Internal combustion engine with a cam phase variation apparatus

Abstract

 This invention concerns internal combustion engines comprising an engine block including a cylinder head unit attached to a cylinder block, a valve actuating mechanism including at least one camshaft, a camshaft drive mechanism including a cam sprocket associated to the camshaft, and a cam phase variation apparatus for varying the angular relation between said camshaft and cam sprocket, said cam phase variation apparatus including an operating mechanism mounted on the camshaft and a hydraulic actuation means connected with said operating mechanism. The engine has been improved in that the hydraulic actuation means forms a pre-assembled unit attached to the engine block from the outside.

Description

[0001] This invention concerns internal combustion engines comprising an engine block including a cylinder head unit attached to a cylinder block, a valve actuating mechanism including at least one camshaft rotatably supported in said cylinder head unit, a camshaft drive mechanism including a cam sprocket associated to the camshaft, and a cam phase variation apparatus for varying the angular relation between said cam shaft and cam sprocket, said cam phase variation apparatus including an operating mechanism mounted on the camshaft and a hydraulic actuation means connected with said operating mechanism.

[0002] In four-cycle engines having an OHC type of valve system, to wit, four-cycle engines in which the camshaft driven by the rotation of the crankshaft by a timing chain, etc., is located above the cylinders and, at the front end of the camshaft, there is an approximately cylindrical casing which houses a helical gear operated by oil pressure. Moreover, at the rear end side of the casing is a cam sprocket engaged by the timing chain, and oil pressure is used to change the phase of the cam sprocket and the phase of the camshaft itself. This technology is known as a cam phase angle variation apparatus (VVT); it changes the valve timing based upon the operational state of the engine. (For example, see Japan Utility Patent Hei 6-12240 (1994)).

[0003] In the cam phase angle variation apparatus of the prior art, wherein oil pressure is used to change the phase of the cam sprocket affixed to the front end of the cam shaft and the phase of the camshaft with respect to the cylindrical casing (the operating control device), in those which employ a solenoid valve in order to regulate the oil pressure that is delivered, the mounting structure for the cam phase angle variation apparatus overall, including the solenoid valve, to the engine unit becomes complex, requiring numerous parts, and increases production costs due the troublesome assembly operations.

[0004] Further, the mounting of the solenoid valve on the engine unit means that a separate oil conduit (an oil passage from the solenoid valve to the operation control device) must be present in the cylinder head to supply oil to the operation control device of the cam phase angle variation apparatus; this feature is additional to the one providing lubricating oil to the bearings which axially support the journal areas of the crankshaft. Consequently the processing steps that must be performed in manufacturing the cylinder head, thus the costs, are increased.

[0005] Accordingly, it is an objective of the present invention to provide an internal combustion engine having an improved mounting structure for the cam phase angle variation apparatus that reduces the number of parts required for mounting the apparatus and that simplifies the mounting operation. Preferably, the fluid passage arrangement in the cylinder head unit should be kept as simple as possible.

[0006] According to the present invention, this objective is performed in that the hydraulic actuation means forms a pre-assembled unit attached to the engine block from the outside.

[0007] According to a preferred embodiment of the invention, said hydraulic actuation means is disposed and attached to the cylinder head unit substantially opposite to one end of the camshaft.

[0008] In a preferred embodiment, said hydraulic actuation means includes a valve means and a fluid transfer unit comprising at least one fluid passage. Preferably said hydraulic transfer unit comprises a projecting portion which extends through an opening formed in a cylinder head wall of the cylinder head unit facing the end of the camshaft and surrounding said projecting portion, said projecting portion being in connection with said operating mechanism.

[0009] According to another preferred embodiment of the invention, an attachment bracket is provided for attaching the hydraulic actuation means, said attachment bracket being attached to a top surface of the cylinder head unit.

[0010] According to yet another preferred embodiment of the invention, a fluid passage arrangement is provided for supplying pressurized fluid to the hydraulic actuation means from a fluid pump. Said fluid passage arrangement preferably forms part of the camshaft lubrication system.

[0011] According to a preferred embodiment of the invention, said fluid passage arrangement comprises a fluid passage formed in the cylinder head unit and communicated with an opening in a cylinder head wall of the cylinder head unit, said opening being connected to the valve means located in front of said cylinder head wall opposite to said opening. Furthermore, a drainage hole is preferably provided in said cylinder head wall of the cylinder head unit and is communicated with a drainage passage, said drainage hole being connected with the said valve means which is located in front of said drainage hole.

[0012] According to yet another preferred embodiment of the invention, the fluid passage arrangement comprises a branch passage communicated with camshaft bearings and said pressurized fluid is a lubricant. Preferably, said branch passage and fluid passage communicated with the valve means are communicated with a common fluid supply passage formed in the cylinder head unit.

[0013] Further preferred embodiments of the invention are laid down in further dependent claims.

[0014] The above described structure provides for a simple operation in attaching the integral assembly of the solenoid valve and the oil transfer unit to the front face of the of the engine after aligning the positions of the operating control device of the cam phase angle variation apparatus on the front end of the camshaft with the oil transfer unit, thereby mounting the entire cam phase angle variation apparatus including the solenoid valve onto the engine unit.

[0015] Also, according to the structure described in the foregoing, after aligning the position of the operating control device of the cam phase angle variation apparatus attached to the front of the crankshaft with the oil transfer unit, the integral assembly of the solenoid valve and the oil transport unit is attached from the front of the engine by the attachment bracket through the opening present by the front end wall of the cylinder head and the attachment bracket, thereby mounting the cam phase angle variation apparatus, including the solenoid valve, to the engine unit.

[0016] In this case, the entire cam phase angle variation apparatus, including the solenoid valve, is affixed to the engine unit, thereby greatly reducing the number of parts required to mount the device by relying on just a single attachment bracket; further, the use of such an attachment bracket contributes to the high durability attachment of the cam phase angle variation apparatus to the engine unit.

[0017] Further, according to the structure described in the foregoing, by simply affixing the solenoid valve and oil transfer unit assembly to the front face of the engine, communication is achieved between the oil inlet of the solenoid valve and the oil passage in the cylinder head.

[0018] Also, according to the structure described above, the need for two separate passages to be present in the cylinder head, namely one oil passage serving the solenoid valve and the other to provide lubricating oil to the camshaft, is eliminated; rather, the number of oil passages in the cylinder head is reduced while still allowing the provision of appropriate amounts of oil to the solenoid valve and the camshaft bearings.

[0019] Furthermore, according to the structure described above, simply attaching the solenoid valve and the oil transfer unit to the front face of the engine connects the solenoid valve's drain hole.

[0020] Hereinafter, the present invention will be illustrated and explained in greater detail by means of a preferred embodiment of the invention in connection with accompanying drawings, wherein:

Figure 1 is an overall front view of a four-cycle internal combustion engine being provided with a cam phase variation apparatus according to a preferred embodiment of the invention,

Figure 2 is a front view of the engine shown in Figure 1 showing the positions of the cam chain.

Figure 3 is a figure used to explain the positionals of the water pump, oil pump and oil cooler in the engine shown in Figure 1.

Figure 4 is a front view of an embodiment of the mounting structure for the cam phase angle variation apparatus.

Figure 5 is a partial sectional top surface view of the mounting structure for the cam phase angle variation apparatus shown in Figure 4.

Figure 6 is a front view showing the attachment on the engine side of the mounting structure for the cam phase angle variation apparatus shown in Figure 4.

Figure 7 is a top surface view with the cylinder head cover removed of the mounting to the engine unit shown in Figure 6.

Figure 8 is a sectional view of the cylinder head along line A-A of Figure 7.

Figure 9 is a side view of the front of the cylinder head when viewed in the direction of arrow B in Figure 7.

Figure 10 is a bottom view of the front of the cylinder head when viewed in the direction of Arrow C in Figure 9.

[0021] Figure 1 shows a view from the front (in the crankshaft direction) of a multi-cylinder four-cycle engine equipped with a twin cam valve system and an upper and lower two-stage chain. From the top down, connected in the engine 1, are the cylinder head cover 2, the cylinder head 3, the cylinder block 4, the crankcase 5 and the oil pan 6, and additionally, a front cover 7 covers the front surface of the cylinder block 4 and the crankcase 5. Mounted on the bottom surface of the crankcase 5 of the engine 1, in an area outside the oil pan 6, is an oil cooler 9 that is rigidly attached to a filter.

[0022] Further, in this engine unit 1, the water pump 10 is part of the cylinder block 4 and the front cover 7, while the auxiliary equipment, consisting of the alternator 11, the power steering pump 12, the air conditioning compressor 13, etc., is mounted around the periphery of the engine 1. Pulleys 18, 19, 20 and 21 are attached, respectively, to the ends of the input shafts 14, 15, 16 and 17 of the water pump 10 and the various auxiliary equipment 11, 12 and 13.

[0023] Further, a pulley 23 is affixed to the end of the output shaft 22 that extends to the outside the front cover 7 from the crankshaft of the engine. The rotation of the output shaft 22 is transmitted to the input shafts of the water pump and the various auxiliary equipment input shafts 14, 15, 16 and 17 by a belt 24 that drives this auxiliary equipment, the belt 24 additionally spans a tensioner 25 composed of the tension pulley 28, the arm member 27, and a spring damper unit 26.

[0024] In the belt tensioner 25, one end of the spring damper 26 is pivotably affixed to the crankcase 5 by means of a shaft 26a while a pivot unit 29 in the center of the arm 27 is pivotably affixed to the alternator support 4a of the cylinder block 4, the other end of the spring damper 26 and one end of the arm 27 being rotatably connected by a shaft 26b, and the tension pulley 28 is rotatably attached to the other end of the arm 27 so that the force applied by the spring in the spring damper 26 keeps the tension pulley 28 constantly pushing against the belt 24 by means of the arm 27.

[0025] As is shown in Figure 1 for the belt tensioner 25, the belt 24 and the arm 27 intersect between the pivot area 29 and the tension pulley 28 and between the pivot area 29 and the spring damper unit 26, so that the pivot area 29, which is in the center of the arm 27, is positioned inside the serpentine belt 24, while the arm 27 is located in front of the belt 24, so that, when viewed from the front (in the crankshaft direction) the respective center lines of the belt 24 and the spring damper unit 26 are in line, thereby entailing a structure that realizes a lighter weight for arm 27, even while improving strength.

[0026] Because of this structure, compared to structures wherein the tensioner pivot is positioned outside the serpentine belt, there is greater latitude in finding a location with respect to the engine for the belt tensioner 25, and it is easy to locate the belt tensioner in a lesser space. Also, because the arm 27 is positioned in front of the belt 24, it can be very compact in the front of the engine (in the crankshaft direction), and the front-to-rear aligning of the center lines of the belt 24 and the spring damper unit 26 enables lightening and strengthening the arm member 27.

[0027] Further, since the tensioner pulley 28 is located near the center of the engine unit 1 in the transverse direction (the cylindrical axis X shown in Figure 2), the tensioner can be very effectively located with respect to the belt 24 that spans the pulleys of the various auxiliary equipment, and the tension pulley can be compactly located beneath the mounting bracket 30.

[0028] Further, in the engine unit 1, there is a mounting bracket 30 for attaching the engine to the vehicle and spanning both the cylinder head 3 and the cylinder block 4; it is affixed by bolts in attachment areas 31, 32, 33. An attachment area 30a is formed on this mounting bracket 30 for attaching it to the vehicle, and the top of the alternator 2 is attached to the attachment area 34 by a bolt.

[0029] As can be seen from Figure 2, the camshaft drive mechanism includes an intermediate shaft 46 which is coupled to the camshafts via a transmission means including a cam chain for driving said camshafts.

[0030] Figure 2 shows the configuration of the cam chan with respect to the engine unit 1, said chains driving the valve system of this twin cam (not shown) 5-valve engine with three air intake valves and two exhaust valves located at the top of the engine for each cylinder.

[0031] The cam chains consist of an upper and lower 2-stage chain system composed of an upper chain 43 engaging the air intake cam sprocket 41 attached to the camshaft 38 for the air intake valves and the exhaust cam sprocket 42 attached to the camshaft 39 for the exhaust valves, and a lower cam chain 43 which engages a sprocket 44 attached to the end of the output shaft 22 of the crankshaft and intermediate sprockets 48, 49 attached to intermediate rotating shaft 46.

[0032] The intermediate rotating shaft 46 is offset to one side with respect to the cylindrical axis X, located roughly at the center of the engine in the transverse direction and it is rotatably attached to the cylinder head 3. The upper chain 43 spans the intermediate sprocket 47 attached to the intermediate rotating shaft 46, the air intake side cam sprocket 41 and the exhaust side cam sprocket 43, while the lower chain 45 spans the intermediate sprocket 48, and the sprocket 44 attached to the output end of the crankshaft.

[0033] An upper chain tensioner 49 is present between the intermediate sprocket 47 and the air intake side cam sprocket 41 and is designed to take up any slack in the upper chain 43. The tension arm 49a of the upper tensioner 49 is pivotally supported at a pivot area 49b affixed to the cylinder head 3, while a rod cylinder 49c housing a push rod pressing on the tension arm 49a is affixed to an attachment hole through a projection 3a from the cylinder head 3 to enable it to be externally serviceable.

[0034] The attachment area 32, which is the attachment area of the mounting bracket 30 that is located close to the center of the engine in the transverse direction (near the cylindrical axis X), is positioned over the pivot area 49b for the upper chain tensioner 49, so that the hole 32a in the front of the pivot area 49b on the cylinder head 3 also functions as the attachment hole 32a for the mounting bracket 30, a blind plug 32b to close hole 32a holding an attachment bolt to attach the mounting bracket 30 to the cylinder head 3.

[0035] A lower chain tensioner 50 is located between the output sprocket 44 and the intermediate sprocket 48 to take up any slack in the lower chain 45. The tension arm 50a of the lower chain tensioner 50 is pivotally supported at the pivot area 50b affixed to the cylinder block 4, and a rod cylinder 50c which contains a push rod to apply pressure upon the tension arm 50a is affixed in a hole that passes through the lower part of the alternator support 4a of the cylinder block 4 to make it externally serviceable.

[0036] Since the alternator support 4a of the cylinder block 4 is rigidly joined to the cylinder block 4 and projects from it to form a lower support for the alternator 11, the alternator 11 is attached at the bottom to support 4a by a bolt to an attachment area 35.

[0037] Figure 3 shows the location of the water pump, oil pump, oil cooler and their related members installed on the engine.

[0038] As is shown in Figure 2, when the oil pump 52 is still, the level of the oil surface of the oil in the oil pan 6 is at L₁, but when the oil pump 52 is running, that level is at L₂; due to the installation of the engine 1 in a tilted fashion, these oil surfaces serve as the horizontal references.

[0039] The water pump 10, oil pump 52 and oil cooler 9 that are installed in various areas of the engine unit 1 are all positioned on the front face side of the engine unit 1. As is shown in Figure 3, the water pump 10, which is installed above the cylinder block 3, and the oil pump 52, which is located inside the oil pan 6 beneath it that runs the length of the crankcase, lie approximately opposite to each other on either side of the output shaft 22 of the crankshaft.

[0040] Due to the engine tilt, the inlets for the coolant and for the oil to the oil cooler 9 lie in the approximate vertical center between the water pump and the oil pump, and are positioned at the apex of a triangle with a line connecting the water pump 10 and the oil pump 52 as its base.

[0041] While not shown in the Figures, the pump housing for the water pump 10 is formed by the stock in the cylinder block 4, the front cover 7 that covers the front face of the cylinder block 4 and the crankcase 5, and an outer cover that covers the front face of the front cover, and the impeller is situated inside this pump housing.

[0042] As is shown in Figure 1, the rotating input shaft 14 of the impeller of the water pump extends outside the front cover 7, and a pulley 18 is attached to its end so that the coolant water that is pumped by the water pump 10, is transported from the opening 66 to the water jacket in the cylinder block to the inside of the cylinder block 4, and additionally, through a coolant passage (not shown in the Figures) present in the front cover 7, to the oil cooler 9, after which it is returned, through a coolant passage present in the cylinder block 4, from the oil cooler 9 to the water pump 10.

[0043] The oil pump 52 is driven by the rotation of the output shaft 22 of the crankshaft by a chain 54 engaging the oil pump output sprocket 53 along with the output sprocket 44 (shown in Figure 2) on the output shaft 22 of the crankshaft. The drive to the oil pump 52 causes the lubricating oil stored in the oil pan 6 to be drawn up through the strainer 55 and be supplied to the oil cooler 9 through the oil conduit pipe 56.

[0044] Inside the oil cooler 9 are an internal cooler element 9a and a filter element 9b, which, as shown in Figure 1, are attached to the bottom surface of the crankcase adjacent to an indent area in the side surface of the oil pan 6.

[0045] The oil that is sent from the oil pump 52 to the oil cooler 9, after being filtered by the filter element 9b, enters the cooler element 9a where coolant supplied by the water pump 10 cools the oil, and from there, it is sent through the oil passage 57 to the main hole 58, from where it is supplied to various areas of the engine. A part of the oil is also supplied to the cylinder head 3 from the main hole 58 through the oil passage 59.

[0046] In the engine of the present embodiment with the above described structure, the cam phase angle variation apparatus situated at the top of the engine varies the phase angle between the air intake side camshaft 38 and the cam sprocket 48 by using the oil that is supplied to the cylinder head 3 through the oil passage 59, and this feature varies the valve timing for the air intake valves (not shown) according to the operational state of the engine.

[0047] As is shown in Figures 4 and 5, this cam phase angle variation apparatus is composed of a hydraulic actuation means including a valve means such as a solenoid valve 81 controlling the oil pressure, an oil transfer unit 82 which is an oil passage to supply oil from the solenoid valve, an operating control device 84 which applies oil pressure to vary the phase angle of the camshaft 38 and cam sprocket 41, and a cover member 83 that covers the front of the operating control device 84.

[0048] Further, the solenoid valve 81, the oil transfer unit 82 and the cover 83 are pre-assembled into a single unit prior to the installation of the cam phase angle variation apparatus on the engine, and the operating control device 84, which utilizes the oil pressure to vary the phase angle of the cam shaft 38 and the cam sprocket 41, is attached to the front end of the camshaft 38 by a bolt 85.

[0049] The attachment area on the engine unit 1 for the mounting of a cam phase angle variation apparatus such as previously described is accomplished by an attachment bracket 70 that is rigidly fastened by bolts 74 from above through to the front end wall 3c of the cylinder head 3, which covers the front of the chain chamber 3b that is formed in the space where the timing chain 43 is located in the cylinder head, thereby creating an opening 71 on the front face of the engine unit 1 which is of adequate diameter to allow the operating control device 84 of the cam phase angle variation apparatus 8 to pass through.

[0050] To wit, as shown in Figure 6, a semi-circular indent area 3d is present on the front end wall 3c of the cylinder head just under the mating surface with the attachment bracket 70, while an upper semicircular area 70a is formed in the attachment bracket 70 above its mating surface with the front end wall 3c. The attachment bracket is affixed to the top surface of the front end wall 3c to form the opening 71, which is of adequate diameter to allow the operating control device 84 of the cam phase angle variation apparatus 8 to pass through.

[0051] The operating control device 84 of this cam phase angle variation apparatus 8 passes through this opening 71 and is attached to the front end of the camshaft 38 by a bolt 85. Then, the assembly of the solenoid valve 81, of oil transfer unit 82 and the cover 83 is positioned in front of the opening 71, and next, with the indent 84a located in front of the bolt 85 of the operating control unit 84 connected to the rearward projecting area 82a of the oil transfer unit 82, the bolts are tightened on the cover member 83, thereby affixing it to the attachment areas 75 on the front end wall of the cylinder head 3 and the attachment bracket 70, and thereby achieving attachment of the cam phase angle variation apparatus, including the solenoid valve 81, to the front face of the engine unit 1.

[0052] At this time, as shown in Figure 6, a connection hole 61a in the front face of the cylinder head 3 connects the solenoid valve 81 to oil passage 61 for its oil supply, and a drain hole 73 drains the oil expelled from the solenoid valve 81, so that by attaching the foregoing unit, as shown in Figure 4, the connections are made to the oil inlet opening 81a and the oil drain opening 81b for the solenoid valve 81.

[0053] In order to supply oil to the connection hole 61a in the front face of the cylinder head 3 for the solenoid 81, as shown in Figure 3, the oil drawn up from the oil pan 6 by the oil pump 52 passes through the oil cooler 9 and then to the main hole 58; and a branch oil passage 60 present in the cylinder head 3 that continues the oil passage 59 from the main hole 58 supplies the oil to the cylinder head 3.

[0054] In other words an oil passage 60 connects with the oil passage 59 in the cylinder block, and, as shown in Figures 7 and 9, it comprises branches, namely an oil passage 61 which supplies oil to the solenoid valve 81 and oil passage 62 which supplies oil to lubricate the camshafts 38, 39. The end 61a of the oil passage 61 supplying oil to the solenoid valve terminates in the front face of the front end wall of the cylinder head 3 where the opening to the solenoid valve 81 is located.

[0055] On the other hand, as shown in Figure 8, the oil passage 62 for lubricating the cam shafts branches into constricted branches 63, 64 which open at the bearings 3e, 3f of the camshafts 38, 39. These constrictions 63, 64 allow the provision of an appropriate amount of oil to the bearings 3e, 3f of the camshafts 38, 39.

[0056] As shown in Figures 5 and 7, 91 represents the head bolt holes, 92 the cam cap bolt holes, and 93 the spark plug holes.

[0057] The above described mounting embodiment of a cam phase angle variation apparatus 8 on an engine is implemented by the end wall 3c of the cylinder head 3 and an attachment bracket 70, whereby the cam phase angle variation apparatus, including the solenoid valve 81, can be very durably attached to the engine unit 1, while greatly reducing the number of parts over those conventionally required for the mounting of the cam phase angle variation apparatus 8.

[0058] Further, the assembly composed of the solenoid valve 81, the oil transfer unit 82 and the cover 83 is connected to the operating control device 84 and the oil transfer unit 82 through the opening 71, so that the mere mounting of the unit to the front wall 3c of the cylinder head and the attachment bracket 70 allows mounting the entire cam phase angle variation apparatus 8, including the solenoid valve 81, to be vastly simplified because it is possible to assemble the solenoid and the oil transfer unit to the operating control device 84 attached to the front end of the camshaft 38.

[0059] Further, because of the openings for the oil passage 61 to the solenoid valve 81 and drain hole 73 in the front end wall 3c of the cylinder head where the solenoid valve 81 is mounted, merely affixing the unit, including the solenoid valve 81, to the front face of the engine, connects the oil inlet opening 81a of the solenoid valve 81 with the oil passage 61 in the cylinder head 3, and, connects the oil outlet 81b of the solenoid valve 81 with the oil drain hole 73.

[0060] Further, the oil passage 60 in the cylinder head 3 connects with the oil passage 59 in the cylinder block 4, and midway, it branches the oil passage 61 to the solenoid valve and oil passage 62 that supplies lubrication for the camshafts. Because of the constricted areas 63, 64 in the branch passage 62 for the camshafts, it is possible to supply appropriate amounts of oil to the bearing areas 3e, 3f of the camshafts 38, 38 and to the solenoid valve 81 without the need for two separate oil passage systems in the cylinder head, thereby reducing the number of oil passages required in the cylinder head.

[0061] As has been explained above, the mounting structure for cam phase angle variation apparatus to engines in this invention enables reduction in the number of parts required for mounting the entire apparatus to the engine and simplifies the mounting operation to reduce costs.

[0062] Further, the structure specified in the foregoing allows high durability mounting of the cam phase angle variation apparatus by an attachment bracket; furthermore, the connection between the solenoid valve and the oil passage in the cylinder head is simplified; moreover, the number of oil passages present in the cylinder head can be reduced; according to the structure described in the foregoing the connection between the solenoid valve and the oil drain hole is simplified; and all the above simplify the assembly or machining operations to bring costs down.

Claims

1. Internal combustion engine comprising an engine block including a cylinder head unit (2, 3) attached to a cylinder block (4), a valve actuating mechanism including at least one camshaft (38, 39) rotatably supported in said cylinder head unit, a camshaft drive mechanism (43, 45, 46, 47, 48) including a cam sprocket (41) associated to the camshaft (38), and a cam phase variation apparatus (8) for varying the angular relation between said camshaft (38) and cam sprocket (41), said cam phase variation apparatus including an operating mechanism (84) mounted on the camshaft (38) and a hydraulic actuation means (81, 82) connected with said operating mechanism,
characterized in that
said hydraulic actuation means (81, 82) forms a preassembled unit attached to the engine block (2, 3, 4) from the outside.

2. Internal combustion engine according to claim 1, characterized in that said hydraulic actuation means (81, 82) is disposed and attached to the cylinder head unit (2, 3) substantially opposite to one end of the camshaft (38).

3. Internal combustion engine according to claim 1 or 2, characterized in that said hydraulic actuation means includes a valve means (81) and a fluid transfer unit (82) comprising at least one fluid passage.

4. Internal combustion engine according to claim 3, characterized in that said hydraulic transfer unit (82) comprises a projecting portion (82a) which extends through an opening (71) formed in a cylinder head wall (3c) of the cylinder head unit (3) facing the end of the camshaft (38) and surrounding said projecting portion (82a), said projecting portion (82a) being in connection with said operating mechanism (84).

5. Internal combustion engine according to claim 3 or 4, characterized in that said hydraulic actuation means comprises a cover member (83) pre-assembled with said valve means (81) and said fluid transfer unit (82), said cover member covering said opening (71) with said projecting portion (82a) extending therethrough.

6. Internal combustion engine according to at least one of claims 1 to 5, characterized in that an attachment bracket (70) is provided for attaching the hydraulic actuation means (81, 82), said attachment bracket being attached to a top surface of the cylinder head unit (2, 3).

7. Internal combustion engine according to at least one of claims 1 to 6, characterized in that a fluid passage arrangement (59, 60, 61) is provided for supplying pressurized fluid to the hydraulic actuation means (81, 82) from a fluid pump (52).

8. Internal combustion engine according to claim 7, characterized in that the said fluid passage arrangement (59, 60) forms part of the camshaft lubrication system.

9. Internal combustion engine according to claim 7 or 8, characterized in that said fluid passage arrangement comprises a fluid passage (61) formed in the cylinder head unit (3) and communicated with an opening (61a) in a cylinder head wall (3c) of the cylinder head unit (3), said opening (61a) being connected to the valve means (81) located in front of said cylinder head wall (3c) opposite to said opening (61a).

10. Internal combustion engine according to at least one of claims 3 to 9, characterized in that a drainage hole (73) is provided in said cylinder head wall (3c) of the cylinder head unit (3) and is communicated with a drainage passage, said drainage hole being connected with the said valve means (81) which is located in front of said drainage hole (73).

11. Internal combustion engine according to at least one of claims 7 to 10, characterized in that the fluid passage arrangement comprises a fluid passage (59) formed in the cylinder block (4) and communicated with the fluid passage (60) formed in the cylinder head unit (3) and with the said fluid pump (52).

12. Internal combustion engine according to at least one of claims 7 to 11, characterized in that said fluid passage arrangement comprises a branch passage (62, 63, 64) communicated with camshaft bearings, and said pressurized fluid is a lubricant.

13. Internal combustion engine according to claim 12, characterized in that said branch passage (62) and the fluid passage (61) communicated with the valve means (81) are communicated with a common fluid supply passage (60) formed in the cylinder head unit (3).

14. Internal combustion engine according to at least one of claims 1 to 13, characterized in that said camshaft drive mechanism includes an intermediate shaft (46) rotatably supported in the cylinder head unit (3), said intermediate shaft being coupled to the camshaft (38) via a transmission means (43) for driving said camshaft (38).

15. Internal combustion engine according to at least one of claims 1 to 14, characterized in that said valve actuating mechanism comprises an intake camshaft (38) and an exhaust camshaft (39) which are rotatably supported in said cylinder head unit (3) for actuating three intake valves and a pair of exhaust valves per cylinder, said cam phase variation apparatus (8) being associated with said intake camshaft (38).

Drawing