JP5667366B2 - Crankcase structure of internal combustion engine - Google Patents

Description

  The present invention relates to a crankcase structure of an internal combustion engine provided with an oil pan below the crankcase.

An internal combustion engine having an oil pan below the crankcase is provided with a lubrication system that pumps up oil stored in the oil pan and supplies it to a required lubrication site that requires lubrication. The lifting mechanism has its oil suction port close to the bottom of the oil pan, so that the oil suction port is always completely immersed in the oil without being affected by the amount of oil stored in the oil pan, so that air is not sucked in. I am doing so.
If air is sucked in, the discharge hydraulic pressure of the oil pump fluctuates due to air biting, and oil cannot be supplied to the lubricated part with a stable hydraulic pressure.

  Therefore, the oil intake port is made close to the bottom surface of the oil pan, and especially when the internal combustion engine is tilted together with the vehicle body in an internal combustion engine mounted on a motorcycle, the oil is sufficiently not to be exposed from the oil surface. Although it is stored in the oil pan, when the internal combustion engine swings suddenly with the vehicle body or acceleration / deceleration acts, the oil level of the oil in the oil pan fluctuates. However, there is a possibility that the oil suction port may be exposed. Therefore, when trying to prevent this, a large amount of oil is stored.

Therefore, when the weight increases and the oil overflows to the crank chamber, the crank web of the crankshaft is immersed in the oil, resulting in an increase in friction associated with the rotation of the crankshaft.
In view of this, an example has been proposed in which a partition wall is formed substantially horizontally in the oil pan to suppress fluctuations in the oil surface of the oil stored in the oil pan (see, for example, Patent Document 1).

JP 2008-223880 A

  The internal combustion engine disclosed in Patent Document 1 is a one-cylinder four-stroke internal combustion engine in which a transmission is disposed behind the crankshaft in a crankcase that houses the crankshaft, and an oil pan is provided below the crankcase. I have.

And the lower partition which partitions up and down from the front-and-back case outer peripheral wall toward the inner side of an oil pan is each extended and formed.
Further, an upper partition is formed above the front lower partition and curved downward along the rotation trajectory of the crank web.
Variations in the oil level of the oil stored in the oil pan can be suppressed by the front and rear lower and upper partition walls.

The front and rear lower partition walls extend from the bottom surface of the oil pan at substantially the same height and approach each other, and a large opening is formed in communication between the upper and lower ends of the both ends.
An oil suction duct is inserted into the opening, and an oil suction port is provided near the bottom of the oil pan at the lower end.

The upper partition below the crankshaft is formed so as to be installed between a pair of vertical bearing walls that support the crankshaft, and has a gap between the outer peripheral wall of the front case and curved downward in the middle. A discharge port part is formed slightly behind the lowest part.
Therefore, the oil accumulated on the upper partition wall flows out from the discharge port portion to the opening between the lower partition walls just before and after, and reduces the friction of the crankshaft caused by the rotating crank web being immersed in the oil. I am doing so.

However, the discharge port portion of the upper partition wall is at a relatively high position, and the oil on the upper partition wall flows out so as to be scraped off from the discharge port portion with the rotation of the crank web. Bubbles are likely to be generated at the opening, and it is highly likely that the bubbles will be sucked into an oil suction port located below the opening, and the discharge hydraulic pressure of the oil pump tends to become unstable due to air engagement.
In addition, since the upper partition wall has a gap between the case outer peripheral wall and the front wall of the case, especially when the internal combustion engine swings back and forth, the oil accumulated on the front lower partition wall is separated from the case outer wall. Backward along the inner surface of the front side wall, the air gap may flow upward and be supplied in a large amount onto the upper partition wall, which may increase crankshaft friction.

  The present invention has been made in view of the above points, and the object of the present invention is to suppress the oil level fluctuation and to suppress the occurrence of air-engagement of the oil pump while suppressing the increase of the friction of the crankshaft or the transmission. It is in the point which provides the crankcase structure of the internal combustion engine which can be prevented.

In order to achieve the above-mentioned object, the invention described in claim 1 is characterized in that a crankshaft is constructed with both sides supported by a pair of opposed vertical bearing walls, and the pair of vertical bearing walls and the outer peripheral wall of the case. In a crankcase structure of an internal combustion engine having an oil pan below a crankcase in which a crank web having a counterweight is provided in a space within the enclosed case and a transmission having a gear train is disposed, an appropriate amount of the oil pan is provided. A lower partition that vertically partitions the lower part of the oil surface when the engine of stored oil is stopped extends from the outer peripheral wall of the case toward the inner space of the case, and is spaced apart from the lower partition by a predetermined distance. and upper partition wall for partitioning the downward and below the a upper crank shaft and the transmission, are formed to extend toward the case inner space from the case outer peripheral wall, said Oirupa An oil suction port of an oil pumping mechanism that pumps up oil stored in the oil pan is formed along the bottom surface of the oil pan, and a case cover is respectively placed on the outside of the pair of vertical bearing walls of the crankcase, A crankshaft side upper partition formed below the crankshaft and a crankshaft side lower partition below the crankshaft are connected to the pair of vertical bearing walls, and the crankshaft side upper partition is a rotation locus of the crank web. Of the vertical bearing wall along the upper surface of the crankshaft side upper partition, and the case inner space above the crankshaft side upper partition and the case cover An upper communication port that communicates with the space in the cover is formed, and the crankshaft side lower side is formed in a portion along the upper surface of the crankshaft side lower partition wall of the vertical bearing wall. A lower communication port (72l, 72r) that communicates the space in the case above the wall and the space in the cover of the case cover is formed, and the case cover is below the crankshaft side lower partition wall of the vertical bearing wall. The crankcase structure of the internal combustion engine is characterized in that an oil return port is formed for returning the oil flowing into the cover inner space to the oil pan .

  According to a second aspect of the present invention, in the crankcase structure of the internal combustion engine according to the first aspect, a breather chamber is formed above the transmission on the side where the transmission is disposed in the space in the case. A communication port that communicates the breather chamber with the space in the case is formed in a lower portion of the chamber.

According to a third aspect of the present invention, in the crankcase structure of the internal combustion engine according to the first or second aspect, the leading end of the crankshaft side upper partition that extends from the case outer peripheral wall toward the case inner space. And a shift drum is disposed between the extended tip of the transmission-side upper partition formed below the transmission .

According to a fourth aspect of the present invention, in the crankcase structure of the internal combustion engine according to the third aspect, the extension tip of the transmission-side upper partition and the extension tip of the lower partition located below the transmission-side upper partition The shift drum is arranged on a line segment connecting the two.

  According to a fifth aspect of the present invention, in the crankcase structure of the internal combustion engine according to any one of the first to fourth aspects, the main shaft and the counter shaft of the transmission parallel to the crank shaft are arranged in this order in the crank shaft. The countershaft is disposed above the crankshaft, and the transmission-side upper partition formed below the transmission is obliquely downward from the case outer peripheral wall on the countershaft side. It is characterized by being formed to extend.

According to a sixth aspect of the present invention, in the crankcase structure of the internal combustion engine according to any one of the first to fifth aspects, the crankshaft side lower partition extending from the case outer peripheral wall is at least mounted on a vehicle body. The extended base end is at a lower position than the extended tip.

According to a seventh aspect of the present invention, in the crankcase structure of the internal combustion engine according to the first aspect, the crankshaft side upper partition wall is formed with a missing portion at a portion overlapping the crankshaft side lower partition wall in the vertical direction. It is characterized by that.

According to an eighth aspect of the present invention, a crankshaft is installed on both sides of a pair of opposing vertical bearing walls, and a counter is installed in a case inner space surrounded by the pair of vertical bearing walls and the outer peripheral wall of the case. In a crankcase structure of an internal combustion engine having an oil pan below a crankcase in which a transmission having a gear train is arranged together with a crank web having a weight, when the engine is stopped when an appropriate amount of oil is stored in the oil pan A lower partition that vertically divides the lower side of the oil surface from the outer peripheral wall of the case toward the inner space of the case, and is above the lower partition and at a predetermined interval, the crankshaft And an upper partition that vertically divides the lower portion of the transmission from the outer peripheral wall of the case toward the inner space of the case, and is formed in the transmission main body parallel to the crankshaft. A shaft and a countershaft are disposed in this order horizontally apart from the crankshaft, the countershaft is disposed above the crankshaft, and a transmission-side upper partition formed below the transmission includes: The crankshaft side upper partition and the lower crankshaft side partition formed below the crankshaft are formed to extend obliquely downward from the outer peripheral wall of the case on the countershaft side, and the pair of vertical The crankshaft side upper partition wall is connected to a bearing wall, and is formed to be curved downward along the outer peripheral edge of the rotation trajectory of the crank web, and the crankshaft side upper partition wall is connected to the crankshaft side lower partition wall. A deficient portion is formed in a portion overlapping in the vertical direction, and an oil suction port of an oil pumping mechanism that pumps up oil stored in the oil pan extends along the bottom surface of the oil pan. A case cover is provided on each of the outer sides of the pair of vertical bearing walls of the crankcase, and a portion of the vertical bearing wall along the upper surface of the crankshaft side lower partition wall is formed on the crankshaft side lower partition wall. A lower communication port is formed to connect the upper space in the case and the space in the cover of the case cover, and flows into the space in the cover of the case cover below the crankshaft side lower partition wall of the vertical bearing wall. The crankcase structure of the internal combustion engine is characterized in that an oil return port is formed for returning the oil to the oil pan.

According to the crankcase structure of the internal combustion engine according to claim 1, the lower partition wall that vertically partitions the lower part of the oil surface when the engine is stopped for the oil stored in the oil pan in an appropriate amount is provided from the case outer peripheral wall to the case inner space. An upper partition that is formed to extend upward and is spaced apart from the lower partition by a predetermined distance and that vertically divides the lower side of the crankshaft and the transmission extends from the outer peripheral wall of the case toward the inner space of the case. When the oil stored in the oil pan below the crankcase is swaying and flowing, the oil flow is effectively suppressed by the double partition wall of the lower partition wall and the upper partition wall, Especially when shaking back and forth during acceleration / deceleration, the oil accumulated on the lower partition wall flows back on the upper partition wall where the crankshaft or the transmission is arranged, going back along the inner surface of the case outer peripheral wall. Since the extended base end portion of the upper partition wall extending from the peripheral wall can be prevented, an increase in the friction of the crankshaft or the transmission due to the oil supplied to the upper partition wall is suppressed as much as possible. it can.
The oil level of the oil in the oil pan is reliably prevented from fluctuating greatly, so that the oil suction port in the oil pan is not exposed and fluctuations in the discharge hydraulic pressure due to the oil biting of the oil pump are prevented. Can do.
Further, the crankshaft side upper partition wall formed by bending downward along the outer peripheral edge of the crank web rotation trajectory by the upper communication port formed in the vertical bearing wall along the upper surface of the crankshaft side upper partition wall. The oil accumulated above flows out into the cover inner space of the case cover, and on the crankshaft side lower partition wall by the lower communication port formed in the vertical bearing wall along the upper surface of the crankshaft side lower partition wall. The accumulated oil flows out into the cover inner space of the case cover, and the oil flowing into the cover inner space of the case cover is returned to the oil pan by the oil return port formed below the lower partition wall on the crankshaft side of the vertical bearing wall. Therefore, the flow of oil return from the lower position of the oil return port away from the oil suction port formed along the bottom surface of the oil pan in the center of the equidistant distance from the pair of vertical bearing walls. In addition, it is difficult for bubbles to be generated due to the return flow of oil from this low position, and even if it occurs, the bubbles generated on the vertical bearing wall side are not sucked from the remote oil intake port in the center, and the oil pump The air pressure fluctuation can be prevented and the hydraulic pressure fluctuation can be suppressed.
In addition, since oil flows out from the upper communication port into the side cover inner space, the oil flow from the extended tip at the relatively high position of the crankshaft side upper partition wall is suppressed. The generation of bubbles is suppressed as much as possible.
In addition, oil flows out from the lower communication port into the side cover inner space, and the oil flow from the extended tip of the crankshaft side lower partition is also suppressed.

  According to the crankcase structure for an internal combustion engine according to claim 2, a breather chamber is formed above the transmission of the crankcase, and a communication port for communicating the breather chamber and the space in the case is formed at a lower portion of the breather chamber. As a result, the blow-by gas can be easily removed and the gas-liquid separated oil can be easily returned to the oil pan, and the upper partition wall extending from the case outer peripheral wall prevents the oil from going back to the inner surface of the case outer peripheral wall. Thus, it is possible to prevent oil from entering the breather chamber from the communication port above the transmission.

According to the crankcase structure of the internal combustion engine according to claim 3, the transmission side upper side formed below the transmission tip of the crankshaft side upper partition extending from the case outer peripheral wall toward the case inner space and the transmission. Since the shift drum is disposed between the extended tip of the partition wall, the upper partition wall and the shift drum cooperate to disperse or flow oil below the upper partition wall, and the upper side where the crankshaft or transmission is disposed. It can prevent as much as possible that it moves to the space in a case on a partition.

According to the crankcase structure of the internal combustion engine according to claim 4, the shift is performed on a line segment connecting the extending tip of the transmission-side upper partition and the extending tip of the lower partition located below the transmission-side upper partition. Since the drum is arranged, the upper part of the opening on the crank chamber side in the space between the lower partition wall and the upper partition wall is blocked by the shift drum adjacent to the extension tip of the upper partition wall, and is accumulated in the same space. It is possible to prevent the oil from scattering or flowing upward, and to further suppress the movement of the oil above the upper partition wall.

  According to the crankcase structure of the internal combustion engine according to claim 5, the transmission-side upper partition formed below the transmission extends obliquely downward from the case outer peripheral wall on the countershaft side disposed above the crankshaft. Therefore, the transmission side upper partition can be formed at a high position while avoiding interference with the counter gear train, and a large space can be secured between the lower lower partition and the oil can be put in the same space. The amount of oil that accumulates on the transmission-side upper partition can be reduced, and the oil on the transmission-side upper partition that extends diagonally downward from the outer peripheral wall of the case flows on the inclined surface and extends forward. It flows down from the bottom and easily returns to the oil pan.

According to the crankcase structure of the internal combustion engine according to claim 6, the crankshaft side lower partition extending from the case outer peripheral wall is at a position where the extended proximal end is lower than the extended distal end at least when mounted on the vehicle body. Therefore, the oil on the crankshaft side lower partition wall is accumulated on the extended base end side, and most of the oil flows out from the lower communication port of the vertical bearing wall to the cover inner space. It is possible to further reduce the amount of oil flowing down above the oil suction port in the center of the oil pan, and to suppress the generation of bubbles and prevent the bubbles from being sucked from the oil suction port as much as possible.

According to the crankcase structure of the internal combustion engine according to claim 7, the crankshaft side upper partition wall is formed with a missing portion in a portion overlapping the crankshaft side lower partition wall in the vertical direction. The upper oil flows down from the missing part onto the lower crankshaft side lower partition wall to suppress the increase in friction caused by the rotation of the crankshaft, and the crankshaft side lower partition wall causes the oil in the oil pan to move to the crankshaft. It is possible to prevent the oil from moving upward and to secure the amount of oil in the oil pan.

According to the crankcase structure of the internal combustion engine according to claim 8 , the lower partition wall that partitions the lower part of the oil surface up and down at the time of engine stoppage of the oil stored in the oil pan in an appropriate amount from the case outer peripheral wall to the case inner space. An upper partition that is formed to extend upward and is spaced apart from the lower partition by a predetermined distance and that vertically divides the lower side of the crankshaft and the transmission extends from the outer peripheral wall of the case toward the inner space of the case. When the oil stored in the oil pan below the crankcase is swaying and flowing, the oil flow is effectively suppressed by the double partition wall of the lower partition wall and the upper partition wall, Especially when shaking back and forth during acceleration / deceleration, the oil accumulated on the lower partition wall flows back on the upper partition wall where the crankshaft or the transmission is arranged, going back along the inner surface of the case outer peripheral wall. Since the extended base end portion of the upper partition wall extending from the peripheral wall can be prevented, an increase in the friction of the crankshaft or the transmission due to the oil supplied to the upper partition wall is suppressed as much as possible. it can.
In addition, since the oil level of the oil in the oil pan is largely prevented from fluctuating, the oil suction port in the oil pan is not exposed, and fluctuations in the discharge hydraulic pressure due to the oil biting of the oil pump are prevented. can do.
In addition, the transmission-side upper partition formed below the transmission is formed to extend obliquely downward from the outer peripheral wall of the counter shaft-side case disposed above the crankshaft. It is formed at a high position while avoiding interference with the gear train, and a large space can be secured between the lower lower partition wall. Oil is stored in the same space and the oil moves on the transmission side upper partition wall. In addition to reducing the amount of oil, the oil on the transmission-side upper partition that extends obliquely downward from the outer peripheral wall of the case flows on the inclined surface, flows downward from the extended tip, and easily returns to the oil pan.
The crankshaft side upper partition formed below the crankshaft is formed with a missing portion in a portion overlapping the lower crankshaft side lower partition in the vertical direction. The oil flows down from the missing part onto the lower crankshaft side lower partition wall to suppress the increase of friction caused by the rotation of the crankshaft, and the oil in the oil pan is located in the crankshaft by the crankshaft side lower partition wall. It is possible to prevent the oil from moving upward and to secure the amount of oil in the oil pan.
Further, the oil that has flowed down from the missing portion of the crankshaft side upper partition wall and accumulated on the crankshaft side lower partition wall is formed in the lower part of the vertical bearing wall formed along the upper surface of the crankshaft side lower partition wall. Oil that flows out into the cover inner space of the case cover through the communication port and flows into the cover inner space of the case cover through the oil return port formed below the lower partition on the crankshaft side of the vertical bearing wall is returned to the oil pan. Therefore, there is a flow of oil return from the lower position of the oil return port away from the oil suction port formed along the bottom surface of the oil pan at the center of the equidistant distance from the pair of vertical bearing walls. Bubbles are unlikely to be generated due to the return flow of the oil, and even if they occur, the bubbles generated on the vertical bearing wall side are not sucked from the remote oil suction port, and the oil pump air It is possible to suppress the pressure fluctuation to prevent.

1 is a right side view of an internal combustion engine for a motorcycle according to an embodiment of the present invention. FIG. 2 is a sectional view of the internal combustion engine shown in FIG. 1 taken along the line II-II. FIG. 3 is a cross-sectional view of the internal combustion engine shown in FIG. 1 taken along line III-III. FIG. 3 is a right side view of the internal combustion engine with a right crankcase cover removed. FIG. 2 is a left side view of the internal combustion engine, with the left crankcase omitted and the right crankcase viewed from the inside with a partial cross section. FIG. 2 is a right side view of the internal combustion engine in which the right crankcase is omitted and the left crankcase is partially sectioned when viewed from the inside. It is the left view which looked at the left crankcase from the outside. FIG. 8 is a cross-sectional view taken along line VIII-VIII of the internal combustion engine shown in FIGS. 4 to 7. It is the IX-IX sectional view taken on the line of the internal combustion engine shown by FIG. 4 thru | or FIG. FIG. 7 is a left side view of the motorcycle internal combustion engine according to another embodiment, with the left crankcase omitted and the right crankcase viewed from the inside, with a partial cross section. FIG. 2 is a right side view of the internal combustion engine in which the right crankcase is omitted and the left crankcase is partially sectioned when viewed from the inside.

Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.
The internal combustion engine 1 according to the present embodiment is a single-cylinder four-stroke internal combustion engine and is mounted horizontally on a motorcycle with the crankshaft 10 oriented in the vehicle body width direction.
In the present specification, the front, rear, left and right are determined based on the motorcycle body.

  FIG. 1 is a right side view of the internal combustion engine 1. Referring to FIG. 1, a cylinder block 3 and a cylinder are disposed diagonally above a crankcase 2 that rotatably supports a crankshaft 10 oriented in the left-right direction. The heads 4 are sequentially stacked and fastened together, and a cylinder head cover 5 is placed on the cylinder head 4, and the cylinder block 3, the cylinder head 4, and the cylinder head cover 5 are tilted slightly forward from the crankcase 2. It is protruding.

  A piston 18 is slidably fitted on the cylinder block 3 projecting obliquely upward from the crankcase 2 and connected to a crank pin 10p installed between the crank webs 10w, 10w of the crankshaft 10 via a connecting rod 19. The crankshaft 10 is rotationally driven according to the movement of the piston 18 (see FIGS. 2, 5, and 6).

A combustion chamber 20 is formed below the cylinder head 4 and above the piston 18.
In the combustion chamber 20, an intake port 21 and an exhaust port 22 are connected, and an intake valve 23 and an exhaust valve 24 that open and close these inner ends are provided.
A throttle body 25 and a fuel injection valve 26 are connected to the intake port 22.
A starter motor 27 and a speed sensor 28 are installed on the rear upper surface of the crankcase 2.

Referring to FIG. 2 which is a sectional view taken along the line II-II of the internal combustion engine shown in FIG. 1, the crankcase 2 is divided into left and right halves, and between the left crankcase 2L and the right crankcase 2R. A space is formed.
The inner space of the case is a space formed between the left and right vertical bearing walls 2Lv and 2Rv facing each other, which will be described later, surrounded by the outer peripheral walls 2Ls and 2Rs, and is accommodated by the crank web 10w constituting the counterweight of the crankshaft 10. The crank chamber 2C and the mission chamber 2M in which the constantly meshing gear transmission M is housed are located in front and back to communicate with each other to form one space.

  The left crankcase cover 6 and the right crankcase cover 7 cover the left and right outer sides of the left crankcase 2L and the right crankcase 2R, and the AC generator G is accommodated in the generator chamber 6G in the left crankcase cover 6 so that the right crank The multi-plate friction clutch C is accommodated in the clutch chamber 7 </ b> C in the case cover 7.

The outer root of the crank web 10w of the crankshaft 10 is pivotally supported via metal bearings 11 and 11 on the left and right vertical bearing walls 2Lv and 2Rv facing each other of the left crankcase 2L and the right crankcase 2R.
An AC generator G is provided on the left side of the crankshaft 10 protruding leftward from the left metal bearing 11, and the AC generator G is covered with a left crankcase cover 6.

As shown in FIG. 3, the left and right metal bearings 11 and 11, left and right vertical bearing wall 2Lv, metal retaining member 11h which is fitted to the circular bearing hole of 2Rv, held together in 11h, the metal retaining member 11h 11h holds the metal bearings 11 and 11 and supplies pressure oil to the gap (oil clearance) between the journal portion of the crankshaft 10 and the metal bearing 11, and the metal bearings 11 and 11 oil the rotating crankshaft 10. It supports through the clearance.

  Referring to FIG. 2, the main shaft 12 and the counter shaft 13 of the constantly meshing gear transmission M are a bearing 12b between the left and right side walls extending rearward of the left and right vertical bearing walls 2Lv and 2Rv of the left and right crankcases 2L and 2R. The drive gear train 12g supported by the main shaft 12 and the driven gear train 13g supported by the counter shaft 13 are always meshed with the corresponding gears and supported in the transmission chamber 2M through the shafts 12b, 13b and 13b. Contained.

A multi-plate friction clutch C is provided on the right side portion that passes through the right vertical bearing wall 2Rv of the main shaft 12 to the right and protrudes into the clutch chamber 7C.
The counter shaft 13 has an output sprocket 16 fitted to the left end portion that protrudes to the left through the left vertical bearing wall 2Lv.
A rear-wheel drive chain 17 is wound around the output sprocket 16.

Referring to FIGS. 1 and 5, main shaft 12 and counter shaft 13 are parallel to crankshaft 10, main shaft 12 is positioned obliquely above rearward of crankshaft 10, and further rearward of main shaft 12. The counter shaft 13 is positioned slightly obliquely below, and the counter shaft 13 is positioned above the crank shaft 10 .
A shift drum 14 is disposed at a position substantially below the main shaft 12 and lower than the counter shaft 13 (see FIG. 5).

3 is a cross-sectional view taken along the line III-III of the internal combustion engine shown in FIG. 1. Referring to FIG. 3 together with FIG. 1, the balancer shaft 15 provided with a balancer weight 15w is provided in front of the crankshaft 10. Are rotatably mounted on the left and right vertical bearing walls 2Lv and 2Rv via ball bearings 15b and 15b.
The balancer drive gear 35a, the cam chain drive sprocket 30, and the primary drive gear 36a are arranged in order from left to right on the right side portion of the crankshaft 10 that is supported by the metal bearing 11 of the right vertical bearing wall 2Rv and protrudes to the right. The crankshaft 10 is fitted so as to rotate integrally.

The balancer drive gear 35a meshes with the balancer driven gear 35b fitted to the balancer shaft 15 to transmit power.
The primary drive gear 36a meshes with a primary driven gear 36b supported by a clutch outer Co of a multi-plate friction clutch C provided on the right side of the main shaft 12, and power is transmitted (see FIG. 2).

Referring to FIG. 3, an oil pump 40 is provided on the right wall surface of right vertical bearing wall 2Rv below the right side of crankshaft 10.
The oil pump 40 is a trochoid pump in which the inner rotor 42i and the outer rotor 42o mesh with each other in the pump housing 41. The oil pump shaft 43 on which the inner rotor 42i is fitted has a pump driven gear 44 at a right end portion protruding rightward from the pump housing 41. Is fitted, the pump driven gear 44 meshes with the primary drive gear 36a, the power is transmitted, and the oil pump 40 is driven.
A relief valve 45 is provided obliquely below the oil pump 40 so as to be sandwiched between the right vertical bearing wall 2Rv and the pump housing 41.

The right crankcase cover 7 is provided with a water pump shaft 46a coaxially with the balancer shaft 15 and provided with a water pump 46.
The water pump shaft 46 a is connected to the balancer shaft 15 and rotates together with the balancer shaft 15.
The right crankcase cover 7 is provided with an oil filter 47 at a corresponding portion in the vicinity of the oil pump 40.

FIG. 4 is a right side view of the internal combustion engine 1 with the right crankcase cover 7 removed, and the right crankcase 2R includes an annular frame wall 2Rt formed to protrude on the right side together with the right vertical bearing wall 2Rv. An annular mating surface 2Rg (portion indicated by a lattice hatch) with the right crankcase cover 7 which is an end surface is shown.
The right crankcase cover 7 covering the right side of the right crankcase 2R has an end face of the outer peripheral wall as a mating surface and abuts with a mating surface 2Rg of the annular frame wall 2Rt of the right crankcase 2R to form a clutch chamber 7C therein. .

  The cam chain drive sprocket 30 that is pivotally supported on the right vertical bearing wall 2Rv of the crankshaft 10 and is fitted to the right side protruding rightward, and the camshaft 31 of the valve mechanism that is pivotally supported on the upper part of the cylinder head 4. , 32, the cam chain 33 is bridged between the cam chain driven sprockets 31s, 32s, and power is transmitted to the valve operating mechanism.

A shift spindle 37 for shifting operation is penetrated from the left outer side below the counter shaft 13 and is rotatably supported. The rotation of the shift spindle 37 operates a gear change mechanism 38 provided with the main shaft 12. Then, the shift drum 14 is rotated, and the shift drum 14 is rotated by moving the shift forks 39a and 39b (see FIG. 5), and the drive gear train 12g and the driven gear of the constantly meshing gear transmission M. A gear pair that effectively transmits power is selected from among the meshing gear pairs in the row 13g to perform speed change.
Below the right side of the crankshaft 10, the oil pump 40 is provided.

FIG. 5 is a left side view of the internal combustion engine 1 in which the left crankcase 2L is omitted and the right crankcase 2R is partially sectioned when viewed from the inside, and the mating surface 2Rf of the right crankcase 2R with the left crankcase 2L is shown. (A portion indicated by a lattice hatch) is shown in an annular shape (a part of the cylinder portion is cut away).
FIG. 6 is a right side view of the internal combustion engine 1 in which the right crankcase 2R is omitted and the left crankcase 2L is a partial cross section viewed from the inside, and the mating surface 2Lf of the left crankcase 2L with the right crankcase 2R is shown. (A portion indicated by a lattice hatch) is shown in an annular shape (a part of the cylinder portion is cut away).
A right side view of the right crankcase 2R viewed from the outside is shown in FIG. 4, and a left side view of the left crankcase 2L viewed from the outside is shown in FIG.

4 to 7, the case outer peripheral walls 2Ls and 2Rs that form the crank chamber 2C and the transmission chamber 2M of the left and right crankcases 2L and 2R together with the left and right vertical bearing walls 2Lv and 2Rv are located in front of the balancer shaft 15. To the lower part of the crankshaft 10 and the lower part of the constantly meshing gear transmission M and to the rear, and the rear part of the continuously meshing gear transmission M to the upper part. The outer periphery is covered so as to reach above M.
The inner end surfaces of the case outer peripheral walls 2Ls and 2Rs are the mating surfaces 2Lf and 2Rf.

  The left and right crankcases 2L and 2R are oils that are recessed below the crank chamber 2C and the transmission chamber 2M so that the left and right vertical bearing walls 2Lv and 2Rv and the case outer peripheral walls 2Ls and 2Rs extend downward to store oil. Bread 2p is formed.

The oil pan 2p needs to always store an appropriate amount of oil, and an average oil surface S of the appropriate amount of stored oil when the engine is stopped is shown by a one-dot chain line in FIGS.
When the internal combustion engine 1 is stopped, if there is an oil surface within the width near the top and bottom of the oil surface S, the amount of oil is an appropriate amount.
When the internal combustion engine 1 is operated, the oil in the oil pan 2p is pumped up by the drive of the oil pump 40 and supplied to each lubrication site, so that the oil surface S is at a position much lower than the height shown in FIGS. .

Referring to FIG. 5, the inner surface of the right crankcase 2R extends from the front side wall of the case outer peripheral wall 2Rs to the rear while being integrally connected to the vertical bearing wall 2Rv above the front half of the bottom surface of the oil pan 2p. An oil suction passage upper wall 51R is formed along the bottom surface, and an oil suction passage upper wall 51L (see FIG. 6) symmetrically formed in the left crankcase 2L and an oil suction passage upper wall 51R are brought into contact with each other to form an oil pan. An oil suction passage 54 is formed between the bottom surface of 2p.
At that time, the flat rectangular openings formed between the rear ends of the oil suction passage upper walls 51L and 51R and the bottom surface of the oil pan 2p are closed on the left and right by the oil suction passage rear walls 52L and 52R. 53 is formed (see FIG. 9).

Referring to FIG. 8, an oil passage 55 that opens to the oil suction passage 54 is perforated upward in the right vertical bearing wall 2Rv of the right crankcase 2R, and the oil passage 55 is in the middle of the annular frame wall 2Rt. Is communicated with a rectangular hole 56 perforated in a flat rectangular shape, and an oil strainer 57 is interposed in the rectangular hole 56 to partition the oil passage 55 from the upstream side (lower side) and the downstream side (upper side).
The right end opening of the rectangular hole 56 is closed by the mating surface of the right crankcase cover 7.
The downstream end (upper end) of the oil passage 55 is bent to the right and communicates with a suction port of the oil pump 40 provided in the clutch chamber 7C.

Therefore, when the internal combustion engine 1 is operated and the oil pump 40 is driven, the oil stored in the oil pan 2p is sucked into the oil suction passage 54 from the oil suction port 53 formed at the bottom center of the oil pan 2p. Then, the oil passage 55 of the right vertical bearing wall 2Rv rises from the oil suction passage 54, and is filtered by the oil strainer 57 on the way and pumped up to the suction port of the oil pump 40.
Then, the pressure oil discharged from the discharge port of the oil pump 40 is supplied to each lubricating portion such as the metal bearing 11 that supports the crankshaft 10 through the oil passage.

As shown in FIG. 5, the inner surface of the right crankcase 2R has a height that partitions the lower part of the oil surface S up and down when the engine is stopped, and a front lower partition wall from the front side wall of the case outer peripheral wall 2Rs toward the rear. (Crankshaft side lower partition) 61R extends, and a rear lower partition (transmission side lower partition) 62R extends forward from the rear side wall toward the front lower partition 61R.
The front lower partition wall 61R and the rear lower partition wall 62R are on the same plane inclined slightly downwardly forward with respect to the oil surface S, the right end is integrally connected to the right vertical bearing wall 2Rv, and the left end surface is The mating surface is the same as the mating surface 2Rf, and the rear end of the front lower partition wall 61R and the front end of the rear lower partition wall 62R are separated by a predetermined distance.

  A front lower partition 61L and a rear lower partition 62L are formed on the inner surface of the left crankcase 2L symmetrically with the front lower partition 61R and the rear lower partition 62R on the inner surface of the right crankcase 2R (FIG. 6). When the left crankcase 2L and the right crankcase 2R are combined, the front lower partition wall 61L and the front lower partition wall 61R come into contact with each other to form the front lower partition walls 61L and 61R that form the same plane. The rear lower partition wall 62L and the rear lower partition wall 62R are in contact with each other and form rear lower partition walls 62L and 62R that are flush with each other.

That is, the front lower partition (crankshaft side lower partition) 61L, 61R and the rear lower partition (transmission side lower partition) 62L, 62R are arranged on the oil surface S when the engine is stopped before and after the oil pan 2p. A rectangular opening communicating with the lower layer space 63 between the rear ends of the front lower partition walls 61L and 61R and the front ends of the rear lower partition walls 62L and 62R, defining the lower layer space 63 of the oil pan 2p by dividing the lower part into upper and lower parts. Form 64.
The rectangular opening 64 is located above the oil suction port 53.

  Further, as shown in FIG. 5, on the inner surface of the right crankcase 2R, there is an upper portion spaced apart from the front lower partition wall 61R and below a crank web 10w provided with a counterweight of the crankshaft 10. Front upper partition wall (crankshaft side) while being curved downward along the outer peripheral edge of the rotation trajectory of the crank web 10w through the lower part of the balancer shaft 15 from the front side wall of the case outer peripheral wall 2Rs to the rear at a height that partitions vertically The upper partition wall (65R) extends, and the rear upper partition wall (transmission side upper partition wall) 66R extends downward along the driven gear train 13g of the transmission M from the rear side wall toward the front.

  The front upper partition 65R has a lower portion slightly immersed in the oil surface S, and the rear upper partition 66R is above the oil surface S and is inclined forward and downward with respect to the oil surface S. The rear upper partition 66R is integrally connected to the right vertical bearing wall 2Rv at the right end, and the left end surface forms the same mating surface as the mating surface 2Rf. The rear end of the front upper partition 65R and the front end of the rear upper partition 66R Is a predetermined distance apart, and the shift drum 14 is disposed therebetween.

  On the inner surface of the left crankcase 2L, a front upper partition 65L and a rear upper partition 66L are formed symmetrically with the front upper partition 65R and the rear upper partition 66R on the inner surface of the right crankcase 2R (see FIG. 6). When the crankcase 2L and the right crankcase 2R are combined, the front upper partition wall 65L and the front upper partition wall 65R contact the mating surfaces to form the front upper partition walls 65L and 65R having the same curved surface, and the rear upper partition wall 66L The rear upper partition 66R constitutes rear upper partitions 66L and 66R that are flush with each other and are flush with each other.

  That is, the front upper partition (crankshaft side upper partition) 65L, 65R and the rear upper partition (transmission side upper partition) 66L, 66R partition the rotation trajectory of the crank web 10w and the lower side along the driven gear train 13g vertically. An upper space 67 of the oil pan 2p is defined between the lower front lower partition walls 61L and 61R and the rear lower partition walls 62L and 62R, and the rear ends of the front upper partition walls 65L and 65R and the rear upper partition walls 66L, A rectangular opening 68 communicating with the upper space 67 is formed between the front end of 66R.

The shift drum 14 is disposed in the rectangular opening 68 so as to block the rectangular opening 68 (see FIG. 5).
Further, as shown in FIG. 5, the shift drum 14 is on a line segment T connecting the front ends (extending front ends) of the rear upper partitions 66L and 66R and the front ends (extending front ends) of the rear lower partitions 62L and 62R. Arranged and the opening toward the front of the rear upper space 67 between the rear upper partition walls 66L and 66R and the rear lower partition walls 62L and 62R is partially blocked.

  Further, the shift spindle 37 is supported by penetrating in the left-right direction below the rear lower partition walls 62L and 62R below the front ends of the rear upper partition walls 66L and 66R, and the shift spindle 37 is supported by the case outer peripheral walls 2Ls and 2Rs of the upper space 67. It exists in the position which partitions off the back back space along the rear side wall from front space.

  As described above, the interior of the crankcase 2 is defined by the front upper partition walls 65L and 65R and the rear upper partition walls 66L and 66R so that the crank chamber 2C and the transmission chamber 2M are defined above the interior of the oil pan 2p below the crank chamber 2C. Is divided into an upper layer space 67 and a lower layer space 63 by front lower partition walls 61L and 61R and rear lower partition walls 62L and 62R, and a rectangular opening 68 is formed between the front upper partition walls 65L and 65R and the rear upper partition walls 66L and 66R. The rectangular openings 64 are formed in the front lower partition walls 61L and 61R and the rear lower partition walls 62L and 62R. The oil surface S when the engine is stopped is the front lower partition walls 61L and 61R and the rear lower partition walls 62L and 62L. Above 62R, the height is high enough to be immersed in the lowermost part of the front upper partition walls 65L, 65R.

Referring to FIG. 5, four upper communication ports 71r (parts provided with dots) are provided at the front and rear at the lowest portion along the upper surface of the front upper partition wall 65R curved downward in the right vertical bearing wall 2Rv of the right crankcase 2R. The upper communication port 71r communicates between the crank chamber 2C and the clutch chamber 7C in the right crankcase cover 7 (see FIG. 8).
Further, in the right vertical bearing wall 2Rv, one lower communication port 72r (a portion provided with dots) is formed in the front portion between the front upper partition wall 65R and the front lower partition wall 61R. 72r communicates the upper layer space 67 and the clutch chamber 7C.

Further, in the right vertical bearing wall 2Rv, an oil return port 73 (a portion provided with dots) is bored slightly below the rectangular opening 64 between the front lower partition wall 61R and the rear lower partition wall 62R.
The oil return port 73 is located at a position lower than the lower communication port 72r. However, as shown in FIG. 4 when the right crankcase 2R is viewed from the outside (right side), the oil return port 73 extends along the upper surface of the lower portion of the annular frame wall 2Rt. Therefore, the clutch chamber 7C is opened to communicate with the lower space 63 of the oil pan 2p (see FIG. 9).

Referring to FIG. 6, there are four upper communication ports 71 l (parts with scattered points) at the lowest part along the upper surface of the front upper partition wall 65 L curved downward in the left vertical bearing wall 2 Lv of the left crankcase 2 L. The upper communication port 71l communicates between the crank chamber 2C and the generator chamber 6G in the left crankcase cover 6.
Further, in the left vertical bearing wall 2Lv, one lower communication port 72l (a portion provided with a dot) is formed in a portion along the upper surface of the front lower partition 61L between the front upper partition 65L and the front lower partition 61L. It is installed.

When the left crankcase 2L is viewed from the outside (left side), FIG. 7 shows an annular mating surface 2Lg with the left crankcase cover 6 which is an end surface of an annular frame wall 2Lt formed on the left side together with the left vertical bearing wall 2Lv. (A portion indicated by a lattice hatch) is shown.
As shown in FIG. 7 , the lower communication port 72l is formed along the upper surface of the lowermost portion of the annular frame wall 2Lt. Therefore, the lower communication port 72l opens to the generator chamber 6G and the bottom of the generator chamber 6G and the oil. The upper space 67 of the bread 2p is communicated (see FIG. 8).

  With the structure as described above, the oil accumulated on the front upper partition walls 65L and 65R curved downward along the outer periphery of the rotation trajectory of the crank web 10w in the crank chamber 2C, as indicated by broken line arrows in FIG. Generator chamber 6G and right crankcase cover covered with left crankcase cover 6 from left and right upper communication ports 71l and 71r formed in left and right vertical bearing walls 2Lv and 2Rv along the upper surface of front upper partition walls 65L and 65R. 7 is separated into left and right into the clutch chamber 7 </ b> C covered with 7.

The oil accumulated in the generator chamber 6G by flowing into the generator chamber 6G from the crank chamber 2C flows out from the lower communication port 72l of the left vertical bearing wall 2Lv to the front upper space 67 above the front lower partition walls 61L and 61R. (See FIG. 8).
Further, the oil accumulated on the front lower partition walls 61L and 61R flows out into the clutch chamber 7C from the lower communication port 72r (shown in a partially sectional view in FIG. 8) of the right vertical bearing wall 2Rv.

  Therefore, the oil accumulated on the front upper partition walls 65L and 65R of the crank chamber 2C flows directly into the right clutch chamber 7C covered with the right crankcase cover 7 from the right upper communication port 71l, and the left generator Oil accumulated in the chamber 6G also flows out from the right lower communication port 72r through the front upper space 67 of the oil pan 2p, and is collected in the right clutch chamber 7C.

  The oil collected in the right clutch chamber 7C is, as shown in FIG. 9, an oil return port on the right side formed in the right vertical bearing wall 2Rv along the upper surface of the lower portion of the annular frame wall 2Rt. 73 flows out into the lower space 63 of the oil pan 2p and is stored in the oil pan 2p.

  Further, the crankcase 2 has an upper wall portion of the mission chamber 2M in the case outer peripheral walls 2Ls, 2Rs of the left and right crankcases 2L, 2R bulging upwards over the left and right crankcases 2L, 2R, and a breather bulging wall 80 is formed. A breather chamber 82 is formed inside the breather bulging wall 80 and partitioned from the mission chamber 2M by a breather chamber bottom wall 81.

In the breather chamber 82, a labyrinth structure is formed by a plurality of inner walls, and a breather chamber inlet 83 is formed at the front of the breather chamber bottom wall 81 formed along the driven gear train 13g above the driven gear train 13g. An oil return hole 84 is formed in the rear portion of the breather chamber bottom wall 81, which is the lowermost portion of the breather chamber 82, in the upper portion of the rear side walls of the case outer peripheral walls 2Ls and 2Rs with the opening facing forward.
A gas discharge pipe 85 serving as a breather chamber outlet projects from the ceiling wall of the breather bulge wall 80 of the left crankcase 2L, and a gas pipe (not shown) extending from the air cleaner is provided in the gas discharge pipe 85. Connected.

  Therefore, the flow-by gas inside the crank chamber 2C and the mission chamber 2M flows into the breather chamber 82 above the mission chamber 2M from the breather chamber inlet 83, and is separated into gas and liquid by the labyrinth structure in the breather chamber 82. The gas is discharged from the gas discharge pipe 85 and sent to the air cleaner, and the separated oil flows out from the oil return hole 84 to the mission chamber 2M and is eventually collected in the oil pan 2p.

Since the crankcase structure according to the present embodiment is configured as described above, the following effects can be obtained.
5 and 6 show an average oil level S when the internal combustion engine 1 is stopped. While the internal combustion engine 1 is in operation, oil is supplied to each lubrication site, and the oil level S is equivalent. For example, the oil surface S is located in the lower layer space 63 lower than the front lower partition walls 61L and 61R and the rear lower partition walls 62L and 62R, and is thus stored in the lower layer space 63 of the oil pan 2p. The oil surface S is suppressed by the upper and lower partition walls 61L, 61R, 62L, 62R and the upper partition walls 65L, 65R, 66L, 66R. Thus, the oil flow is effectively suppressed.

  In particular, when the oil in the oil pan 2p greatly shakes back and forth during acceleration / deceleration, the oil accumulated on the front lower partition walls 61L and 61R goes back along the inner surfaces of the case outer peripheral walls 2Ls and 2Rs and the crankshaft 10 The movement of the upper upper partition walls 65L and 65R to be disposed can be prevented by the extending base end portions of the front upper partition walls 65L and 65R extending from the front side walls of the case outer peripheral walls 2Ls and 2Rs. Further, the oil accumulated on the rear lower partition walls 62L and 62R moves back along the inner surfaces of the rear outer walls of the case outer peripheral walls 2Ls and 2Rs and onto the rear upper partition walls 66L and 66R where the transmission M is disposed. Can be prevented by the extending base end portions of the rear upper partition walls 66L, 66R extending from the rear side walls of the case outer peripheral walls 2Ls, 2Rs, so that oil is supplied onto the upper partition walls 65L, 65R, 66L, 66R. Increased friction of crankshaft 10 and transmission M It can be suppressed as much as possible.

  Further, the oil surface S is suppressed by the upper and lower partition walls 61L, 61R, 62L, and 62R and the upper partition walls 65L, 65R, 66L, and 66R, so that the oil suction port along the bottom surface of the oil pan 2p. 53 is not exposed even momentarily, and it is possible to prevent the oil pump 40 from sucking air from the oil suction port 53 and causing air engagement.

  As shown in FIGS. 5 and 6, the crankcase 2 has a breather chamber 82 formed above the transmission M in order to make it easy to extract blow-by gas, and the oil separated from the breather chamber 82 is separated from the oil. An oil return hole 84 for returning to the pan is perforated at the rear part of the breather chamber bottom wall 81 at the upper part of the rear side wall of the case outer peripheral wall 2Ls, 2Rs, but the rear lower side by the extended base end part of the rear upper partition walls 66L, 66R. Since the oil accumulated on the partition walls 62L and 62R is prevented from going back along the inner surface of the rear side wall of the case outer peripheral walls 2Ls and 2Rs, the oil does not go back to the oil return hole 84. The oil is prevented from entering the breather chamber 82.

  As also shown in FIG. 5, the front ends of the front upper partition walls 65L and 65R extending rearward from the front side walls of the case outer peripheral walls 2Ls and 2Rs, and the front end extending from the rear side walls of the case outer peripheral walls 2Ls and 2Rs. Since the shift drum 14 is disposed so as to block the rectangular opening 68 between the extending ends of the upper partition walls 66L, 66R, the front and rear upper partition walls 65L, 65R, 66L, 66R and the shift drum 14 cooperate. The oil below the upper partition walls 65L, 65R, 66L, 66R is scattered or flows to prevent the oil from moving on the upper partition walls 65L, 65R, 66L, 66R where the crankshaft 10 or the transmission M is disposed. Therefore, increase in the friction of the crankshaft 10 and the transmission M can be suppressed.

In particular, the shift drum is on a line segment T connecting the extended tip of the rear upper partition walls 66L, 66R extending forward from the rear side wall of the case outer peripheral walls 2Ls, 2Rs and the extended tip of the rear lower partition walls 62L, 62R. 14 is disposed, the upper part of the front opening of the rear upper layer space 67 between the rear lower partition walls 62L and 62R and the rear upper partition walls 66L and 66R is blocked by the shift drum 14 (see FIG. 5). Thereafter, the oil accumulated in the upper space 67 is effectively prevented from scattering or flowing upward, and can be further suppressed from moving on the upper partition walls 65L, 65R, 66L, 66R.
Further, the fact that the shift spindle 37 penetrates the rear upper layer space 67 also suppresses the flow of oil in the rear upper layer space 67, and the oil moves on the upper partition walls 65L, 65R, 66L, 66R. Is suppressed as much as possible.

As described above, the upper partition wall 65L, 65R, 66L, it is suppressed that the oil in the oil pan 2p on the 66R is moved, the upper partition wall 65L, 65R, 66L, the crank shaft 10 on the 66R The oil that lubricated the transmission M gathers and accumulates.
As shown in FIGS. 5 and 6, the rear upper partition walls 66L, 66R below the transmission M in the transmission chamber 2M are located behind the case outer peripheral walls 2Ls, 2Rs on the counter shaft 13 side disposed above the crankshaft 10. Since the rear upper partition walls 66L and 66R are formed at a high position while avoiding interference with the counter gear train 13g, a large rear upper layer space 67 is secured below the rear upper partition walls 66L and 66R. The amount of oil moving on the rear upper partition walls 66L, 66R can be reduced by storing oil in the rear upper space 67, and obliquely downward from the rear side walls of the case outer peripheral walls 2Ls, 2Rs. After the extension, the oil on the upper partition walls 66L, 66R flows on the inclined surface, flows downward from the extension tip, and easily returns to the oil pan 2p.

  As shown in FIGS. 5 and 6, the rear lower partition walls 62L and 62R extend farther forward than the rear upper partition walls 66L and 66R, so that the rear upper partition walls 66L and 66R extend from the leading ends of the rear upper partition walls 66L and 66R. The oil that has flowed down is first received by the rear lower partition walls 62L and 62R, and does not fall directly onto the oil surface S of the stored oil in the lower space 63 of the oil pan 2p. Therefore, the generation of bubbles is suppressed, and the rear lower partition walls 62L and 62R The possibility that bubbles are sucked from the oil suction port 53 provided along the bottom surface of the oil pan 2p of the lower layer space 63 divided into two is extremely low.

  In the crank chamber 2C, the oil accumulated on the front upper partition walls 65L and 65R curved downward along the outer periphery of the rotation trajectory of the crank web 10w, as described above, is supplied from the left and right upper communication ports 71l and 71r to the left generator. Since the flow is divided into left and right into the chamber 6G and the right clutch chamber 7C, an increase in friction due to oil accompanying rotation of the crank web 10w can be suppressed as much as possible.

In addition, since the oil on the front upper partition walls 65L and 65R flows out from the left and right upper communication ports 71l and 71r, the oil flowing down from the rectangular opening 68 opened at the rear end of the front upper partition walls 65L and 65R It can be suppressed.
The oil that flows down from the rectangular opening 68 at a relatively high position flows down toward the rectangular opening 64 below it, which may generate bubbles on the oil surface. There is a possibility that the oil pump 40 sucked from the suction port 53 may cause air biting. However, by suppressing the oil flowing down from the rectangular opening 68, generation of bubbles can be suppressed and air biting can be prevented as much as possible.

Further, as shown in FIGS. 5 and 6, the front lower partition walls 61L and 61R extend rearward and obliquely upward from the front side walls of the case outer peripheral walls 2Ls and 2Rs, and extend toward the base end from the extension tip. Therefore, the oil above the front lower partition walls 61L and 61R accumulates on the extending base end side, and most of the oil flows out from the lower communication port 72r of the right vertical bearing wall 2Rv to the right clutch chamber 7C.
Therefore, the amount of oil flowing down from the rectangular opening 64 at the leading end of the front lower partition walls 61L and 61R onto the oil suction port 53 at the center of the oil pan 2p can be further reduced, and the generation of bubbles is suppressed. It is possible to prevent the bubbles from being sucked from the suction port 53 as much as possible.

As shown in FIG. 9, the oil collected in the right clutch chamber 7C flows into the lower space 63 of the oil pan 2p from the oil return port 73 of the right vertical bearing wall 2Rv.
The oil return port 73 is relatively close to the bottom surface of the oil pan 2p, and is less likely to generate bubbles when the oil flows. The oil return port 73 is located on the right side and is located in the center in the left-right direction. Since it is away from the suction port 53, even if bubbles are generated by the inflow of oil from the oil return port 73, the possibility that the bubbles are sucked into the oil suction port 53 is extremely low.

  As described above, it is possible to prevent air from being sucked from the oil suction port 53 as much as possible, to prevent the oil pump 40 from generating air engagement, and to suppress and stabilize the fluctuation of the discharge hydraulic pressure of the oil pump 40. Therefore, it is possible to employ the metal bearing 11 that requires a stable supply hydraulic pressure for the bearing such as the crankshaft 10.

Next, a crankcase structure of an internal combustion engine according to another embodiment will be described with reference to FIGS.
The internal combustion engine 90 of the present embodiment is the same as the internal combustion engine 1 of the above embodiment except that the front upper partition walls 65L and 65R on the crankshaft 10 side of the left and right crankcases 2L and 2R are the same. The same reference numerals are used except for the upper partition walls 65L and 65R.

  The front upper partition walls 91L, 91R on the crankshaft 10 side in the left and right crankcases 2L, 2R of the internal combustion engine 90 are curved downward along the outer peripheral edge of the rotation locus of the crank web 10w, and the lower crankshaft A deficient portion 92 is formed in a portion overlapping with the front lower partition walls 61L and 61R on the 10 side in the vertical direction.

  The oil above the front upper partition walls 91L and 91R formed by curving downward along the outer peripheral edge of the rotation trajectory of the crank web 10w flows down from the defective portion 92 onto the lower front lower partition walls 61L and 61R. Since it is difficult to accumulate on the front upper partition walls 91L and 91R, an increase in friction due to the rotation of the crankshaft 10 is suppressed, and the oil in the oil pan 2p is moved upward with the crankshaft 10 by the front lower partition walls 61L and 61R. It is possible to easily prevent the oil amount in the oil pan 2p.

  The oil that flows down from the missing portions 92 of the front upper partition walls 91L and 91R on the crankshaft 10 side and accumulates on the front lower partition walls 61L and 61R on the crankshaft 10 side is the front lower side of the vertical bearing walls 2Lv and 2Rv. The lower communication port 72r formed in the portion along the upper surface of the partition wall 61R flows out into the clutch chamber 7C, which is the cover inner space of the case cover 7, and flows into the clutch chamber 7C of the case cover 7 with reference to FIG. Since the oil is returned to the oil pan 2p by the oil return port 73 formed below the front lower partition wall 61R of the right vertical bearing wall 2Rv, the oil is provided at the center at a substantially equal distance from the pair of left and right vertical bearing walls 2Lv and 2Rv. There is an oil return flow from a low position of the oil return port 73 that is separated from the oil suction port 53 formed along the bottom surface of the pan 2p, and bubbles are hardly generated by the oil return flow from the low position. Even if it happens, right Bubbles generated in the linear bearing wall 2Rv side is not to be sucked from the center of the oil suction port 53 away, it is possible to suppress the pressure fluctuation to prevent trapping air in the oil pump 40.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2, 2L, 2R ... Crank case, 2Lv, 2Rv ... Vertical bearing wall, 2Ls, 2Rs ... Case outer peripheral wall, 2C ... Crank chamber, 2M ... Transmission chamber, 3 ... Cylinder block, 4 ... Cylinder head, 5 ... Cylinder head cover, 6 ... Left crankcase cover, 6G ... Generator chamber, 7 ... Right crankcase cover, 7C ... Clutch chamber,
M: Constant mesh gear transmission, G: AC generator, C: Multi-plate friction clutch,
10 ... Crank shaft, 11 ... Metal bearing, 12 ... Main shaft, 13 ... Counter shaft, 14 ... Shift drum, 37 ... Shift spindle,
40 ... Oil pump, 51L, 51R ... Upper wall of oil suction passage, 53 ... Oil suction port,
61L, 61R ... front lower partition, 62L, 62R ... rear lower partition, 63 ... lower layer space, 64 ... rectangular opening, 65L, 65R ... front upper partition, 66L, 66R ... rear upper partition, 67 ... upper layer space, 68 ... rectangular opening,
71l, 71r ... upper communication port, 72l, 72r ... lower communication port, 73 ... oil return port,
80 ... Breather bulging wall, 81 ... Breather chamber bottom wall, 82 ... Breather chamber, 83 ... Breather chamber inlet, 84 ... Oil return hole, 85 ... Gas exhaust pipe,
90 ... Internal combustion engine, 91L, 91R ... Front upper partition, 92 ... Defect.

Claims (8)

A pair of vertical bearing walls (2Lv, 2Rv) opposed to each other are pivotally supported on both sides, and a crankshaft (10) is installed, and the pair of vertical bearing walls (2Lv, 2Rv) and the case outer peripheral wall (2Ls, 2Rs) An oil pan (2p) is provided below the crankcase (2) in which a transmission (M) having a gear train is disposed together with a crank web (10w) having a counterweight in a case inner space surrounded by In the crankcase structure of an internal combustion engine,
A lower partition wall (61L, 61R: 62L, 62R) that divides the lower part of the oil surface (S) of the oil stored in an appropriate amount in the oil pan (2p) into upper and lower parts when the engine is stopped, the case outer peripheral wall (2Ls, 2Rs) and extending toward the inner space of the case,
Upper partition walls (65L, 65R; above the lower partition walls (61L, 61R: 62L, 62R) and above and below the crankshaft (10) and the transmission (M) above and below the transmission (M). 66L, 66R) is formed to extend from the case outer peripheral wall (2Ls, 2Rs) toward the case inner space,
An oil suction port (53) of an oil pumping mechanism for pumping oil stored in the oil pan (2p) is formed along the bottom surface of the oil pan (2p), and the pair of crankcases (2) Case covers (6, 7) are placed outside the vertical bearing walls (2Lv, 2Rv),
The crankshaft side upper partition wall (65L, 65R) formed below the crankshaft (10) and the crankshaft side lower partition wall (61L, 61R) therebelow are both the pair of vertical bearing walls (2Lv, 2Rv). )
The crankshaft side upper partition (65L, 65R) is formed to curve downward along the outer peripheral edge of the rotation locus of the crank web (10w),
In the portion along the upper surface of the crankshaft side upper partition wall (65L, 65R) of the vertical bearing wall (2Lv, 2Rv), a space in the case (2C) above the crankshaft side upper partition wall (65L, 65R) and Upper communication ports (71l, 71r) that communicate with the cover inner space (6G, 7C) of the case cover (6, 7) are formed,
In the portion along the upper surface of the crankshaft side lower partition wall (61L, 61R) of the vertical bearing wall (2Lv, 2Rv), the space in the case above the crankshaft side lower partition wall (61L, 61R) (67 ) And the cover inner space (6G, 7C) of the case cover (6, 7) are formed with lower communication ports (72l, 72r),
Oil flowing into the cover inner space (7C) of the case cover (6, 7) below the crankshaft side lower partition wall (61L, 61R) of the vertical bearing wall (2Lv, 2Rv) is supplied to the oil pan ( 2. A crankcase structure for an internal combustion engine, wherein an oil return port (73) for returning to 2p) is formed. A breather chamber (82) is formed above the transmission (M) on the side where the transmission (M) is disposed in the space in the case,
The crankcase of an internal combustion engine according to claim 1, wherein a communication port (83, 84) for communicating the breather chamber (82) and the space in the case is formed in a lower portion of the breather chamber (82). Construction.   A transmission formed at the extension tip of the crankshaft side upper partition wall (65L, 65R) extending from the case outer peripheral wall (2Ls, 2Rs) toward the case inner space and below the transmission (M) The crankcase structure for an internal combustion engine according to claim 1 or 2, characterized in that a shift drum (14) is disposed between the extended tip of the side upper partition (66L, 66R).   A line segment (T) connecting the extension tip of the transmission side upper partition wall (66L, 66R) and the extension tip of the lower partition wall (62L, 62R) below the transmission side upper partition wall (66L, 66R) The crankcase structure for an internal combustion engine according to claim 3, wherein the shift drum (14) is arranged on the upper part. The main shaft (12) and the counter shaft (13) of the transmission (M) parallel to the crankshaft (10) are arranged in this order apart from the crankshaft (10) in the horizontal direction,
The counter shaft (13) is disposed above the crank shaft (10),
The transmission side upper partition walls (66L, 66R) formed below the transmission (M) are formed to extend obliquely downward from the case outer peripheral wall (2Ls, 2Rs) on the counter shaft (13) side. The crankcase structure for an internal combustion engine according to any one of claims 1 to 4, wherein the structure is a crankcase structure.   The crankshaft side lower partition wall (61L, 61R) extending from the case outer peripheral wall (2Ls, 2Rs) is located at a position where the extended base end is lower than the extending distal end at least when mounted on the vehicle body. A crankcase structure for an internal combustion engine according to any one of claims 1 to 5.   The crankshaft side upper partition wall (65L, 65R) is characterized in that a missing portion (92) is formed in a portion overlapping the crankshaft side lower partition wall (61L, 61R) in the vertical direction. The crankcase structure of the internal combustion engine described. A pair of vertical bearing walls (2Lv, 2Rv) opposed to each other are pivotally supported on both sides, and a crankshaft (10) is installed, and the pair of vertical bearing walls (2Lv, 2Rv) and the case outer peripheral wall (2Ls, 2Rs) An oil pan (2p) is provided below the crankcase (2) in which a transmission (M) having a gear train is disposed together with a crank web (10w) having a counterweight in a case inner space surrounded by In the crankcase structure of an internal combustion engine,
A lower partition wall (61L, 61R: 62L, 62R) that divides the lower part of the oil surface (S) of the oil stored in an appropriate amount in the oil pan (2p) into upper and lower parts when the engine is stopped, the case outer peripheral wall (2Ls, 2Rs) and extending toward the inner space of the case,
Upper partition walls (65L, 65R; above the lower partition walls (61L, 61R: 62L, 62R) and above and below the crankshaft (10) and the transmission (M) above and below the transmission (M). 66L, 66R) is formed to extend from the case outer peripheral wall (2Ls, 2Rs) toward the case inner space,
The main shaft (12) and the counter shaft (13) of the transmission (M) parallel to the crankshaft (10) are arranged in this order apart from the crankshaft (10) in the horizontal direction,
The counter shaft (13) is disposed above the crank shaft (10),
The transmission side upper partition walls (66L, 66R) formed below the transmission (M) are formed to extend obliquely downward from the case outer peripheral wall (2Ls, 2Rs) on the counter shaft (13) side. ,
The crankshaft side upper partition wall (65L, 65R) formed below the crankshaft (10) and the crankshaft side lower partition wall (61L, 61R) therebelow are both the pair of vertical bearing walls (2Lv, 2Rv). )
The crankshaft side upper partition (65L, 65R) is formed to curve downward along the outer peripheral edge of the rotation locus of the crank web (10w),
The crankshaft side upper partition wall (65L, 65R) is formed with a missing portion (92) in a portion overlapping the crankshaft side lower partition wall (61L, 61R) in the vertical direction,
An oil suction port (53) of an oil pumping mechanism for pumping oil stored in the oil pan (2p) is formed along the bottom surface of the oil pan (2p), and the pair of crankcases (2) Case covers (6, 7) are placed outside the vertical bearing walls (2Lv, 2Rv),
The space in the case (67) above the crankshaft side lower partition wall (61L, 61R) in a portion along the upper surface of the crankshaft side lower partition wall (61L, 61R) of the vertical bearing wall (2Lv, 2Rv) ) And the cover inner space (6G, 7C) of the case cover (6, 7) are formed with lower communication ports (72l, 72r),
Oil flowing into the cover inner space (6G, 7C) of the case cover (6, 7) below the crankshaft side lower partition (61L, 61R) of the vertical bearing wall (2Lv, 2Rv) A crankcase structure for an internal combustion engine, wherein an oil return port (73) for returning to the pan (2p) is formed.

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