Engine oil passage structure

Abstract

To provide an engine oil passage structure capable of curbing an increase in an oil temperature.SOLUTION: An oil passage structure of an engine 1, for circulating oil stored in an oil pan 30 arranged beneath a cylinder block 3 of an engine body 10 with an oil pump 31 in a manner that transfers and supplies the same to a lubricated section and returns the same to the oil pan 30, comprises a cylinder side oil return passage 43a which is installed on the cylinder block 3 and allows the oil to be returned from the cylinder head 4 of the engine body 10 to the oil pan 30. The cylinder side oil return passage 43a is arranged adjacent to a cooling section 13 installed in the cylinder block 3. An inner peripheral surface of the cylinder side oil return passage 43a has a wettability changing section in which wettability with respect to the oil is changed in a direction of a flow direction of the cylinder side oil return passage 43a so as to limit an oil flow on the inner peripheral surface.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an oil passage structure for an engine mounted on a vehicle such as an automobile. [Background technology]

[0002] Engines mounted on vehicles are generally configured so that oil stored in an oil pan located below the cylinder block of the engine is sucked out by an oil pump and supplied to lubricated parts of the engine, such as cylinders, pistons, and cams.

[0003] The oil supplied to the lubricated parts lubricates the lubricated parts, receives (absorbs) heat such as frictional heat from the lubricated parts, and is returned to the oil pan via an oil return passage provided in the engine body.

[0004] The oil supplied to the parts to be lubricated may receive heat from the parts to be lubricated and its temperature may rise depending on the temperature of the parts to be lubricated. In this case, it is preferable to cool the oil because the oil's viscosity decreases due to the increase in oil temperature, resulting in a decrease in lubrication.

[0005] Patent Document 1 discloses an oil return passage structure for an engine formed in a cylinder block with multiple cylinders and a cylinder head disposed on the upper surface of the cylinder block and forming a combustion chamber together with pistons. The oil return passage includes a head-side return passage and a block-side return passage formed in the cylinder head and the cylinder block, respectively, and communicating with each other.

[0006] A water jacket for circulating cooling water for cooling the cylinder is provided radially outside the cylinder of the cylinder block so as to surround the outer periphery of the cylinder. The block-side return passage is provided radially outside the water jacket and extends in the vertical direction. A plurality of fins are provided on the inner surface of the block-side return passage on the water jacket side, and the cooling water flowing inside the water jacket is used to promote heat dissipation of the oil passing through the oil return passage, thereby suppressing an increase in temperature of the oil. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-148227 A Summary of the Invention [Problem to be solved by the invention]

[0008] When using low-viscosity oil, which has a lower upper limit temperature than oil with normal viscosity, to improve fuel efficiency, or when eliminating the oil cooler to reduce costs and the number of parts, there is an additional need to suppress the rise in temperature of the oil itself.

[0009] An object of the present invention is to provide an oil passage structure for an engine that can suppress an increase in oil temperature. [Means for solving the problem]

[0010] The present invention provides an oil passage structure for an engine in which oil stored in an oil pan disposed below a cylinder block of an engine body is transported by an oil pump to be supplied to a lubricated part, and then circulated back to the oil pan, a cylinder-side oil return passage provided in the cylinder block for returning oil from a cylinder head side of the engine body to the oil pan; The cylinder side oil return passage is disposed adjacent to a cooling portion provided in the cylinder block, The inner circumferential surface of the cylinder side oil return passage has a wettability changing portion that changes the wettability with respect to the oil in the flow direction of the cylinder side oil return passage to limit the flow of oil flowing along the inner circumferential surface. To provide an oil passage structure for an engine.

[0011] According to the present invention, the wettability changing portion can change the wettability of the oil in the cylinder-side oil return passage in the flow direction of the cylinder-side oil return passage, thereby suppressing the flow of oil from the upstream side to the downstream side of the cylinder-side oil return passage and increasing the residence time of the oil in the cylinder-side oil return passage.

[0012] When the cylinder side oil return passage is arranged adjacent to a cooling section such as a water jacket provided on the engine body, the residence time of oil in the cylinder side oil return passage can be increased, heat dissipation to the wall of the cylinder side oil return passage is promoted, and the rise in oil temperature can be reduced.

[0013] The wettability changing portion may include a plurality of recesses formed on the inner circumferential surface of the cylinder side oil return passage such that oil repellency increases from the upstream portion to the downstream portion of the cylinder side oil return passage.

[0014] With this configuration, the wettability changing portion is formed by forming multiple recesses on the inner surface of the cylinder side oil return passage. With a relatively simple configuration using multiple recesses, the oil repellency is increased from the upstream side to the downstream side of the cylinder side oil return passage, thereby suppressing the flow of oil flowing from the upstream side to the downstream side of the cylinder side oil return passage and increasing the residence time of oil in the cylinder side oil return passage.

[0015] The cylinder block is made of a metal material, The plurality of recesses may be formed so that their depths become shallower from the upstream portion toward the downstream portion of the cylinder side oil return passage.

[0016] With this configuration, the oil repellency can be increased from the upstream side to the downstream side of the cylinder side oil return passage by forming a plurality of recesses on the inner surface of the cylinder side oil return passage that become shallower from the upstream side to the downstream side of the cylinder side oil return passage.

[0017] A layer made of a fluororesin material may be provided on the inner surface of the cylinder side oil return passage, and the multiple recesses may be formed so that their depth increases from the upstream portion to the downstream portion of the cylinder side oil return passage.

[0018] With this configuration, the oil repellency can be increased from the upstream side to the downstream side of the cylinder side oil return passage by forming a plurality of recesses on the inner surface of the cylinder side oil return passage, the depth of which increases from the upstream side to the downstream side of the cylinder side oil return passage.

[0019] The cylinder block is made of a metal material, The plurality of recesses may be formed so that their widths decrease from the upstream portion to the downstream portion of the cylinder side oil return passage.

[0020] With this configuration, the oil repellency can be further increased from the upstream side to the downstream side of the cylinder side oil return passage by forming a plurality of recesses on the inner surface of the cylinder side oil return passage whose width decreases from the upstream side to the downstream side of the cylinder side oil return passage.

[0021] A layer made of a fluororesin material may be provided on the inner surface of the cylinder side oil return passage, and the multiple recesses may be formed so that their width decreases from the upstream portion to the downstream portion of the cylinder side oil return passage.

[0022] With this configuration, the oil affinity can be further increased from the upstream side to the downstream side of the cylinder side oil return passage by forming a plurality of recesses on the inner surface of the cylinder side oil return passage, the width of which decreases from the upstream side to the downstream side of the cylinder side oil return passage.

[0023] The engine body is provided with a water jacket through which cooling water from a water pump flows, The cooling portion may be constituted by the water jacket.

[0024] Since the cylinder-side oil return passage is disposed adjacent to the water jacket, the inner peripheral surface of the cylinder-side oil return passage can be cooled by the cooling water flowing through the water jacket, which promotes heat dissipation from the oil and suppresses an increase in oil temperature. Effect of the Invention

[0025] According to the engine oil passage structure of the present invention, an increase in oil temperature can be suppressed. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic diagram showing a configuration of an engine according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the cylinder head taken along line II-II in FIG. [Diagram 3] FIG. 2 is a cross-sectional view of the cylinder block taken along line III-III in FIG. [Figure 4] 1 is a cross-sectional view showing an oil passage of an engine according to an embodiment of the present invention. [Diagram 5] 1 is a schematic diagram showing an oil supply passage of an engine according to an embodiment of the present invention. [Figure 6] FIG. 4 is another cross-sectional view showing the oil passage of the engine according to the embodiment of the present invention. [Figure 7] 7 is a schematic cross-sectional view of a cylinder-side oil return passage indicated by an arrow VII in FIG. 4. [Figure 8] FIG. 2 is an explanatory diagram for explaining wettability with oil. [Figure 9] 9 is a diagram showing a modified example of the cylinder side oil return passage shown in FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0028] An oil passage structure according to an embodiment of the present invention is applied to an engine 1. As shown in Fig. 1, the engine 1 according to an embodiment of the present invention is a so-called vertically mounted engine 1 that is mounted on a vehicle such as an automobile and has a crankshaft 6a extending in the front-rear direction. The engine 1 includes an engine body 10, which includes a cylinder block 3 in which cylinders 2 are formed, and a cylinder head 4 disposed on the cylinders 2. The cylinder block 3 and the cylinder head 4 are formed of a metal material such as an aluminum alloy.

[0029] A piston 5 is arranged reciprocably within the cylinder 2. The piston 5 is connected via a connecting rod 7 to a crankshaft 6 that is rotatably supported at the bottom of the cylinder block 3, so that the reciprocating motion of the piston 5 is converted into the rotational motion of the crankshaft 6.

[0030] An intake port 15 and an exhaust port 16 are formed in the cylinder head 4. Two intake ports 15 and two exhaust ports 16 are provided in each cylinder 2, and the two intake ports 15 and the two exhaust ports 16 are provided spaced apart in the axial direction of the crankshaft 6a that is perpendicular to the central axis 2a of the cylinder 2.

[0031] An intake passage (not shown) that supplies air to the combustion chamber 8 is connected to the intake port 15, and an exhaust passage (not shown) that discharges exhaust gas, which is combustion gas, from the combustion chamber 8 is connected to the exhaust port 16. A catalytic device 11 equipped with a catalyst that purifies the exhaust gas, and an exhaust pipe 12, which serve as an exhaust device, are connected to the exhaust passage. The catalytic device 11 and the engine 1 are arranged side by side in the vehicle body width direction.

[0032] As shown by imaginary lines, an intake valve and an exhaust valve are disposed on the upper part of the cylinder head 4 for opening and closing an intake port 15 and an exhaust port 16, respectively. The intake valve opens and closes the intake port 15 at a predetermined timing by an intake camshaft 17 drivingly connected to the crankshaft 6, and supplies air to the combustion chamber 8 during the intake stroke. The exhaust valve opens and closes the exhaust port 16 at a predetermined timing by an exhaust camshaft 18 drivingly connected to the crankshaft 6, and exhausts exhaust gas from the combustion chamber 8 during the exhaust stroke.

[0033] A head-side water jacket 14, through which cooling water circulates, is formed inside the cylinder head 4. The head-side water jacket 14 is provided above the combustion chambers 8, between the intake port 15 and the exhaust port 16 in the cross section shown in Fig. 1. The head-side water jacket 14 is formed so as to surround the upper part of each combustion chamber 8. The cylinder head 4 has a deck surface 4a above the head-side water jacket 14, approximately near the center of the cylinder head 4 in the vertical direction.

[0034] 2, the cylinder head 4 extends in the cylinder direction and has a rectangular shape in a plan view. A boss portion 51 for mounting an ignition plug (not shown) for each cylinder 2 is provided on the deck surface 4a. An intake boss portion 52 and an exhaust boss portion 53 are provided on the intake side and exhaust side of the boss portion 51, respectively, on the deck surface 4a. An intake valve is disposed on the intake boss portion 52, and an exhaust valve is disposed on the exhaust boss portion 53.

[0035] The deck surface 4a is provided with a plurality of head bolt insertion holes 54a for each cylinder, through which head bolts (not shown) for attaching the cylinder head 4 to the cylinder block 3 are inserted, surrounding the cylinder 2. The deck surface 4a is provided with head side return passages 42, 46, which will be described later, on the side wall side opposite the crankshaft of the head bolt insertion holes 54a.

[0036] 1, the cylinder head 4 has an intake side inclined surface 4b and an exhaust side inclined surface 4c that extend upward and outward from both sides of the deck surface 4a in the width direction perpendicular to the crankshaft, and a front surface 4d and a rear surface 4e that rise from one end side and the other end side of the crankshaft of the deck surface 4a (see FIG. 2). The front surface 4d and the rear surface 4e are provided with recesses for arranging the intake camshaft 17 and the exhaust camshaft 18.

[0037] 1, the exhaust-side inclined surface 4c constitutes a part of the inner surface of the side wall of the cylinder head 2 and is adjacent to the catalytic device 11, so that the exhaust-side inclined surface 4c becomes hotter than the deck surface 4a due to the exhaust gas from the catalytic device 11. The center of the deck surface 4a in the width direction is located above the head-side water jacket 14, so that the center of the deck surface 4a is cooled more than both sides of the deck surface 4a.

[0038] As shown in Fig. 3, a cylinder-side water jacket 13 serving as a cooling section through which cooling water flows is provided on the upper side of the cylinder block 3 so as to surround the cylinder 2 on the radial outside of the cylinder 2. The cylinder-side water jacket 13 has a closed loop structure surrounding the radial outside of the cylinder 2 of the cylinder row. The cylinder-side water jacket 13 is formed so as to open upward.

[0039] The cylinder side water jacket 13 has a plurality of arc-shaped portions 13a that partially surround the cylinders 2 and a plurality of recesses 13b that extend between the cylinders 2 in the axial direction of the crankshaft 6a. The cylinder side water jacket 13 has the arc-shaped portions 13a and the recesses 13b arranged alternately and continuously on both sides of the axial direction of the cylinder row. At the front and rear ends of the cylinder row, front end portions 13c and rear end portions 13c that connect the arc-shaped portions 13a and surround the front and rear ends of the cylinders 2 are arranged, respectively.

[0040] A plurality of screw holes 54b for screwing in head bolts for fixing the cylinder head 4 are provided on both sides of the cylinder row of the cylinder block 3. The screw holes 54b are arranged outside the recess 13b, the front end 13c, and the rear end 13c of the cylinder side water jacket 13 in a plan view.

[0041] 4, the cylinder block 3 has an upper cylinder block 3a located on the upper side and a lower cylinder block 3b arranged below the upper cylinder block 3a, and the cylinder side water jacket 13 is provided in the upper region of the upper cylinder block 3a. The cylinder side water jacket 13 is formed to a depth that extends downward from the upper end of the cylinder block 3 to near the top of a main gallery 37a (described later).

[0042] In this embodiment, an oil pan 30 for storing oil for lubricating parts to be lubricated, such as the piston 5, the crankshaft 6, the camshafts 17, 18, etc., is disposed at the lower end of the cylinder block lower 3b.

[0043] In this embodiment, the engine 1 is mounted on the vehicle and supported by a body frame with the central axis 2a of the cylinder 2 extending in a direction inclined toward the exhaust side at a predetermined angle θ1, such as 10 degrees, from the vertical, as shown in FIG.

[0044] 1 and 4 to 6, engine 1 is provided with an oil passage 20 that circulates oil for lubricating parts to be lubricated (piston 5, crankshaft 6, camshafts 17, 18, etc.) within engine 1. Oil passage 20 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 supplied to the parts to be lubricated to the oil pan.

[0045] As shown in FIG. 5, the oil supply passage 21 includes an oil pump 31 that sucks 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.

[0046] 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 3, 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.

[0047] 1 and 5, the oil pump 31 is driven by the crankshaft 6. The oil discharged from the oil pump 31 flows through a first oil supply passage 36 into the oil filter 32 where it is filtered, and then flows into the oil cooler 33 where it is cooled. The oil cooled in the oil cooler 33 is supplied to a second oil supply passage 37 of the cylinder block 3 through a first communication oil passage 39.

[0048] As shown in Figures 1, 4 and 5, the first supply oil passage 36 includes an oil passage 36a that is provided in the oil pan 30 and connects the oil pump 31 and the oil filter 32, an oil passage 36b that is provided adjacent to the exhaust side of the oil pan 30 and connects the oil filter 32 and the oil cooler 33, and an oil passage 36c that extends upward from the oil cooler 33 and is connected to a first communicating oil passage 39 provided in the cylinder block 3.

[0049] As shown in Figures 4 and 5, the first communicating oil passage 39 includes an oil passage 39a that is provided in the cylinder block lower 3b, opens to the exhaust side, and extends in the radial direction of the cylinder 2 (in the width direction of the engine body 10), an oil passage 39b that extends upward from the radially inner end of the oil passage 39a and opens upward into the cylinder block lower 3b, and an oil passage 39c that is provided in the cylinder block upper 3a and extends upward, communicating with the oil passage 39b.

[0050] The second supply oil passage 37 includes a main gallery 37a to which oil passage 39c is connected and which extends in the cylinder row direction, and a plurality of branch oil passages 37b which branch off from the main gallery 37a and extend downward toward the crankshaft 6a to supply oil to the lubricated parts of the crankshaft 6.

[0051] The main gallery 37a is located on the exhaust side of the cylinder block 3 in a width direction perpendicular to the cylinder row direction of the cylinder block 3, near the lower end of the cylinder 2. The downstream ends of the branched oil passages 37b each open toward the crankshaft 6a of the cylinder block 3.

[0052] As shown in FIGS. 5 and 6, the second supply oil passage 37 further includes an oil passage 37c that branches off from one end of the main gallery 37a, extends in the width direction, and communicates with the second communication oil passage .

[0053] The second communicating oil passage 40 includes an oil passage 40a provided in the cylinder block upper 3a and extending upward from the end of the oil passage 37c on the main gallery 37a side, and an oil passage 40b provided in the cylinder head 4, communicating with the oil passage 40a and extending upward.

[0054] The third supply oil passage 38 includes an oil passage 38a extending from the upper end of the oil passage 40b on 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 in the cylinder row direction from the oil passage 38b. 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 on the intake side and the exhaust side of the camshafts 17, 18.

[0055] In addition to the above-mentioned configuration, the oil supply passage 21 is formed so as to supply oil to, for example, an oil jet for cooling a piston.

[0056] As shown in FIG. 4, oil supplied to the camshafts 17, 18, which are lubricated parts of the engine 1, through the oil supply passage 21 drips onto the intake side and exhaust side inclined surfaces 4b, 4c and the deck surface 4a of the cylinder head 4 (arrow a), and is returned to the oil pan 30 through the head side return passages 42, 46 that constitute the oil return passage 22 provided on the deck surface 4a.

[0057] When the engine 1 is mounted on the vehicle body, the deck surface 4a is inclined with respect to the horizontal plane 2b so that the exhaust side is lower than the intake side. Therefore, oil that drips onto the deck surface 4a is easily guided to the head-side return passage 42 on the exhaust side.

[0058] The oil return passage 22 includes a plurality of exhaust-side return passages 41 and intake-side return passages 45 through which oil supplied to the camshafts 17, 18 as lubricated parts flows separately to the exhaust port 16 side and the intake port 15 side. The exhaust-side return passage 41 and the intake-side return passage 45 include head-side return passages 42, 46 provided in the cylinder head 4 and block-side return passages 43, 47 provided in the cylinder block 3. Since the exhaust-side return passage 41 and the intake-side return passage 45 have the same configuration, only the exhaust-side return passage 41 will be described.

[0059] The head-side return passage 42 is formed in a substantially circular shape in a plan view and extends in the vertical direction. A plurality of head-side return passages 42 are provided on the exhaust side of the cylinder head 4 and are connected to the block-side return passage 43. The head-side return passages 42 are disposed between each cylinder 2 at positions offset from each cylinder 2 in the cylinder row direction.

[0060] The block-side return passage 43 is formed in a substantially circular shape in a plan view and extends in the vertical direction. The block-side return passage 43 includes upper-side passage returns 43a, 43b that extend in the vertical direction from the upper end to the lower end of the upper cylinder block 3a, and a lower-side return passage 43f that extends downward from the upper end of the lower cylinder block 3b and opens into the oil pan 30.

[0061] The upper return passages 43a, 43b include an upper return passage 43a located above the upper cylinder block 3a, and a lower return passage 43b located below the upper cylinder block 3a.

[0062] 3 and 4, the upper return passage 43a is adjacent to the cylinder side water jacket 13 and is provided along the cylinder side water jacket 13. The upper return passage 43a extends from the upper end of the cylinder block 3 to near the lower end of the cylinder side water jacket 13. The upper return passage 43a is formed to approximately the same depth as the cylinder side water jacket 13.

[0063] The upper return passage 43a is located between the arc-shaped portions 13a of the cylinder-side water jacket 13 and outside the recesses 13b that are disposed between the cylinders 2. Between the cylinders 2, the upper return passage 43a is offset in the cylinder row direction from the central axes 2a of the cylinders 2.

[0064] The lower return passage 43b is adjacent to the outside of the oil passage 39c of the first communicating oil passage 39 of the oil supply passage 21 and is provided along the oil passage 39c. The lower return passage 43b extends from near the main gallery 37a to the lower end of the upper cylinder block 3a.

[0065] The upper return passage 43a and the lower return passage 43b are offset in the width direction perpendicular to the cylinder row direction, and the lower return passage 43b is disposed closer to the outer wall of the engine body 10 than the upper return passage 43a. A radial passage 43c is provided between the upper return passage 43a and the lower return passage 43b to communicate between the upper return passage 43a and the lower return passage 43b.

[0066] The radial passage 43c has a substantially circular shape and extends in a direction perpendicular to the upper return passage 43a and the lower return passage 43b from the outer wall portion of the cylinder block 3 toward the lower side of the cylinder side water jacket 13. The lower end portion of the upper return passage 43a is communicated with the radial passage 43c, and the upper end portion of the lower return passage 43b is communicated with the radial passage 43c, so that the upper return passage 43a and the lower return passage 43b are communicated with each other via the radial passage 43c.

[0067] The lower passage 43f extends vertically from the upper end to the lower end of the cylinder block lower 3b. The lower passage 43f communicates with the lower return passage 43b and is formed to open to the oil pan 30.

[0068] When the engine 1 starts operating, the oil pump 31 is driven in response to the rotation of the crankshaft 6. Then, as shown by the arrow in Fig. 5, the oil pump 31 draws oil stored in the oil pan 30 through the suction port 31a of the oil pump 31, and supplies the drawn oil to parts to be lubricated in the engine body 10 via the first supply oil passage 36, the first communicating oil passage 39, the second supply oil passage 37, the second communicating oil passage 40, and the third supply oil passage 38 in this order.

[0069] The oil supplied to the lubricated parts in this manner lubricates the lubricated parts via the oil supply passage 21 and, after absorbing heat such as frictional heat generated during operation of the lubricated parts, is returned to the oil pan 30 via the oil return passage 22.

[0070] The oil flowing into the oil return passage 22 is warmed by absorbing heat such as frictional heat generated during operation of the lubricated parts, and is then cooled by dissipating the heat of the oil at the deck surface 4a, which is located at a position including above the head side water jacket 14, and at the upper return passage 43a, which is located adjacent to the cylinder side water jacket 13, and is returned to the oil pan 30.

[0071] 7 is a cross-sectional view of the upper return passage 43a shown in FIG. 4. FIG. 7 shows a schematic cross-sectional view of the upper return passage 43a (oil return passage) of the block-side return passage 43 in the embodiment of the present invention. As described above, the upper return passage 43a is disposed adjacent to the radial outside of the block-side water jacket 13, and therefore has a lower temperature than the head-side return passage 42 and the lower return passage 43b. In this embodiment, the wettability to oil is changed in the flow direction of the upper return passage 43a so that the oil repellency increases from the upstream side to the downstream side of the upper return passage 43a, thereby making it easier to restrict the flow of oil flowing along the inner circumferential surface of the upper return passage 43a, thereby suppressing the rise in temperature of the oil.

[0072] As shown in FIG. 7, the upper return passage 43a is provided with a wettability changing section 60 in which the wettability to oil is changed in the flow direction of the upper return passage 43a so that the oil repellency increases from the upstream side to the downstream side of the upper return passage 43a.

[0073] The wettability changing portion 60 includes a plurality of grooves 61 as a plurality of recesses formed on the inner circumferential surface of the upper return passage 43a such that the oil repellency increases from the upstream side to the downstream side of the upper return passage 43a. Each of the plurality of grooves 61 is formed to extend in the circumferential direction of the upper return passage 43a over the entire circumferential direction of the upper return passage 43a, and the plurality of grooves 61 are formed spaced apart from each other from the upstream side to the downstream side of the upper return passage 43a.

[0074] Each of the grooves 61 is formed in a U-shape having a predetermined width W1 and a predetermined depth D1. The widths W1 of the grooves 61 are set to be the same, and the depths D1 of the grooves 61 are set to become shallower from the upstream side to the downstream side of the head-side return passage 42.

[0075] In this way, the plurality of grooves 61 are formed so that the depth D1 becomes shallower from the upstream side to the downstream side of the upper return passage 43a, and thus the oil repellency becomes higher from the upstream side to the downstream side of the upper return passage 43a. In Fig. 7, the grooves 61 are shown enlarged to make the drawing easier to see, but the grooves 61 are fine grooves having widths and depths within the range of several µm to several tens of µm.

[0076] Fig. 8 is an explanatory diagram for explaining the wettability with respect to oil. Fig. 8(a) shows a state in which oil 100 is attached to a wall surface 101, and Fig. 8(b) shows a state in which oil 100 has entered a groove portion 102 provided in the wall surface 101. In Fig. 8, the width of groove portion 102 is represented as W, the depth of groove portion 102 is represented as D, the opening area of ​​groove portion 102 is represented as a1, and the area of ​​groove portion 102 is represented as a2.

[0077] When the oil 100 changes from the state shown in Fig. 8(a) to the state shown in Fig. 8(b) and the energy required for the oil 100 to create a new surface is denoted as E1, the energy E1 can be expressed by the following formula: E1 = Esurf × (a2 - a1), where Esurf represents the surface free energy of the oil 100.

[0078] Also, when the oil 100 deforms from the state shown in FIG. 8(b) to the state shown in FIG. 8(a) and the energy required to peel the oil 100 from the wall surface 101, specifically the wall surface 101 of the groove portion 102, is denoted as E2, the energy E2 can be expressed by the following formula: E2 = Einterface × a2. Here, Einterface represents the interfacial interaction energy of the oil 100.

[0079] The lipophilicity degree of the oil 100 with respect to the wall surface 101, which is the lipophilic degree, can be expressed as (E2 - E1). When E1 < E2, as shown in FIG. 8(b), the state where the oil 100 penetrates into the groove portion 102 of the wall surface 101 is stable (lipophilic), and the greater the difference (E2 - E1) between the energy E1 and the energy E2, the higher the lipophilic degree. When E1 > E2, as shown in FIG. 8(a), the state where the oil 100 adheres to the wall surface 101 is stable (oleophobic).

[0080] The lipophilic degree (E2 - E1) is expressed as (Einterface - Esurf) × a2 + Esurf × a1. When the groove portion 102 is formed of a metal material satisfying the formula: Einterface > Esurf, as the depth D of the groove portion 102 increases, the area a2 of the groove portion 102 increases, so the lipophilic degree increases, the lipophilicity increases, and the oleophobicity decreases. On the other hand, when the depth D is decreased, the area a2 of the groove portion 102 decreases, so the lipophilic degree decreases, and the oleophobicity increases.

[0081] When the groove portion 102 is formed of a fluororesin material satisfying the formula: Einterface < Esurf, as the depth D of the groove portion 102 increases, the area a2 of the groove portion 102 increases, so the lipophilic degree decreases, the lipophilicity decreases, and the oleophobicity increases. On the other hand, when the depth D is decreased, the area a2 of the groove portion 102 decreases, so the lipophilicity increases, and the oleophobicity decreases.

[0082] Furthermore, when the width W of groove portion 102 is increased, the difference between the area a2 of groove portion 102 and the opening area a1 of groove portion 102 becomes smaller, and the energy E1 becomes smaller. Therefore, regardless of whether groove portion 102 is made of a metal material or a fluororesin material, the lipophilicity increases and the lipophilicity becomes higher.

[0083] In the upper return passage 43a shown in Figure 7, the multiple groove portions 61 are formed so that the depth D1 becomes shallower from the upstream side to the downstream side of the upper return passage 43a, and the oil repellency becomes higher from the upstream side to the downstream side of the upper return passage 43a.

[0084] In this way, by changing the oil wettability so that the oil repellency increases from the upstream side to the downstream side of the upper return passage 43a, the flow of oil from the upstream side to the downstream side of the upper return passage 43a can be suppressed, and the residence time of oil in the upper return passage 43a can be increased.

[0085] When the upper return passage 43a is positioned adjacent to a cooling section such as the block side water jacket 13, the residence time of oil in the upper return passage 43a can be increased, heat dissipation to the wall of the upper return passage 43a is promoted, and the rise in oil temperature can be reduced.

[0086] In the wettability changing portion 60, the groove portions 61 are formed as a plurality of recesses in the inner circumferential surface of the upper return passage 43a. Therefore, the wettability changing portion 60 can be formed with a relatively simple configuration by forming the plurality of recesses 61.

[0087] Fig. 9 is a cross-sectional view showing a modified example of the upper return passage 43a shown in Fig. 7. The upper return passage 43a shown in Fig. 9 has a layer 43g made of a fluororesin such as PTFE (polytetrafluoroethylene) provided on the inner circumferential surface. The layer 43g made of the fluororesin is formed to a thickness of, for example, several hundred µm. The layer 42b made of the fluororesin has oil repellency.

[0088] The upper return passage 43a shown in Fig. 9 is also provided with a wettability changing section 70 in which the wettability to oil is changed in the flow direction of the upper return passage 43a so that the oil repellency increases from the upstream side to the downstream side of the upper return passage 43a, similarly to the upper return passage 43a shown in Fig. 7. The wettability changing section 70 may include a plurality of grooves 71 formed on the inner circumferential surface 42h of the layer 42g made of fluororesin of the upper return passage 43a so that the oil repellency increases from the upstream side to the downstream side.

[0089] The multiple groove portions 71 formed on the inner surface 43h of the layer 43g made of fluororesin are each formed to extend in the circumferential direction of the upper return passage 43a over the entire circumferential direction of the upper return passage 43a, and the multiple groove portions 71 are each formed at a distance from the upper end side to the lower end side of the upper return passage 43a.

[0090] Each of the grooves 71 has a predetermined width W2 and a predetermined depth D2 and is formed in a U-shaped cross section. The widths W2 of the grooves 71 are set to be the same, and the depths D2 of the grooves 71 are set to become deeper from the upstream side to the downstream side of the upper return passage 43a.

[0091] The multiple groove portions 71 are formed so that the depth D2 becomes deeper from the upstream side to the downstream side of the upper return passage 43a, thereby increasing the oil repellency from the upstream side to the downstream side of the upper return passage 43a.

[0092] In this way, by changing the oil wettability so that the oil repellency increases from the upstream side to the downstream side of the upper return passage 43a, the flow of oil from the upstream side to the downstream side of the upper return passage 43a can be suppressed, and the residence time of oil in the oil return passage can be increased.

[0093] In this embodiment, the multiple groove portions 61 formed in the upper return passage 43a are formed so that the width W1 is set to the same and the depth D1 becomes shallower from the upstream side to the downstream side of the upper return passage 43a, but the depth D1 may be set constant and the width W1 may be formed so that it becomes smaller from the upstream side to the downstream side of the upper return passage 43a.

[0094] In this embodiment, in the upper return passage 43a, the multiple groove portions 71 formed on the inner surface 43h of the layer 43g made of fluororesin are formed so that the width W2 is set to be the same and the depth D2 becomes deeper from the upstream side to the downstream side of the upper return passage 43a. However, the depth D2 may be set constant and the width W2 may become smaller from the upstream side to the downstream side of the upper return passage 43a.

[0095] In this embodiment, the multiple grooves 61, 71 are formed to have a U-shaped cross section, but they may also be formed to have other cross-sectional shapes such as a rectangular cross section, a triangular cross section, etc. The multiple grooves 61, 71 are formed to extend in the circumferential direction of the upper return passage 43a over the entire circumferential direction of the upper return passage 43a, but they may be formed to extend in the circumferential direction of the head side return passage 42 only in a part of the circumferential direction of the upper return passage 43a, for example, on the exhaust side.

[0096] In this embodiment, the grooves 61 formed in the upper return passage 43a are formed so that the width W1 is set to be the same and the depth D1 becomes shallower from the upstream side to the downstream side of the upper return passage 43a, but in addition to the change in the depth D1, the width W1 may be formed so as to become smaller from the upstream side to the downstream side of the upper return passage 43a. This further enhances the oil repellency from the upstream side to the downstream side of the upper return passage 43a.

[0097] In the present embodiment, the grooves 71 formed in the inner circumferential surface 43h of the layer 43g made of fluororesin in the upper return passage 43a are formed so that the width W2 is set to be the same and the depth D2 is deepened from the upstream side to the downstream side of the upper return passage 43a, but in addition to the change in the depth D2, the width W2 may be formed to be smaller from the upstream side to the downstream side of the upper return passage 43a. This further enhances the oil repellency from the upstream side to the downstream side of the upper return passage 43a.

[0098] In this embodiment, the multiple recesses provided in the wettability changing portion 60, 70 of the upper return passage 43a are formed by multiple grooves 61, 71, but the multiple recesses may be formed by arranging multiple dimple rows arranged in the circumferential direction on the inner circumferential surface of the upper return passage 43a in the flow path direction. The dimple row may be, for example, a circular shape in a plan view, and multiple dimples having an arc shape whose cross section is concave on the radially outer side of the upper return passage 43a arranged in the circumferential direction. The multiple dimples constituting the dimple row arranged in the circumferential direction are formed with the same depth and width diameter. The depth and width diameter of the dimple row arranged in the flow path direction may be set so that the lipophilicity changes in the flow path direction, similar to the multiple grooves 61, 71. This increases the oil repellency from the upstream side to the downstream side of the upper return passage 43a.

[0099] The present invention is not limited to the exemplified embodiments, and various improvements and design modifications are possible without departing from the gist of the present invention. [Industrial Applicability]

[0100] INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to provide an engine oil passage structure capable of suppressing an increase in oil temperature, and therefore the present invention may be suitably used in the engine manufacturing industry. [Explanation of symbols]

[0101] 1 Engine 3 Cylinder block 10 Engine body 11 Exhaust system 13 Cooling section 20 Oil passage 30 Oil pan 31 Oil pump 43a Upper return passage (cylinder side oil return passage) 60 Wettability change area 61 Multiple grooves (multiple recesses) D1 Depth W1 width

Claims

1. An oil passage structure for an engine in which oil stored in an oil pan disposed below a cylinder block of an engine body is transported by an oil pump to be supplied to a lubricated part, and then circulated back to the oil pan, a cylinder-side oil return passage provided in the cylinder block for returning oil from a cylinder head side of the engine body to the oil pan; The cylinder side oil return passage is disposed adjacent to a cooling portion provided in the cylinder block, The inner circumferential surface of the cylinder side oil return passage has a wettability changing portion that changes the wettability with respect to the oil in the flow direction of the cylinder side oil return passage to limit the flow of oil flowing along the inner circumferential surface. Engine oil passage structure.

2. The wettability changing portion includes a plurality of recesses formed on the inner peripheral surface of the cylinder side oil return passage such that the oil repellency increases from the upstream portion toward the downstream portion of the oil return passage.

2. The engine oil passage structure according to claim 1.

3. The cylinder block is made of a metal material, The plurality of recesses are formed so that their depths become shallower from the upstream portion toward the downstream portion of the cylinder side oil return passage.

3. An oil passage structure for an engine according to claim 2.

4. a layer made of a fluororesin material is provided on the inner circumferential surface of the cylinder side oil return passage, The plurality of recesses are formed so that their depth increases from the upstream portion toward the downstream portion of the cylinder side oil return passage.

3. An oil passage structure for an engine according to claim 2.

5. The cylinder block is made of a metal material, The plurality of recesses are formed so that their widths become smaller from the upstream portion to the downstream portion of the cylinder side oil return passage.

4. An engine oil passage structure according to claim 2 or 3.

6. a layer made of a fluororesin material is provided on the inner circumferential surface of the cylinder side oil return passage, The plurality of recesses are formed so that their widths become smaller from the upstream portion to the downstream portion of the cylinder side oil return passage.

5. An oil passage structure for an engine according to claim 2 or 4.

7. The cylinder block is provided with a water jacket through which cooling water from a water pump flows.

6. The engine oil passage structure according to claim 1, wherein the cooling portion is formed by the water jacket.

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