Intake duct structure of motorcycle

An intake duct structure of a motorcycle includes front forks disposed on both of right and left sides of a head pipe of a body frame and a main frame extending obliquely backward and downward from the head pipe, wherein the intake duct structure extends from a front end of the motorcycle toward the head pipe and is formed in such a manner that an interfered area where a rotational orbit of the front forks at a time of steering overlaps the intake duct structure is elastically deformable.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority of Japanese Patent Application No. 2018-218438, filed Nov. 21, 2018, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present invention relate to an intake duct structure of a motorcycle configured to lead traveling wind taken from the front surface of the motorcycle to its air cleaner.

Description of the Related Art

A layout for taking in air supplied to the engine from around the head pipe is superior in terms of the intake efficiency and the placement efficiency of the component. For instance, JP H10-035559 A discloses a layout of this type in which traveling wind taken in from the front of the vehicle is allowed to pass through an air passage provided through the front of the body frame.

The intake duct for taking in traveling wind through the space between the right and left front forks is disposed to have some clearance from the front forks such that the intake duct does not interfere with the movement of the front forks even when the handlebar is steered to the maximum.

However, in the conventional technique, there is a problem that the cross-sectional area of the intake duct is limited to make the orbital movement of the front forks ensured and the efficiency of introducing traveling wind to the engine cannot be enhanced.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an intake duct structure of a motorcycle that allows large handling and is improved in efficiency of introducing travelling wind to the engine.

An intake duct structure of a motorcycle includes front forks disposed on both of right and left sides of a head pipe of a body frame and a main frame extending obliquely backward and downward from the head pipe, wherein the intake duct structure extends from a front end of the motorcycle toward the head pipe and is formed in such a manner that an interfered area where a rotational orbit of the front forks at a time of steering overlaps the intake duct structure is elastically deformable.

According to the present invention, the intake duct structure of the motorcycle that allows large handling and is improved in efficiency of introducing travelling wind to the engine is provided.

DETAILED DESCRIPTION

Hereinbelow, embodiments of the present invention will be described by referring to the accompanying drawings.

As to an intake duct structure of a motorcycle according to the present invention (hereinafter simply referred to as “the intake duct structure”), the following embodiment will be described for a case where the body frame is a twin spar type; however, the intake duct structure is applicable not only to the twin spar type but also to other types such a double cradle frame and a monocoque frame. Further, the term “motorcycle” may also include a three-wheeled motor vehicle (i.e., motor tricycle) which has two rear wheels.

In the following embodiment, directional terms such as upper, upward, lower, downward, right, left, front, and rear are used with reference to a rider (driver) riding on the vehicle. In each figure, the forward direction of the vehicle is indicated by an arrow FW, the backward direction of the vehicle is indicated by an arrow BW, the left direction of the vehicle is indicated by an arrow L, the right direction of the vehicle is indicated by an arrow R, the upward direction of the vehicle is indicated by an arrow U, and the downward direction of the vehicle is indicated by an arrow D, when necessary. In each figure, some components are omitted for simplifying the description when deemed unnecessary.

First, a structure around a body frame11of the motorcycle equipped with an intake duct10according to the embodiment will be described by referring toFIG. 1toFIG. 3.

FIG. 1is a schematic right side view of the body frame11, to which the intake duct10according to the embodiment is attached, and the peripheral components of the intake duct10.

FIG. 2is an exploded perspective view of the body frame11and its peripheral components as viewed from the rear upper right side.

FIG. 3is a rear view around a head pipe13as viewed from within the space12of the body frame11.

As shown inFIG. 1andFIG. 2, the body frame11is, e.g., a so-called twin spar frame which is preferably applied to a vehicle to which high speed performance is required.

In the body frame11, the main frame20branches toward right and left from the rear of the head pipe13to the rear and extends rearward and downward so as to form an annular shape including the head pipe13in plan view. The body frame11has a vertical width (i.e., width in the up-and-down direction) that is almost equal to the length of the head pipe13. At the rear of the body frame11, a seat rail support14for fixing a seat rail which inclines backward and upward is provided. Under the seat rail support14in the rear portion of the body frame11, a pivot16for supporting a swing arm is provided in such a manner that the swing arm can swing in the up-and-down direction.

In the body frame11, an engine unit17is suspended by plural engine mounts15so as to be held by the body frame11.

The engine of the engine unit17is, e.g., a four-stroke multi-cylinder engine, typically a parallel four-cylinder engine. The engine unit17is formed by sequentially and integrally connecting a cylinder17B, a cylinder head17C, and a cylinder head cover17D on the top portion of a crankcase17A. The engine unit17is integrally joined to and supported by the body frame11and thereby functions as a rigid member of the body frame11.

A fuel tank is mounted on the body frame11above the engine unit17.

In the egg-shaped space12of the body frame11, an air cleaner box18above the cylinder head17C is supported by the body frame11and its peripheral components. The air cleaner box18is connected to an intake port at the rear of the cylinder head17C by an intake passage19. Air is drawn into the intake passage19by the engine negative pressure, mixed with the fuel supplied from a fuel supply device, and supplied into the cylinder head17C. When the intake duct10according to the embodiment is applied to a motorcycle for traveling on a public road, an air filter is provided in the air cleaner box18.

At the front of the body frame11, a stem shaft22is inserted into the head pipe13by a bearing as shown inFIG. 4. The stem shaft22serves as the rotation center related to steering of a steering mechanism23described below.

On the right and left of the head pipe13as shown inFIG. 2andFIG. 3, respective holes24penetrating the body frame11in the vehicle longitudinal direction (i.e., in the front-and-rear direction of the vehicle body) are formed.

A supporter26of the head pipe13forming the side surface of each hole24on the axle side has an approximately oval shape, and the long side of which extends in the vehicle longitudinal direction.

Two forked duct members (also referred to as a front intake duct and a rear intake duct)10aand10bconstituting the intake duct10are inserted so as to encircle the head pipe supporter26in the front-and-rear direction.

As shown inFIG. 2, the forked duct members10aand10bare coupled to each other by fasteners25inside the right and left holes24in the front-and-rear direction.

Of the components of the intake duct10, the front intake duct10ainserted into the holes24from the front of the vehicle body is fixed to the front end of the head pipe supporter26at, e.g., two upper and lower positions with screws27.

Of the components of the intake duct10, the rear intake duct10bdisposed inside the space12of the body frame11is inserted into the holes from the rear and fixed to the head pipe supporter26with screws28.

The rear end opening29of the rear bifurcated portion in the front intake duct10ais connected to the front open end30of the front bifurcated portion of the rear intake duct10b, so that the forked duct members (front and rear intake ducts)10aand10bconstitute, as a whole, the intake duct10.

FIG. 4is a partial plan view around the stem mechanism23of the motorcycle to which the intake duct10according to the embodiment is attached.

As shown inFIG. 4, the steering mechanism23is formed by fixing a pair of right and left front forks33for supporting the front wheel to a top bridge32, which is in the shape of an inverted triangle and fixed to the upper end portion of the stem shaft22.

Further, a handlebar is fixed to the top bridge32via a non-illustrated handle clamp.

The right and left front forks33are further fixed to an under bracket35at the lower portion of the head pipe13, and receive steering by the handlebar in a state in which the distance between the right and left front forks33is maintained.

The intake duct10is disposed, e.g., between the right and left front forks33. The collective opening36at the front end of the front intake duct10acommunicates with (i.e., is spatially connected to) an air intake port38opened at the front surface of the front cowl37via a communicating cowl39.

The communicating cowl39is a duct which functions to extend the air intake port38into the front cowl37to connect the air intake port38with the front intake duct10a. Electrical devices such as a meter panel41are put and fixed to the communicating cowl39. The front cowl37covers the front portion of the communicating cowl39and the meter panel41, and is fixedly supported by a stay42integrally formed on the meter panel41. The air cleaner box18is connected to the rear of the rear intake duct10b.

The above-described connection of the front cowl37, the communicating cowl39, the front intake duct10a, the rear intake duct10b, the air cleaner box18, and the intake passage19causes the traveling wind taken in from the front of the vehicle to pass through the both side surfaces of the head pipe13and to be blown to the engine unit17.

Next, the intake duct10according to the embodiment will be described in more detail usingFIG. 5toFIG. 7.

FIG. 5is a partial plan view for illustrating a state in which the handlebar is turned to the right inFIG. 4.

FIG. 6is a perspective view for illustrating one aspect of the front intake duct10aaccording to the embodiment.

FIG. 7is a perspective view of the vicinity of the head pipe13of the motorcycle to which the intake duct10according to the embodiment is attached.

InFIG. 5andFIG. 7, the front cowl37and the top bridge32are not shown.

The intake duct10is mainly composed of a material that withstands traveling wind and load of the front cowl37and the communicating cowl39for supporting the meter panel41. That is, the intake duct10is desirably made of a material that has sufficient rigidity for functioning as a cowl brace capable of supporting the front cowl37.

The materials which can be used for the intake duct10are, e.g., FRP (Fiber Reinforced Plastics), CFRP (Carbon Fiber Reinforced Plastics), metal, polypropylene, ABS resin, or NBR (nitrile rubber).

As shown inFIG. 5, when the handlebar is steered, the front forks33rotate around the head pipe13(stem shaft22) in plan view and the front forks33come closer to the vehicle body center C extending in the vehicle longitudinal direction by this rotation.

For this reason, as shown inFIG. 4andFIG. 5, the intake duct10is formed so as to overlap or interfere with the orbital movement (rotation) of the front forks33at the maximum steering of the handlebar. The interfered area43of this intake duct10is made of an elastic member such as silicon and is formed to be elastically deformable with respect to the pressure from the front forks33as shown inFIG. 4toFIG. 7. Hereinafter, the interfered area43made of a flexible material is also referred to as an elastic portion43awhen necessary.

Depending on the type of motorcycle, only one of the front intake duct10aand the rear intake duct10bmight interfere with the movement of the front forks33. In these cases, it is sufficient when the elastic portion43ais provided on either the front intake duct10aor the rear intake duct10bwhich interferes with the movement of the front forks33.

The elastic portion43a, which is elastically deformable, in the front intake duct10amay include the peripheral portion of the interfered area43and may be larger than the interfered area43. Additionally, the entirety of the front intake duct10amay be made of elastic material so as to be deformed in the whole body when pressed by the front forks33.

The elastic portion43aof the front intake duct10ais designed to have a shape and a range capable of absorbing a handlebar turning angle of at least about 5° to each of the right and left sides, and the handlebar turning angle of about 5° is a displacement range by self-aligning of the handlebar during traveling.

In order to satisfy the ease of handling, the motorcycle is preferably designed so as to be able to absorb the handlebar turning angle of about 30° to each of the right and left.

As to the handlebar turning angle larger than the self-aligning displacement range, there is no hindrance because it is usually operated by the driver's intention.

According to the intake duct10configured as described above, the following effects can be obtained.

(1) Since an elastic material is used for the interfered area43on the intake duct10interfered by the front forks33, the intake duct10is formed to be elastically deformable when pressed by the front forks33.

Since the intake duct10is configured to be elastically deformable, there is no need to provide a clearance between the intake duct10and the front forks33, the intake duct10can have a large diameter.

In other words, the intake duct10can be increased in diameter and the intake efficiency of air to the engine unit17can be enhanced without inhibiting the displacement of the front forks33.

(2) The intake duct10is disposed to pass between the right and left front forks33.

Generally, when the handlebar is largely turned, the traveling speed is reduced and a large amount of air supply is not required. That is, what is required for improving the engine efficiency is that the intake duct10elastically deformed is recovered to the initial form to ensure a large-diameter duct cross-sectional area at the time of running straight. In other words, what is required for improving the engine efficiency is to increase the cross-sectional area of the intake duct10at the time when the front forks33are not displaced.

In the arrangement relationship between the intake duct10and the front forks33according to the embodiment, when the motorcycle travels straight to perform medium to high speed traveling requiring a large amount of intake, the elastic portion43ais restored from deformation and thereby the maximum opening state of the intake duct10is achieved. That is, the intake duct10does not inhibit the displacement of the front forks33in the handlebar displacement range during straight traveling requiring a large amount of intake.

Thus, the diameter of the air supply passage can be increased without impairing the steering stability.

(3) The handlebar turning angle at which the front forks33does not abut or interfere with the functioning of the intake duct10is set at least 5° or more to the right and left sides from the straight state.

Since the handlebar turning angle operated by self-alignment during normal driving is generally 5° to the right and left, steering stability during driving can be achieved by designing the elastic portion43asuch that the handlebar turning angle of at least 5° to the right and left is ensured. In addition, turning of the handlebar in the stopped state (i.e., when the motorcycle is not running) is achieved by designing it to ensure a handlebar turning angle of about 30° to both right and left.

According to the present inventions, intake duct structures of motorcycles that allow large handling and are improved in efficiency of introducing travelling wind to the engine are provided.

The embodiments of the present invention have been described heretofore. However, the embodiments are merely given for the sake of example, and do not intend to limit the scope of the invention. The embodiments can be carried out in other various modes, and various omissions, replacements, and changes may be made thereto without departing from the gist of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

For instance, the intake duct structure may be disposed so as to pass through the outside of the front forks33. In this case, the interfered area43with the front forks33is the side surface on the vehicle center side of the intake duct structure.