Engine oil passage structure

Abstract

To provide an oil passage structure capable of efficiently cooling oil when an engine is warm and suppressing cooling of the oil when the engine is cold.SOLUTION: An oil passage structure for an engine includes an exhaust side return passage 41 provided in an engine body 10 to return oil from a cylinder head 4 of the engine body 10 to an oil pan. The exhaust side return passage 41 includes: a main passage 44 formed in the vicinity of an exhaust port 16 of the cylinder head 4; and an auxiliary passage 45 formed to branch from the main passage 44 in the cylinder head 4. An upper opening part 45a of the auxiliary passage 45 is located on the upper side of an upper opening part 44a of the main passage 44, and the auxiliary passage 45 is disposed at a position near to a cooling part in the cylinder head 4 relative to the main passage 44.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The technology disclosed herein belongs to the technical field relating to oil passage structures of engines. [Background technology]

[0002] In recent years, there has been a trend toward using low-viscosity oils, which have a lower upper temperature limit than oils with normal viscosity, in order to improve engine fuel efficiency. However, because low-viscosity oils have reduced lubrication properties, when low-viscosity oils are used, it is necessary to actively cool the oil, especially when the engine is warm.

[0003] Patent document 1 discloses a structure in which the upper part of an oil return passage formed in a cylinder block is formed as an expanded section that widens to partially surround the water jacket, and multiple fins are formed on the inner surface of the expanded section that is located on the water jacket side.

[0004] Patent Document 2 also discloses an oil passage structure having a main passage that is formed substantially parallel to and below the cylinder axis and that connects the cylinder head and crankcase of an internal combustion engine, a first branch passage that branches from a lower part of the main passage toward the cylinder axis and opens into the crankcase, and a second branch passage that branches from an upper part of the main passage toward the cylinder axis and opens into the cylinder head. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-148227 [Patent Document 2] Patent No. 3741159 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the engine is cold, there is a demand to raise the oil temperature as much as possible in order to quickly warm up the engine. The configuration as disclosed in Patent Document 1 can actively cool the oil, but does not provide an advantageous effect in suppressing the cooling of the oil when the engine is cold.

[0007] In addition, in Patent Document 2, a branch passage is provided to ensure a passage for blow-by gas, but it is not intended for oil returning to the oil pan to flow through the branch passage, and therefore this branch passage does not contribute to cooling or heating the oil.

[0008] Therefore, there is room for improvement in achieving the conflicting requirements of efficiently cooling the oil when the engine is warm, while suppressing the cooling of the oil when the engine is cold.

[0009] The technology disclosed herein has been developed in consideration of these points, and its purpose is to provide an oil passage structure that can efficiently cool oil when the engine is warm, while suppressing oil cooling when the engine is cold. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, a first aspect of the technology disclosed herein is directed to an oil passage structure of an engine in which oil stored in an oil pan located below a cylinder block of an engine body is supplied by an oil pump to lubricated parts of a cylinder head, and then returned to the oil pan and circulated. The oil return passage is provided in the engine body for returning oil from the cylinder head of the engine body to the oil pan, and the oil return passage has a main passage formed near an exhaust port of the cylinder head and a secondary passage formed within the cylinder head by branching off from the main passage, and the main passage and the secondary passage each have upper openings that open upward within the cylinder head, the upper opening of the secondary passage being located higher than the upper opening of the main passage, and the secondary passage being located closer to a cooling part within the cylinder head than the main passage.

[0011] With this configuration, when the engine is cold and the amount of oil supplied is small, the oil level in the cylinder head is unlikely to reach the upper opening of the secondary passage, so the oil mainly flows through the primary passage. Because the primary passage is close to the exhaust port, the oil passing through the primary passage is warmed by exhaust heat. This suppresses oil cooling when the engine is cold. On the other hand, when the engine is warm, the amount of oil supplied increases, so the oil level in the cylinder head rises and reaches the upper opening of the secondary passage. Because the secondary passage is close to the cooling unit, the oil passing through the secondary passage is cooled by the cooling unit. This returns the cooled oil to the oil pan, actively cooling the oil. Therefore, it is possible to achieve both oil cooling when the engine is warm and suppression of oil cooling when the engine is cold.

[0012] A second aspect of the technology disclosed herein may be configured in the first aspect such that a flow path cross-sectional area of ​​the sub-passage is larger than a flow path cross-sectional area of ​​the main passage.

[0013] With this configuration, the flow rate of oil passing through the bypass passage can be increased as much as possible when the engine is warm, thereby enabling more active cooling of the oil when the engine is warm.

[0014] A third aspect of the technology disclosed herein may be configured such that, in the first or second aspect, the cylinder head is provided with a water jacket through which cooling water flows, the cooling portion is formed by the water jacket, and the sub-passage is adjacent to the water jacket.

[0015] With this configuration, the bypass passage is adjacent to the water jacket, and the wall of the bypass passage is cooled by the coolant flowing through the water jacket, which promotes heat dissipation from the oil and allows for more effective cooling of the oil when the engine is warm.

[0016] According to a fourth aspect of the technology disclosed herein, in the first aspect, the upper opening of the auxiliary passage may be located closer to the intake side than the upper opening of the main passage, and a guide portion may be provided within the cylinder head to guide oil, after it has been supplied to the lubricated parts located above the upper openings of the main passage and the auxiliary passage, to the intake side of the upper openings of the auxiliary passage.

[0017] This configuration allows lubricating oil supplied to the exhaust-side cam journal and other components to flow into the bypass passage. It also creates an oil flow from the intake side to the exhaust side, actively circulating the oil through the bypass passage. This allows for more efficient oil cooling when the engine is warm. [Effects of the Invention]

[0018] As described above, the technology disclosed herein makes it possible to efficiently cool oil when the engine is warm and efficiently heat oil when the engine is cold. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view showing an engine body having an oil passage structure according to an exemplary embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an oil supply passage of the engine. [Figure 3] FIG. 3 is a cross-sectional view showing an oil return passage of the engine. [Figure 4] FIG. 4 is a view of the middle deck of the cylinder head as seen from above. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is an enlarged perspective view showing the vicinity of the sub-passage. [Figure 7A] FIG. 7A is a graph showing the relationship between oil temperature and oil flow rate. [Figure 7B] FIG. 7B is a graph showing the relationship between the oil flow rate and the oil level in the cylinder head. [Figure 8] FIG. 8 is a time chart showing the oil temperature, the oil flow rate in the main passage, and the oil flow rate in the sub-passage. [Figure 9] FIG. 9 is a view equivalent to FIG. 5, showing a modified example of the sub-passage. DETAILED DESCRIPTION OF THE INVENTION

[0020] Exemplary embodiments will now be described in detail with reference to the drawings.

[0021] 1 shows an engine body 10 having an oil passage structure according to an embodiment. The engine body 10 is disposed in the engine compartment of an automobile. The engine body 10 includes a cylinder block 3, a cylinder head 4 disposed above the cylinder block 3, and an oil pan 30 disposed below the cylinder block 3.

[0022] The cylinder block 3 has a plurality of (four in this example) cylinders 2. The cylinders 2 are arranged side by side in the direction of the paper surface of FIG. 1 (hereinafter referred to as the cylinder row direction) with their cylinder axes parallel to one another. Pistons 5 are arranged reciprocatingly within the cylinders 2. The pistons 5 are connected via connecting rods 7 to a crankshaft 6, which is rotatably supported at the bottom of the cylinder block 3. The reciprocating motion of the pistons 5 within the cylinders 2 causes the crankshaft 6 to rotate. A combustion chamber 8 is formed by the upper surfaces of the pistons 5, the cylinders 2, and part of the cylinder head 4.

[0023] A block-side water jacket 11 through which cooling water flows is provided on the cylinder block 3. The block-side water jacket 11 is provided on the outer periphery of the cylinder 2 so as to surround the cylinder 2 and communicate with the cylinders in the cylinder row direction.

[0024] The cylinder head 4 is divided into upper and lower parts by a middle deck 4a, and has intake ports 15 and exhaust ports 16 below the middle deck 4a. Two intake ports 15 and two exhaust ports 16 are provided for each cylinder 2. The middle deck 4a is formed so as to be horizontal when the engine body 10 is placed in the engine room.

[0025] The cylinder head 4 is provided with an intake valve 15a for opening and closing the intake port 15, and an exhaust valve 16a for opening and closing the exhaust port 16. The cylinder head 4 also is provided with an intake camshaft 17 for opening and closing the intake valve 15a, and an exhaust camshaft 18 for opening and closing the exhaust valve 16a. The intake camshaft 17 and the exhaust camshaft 18 are each drivingly connected to the crankshaft 6. As a result, the intake valve 15a and the exhaust valve 16a open and close the intake port 15 and the exhaust port 16, respectively, in accordance with the rotation of the crankshaft 6.

[0026] The cylinder head 4 is provided with a head-side water jacket 19 (see FIG. 3 ) through which cooling water flows. The head-side water jacket 19 is formed in a portion between the intake port 15 and the exhaust port 16 and communicates in the cylinder row direction. The head-side water jacket 19 communicates with the block-side water jacket 11, and cooling water flows into the head-side water jacket 19 from the block-side water jacket 11. The head-side water jacket 19 constitutes a cooling section of the engine body 10.

[0027] The oil pan 30 stores oil for lubricating parts to be lubricated, such as the piston 5, the crankshaft 6, the intake camshaft 17, and the exhaust camshaft 18.

[0028] In this embodiment, as shown in FIG. 1, the engine body 10 is supported by the vehicle body frame and placed in the engine compartment with the cylinders 2 extending in a direction inclined toward the exhaust side.

[0029] 2 and 3, the engine body is provided with an oil passage that circulates oil that lubricates the parts to be lubricated (piston 5, crankshaft 6, intake camshaft 17, exhaust camshaft 18, etc.) within the engine body 10. The oil passage has an oil supply passage 21 that supplies oil to the parts to be lubricated, and an oil return passage 22 that returns the oil that has been supplied to the parts to be lubricated to the oil pan.

[0030] The oil supply passage 21 includes an oil pump 31 that draws up oil stored in an oil pan 30, an oil filter 32 that filters the oil discharged from the oil pump 31, an oil cooler 33 that cools the oil discharged from the oil pump 31, and an oil supply passage 35 provided in the engine body 10.

[0031] The supply oil passage 35 includes a first supply oil passage 36 provided on the oil pan 30 side, a second supply oil passage 37 provided in the cylinder block, a third supply oil passage 38 provided in the cylinder head 4, a first communicating oil passage 39 connecting the first supply oil passage 36 and the second supply oil passage 37, and a second communicating oil passage 40 connecting the second supply oil passage 37 and the third supply oil passage 38.

[0032] As shown in FIG. 2, the first oil supply passage 36 includes an oil passage provided within the oil pan 30 and connecting the oil pump 31 and the oil filter 32, and an oil passage provided adjacent to the exhaust side of the oil pan 30 and connecting the oil filter 32 and the oil cooler 33.

[0033] As shown in FIG. 2, the first communication oil passage 39 extends upward from the oil cooler 33 within the cylinder block 3, extends in a width direction perpendicular to both the vertical direction and the cylinder row direction, and then extends upward again.

[0034] The second oil supply passage 37 includes a main gallery 37a connected to the first communication oil passage 39 and extending in the cylinder row direction, a plurality of branch oil passages 37b branching from the main gallery 37a and extending downward to supply oil to lubricated parts of the crankshaft 6, and an oil passage 37c branching from one end of the main gallery 37a, extending in the width direction, and communicating with the second communication oil passage 40. The main gallery 37a is located on the exhaust side of the cylinder block 3 in the width direction perpendicular to the cylinder row direction of the cylinder block 3, near the lower end of the cylinder 2.

[0035] The second communication oil passage 40 extends upward from the end of the oil passage 37c on the main gallery 37a side. The second communication oil passage 40 has a lower portion provided in the cylinder block 3 and an upper portion provided in the cylinder head 4.

[0036] The third oil supply passage 38 includes an oil passage 38a extending from the upper end of the second communication oil passage 40 to both sides in the width direction, a pair of oil passages 38b extending upward from the exhaust side and the intake side of the oil passage 38a, and a head-side gallery 38c extending from the oil passage 38b in the cylinder row direction. The head-side gallery 38c includes a plurality of branched oil passages 38d formed to supply oil from the head-side gallery 38c to the cam journals of the intake camshaft 17 and the exhaust camshaft 18, etc.

[0037] Although not shown in the drawings, the oil supply passage 21 is configured to supply oil to an oil jet for cooling a piston, for example, in addition to the above-mentioned configuration.

[0038] The oil supplied to the lubricated parts of the engine body 10 is returned to the oil pan 30 through the oil return passage 22 after cooling and lubricating the lubricated parts.

[0039] 3, the oil return passage 22 includes multiple exhaust-side return passages 41 through which oil supplied to the intake camshaft 17 and the exhaust camshaft 18, which are lubricated parts, flows separately toward the exhaust port 16 and the intake port 15, and one intake-side return passage 51. The exhaust-side return passage 41 and the intake-side return passage 51 include head-side return passages 42, 52 provided in the cylinder head 4 and block-side return passages 43, 53 provided in the cylinder block 3. The configuration of the intake-side return passage 51 is the same as that of the exhaust-side return passage 41 except that it does not include a sub-passage 45, which will be described later. Therefore, the following description will focus on the exhaust-side return passage 41, and a detailed description of the intake-side return passage 51 will be omitted.

[0040] The head-side return passage 42 has a main passage 44 and a sub-passage 45. The main passage 44 will be described below, and the sub-passage 45 will be described later.

[0041] The main passage 44 has a generally circular cross section and extends in the vertical direction. A plurality of main passages 44 are provided on the exhaust side of the cylinder head 4 (see FIG. 4). The lower ends of the main passages 44 are connected to the block-side return passage 43. The main passages 44 are arranged between the cylinders 2 at positions offset from the cylinders 2 in the cylinder row direction. Specifically, the main passages 44 are arranged adjacent to the exhaust ports 16.

[0042] The upper opening 44a of the main passage 44 is provided in the middle deck 4a of the cylinder head 4. The main passage 44 is disposed adjacent to a bolt hole 61 into which a connecting bolt 60 (see FIG. 5) that connects the cylinder head 4 and the cylinder block 3 is fastened. The upper opening 44a of the main passage 44 is formed at a position lower than the upper end of the bolt hole 61.

[0043] The block-side return passage 43 is formed in a substantially circular shape and extends from the upper end to the lower end of the cylinder block 3. The lower end of the block-side return passage 43 opens into the oil pan 30.

[0044] When the engine starts operating, the oil pump 31 is driven in response to the rotation of the crankshaft 6. Then, as shown by the arrow in Figure 2, the oil pump 31 draws in oil stored in the oil pan 30 and supplies the drawn-in oil to parts to be lubricated in the engine body 10 via the first oil supply passage 36, the first communication oil passage 39, the second oil supply passage 37, the second communication oil passage 40, and the third oil supply passage 38 in that order.

[0045] The oil supplied to the parts to be lubricated lubricates the parts through the oil supply passage 21 and absorbs heat, such as frictional heat, generated when the parts to be lubricated operate. The oil supplied to the cylinder head 4 is stored in the cylinder head 4 and flows through the middle deck 4a into the head-side return passage 42. It is then returned to the oil pan 30 through the oil return passage 22.

[0046] In recent years, there has been a trend toward using low-viscosity oils, which have a lower upper temperature limit than oils with normal viscosities, in order to improve engine fuel economy. When using low-viscosity oils, it is necessary to actively cool the oil to prevent a decrease in lubrication, especially when the engine is warm. On the other hand, when the engine is cold, there is a demand to warm the oil as much as possible to raise the engine temperature.

[0047] Therefore, in this embodiment, a sub-passage 45 branching off from the main passage 44 is formed in the head-side return passage 42 .

[0048] 3 and 5, the bypass passage 45 branches off from the lower end of the main passage 44 and extends at an angle so that the upper end is positioned closer to the intake side. In this embodiment, the upper end of the bypass passage 45 is positioned closer to the intake side than the bolt head 60a of the connecting bolt 60. More specifically, the bypass passage 45 is disposed at the middle deck 4a of the cylinder head 4 so that the bolt head 60a is positioned between the main passage 44 and the bypass passage 45.

[0049] In this embodiment, the sub-passage 45 is formed by a pipe. As shown in Figures 5 and 6, a portion of the pipe that forms the sub-passage 45 is located inside the head-side water jacket 19. As a result, the sub-passage 45 is adjacent to the head-side water jacket 19 via the wall surface of the pipe, and is located closer to the head-side water jacket 19 than the main passage 44.

[0050] The sub-passage 45 is formed so that its flow path cross-sectional area is larger than the flow path cross-sectional area of ​​the main passage 44.

[0051] The upper opening 45a of the sub-passage 45 is located closer to the intake port than the upper opening 44a of the main passage 44. The upper opening 45a of the sub-passage 45 is located above the upper opening 44a of the main passage 44, and is provided at a height h above the upper surface of the middle deck 4a.

[0052] The height h of the upper opening 45a of the bypass passage 45 is set based on the oil flow rate when the engine body 10 has finished warming up. Specifically, first, the oil flow rate when the engine has finished warming up (hereinafter referred to as the specific flow rate OF) is calculated. As shown in FIG. 7, the oil flow rate is basically controlled to increase in proportion to the oil temperature (hereinafter referred to as the oil temperature). Since the oil temperature can be regarded as the temperature of the engine body 10, the temperature when the engine body 10 has finished warming up is regarded as the oil temperature when the engine body 10 has finished warming up (hereinafter referred to as the specific oil temperature OT), and the specific flow rate OF is calculated from a graph such as that shown in FIG. 7A. Next, the height of the oil level in the cylinder head 4 when the engine body 10 has finished warming up (height from the upper surface of the middle deck 4a, hereinafter referred to as the specific height OH) is calculated from the calculated specific flow rate OF. In this embodiment, the relationship between the oil flow rate and the height of the oil level in the cylinder head 4 is linear, as shown in FIG. 7B. From this, the specific height OH is calculated. This specific height OH is set to the height h of the upper opening 45a of the auxiliary passage 45. The specific height OH is set to, for example, 4 mm based on the specific oil temperature OT and the specific flow rate OF. If the set temperature of the specific oil temperature OT changes, the specific flow rate OF and the specific height OH also change accordingly.

[0053] Depending on the internal structure of the cylinder head 4, the relationship between the oil flow rate and the oil level in the cylinder head 4 may not be linear as shown in Figure 7B. In such cases, a graph showing the relationship between the oil flow rate and the oil level in the cylinder head 4 can be created separately and the specific height OH can be calculated.

[0054] In this way, by setting the height h of the upper opening 45a of the auxiliary passage 45 based on the height of the oil level when the engine body 10 has finished warming up, the oil is actively cooled when the engine is warm, and an increase in oil temperature can be suppressed. This will be explained with reference to FIG. 8.

[0055] 8 shows the relationship between oil temperature, the flow rate in the main passage 44, and the flow rate in the bypass passage 45. First, when the engine is cold and the oil temperature is low, the oil level does not reach the upper opening 45a of the bypass passage 45, so the oil does not flow into the bypass passage 45 but only into the main passage 44. Because the main passage 44 is adjacent to the exhaust port 16, the oil passing through the main passage 44 is warmed, and the oil temperature rises. Accordingly, the oil flow rate also increases.

[0056] When the oil temperature reaches the specific oil temperature OT, the oil flow rate reaches the specific flow rate OF, and the height of the oil surface from the middle deck 4a reaches the specific height OH, and the oil surface reaches the upper opening 45a of the sub-passage 45.

[0057] Then, when the oil temperature rises further, the oil flows into the bypass passage 45. Because the bypass passage 45 branches off from the main passage 44, when the oil flows into the bypass passage 45, the amount of oil flowing in from the main passage 44 decreases. By the oil flowing into the bypass passage 45, the oil is more easily cooled, and the rise in oil temperature is suppressed.

[0058] Thereafter, when the flow rate in the sub-passage 45 reaches a maximum, the oil temperature becomes substantially constant. The temperature at this time is lower than when the sub-passage 45 is not provided (shown by the two-dot chain line in FIG. 8).

[0059] In this way, by providing the sub-passage 45, it is possible to warm the oil when the engine is cold to quickly warm up the engine, and to suppress an increase in oil temperature when the engine is warm.

[0060] 4, if the upper opening 45a of the bypass passage 45 is located closer to the intake side than the upper opening 44a of the main passage 44, the upper opening 45a of the bypass passage 45 will be located farther from the exhaust camshaft 18 than the upper opening 44a of the main passage 44. Since the exhaust camshaft 18 is located above the upper openings 44a, 45a of the main passage 44 and the bypass passage 45, oil that has lubricated the exhaust camshaft 18 normally flows directly into the main passage 44 along the inner wall surface of the cylinder head 4. However, in order to actively cool the oil when the engine is warm, it is desirable to allow the oil that has lubricated the exhaust camshaft 18 to also pass through the bypass passage 45.

[0061] 4 and 5, the present embodiment provides a guide portion 46 that guides the oil, after it has been supplied to the exhaust camshaft 18 located above the upper openings 44a, 45a of the main passage 44 and the sub-passage 45, toward the intake side of the upper opening 45a of the sub-passage 45. Note that the guide portion 46 is omitted in FIG. 6.

[0062] A plurality of guide portions 46 are provided corresponding to the positions of the exhaust-side return passage 41. Each guide portion 46 has a receiving portion that receives oil and a transmission portion that directs the oil received by the receiving portion toward the intake side. Each receiving portion extends from the transmission portion in the axial direction of the exhaust camshaft 18 and is located directly below the cam journal of the exhaust camshaft 18. Each transmission portion passes directly above the secondary passage 45 and extends to a position on the intake side of the upper opening 45a of the secondary passage 45.

[0063] As a result, the oil after lubricating the exhaust camshaft 18 is received by the receiving portion, passes through the transmission portion, and is discharged to a position on the intake side of the upper opening 45a of the bypass passage 45. As a result, the oil after lubricating the exhaust camshaft 18 can also pass through the bypass passage 45 and be cooled.

[0064] Furthermore, by transmitting the oil that lubricates the exhaust camshaft 18 to the intake side using the guide portion 46, the amount of oil supplied to the intake side is greater than that to the exhaust side on the middle deck 4a. On the other hand, because there are more exhaust-side return passages 41 than there are intake-side return passages 51, more oil is discharged from the cylinder head 4 on the exhaust side than on the intake side. For this reason, providing the guide portion 46 causes an oil flow from the intake side to the exhaust side. This allows oil to actively flow into the sub-passage 45, which is located closer to the intake side (upstream of the flow) than the main passage 44, thereby actively cooling the oil.

[0065] 5 and 6, since the bolt head 60a of the connecting bolt 60 is located on the exhaust side of the upper opening 45a of the bypass passage 45, when oil flows from the intake side to the exhaust side, the bolt head 60a temporarily blocks the oil flow. This makes it easier for oil to flow through the bypass passage 45.

[0066] Therefore, in this embodiment, the engine body 10 is provided with an exhaust-side return passage 41 for returning oil from the cylinder head 4 of the engine body 10 to the oil pan 30, and the exhaust-side return passage 41 has a main passage 44 formed near the exhaust port 16 of the cylinder head 4 and a secondary passage 45 formed within the cylinder head 4 by branching off from the main passage 44, and the main passage 44 and the secondary passage 45 each have upper openings 44a, 45a that open upward within the cylinder head 4, and the upper opening 45a of the secondary passage 45 is located above the upper opening 44a of the main passage 44, and the secondary passage 45 is located closer to the head-side water jacket 19 within the cylinder head 4 than the main passage 44. As a result, when the engine is cold and the amount of oil supplied is small, the oil level in the cylinder head 4 is unlikely to reach the upper opening 45a of the secondary passage 45, so that the oil mainly flows through the main passage 44. Because the main passage 44 is close to the exhaust port 16, the oil passing through the main passage 44 is warmed by exhaust heat. As a result, oil cooling is suppressed when the engine is cold. On the other hand, when the engine is warm, the amount of oil supplied increases, causing the oil level in the cylinder head 4 to rise and reach the upper opening 45a of the secondary passage 45. Because the secondary passage 45 is close to the head-side water jacket 19, the oil passing through the secondary passage 45 is cooled by the head-side water jacket 19. As a result, the cooled oil is returned to the oil pan 30, so the oil is actively cooled. Therefore, it is possible to both cool the oil when the engine is warm and suppress cooling of the oil when the engine is cold.

[0067] In particular, in this embodiment, the height of the upper opening 45a of the sub-passage 45 from the middle deck 4a is set based on the height of the oil surface in the cylinder head 4 when the engine body 10 has finished warming up (when the oil temperature has reached the warm-up completion temperature). This allows the oil to be warmed efficiently when the engine is cold.

[0068] In this embodiment, the cross-sectional area of ​​the bypass passage 45 is larger than the cross-sectional area of ​​the main passage 44. This allows the flow rate of oil passing through the bypass passage 45 to be as large as possible when the engine is warm. This allows the oil to be cooled more actively when the engine is warm.

[0069] In this embodiment, the upper opening 45a of the secondary passage 45 is located closer to the intake side than the upper opening 44a of the main passage 44. A guide portion 46 is provided in the cylinder head 4 to guide the oil, after it has been supplied to a lubricated part (here, the exhaust camshaft 18) located above the upper openings 44a, 45a of the main passage 44 and the secondary passage 45, toward the intake side of the upper opening 45a of the secondary passage 45. This allows lubricating oil supplied to the exhaust camshaft 18 and the like to also flow into the secondary passage 45. This also allows the oil to flow from the intake side toward the exhaust side, thereby actively circulating the oil through the secondary passage 45. This allows the oil to be cooled more actively when the engine is warm.

[0070] In this embodiment, the bolt head 60a of the connecting bolt 60 is located between the upper opening 45a of the secondary passage 45 and the upper opening 44a of the main passage 44 in the width direction of the engine body 10. As a result, when oil flows from the intake side to the exhaust side, the bolt head 60a temporarily blocks the oil flow. This makes it easier for oil to flow through the secondary passage 45.

[0071] The technology disclosed herein is not limited to the above-described embodiments, and can be substituted within the scope of the claims.

[0072] For example, in the above-described embodiment, the bypass passage 45 is formed by a pipe. However, this is not limiting, and the bypass passage 45 may be formed by drilling the cylinder head 4. In this case, as shown in FIG. 9 , a protruding portion 247 that protrudes upward is formed in the middle deck 4a, and the upper end of the bypass passage 245 is formed in the protruding portion 247. This allows the upper opening of the bypass passage 245 to be positioned above the upper opening 44a of the main passage 44, even when the bypass passage 245 is formed by drilling the cylinder head 4.

[0073] The above-described embodiments are merely examples and should not be construed as limiting the scope of the present disclosure. The scope of the present disclosure is defined by the claims, and all modifications and variations that fall within the scope of the claims equivalents are within the scope of the present disclosure. [Industrial Applicability]

[0074] The technology disclosed herein is useful for an engine oil passage structure in which oil stored in an oil pan located below the cylinder block of the engine body is supplied to the lubricated parts of the cylinder head by an oil pump, and then returned to the oil pan for circulating. [Explanation of symbols]

[0075] 3 Cylinder block 4 Cylinder head 10 Engine body 16 Exhaust port 22 Oil return passage 30 Oil pan 31 Oil pump 44 Main passage 44a Upper opening 45 Sub-aisle 45a Upper opening 46 Guide part 245 Sub-aisle 245a Upper opening 247 Protrusion

Claims

1. An oil passage structure for an engine in which oil stored in an oil pan arranged below a cylinder block of an engine body is supplied to a lubricated part of a cylinder head by an oil pump and then returned to the oil pan for circulation, an oil return passage provided in the engine body for returning oil from a cylinder head of the engine body to the oil pan; The oil return passage a main passage formed in the vicinity of the exhaust port of the cylinder head; a sub-passage formed in the cylinder head by branching off from the main passage; and the main passage and the sub-passage each have an upper opening that opens upward within the cylinder head, the upper opening of the sub-passage is located above the upper opening of the main passage, 10. An oil passage structure for an engine, wherein the sub-passage is located closer to a cooling portion in the cylinder head than the main passage.

2. 2. The engine oil passage structure according to claim 1, 1. An oil passage structure for an engine, wherein a flow path cross-sectional area of ​​the sub-passage is larger than a flow path cross-sectional area of ​​the main passage.

3. 3. The engine oil passage structure according to claim 1, The cylinder head is provided with a water jacket through which cooling water flows, the cooling section is constituted by the water jacket, 1. An oil passage structure for an engine, wherein the sub-passage is adjacent to the water jacket.

4. 3. The engine oil passage structure according to claim 1, the upper opening of the sub-passage is located closer to the intake side than the upper opening of the main passage, and a guide portion is provided in the cylinder head to guide oil, after it has been supplied to the lubricated parts located above the upper openings of the main passage and the sub-passage, toward the intake side of the upper opening of the sub-passage.

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