JP2022153886A - engine - Google Patents

Abstract

To prevent vibration, noise and deterioration of sealability, and simply form a PCV separator passage, in constructing a bearing part of a camshaft separately from a cylinder head.SOLUTION: A cam housing 17 is arranged inside a head cover 4, and cam shafts 15, 16 are rotatably held by an upper bearing part 20 formed in the cam housing 17 and a cam chamber part cam cap 19 overlapping the upper bearing part from below. The cam housing 17 and the cam chamber part cam cap 19 are fastened together to a cylinder head 2 with a plurality of bolts 23, for example, between the cam shafts 15, 16. A PCV separator passage 42 and a fresh air passage 43 are formed between the head cover 4 and the cam housing 17.SELECTED DRAWING: Figure 4

Description

The present invention relates to an engine having a camshaft.

In a gasoline engine or a diesel engine, intake valves and exhaust valves are driven to open and close by a camshaft, and both sides of the camshaft are rotatable on the cylinder head by a lower bearing and an upper bearing. held.

In many cases, the camshaft is supported by forming the lower bearing part integrally with the cylinder head, forming the upper bearing part as a cam cap, and fixing the upper bearing part to the lower bearing part with bolts. It has also been proposed to configure the bearing portion with a member separate from the cylinder head.

As an example, in Patent Document 1, each lower bearing portion is integrally formed with a bearing cage arranged in a cam chamber of a cylinder head, while each upper bearing portion is integrally formed with a head cover. The part between the exhaust camshaft and the exhaust camshaft is bolted together to the cylinder head, and the outer part sandwiching both camshafts is the upper bearing part (head cover) and the lower bearing part (bearing casing). A bolted fastening is disclosed.

Patent Document 2 also discloses that a lower cam carrier formed separately from a cylinder head is integrally formed with a lower bearing portion, while each upper bearing portion is integrally formed with a head cover. In Patent Document 2, the lower cam carrier is superimposed on the upper surface of the cylinder head, and the left and right side portions of the head cover and the left and right side portions of the lower cam carrier are bolted together to the cylinder head.

On the other hand, in Patent Document 3, a cam shaft is rotatably held by a lower cam carrier integrally formed with lower bearing portions and a plurality of upper cam carriers forming an upper cam carrier. is covered with a head cover, and the head cover and the lower cam carrier are bolted together to the upper surface of the cylinder head.

When the lower bearing portion is configured separately from the cylinder head as in each of the patent documents, there is an advantage that the structure of the cylinder head can be simplified and the accuracy and yield of casting can be improved. In any of the patent documents, the bearing casing or lower cam carrier in which each lower bearing portion is formed has a ladder frame structure, so that it has high rigidity and excellent assembly accuracy.

JP-A-07-166956 JP 2007-192104 A JP 2007-192105 A

Each patent document has the above advantages, but if the upper bearing portion is formed integrally with the head cover as in Patent Documents 1 and 2, there is concern that membrane vibration will be induced and noise and vibration will increase. More specifically, since the intake valves and exhaust valves are urged upward by springs, an upward force acts on the upper bearing portion in small increments as the engine runs, but the upper bearing portion is formed on the top plate of the head cover. Therefore, there is concern that the top plate of the head cover will be pushed up by the impact caused by the rise of the valve, and membrane vibration will easily occur.

Another problem is that the urging force of the valve acts to reduce the sealing performance of the head cover, which is fixed to the cylinder head via a sealing material. To elaborate on this point, since the head cover is fixed with bolts by compressing the sealing material, the elastic restoring force of the sealing material acts to move the head cover away from the cylinder head. Since the urging force of the valve acts to reduce the elastic restoring force of the sealing material, there is concern about deterioration in sealing performance.

In addition, in Patent Documents 1 and 2, the camshaft tends to move up and down due to elastic deformation of the top plate of the head cover, etc. Therefore, the smooth rotation of the camshaft is hindered, which increases the mechanical loss and increases the VVT device (variable There is also concern about increased mechanical loss due to misalignment with the valve timing device.

Furthermore, as in Patent Documents 2 and 3, when the head cover and the lower cam carrier are bolted together to the cylinder head, the overlapping surface of the cylinder head and the lower cam carrier and the overlapping surface of the head cover with the lower cam carrier Since sealing materials must be arranged for each of them, there is a particular concern about deterioration in sealing performance. In addition, since the lower cam carrier has the same width as the cylinder head, there is a concern that fuel consumption may deteriorate due to the increased weight.

Now, in a reciprocating engine, there is a phenomenon in which blow-by gas (PCV gas) blows into the crankcase. Therefore, the blow-by gas is recirculated to the intake system, but since the blow-by gas contains oil, an oil separator chamber is required to remove (collect) the oil. By attaching the baffle plate, the space formed between the top plate of the head cover and the baffle plate is often used as a PCV separator passage (oil separator chamber). In many cases, a fresh air introduction passage for taking in fresh air for preventing deterioration of the oil is provided side by side.

However, when the baffle plate is attached to the head cover, there is a problem that the number of parts increases and the structure becomes complicated.

The present invention is intended to improve such a situation.

The present application includes two inventions specified in claims 1 and 2, and both inventions are
"Intake camshafts and exhaust camshafts arranged in parallel are rotatably held by the cylinder head via upper bearing portions and lower bearing portions at a plurality of axially separated locations.
The cylinder head is surrounded by a peripheral wall and has a bottom surface of a cam chamber that opens upward, and a head cover that surrounds the cam shaft to form a valve operating chamber is fixed to the upper surface of the peripheral wall of the cylinder head.
It has a basic configuration.

And in the invention of claim 1, in the above basic configuration,
"Each of the upper bearing portions is integrally formed with one cam housing accommodated inside the head cover, and a cam cap that constitutes the lower bearing portion overlaps with each upper bearing portion from below,
The cam housing and the cam caps are fastened together to the cylinder head with bolts passing through the cam housing and the cam caps in at least a plurality of locations.
It is configured.

On the other hand, the invention of claim 2, in the above basic configuration,
Each of the upper bearing portions is integrally formed with one cam housing that is accommodated inside the head cover. and each cam cap are fastened together to the cylinder head with bolts at least at a portion between the exhaust camshaft and the intake camshaft,
At least one of a PCV separator passage for collecting oil from blow-by gas and a fresh air passage for introducing fresh air into the engine is formed between the top plate of the head cover and the top plate of the cam housing.
It is configured.

In the invention of claim 2, the portion of the cam cap (lower bearing portion) located outside of the camshaft may be fastened together with the cam housing to the cylinder head, or may be not fastened together. It may be fixed to the cam housing by bolts inserted from below.

The lower end of the cam cap can be brought into contact with the bottom surface of the cam chamber of the cylinder head. When the bottom surface of the camshaft is overlapped, the boss and the peripheral wall can be accurately machined to the same height by milling after casting, so that the camshaft can be mounted with high accuracy.

In the two inventions of the present application, since the cam housing is separate from the head cover, the shock associated with the reciprocating motion of the valve does not act on the head cover. Therefore, it is possible to prevent membrane vibration and the resulting noise. That is, it is excellent in quietness.

Further, since the cam housing and the cam cap are fixed to the cylinder head, the reciprocating motion of the valve does not tend to move the cam shaft up and down. Therefore, smooth rotation of the camshaft can be maintained, and misalignment with the VVT device does not occur, and mechanical loss does not increase.

In both inventions of the present application, the cam housing is arranged inside the head cover and bolted together with the cam cap to the cam chamber of the cylinder head. It is smaller than the lower cam carrier. Therefore, the weight of the cam housing can be reduced to contribute to the improvement of fuel efficiency. Moreover, since a seal between the cam housing and the cylinder head is not required, the problem of deterioration of sealing does not occur in the first place, and high sealing performance can be ensured.

In the second aspect, the cam housing as a bearing member can be used to form the PCV separator passage or the fresh air introduction passage, so the conventional baffle plate can be eliminated. Therefore, in addition to the above effect, there is an effect that the PCV separator passage or the fresh air introduction passage can be formed while reducing the number of members and simplifying the structure.

1 is a schematic exploded perspective view of an embodiment; FIG. 1 is a plan view of an embodiment; FIG. FIG. 3 is a front view taken along line III-III in FIG. 2; FIG. 3 is a sectional view taken along line IV-IV of FIG. 2;

Next, embodiments of the present invention will be described based on the drawings. This embodiment is applied to an automotive gasoline engine. In the present application, terms such as front-rear and left-right are used to specify directions, and the front-rear direction is the direction of the crank axis, and the left-right direction is the direction perpendicular to the crank axis and the cylinder bore axis.

Regarding the distinction between front and rear, the side where the timing chain is arranged is the front, and the side where the transmission case is arranged is the rear. A plan view is a diagram viewed from the axial direction of the cylinder bore, and in a slant type engine, it may not coincide with the vertical direction. 1 and 2 clearly show the directions of front and rear, left and right.

(1).Basic structure The engine consists of a cylinder block 1 shown in Fig. 3, a cylinder head 2 fixed to the upper surface of the cylinder block 1, and a chain cover (front cover ) 3. A head cover 4 is overlapped and fixed on the upper surface of the cylinder head 2 . The cylinder head 2 and head cover 4 are clearly shown in FIGS.

As clearly shown in FIG. 1, the cylinder head 2 has left and right side walls 5, a front wall 6 continuous to the front ends of the side walls 5, and a rear wall 7 continuous to the rear ends of the side walls 5. The inside surrounded by the walls 5 to 7 of is a cam chamber (recess) 8 having a bottom surface. As shown in FIGS. 1 and 2, four pairs of intake ports 9 are opened on the intake side surface 2a of the cylinder head 2. As shown in FIGS. Therefore, the engine of this embodiment has four cylinders.

As shown in FIGS. 1 and 2, an injector insertion hole 10 for mounting a fuel injector (not shown) is formed on the intake side surface 2a of the cylinder head 2 above each intake port 9. . In the drawing, the injector insertion hole 10 is drawn in a tubular shape for easy viewing, but it may not be formed in a tubular shape. Also, the injector insertion hole 10 is drawn smaller than it actually is.

There is also a system in which an injector is attached to an intake manifold (not shown) to inject atomized fuel into the intake manifold. In any case, in this embodiment, a pair of front and rear intake ports 9 are formed for one cylinder, and an injector is arranged corresponding to each intake port 9 . That is, it is a 2-port, 2-injector system.

Exhaust gas is discharged from the exhaust side, but the exhaust ports of the cylinders are gathered into one and discharged from one exhaust outlet. Reference numeral 12 shown in FIG. 4 is a cooling water jacket, and reference numeral 13 is a head bolt insertion hole.

As shown in FIG. 3, a chain cover 3 is fixed to the front surfaces of the cylinder head 2 and the cylinder block 1 with a large number of bolts. is formed, and a driving portion 14 of an electric intake valve VVT device (variable valve timing device) is fixed to the upper support portion 3a with bolts. Since the front end portion 4a of the head cover 4 overlaps the upper support portion 3a of the chain cover 3, the head cover 4 opens forward as shown in FIG.

(2) Camshaft Support Structure As shown in FIGS. The cam shafts 15 and 16 are rotatably held by one cam housing 17 and a plurality of cam caps (lower bearing portions) 18 and 19 arranged side by side. Accordingly, the cam housing 17 is integrally formed with an upper bearing portion 20 having a downwardly opening semicircular hole so as to overlap the upper halves of the camshafts 15 and 16 . The cam caps 18 and 19 are formed with semicircular holes that open upward.

Since this embodiment has four cylinders, the cam shafts 15 and 16 have four cam portions, and the front and rear portions sandwiching each cam portion are rotated by the upper bearing portion 20 and the cam caps 18 and 19. freely held. The upper bearing portion 20 and the cam caps 18 and 19 are plate-shaped, and the cam housing 17 has a ladder frame structure in which each upper bearing portion 20 protrudes downward from a top plate 21 . The cam housing 17 is entirely housed inside the head cover 4 .

As can be seen from FIG. 1, the front cam cap 18 located at the front end of the cam caps 18 and 19 overlaps the front wall 6 of the cylinder head 2 from above, while the cam chamber excluding the front cam cap 18 The cam cap 19 overlaps bosses 22 erected on the bottom surface of the cam chamber 8 of the cylinder head 2 at two locations between the cam shafts 15 and 16 .

As shown in FIG. 4, each boss portion 22 of the cylinder head 2 has the same height as the upper surface of each wall 5 to 7 in the cylinder head 2, and the cam housing 17 and each cam chamber portion cam cap 19 are At a position between the two cam shafts 15 and 16, two left and right intermediate portions 23 are fastened together to the boss portion 21 of the cylinder head 2. As shown in FIG. A top plate 21 of the cam housing 17 is formed with a cylindrical reinforcing rib 24 through which an intermediate bolt 23 passes.

The cam chamber portion cam cap 19 and the upper bearing portion 20 on which it overlaps have overhang portions 26 and 27 that are not fixed to the cylinder head 2 and protrude to the left and right outside of the boss portion 22 . , 27 sandwich the camshafts 15 and 16 . Basically, the left and right ends of the overhangs 26 and 27 are integrally fastened (fixed) by end bolts 25 inserted through the cam chamber cam cap 19 from below.

In addition, the lower surface of the overhang portion 27 of the cam chamber cam cap 19 is thinned and thinned, and the portions of the cam chamber cam cap 19 between the left and right intermediate bolts 23 are also thinned. there is Therefore, the cam chamber portion cam cap 19 has two left and right leg portions 19 a fixed to the boss portion 22 of the cylinder head 2 .

Overhang portions 26 and 27 between the upper bearing portion 20 and the cam chamber portion cam cap 19 are basically fastened together by end bolts 25 inserted from below. As for the upper cam cap 19, the end of the overhang 27 on the intake side overlaps the upper surface of the cylinder head 2, and the outer ends of the overhangs 26, 27 are provided with an upper PCV introduction passage 28 that is open vertically. vacant. In order to match this, a lower PCV introduction passage 29 communicating with the upper PCV introduction passage 27 is formed in a portion of the cylinder head 2 where the cam chamber portion cam cap 19 located at the forefront overlaps.

The lower PCV introduction passage 29 opens into the crank chamber via a passage (not shown) formed in the cylinder block 1, and the blow-by gas blown into the crank chamber passes through the PCV introduction passages 28, 29 to the cam. It jets out above the housing 17 . As shown in FIG. 2, the upper PCV introduction passage 27 (and the lower PCV introduction passage 29) are located outside the inter-bore portion (the portion between adjacent cylinders).

The front cam cap 18 is fixed to the front wall 6 of the cylinder head 2 with bolts (not shown) together with an upper bearing portion 20 at the front end of the cam housing 17 . Accordingly, four bolt insertion holes 29 are formed in the front end portion of the cam housing 17 and the front cam cap 18, and four female screw holes 30 are formed in the front wall 6 of the cylinder head 2. As shown in FIG.

Since the intake side end of the cam cap 19 of the frontmost cam chamber overlaps the side wall 5 of the cylinder head 2, as shown in FIG. there is

(3) Head Cover and Related Structure The head cover 4 includes left and right side walls 31, left and right top plates 32 connected to the left and right side walls, and a rear wall (not shown) connected to the rear ends of the left and right side walls 31. The side walls 31 and the rear wall overlap the upper surface of the cylinder head 2 . An outward flange 33 is projected from the lower end of the side wall 31 , and the flange 33 is fixed to the upper surface of the cylinder head 2 with bolts 34 .

As shown in FIG. 4, a long groove 35 extending over the entire length is formed in the lower end surface of the peripheral wall of the head cover 4, and a sealing member 36 is arranged in the long groove 35. As shown in FIG. The sealing material 36 may be a fitting type such as an O-ring, or may be a liquid type that is applied using a dispenser. The long groove 35 and the sealing material 36 are also provided on the inner surface of the front end portion 4 of the head cover 4 . Therefore, it is provided on the entire circumference of the head cover 4 .

As clearly shown in FIG. 1, the top plate 32 of the head cover 4, except for the front end portion 4a, is formed with a long groove 37 opening upward. An ignition hole cylindrical portion 38 for fitting is formed. An ignition hole 39 is also formed in the cam housing 17 and the cylinder head 2 .

As clearly shown in FIG. 4, the top plate 32 of the head cover 4 has downward gutter-like portions 40 and 41 that are elongated in the front-rear direction on both the left and right sides of the long groove 37, and the downward gutter-like portion 41 on the intake side. A PCV separator passage (oil separator passage) 42 is formed between and the cam housing 17 , and a fresh air passage 43 is formed between the downward gutter-shaped portion 41 on the exhaust side and the cam housing 17 .

As shown in FIG. 4, the downward gutter-shaped portions 40 and 41 of the head cover 4 are formed with partition ribs 44 that abut on the top surface of the top plate 21 of the cam housing 17. is filled with a sealing material 45 . The sealing material 45 may also be a fitting type such as an O-ring or a liquid coating type. Although the cam housing 17 and the cam chamber cam cap 19 overlap the side wall 31 of the head cover 4 in FIG. 4, there is actually a slight gap between them.

As shown in FIG. 2, partition ribs 44 are also formed at the front and rear ends of the downward gutter-like portions 40 and 41 . Therefore, the partition rib 44 has a loop shape and overlaps the cam housing 17 with the sealing material 45 interposed therebetween. Therefore, blow-by gas and fresh air do not leak from the boundary between the head cover 4 and the cam housing 17. FIG. Although not shown, an oil drop hole is formed in the top plate 21 of the cam housing 17 at a portion corresponding to the PCV separator passage 42 to allow collected oil to flow down to the valve gear chamber.

The front end of the PCV separator passage 42 communicates with the upper PCV introduction passage 28, and the blow-by gas flows from the upper PCV introduction passage 28 into the PCV separator passage 42 and flows rearward. A discharge port 46 that opens upward is formed at the rear end of the PCV separator passage 42 , and a PCV valve (not shown) is attached to the discharge port 46 . When the intake system of the engine becomes negative pressure, the PCV valve opens and blow-by gas is recirculated to the intake system (for example, the intake manifold).

As shown in FIGS. 2 and 4, in the PCV separator passage 42, baffle plates 47 for collecting oil mist are arranged side by side in the front-rear direction. The baffle plate 47 shown in FIG. 4 protrudes downward from the head cover 4, and the downward protruding portion on the head cover 4 and the upward protruding portion on the top plate 21 of the cam housing 17 are alternately arranged. Placement is preferred. In this case, the blow-by gas meanders vertically, but it is also possible to cause the blow-by gas to meander left and right by alternately shifting the baffle plate 47 in the left-right direction. Alternatively, it is possible to combine meandering in the vertical direction and meandering in the horizontal direction.

As shown in FIG. 2, a fresh air introduction port 48 is provided at the rear end of the fresh air passage 43, and a fresh air discharge port 49 is opened downward at the front end of the fresh air passage 43. . Accordingly, the fresh air inlet 48 is provided in the top plate 32 of the head cover 4 and the fresh air outlet 48 is provided in the top plate 21 of the cam housing 17 .

(4) Summary In the above configuration, the cam housing 17 is separate from the head cover 4, so the impact force of the valve does not act on the head cover 4 while the engine is running. Therefore, the head cover 4 does not vibrate or generate noise due to movement of the valve, and is excellent in quietness. In the present embodiment, the cam housing 17 is pushed downward by the head cover 4 through the sealing material 45, but the upward force acting on the cam housing 17 is absorbed by the sealing material 45, so that the head cover 4 vibrates. never do.

In addition, since the cam housing 17 is entirely hidden inside the head cover 4, it is not necessary to consider the sealing performance when attaching it to the cylinder head 2. Therefore, the provision of the cam housing 17 does not reduce the sealing performance at all. does not occur. Rather, there is an advantage that high sealing performance can be ensured between the head cover 4 and the cylinder head 2 because the head cover 4 does not need to be processed in a complicated manner.

The left and right ends of the cam chamber cam cap 19 can be tightened together with the cylinder head 2. When the left and right ends are fixed to the upper bearing portion 20 of the cam housing 17 with the end bolts 25 from below, the weight of the cam chamber cam cap 19 and the cylinder head 2 can be reduced to contribute to the improvement of fuel efficiency. Since the cap 19, the cam housing 17, and the cam shafts 15 and 16 can be unitized in advance, there is an advantage that the labor for assembly can be reduced.

Furthermore, in this embodiment, each cam chamber portion cam cap 19 is also thinned out between the left and right intermediate portion bolts 23, so that weight reduction can be further promoted. It is also possible to remove the portion of the upper bearing portion 20 of the cam housing 17 between the left and right intermediate bolts 23 .

In addition, since the PCV separator passage 42 is formed in a portion surrounded by the head cover 4 and the cam housing 17, no baffle plate is required, which simplifies the structure and reduces the cost. In addition, since the blow-by gas flows from the upper PCV introduction passage 28 formed in the head cover 4, the oil mist floating in the valve gear chamber is not mixed with the blow-by gas. can promote.

Although the upper PCV introduction passage 28 is also formed in the cylinder head 2, it requires a certain cross-sectional area. In this regard, when only one fuel injection injector is arranged for two intake ports 9, the injector is positioned between the pair of intake ports 9, so the lateral injection force between the bores of the cylinder head 2 is In addition, a female threaded hole into which a bolt for fixing the intake side end of the cam chamber cam cap 19 is screwed, and the upper PCV introduction passage 28 can be formed side by side.

However, if there is a pair of injectors corresponding to a pair of intake ports 9, the injector insertion hole 10 enters between the pair of adjacent intake ports. Therefore, if the intake side end of the cam chamber cam cap 19 is fixed to the cylinder head 2 with a bolt, the upper PCV introduction passage 28 cannot be formed.

On the other hand, in the present embodiment, the intake side end of the cam chamber portion cam cap 19 is not fixed with a bolt, and the upper PCV introduction passage 28 is formed in the portion to be the bolt insertion hole.・Blow-by gas can be taken in through the head cover 4 even in a two-injector engine.

At the location of the upper PCV introduction passage 28, the intake side end of the cam chamber cam cap 19 is sandwiched between the upper bearing portion 20 of the cam housing 17 and the cylinder head 2, but the cam housing 17 has high rigidity. Therefore, the pressing force of the two intermediate bolts 23 positioned between the camshafts 15 and 16 is also applied to the PCV separator passage 42, so that the intake camshaft 15 can be held stably. In addition, since the cam housing 17 is held by the head cover 4 via the seal member 45, the intake camshaft 15 can be stably held.

4, the head cover 4 and the cylinder head 2 are provided with a flange 50 projecting outward from the upper PCV introduction passage 28, so that bolts 34 are also attached to the head cover outside the upper PCV introduction passage 28. 4 can be fixed to the cylinder head 2 . In this case, the cam housing 17 and the cam chamber cam cap 19 are pushed by the cylinder head 2 via the sealing material 45, so that the stability of the intake camshaft 15 is further improved.

Although the embodiments of the present invention have been described above, the present invention can be embodied in various other ways. For example, the top plate forming the upper surface of the cam housing may be provided with relief holes except for the PCV separator passage and fresh air passage 42 . Blow-by gas may be introduced into the PCV separator passage from the valve gear chamber.

In the embodiment, the two intermediate bolts 23 are used as common tightening bolts, but at least two of the four bolts 23 and 25 (three at the location where the PCV passage is provided) are used as common tightening bolts. you should do it.

The present invention can be embodied in an engine with a camshaft. Therefore, it can be used industrially.

2 cylinder head 3 chain cover 4 head cover 5 side wall of cylinder head 6 front wall of cylinder head 8 cam chamber of cylinder head 9 intake port 10 injector insertion hole 15 intake camshaft 16 exhaust camshaft 17 cam housing 18 front cam cap 19 Cam chamber portion cam cap 20 Upper bearing portion 21 Top plate of cam housing 23 Intermediate portion bolt (co-tightening bolt)
25 End bolt 28 Upper PCV introduction passage 31 Side wall of head cover 32 Top plate of head cover 36 Sealing material between head cover and cylinder head 42 PCV separator passage 43 Fresh air passage 45 Sealing material between head cover and cam housing

Claims (2)

The intake and exhaust camshafts arranged in parallel are rotatably held by the cylinder head via the upper bearing portion and the lower bearing portion at a plurality of locations separated in the axial direction,
The cylinder head is surrounded by a peripheral wall and has a bottom surface of a cam chamber that opens upward, and a head cover that surrounds the cam shaft to form a valve operating chamber is fixed to the upper surface of the peripheral wall of the cylinder head. There is
Each of the upper bearing portions is integrally formed with one cam housing accommodated inside the head cover, and a cam cap constituting the lower bearing portion overlaps with each upper bearing portion from below,
The cam housing and the cam caps are fastened together to the cylinder head with bolts passing through the cam housing and the cam caps in at least a plurality of locations.
engine. The intake and exhaust camshafts arranged in parallel are rotatably held by the cylinder head via the upper bearing portion and the lower bearing portion at a plurality of locations separated in the axial direction,
The cylinder head is surrounded by a peripheral wall and has a bottom surface of a cam chamber that opens upward, and a head cover that surrounds the cam shaft to form a valve operating chamber is fixed to the upper surface of the peripheral wall of the cylinder head. There is
Each of the upper bearing portions is integrally formed with one cam housing accommodated inside the head cover, and a cam cap forming the lower bearing portion overlaps with each upper bearing portion from below. Each cam cap is fastened together with the cylinder head with a bolt at least at a portion between the exhaust camshaft and the intake camshaft,
At least one of a PCV separator passage for collecting oil from blow-by gas and a fresh air passage for introducing fresh air into the engine is formed between the top plate of the head cover and the top plate of the cam housing.
engine.

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