Patent Description:
Patent Document <NUM> below describes that an intake passage provided between a throttle valve and an intake valve is defined as a main passage and a tumble passage along the passage direction, for example. In Patent Document <NUM> described below, the tumble passage has a circular cross section, and there is room for improvement in order for intake air to efficiently pass through a port opening, which is a flat passage, between the intake valve and an intake valve valve seat.

Further, for example, Patent Document <NUM> below describes a configuration in which a tumble passage is flattened, but since the tumble passage directly faces the intake valve port, there is a problem that a valve shaft of the intake valve interferes with an intake air flow from the tumble passage.

Last, Patent Document <NUM> below discloses another configuration wherein a flattened tumble passage splits into two symmetrical branches upstream of the intake valve port.

In view of the above prior art, an object of the present invention is to provide an intake structure of an internal combustion engine, in which an intake passage provided between a throttle valve and an intake valve is formed in a main passage and a tumble passage, and an intake air flow during low-load operation easily flows between the intake valve and an intake valve valve seat along the tumble passage, and flows into a combustion chamber to strengthen the tumble flow, thereby improving fuel consumption performance.

In order to solve the above problems, the present invention provides.

According to the above configuration,
the intake air flow during the low-load operation of the internal combustion engine is rectified along the tumble passage having the transverse cross section formed in a horizontally long oval shape with the passage width direction as the longitudinal direction, and easily flows between the intake valve and the intake valve valve seat, and collision interference with the intake valve seat is reduced to flow into a combustion chamber, and the tumble flow is strengthened. Therefore, atomization of an air-fuel mixture by the tumble flow during the low-load operation is promoted, rapid combustion and lean combustion are possible, and the fuel consumption performance can be improved.

Further, the intake air flow flowing through the tumble passage can linearly flow into the combustion chamber through the intake valve port, and the longitudinal width w of the transverse cross section of the tumble passage gradually decreases, so that the passage cross-sectional area gradually decreases and the flow velocity gradually increases. Therefore, the tumble flow T is strengthened in the combustion chamber, atomization of the air-fuel mixture is further promoted, leaner combustion is possible, and fuel consumption performance can be improved.

Further, the internal combustion engine includes a pair of an exhaust valve and the intake valve in which shaft portions of the exhaust valve and the intake valve are oriented to be opened in a V shape in a front-rear direction above a combustion chamber, a virtual extension line of the other end of the tumble passage passes through a vicinity of the shaft portion of the intake valve, and an ignition plug is disposed on a peripheral portion of the combustion chamber on a side of the other end.

Therefore, since the intake air flow flowing on the other end side of the tumble passage flows so as to be in contact with the valve shaft of the intake valve, the flow velocity is reduced on the other end side of the intake air flow linearly flowing through the port opening between the upper surface of the umbrella portion of the intake valve and the intake valve valve seat of the intake valve port, and a swirl flow toward the other end side is generated. By the effect of guiding the air-fuel mixture to the ignition plug provided on the other end side of the intake air flow, ignitability in the ignition plug is enhanced, combustion stability is obtained, lean combustion is improved, and fuel performance can be improved.

According to a preferred embodiment of the present invention,
the main passage is provided with a reed valve that closes the intake air flow when the internal combustion engine is in the low-load operation.

Therefore, the intake air flowing through the main passage can be restricted by the reed valve during the low-load operation of the internal combustion engine, and the intake air flow can mainly flow to the tumble passage, so that the tumble flow can be further enhanced.

According to a preferred embodiment of the present invention,
the reed valve is provided between the throttle valve and an inlet manifold, and the reed valve element that restricts the intake air flow of the main passage has one end portion on an upstream side attached to the reed valve body of the reed valve so as to cover a main-passage-side outlet opening of the reed valve, and an opening-side edge portion on a downstream side formed in a direction parallel to the passage width direction of the tumble passage.

Therefore, since the passage-width-direction operation region of the reed valve element can be formed to be large along the passage-width direction of the tumble passage having the transverse cross section, the main-passage-side outlet opening of the reed valve can be provided to be large, and the flow passage resistance of both the main passage and the tumble passage can be reduced to improve the intake efficiency.

According to a preferred embodiment of the present invention,
the reed valve body of the reed valve is formed by a mold combined from two directions against each other in which the main passage is molded by a molding die from a downstream side and the tumble passage is molded by a molding die from an upstream side.

Therefore, due to the draft angle of the molding die for forming the reed valve body, the passage area of the main passage is enlarged from the inlet toward the outlet, while the tumble passage is conversely reduced, so that the change in the total passage area of the passages is reduced, the disturbance of the flow velocity of the intake air flow during a high-load operation can be prevented, and the engine performance is improved.

According to a preferred not claimed embodiment
a main-passage-side outlet opening width of the main-passage-side outlet opening of the reed valve body is wider than an inlet opening width of an inlet opening (<NUM>) of the reed valve body.

Therefore, the intake air flow at a high load can smoothly flow toward the main passage, and the engine performance can be improved.

According to a preferred not claimed embodiment
in the valve intake path in the reed valve body, a tumble-passage-side outlet opening is made narrow and provided below and vertically adjacent to the main-passage-side outlet opening, tumble-passage-side outlet opening being narrowed by step portions provided on both sides of a lower portion of the main-passage-side outlet opening.

Therefore, the tumble-passage-side outlet opening is narrowed by the step portions, the flow velocity of the tumble passage is increased at the time of low load, the lean combustion is improved, and the fuel consumption is improved.

According to the intake structure of the internal combustion engine according to the present invention,
the intake air flow during the low-load operation of the internal combustion engine is rectified along the tumble passage having the transverse cross section formed in a horizontally long oval shape with the passage width direction as the longitudinal direction, and easily flows between the intake valve and the intake valve valve seat, and collision interference with the intake valve seat is reduced to flow into a combustion chamber, and the tumble flow is strengthened. Therefore, atomization of an air-fuel mixture by the tumble flow during the low-load operation is promoted, rapid combustion and lean combustion are possible, and the fuel consumption performance can be improved.

An intake structure of an internal combustion engine according to an embodiment of the present invention will be described with reference to <FIG>.

Note that directions such as front, rear, left, right, up, and down in the description and claims of the present specification follow a vehicle orientation of a straddle type vehicle in a case where the internal combustion engine according to the present embodiment is mounted on a straddle type vehicle. In this embodiment, a straddle type vehicle specifically is a scooter-type motorcycle (hereinafter simply referred to as a "motorcycle").

In the drawing, the arrows FR, LH, RH, and UP indicate the front, the left, the right, and an upper part of the vehicle, respectively.

<FIG> illustrates an outline of a left side surface of a motorcycle <NUM> including an intake structure of an internal combustion engine according to the present embodiment.

In the motorcycle <NUM> of this embodiment, a vehicle body front portion 1A and a vehicle body rear portion 1B are connected to each other via a low floor portion 1C (foot placing portion), and a vehicle body frame <NUM> forming a framework of the vehicle body is basically formed of a down frame <NUM> and a main frame <NUM>.

That is, the down frame <NUM> extends downward from a head pipe <NUM> of the vehicle body front portion 1A and is connected to a pair of left and right lower frame portions 22a of the main frame <NUM> extending substantially horizontally rearward from the lower end of the down frame <NUM>. The main frame <NUM> extending to an obliquely rear and upper side from the rear ends of the lower frame portions 22a forms a pair of right and left inclined portions 22b, and the upper portions of the inclined portions 22b further bend to form a pair of right and left horizontal portions 22c extending substantially horizontally to the rear side.

The inclined portions 22b and the horizontal portions 22c of the main frame <NUM> support a storage box (also referred to as a helmet box) <NUM>, and an occupant seat <NUM> is arranged to cover the upper side of the storage box.

In contrast, in the vehicle body front portion 1A, a handle bar <NUM> is provided on an upper side of the head pipe <NUM> so as to be pivotably supported thereby, a front fork <NUM> extends downward, and a front wheel <NUM> is pivotably supported at a lower end thereof.

A power unit support bracket <NUM> is provided to project rearward in the inclined portions 22b of the main frame <NUM>, and a swing type power unit (hereinafter simply referred to as a "power unit") <NUM> is connected and supported to the power unit support bracket <NUM> via a link member <NUM> so as to be vertically swingable.

That is, the motorcycle <NUM> of this embodiment adopts an upper link-type supporting structure of a power unit <NUM>, and as a result, a space provided with a catalyst device <NUM> below the front portion of the power unit <NUM> is obtained.

In the vehicle body front portion 1A, the head pipe <NUM> and the down frame <NUM> are covered from the front and rear sides with a front cover 10a and a leg shield 10b of a vehicle body cover <NUM>.

A floor portion 1C is provided on the pair of left and right lower frame portions 22a of the main frame <NUM> of the vehicle body frame <NUM>. An upper portion of the lower frame portion 22a is covered with a floor cover 10c, left and right portions thereof are covered with a floor side cover 10d in the front-rear direction, and a lower portion thereof is covered with an under cover 10e.

In the vehicle body rear portion 1B, a fuel tank <NUM> is provided on the horizontal portion 22c of the main frame <NUM> below the rear portion of the occupant seat <NUM> and above a rear wheel <NUM>, and the inclined portion 22b and the horizontal portion 22c of the main frame <NUM> are covered on the left, right, and rear sides by a body cover 10f. Further, a front fender <NUM> is provided above the front wheel <NUM>.

Each of the covers 10a to <NUM> configuring the vehicle body cover <NUM> is formed of a suitable material such as a resin material.

In the power unit <NUM>, an internal combustion engine <NUM> is provided, and a power transmission part <NUM> internally provided with a belt type stepless transmission <NUM> is provided behind the internal combustion engine <NUM>. A reduction gear mechanism <NUM> which is transmitted from the belt type stepless transmission <NUM> is provided at a rear portion of the power transmission part <NUM>, and the rear wheel <NUM> is provided on a rear axle 52a which is an output shaft of the reduction gear mechanism.

A rear cushion <NUM> is interposed between the rear portion of the power transmission part <NUM> and the rear horizontal portion 22c of the main frame <NUM>.

The internal combustion engine <NUM> is a single-cylinder air-cooled <NUM>-stroke cycle internal combustion engine, in which a crankshaft <NUM> is rotatably supported by a crankcase <NUM> so as to be directed in the vehicle width direction, that is, the left-right direction, and a cylinder block <NUM>, a cylinder head <NUM>, and a head cover <NUM> are sequentially overlapped so as to protrude from the front portion of the crankcase <NUM>, and fastened with the cylinder axis C being substantially horizontal and greatly inclined forward.

An inlet manifold <NUM> and a throttle body <NUM> are provided above the power unit <NUM>, the cylinder head <NUM>, and the crankcase <NUM>. The inlet manifold <NUM> is connected to an intake port inlet 45a in an upper portion of the cylinder head <NUM>, which is greatly forward inclined. The inlet manifold <NUM> extends with its upstream side bent backward and connected to the throttle body <NUM>.

The upstream side of the throttle body <NUM> is connected via a connecting tube <NUM> to an air cleaner <NUM> attached to the upper portion of the power transmission part <NUM>.

An intake passage <NUM> is formed from the connecting tube <NUM> through the throttle body <NUM>, the inlet manifold <NUM>, and an intake port <NUM> of the cylinder head <NUM>, and leads to a combustion chamber <NUM>.

In an upstream exhaust pipe 48a connected to an exhaust port outlet 47a at the lower portion of the cylinder head <NUM>, the catalyst device <NUM> having a substantially cylindrical shape directed in the vehicle width direction is interposed, and a catalyst such as a three-way catalyst for purifying exhaust gas is loaded in the inside thereof.

A downstream exhaust pipe 49b connected to the outlet of the catalyst device <NUM> is bent rearward, extends rearward along the right side of the vehicle, and is connected to a muffler (not illustrated) on the right side of the rear wheel <NUM>.

<FIG> is a right cross-sectional side view of the cylinder block <NUM>, the cylinder head <NUM>, the head cover <NUM>, and the periphery thereof of the power unit <NUM> in <FIG>, taken along the cylinder axis C.

The crankcase <NUM> is configured by combining a left case half body <NUM> and a right case half body (not illustrated) which are divided into right and left, and the left case half body <NUM> extends rearward to form a power transmission part <NUM> that accommodates a transmission device including a long belt type stepless transmission <NUM> (not illustrated), a reduction gear mechanism <NUM>, and the like between the crankshaft <NUM> and the rear axle 52a of the rear wheel <NUM>.

A piston <NUM> reciprocating in a cylinder bore 42a of the cylinder block <NUM> is connected to a crank pin 41a of the crankshaft <NUM> of the crankcase <NUM> by a connecting rod <NUM>.

The combustion chamber <NUM> is formed between a top surface 33a of the piston <NUM> slidably fitted in the cylinder bore 42a of the cylinder block <NUM> and a combustion chamber ceiling surface 43a of the cylinder head <NUM> to which the top surface 33a is facing.

As illustrated in <FIG>, in the present embodiment, the throttle body <NUM> is fastened and connected to the inlet manifold <NUM> connected to the intake port inlet <NUM> of the cylinder head <NUM> on the upstream side via a reed valve <NUM> described later.

In the throttle body <NUM>, a throttle valve 62a is incorporated in the intake passage <NUM>, and rotates around a throttle valve shaft 62b to open and close the intake passage <NUM> and adjust an intake flow rate.

In <FIG>, <NUM> represents a bracket portion that protrudes upward from the upper portion of the crankcase <NUM> and suspends the power unit <NUM> to the vehicle body frame <NUM>. As illustrated in <FIG>, the bracket portion <NUM> is pivotally supported by a power unit support bracket <NUM> protruding rearward from the inclined portion 22b of the main frame <NUM> via a link member <NUM>, and the power unit <NUM> swings up and down with respect to the vehicle body frame <NUM>.

The rear end of the power unit <NUM> that vertically swings is supported by the horizontal portion 22c of the main frame <NUM> by the rear cushion <NUM>.

As illustrated in <FIG>, an inlet manifold <NUM> is connected to the front side of the throttle body <NUM>, that is, the downstream side of the intake air and is bent downward, and is connected to the intake port inlet 45a in the upper portion of the cylinder head <NUM> with an insulator <NUM> interposed therebetween.

A fuel injection valve <NUM> is attached to a downstream end of the inlet manifold <NUM>, and fuel is injected toward the intake valve port <NUM>.

Since the fuel injection has a certain spread with respect to the injection center line I illustrated in <FIG>, a fuel injection avoiding recess 67a that avoids the injected fuel is provided in a later described main passage head inlet opening <NUM> on the downstream side (see <FIG>).

A fuel hose (not illustrated) connected to the fuel injection valve <NUM> is routed rearward and connected to a fuel tank <NUM> provided above the rear wheel <NUM> via a fuel pump device (not illustrated).

In the present embodiment, the internal combustion engine <NUM> employs a single-cylinder SOHC type two-valve system, and a valve mechanism <NUM> is provided in the cylinder head <NUM>. The cylinder head <NUM> is covered with the head cover <NUM> so as to cover the valve mechanism <NUM>.

In order to transmit power to the valve mechanism <NUM> in the head cover <NUM>, an endless cam chain (not illustrated) passes through a cam chain chamber (not illustrated) provided on one side of the crankcase <NUM>, the cylinder block <NUM>, and the cylinder head <NUM> in the direction of the crankshaft <NUM>, and is installed between the camshaft <NUM> and the crankshaft <NUM>, and the camshaft <NUM> rotates at a rotation speed of <NUM>/<NUM> in synchronization with the crankshaft <NUM>.

Here, an ignition plug <NUM> (see <FIG>) is fitted into the cylinder head <NUM> from the side opposite to the cam chain chamber (the other side in the direction of the crankshaft <NUM>) toward the inside of the combustion chamber <NUM>.

In the cylinder head <NUM> in which the cylinder axis C is substantially horizontal and greatly inclined forward, the intake port <NUM> and an exhaust port <NUM> are formed to extend while being curved in directions vertically away from each other from the intake valve port <NUM> and an exhaust valve port <NUM> opened to the combustion chamber ceiling surface 43a, respectively.

An upstream end of the intake port <NUM> opens upward from the cylinder head <NUM> to form an intake port inlet <NUM>, and is connected to the inlet manifold <NUM> to form a continuous intake passage <NUM>. The throttle body <NUM> is connected to the upstream side of the inlet manifold <NUM>.

A downstream end of the exhaust port <NUM> forms an exhaust port outlet <NUM>, opens downward of the cylinder head <NUM>, and is connected the upstream exhaust pipe 48a (see <FIG>).

A cylindrical intake valve guide <NUM> is integrally fitted to the curved outer wall portion 37a of the intake port <NUM> in the cylinder head <NUM>, and an intake valve <NUM> slidably supported by the intake valve guide <NUM> opens and closes the intake valve port <NUM> facing the combustion chamber <NUM> of the intake port <NUM>.

In addition, an exhaust valve <NUM> slidably supported by the exhaust valve guide <NUM> integrally fitted to the curved outer wall portion 38a of the exhaust port <NUM> in the cylinder head <NUM> opens and closes the exhaust valve port <NUM> facing the combustion chamber <NUM> of the exhaust port <NUM>.

The intake valve <NUM> and the exhaust valve <NUM> are biased upward by a valve spring <NUM> such that the umbrella portions 73a and 74a close the intake valve port <NUM> and the exhaust valve port <NUM> facing the combustion chamber <NUM>, respectively. However, stem ends 73b and 74b of the intake valve <NUM> and the exhaust valve <NUM> are pushed down by an intake rocker arm <NUM> and an exhaust rocker arm <NUM> that swing in contact with an intake cam and an exhaust cam of the camshaft <NUM>, the intake valve <NUM> and the exhaust valve <NUM> are opened at a predetermined timing, the intake port <NUM> and the combustion chamber <NUM>, and the exhaust port <NUM> and the combustion chamber <NUM> communicate with each other, and intake and exhaust are performed at a predetermined timing.

In the internal combustion engine <NUM> of the present embodiment as described above, in order to obtain more preferable combustion in the combustion chamber <NUM>, an intake structure for giving a longitudinal rotating vortex (rotating vortex on a virtual plane along the cylinder axis C) of the fuel-air mixture in the combustion chamber <NUM>, that is, a tumble flow T, and a lateral rotating vortex (rotating vortex on a virtual plane orthogonal to the cylinder axis C), that is, a swirl flow S is configured.

The inlet manifold <NUM> is connected to an upstream end of the intake port <NUM> of the internal combustion engine <NUM> via an insulator <NUM> to form the continuous intake passage <NUM>, and the throttle body <NUM> is connected to an upstream side of the inlet manifold <NUM> via the reed valve <NUM> to be described later.

The throttle body <NUM> has an intake path 62c having a substantially circular cross section and constituting a part of the intake passage <NUM> connected to a combustion chamber <NUM> of the internal combustion engine <NUM>, and an upstream side thereof is connected to the air cleaner <NUM> (see <FIG>) via the connecting tube <NUM>.

The throttle body <NUM> includes the single butterfly throttle valve 62a that is rotatably and pivotally supported in the throttle body <NUM> by the throttle valve shaft 62b that is oriented vertically to the intake flow direction F of the intake path 62c, that is, vertically to the center axis X of the intake path 62c, to substantially horizontally to variably control the flow path area of the intake path 62c and open and close the intake path 62c.

The throttle valve 62a is rotatable in a valve opening direction in a clockwise direction in <FIG> by a driver's operation or the like, and is biased in a valve closing direction in a counterclockwise direction by a return spring (not illustrated).

According to the present embodiment, the intake path 62c of the throttle body <NUM> is oriented substantially horizontally.

According to the present embodiment, the intake passage <NUM> is divided into upper and lower parts along the intake flow direction by a partition wall <NUM> following from the inlet manifold <NUM> to the intake port <NUM>, and is partitioned into a tumble passage 6A on the lower side in the drawing and a main passage 6B on the upper side in the drawing except for the tumble passage 6A, the tumble passage 6A being configured to generate a tumble flow T in the combustion chamber <NUM>.

According to the present invention, the "tumble passage" is a passage for intake air for generating the tumble flow T in the combustion chamber <NUM> when the throttle valve 62a has a low opening, that is, when the internal combustion engine <NUM> has a low load.

Note that, in the present invention, the vertical arrangement of the tumble passage 6A and the main passage 6B is not limited to that of the embodiment.

The partition wall <NUM> is configured such that an inlet-manifold-side partition wall 65A, an insulator-side partition wall 65B, and an intake-port-side partition wall 65C are continuously positioned from the upstream side to the downstream side of the intake air flow.

The main passage 6B on the upper side in the drawing and the tumble passage 6A on the lower side in the drawing are defined by vertically partitioning the intake passage <NUM> on the downstream side of the throttle body <NUM> from the inlet manifold <NUM> to the intake port <NUM> by the partition wall <NUM>. As illustrated in <FIG>, the reed valve <NUM> formed in a substantially triangular shape in a cross section of the intake passage <NUM> in a side view is interposed between the throttle body <NUM> and the inlet manifold <NUM>.

<FIG> is a perspective view of an upstream side of a reed valve body <NUM> of the reed valve <NUM>, in which the intake passage <NUM> is illustrated to be opened in the mounting flange portion <NUM>, and the main-passage-side outlet opening <NUM> and the tumble-passage-side outlet opening <NUM> are seen at a depth of the valve intake path <NUM> inside.

<FIG> is a perspective view of the downstream side of the reed valve body <NUM> of the reed valve <NUM>, and illustrates the back portion of the mounting flange portion <NUM>, the main-passage-side outlet opening <NUM> of the inclined surface 81a, the tumble-passage-side outlet opening <NUM> of the downstream end <NUM>, and the like.

<FIG> is a perspective view of the downstream side of the reed valve <NUM> having the same orientation as that of <FIG>, and illustrates a state in which the reed valve element <NUM> is fastened to the reed valve body <NUM>.

The reed valve <NUM> includes the reed valve body <NUM> that forms the whole shape, and the mounting flange portion <NUM> thereof is sandwiched and fastened between a downstream end portion of the throttle body <NUM> and an upstream end portion of the inlet manifold <NUM>.

An inlet opening <NUM> coinciding with a downstream opening 62d of the throttle body <NUM> is provided on a surface of the reed valve body <NUM> to be attached to the throttle body <NUM>, and the valve intake path <NUM> communicating with the intake path 62c of the throttle body <NUM> is formed in the reed valve body <NUM>.

The downstream end <NUM> of the reed valve body <NUM> is provided with the tumble-passage-side outlet opening <NUM> that abuts against an upstream end 65Aa of the inlet-manifold-side partition wall 65A and matches an upstream end opening 6Aa of the tumble passage 6A of the inlet manifold <NUM>.

The upper portion of the reed valve body <NUM> is formed to be inclined from the back portion of the mounting flange portion <NUM> to the lower portion on the downstream side of the reed valve <NUM>, and the inclined surface 81a is formed with the main-passage-side outlet opening <NUM> that communicates the valve intake path <NUM> in the reed valve body <NUM> and the main passage 6B of the inlet manifold <NUM>.

The reed valve element <NUM> is fastened to the outer surface of the main-passage-side outlet opening <NUM> by a reed valve element screw 87c at one end portion 87a on the upstream side to the back portion of the mounting flange portion <NUM> so as to cover the main-passage-side outlet opening <NUM>.

An opening-side edge portion 87b on the other end side of the reed valve element <NUM> is a swing free end, and contacts the reed valve body <NUM> in the upper portion of the tumble-passage-side outlet opening <NUM> of the downstream end <NUM> of the reed valve body <NUM>. When the negative pressure on the downstream side of the reed valve element <NUM> is smaller than a certain value, a state in which the main-passage-side outlet opening <NUM> is closed is maintained, and the intake air flows exclusively from the valve intake path <NUM> in the reed valve body <NUM> to the tumble passage 6A of the inlet manifold <NUM>.

When the throttle valve 62a has a high opening degree, that is, when the internal combustion engine <NUM> has a high load and the negative pressure on the downstream side of the reed valve element <NUM> becomes larger than a certain value, the opening-side edge portion 87b on the downstream side of the reed valve element <NUM> bends so as to open the main-passage-side outlet opening <NUM>, and the intake air flows from the valve intake path <NUM> in the reed valve body <NUM> to the main passage 6B of the inlet manifold <NUM>.

Therefore, the upstream end opening 6Aa of the tumble passage 6A of the intake passage <NUM> of the inlet manifold <NUM> connected to the downstream side of the valve intake path <NUM> of the reed valve <NUM> is connected to the downstream side of the tumble-passage-side outlet opening <NUM> of the downstream end <NUM> of the reed valve <NUM> to open, and the upstream end opening 6Ba of the main passage 6B is connected to the downstream side of the main-passage-side outlet opening <NUM> of the inclined surface 81a of the reed valve <NUM> to open.

In the present embodiment, as illustrated in <FIG>, the throttle valve 62a is provided near the downstream end of the intake path <NUM> of the throttle body <NUM>, and the tumble-passage-side outlet opening <NUM> and the main-passage-side outlet opening <NUM> of the reed valve <NUM> are connected via the valve intake path <NUM> having a suppressed volume. Therefore, the response of the reed valve element <NUM> of the main-passage-side outlet opening <NUM> to the state of the throttle valve 62a is fast, and the response of the intake air flow switching between the tumble passage 6A and the main passage 6B is high.

Further, the reed valve <NUM> is provided between the throttle body <NUM> and the inlet manifold <NUM>, and as illustrated in <FIG>, in the tumble-passage-side outlet opening <NUM>, a transverse cross section <NUM> is wide and the opening cross section is large on the lower side of the intake passage <NUM>.

In the reed valve element <NUM> that restricts the intake air flow of the main passage 6B, the one end portion 87a on the upstream side is attached to the reed valve body <NUM> so as to cover the main-passage-side outlet opening <NUM> of the reed valve <NUM>, and the opening-side edge portion 87b on the downstream side is formed in a direction parallel to the passage width direction of the tumble passage 6A.

Therefore, since the passage-width-direction operation region of the reed valve element <NUM> can be formed to be large along the passage-width direction of the tumble passage 6A having the transverse cross section <NUM>, the main-passage-side outlet opening <NUM> of the reed valve <NUM> can be provided to be large, and the flow passage resistance of both the main passage 6B and the tumble passage 6A is reduced to improve the intake efficiency.

Further, the reed valve body <NUM> of the reed valve <NUM> is integrally molded by a mold combined from two directions against each other, the main passage 6B of the reed valve body <NUM> is molded by a molding die from the downstream side, and the tumble passage 6A of the reed valve body <NUM> is molded by a molding die from the upstream side.

Therefore, as illustrated in <FIG>, the main passage 9B in the reed valve <NUM> is formed at an angle β widening toward the downstream side due to the draft angle of the molding die.

The tumble passage 6A in the reed valve <NUM> is formed at an angle α that narrows toward the downstream side due to the draft angle of the molding die.

That is, due to the draft angle of the molding die for forming the reed valve body <NUM>, the passage area of the main passage 6B is enlarged from the inlet toward the outlet, while the tumble passage 6A is conversely reduced, so that the change in the total passage area of the passages 6A and 6B is reduced, the disturbance of the flow velocity of the intake air flow during the high load operation can be prevented, and the engine performance is improved.

To the inlet manifold <NUM>, the fuel injection valve <NUM> is attached, which penetrates the main passage 6B from the upper outside and injects and supplies fuel toward the intake valve port <NUM>.

According to the present embodiment, the fuel injection valve <NUM> is disposed in the inlet manifold <NUM>, but a direct injection structure in which the fuel injection valve <NUM> is disposed in the cylinder head <NUM> or the cylinder block <NUM> and fuel is injected into the combustion chamber <NUM> may be used.

As illustrated in <FIG>, the tumble-passage-side outlet opening <NUM> of the downstream end <NUM> of the reed valve <NUM> is formed in a horizontally long cross section having a horizontally long oval shape elongated in the passage width direction.

Therefore, the tumble passage 6A of the inlet manifold <NUM> connected to the tumble-passage-side outlet opening <NUM> is also formed such that the intake passage <NUM> is partitioned by the inlet-manifold-side partition wall 65A, and the transverse cross section <NUM> is formed in a horizontally long oval cross section long in the passage width direction.

The main-passage-side outlet opening width 86W of the main-passage-side outlet opening <NUM> of the reed valve body <NUM> illustrated in <FIG> is formed to be wider than the inlet opening width 82W of the inlet opening <NUM> of the reed valve body <NUM> illustrated in <FIG>.

Therefore, the intake air flow at a high load of the internal combustion engine <NUM> can smoothly flow toward the main passage 6B, and the engine performance can be improved.

Further, as illustrated in <FIG> and <FIG>, in the valve intake path <NUM> in the reed valve body <NUM>, the tumble-passage-side outlet opening <NUM> is provided to be narrower than the main-passage-side outlet opening <NUM> by step portions <NUM> provided on both sides of the lower portion of the main-passage-side outlet opening <NUM>, the tumble-passage-side outlet opening <NUM> being vertically adjacent to the main-passage-side outlet opening <NUM> below.

Therefore, the tumble-passage-side outlet opening <NUM> is narrowed by the step portions <NUM>, the flow velocity of the tumble passage 6A is increased at the time of low load of the internal combustion engine <NUM>, the lean combustion is improved, and the fuel consumption is improved.

As described above, since the reed valve element <NUM> of the reed valve <NUM> that closes the intake flow during the low-load operation of the internal combustion engine <NUM> is provided in the main passage 6B of the intake passage <NUM>, the intake air flowing through the main passage 6B can be restricted by the reed valve element <NUM> of the reed valve <NUM> during the low-load operation of the internal combustion engine <NUM>, and the intake flow can mainly flow to the tumble passage 6A, so that the tumble flow T in the combustion chamber <NUM> can be further increased.

The tumble flow T indicated by the two-dot chain line in <FIG> schematically indicates the tumble flow T in the combustion chamber <NUM> when the piston <NUM> descends in the cylinder bore 42a as indicated by a two-dot chain line.

<FIG> is a top view of the cylinder head <NUM> as viewed in a direction of the arrows VI-VI in <FIG>, and the intake port inlet <NUM> is illustrated behind the intake side flange surface 43b to which the inlet manifold <NUM> is fastened via the insulator <NUM>.

The intake port inlet <NUM> is partitioned by the intake-port-side partition wall 65C, and the tumble passage head inlet opening <NUM> and the main passage head inlet opening <NUM> are opened, whereas the tumble passage head inlet opening <NUM> is also formed in a laterally long oval cross section <NUM> that is long in the passage width direction similarly to the tumble passage 6A of the inlet manifold <NUM>.

In the main passage head inlet opening <NUM>, as described above, the fuel injection avoiding recess 67a that avoids the fuel injected from the fuel injection valve <NUM> is formed (see <FIG>).

According to the present embodiment, the tumble passage 6A of the cylinder head <NUM> is formed by casting at the time of casting the cylinder head <NUM>, but may be formed by machining after forming the cylinder head <NUM>.

However, since the tumble passage 6A is formed in a horizontally long oval cross section in which the transverse cross section <NUM> is long in the passage width direction as described above, molding at the time of casting is easy and preferable.

As illustrated in <FIG>, the tumble passage 6A of the cylinder head <NUM> is formed with a uniform passage sectional height h from the tumble passage head inlet opening <NUM> to the tumble passage outlet <NUM>.

The orientation of the tumble passage 6A of the cylinder head <NUM> and the passage sectional height h are set such that the intake air flow f that has passed through the tumble passage 6A of the cylinder head <NUM> and jetted into the intake port <NUM> is directed between the umbrella portion 73a of the opened intake valve <NUM> and an intake valve valve seat <NUM> as indicated by a two-dot chain line in <FIG>.

Further, in <FIG>, the intake valve guide <NUM> fitted to the curved outer wall portion 37a of the intake port <NUM> and the shaft portion of the intake valve <NUM> slidably supported by the intake valve guide <NUM> are illustrated at the back of the main passage head inlet opening <NUM>.

As described above, since the transverse cross section <NUM> of the tumble passage 6A formed by the partition wall <NUM> in the intake passage <NUM> is formed in the oblong oval cross section long in the passage width direction, the intake air flow during the low-load operation of the internal combustion engine <NUM> is rectified along the tumble passage 6A, the collision interference of the intake valve seat of the intake valve port <NUM> with the intake air flow is reduced, the intake air flow flows into the combustion chamber <NUM>, and the tumble flow T is strengthened. Therefore, atomization of the air-fuel mixture by the tumble flow T during the low-load operation is promoted, rapid combustion and lean combustion are possible, and fuel consumption performance can be improved.

<FIG> is a perspective view of a cross section, viewed from the head cover <NUM> side, which slightly obliquely intersects with the cylinder axis C rather than being orthogonal to the cylinder axis C, generally along the tumble passage 6A of the cylinder head <NUM> as viewed in a direction of the arrows VII-VII in <FIG>.

In the cylinder head <NUM>, one end 69a in the longitudinal direction of the transverse cross section <NUM> of the tumble passage 6A is oriented along the tangential direction of an opening edge 35a of the intake valve port <NUM>, and the other end 69b is oriented to gradually narrow the longitudinal width w of the transverse cross section <NUM> toward the intake valve port <NUM>.

Therefore, according to the present embodiment, the intake air flow flowing through the tumble passage 6A can linearly flow into the combustion chamber <NUM> through the intake valve port <NUM>, and the longitudinal width w of the transverse cross section <NUM> of the tumble passage 6A gradually decreases, so that the passage cross-sectional area gradually decreases and the flow velocity gradually increases. Therefore, the tumble flow T is strengthened in the combustion chamber <NUM>, atomization of the air-fuel mixture is further promoted, leaner combustion is possible, and fuel consumption performance can be improved.

As illustrated in <FIG>, the internal combustion engine <NUM> is provided with a pair of the intake valve <NUM> and the exhaust valve <NUM> above the combustion chamber <NUM>, and the shaft portion 73c and a shaft portion 74c of the intake valves and the exhaust valves are opened and oriented in a V shape in the front-rear direction.

As illustrated in <FIG>, in the cylinder head <NUM>, a virtual extension line b in the passage direction of the other end 69b of the tumble passage 6A passes through the vicinity of the shaft portion 73c of the intake valve <NUM>, and the ignition plug <NUM> is disposed on a peripheral portion of the combustion chamber <NUM> on the other end 69b side.

Therefore, since the intake air flow flowing out from the other end 69b side of the tumble passage 6A flows so as to be in contact with the shaft portion 73c of the intake valve <NUM>, the intake air flow on the other end 69b side directly flowing in through the port opening <NUM> between the upper surface of the umbrella portion 73a of the intake valve <NUM> and the intake valve valve seat <NUM> of the intake valve port <NUM> comes into contact with the shaft portion 73c to reduce the flow velocity, and a swirl flow S directed toward the other end 69b side is generated.

Therefore, the tumble flow T is inclined in the direction of the swirl flow S, and the air-fuel mixture is guided to the ignition plug <NUM> provided on a position on the other end 69b side of the tumble passage 6A. Therefore, ignitability in the ignition plug <NUM> is enhanced, combustion stability is obtained, lean combustion is improved, and fuel performance is improved.

The swirl flow S indicated by the two-dot chain line in <FIG> schematically illustrates the swirl flow S in the combustion chamber <NUM> when the piston <NUM> descends in the cylinder bore 42a as indicated by the two-dot chain line in <FIG>.

In addition, as illustrated in <FIG>, in the cylinder head <NUM>, the tumble passage 80A is linearly formed to be directed between the umbrella portion 73a when the intake valve <NUM> is opened and the intake valve valve seat <NUM> on the exhaust valve port <NUM> side of the intake valve port <NUM> in a side view with respect to the cross section along the cylinder axis C.

Therefore, as indicated by a two-dot chain line in <FIG>, the intake air flow f flowing out of the tumble passage 6A can pass above the umbrella portion 73a of the intake valve <NUM> and then directly flow into the cylinder bore 42a by reducing collision interference with the intake valve seat <NUM>, so that the tumble flow T is easily generated in the combustion chamber <NUM>.

<FIG> is a top perspective view of the cylinder head <NUM> as viewed from the upper right rear portion as viewed from the arrow VIII in <FIG>, and illustrates that the inlet manifold <NUM>, the reed valve <NUM>, and the throttle body <NUM> are sequentially attached to the upper surface of the cylinder head <NUM>, and the ignition plug <NUM> is attached from the right side.

Since the reed valve element <NUM> of the main passage 6B of the inserted reed valve <NUM> has a substantially rectangular shape that is wide in the passage width direction and moves up and down, an upper surface 61a of the inlet manifold <NUM> is formed in a planar manner so as to match the rectangular shape (see also <FIG>).

Claim 1:
An internal combustion engine with an intake structure in which a main passage (6B) and a tumble passage (6A) are formed by a partition wall (<NUM>) that partitions an intake passage (<NUM>) provided between a throttle valve (62a) and an intake valve (<NUM>) vertically along the passage direction, and configured to guide intake air into the tumble passage (6A) when the internal combustion engine (<NUM>) is in a low-load operation, wherein
a transverse cross section (<NUM>) of the tumble passage (6A) formed by the partition wall (<NUM>) is formed in a horizontally long oval shape whose longitudinal direction is a passage width direction,
one end (69a) in a longitudinal direction of the transverse cross section (<NUM>) of the tumble passage (6A) is oriented along a tangential direction of an opening edge (35a) of an intake valve port (<NUM>), and another end (69b) is oriented to gradually narrow a longitudinal width (w) of the transverse cross section (<NUM>) toward the intake valve port (<NUM>), and
the internal combustion engine (<NUM>) includes a pair of an exhaust valve (<NUM>) and the intake valve (<NUM>) in which shaft portions (74c, 73c) of the exhaust valve (<NUM>) and the intake valve (<NUM>) are oriented to be opened in a V shape in a front-rear direction above a combustion chamber (<NUM>), a virtual extension line (b) of the other end (69b) of the tumble passage (6A) passes through a vicinity of the shaft portion (73c) of the intake valve (<NUM>) on a side opposite to the one end (69a) with respect to the shaft portion (73d), and an ignition plug (<NUM>) is disposed on a peripheral portion of the combustion chamber (<NUM>) on a side of the other end (69b).