Patent Description:
For an object of high output, low fuel consumption, and low exhaust gas, a variable valve timing system is employed, which controls an opening and closing timing of a valve by a variable valve device according to an operation state of an engine. As a variable valve timing system, there is a system in which an oil control valve disposed on an outer surface of a cylinder head controls a hydraulic pressure with respect to a variable valve device (see, for example, Patent Literature <NUM>). Oil controlled by the oil control valve is supplied to the variable valve device, and the variable valve device switches between a low-speed rotation cam and a highspeed rotation cam to adjust an opening and closing timing of a valve.

<CIT> and <CIT> concern an installation structure of an oil control valve unit and a vehicle.

However, in the variable valve timing system described in Patent Literature <NUM>, a position relationship between a vehicle body frame and the oil control valve, and effects of vibration and heat of an engine have not been sufficiently studied. Therefore, disposing the oil control valve on the outer surface of the cylinder head may have a disadvantageous effect.

The present invention has been made in view of the above, and an object thereof is to provide a variable valve timing system suitable for a layout where an oil control valve is provided on an outer surface of an engine.

Aspects of the present invention are defined in the accompanying claims. According to a first aspect there is provided a vehicle in accordance with claim <NUM>. Preferred optional features are defined in the dependent claims. There is provided a variable valve timing system for an engine in which a cylinder head fixed on a cylinder is suspended on a vehicle body frame and a cam chain chamber is formed in the cylinder and the cylinder head, the variable valve timing system including: a variable valve device configured to change an opening and closing timing of a valve by a hydraulic pressure; and an oil control valve configured to control the hydraulic pressure with respect to the variable valve device. The oil control valve is disposed on an outer surface of the cylinder, which is an outer wall of the cam chain chamber, and the variable valve device is disposed inside the cylinder head. An oil path for hydraulic pressure control enters the outer wall of the cam chain chamber from the oil control valve, extends from a side of the cylinder to a side of the cylinder head, and crosses the cam chain chamber to the variable valve device through an inner wall of the cam chain chamber.

According to the variable valve timing system of the aspect of the present invention, the oil control valve is disposed on the outer surface of the cylinder and separated from the vehicle body frame on which the cylinder head is suspended. A size of the vehicle body frame does not become large in a vehicle width direction due to the oil control valve, and an increase in a size of a vehicle is suppressed. Since the oil control valve is brought closer to the center of gravity of the engine, transmission of vibration to the oil control valve is reduced and durability of the oil control valve is improved. The oil path bypasses a cylinder bore through the outer wall of the cam chain chamber, so that a temperature of oil in the oil path can be stabilized and an operation of the variable valve device can be stabilized.

A variable valve timing system according to an aspect of the present invention is mounted on an engine in which a cam chain chamber is formed in a cylinder and a cylinder head. The variable valve timing system is provided with a variable valve device disposed inside the cylinder head, and an oil control valve disposed on an outer surface of the cylinder, which is an outer wall of the cam chain chamber. The oil control valve controls a hydraulic pressure with respect to the variable valve device, and the variable valve device changes an opening and closing timing of a valve. The cylinder head fixed on the cylinder is suspended on a vehicle body frame, and the oil control valve on the outer surface of the cylinder is separated from the vehicle body frame. A size of the vehicle body frame does not become large in a vehicle width direction due to the oil control valve, and an increase in a size of a vehicle is suppressed. Since the oil control valve is brought closer to the center of gravity of the engine, transmission of vibration to the oil control valve is reduced and durability of the oil control valve is improved. The oil path for hydraulic pressure control enters the outer wall of the cam chain chamber from the oil control valve, and after goes from a cylinder side to a cylinder head side, the oil path crosses the cam chain chamber toward the variable valve device through an inner wall of the cam chain chamber. The oil path bypasses a cylinder bore through the outer wall of the cam chain chamber, so that a temperature of oil in the oil path can be stabilized and an operation of the variable valve device can be stabilized.

Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings. <FIG> is a right side view of a vehicle front portion according to the present embodiment. In the following drawings, an arrow FR indicates a vehicle front side, an arrow RE indicates a vehicle rear side, an arrow L indicates a vehicle left side, and an arrow R indicates a vehicle right side.

As shown in <FIG>, a straddle-type vehicle <NUM> includes various components such as an engine <NUM> and an electrical system that are mounted on a twin spar-type vehicle body frame <NUM>. The vehicle body frame <NUM> includes a pair of main frames <NUM> that are branched off from a head pipe <NUM> to the left and right and extend rearward, and a pair of down frames <NUM> that extend downward from front portions of the pair of main frames <NUM>. The pair of main frames <NUM> are curved so as to pass over the engine <NUM> and wrap around to the rear of the engine <NUM>. An upper side and a rear side of the engine <NUM> are suspended by the pair of main frames <NUM>, and a front side of the engine <NUM> is suspended by the pair of down frames <NUM>.

A front fork <NUM> is steerably supported by the head pipe <NUM> via a steering shaft (not shown). A front wheel <NUM> is rotatably supported at a lower portion of the front fork <NUM>. A radiator (heat exchanger) <NUM> that dissipates heat from cooling water of the engine <NUM> is provided in front of the engine <NUM>. An upper portion of the radiator <NUM> is supported by the main frames <NUM> via an upper bracket <NUM>, and a lower portion of the radiator <NUM> is supported by the engine <NUM> via a lower bracket <NUM>. A cooling fan <NUM> that takes in hot air from the radiator <NUM> when the vehicle is stopped is attached to a rear surface of the radiator <NUM>.

The engine <NUM> is a parallel <NUM>-cylinder engine in which four cylinders are arranged in left and right directions, and includes a crankcase <NUM> accommodating a crankshaft (not shown). A cylinder assembly in which a cylinder <NUM>, a cylinder head <NUM>, and a cylinder head cover <NUM> are laminated is attached to an upper portion of the crankcase <NUM>. An oil pan <NUM> in which oil for lubrication and cooling is stored is attached to a lower portion of the crankcase <NUM>. Engine covers such as a clutch cover <NUM> and starter gear covers <NUM> and <NUM> are attached to a left side surface of the crankcase <NUM>. A plurality of exhaust pipes <NUM> extend downward from a front surface of the engine <NUM>.

The engine <NUM> is mounted with a hydraulically controlled variable valve timing system that controls an opening and closing timing of an intake valve (not shown). A variable valve device <NUM> (see <FIG>) is accommodated inside the cylinder head <NUM> and the cylinder head cover <NUM>, and an oil control valve <NUM> is disposed on an outer surface of the cylinder <NUM>. The variable valve device <NUM> and the oil control valve <NUM> are connected through various oil paths in the engine <NUM>. The oil control valve <NUM> controls a hydraulic pressure with respect to the variable valve device <NUM>, so that the opening and closing timing of the intake valve is changed by the hydraulic pressure with respect to the variable valve device <NUM>.

Since such an engine <NUM> is suspended on the vehicle body frame <NUM>, the oil control valve <NUM> is disposed so as to avoid interference with the vehicle body frame <NUM>. If the oil control valve <NUM> protrudes greatly outward in the vehicle width direction, the vehicle body frame <NUM> protrudes outward in the vehicle width direction, resulting in the increase in the size of the vehicle. If the oil control valve <NUM> is too far from the center of gravity of the engine <NUM>, vibration of the oil control valve <NUM> increases and durability of the oil control valve <NUM> decreases. Further, heat of the engine <NUM> may destabilize an operation of the variable valve device <NUM>.

Therefore, in the variable valve timing system of the present embodiment, the oil control valve <NUM> is disposed on the outer surface of the cylinder <NUM> sufficiently away from the vehicle body frame <NUM> and close to the center of gravity of the engine <NUM>. A cam chain chamber <NUM> (see <FIG>) is formed in the engine <NUM>, and an oil path extending from the oil control valve <NUM> to the variable valve device <NUM> is formed so as to avoid a combustion point of the engine <NUM> by using the cam chain chamber <NUM>. Accordingly, the variable valve timing system suitable for a layout where the oil control valve <NUM> is disposed on an outer surface of the engine <NUM> is employed in the engine <NUM>.

The layout of the oil control valve will be described with reference to <FIG> and <FIG>. <FIG> is a right side view showing the periphery of the engine according to the present embodiment. <FIG> is a front view of the periphery of the engine according to the present embodiment.

As shown in <FIG>, the crankcase <NUM> of the engine <NUM> has a vertically divided structure including an upper case <NUM> and a lower case <NUM>. Various shafts such as a crankshaft are supported by a mating surface between the upper case <NUM> and the lower case <NUM>. The oil pan <NUM> is fixed to a lower surface of the lower case <NUM> and the cylinder <NUM> is fixed to an upper surface of the upper case <NUM>. The cylinder head <NUM> is fixed to an upper surface of the cylinder <NUM>, and the cylinder head cover <NUM> is fixed to an upper surface of the cylinder head <NUM>. The cylinder head <NUM> and the crankcase <NUM> are suspended on the vehicle body frame <NUM>.

A front portion of the vehicle body frame <NUM> branches into the main frames <NUM> and the down frames <NUM>. The main frame <NUM> obliquely crosses a side of the cylinder head <NUM> from the upper surface to a rear surface, and the down frame <NUM> is formed in a substantially triangular shape in a side view such that a front-to-rear width narrows downward. The main frame <NUM> laterally covers a rear side of the cylinder head <NUM>, and the down frame <NUM> laterally covers a front side of the cylinder head <NUM>. The rear side of the cylinder head <NUM> is suspended on a middle portion of the main frame <NUM> in an extension direction, and the front side of the cylinder head <NUM> is suspended on a lower head portion of the down frame <NUM>.

A triangular area (area) surrounded by a lower edge of the main frame <NUM>, a rear edge of the down frame <NUM>, and a lower surface of the cylinder head <NUM> is formed on a side surface of the cylinder head <NUM> in a side view of the vehicle. Although the triangular area of the cylinder head <NUM> is exposed to the side from between the main frame <NUM> and the down frame <NUM>, the triangular area is not wide enough for the oil control valve <NUM>. Therefore, the oil control valve <NUM> is disposed on a side surface (outer surface) of the cylinder <NUM> below the triangular area of the cylinder head <NUM>. The side surface of the cylinder <NUM> is formed by an outer wall of the cam chain chamber <NUM> (see <FIG>).

A pair of plug caps <NUM> and <NUM> that close insertion openings for a pair of oil pipes <NUM> and <NUM> (see <FIG>) which will be described later are disposed in the triangular area of the cylinder head <NUM>. Since the plug caps <NUM> and <NUM> avoid the vehicle body frame <NUM> in the side view of the vehicle, the oil pipes <NUM> and <NUM> can be attached and detached through the plug caps <NUM> and <NUM> even when the engine <NUM> is suspended on the vehicle body frame <NUM>, and maintainability is improved. Since the plug caps <NUM> and <NUM> are disposed along the rear edge of the down frame <NUM>, there is no need to modify a shape of the down frame <NUM>. In this case, the plug cap <NUM> at the rear of the vehicle is positioned higher than the plug cap <NUM> at the front of the vehicle, and the plug caps <NUM> and <NUM> are partially overlapped with each other in an up-down direction, so that a disposing area of the plug caps <NUM> and <NUM> is narrowed.

The oil control valve <NUM> is formed in a substantially cylindrical shape by a valve housing <NUM> in which a valve spool (not shown) is accommodated and a solenoid <NUM> that advances and retracts the valve spool. The oil path in the oil control valve <NUM> is switched by advancing and retracting the valve spool by the solenoid <NUM>. The oil control valve <NUM> is tilted such that an axial direction of the oil control valve <NUM> is parallel to a mating surface between the cylinder head <NUM> and the cylinder <NUM>. The solenoid <NUM> is provided on a rear side of the valve housing <NUM> and positioned above the valve housing <NUM>.

A contamination such as metal powder may occur inside the valve housing <NUM>, but it is difficult for the contamination to enter the solenoid <NUM> from the valve housing <NUM>. That is, since the oil control valve <NUM> is tilted such that the solenoid <NUM> is higher than the valve housing <NUM>, the contamination is suppressed from being transferred from the valve housing <NUM> to the solenoid <NUM> by the oil. Since the contamination does not accumulate on a solenoid <NUM> side, damage to the oil control valve <NUM> due to the contamination is suppressed. Details of the oil control valve <NUM> will be described later.

Since the oil control valve <NUM> is disposed on the outer surface of the cylinder <NUM>, the oil control valve <NUM> does not interfere with the vehicle body frame <NUM> on which the cylinder head <NUM> is suspended. Therefore, the vehicle body frame <NUM> does not protrude outward in the vehicle width direction, and an increase in a size of the straddle-type vehicle <NUM> is suppressed. Since the center of gravity of the engine <NUM> is located in the crankcase <NUM>, the oil control valve <NUM> is brought closer to the center of gravity of the engine <NUM>. Therefore, transmission of vibration from the crankcase <NUM> to the oil control valve <NUM> is reduced, and the durability of the oil control valve <NUM> is improved.

In the side view of the vehicle, the cylinder head <NUM> and the cylinder <NUM> are fixed by two bolts <NUM> on both sides of a cylinder axis, and the cylinder <NUM> and the crankcase <NUM> are fixed by two bolts <NUM> on the both sides of the cylinder axis. The oil control valve <NUM> is disposed so as not to overlap with these four bolts <NUM> and <NUM>, and the oil control valve <NUM> is suppressed from protruding outward in the vehicle width direction. In this case, an interval between the two bolts <NUM> on an upper side is wider than an interval between the two bolts <NUM> on a lower side, and the oil control valve <NUM> is positioned closer to the cylinder head <NUM>.

The starter gear covers <NUM> and <NUM> that laterally cover starter gears (not shown) are provided below the oil control valve <NUM>. The clutch cover <NUM> that laterally covers the clutch (not shown) is provided behind the starter gear covers <NUM> and <NUM>. An upper portion of the starter gear cover <NUM> protrudes toward the cylinder <NUM>, but interference between the starter gear cover <NUM> and the solenoid <NUM> is suppressed. The starter gear covers <NUM> and <NUM> and the clutch cover <NUM> are formed as separate engine covers, but the starter gear covers <NUM> and <NUM> and the clutch cover <NUM> may be formed as one engine cover.

As shown in <FIG> and <FIG>, the starter gear covers <NUM> and <NUM> and the clutch cover <NUM> bulge outward from a side surface of the cylinder <NUM> in the vehicle width direction. In a front view of the vehicle, the oil control valve <NUM> is positioned inside the starter gear covers <NUM> and <NUM>, the clutch cover <NUM>, and the down frames <NUM> in the vehicle width direction. The oil control valve <NUM> is positioned between the starter gear covers <NUM> and <NUM> and the down frames <NUM>. The oil control valve <NUM> is protected by the starter gear covers <NUM> and <NUM>, the clutch cover <NUM>, and the down frames <NUM> when the vehicle overturns.

A main gallery <NUM> of the oil is formed in the crankcase <NUM>, and the main gallery <NUM> and the oil control valve <NUM> are connected by an external pipe <NUM>. Accordingly, the oil is directly supplied to the oil control valve <NUM> from the main gallery <NUM> with high hydraulic pressure through the external pipe <NUM>. The oil is supplied from the main gallery <NUM> to the oil control valve <NUM> without passing through the oil path in the crankcase <NUM>, so that pressure loss in the oil path is suppressed, and the oil with high hydraulic pressure can be supplied to the oil control valve <NUM>.

The external pipe <NUM> extends forward of the vehicle from the main gallery <NUM>, wraps around the crankcase <NUM> from below, and extends upward. The external pipe <NUM> is bent toward the rear of the vehicle below the down frame <NUM> and connected to the valve housing <NUM> of the oil control valve <NUM>. In the front view of the vehicle, the external pipe <NUM> passes through inner sides of the starter gear covers <NUM> and <NUM>, the clutch cover <NUM>, and the down frames <NUM> in the vehicle width direction, and is connected to the oil control valve <NUM> below the down frames <NUM>. The external pipe <NUM> is protected by the starter gear covers <NUM> and <NUM>, the clutch cover <NUM>, and the down frames <NUM> when the vehicle overturns.

The radiator <NUM> having a rectangular shape in the front view is provided in front of the cylinder head <NUM>. The radiator <NUM> is tilted such that the upper portion is located forward of the lower portion. The radiator <NUM> is a round radiator curved into an arch shape in a top view, and the cooling fan <NUM> is attached to the rear surface of the radiator <NUM> on an oil control valve <NUM> side (right side) in the vehicle width direction. In the front view of the vehicle, the oil control valve <NUM> is disposed outside the radiator <NUM> in the vehicle width direction and below the down frame <NUM>, and it is difficult for the radiator <NUM> and the down frames <NUM> to block running wind in front of the oil control valve <NUM>.

Since the oil control valve <NUM> is a solenoid valve, the oil control valve <NUM> is likely to generate heat when the solenoid <NUM> is energized. Therefore, the oil control valve <NUM> is cooled by the running wind, so that deterioration of operability of the variable valve device <NUM> due to temperature rise of the oil control valve <NUM> and the oil is suppressed. As described above, the solenoid <NUM> is positioned at the rear side of the valve housing <NUM>, and the solenoid <NUM> is separated from the radiator <NUM>. The heat from the radiator <NUM> is less likely to be transmitted to the solenoid <NUM>, and temperature rise of the solenoid <NUM> is suppressed.

In the side view of the vehicle, a lower end of the down frame <NUM> is positioned on an extension line L extending from a lower end of the cooling fan <NUM> in a blowing direction, and the oil control valve <NUM> is positioned below the extension line L. Exhaust air from the radiator <NUM> is less likely to hit the oil control valve <NUM>, and the deterioration of the operability of the variable valve device <NUM> due to the temperature rise of the oil control valve <NUM> and the oil is suppressed. In the front view of the vehicle, the solenoid <NUM> of the oil control valve <NUM> is covered by the down frames <NUM>, and the exhaust air from the radiator <NUM> is blocked by the down frames <NUM> to suppress the temperature rise of the solenoid <NUM>.

The oil control valve will be described with reference to <FIG> are front and rear views of the oil control valve according to the present embodiment. <FIG> shows the front view of the oil control valve, and <FIG> shows the rear view of the oil control valve.

As shown in <FIG>, the valve housing <NUM> of the oil control valve <NUM> includes a disposing plate <NUM> disposed on the side surface of the cylinder <NUM>, and a cylindrical case <NUM> bulging outward from the disposing plate <NUM>. Three fixing holes <NUM> for screwing are formed in an outer edge of the disposing plate <NUM> so as to surround the cylindrical case <NUM>. A supply port <NUM> to which the external pipe <NUM> (see <FIG>) is connected is formed in a lower portion of the disposing plate <NUM>. The valve spool extending from the solenoid <NUM> is inserted into the cylindrical case <NUM>. A destination of the oil entering from the supply port <NUM> is switched by the valve spool.

An O-ring <NUM> that seals a gap between a rear surface of the disposing plate <NUM> and the side surface of the cylinder <NUM> is attached to the rear surface of the disposing plate <NUM>. The supply port <NUM>, an input port <NUM>, an advance port <NUM>, a retard port <NUM>, and a drain port <NUM> are formed inside the O-ring <NUM>. The supply port <NUM> communicates with the input port <NUM> through the oil path formed in the cylinder <NUM>. A filter <NUM> is disposed in the input port <NUM>, and the oil is filtered by passing through the filter <NUM>. The input port <NUM> communicates with any one of the advance port <NUM>, the retard port <NUM>, and the drain port <NUM> depending on a position of the valve spool.

When the oil enters the input port <NUM> from the supply port <NUM>, the oil filtered by the filter <NUM> of the input port <NUM> is input to the cylindrical case <NUM>. By moving the valve spool by the solenoid <NUM>, the input port <NUM> is communicated with either the advance port <NUM> or the retard port <NUM>, and the drain port <NUM> is communicated with the other of the advance port <NUM> and the retard port <NUM>. Accordingly, the oil is supplied from the oil control valve <NUM> toward either an advance chamber S1 or a retard chamber S2 of the variable valve device <NUM> (see <FIG>) which will be described later, and the excess oil is discharged from the other of advance chamber S1 and the retard chamber S2 toward the oil control valve <NUM>.

The oil path in the engine will be described with reference to <FIG>, <FIG>, and <FIG>. <FIG> is a schematic diagram of the oil path according to the present embodiment. <FIG> is a cross-sectional view of the engine in <FIG> taken along a line A-A. <FIG> is a perspective view of the oil pipe according to the present embodiment. <FIG> are cross-sectional views of a disposing location of the oil pipe according to the present embodiment. <FIG>, and <FIG> are explanatory diagrams of the oil path in the cam housing according to the present embodiment. In <FIG>, a cam chain is omitted for convenience of description. <FIG> shows a state with the plug cap attached, and <FIG> shows a state with the plug cap removed. <FIG> shows a lower housing viewed from below,.

<FIG> shows an upper housing viewed from below, and <FIG> shows a state with a camshaft removed.

As shown in <FIG>, the cam chain chamber <NUM> is formed in the cylinder <NUM> and cylinder head <NUM> of the engine <NUM>. A cam chain <NUM> is accommodated in the cam chain chamber <NUM>, and the cam chain <NUM> is stretched over an intake side cam sprocket <NUM> and an exhaust side cam sprocket <NUM>. An intake side camshaft <NUM> is fixed to the intake side cam sprocket <NUM>, and an exhaust side camshaft <NUM> is fixed to the exhaust side cam sprocket <NUM>. The crankshaft (not shown) is connected to the intake side camshaft <NUM> and the exhaust side camshaft <NUM> via the cam chain <NUM>.

The intake side camshaft <NUM> and the exhaust side camshaft <NUM> are rotatably supported by a cam housing <NUM>. The cam housing <NUM> is a support wall fixed on the cylinder head <NUM>, and includes an upper housing <NUM> that supports upper half portions of the camshafts <NUM> and <NUM> and a lower housing <NUM> that supports lower half portions of the camshafts <NUM> and <NUM>. The variable valve device <NUM> is attached to one end portion of the intake side camshaft <NUM> inside the cylinder head <NUM>. The variable valve device <NUM> advances or retards the intake side camshaft <NUM> by the hydraulic pressure to change the opening and closing timing of the intake valve (not shown).

The oil control valve <NUM> is disposed on the outer surface (side surface) of the cylinder <NUM> which is the outer wall of the cam chain chamber <NUM>. The oil control valve <NUM> controls the hydraulic pressure with respect to the variable valve device <NUM>. An advance path <NUM> extends from the advance port <NUM> (see <FIG>) of the oil control valve <NUM> toward the variable valve device <NUM>, and a retard path <NUM> extends from the retard port <NUM> (see <FIG>) of the oil control valve <NUM> toward the variable valve device <NUM>. The oil for advancing the opening and closing timing of the intake valve passes through the advance path <NUM>, and the oil for retarding the opening and closing timing of the intake valve passes through the retard path <NUM>.

The advance path <NUM> and the retard path <NUM> for the hydraulic pressure control enter the outer wall of the cam chain chamber <NUM> from the oil control valve <NUM>. The advance path <NUM> and the retard path <NUM> are directed from a cylinder <NUM> side to a cylinder head <NUM> side, then cross the cam chain chamber <NUM> toward the variable valve device <NUM> through an inner wall of the cam chain chamber <NUM>. In this case, the outer wall of the cam chain chamber <NUM> is formed by an outer wall of the cylinder <NUM>, an outer wall of the cylinder head <NUM>, and an outer wall of the crankcase <NUM>, and the inner wall of the cam chain chamber <NUM> is formed by an inner wall of the cylinder <NUM>, an inner wall of the cylinder head <NUM>, an inner wall of the crankcase <NUM>, and the cam housing <NUM>.

The outer wall and the inner wall of the cylinder head <NUM> are connected by the pair of oil pipes <NUM> and <NUM>. The pair of oil pipes <NUM> and <NUM> cross the cam chain chamber <NUM> through the inside of the cam chain <NUM>. Since the oil pipes <NUM> and <NUM> are detachably disposed, the pair of oil pipes <NUM> and <NUM> do not interfere when the cam chain <NUM> is assembled. Since the oil pipes <NUM> and <NUM> are detachable, the pair of oil pipes <NUM> and <NUM> can be inserted after the cam chain <NUM> is assembled to the engine <NUM>. Accordingly, a dead space inside the cam chain <NUM> can be effectively utilized.

In the outer wall of the cam chain chamber <NUM>, the advance path <NUM> and the retard path <NUM> extend from the outer wall of the cylinder <NUM> toward the outer wall of the cylinder head <NUM> in parallel with the cylinder axis. In this case, the advance path <NUM> is positioned on the front side and the retard path <NUM> is positioned on the rear side, and the retard path <NUM> extends to a position higher than the advance path <NUM>. Between the outer wall and the inner wall of the cam chain chamber <NUM>, the advance path <NUM> and the retard path <NUM> pass through the pair of oil pipes <NUM> and <NUM> and extend in a direction orthogonal to the cylinder axis. Accordingly, the pair of oil pipes <NUM> and <NUM> form crossing points of the advance path <NUM> and the retard path <NUM>.

In the inner wall of the cam chain chamber <NUM>, the advance path <NUM> and the retard path <NUM> extend from the outer wall of the cylinder head <NUM> toward the cam housing <NUM> in parallel with the cylinder axis. The advance path <NUM> passes through the lower housing <NUM> and extends to a mating surface <NUM> between the lower housing <NUM> and the upper housing <NUM>, and then passes through the mating surface <NUM>, and is connected to an advance groove <NUM> laterally. The retard path <NUM> passes through a mating surface <NUM> between the cylinder head <NUM> and the lower housing <NUM> and extends below a retard groove <NUM>, and then passes through the lower housing <NUM>, and is connected to the retard groove <NUM> from below. The advance groove <NUM> and the retard groove <NUM> are connected to the variable valve device <NUM> through the intake side camshaft <NUM>.

The advance path <NUM> and the retard path <NUM> are formed in the cylinder <NUM> and the cylinder head <NUM> by a straight path parallel to the cylinder axis and an orthogonal path orthogonal to the straight path. Therefore, the pressure loss of the oil in the advance path <NUM> and the retard path <NUM> is reduced, and the advance path <NUM> and the retard path <NUM> can be easily machined with respect to the cylinder <NUM> and the cylinder head <NUM>. In the cylinder <NUM> and the cylinder head <NUM>, the advance path <NUM> and the retard path <NUM> are arranged in parallel. Therefore, the advance path <NUM> and the retard path <NUM> are brought closer in a front-rear direction, and an increase in the size of the engine <NUM> is suppressed.

A drain hole <NUM> (see, in particular, <FIG>) communicating with the drain port <NUM> (see <FIG>) of the oil control valve <NUM> is formed on the cylinder <NUM> side of the outer wall of the cam chain chamber <NUM>. An inner peripheral surface of the cam chain <NUM> is positioned below the drain hole <NUM>, and the oil is discharged from the drain hole <NUM> toward the cam chain <NUM>. The oil dropped from the drain hole <NUM> is supplied to the cam chain <NUM>, and a meshing point between the cam chain <NUM> and the intake side cam sprocket <NUM> and a meshing point between the cam chain <NUM> and the exhaust side cam sprocket <NUM> are properly lubricated, and durability of the cam chain <NUM> is improved. No guide or complicated machining for directing the oil to the cam chain <NUM> is required.

As shown in <FIG>, a cylindrical cylinder bore <NUM> is formed in the cylinder <NUM>, and a piston (not shown) is slidably accommodated in the cylinder bore <NUM>. A ceiling surface covering the cylinder bore <NUM> is formed in the cylinder head <NUM>, and a combustion chamber <NUM> is formed between a top surface of the piston and the ceiling surface of the cylinder head <NUM>. A water jacket <NUM> that cools the combustion chamber <NUM> is formed on the inner walls of the cylinder <NUM> and the cylinder head <NUM>. As described above, the cam chain chamber <NUM> is formed between the outer and inner walls of the cylinder <NUM> and the cylinder head <NUM> on one side (right side) of the engine <NUM> in the vehicle width direction.

The advance path <NUM> is formed from the disposing location of the oil control valve <NUM> on the outer wall of the cylinder <NUM> to the outer wall of the cylinder head <NUM>. The outer wall and the inner wall of the cylinder head <NUM> are connected via the oil pipe <NUM>, and the advance path <NUM> crosses the cam chain chamber <NUM> through the oil pipe <NUM> above the combustion chamber <NUM>. In this case, the advance path <NUM> crosses the cam chain chamber <NUM> toward an upper portion of the water jacket <NUM>, and the advance path <NUM> is formed so as to pass next to the water jacket <NUM> on the inner wall of the cylinder head <NUM>. The retard path <NUM> is also formed in substantially the same manner as the advance path <NUM>.

The advance path <NUM> and the retard path <NUM> are formed so as to bypass the combustion chamber <NUM>. Since the advance path <NUM> and the retard path <NUM> pass next to the water jacket <NUM>, the oil in the advance path <NUM> and the retard path <NUM> is cooled by the water jacket <NUM>. The cam chain chamber <NUM> and the water jacket <NUM> are formed between the advance path <NUM> and the combustion chamber <NUM> and between the retard path <NUM> and the combustion chamber <NUM>, and the heat is less likely to be transferred from the combustion chamber <NUM> to the oil in the advance path <NUM> and the retard path <NUM>. Therefore, a temperature of the oil in the advance path <NUM> and the retard path <NUM> is stabilized, and an operation of the variable valve device <NUM> is stabilized.

As shown in <FIG> and <FIG>, a first seal surface <NUM> disposed on the outer wall of the cam chain chamber <NUM> (cylinder head <NUM>) is formed on one end side of an outer peripheral surface of the oil pipe <NUM>, and a second seal surface <NUM> disposed on the inner wall of the cam chain chamber <NUM> is formed on the other end side of the outer peripheral surface of the oil pipe <NUM>. The first seal surface <NUM> is slightly larger in diameter than the second seal surface <NUM>, and a space between the first and second seal surfaces <NUM> and <NUM> is formed to have the same diameter as the second seal surface <NUM>. One end portion of the oil pipe <NUM> which is the one end side of the first seal surface <NUM> is a diameter-reduced portion <NUM> having a diameter smaller than those of the first and second seal surfaces <NUM> and <NUM>.

A first seal groove <NUM> is formed in the first seal surface <NUM>, and a first O-ring <NUM> is mounted in the first seal groove <NUM>. A second seal groove <NUM> is formed in the second seal surface <NUM>, and a second O-ring <NUM> is mounted in the second seal groove <NUM>. Through holes <NUM> penetrate through the diameter-reduced portion <NUM> of the oil pipe <NUM> so as to intersect in a cross shape, and the oil pipe <NUM> and the advance path <NUM> are communicated through the through holes <NUM>. The oil flows to the one end side of the oil pipe <NUM> in a radial direction through the through holes <NUM>, and flows out from the other end side of the oil pipe <NUM> in the axial direction.

First and second disposing holes <NUM> and <NUM> are formed in the outer and inner walls of the cam chain chamber <NUM> (cylinder head <NUM>). The first seal surface <NUM> of the oil pipe <NUM> is disposed in the first disposing hole <NUM> on an outer wall side, and the second seal surface <NUM> of the oil pipe <NUM> is disposed in the second disposing hole <NUM> on an inner wall side. The first seal surface <NUM> and an inner peripheral surface of the first disposing hole <NUM> are liquid-tightly sealed with the first O-ring <NUM>, and the second seal surface <NUM> and an inner peripheral surface of the second disposing hole <NUM> are liquid-tightly sealed with the second O-ring <NUM>. The first and second seal surfaces <NUM> and <NUM> suppress oil leakage from the oil pipe <NUM> on the outer and inner walls of the cam chain chamber <NUM>.

The outer wall of the cam chain chamber <NUM> is formed with an insertion opening <NUM> for the oil pipe <NUM>, and the insertion opening <NUM> is closed by the plug cap <NUM>. A female screw is threaded on the inner peripheral surface of the insertion opening <NUM>, and a male screw of the plug cap <NUM> is fitted into the female screw of the insertion opening <NUM>. The insertion opening <NUM> has a larger diameter than those of the first and second disposing holes <NUM> and <NUM>. The diameter-reduced portion <NUM> of the oil pipe <NUM> is positioned inside the female screw of the insertion opening <NUM>, and the through holes <NUM> of the diameter-reduced portion <NUM> communicate with the oil path opening to the female screw. The oil can easily enter the oil pipe <NUM> from the insertion opening <NUM> through the plurality of through holes <NUM>, and the pressure loss at one end side of the oil pipe <NUM> can be reduced.

In this case, after the second disposing hole <NUM> of φ12 (hole diameter <NUM>) is formed in the inner wall of the cam chain chamber <NUM>, a pilot hole of φ14 (hole diameter <NUM>) is formed so as to chamfer the second disposing hole <NUM>. The pilot hole forms the first disposing hole <NUM> in the outer wall of the cam chain chamber <NUM>. A female screw of M16 (screw diameter <NUM>) is threaded at an entrance side of the pilot hole to form the insertion opening <NUM>. Accordingly, by forming the pilot hole for the female screw, the second disposing hole <NUM> is chamfered and the first disposing hole <NUM> is formed. An inner diameter of the oil pipe <NUM> and an inner diameter of the through hole <NUM> are each formed to be φ6 (hole diameter <NUM>).

The one end portion of the oil pipe <NUM> is closed with the plug cap <NUM>. A slight gap is provided between the one end portion of the oil pipe <NUM> and the plug cap <NUM>, but the one end portion of the oil pipe <NUM> and the plug cap <NUM> may be brought into contact with each other. Tensioning of the oil pipe <NUM> also serves as a countermeasure against noise on the wall surface of the cam chain chamber <NUM>. The outer wall of the cylinder head <NUM> bulges outward in the vehicle width direction at a location where the variable valve device <NUM> (see <FIG>) is accommodated, and an amount of protrusion of the plug caps <NUM> and <NUM> in the vehicle width direction is equal to or less than an amount of bulging of a bulging portion <NUM> of the outer wall. Accordingly, the engine <NUM> is easily assembled to the vehicle body frame <NUM>.

As shown in <FIG>, the one end portion of the oil pipe <NUM> is the diameter-reduced portion <NUM>, and thus a sufficient interval is provided between the insertion opening <NUM> and the diameter-reduced portion <NUM>, and removal of the oil pipe <NUM> is improved. For example, the plug cap <NUM> is removed from the insertion opening <NUM>, the diameter-reduced portion <NUM> of the oil pipe <NUM> can be grasped and pulled out with a tool <NUM> such as a needle pliers, or the hook <NUM> can be hooked into the through hole <NUM> of the diameter-reduced portion <NUM> to pull out the diameter-reduced portion <NUM>. The oil pipe <NUM> and the plug cap <NUM> for advancement have been described, and the angle oil pipe <NUM> and plug cap <NUM> for retardation are similarly constructed.

As shown in <FIG>, journals <NUM> and <NUM> of the intake side camshaft <NUM> and the exhaust side camshaft <NUM> are supported by the upper housing (support wall) <NUM> and the lower housing (support wall) <NUM>. The intake side cam sprocket <NUM> and the variable valve device <NUM> are attached to one end portion of the intake side camshaft <NUM>, and the exhaust side cam sprocket <NUM> is attached to one end portion of the exhaust side camshaft <NUM>. Thrust stoppers <NUM> and <NUM> for positioning in the axial direction (thrust direction) are formed on outer peripheral surfaces of the respective journals <NUM> and <NUM> of the intake side camshaft <NUM> and the exhaust side camshaft <NUM>, respectively.

The advance groove <NUM>, the retard groove <NUM>, and an accommodation groove <NUM> are formed in a bearing surface <NUM> at an intake side of the upper housing <NUM> and the lower housing <NUM> (bearing surface of the lower housing <NUM> is not shown). The oil for advancing the intake side camshaft <NUM> enters the advance groove <NUM>, the oil for retarding the intake side camshaft <NUM> enters the retard groove <NUM>, and the thrust stopper <NUM> of the intake side camshaft <NUM> is accommodated in the accommodation groove <NUM>. At the bearing surface <NUM> at the intake side, the retard groove <NUM> is positioned on one wall surface <NUM> side of the upper housing <NUM>, the accommodation groove <NUM> is positioned on the other wall surface <NUM> side of the upper housing <NUM>, and the advance groove <NUM> is positioned between the retard groove <NUM> and the accommodation groove <NUM>. Each groove is similarly formed in the lower housing <NUM>.

Four bolt holes 137a to 137d are formed in the upper housing <NUM> and the lower housing <NUM> so as to sandwich the intake side camshaft <NUM> and the exhaust side camshaft <NUM> therebetween. At a center of a lower surface of the lower housing <NUM>, an advance through path <NUM> extends through the lower housing <NUM> in the up-down direction, and a retard path groove <NUM> (see <FIG>) extends from the center of the lower surface of the lower housing <NUM> to the intake side through the side of the bolt hole 137c. Parts of the advance through path <NUM> and the retard path groove <NUM> are sandwiched by bolts tightened in the bolt holes 137b and 137c. The lower surface of the lower housing <NUM> is the mating surface <NUM> between the cylinder head <NUM> and the lower housing <NUM>, and the mating surface <NUM> increases a surface pressure in the vicinity of the advance through path <NUM> and the retard path groove <NUM> to suppress the oil leakage.

The advance through path <NUM> extends to the mating surface <NUM> between the lower housing <NUM> and the upper housing <NUM>, and an advance path groove <NUM> (see <FIG>) extending from an upper end of the advance through path <NUM> toward the advance groove <NUM> is formed in the mating surface <NUM>. The retard path groove <NUM> extends below the retard groove <NUM>, and a retard through path <NUM> penetrates the lower housing <NUM> in the up-down direction so as to connect the retard path groove <NUM> and the retard groove <NUM>. Accordingly, the advance path <NUM> that laterally supplies the oil to the advance groove <NUM> is formed by the advance through path <NUM> and the advance path groove <NUM>, and the retard path <NUM> that supplies the oil to the retard groove <NUM> from below is formed by the retard path groove <NUM> and the retard through path <NUM>.

The journal <NUM> of the intake side camshaft <NUM> is formed with an advance hole <NUM> corresponding to the advance groove <NUM> and a retard hole <NUM> corresponding to the retard groove <NUM>. The advance hole <NUM> communicates with the advance chamber S1 (see <FIG>) of the variable valve device <NUM> through the path in the intake side camshaft <NUM>. The retard hole <NUM> communicates with the retard chamber S2 (see <FIG>) of the variable valve device <NUM> through the path in the intake side camshaft <NUM>. The intake side camshaft <NUM> is advanced by supplying the oil from the advance groove <NUM> to the advance chamber S1 of the variable valve device <NUM>, and the intake side camshaft <NUM> is retarded by supplying the oil from the retard groove <NUM> to the retard chamber S2 of the variable valve device <NUM>.

Here, power is transmitted from the cam chain <NUM> (see <FIG>) to the intake side camshaft <NUM> via the variable valve device <NUM>. The variable valve device <NUM> continues to receive torque from the intake side camshaft <NUM> in a direction of retarding an inner rotor <NUM> (see <FIG>), and a larger hydraulic pressure is required to advance the intake side camshaft <NUM> than to retard the intake side camshaft <NUM>. Since the advance groove <NUM> is disposed between the retard groove <NUM> and the accommodation groove <NUM> in the bearing surface <NUM>, the advance groove <NUM> is separated from one wall surface <NUM> and the other wall surface <NUM>. A counter hydraulic pressure that delays the oil leakage of the advance groove <NUM> is generated in the retard groove <NUM> and the accommodation groove <NUM>, the oil leakage from the advance groove <NUM> is suppressed, and the variable valve device <NUM> can be stably operated with an appropriate hydraulic pressure.

Since the hydraulic pressure required for the retard groove <NUM> is smaller than that for the advance groove <NUM>, even if some oil leaks from the retard groove <NUM>, the operation of the variable valve device <NUM> is not affected. The accommodation groove <NUM> not only lubricates the thrust stopper <NUM> with the oil, but also generates the counter hydraulic pressure against the oil leakage of the advance groove <NUM>. Since a main purpose of the accommodation groove <NUM> is lubrication and the counter hydraulic pressure, even if some oil leaks from the accommodation groove <NUM>, the operation of the variable valve device <NUM> is not affected. The upper housing <NUM> and the lower housing <NUM> are separate components from the cylinder head <NUM>, and thus the mating surface <NUM> between the upper housing <NUM> and the lower housing <NUM> has high planar accuracy, and the advance groove <NUM>, the retard groove <NUM>, and the accommodation groove <NUM> are formed with high precision.

A lubrication groove <NUM> and an accommodation groove <NUM> are formed on a bearing surface <NUM> on an exhaust side of the upper housing <NUM> and the lower housing <NUM> (bearing surface of the lower housing <NUM> is not shown). The oil for lubrication enters the lubrication groove <NUM>, and the thrust stopper <NUM> of the exhaust side camshaft <NUM> is accommodated in the accommodation groove <NUM>. The lubrication groove <NUM> is positioned on the one wall surface <NUM> side of the upper housing <NUM>, and the accommodation groove <NUM> is positioned on the other wall surface <NUM> side of the upper housing <NUM>. Each groove is similarly formed in the lower housing <NUM>. The journal <NUM> of the exhaust side camshaft <NUM> is formed with an oil hole <NUM> through which the oil for lubrication passes from the path in the exhaust side camshaft <NUM> to the lubrication groove <NUM>.

The mating surface <NUM> between the lower housing <NUM> and the upper housing <NUM> is formed with a lubrication path groove <NUM> through which the oil for lubrication passes from the lubrication groove <NUM> of the exhaust side camshaft <NUM> toward the accommodation groove <NUM> of the intake side camshaft <NUM>. Accordingly, the lubrication groove <NUM> and the lubrication path groove <NUM> form a lubrication path that laterally supplies the oil to the accommodation groove <NUM>. At the mating surface <NUM> between the housings, the lubrication path groove <NUM> bypasses the advance path groove <NUM> so as to pass through the inside of the engine <NUM>, passes next to the advance path groove <NUM>, and continues to the accommodation groove <NUM>. The thrust stopper <NUM> of the intake side camshaft <NUM> is lubricated by supplying the oil from the lubrication path groove <NUM> to the accommodation groove <NUM>.

Since the lubrication path groove <NUM> passes next to the advance path groove <NUM>, the oil leakage of the advance path groove <NUM> is suppressed by generating, in the lubrication path groove <NUM>, the counter hydraulic pressure against the oil leakage of the advance path groove <NUM>. The advance path groove <NUM> is formed wider than the lubrication path groove <NUM> at the mating surface <NUM> between the housings, and the advance path groove <NUM> secures the amount of the oil required to advance the intake side camshaft <NUM>. The oil path extending from the exhaust side camshaft <NUM> to the intake side camshaft <NUM> is formed by the lower housing <NUM> and the upper housing <NUM>, and thus members such as pipes are not required, and space saving is achieved.

The variable valve timing system will be described with reference to <FIG> is a schematic diagram of the variable valve timing system according to the present embodiment.

As shown in <FIG>, a drive gear <NUM> for the cam chain <NUM> is provided below the oil control valve <NUM>. A crankshaft (not shown) is connected to the drive gear <NUM> via a gear train. A lower portion of the cam chain <NUM> is wound around the drive gear <NUM>, and an upper portion of the cam chain <NUM> is wound around the intake side cam sprocket <NUM> and the exhaust side cam sprocket <NUM>. As the drive gear <NUM> rotates and the cam chain <NUM> rotates in a circle, the intake side camshaft <NUM> is rotated integrally with the intake side cam sprocket <NUM>, and the exhaust side camshaft <NUM> is rotated integrally with the exhaust side cam sprocket <NUM>.

The cam chain <NUM> is guided by a lever guide <NUM> and a chain guide <NUM>. The cam chain <NUM> sent from the drive gear <NUM> to the intake side cam sprocket <NUM> is guided by the lever guide <NUM>, and the cam chain <NUM> drawn to the drive gear <NUM> from the exhaust side cam sprocket <NUM> is guided by the chain guide <NUM>. The cam chain <NUM> extending from the drive gear <NUM> to the intake side cam sprocket <NUM> becomes loose, and thus a chain tensioner (not shown) presses the lever guide <NUM> against the cam chain <NUM> to give tension to the cam chain <NUM>.

The intake valve and an exhaust valve are opened and closed by the rotation of the intake side camshaft <NUM> and the exhaust side camshaft <NUM>, but the opening and closing timing of the intake valve is changed by the variable valve timing system. The variable valve timing system is provided with the variable valve device <NUM> which changes a relative rotational phase of the intake side camshaft <NUM> with respect to the crankshaft. The variable valve device <NUM> includes a case <NUM> fixed to the intake side cam sprocket <NUM> and the inner rotor <NUM> fixed to the intake side camshaft <NUM>. The inner rotor <NUM> is accommodated inside the case <NUM> so as to be relatively rotatable.

A plurality of hydraulic pressure chambers are formed in the case <NUM> of the variable valve device <NUM>, and a plurality of vanes <NUM> extend radially outward from the inner rotor <NUM>. The vane <NUM> of the inner rotor <NUM> is accommodated in each of the hydraulic pressure chambers of the case <NUM>, and each of the hydraulic pressure chambers is partitioned by the vane <NUM> into the advance chamber S1 and the retard chamber S2. When a volume of the advance chamber S1 is increased by the hydraulic pressure, the inner rotor <NUM> is rotated to an advance side relative to the case <NUM>, and the intake side camshaft <NUM> is advanced. When a volume of the retard chamber S2 is increased by the hydraulic pressure, the inner rotor <NUM> is rotated to a retard side relative to the case <NUM>, and the intake side camshaft <NUM> is retarded.

The variable valve device <NUM> is operated by the hydraulic pressure from the oil control valve <NUM>. The oil is supplied to the oil control valve <NUM> from the main gallery <NUM> (see <FIG>) through the external pipe <NUM>. According to a communication state between the ports of the oil control valve <NUM>, an oil supply destination from the oil control valve <NUM> is switched between the advance chamber S1 and the retard chamber S2 of the variable valve device <NUM>. The oil is supplied from the oil control valve <NUM> through the advance path <NUM> to the advance chamber S1, and the oil is supplied from the oil control valve <NUM> through the retard path <NUM> to the retard chamber S2.

As described above, the advance path <NUM> and the retard path <NUM> cross the cam chain chamber <NUM> (see <FIG>), and the oil pipes <NUM> and <NUM> are used to cross the cam chain chamber <NUM>. The oil pipes <NUM> and <NUM> are disposed inside the cam chain <NUM> between the lever guide <NUM> and the chain guide <NUM>. The oil pipes <NUM> and <NUM> are arranged in the front-rear direction while being separated from each other in the up-down direction, and the disposing area of the oil pipes <NUM> and <NUM> is narrowed, and the oil pipes <NUM> and <NUM> are disposed inside the cam chain <NUM> with ample space. Even when the cam chain <NUM> is pushed by the lever guide <NUM>, the cam chain <NUM> does not interfere with the oil pipes <NUM> and <NUM>.

As described above, according to the present embodiment, the oil control valve <NUM> is disposed on the outer surface of the cylinder <NUM>, and the oil control valve <NUM> is separated from the vehicle body frame <NUM> on which the cylinder head <NUM> is suspended. A size of the vehicle body frame <NUM> does not become large in the vehicle width direction due to the oil control valve <NUM>, and the increase in the size of the vehicle is suppressed. Since the oil control valve <NUM> is brought closer to the center of gravity of the engine <NUM>, the transmission of the vibration to the oil control valve <NUM> is reduced and the durability of the oil control valve <NUM> is improved. The oil path bypasses the cylinder bore <NUM> through the outer wall of the cam chain chamber <NUM>, so that the temperature of the oil in the oil path can be stabilized, and the operation of the variable valve device <NUM> can be stabilized.

In the present embodiment, the parallel <NUM>-cylinder engine is exemplified as the engine, but the type of the engine is not particularly limited.

In the present embodiment, a twin spar frame is exemplified as the vehicle body frame, but the type of vehicle body frame is not particularly limited as long as the vehicle body frame can suspend the cylinder head. For example, the vehicle body frame may be a cradle frame.

The oil control valve is disposed on a right side surface of the engine in the present embodiment, but the oil control valve may be disposed on a left side surface of the engine.

In the present embodiment, the solenoid valve is used as an example of the oil control valve, but the type of the oil control valve is not particularly limited as long as the oil control valve is a valve that can control the hydraulic pressure with respect to the variable valve device.

In the present embodiment, the intake side camshaft is provided with the variable valve device, but at least one of the intake side camshaft and the exhaust side camshaft may be provided with the variable valve device.

In the present embodiment, the oil control valve and the main gallery are connected by the external pipe, but the oil control valve and the main gallery may be connected by the oil path inside the engine.

In the present embodiment, the detachable oil pipe forms a crossing path in the cam chain chamber, but the crossing path in the cam chain chamber may be formed so as to allow the oil to move between the inner wall and the outer wall of the cam chain chamber. For example, one of the inner wall and the outer wall of the cylinder head may protrude toward the other side to form the crossing path.

In the present embodiment, the advance path and the retard path are partially formed in parallel, but the advance path and the retard path may be formed entirely non-parallel if the size of the engine is large enough.

In the present embodiment, the advance path and the retard path pass above the combustion chamber, but routes of the advance path and the retard path are not particularly limited. The advance path and the retard path may extend from the oil control valve across the cam chain chamber toward the variable valve device.

In the present embodiment, the oil control valve is disposed so as not to overlap with the bolt on the outer surface of the cylinder, but the oil control valve may overlap with the bolt if the oil control valve does not protrude excessively from the outer surface of the engine.

In the present embodiment, inside the cam chain, the pair of oil pipes are arranged in the front-rear direction while being separated from each other in the up-down direction, but the disposing location of the pair of oil pipes is not particularly limited as long as the pair of oil pipes do not interfere with the cam chain.

In the present embodiment, the pair of plug caps are disposed along the rear edge of the down frame, but the disposing location of the pair of plug caps is not particularly limited as long as the pair of plug caps do not interfere with the vehicle body frame.

In the present embodiment, the oil pipe and the plug cap are formed separately, but the oil pipe and the plug cap may be formed integrally.

In the present embodiment, the diameter of the one end portion of the oil pipe is reduced, and the through hole is formed in the one end portion in the radial direction, but the shape of the oil pipe is not particularly limited as long as the oil pipe can cross the cam chain chamber.

In the present embodiment, the support wall of the camshaft is the cam housing separate from the cylinder head, but the support wall of the camshaft may be formed integrally with the cylinder head.

In the present embodiment, the retard path of the cam housing connects to the retard groove from below, and the advance path of the cam housing connects to the advance groove laterally, but the routes of the advance path and the retard path of the cam housing are not particularly limited. For example, the retard path may connect to the retard groove laterally, and the advance path may connect to the advance groove from below.

In the present embodiment, the lubrication path groove is formed from the exhaust side camshaft toward the intake side camshaft, but the oil may be supplied from the intake side camshaft to the accommodation groove without forming the lubrication path groove.

In the present embodiment, the oil control valve is positioned outside the radiator in the vehicle width direction and below the down frame, but a position relationship between the radiator and the oil control valve is not particularly limited.

In the present embodiment, the oil control valve is positioned below the extension line extending from the lower end of the cooling fan in the blowing direction, but a position relationship between the cooling fan and the oil control valve is not particularly limited.

In the present embodiment, the oil control valve is positioned inside the engine cover and the down frames in the vehicle width direction, but the oil control valve may be positioned outside the engine cover and the down frames in the vehicle width direction.

In the present embodiment, the external pipe is positioned inside the engine cover and the down frames in the vehicle width direction, but the external pipe may be positioned outside the engine cover and the down frames in the vehicle width direction.

In the present embodiment, an area surrounded by the main frame, the down frame, and the lower surface of the cylinder head is formed in a triangle shape, but the shape of the area surrounded by the main frame, the down frame, and the lower surface of the cylinder head is not particularly limited.

The variable valve timing system may be applied not only to the shown straddle-type vehicle, but also to other types of straddle-type vehicles. The straddle-type vehicle is not limited to general vehicles on which a rider rides in a posture of straddling a seat, and also includes a small-sized scooter-type vehicle on which a rider rides without straddling a seat.

As described above, the variable valve timing system according to the present embodiment is a variable valve timing system of an engine (<NUM>) in which a cylinder head (<NUM>) fixed on a cylinder (<NUM>) is suspended on a vehicle body frame (<NUM>), and a cam chain chamber (<NUM>) is formed in the cylinder and the cylinder head, the variable valve timing system including: a variable valve device (<NUM>) configured to change an opening and closing timing of a valve by a hydraulic pressure; and an oil control valve (<NUM>) configured to control the hydraulic pressure with respect to the variable valve device. The oil control valve is disposed on an outer surface of the cylinder, which is an outer wall of the cam chain chamber, and the variable valve device is disposed inside the cylinder head. An oil path for hydraulic pressure control enters the outer wall of the cam chain chamber from the oil control valve, extends from a side of the cylinder to a side of the cylinder head, and crosses the cam chain chamber toward the variable valve device through an inner wall of the cam chain chamber. According to the configuration, the oil control valve is disposed on the outer surface of the cylinder, and the oil control valve is separated from the vehicle body frame on which the cylinder head is suspended. A size of the vehicle body frame does not become large in a vehicle width direction due to the oil control valve, and an increase in a size of the vehicle is suppressed. Since the oil control valve is brought closer to the center of gravity of the engine, transmission of vibration to the oil control valve is reduced and durability of the oil control valve is improved. The oil path bypasses a cylinder bore through the outer wall of the cam chain chamber, so that a temperature of oil in the oil path can be stabilized, and an operation of the variable valve device can be stabilized.

In the variable valve timing system of the present embodiment, the oil path crosses the cam chain chamber above a combustion chamber (<NUM>) of the engine. According to the configuration, the oil path bypasses the combustion chamber, so that the temperature of the oil in the oil path can be stabilized, and the operation of the variable valve device can be stabilized.

In the variable valve timing system according to the present embodiment, a water jacket (<NUM>) configured to cool the combustion chamber is formed on the inner wall of the cam chain chamber, and the oil path crosses the cam chain chamber toward the water jacket and passes next to the water jacket on the inner wall of the cam chain chamber toward the variable valve device. According to the configuration, the water jacket cools the oil in the oil path, the temperature of the oil can be stabilized, and the operation of the variable valve device can be stabilized.

In the variable valve timing system according to the present embodiment, a part of the oil path is formed by a straight path parallel to a cylinder axis and an orthogonal path orthogonal to the straight path. According to the configuration, the oil path is formed by the straight path and the orthogonal path, and thus pressure loss of the oil can be reduced and the path can be easily machined.

In the variable valve timing system according to the present embodiment, the oil path includes an advance path (<NUM>) through which oil for advancing the opening and closing timing of the valve is to pass, and a retard path (<NUM>) through which oil for retarding the opening and closing timing of the valve is to pass, and parts of the advance path and the retard path are arranged in parallel. According to the configuration, the advance path and the retard path can be brought close to each other, and the increase in the size of the engine can be suppressed.

In the variable valve timing system according to the present embodiment, a drain hole (<NUM>) connected to a drain port (<NUM>) of the oil control valve is formed on the side of the cylinder of the outer wall of the cam chain chamber, and oil is discharged from the drain hole toward an inner peripheral surface of the cam chain accommodated in the cam chain chamber. According to the configuration, the oil discharged from the oil control valve can be supplied to the cam chain. No guide or complicated machining for directing the oil to the cam chain is required.

In the variable valve timing system according to the present embodiment, the cylinder is fixed on a crankcase, in a side view of a vehicle, the cylinder head and the cylinder are fixed by two bolts (<NUM>) on both sides of a cylinder axis, and the cylinder and the crankcase are fixed by two bolts (<NUM>) on the both sides of the cylinder axis, and the oil control valve is disposed so as not to overlap with the four bolts. According to the configuration, in order to avoid interference between the four bolts and the oil control valve, the oil control valve is not required to protrude outward in the vehicle width direction, and the increase in the size of the engine can be suppressed.

Although the present embodiment has been described, the embodiment described above and modifications may be combined entirely or partially as another embodiment.

Claim 1:
A vehicle (<NUM>) comprising:
a vehicle body frame (<NUM>);
an engine (<NUM>) in which a cylinder head (<NUM>) fixed on a cylinder (<NUM>) is suspended on the vehicle body frame (<NUM>) and a cam chain chamber (<NUM>) is formed in the cylinder (<NUM>) and the cylinder head (<NUM>);
a variable valve device (<NUM>) configured to change an opening and closing timing of a valve by a hydraulic pressure; and
an oil control valve (<NUM>) configured to control the hydraulic pressure with respect to the variable valve device (<NUM>),
wherein the oil control valve (<NUM>) is disposed on an outer surface of the cylinder (<NUM>), which is an outer wall of the cam chain chamber (<NUM>), and the variable valve device (<NUM>) is disposed inside the cylinder head (<NUM>),
characterized in that:
an oil path for hydraulic pressure control enters the outer wall of the cam chain chamber (<NUM>) from the oil control valve (<NUM>), extends from a side of the cylinder (<NUM>) to a side of the cylinder head (<NUM>), and crosses the cam chain chamber (<NUM>) to the variable valve device (<NUM>) through an inner wall of the cam chain chamber (<NUM>).