Oil supply mechanism for internal combustion engine

Abstract

 An oil supply mechanism for an internal combustion engine (1) is provided. The oil supply mechanism includes a cylinder head (3) that is fixed to an upper portion of a cylinder block (2) and has a valve chamber (9) therein. A sidewall of the cylinder head has an oil removing hole (41, 42, 51) through which oil is supplied from the valve chamber to a timing chain (22) provided on the side of the cylinder head. The oil removing hole communicates with the valve chamber, and the shape of the oil removing hole changes in the vertical direction.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] This invention relates to an oil supply mechanism for an internal combustion engine, in particular, an oil supply mechanism for an internal combustion engine having an oil removing (dropping) hole that supplies oil from a valve chamber in a cylinder head to a timing chain.

2. Description of the Related Art

[0002] Generally, a cylinder head is fixed to an upper portion of a cylinder block of an internal combustion engine. In the cylinder head, a valve chamber that accommodates an intake camshaft and an exhaust camshaft is provided. Oil stored in an oil pan is supplied to the valve chamber via an oil pump or an oil supply passage to lubricate the intake camshaft and the exhaust camshaft.

[0003] Further, a belt chain is provided at the side of the cylinder block and cylinder head. The belt chain is wound around a sprocket provided at an end portion of a crankshaft, a sprocket provided at an end portion of the intake camshaft and a sprocket provided at an end portion of the exhaust camshaft. Therefore, the rotation of the crankshaft is transmitted to the intake camshaft and the exhaust camshaft.

[0004] Further, oil that lubricates the intake camshaft and the exhaust camshaft falls into the valve chamber, and then is supplied to the timing chain through an oil removing hole provided in a sidewall of the cylinder head. Then, after the oil lubricates the timing chain, the oil flows back to the oil pan provided below the cylinder block (see, for example, Japanese patent application publication 2000-97103 (JP-A-2000-97103)).

[0005] In the above-described oil supply mechanism for an internal combustion engine, however, because an opening area of the oil removing hole is large, the oil supplied to the timing chain through the oil removing hole causes a large friction with the timing chain. Therefore, drive loss of the timing chain may occur.

[0006] More specifically, if the opening area of the oil removing hole is reduced, the amount of oil supplied from the valve chamber to the timing chain through the oil removing oil hole is also reduced. However, a sufficient amount of oil to flow back to the oil pan through the oil removing hole must be secured in all operation regions, i.e., from a low engine speed to a high engine speed.

[0007] In particular, because the oil pump rotates in proportion to the rotation speed of the crankshaft, the amount of oil supplied to the valve chamber increases in an engine high speed operation region. Therefore, efficient oil return must be secured when an excessive amount of oil is supplied.

[0008] If the opening area of the oil removing hole is reduced, generation of timing chain drive loss is minimized by reducing the amount of oil to be retuned to the oil pan. However, in reality, it is difficult to reduce the opening area of the oil removing hole, because efficient oil return must be secured when the oil is excessively supplied.

[0009] Thus, with relatively large opening area of the oil removing hole, because the amount of oil that is supplied to the valve chamber and returns to the oil pan increases during the period of the engine low speed operation region and engine middle speed operation region, the oil causes a large friction with the timing chain and timing chain drive loss is generated. The generation of timing chain drive loss may deteriorate fuel efficiency.

SUMMARY OF THE INVENTION

[0010] The present invention provides an oil supply mechanism for an internal combustion engine that prevents increase in timing chain drive loss caused by the oil supplied to the timing chain, and secures sufficient oil return.

[0011] A first aspect of the present invention provides an oil supply mechanism for an internal combustion engine that includes a cylinder head that is fixed to an upper portion of a cylinder block and has a valve chamber therein. A sidewall of the cylinder head has an oil removing hole through which oil is supplied from the valve chamber to a timing chain provided on the side of the cylinder head. The oil removing hole communicates with the valve chamber and the shape of the oil removing hole changes along the vertical direction.

[0012] According to the aspect of the present invention, when the volume of oil supplied to the valve chamber is relatively small, i.e., for example, when the internal combustion engine is in a low or middle speed operation region, oil is supplied to the timing chain only through the lower portion of the oil removing hole, rather than through the entire oil removing hole. Accordingly, oil is prevented from being supplied to the timing chain more than necessary, and the drive loss of the timing chain is prevented from being increased. As a result, decrease in the fuel efficiency can be prevented.

[0013] Further, when a large volume of oil is supplied to the valve chamber, i.e., for example, when the internal combustion engine is in a high speed operation region, oil can return to an oil pan from the entire oil removing hole. Therefore, a large volume of oil can be returned from the oil removing hole to the oil pan while the timing chain is lubricated. Thus, efficient oil return can be secured.

[0014] Thus, the valve chamber is prevented from being filled with the oil excessively supplied to the valve chamber. Therefore, the oil level is prevented from exceeding the opening end of the PCV passage, which communicates between the cylinder head and the intake passage, on the side of the cylinder head, and thus oil is prevented from flowing into the PCV passage 43.

[0015] The oil removing hole may include more than one opening portions that are formed at different positions in the vertical direction.

[0016] According to this construction, when the internal combustion engine is in the low or middle operation region and the volume of oil supplied to the valve chamber is relatively low, oil is supplied to the timing chain through the opening portion located at the lower position, rather than through the entire oil removing hole. Therefore, oil is prevented from being supplied to the timing chain more than necessary, and the drive loss of the timing chain is prevented from being increased.

[0017] Furthermore, when the engine is in a high speed operation region and a large volume of oil is supplied to the valve chamber, oil can be returned to the oil pan from the entire opening portion. Thus, a large volume of oil can return to the oil pan through the oil removing hole while the timing chain is lubricated. Thus, efficient oil return can be secured.

[0018] An upper-most opening portion among the opening portions may be positioned directly above the timing chain.

[0019] According to this construction, when the engine is in a high speed operation region and a large volume of oil must be supplied to the timing chain to lubricate the timing chain, oil is supplied from the opening portion located at higher position as well as the opening portion located at lower position. At this time, because the upper opening located directly above the timing chain, oil is effectively supplied to the timing chain to lubricate the timing chain.

[0020] The oil removing hole may be a single opening portion in which an opening area of a lower portion is smaller than an opening area of an upper portion.

[0021] According to this construction, when the internal combustion engine is in a low or middle speed operation region and the volume of oil supplied to the valve chamber is relatively small, oil is supplied to the timing chain from the lower portion of the single opening portion, rather than the entire oil removing hole. Therefore, oil is prevented from being supplied to the timing chain more than necessary, and the drive loss of the timing chain is prevented from being increased.

[0022] Furthermore, when the engine is in a high speed operation region and a large volume of oil is supplied to the valve chamber, oil can return to the oil pan through the entire opening portion. Thus, a large volume of oil can be retuned to the oil pan through the oil removing hole while the timing chain is lubricated. Thus, efficient oil return can be secured.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG.1 is an exploded view of an internal combustion engine illustrating an oil supply mechanism for the internal combustion engine according to a first embodiment of the present invention;

FIG.2 is a cross-sectional view of the internal combustion engine in the vicinity of a timing chain to illustrate the oil supply mechanism for the internal combustion engine according to the first embodiment of the present invention;

FIG.3 is an exploded view of a cylinder head gasket, a cylinder head, a cam housing, a cylinder head cover gasket and a cylinder head cover to illustrate the oil supply mechanism for the internal combustion engine according to the first embodiment of the present invention;

FIG 4 is a view illustrating paths through which lubricating oil flows in the oil supply mechanism for the internal combustion engine according to the first embodiment of the present invention;

FIG 5 is an elevation view of the timing chain and the cylinder head viewed from a front side of the internal combustion engine to illustrate the oil supply mechanism for the internal combustion engine according to the first embodiment of the present invention; and

FIG 6 is an elevation view of a timing chain and a cylinder head viewed from a front side of the internal combustion engine to illustrate an oil supply mechanism for the internal combustion engine according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0024] An oil supply mechanism for an internal combustion engine according to embodiments of the present invention will be described hereinafter with reference to drawings.

[0025] FIGs. 1 to 5 show an oil supply mechanism for an internal combustion engine according to a first embodiment of the present invention. A construction thereof will be explained first. In FIGs. 1 and 2, an engine 1, served as an internal combustion engine, includes an cylinder block 2, a cylinder head 3 that is fixed to an upper portion of the cylinder block 2, a crank case 4 that is fixed to a lower portion of the cylinder block 2, and an oil pan 5 that is fixed to a lower portion of the crank case 4.

[0026] A cam housing 6 is fixed to an upper portion of the cylinder head 3. As shown in FIG 4, an intake camshaft 7 having an intake cam 7a and an exhaust camshaft 8 having an exhaust cam 8a are rotatably supported by the cam housing 6.

[0027] As shown in FIG. 3, a valve chamber 9 is provided in the cylinder head 3. As described later, oil that has been lubricated the intake camshaft 7 and the exhaust camshaft 8 falls in the valve chamber 9. The bottom surface 9a of the valve chamber 9 in the cylinder head 3 extends substantially horizontally.

[0028] As shown in FIG 3, a cylinder head cover 11 is fixed to the cam housing 6 via a cylinder head cover gasket 10, and the cylinder head 3 is fixed to the cylinder block 2 via the cylinder head gasket 12.

[0029] A shower pipe 13 (see FIG. 4) is provided in the cam housing 6 and the cylinder head cover 11. The shower pipe 13 delivers oil by drops onto the intake camshaft 7 and the exhaust camshaft 8.

[0030] Cylinder bores (not shown) are formed in the cylinder block 2. A piston 14 (see FIG 4) is slidably provided in each of the cylinder bore. Intake ports that communicate with an intake passage (not shown) and exhaust ports that communicate with an exhaust passage (not shown) are provided in the cylinder head 3. The cylinder head 3 has an intake valve 15 that opens and closes each intake port to communicate and discommunicate between the intake pipe and the cylinder bore, and an exhaust valve 16 that opens and closes the exhaust port to communicate and discommunicate between the exhaust pipe and the cylinder bore (see FIG. 4).

[0031] A rocker arm 32 is disposed between the intake valve 15 and the intake camshaft 7. The rocker arm 32 swings along with the rotation of the intake camshaft 7 to open and close the intake valve 15.

[0032] A rocker arm (not shown) is disposed between the exhaust valve 16 and the exhaust camshaft 8. The rocker arm swings along with the rotation of the exhaust camshaft 8 to open and close the exhaust valve 16.

[0033] A crankshaft 17 is disposed in the crank case 4. A camshaft drive mechanism 18 is disposed between the crankshaft 17 and the intake camshaft 7 and exhaust camshaft 8. The rotation of the crankshaft 17 is transmitted to the intake camshaft 7 and the exhaust camshaft 8 via the camshaft drive mechanism 18, thereby driving the rotation of the intake camshaft 7 and the exhaust camshaft 8.

[0034] The camshaft drive mechanism 18 includes a crank sprocket 19, an intake cam sprocket 20, an exhaust cam sprocket 21 and a timing chain 22. The crank sprocket 19 is connected to an axial end of the crankshaft 17. The intake cam sprocket 20 is connected to an axial end of the intake camshaft 7 in the cylinder head 3. The exhaust cam sprocket 21 is connected to an axial end of the exhaust camshaft 8 in the cylinder block 3. The timing chain 22 is wound around the crank sprocket 19, the intake cam sprocket 20 and the exhaust cam sprocket 21, and transmits the rotation of the crank sprocket 19 to the intake cam sprocket 20 and the exhaust cam sprocket 21 to rotate them.

[0035] The timing chain 22 is disposed at the front surface (side surface) of the cylinder block 2, crank case 4 and cylinder head 3. Note that in this embodiment, the side at which the camshaft drive mechanism 18 is disposed is the front side of the vehicle.

[0036] In the camshaft drive mechanism 18, there is a large vertical distance between the crank sprocket 19 and the intake cam sprocket 20 and exhaust cam sprocket 21, because the intake camshaft 7 and the exhaust camshaft 8 are disposed in the cylinder head 3 located above the cylinder block 2, and the crankshaft 17 is disposed in the crank case 4 located below the cylinder block 2.

[0037] An oil pump mechanism 24 that drives the rotation of the oil pump 23 using the crankshaft 17 is provided below the camshaft drive mechanism 18. The oil pump drive mechanism 24 includes a crank sprocket 25, an oil pump sprocket 26 and an oil pump drive chain 27. The crank sprocket 25 is connected to the crankshaft 17, and is located closer to the crank case 4 than the crank sprocket 19. Thus, in FIG 2, crank sprocket 25 is on the right side (in FIG. 2) of the crank sprocket 19. The oil pump sprocket 26 is connected to an axial end of the rotating shaft of the oil pump 23. The oil pump drive chain 27 is wound around the crank sprocket 25 and the oil pump sprocket 26, and transmits the rotation of the crank sprocket 19 to the oil pump sprocket 26 to rotate it.

[0038] The camshaft drive mechanism 18 and the oil pump drive mechanism 24 are covered by a timing chain cover 28 from the outside and is accommodated therein. The timing chain cover 28 is made of aluminum alloy and is attached on the front side of the cylinder head 3, cylinder block 2 and crank case 4, that is, attached on one side in the axial direction thereof.

[0039] A chain tensioner device 29 is provided between the crank sprocket 19 and the exhaust cam sprocket 21. The chain tensioner device 29 adjusts the tensile force of the timing chain 22 at a portion suspended between the crank sprocket 19 and the exhaust cam sprocket 21 under tension. Further, a chain guide 30 is provided between the intake cam sprocket 20 and the crank sprocket 19. The chain guide 30 slidably contacts a portion of the timing chain 22 suspended between the intake cam sprocket 20 and the crank sprocket 19 under tension to guide the timing chain 22. In this case, one axial end of the crankshaft 17 protrudes outside the timing chain cover 28, and a crank pulley 31 is connected to the axial end of the crankshaft 17.

[0040] Further, an oil passage (not shown) is formed in the intake camshaft 7 and the exhaust camshaft 8. The oil passage extends along the axial direction of the intake camshaft 7 and the exhaust camshaft 8.

[0041] An oil passage is formed in the cylinder block 2 and the cylinder head 3 extending in a vertical direction. Oil pumped from the oil pan 5 by the oil pump 23 passes through the oil passage in the cylinder block 2 and the cylinder head 3 and is supplied to the oil passage in the intake camshaft 7 and the exhaust camshaft 8.

[0042] As shown in FIG 5, an opening portion 41 and an opening portion 42, which are served as oil removing holes, are formed in a sidewall 3a on the front side of the cylinder head 3. The opening portion 41 and the opening portion 42 communicate with the valve chamber 9, and discharge or remove the oil dropped or fallen into the valve chamber 9 from the valve chamber 9 to supply the oil to the timing chain 22. The oil returns to the oil pan 5 through the space formed between the cylinder block 2 and crank case 4 and the timing chain cover 28.

[0043] As shown in FIG. 2, the bottom surface 9a of the valve chamber 9 is formed of a first bottom surface 9b and a second bottom surface 9c. The second bottom surface 9c is positioned on the front side of the cylinder head 3 and is lower than the first bottom surface 9b.

[0044] The opening portion 41 has a circular shape and at least a portion of the first opening portion 41 is located above the first bottom surface 9b. The lower end of the first opening portion 41 is below the first bottom surface 9b and above the second bottom surface 9c. The opening portion 42 has a generally rectangular shape having an area larger than the opening portion 41. The center portion of the opening portion 42 in the vertical direction is located at the first bottom surface 9b. The lower end of the opening portion 42 is located below the second bottom surface 9c. The opening portion 41 located higher than the opening portion 42 is located directly above the timing chain 22.

[0045] The total opening area of the first opening portion 41 and the second opening portion 42 is set such that, when the engine 1 is in a high speed operation region and oil is excessively supplied to the valve chamber 9 to lubricate the intake camshaft 7 and the exhaust camshaft 8, a sufficient amount of oil can return to the oil pan 5 without staying in the valve chamber 9.

[0046] An end of a blowby gas recirculation passage (hereinafter, referred to as a "PCV passage") 43 is attached at the upper portion of the cylinder head 3. The other end of the PCV passage 43 is attached to an intake manifold (not shown). The PCV passage 43 is known as a passage that conducts the gas blowing through the gap between the cylinder and the piston 14 of the engine 1 to the engine 1 through the intake manifold to combust the gas again.

[0047] The action or effect of the above construction will be described below. As shown in FIG 4, oil stored in the oil pan 5 is pumped up by the oil pump 23 in the direction shown by arrows, and is supplied to components to be lubricated, such as the crankshaft 17, the piston 14, the intake camshaft 7 and the exhaust camshaft 8. Oil is also supplied to the intake cam 7a, the exhaust cam 8a and the rocker arm 32 via the shower pipe 13.

[0048] Further, the oil supplied to the intake camshaft 7, exhaust camshaft 8, intake cam 7a, exhaust cam 8a and the rocker arm 32 falls on the bottom surface 9a of the valve chamber 9 and is stored in the valve chamber 9.

[0049] Here, when the speed of the engine 1 is in a low speed operation region or in a middle speed operation region, because the volume of oil supplied to the valve chamber 9 is relatively small, the oil fallen on the bottom surface 9a of the valve chamber 9 moves from the first bottom surface 9b to the second bottom surface 9c and is discharged from the opening portion 42. The oil discharged from the opening portion 42 lubricates the timing chain 22, the chain tensioner device 29 and the chain guide 30, and then returns to the oil pan 5. At this time, because the volume of oil supplied to the valve chamber 9 is relatively small, even if the oil returns to the oil pan 5 only through the opening portion 42, oil return efficiency is not much affected thereby.

[0050] When the speed of the engine 1 is in a high speed operation region, because a large volume of oil is supplied to the valve chamber 9, the oil fallen on the bottom surface 9a of the valve chamber 9 moves from the first bottom surface 9b to the second bottom surface 9c, and is discharged from both the opening portion 41 and the opening portion 42.

[0051] The oil discharged from the opening portion 41 and the opening portion 42 lubricates the timing chain 22, the chain tensioner device 29 and the chain guide 30, and then returns to the oil pan 5. Further, because the opening portion 42 is formed directly or immediately above the timing chain 22, the oil discharged from the opening portion 42 is supplied immediately and directly to the timing chain 22.

[0052] As described above, according to this embodiment, the opening portion 41 and the opening portion 42, which have opening areas different from each other, are formed as oil removing holes in the sidewall of the cylinder head 3. The opening portion 41 having a smaller opening area is disposed at a higher position than the opening portion 42 having a greater opening area. Therefore, when the volume of oil supplied to the valve chamber 9 is relatively small, oil can be supplied to the timing chain 22 from the opening portion 42 positioned at a lower place.

[0053] Accordingly, oil is prevented from being excessively supplied to the timing chain 22, and the drive loss of the timing chain 22 is prevented from being increased. As a result, the deterioration in fuel efficiency is prevented.

[0054] When a large volume of oil is supplied to the valve chamber 9, because oil returns to the oil pan 5 through both the opening portion 41 and the opening portion 42, a large volume of oil can be used to lubricate the timing chain 22 and can return to the oil pan 5. Thus, efficient oil return can be secured.

[0055] In particular, in this embodiment, the total opening area of the opening portion 41 and the opening portion 42 is set such that, when oil is excessively supplied to the valve chamber 9 to lubricate the intake camshaft 7 and the exhaust camshaft 8, a sufficient volume of oil can return to the oil pan 5 without staying in the valve chamber 9. Thus, sufficient oil return is secured.

[0056] Further, the valve chamber 9 is prevented from being filled with the oil excessively supplied to the valve chamber 9. Therefore, the oil level is prevented from exceeding the height (level) of the opening end of the PCV passage 43 on the side of the cylinder head 3, and oil is prevented from flowing into the PCV passage 43.

[0057] In the above-described embodiment, because the opening portion 41, which is disposed at a higher position, is located directly above the timing chain 22, when a large volume of oil returns to the oil pan 5 and a large volume of oil is required to lubricate the timing chain 22, oil is effectively supplied to the timing chain 22 from the opening portion 41 to lubricate the timing chain 22.

[0058] Further, when a large volume of oil is supplied to the valve chamber 9 in a high speed operation region of the internal combustion engine, oil can return to the oil pan 5 through both the opening portion 41 and the opening portion 42. Thus, while the timing chain 22 is lubricated, a large volume of oil can return to the oil pan 5 from both the opening portion 41 and the opening portion 42. Therefore, efficient oil return can be secured.

[0059] As a result, the valve chamber 9 is prevented from being excessively filled with oil that is excessively supplied to the valve chamber 9. For example, oil level is prevented from exceeding the opening end of the PCV passage 43, which communicates between the cylinder head 3 and the intake passage, on the side of the cylinder head, and the oil is prevented from flowing into the PCT passage.

[0060] Further, the total opening area of the opening portion 41 and opening portion 42 is set such that, when the engine 1 is in a high speed operation region and the oil is excessively supplied to the valve chamber 9 to lubricate the intake camshaft 7 and the exhaust camshaft 8, the oil can return to the oil pan 5 without staying in the valve chamber 9. Accordingly, when the engine 1 is in a high speed operation region, sufficient oil return can be secured.

[0061] FIG. 6 is an oil supply mechanism for an internal combustion engine according to a second embodiment of the present invention. The elements same as those in the first embodiment are denoted by the same reference numerals, and detailed explanation thereof will be omitted. In FIG 6, an inverted triangular opening portion 51, which is served as an oil removing hole, is formed in the sidewall 3a of the cylinder head 3. Thus, the opening area or shape of the opening portion 51 changes in the vertical direction. In other words, the horizontal width of the opening 51 changes along its height. In this embodiment, the horizontal width of the opening 51 increases, as the position becomes higher.

[0062] In other words, the single opening portion 51 has an upper opening portion 51a and a lower opening portion 51b. The opening area of the upper opening portion 51a is greater than the opening area of the lower opening portion 51b. In addition, the lower end of the lower opening portion 51b is located below the second bottom surface 9c. Note that the upper opening portion 51a and the lower opening portion 51b are divided by the center of the opening portion 51 in the vertical direction. That is, the upper opening portion 51a is a portion located above the center of the opening portion 51 in the vertical direction, and the lower opening portion 51b is a portion located below the center of the opening portion 51 in the vertical direction.

[0063] The opening area of the opening portion 51 is set such that, when the engine 1 is in a high speed operation region and the oil is excessively supplied to the valve chamber 9 to lubricate the intake camshaft 7 and the exhaust camshaft 8, a sufficient volume of oil returns to the oil pan 5 without staying in the valve chamber 9.

[0064] In the second embodiment, when the volume of oil supplied to the valve chamber 9 is relatively small, the oil fallen on the bottom surface 9a moves from the first bottom surface 9b to the second bottom surface 9c and is discharged from the lower opening portion 51b. The oil discharged from the lower opening portion 51b lubricates the timing chain 22, the chain tensioner device 29 and the chain guide 30, and then returns to the oil pan 5. In this case, because the volume of oil supplied to the valve chamber 9 is relatively small, even if the oil returns to the oil pan 5 only through the lower opening portion 51b, oil return efficiency is not affected.

[0065] Further, when a large volume of oil is supplied to the valve chamber 9, the oil fallen on the bottom surface 9a is discharged from both the upper opening portion 51a and the lower opening portion 51b, i.e., from the whole area of the opening portion 51.

[0066] The oil discharged from the opening portion 51 lubricates the timing chain 22, the chain tensioner device 29 and the chain guide 30, and then returns to the oil pan 5.

[0067] As described above, according to the second embodiment, a single opening portion 51 is formed as an oil removing hole in the sidewall of the cylinder head 3. The opening area of the upper opening portion 51a located in a higher position is formed larger than the opening area of the lower opening portion 51b, which is located below the upper opening portion 51a. Therefore, when the volume of oil supplied to the valve chamber 9 is relatively small, the oil is supplied to the timing chain 22 only through the lower opening portion 51b.

[0068] Accordingly, oil is prevented from being supplied to the timing chain 22 more than necessary, and the drive loss of the timing chain 22 is prevented from being increased. As a result, deterioration in fuel efficiency is prevented. Further, when a large volume of oil is supplied to the valve chamber 9, oil can return to the oil pan from the whole area of the opening portion 51. Therefore, while the timing chain 22 is lubricated, a large volume of oil can return to the oil pan 5 through the opening portion 51. Thus, efficient oil return can be secured.

[0069] In particular, in this embodiment, the opening area of the opening portion 51 is set such that, when oil is excessively supplied to the valve chamber 9 to lubricate the intake camshaft 7 and the exhaust camshaft 8, a sufficient volume of oil can return to the oil pan 5 without staying in the valve chamber 9. Thus, sufficient oil return is secured.

[0070] In the first embodiment, two opening portions, i.e., the opening portion 41 and the opening portion 42 are formed at the different heights. In the second embodiment, a single inverted triangular opening portion 51 in which the lower opening area is smaller than the upper opening area is formed. However, more than two opening portions may be formed.

[0071] While some embodiments of the invention have been illustrated above, it is to be understood that the invention is not limited to details of the illustrated embodiments, but may be embodied with various changes, modifications or improvements, which may occur to those skilled in the art, without departing from the spirit and scope of the invention.

[0072] As described above, the oil supply mechanism for an internal combustion engine of the present invention can prevent the drive loss of the timing chain caused by the oil supplied to the timing chain from being increased, and sufficient oil return can be secured. Thus, the oil supply mechanism is useful when it is applied to an internal combustion engine having an oil removing hole to supply oil to a timing chain from a valve chamber in a cylinder head.

Claims

1. An oil supply mechanism for an internal combustion engine (1) that includes a cylinder head (3) that is fixed to an upper portion of a cylinder block (2) and has a valve chamber (9) therein, wherein a sidewall of the cylinder head has an oil removing hole (41, 42, 51) through which oil is supplied from the valve chamber to a timing chain (22) provided on the side of the cylinder head, characterized in that:

the oil removing hole communicates with the valve chamber, and the shape of the oil removing hole changes along the vertical direction.

2. The oil supply mechanism according to claim 1, wherein the oil removing hole (41, 42) includes more than one opening portions that are formed at different positions in the vertical direction.

3. The oil supply mechanism according to claim 2, wherein an upper-most opening portion (41) among the opening portions is positioned directly above the timing chain.

4. The oil supply mechanism according to claim 2 or 3, wherein a lower end of a lower-most opening portion (42) among the opening portions is positioned below a bottom surface (9a) of the valve chamber.

5. The oil supply mechanism according to claim 2 or 3, wherein the valve chamber has a first bottom surface (9b) and a second bottom surface (9c) that is positioned lower than the first bottom surface, and at least a portion of the upper-most opening portion (41) is positioned above the first bottom surface.

6. The oil supply mechanism according to claim 2 or 3, wherein the valve chamber has a first bottom surface and a second bottom surface that is positioned lower than the first bottom surface, and a lower end of an upper-most opening portion is located below the first bottom surface and above the second bottom surface.

7. The oil supply mechanism according to claim 2, wherein the opening area of the upper-most opening portion is smaller than the opening area of the lower-most opening portion.

8. The oil supply mechanism according to claim 1, wherein the oil removing hole (51) is a single opening portion in which the opening area of a lower portion is smaller than the opening area of the upper portion.

9. The oil supply mechanism according to claim 8, wherein the single opening portion is formed in an inverted triangle.

10. The oil supply mechanism according to claim 8 or 9, wherein a lower end of the single opening portion is positioned lower than the bottom surface (9a) of the valve chamber.

11. The oil supply mechanism according to claim 8 or 9, wherein the valve chamber has a first bottom surface and a second bottom surface that is positioned lower than the first bottom surface, and a lower end of the single opening portion is positioned below the second bottom surface and an upper end of the single opening portion is positioned above the first bottom surface.

Drawing