阅读说明：本技术 发动机的通风器结构 (Ventilator structure of engine ) 是由 小西幸生 上野光 于 2019-06-17 设计创作，主要内容包括：本发明的发动机的通风器结构防止利用通风腔从窜气中分离并排出至动阀室的油从通风腔与动阀室之间的通风腔结合面漏出至外部。通风腔(30)具备与动阀室(24)连通的筒状的排油通路(41c)、(41d),排油通路(41c)、(41d)的前端超过汽缸头(22)及头盖(23)的通风腔结合面(22a)、(23a)而从开口部(36a)、(36b)向动阀室(24)侧突出,因而能够将通风腔(30)中从窜气中分离的油可靠地排出至动阀室(24)而防止从通风腔结合面(22a)、(23a)漏出到外部。(The invention provides a ventilator structure of an engine, which prevents oil separated from blow-by gas by a ventilation cavity and discharged to a valve chamber from leaking to the outside from a ventilation cavity joint surface between the ventilation cavity and the valve chamber. The vent chamber (30) is provided with tubular drain passages (41c, 41d) that communicate with the valve chamber (24), and the tips of the drain passages (41c, 41d) project from the openings (36a, 36b) toward the valve chamber (24) beyond the vent chamber coupling surfaces (22a, 23a) of the cylinder head (22) and the head cover (23), so that oil separated from blow-by gas in the vent chamber (30) can be reliably discharged to the valve chamber (24) and prevented from leaking from the vent chamber coupling surfaces (22a, 23a) to the outside.)

1. A breather structure of an engine, wherein a movable valve chamber (24) for accommodating camshafts (33, 34) is defined between a cylinder head (22) common to both banks (12) of a V-type engine and a head cover (23) coupled to the cylinder head (22), openings (36a, 36b) facing the axial ends of the camshafts (33, 34) are formed in ventilation chamber coupling surfaces (22a, 23a) extending across the cylinder head (22) and the head cover (23), and the ventilation chamber coupling surfaces (22a, 23a) are coupled to a ventilation chamber (30) which communicates an intake passage (20) on the upstream side of a throttle valve (21) with the movable valve chamber (24),

the ventilation chamber (30) is provided with tubular oil drain passages (41c, 41d) that communicate with the valve chamber (24), and the tips of the oil drain passages (41c, 41d) project from the openings (36a, 36b) toward the valve chamber (24) beyond the ventilation chamber connection surfaces (22a, 23 a).

2. The ventilator structure of an engine according to claim 1, wherein a first opening (36a) and a second opening (36b) facing axial ends of an intake camshaft (33) and an exhaust camshaft (34) are formed in the ventilation chamber coupling surfaces (22a, 23a), the ventilation chamber (30) includes at least a first chamber (A, B, C) and a second chamber (D) partitioned by an oil separating member (44) separating oil from blow-by gas, a first oil discharge passage (41c) of the first chamber (A, B, C) protrudes from the first opening (36a) toward the valve chamber (24), and a second oil discharge passage (41D) of the second chamber (D) protrudes from the second opening (36b) toward the valve chamber (24).

3. The ventilator structure of an engine according to claim 2, wherein the oil separating member (44) has a plurality of orifices (46a) through which blow-by gas passes, and a collision wall (46b) against which blow-by gas passing through the orifices (46a) collides.

4. The ventilator structure of an engine according to claim 3, wherein the oil separation member (44) is provided with a filter (47) disposed between the orifice (46a) and the collision wall (46 b).

5. The ventilator structure of engine according to claim 2, characterized in that the volume of said second chamber (D) communicating with said air intake passage (20) is larger with respect to the volume of said first chamber (A, B, C) communicating with said valve chamber (24).

6. The ventilator structure for an engine according to claim 5, wherein the ventilation chamber (30) includes a case (41) joined to the ventilation chamber joining surfaces (22a, 23a), a cover (42) joined to the case (41), and a partition member (43) sandwiched between the case (41) and the cover (42).

7. The ventilator structure of the engine according to claim 5, wherein a variation amount of a flow path sectional area of the labyrinth-shaped flow path formed in the first chamber (A, B, C) is larger than a variation amount of a flow path sectional area of the labyrinth-shaped flow path formed in the second chamber (D).

8. The ventilator structure for an engine according to claim 7, wherein the first chamber (A, B, C) is partitioned by sandwiching a partition member (43) having communication holes (43B, 43c, 43e) between a case (41) and a cover (42), and a flow path cross-sectional area of a chamber (B) formed between the partition member (43) and the cover (42) is larger than a flow path cross-sectional area of a chamber (A, C) formed between the case (41) and the partition member (43).

Technical Field

The present invention relates to a breather (break) structure of an engine in which a movable valve chamber for accommodating a camshaft is defined between a cylinder head shared by two cylinder banks of a V-type engine and a head cover coupled to the cylinder head, an opening portion to which a shaft end of the camshaft faces is formed at a vent chamber coupling surface spanning the cylinder head and the head cover, and the vent chamber coupling surface is coupled to a vent chamber which communicates an intake passage on an upstream side of a throttle valve to the movable valve chamber.

Background

From the following patent document 1, the following is known: a shaft end of a camshaft housed in a valve chamber of a cylinder head (cylinder head) is supported by a bearing, an oil separation space facing the shaft end of the camshaft is defined inside a fitting (fitting) coupled to an outer side surface of the bearing, oil contained in blow-by gas supplied from a crankcase into the camshaft is separated by centrifugal force, the blow-by gas is discharged from the oil separation space to the valve chamber, and the blow-by gas having the separated oil is returned from the oil separation space to an intake system of an engine.

Further, according to the following patent document 2, it is known that: an oil separator (oil separator) that is housed in a valve chamber of an engine and separates oil from blow-by gas includes an oil separating mechanism including a restrictor plate, a trap plate, and a backflow prevention plate that are disposed in a blow-by gas passage that connects an inflow port and an outflow port of blow-by gas.

Further, according to the following patent document 3, it is known that: an oil separator for separating oil from blow-by gas includes a first oil separator and a second oil separator provided inside a housing, and the first oil separator and the second oil separator are used for separating oil independently from each other.

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent No. 2504073 publication

[ patent document 2] Japanese patent No. 4581829 publication

[ patent document 3] Japanese patent No. 4425951

Disclosure of Invention

[ problems to be solved by the invention ]

Further, when the ventilation chamber coupling surface is formed so as to extend across both side surfaces of the cylinder head and the head cover of the engine, and the oil separated from the blow-by gas by the ventilation chamber coupled to the ventilation chamber coupling surface is discharged to the valve chamber formed inside the cylinder head and the head cover, the sealability of the divided ventilation chamber coupling surface is easily reduced, and the oil discharged from the ventilation chamber may leak to the outside from the ventilation chamber coupling surface.

The present invention has been made in view of the above circumstances, and an object thereof is to prevent oil separated from blow-by gas by a vent chamber and discharged to a valve chamber from leaking to the outside from a vent chamber coupling surface between the vent chamber and the valve chamber.

[ means for solving problems ]

In order to achieve the above object, according to the invention described in claim 1, there is provided a breather structure of an engine in which a movable valve chamber for accommodating a camshaft is defined between a cylinder head common to both cylinder banks of a V-type engine and a head cover coupled to the cylinder head, an opening portion facing a shaft end of the camshaft is formed in a vent chamber coupling surface spanning the cylinder head and the head cover, the vent chamber coupling surface is coupled to a vent chamber communicating an intake passage on an upstream side of a throttle valve with the movable valve chamber, wherein the vent chamber includes a cylindrical oil drain passage communicating with the movable valve chamber, and a tip end of the oil drain passage protrudes from the opening portion toward the movable valve chamber side beyond the vent chamber coupling surface.

Further, according to the invention described in claim 2, in addition to the structure of claim 1, a first opening portion and a second opening portion that face axial ends of the intake camshaft and the exhaust camshaft are formed on the vent chamber coupling surface, the vent chamber includes at least a first chamber and a second chamber that are partitioned by an oil separating member that separates oil from blow-by gas, a first oil discharge passage of the first chamber protrudes from the first opening portion toward the valve chamber side, and a second oil discharge passage of the second chamber protrudes from the second opening portion toward the valve chamber side.

Further, according to the invention described in claim 3, in addition to the structure of claim 2, there is provided the breather structure of an engine in which the oil separating member includes a plurality of orifices through which blow-by gas passes and a collision wall against which blow-by gas passing through the orifices collides.

Further, according to the invention described in claim 4, in addition to the structure of claim 3, there is provided the ventilator structure for an engine, wherein the oil separating member includes a filter disposed between the orifice and the collision wall.

Further, according to the invention described in claim 5, in addition to the structure described in any one of claims 2 to 4, there is provided a ventilator structure for an engine in which a volume of the second chamber communicating with the intake passage is larger than a volume of the first chamber communicating with the movable valve chamber.

Further, according to the invention described in claim 6, in addition to the structure of claim 5, the ventilation chamber includes a case coupled to the ventilation chamber coupling surface, a cover coupled to the case, and a partition member interposed between the case and the cover.

Further, the airflow pipe 20 of the embodiment corresponds to the intake passage of the present invention, the intake camshaft 33 and the exhaust camshaft 34 of the embodiment correspond to the camshaft of the present invention, the first opening portion 36a and the second opening portion 36b of the embodiment correspond to the opening portions of the present invention, the first drain passage 41c and the second drain passage 41d of the embodiment correspond to the drain passage of the present invention, and the first communication hole 43b, the second communication hole 43c, and the third communication hole 43d of the embodiment correspond to the communication holes of the present invention.

[ Effect of the invention ]

According to the configuration of claim 1, since the valve chamber for accommodating the camshaft is defined between the cylinder head common to both the cylinder banks of the V-type engine and the head cover coupled to the cylinder head, the opening portion facing the shaft end of the camshaft is formed on the ventilation cavity coupling surface spanning the cylinder head and the head cover, and the ventilation cavity coupling surface is coupled to the ventilation cavity which communicates the intake passage on the upstream side of the throttle valve to the valve chamber, when the blowby gas in the valve chamber flows backward toward the intake passage side, the oil separated from the blowby gas in the ventilation cavity can be discharged to the valve chamber, thereby preventing the oil from adhering to the throttle valve on the downstream side of the intake passage.

The vent chamber includes a cylindrical oil drain passage communicating with the valve chamber, and a tip end of the oil drain passage protrudes from the opening portion toward the valve chamber side beyond the vent chamber coupling surface, so that oil separated from blow-by gas in the vent chamber can be reliably discharged to the valve chamber, and leakage from the vent chamber coupling surface to the outside can be prevented.

Further, according to the configuration of claim 2, since the first opening and the second opening facing the shaft ends of the intake camshaft and the exhaust camshaft are formed on the vent chamber coupling surface, and the vent chamber includes at least the first chamber and the second chamber partitioned by the oil separating member that separates oil from blow-by gas, the first oil discharge passage of the first chamber protrudes from the first opening toward the valve chamber side, and the second oil discharge passage of the second chamber protrudes from the second opening toward the valve chamber side, the oil contained in blow-by gas is separated in three stages in the first chamber, the oil separating member, and the second chamber, and therefore, the oil retained in the first chamber and the second chamber can be reliably discharged to the valve chamber by the first oil discharge passage and the second oil discharge passage while the oil contained in the blow-by gas is separated in three stages in the first chamber, the oil separating member, and the second chamber.

Further, according to the structure of claim 3, since the oil separating member includes the plurality of orifices through which the blow-by gas passes and the collision wall against which the blow-by gas passing through the orifices collides, the blow-by gas accelerated through the orifices collides with the collision wall at high speed, and the oil can be efficiently separated.

Further, according to the structure of claim 4, since the oil separating member includes the filter disposed between the orifice and the collision wall, the oil contained in the blow-by gas can be captured and separated more effectively.

Further, according to the structure of claim 5, since the volume of the second chamber communicating with the intake passage is larger than the volume of the first chamber communicating with the movable valve chamber, when the blowby gas containing the oil mist flows back from the driven valve chamber to the intake passage side, not only can the flow velocity of the blowby gas be reduced by the second chamber having a large volume, but also the oil in the blowby gas not completely removed by the oil separating member can be efficiently removed, and the oil in the second chamber can be prevented from being blown off to the intake member side.

Further, according to the configuration of claim 6, since the ventilation chamber includes the case coupled to the ventilation chamber coupling surface, the cover coupled to the case, and the partition member sandwiched between the case and the cover, a plurality of chambers having different volumes can be easily and compactly formed between the case and the cover.

Drawings

Fig. 1 is a plan view of a V-type multi-cylinder engine.

Fig. 2 is a 2-way arrow view of fig. 1.

Fig. 3 is a sectional view corresponding to fig. 2.

Fig. 4 is an exploded perspective view of the vent lumen.

Fig. 5(a) to 5(C) are arrow views in the 5A direction, 5B direction, and 5C direction of fig. 4.

Fig. 6(a) and 6(B) are arrow views in the 6A direction and 6B direction of fig. 4.

FIGS. 7(A) and 7(B) are sectional views taken along line 7A-7A and 7B-7B of FIG. 3.

[ description of symbols ]

12: cylinder block

20: airflow pipe (suction channel)

21: throttle valve

22: cylinder head

22 a: joint surface of ventilation cavity

23: head cover

23 a: joint surface of ventilation cavity

24: movable valve chamber

30: ventilation cavity

33: air intake camshaft (camshaft)

34: exhaust camshaft (camshaft)

36 a: first opening (opening)

36 b: second opening (opening)

41: box

41 c: first oil discharge passage (oil discharge passage)

41 d: second oil discharge passage (oil discharge passage)

41 h-41 k: partition wall

42: cover

42c to 42 e: partition wall

43: partition member

43b, 43c, 43 e: first to third communication holes (communication holes)

44: oil separating member

46 a: orifice

46 b: impact wall

47: filter

A. B, C: first chamber (cavity)

D: second chamber

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to fig. 1 to 7(a) and 7 (B).

As shown in fig. 1 to 3, a pair of front and rear banks (banks) 12 are formed on an upper portion of a cylinder block (cylinder block)11 of a V-type multi-cylinder engine, and a piston 14 slidably fitted in a cylinder 13 disposed in each bank 12 is connected to a crankshaft 16 via a connecting rod 15. An intake manifold 18 communicating with a combustion chamber 17 formed at the upper end of the cylinder 13 is disposed between the two banks 12, and an air cleaner (air) 19 disposed above the intake manifold 18 is connected to a throttle valve 21 via an air flow tube 20 bent in a U shape.

Each of the banks 12 includes a valve chamber 24 defined between the head 22 and the head cover 23, and the valve chamber 24 communicates with the interior of a bottom oil tank 26 provided in the lower portion of the cylinder body 11 via an oil return passage 25 penetrating the interior of the head 22 and the cylinder body 11 of each of the banks 12.

A PCV chamber 28 having a Positive Crankcase Ventilation (PCV) valve 27 is provided on the upper surface of the head cover 23 of the front cylinder block 12, and this PCV chamber 28 is connected to the intake manifold 18 via a PCV pipe 29. Further, a ventilation chamber 30 communicating with the valve operating chamber 24 is provided on the left end surface of the rear bank 12, and this ventilation chamber 30 is connected to the airflow duct 20 upstream of the throttle valve 21 via a ventilation duct 31.

As shown by the solid arrows in fig. 3, a part of the air-fuel mixture supplied to the combustion chamber 17 passes through the gap between the piston 14 and the cylinder 13 as blow-by gas including fuel vapor and mist oil and is accumulated in the crankcase as the engine operates. During operation of the engine, the negative pressure of the intake air of the engine acts on the inside of the intake manifold 18, and therefore the PCV valve 27 including a check valve (check valve) opens, and the blowby gas in the crankcase is returned to the combustion chamber 17 of the front side cylinder block 12 together with the intake air through the oil return passage 25 of the front side cylinder block 12, the PCV valve 27, the PCV chamber 28, the PCV pipe 29, and the intake manifold 18, and is combusted therein, thereby preventing the release of the fuel vapor in the blowby gas to the atmosphere. At this time, oil is separated from the blow-by gas in the PCV chamber 28, and the separated oil is returned from the valve operating chamber 24 of the front side cylinder bank 12 into the bottom tank 26 through the oil return passage 25 of the front side cylinder bank 12.

When the blowby gas in the crankcase is continuously sucked into the intake manifold 18, the suction of the blowby gas is hindered due to a negative pressure in the crankcase, and therefore, it is necessary to suppress the decrease in the internal pressure by replenishing the fresh air in the crankcase. That is, as the internal pressure of the crankcase decreases, the fresh air in the airflow duct 20 upstream of the throttle valve 21 at the atmospheric pressure is supplied into the crankcase through the ventilation duct 31, the ventilation chamber 30, the valve operating chamber 24 of the rear bank 12, and the oil return passage 25 of the rear bank 12.

Further, if only the fresh air in the airflow duct 20 is supplied into the crankcase, it is not necessary to provide the ventilation chamber 30 having the oil separating function in the path thereof. The reason for the need to vent the chamber 30 is as follows.

Except for the case where the opening degree of the throttle valve 21 is a high opening degree equal to or greater than a predetermined value, the blow-by gas in the crankcase may flow backward toward the blow-by gas pipe 20 as shown by the broken line arrow in fig. 3 because the blow-by gas in the crankcase is caused to flow backward toward the blow-by gas pipe 20 because the blow-by gas in the blow-by gas pipe 20 flows toward the crankcase because the fresh air in the blow-by gas pipe 20 is maintained at substantially atmospheric pressure upstream of the throttle valve 21, but when the opening degree of the throttle valve 21 is a high opening degree equal to or greater than the predetermined value. When the blow-by gas containing the mist oil flows backward toward the gas flow pipe 20, the oil may adhere to the throttle valve 21 located downstream of the gas flow pipe 20, causing contamination or malfunction. In order to prevent this, a ventilation chamber 30 having an oil separation function is provided in the reverse flow path of the blow-by gas, and the oil contained in the blow-by gas is separated and returned to the sump 26.

Next, the ventilation chamber 30 and its peripheral structure will be explained.

As shown in fig. 2, 7(a) and 7(B), the vent chamber 30 is fixed to flat vent chamber coupling surfaces 22a and 23a by four screws 32, and the vent chamber coupling surfaces 22a and 23a are formed on left end surfaces of the head cover 23 and the head 22 that are fastened to overlap with the upper end of the cylinder block 12 on the rear side of the cylinder body 11.

An intake camshaft 33 and an exhaust camshaft 34 are rotatably supported between a plurality of journal supporting portions 22b provided on the cylinder head 22 and a plurality of journal supporting portions 23c formed on a cam holder 23b provided on the head cover 23 side, and these intake camshaft 33 and exhaust camshaft 34 are connected to and driven by the crankshaft 16 via a timing belt 35 (see fig. 1) disposed on the right side surface of the engine.

In addition, in a general V-type multi-cylinder engine, since a pair of cylinder heads provided in front and rear cylinder banks are configured by different members having mirror-like object shapes, a chain (sprocket) is provided at an axial end of a camshaft protruding from an opening portion formed at one end side (timing belt side) of the cylinder head, and the other end side (opposite side to the timing belt) of the cylinder head, from which the axial end of the camshaft does not protrude, is not provided with the opening portion and is closed in advance.

However, in order to reduce the equipment cost of the mold for casting the cylinder head, the cylinder head 22 of the present embodiment shares the same shape for the front and rear banks 12. In this way, the cylinder head 22 of the present embodiment, which is common to the left and right banks 12, has opening portions for protruding the intake camshaft 33 and the exhaust camshaft 34 formed on both end sides thereof.

Focusing on the rear bank 12 to which the ventilation chambers 30 are attached, as shown in fig. 7(a) and 7(B), first and second openings 36a and 36B through which the intake camshaft 33 and the exhaust camshaft 34 can be inserted are formed in ventilation chamber connection surfaces 22a and 23a formed at the left ends of the cylinder head 22 and the head cover 23, respectively, and journal support portions 22B and 23c that can support the journals of the intake camshaft 33 and the exhaust camshaft 34 are formed so as to be adjacent to the first and second openings 36a and 36B.

However, since the intake camshaft 33 and the exhaust camshaft 34 do not protrude to the outside at the left end portion of the cylinder head 22 of the rear bank 12 to which the ventilation chamber 30 is attached, the first opening portion 36a, the second opening portion 36b, and the journal support portions 22b, 23c are not used to support the intake camshaft 33 and the exhaust camshaft 34, and the first opening portion 36a and the second opening portion 36b are closed by the ventilation chamber 30.

The first opening 36a and the second opening 36b and the journal supporting portions 22b and 23c at the left ends of the head 22 and the head cover 23 of the front bank 12 are also not used for supporting the intake camshaft 33 and the exhaust camshaft 34, and therefore the first opening 36a and the second opening 36b are closed by a member such as a cap (cap).

As shown in fig. 4 to 7(B), the ventilation chamber 30 includes: a synthetic resin case 41 fastened to the ventilation cavity coupling surfaces 22a, 23a of the head cover 23 and the cylinder head 22 by four screws 32; a synthetic resin cover 42 vibration-welded to the left end of the case 41; a synthetic resin partition member 43 sandwiched between the case 41 and the cover 42; and an oil separating member 44 for separating oil from the blow-by gas flowing in the ventilation chamber 30. The split surfaces of the case 41 and the lid 42 by vibration welding are shown in fig. 5(a) to 5(C) and fig. 6(a) and 6(B) by hatching.

The right side surface (see fig. 5 a) of the case 41 coupled to the ventilation chamber coupling surfaces 22a and 23a of the head cover 23 and the cylinder head 22 is substantially flat, and is formed with: a seal groove 41a into which a seal member 45 for sealing between the vent chamber coupling surfaces 22a and 23a is fitted; an opening 41b communicating with the interior of the valve chamber 24; two cylindrical first and second oil discharge passages 41c and 41d projecting toward the cylinder head 22 and the head cover 23; and four base portions 41e through which the four screws 32 screwed to the ventilation chamber coupling surfaces 22a, 23a are inserted.

A concave space whose outer periphery is substantially surrounded by the peripheral wall 41f is formed in the left side surface of the tank 41 coupled to the cover 42 (see fig. 4 and 5B), a shallow step portion 41g into which the partition member 43 is fitted and a plurality of partition walls 41h to 41k constituting a labyrinth are provided inside the peripheral wall 41f, an oil hole 41m including a notch is formed in the partition wall 41h, two oil holes 41n and 41o including notches are formed in the partition wall 41j, and an oil separating member support groove 41p into which the oil separating member 44 is fitted is formed between the peripheral wall 41f and the partition wall 41 i.

The partition member 43 (see fig. 4, 5C, and 6a) fitted to the step portion 41g of the case 41 and held by the cover 42 includes a flat partition wall 43a, a first communication hole 43b and a second communication hole 43C penetrating the partition wall 43a, a protrusion 43d protruding in a bag shape from the lower half of the partition wall 43a toward the case 41 side, and a third communication hole 43e opening at the bottom of the protrusion 43 d.

A concave space whose outer periphery is substantially surrounded by the peripheral wall 42a is formed on the right side surface (see fig. 6B) of the cover 42 coupled to the tank 41, a joint portion 42B for connecting the ventilation duct 31 is provided in the peripheral wall 42a so as to protrude upward, and a plurality of partition walls 42c to 42e forming a labyrinth are formed inside the peripheral wall 42 a.

The oil separating member 44 fitted in the oil separating member support groove 41p of the tank 41 and held by the cover 42 includes a frame 46 bent in a U shape, and a plurality of orifices 46a are formed in one leg of the frame 46, and the other leg constitutes a collision wall 46b facing the orifices 46 a. Further, a filter 47 made of soft fluffed fiber material made of polyethylene terephthalate (flece) is fixed to the collision wall 46b so as to face the orifice 46 a.

In the ventilation chamber 30 in which the tank 41, the lid 42, the partition member 43, and the oil separating member 44 configured as described above are assembled, when the blowby gas flows backward, that is, when the blowby gas in the valve chamber 24 flows in from the opening 41b of the tank 41 and flows out from the joint portion 42b of the lid 42 to the gas flow pipe 20, the first chamber A, B, C is defined in the range from the opening 41b to the oil separating member 44, which is the upstream side thereof, and the second chamber D is defined in the range from the oil separating member 44 to the joint portion 42b, which is the downstream side thereof.

As shown in fig. 5(B), 6(B), 7(a) and 7(B), since the chambers a and C are partitioned between the case 41 and the partition member 43, the upper chamber a communicates with the movable valve chamber 24 through the opening 41B of the case 41, and communicates with the lower chamber C through the communication hole 41m of the partition wall 41 h. The chamber C communicates with the valve chamber 24 via the first oil discharge passage 41C of the tank 41.

The chamber B is divided between the partition member 43 and the cover 42, and thus communicates with the chamber a via the first communication hole 43B of the partition member 43, and communicates with the chamber C via the third communication hole 43e of the projection 43d of the partition member 43. Further, the chamber B communicates with the oil separating member 44 via the second communication hole 43c of the partition member 43.

The second chamber D, which is partitioned between the tank 41 and the cover 42 and communicates with the chamber B via the oil separating member 44, is formed in a labyrinth shape by the partition walls 41j, 41k of the tank 41 and the partition walls 42D, 42e of the cover 42 abutting against each other, and two oil holes 41n, 41o are formed in the partition wall 41j of the tank 41. The second chamber D communicates with the valve chamber 24 via a second drain passage 41D provided in a lower portion of the tank 41.

When the blowby gas flows backward, the volume of the second chamber D located on the downstream side is set larger than the volume of the first chamber A, B, C located on the upstream side of the oil separation member 44.

As is clear from fig. 7(a) and 7(B), the tip end of the first oil discharge passage 41C extending from the cavity C of the vent cavity 30 extends from the first opening 36a to the valve chamber 24 side beyond the vent cavity coupling surfaces 22a, 23a of the head cover 23 and the cylinder head 22. The first oil discharge passage 41c is relatively short, and therefore its tip is positioned closer to the first opening 36a than the unused journal supporting portions 22b, 23 c.

The tip end of the second drain passage 41D extending from the second chamber D of the ventilation chamber 30 extends beyond the ventilation chamber coupling surfaces 22a, 23a of the cylinder head 22 and the head cover 23, penetrates the second opening 36b, and extends into the valve chamber 24. The second drain passage 41d is relatively long, and therefore its tip end extends beyond the unused journal support portions 22b and 23c to reach the interior of the valve chamber 24. A check valve (not shown) that allows oil to pass from the vent chamber 30 side to the valve chamber 24 side is provided at the tip end of the second drain passage 41 d.

A recess 22c in which oil can be retained is formed between the first and second opening portions 36a, 36b and the journal support portions 22b, 23c of the intake camshaft 33 and the exhaust camshaft 34, and the recess 22c communicates with the interior of the valve chamber 24 through an oil discharge hole 22d that penetrates below the journal support portions 22b, 23 c.

Next, the operation of the ventilation chamber 30 having the above-described structure will be described.

When the throttle valve 21 is opened to a high degree and the blowby gas in the crankcase flows backward toward the airflow pipe 20, the blowby gas in the valve chamber 24 flows into the chamber a from the opening 41B of the case 41 of the ventilation chamber 30, collides with the partition wall portion 43a of the partition member 43, changes its direction at a right angle, and flows into the chamber B from the first communication hole 43B of the partition member 43. At this time, the oil separated from the blow-by gas in the chamber a passes through the oil hole 41m of the partition wall 41h constituting the bottom wall of the chamber a, and is discharged from the chamber C therebelow to the valve operating chamber 24 via the first oil discharge passage 41C of the tank 41.

The oil separated from the blow-by gas in the chamber B flows into the chamber C from the third communication hole 43e provided in the bottom of the projection 43d of the partition member 43, and is discharged from the first oil discharge passage 41C of the tank 41 to the valve chamber 24 together with the oil separated in the chamber a.

The blowby gas of the chamber B is supplied to the oil separating member 44 through the second communication hole 43c of the partition member 43, and the blowby gas whose flow velocity is increased through the orifice 46a of the oil separating member 44 collides with the collision wall 46B, thereby separating the oil. At this time, the blow-by gas passes through the filter 47 disposed between the orifice 46a and the collision wall 46b, whereby the filter 47 traps the oil and promotes separation. The oil separated by the oil separating member 44 is discharged from the bottom of the second chamber D to the valve chamber 24 through the second drain passage 41D provided in the tank 41.

The blow-by gas flowing into the second chamber D from the oil separating member 44 flows through the labyrinth passage before reaching the joint 42b of the cover 42 serving as an outlet thereof, and the oil separated from the blow-by gas during the flow-by gas flows downward through the oil holes 41n and 41o of the partition wall 41j and is discharged to the valve chamber 24 through the second drain passage 41D.

The labyrinth-like flow path formed in the first chamber A, B, C is formed by the chamber a, the chamber B, the chamber C, the first communication hole 43B, the second communication hole 42C, and the third communication hole 43e, and the amount of change in the flow path cross-sectional area is large, so that the flow velocity of the blow-by gas can be increased or decreased to achieve efficient separation of oil by the inertial force. On the other hand, since the change amount of the flow path cross-sectional area of the labyrinth-shaped flow path formed in the second chamber D is small, the change in the flow velocity of the blow-by gas in the second chamber D can be suppressed, and the oil is dropped by gravity to promote separation, thereby preventing the oil from being blown off together with the blow-by gas and permeating into the gas flow pipe 20 side.

Also, the volume of the second chamber D is set larger relative to the volume of the first chamber A, B, C, so the flow rate of the blowby gas flowing into the second chamber D through the oil separating member 44 is drastically reduced, thereby facilitating oil separation by gravity in the second chamber D, and the oil is made more difficult to permeate into the gas flow pipe 20 side by the reduction in the flow rate of the blowby gas in the second chamber D.

In the case of separating oil from blow-by gas by the ventilation chamber, it is not sufficient to separate oil only by collision of blow-by gas against the collision wall or by circling of blow-by gas, and it is necessary to combine oil separating members in multiple stages to achieve reliable oil separation, but in the present embodiment, oil is separated in three stages by the first chamber A, B, C, the oil separating member 44, and the second chamber D of the ventilation chamber 30, and therefore oil separation can be performed reliably. This prevents the blow-by gas containing oil from being supplied to the gas flow pipe 20, and prevents the oil from adhering to the throttle valve 21 located on the downstream side of the gas flow pipe 20, which may cause contamination or malfunction.

Further, since the ventilation chamber 30 is configured by coupling the case 41 having the partition walls 41h to 41k, the cover 42 having the partition walls 42c to 42e, and the partition member 43 having the first communication hole 43b, the second communication hole 43c, and the third communication hole 43e, the ventilation chamber 30 having a plurality of chambers with different volumes can be formed easily and compactly.

If the case 41 of the vent chamber 30 does not include the first and second tubular drain passages 41c and 41d and drain holes are opened only in the first and second openings 36a and 36b of the vent chamber coupling surfaces 22a and 23a of the cylinder head 22 and the head cover 23, there is a possibility that oil flowing out of the drain holes leaks to the outside from the coupling surfaces of the vent chamber coupling surfaces 22a and 23a of the cylinder head 22 and the head cover 23 and the case 41 of the vent chamber 30.

However, according to the present embodiment, the tips of the first and second drain passages 41c, 41d of the case 41 provided in the vent chamber 30 project beyond the vent chamber coupling surfaces 22a, 23a of the cylinder head 22 and the head cover 23 toward the valve chamber 24, so that the oil separated from the blow-by gas in the vent chamber 30 can be reliably discharged to the valve chamber 24, and leakage from the vent chamber coupling surfaces 22a, 23a to the outside can be prevented.

The oil flowing out from the distal ends of the first and second oil discharge passages 41c, 41d, particularly the oil flowing out from the relatively short first oil discharge passage 41c, is likely to accumulate in the recess 22c on the near side of the journal support portion 22B and flow into the vent chamber coupling surfaces 22a, 23a, but the oil accumulated in this recess 22c is discharged into the valve chamber 24 through the oil discharge hole 22d (see fig. 7a and 7B) penetrating below the journal support portions 22B, 23c, and thus the oil can be more reliably prevented from leaking out from the vent chamber coupling surfaces 22a, 23 a.

While the embodiments of the present invention have been described above, the present invention may be variously modified in design without departing from the scope of the present invention.

For example, in the embodiment, the vent chamber 30 includes the first drain passage 41c and the second drain passage 41d, but the number of the drain passages is arbitrary.

In the embodiment, both the case 41 and the cover 42 of the ventilation chamber 30 include the partition walls 41h to 41k and 42c to 42e, but at least one of the case 41 and the cover 42 may include the partition wall.