CYLINDER HEAD STRUCTURE FOR INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

[0001]The present invention relates to a cylinder head structure for an internal combustion engine including a hydraulic lash adjuster, and in particular, relates to improvement in layout of an oil passage supplying oil to the lash adjuster.

BACKGROUND ART

[0002]Hydraulic lash adjusters are known for automatically adjusting a valve clearance to zero in a valve operation mechanism of an intake valve or an exhaust valve of an internal combustion engine. In case of a hydraulic lash adjuster included in a cylinder head, an oil passage is generally required in order to guide oil supplied from a cylinder block side to the hydraulic lash adjuster.

[0003]Patent Document 1 discloses forming an oil reservoir covered by a cam cap, between an intake camshaft and an exhaust camshaft of a cylinder head, and forming an oil passage leading from a lower part of the oil reservoir to hydraulic lash adjusters.

[0004]As disclosed in Patent Document 1, conventional arts form an entire part of an oil passage for a hydraulic lash adjuster inside a cylinder head by a method such as drilling. This deteriorates flexibility in design, and may make arrangement of the oil passage difficult due to interference with other components.

PRIOR ART DOCUMENT(S)

Patent Document(s)

SUMMARY OF THE INVENTION

[0006]According to an aspect of the present invention, a cylinder head structure for an internal combustion engine includes: a cylinder head; a first camshaft and a second camshaft one of which is structured for an intake valve and the other is structured for an exhaust valve; a first hydraulic lash adjuster disposed in the cylinder head, corresponding to the first camshaft; a cam carrier that is fixed to an upper part of the cylinder head and supports the first camshaft; an oil source-pressure passage disposed inside the cylinder head and positioned between the first and second camshafts when viewed in a direction of a cylinder axis; and an oil passage that leads from the oil source-pressure passage to the first hydraulic lash adjuster and includes a cam carrier internal passage passing inside the cam carrier.

[0007]Pressurized oil is supplied from a cylinder block side to the oil source-pressure passage inside the cylinder head, and is then delivered to the hydraulic lash adjuster via the oil passage. The oil passage includes a part passing inside the cam carrier. This reduces constraints on arrangement of the oil passage caused due to interference with other components in the cylinder head.

[0008]The cam carrier is positioned relatively high in the vertical direction in the internal combustion engine. This increases a vertical distance to the lash adjuster, and serves to retain oil even when the internal combustion engine has been left unused for a long period. Accordingly, oil is reliably supplied to the lash adjuster from an initial stage of a next engine start.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a front view of a cylinder head including a cam carrier.

[0010]FIG. 2 is a plan view of the cam carrier.

[0011]FIG. 3 is a sectional view of the cylinder head including the cam carrier.

[0012]FIG. 4 is an illustrative view showing an oil passage layout.

[0013]FIG. 5 is a top view of the cylinder head.

[0014]FIG. 6 is an illustrative view showing a valve operation mechanism.

MODE(S) FOR CARRYING OUT THE INVENTION

[0015]The following details a first embodiment of the present invention with reference to the drawings. FIG. 1 is a front view showing a cylinder head 1 of an internal combustion engine according to the present invention, together with a cam carrier 2. Cylinder head 1 is integrally cast using a metallic material such as an aluminum alloy, and is attached to an upper face of a cylinder block 3. The internal combustion engine according to the present embodiment is a straight-three spark-ignition internal combustion engine, i.e., a gasoline engine, and is mounted in a transverse orientation in a front part of a vehicle. When mounted in the vehicle, the internal combustion engine has a cylinder center axis being substantially vertical. Accordingly, FIG. 1 substantially corresponds to the orientation of the internal combustion engine when mounted in the vehicle.

[0016]The internal combustion engine according to the present embodiment includes a pent-roof combustion chamber including at its center a spark plug and a fuel injection valve. Each of the cylinders is provided with a pair of an intake valve and an exhaust valve.

[0017]Cylinder head 1 includes an intake camshaft 5 for the intake valve and an exhaust camshaft 6 for the exhaust valve. Cam carrier 2 is shaped as a cover covering an upper face opening of cylinder head 1, and is joined and fixed to an upper face of cylinder head 1 via an appropriate sealing member such as a liquid gasket. Cam carrier 2 includes an intake-side camshaft bearing 11 and an exhaust-side camshaft bearing 12 each of which has a substantially semicircular shape open downward. Cam brackets 13 and 14 are respectively mounted to camshaft bearings 11 and 12 so as to face camshaft bearings 11 and 12. Thus, cam brackets 13 and 14 and camshaft bearings 11 and 12 rotatably support intake camshaft 5 and exhaust camshaft 6 therebetween.

[0018]As shown in FIG. 1, intake camshaft 5 is positioned lower than exhaust camshaft 6 in height position along the cylinder center axis. Correspondingly, cam carrier 2 covering the upper side of camshafts 5 and 6 includes an upper edge shaped to be lower in height position in an intake camshaft 5 side than in an exhaust camshaft 6 side. In the present embodiment, the internal combustion engine is mounted in an engine room in the front part of the vehicle, in an orientation to direct intake camshaft 5 to a front side of the vehicle and direct exhaust camshaft 6 to a rear side of the vehicle. This maintains an appropriate clearance between cam carrier 2 and an engine hood (indicated by a virtual line L) of the vehicle in both the intake camshaft 5 side and the exhaust camshaft 6 side, in consideration of inclination of the engine hood including a front end positioned lower.

[0019]As shown in FIG. 2, cam carrier 2 according to the first embodiment includes a pair of camshaft containers 21 and 22 elongated and extending in a cylinder row direction, and has a ladder-like structure in which camshaft containers 21 and 22 are connected to each other at positions corresponding to gaps between the cylinders. Cam carrier 2 includes injector openings 23 being relatively large. Injector openings 23 are formed between camshaft containers 21 and 22, at three positions corresponding to positions of the cylinders in the cylinder row direction. Cam carrier 2 further includes plug holes 24 in which spark plugs are inserted. Plug holes 24 are shaped cylindrically, and are positioned closer to exhaust camshaft 6 (i.e., closer to camshaft container 22) than injector openings 23. Cam carrier 2 is made of a metallic material such as an aluminum alloy, and is integrally cast.

[0020]FIG. 3 is a sectional view of cylinder head 1 and cam carrier 2 shown in FIG. 1, at a section passing through centers of the intake and exhaust valves. As described above, the internal combustion engine includes pent-roof combustion chamber 31 connected to an intake port 32 and an exhaust port 33. Although the valve operation mechanism is omitted in FIG. 3, as is known to those skilled in the art, the internal combustion engine includes stem guide mounting holes 34 and 35 to which cylindrical stem guides are mounted respectively and therein the poppet-type intake and exhaust valves are installed together with valve springs.

[0021]FIG. 6 is an illustrative view schematically showing the valve operation mechanism omitted in FIG. 3. The valve operation mechanism includes a rocker arm 101 including an end supported by a hydraulic lash adjuster 36. Rocker arm 101 is structured to swing in response to cam action of intake camshaft 5, and thereby open and close intake valve 103. Similarly, the valve operation mechanism includes a rocker arm 102 including an end supported by a hydraulic lash adjuster 37. Rocker arm 102 is structured to swing in response to cam action of exhaust camshaft 6, and thereby open and close exhaust valve 104. Reference numeral 105 represents the fuel injection valve. Reference numeral 103 represents the spark plug. Each of the hydraulic lash adjusters has a substantially cylindrical shape, is structured to extend to adjust a valve clearance to zero with use of an internal spring thereof, and receives reaction force upon valve lifting with oil filled inside the hydraulic lash adjuster. Further detailed explanations of the hydraulic lash adjusters themselves are omitted because they have known configurations. In addition, FIG. 6 merely illustrates a mechanism, and does not show strict arrangement of respective components.

[0022]In FIG. 3, line M1 represents a centerline of the intake valve stem, and line M2 represents a centerline of the exhaust valve stem. As shown in FIG. 3, intake valve centerline M1 passes further inward in a widthwise direction of cylinder head 1 (i.e., the right-and-left direction in FIG. 3) than a center O1 of intake camshaft 5. On the other hand, exhaust valve centerline M2 passes further outward in the widthwise direction of cylinder head 1 than a center O2 of exhaust camshaft 6.

[0023]Each of the intake valve and the exhaust valve is provided with a corresponding one of hydraulic lash adjusters 36 and 37. Hydraulic lash adjusters 36 and 37 are respectively installed in lash adjuster installation holes 38 and 39 shaped cylindrically and formed in cylinder head 1, and receive supply of hydraulic pressure.

[0024]The intake-side hydraulic lash adjuster 36 is positioned further outward in the widthwise direction of cylinder head 1 than intake valve centerline M1, and in the shown example, is disposed substantially directly under intake camshaft 5. The exhaust-side hydraulic lash adjuster 37 is positioned further inward in the widthwise direction of cylinder head 1 than exhaust valve centerline M2, and in the shown example, is disposed at a position higher than the intake-side hydraulic lash adjuster 36.

[0025]As a whole of cylinder heads 1 of the straight-three engine, six intake-side hydraulic lash adjusters 36 and six exhaust-side hydraulic lash adjusters 37 are provided. Lash adjuster installation holes 38 and 39 are respectively in communication with lash adjuster oil galleries 41 and 42 extending in the cylinder row direction. Lash adjuster oil galleries 41 and 42 are, for example, formed by drilling in the cylinder row direction. Ends of lash adjuster oil galleries 41 and 42, which are shown in FIG. 1, are respectively closed by plugs.

[0026]The following describes configurations of oil passages with reference to FIG. 4, which is a chief part of the present invention. FIG. 4 shows oil passages in a transparent view in the cylinder row direction, for showing the oil passages inside cylinder head 1 and cam carrier 2. Most of the oil passages except for lash adjuster oil galleries 41 and 42 are formed in cylinder head 1 and a front end of cam carrier 2 (i.e., a lower part in FIG. 2). Similarly to lash adjuster oil galleries 41 and 42, the oil passages are formed by a combination of straight drilling processes, while unnecessary open ends of the oil passages are closed by plugs.

[0027]An oil source-pressure passage 45 extending vertically is formed at a substantially middle in the widthwise direction of cylinder head 1, that is, formed between intake camshaft 5 and exhaust camshaft 6 when viewed in the cylinder axial direction. Oil source-pressure passage 45 includes a lower end being in communication with a main oil gallery (not shown) of cylinder block 3. Accordingly, oil source-pressure passage 45 is supplied with pressurized oil from an oil pump.

[0028]Oil source-pressure passage 45 includes an upper end open to a lower face of an oil reservoir 46 formed in an upper portion of cylinder head 1. Oil reservoir 46 is formed as a bathtub-shaped depression in a joint surface between cylinder head 1 and cam carrier 2 (see FIG. 5), and is positioned between intake camshaft 5 and exhaust camshaft 6. Oil reservoir 46 is covered by a lower surface of cam carrier 2 and thereby shaped to define a closed space. Joint surface 47 between cylinder head 1 and cam carrier 2 around oil reservoir 46 is sealed by an appropriate sealing member such as a liquid gasket as described above.

[0029]As shown in FIG. 4, oil reservoir 46 includes a side surface 46a on the exhaust camshaft 6 side. Side surface 46a is an inclined surface, wherein an end of an exhaust-side oil passage 51 is open at a center of side surface 46a. Exhaust-side oil passage 51 is shaped to be straight and inclined with respect to joint surface 47 (in other words, the upper face of cylinder head 1) by an angle such as 40 to 50 degrees, and includes a tip being in communication with the exhaust-side lash adjuster oil gallery 42. Thus, oil is supplied from oil reservoir 46 to exhaust-side lash adjuster installation hole 39 via exhaust-side oil passage 51 and lash adjuster oil gallery 42.

[0030]Cam carrier 2 includes a cam carrier internal passage 52 as a part of the oil passages leading from oil reservoir 46 to intake-side hydraulic lash adjuster 36. Cam carrier internal passage 52 passes an interior of cam carrier 2, and is formed by connecting a plurality of straight sections. Cam carrier internal passage 52 includes a straight section 52a, a straight section 52b, and a straight section 52c. Straight section 52a extends obliquely upward from oil reservoir 46. Straight section 52b extends parallel with joint surface 47, above intake camshaft 5. Straight section 52c extends downward, and is positioned further outward in the widthwise direction of cylinder head 1 than intake camshaft 5. Thus, cam carrier internal passage 52 includes an inlet portion 52d facing oil reservoir 46 between intake camshaft 5 and exhaust camshaft 6, and an outlet portion 52e extending toward the upper face of cylinder head 1 outside intake camshaft 5 and exhaust camshaft 6. Straight section 52b extending parallel with joint surface 47 includes at its middle a camshaft lubrication oil passage 56 branching from cam carrier internal passage 52 and leading to intake-side camshaft bearing 11 for intake camshaft 5. Oil flowing via camshaft lubrication oil passage 56 serves for lubrication of a journal portion of intake camshaft 5.

[0031]Outlet portion 52e of cam carrier internal passage 52 is connected to an intake-side oil passage 53 formed in the cylinder head 1 side. Intake-side oil passage 53 includes a straight section 53a extending vertically and a straight section 53b extending obliquely downward from an outer periphery of cylinder head 1. Straight section 53b includes a tip being in communication with intake-side lash adjuster oil gallery 41. A connection part between intake-side oil passage 53 and lash adjuster oil gallery 41 is surrounded and sealed by the sealing member for joint surface 47 between cylinder head 1 and cam carrier 2. FIG. 5 shows an upper end opening of straight section 53a of intake-side oil passage 53. Accordingly, oil is supplied from oil reservoir 46 to intake-side lash adjuster installation hole 38 via cam carrier internal passage 52, intake-side oil passage 53, and lash adjuster oil gallery 41.

[0032]As described above, the present embodiment is configured to supply oil from oil reservoir 46 to intake-side lash adjuster installation hole 38 via cam carrier internal passage 52. This facilitates layout of the oil passages in comparison with a case of forming the entire part of the needed oil passages inside the cylinder head 1, and thereby allows the oil passages to be formed while avoiding interference with other components. For example, the configuration of forming cam carrier internal passage 52 inside the cam carrier 2 allows the oil passages to be routed while avoiding interference with the intake valve that is interposed between oil source-pressure passage 45 and intake-side lash adjuster installation hole 38 (see FIG. 6). Furthermore, since cam carrier internal passage 52 passes above intake camshaft 5, there is no need to form in cylinder head 1 an oil passage that passes below intake camshaft 5.

[0033]Cam carrier internal passage 52 is positioned higher than hydraulic lash adjusters 36 and 37, and forms a relatively long path leading to hydraulic lash adjusters 36 and 37. This contributes to retention of oil during stopping of the internal combustion engine, and thereby improves oil retention in case such as the internal combustion engine left unused for a long period. As a result, when the internal combustion engine is started after being left unused, oil is promptly supplied to hydraulic lash adjusters 36 and 37, suppressing oil shortage and air intake.

[0034]Exhaust-side hydraulic lash adjuster 37 is positioned between the exhaust valve and oil source-pressure passage 45. Accordingly, a simple structure can be achieved by, as described above, forming exhaust-side oil passage 51 as a straight passage extending from oil reservoir 46 located centrally. Although exhaust-side hydraulic lash adjuster 37 is not provided with an oil-retaining passage passing inside cam carrier 2, oil reservoir 46 retains oil and thereby suppresses oil shortage and air intake. Thus, the sections with the oil-retaining function are separately provided for intake-side hydraulic lash adjuster 36 and exhaust-side hydraulic lash adjuster 37. This ensures reliable suppression of oil shortage for each hydraulic lash adjuster.

[0035]The present invention is not limited to the first embodiment described above, but may be variously modified. For example, the cam carrier is not limited to the ladder-like structure as in the above embodiment, but may be modified as long as including at least one camshaft bearing. Furthermore, the camshafts may be rotatably supported between cylinder head 1 and cam carrier.