Internal combustion engine

Side surfaces of an end cam cap and a pair of side surfaces of a recess for cam cap form two cross-sectional area gradually changing gaps therebetween. A gasket is filled between an inner surface of the recess for cam cap and an outer surface of the end cam cap. The inner surface includes the side surfaces of the recess for cam cap and the outer surface includes the side surfaces of the end cam cap.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Japanese Patent Application No. 2016-116854 filed on Jun. 13, 2016, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an internal combustion engine that has a dual lubricating oil circulation passage.

2. Description of the Related Art

There is known an internal combustion engine having a dual lubricating oil circulation passage.

Such an internal combustion engine includes a cylinder block, a cylinder head, a cylinder head cover, an oil pan and a chain cover.

A cylinder bore is formed inside the cylinder block. A pistons is slidably provided in the cylinder bore.

The oil pan is connected to the bottom portion of the cylinder block. The lower space of the cylinder block and a crank shaft storage space, which is the interior space of the oil pan, are communicated with the cylinder bore. In addition, the crank shaft storage space stores a crank shaft that rotates in conjunction with the operation of the piston.

The cylinder head is connected to the upper portion of the cylinder block. The space defined by a recess formed in the bottom portion of the cylinder head, the cylinder bore, and the upper end surface of the piston constitutes a combustion chamber. An intake valve and an exhaust valve, both of which can move upward and downward, are provided inside the cylinder head. Additionally, an inlet port and an exhaust port, which communicate with the recess (the combustion chamber) and are opened and closed by the intake valve and the exhaust valve respectively, are formed in the cylinder head.

A camshaft storage space is formed inside the cylinder head. The camshaft storage space, whose top surface is opened, is independent from the recess (the combustion chamber), the inlet port and the exhaust port. In other words, the camshaft storage space does not communicate with the recess, the inlet port and the exhaust port.

A camshaft, which extends linearly and is rotatable about its own axis, is disposed in the camshaft storage space. A through-hole is formed through a chain cover adjacent wall that constitutes a part of the outer peripheral wall of the cylinder head. One end of the camshaft passes through this through-hole and protrudes out of the cylinder head. An oil seal is provided between the inner peripheral surface of the through-hole and the outer peripheral surface of the camshaft. This oil seal is in contact with the inner peripheral surface of the through-hole and the outer peripheral surface of the camshaft in an air-tight and water-tight manner.

As is well known, both the intake valve and the exhaust valve are interlocked with the camshaft. Namely, when the camshaft rotates, the intake valve and the exhaust valve operate to open and close the inlet port and the exhaust port, respectively.

The cylinder head cover is fixed to the top surface of the cylinder head. Namely, the top surface of the cylinder head is covered with the cylinder head cover.

The chain cover is fixed to the cylinder block, the cylinder head, and the oil pan.

A chain storage space is formed inside the chain cover. This chain storage space communicates with the crank shaft storage space of the oil pan. On the other hand, the chain storage space does not communicate with the camshaft storage space. Namely, the chain cover adjacent wall of the cylinder head separates the camshaft storage space from the chain storage space in an in-air-tight and water-tight manner.

The one end of the camshaft, which passes through the through-hole of the chain cover adjacent wall, is located in the chain storage space. A timing chain, which is arranged in both the chain storage space and the interior space of the oil pan, is wounded around a sprocket provided at one end of the camshaft and a sprocket provided at one end of the crank shaft. Namely, the crank shaft and the camshaft are interlocked by the timing chain so that the camshaft is rotated by the rotational force of the crank shaft.

The crank shaft storage space of the oil pan is filled with a first lubricating oil.

In addition, the crank shaft storage space is equipped with a first oil pump to circulate the first lubricating oil through the crank shaft storage space, the interior space of the cylinder block, and the chain storage space. Namely, a first lubricating oil circulation passage is formed so as to pass through the crank shaft storage space, the interior space of the cylinder block, and the chain storage space.

On the other hand, a sub oil pan, which communicates with the camshaft storage space, is formed in the cylinder head. The sub oil pan is filled with a second lubricating oil.

In addition, the camshaft storage space is equipped with a second oil pump to circulate the second lubricating oil through the sub oil pan and the camshaft storage space. Namely, a second lubricating oil circulation passage is formed so as pass through the sub oil pan and the camshaft storage space.

Then, when the first oil pump is operated, the first lubricating oil circulates through the first lubricating oil circulation passage, and when the second oil pump is operated, the second lubricating oil circulates through the second lubricating oil circulation passage.

The first lubricating oil circulating through the first lubricating oil circulation passage enables the piston, the crank shaft, and the timing chain to operate smoothly. Furthermore, the second lubricating oil circulating through the second lubricating oil circulation passage enables the camshaft, the intake valve, and the exhaust valve to operate smoothly.

As described above, the camshaft storage space is independent from the recess (the combustion chamber) of the cylinder head, the inlet port, and the exhaust port. Additionally, the chain cover adjacent wall of the cylinder head separates the camshaft storage space from the chain storage space in an air-tight and water-tight manner.

Therefore, the first lubricating oil circulation passage and the second lubricating oil circulation passage are independent from each other. In other words, the first lubricating oil does not flow into the second lubricating oil circulation passage and the second lubricating oil does not flow into the first lubricating oil circulation passage.

By the way, when the internal combustion engine operates, so-called blowby gas is generated in the combustion chamber. This blowby gas flows through the gap between the inner circumferential surface of the cylinder bore and the end gap of the piston ring attached to the piston, and flows into the crank shaft storage space. The blowby gas comes in contact with the first lubricating oil, and then the first lubricating oil deteriorates. Then, the first lubricating oil needs to be replaced with new lubricating oil with a certain frequency.

On the other hand, the recess (the combustion chamber) and the camshaft storage space are independent from each other. Then, the blowby gas does not flow into the camshaft storage space to come into contact with the second lubricating oil.

Additionally, since the chain cover adjacent wall separates the camshaft storage space from the chain storage space in an air-tight and water-tight manner, the blowby gas does not flow into the camshaft storage space from the chain storage space to come into contact with the second lubricating oil.

Therefore, the second lubricating oil is harder to deteriorate than the first lubricating oil. Then, the exchange frequency of the second lubricating oil with new lubricating oil is lower than that of the first lubricating oil.

It should be noted that Japanese Unexamined Patent Application Publication No. H08-246831 and Japanese Unexamined Patent Application Publication No. 2011-190721 disclose a background technology related to the present invention.

SUMMARY OF THE INVENTION

Typically, a plurality of portions of the lower half portion of the camshaft, which are separated from each other in the axial direction of the camshaft, are rotatably supported by a plurality of journal bearings, which are disposed inside the cylinder head along the axial direction thereof, respectively.

Furthermore, a plurality of cam caps, which are disposed in the camshaft storage space, are mounted on a plurality of portions of the upper half portion of the camshaft, which are separated from each other in the axial direction, from above, respectively. Each of the cam caps rotatably supports the upper half portion of the camshaft. In addition, each of the cam caps is fixed to corresponding one of journal bearings.

The cam cap positioned on the most chain cover adjacent wall side is disposed in the camshaft storage space so as to be close to the inner surface (the side surface that defines the camshaft storage space) of the chain cover adjacent wall.

Incidentally, the axial direction dimension of the camshaft storage space (i.e., the cylinder head) is the dimension including the thickness of the chain cover adjacent wall and the thickness of all the cam caps.

Then, the internal combustion engine having the above structure, in which the chain cover adjacent wall and all the cam caps are arranged in the axial direction, has difficulty in reducing both the axial direction dimension of the cylinder head and the axial direction dimension of the entire internal combustion engine.

The present invention has been made to cope with the above problems, and has an object to provide an internal combustion engine that can securely prevent the first lubricating oil circulation passage and the second lubricating oil circulation passage from communicating with each other between the camshaft storage space and the chain storage space, and can reduce the dimension of the entire internal combustion engine in the axial direction of the camshaft.

In order to achieve the object, an internal combustion engine comprises:

a cylinder block (20) including a cylinder bore (21) which supports a piston (23) so as to be slidable;

an oil pan (30) provided therein with a crank shaft storage space (32) for storing a crank shaft (25) rotating in conjunction with an operation of the piston, the oil pan connected to the cylinder block;

a cylinder head (35) provided therein with a port (42,43), which is communicated with the cylinder bore and made to be opened and closed by a valve (44,45) reciprocating in conjunction with the operation of the piston, a sub oil pan (40a), and a camshaft storage space (47a), which has no communication with an interior of the oil pan, the crank shaft storage space, and the cylinder bore;

a camshaft (65,70) disposed in the camshaft storage space, the camshaft including a plurality of supported portions (66,71) whose lower portions are rotatably supported by the cylinder head so that the camshaft rotates about its own axis to reciprocate the valve, the supported portions arranged at an interval in an axial direction of the camshaft;

a plurality of cam caps (75,80), fixed to the cylinder head, for rotatably supporting upper portions of the supported portions of the camshaft;

a cover member (88) connected to the oil pan and the cylinder head so that the cover member is provided therein with an interlocking member storage space (89), the interlocking member storage space storing an annular interlocking member (86) interlocking the crank shaft and the camshaft, the interlocking member storage space having communication with the crank shaft storage space and having no communication with the camshaft storage space;

a first lubricating oil (91) filled in the oil pan so as to circulate through the interior of the oil pan, the crank shaft storage space, the cylinder bore and the interlocking member storage space;

a second lubricating oil (101) filled in the sub oil pan so as to circulate through the an interior of the sub oil pan and the camshaft storage space; and

a cover adjacent wall (48) for forming part of the cylinder head and for separating the interlocking member storage space from the camshaft storage space.

Atmosphere pressure of the interlocking member storage space is kept lower than atmosphere pressure of the camshaft storage space.

A recess for cam cap (51) is formed on an upper end surface of the cover adjacent wall so as to penetrate through the cover adjacent wall in the axial direction of the camshaft.

One of the plurality of the cam caps, which is disposed in the recess for cam cap and is located closest to the cover member among the cam caps, is an end cam cap (80).

The end cam cap is provided with a pair of side surfaces which are spaced from each other in a direction orthogonal to the axial direction.

The side surfaces of the end cam cap and a pair of side surfaces (51b) of the recess for cam cap form two cross-sectional area gradually changing gaps (S) therebetween. Each of the cross-sectional area gradually changing gaps has both open ends which are separated from each other in the axial direction and each of the cross-sectional area gradually changing gaps has a cross-sectional area which gradually decreases as approaching to the interlocking member storage space from an intermediate portion thereof in the axial direction or a portion thereof farther from the interlocking member storage space than the intermediate portion in the axial direction.

A gasket (G) is filled between an inner surface of the recess for cam cap and an outer surface of the end cam cap. The inner surface includes the side surfaces of the recess for cam cap and the outer surface includes the side surfaces of the end cam cap.

In the internal combustion engine of the present invention, the end cam cap is disposed in the recess for cam cap formed on the upper end surface of the cover adjacent wall of the cylinder head. Namely, the cover adjacent wall and the end cam cap are disposed at the same position in the axial direction of the camshaft.

Therefore, compared with a conventional internal combustion engine, the present invention can reduce both the dimension of the cylinder head and the dimension of the entire internal combustion engine in the axial direction of the camshaft.

Furthermore, since an atmosphere pressure of the interlocking member storage space is lower than an atmosphere pressure of the camshaft storage space, the second lubricating oil in the camshaft storage space always attempt to flow into the interlocking member storage space via a gap between the recess for cam cap and the end cam cap.

However, a semi-solidified gasket is filled in the gap between the outer surface of the cam cap and the inner surface of the recess for cam cap.

Therefore, the second lubricating oil does not leak to the interlocking member storage space via the gap between the recess for cam cap and the end cam cap, and thus does not mix with the first lubricating oil.

Therefore, the second lubricating oil does not decrease.

Furthermore, gaps need to be formed between both side surfaces of the end cam cap and both side surfaces of the recess for cam cap in order to dispose the end cam cap in the recess for cam cap. In other words, the dimension between the both side surfaces of the end cam cap needs to be smaller than the dimension between the both side surfaces of the recess for cam cap.

In the present invention, the cross-sectional area gradually changing gaps, each of which has both open ends separated from each other in the axial direction and has a cross-sectional area gradually decreasing as approaching to the interlocking member storage space from the intermediate portion thereof in the axial direction or the portion thereof farther from the interlocking member storage space than the intermediate portion in the axial direction, are formed between both side surfaces of the end cam cap and both side surfaces of the recess for cam cap.

Since the atmosphere pressure of the interlocking member storage space is lower than the atmosphere pressure of the camshaft storage space, a pressure is applied from the camshaft storage space to the gasket that is semi-solidified in this cross-sectional area gradually changing gap.

However, the cross-sectional area of the interlocking member storage space side end of the cross-sectional area gradually changing gap is smaller than the cross-sectional area of the intermediate portion of the cross-sectional area gradually changing gap. Then, the interlocking member storage space side end of the cross-sectional area gradually changing gap generates a large resistance force to prevent the gasket from moving to the interlocking member storage space.

Therefore, the gasket hardly discharged to the interlocking member storage space via the cross-sectional area gradually changing gap.

Therefore, a chance that the second lubricating oil filled in the camshaft storage space of the cylinder head leaks to the interlocking member storage space via the cross-sectional area gradually changing gap is much smaller compared with the case where the side surfaces of the recess for cam cap and the side surfaces of the end cam cap are flat surfaces parallel to each other.

An interlocking member storage space side end of each of the cross-sectional area gradually changing gaps may be located closer to the camshaft storage space than an interlocking member storage space side surface of the cover adjacent wall.

The side surfaces of the end cam cap and the side surfaces of the recess for cam cap may be flat surfaces.

Each of the side surfaces of the end cam cap and each of the side surfaces of the recess for cam cap may face each other so as to form a minute gap therebetween and be parallel to each other at a position between each of the cross-sectional area gradually changing gaps and the interlocking member storage space.

This “parallel” includes not only “complete parallel” but also “substantially parallel”.

Between the interlocking member storage space side end of the cross-sectional area gradually changing gap and the interlocking member storage space side surface of the cover adjacent wall, the side flat surfaces of the end cam cap and the side flat surfaces of the recess for cam cap surface face with each other so as to form the minute gaps therebetween and be parallel to each other.

Therefore, a chance that the gasket is discharged to the interlocking member storage space via the cross-sectional area gradually changing gap become much smaller compared with the case where the interlocking member storage space side end of the cross-sectional area gradually changing gap is positioned at the same position as the interlocking member storage space side surface of the cover adjacent wall. Namely, the chance that the second lubricating oil leaks to the interlocking member storage space via the cross-sectional area gradually changing gap becomes much smaller.

A bottom surface (51a) of the recess for cam cap and a bottom surface of the end cam cap may be horizontal flat surfaces.

If the cross-sectional area gradually changing gap is formed between the bottom surface of the end cam cap and the bottom surface of the recess for cam cap and the gasket is filled in this cross-sectional area gradually changing gap, the bottom surface of the recess for cam cap supports the end cam cap unstably.

However, when the present invention is configured in this way, the supporting state of the end cam cap by the bottom surface of the recess for cam cap can become stable.

A cutout may be formed on each of the side surfaces of the end cam cap.

Each of the cutouts and each of the side surfaces of the recess for cam cap may form the cross-sectional area gradually changing gap therebetween when the end cam cap is disposed in the recess for cam cap.

The cutout for forming the cross-sectional area gradually changing gap between the side surfaces of the end cam cap and the side surfaces of the recess for cam cap can be easily formed on the side surfaces of the end cam cap than the side surfaces of the recess for cam cap.

Therefore, when the present invention is configured in this way, the productivity of the internal combustion engine can be increased.

In the above description, references used in the following descriptions regarding embodiments are added with parentheses to the elements of the present invention, in order to understand the invention. However, those references should not be used to limit the scope of the present invention.

Other objects, other features, and accompanying advantages of the present invention are easily understood from the description of embodiments of the present invention to be given referring to the following drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An internal combustion engine of the present invention will be described hereinafter with reference to the accompanying figures.

FIGS. 1 and 2show a schematic configuration of a multi-cylinder (for example, a four-cylinder) internal combustion engine10. Note that,FIG. 2shows a cross section of a cylinder. However, the other cylinders have the same configurations as this cylinder. This internal combustion engine10is installed in a vehicle, which is not shown, as a driving source of the vehicle.

This internal combustion engine10is provided with a cylinder block20, an oil pan30, a cylinder head body40, a camshaft housing47, an intake system60, an exhaust system61, an exhaust camshaft65, an intake camshaft70, a cam cap75, an end cam cap80, a timing chain86, a cylinder head cover87, a cover member88, a first lubricating oil circulation system90, a second lubricating oil circulation system100, a fresh air inlet pipe108, and a blowby gas circulation pipe109, as main components.

As shown inFIG. 2, a cylinder bore21is formed in an upper side portion of the cylinder block20. A lower space22communicating with the cylinder bore21is formed in the lower side portion of the cylinder block20. A piston23is provided in the cylinder bore21so as to be able to slide in the axial direction of the cylinder bore21.

The upper portion of the connecting rod24is rotatably connected to the piston23.

The upper surface of the oil pan30is in contact with the lower surface of the cylinder block20in an air-tight and water-tight manner. The cylinder block20and the oil pan30are fixed with each other by using a bolt and a nut. As shown inFIG. 1, the forward and rearward direction length of the oil pan30is longer than that of the cylinder block20. The front end portion of the oil pan30is positioned at a more forward position than the front end portion of the cylinder block20.

A crankshaft bearing (not shown) provided at the bottom of the cylinder block20rotatably supports a crank shaft25extending in the forward and rearward direction. Furthermore, the lower end portion of the connecting rod24is rotatably connected to the connecting rod bearing (not shown) formed in the crank shaft25. A sprocket (not shown) is fixed to the front portion of the crank shaft25.

The interior space of the oil pan30constitutes a first lubricating oil storage room31. Furthermore, the lower space22of the cylinder block20and the first lubricating oil storage room31of the oil pan30constitute a crank shaft storage space32communicating with the cylinder bore21.

A cylinder head35is fixed to the upper end portion of the cylinder block20. The cylinder head35is provided with the cylinder head body40and the camshaft housing47.

The lower end surface of the cylinder head body40is in contact with the upper end surface of the cylinder block20in an air-tight and water-tight manner. The cylinder head body40and the cylinder block20are fixed to each other by using a bolt. As shown inFIGS. 3 and 4, the sectional shape of the cylinder head body40, which is formed by cutting the cylinder head body40along a horizontal plane, has a subsequently rectangular shape which is long in the forward and rearward direction. The upper end surface of the cylinder head body40is a flat surface.

As shown inFIG. 2, a recess formed at the bottom of the cylinder head body40, the cylinder bore21, and the upper end surface of the piston23define (form) the combustion chamber41.

Furthermore, an inlet port42and an exhaust port43, both of which communicate with the combustion chamber41, are formed in the cylinder head body40. In addition, an intake valve guide42aand an exhaust valve guide43a, both of which have cylindrical shapes, are fixed to the cylinder head body40. The lower end of the intake valve guide42ais connected to the inlet port42, and the lower end of the exhaust valve guide43ais connected to the exhaust port43. Further, cylindrical seal members (not shown) are fixed to the upper portion of each intake valve guide42aand the upper portion of each exhaust valve guide43a, respectively. An intake valve44and an exhaust valve45are inserted into each intake valve guide42aand each exhaust valve guide43a, respectively. The intake valve44and the exhaust valve45are movable in the axial direction of the intake valve guide42aand the axial direction of the exhaust valve guide43a, respectively. A stem portion of each of the intake valves44is slidably supported by each intake valve guide42aand a stem portion of each of the exhaust valves45is slidably supported by each exhaust valve guide43a. As is well known, each of the intake valves44and each of the exhaust valves45open and close the corresponding inlet port42and the corresponding exhaust port43respectively by reciprocating in the axial direction of the intake valve guide42aand the axial direction of the exhaust valve guide43a, respectively.

An ignition plug46a, an igniter46bthat generates a high voltage given to the ignition plug46a, and an injector46cthat injects the fuel into the inlet port42are provided inside the cylinder head body40.

The camshaft housing47is provided on the upper end surface of the cylinder head body40.

As shown inFIGS. 3 and 4, the camshaft housing47is a frame body having a substantially rectangular shape in a plane view. Both upper and lower surfaces of the camshaft housing47are opened. The upper and lower surfaces of the camshaft housing47are flat surfaces. The upper end surface of the cylinder head body40and the lower end surface of the camshaft housing47are in contact with each other in an air-tight and water-tight manner. Furthermore, the cylinder head body40and the camshaft housing47are fixed to each other by a bolt.

The camshaft housing47includes a chain cover adjacent wall48, a pair of the side walls49, and a rear wall50(seeFIG. 1). The chain cover adjacent wall48constitutes the front surface of the camshaft housing47. The pair of the side walls49constitute the left and right side surfaces of the camshaft housing47, respectively. The rear wall50constitutes the rear surface of the camshaft housing47.

A camshaft storage space47a, whose top is opened, is formed inside the camshaft housing47.

The camshaft storage space47ais independent from the recess (the combustion chamber41) formed at the bottom of the cylinder head body40. In other words, the camshaft storage space47aand this combustion chamber41do not communicate with each other. Since each seal member is fixed to the upper portion of each of the intake valve guides42aand the upper portion of each of the exhaust valve guides43arespectively, the camshaft storage space47ais independent from each of the inlet ports42and each of the exhaust ports43. Namely, the camshaft storage space47adose not communicate with the inlet ports42and the exhaust ports43.

As shown inFIGS. 3 and 4, a recess for cam cap51having a rectangular shape in a front view is formed at the upper end portion of the chain cover adjacent wall48. The recess for cam cap51penetrates through the chain cover adjacent wall48in the forward and rearward direction.

The bottom surface51aof the recess for cam cap51is a horizontal flat surface. The left and right side surfaces51bof the recess for cam cap51are flat surfaces that are parallel to each other and are orthogonal to the lateral direction (left and right direction).

A pair of left and right bearing recesses52a,52bare formed on the bottom surface51a. The cross-sectional shape of the left bearing recess52aand the cross-sectional shape of the right bearing recess52bare semicircular shapes, which are the same as each other, respectively. Four female screw holes53are formed on the bottom surface51aof the recess for cam cap51so as to separate from the bearing recesses52a,52b.

Furthermore, the camshaft housing47is provided integrally with a plurality of journal bearings56that are arranged at approximately equal intervals in the forward and rearward direction. The upper end surface of each journal bearing56is a flat surface located on a plane on which the bottom surface51aof the recess for cam cap51is located.

A pair of left and right bearing recesses57a,57b, each of which has a semicircular shaped cross-section, are formed on the upper surface of each of the journal bearings56. Furthermore, each of the bearing recesses57ais coaxial with the bearing recess52a, and each of the bearing recesses57bis coaxial with the bearing recess52b. Four female screw holes58are formed on the upper end surface of each of the journal bearings56so as to separate from the bearing recesses57a,57b.

As shown inFIG. 2, one end of the intake system60and one end of the exhaust system61are respectively connected to the upstream end of each of the inlet ports42and the downstream end of each of the exhaust ports43of the cylinder head body40. The intake system60supplies air-fuel mixture including fuel (e.g., gasoline) and air to the cylinder block20. The exhaust system61emits exhaust gas from the cylinder block20to the outside of the internal combustion engine10.

The intake system60is provided with an intake manifold60aconnected to the upstream end of each inlet port42, a surge tank60bconnected to the intake manifold60a, a throttle body connected to the surge tank60b, and an intake duct60cconnected to the throttle body. The throttle body is provided integrally with a throttle valve60dand an actuator for throttle valve60e.

The exhaust system61comprises an exhaust pipe61b, which includes an exhaust manifold61acommunicating with the downstream end of each exhaust port43, and a catalyst apparatus61c, which is arranged in the exhaust pipe61b.

As shown inFIGS. 3 and 4, a plurality of portions of the lower half portion of the exhaust camshaft65are rotatably supported by the bearing recesses52aand the bearing recesses57aof the camshaft housing47. Likewise, a plurality of portions of the lower half portion of the intake camshaft70are rotatably supported by the bearing recesses52band the bearing recesses57b.

The exhaust camshaft65and the intake camshaft70are elongated members whose axes extend in the forward and rearward direction. The exhaust camshaft65and the intake camshaft70have the supported portions66and the supported portions71, respectively. The number of the supported portions66and the number of the supported portions71are the same as the total number of the chain cover adjacent wall48and all the journal bearings56. Each of the outer peripheral surfaces of the supported portions66,71is a cylindrical surface that has the same curvature as that of corresponding one of the bearing recesses52a,52b,57a,57b, respectively. Furthermore, the exhaust camshaft65has multiple pairs of the cams67formed at different positions from the supported portions66. Likewise, the intake camshaft70has multiple pairs of the cams72formed at different positions from the supported portions71. Furthermore, sprockets68,73are fixed to the vicinity of the front end of the exhaust camshaft65and the vicinity of the front end of the intake camshaft70, respectively.

The lower half portion of the foremost supported portion66of the exhaust camshaft65and the lower half portion of the foremost supported portion71of the intake camshaft70are supported by the bearing recess52aand the bearing recess52bof the camshaft housing47, respectively. On the other hand, the lower half portions of the remaining supported portions66of the exhaust camshaft65are rotatably supported by each of the bearing recesses57aof the journal bearings56, respectively, and the lower half portions of the remaining supported portions71of the intake camshaft70are rotatably supported by each of the bearing recesses57bof the journal bearings56, respectively. Furthermore, the sprocket68of the exhaust camshaft65and the sprocket73of the intake camshaft70are located at a more forward position than the chain cover adjacent wall48of the camshaft housing47.

Further, a VVT74(variable valve timing mechanism) is provided at the front end portion of each of the exhaust camshaft65and the intake camshaft70, respectively (seeFIG. 7. The VVT74of the exhaust camshaft65is not shown). Each of these VVTs74is operated by a driving force of an actuator for VVT.

The cam caps75are mounted on the upper end surface of each of the journal bearings56of the camshaft housing47from above, respectively.

Each of the cam caps75is a plate material that has a substantially rectangular shape in the front view, and its lateral dimension (a dimension in the left and right direction) is shorter than the lateral dimension between the inner surfaces of the left and right side walls49of the camshaft housing47. Further, a pair of left and right bearing recesses76a,76bare formed on the bottom surface of each of the cam caps75. The cross-sectional shapes of the bearing recesses76a,76bare semicircular shapes that are vertically symmetrical with the bearing recesses57a,57b. In addition, four through-holes77are formed in each of the cam caps75so as to be at positions different from those of the bearing recesses57a,57b. Each of the through-holes77penetrates through the cam caps75in the vertical direction.

The lower surface of each of the cam caps75are in contact with the corresponding one of upper surfaces of the journal bearings56. Furthermore, each of the cam caps75is fixed to corresponding one of the journal bearings56by screwing the lower end of each of bolts (not shown), which are inserted into through-holes77of each journal bearing56from above, into corresponding one of the female screw holes58.

The bearing recess76aof each cam cap75rotatably supports the upper half portion of corresponding one of the supported portions66of the exhaust camshaft65, respectively. Likewise, the bearing recess76bof each cam cap75rotatably supports the upper half portion of corresponding one of the supported portions71of the intake camshaft70, respectively.

The end cam cap80is detachably mounted to the recess for cam cap51of the camshaft housing47.

The dimension in the forward and rearward direction of the end cam cap80is the same as that of the recess for cam cap51. The vertical dimension of the end cam cap80is the same as that of the recess for cam cap51. However, the dimension in the forward and rearward direction of the end cam cap80does not have to be the same as that of the recess for cam cap51as long as the vertical dimensions of the left and right ends of the end cam cap80are the same as that of the recess for cam cap51. On the other hand, the lateral dimension of the end cam cap80is slightly smaller than that of the recess for cam cap51.

The six surfaces that form the entire outer surface of the end cam cap80are flat surfaces. Furthermore, the upper surface and the lower surface of the end cam cap80are horizontal flat planes. However, the entire outer surface excluding the lower surface of the end cam cap80does not have to be a flat surface (flat surfaces) while the lower surface of the end cam cap80must be a flat surface.

A pair of left and right bearing recesses81a,81bare formed on the bottom surface of the end cam cap80. The cross-sectional shapes of the bearing recesses81a,81bare semicircular shapes that are vertically symmetrical with the bearing recesses52a,52b, respectively. Four through-holes82are formed in the end cam cap80so as to be at positions different from those of the bearing recesses81a,81b. Each of the through-holes82penetrates through the end cam cap80in the vertical direction.

The end cam cap80has a pair of left and right side surfaces that are spaced apart from each other in a direction orthogonal to the axial directions of the exhaust camshaft65and the intake camshaft70. As shown inFIG. 7, the right side surface of the end cam cap80is constituted by a gap forming surface83that is a flat surface in the plane view. The gap forming surface83gradually approaches the center portion of the end cam cap80as approaching from the front thereof to the rear thereof in the plane view. This gap forming surface83is inclined with respect to the forward and rearward direction in the plane view. In other words, the right side portion of the end cam cap80is cut out (notched) so as to form the gap forming surface83.

Likewise, although not shown, the left side portion of the end cam cap80is constituted by a gap forming surface83that is bilaterally symmetrical with this right side gap forming surface83. In other words, the left side portion of the end cam cap80is cut out (notched) so as to form this gap forming surface83.

Pasty gasket G, which is called FIPG (Formed In Place Gasket) and is an oil resistant sealing material, is applied to the entire bottom surface of the end cam cap80, the entire left gap forming surface83of the end cam cap80, and the entire right gap forming surface83of the end cam cap80. Specific example of this gasket G is a gasket that includes a room temperature vulcanizing silicone rubber which is paste and contains a base silicone oil, a cross-linking agent, a filler, and an adhesion imparting agent. This gasket G is pasty when it is placed in a tube (container) not shown (namely, when it is not in contact with the air). Further, the gasket G is turned into semi-solidified with the lapse of time when it comes into contact with the air. The end cam cap80to which the gasket G is applied is fitted into the recess for cam cap51. Since the lateral dimension of the end cam cap80is slightly smaller than that of the recess for cam cap51, the end cam cap80can be smoothly fitted into the recess for cam cap51.

Furthermore, bolts (not shown) are inserted into each of the through-holes82of the end cam cap80from above, and the lower end of each of bolts is screwed into each of the female screw holes53formed in the recess for cam cap51.

The end cam cap80is thus fixed to the recess for cam cap51. As a result, the upper surface (at least the upper surfaces of the left and right end portions) of the end cam cap80is located on a flat (plane) on which the upper surface of the camshaft housing47is located.

When the end cam cap80is fixed to the recess for cam cap51, the bearing recess81aand the bearing recess52arotatably support the foremost supported portion66of the exhaust camshaft65. Likewise, the bearing recess81band the bearing recess52brotatably support the foremost supported portion71of the intake camshaft70. Then, the exhaust camshaft65and the intake camshaft70are allowed to rotate relative to the camshaft housing47about their own axes.

Further, as shown inFIG. 7, when the end cam cap80is fixed to the recess for cam cap51, cross-sectional area gradually changing gaps S, which are triangle-shapes in the plane view, are formed between the left and right gap forming surfaces83of the end cam cap80and the left and right side surfaces51bof the recess for cam cap51, respectively. Both the front end and the rear end of each of the left and right cross-sectional area gradually changing gaps S are opened. Furthermore, the cross-sectional area of each of the cross-sectional area gradually changing gaps S, which is formed by cutting each of the cross-sectional area gradually changing gaps S with a plane orthogonal to the forward and rearward direction, is gradually reduced as approaching from the rear thereof to the front thereof.

At the moment when the gasket G is applied to the end cam cap80, the gasket G is pasty. However, the gasket G is turned into semi-solidified gradually with the lapse of time. When a certain period of time elapses after the end cam cap80is fitted into the recess for cam cap51, the left and right gap forming surfaces83and the bottom surface of the end cam cap80and the inner surface of the recess for cam cap51are fixed to each other by the semi-solidified gasket G.

The space between both side surfaces and the bottom surface of the end cam cap80and the inner surface of the recess for cam cap51is filled with the semi-solidified gasket G. Namely, the semi-solidified the gasket G comes into contact with the left and right gap forming surfaces83, the bottom surface of the end cam cap80, and the inner surface of the recess for cam cap51in an air-tight and water-tight manner. Furthermore, a portion of the gasket G, which is semi-solidified between the bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51, and another portions of the gasket G, which are semi-solidified between the left and right gap forming surfaces83of the end cam cap80and the left and right surfaces51bof the recess for cam cap51, are continuous with each other.

As shown inFIG. 2, a plurality of rocker arms84are provided inside the camshaft housing47so as to be swingable. Half the number of the rocker arms84are in contact with the upper end of each of the exhaust valves45from above respectively, and are in contact with each cam67from below. On the other hand, the remaining half the number of the rocker arms84come in contact with the upper end of each of the intake valves44from above respectively, and are in contact with each cam72from below. Further, HLAs85(hydraulic lash adjusters) are provided inside the camshaft housing47. Each of HLAs85is connected to an end of each rocker arm84. This end of each rocker arm84is opposite to the contacting end of each rocker arm84, which comes into contact with the intake valves44or the exhaust valves45.

As shown inFIG. 4, the timing chain86, which is a ring member, is wound around the sprocket of the crank shaft25, the sprocket68of the exhaust camshaft65, and the sprocket73of the intake camshaft70.

As shown inFIG. 1, the lower end surface of the cylinder head cover87is in contact with the upper end surfaces of the camshaft housing47and the end cam cap80in an air-tight and water-tight manner. In addition, the camshaft housing47and the cylinder head cover87are fixed to each other by using a bolt. Namely, the cylinder head cover87covers up the upper end opening of the camshaft storage space47aof the camshaft housing47.

Thus, the camshaft storage space47aof the camshaft housing47and the interior space of the cylinder head cover87communicate with each other. These spaces have no communication with the external space outside of the cylinder head body40, the camshaft housing47, and the cylinder head cover87. Therefore, the atmosphere pressure of each of the camshaft storage space47aof the camshaft housing47and the atmosphere pressure of the interior space of the cylinder head cover87are always the same as the outside air pressure (the atmospheric pressure outside of the vehicle).

Further, as shown inFIG. 1, the cover member88is in contact with the front surfaces of the cylinder block20, the cylinder head body40, the camshaft housing47and the cylinder head cover87and the upper surface of the front portion of the oil pan30in an air-tight and water-tight manner. The cover member88is fixed to the cylinder block20, the cylinder head body40, the camshaft housing47, the cylinder head cover87, and the oil pan30by using bolts.

The rear surface and the bottom surface of the cover member88are only opened in the cover member88.

The chain storage space89is formed inside the cover member88(seeFIG. 7).

The lower end portion of the cover member88is connected to the upper end surface of the front portion of the oil pan30. Namely, the lower end of the chain storage space89and the front end portion of the first lubricating oil storage room31(the crank shaft storage space32) communicate with each other.

As shown inFIGS. 1, 5 and 6, the first lubricating oil circulation system90and the second lubricating oil circulation system100are formed inside the internal combustion engine10.

As shown inFIGS. 1 and 5, the first lubricating oil circulation system90is provided with the oil pan30, a first lubricating oil91, a main gallery92, an oil strainer93, an oil pump94, a relief valve95, an oil filter96, a piston jet97, a chain jet98, the crankshaft bearing, and the connecting rod bearing.

The first lubricating oil storage room31of the oil pan30is always filled with the first lubricating oil91.The main gallery92is formed inside the cylinder block20. The main gallery92is a flow path of the first lubricating oil91.

The oil strainer93, the oil pump94and the oil filter96are disposed in the cylinder block20. The oil strainer93, the oil pump94and the oil filter96are connected to each other via oil paths (not shown). The oil strainer93is in contact with the first lubricating oil91in the first lubricating oil storage room31. The oil pump94is interlocked with the crank shaft25via members including a chain (not shown). The oil pump94is provided integrally with the relief valve95.

The main gallery92is connected to each of the crankshaft bearings and the piston jet97. This piston jet97is provided in the cylinder block20so as to be close to the cylinder bore21and the piston23. Further, the main gallery92is connected to the chain jet98. This chain jet98is fixed to the cylinder head body40or the cylinder block20. The chain jet98is exposed in the chain storage space89and is close to the timing chain86.

As shown inFIGS. 1 and 6, the second lubricating oil circulation system100is provided with a sub oil pan40a, a second lubricating oil101, a sub oil strainer102, a sub oil pump103, a relief valve104, a sub oil filter105, a HLA gallery106, and a lubricating oil passage107.

The cylinder head body40is provided with the sub oil pan40athat is a recess formed inside the cylinder head body40. This the sub oil pan40ais always filled with the second lubricating oil101.

The sub oil strainer102, the sub oil pump103and the sub oil filter105are provided inside the cylinder head body40. The sub oil pump103is interlocked with the crank shaft25via the exhaust camshaft65, the intake camshaft70and the chain or the like, and is provide integrally with the relief valve104. Note that, the sub oil pump103may be an electric pump.

The sub oil strainer102, the sub oil pump103and the sub oil filter105are connected to each other via the lubricating oil passage107formed inside the cylinder head body40. The sub oil strainer102is in contact with the second lubricating oil101in the sub oil pan40a.

Furthermore, the lubricating oil passage107is connected to grooves (not shown) formed on the inner surfaces of the bearing recesses52a,52bof the chain cover adjacent wall48. An oil passage for VVT (not shown) is formed inside the front portion of each of the exhaust camshaft65and the intake camshaft70. Furthermore, the entrance end of each oil passage for VVT is formed on the surface of each of the foremost supported portions66,71of the exhaust camshaft65and the intake camshaft70. Each oil passage for VVT passes through the corresponding VVT74, and further is connected to the front end of each oil passage48a(seeFIG. 3) that passes through the chain cover adjacent wall48in the forward and rearward direction and is positioned below the bearing recesses52a,52b. Furthermore, an oil seal is provided between a rotating portion (not shown) of each VVT74and the front surface of the chain cover adjacent wall48. This oil seal prevents the second lubricating oil101from flowing from the camshaft storage space47ato the chain storage space89and prevents the first lubricating oil91and blowby gas described below from flowing from the chain storage space89to the camshaft storage space47a. Furthermore, the lubricating oil passage107is connected to one end of the HLA gallery106formed inside the cylinder head body40via the grooves formed on the inner surfaces of the bearing recess52a,52bof the chain cover adjacent wall48. The HLA gallery106is a flow path of the second lubricating oil101. The HLA gallery106is connected to the HLA85and the journal bearings56.

Furthermore, as shown inFIG. 1, the internal combustion engine10is provided with the blowby gas circulation pipe109and the fresh air inlet pipe108.

One end of the fresh air inlet pipe108is connected to the cover member88, and the other end of the fresh air inlet pipe108is connected to the intake system60at a position upstream of the throttle valve60d.

One end of the blowby gas circulation pipe109is connected to the cylinder block20, and the other end of the blowby gas circulation pipe109is connected to the intake system60at a position downstream of throttle valve60d. A valve (not shown) is provided in the blowby gas circulation pipe109.

Further, as shown inFIG. 2, the internal combustion engine10is connected to a crank position sensor CS, a wheel speed sensor (not shown), an accelerator opening sensor APS, a break sensor BPS, and an electronic control unit110.

The crank position sensor CS outputs signal every time the crank shaft25rotates by a predetermined angle. This signal is used to obtain rotating speed NE of the internal combustion engine10. The rotating speed NE represents the number of rotations of the crank shaft25per minute.

The wheel speed sensor outputs a signal representing a rotating speed of each wheel of the vehicle. A vehicle speed SPD is acquired based on average value of the rotating speeds of the wheels.

The accelerator opening sensor APS detects an operation amount of the accelerator pedal AP operated by a driver and outputs a signal representing this operation amount.

The break sensor BPS detects an operation amount of the brake pedal BP operated by the driver and outputs a signal representing this operation amount.

The electronic control unit110(hereinafter it is referred to as ECU110) is a micro-computer including a CPU111, a ROM112, a RAM113, a backup RAM114and an interface115, all of which are connected to each other via a bus. Data, which includes a program executed by the CPU111, a look-up table (a map), and constants, are stored in the ROM112in advance so that the data are held. The RAM113temporarily holds data according to the instruction from the CPU111. The backup RAM114holds data not only when the internal combustion engine10is in the driving state but also when the internal combustion engine10is not in the driving state. The interface115includes an AD converter.

The interface115is connected to an ignition switch (not shown), the crank position sensor CS, the wheel speed sensor, the accelerator opening sensor APS, and the break sensor BPS. Output signals of the ignition switch, the crank position sensor CS, the wheel speed sensor, the accelerator opening sensor APS, and the break sensor BPS are transmitted to the CPU111. As is well known, the ignition switch can be switched to any one of an OFF position, an ON position and an accessory position by operating a key (not shown).

Next, the operation of the internal combustion engine10in accordance with the control of the ECU110will be described.

When the ignition switch is operated by operation of the key, the internal combustion engine10starts to rotate. Then, the CPU111sends a driving signal (instruction signal) to the igniter46b, the injector46c, the actuator for throttle valve60e, and the actuator for VVT.

Then, an air-fuel mixture including the fuel and air is supplied from the intake system60to the combustion chamber41, and this air-fuel mixture burns in the combustion chamber41. Then, each piston23reciprocates in the vertical direction in the corresponding cylinder bore21of the cylinder block20. Then, the movement of each piston23is transmitted to the crank shaft25through the connecting rod24, and then the crank shaft25rotates about its axis. Then, since rotational force of the crank shaft25is transmitted to the sprocket68of the exhaust camshaft65and the sprocket73of the intake camshaft70through the timing chain86, each of the exhaust camshaft65and the intake camshaft70rotates about its own axis. As a result, each cam67of the exhaust camshaft65rotates to move corresponding one of the rocker arms84upward and downward. Then, each exhaust valve45connected to corresponding one of the rocker arms84moves upward and downward to open and close each exhaust port43. Additionally, each cam72of the intake camshaft70rotates to move corresponding one of the rocker arms84upward and downward. Then, each intake valve44connected to corresponding one of these rocker arms84moves upward and downward to open and close each inlet port42.

When the CPU111sends a driving signal to the actuator for VVT connected to the VVT74provided in the exhaust camshaft65, the driving force of the actuator for VVT causes the rotation position of the exhaust camshaft65(rotation phase) to change with respect to the crank shaft25. Therefore, the valve timing (INVT) of each of the exhaust valves45changes to the advance angle side or the delay angle side. Likewise, when the CPU111sends a driving signal to the actuator for VVT connected to the VVT74provided in the intake camshaft70, the driving force of this actuator for VVT causes the rotation position of the intake camshaft70to change with respect to the crank shaft25. Therefore, the valve timing of each of the intake valves44changes to the advance angle side or the delay angle side.

Furthermore, when the crank shaft25rotates, this rotational force is transmitted to the oil pump94and the sub oil pump103via members including the chain, and then the oil pump94and the sub oil pump103start their suction operation.

As shown inFIG. 5, when the oil pump94starts its suction operation, the first lubricating oil91in the first lubricating oil storage room31of the oil pan30is sucked by the oil pump94via the oil strainer93. Then, the first lubricating oil91discharged from the oil pump94flows to the main gallery92after passing through the oil filter96.

In addition, the first lubricating oil91is supplied from the main gallery92to the crankshaft bearing. Part of the first lubricating oil91supplied to the crankshaft bearing returns to the oil pan30by gravity. The remaining first lubricating oil91supplied to the crankshaft bearing is supplied to the connecting rod bearing of the crank shaft25and returns to the oil pan30by gravity.

In addition, part of the first lubricating oil91is supplied from the main gallery92to the piston jet97. Then, the piston jet97injects the first lubricating oil91to the cylinder bore21and the piston23. The first lubricating oil91fed to the cylinder bore21and the piston23returns to the oil pan30by gravity.

In this way, the first lubricating oil91circulates through the first lubricating oil storage room31of the oil pan30and the interior space of the cylinder block20by the sucking force of the oil pump94. The circulation passage of this first lubricating oil91is a block side first lubricating oil circulation passage90ashown inFIG. 1.

Further, the first lubricating oil91flowing into the main gallery92is supplied from the main gallery92to the chain jet98. Then, the chain jet98injects the first lubricating oil91to the timing chain86. The first lubricating oil91supplied to the timing chain86returns to the oil pan30by gravity.

In this way, the first lubricating oil91in the first lubricating oil storage room31of the oil pan30circulates through the inside space of the oil pan30, the inside space of the cylinder block20, and the chain storage space89of cover member88by the sucking force of the oil pump94. The circulation passage of this first lubricating oil91is a chain side first lubricating oil circulation passage90bshown inFIG. 1.

On the other hand, as shown inFIG. 6, when the sub oil pump103starts its suction operation, the second lubricating oil101in the sub oil pan40ais sucked by the sub oil pump103via the sub oil strainer102and the lubricating oil passage107. The second lubricating oil101discharged from the sub oil pump103is supplied to the grooves of the bearing recesses52a,52bof the chain cover adjacent wall48, the oil passage for VVT, and the HLA gallery106after passing through the lubricating oil passage107and the sub oil filter105.

The second lubricating oil101, which has lubricated the interior of each VVT74, passes through the oil passage48aof the chain cover adjacent wall48and returns to the sub oil pan40aby gravity.

The second lubricating oil101supplied to the HLA gallery106is supplied to the HLA85through the HLA gallery106. Furthermore, part of the second lubricating oil101supplied to the HLA85returns to the sub oil pan40aby gravity. In addition, part of the second lubricating oil101supplied to the HLA gallery106is supplied to the inner surfaces of the bearing recesses57a,57bof each of the bearing journals56through the HLA gallery106.

Part of the second lubricating oil101supplied to the journal bearings56returns to the sub oil pan40aby gravity. The remaining second lubricating oil101supplied to the journal bearings56is supplied to the rocker arms84. Furthermore, the second lubricating oil101supplied to the rocker arms84returns to the sub oil pan40aby gravity.

In this way, the second lubricating oil101in the sub oil pan40acirculates through the interior of the camshaft housing47and the interior of the cylinder head cover87by the sucking force of the sub oil pump103. The circulation passage of this second lubricating oil101is a second lubricating oil circulation passage100ashown inFIG. 1.

As is well known, when the internal combustion engine10is in an operation state, part of the combustion gas generated in the combustion chamber41flows into the crank shaft storage space32after passing through a gap between the inner peripheral surface of the cylinder bore21and the piston ring end gaps of piston rings, which are mounted on each of the pistons23respectively, to become blowby gas.

Then, the blowby gas comes into contact with the first lubricating oil91in the first lubricating oil storage room31of the oil pan30. As a result, since the blowby gas is mixed with the first lubricating oil91, the first lubricating oil91is deteriorated.

On the other hand, as described above, the camshaft storage space47aof the camshaft housing47and the recess (the combustion chamber41) of the cylinder head body40have no communication with each other. Furthermore, the seal members, which are fixed to the upper portion of each of the intake valve guides42aand the exhaust valve guides43arespectively, cause the inlet ports42and the exhaust ports43not to communicate with the camshaft storage space47a.

Therefore, the blowby gas staying in the cylinder block20and the oil pan30does not flow into the camshaft housing47via the recess (the combustion chamber41), each intake valve guide42aand each exhaust valve guide43a. Namely, the blowby gas does not come in contact with the second lubricating oil101disposed inside the camshaft housing47and the cylinder head cover87via the combustion chamber41, the intake valve guide42a, and the exhaust valve guide43a.

In addition, the second lubricating oil101in the camshaft housing47does not flow into the cylinder block20and the oil pan30via the combustion chamber41, the intake valve guide42a, and the exhaust valve guide43a. Namely, the second lubricating oil circulation passage100aand the block side first lubricating oil circulation passage90a(and the chain side first lubricating oil circulation passage90b) are independent from each other.

By the way, the blowby gas in the crank shaft storage space32and the chain storage space89flows into the combustion chamber41via the blowby gas circulation pipe109and the intake system60ato be burned in the combustion chamber41.

On the other hand, fresh air (which excludes exhaust gas and fuel) flowing from the upstream side of the intake duct60cto the downstream side of the intake duct60cis always supplied to the chain storage space89and the crank shaft storage space32via the fresh air inlet pipe108.

Thus, a negative pressure is always applied to the chain storage space89of the cover member88and the inside of the cylinder block20. Therefore, the atmosphere pressure of the chain storage space89is always lower than those of the camshaft storage space47aof the camshaft housing47and the interior space of the cylinder head cover87(i.e., the outside air pressure or the atmospheric pressure outside of the vehicle). Since there is a difference in atmosphere pressure between the camshaft storage space47aof the camshaft housing47and the chain storage space89, if there is a gap that makes the camshaft storage space47aand the chain storage space89communicate with each other therebetween, a sucking force heading to the chain storage space89is always applied to the second lubricating oil101.

However, the spaces (the cross-sectional area gradually changing gaps S) between the left and right gap forming surfaces83of the end cam cap80and the left and right side surfaces51bof the recess for cam cap51are filled with the gasket G in an air-tight and water-tight manner. Furthermore, the space between the bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51is also filled with the gasket G in an air-tight and water-tight manner.

Then, the second lubricating oil101in the camshaft storage space47adoes not pass through a gap between the end cam cap80and the recess for cam cap51to leak to the chain storage space89. Then, the second lubricating oil101in the camshaft storage space47adoes not mix with the first lubricating oil91.

Then, the second lubricating oil101in the camshaft storage space47adoes not decrease.

The bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51are substantially parallel to each other. In other words, the cross-sectional area of the gap between the bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51is substantially constant at any position in the forward and rearward direction. Namely, the cross-sectional area of the gap between the front end portion of the bottom surface of the end cam cap80and the front end portion of the bottom surface51aof the recess for cam cap51is substantially the same as the cross-sectional area of the gap formed between a remaining portion of the bottom surface of the end cam cap80, which excludes the front end portion of the bottom surface of the end cam cap80, and a remaining portion of the bottom surface51aof the recess for cam cap51, which excludes the front end portion of the bottom surface51a.

Then, the front end portion of the bottom surface of the end cam cap80and the front end portion of the bottom surface51aof the recess for cam cap51may hardly generate a resistance force to prevent the gasket G positioned between the bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51from moving to the chain storage space89when the negative pressure in the chain storage space89is exerted on the gasket G. This problem occurs when the end cam cap80and the recess for cam cap51are not tightly fixed by using the bolts and each of the female screw holes53. Then, in this case, there is a slight possibility of the gasket G being discharged to the chain storage space89via the gap between the front end portion of the bottom surface of the end cam cap80and the front end portion of the bottom surface51a.

However, in the present embodiment, the gasket G is sandwiched between the bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51with a strong force by using the bolts and each of the female screw holes53. Therefore, the gasket G is not discharged to the chain storage space89via the gap between the front end portion of the bottom surface of the end cam cap80and the front end portion of the bottom surface51a.

Furthermore, the negative pressure in the chain storage space89is also exerted on the gasket G that is semi-solidified in the left and right cross-sectional area gradually changing gaps S.

However, the cross-sectional area of each of the cross-sectional area gradually changing gaps S gradually decreases as approaching from the rear end of each of the cross-sectional area gradually changing gaps S to the front end of each of the cross-sectional area gradually changing gaps S.

Then, the front end portions of the side surfaces of the end cam cap80and the front end portions of the side surfaces51bof the recess for cam cap51generate a large resistance force to prevent the gasket G from moving to the chain storage space89.

Therefore, the gasket G does not pass through the front end portion of each of the cross-sectional area gradually changing gaps S and is not discharged to the chain storage space89.

The left and right side surfaces of the end cam cap80may be constituted by flat surfaces parallel to the left and right side surfaces51bof the recess for cam cap51.

In this case, however, the same problem as the above problem on the bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51, which occurs when the bolts are not threaded to each of the female screw holes53, occurs. Namely, a chance that the semi-solidified gasket G is discharged to the chain storage space89via the gap between the left and right side surfaces of the end cam cap80and the left and right side surfaces51bof the recess for cam cap51becomes larger compared with the case where the cross-sectional area gradually changing gaps S are formed between the end cam cap80and the recess for cam cap51.

In contrast, in the present embodiment, since the cross-sectional area gradually changing gaps S are formed between the left and right gap forming surfaces83of the end cam cap80and the left and right side surfaces51bof the recess for cam cap51, such a problem does not occur.

Thus, in the internal combustion engine10, the second lubricating oil101in the camshaft storage space47aof the camshaft housing47and the interior space of the cylinder head cover87does not flow into the cylinder block20and the oil pan30, and then does not leak to the chain storage space89.

Therefore, the amount of the second lubricating oil101in the camshaft storage space47aof the camshaft housing47and the interior space of the cylinder head cover87does not decrease.

Then, the intake valves44, the exhaust valves45, the exhaust camshaft65, the intake camshaft70, the rocker arms84, and the HLAs85can always operate smoothly.

Noted that, a gap forming surface, which is constituted by an inclined surface corresponding to the gap forming surface83, may be formed on the bottom surface of the end cam cap80, and then a cross-sectional area gradually changing gap S having a triangular shape in a side view may be formed between the bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51. In this case, this cross-sectional area gradually changing gap S is filled with the gasket G.

However, in this case the bottom surface51aof the recess for cam cap51supports the end cam cap80unstably.

On the other hand, in the present embodiment, since the bottom surface of the end cam cap80, which is a horizontal flat surface, is supported by the bottom surface51aof the recess for cam cap51, which is a horizontal flat surface, such a problem does not occur.

Furthermore, in the internal combustion engine10, the end cam cap80is disposed in the recess for cam cap51formed in the chain cover adjacent wall48of the camshaft housing47. In other words, the cover adjacent wall48and the end cam cap80are disposed at the same position in the forward and rearward direction.

Therefore, compared with a conventional internal combustion engines, the present invention can reduce the forward and rearward direction dimensions of the camshaft housing47and the entire internal combustion engine10.

Although, the present invention has been described based on the above embodiment. However, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the object of the present invention.

For example,FIGS. 8 through 10show first through third modified embodiments of the present invention, respectively.

In the first modified embodiment shown inFIG. 8, the left and right side surfaces of the end cam cap80are constituted by gap forming surfaces120that are curved surfaces and gradually approach the center portion of the end cam cap80as approaching from the front thereof to the rear thereof in the plane view. In other words, the left and right side portions of the end cam cap80are cut out (notched) so as to form the gap forming surfaces120, respectively.

In the second modified embodiment shown inFIG. 9, the left and right side surfaces of the end cam cap80are constituted by gap forming surfaces121. Each of the gap forming surfaces121comprises a flat surface121aand a flat surface121b. Each of flat surfaces121aextends linearly in the forward and rearward direction from the rear surface of the end cam cap80to the front thereof in the plane view. Each of flat surfaces121bextends linearly from the front end of the corresponding flat surface121ato the side end of the front surface of the end cam cap80while inclining with respect to the forward and rearward direction. Namely, the left and right side portions of this end cam cap80are cut out (notched) so as to form the gap forming surfaces121, respectively.

In the third modified embodiment shown inFIG. 10, the front portion of each of the left and right side surfaces of the end cam cap80is constituted by a gap forming surface122, respectively. Each of the gap forming surfaces122comprises a flat surface122a, a flat surface122b, and a flat surface122c. Each of flat surfaces122aextends linearly in the lateral direction from the side surface of the end cam cap80in the plane view. Each of flat surfaces122bextends linearly from the inner end of the corresponding flat surface122ato the front. Each of flat surfaces122cextends linearly from the front end of the corresponding flat surface122bto the side end of the front surface of the end cam cap80while inclining with respect to the forward and rearward direction. Namely, the left and right side portions of this end cam cap80are cut out (notched) so as to form the gap forming surfaces122, respectively.

In each of the modified embodiments shown inFIGS. 8 through 10, the cross-sectional area gradually changing gaps S1, S2, and S3, whose shapes are different from each other, are formed between each of the gap forming surfaces120,121,122of the end cam caps80and each of the side surfaces51bof each recess for cam cap51, respectively. The gaps between the left and right side surfaces of each of the end cam caps80and the left and right side surfaces51bof each recess for cam cap51are filled with the gasket G. The gap between the bottom surface of each of the end cam caps80and the bottom surface51aof each recess for cam cap51is filled with the gasket G. In these modified embodiments as well, the gaskets G, which are between the left and right side surfaces of each end cam cap80and the left and right side surfaces51bof each recess for cam cap51, and the gasket G, which is between the bottom surface of each end cam cap80and the bottom surface51aof each recess for cam cap51, are continuous with each other.

Furthermore, the cross-sectional area of the cross-sectional area gradually changing gap S1of the first modified embodiment, which is formed by cutting this cross-sectional area gradually changing gap S1with a plane orthogonal to the forward and rearward direction, is gradually reduced as approaching from the rear thereof to the front thereof (i.e., the front surface of the end cam cap80). In addition, the cross-sectional area of the cross-sectional area gradually changing gap S2of the second modified embodiment, which is formed by cutting this cross-sectional area gradually changing gap S2with a plane orthogonal to the forward and rearward direction, is gradually reduced as approaching from the front end of the flat surface121ato the front thereof. Furthermore, the cross-sectional area of the cross-sectional area gradually changing gap S3of the third modified embodiment, which is formed by cutting this cross-sectional area gradually changing gap S3with a plane orthogonal to the forward and rearward direction, is gradually reduced as approaching from the front end of the flat surface122bto the front thereof.

Therefore, each of these modified embodiments can produce the same effect as that of the above embodiment.

In the fourth modified embodiment shown inFIG. 11, the rear portion of each of the left and right side surfaces of the end cam cap80is constituted by a gap forming surface123. Each of the gap forming surfaces123comprises a flat surface123aand a flat surface123b. Each of flat surfaces123aextends linearly from the rear surface of the end cam cap80to the front in the plane view. Each of flat surfaces123bextends linearly from the front end of the corresponding flat surface123ato a middle portion of each of side surfaces of the end cam cap80in the forward and rearward direction while inclining with respect to the forward and rearward direction. Namely, the left and right side portions of this end cam cap80are cut out (notched) so as to form the gap forming surfaces123, respectively. The front portion of each of the left and right side surfaces of the end cam cap80is constituted by a flat surface parallel to the side surfaces51bof the recess for cam cap51.

In this modified embodiment, each of the cross-sectional area gradually changing gaps S4formed between the gap forming surfaces123and the side surfaces51bare filled with the gasket G, respectively. Furthermore, a gap between the bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51is filled with the gasket G. In this modified embodiment as well, the gaskets G, which are between the left and right side surfaces of the end cam cap80and the left and right side surfaces51bof the recess for cam cap51, and the gasket G, which is between the bottom surface of the end cam cap80and the bottom surface51aof the recess for cam cap51, are continuous with each other.

The gasket G filled in the front portion of each of the cross-sectional area gradually changing gaps S4receives the negative pressure from the chain storage space89.

However, in this modified embodiment, the front portion of each of left and right side surfaces of the end cam cap80and the front portion of each of side surfaces51bfaces with each other so as to form a minute gap and be parallel to each other. No gasket G is filled in a gap between the front portion of each of the left and right side surfaces of the end cam cap80and the front portion of each of side surfaces51b.

Then, the gasket G filled in the front portion of each of the cross-sectional area gradually changing gaps S4hardly move to the gap between the front portion of each of left and right side surfaces of the end cam cap80and the front portion of each of the side surfaces51b. Namely, there is an extremely small possibility that the gasket G is discharged to the chain storage space89after passing through the gap between the front portion of each of the left and right side surfaces of the end cam cap80and the front portion of each of side surfaces51b. Therefore, a chance that the second lubricating oil101in the interior spaces of the camshaft storage space47aand the cylinder head cover87leaks to the chain storage space89after passing through the gaps between the side surfaces of the end cam cap80and the side surfaces51bof the recess for cam cap51is much smaller compared with the case where the front end portion of each of the cross-sectional area gradually changing gaps S4is positioned at the same position as the front surface of the end cam cap80.

Both side surfaces of each of the end cam caps80may be constituted by flat surfaces that are parallel to each other and the both side portions of each recess for cam cap51may be cut out (notched) so that the both side surfaces of each recess for cam cap51and the both side surfaces of each of the end cam caps80form each of the cross-sectional area gradually changing gaps S, S1, S2, S3, S4therebetween, respectively.

The internal combustion engine10may comprise an annular timing belt (an annular interlocking member) that interlocks the crank shaft25, the exhaust camshaft65, and the intake camshaft70each other instead of the timing chain86.

The internal combustion engine10may be configured so that the intake valves44and the exhaust valves45are opened and closed by one camshaft.

The internal combustion engine10may be configured as the fifth modified embodiment shown inFIG. 12or the sixth modified embodiment shown inFIG. 13.

The cover member88of the internal combustion engine10inFIG. 12is opened only at its rear surface and the front surface of the oil pan30is opened. The lower portion of the rear surface of the cover member88is fixed to the front surface of the oil pan30, and the lower opening of the rear surface of the cover member88is connected to the opening of the front surface of the oil pan30.

The cover member88of the internal combustion engine10inFIG. 13is opened only at its rear surface and upper surface. The upper surface of the cover member88is fixed to the front portion of the opened lower surface of the cylinder head cover87. As shown inFIG. 13, a partition wall87ais provided inside the cylinder head cover87. A rubber gasket (not shown) is provided between the upper surface of the end cam cap80and the lower surface of the partition wall87a. Therefore, the blowby gas, the first lubricating oil91, and the second lubricating oil101do not flow between the space at a more forward portion of the cylinder head cover87than the partition wall87a(and the upper space of the cover member88) and the space at a more rearward portion of the cylinder head cover87than the partition wall87a.