Engine lubrication structure

Abstract

To increase oil pressure for a variable valve mechanism without increasing the discharge amount of an oil pump. [Solution] The engine is equipped with a variable valve train (12) that can change valve operation. The lubrication structure of this engine is provided with a relief valve (21) that adjusts the oil pressure of oil discharged from an oil pump (16), a main gallery (19) that supplies oil as lubricating oil to engine parts (13a-13c), and an oil control valve (18) that controls the oil pressure for the variable valve train. The main gallery is supplied with oil downstream of a relief hole in the relief valve, and the oil control valve is supplied with oil upstream of the relief hole.

Description

[Technical Field]

[0001] The present invention relates to a lubrication structure for an engine. [Background technology]

[0002] Conventionally, a known engine lubrication structure operates a variable valve train using oil from an oil pump (see, for example, Patent Document 1). In the lubrication structure described in Patent Document 1, oil is pumped up from an oil pan by an oil pump and supplied to an oil control valve through an oil filter and a main gallery. The oil control valve controls the oil pressure for the variable valve train, and the variable valve train is operated by oil from the oil control valve. In addition, oil is supplied from the main gallery to various engine components for lubrication. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-154209 Summary of the Invention [Problem to be solved by the invention]

[0004] As mentioned above, because oil is also used to lubricate engine parts, there are cases where sufficient oil pressure is not obtained to operate the variable valve mechanism. While oil pressure can be increased by increasing the oil pump discharge rate, this increases the pump size and the engine size, and also increases mechanical loss when the pump is driven, which can reduce engine output and fuel efficiency.

[0005] The present invention has been made in view of the above points, and has as its object to provide an engine lubrication structure that can increase the oil pressure applied to a variable valve mechanism without increasing the discharge volume of the oil pump. [Means for solving the problem]

[0006] One embodiment of the engine lubrication structure of the present invention is a lubrication structure for an engine equipped with a variable valve operating device that can change valve operation, and includes a relief valve that adjusts the oil pressure of oil discharged from an oil pump, a main gallery for supplying oil as lubricating oil to engine components, and an oil control valve that controls the oil pressure to the variable valve operating device, and the above-mentioned problem is solved by supplying oil downstream of the relief hole of the relief valve to the main gallery and oil upstream of the relief hole to the oil control valve. [Effects of the Invention]

[0007] According to one aspect of the engine lubrication structure of the present invention, the oil pressure upstream of the relief hole is increased and supplied to the oil control valve until the relief hole of the relief valve is opened. Therefore, even at extremely low engine speeds immediately after engine start, oil is preferentially supplied to the oil control valve, enabling the variable valve mechanism to operate. When the oil pressure is sufficiently increased to open the relief hole, operating oil is supplied to the oil control valve, and lubricating oil is also supplied to various engine components through the main gallery. Because there is no need to increase the oil pump discharge rate, mechanical loss during pump operation is reduced, improving engine output and fuel economy. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a lubrication structure for an engine according to a first embodiment. [Figure 2] FIG. 4 is a schematic diagram of a lubrication structure for an engine according to a second embodiment. [Figure 3] FIG. 10 is a schematic diagram of a lubrication structure for an engine according to a third embodiment. [Figure 4] FIG. 10 is a schematic diagram of a lubrication structure for an engine according to a fourth embodiment. [Figure 5] FIG. 2 is a schematic diagram of a lubrication structure of an engine of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] An engine according to one embodiment of the present invention is equipped with a variable valve train capable of varying valve operation. In this engine's lubrication structure, the oil pressure of oil discharged from the oil pump is adjusted by a relief valve. Oil downstream of the relief hole of the relief valve is supplied to a main gallery, which supplies the oil to engine components as lubricating oil. Oil upstream of the relief hole is supplied to an oil control valve, which controls the oil pressure for the variable valve train. Until the relief hole of the relief valve is opened, the oil pressure of the oil upstream of the relief hole is increased and supplied to the oil control valve. Therefore, even at extremely low engine speeds immediately after engine start, oil is preferentially supplied to the oil control valve, enabling the variable valve train to operate. When the oil pressure is sufficiently increased to open the relief hole, operating oil is supplied to the oil control valve, and lubricating oil is also supplied to various engine components via the main gallery. Since there is no need to increase the oil pump discharge rate, mechanical loss during pump operation is reduced, improving engine output and fuel economy. [Example]

[0010] Generally, the engines of saddle-type vehicles are equipped with variable valve train mechanisms such as a VVT (Variable Valve Timing) mechanism or a VVL (Variable Valve Lift) mechanism. Oil is pumped from an oil pan and supplied to the variable valve train mechanism via an oil control valve. The variable valve train mechanism is operated by hydraulic pressure to adjust valve timing, valve lift, etc. In such saddle-type vehicles, oil is also supplied to lubricate piston and crank system engine parts such as ball bearings, metal bearings, and piston cooling jets.

[0011] In such engines, sufficient oil pressure may not be obtained to operate the variable valve mechanism due to factors such as the large surface area of ​​the supply holes open to the atmosphere for lubricating the pistons and crankshaft components, and the small oil pump discharge rate. When ball bearings are used for the crankshaft, as in small scooters, more oil is required to lubricate the ball bearings than to lubricate metal bearings, so the oil supply holes for lubrication are large and jet-like. Furthermore, the small oil pumps of single-cylinder engines do not discharge enough oil.

[0012] 5, in the engine of the comparative example, oil is pumped up from an oil pan 91 by a small oil pump 92 and sent to a main gallery 94 through an oil filter 93. A variable valve train 96 is connected to the main gallery 94 via an oil control valve 95, and oil passages leading to various engine components 97a-97c such as ball bearings are also connected to the main gallery 94. Oil for operating the variable valve train 96 is supplied from the main gallery 94 to the oil control valve 95, and oil for lubrication is supplied from the main gallery 94 to the engine components 97a-97c.

[0013] A relief valve 98 is connected midway in the oil passage leading from the oil pump 92 to the oil filter 93. When the oil pressure of the oil discharged from the oil pump 92 rises due to an increase in engine speed, the excess oil is released from the relief valve 98 to the oil pan 91, thereby maintaining a constant pressure of the oil leading from the oil filter 93 to the main gallery 94. Oil supply holes are formed beyond the main gallery 94 to lubricate engine parts 97a-97c, and as the area of ​​the multiple supply holes increases, the oil pressure in the main gallery 94 drops, resulting in an insufficient oil pressure for operating the variable valve train 96.

[0014] Therefore, the engine lubrication structure of the first embodiment has separate oil passages formed for operating the variable valve train and for lubricating the engine components. The relief hole of the relief valve serves as the boundary, with the variable valve train connected to the oil passage upstream of the relief hole via an oil control valve, and the engine components connected to the oil passage downstream of the relief hole via a main gallery. Relatively high-pressure oil upstream of the relief hole is supplied to the variable valve train via the oil control valve, and oil released from the relief valve is supplied to the engine components via the main gallery.

[0015] <First Example> Hereinafter, a lubrication structure for an engine according to a first embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of the lubrication structure for an engine according to the first embodiment. In the following, an example in which the lubrication structure for an engine is applied to a single-cylinder engine of a small scooter will be described.

[0016] As shown in Figure 1, the engine's lubrication structure has oil passages 14a-14f extending from an oil pan 11 to a variable valve train 12, such as a VVT mechanism or a VVL mechanism, and engine components 13a-13c, such as ball bearings. An oil strainer 15 is installed at the upstream end of oil passage 14a and extends into the oil pan 11. An oil pump 16 is installed downstream of oil strainer 15, and oil is pumped up from the oil pan 11 by the oil pump 16. An oil filter 17 is installed midway along oil passage 14b downstream of oil pump 16, and the oil discharged from oil pump 16 is filtered by the oil filter 17.

[0017] Oil passage 14c branches off from oil passage 14b downstream of oil filter 17, and relief valve 21 is connected to oil passage 14c. A valve case 22 of relief valve 21 is formed with an inlet 23 and a relief hole 24, and oil passage 14c is connected to inlet 23 of relief valve 21, and oil passage 14d is connected to relief hole 24 of relief valve 21. Inside valve case 22, a valve spring 25 presses a plunger 26 in the direction of closing relief hole 24. The expansion and contraction of valve spring 25 causes plunger 26 to open and close relief hole 24, thereby adjusting the oil pressure of the oil discharged from oil pump 16.

[0018] Furthermore, oil passage 14e branches off from oil passage 14b downstream of oil filter 17, and oil control valve 18 is connected to oil passage 14e. Oil filtered by oil filter 17 is supplied to variable valve train 12 through oil control valve 18. A valve spool (not shown) is housed in oil control valve 18, and the hydraulic pressure applied to variable valve train 12 is controlled by the advancement and retreat of the valve spool, thereby operating variable valve train 12. Immediately after engine start-up, relief valve 21 is closed, and relatively high-pressure oil is preferentially supplied to oil control valve 18, operating variable valve train 12.

[0019] The relief hole 24 of the relief valve 21 is connected to the main gallery 19 through oil passages 14d and 14f. Oil is supplied as lubricating oil from the main gallery 19 to the engine components 13a-13c. The oil passage 14e, which leads the oil upstream of the relief hole 24 to the oil control valve 18, is formed smaller than the oil passage 14d, which leads the oil downstream of the relief hole 24 to the main gallery 19. The variable valve mechanism 12 requires high oil pressure but does not need a large amount of oil, so by narrowing the cross-sectional area of ​​the oil passage 14e, a sufficient amount of oil is ensured to be supplied to the engine components 13a-13c through the main gallery 19.

[0020] When the engine is running at extremely low speeds immediately after starting, the amount of oil discharged from oil pump 16 to oil passage 14b is small. Oil flows from oil passage 14b through oil passage 14c into inlet 23 of relief valve 21, but the repulsive force of valve spring 25 is greater than the hydraulic pressure at inlet 23 of relief valve 21. The hydraulic pressure at inlet 23 does not push plunger 26, so plunger 26 closes relief hole 24. Because oil is not released from relief hole 24, oil is not supplied to engine components 13a-13c through oil passages 14d, 14f and main gallery 19.

[0021] Furthermore, by closing the relief hole 24, the oil pressure of the oil upstream of the relief hole 24 is increased. As a result, relatively high-pressure oil is supplied to the oil control valve 18 from the oil passage 14b through the oil passage 14e. As described above, the amount of oil discharged from the oil pump 16 is small, but the amount of oil required for the oil control valve 18 and the variable valve train 12 is small, so the variable valve train 12 is operated with a small amount of oil via the oil control valve 18. The valve timing and valve lift are adjusted by the operation of the variable valve train 12.

[0022] When the engine speed increases and the amount of oil discharged from oil pump 16 to oil passage 14b increases, the amount of oil flowing from oil passage 14b to oil passage 14c increases, causing the oil pressure at inlet 23 of relief valve 21 to rise. The oil pressure at inlet 23 exceeds the repulsive force of valve spring 25, causing plunger 26 to be pushed against the repulsive force of valve spring 25 and opening relief hole 24. Oil is released from relief hole 24 through oil passages 14d and 14f to main gallery 19, adjusting the pressure in oil passage 14b. Oil is also supplied from main gallery 19 to lubricate each of engine components 13a-13c.

[0023] Oil is also supplied from oil passage 14b through oil passage 14e to the oil control valve 18 to operate the variable valve train 12. In this case, the oil control valve 18 and main gallery 19 are connected via oil passages 14b-14f, which reduces the oil pressure in the entire oil passage, while the engine speed increases to increase the oil pressure in the entire oil passage, ensuring sufficient oil pressure to operate the variable valve train 12. In this way, the main gallery 19 is supplied with oil from the downstream side of the relief hole 24, and the oil control valve 18 is supplied with oil from the upstream side of the relief hole 24.

[0024] As described above, according to the engine lubrication structure of the first embodiment, the oil pressure on the upstream side of the relief hole 24 of the relief valve 21 is increased and supplied to the oil control valve 18 until the relief hole 24 is opened. Therefore, even at extremely low engine speeds immediately after the engine is started, oil is preferentially supplied to the oil control valve 18, enabling the variable valve train 12 to operate. When the oil pressure is sufficiently increased to open the relief hole 24, operating oil is supplied to the oil control valve 18, and lubricating oil is also supplied to the engine components 13a-13c of the engine via the main gallery 19. Because there is no need to increase the discharge rate of the oil pump 16, mechanical loss during pump operation is reduced, improving engine output and fuel economy.

[0025] <Second Example> Next, a lubrication structure for an engine according to a second embodiment will be described. FIG. 2 is a schematic diagram of the lubrication structure for an engine according to the second embodiment. The lubrication structure for an engine according to the second embodiment differs from the lubrication structure for an engine according to the first embodiment in that another relief valve is installed downstream of the relief hole of the relief valve. Therefore, a description of the same configuration as that of the first embodiment will be omitted for the second embodiment.

[0026] 2, in the engine lubrication structure of the second embodiment, oil passages 34a-34f extend from oil pan 31 toward variable valve train 32 and engine components 33a-33c, similar to the engine lubrication structure of the first embodiment. Oil is pumped up from oil pan 31 through oil strainer 35 by oil pump 36, and the oil discharged from oil pump 36 is filtered by oil filter 37. Downstream of oil filter 37, relief valve 41a is connected to oil passage 34c branching off from oil passage 34b, and oil control valve 38 is connected to oil passage 34e branching off from oil passage 34b.

[0027] A relief hole 44a of the relief valve 41a is connected to the main gallery 39 via oil passages 34d and 34f, and oil is supplied from the main gallery 39 to the engine components 33a-33c. A relief valve (another relief valve) 41b with a higher valve opening pressure than the relief valve 41a is connected midway through the oil passage 34d. The relief valve 41b has the same configuration as the relief valve 41a, but the relief hole 44b of the relief valve 41b is open to the atmosphere above the oil pan 31. By releasing oil from the relief hole 44b into the oil pan 31, the oil pressure of the oil passages 34d and 34f, which are downstream of the relief hole 44a, is adjusted.

[0028] In this engine lubrication structure, the amount of oil discharged from the oil pump 36 to the oil passage 34b is small when the engine is running at extremely low speeds immediately after starting. The repulsive force of the valve spring 45a is greater than the oil pressure at the inlet 43a of the relief valve 41a, and the relief hole 44a is closed by the plunger 46a. The oil pressure upstream of the relief hole 44a increases, and relatively high-pressure oil is supplied from the oil passage 34e to the oil control valve 38, which then operates the variable valve train 32. In this way, as with the first embodiment, oil is preferentially supplied to the variable valve train 32 when the engine is running at extremely low speeds.

[0029] When the engine speed increases and the amount of oil discharged from the oil pump 36 to the oil passage 34b increases, the oil pressure at the inlet 43a exceeds the repulsive force of the valve spring 45a, pushing the plunger 46a and opening the relief hole 44a. Oil is released from the relief hole 44a through oil passages 34d and 34f to the main gallery 39, and is then supplied from the main gallery 39 to each of the engine components 33a-33c. The oil pressure in the oil passage 34b is adjusted to a predetermined pressure or lower, but is still equal to or higher than the operating pressure of the variable valve train 32, so oil is also supplied to the oil control valve 38 through the oil passage 34e, and the variable valve train 32 is operated.

[0030] Furthermore, when the engine is running at high speeds, the amount of oil discharged from the oil pump 36 to the oil passage 14b increases, and a large amount of oil is released from the relief hole 44a of the relief valve 41a into the oil passage 34d. The amount of oil flowing from the oil passage 34d into the inlet 43b of the relief valve 41b increases, causing the oil pressure at the inlet 43b to increase. The oil pressure at the inlet 43b becomes greater than the repulsive force of the valve spring 45b, pushing the plunger 46b and opening the relief hole 44b. Excess oil is returned to the oil pan 31 from the relief hole 44b, adjusting the oil pressure in each oil passage and the main gallery 39.

[0031] As described above, in the engine lubrication structure of the second embodiment, oil is preferentially supplied to the oil control valve 38 to operate the variable valve mechanism 32. Also, because there is no need to increase the discharge rate of the oil pump 36, mechanical loss during pump operation is reduced, improving engine output and fuel economy. Furthermore, when the engine is running at high speeds, excess oil is discharged from the relief valve 41b, stabilizing the oil pressure of the oil released from the relief valve 41a toward the main gallery 39.

[0032] <Third Example> Next, a lubrication structure for an engine according to a third embodiment will be described. Fig. 3 is a schematic diagram of the lubrication structure for an engine according to the third embodiment. The lubrication structure for an engine according to the third embodiment differs from the lubrication structure for an engine according to the first embodiment in that the upstream side and downstream side of the relief hole of the relief valve are connected by a bypass passage. Therefore, a description of the same configuration as that of the first embodiment will be omitted for the third embodiment.

[0033] 3, in the engine lubrication structure of the third embodiment, oil passages 54a-54f extend from oil pan 51 toward variable valve train 52 and engine components 53a-53c, similar to the engine lubrication structure of the first embodiment. Oil is pumped up from oil pan 51 through oil strainer 55 by oil pump 56, and the oil discharged from oil pump 56 is filtered by oil filter 57. Downstream of oil filter 57, a relief valve 61 is connected to oil passage 54c branching off from oil passage 54b, and an oil control valve 58 is connected to oil passage 54e branching off from oil passage 54b.

[0034] The relief hole 64 of the relief valve 61 is connected to the main gallery 59 through oil passages 54d and 54f, and oil is supplied from the main gallery 59 to the engine components 53a-53c. The oil passage 54b on the upstream side of the relief hole 64 and the oil passage 54f on the downstream side of the relief hole 64 are connected through a bypass passage 69. The bypass passage 69 is an orifice jet, and the cross-sectional area of ​​the bypass passage 69 is smaller than the cross-sectional area of ​​the oil passage 54b that guides oil from the oil pump 56 to the relief valve 61. Even when the relief valve 61 is closed, oil is supplied to the main gallery 59 through the bypass passage 69.

[0035] In this engine lubrication structure, the amount of oil discharged from the oil pump 56 to the oil passage 54b is small when the engine is running at extremely low speeds immediately after starting. The repulsive force of the valve spring 65 is greater than the oil pressure at the inlet 63 of the relief valve 61, so the plunger 66 closes the relief hole 64, but oil is gradually supplied to the main gallery 59 through the bypass passage 69. Even at extremely low engine speeds where the relief valve 61 does not open, oil is supplied to engine components 53a-53c. The oil pressure increases upstream of the relief hole 64, and relatively high-pressure oil is supplied from the oil passage 54e to the oil control valve 58, which then operates the variable valve train 52.

[0036] When the engine speed increases and the amount of oil discharged from the oil pump 56 to the oil passage 54b increases, the oil pressure at the inlet 63 exceeds the repulsive force of the valve spring 65, pushing the plunger 66 and opening the relief hole 64. Oil is released from the relief hole 64 through oil passages 54d and 54f to the main gallery 59, and is supplied from the main gallery 59 to each of the engine components 53a-53c. The oil pressure in the oil passage 54b is adjusted to a predetermined pressure or lower, but is still equal to or higher than the operating pressure of the variable valve train 52, so oil is also supplied to the oil control valve 58 through the oil passage 54e, and the variable valve train 52 is operated.

[0037] As described above, in the engine lubrication structure of the third embodiment, oil is preferentially supplied to the oil control valve 58 to operate the variable valve mechanism 52. Furthermore, since there is no need to increase the discharge rate of the oil pump 56, mechanical loss during pump operation is reduced, improving engine output and fuel economy. Furthermore, even at extremely low engine speeds where the relief valve 61 does not open, oil is supplied from the oil pump 56 to the engine components 53a-53c through the bypass passage 69 and the main gallery 59.

[0038] <Fourth Example> Next, a lubrication structure for an engine according to a fourth embodiment will be described. Fig. 4 is a schematic diagram of the lubrication structure for an engine according to the fourth embodiment. The lubrication structure for an engine according to the fourth embodiment differs from the lubrication structure for an engine according to the first embodiment in that a bypass passage connects the upstream and downstream sides of the relief hole of the relief valve, and another relief valve is installed downstream of the relief hole of the relief valve. Therefore, a description of the same configuration of the fourth embodiment as that of the first embodiment will be omitted.

[0039] 4, in the engine lubrication structure of the fourth embodiment, oil passages 74a-74f extend from oil pan 71 toward variable valve train 72 and engine components 73a-73c, similar to the engine lubrication structure of the first embodiment. Oil is pumped up from oil pan 71 through oil strainer 75 by oil pump 76, and the oil discharged from oil pump 76 is filtered by oil filter 77. Downstream of oil filter 77, relief valve 81a is connected to oil passage 74c branching off from oil passage 74b, and oil control valve 78 is connected to oil passage 74e branching off from oil passage 74b.

[0040] A relief hole 84a of the relief valve 81a is connected to the main gallery 79 via oil passages 74d and 74f, and oil is supplied from the main gallery 79 to the engine components 73a-73c. A relief valve (another relief valve) 81b with a higher valve opening pressure than the relief valve 81a is connected midway through the oil passage 74d. The relief valve 81b has the same configuration as the relief valve 81a, but the relief hole 84b of the relief valve 81b is open to the atmosphere above the oil pan 71. By releasing oil from the relief hole 84b into the oil pan 71, the oil pressure of the oil passages 74d and 74f downstream of the relief hole 84a is adjusted.

[0041] The oil passage 74b upstream of the relief hole 84a and the oil passage 74f downstream of the relief hole 84a are connected via a bypass passage 89. The oil passage 74f is located closer to the main gallery 79 than the relief valve 81b, and the bypass passage 89 is formed to bypass the two relief valves 81a, 81b. The bypass passage 89 is an orifice jet, and the cross-sectional area of ​​the bypass passage 89 is formed to be smaller than the cross-sectional area of ​​the oil passage 74b. Even when the relief valve 81a is closed, oil is supplied to the main gallery 79 through the bypass passage 89.

[0042] In this engine lubrication structure, the amount of oil discharged from the oil pump 76 to the oil passage 74b is small when the engine is running at extremely low speeds immediately after starting. The repulsive force of the valve spring 85a is greater than the oil pressure at the inlet 83a of the relief valve 81a, so the plunger 86a closes the relief hole 84a, but oil is gradually supplied to the main gallery 79 through the bypass passage 89. Even at extremely low engine speeds where the relief valve 81a does not open, oil is supplied to the engine components 73a-73c. The oil pressure increases upstream of the relief hole 84a, and relatively high-pressure oil is supplied from the oil passage 74e to the oil control valve 78, which then operates the variable valve train 72.

[0043] When the engine speed increases and the amount of oil discharged from the oil pump 76 to the oil passage 74b increases, the oil pressure at the inlet 83a exceeds the repulsive force of the valve spring 85a, pushing the plunger 86a and opening the relief hole 84a. Oil is released from the relief hole 84a through oil passages 74d and 74f to the main gallery 79, and the oil is supplied from the main gallery 79 to each of the engine components 73a-73c. The oil pressure in the oil passage 74b is adjusted to a predetermined pressure or lower, but is still above the operating pressure of the variable valve train 72, so oil is also supplied to the oil control valve 78 through the oil passage 74e, and the variable valve train 72 is operated.

[0044] Furthermore, when the engine is running at high speeds, the amount of oil discharged from the oil pump 76 to the oil passage 74b increases, and a large amount of oil is released from the relief hole 84a of the relief valve 81a into the oil passage 74d. The amount of oil flowing from the oil passage 74d into the inlet 83b of the relief valve 81b increases, causing the oil pressure at the inlet 83b to increase. The oil pressure at the inlet 83b becomes greater than the repulsive force of the valve spring 85b, pushing the plunger 86b in and opening the relief hole 84b. Excess oil is returned to the oil pan 71 from the relief hole 84b, adjusting the oil pressure in each oil passage and the main gallery 79.

[0045] As described above, according to the engine lubrication structure of the fourth embodiment, oil is preferentially supplied to the oil control valve 78 to operate the variable valve mechanism 72. Also, because there is no need to increase the discharge rate of the oil pump 76, mechanical loss during pump operation is reduced, improving engine output and fuel economy. Furthermore, even at extremely low engine speeds where the relief valves 81a, 81b do not open, oil is supplied from the oil pump 76 to the engine components 73a-73c through the bypass passage 89 and the main gallery 79.

[0046] In each embodiment, the oil passage extending from the oil filter branches off to the oil control valve at a location farther from the oil filter than the relief valve, but this configuration is not limiting. The oil passage extending downstream from the oil filter may branch off to the oil control valve at a location closer to the oil filter than the relief valve.

[0047] In the second and fourth embodiments, the other relief valve is connected to the oil passage extending from the relief hole of the relief valve, but the present invention is not limited to this configuration. The other relief valve may be connected to the oil passage between the relief hole of the relief valve and the main gallery.

[0048] In the third and fourth embodiments, the oil passage extending from the oil filter and the oil passage leading to the main gallery are connected by a bypass passage, but this configuration is not limiting. The bypass passage may be any passage that can connect the upstream and downstream sides of the relief hole.

[0049] Furthermore, the engine lubrication structure of this embodiment is not limited to small scooters, but may also be used in other types of straddle-type vehicles and other vehicles.

[0050] As described above, the first aspect is a lubrication structure for an engine equipped with a variable valve train (12, 32, 52, 72) in which valve operation can be changed, and includes a relief valve (21, 41a, 61, 81a) that adjusts the oil pressure of oil discharged from an oil pump (16, 36, 56, 76), a main gallery (19, 39, 59, 79) for supplying oil as lubricating oil to engine components, and an oil control valve (18, 38, 58, 78) that controls the oil pressure for the variable valve train, wherein the main gallery is supplied with oil downstream of a relief hole (24, 44a, 64, 84a) of the relief valve, and the oil control valve is supplied with oil upstream of the relief hole. With this configuration, until the relief hole of the relief valve is opened, the oil pressure of the oil upstream of the relief hole is increased and supplied to the oil control valve. As a result, even at extremely low engine speeds immediately after starting the engine, oil is supplied preferentially to the oil control valve, allowing the variable valve mechanism to operate. When the oil pressure is sufficiently increased to open the relief hole, oil for operation is supplied to the oil control valve, and oil for lubrication is also supplied to various engine parts through the main gallery. Because there is no need to increase the oil pump discharge volume, mechanical loss during pump operation is reduced, improving engine output and fuel efficiency.

[0051] In the second aspect, in the first aspect, the relief valve is installed downstream of the oil filter (17, 37, 57, 77), and the oil control valve is supplied with oil downstream of the oil filter. With this configuration, the oil filtered by the oil filter can be supplied to the variable valve mechanism through the oil control valve.

[0052] In the third aspect, in the first or second aspect, the cross-sectional area of ​​the oil passage (14e, 34e, 54e, 74e) that guides oil upstream of the relief hole to the oil control valve is smaller than the cross-sectional area of ​​the oil passage (14d, 34d, 54d, 74d) that guides oil downstream of the relief hole to the main gallery. With this configuration, the variable valve mechanism requires high oil pressure but does not need a large amount of oil. Therefore, by narrowing the cross-sectional area of ​​the oil passage that guides oil to the oil control valve, a sufficient amount of oil can be supplied to engine components through the main gallery.

[0053] A fourth aspect is any one of the first to third aspects, further comprising another relief valve (41b) having a valve opening pressure set higher than that of the relief valve, and the other relief valve adjusts the oil pressure of the oil downstream of the relief hole of the relief valve. With this configuration, excess oil is discharged from the other relief valve when the engine is running at high speed, and the oil pressure of the oil released from the relief valve toward the main gallery can be stabilized.

[0054] A fifth aspect is any one of the first to third aspects, in which a bypass passage (69, 89) is formed connecting the upstream side and the downstream side of the relief hole, and the cross-sectional area of ​​the bypass passage is formed smaller than the cross-sectional area of ​​the oil passage that guides oil from the oil pump to the relief valve. With this configuration, even at extremely low engine speeds where the relief valve does not open, oil can be supplied to engine components from the oil pump through the bypass passage and the main gallery.

[0055] In a sixth aspect, the fifth aspect is configured so that another relief valve (81b) having a valve opening pressure set higher than that of the relief valve is provided, the other relief valve adjusts the oil pressure of the oil downstream of the relief hole, and the bypass passage connects the oil passage (74b) upstream of the relief hole with an oil passage (74f) closer to the main gallery than the other relief valve. With this configuration, even at extremely low engine speeds where the relief valve and the other relief valve do not open, oil can be supplied from the oil pump to the engine components through the bypass passage and the main gallery.

[0056] Although the present embodiment has been described, other embodiments may be made by combining the above-described embodiments and modifications in whole or in part.

[0057] Furthermore, the technology of the present invention is not limited to the above-described embodiments, and various changes, substitutions, and modifications may be made without departing from the spirit of the technical idea. Furthermore, if the technical idea can be realized in a different way due to technological advances or other derived technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea. [Explanation of symbols]

[0058] 12, 32, 52, 72: Variable valve train 16, 36, 56, 76: Oil pump 17, 37, 57, 77: Oil filter 18, 38, 58, 78: Oil control valve 19, 39, 59, 79: Main Gallery 21, 41a, 61, 81a: Relief valve 24, 44a, 64, 84a: Relief holes 41b, 81b: Other relief valves 69, 89: Bypass passage

Claims

1. A lubrication structure for an engine equipped with a variable valve mechanism capable of changing valve operation, a relief valve that adjusts the oil pressure of the oil discharged from the oil pump; The main gallery supplies oil to the engine parts as a lubricant, an oil control valve that controls hydraulic pressure for the variable valve mechanism, An engine lubrication structure characterized in that the main gallery is supplied with oil downstream of the relief hole of the relief valve, and the oil control valve is supplied with oil upstream of the relief hole.

2. 2. The lubrication structure for an engine according to claim 1, wherein the relief valve is installed downstream of an oil filter, and the oil control valve is supplied with oil downstream of the oil filter.

3. 3. An engine lubrication structure as described in claim 1 or claim 2, characterized in that the cross-sectional area of ​​the oil passage that leads oil upstream of the relief hole to the oil control valve is smaller than the cross-sectional area of ​​the oil passage that leads oil downstream of the relief hole to the main gallery.

4. another relief valve having a valve opening pressure set higher than that of the relief valve; 3. The lubrication structure for an engine according to claim 1, wherein the other relief valve adjusts the oil pressure of the oil downstream of the relief hole of the relief valve.

5. a bypass passage is formed connecting the upstream side and downstream side of the relief hole; 3. The engine lubrication structure according to claim 1, wherein the cross-sectional area of ​​the bypass passage is smaller than the cross-sectional area of ​​an oil passage that guides oil from the oil pump to the relief valve.

6. another relief valve having a valve opening pressure set higher than that of the relief valve; the other relief valve adjusts the oil pressure of the oil downstream of the relief hole; 6. The lubrication structure for an engine according to claim 5, wherein the bypass passage connects the oil passage upstream of the relief hole with the oil passage located closer to the main gallery than the other relief valve.

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