STRADDLED VEHICLE

Abstract

 A straddled vehicle is capable of supplying clean lubricant, which has been removed of foreign matter, to a transmission. A straddled vehicle includes an annular plate (47) fixed to a first side wall (31a) of a first crank web (31), with a part of the annular plate (47) being spaced apart from the first side wall (31a). The first side wall (31a) and the annular plate (47) together form a centrifugal filter (50) that is closed on the radially outer side and is open on the radially inner side. The straddled vehicle further includes a first oil path (81) configured to guide lubricant to the centrifugal filter (50), and a second oil path (82) configured to guide lubricant from the centrifugal filter (50) to a gap between a connecting rod (19) and a crankpin (36). A front end of a transmission is located rearward of a rear end of a cylinder (6). The transmission is placed rearward of the centrifugal filter (50) . A part of the transmission overlaps with the centrifugal filter (50), as the vehicle is seen from the front.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to a straddled vehicle having an internal combustion engine.

Description of the Related Art

[0002] Straddled vehicles having an internal combustion engine placed inside a crankcase, and a V-belt continuously variable transmission placed outside the crankcase are known in the art. Also, straddled vehicles having an internal combustion engine placed inside a crankcase, and a transmission including a plurality of gears placed inside the crankcase are known in the art. With such a straddled vehicle, in which the transmission is placed inside the crankcase, foreign matter generated by abrasion of the transmission may contaminate the lubricant inside the crankcase. Therefore, such a straddled vehicle may have a larger amount of foreign matter contaminating the lubricant, as compared with a straddled vehicle in which the transmission is placed outside the crankcase.

[0003] Japanese Laid-Open Patent Publication No. 2014-70568 discloses a straddled vehicle having a first oil path provided inside a crankshaft, a second oil path provided inside the crankshaft, and a centrifugal filter attached to the crankshaft. The centrifugal filter communicates with the first oil path via a first communicating hole, and communicates with the second oil path via a second communicating hole. With this straddled vehicle, if the lubricant flowing through the first oil path is contaminated with foreign matter, the foreign matter is removed by the centrifugal filter. The lubricant, which has been removed of the foreign matter, is supplied to the second oil path.

SUMMARY OF THE INVENTION

[0004] It is an object of the present invention to provide a straddled vehicle with which it is possible to supply clean lubricant, which has been removed of foreign matter, to the transmission.

[0005] This object is achieved by a straddled vehicle as defined in the independent claim.

[0006] With the known straddled vehicle described above, the lubricant, which has been removed of the foreign matter by the centrifugal filter, flows through the second oil path inside the crankshaft and is guided to the big end of the connecting rod. The lubricant in the centrifugal filter needs to be pressurized in order for the lubricant in the centrifugal filter to flow into the second oil path inside the crankshaft against the centrifugal force. Therefore, the space inside the centrifugal filter is sealed except for the first communicating hole and the second communicating hole. The lubricant, having flowed into the second oil path inside the crankshaft, is used for lubricating sliding parts, such as the big end and the small end of the connecting rod, and for cooling the piston. The lubrication of the small end of the connecting rod and the cooling of the piston are done by the lubricant being ejected upward from between the big end of the connecting rod and the crank web.

[0007] When a crankshaft is provided with a centrifugal filter, as in the straddled vehicle described above, the filter maintainability is better than that of a vehicle provided with an oil filter. When a crankshaft is provided with a centrifugal filter, however, it is difficult to supply, to the transmission, clean lubricant, which has been removed of the foreign matter by the centrifugal filter. This is because all of the lubricant, which has been removed of the foreign matter by the centrifugal filter, flows into the second oil path to lubricate and cool the piston and the connecting rod in the cylinder, after which the lubricant freefalls to be collected in an oil pan, but the transmission is absent in the path of free fall of the lubricant. In addition, when a crankshaft is provided with a centrifugal filter, it is often the case that only a simple oil filter, such as a meshed filter, is provided along the lubricant path from the oil pan to the transmission. In such a case, foreign matter having a size larger than the mesh size is removed but relatively small foreign matter is not removed. Therefore, with the straddled vehicle described above, it is not possible to supply clean lubricant, which has been removed of finer foreign matter by the centrifugal filter, to the transmission.

[0008] A straddled vehicle of the present invention includes a crankcase, a cylinder, a crankshaft, a transmission, a connecting rod, a piston, a bearing, an annular plate, a first oil path, and a second oil path. The crankcase includes a wall with a hole therein. The cylinder is connected to the crankcase, at least a part of the cylinder being located above the crankcase. The crankshaft is placed inside the crankcase and includes a first crank web including a first side wall and a second side wall on an opposite side from the first side wall, a second crank web facing the second side wall of the first crank web, a crankpin connected to the first crank web and the second crank web, and a first shaft provided on the first side wall of the first crank web. The transmission is placed inside the crankcase and includes a first rotation shaft, a second rotation shaft, a plurality of first gears provided on the first rotation shaft, and a plurality of second gears provided on the second rotation shaft and meshing with the first gears. The connecting rod includes a big end and a small end, the big end including a pin hole in which the crankpin is inserted. The piston is placed inside the cylinder and connected to the small end of the connecting rod. The bearing is placed in the hole of the wall of the crankcase and configured to rotatably support the first shaft. The annular plate is fixed to the first side wall of the first crank web, a part of the annular plate being spaced apart from the first side wall. The centrifugal filter is formed by the first side wall and the annular plate, the centrifugal filter being closed on a radially outer side and being open on a radially inner side. The first oil path communicates with the centrifugal filter and is configured to guide lubricant to the centrifugal filter. The second oil path is configured to connect between the centrifugal filter and a gap between the connecting rod and the crankpin. The second oil path includes a first channel hole formed inside the crankpin and extending in an axial direction of the crankpin, and a second channel hole formed inside the crankpin and extending in a radial direction of the crankpin, the second channel hole communicating with the first channel hole. A front end of the transmission is located rearward of a rear end of the cylinder. The transmission is placed rearward of the centrifugal filter. A part of the transmission overlaps with the centrifugal filter, as the vehicle is seen from the front.

[0009] With the straddled vehicle described above, if the lubricant having been guided from the first oil path to the centrifugal filter has been contaminated with foreign matter, the foreign matter is collected on the outer side in the radial direction of the centrifugal filter by virtue of the centrifugal force from the rotation. As a result, the foreign matter is separated from the lubricant, and clean lubricant, which has been removed of the foreign matter, is sent from the centrifugal filter to the second oil path. Clean lubricant, which has been removed of foreign matter, is supplied to the gap between the connecting rod and the crankpin. With the straddled vehicle, at least a part of the cylinder is placed upward of the crankcase, and the front end of the transmission is located rearward of the rear end of the cylinder. Therefore, lubricant freefalling from the gap between the connecting rod and the crankpin is unlikely to be supplied to the transmission. However, with the straddled vehicle, since the centrifugal filter is open on the radially inner side, not all of the lubricant, which has been removed of foreign matter by the centrifugal filter, does not flow into the second oil path. A part of the clean lubricant, which has been removed of foreign matter by the centrifugal filter, overflows the centrifugal filter to be scattered outward in the radial direction of the crankshaft by virtue of the centrifugal force. Since the transmission is placed rearward of the centrifugal filter, the lubricant that has been scattered from the centrifugal filter is supplied to the transmission. Therefore, with the straddled vehicle, clean lubricant, which has been removed of foreign matter by the centrifugal filter, can be supplied to the transmission.

[0010] According to a preferred embodiment of the present invention, the first side wall of the first crank web includes an outer edge wall located radially outward of the first shaft and a depressed wall located radially inward of the outer edge wall and depressed relative to the outer edge wall. The annular plate is spaced apart from at least a part of the depressed wall. The depressed wall and the annular plate together form the centrifugal filter.

[0011] According to the above embodiment, a desirable centrifugal filter is formed by the depressedwall and the annular plate.

[0012] According to another preferred embodiment of the present invention, the centrifugal filter includes an oil reservoir space defined by the first side wall and the annular plate.

[0013] According to the above embodiment, foreign matter is removed from lubricant by using the centrifugal force in the oil reservoir space.

[0014] According to another preferred embodiment of the present invention, the annular plate includes an inner circumferential edge spaced apart from the bearing in a radially outward direction.

[0015] According to the above embodiment, it is possible, with a simple configuration, to form a centrifugal filter that is closed on the radially outer side and is open on the radially inner side.

[0016] According to another preferred embodiment of the present invention, the first oil path is formed in the wall of the crankcase and includes an opening, at least a part of the opening being located radially inward of the inner circumferential edge of the annular plate.

[0017] According to the above embodiment, lubricant can be guided to the centrifugal filter through the opening formed in the wall of the crankcase.

[0018] According to another preferred embodiment of the present invention, an oil path in which lubricant flows is absent inside the first shaft.

[0019] According to the above embodiment, since there is no need to machine an oil path inside the first shaft, it is possible to reduce the machining cost and to decrease the radius of the first shaft.

[0020] According to another preferred embodiment of the present invention, the first oil path is formed in the first shaft and includes an opening, the opening being located radially inward of the inner circumferential edge of the annular plate and between the annular plate and the first side wall with respect to an axial direction of the crankshaft.

[0021] According to the above embodiment, lubricant can be guided to the centrifugal filter through the opening formed in the first shaft.

[0022] According to another preferred embodiment of the present invention, a gap in a radial direction between the inner circumferential edge of the annular plate and the bearing is smaller than a dimension of the bearing in the radial direction.

[0023] According to the above embodiment, a desirable centrifugal filter is obtained, whichmakes it possible to supply clean lubricant to the gap between the connecting rod and the crankpin and to the transmission.

[0024] According to another preferred embodiment of the present invention, a gap in a radial direction between the inner circumferential edge of the annular plate and the bearing is smaller than a dimension in the radial direction between the inner circumferential edge and an outer circumferential edge of the annular plate.

[0025] According to the above embodiment, a desirable centrifugal filter is obtained, whichmakes it possible to supply clean lubricant to the transmission.

[0026] According to another preferred embodiment of the present invention, the crankcase includes another wall including an oil path and a discharge port formed therein, wherein lubricant flows in the oil path, and the discharge port is connected to the oil path and includes an opening facing the transmission. The discharge port is placed so as to be aligned with a part of the transmission with respect to an axial direction of the crankshaft.

[0027] According to the above embodiment, it is possible not only to supply lubricant that has overflowed the centrifugal filter to the transmission, but also to supply lubricant to the transmission via the discharge port. Therefore, it is possible to supply a sufficient amount of lubricant to the transmission.

Advantageous Effects Of Invention

[0028] According to the present invention, it is possible to provide a straddled vehicle that can supply clean lubricant, which has been removed of foreign matter, to the transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 

FIG. 1 is a side view of a motorcycle according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a power unit of the motorcycle.

FIG. 3 is a schematic view showing a positional relationship between main parts of the power unit.

FIG. 4 is a cross-sectional view of a centrifugal filter and other members around the centrifugal filter.

FIG. 5 shows a part of a crankshaft and a part of a transmission, as the vehicle is seen from the front.

FIG. 6 is a schematic view showing a configuration of an oil supply system.

FIG. 7 is a cross-sectional view showing an oil path provided in the crankcase wall and a part of the transmission.

FIG. 8 is a cross-sectional view of a power unit according to another embodiment.

FIG. 9 is a cross-sectional view of a power unit according to another embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] One embodiment of the present invention will now be described with reference to the drawings. As shown in FIG. 1, a vehicle of the present embodiment is a motorcycle 1, which is an example straddled vehicle to be straddled by a passenger. Note however that the vehicle of the present invention is not limited to the motorcycle 1, but may be any other straddled vehicle to be straddled by a passenger, such as a three-wheeled vehicle, an all terrain vehicle (ATV) and a snowmobile.

[0031] The terms front, rear, left, right, up and down, as used in the description below, refer to these directions as seen from a passenger seated in a seat 4 while the motorcycle 1 is stationary in an upright position on a horizontal surface, unless specified otherwise. The designations F, Re, L, R, U and D, as used in the figures, refer to front, rear, left, right, up and down, respectively. The terms forward and rearward refer to these directions in the vehicle front-rear direction, unless specified otherwise. The terms upward and downward refer to these directions in the vehicle up-down direction. The terms leftward and rightward refer to these directions in the vehicle left-right direction.

[0032] As shown in FIG. 1, the motorcycle 1 includes a vehicle body frame 2 including a head pipe 12, a power unit 3 supported on the vehicle body frame 2, a front wheel 20 and a rear wheel 30. A steering shaft 13 is rotatably supported on the head pipe 12. A handle bar 11 is fixed on an upper portion of the steering shaft 13, and a front fork 14 is fixed on a lower portion of the steering shaft 13. The front wheel 20 is attached to the front fork 14. A fuel tank 10 is placed upward of the power unit 3. The seat 4 is placed rearward of the fuel tank 10. The power unit 3 is linked to the rear wheel 30 via a transmission member such as a chain 26 (not shown in FIG. 1; see FIG. 2).

[0033] Next, a configuration of the power unit 3 will be described. As shown in FIG. 2, the power unit 3 includes an internal combustion engine 5. The power unit 3 drives the rear wheel 30 using the power from the internal combustion engine 5. In the present embodiment, the internal combustion engine 5 is a single-cylinder internal combustion engine including a single cylinder 6. Note however that the internal combustion engine 5 may be a multi-cylinder internal combustion engine including a plurality of cylinders.

[0034] The power unit 3 includes a crankcase 7, a cylinder block 8 fixed on the crankcase 7, a cylinder head 9 fixed on the cylinder block 8, and a cylinder head cover 15 fixed on the cylinder head 9. The cylinder 6 is provided inside the cylinder block 8, and a piston 16 is placed inside the cylinder 6. Note that although the cylinder 6 is a part of the cylinder block 8, the cylinder 6 in the present embodiment is a cylinder sleeve, which is separate from the other part of the cylinder block 8. Note however that the present invention is not limited to this. The cylinder 6 may be integral with the other part of the cylinder block 8. For example, the cylinder 6 may be provided by, for example, plating the wall surface of the circular hole of the cylinder block 8. A combustion chamber 17 is defined by the piston 16, the cylinder 6 and the cylinder head 9. At least a part of the cylinder block 8 is placed upward of the crankcase 7 (see FIG. 3). Therefore, at least a part of the cylinder 6 is placed upward of the crankcase 7.

[0035] A crankshaft 18 is placed inside the crankcase 7. The crankshaft 18 and the piston 16 are linked together by a connecting rod 19. The piston 16 is connected to a small end 19a of the connecting rod 19. The crankshaft 18 is connected to a big end 19b of the connecting rod 19. The small end 19a is placed upward of the big end 19b. A generator 21 is attached to the left end of the crankshaft 18. A gear 28 is placed at the right end of the crankshaft 18.

[0036] A main shaft 23 and a drive shaft 24 are placed inside the crankcase 7. The main shaft 23 and the drive shaft 24 are an example of the "first rotation shaft" and an example of the "second rotation shaft", respectively. The main shaft 23 and the drive shaft 24 are placed parallel to the crankshaft 18. A plurality of transmission gears 25A are provided on the main shaft 23. Transmission gears 25B, meshing with the transmission gears 25A, are provided on the drive shaft 24. The transmission gears 25A and 25B are an example of the "first gears" and an example of the "second gears", respectively. The main shaft 23, the transmission gears 25A, the transmission gears 25B and the drive shaft 24 together form a transmission 35 placed inside the crankcase 7. The left end 24a of the drive shaft 24 is placed outside the crankcase 7. A sprocket 26A is fixed at the left end 24a of the drive shaft 24, with the chain 26 wrapped around the sprocket 26A.

[0037] As shown in FIG. 3, a front end 35f of the transmission 35 is located rearward of a rear end 6b of the cylinder 6. Note that the front end 35f of the transmission 35 is the most forward part of the transmission 35 in the vehicle front-rear direction. In the present embodiment, the most forward part of the transmission gears 25A in the vehicle front-rear direction is the front end 35f. The rear end 6b of the cylinder 6 is the most rearward part of the cylinder 6 in the vehicle front-rear direction. Thus, the transmission 35 is absent directly below the cylinder 6. The transmission 35 is absent in the path in which the lubricant freefalls from the cylinder 6.

[0038] As shown in FIG. 2, a clutch 40 is provided at the right end of the main shaft 23. While the clutch 40 is a wet multiple-disc clutch in the present embodiment, there is no particular limitation on the type of the clutch 40. The clutch 40 includes a clutch housing 41 rotatably supported on the main shaft 23, a clutch boss 42 non-rotatably supported on the main shaft 23, a plurality of plates 27 which are supported on the clutch housing 41 and rotate together with the clutch housing 41, a plurality of plates 29 which are supported on the clutch boss 42 and rotate together with the clutch boss 42, a pressure plate 43 configured to press the plates 27 and the plates 29 against each other, and a spring 45 configured to urge the pressure plate 43 toward the plates 27 and the plates 29.

[0039] The crankshaft 18 includes a first crank web 31, a second crank web 32, a first shaft 33 and a second shaft 34. The first crank web 31 and the first shaft 33 are provided as an integral part, and the second crank web 32 and the second shaft 34 are provided as an integral part. As shown in FIG. 4, the first crank web 31 includes a first side wall 31a, and a second side wall 31b on the opposite side from the first side wall 31a. The second crank web 32 is facing the second side wall 31b of the first crank web 31. The first shaft 33 is provided on the first side wall 31a of the first crank web 31. In the present embodiment, the first side wall 31a and the second side wall 31b are the right side wall and the left side wall, respectively, of the first crank web 31. The first shaft 33 extends rightward from the first side wall 31a. The second shaft 34 extends leftward from the second crank web 32.

[0040] The first crank web 31 includes a pin hole 31c, and the second crank web 32 includes a pin hole 32c. A pin hole 19c is provided in the big end 19b of the connecting rod 19. A crankpin 36 is inserted through these pin holes 31c, 32c and 19c. The crankpin 36 is connected to the first crank web 31, the big end 19b of the connecting rod 19 and the second crank web 32. The first crank web 31, the big end 19b of the connecting rod 19 and the second crank web 32 are linked together by the crankpin 36.

[0041] As shown in FIG. 2, the crankcase 7 includes a wall 38 with a hole 37 therein, and a wall 44 with a hole 66 therein. A bearing 39 rotatably supporting the first shaft 33 and a metal sleeve 85 are placed in the hole 37. Note that the sleeve 85 is not always needed, and it may be omitted. A bearing 46 rotatably supporting the second shaft 34 is placed in the hole 66. The bearings 39 and 46 are ball bearings in the present embodiment. Note however that the bearings 39 and 46 are not limited to ball bearings.

[0042] As shown in FIG. 4, an annular plate 47 is fixed to the first side wall 31a of the first crank web 31. The first side wall 31a includes an outer edge wall 31d located radially outward of the first shaft 33, and a depressed wall 31e located radially inward of the outer edge wall 31d and depressed relative to the outer edge wall 31d. Note that the terms radially inward and radially outward refer to a direction toward an axis 18c of the crankshaft 18 and a direction away from the axis 18c, respectively. The annular plate 47 includes a flat portion 47a perpendicular to the direction of the axis 18c of the crankshaft *18 (hereinafter referred to as the axis direction), and a depressed portion 47b located radially outward of the flat portion 47a and depressed toward the first side wall 31a relative to the flat portion 47a. In the present embodiment, the depressed portion 47b of the annular plate 47 is in contact with the first side wall 31a. The flat portion 47a of the annular plate 47 is spaced apart from at least a part of the depressed wall 31e. The flat portion 47a of the annular plate 47 is spaced apart in the axis direction from the part of the depressed wall 31e. Herein, the flat portion 47a of the annular plate 47 is spaced apart rightward from the part of the depressed wall 31e. The most radially inward portion of the flat portion 47a is an inner circumferential edge 47c of the annular plate 47. The inner circumferential edge 47c is spaced apart from the bearing 39 in the radially outward direction. There is a gap between the inner circumferential edge 47c and the bearing 39.

[0043] The first side wall 31a and the annular plate 47 together form a centrifugal filter 50 that is closed on the radially outer side and is open on the radially inner side. Note that in the present embodiment, the gap between the inner circumferential edge 47c of the annular plate 47 and the bearing 39 is the opening of the centrifugal filter 50. As described above, the annular plate 47 is in contact with the depressed wall 31e of the first side wall 31a in the present embodiment. Therefore, the centrifugal filter 50 is formed by the depressed wall 31e and the annular plate 47. The centrifugal filter 50 includes an oil reservoir space 51 defined by the first side wall 31a and the annular plate 47. While there is no particular limitation on the gap G1 in the radial direction between the inner circumferential edge 47c of the annular plate 47 and the bearing 39, the gap G1 is herein smaller than the width G2 of the bearing 39 in the radial direction. The gap G1 is smaller than the distance G3 in the radial direction between the inner circumferential edge 47c and the outer circumferential edge of the annular plate 47.

[0044] As shown in FIG. 3, the transmission 35 is placed rearward of the centrifugal filter 50. The front end 35f of the transmission 35 is placed rearward of a rear end 50b of the centrifugal filter 50. As shown in FIG. 5, a part of the transmission 35 overlaps the centrifugal filter 50. Note that hatching representing the cross section of the crankshaft 18 and the connecting rod 19 is omitted in FIG. 5 for a better view of the transmission 35 located rearward of the crankshaft 18 and the connecting rod 19.

[0045] The power unit 3 includes a number of sliding parts. Therefore, the power unit 3 includes an oil supply system 70 configured to supply lubricant to the sliding parts. FIG. 6 is a schematic view showing a configuration of the oil supply system 70. Arrows in FIG. 6 each represent a lubricant flow.

[0046] The oil supply system 70 includes an oil pan 61, a meshed oil filter 61A, an oil pump 62 and the centrifugal filter 50 described above. The oil pan 61 is provided at the bottom of the crankcase 7. Lubricant, having lubricated sliding parts of the power unit 3, is collected in the oil pan 61. The oil pan 61 and an inlet 62i of the oil pump 62 are connected to each other by an oil path 71. The oil filter 61A is provided in the oil path 71 and is configured to filter oil which is sucked into the oil pump 62 from the oil pan 61. Oil having been cleaned through the oil filter 61A is supplied to the oil pump 62. An oil path 72 is connected to an outlet 62o of the oil pump 62. The oil path 72 diverges into an oil path 73 and an oil path 76.

[0047] The oil path 73 further diverges into an oil path 74 and an oil path 75. The oil path 74 extends to the cylinder head cover 15 via the crankcase 7, the cylinder block 8 and the cylinder head 9. Oil supply ports 74a and 74b provided along the oil path 74 are configured to supply lubricant from above to an intake valve 67, an intake cam 67a (see FIG. 2), an exhaust valve 48 and an exhaust cam 48a (see FIG. 2).

[0048] A discharge port 75a provided along the oil path 75 is configured to supply lubricant to the transmission 35. As shown in FIG. 7, the discharge port 75a is provided in a wall 49 of the crankcase 7, and has an opening facing toward the transmission 35. The oil path 75 includes an oil path 75b formed inside the wall 49. The oil path 75b is connected to the discharge port 75a. The discharge port 75a is placed so as to be aligned with a part of the transmission 35 with respect to the axial direction of the crankshaft 18 (the left-right direction of FIG. 7). The discharge port 75a is configured to inject lubricant toward the transmission 35. In the present embodiment, the discharge port 75a has an opening facing toward transmission gear 25A that is the first gear. Note however that the opening of the discharge port 75a may be facing toward a transmission gear 25A that is other than the first gear. The opening of the discharge port 75a may be facing the main shaft 23, the drive shaft 24 and/or the transmission gears 25B. There is no particular limitation on the number of the discharge ports 75a.

[0049] As shown in FIG. 6, the oil path 76 is connected to a first oil path 81 configured to guide oil to the centrifugal filter 50. As shown in FIG. 4, the first oil path 81 is formed inside the wall 38 of the crankcase 7. The first oil path 81 includes an opening 81o for discharging oil. The opening 81o is formed in the wall 38. In the present embodiment, the opening 81o is defined by the gap, in the hole 37 of the wall 38, between the bearing 39 and the sleeve 85. Note however that the position and the configuration of the opening 81o are not limited to those of the present embodiment. At least a part of the opening 81o is located radially inward of the inner circumferential edge 47c of the annular plate 47. The opening 81o is facing toward the first side wall 31a of the first crank web 31.

[0050] A gap 55 is formed between the big end 19b of the connecting rod 19 and the crankpin 36. The gap 55 includes a gap 55a between the crankpin 36 and a needle bearing 39B, a gap 55b between the needle bearing 39B and the big end 19b, and a gap 55c between the big end 19b and the crank webs 31 and 32. The centrifugal filter 50 and the gap 55 communicate with each other via a second oil path 82. The second oil path 82 includes a first channel hole 82a formed inside the crankpin 36 and extending in the axial direction of the crankpin 36, and a second channel hole 82b formed inside the crankpin 36 and extending in the radial direction of the crankpin 36. The first channel hole 82a and the second channel hole 82b communicate with each other. Note that as used herein, "extending in the axial direction of the crankpin 36" may refer not only to extending in the axis direction of the crankpin 36, but also to extending in a direction inclined from the axis direction. As used herein, "extending in the radial direction of the crankpin 36" may refer not only to extending in a direction perpendicular to the axis direction of the crankpin 36, but also to extending in a direction inclined from the direction perpendicular to the axis direction.

[0051] As shown in FIG. 2, an oil path in which lubricant flows is absent inside the first shaft 33 of the crankshaft 18. An oil path in which lubricant flows is also absent inside the second shaft 34. Note however that it is possible to form an oil path inside the first shaft 33, in addition to the first oil path 81.

[0052] The power unit 3 is configured as described above. Next, oil circulation in the power unit 3 will be described.

[0053] Lubricant is stored in the oil pan 61. Note however that the lubricant stored in the oil pan 61 is lubricant having lubricated sliding parts (e.g. , the intake cam 67a, the exhaust cam 48a, the transmission 35, etc.). For example, the lubricant stored in the oil pan 61 may include foreign matter from lubricated parts like the intake cam. Therefore, foreign matter may be contained in the lubricant stored in the oil pan 61. The lubricant stored in the oil pan 61 is guided to the oil path 72 by the oil pump 62. The lubricant in the oil path 72 diverges into the oil path 73 and the oil path 76, and the lubricant in the oil path 73 diverges into the oil path 74 and the oil path 75.

[0054] The lubricant in the oil path 74 is supplied to the intake cam 67a and the intake valve 67 via the oil supply port 74a, and to the exhaust cam 48a and the exhaust valve 48 via the oil supply port 74b. These streams of lubricant fall down by virtue of gravity to lubricate the intake cam 67a, the intake valve 67, the exhaust cam 48a and the exhaust valve 48, and are supplied further to a cam chain 54, etc., to be collected in the oil pan 61.

[0055] The lubricant in the oil path 75 is supplied to the transmission 35 via the discharge port 75a. The lubricant injected from the discharge port 75a is supplied to the transmission 35 in the form of mist. Thus, the transmission 35 is lubricated and cooled. Oil supplied to the transmission 35 falls down under the influence of gravity to be collected in the oil pan 61.

[0056] The lubricant in the oil path 76 flows through the first oil path 81, and is guided to the centrifugal filter 50 via the opening 81o. When the lubricant having been guided to the centrifugal filter 50 contains foreign matter therein, the foreign matter, which has a greater specific gravity, is collected on the outer side in the radial direction. Therefore, in the centrifugal filter 50, foreign matter is separated from lubricant. The centrifugal filter 50 is closed on the radially outer side. Therefore, foreign matter is caught in a radially outward area of the centrifugal filter 50. A part of clean lubricant, which has been removed of foreign matter, flows through the second oil path 82 to be supplied to the gap 55 between the connecting rod 19 and the crankpin 36. This lubricant lubricates the connecting rod 19 and the crankpin 36. A part of the lubricant having flown through the gap 55 is scattered toward the piston 16. The lubricant having been scattered toward the piston 16 lubricates the piston 16 and the cylinder 6 and cools the piston 16. The lubricant falls down under the influence of gravity to be collected in the oil pan 61.

[0057] Since the centrifugal filter 50 is open on the radially inner side, lubricant, which has overflowed the oil reservoir space 51, is scattered around the first crank web 31. Since the first crankweb 31 is rotating, oil to be scattered is scattered radially outward. Oil is scattered also from the gap 55c between the big end 19b of the connecting rod 19 and the crank webs 31 and 32. As shown in FIG. 3, the transmission 35 is placed rearward of the centrifugal filter 50. As shown in FIG. 5, the centrifugal filter 50 overlaps the transmission 35, as the vehicle is seen from the front. Therefore, a part of clean lubricant, which has overflowed the radially inner side of the centrifugal filter 50, is supplied to the transmission 35. The lubricant is supplied directly to the transmission 35. Thus, lubricant is supplied to the transmission 35 via the discharge port 75a of the oil path 75, and clean lubricant is supplied thereto from the centrifugal filter 50.

[0058] As described above, with the motorcycle 1 of the present embodiment, if the lubricant having been guided from the first oil path 81 to the centrifugal filter 50 has been contaminated with foreign matter, the foreign matter is collected on the outer side in the radial direction of the centrifugal filter 50 by virtue of the centrifugal force from the rotation of the crankshaft 18. As a result, the foreign matter is separated from the lubricant, and clean oil, which has been removed of the foreign matter, is sent from the centrifugal filter 50 to the second oil path 82. Clean lubricant, which has been removed of foreignmatter, is supplied to the gap 55 between the connecting rod 19 and the crankpin 36. With the motorcycle 1, at least a part of the cylinder 6 is placed upward of the crankcase 7, and the front end 35f of the transmission 35 is located rearward of the rear end 6b of the cylinder 6. Therefore, oil freefalling from the gap 55 between the connecting rod 19 and the crankpin 36 is unlikely to be supplied to the transmission 35. However, since the centrifugal filter 50 is open on the radially inner side, a part of the clean lubricant, which has been removed of foreign matter by the centrifugal filter 50, overflows the centrifugal filter 50 to be scattered outward in the radial direction of the crankshaft 18 by virtue of the centrifugal force. Since the transmission 35 is placed rearward of the centrifugal filter 50, the lubricant that has been scattered from the centrifugal filter 50 is supplied to the transmission 35. Therefore, with the motorcycle 1 of the present embodiment, clean lubricant, which has been removed of foreign matter by the centrifugal filter 50, can be supplied to the transmission 35.

[0059] According to the present embodiment, the centrifugal filter 50 is formed by the depressed wall 31e of the first side wall 31a of the first crank web 31 and the annular plate 47. The centrifugal filter 50 can be provided by such a simple configuration.

[0060] According to the present embodiment, the opening 81o of the first oil path 81 is formed in the wall 38 of the crankcase 7. Oil can be guided from the first oil path 81 to the centrifugal filter 50 through the opening 81o formed in the wall 38 of the crankcase 7. According to the present embodiment, an oil path in which lubricant flows is not needed inside the first shaft 33 of the crankshaft 18. According to the present embodiment, since there is no need to machine an oil path inside the first shaft 33, it is possible to reduce the machining cost and to decrease the radius of the first shaft 33.

[0061] According to the present embodiment, the gap G1 in the radial direction between the inner circumferential edge 47c of the annular plate 47 and the bearing 39 is smaller than the dimension G2 of the bearing 39 in the radial direction. The gap G1 is smaller than the dimension G3 in the radial direction between the inner circumferential edge 47c and the outer circumferential edge of the annular plate 47. With the gap G1 being relatively small, clean lubricant can be desirably supplied both to the gap 55 between the connecting rod 19 and the crankpin 36 and to the transmission 35.

[0062] In the present embodiment, the discharge port 75a and the oil path 75b are formed in the wall 49 of the crankcase 7, and the discharge port 75a is placed so as to be aligned with a part of the transmission 35 with respect to the axial direction of the crankshaft 18. Therefore, oil can be supplied to the transmission 35 not only from the centrifugal filter 50 but also from the discharge port 75a. Thus, it is possible to supply a sufficient amount of oil to the transmission 35.

[0063] While one embodiment of the present invention has been described above, it is understood that the present invention is not limited to the embodiment described above. Next, some alternative embodiments will be described.

[0064] While the motorcycle 1 of the embodiment described above includes the first oil path 81 formed in the wall 38 of the crankcase 7, there is no particular limitation on the member in which the first oil path 81 is formed. For example, the first oil path 81 may be formed in the first shaft 33 of the crankshaft 18 as shown in FIG. 8, instead of the first oil path 81 formed in the wall 38 of the crankcase 7. In the following description, like elements to those of the embodiment described above will be denoted by like reference numerals and will not be further discussed below.

[0065] In the motorcycle 1 according to an alternative embodiment shown in FIG. 8, the first oil path 81 includes an oil path 81a extending in the axial direction of the first shaft 33, and an oil path 81b connected to the oil path 81a and extending in the radial direction of the first shaft 33. Note that "extending in the axial direction of the first shaft 33" may refer both to extending in the axial direction of the first shaft 33, and to extending in a direction inclined from the axial direction. As used herein, "extending in the radial direction of the first shaft 33" may refer both to extending in a direction perpendicular to the axial direction of the first shaft 33, and to extending in a direction inclined from the direction perpendicular to the axial direction. The first oil path 81 includes the opening 81o through which lubricant is discharged. The opening 81o is provided at the downstream end of the oil path 81b. The opening 81o is formed in the outer circumferential surface of the first shaft 33. The opening 81o is located radially inward of the inner circumferential edge 47c of the annular plate 47 and between the annular plate 47 and the first side wall 31a with respect to the axial direction of the crankshaft 18. Lubricant is supplied to the centrifugal filter 50 via the opening 81o of the first oil path 81.

[0066] In the present embodiment, the inner circumferential edge 47c of the annular plate 47 is located radially inward of the radially outer end of the bearing 39. Also in the present embodiment, the centrifugal filter 50 is formed by the first side wall 31a of the first crank web 31 and the annular plate 47. The centrifugal filter 50 is closed on the radially outer side and is open on the radially inner side.

[0067] Also in the present embodiment, lubricant, which has been scattered from the centrifugal filter 50, is supplied to the transmission 35. Therefore, cleanlubricant,which hasbeen removed of foreign matter by the centrifugal filter 50, can be supplied to the transmission 35. It is possible, with a simple configuration, to form the centrifugal filter 50 that is closed on the radially outer side and is open on the radially inner side.

[0068] In the embodiment described above, a ball bearing is used as the bearing 39, which is placed in the hole 37 of the wall 38 of the crankcase 7 and is configured to rotatably support the first shaft 33. However, the type of the bearing 39 is not limited to a ball bearing. For example, the bearing 39 may be a cylindrical roller bearing, as shown in FIG. 9.

[0069] In the embodiment described above, the depressed wall 31e is formed in the first side wall 31a of the first crank web 31. However, the depressed wall 31e may not be needed as long as the centrifugal filter 50 is formed by the first side wall 31a and the annular plate 47.

[0070] As shown in FIG. 2, the centrifugal filter 50 is placed rightward of the cylinder axis CA in the embodiment described above. However, the configuration of the embodiment described above may be placed in left-right symmetry with respect to a plane that includes the cylinder axis CA therein and is perpendicular to the crankshaft 18. The annular plate 47 may be attached to the side wall, on which the second shaft 34 of the second crank web 32 is provided, and the centrifugal filter 50 may be formed by this side wall and the annular plate 47. In such a case, the first oil path 81 may be formed in the wall 44 of the crankcase 7 or the second shaft 34.

[0071] The positional relationships, etc., between different parts of the power unit 3 have been described above based on directions as seen from a passenger seated in the seat 4 while the motorcycle 1 is stationary in an upright position on a horizontal surface. In other words, the positional relationships, etc., between different parts of the power unit 3 have been described based on a state (i.e., a mounted state) in which the power unit 3 is supported on the vehicle body frame 2. However, the mounted state of the power unit 3 is not limited to that of the embodiment described above. For example, the power unit 3 may be supported on the vehicle body frame 2 in an orientation that is inclined with respect to a horizontal plane from the embodiment described above. Even when the mounted state of the power unit 3 is different from that of the embodiment described above, it is possible to uniquely specify the positional relationships between different parts of the power unit by itself, irrespective of the mounted state, by re-defining the terms forward, rearward, leftward, rightward, upward and downward to mean forward, rearward, leftward, rightward, upward and downward when the bottom of the crankcase 7 of the power unit 3 is placed on a horizontal plane in such an orientation that the crankshaft 18 extends in the left-right direction and the transmission 35 is located rearward of the crankshaft 18.

[0072] The terms and expressions used herein are used for explanation purposes and should not be construed as being restrictive. It should be appreciated that the terms and expressions used herein do not eliminate any equivalents of features illustrated and mentioned herein, but include various modifications falling within the claimed scope of the present invention. The present invention may be embodied in many different forms. The present disclosure is to be considered as providing examples of the principles of the invention. These examples are described herein with the understanding that such examples are not intended to limit the present invention to preferred embodiments described herein and/or illustrated herein. Hence, the present invention is not limited to the preferred embodiments described herein. The present invention includes any and all preferred embodiments including equivalent elements, modifications, omissions, combinations, adaptations and/or alterations as would be appreciated by those skilled in the art on the basis of the present disclosure. The limitations in the claims are to be interpreted broadly based on the language included in the claims and not limited to examples described in the present specification or during the prosecution of the application.

Reference Signs List

1	Motorcycle (straddled vehicle)
6	Cylinder
7	Crankcase
16	Piston
18	Crankshaft
19	Connecting rod
23	Main shaft (first rotation shaft)
24	Drive shaft (second rotation shaft)
25A	Transmission gear (first gear)
25B	Transmission gear (second gear)
31	First crank web
31a	First side wall
31b	Second side wall
32	Second crank web
33	First shaft
35	Transmission
36	Crankpin
37	Hole
38	Wall
39	Bearing
47	Annular plate
50	Centrifugal filter
81	First oil path
82	Second oil path
82a	First channel hole
82b	Second channel hole

Claims

1. A straddled vehicle comprising:

a crankcase (7) including a wall (38) with a hole (37) therein;

a cylinder (6) connected to the crankcase (7), at least a part of the cylinder (6) being located above the crankcase (7) ;

a crankshaft (18) placed inside the crankcase (7) and including a first crank web (31) including a first side wall (31a) and a second side wall (31b) on an opposite side from the first side wall (31a), a second crank web (32) facing the second side wall (31b) of the first crank web (31), a crankpin (36) connected to the first crank web (31) and the second crank web (32), and a first shaft (33) provided on the first side wall (31a) of the first crank web (31);

a transmission (35) placed inside the crankcase (7) and including a first rotation shaft (23), a second rotation shaft (24), a plurality of first gears (25A) provided on the first rotation shaft (23), and a plurality of second gears (25B) provided on the second rotation shaft (24) and meshing with the first gears (25A);

a connecting rod (19) including a big end (19b) and a small end (19a), the big end (19b) including a pin hole (19c) in which the crankpin (36) is inserted;

a piston (16) placed inside the cylinder (6) and connected to the small end (19a) of the connecting rod (19);

a bearing (39) placed in the hole (37) of the wall (38) of the crankcase (7) and configured to rotatably support the first shaft (33);

an annular plate (47) fixed to the first side wall (31a) of the first crank web (31), a part of the annular plate (47) being spaced apart from the first side wall (31a),

a centrifugal filter (50) formed by the first side wall (31a) and the annular plate (47), the centrifugal filter (50) being closed on a radially outer side and being open on a radially inner side;

a first oil path (81) communicating with the centrifugal filter (50) and configured to guide lubricant to the centrifugal filter (50); and

a second oil path (82) configured to connect between the centrifugal filter (50) and a gap (55) between the connecting rod (19) and the crankpin (36), wherein:

the second oil path (82) includes a first channel hole (82a) formed inside the crankpin (36) and extending in an axial direction of the crankpin (36), and a second channel hole (82b) formed inside the crankpin (36) and extending in a radial direction of the crankpin (36), the second channel hole (82b) communicating with the first channel hole (82a);

a front end of the transmission (35) is located rearward of a rear end of the cylinder (6);

the transmission (35) is placed rearward of the centrifugal filter (50); and

a part of the transmission (35) overlaps with the centrifugal filter (50), as the vehicle is seen from the front.

2. The straddled vehicle according to claim 1, wherein:

the first side wall (31a) of the first crank web (31) includes an outer edge wall (31d) located radially outward of the first shaft (33) and a depressed wall (31e) located radially inward of the outer edge wall (31d) and depressed relative to the outer edge wall (31d);

the annular plate (47) is spaced apart from at least a part of the depressed wall (31e); and

the depressed wall (31e) and the annular plate (47) together form the centrifugal filter (50).

3. The straddled vehicle according to claim 1 or 2, wherein the centrifugal filter (50) includes an oil reservoir space (51) defined by the first side wall (31a) and the annular plate (47).

4. The straddled vehicle according to any one of claims 1 to 3, wherein the annular plate (47) includes an inner circumferential edge (47c) spaced apart from the bearing (39) in a radially outward direction.

5. The straddled vehicle according to claim 4, wherein the first oil path (81) is formed in the wall (38) of the crankcase (7) and includes an opening (81o), at least a part of the opening (81o) being located radially inward of the inner circumferential edge (47c) of the annular plate (47).

6. The straddled vehicle according to claim 4, wherein the first oil path (81) is formed in the first shaft (33) and includes an opening (81o), the opening (81o) being located radially inward of the inner circumferential edge (47c) of the annular plate (47) and between the annular plate (47) and the first side wall (31a) with respect to an axial direction of the crankshaft (18).

7. The straddled vehicle according to any one of claims 4 to 6, wherein a gap (G1) in a radial direction between the inner circumferential edge (47c) of the annular plate (47) and the bearing (39) is smaller than a dimension (G2) of the bearing (39) in the radial direction.

8. The straddled vehicle according to any one of claims 4 to 7, wherein a gap (G1) in a radial direction between the inner circumferential edge (47c) of the annular plate (47) and the bearing (39) is smaller than a dimension (G3) in the radial direction between the inner circumferential edge (47c) and an outer circumferential edge of the annular plate (47).

9. The straddled vehicle according to any one of claims 1 to 5, wherein an oil path in which lubricant flows is absent inside the first shaft (33).

10. The straddled vehicle according to any one of claims 1 to 9, wherein:

the crankcase (7) includes another wall including an oil path (75) and a discharge port (75a) formed therein, wherein lubricant flows in the oil path (75), and the discharge port (75a) is connected to the oil path (75) and includes an opening facing the transmission(35); and

the discharge port (75a) is placed so as to be aligned with a part of the transmission (35) with respect to an axial direction of the crankshaft (18).

Drawing