Patent Description:
Prior art document <CIT> discloses a motorcycle accommodates an enlarged rear tire by interposing an intermediate shaft between the transmission output gear and the rear wheel drive gear. The intermediate shaft includes a power input gear disposed in the same vertical plane as the transmission output gear, and a first drive belt couples the two together. The intermediate shaft also includes a power output gear disposed in the same vertical plane as the rear wheel drive gear, and a second drive belt couples the two together. The first vertical plane lies closer to the central longitudinal axis of the support frame than does the second vertical plane, allowing the center of mass of the engine and transmission to be maintained substantially along the central longitudinal axis. When incorporated into a soft-tail type motorcycle frame, the intermediate shaft is coincident with the pivot axis of the soft-tail suspension.

Prior art document <CIT> discloses a scooter type two-wheeled motor vehicle comprising: an engine unit including an engine with a crankshaft, a speed change mechanism for changing speed of rotation outputted from the crankshaft of the engine, and an output shaft for receiving power from the speed change mechanism, wherein the speed change mechanism has a V-belt type continuously variable transmission; a first pulley fixed to the output shaft; a second pulley connected to a drive wheel;a chain extending between and wound around the first pulley and the second pulley for transmitting power from the output shaft to the drive wheel; and a swing arm for supporting the drive wheel to be swingable about the output shaft, wherein the speed change mechanism is the V-belt type continuously variable transmission having a drive shaft, a driven shaft and the V-belt, the speed change mechanism has a gear reduction mechanism for decelerating output from the V-belt type continuously variable transmission and the output from the continuously variable transmission is transmitted to the output shaft through the clutch mechanism and the gear reduction mechanism.

Conventionally, there are two types of device for transmitting power between the engine unit and a rear wheel acting as the drive wheel; one using a chain, and the other using a toothed belt. Either type is provided to extend parallel to a swing arm, and the chain or toothed belt is swingable with swinging of the swing arm. Patent Document <NUM> describes a two-wheeled motor vehicle which uses a chain for power transmission between the engine unit and drive wheel. Patent Document <NUM> describes a two-wheeled motor vehicle which uses a toothed belt for power transmission between the engine unit and drive wheel.

The two-wheeled motor vehicle described in Patent Document <NUM> (<CIT>) has a secondary reduction mechanism with a chain for transmitting power from the output shaft to the rear wheel. Since the chain can be rusted through exposure to rain water, a chain case is provided for covering substantially the entire chain.

The two-wheeled motor vehicle described in Patent Document <NUM> (<CIT>) has a secondary reduction mechanism with a toothed belt for transmitting power from the output shaft to the rear wheel. Compared with the chain, the toothed belt has a possibility of tooth jumping in which the toothed belt separates from a pulley of the output shaft. So, the toothed belt is provided with tooth jump prevention rollers.

The two-wheeled motor vehicle described in Patent Document <NUM> has a problem that the chain can be rusted not only by rain water but also by moisture in the air. In one method of preventing formation of rust, the chain is enclosed in a chain case, and the chain case is filled with lubricating oil. This can reduce formation of rust and can reduce frequency of maintenance. Sprockets around which the chain is wound are highly rigid, and thus the teeth of the sprockets will not deform easily. Since the chain is also highly rigid, the chain can be kept in high tension and will not loosen easily. With these features, tooth jumping hardly occurs with the chain wound around the two sprockets. However, since the chain case swings up and down with the chain, there is a problem of the swingable members becoming heavy.

The two-wheeled motor vehicle described in Patent Document <NUM> requires no lubrication and is free from the problem of rust formation since the toothed belt is used for power transmission from the output shaft to the rear wheel. Thus, there is no need to provide a chain case, and the material for the swingable members can be reduced. Further, the toothed belt can reduce frequency of maintenance, as compared with a chain. However, tooth jump prevention rollers must be arranged in order to prevent tooth jumping in which the toothed belt separates from the pulley of the output shaft. Although tooth jumping can be prevented by arranging the rollers to press down the toothed belt, a large space is required around the output shaft for installing the rollers, which enlarges the vehicle size. As another method of preventing tooth jumping, the diameter of the pulley of the output shaft may be increased. However, with an increase in the diameter of the pulley of the output shaft, the rear wheel must have a drive shaft with an increased pulley diameter, which makes it impossible to secure a banking angle.

This invention has been made having regard to the state of the art noted above, and its object is to provide a scooter type two-wheeled motor vehicle which can maintain a vehicle size and a banking angle similar to those in the prior art while reducing the frequency of maintenance and reducing the weight of swingable members.

Inventor herein has attained the findings that, with a pivot shaft provided coaxially with an output shaft, a swing arm and a toothed belt can be swung synchronously, thereby to prevent the toothed belt becoming detached. This measure can maintain a vehicle size and a banking angle similar to those in the prior art while reducing the frequency of maintenance and reducing the weight of swingable members.

According to the present invention said object is solved by a scooter type two-wheeled motor vehicle having the features of independent claim <NUM>. Preferred embodiments are laid down in the dependent claims.

A two-wheeled motor vehicle comprises an engine unit including an engine with a crankshaft, a speed change mechanism for changing speed of rotation outputted from the crankshaft of the engine, and an output shaft for receiving power from the speed change mechanism; a first pulley fixed to the output shaft; a second pulley connected to a drive wheel; a toothed belt extending between and wound around the first pulley and the second pulley for transmitting power from the output shaft to the drive wheel; and a swing arm for supporting the drive wheel to be swingable about the output shaft.

Accordingly, the speed of rotation outputted from the crankshaft of the engine is changed by the speed change mechanism. Further, power is transmitted from the speed change mechanism to the output shaft. The engine unit has these components, i.e. the engine, speed change mechanism and output shaft. The output shaft has the first pulley fixed thereto. The second pulley is connected to the drive wheel. The toothed belt extends between and is wound around the first pulley and second pulley. The toothed belt transmits power from the output shaft to the drive wheel through the first pulley and second pulley. The swing arm supports the drive wheel to be swingable about the output shaft.

By employing the toothed belt for power transmission from the output shaft to the drive wheel, a die-cast case can be omitted to realize weight saving of the construction around the drive wheel. A further weight saving is achieved by omitting the oil stored in the case. Further, the swing arm swings about the axis of the output shaft, which synchronizes with swinging of the toothed belt, whereby the toothed belt does not easily come off the first pulley and second pulley. These features realize the two-wheeled motor vehicle which, while reducing the frequency of maintenance, and reducing the weight of the swinging members, can maintain a vehicle size and a banking angle similar to those in the prior art.

For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown.

Embodiment <NUM> of this invention will be described hereinafter with reference to the drawings.

In the following description, the front, rear, right and left are directions seen from the rider seated on a two-wheeled motor vehicle.

Reference is made to <FIG> and <FIG>. <FIG> is a side view showing an outline construction of a two-wheeled motor vehicle <NUM> according to this invention.

<FIG> is a side view showing an outline construction in a body cover of the two-wheeled motor vehicle. The two-wheeled motor vehicle <NUM> is a scooter type vehicle having a diamond frame type body frame <NUM> with an arcuate shape extending downward from a front end. The body frame <NUM> is not limited to this type, but may be the underbone type. A head tube <NUM> is disposed in an upper front portion of the body frame <NUM>. The head tube <NUM> rotatably supports a front fork <NUM>. A handlebar <NUM> is connected to an upper end of the front fork <NUM>, and the front fork <NUM> is rotatable by operation of the handlebar <NUM>. A front wheel <NUM> is rotatably attached to a lower end of the front fork <NUM>.

An engine unit <NUM> is attached to the body frame <NUM> through a bracket 2a. By fixing the engine unit <NUM> to be body frame <NUM>, the engine unit <NUM> functions as part of the frame. This realizes a reduction of frame pipes, which allows the vehicle body to be small and lightweight.

A swing arm <NUM> is connected to the rear of the engine unit <NUM> to be swingable up and down. A rear wheel <NUM> is rotatably supported at the rear of the swing arm <NUM>. A rear suspension <NUM> is disposed between the rear of the body frame <NUM> and the rear wheel <NUM> for absorbing swings of the swing arm <NUM>.

A main stand <NUM> is pivotably connected to a lower portion at the rear of the engine unit <NUM> through a bracket <NUM>. The main stand <NUM> is pivotable on a pivot shaft <NUM> of the bracket <NUM>. The rear wheel <NUM> contacts a road surface when the main stand <NUM> does not contact the road surface, i.e. in a contained state. The rear wheel <NUM> is separated from the road surface when the main stand <NUM> contacts the road surface, i.e. in a standing state. The main stand <NUM> in the contained state overlaps the rear wheel <NUM> in a side view, and a first pulley <NUM> is disposed at the rear of the engine unit <NUM> and above the main stand <NUM>.

A fuel tank <NUM> is disposed above the engine unit <NUM>. A seat <NUM> for seating the rider is disposed above the fuel tank <NUM>. Between the handlebar <NUM> and seat <NUM> are low-floor footrests <NUM> for receiving the rider's feet. The footrests <NUM> extend forward from right and left sides of the seat <NUM>. Tandem footrests <NUM> for receiving a passenger's feet are provided above the first pulley <NUM> connected to the engine unit <NUM> and below the seat <NUM>. The body frame <NUM> is covered with a body cover <NUM> divided into parts. In particular, a cover 20a projects forward from the seat <NUM> and upward from between the right and left footrests <NUM>. Below the cover 20a, an engine <NUM> of the engine unit <NUM> is disposed, and particularly a cylinder block <NUM> of the engine <NUM> is disposed. The cylinder block <NUM> is located forward of a crankcase <NUM>.

A storage box <NUM> is disposed rearward of the fuel tank <NUM>. The storage box <NUM> can store helmets. The seat <NUM> is disposed above the fuel tank <NUM> and storage box <NUM> to be pivotable about a hinge <NUM> provided at a forward end of the seat <NUM>. The seat <NUM> includes a main seat 17a for seating the rider, and a tandem seat 17b for seating a passenger rearward of the main seat 17a. A projection 17c is formed between the main seat 17a and tandem seat 17b. A glove bar <NUM> is disposed around the tandem seat 17b to be held by the passenger. A storage lockbox <NUM> is attached below the glove bar <NUM>.

Next, reference is made to <FIG> is a schematic view of the seat and adjacent components seen in a direction of arrow III of <FIG>. The storage lockbox <NUM> is fixed to the rear end of the glove bar <NUM> with bolts <NUM>. The storage lockbox <NUM> has a key cylinder 26a and a case lid 26b slidable right and left. The case lid 26b is slidable when the key cylinder 26a is in an open state, and is not slidable when the key cylinder 26a is in a closed state.

Next, reference is made to <FIG> is a schematic view of the seat and adjacent components seen in the direction of arrow III of <FIG>, in which the case lid of the storage lockbox is opened. A communication device <NUM> is stored inside the storage lockbox <NUM>. Locking the storage lockbox <NUM> can prevent theft of a communication card of a toll collection system inserted in the communication device <NUM>. An ignition key of the two-wheeled motor vehicle <NUM> may be used as the key for opening and closing the key cylinder 26a.

The construction of the engine unit <NUM> provided for the two-wheeled motor vehicle <NUM> will be described with reference to <FIG> is a developed sectional view taken on line V-V of <FIG> and showing the engine unit and swing arm.

The engine unit <NUM> includes the engine <NUM>, a V-belt type continuously variable transmission (hereinafter called CVT) <NUM> disposed rightward and rearward of the engine <NUM>, a clutch mechanism <NUM> disposed leftward of a rear portion of the CVT <NUM>, a reduction gear mechanism <NUM> disposed leftward and rearward of the CVT <NUM>, and an output shaft <NUM> disposed rearward of the reduction gear mechanism <NUM>. The CVT <NUM> and reduction gear mechanism <NUM> constitute a speed change mechanism <NUM> for outputting, in varied speeds, rotation outputted from a crankshaft <NUM> of the engine <NUM> to the output shaft <NUM>.

The engine <NUM> is a <NUM>-cycle parallel <NUM>-cylinder engine. The engine <NUM> is disposed in a position inclined a large degree forward to a near horizontal state, with the cylinder block <NUM>, cylinder head <NUM> and cylinder head cover <NUM> connected to the front of the crankcase <NUM>. The crankcase <NUM> is split transversely into a left crankcase 36a and a right crankcase 36b. The crankcase <NUM> houses a middle portion of the crankshaft <NUM> and the reduction gear mechanism <NUM>. Pistons <NUM> are connected to the crankshaft <NUM> such that reciprocating movement of the pistons <NUM> produces rotation of the crankshaft <NUM>. A balancer <NUM> is provided between the two pistons <NUM>.

A left portion of the crankshaft <NUM> is connected to an alternator <NUM>. With rotation of the crankshaft <NUM>, the alternator <NUM> generates AC power. The alternator <NUM> is housed in a dynamo cover <NUM> connected to the left crankcase 36a.

A right portion of the crankshaft <NUM> is connected to the CVT <NUM>. The CVT <NUM> includes a CVT first pulley <NUM>, a CVT second pulley <NUM>, and a V-belt <NUM> wound around the CVT first pulley <NUM> and CVT second pulley <NUM>. The CVT <NUM> is housed in a speed changer case <NUM>. The speed changer case <NUM> is split transversely into a left speed changer case 50a and a right speed changer case 50b. The speed changer case <NUM> is disposed on the right side of the crankcase <NUM>, with the left speed changer case 50a fixed to the right side of the right crankcase 36b.

The CVT first pulley <NUM> is rotatable with the crankshaft <NUM>. The crankshaft <NUM> acts also as drive shaft of the CVT first pulley <NUM>. Rearward of the CVT first pulley <NUM> is the CVT second pulley <NUM> supported by a driven shaft <NUM>. The driven shaft <NUM> is disposed parallel to the crankshaft <NUM>. Rotation of the crankshaft <NUM> is transmitted to the driven shaft <NUM> through the CVT first pulley <NUM>, V-belt <NUM> and CVT second pulley <NUM>.

The CVT first pulley <NUM> includes a fixed pulley body <NUM> located leftward transversely of the vehicle body, i.e. inward in the direction of width of the vehicle with respect to a center line II of the main frame <NUM>, and a movable pulley body <NUM> located rightward transversely of the vehicle body, i.e. outward in the direction of width of the vehicle, and opposed to the fixed pulley body <NUM>. The fixed pulley body <NUM> is fixed to the crankshaft <NUM> to be rotatable with the crankshaft <NUM>. The movable pulley body <NUM> is disposed rightward of the fixed pulley body <NUM>, and is mounted to be slidable along the crankshaft <NUM>. Roller weights <NUM> are arranged on a right portion of the movable pulley body <NUM>. With this construction, the movable pulley body <NUM>, while rotating with the crankshaft <NUM>, is slidable axially of the crankshaft <NUM> by rotation of the latter.

The CVT second pulley <NUM> includes a fixed pulley body <NUM> located rightward transversely of the vehicle body, and a movable pulley body <NUM> located leftward transversely of the vehicle body and opposed to the fixed pulley body <NUM>. The movable pulley body <NUM> is slidable axially of the driven shaft <NUM> while rotating with the driven shaft <NUM>.

The CVT <NUM> transmits power of the crankshaft <NUM> to the driven shaft <NUM> through the V-belt <NUM>. An increase in the rotating speed of the crankshaft <NUM> causes centrifugal movement of the roller weights <NUM>, whereby the movable pulley body <NUM> of CVT first pulley <NUM> approaches the fixed pulley body <NUM>. This increases the winding diameter of the V-belt <NUM> fitted between the fixed pulley body <NUM> and movable pulley body <NUM>. Conversely, the winding diameter of the V-belt <NUM> fitted between the fixed pulley body <NUM> and movable pulley body <NUM> of the CVT second pulley <NUM> becomes smaller, thereby automatically providing varied speeds.

Next, reference is made to <FIG> is an enlarged view of the reduction gear mechanism and adjacent components shown in <FIG>. The clutch mechanism <NUM> is disposed leftward of the driven shaft <NUM>. The clutch mechanism <NUM> is disposed coaxially with the driven shaft <NUM>. The driven shaft <NUM> is connected to the reduction gear mechanism <NUM> between the CVT second pulley <NUM> and clutch mechanism <NUM>. The reduction gear mechanism <NUM> includes, arranged between the driven shaft <NUM> and output shaft <NUM>, an intermediate shaft <NUM> extending parallel to the driven shaft <NUM> and output shaft <NUM>, and a group of gears mounted on these shafts. Rotative power of the engine unit <NUM> is outputted from the output shaft <NUM>.

The clutch mechanism <NUM> is constructed such that, when the rotating speed of the driven shaft <NUM> exceeds a predetermined speed, clutch weights <NUM> in centrifugal movement move toward a pressure plate <NUM>. Consequently, the pressure plate <NUM> is pushed in the direction of the CVT <NUM>, to engage the clutch. With the engagement of the clutch, a clutch output gear <NUM> also rotates. The clutch output gear <NUM> is meshed with an intermediate shaft first gear <NUM> fixed to the intermediate shaft <NUM>. The clutch output gear <NUM> has a smaller diameter than the intermediate shaft first gear <NUM>.

An intermediate shaft second gear <NUM> fixed to the intermediate shaft <NUM> is meshed with an output shaft gear <NUM> fixed to the output shaft <NUM>. The intermediate shaft second gear <NUM> has a smaller diameter than the output shaft gear <NUM>. Thus, the reduction gear mechanism <NUM> provides deceleration in two steps.

The intermediate shaft <NUM> has a left end thereof supported by the left crankcase 36a through a bearing <NUM>. The intermediate shaft <NUM> has a right end thereof supported by the right crankcase 36b through a bearing <NUM>. The output shaft <NUM> has a right end thereof supported by the right crankcase 36b through a bearing <NUM>. The output shaft <NUM> is supported adjacent the middle position thereof by the left crankcase 36a through a bearing <NUM>.

<FIG> is a side view of a toothed belt. As shown in <FIG> and <FIG>, a secondary reduction mechanism <NUM> includes a first pulley <NUM> fixed to a left portion of the output shaft <NUM>, a second pulley <NUM> fixed to a left portion of a wheel body <NUM> of the rear wheel <NUM>, and a toothed belt <NUM> wound around the first pulley <NUM> and second pulley <NUM>.

The first pulley <NUM> has a diameter of <NUM>, and the second pulley <NUM> a diameter of <NUM>. Thus, the first pulley <NUM> is smaller in diameter than the second pulley <NUM>. The first pulley <NUM> is smaller in diameter than pulleys of output shafts of other, sport type and cruiser type two-wheeled motor vehicles. This is because a large space cannot be secured under the seat <NUM> of the scooter type two-wheeled motor vehicle.

The toothed belt <NUM> has belt teeth 76a. The first pulley <NUM> and second pulley <NUM> also have teeth for meshing with the belt teeth 76a. The toothed belt <NUM> transmits rotative power of the output shaft <NUM> to the rear wheel <NUM>.

The rear wheel <NUM> has a rim portion <NUM> and the wheel body <NUM>. The second pulley <NUM> is fastened directly to the wheel body <NUM> with bolts <NUM>, without using a hub clutch and a hub damper. The wheel body <NUM> is rotatable with the second pulley <NUM>. The rotation of the wheel body <NUM> rotates the rear wheel <NUM> acting as drive wheel. The bolts <NUM> correspond to the fastening members in this invention, and the rear wheel <NUM> corresponds to the drive wheel in this invention.

The secondary reduction mechanism <NUM> is a one-step reduction mechanism. With this, a three-step speed reduction is carried out in the course of power transmission from the CVT <NUM> to the rear wheel <NUM>. The speed reduction by the CVT <NUM> has a limited range of reduction ratios compared with a gear transmission mechanism. In this embodiment, the diameter Rg of the output shaft gear <NUM> and the diameter Rp of the first pulley <NUM> are equal (see <FIG>). Consequently, a larger number of meshing teeth can be secured between the first pulley <NUM> and the belt teeth 76a of the toothed belt <NUM> than in the case where the diameter of the pulley is made just equal to the diameter of a conventional sprocket. It is also possible to prevent the toothed belt <NUM> from contacting the engine unit <NUM>. Since the diameter of the second pulley <NUM> is not excessively large, a sufficient banking angle of the two-wheeled motor vehicle <NUM> can be secured.

The swing arm <NUM> is divided into two halves, i.e. a left divided part <NUM> and a right divided part <NUM>. A mounting boss 81a of the left divided part <NUM> and a mounting boss 82a of the right divided part <NUM> are in an end-to-end abutment against each other. <FIG> is a side view of the swing arm. As shown in <FIG>, the left divided part <NUM> and right divided part <NUM> are connected by bolts <NUM> and <NUM>. The swing arm <NUM> is swingably attached to the rear end of the rear suspension <NUM> through a shaft <NUM>.

An upper belt cover <NUM> covering the toothed belt <NUM> is fixed to an upper portion of the left divided part <NUM> by bolts <NUM> and <NUM>. A lower belt cover <NUM> covering the toothed belt <NUM> is fixed to a lower portion of the left divided part <NUM> by bolts <NUM> and <NUM>. These covers <NUM> and <NUM> prevent gravels and the like becoming caught between the first pulley <NUM> and second pulley <NUM>, and the toothed belt <NUM>. In this way, a large part of the toothed belt <NUM> extending from the first pulley <NUM> to the second pulley <NUM> is covered by the upper belt cover <NUM> and lower belt cover <NUM>. A forward portion of the toothed belt <NUM> wound around the first pulley <NUM> and a rearward portion of the toothed belt <NUM> wound around the second pulley <NUM> are exposed. A window <NUM> is formed in a middle position of the lower belt cover <NUM>, and the toothed belt <NUM> is exposed through the window <NUM>.

As shown in <FIG>, the right divided part <NUM> has a forward end thereof connected to the rear of the right crankcase 36b by a bolt <NUM> to be swingable up and down. A left end of the bolt <NUM> is rotatably supported by the right crankcase 36b through a bearing <NUM>. The bolt <NUM> is the pivot shaft in this invention.

The left divided part <NUM> has a forward end thereof connected to the rear of the left crankcase 36a through a holder <NUM> to be swingable up and down. The holder <NUM> is open at both right and left sides, and the output shaft <NUM> extends through the centers of the openings. The holder <NUM> is fixed to the left crankcase 36a by bolts <NUM>. The left divided part <NUM> is swingably supported by the holder <NUM> through a bearing <NUM>. Thus, the left divided part <NUM> is connected to the left crankcase 36a by the holder <NUM> to be swingable about the output shaft <NUM> acting as central axis. Shocks due to swinging of the left divided part <NUM> are transmitted to the left crankcase 36a through the holder <NUM>, whereby the shocks are mitigated for the output shaft <NUM>. In this construction, since the bolt <NUM> and output shaft <NUM> are arranged coaxially, the output shaft <NUM>, although performing the function as the central axis of swinging of the left divided part <NUM>, hardly undergoes the shocks of swinging of the left divided part <NUM>.

Since the bolt <NUM> and output shaft <NUM> are arranged coaxially, up-and-down swinging of the toothed belt <NUM> synchronizes with up-and-down swinging of the swing arm <NUM>. This reduces the influence of the swinging of the swing arm <NUM> on the tension applied to the toothed belt <NUM>. The bolt <NUM> and output shaft <NUM> act as pivot shaft of the swing arm <NUM>.

The swing arm <NUM> is connected to the engine unit <NUM>, but not to the body frame <NUM>. That is, the swing arm <NUM> is connected to the body frame <NUM> through the engine unit <NUM>. Consequently, vibration of the swing arm <NUM> is absorbed not only by the rear suspension <NUM> but also by the V-belt <NUM>, thereby preventing the vibration of the swing arm <NUM> from being transmitted directly to the body frame <NUM>. This can also reduce the vibration transmitted to the rider on the seat <NUM> through the body frame <NUM>.

Referring to <FIG>, the first pulley <NUM> is fixed to the output shaft <NUM> in a position outward of the left divided part <NUM> transversely of the vehicle body. To the left of the first pulley <NUM>, an output shaft cover <NUM> supports the left end of the output shaft <NUM> through a bearing <NUM>. The output shaft cover <NUM> is fixed to the left divided part <NUM> by bolts <NUM>, <NUM> and <NUM>. The second pulley <NUM> is fixed to the wheel body <NUM> in a position inward of the left divided part <NUM> transversely of the vehicle body. Consequently, the second pulley <NUM> is protected by the left divided part <NUM> also when the two-wheeled motor vehicle <NUM> makes turns.

The left divided part <NUM> which is a half body of the swing arm <NUM> extends through a space between upper and lower portions of the toothed belt <NUM> rotating between the first pulley <NUM> and second pulley <NUM>. Thus, the left divided part <NUM> and left crankcase 36a can be pivotably connected through the holder <NUM> in a position inward of the first pulley <NUM> transversely of the vehicle body. This reduces the influence of swinging of the left divided part <NUM> on the output shaft <NUM>. A rear wheel axle <NUM> is fixed to rear ends of the left divided part <NUM> and right divided part <NUM>. The rear wheel axle <NUM> supports the rear wheel <NUM>.

A brake mechanism <NUM> is disposed on the right side of the rear wheel <NUM>. The brake mechanism <NUM> has a brake disc <NUM> and a caliper <NUM>. The brake disc <NUM> is fixed to the right side of the wheel body <NUM>. The caliper <NUM> of the brake disc <NUM> is disposed on the right divided part <NUM>. The caliper <NUM> has a pad for pressing on the brake disc <NUM> to apply a braking force thereto (see <FIG>). The brake disc <NUM> and caliper <NUM> are arranged opposite the secondary reduction mechanism <NUM> across the rear wheel <NUM>, which arrangement can keep an excellent right and left weight balance of the rear wheel <NUM>.

According to the embodiment, since the bolt <NUM>, which is the pivot shaft of the swing arm <NUM>, and the output shaft <NUM> are arranged coaxially, the swinging of the swing arm <NUM> synchronizes with that of the toothed belt <NUM>, thereby to prevent the toothed belt <NUM> from coming off the first pulley <NUM> and second pulley <NUM>. Since the output shaft <NUM> and the bolt <NUM> acting as the pivot shaft are coaxial, even when the swing arm <NUM> swings up and down, the tension of the toothed belt <NUM> can be maintained unchanged without being influenced by different strokes of the rear suspension <NUM>. Since the tension of the toothed belt <NUM> is not influenced by swinging of the swing arm <NUM>, the toothed belt <NUM> is prevented from coming off the first pulley <NUM> and second pulley <NUM> due to conditions of a road surface on which the two-wheeled motor vehicle <NUM> is running. The first pulley <NUM> is made small in diameter, compared with other, cruiser type and sport type two-wheeled motor vehicles. Although this renders the toothed belt <NUM> easily detachable from the pulley, it is possible to prevent detachment of the toothed belt <NUM> and chipping of the belt teeth 76a. Preventing chipping of the belt teeth 76a can prevent lowering of the transmission efficiency of the secondary reduction mechanism <NUM>. Further, lowering of the durability of the toothed belt <NUM> can be prevented.

The swing arm <NUM> swings about the axis of the output shaft <NUM>, which synchronizes with swinging of the toothed belt <NUM>, whereby the toothed belt <NUM> does not easily come off the first pulley <NUM> and second pulley <NUM>. Thus, there is no need to provide rollers to prevent tooth jumping of the toothed belt <NUM>, or to provide a large space around the output shaft <NUM>. This can maintain a vehicle size similar to that in the prior art. The pulley diameter of the output shaft <NUM> is not made excessively large in order to prevent tooth jumping. This can prevent enlargement of the pulley diameter of the rear wheel axle <NUM> which is the drive shaft of the rear wheel <NUM>, thereby to maintain a banking angle similar to that in the prior art.

By employing the toothed belt <NUM> for power transmission from the output shaft <NUM> to the rear wheel <NUM>, a conventional die-cast case can be omitted to realize weight saving of the construction around the rear wheel <NUM>. A further weight saving is achieved by omitting the oil conventionally stored in the die-cast case. This can reduce the frequency of maintenance, and the weight of the swinging members. Further, the weight saving of the construction around the rear wheel <NUM> results in a uniformed weight distribution longitudinally of the two-wheeled motor vehicle <NUM>. The rear wheel <NUM> has an improved road following capability, and the rider can enjoy improved comfort. The weight saving of the construction around the rear wheel <NUM> provides weight saving also of the two-wheeled motor vehicle <NUM>, which can reduce manufacturing cost, and improve fuel consumption.

Since vibration of the rear wheel <NUM> is absorbed by the toothed belt <NUM>, the transmission of vibration from the rear wheel <NUM> to the engine unit <NUM> is reduced, and the second pulley <NUM> and rear wheel <NUM> can be directly fastened to each other with the bolts <NUM>. By fastening the second pulley <NUM> and rear wheel <NUM> directly, a clutch damper and a hub clutch conventionally attached to the rear wheel <NUM> can be omitted, to achieve a further weight saving of the construction around the rear wheel <NUM>.

The engine unit <NUM> is disposed below the fuel tank <NUM> below the seat <NUM>, with the engine <NUM> laid in a horizontal position. Consequently, the space between the engine unit <NUM> and rear wheel <NUM> is smaller than that of a cruiser type two-wheeled motor vehicle or sport type two-wheeled motor vehicle. The first pulley <NUM> has a size to fit in a position rearward of the engine unit <NUM> disposed below the fuel tank <NUM> and above the main stand <NUM>. Thus, although the two-wheeled motor vehicle <NUM> is the scooter type, the toothed belt <NUM> can be employed conveniently as the secondary reduction mechanism.

Since the CVT <NUM> with the V-belt <NUM> acts as the speed change mechanism for changing speed of the rotation output of the engine <NUM>, the vibration produced by the engine <NUM> can be reduced. The V-belt <NUM> and toothed belt <NUM> are arranged at opposite sides of the center line II-II transversely of the two-wheeled motor vehicle <NUM>. Vibration of each of the right and left sides of the two-wheeled motor vehicle <NUM> is absorbed by each belt, thereby to reduce the vibration transmitted to the rider. That the V-belt <NUM> and toothed belt <NUM> are belts provides an improved right and left weight balance of the two-wheeled motor vehicle <NUM>.

The V-belt <NUM> is disposed forward of the output shaft <NUM>, while the toothed belt <NUM> is disposed rearward of the output shaft <NUM>. Thus, each belt absorbs vibration transmitted from the forward portion or rearward portion of the two-wheeled motor vehicle <NUM>. This can reduce vibration due to irregularity of a road surface before transmission to the rider. The V-belt <NUM> can reduce vibration transmitted from the front wheel <NUM> to the engine unit <NUM> through the front fork <NUM> and body frame <NUM>. The toothed belt <NUM> can reduce vibration transmitted from the rear wheel <NUM> to the engine unit <NUM>. Thus, the vibrations transmitted to the seat <NUM> are reduced by the two belts arranged below and forward and backward of the seat <NUM>.

Conventionally, a two-wheeled motor vehicle with a belt type continuously variable transmission has a limited reduction ratio by the CVT. In order to secure a sufficient reduction ratio, a sprocket of a secondary reduction mechanism has a smaller diameter than a gear fixed to the output shaft. In the above embodiment, the toothed belt <NUM> is prevented from coming off the first pulley <NUM> by arranging that the first pulley <NUM> is equal in diameter to the output shaft gear <NUM>. Further, a space can be provided between the first pulley <NUM> and the dynamo cover <NUM> disposed forward of the first pulley <NUM> to prevent contact between the toothed belt <NUM> and dynamo cover <NUM>.

In this invention, it is preferred that the swing arm is supported by the engine unit to be rotatable about the output shaft between the first pulley and the engine unit. This construction can reduce transmission to the output shaft of shocks produced by swinging of the swing arm.

In this invention, it is preferred that the swing arm is formed of two halves, which are a first half located at one side of the drive wheel and a second half located at the other side of the drive wheel; the first half being disposed between the first pulley and the engine unit, and supported by the engine unit to be rotatable about the output shaft; and the second half having a support shaft disposed in the engine unit to be coaxial with the output shaft, the second half being disposed at the other side of the engine unit, and rotatably supported by the support shaft. This construction can reduce transmission to the output shaft of shocks produced by swinging of the swing arm.

In this invention, it is preferred that the vehicle further comprises fastening members for directly fastening the second pulley and the drive wheel together. Since vibration of the rear wheel is absorbed by the toothed belt, the transmission of vibration from the rear wheel to the engine unit is reduced, and the second pulley and rear wheel can be directly fastened to each other with the fastening members. By fastening the second pulley and rear wheel directly, this construction can omit a clutch damper and a hub clutch attached to the rear wheel. This achieves a further weight saving of the construction around the rear wheel.

In this invention, it is preferred that the fastening members are bolts. Since the fastening members are bolts according to this construction, the swing arm and drive wheel can be fastened together effectively.

In this invention, it is preferred that the vehicle further comprises a braking mechanism for braking rotation of the drive wheel, wherein the second pulley is disposed at one side of the drive wheel, and the braking mechanism is disposed at the other side of the drive wheel. With the brake mechanism and second pulley arranged at opposite sides of the drive wheel, the second pulley is not disposed outward of the vehicle body, thereby to secure a banking angle. Further, the first pulley also is disposed inward of the vehicle body, thereby to inhibit enlargement of the vehicle body.

In this invention, it is preferred that the vehicle further comprises a seat for seating a rider; a fuel tank disposed below the seat and above the engine unit; and a main stand connected to a lower position of the engine unit for lowering the drive wheel to a road surface, and raising the drive wheel from the road surface; wherein, when the main stand is in a contained state, the main stand and the rear wheel overlap in a side view; and the first pulley is disposed rearward of the engine unit and above the main stand.

According to the above construction, since the engine unit is disposed below the fuel tank below the seat, the engine unit cannot be placed to have the cylinder block located above the crankcase. So the engine unit is placed to have the cylinder block located forward of the crankcase. Consequently, the space between the engine unit and rear wheel is smaller than that of a cruiser type two-wheeled motor vehicle. The first pulley has a size to fit in a position rearward of the engine unit disposed below the fuel tank and above the main stand. Thus, although this is a two-wheeled motor vehicle, the belt can be employed conveniently as the secondary reduction mechanism.

In this invention, it is preferred that the speed change mechanism has a V-belt type continuously variable transmission. An engine with stepped change speed requires a gear change and clutch engagement and disengagement for each shifting operation. Engine speed and transmission torque also change discontinuously for each shifting operation. On the other hand, the V-belt type continuously variable transmission changes speed continuously, and the V- belt itself absorbs vibration. Since the speed change mechanism has the continuously variable transmission with the V-belt, vibration produced by the engine can be reduced as compared with the engine with stepped change speed.

In this invention, it is preferred that the V-belt and the toothed belt are opposed to each other across a center line of the two-wheeled motor vehicle transversely of a vehicle body. According to this construction, the V-belt and toothed belt are arranged at opposite sides of the center line transversely of the two-wheeled motor vehicle. Vibration of each of the right and left sides is absorbed by each belt, thereby to reduce the vibration transmitted to the rider. Since both the V-belt and toothed belt are belts, the right and left weight balance is improved.

In this invention, it is preferred that the V-belt is disposed forward of the output shaft, and the toothed belt is disposed rearward of the output shaft. According to this construction, each belt absorbs vibration transmitted from the forward portion or rearward portion. This can reduce vibration due to irregularity of a road surface before transmission to the rider. The V-belt can reduce vibration transmitted from the front wheel to the engine unit through the frame. The toothed belt can reduce vibration transmitted from the rear wheel to the engine unit. Thus, the vibrations transmitted to the seat are reduced by the two belts arranged below the seat.

In this invention, it is preferred that the speed change mechanism has a gear reduction mechanism for decelerating output from the V-belt type continuously variable transmission, wherein the first pulley is equal in diameter to a gear of the reduction mechanism fixed to the output shaft. According to this construction, output from the V-belt type continuously variable transmission is decelerated by the gear reduction mechanism to be transmitted to the output shaft. Consequently, a reduction mechanism for providing a plurality of speeds is disposed from the V-belt type continuously variable transmission to the drive wheel. The gear of the reduction mechanism fixed to the output shaft is equal in diameter to the first pulley. This secures a sufficient number of meshing teeth of the first pulley and toothed belt to prevent the toothed belt from coming off the first pulley.

In this invention, it is preferred that the speed change mechanism is a V-belt type continuously variable transmission having a drive shaft, a driven shaft and the V-belt; the engine unit has a clutch mechanism disposed coaxially with the driven shaft, and the gear reduction mechanism disposed between the continuously variable transmission and the clutch mechanism; and output from the continuously variable transmission is transmitted to the output shaft through the clutch mechanism and the gear reduction mechanism. According to this construction, the first pulley is located on the output shaft which is a different shaft to the driven shaft of the speed change mechanism, and the gear reduction mechanism for transmitting power to the output shaft is disposed between the continuously variable transmission and the clutch mechanism. This can inhibit the first pulley from being located remote from the center of the engine unit, thereby to inhibit enlargement of the vehicle.

In this invention, it is preferred that the speed change mechanism is a V-belt type continuously variable transmission having a drive shaft, a driven shaft and the V-belt; the engine unit has the gear reduction mechanism for transmitting power between the driven shaft of the continuously variable transmission and the output shaft; and the first pulley is disposed between right and left ends of the engine unit transversely of the vehicle body. According to this construction, the first pulley is disposed within the engine unit transversely of the vehicle body, which can inhibit enlargement of the vehicle.

In this invention, it is preferred that the vehicle further comprises a seat for seating a rider; right and left footrests extending forward from sides of the seat; and a cover member located between the right and left footrests and forward of the seat, and projecting upward from the footrests; wherein the engine unit includes an engine disposed forward of a front end of the seat and below the cover member, and an output shaft disposed rearward of the front end of the seat and rearward of the footrests. According to this construction, the two-wheeled motor vehicle has the engine unit and drive wheel arranged close to each other, with the engine unit extending long rearward from a position forward of the front end of the seat. This invention is particularly effective for the two-wheeled motor vehicle having such configuration since the engine unit is not enlarged.

Claim 1:
A scooter type two-wheeled motor vehicle (<NUM>) comprising:
an engine unit (<NUM>) including an engine (<NUM>) with a crankshaft (<NUM>), a speed change mechanism (<NUM>) for changing speed of rotation outputted from the crankshaft (<NUM>) of the engine (<NUM>), and an output shaft (<NUM>) for receiving power from the speed change mechanism (<NUM>), wherein the speed change mechanism (<NUM>) has a V-belt type continuously variable transmission (<NUM>);
a first pulley (<NUM>) fixed to the output shaft (<NUM>);
a second pulley (<NUM>) connected to a drive wheel (<NUM>);
a toothed belt (<NUM>) extending between and wound around the first pulley (<NUM>) and the second pulley (<NUM>) for transmitting power from the output shaft (<NUM>) to the drive wheel (<NUM>); and
a swing arm (<NUM>) for supporting the drive wheel (<NUM>) to be swingable about the output shaft (<NUM>), wherein the speed change mechanism (<NUM>) is the V-belt type continuously variable transmission (<NUM>) having a drive shaft (<NUM>), a driven shaft (<NUM>) and the V-belt (<NUM>), the speed change mechanism (<NUM>) has a gear reduction mechanism (<NUM>) for decelerating output from the V-belt type continuously variable transmission (<NUM>), the first pulley (<NUM>) is equal in diameter to a gear (<NUM>) of the reduction mechanism (<NUM>) fixed to the output shaft (<NUM>);
the engine unit (<NUM>) has a clutch mechanism (<NUM>) disposed coaxially with the driven shaft (<NUM>), and the gear reduction mechanism (<NUM>) disposed between the continuously variable transmission (<NUM>) and the clutch mechanism (<NUM>); and
output from the continuously variable transmission (<NUM>) is transmitted to the output shaft (<NUM>) through the clutch mechanism (<NUM>) and the gear reduction mechanism (<NUM>).