CN109209552B

CN109209552B - Crankshaft for internal combustion engine

Info

Publication number: CN109209552B
Application number: CN201810745298.7A
Authority: CN
Inventors: G·拉梅什库马; T·S·维宾; S·约瑟夫; M·D·尤美特; T·纳文; C·萨布兰尼安
Original assignee: TVS Motor Co Ltd
Current assignee: TVS Motor Co Ltd
Priority date: 2017-07-07
Filing date: 2018-07-09
Publication date: 2022-09-20
Anticipated expiration: 2038-07-09
Also published as: CN109209552A

Abstract

An internal combustion engine (101) includes a crankshaft (300) enclosed and supported within a crankcase (204). A pair of roller bearings (307, 312) support the crankshaft (300) on a crankcase (204). The crankshaft (300) includes a pair of non-circular T-shaped counterweights (410, 412) disposed on both sides of the connecting rod (304) and connected to each other by a crank pin (414), each of the pair of counterweights (410, 412) includes a connecting neck portion (450) fixed to the connecting rod (304), and an enlarged portion (460) having a circular outer circumference, and mass is concentrated in the enlarged portion (460). A lubricating oil path (701, 703, 414a) for supplying oil by oil splash to lubricate the piston (303) is present in the crankshaft (300). An oil filter assembly (401) is disposed on at least one side of the crankshaft (300), the oil filter assembly (401) being circular and fixed to at least one of the pair of counterweights (410), and the oil filter assembly (401) forming part of a lubrication oil path (701, 703, 414a) to filter oil before passing through the oil splash lubrication piston (303).

Description

Crankshaft for internal combustion engine

Technical Field

The present invention generally relates to an internal combustion engine. More specifically, the invention relates to a crankshaft employed in an internal combustion engine of a two-wheeled vehicle.

Background

Internal combustion engines convert the thermal energy obtained from the combustion of fuel and oxidant (air) into mechanical energy that can be used to perform some mechanical work. It is used in a wide range of applications, including powering the movement of vehicles. The main components of the engine include a cylinder head, a reciprocating piston on the cylinder block, and a connecting rod connecting the piston to a reciprocating crankshaft. Connecting rods in the engine transmit power generated by reciprocating pistons in the engine block and convert it into rotational motion of a crankshaft, collectively forming a slider-crank mechanism. In a two-wheeled vehicle having a single cylinder, the crankshaft generally includes a left side of the crankshaft and a right side of the crankshaft assembled on both sides of a large end of a connecting rod. The crankpins are interposed between the large ends of the connecting rods, and the crankpins are commonly connected by the right side of the crankshaft and the left side of the crankshaft to collectively form a crankshaft assembly. Generally, in two-wheeled vehicles (including motorcycles and scooters) having a single cylinder engine, the crank assembly is split, and the configuration is divided into right and left sides. Further, typically each of the right side of the crankshaft and the left side of the crankshaft has a right crank arm and a left crank arm forming a counterweight. The crank arm counterweights are used as reciprocating masses to improve crankshaft balance and to resist reaction forces due to crankshaft rotation. Typically, the crank arm of a single cylinder two-wheeled vehicle has a circular cross-section. This is particularly true in step-type straddle vehicles. It is desirable to eliminate the circular cross-section of the crank arm and change it to a more eccentric weight design. However, this is difficult in view of the lubrication requirements of the piston and connecting rod. Therefore, there is a need for a crankshaft design with an eccentrically loaded counterweight that is also capable of lubricating the pistons and connecting rods.

Drawings

The detailed description is illustrated by reference to the accompanying drawings. Throughout the drawings, the same reference numerals are used to denote the same features and components.

Fig. 1 shows a side view of a two-wheeled vehicle employing an embodiment of the present subject matter.

Fig. 2 shows an isometric view of an internal combustion engine employing an embodiment of the present subject matter.

FIG. 3 illustrates a cross-sectional view of an internal combustion engine illustrating an oil filter assembly according to an embodiment of the present subject matter.

FIG. 4 illustrates an isometric view of a crankshaft and connecting rod according to an embodiment of the present subject matter.

FIG. 5 illustrates an exploded view of a crankshaft illustrating an oil filter assembly according to an embodiment of the present subject matter.

FIG. 6a shows an isometric view of an oil filter assembly secured to one side of a crankshaft according to an embodiment of the present subject matter.

Fig. 6b and 6c show front and side views of an oil filter assembly according to an embodiment of the present subject matter.

Fig. 7 shows an enlarged cross-sectional view of an internal combustion engine demonstrating an oil lubrication path, according to embodiments of the present subject matter.

FIG. 8a shows an enlarged cross-sectional view of a crankshaft supported by a crankcase through a right-hand (RH) roller bearing according to an embodiment of the present invention.

FIG. 8b shows an exploded view of the right half of the crankshaft with oil filter assembly assembled within an RH housing according to an embodiment of the present invention.

Detailed Description

Various features and embodiments of the invention will become apparent from the further description which follows. According to an embodiment, an Internal Combustion (IC) engine described herein operates in four cycles. Internal combustion engines are mounted in two-wheeled striding vehicles, commonly known as scooters. It is noted that the internal combustion engine may be mounted in different arrangements in the two-wheeled vehicle, such as in a transverse manner and a longitudinal manner. However, in the following description, such an engine is laterally installed at a lower portion of a two-wheeled straddle-type vehicle. It is contemplated that the concepts of the present invention may be used with other types of vehicles, such as a straddle type motorcycle, within the spirit and scope of the present invention. The "front" and "rear" and the "left" and "right" mentioned in the description of the embodiment shown below refer to the front and rear directions, the left direction and the right direction as seen from the rear of the internal combustion engine and from the previous view. Detailed descriptions of the components constituting the essential parts other than the present invention are omitted where appropriate.

Generally, in a two-wheeled vehicle such as a scooter, a swing type internal combustion engine having a single cylinder is located below a seat at a lower rear portion of the vehicle. Internal combustion engines have, among other components, a cylinder block that includes a cylinder head at the top or front of the block, and the block may receive reciprocating pistons from the bottom or rear. In the case where the air-fuel mixture is combusted, the piston transmits energy generated during combustion to the crankshaft through the connecting rod, thereby driving the crankshaft. In this way, the reciprocating motion of the piston is converted into rotational motion of the crankshaft. The crankshaft is accommodated in a crankcase below or behind the cylinder block. In order to move the vehicle, the power supplied to the crankshaft of the internal combustion engine is transmitted in a controlled manner to the wheels of the vehicle via a transmission system. The transmission system in a conventional vehicle employs a centrifugal clutch and a continuously variable transmission system including two pulleys connected by a continuous belt. The speed change mechanism connecting the drive-side pulleys enables the movement of the pulleys to change diameter due to centrifugal force. Due to this change in the effective diameter of the pulleys, a gear change is obtained.

Traditionally, internal combustion engines are provided with engine lubrication passages that are capable of lubricating moving engine components during engine operation. Lubrication channels involve the transfer of oil through specific channels to achieve the lubrication and cooling required of engine components. In internal combustion engines, lubricating oil functions as a lubricant and a coolant. Oil used for this purpose may be stored in the oil pan, which also serves as a reservoir for oil drained from the engine components as a result of their operation. The oil is pumped by an oil pump and delivered to a desired location within the engine for lubrication and cooling at low, medium or high engine speeds. Circulating lubrication oil reduces wear and friction of engine components and also ensures that the engine is continuously maintained at an optimum temperature, thereby improving engine performance, engine component life, and lubricant service life. Typically, the sump is formed within the crankcase assembly.

In many two-wheeled vehicles, piston lubrication (by splash lubrication) occurs by circulation of oil in oil holes in the crankshaft, which merges at the large end hole of the connecting rod and splashes from the bottom to the piston. This system also has a special oil filter in the lubrication circuit and oil circulates to the crankpin through a hole through the crankshaft. However, in a small single cylinder compact scooter engine, various engine components need to be mounted on both sides of the crankshaft. Typically, the magneto assembly is mounted at one end on the right side and the centrifugal clutch for the drive train is mounted at the end on the left side. Since the engine components are mounted on either side, it is difficult to drill oil holes through the crankshaft to circulate the oil. The cross-sectional diameter of the crankshaft is small, cannot withstand axial loads on the crankshaft, and may fail. Thus, in such small single cylinder compact scooter engines, lubrication oil is transported from the oil pan through the left housing of the crankcase assembly to the right housing of the crankcase assembly. In the right housing, one passage from the main lubrication passage is used for supplying oil to lubricate the crankshaft bearings, the connecting rod, and the piston in the cylinder block by splash lubrication. The crankshaft is fixed in the crankcase by means of two roller bearings, on which an axial load is exerted. A crankshaft lubrication passage is disposed in the right housing and merges with the right roller bearing of the crankshaft and passes through the crankshaft into the crankpin. The connecting rod has a small oil groove at one end of the shank toward the large end bore to allow oil flow for lubrication, which lubricates the crank pin, the large end bore and allows oil to splash onto the piston.

During the supply of lubricating oil from the crankcase to the crank pin through the right side of the crank arm, an oil filter assembly is usually arranged. The oil filter assembly may function to filter debris, burrs, dust, and other heavier particles before the oil is splashed onto the piston by the connecting rod. Typically, the crank arm is circular and a front plate member having an annular opening is arranged at the front of the crank arm. The front plate member forms an oil filter assembly that centrifugally throws out burrs, dust and other heavier particles toward the edges while filtered oil passes through the crankshaft to the crank pin.

Typically, the crank arms are circular in shape to facilitate such filtration of the lubricating oil. However, this shape of the crank arm also makes the crankshaft too heavy, too much machining and too much material used. This ultimately increases the cost of the two-wheeled vehicle. Therefore, in order to reduce costs and alleviate the above drawbacks, it is necessary to obtain crank arms of eccentric configuration with only counterweights. The eccentric crank arm may be bell-shaped, having a narrow tip and a wide tip. A counterweight is disposed on the wide tip and a crank pin for mounting a connecting rod is disposed on the narrow end. This design has advantages such as reduced raw material usage, reduced manufacturing cycle time (forging weight savings), and reduced cost. In addition, the eccentric crank arm realizes the emission reduction of carbon dioxide and the like by reducing the inertia force of the crank shaft. This reduction is achieved without compromising the balance mass, as compared to a round crankshaft. However, the proposed arrangement does not provide the cross-sectional support required to accommodate the front plate member and does not provide a means to facilitate the entry of lubrication oil from the right housing into the crank pin interior. The present invention thus provides a novel oil filter assembly for an eccentric crankshaft and means for securely attaching the same to the crankshaft.

An internal combustion engine includes a crankshaft enclosed and supported within a crankcase. A pair of roller bearings supporting the crankshaft on a crankcase. The crankshaft includes a pair of non-circular T-shaped counterweights disposed on both sides of the connecting rod and connected to each other by the crank pin, each of the pair of counterweights including a connecting neck portion fixed to the connecting rod, and an enlarged portion having a circular outer periphery and having mass concentrated thereon. A lubricating oil path exists in the crankshaft for supplying oil to lubricate the pistons by oil splash. An oil filter assembly disposed on at least one side of the crankshaft, the oil filter assembly being circular and secured to at least one of the pair of counterweights; and the oil filter assembly forms a portion of the lubrication oil path to filter the oil prior to lubricating the piston by oil splash.

Further, the oil filter assembly includes a circular back plate having a circular profile corresponding to the T-weight and an annular front plate attached to the back plate.

In addition, an oil filter assembly is secured by a spacer disposed adjacent to and securing the oil filter assembly, the spacer being retained on the crankshaft by a transition fit. The roller bearing has an inner diameter secured to the crankshaft by an interference fit and an outer surface of the roller bearing is secured to the crankcase by an interference fit such that the oil filter assembly is securely retained when the crankshaft is secured within the crankcase due to the roller bearing exerting an axial force on the spacer.

According to the invention proposed above, advantages can be obtained such as preventing foreign matter such as debris from entering into the crank pin by providing a fixed support to the oil filter assembly to lubricate the reciprocating piston. The proposed oil filter assembly can itself be used as a jacket for the lubricating oil path on the crankshaft with an effective filtering action. The assembly of the oil filter assembly is simple during manufacture and assembly and can be accomplished by a simple operation such as press fitting. Therefore, the weight of the T-shaped crank arm is light and the material used is small in consideration of the filtering function of the lubricating oil. This contributes to a significant cost and weight reduction.

The invention, as well as the accompanying embodiments and other advantages, will be described in more detail in conjunction with the accompanying drawings in the following paragraphs.

Fig. 1 shows a two-wheeled vehicle 100 according to one embodiment of the invention. The vehicle includes a frame, typically a lower frame chassis frame, that provides a generally open central area to allow a rider to sit "striding" for safety. Typically, the frame assembly includes a head tube 102, a main tube 107, and a pair of side tubes 109 (only one shown). The two-wheeled vehicle extends from the front F to the rear R in the longitudinal axis direction. The head pipe 102 is arranged toward the front F, and the main pipe 107 extends downward and rearward from the head pipe 102 to form a flat horizontal stride portion 117. A pair of side pipes 109 extend rearward from the other end of the main pipe 107 and support accessories of the vehicle, such as a seat 108, a fuel tank assembly (not shown), a tool box (not shown), and a rear seat armrest 118. The head tube 102 supports the steer tube 104 and is further connected at a lower end to a front suspension system 121. The handlebar support member 124 is connected to an upper end of the steerer tube 104 and supports the handlebar assembly 106. Two telescoping front suspension systems 121 (only one shown) support the front wheels 119. The upper portion of the front wheel 119 is covered by a front fender 103 mounted to the lower portion of the steering tube 104. Front brakes (not shown) and rear brakes 114 are provided on the front wheels 119 and rear wheels 113, respectively. The rear wheel 113 is supported toward the rear side of the frame by the internal combustion engine 101, and the internal combustion engine 101 is swingably coupled horizontally to the rear of the frame assembly of the two-wheeled vehicle through a rear suspension system 115. Since the internal combustion engine 101 is directly coupled to the rear wheels 113, the internal combustion engine 101 can directly transmit drive to the rear wheels 113. The internal combustion engine 101 includes a Continuously Variable Transmission (CVT) system that is arranged on the left side of the internal combustion engine 101 in the vehicle width direction. The rear wheel 113 is surrounded by a tailgate 110 connected to the frame assembly.

Fig. 2 shows an isometric view of an internal combustion engine 101 according to an embodiment of the present subject matter. The internal combustion engine 101 is composed of a cylinder head cover 201, a cylinder head 202, a cylinder block 203, and a crankcase 204. The crankcase 204 is composed of a right-side case (RH case 204a) and a left-side case (LH case 204b), and the crankcase 204 encloses the crankshaft 300 therein. The RH case 204a supports the right side of the crankshaft 411, and the LH case 204b supports the left side of the crankshaft 413. Crankshaft 300 is disposed transverse to the longitudinal cylinder axis. The CVT mechanism is disposed on the left side of LH housing 204b, and is surrounded by CVT case 205 that surrounds the leftmost portion of internal combustion engine 101. Openings 205a in the CVT cover 205 allow air to enter the CVT cover to cool the CVT transmission components.

Fig. 3 shows a cross-sectional view of an internal combustion engine 101 according to an embodiment of the invention, illustrating the main components of the internal combustion engine. The internal combustion engine includes reciprocating pistons 303 enclosed within a cylinder block 203, connecting rods 304 connecting the reciprocating pistons 303 to a rotatable crankshaft 300. The cylinder head 202 is disposed above the cylinder block 203, and a combustion chamber 314 is formed at the junction of the cylinder head 202 and the cylinder block 203. During operation, combustion of fuel and oxidant occurs within combustion chamber 314 and transfers mechanical energy to reciprocating piston 303, which, due to the slider-crank mechanism, reciprocating piston 303 transfers mechanical energy to power-generating crankshaft 300. Cylinder head 202 includes at least one inlet valve (not shown) and at least one outlet valve (not shown) operated by a rocker arm (not shown) and a camshaft 301, camshaft 301 including at least one inlet cam lobe (not shown) and at least one outlet cam lobe (not shown) that actuate the rocker arm (not shown) when desired. The cam chain 313 is engaged between the crankshaft 300 and the camshaft 301 to drive the camshaft 301 in the cylinder head 202. An intake air-fuel mixture from a throttle body (not shown) is connected to an intake port of the internal combustion engine 101 in the cylinder head 202, and an exhaust system including a muffler (not shown) is connected to an exhaust port of the cylinder head 202. CVT system 311 is attached to one end of crankshaft 300 and magneto assembly 308 is disposed at the other end of crankshaft 300. CVT system 311 includes a V-belt located between two fixed pulleys and one of the pulleys includes a variator. The CVT cover 205 forms the outside of the internal combustion engine 101 and surrounds the CVT system. The CVT cover 205 includes a foot actuator assembly that includes a foot actuator lever 206, the foot actuator lever 206 being assembled over a return spring 309 and a ratchet mechanism 350. The ratchet mechanism 350 is configured to engage the crankshaft 300 on the front side of the internal combustion engine 101.

Fig. 4 illustrates an isometric view of a crankshaft 300 and a connecting rod 304, according to an embodiment of the present subject matter. The crankshaft 300 is accommodated in the crank case 204, and is rotatably supported by the crank case 204 on both sides. In particular, crankshaft 300 is rotatably supported by a pair of RH and

LH roller bearings

307, 312 disposed within crankcase 204. Crankshaft 300 includes a pair of laterally extending arms having

respective counterweights

410, 412, including an RH arm 411 and an LH arm 413, and respective RH counterweight 410 and LH counterweight 412 extending laterally from connecting rod large end 304a thereof. The pair of

roller bearings

307, 312 are disposed on both sides of the link 304 to rotatably support the pair of laterally extending

arms

411, 413. The crankshaft further defines a pair of non-circular T-shaped

counterweights

410, 412 disposed on either side of the connecting rod big end 304a and connected to each other by a crankpin 414. Each of the pair of

weights

410, 412 includes a long narrow connecting neck 450 fixed to the connecting rod large end 304a, and an enlarged portion 460 having a circular outer periphery, and mass is concentrated on the enlarged portion 460. This improved eccentric shaped weight acts as a crank arm and is superior to a circular crank arm with weights because of the savings in excess material toward the left and right sides of the top of the mass concentration zone. This reduces the weight of the crankshaft and reduces its manufacturing cost.

Fig. 5 shows an exploded view of a crankshaft of the internal combustion engine 101 employing an embodiment of the present invention, and the crankshaft is housed in a crankcase 204. The crankshaft of the split design has an RH arm 411 as the magneto 308 side and an LH arm 413 as the CVT 311 side. The crank pin 414 is inserted through the large end 304a of the connecting rod 304 and frictionally engages both sides of the connecting neck 450 through the holes present in the counterweight 410 and the counterweight 412. The needle bearing 304b is disposed between the crank pin 414 and the large end 304a of the connecting rod 304, and the needle bearing 304b is assembled in such a manner that the inwardly facing circumferential surface of the large end 304a serves as a bearing running area for the needle bearing 304 b.

FIG. 6a shows an isometric view of oil filter assembly 401 secured to one side of crankshaft 300. Fig. 6b and 6c show front and side views of oil filter assembly 401 according to an embodiment of the present subject matter. According to the invention, an oil filter assembly 401 is arranged on at least one side of the crankshaft 300. In this embodiment, oil filter assembly 401 is disposed on the right side of crankshaft 401 and is secured to RH arm 411 proximate to RH weight 410. The oil filter assembly is circular and forms part of a lubrication oil path to filter oil to lubricate the piston by oil splashing. Oil filter assembly 401 includes a circular back plate 401b and a slightly bowl-shaped front plate 401a with an annular aperture 401d in the center of front plate 401 a. The front plate 401a is fixed to a side surface of the back plate 401b to define a centrifugal separation chamber 401e inside in cooperation with a side surface of the back plate 401 b. The oil filter assembly 401 is arranged between the oil paths so that the oil is forced under pressure into the centrifugal separation chamber 401e under pressure. Since the oil filter assembly 401 is securely attached to the crankshaft 300, during operation, the oil filter assembly 401 rotates with the crankshaft 300. The centrifugal force of oil filter assembly 401 forces foreign particles and suspended solids in the oil in centrifugal separation chamber 401e to be centrifugally thrown toward the outer lip of rear plate 401 b. Thus, the remaining filtered and cleaned oil is forced into the crank pin opening 401c, which crank pin opening 401c is configured to communicate with the crank pin bore 414a to supply filtered oil to the crank pin 414 for lubrication of the reciprocating piston 303 within the cylinder block 203 by oil splash lubrication. Foreign particles and other suspended solids include dust, swarf, and the like. The back plate 401b of the oil filter assembly 401 is circular and has a circular profile. When back plate 401b is secured to T-weight 410, the circular profile of back plate 401b matches the circular profile of T-weight 410. In this way, the necessity of a counterweight having a circular shape is avoided, and an oil filtering function can be effectively performed by the oil filter assembly 401 proposed by the present invention. In one embodiment, back plate 401b and front plate 401a are made of a steel alloy material.

FIG. 7 shows an enlarged cross-sectional view of an internal combustion engine illustrating oil lubrication paths within the crankshaft according to an embodiment of the present subject matter. In the present embodiment, the lubricating oil is supplied from the RH housing 204a to the oil filter assembly 401. RH housing 204a includes oil passages 701 through which lubricating oil flows under pressure to crankshaft 300. There is a small notch 703 on the contact surface between the RH crankshaft bearings 307, and the oil passages 701 meet at the notch 703. The recess 703 defines a lubrication oil path in the crankshaft that lubricates the piston by splashing supply oil from the bottom of the connecting rod, allowing oil 700 to flow from the oil gallery 701 to the oil filter assembly 401. The lubricating oil 700 is further filtered by the oil filter assembly 401 and flows in toward the crank pin hole 414a through the rear plate opening 401 c. The crank pin 414 includes a crank pin oil passage 414b that allows oil to flow from the crank pin bore 414a to the connecting rod big end 304 a. The shape of the large end 304a of the connecting rod is such that the lubricating oil 700 is under pressure at each rotation of the crankshaft 300, and the lubricating oil splashes into the piston 303 from the inside of the entire cylinder block 203.

Fig. 8a shows an enlarged sectional view of a crankshaft according to an embodiment of the invention, the crankshaft being supported by an RH housing by means of an RH roller bearing 307. The oil filter assembly 401 is held by a spacer 501, the spacer 501 being arranged adjacent to the oil filter assembly 401 and holding the oil filter assembly 401, the spacer 501 being held on the crankshaft 300 by a transition fit. The inner diameter of the RH roller bearing 307 is fixed to the RH crankshaft surface 411a by interference fit, and the outer surface of the RH roller bearing 307 is fixed to the RH housing 204a by interference fit. When the RH housing 204a is assembled in connection with the LH housing 204b, the gasket 501 is subjected to an axial force applied to the gasket 501 by the roller bearing 307. This axial force F on the washer 501 holds the oil filter assembly 401 firmly in place on the crankshaft 300. The diameter of the shim may vary based on the clamping force applied by the roller bearing. The shim 501 is made of alloy steel.

FIG. 8b shows an exploded view of the right half of the crankshaft with oil filter assembly assembled within an RH housing according to an embodiment of the present invention. As can be seen, the washer 501 is assembled on the RH crankshaft surface 411a by a transition fit so that the oil filter assembly 401 is securely held on the RH crankshaft surface 411 a. However, to ensure that oil filter assembly 401 can be tightly and securely fit on crankshaft 300, the inner diameter of RH roller bearing 307 is secured to RH crankshaft surface 411a by an interference fit, and further, the outer diameter of the RH roller bearing is secured to RH housing 204a by an interference fit, and RH housing 204a and LH housing 204b are clamped together upon assembly. This therefore provides an axial clamping force on the washer 501 and thereby holds the oil filter assembly 401 securely in place.

Many modifications and variations of the present subject matter are possible in light of the above disclosure. Therefore, within the scope of the subject claims, the disclosure may be practiced other than as specifically described.

Claims

1. An internal combustion engine (101), comprising:

a crankcase (204) composed of a right-side crankcase (204a) and a left-side crankcase (204 b);

a cylinder block (203) disposed above the crankcase (204);

a piston (303) reciprocating within the cylinder block (203);

a crankshaft (300) enclosed and supported within the crankcase (204), the piston (303) and the crankshaft (300) being connected by a connecting rod (304) for converting reciprocating motion of the piston (303) into rotational motion of the crankshaft (300);

a pair of roller bearings (307, 312) for supporting the crankshaft (300) on the crankcase (204);

the crankshaft (300) includes a pair of non-circular T-shaped counterweights (410, 412), the pair of non-circular T-shaped counterweights (410, 412) being disposed on both sides of the connecting rod (304) and connected to each other by a crank pin (414), and each of the pair of counterweights (410, 412) includes a connecting neck portion (450) and an enlarged portion (460), the connecting neck portion (450) being fixed to the connecting rod (304), and the enlarged portion (460) being configured to have a circular outer circumference, and each mass of the pair of counterweights (410, 412) being concentrated at the enlarged portion (460);

a lubrication oil path (701, 703) provided in the crankshaft (300) for lubricating the piston (303) by oil splash supply from a bottom surface of the connecting rod (304), wherein the crankcase (204) supplies oil to the lubrication oil path (701, 703);

wherein the content of the first and second substances,

an oil filter assembly (401) separately mounted on at least one side of the crankshaft (300); and the oil filter assembly (401) is circular and fixed to at least one of the pair of weights (410, 412); and the oil filter assembly (401) is configured to form part of the lubrication oil path (701, 703) to filter oil prior to lubricating the piston (303) by oil splash; and is

Wherein the oil filter assembly (401) is secured to the crankshaft (300) by a spacer (501), wherein the spacer (501) is disposed between the oil filter assembly (401) and one of the pair of roller bearings (307, 312);

wherein one of the pair of roller bearings (307, 312) has an inner diameter fixed to the crankshaft (300) by interference fit, and an outer surface of the one of the pair of roller bearings (307, 312) is fixed to one of the right-side crankcase (204a) and the left-side crankcase (204b) by interference fit.

2. The internal combustion engine (101) of claim 1, wherein the oil filter assembly (401) comprises a circular back plate (401b) and an annular front plate (401a), wherein the annular front plate (401a) is connected to the circular back plate (401b) and the circular back plate (401b) has a circular profile corresponding to the outer shape of the T-shaped counterweight (410, 412).

3. The internal combustion engine (101) of claim 1, wherein the spacer (501) is disposed adjacent to the oil filter assembly (401) and secures the oil filter assembly (401), wherein the spacer (501) is retained on the crankshaft (300) by a transition fit.

4. The internal combustion engine (101) of claim 1, wherein the oil filter assembly (401) is securely retained to the crankshaft (300) by one of the pair of roller bearings (307, 312) exerting an axial force on the shim (501) when the crankshaft (300) is secured within the crankcase (204).

5. The internal combustion engine (101) of claim 2, wherein the back plate (401b) includes a crankpin opening (401d), the crankpin opening (401d) configured to communicate with a bore (414a) disposed within the crankpin (414), thereby forming a portion of the lubrication oil path (701, 703, 414a) to supply filtered oil to the crankpin (414) for lubrication of the piston (303) within the cylinder block (203).

6. The internal combustion engine (101) of claim 2, wherein the back plate (401b) and the front plate (401a) are made of alloy steel, and the shim (501) is made of alloy steel.

7. The internal combustion engine (101) of claim 1, wherein a continuously variable transmission system (311) is connected to one end of the crankshaft (300) and a magneto assembly (308) is arranged at the other end of the crankshaft (300).

8. The internal combustion engine (101) of claim 1, wherein the oil filter assembly (401) is disposed on a right side of the crankshaft (300) and oil is supplied to the oil filter assembly (401) from a crankcase (204a) on the right side.

9. The internal combustion engine (101) of claim 4, wherein a diameter of the shim (501) is predetermined based on the axial force applied by the roller bearing (307) for clamping the shim (501).

10. A two-wheeled scooter-type vehicle (100) comprising an internal combustion engine (101) as claimed in any one of the preceding claims.