange portion is provided that is extending between the first portion and the second portion. The first portion and the second portion are disposed substantially radially opposite to each other, and the first portion and the second portion of the first counterweight member are having a width, taken in axial direction, being substantially greater than a width the flange portion. The first counterweight member disposed away from the transmission system comprises the first cross-sectional area greater than the second cross-sectional area of the first counterweight member. The first counterweight member comprises a first arm extending along axis of rotation, wherein the first arm is capable of supporting an electrical machine like a magneto or an integrated starter-generator. [00031] The present subject matter, in accordance with one embodiment, provides the first arm (of first counterweight member) having an arm length smaller than an arm length of the second arm (of second counterweight member). Thus, the second counterweight member with smaller cross-sectional area comprises a longer arm length providing required mass for offering momentum.

[00032] The present subject matter, in accordance with one embodiment, provides the first counterweight member comprises an outward facing axial side provided with a first recess portion, which is substantially circular and wherein an oil cleaner is secured at the outward facing axial side thereof. In one embodiment, the oil cleaner is a centrifugal oil filter.

[00033] The present subject matter, in accordance with one embodiment, provides the second counterweight member having a first imaginary line passing through an outer periphery of a first radial outward end and a second imaginary line passing through a second radial outward end, and the first imaginary line and the second imaginary line are passing through an axis of the translating member. The first imaginary line and the second imaginary line are disposed at a predetermined sector angle. The sector angle is greater than the acute angle formed between the radial sides, whereby a greater mass is provided at the body second portion at the radial end portion offering the required mass for counterweight.

[00034] The present subject matter, in accordance with one embodiment, provides the transmission system including a continuously variable transmission system supported by a second side casing, which is extending in a longitudinal direction orthogonal to an axis of the translating member. The transmission system is functionally connected to the translating member.

[00035] The present subject matter, in accordance with one embodiment, provides a motor vehicle, like a two-wheeler or a three-wheeler, with a single cylinder-type having a cylinder axis disposed in at least one of a vertical direction and a forward inclination with respect to said vertical direction.

[00036] These and other advantages of the present subject matter would be described in greater detail in conjunction with one or more embodiments with the corresponding figures in the following description. In the figures F represents forward direction, R represents rearward direction, RH represents right side and LH represents left side with respect to vehicle as reference.

[00037] Fig. 1 depicts a right-side view of an exemplary motor vehicle 100, in accordance with an embodiment of the present subject matter. The motor vehicle 100 comprises a frame assembly 105 supporting a front wheel 130 and a rear wheel 132. The front wheel 130 and the rear wheel 132 are rotatably supported by front suspension system and the rear suspension system (not shown), respectively. In one embodiment, the rear wheel 132 may be additionally supported by a swingarm (not shown). In the depicted embodiment, the frame assembly 105 comprises a main tube 107 which extends rearwardly downward from a head tube 106 and one or more rear frames 108 which extend inclinedly rearward towards a rear portion of the vehicle 100. The frame assembly 105 defines a step-through portion 140 thereof, which can be used for load carrying or for the user to rest feet.

[00038] In the present embodiment, a power unit 200 is swingably mounted to one of the main tube 107 or the rear tubes 108 of the frame assembly 105 and is disposed substantially rearward of the step-through portion 140. In another embodiment, the power unit may be fixedly mounted to the main tube 107 of the frame assembly 105. The power unit 200 is connected to a muffler 155 which is part of an exhaust system, and is capable of attenuating noise and treating harmful exhaust gases before emitting the exhaust gases to the atmosphere. The power unit 200 is coupled to a transmission system 240 (shown in Fig. 3) for transferring power to the rear wheel 132. Further, the front wheel 130 is steerable by a handle bar assembly 150, which is functionally connected to the front wheel 130 for maneuvering the vehicle 100. The handle bar assembly 150 supports an instrument cluster, vehicle controls including throttle, clutch, or electrical switches.

[00039] Further, a seat assembly 150 is mounted to the frame assembly 105 and disposed rearward of the step-through portion 140. The rider can operate the vehicle 100 in a seated position on the seat assembly 155. Further, the vehicle 100 is provided with plurality of panels 170A, 170B mounted to the frame assembly 105 and covering the frame assembly 105 and/or parts of the vehicle 100. Also, the vehicle 100 may be provided with plurality of mechanical, electronic, and electromechanical system including an anti-lock braking system, a vehicle safety system, or an electronic control system.

[00040] Fig. 2 illustrates a detailed left side view of a power unit, in accordance with an embodiment of the present subject matter. The power unit 200 comprises a cylinder head cover 201, a cylinder head 202, a cylinder block 203, and a crankcase 204. The power unit 200 comprises an intake port 208 to which an air- control device 209 like a carburetor or a throttle body with a fuel injector is connected. In one embodiment, the crankcase 204 is made of a first side casing 205 and a second side casing 206, which is capable of rotatably supporting various parts of the power unit 200 including a translating member 300. Further, the crankcase 240 also comprises a sump portion at a bottom portion for storing oil for lubrication and/or cooling. The second side casing 206 (shown in Fig 3) extends substantially rearward with respect to a first side casing 205 (shown in Fig. 3) in order to support a transmission system 240 and a final drive system 246. The cylinder block 203 is supported by the crankcase 204. The cylinder block 203 comprises a cylinder portion about which a reciprocating member 214 (shown in Fig. 3) is movable. The cylinder head 202 is mounted to the cylinder bock 203 and the cylinder head 202 is supporting a camshaft 210 and plurality of valves (not shown). The translating member 300 is disposed transverse with respect to a longitudinal axis F-R of the power unit 200.

[00041] The power unit 200 comprises a connecting rod 212 connecting the reciprocating member 214 to a translating member 300. During the combustion process transfer of mechanical energy occurs from the reciprocating member 214 to the translating member 300, which generates power due to the slider crank mechanism. The translating member 300 is rotatably supported on the crankcase 204 by bearing members, wherein a first bearing member 218 is disposed on one side of the translating member 300 and a second bearing member 220 is disposed on other side thereof. An oil cleaner is connected to the translating member 300, wherein the oil cleaner filters the lubrication oil before transferring to the piston. The transmission system 240 is disposed towards one lateral side of the power unit 200 and is supported on the second casing 206. The transmission system 240, in the present embodiment, is a continuously variable transmission 240 that engages with one end of the translating member 300. The transmission system 240 comprises a belt 242 that connects drive pulley 241 with a driven pulley 244. Thus, the one end of the translating member 200 is connected to the transmission system 240, wherein the transmission system 240 is capable of offering a variable transmission that is similar to a multi-stage gear system. Further, the output of the transmission system 240 is provided to a final reduction system 246 that is supported on the second casing 206. A cover member 225 is detachably attached to the casing 204, wherein the cover member 225 forms at least an outer portion of the power unit 200. The power unit 200 comprises a kick-starter system with a kick-start lever 226.

[00042] Fig. 4 illustrates a perspective view of a translating member, in accordance with an embodiment of the present subject matter. Fig. 5 (a) depicts partial exploded view of the translating member 300, in accordance with an embodiment of the present subject matter. The translating member 300 is rotatably supported by bearings 218, 220, wherein the bearings 218, 220 gets sandwiched between the translating member 300 and the crankcase 204. The translating member 300 comprises a first counterweight member 310 and a second counterweight member 330. The first counterweight member 310 is disposed on one side of the connecting rod 212 and the second counterweight member 330 is disposed on other side of the connecting rod 212. The first counter weight member 310 and the second counter weight member 330 are connected to each other through a crankpin 222. The second counterweight member 330 comprises a second cross-sectional area CA2 being smaller than a first cross-sectional area CA1 of a first counterweight member 310, wherein the second counterweight member 330 is disposed to be engaging with the transmission system 240. The first counterweight member 310 comprises the first cross-sectional area CA1 (cross-sectional taken along a plane orthogonal to the axis of rotation) being about 1.2 to 1.6 times of the second cross-sectional area CA2 of the second counterweight member 330 whereby the overall cross-sectional area of the translating member is reduced. Thus, the translating member 300 comprises reduced inertia that would improve the efficiency due to reduced effort in rotating the translating member. Further, the range 1.2 to 1.6 enables in retaining the structural integrity of the second counterweight member with respect to the first counterweight member.

[00043] The translating member 300 comprises a pair of laterally extending arms corresponding to the two counterweight members 310, 330, wherein a first counter weight member 310 comprises a first arm 312 extending outward in an axial direction C-C’ of the translating member and a second arm 332 extending outward in the axial direction C-C’ but opposite to direction of extension of the first arm 332. In one embodiment, the second arm 332 comprises an axial length greater than an axial length of the first arm 312.

[00044] The first counterweight member 310 comprises a substantially circular cross-section and the second counterweight member 330 comprises a non-circular cross-section. In the depicted embodiment, the second counterweight member 330 comprises a substantial sector-shaped profile with one or more outer peripheries having arc shaped.

[00045] The second counterweight member 330 comprises a connection portion 334 at which the connecting rod 212 get connected to the second counterweight member 330. Similarly, a connection portion 314 is provided on the first counterweight member 310 at which the connecting rod 212 gets connected to the first counterweight member 310. The crankpin 222 passes through the connection portions 314, 334 along the crankpin axis CP for connection of the crankpin 222. [00046] The second counterweight member 330 comprises a body portion 336 that is extending from connection portion 334 and expanding in a radial direction. The body portion 336 comprises a first portion 337 and a second portion 338, wherein the first portion 337 and the second 338 are having a thickness/width W21, W22 (in axial direction) substantially greater than rest of the body portion 337. Further, the second arm 332 is disposed along the axis of rotation C-C’. As seen in Fig. 5 (a), an axial outward side of the second counterweight member 330 is provided with a second recess portion 350, whereby weight of the second member counterweight member 330 is reduced. Further, the first portion 337, which is farthest from the connection portion 334, comprises an angular region substantially greater than an angular region of the second portion 338. The first portion 337 provides the requisite counter mass for creating the momentum for the translating member 300.

[00047] Similarly, the first counterweight member 310 comprises a body portion 316 that is extending from the connection portion 334 and expanding forming a circular profile, with the center thereof aligning with the first arm 312. The body portion 316 comprises a first portion 317, a second portion 318, and a flange portion 319. The body portion 316 of the first counterweight member 310 excluding the flange portion 319 forms a mirror image of the second counterweight member 330. Thus, the first counterweight member 310 is also having peripheral area at the first portion 317 and the second portion 318 being greater than the rest of the body portion 316.

[00048] In the depicted embodiment, the second counterweight member 330 is having a smaller cross-sectional area (compared to first counter weight member 310) and has a substantially sector shaped profile. A connection portion 334 for connecting with the first counterweight member 310 being disposed towards a narrow end and a cross-section CA (shown in dotted line) is increasing when moving towards a wider end of the sector shaped profile. Thus, the second counterweight member 330 has mass accumulated at an end away from the connection portion 334 thereby creating counter rotational force in achieving the desired momentum.

[00049] The translating member 300 is provided with an at least partial circular periphery on the first counterweight member 310 that is capable of supporting an oil cleaner (not shown) secured on the outer axial side. In one embodiment, the oil cleaner is substantially circular in shape and can be secured to the first counterweight member 310. The oil cleaner, in one embodiment, comprises of a circular bowl-shaped plate with an annular hole at its center, wherein the bowl shaped-plate is mounted to the first counterweight member 310. In one embodiment, the bowl shaped-plate is press-fitted to the first counterweight member 310. In another embodiment, a back-plate may be provided on the first counterweight member 310 and the bowl-shaped plate may be mounted to the back-plate. [00050] Fig. 5 (b) depicts another perspective view of a portion of the translating member, in accordance with an embodiment of the present subject matter. The second portion 318 substantially surrounds the connection portion 314 and comprises a thickness substantially greater than the flange portion 319 thereby providing the structural strength to withstand the force from the connecting rod 212. Further, in one embodiment, the second portion 318 is also provided with a thickness substantially greater than a thickness of the flange portion 319, which acts like a concentrated mass for providing the momentum required for rotation of the translating member 300. The separation of the flange portion 319 is shown in dotted line (in the current Fig. 5 (b)). The bulging due to larger width (in axial direction) of the first portion 317 and the second portion 318 are provided on the inward facing axial side AS1 of the first counterweight member 310 and the outward facing axial side AS2 comprises a recess portion 340 with a depth 342, wherein the oil cleaner can be accommodated at the first recess portion 340. [00051] Further, referring to Fig. 5 (a), the first portion 317 comprises a first peripheral region PR1, the second portion 318 comprises a second peripheral region PR2, which will come in contact with lubrication oil for splashing oil towards the reciprocating member 214 for lubrication. Further, the flange portion 319 comprises a substantially small thickness or width W13 (compared to width Wll, W12 of the first portion 317 and the second portion 318) whereby the drag from the lubrication oil in the sump thereon is very low whereby the desired improvement in momentum is obtained. Similarly, the first portion 337 of the second counterweight member 330 comprises a first peripheral region PR4, and the second portion 338 comprises a second peripheral region PR5, which will come in contact with lubrication oil for splashing oil. However, the second counterweight member 330 comprises radial sides with a flange peripheral region PR6 that is substantially inward and would not coming in contact with the lubrication oil whereby the drag from the lubrication oil in the sump is only due to the first peripheral region PR4 and the second peripheral region PR5 whereby overall drag is reduced.

[00052] Further, the first counterweight member 310 supports an electrical machine like a magneto or an integrated starter generator (ISG), wherein it has one rotating member that rotates independent of other parameters. The first counterweight member 310 comprises a cross-sectional area less than the cross- sectional area of the second counterweight member 330. Whereas, the second counterweight member 330 is connected to a transmission system 240, wherein the transmission system 240 that has a varying transmission ratio and the transmission system 240 is further connected to the rear wheel 132, which exerts additional inertia on the second counterweight member 330. The second counterweight member 330 with this additional inertia acting thereon is balance by the reduced cross-section of the second counterweight member 330 whereby the drag effect is reduced.

[00053] Fig. 6 depicts an inner axial side view of a second counterweight member 330, in accordance with an embodiment of the present subject matter. The second counterweight member 330 comprises a cross-sectional area less than a cross- sectional area of the first counterweight member 310, whereby overall weight of the translating member 300 is reduced. In one embodiment, the second counterweight member 330 is substantially having a non-circular shaped profile. As shown in Fig. 6, the dotted line depicts an imaginary outer periphery of the first counterweight member 310. The second counterweight member 330 comprises the body portion 336, which is substantially in the shape of an arc with a narrow end disposed near the connection portion 334. The body portion 336 comprises the first portion 337 and the second portion 338 and in one embodiment the portion 337, 338 are at least partially having a thickness substantially greater than a thickness of rest of the body portion 336. The second counterweight member 330 comprises a first radial side 352 and second radial side 353, which are disposed to be extending between the first portion 337 and the second portion 338. An outward radial end 354, 355 of the first radial side 352 and the second radial side 353 are further extending outward at an acute angle a from the rest of the radial side 352, 353.

[00054] A first radial line R1 and a second radial line R2 are passing along the first radial side 352 and the radial side 353, respectively. In one embodiment, the first radial line R1 and the second radial line R2 are secant lines cutting through an imaginary circle. Each of the radial outward ends 354, 355 are disposed at an acute angle a with respect to an imaginary line El or E2 drawn radially, wherein a requisite amount of counter mass is accumulated farther from the connection portion 334. The radial outward end 354, 355 acts as an extended portion of the second counterweight member 330 with mass concentration. The radial outward end 354, 355 has an imaginary line El, E2 passing therethrough and the acute angle a is provided in the range of 20-60 degrees.

[00055] In one embodiment, the second counterweight member 330 comprises a linear arm portion 357 (similar linear arm portion 356 may be provided for the first counterweight member as shown in Fig. 5 (b)) extending between radial outward ends 354, 355. The linear arm portion 357 is disposed at a first radial distance RD1 from an axis of rotation C-C’ of the translating member 300. The linear arm portion 357 forms a side of the first peripheral portion 317 that is facing the axis of rotation C-C’. The first radial distance is varied to adjust the center of gravity of the translating member 300 for creating balanced rotation. Further, the linear arm portion 357 may be disposed at a certain angle for balancing requirements.

[00056] Further, a sector angle b between the imaginary lines El, E2 passing through the radial outward ends 354, 355 is varied depending on balancing requirement, which is analogous to the counter mass required. The sector angle b is kept in the range of 100-180 degrees to match to the required counter mass requirement. In a preferred embodiment, the sector angle b is kept in the range of 100-140 degrees thereby reducing the outer peripheral area. This reduces the drag force from splash oil lubrication thereby improving angular momentum of the translating member. [00057] The second peripheral region PR5 is disposed inward with respect to an outer periphery of the first counterweight member 310. Thus, a depth reached by the second peripheral region PR5 is lower than the depth reached by the second peripheral region PR2 of the first counterweight member 310 in an oil sump. Thus, the amount of drag or resistance on the second counterweight member 330 side is lower when compared to the first counterweight member 310, whereby the translating member 300 undergoes an overall balance of forces acting thereon from the transmission system on one side and oil drag on other side. [00058] The first peripheral portion 337 is comprising a first peripheral portion PR4 covering a first angular area gΐ and the second peripheral portion 338 is comprising a second peripheral portion PR5 covering a second angular area g2, and wherein the first angular area gΐ is substantially greater than the second angular area j2. Thus, the first angular area gΐ offers larger mass at certain angular region/ area thereby creating desired counterweight effect.

[00059] The second counterweight member 330 is comprising a first radial side 352 and a second radial side 353. The first radial side 352 and the second radial side 353 are comprising a radial outward end 354, 355 disposed at an acute angle a with respect to an imaginary line Rl, R2 passing substantially along the first radial side 352 and the second radial side 353.

[00060] The second counterweight member 330 is comprising an outward facing axial side AS2 and a second arm 332 is extending about an axis of rotation C-C’ therefrom, and the outward facing axial side AS2 is provided with a second recess portion 350.

[00061] Fig. 7 represents a schematic polar plot of unbalanced mass versus crank angle for translating member(s). The plot depicts a curve- B, for the translating member 300 in accordance with the present subject matter. The curve- B depicts a reduced unbalanced mass of the translating member 300. Radial distance of the curve- B from the center towards the outward side of the graph is reduced as the translating member 300 offers balanced counterweight that would balance the rotation of the translating member 300. The present subject matter offers a power unit having the second counterweight member having a second cross-sectional area disposed towards the transmission side and the first counterweight member having the first cross-sectional area, which is greater than the second cross- sectional area, is disposed away from the transmission system thereby offering a translating member with balanced forces acting thereon. This helps in retaining the center of gravity of the translating member near to the axis of rotation as the intermittent forces acting on the translating member from the transmission system get balanced due to the profile of the translating member

[00062] Further, the translating member offers an overall reduced drag from the lubrication oil as the translating member undergoes some resistance towards the transmission system whereby the overall drag experienced by the translating member is lower and is more balanced. This improves the functional performance of the translating member like reduced overall drag or lower frictional resistance, lower rotational inertia or improved angular momentum, balanced forces acting on the translating member etc. thereby improving longevity of the part and other life of the ancillary parts like reciprocating member etc. Further, the present subject matter reduces vibration due to the balance attained by the translating member.

[00063] It is to be understood that the aspects of the embodiments are not necessarily limited to the features described herein. Many modifications and variations of the present subject matter are possible in the light of above disclosure. Therefore, within the scope of claims of the present subject matter, the present disclosure may be practiced other than as specifically described.

List of reference signs:

100 motor vehicle 30 226 kick-start lever

105 frame assembly 240 transmission system

106 head pipe 242 belt 107 main frame

108 rear frames 241 drive pulley

130 front wheel 242 driven pulley

132 rear wheel 35 246 final drive/ final reduction

140 step-through portion system 150 seat assembly 300 translating member

151 handlebar assembly

310 first counterweight member 155 muffler

170A/170B 312 first arm panel 314 connection portion 200 power unit 316 body portion

201 cylinder head cover

317 first portion

202 cylinder head

318 second portion

203 cylinder block

319 flange portion

204 crankcase 330 second counterweight 205 first side casing member

206 second side casing 332 second arm

208 intake port 334 connection portion

209 air control device 336 body portion 212 connecting rod 50 337 first portion 214 reciprocating member 338 second portion

218 first bearing member 340 first recess portion 220 second bearing member 350 second recess portion 222 crankpin 352 first radial side

225 first cover 55 353 second radial side 354\355 outward radial end PR1 first peripheral region

357 linear arm portion PR2 second peripheral region AS 1 inward facing axial side PR4 first peripheral region AS2 outward facing axial side PR5 second peripheral region R1\R2 radial line 15 PR6 flange peripheral region

CA1 first cross-sectional area W11/W12/W13/W21/W22 CA2 second cross-sectional area width CP crankpin axis a an acute angle C-C’ axis of rotation b sector angle E1YE2 imaginary line 20 g1/ g2 angular area