variable valve timing system

Abstract

To provide a variable valve timing system suitable for a layout where an oil control valve is installed on an outer surface of an engine.SOLUTION: A variable valve timing system is mounted on an engine (21) in which a cylinder head (26) on a cylinder (25) is suspended on a vehicle body frame (10). The variable valve timing system is provided with: a variable valve device configured to change an opening and closing timing of a valve by a hydraulic pressure; and an oil control valve (40) which controls the hydraulic pressure applied to the variable valve device. The vehicle body frame includes: a main frame (12) configured to laterally cover the rear side of the cylinder head; and a down frame (13) configured to laterally cover the front side of the cylinder head. In a side view of a vehicle, the oil control valve is detachably installed on an outer surface of the engine below an area surrounded by the main frame, the down frame, and a lower surface of the cylinder head.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a variable valve timing system. [Background technology]

[0002] Variable valve timing systems are being adopted to achieve high power output, low fuel consumption, and low exhaust gas emissions, in which the valve opening and closing timing is controlled by a variable valve timing mechanism depending on the engine's operating conditions. One known variable valve timing system controls the oil pressure for the variable valve timing mechanism using an oil control valve installed on the outer surface of the cylinder head (see, for example, Patent Document 1). Oil controlled by the oil control valve is supplied to the variable valve timing mechanism, and the variable valve timing mechanism switches between a cam for low speed rotation and a cam for high speed rotation, adjusting the valve opening and closing timing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5345448 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the variable valve timing system described in Patent Document 1 does not fully consider the effects of the relative positions of the oil control valve and the body frame, the ease of mounting the engine on the body frame, the ease of installing the oil control valve, etc. Therefore, installing the oil control valve on the outer surface of the cylinder head may have a disadvantageous effect.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to provide a variable valve timing system that is suitable for a layout in which an oil control valve is installed on the outer surface of an engine. [Means for solving the problem]

[0006] One aspect of the variable valve timing system of the present invention is a variable valve timing system for an engine in which a cylinder head is fixed onto a cylinder and the cylinder head is suspended from a body frame, and the system comprises a variable valve train that changes the timing at which the valve opens and closes using hydraulic pressure, and an oil control valve that controls the hydraulic pressure for the variable valve train, wherein the body frame has a main frame that covers the rear side of the cylinder head from the side, and a down frame that covers the front side of the cylinder head from the side, and the above-mentioned problem is solved by the oil control valve being detachably installed on the outer surface of the engine below the area surrounded by the main frame, the down frame, and the underside of the cylinder head when viewed from the side of the vehicle. [Effects of the Invention]

[0007] According to one aspect of the variable valve timing system of the present invention, the oil control valve is separated from the body frame on which the cylinder head is suspended, thereby improving the flexibility of the body frame's shape and preventing the vehicle from becoming too large. Furthermore, the oil control valve is detachably mounted on the outer surface of the engine, improving the ease of mounting the engine and the ease of installing the oil control valve on the body frame. Since the oil control valve is located closer to the center of gravity of the engine, the transmission of vibration to the oil control valve is reduced, improving the durability of the oil control valve. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a right side view of the front part of the vehicle according to the present embodiment. [Figure 2] FIG. 2 is a right side view of the engine and its surroundings according to the present embodiment. [Figure 3] FIG. 2 is a front view of the engine and its surroundings according to the present embodiment. [Figure 4] 2A and 2B are a front view and a rear view of the oil control valve of the present embodiment. [Figure 5]FIG. 2 is a schematic diagram of an oil passage according to the present embodiment. [Figure 6] FIG. 3 is a cross-sectional view of the engine of FIG. 2 taken along line AA. [Figure 7] FIG. 2 is a perspective view of the oil pipe of the present embodiment. [Figure 8] FIG. 2 is a cross-sectional view of an installation location of an oil pipe in this embodiment. [Figure 9] FIG. 4 is an explanatory diagram of an oil passage in the cam housing of the present embodiment. [Figure 10] 1 is a schematic diagram of a variable valve timing system according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0009] A variable valve timing system according to one aspect of the present invention is mounted on an engine in which a cylinder head on a cylinder is suspended from a body frame. In the variable valve timing system, a variable valve timing mechanism changes the opening and closing timing of a valve, and an oil control valve controls hydraulic pressure for the variable valve timing mechanism. The body frame includes a main frame that laterally covers the rear side of the cylinder head and a down frame that laterally covers the front side of the cylinder head. In a side view of the vehicle, an oil control valve is detachably mounted on the outer surface of the engine below an area surrounded by the main frame, the down frame, and the underside of the cylinder head. Because the oil control valve is separated from the body frame on which the cylinder head is suspended, flexibility in the shape of the body frame is improved and an increase in vehicle size is suppressed. Furthermore, because the oil control valve is detachably mounted on the outer surface of the engine, ease of mounting the engine on the body frame and ease of installing the oil control valve are improved. Because the oil control valve is located closer to the center of gravity of the engine, vibration transmission to the oil control valve is reduced, improving the durability of the oil control valve. [Example]

[0010] This embodiment will be described in detail below with reference to the accompanying drawings. Fig. 1 is a right side view of the front of the vehicle of this embodiment. In the following drawings, arrow FR indicates the front of the vehicle, arrow RE indicates the rear of the vehicle, arrow L indicates the left side of the vehicle, and arrow R indicates the right side of the vehicle.

[0011] As shown in Fig. 1, the saddle-ride type vehicle 1 is configured by mounting an engine 21, an electrical system, and various other components on a twin-spar body frame 10. The body frame 10 has a pair of main frames 12 that branch off to the left and right from a head pipe 11 and extend rearward, and a pair of down frames 13 that extend downward from the front portions of the pair of main frames 12. The pair of main frames 12 pass above the engine 21 and curve around to the rear of the engine 21. The upper and rear sides of the engine 21 are suspended by the pair of main frames 12, and the front side of the engine 21 is suspended by the pair of down frames 13.

[0012] A front fork 14 is steerably supported on the head pipe 11 via a steering shaft (not shown). A front wheel 15 is rotatably supported on the lower part of the front fork 14. A radiator (heat exchanger) 16 that dissipates heat from the coolant for the engine 21 is provided in front of the engine 21. An upper part of the radiator 16 is supported on the main frame 12 via an upper bracket 17, and a lower part of the radiator 16 is supported on the engine 21 via a lower bracket 18. A cooling fan 19 is attached to the back of the radiator 16 to draw in hot air from the radiator 16 when the vehicle is stopped, etc.

[0013] The engine 21 is an in-line four-cylinder engine with four cylinders aligned laterally, and has a crankcase 22 that houses a crankshaft (not shown). A cylinder assembly, which is made up of a stack of cylinders 25, a cylinder head 26, and a cylinder head cover 27, is attached to the top of the crankcase 22. An oil pan 28 that stores oil for lubrication and cooling is attached to the bottom of the crankcase 22. Engine covers such as a clutch cover 31 and starter gear covers 32 and 33 are attached to the left side of the crankcase 22. Multiple exhaust pipes 34 extend downward from the front of the engine 21.

[0014] The engine 21 is equipped with a hydraulically controlled variable valve timing system that controls the opening and closing timing of intake valves (not shown). A variable valve train 60 (see FIG. 9) is housed inside the cylinder head 26 and cylinder head cover 27, and an oil control valve 40 is installed on the outer surface of the cylinder 25. The variable valve train 60 and the oil control valve 40 are connected via various oil passages within the engine 21. The oil control valve 40 controls the hydraulic pressure to the variable valve train 60, and the opening and closing timing of the intake valve is changed by the hydraulic pressure to the variable valve train 60.

[0015] Because such an engine 21 is suspended from the body frame 10, the oil control valve 40 needs to be installed so as to avoid interference with the body frame 10. If the oil control valve 40 protrudes significantly outward in the vehicle width direction, the body frame 10 will protrude outward in the vehicle width direction, increasing the size of the vehicle. This limits the degree of freedom in the shape of the body frame 10 and also makes it difficult to mount the engine 21 on the body frame 10. Furthermore, if the oil control valve 40 is located too far from the center of gravity of the engine 21, vibration of the oil control valve 40 will increase, reducing the durability of the oil control valve 40.

[0016] Therefore, in the variable valve timing system of this embodiment, the oil control valve 40 is installed on the outer surface of the cylinder 25, which is sufficiently separated from the body frame 10 and close to the center of gravity of the engine 21. In addition, because the oil control valve 40 is detachable, it can be installed on the outer surface of the cylinder 25 after the engine 21 is mounted on the body frame 10. In this way, a variable valve timing system suitable for a layout in which the oil control valve 40 is installed on the outer surface of the engine 21 is adopted for the engine 21.

[0017] The layout of the oil control valve will be described with reference to Figures 2 and 3. Figure 2 is a right side view of the engine and its periphery in this embodiment. Figure 3 is a front view of the engine and its periphery in this embodiment.

[0018] As shown in Figure 2, the crankcase 22 of the engine 21 has an upper and lower split structure including an upper case 23 and a lower case 24. Various shafts, such as the crankshaft, are supported on the mating surfaces of the upper case 23 and the lower case 24. An oil pan 28 is fixed to the underside of the lower case 24, and a cylinder 25 is fixed to the top surface of the upper case 23. A cylinder head 26 is fixed to the top surface of the cylinder 25, and a cylinder head cover 27 is fixed to the top surface of the cylinder head 26. The cylinder head 26 and crankcase 22 are suspended from the body frame 10.

[0019] The front portion of the body frame 10 branches into a main frame 12 and a down frame 13. The main frame 12 crosses the side of the cylinder head 26 diagonally from the top to the rear, and the down frame 13 is formed in a generally triangular shape in side view so that its front-to-rear width narrows downward. The main frame 12 covers the rear side of the cylinder head 26 from the sides, and the down frame 13 covers the front side of the cylinder head 26 from the sides. The rear side of the cylinder head 26 is suspended from a midpoint in the extension direction of the main frame 12, and the front side of the cylinder head 26 is suspended from the lower top of the down frame 13.

[0020] In a side view of the vehicle, a triangular area (region) is formed on the side of the cylinder head 26, surrounded by the lower edge of the main frame 12, the rear edge of the down frame 13, and the underside of the cylinder head 26. The triangular area of ​​the cylinder head 26 is exposed laterally between the main frame 12 and the down frame 13, but the triangular area is not large enough for the oil control valve 40. For this reason, the oil control valve 40 is installed on the side (outer surface) of the cylinder 25, which is below the triangular area of ​​the cylinder head 26. The side of this cylinder 25 is formed by the outer wall of the cam chain chamber 58 (see FIG. 6).

[0021] A pair of plug caps 66, 67 are installed in a triangular region of the cylinder head 26 to close insertion openings for a pair of oil pipes 64, 65 (see FIG. 6), which will be described later. Because the plug caps 66, 67 avoid the body frame 10 in a side view of the vehicle, the oil pipes 64, 65 can be attached and detached via the plug caps 66, 67 even when the engine 21 is suspended from the body frame 10, improving maintainability. Because the plug caps 66, 67 are installed along the rear edge of the down frame 13, there is no need to modify the shape of the down frame 13. In this case, the plug cap 67 at the rear of the vehicle is positioned higher than the plug cap 66 at the front of the vehicle, and the plug caps 66, 67 partially overlap in the vertical direction, thereby narrowing the installation area for the plug caps 66, 67.

[0022] The oil control valve 40 is formed into a substantially cylindrical shape and includes a valve housing 41 that houses a valve spool (not shown) and a solenoid 42 that moves the valve spool back and forth. The solenoid 42 moves the valve spool back and forth, thereby switching the oil passage within the oil control valve 40. The oil control valve 40 is tilted so that its axial direction is parallel to the mating surface between the cylinder head 26 and the cylinder 25. The solenoid 42 is provided on the rear side of the valve housing 41 and is positioned higher than the valve housing 41.

[0023] Although there is a risk of contamination such as metal powder forming inside the valve housing 41, it is difficult for the contamination to get from the valve housing 41 into the solenoid 42. In other words, the oil control valve 40 is tilted so that the solenoid 42 is higher than the valve housing 41, which prevents the oil from carrying the contamination from the valve housing 41 to the solenoid 42. Because the contamination does not accumulate on the solenoid 42 side, the oil control valve 40 is prevented from being damaged by the contamination. Details of the oil control valve 40 will be described later.

[0024] Because the oil control valve 40 is installed on the outer surface of the cylinder 25, the oil control valve 40 does not interfere with the body frame 10 that suspends the cylinder head 26. Therefore, the body frame 10 does not protrude outward in the vehicle width direction, and an increase in the size of the saddle-ride type vehicle 1 is suppressed. Furthermore, because the center of gravity of the engine 21 is located in the crankcase 22, the oil control valve 40 is located close to the center of gravity of the engine 21. Therefore, transmission of vibration from the crankcase 22 to the oil control valve 40 is reduced, improving the durability of the oil control valve 40.

[0025] In a side view of the vehicle, the cylinder head 26 and cylinder 25 are fixed on either side of the cylinder axis by two bolts 36, and the cylinder 25 and crankcase 22 are fixed on either side of the cylinder axis by two bolts 37. The oil control valve 40 is installed so as not to overlap these four bolts 36, 37, preventing the oil control valve 40 from protruding outward in the vehicle width direction. In this case, the distance between the two upper bolts 36 is wider than the distance between the two lower bolts 37, and the oil control valve 40 is positioned closer to the cylinder head 26.

[0026] Starter gear covers 32, 33 that cover the starter gear (not shown) from the sides are provided below the oil control valve 40. A clutch cover 31 that covers the clutch (not shown) from the sides is provided behind the starter gear covers 32, 33. The upper part of the starter gear cover 32 protrudes toward the cylinder 25, but interference between the starter gear cover 33 and the solenoid 42 is minimized. Note that although the starter gear covers 32, 33 and the clutch cover 31 are formed as separate engine covers, the starter gear covers 32, 33 and the clutch cover 31 may also be formed as a single engine cover.

[0027] 2 and 3, the starter gear covers 32, 33 and the clutch cover 31 bulge outward in the vehicle width direction beyond the side surfaces of the cylinder 25. In a front view of the vehicle, the oil control valve 40 is positioned more inward in the vehicle width direction than the starter gear covers 32, 33, the clutch cover 31, and the down frame 13. In addition, the oil control valve 40 is positioned between the starter gear covers 32, 33 and the down frame 13. When the vehicle falls over, the oil control valve 40 is protected by the starter gear covers 32, 33, the clutch cover 31, and the down frame 13.

[0028] An oil main gallery 38 is formed in the crankcase 22, and the main gallery 38 and oil control valve 40 are connected by external piping 39. As a result, oil is supplied directly from the main gallery 38, which has a high oil pressure, to the oil control valve 40 via the external piping 39. By supplying oil from the main gallery 38 to the oil control valve 40 without passing through the oil passages in the crankcase 22, pressure loss in the oil passages is reduced and oil at a high oil pressure can be supplied to the oil control valve 40.

[0029] The external piping 39 extends from the main gallery 38 toward the front of the vehicle, wraps around the crankcase 22 from below, and extends upward. The external piping 39 is then bent toward the rear of the vehicle below the down frame 13 and connected to a valve housing 41 of an oil control valve 40. In a front view of the vehicle, the external piping 39 passes inside the starter gear covers 32, 33, the clutch cover 31, and the down frame 13 in the vehicle width direction, and is connected to the oil control valve 40 below the down frame 13. When the vehicle turns over, the external piping 39 is protected by the starter gear covers 32, 33, the clutch cover 31, and the down frame 13.

[0030] A radiator 16 having a rectangular shape in front view is provided in front of the cylinder head 26. The radiator 16 is tilted so that its upper portion is positioned further forward than its lower portion. The radiator 16 is a round radiator that is curved in an arch shape in top view, and a cooling fan 19 is attached to the back of the radiator 16 on the oil control valve 40 side (right side) in the vehicle width direction. When viewed from the front of the vehicle, the oil control valve 40 is installed outside the radiator 16 in the vehicle width direction and below the down frame 13, so that the wind generated by traveling is less likely to be blocked by the radiator 16 and the down frame 13 in front of the oil control valve 40.

[0031] Because the oil control valve 40 is a solenoid valve, the oil control valve 40 is prone to heat generation when the solenoid 42 is energized. Therefore, the oil control valve 40 is cooled by the wind while the vehicle is running, which prevents deterioration in the operability of the variable valve mechanism 60 due to a rise in the temperature of the oil control valve 40 and the oil. As described above, the solenoid 42 is positioned on the rear side of the valve housing 41, and is separated from the radiator 16. Heat from the radiator 16 is less likely to be transmitted to the solenoid 42, which prevents a rise in temperature of the solenoid 42.

[0032] In a side view of the vehicle, the lower end of the down frame 13 is positioned on an extension line L extending from the lower end of the cooling fan 19 in the air blowing direction, and the oil control valve 40 is positioned below this extension line L. The exhaust air from the radiator 16 is less likely to hit the oil control valve 40, which prevents deterioration in the operability of the variable valve mechanism 60 caused by a rise in the temperatures of the oil control valve 40 and the oil. In addition, in a front view of the vehicle, the down frame 13 covers the solenoid 42 of the oil control valve 40, which blocks the exhaust air from the radiator 16 and prevents a rise in the temperature of the solenoid 42.

[0033] The oil control valve will be described with reference to Fig. 4. Fig. 4 shows a front view and a rear view of the oil control valve of this embodiment. Fig. 4(A) shows the front view of the oil control valve, and Fig. 4(B) shows the rear view of the oil control valve.

[0034] As shown in Figures 4(A) and 4(B), the valve housing 41 of the oil control valve 40 has a mounting plate 43 that is mounted on the side of the cylinder 25, and a cylindrical case 44 that bulges outward from the mounting plate 43. Fixing holes 45 for screwing are formed in three locations around the outer edge of the mounting plate 43 surrounding the cylindrical case 44. In addition, a supply port 46 to which the external piping 39 (see Figure 2) is connected is formed in the lower part of the mounting plate 43. A valve spool extending from the solenoid 42 is inserted into the cylindrical case 44. The destination of the oil that enters through the supply port 46 is switched by the valve spool.

[0035] An O-ring 47 is attached to the back surface of the installation plate 43, sealing the gap between the back surface of the installation plate 43 and the side surface of the cylinder 25. A supply port 46, an input port 51, an advance port 52, a retard port 53, and a drain port 54 are formed inside the O-ring 47. The supply port 46 is connected to the input port 51 through an oil passage formed in the cylinder 25. A filter 55 is installed in the input port 51, and the oil is filtered by passing through the filter 55. The input port 51 is connected to one of the advance port 52, retard port 53, and drain port 54, depending on the position of the valve spool.

[0036] When oil flows into the input port 51 from the supply port 46, the oil is filtered by the filter 55 of the input port 51 and then input into the cylindrical case 44. When the valve spool is moved by the solenoid 42, the input port 51 is connected to either the advance port 52 or the retard port 53, and the drain port 54 is connected to the other of the advance port 52 or the retard port 53. As a result, oil is supplied from the oil control valve 40 to either the advance chamber S1 or the retard chamber S2 of the variable valve mechanism 60 (see FIG. 10 ), which will be described later, and excess oil is discharged from the other of the chambers toward the oil control valve 40.

[0037] The oil passages in the engine will be described with reference to Figures 5 to 9. Figure 5 is a schematic diagram of the oil passages in this embodiment. Figure 6 is a cross-sectional view of the engine in Figure 2 taken along line AA. Figure 7 is a perspective view of the oil pipe in this embodiment. Figure 8 is a cross-sectional view of the installation location of the oil pipe in this embodiment. Figure 9 is an explanatory diagram of the oil passages in the cam housing in this embodiment. Note that the cam chain is omitted from Figure 6 for ease of explanation. Figure 8(A) shows the state with the plug cap installed, and Figure 8(B) shows the state with the plug cap removed. Figure 9(A) shows the state where the lower housing is viewed from below, Figure 9(B) shows the state where the upper housing is viewed from below, and Figure 9(C) shows the state where the camshaft is removed.

[0038] As shown in Figure 5, a cam chain chamber 58 is formed in the cylinder 25 and cylinder head 26 of the engine 21. A cam chain 59 is housed in the cam chain chamber 58, and the cam chain 59 is stretched over an intake cam sprocket 71 and an exhaust cam sprocket 81. An intake camshaft 72 is fixed to the intake cam sprocket 71, and an exhaust camshaft 82 is fixed to the exhaust cam sprocket 81. A crankshaft (not shown) is connected to the intake camshaft 72 and the exhaust camshaft 82 via the cam chain 59.

[0039] The intake camshaft 72 and the exhaust camshaft 82 are rotatably supported by a cam housing 91. The cam housing 91 is a support wall fixed to the cylinder head 26, and has an upper housing 92 that supports the upper halves of the camshafts 72, 82, and a lower housing 93 that supports the lower halves of the camshafts 72, 82. A variable valve train 60 is attached to one end of the intake camshaft 72 inside the cylinder head 26. The variable valve train 60 uses hydraulic pressure to advance or retard the intake camshaft 72, thereby changing the opening and closing timing of the intake valve (not shown).

[0040] An oil control valve 40 is installed on the outer surface (side surface) of the cylinder 25, which forms the outer wall of the cam chain chamber 58. The oil control valve 40 controls the oil pressure to the variable valve train 60. An advance passage 100 extends from an advance port 52 (see FIG. 4B) of the oil control valve 40 toward the variable valve train 60, and a retard passage 105 extends from a retard port 53 (see FIG. 4B) of the oil control valve 40 toward the variable valve train 60. Oil that advances the opening and closing timing of the intake valve flows through the advance passage 100, and oil that retards the opening and closing timing of the intake valve flows through the retard passage 105.

[0041] The advance passage 100 and retard passage 105 for hydraulic control enter the outer wall of the cam chain chamber 58 from the oil control valve 40. The advance passage 100 and retard passage 105 then flow from the cylinder 25 side toward the cylinder head 26 side, cross the cam chain chamber 58, and flow toward the variable valve mechanism 60 through the inner wall of the cam chain chamber 58. In this case, the outer wall of the cam chain chamber 58 is formed by the outer wall of the cylinder 25, the outer wall of the cylinder head 26, and the outer wall of the crankcase 22, while the inner wall of the cam chain chamber 58 is formed by the inner wall of the cylinder 25, the inner wall of the cylinder head 26, the inner wall of the crankcase 22, and the cam housing 91.

[0042] The outer wall and inner wall of the cylinder head 26 are connected by a pair of oil pipes 64, 65. The pair of oil pipes 64, 65 pass inside the cam chain 59 and cross the cam chain chamber 58. Because the oil pipes 64, 65 are installed detachably, the pair of oil pipes 64, 65 do not become an obstacle when assembling the cam chain 59. Because the pair of oil pipes 64, 65 are detachable, the pair of oil pipes 64, 65 can be inserted after assembling the cam chain 59 to the engine 21. This makes effective use of the dead space inside the cam chain 59.

[0043] In the outer wall of the cam chain chamber 58, the advance passage 100 and the retard passage 105 extend parallel to the cylinder axis from the outer wall of the cylinder 25 toward the outer wall of the cylinder head 26. In this case, the advance passage 100 is positioned on the front side, and the retard passage 105 is positioned on the rear side, with the retard passage 105 extending to a position higher than the advance passage 100. Between the outer wall and inner wall of the cam chain chamber 58, the advance passage 100 and the retard passage 105 extend perpendicular to the cylinder axis, passing inside the pair of oil pipes 64, 65. In this way, the pair of oil pipes 64, 65 form a crossing point of the advance passage 100 and the retard passage 105.

[0044] In the inner wall of the cam chain chamber 58, an advance passage 100 and a retard passage 105 extend parallel to the cylinder axis from the outer wall of the cylinder head 26 toward the cam housing 91. The advance passage 100 passes through the lower housing 93 and extends to a mating surface 151 between the lower housing 93 and the upper housing 92, and then passes through the mating surface 151 to connect to the advance groove 131 from the side. The retard passage 105 passes through the mating surface 152 between the cylinder head 26 and the lower housing 93 and extends to below the retard groove 132, and then passes through the lower housing 93 to connect to the retard groove 132 from below. The advance groove 131 and the retard groove 132 are connected to the variable valve train 60 via the intake camshaft 72.

[0045] In the cylinder 25 and the cylinder head 26, the advance passage 100 and the retard passage 105 are formed by a straight passage parallel to the cylinder axis and an orthogonal passage perpendicular to the straight passage. This reduces oil pressure loss in the advance passage 100 and the retard passage 105 and allows the advance passage 100 and the retard passage 105 to be easily machined into the cylinder 25 and the cylinder head 26. In the cylinder 25 and the cylinder head 26, the advance passage 100 and the retard passage 105 are aligned in parallel. This allows the advance passage 100 and the retard passage 105 to be close to each other in the front-to-rear direction, preventing the engine 21 from becoming larger.

[0046] A drain hole 109 (see FIG. 10 in particular) that connects to the drain port 54 (see FIG. 4B) of the oil control valve 40 is formed in the outer wall of the cam chain chamber 58 on the cylinder 25 side. The inner peripheral surface of the cam chain 59 is positioned below the drain hole 109, and oil is discharged from the drain hole 109 toward the cam chain 59. The oil that drops from the drain hole 109 is supplied to the cam chain 59, appropriately lubricating the meshing portions of the cam chain 59 with the intake cam sprocket 71 and the exhaust cam sprocket 81, improving the durability of the cam chain 59. In addition, no guides or complex machining are required to direct the oil toward the cam chain 59.

[0047] As shown in Figure 6, a cylindrical cylinder bore 95 is formed in the cylinder 25, and a piston (not shown) is slidably housed in the cylinder bore 95. A ceiling surface is formed in the cylinder head 26 that covers the cylinder bore 95, and a combustion chamber 96 is formed between the top surface of the piston and the ceiling surface of the cylinder head 26. A water jacket 97 that cools the combustion chamber 96 is formed on the inner walls of the cylinder 25 and the cylinder head 26. As described above, on one side (right side) of the engine 21 in the vehicle width direction, a cam chain chamber 58 is formed between the outer and inner walls of the cylinder 25 and the cylinder head 26.

[0048] An advance passage 100 is formed from the location of the oil control valve 40 on the outer wall of the cylinder 25 to the outer wall of the cylinder head 26. The outer and inner walls of the cylinder head 26 are connected via an oil pipe 64, and the advance passage 100 crosses the cam chain chamber 58 via the oil pipe 64 above the combustion chamber 96. At this time, the advance passage 100 crosses the cam chain chamber 58 toward the top of the water jacket 97, and is formed so as to pass next to the water jacket 97 on the inner wall of the cylinder head 26. The retard passage 105 is formed in substantially the same manner as the advance passage 100.

[0049] The advance passage 100 and the retard passage 105 are formed so as to bypass the combustion chamber 96. Furthermore, the advance passage 100 and the retard passage 105 pass next to the water jacket 97, which cools the oil in the advance passage 100 and the retard passage 105. Furthermore, the cam chain chamber 58 and the water jacket 97 are formed between the advance passage 100 and the combustion chamber 96 and between the retard passage 105 and the combustion chamber 96, making it difficult for heat to be transferred from the combustion chamber 96 to the oil in the advance passage 100 and the retard passage 105. Therefore, the oil temperature in the advance passage 100 and the retard passage 105 is stabilized, and the operation of the variable valve mechanism 60 is stabilized.

[0050] 7 and 8A, a first seal surface 111 is formed on one end of the outer peripheral surface of the oil pipe 64, and the first seal surface 111 is attached to the outer wall of the cam chain chamber 58 (cylinder head 26). The second seal surface 115 is formed on the other end of the outer peripheral surface of the oil pipe 64, and the second seal surface 115 is attached to the inner wall of the cam chain chamber 58. The first seal surface 111 has a slightly larger diameter than the second seal surface 115, and the space between the first and second seal surfaces 111, 115 has the same diameter as the second seal surface 115. One end of the oil pipe 64, which is closer to the first seal surface 111 than the first seal surface 111, forms a reduced-diameter portion 119 that is smaller in diameter than the first and second seal surfaces 111, 115.

[0051] A first seal groove 112 is formed in the first seal surface 111, and a first O-ring 113 is fitted in the first seal groove 112. A second seal groove 116 is formed in the second seal surface 115, and a second O-ring 117 is fitted in the second seal groove 116. Through holes 120 extend through the reduced diameter portion 119 of the oil pipe 64 so as to intersect in a cross shape, and the oil pipe 64 and the advance passage 100 are connected through the through holes 120. Oil flows in from the radial direction through the through holes 120 at one end of the oil pipe 64, and oil flows out from the axial direction at the other end of the oil pipe 64.

[0052] First and second mounting holes 114, 118 are formed in the outer and inner walls of the cam chain chamber 58 (cylinder head 26). A first seal surface 111 of the oil pipe 64 is installed in the first mounting hole 114 on the outer wall side, and a second seal surface 115 of the oil pipe 64 is installed in the second mounting hole 118 on the inner wall side. A first O-ring 113 provides a liquid-tight seal between the first seal surface 111 and the inner circumferential surface of the first mounting hole 114, and a second O-ring 117 provides a liquid-tight seal between the second seal surface 115 and the inner circumferential surface of the second mounting hole 118. The first and second seal surfaces 111, 115 prevent oil leakage from the oil pipe 64 at the outer and inner walls of the cam chain chamber 58.

[0053] An insertion port 98 for the oil pipe 64 is formed in the outer wall of the cam chain chamber 58, and the insertion port 98 is closed by the plug cap 66. An internal thread is formed on the inner peripheral surface of the insertion port 98, and the external threads of the plug cap 66 are fitted into the internal threads of the insertion port 98. The insertion port 98 has a larger diameter than the first and second installation holes 114, 118. A reduced-diameter portion 119 of the oil pipe 64 is positioned inside the internal threads of the insertion port 98, and a through-hole 120 in the reduced-diameter portion 119 is connected to an oil passage that opens into the internal threads. Oil can easily enter the oil pipe 64 from the insertion port 98 through the multiple through-holes 120, reducing pressure loss at one end of the oil pipe 64.

[0054] In this case, after a second installation hole 118 of φ12 (hole diameter 12 mm) is formed in the inner wall of the cam chain chamber 58, a pilot hole of φ14 (hole diameter 14 mm) is formed so as to chamfer the second installation hole 118. This pilot hole forms the first installation hole 114 in the outer wall of the cam chain chamber 58. An M16 (thread diameter 16 mm) female thread is cut on the inlet side of the pilot hole to form the insertion port 98. By forming the female-threaded pilot hole in this manner, the second installation hole 118 is chamfered and the first installation hole 114 is formed. The inner diameter of the oil pipe 64 and the inner diameter of the through-hole 120 are each formed to φ6 (hole diameter 6 mm).

[0055] One end of the oil pipe 64 is closed by a plug cap 66. There is a small gap between one end of the oil pipe 64 and the plug cap 66, but the one end of the oil pipe 64 and the plug cap 66 may also come into contact. The tension of the oil pipe 64 also serves to reduce noise from the wall of the cam chain chamber 58. In addition, the outer wall of the cylinder head 26 bulges outward in the vehicle width direction at the location where the variable valve train 60 (see Figure 9) is housed, and the amount of protrusion of the plug caps 66, 67 in the vehicle width direction is less than the amount of bulge of the bulging portion 99 of the outer wall. This makes it easier to assemble the engine 21 to the body frame 10.

[0056] As shown in Figure 8(B), one end of the oil pipe 64 forms a reduced diameter portion 119, and therefore there is a sufficient gap between the insertion opening 98 and the reduced diameter portion 119, improving the ease of removal of the oil pipe 64. For example, after removing the plug cap 66 from the insertion opening 98, the oil pipe 64 can be pulled out by grasping the reduced diameter portion 119 of the oil pipe 64 with a tool 121 such as pliers, or by hooking a hook 122 into the through hole 120 of the reduced diameter portion 119. Note that while the advance oil pipe 64 and plug cap 66 have been described above, the retard oil pipe 65 and plug cap 67 are configured in the same way.

[0057] 9(A) to 9(C), the journals 73, 83 of the intake camshaft 72 and the exhaust camshaft 82 are supported by an upper housing (support wall) 92 and a lower housing (support wall) 93. The intake cam sprocket 71 and the variable valve train 60 are attached to one end of the intake camshaft 72, and the exhaust cam sprocket 81 is attached to one end of the exhaust camshaft 82. Thrust stops 74, 84 for positioning in the axial direction (thrust direction) are formed on the outer circumferential surfaces of the journals 73, 83 of the intake camshaft 72 and the exhaust camshaft 82.

[0058] An advance groove 131, a retard groove 132, and a storage groove 133 are formed in an intake-side bearing surface 130 of the upper housing 92 and the lower housing 93 (the bearing surface of the lower housing 93 is not shown). Oil that advances the intake-side camshaft 72 enters the advance groove 131, oil that retards the intake-side camshaft 72 enters the retard groove 132, and the storage groove 133 accommodates the thrust stopper 74 of the intake-side camshaft 72. On the intake-side bearing surface 130, the retard groove 132 is positioned on one wall surface 135 of the upper housing 92, the storage groove 133 is positioned on another wall surface 136 of the upper housing 92, and the advance groove 131 is positioned between the retard groove 132 and the storage groove 133. The lower housing 93 also has similar grooves formed therein.

[0059] The upper housing 92 and the lower housing 93 have bolt holes 137a-137d formed in four locations sandwiching the intake camshaft 72 and the exhaust camshaft 82. An advance angle through-passage 102 penetrates the lower housing 93 from top to bottom at the center of the underside of the lower housing 93, and a retard angle passage groove 107 (see FIG. 9A) extends from the center of the underside of the lower housing 93 to the intake side, passing next to the bolt hole 137c. Portions of the advance angle through-passage 102 and the retard angle passage groove 107 are sandwiched between bolts fastened in the bolt holes 137b and 137c. The underside of the lower housing 93 forms a mating surface 152 between the cylinder head 26 and the lower housing 93, and the mating surface 152 increases the surface pressure near the advance angle through-passage 102 and the retard angle passage groove 107, thereby suppressing oil leakage.

[0060] The advance angle through-passage 102 extends to a mating surface 151 between the lower housing 93 and the upper housing 92, and an advance angle passage groove 103 (see FIG. 9B) is formed in the mating surface 151, extending from the upper end of the advance angle through-passage 102 toward the advance angle groove 131. The retard angle passage groove 107 extends to below the retard angle groove 132, and a retard angle through-passage 108 passes through the lower housing 93 from top to bottom to connect the retard angle passage groove 107 and the retard angle groove 132. In this way, the advance angle through-passage 100 that supplies oil to the advance angle groove 131 from the side is formed by the advance angle through-passage 102 and the advance angle passage groove 103, and the retard angle passage groove 107 and the retard angle through-passage 108 form a retard angle passage 105 that supplies oil to the retard angle groove 132 from below.

[0061] Advance holes 75 are formed in the journal 73 of the intake camshaft 72 in correspondence with the advance grooves 131, and retard holes 76 are formed in correspondence with the retard grooves 132. The advance holes 75 pass through passages in the intake camshaft 72 and communicate with advance chambers S1 (see FIG. 10) of the variable valve train 60. The retard holes 76 pass through passages in the intake camshaft 72 and communicate with retard chambers S2 (see FIG. 10) of the variable valve train 60. The intake camshaft 72 is advanced by supplying oil from the advance grooves 131 to the advance chambers S1 of the variable valve train 60, and the intake camshaft 72 is retarded by supplying oil from the retard grooves 132 to the retard chambers S2 of the variable valve train 60.

[0062] Here, power is transmitted from the cam chain 59 (see FIG. 10) to the intake camshaft 72 via the variable valve train 60. The variable valve train 60 continues to receive torque from the intake camshaft 72 in a direction that retards the inner rotor 62 (see FIG. 10), and therefore, greater hydraulic pressure is required to advance the intake camshaft 72 than to retard it. Because the advance grooves 131 are located between the retard grooves 132 and the accommodation groove 133 on the bearing surface 130, the advance grooves 131 are separated from one wall surface 135 and the other wall surface 136. Counteracting hydraulic pressure that retards oil leakage from the advance grooves 131 is generated in the retard grooves 132 and the accommodation groove 133, suppressing oil leakage from the advance grooves 131 and allowing the variable valve train 60 to operate stably with appropriate hydraulic pressure.

[0063] Furthermore, because the oil pressure required for the retard grooves 132 is smaller than that required for the advance grooves 131, even if a small amount of oil leaks from the retard grooves 132, it does not affect the operation of the variable valve train 60. Furthermore, the accommodating grooves 133 not only lubricate the thrust stoppers 74 with oil, but also generate a counter oil pressure against the oil leakage from the advance grooves 131. Because the main purposes of the accommodating grooves 133 are lubrication and counter oil pressure, even if a small amount of oil leaks from the accommodating grooves 133, it does not affect the operation of the variable valve train 60. Furthermore, because the upper housing 92 and the lower housing 93 are separate parts from the cylinder head 26, the mating surfaces 151 of the upper housing 92 and the lower housing 93 have high flatness precision, and the advance grooves 131, retard grooves 132, and accommodating grooves 133 are formed with high precision.

[0064] A lubrication groove 141 and an accommodation groove 142 are formed in exhaust-side bearing surfaces 140 of the upper housing 92 and the lower housing 93 (the bearing surface of the lower housing 93 is not shown). Lubricating oil enters the lubrication groove 141, and the accommodation groove 142 accommodates the thrust stopper 84 of the exhaust-side camshaft 82. The lubrication groove 141 is positioned on one wall surface 135 side of the upper housing 92, and the accommodation groove 142 is positioned on the other wall surface 136 side of the upper housing 92. Similar grooves are formed in the lower housing 93. An oil hole 85 is formed in the journal 83 of the exhaust-side camshaft 82 to pass lubricating oil from a passage in the exhaust-side camshaft 82 to the lubrication groove 141.

[0065] A lubrication passage groove 143 is formed in a mating surface 151 between the lower housing 93 and the upper housing 92, through which lubricating oil flows from the lubrication groove 141 of the exhaust-side camshaft 82 toward the accommodation groove 133 of the intake-side camshaft 72. In this way, the lubrication groove 141 and the lubrication passage groove 143 form a lubrication passage that supplies oil from the side to the accommodation groove 133. At the housing mating surface 151, the lubrication passage groove 143 bypasses the advance passage groove 103 so as to pass inside the engine 21, passes next to the advance passage groove 103, and continues to the accommodation groove 133. The supply of oil from the lubrication passage groove 143 to the accommodation groove 133 lubricates the thrust stopper 74 of the intake-side camshaft 72.

[0066] Furthermore, since the lubrication passage groove 143 passes adjacent to the advance passage groove 103, a counter oil pressure is generated in the lubrication passage groove 143 against oil leakage from the advance passage groove 103, thereby suppressing oil leakage from the advance passage groove 103. At the mating surface 151 of the housing, the advance passage groove 103 is formed wider than the lubrication passage groove 143, and the advance passage groove 103 ensures the amount of oil necessary to advance the intake camshaft 72. Because the lower housing 93 and the upper housing 92 form an oil passage from the exhaust camshaft 82 to the intake camshaft 72, components such as piping are not required, thereby saving space.

[0067] The variable valve timing system will be described with reference to Fig. 10. Fig. 10 is a schematic diagram of the variable valve timing system of this embodiment.

[0068] As shown in Figure 10, a drive gear 155 for the cam chain 59 is provided below the oil control valve 40. A crankshaft (not shown) is connected to the drive gear 155 via a gear train. The lower part of the cam chain 59 is hooked onto the drive gear 155, and the upper part of the cam chain 59 is hooked onto the intake side cam sprocket 71 and the exhaust side cam sprocket 81. When the drive gear 155 rotates and the cam chain 59 moves around, the intake side camshaft 72 rotates integrally with the intake side cam sprocket 71, and the exhaust side camshaft 82 rotates integrally with the exhaust side cam sprocket 81.

[0069] The cam chain 59 is guided by a lever guide 156 and a chain guide 157. The cam chain 59 that is sent out from the drive gear 155 to the intake side cam sprocket 71 is guided by the lever guide 156, and the cam chain 59 that is pulled from the exhaust side cam sprocket 81 to the drive gear 155 is guided by the chain guide 157. Because slack occurs in the cam chain 59 that goes from the drive gear 155 to the intake side cam sprocket 71, a chain tensioner (not shown) presses the lever guide 156 against the cam chain 59, applying tension to the cam chain 59.

[0070] The intake valve and exhaust valve are opened and closed by the rotation of the intake camshaft 72 and the exhaust camshaft 82, but the timing of opening and closing the intake valve is changed by a variable valve timing system. The variable valve timing system is provided with a variable valve train 60 that changes the relative rotational phase of the intake camshaft 72 with respect to the crankshaft. The variable valve train 60 has a case 61 fixed to the intake cam sprocket 71 and an inner rotor 62 fixed to the intake camshaft 72. The inner rotor 62 is housed inside the case 61 so as to be able to rotate relative to the crankshaft.

[0071] A case 61 of the variable valve mechanism 60 is formed with a plurality of hydraulic chambers, and a plurality of vanes 63 extend radially outward from an inner rotor 62. A vane 63 of the inner rotor 62 is housed in each hydraulic chamber of the case 61, and each hydraulic chamber is divided by the vanes 63 into an advance chamber S1 and a retard chamber S2. When the volume of the advance chamber S1 expands due to hydraulic pressure, the inner rotor 62 rotates relatively to the case 61 toward the advance side, and the intake camshaft 72 is advanced. When the volume of the retard chamber S2 expands due to hydraulic pressure, the inner rotor 62 rotates relatively to the case 61 toward the retard side, and the intake camshaft 72 is retarded.

[0072] The variable valve train 60 is operated by hydraulic pressure from the oil control valve 40. Oil is supplied to the oil control valve 40 from the main gallery 38 (see FIG. 2) through external piping 39. Depending on the communication state between the ports of the oil control valve 40, the destination of the oil supplied from the oil control valve 40 is switched between the advance chamber S1 and the retard chamber S2 of the variable valve train 60. Oil is supplied to the advance chamber S1 from the oil control valve 40 through an advance passage 100, and oil is supplied to the retard chamber S2 from the oil control valve 40 through a retard passage 105.

[0073] As described above, the advance passage 100 and the retard passage 105 traverse the cam chain chamber 58 (see FIG. 6 ), and the oil pipes 64, 65 are used to traverse the cam chain chamber 58. The oil pipes 64, 65 are installed inside the cam chain 59 between the lever guide 156 and the chain guide 157. The oil pipes 64, 65 are lined up in the front and rear with a space between them in the vertical direction, which narrows the installation area for the oil pipes 64, 65 and allows the oil pipes 64, 65 to be installed inside the cam chain 59 with ample space between them. Even when the cam chain 59 is pushed in by the lever guide 156, the cam chain 59 does not interfere with the oil pipes 64, 65.

[0074] As described above, according to this embodiment, the oil control valve 40 is separated from the body frame 10 on which the cylinder head 26 is suspended, which improves the flexibility of the shape of the body frame 10 and prevents the vehicle from becoming larger. Furthermore, the oil control valve 40 is detachably mounted on the outer surface of the cylinder 25, which improves the ease of mounting the engine 21 on the body frame 10 and the ease of installing the oil control valve 40. In other words, the oil control valve 40 can be installed on the engine 21 after the engine 21 is mounted on the body frame 10. Since the oil control valve 40 is located closer to the center of gravity of the engine 21, the transmission of vibration to the oil control valve 40 is reduced, which improves the durability of the oil control valve 40.

[0075] In this embodiment, an in-line four-cylinder engine is used as an example of the engine, but the type of engine is not particularly limited.

[0076] In addition, in this embodiment, a twin-spar frame is used as an example of the body frame, but the type of body frame is not particularly limited as long as it is a body frame capable of suspending a cylinder head. For example, the body frame may be a cradle frame.

[0077] Furthermore, in this embodiment, the oil control valve is installed on the right side of the engine, but the oil control valve may be installed on the left side of the engine.

[0078] In addition, in this embodiment, the oil control valve is installed on the outer surface of the cylinder, but the oil control valve may be installed on the outer surface of the engine. For example, the oil control valve may be installed on the outer surface of the crankcase.

[0079] Furthermore, in this embodiment, a solenoid valve is used as an example of the oil control valve, but the type of oil control valve is not particularly limited as long as it is a valve that can control the oil pressure for the variable valve mechanism.

[0080] Furthermore, in this embodiment, the intake camshaft is provided with a variable valve operating device, but it is sufficient that at least one of the intake camshaft and the exhaust camshaft is provided with a variable valve operating device.

[0081] Furthermore, in this embodiment, the oil control valve and the main gallery are connected by an external pipe, but the oil control valve and the main gallery may also be connected by an oil passage within the engine.

[0082] In this embodiment, the cross passage of the cam chain chamber is formed by a detachable oil pipe, but the cross passage of the cam chain chamber may be formed in any manner that allows oil to move between the inner and outer walls of the cam chain chamber. For example, the cross passage may be formed by protruding one of the inner and outer walls of the cylinder head toward the other.

[0083] In addition, in this embodiment, the advance passage and the retard passage are partially formed parallel to each other, but if the engine is large enough, the advance passage and the retard passage may be formed non-parallel to each other as a whole.

[0084] In addition, in this embodiment, the advance passage and the retard passage pass above the combustion chamber, but the routes of the advance passage and the retard passage are not particularly limited as long as they extend from the oil control valve, cross the cam chain chamber, and toward the variable valve mechanism.

[0085] In addition, in this embodiment, the oil control valve is installed so as not to overlap the bolts on the outer surface of the cylinder, but the oil control valve may overlap the bolts as long as it does not protrude excessively from the outer surface of the engine.

[0086] In addition, in this embodiment, a pair of oil pipes are arranged in front and behind the cam chain with a space between them in the vertical direction, but the location where the pair of oil pipes are installed is not particularly limited as long as the pair of oil pipes do not interfere with the cam chain.

[0087] In addition, in this embodiment, a pair of plug caps are installed along the rear edge of the down frame, but the installation locations of the pair of plug caps are not particularly limited as long as the pair of plug caps do not interfere with the vehicle body frame.

[0088] Furthermore, in this embodiment, the oil pipe and the plug cap are formed as separate bodies, but the oil pipe and the plug cap may be formed as one body.

[0089] In addition, in this embodiment, one end of the oil pipe is reduced in diameter and a through hole is formed in the radial direction at this end, but the shape of the oil pipe is not particularly limited as long as the oil pipe can cross the cam chain chamber.

[0090] Furthermore, in this embodiment, the support wall of the camshaft is a cam housing that is separate from the cylinder head, but the support wall of the camshaft may be formed integrally with the cylinder head.

[0091] In this embodiment, the retard passages of the cam housing are connected to the retard grooves from below, and the advance passages of the cam housing are connected to the advance grooves from the sides, but the routes of the advance and retard passages of the cam housing are not particularly limited. For example, the retard passages may be connected to the retard grooves from the sides, and the advance passages may be connected to the advance grooves from below.

[0092] In addition, in this embodiment, a lubrication passage groove is formed from the exhaust side camshaft to the intake side camshaft, but the lubrication passage groove may not be formed and oil may be supplied from the intake side camshaft to the accommodation groove.

[0093] In addition, in this embodiment, the oil control valve is positioned further outward in the vehicle width direction than the radiator and lower than the down frame, but the positional relationship between the radiator and the oil control valve is not particularly limited.

[0094] In addition, in this embodiment, the oil control valve is positioned below the extension line of the lower end of the cooling fan in the air blowing direction, but the positional relationship between the cooling fan and the oil control valve is not particularly limited.

[0095] Furthermore, in this embodiment, the oil control valve is positioned more inward in the vehicle width direction than the engine cover and the down frame, but the oil control valve may be positioned more outward in the vehicle width direction than the engine cover and the down frame.

[0096] Furthermore, in this embodiment, the external piping is positioned more inward in the vehicle width direction than the engine cover and the down frame, but the external piping may also be positioned more outward in the vehicle width direction than the engine cover and the down frame.

[0097] Furthermore, in this embodiment, the area surrounded by the lower surfaces of the main frame, down frame, and cylinder head is formed in a triangular shape, but the shape of the area surrounded by the lower surfaces of the main frame, down frame, and cylinder head is not particularly limited.

[0098] Furthermore, the variable valve timing system is not limited to the illustrated saddle-ride type vehicle, and may be employed in other types of saddle-ride type vehicles. A saddle-ride type vehicle is not limited to all vehicles in which a rider sits astride a seat, but also includes small scooter-type vehicles in which a rider does not sit astride a seat.

[0099] As described above, the variable valve timing system of this embodiment is a variable valve timing system for an engine (21) in which a cylinder head (26) is fixed onto a cylinder (25) and the cylinder head is suspended from a body frame (10), and includes a variable valve train (60) that changes the valve opening / closing timing using hydraulic pressure, and an oil control valve (40) that controls the hydraulic pressure for the variable valve train, and the body frame has a main frame (12) that covers the rear side of the cylinder head from the sides and a down frame (13) that covers the front side of the cylinder head from the sides, and the oil control valve is detachably installed on the outer surface of the engine below the area surrounded by the main frame, the down frame, and the underside of the cylinder head in a side view of the vehicle. With this configuration, the oil control valve is separated from the body frame on which the cylinder head is suspended, thereby improving the flexibility of the shape of the body frame and preventing the vehicle from becoming larger. Furthermore, by detachably installing the oil control valve on the outer surface of the engine at a position that avoids the body frame, the ease of mounting the engine on the body frame and the ease of installing the oil control valve are improved.Since the oil control valve is located closer to the center of gravity of the engine, the transmission of vibration to the oil control valve is reduced, improving the durability of the oil control valve.

[0100] In the variable valve timing system of this embodiment, a heat exchanger (radiator 16) is installed in front of the engine, and the oil control valve is positioned outboard of the heat exchanger in the vehicle width direction and below the down frame when viewed from the front of the vehicle. This configuration makes it less likely that the airflow from the vehicle traveling will block the oil control valve. This allows the oil control valve to be cooled by the airflow, preventing deterioration in the operability of the variable valve timing system due to temperature increases in the oil and oil control valve.

[0101] In the variable valve timing system of this embodiment, a heat exchanger is installed in front of the engine, a cooling fan (19) is attached to the rear of the heat exchanger, the lower end of the down frame is positioned on an extension of the lower end of the cooling fan in the direction of airflow, and the oil control valve is positioned below this extension, in a side view of the vehicle. With this configuration, the exhaust air from the heat exchanger is less likely to hit the oil control valve, and deterioration of the operability of the variable valve timing device due to temperature increases in the oil and oil control valve is suppressed.

[0102] In the variable valve timing system of this embodiment, the engine covers (clutch cover 31, starter gear covers 32, 33) bulge outward in the vehicle width direction from the outer surfaces of the cylinders, and the oil control valve is positioned inward in the vehicle width direction from the engine cover and down frame, and is positioned between the engine cover and down frame, in a front view of the vehicle. With this configuration, the oil control valve is protected by the engine cover and down frame when the vehicle rolls over.

[0103] In the variable valve timing system of this embodiment, the engine cover bulges outward in the vehicle width direction beyond the outer surface of the cylinder, a main oil gallery (38) is formed in the engine, an external pipe (39) extends from the main gallery to the oil control valve, and in front view of the vehicle, the external pipe passes inside the down frame and engine cover in the vehicle width direction and is connected to the oil control valve below the down frame. With this configuration, the external pipe is protected by the engine cover and down frame when the vehicle rolls over.

[0104] In the variable valve timing system of this embodiment, a cam chain chamber (58) is formed in the cylinder and cylinder head, and an oil pipe (64, 65) is removably installed across the cam chain chamber. An oil passage for hydraulic control enters the outer wall of the cam chain chamber from the oil control valve, flows from the cylinder side to the cylinder head side, passes through the oil pipe, and then flows through the inner wall of the cam chain chamber to the variable valve train. In a side view of the vehicle, the oil pipe is positioned in an area surrounded by the main frame, down frame, and underside of the cylinder head. With this configuration, the oil pipe can be installed in the narrow area surrounded by the underside of the main frame, down frame, and cylinder head. Furthermore, since the installation location of the oil pipe is exposed to the side of the vehicle, the oil pipe can be easily installed and removed.

[0105] 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.

[0106] 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]

[0107] 10: Body frame 12: Mainframe 13: Down frame 16: Radiator 19: Cooling fan 21: Engine 25: Cylinder 26: Cylinder head 31: Clutch cover (engine cover) 32, 33: Starter gear cover (engine cover) 38: Main Gallery 39: External piping 40: Oil control valve 58: Cam chain compartment 60: Variable valve train 64, 65: Oil pipe L: Extension line

Claims

1. A variable valve timing system for an engine in which a cylinder head is fixed on a cylinder and the cylinder head is suspended from a vehicle body frame, a variable valve mechanism that changes the valve opening and closing timing using hydraulic pressure; an oil control valve that controls hydraulic pressure for the variable valve mechanism, the vehicle body frame includes a main frame that covers a rear side of the cylinder head from the side, and a down frame that covers a front side of the cylinder head from the side, a variable valve timing system characterized in that, in a side view of the vehicle, the oil control valve is detachably installed on an outer surface of the engine below an area surrounded by the main frame, the down frame, and a lower surface of the cylinder head.

2. A heat exchanger is installed in front of the engine, 2. The variable valve timing system according to claim 1, wherein the oil control valve is positioned outward in the vehicle width direction from the heat exchanger and below the down frame when viewed from the front of the vehicle.

3. A heat exchanger is installed in front of the engine, and a cooling fan is attached to the rear of the heat exchanger.

3. The variable valve timing system according to claim 1, wherein, in a side view of the vehicle, a lower end of the down frame is positioned on an extension line of a lower end of the cooling fan extended in the air blowing direction, and the oil control valve is positioned below the extension line.

4. The engine cover bulges outward in the vehicle width direction beyond the outer surface of the cylinder, 4. The variable valve timing system according to claim 1, wherein the oil control valve is positioned inward in the vehicle width direction relative to the engine cover and the down frame, and is positioned between the engine cover and the down frame, when viewed from the front of the vehicle.

5. The engine cover bulges outward in the vehicle width direction beyond the outer surface of the cylinder, An oil main gallery is formed in the engine, and an external pipe extends from the main gallery to the oil control valve, 5. The variable valve timing system according to claim 1, wherein, in a front view of the vehicle, the external piping passes inside the down frame and the engine cover in the vehicle width direction and is connected to the oil control valve below the down frame.

6. A cam chain chamber is formed in the cylinder and the cylinder head. An oil pipe is detachably installed so as to cross the cam chain chamber, an oil passage for hydraulic control runs from the oil control valve into the outer wall of the cam chain chamber, flows from the cylinder side toward the cylinder head side, passes through the oil pipe, and flows through the inner wall of the cam chain chamber toward the variable valve mechanism; 6. The variable valve timing system according to claim 1, wherein the oil pipe is positioned in an area surrounded by the main frame, the down frame, and a lower surface of the cylinder head in a side view of the vehicle.

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