JP5808541B2 - Breather chamber structure of internal combustion engine - Google Patents

Description

  The present invention relates to a breather chamber structure for an internal combustion engine.

  The purpose of the breather device is to make the piston move smoothly by discharging the gas in the crank chamber when the internal pressure of the crank chamber increases and introducing air into the crank chamber when the internal pressure of the crank chamber decreases when the internal combustion engine is operating. The crank chamber breathing device.

  In a four-stroke cycle internal combustion engine, blow-by gas flows out of the combustion chamber into the crank chamber through a gap between the piston ring and the inner wall surface of the cylinder liner in a stroke in which the piston reciprocates in the cylinder. Most of this blow-by gas is unburned gas (unburned gas mixture) generated in the compression stroke and contains a large amount of air pollutant hydrocarbons (HC), so this unburned gas is led to the intake system, Mixed with intake air, recirculated to combustion chamber, and burned.

  Further, during operation of the internal combustion engine, the lubricating oil in the crank chamber is vigorously agitated by the high speed rotation of the crankshaft and the power transmission gear to become oil mist, which fills the crank chamber. For this reason, when unburned gas is discharged from the crank chamber, oil mist is also discharged at the same time. Generally, in order to prevent the oil mist from returning to the combustion chamber and to prevent the consumption of lubricating oil, the unburned gas is not discharged in the breather chamber. The oil is separated from the gas, the unburned gas from which the oil has been separated is returned to the combustion chamber, and the separated oil is returned to the crank chamber.

  The breather chamber of the internal combustion engine disclosed in Patent Document 1 is provided in the cylinder head cover, and a plurality of labyrinth walls are provided in the breather chamber to form a labyrinth flow path. When the rotational speed of the internal combustion engine is relatively low, gas-liquid separation is promoted by the labyrinth wall, but when the internal combustion engine is used at a high rotational speed, the cam in the cylinder head etc. The amount of lubricating oil that enters is so great that it can flow into the unburned gas discharge pipe along the labyrinth wall.

JP-A-7-269327

  Even in a use state where the rotational speed of the internal combustion engine is high, the oil does not easily enter the breather chamber, and the oil does not easily enter the gas discharge pipe.

The present invention solves the above problems, and the invention according to claim 1
Breather chamber inlet (45) provided in the lower wall (35) that forms a boundary with the cylinder head (15) of the breather chamber (31) provided in the cylinder head cover (16) above the cylinder head (15) Then, the unburned gas containing the oil in the crankcase (13) flows into the breather chamber (31), gas-liquid separation is performed in the breather chamber (31), and the unburned gas separated from the liquid is discharged into the gas discharge pipe. In the breather chamber structure of the internal combustion engine (2) that discharges out of the breather chamber (31) through (43), the breather chamber (31) comprises a single space without a labyrinth wall, and the gas discharge pipe The inlet (43a) of (43) is provided in the central part of the breather chamber (31), and the breather chamber (31) and the portion of the gas discharge pipe (43) located in the breather chamber (31) internal combustion engine, wherein a small hole (44) is provided for communicating the gas passage of the gas discharge pipe (43) (43c) A breather chamber structure.

The invention according to claim 2 is the breather chamber structure of the internal combustion engine according to claim 1 ,
The small hole (44) provided in a portion of the gas discharge pipe (43) located in the breather chamber (31) is opened in a direction perpendicular to the vertical direction. To do.

The invention according to claim 3 is the breather chamber structure of the internal combustion engine according to claim 1 or 2 ,
The cylinder (12) of the internal combustion engine (2) is inclined to one side, and the gas discharge pipe (43) is attached so as to discharge unburned gas from the inclined upper end side of the inclined cylinder head cover (16). The gas discharge pipe inlet (43a) is provided toward the inclined lower end side.

The invention according to claim 4 is the breather chamber structure of the internal combustion engine according to claim 3 ,
A plurality of breather chamber inlets (45) provided on the lower wall (35) of the breather chamber are arranged more toward the inclined lower end side than the inclined upper end side of the breather chamber (31). .

The invention according to claim 5 is the breather chamber structure of the internal combustion engine according to claim 4 ,
A rib (47) for preventing oil ingress is provided on the inclined upper end side of the breather chamber inlet (45) provided in the lower wall (35) of the breather chamber (31).

The invention according to claim 6 is the breather chamber structure of the internal combustion engine according to claim 5 ,
The lower wall (35) of the breather chamber (31) is an upward convex arcuate cross section (40) partially adjacent to the rotating body provided on the cylinder head (15). The arc-shaped cross section (40) is provided with a plurality of breather chamber inlets (45) having ribs (47) for preventing oil intrusion, and the breather chamber closer to the inclined upper end side than the top of the arc-shaped cross section (40). The rib (47) of the inlet (45) is provided on the indoor side of the breather chamber (31), and the rib (47) of the breather chamber inlet (45) closer to the inclined lower end side than the top of the arcuate section (40). Is provided on the cylinder head (15) side.

The invention according to claim 7 is the breather chamber structure of the internal combustion engine according to claim 6 ,
The oil intrusion prevention rib (47) provided toward the indoor side of the breather chamber (31) is continuously provided in a U shape so as to surround the inclined upper end side of the breather chamber inlet (45). It is characterized by being.

The invention according to claim 8 is the breather chamber structure of the internal combustion engine according to claim 5 ,
The rib (47) for preventing oil intrusion at the breather chamber inlet (45) is provided around the breather chamber inlet (45) on the lower surface of the lower wall (35).

According to the invention of claim 1,
Since the labyrinth wall is not provided in the breather chamber (31), the inlet of the gas exhaust pipe (43) provided at the center of the breather chamber (31) is connected to the wall surface of the breather chamber (31). The distance from the gas discharge pipe inlet (43a) can be increased, and the oil flowing along the wall surface does not easily enter the gas discharge pipe (43).
Further, since the pressure drop at the gas discharge pipe inlet (43a) is alleviated, the oil reaching the vicinity of the gas discharge pipe inlet (43a) is less likely to enter the gas discharge pipe (43).

According to the invention of claim 2 ,
Since the breather chamber (31) is provided in the cylinder head cover (16), it is generally made thin in the vertical direction in order to reduce the overall height of the engine. By opening the small hole (44) in a direction perpendicular to the vertical direction, the small hole (44) has a greater distance from the wall surface, so that oil flows from the small hole (44) to the gas discharge pipe ( 43) Difficult to get inside.

According to the invention of claim 3 ,
Oil that has entered the gas discharge pipe (43) is easily discharged from the gas discharge pipe inlet (43a).

According to the invention of claim 4 ,
Since the oil that has entered the breather chamber (31) flows along the inclination of the lower wall (35), it easily returns to the cylinder head side.

According to the invention of claim 5 ,
Most of the oil mist blown off from the cam nose by the rotation of the cam shaft (28) collides with these ribs (47) and liquefies and flows downward, so that it hardly enters the breather chamber (31).

According to the invention of claim 6 ,
The upward ribs (47B, 47C) promote liquefaction due to the collision of the oil mist bounced off from the cam nose, and also enable liquefaction of the oil mist due to the collision when the gas moves in the breather chamber (31). Also, the downward rib (47D) promotes gas-liquid separation mainly by the oil mist bounced off from the cam nose colliding at a short distance.

According to the invention of claim 7 ,
Since it is difficult for gas to move in the breather chamber (31), the collision liquefaction of the oil mist blown off from the cam nose is further accelerated by the rotation of the cam shaft (28), and the oil mist enters the breather chamber (31). It becomes difficult.

According to the invention of claim 8 ,
By the ribs (47A, 47E), the oil blown off by the cam nose collides with the ribs (47A, 47E) on the way to the breather chamber inlet (45), so that gas-liquid separation is promoted, and the oil is breathed in the breather chamber (31). Hard to get into.

1 is a left side view of a motorcycle according to an embodiment of the present invention. It is a left view of the principal part cross section of the internal combustion engine of the said motorcycle. It is a top view of the cylinder head cover of a rear cylinder. It is IV-IV sectional drawing of FIG. It is VV sectional drawing of FIG. It is VI-VI sectional drawing of FIG.

  FIG. 1 is a left side view of a motorcycle 1 according to an embodiment of the present invention. The motorcycle 1 is equipped with an internal combustion engine 2 having a breather chamber structure according to the present invention. A front fork 4 is provided at the front end of the main frame 3 of the motorcycle 1 so as to be able to turn left and right. A steering handle 5 is integrally attached to the upper end of the front fork 4, and a front wheel 6 is attached to the lower portion of the front fork 4. It is pivotally supported. A rear fork 7 is provided at the rear portion of the main frame 3 so as to be swingable up and down, and a rear wheel 8 is pivotally supported at the rear end thereof. The rear wheel 8 is rotationally driven via a chain 9 by the power of the internal combustion engine 2.

  FIG. 2 is a left side view of a cross section of the main part of the internal combustion engine 2. In the following drawings, directions are indicated by arrows as forward Fr, backward Re, upward Up, downward Dn, left L, right R. The internal combustion engine 2 is a four-cylinder V-type OHC internal combustion engine in which a cylinder axis is branched back and forth around a crankshaft 11 and two cylinders 12 are arranged in each cylinder. The crankcase 13 is of an upper and lower split type consisting of an upper crankcase 13U and a lower crankcase 13L. The upper crankcase 13U is integrally formed with front and rear cylinder blocks 14. A cylinder head 15 is coupled to the upper part of each cylinder block 14, and a cylinder head cover 16 is attached to the upper part of each cylinder head 15. An air cleaner 17 (FIG. 1) is disposed above the internal combustion engine 2.

  Pistons 18 are slidably fitted to the front and rear cylinders 12, respectively. A crankshaft 11 is rotatably supported on a mating surface between the upper crankcase 13U and the lower crankcase 13L. Both ends of a connecting rod 19 are pivotally attached to the piston 18 and the crankshaft 11, and the crankshaft 11 is rotationally driven in response to the vertical movement of the piston 18.

  An intake port 21 is disposed on the inner side where the front and rear cylinder heads 15 approach each other, and an exhaust port 22 is disposed on the outer front and rear sides of the cylinder head 15, respectively. A throttle body mounting member 23 is provided on the upper portion of the intake port 21, and a throttle body (not shown) is mounted on the upper surface thereof. The upper part of the throttle body is connected to an air cleaner 17 (FIG. 1). A fuel injection valve 24 is mounted on the throttle body mounting member 23 with its tip directed toward the intake port 21. An exhaust pipe 25 (FIG. 1) is connected to the exhaust ports 22 outside the front and rear of the cylinder head 15.

  The intake port 21 and the exhaust port 22 are respectively provided with an intake valve 26 and an exhaust valve 27 that can be opened and closed. An intake cam shaft 28I and an exhaust cam shaft 28E are rotatably provided between the cylinder head 15 and the cylinder head cover 16. A drive gear (not shown) provided on the crankshaft 11 and a driven gear (not shown) provided on each camshaft 28 are connected by a gear train (not shown) provided therebetween, and the camshaft 28 is Each time the crankshaft 11 makes two revolutions, the crankshaft 11 makes one revolution, and the intake valve 26 and the exhaust valve 27 are opened and closed by the cam of the camshaft 28. The inside of the crankcase 13 and the inside of the cylinder head 15 communicate with each other through a gear train chamber 29 (FIG. 3), and unburned gas and air circulate therethrough. A breather chamber 31 is provided on the upper surface of the cylinder head cover 16 of the rear cylinder 30R. The breather chamber 31 is provided only in the rear cylinder 30R. Unburned gas generated from the front cylinder 30F is also processed in the breather chamber 31 provided in the rear cylinder 30R through the common crankcase 13 and the gear train chamber 29 of the rear cylinder 30R.

  3 is a top view of the cylinder head cover 16 of the rear cylinder 30R, FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3, FIG. 5 is a sectional view taken along the line V-V in FIG. FIG. In FIG. 6, H is a horizontal plane, and C is a cylinder axis of the rear cylinder 30R.

  3 and 4, the cylinder head cover 16 is attached to the upper surface of the cylinder head 15 that covers the upper portions of the two cylinders 12 arranged in the left-right direction in the rear cylinder 30R. As described above, the rear cylinder 30R of the internal combustion engine 2 is a two-cylinder, and the cylinder head cover 16 is provided with a spark plug mounting hole 32 corresponding to each cylinder. The right end is a gear train chamber 29 for driving the camshaft.

  3, 4, and 5, the upper member 33 that covers the upper surface of the cylinder head cover 16 is cast integrally with the cylinder head cover 16 in the front-rear direction at the center in the left-right direction of the cylinder head cover 16 to form a cavity therein. Has been. This cavity is the breather chamber 31.

  6 is a view showing a cross section taken along line VI-VI in FIG. This is an enlarged left side view of the breather chamber 31 in cross section. The breather chamber 31 shown in FIG. 3 shows the III-III cross section of FIG. That is, the inside of the breather chamber 31 as viewed from above is shown. 6 and 3, the breather chamber 31 is surrounded by an upper wall 34, a lower wall 35, a front wall 36, a rear wall 37, and left and right side walls 38. The upper wall 34 is a part of the upper member 33, and the lower wall 35 is a part of the cylinder head cover 16. The breather chamber 31 and the valve operating chamber 42 in the cylinder head 15 are partitioned by a lower wall 35 of the breather chamber 31.

  In FIG. 6, an intake cam shaft 28I and an exhaust cam shaft 28E are provided below the cylinder head cover 16. The portion of the cylinder head cover 16 covering these cam shafts 28 has an arcuate cross section along the cam nose locus 39 (see also the cross section of the cylinder head cover 16 of the front cylinder 30F in FIG. 2).

  In FIG. 6, the lower wall 35 at the rear part of the breather chamber 31 has an arcuate cross-sectional portion 40, similar to the portion covering the exhaust camshaft 28 </ b> E of the cylinder head cover 16. However, the lower wall 35 below the gas discharge pipe 43 at the front portion of the breather chamber 31 has a rectangular cross section 41 for convenience of mounting the gas discharge pipe 43.

  3 and 6, a gas discharge pipe 43 is attached from the front wall 36 of the breather chamber 31 toward the inside of the breather chamber 31. The gas discharge pipe inlet 43 a is located substantially at the center of the internal space of the breather chamber 31. The gas discharge pipe 43 is bent outside the breather chamber 31, and a gas discharge pipe outlet 43b is provided at the end thereof. The gas discharge pipe outlet 43b is connected to the clean side of the air cleaner 17 via a hose. A small hole 44 that communicates between the breather chamber 31 and the gas passage 43c in the gas discharge pipe 43 is located in a portion of the gas discharge pipe 43 located in the breather chamber 31 in a lateral direction (a direction perpendicular to the vertical direction). It is provided.

  3 and 6, the breather chamber lower wall 35 is provided with a plurality of breather chamber inlets 45. The breather chamber entrances 45A, 45B, 45C, and 45D are named in order from the front entrance. The breather chamber inlet 45A is provided below the gas discharge pipe 43. The breather chamber inlets 45B, 45C and 45D are provided in the arcuate cross section 40. These breather chamber inlets 45 are square holes as seen in FIG. 3, 4, and 6, a member denoted by reference numeral 46 is a lid that closes a hole for removing a core used in the process of casting the breather chamber 31.

  As shown in FIG. 3 and FIG. 6, upward or downward oil intrusion prevention ribs 47 are provided around the breather chamber inlet 45, on the front side, and on the lateral side. A downward rib 47A surrounding the hole is provided below the breather chamber entrance 45A. An upward rib 47B is provided in front of the breather chamber entrance 45B. The breather chamber entrance 45C is provided with an upward rib 47C that surrounds the front side and a part of the side and is U-shaped when viewed from above. A downward rib 47D is provided below the front side of the breather chamber entrance 45D. As shown in FIGS. 3, 5, and 6, a common downward rib 47E is provided on the lower left and right sides of the breather chamber inlets 45B, 45C, 45D.

  In the breather chamber 31 configured as described above, unburned gas containing oil in the crankcase 13 is geared from the breather chamber inlet 45 provided in the lower wall 35 that forms a boundary with the cylinder head 15 into the breather chamber 31. It flows in through the train chamber 29 and the valve operating chamber 42, performs gas-liquid separation in the breather chamber 31, and the unburned gas from which the liquid has been separated is discharged out of the breather chamber 31 through the gas discharge pipe 43. The separated oil returns to the crankcase 13 via the cylinder head 15 and the gear train chamber 29.

  The breather chamber 31 is composed of a single space without a labyrinth wall. However, the oil mist stirred by the cam nose collides with the upward ribs 47B and 47C or the downward ribs 47A, 47D and 47E. Liquid separation is performed. Since the inlet 43a of the gas exhaust pipe 43 is provided in the central portion of the breather chamber 31, the distance between the wall of the breather chamber 31 and the inlet of the gas exhaust pipe 43 can be increased, and oil flowing along the wall Is difficult to enter the gas discharge pipe 43.

  Since the pressure drop at the gas discharge pipe inlet 43a is alleviated by the small hole 44 provided in the breather chamber 31 of the gas discharge pipe 43, the oil mist that has reached the vicinity of the inlet 43a of the gas discharge pipe 43 Is difficult to enter the gas discharge pipe 43.

  The breather chamber 31 is provided on the upper surface of the cylinder head cover 16, and is thin in the vertical direction and wide in the horizontal direction in order to reduce the overall height of the engine. Since the small hole 44 of the gas discharge pipe 43 is opened in the lateral direction, that is, in a direction orthogonal to the vertical direction, the distance between the small hole 44 and the side wall 38 is large, and the oil adhering to the wall surface Is prevented from entering the gas discharge pipe 43 from the small hole 44.

  The cylinder 12 of the rear cylinder 30R is inclined rearward, and the gas discharge pipe 43 is mounted so as to discharge unburned gas from the inclined upper end side of the inclined cylinder head cover 16, and the inlet 43a of the gas discharge pipe 43 is It is provided toward the inclined lower end side direction. Therefore, the oil that has entered the gas discharge pipe 43 is discharged from the gas discharge pipe inlet 43a.

  Of the four breather chamber inlets 45 provided on the lower wall 35 of the breather chamber 31, more than half of the three are disposed on the inclined lower end side of the breather chamber 31, that is, closer to the rear. Since the oil that has entered the breather chamber 31 flows rearward and downward along the inclination of the lower wall 35, the oil easily returns to the cylinder head 15 side.

  On the inclined upper end side of the breather chamber inlet 45 provided in the lower wall 35 of the breather chamber 31, a rib 47 for preventing oil ingress is provided. Most of the oil mist blown off from the cam nose by the rotation of the cam shaft 28 collides with the ribs 47 and liquefies and flows downward, so that it hardly enters the breather chamber 31.

  The rear part of the lower wall 35 of the breather chamber 31 has an arcuate cross section 40 that protrudes upward like the part covering the rotating body provided in the cylinder head 15, and the arcuate cross section 40 includes oil. A plurality of breather chamber inlets 45 provided with ribs 47 for preventing intrusion are provided. The ribs 47B and 47C of the breather chamber inlets 45B and 45C closer to the inclined upper end side than the apex portion or the apex portion of the arc-shaped cross section 40 are provided on the indoor side (upward) of the breather chamber 31, and A rib 47D of the breather chamber inlet 45D closer to the side is provided on the cylinder head 15 side (downward). The upward ribs 47B and 47C promote liquefaction due to collision of oil mist bounced off from the cam nose, and also enable liquefaction of oil mist due to collision during movement of gas in the breather chamber. In addition, the downward rib 47D mainly promotes gas-liquid separation when oil mist bounced off from the cam nose collides at a short distance.

  The rib 47C provided toward the indoor side of the breather chamber inlet 45C is continuously provided in a U shape so as to surround the inclined upper end side of the breather chamber inlet 45C. This makes it difficult for the gas to move in the breather chamber 31, so that the collision liquefaction of the oil mist blown off from the cam nose by the rotation of the cam shaft 28 is further promoted, and the oil mist is less likely to enter the breather chamber 31.

  The downward rib 47A of the breather chamber entrance 45A is provided around the breather chamber entrance 45A. Further, on the side of the breather chamber inlets 45B, 45C, 45D, downward ribs 47E are provided on the lower surface of the lower wall 35 so as to collectively surround the breather chamber inlets 45B, 45C, 45D. By these ribs 47A and 47E, the oil blown off by the cam nose collides with the ribs 47A and 47E on the way to the breather chamber inlet 45, so that gas-liquid separation is promoted and the oil hardly enters the breather chamber 31.

As described in detail above, the following effects are brought about in the above embodiment.
(1) Since the gas discharge pipe inlet 43a is provided in the central portion of the breather chamber 31, the oil is difficult to enter the gas discharge pipe 43 through the wall surface.
(2) The small hole 44 that connects the breather chamber 31 and the gas passage 43c in the gas discharge pipe 43 alleviates the pressure drop at the gas discharge pipe inlet 43a and reduces the entry of oil mist into the gas discharge pipe.
(3) Since the small hole 44 is opened in the lateral direction, the oil on the wall surface hardly enters the gas discharge pipe 43 from the small hole 44.
(4) Since the gas discharge pipe inlet 43a is provided toward the inclined lower end side, the oil that has entered the gas discharge pipe 43 is easily discharged from the gas discharge pipe inlet 43a.
(5) Since a plurality of inlets of the breather chamber 31 are arranged on the inclined lower end side of the breather chamber 31, the oil flowing along the inclination in the breather chamber 31 easily returns to the cylinder head 15 side. .
(6) Since the oil mist blown off from the cam nose collides with the rib 47 on the inclined upper end side of the inlet 45 of the breather chamber 45, it is difficult to enter the breather chamber.
(7) The upward ribs 47B and 47C promote liquefaction due to collision of oil mist bounced off from the cam nose, and also enable liquefaction of oil mist due to collision during movement of gas in the breather chamber. The downward rib 47D mainly promotes gas-liquid separation by colliding at a short distance from the oil mist bounced off from the cam nose.
(8) The rib 47C provided toward the indoor side, which is continuously provided in a U-shape so as to surround the inclined upper end side of the inlet 45C of the breather chamber, allows oil mist blown off from the cam nose to enter the breather chamber 31. Hateful.
(9) Since the oil mist blown off by the cam nose collides with ribs 47A and 47E provided around the lower surface of the breather chamber inlet 45 on the way to the breather chamber inlet 45, gas-liquid separation is promoted, Difficult to enter Breather Chamber 31.

2 ... Internal combustion engine, 12 ... Cylinder, 15 ... Cylinder head, 16 ... Cylinder head cover, 31 ... Breather chamber, 35 ... Lower wall, 40 ... Arc-shaped cross section, 43 ... Gas exhaust pipe, 43a ... Gas exhaust pipe inlet, 43c ... Gas passage in the gas discharge pipe, 44 ... small hole, 45 ... breather chamber inlet, 45A, 45B, 45C, 45D ... breather chamber inlet, 47 ... rib, 47A, 47B, 47C, 47D, 47E ... rib, H ... Horizontal plane, C ... Cylinder axis of rear cylinder

Claims (8)

Breather chamber inlet (45) provided in the lower wall (35) that forms a boundary with the cylinder head (15) of the breather chamber (31) provided in the cylinder head cover (16) above the cylinder head (15) Then, the unburned gas containing the oil in the crankcase (13) flows into the breather chamber (31), gas-liquid separation is performed in the breather chamber (31), and the unburned gas separated from the liquid is discharged into the gas discharge pipe. In the breather chamber structure of the internal combustion engine (2) that discharges out of the breather chamber (31) through (43),
The breather chamber (31) consists of a single space without a labyrinth wall, and the inlet (43a) of the gas discharge pipe (43) is provided at the center of the breather chamber (31) ,
A small hole (44) communicating the breather chamber (31) and the gas passage (43c) in the gas discharge pipe (43) with a portion of the gas discharge pipe (43) located in the breather chamber (31). ) . A breather chamber structure for an internal combustion engine. The small hole (44) provided in a portion of the gas discharge pipe (43) located in the breather chamber (31) is opened in a direction perpendicular to the vertical direction. The breather chamber structure for an internal combustion engine according to claim 1 . The cylinder (12) of the internal combustion engine (2) is inclined to one side, and the gas discharge pipe (43) is attached so as to discharge unburned gas from the inclined upper end side of the inclined cylinder head cover (16). The breather chamber structure for an internal combustion engine according to claim 1 or 2 , wherein the gas discharge pipe inlet (43a) is provided in a direction toward the inclined lower end side. A plurality of breather chamber inlets (45) provided on the lower wall (35) of the breather chamber are arranged more toward the inclined lower end side than the inclined upper end side of the breather chamber (31). The breather chamber structure of the internal combustion engine according to claim 3 . The rib (47) for preventing oil ingress is provided on the inclined upper end side of the breather chamber inlet (45) provided in the lower wall (35) of the breather chamber (31). 5. A breather chamber structure for an internal combustion engine according to 4 . The lower wall (35) of the breather chamber (31) is an upward convex arcuate cross section (40) partially adjacent to the rotating body provided on the cylinder head (15). The arc-shaped cross section (40) is provided with a plurality of breather chamber inlets (45) having ribs (47) for preventing oil intrusion, and the breather chamber closer to the inclined upper end side than the top of the arc-shaped cross section (40). The rib (47) of the inlet (45) is provided on the indoor side of the breather chamber (31), and the rib (47) of the breather chamber inlet (45) closer to the inclined lower end side than the top of the arcuate section (40). The breather chamber structure for an internal combustion engine according to claim 5 , wherein is provided on the cylinder head (15) side. The oil intrusion prevention rib (47) provided toward the indoor side of the breather chamber (31) is continuously provided in a U shape so as to surround the inclined upper end side of the breather chamber inlet (45). The breather chamber structure for an internal combustion engine according to claim 6 . The breather chamber inlet for oil entering prevention of (45) ribs (47), in the lower wall (35) lower surface, claim 5, characterized in that provided on the periphery of the breather chamber inlet (45) The breather chamber structure of the internal combustion engine described in 1.

Images