Sound insulation structure with resonator

To enhance the noise reducing effect of a sound insulation structure which includes a cover member for covering a power unit from the outside so as to reduce the radiant sound generated from the power unit, and a resonator. A sound insulation structure includes an armor cover for covering a left case half and a left cover constituting a side part cover of the power unit from the left side so as to reduce the radiant sound generated from the side part cover and enhance an appearance quality of the power unit, and the resonator capable of resonating at a specified frequency of the radiant sound. The resonator is disposed in a space formed between the side part cover and the armor cover in the state of being out of contact with the armor cover, and is attached to the side part cover in contact with the latter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2008-039402, filed in Japan on Feb. 20, 2008, the entirety of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sound insulation structure including a cover member for reducing radiant sound generated from a power unit for generating motive power, and a resonator for reducing the radiant sound. More particularly, the present invention relates to the layout of the resonator in relation to the power unit and the cover member.

2. Background of the Invention

An internal combustion engine as a power unit is know to have a cover member attached thereto for reducing radiant sound generated from an internal combustion engine. A resonator is formed inside the cover member integrally with the cover member so as to reduce the noise in a space defined by the internal combustion engine and the cover member. In addition, a neck part of the resonator is opened into the space (refer to, for example, Japanese Patent Laid-open No. Hei 8-144783).

In addition, a system is known wherein a power unit includes an internal combustion engine and a transmission supplied with motive power of the internal combustion engine and in which the transmission is composed of a swash plate type hydrostatic continuously variable transmission (refer to, for example, Japanese Patent Laid-open No. 2005-248838 and Japanese Patent Laid-open No. 2005-263143).

SUMMARY OF THE INVENTION

In the case where a resonator disposed in a space formed between an internal combustion engine and a cover member covering the internal combustion engine is formed as one body with the cover member, the resonator itself is vibrated together with the cover member. The vibration of the resonator itself in this instance is, in many cases, a vibration at a frequency different from the specified frequency of the radiant sound to be reduced through resonance of the resonator. Particularly, in the case where the cover member is attached to the internal combustion engine through a vibration isolating member such as a rubber vibration isolator, the frequency of vibration of the resonator itself is more frequently different from the specified frequency. Therefore, in some cases, the reducing effect of the resonator on the radiant sound at the specified frequency has not been sufficiently obtainable.

The present invention has been made in consideration of the above-mentioned circumstances. Accordingly, an object of the present invention is to enhance the noise reducing effect of a sound insulation structure, which includes a cover member covering a power unit externally so as to reduce radiant sound generated from the power unit, and a resonator. Furthermore, an object of the present invention is to enhance the noise reducing effect of a resonator for the rider(s).

According to a first aspect of the present invention, a sound insulation structure includes a cover member (C1) with which a noise source device (P) generating a radiant sound is covered on the outside thereof from a predetermined direction thereof so as to reduce the radiant sound, and a resonator (120) which resonates at a specified frequency of the radiant sound, wherein the resonator (120) is disposed, out of contact with the cover member (C1), in a space (S) formed between the noise source device (P) and the cover member (C1), and is attached to and in contact with the noise source device (P).

According to a second aspect of the present invention, the cover member (C1) includes a cover part (Ca) covering the noise source device (P) from the predetermined direction, and an outer peripheral part (Cb) bent toward a direction opposite to the predetermined direction so as to approach the noise source device (P), the outer peripheral part (Cb) covers the noise source device (P) from an orthogonal direction orthogonal to the predetermined direction, and a sound absorbing material (115) is disposed in the space (S) along an inner surface (Ci) of the cover member (C1) and between the cover member (C1) and the resonator (120).

According to a third aspect of the present invention, the resonator (120) is mounted in the vicinity of an oscillation source (60) of the radiant sound at a specified frequency, and an aperture part (127) of a neck part (126) of the resonator (120) is opened in the space (S) in a direction along the cover member (C1) and in a sense (A1) toward the inner side in the space (S) in relation to the position of the aperture part (127).

According to a fourth aspect of the present invention, the noise source device (P) is a power unit (P) disposed below a rider's seat (9) in a motorcycle (V), the aperture part (127) is located on the front side relative to the seat (9), and the sense (A1) in which the aperture part (127) is opened is an upward sense.

According to the first aspect of the present invention, the radiant sound generated from the power unit in the space between the power unit and the cover member is reduced by the resonator disposed in the space. In this case, since the resonator is not in contact with the cover member, the vibration of the cover member is prevented from suppressing the vibration of the resonator itself being in a resonant state so as to hamper the resonance of the resonator. Moreover, since the resonator itself is attached directly to the power unit, the resonator itself is also oscillated directly at the specified frequency and, hence, the resonance at the specified frequency is promoted by the vibration of the resonator itself. As a result, the noise reducing effect of the resonator is enhanced, and the noise reducing effect of the sound insulation structure is enhanced.

According to the second aspect of the present invention, the cover member not only covers the noise source device from a predetermined direction with its cover part but also covers the noise source device from an orthogonal direction orthogonal to the predetermined direction with its outer peripheral part, and, therefore, the noise reducing effect of the cover member is enhanced.

In addition, by utilizing the fact that the resonator is not in contact with the cover member, the sound absorbing material can be disposed in the space over a wide range along the inner surface of the cover member, without being blocked by the resonator. As a result, in addition to the noise reducing effect of the resonator on the radiant sound at the specified frequency, the noise of the whole radiant sound inclusive of the radiant sound at the specified frequency can be reduced by the sound absorbing material disposed along the inner surface of the cover member, so that the noise reducing effect is enhanced.

According to the third aspect of the present invention, the aperture part of the resonator is opened toward the wider side of the space along the cover member defining the space, so that it is made easier for the resonance at the resonator to occur. In addition, since the neck part is opened in a direction along the cover member, the radiant sound at the specified frequency, of the radiant sounds transmitted along the cover member, can be reduced by the resonator.

Furthermore, the resonator is mounted in the vicinity of the oscillation source. Therefore, the resonator itself is effectively oscillated at the specified frequency, so that the resonance at the specified frequency is more promoted. As a result, the noise reducing effect of the resonator is enhanced, and the noise reducing effect of the sound insulation structure is enhanced.

According to the fourth aspect of the present invention, the radiant sound coming from the power unit toward the rider(s) on the motorcycle is effectively reduced by the resonator. Therefore, the noise reducing effect for the rider(s) is enhanced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference to the accompanying drawings, wherein the same reference numerals will be used to identify the same or similar elements throughout the several views. Now, an embodiment of the present invention will be described referring toFIGS. 1 to 4.

Referring toFIG. 1, in this embodiment, a sound insulation structure to which the present invention is applied is provided in a motorcycle V as a vehicle. The sound insulation structure includes an armor cover C1that covers a power unit P on the outside thereof, and a resonator120, as will be described later.

In this embodiment, the left-right direction and the front-rear direction coincide with the left-right direction and the front-rear direction with respect to the motorcycle V on which the power unit P is mounted, and the up-down direction is the vertical direction. The axial direction, which term will be used in relation to each rotary shaft to be described later, means the direction of the axis of rotation of the shaft. The axial direction of a crankshaft33(seeFIG. 3) provided in an internal combustion engine E coincides with the left-right direction in this embodiment. When either one of the rightward sense and the leftward sense is assumed to be one sense of the axial direction of the crankshaft33, the other of the rightward sense and the leftward sense is the other sense of the axial direction of the crankshaft33.

The motorcycle V includes: a body frame F having a head pipe1, a main frame2and a down tube3; a power unit P supported on the body frame F; a front wheel6rotatably supported on a front fork4steerably supported on the head pipe1; a rear wheel7rotatably supported on a swing arm5swingably supported on the main frame2; and a fuel tank8and a riders' seat9which are supported on the body frame F. The power unit P is disposed below the riders' seat9in the motorcycle V.

Referring toFIGS. 2 and 3, the power unit P includes an internal combustion engine E, which is a water-cooled type multi-cylinder 4-stroke internal combustion engine, and a mission unit M having a transmission60(seeFIG. 3) to which motive power from the internal combustion engine E is inputted. The internal combustion engine E and the mission unit M constitute a united apparatus, which outputs motive power for driving the rear wheel7serving as an object of driving.

The internal combustion engine E supported on the body frame F in a transverse layout with the crankshaft33oriented in the vehicle width direction is a V-type internal combustion engine having a front bank B1and a rear bank B2. The transmission60is a hydrostatic type continuously variable transmission having a hydraulic pump61and a hydraulic motor62.

The motive power generated by the internal combustion engine E is inputted to the mission unit M, and is then transmitted from a power take-off shaft91of the mission unit M to the rear wheel7, serving as a drive wheel, through a final transmission mechanism140having a drive shaft142, which is connected to the power take-off shaft91through a universal joint141. The final transmission mechanism140is contained in the swing arm5.

The internal combustion engine E has an engine main body composed of: a cylinder block10having a plurality of (in this embodiment, two) cylinders10aarranged so as to constitute a V-shaped pair of banks B1and B2; a pair of cylinder heads11connected to upper end parts of the cylinders10ain the banks B1and B2, respectively; a pair of cylinder head covers12connected to upper end parts of the cylinder heads11, respectively; and a crankcase13connected to a lower end part of the cylinder block10.

Incidentally, both the banks B1and B2are basically the same in the structure pertaining to the cylinder10a, the cylinder head11and the cylinder head cover12. In the following, therefore, description will be made referring mainly to the structure of the rear bank B2.

Referring toFIGS. 2 and 3, the cylinder head11is provided with: a combustion chamber21opposed to a piston20in the cylinder axial direction; an intake port24through which a gaseous mixture of intake air fed from an intake system22having a throttle body22aconnected to the cylinder head11and a fuel from a fuel injection valve (not shown) is introduced into the combustion chamber21; an exhaust port25through which an exhaust gas from the combustion chamber21is introduced into an exhaust system23having an exhaust pipe23aconnected to the cylinder head11; a spark plug26fronting on the combustion chamber21; and an intake vale27and an exhaust valve28for opening and closing the intake port24and the exhaust port25, respectively.

A valve system30for opening and closing the intake valve27and the exhaust valve28includes a camshaft30ahaving a valve cam30b, and rocker arms30c,30dmaking contact with the intake valve27and the exhaust valve28and driven by the valve cam30bto rock. The valve cam30bopens and closes the intake valve27and the exhaust valve28through the rocker arms30c,30drockably supported on rocker shafts30e,30f, respectively.

A valve-operating power transmission mechanism31for driving the camshaft30ato rotate by a torque of the crankshaft33includes a drive sprocket31aprovided at both end parts33a,33bof the crankshaft33, a cam sprocket31bprovided on the camshaft30a, and a chain31cwrapped around both the sprockets31a,31b.

The crankcase13is a left-right split crankcase having a configuration in which a pair of case halves13a,13bas case parts split into a plurality in the vehicle width direction (left-right direction) are coupled. The crankshaft33, which is connected to pistons20through connecting rods32, is contained in a crank chamber34formed by the crankcase13, and is rotatably supported on both the case halves13a,13bthrough a pair of main bearings35. A part of the crankcase13constitutes a mission case Mc of the mission unit M.

In addition, the internal combustion engine E has a pair of covers14,15connected respectively to the left and right case halves13a,13bthrough a multiplicity of bolts.

Of the crankshaft33, a shaft end part33aon one side which projects leftwards from the inside of the crank chamber34extends into a power transmission chamber36formed as a left chamber by the left case half13aand the left cover14, and a shaft end part33bon the other side which projects rightward from the inside of the crank chamber34extends into an accessory chamber37formed as a right chamber by the right case half13band the right cover15. An input-side transmission mechanism50of the mission unit M and a drive sprocket41aaround which to wrap a chain41cof a power transmission mechanism41for driving an oil pump40are provided at the shaft end part33a. On the other hand, an AC generator42is provided at the shaft end part33b. The mission unit M, the oil pump40and the AC generator42are all driven units which are driven by the torque of the crankshaft33.

The mission unit M includes the transmission60driven to rotate by the torque of the crankshaft33, the input-side transmission mechanism50for inputting the torque of the crankshaft33to the transmission60, an output-side transmission mechanism T to which the torque outputted from the transmission60is inputted, and the mission case Mc forming a mission chamber38in which the transmission60and both the transmission mechanisms50, T are contained.

The torque (or motive power) generated by the internal combustion engine E is transmitted from the crankshaft33serving as an engine output shaft to the rear wheel7(seeFIG. 1) through a torque transmission path composed of the input-side power transmission mechanism50, the transmission60, the output-side power transmission mechanism T and the final transmission mechanism140(seeFIG. 1) (hereinafter referred to as “torque transmission path”). The torque transmission path includes, with the transmission60as a boundary, an input-side transmission path between the crankshaft33and the transmission60, the transmission60itself, and an output-side torque transmission path between the transmission60and the rear wheel7. Therefore, the input-side torque transmission path is composed of the input-side transmission mechanism50, whereas the output-side torque transmission path is composed of the output-side transmission mechanism T and the final transmission mechanism140to which the torque from the output-side transmission mechanism T is inputted.

The mission case Mc includes the pair of case halves13a,13b, the left cover14serving also as a left mission cover, the right cover16which is a right mission cover connected to the right case half13b, and a gear cover17which is a cover connected to a rear part of the left case half13atogether with a bearing housing96. Of the first and second power transmission chambers36,37constituting the mission chamber38, the first power transmission chamber36in which the transmission60, the input-side transmission mechanism50and most part of the output-side transmission mechanism T exclusive of a part such as a running clutch70are disposed is defined by both the case halves13a,13band the left cover14, whereas the second transmission chamber37serving as a clutch chamber in which to dispose the running clutch70is defined by the right case half13band the right cover16. The crankcase13, the left cover14, both the right covers15,16and the gear cover17constitute a power case of the power unit P.

The input-side transmission mechanism50includes a gear mechanism51,52for transmitting the torque of the crankshaft33to the transmission60, and an input-side torque damper54for absorbing excess torque generated in the input-side torque transmission path.

The gear mechanism51,52includes a drive gear51connected to the crankshaft33through a transmission mechanism, which is composed of a collar53spline fitted over the shaft end part33aand an input cam member55spline fitted over the collar53. A driven gear52is integrally rotatably provided on the pump housing61a, which serves as an input rotary body in the transmission60. The drive gear51is rotatably supported on the collar53, and is provided at the shaft end part33athrough the collar53.

The torque damper54of a cam type includes an input cam member55as an input member movable in the axial direction relatively to the shaft end part33a. The drive gear51being an output cam member is an output member, which is engaged with the input cam member55and to which the torque of the crankshaft33is inputted through the input cam member55. A damper spring56is an urging member for urging the input cam member55in the axial direction so as to bring the input cam member55into contact with the drive gear51. The damper spring56, which is composed of a plurality of disc springs, is disposed between a spring retainer57held by the collar53and the input cam member55. The input cam member55has an input cam part55a, whereas the drive gear51has an output cam part51a. The input cam part55aand the output cam part51amake contact with each other in the axial direction and in the circumferential direction under the urging force of the damper spring56, and are relatively slidable in the circumferential direction.

The torque damper54rotates the input cam member55and the drive gear51as one body when a torque of not more than a preset first set torque acts between the input cam member55and the drive gear51. When an excess torque of more than the first set torque acts at the time of deceleration of the motorcycle V (seeFIG. 1) or the internal combustion engine E or in similar situations, for example, at the time of engine brake of the motorcycle V, sliding in the circumferential direction occurs between the input cam member55and the drive gear51. Therefore, the input cam member55and the drive gear51are rotated relative to each other while the input cam member55driven by the output cam part51ais being moved in the axial direction against the urging force of the damper spring56, whereby the excess torque is absorbed.

The transmission60is similar to the transmissions disclosed in the above-mentioned Japanese Patent Laid-open Nos. 2005-248838 and 2005-263143. The transmission60includes a swash plate type hydraulic pump61, a swash plate type hydraulic motor62, a valve mechanism63for controlling the flow of a working fluid between the hydraulic pump61and the hydraulic motor62, a transmission output shaft64as an output rotary body, and an input-side clutch65which is a starting clutch for switching between stoppage and rotation of the transmission output shaft64.

The hydraulic pump61includes a pump housing61arotatably supported on the left cover14through a bearing66. A pump swash plate61bis contained in the pump housing61a. A pump body61cis disposed opposite to the pump swash plate61bin the axial direction. A plurality of pump plungers61dare reciprocatably fitted in the pump body61cand driven by the pump swash plate61bto perform suction and discharge of the working fluid.

The hydraulic motor62includes a motor housing62afixed to the right case half13b. A support member62eis swingably supported on a spherical supporting surface formed as part of the motor housing62a. A motor swash plate62bis rotatably supported on the support member62e. A motor body62cis disposed opposite to the motor swash plate62bin the axial direction. A plurality of motor plungers62dis reciprocatably fitted in the motor body62cand is driven by the working fluid discharged from the hydraulic pump61. An electric motor67is provided as an actuator for driving the support member62e. With the support member62edriven by the electric motor67to swing, the inclination angle of the motor swash plate62bis changed, whereby the rotating speed of the transmission output shaft64in relation to the rotating speed of the crankshaft33is changed, and the rotating speed of the crankshaft33is changed.

The valve mechanism63provided between the hydraulic pump61and the hydraulic motor62in the axial direction includes a plurality of spools63afor controlling the flow of the working fluid as an oil discharged from the oil pump40and supplied from an oil passage formed in the right cover16through an oil passage68formed in the transmission output shaft64. Control rings63bare provided for controlling the positions of the spools63aaccording to the rotating position of the pump housing61a.

The transmission output shaft64, which is spline fitted in the motor body62c, is rotatably supported on the pump housing61a, the motor housing62aand the right cover16through bearings69a,69b,69c, respectively. The transmission output shaft64has a rotational center line L2parallel to the rotational center line L1(seeFIG. 2) of the crankshaft. In addition, rotational center lines L3and L4of an output shaft72and an intermediate shaft90, which will be described later, are parallel to both the rotational center lines L1, L2.

The clutch65, which is disposed at an end part nearer to the left cover14in the axial direction in the transmission60, makes and breaks transmission of a torque from the driven gear52to the transmission output shaft64. The clutch65includes an input member65arotated as one body with the pump housing61a. A centrifugal weight is supported by the input member65aand can be moved in the radial direction while being guided by the input member65aunder a centrifugal force generated according to the rotating speed of the input member65a. An output member65ccan be moved in the axial direction according to the position of the centrifugal weight65band is rotated as one body with the input member65a. A clutch spring65eis disposed between the input member65aand the output member65cand presses the centrifugal weight65bagainst the input member65athrough the output member65c. The output member65chas a spool65d, which constitutes a spool valve with the transmission output shaft64as a sleeve.

When the engine rotating speed of the internal combustion engine E is not more than an idling speed, the clutch65is in a torque interruption position shown inFIG. 3. In this instance, the working fluid discharged from the hydraulic pump61returns to the hydraulic pump61without rotating the hydraulic motor62. Besides, when the engine rotating speed exceeds the idling speed, the spool65is moved rightward while being driven by the centrifugal weight65bmoved radially outwards under a centrifugal force, and the clutch65takes a torque transmission position. With the clutch65in this torque transmission position, the working fluid discharged from the hydraulic pump61flows into the hydraulic motor62, the hydraulic motor62is thereby driven to rotate, and the torque of the crankshaft33is transmitted to the transmission output shaft64. In an engine rotating speed region in excess of the idling speed, the transmission output shaft64is rotated at a rotating speed changed according to the inclination angle of the motor swash plate62b.

The output-side transmission mechanism T includes an input mechanism Ti composed of an output gear64oprovided on the transmission output shaft64and rotated as one body with the transmission output shaft64. The running clutch70as an output-side clutch switches between a drive position and a neutral position by making and breaking the transmission of the torque from the transmission60to the rear wheel7. An output mechanism To as a transmission mechanism transmits to the final transmission mechanism140(seeFIG. 1) the torque transmitted from the transmission60through the running clutch70.

The output gear64oas the output rotary body is spline fitted over the shaft end part64a, projecting rightwards from the bearing69bto extend into the second power transmission chamber37, of the transmission output shaft64, and is meshed with an input gear71of the running clutch70.

Referring toFIG. 3, the running clutch70, which is a hydraulic type multiple-disk frictional clutch, includes an output shaft72as an output member which is rotatably borne on the right case half13band the right cover16through bearings. An input gear71as an input member is rotatably supported on the output shaft72and a torque from the transmission output shaft64serving as an input shaft is inputted through the output gear64o. A plurality of clutch disks74are alternately stacked. A housing75as an intermediate member is spline fitted over the output shaft72and is rotated as one body with the latter. A pushing piston76as a pushing member is reciprocatably fitted in the housing75capable of transmitting to the output shaft72the torque from the input gear71transmitted through the clutch74in its connected state and is capable of pushing the clutch disks74to bring the latter into mutual contact. A clutch spring77urges the pushing piston76so as to separate the clutch disks74from each other.

The running clutch70as a hydraulic operating unit capable of operating by a hydraulic pressure is provided with a hydraulic pressure chamber78into which the working fluid for driving the pushing piston76is conducted, by the housing75and the pushing piston76. The working fluid here is a portion of the oil discharged from the oil pump40(seeFIG. 2) driven by a power transmission mechanism41.

The hydraulic pressure in the hydraulic pressure chamber78is controlled by a hydraulic pressure controller for controlling the supply and discharge of the oil into and from the hydraulic pressure chamber78. The hydraulic pressure controller is composed of a hydraulic pressure control valve79provided at the right cover16and controlled by a controller according to an operation of a speed change position operating member, and an oil circuit through which the oil controlled by the hydraulic pressure control valve79flows.

The oil circuit provided as a passage for supplying the oil into the hydraulic pressure chamber78and discharging the oil from the hydraulic pressure chamber78is composed of an oil passage formed in a connection member80connected to the hydraulic pressure control valve79having a part of the right cover16as a valve body. An oil passage82is connected to the oil passage81and is formed in the right cover16. An oil passage83communicates between the oil passage82and the hydraulic pressure chamber78.

In addition, in order to monitor the operating condition of the running clutch70by detecting the hydraulic pressure condition at the running clutch70, a hydraulic pressure sensor88for detecting the hydraulic pressure in the oil circuit is mounted to the right cover16. The hydraulic pressure sensor88detects the hydraulic pressure in the oil passage82.

In the running clutch70as above, when the hydraulic pressure chamber78is supplied with a high-pressure oil and a high hydraulic pressure is established in the hydraulic pressure chamber78, the pushing piston76presses the clutch disks74against the springy force of the clutch spring77. This results in a connected condition in which the input gear71and the housing75are rotated as one body under the function of friction between the clutch disks74, and the torque of the transmission output shaft64is transmitted through both the gears64oand71to the output shaft72. On the other hand, when the working fluid is discharged from the hydraulic pressure chamber78and a low hydraulic pressure is established in the hydraulic pressure chamber78, the clutch disks74are separated from each other by the springy force of the clutch spring77. This results in a disconnected condition in which the transmission of torque between the input gear71and the housing75is interrupted, and the transmission of the torque of the transmission output shaft64to the output shaft72is interrupted. In this manner, the supply and discharge of the oil into and from the hydraulic pressure chamber78through the oil passages81,82and83are controlled, whereby the connection and disconnection of the running clutch70are controlled.

The above-mentioned output mechanism To includes an intermediate shaft90being a first power take-off shaft as a driven rotary shaft driven to rotate by the output shaft72serving as a driving rotary shaft. A second power take-off shaft91as a driven rotary shaft driven to rotate by the intermediate shaft90is operative to drive a drive shaft142(seeFIG. 1) to rotate. A first transmission mechanism is disposed between the output shaft72and the intermediate shaft90in the output-side torque transmission path. The torque of the output shaft72is inputted to the intermediate shaft90through the first transmission mechanism. A second transmission mechanism is disposed between the intermediate shaft90and the power take-off shaft91in the output-side torque transmission path. The torque of the intermediate shaft90is inputted to the power take-off shaft91through the second transmission mechanism. An output-side torque damper100is disposed between the transmission60and the power take-off shaft91in the output-side torque transmission path and which absorbs an excess torque generated in the output-side torque transmission path.

The first transmission mechanism is composed of a drive gear92as a driving rotary body rotated as one body with the output shaft72, and a driven gear93as an input rotary body which is meshed with the drive gear92and by which the torque of the output shaft72is inputted to the intermediate shaft90. The driven gear93is so provided as to be spline fitted on an input cam member101of the torque damper100and to be rotated as one body with the input cam member101, and is connected to the intermediate shaft90through the torque damper100.

The intermediate shaft90, at its shaft part on the right side, is rotatably supported on the right case half13bthrough the input cam member101and a bearing94. The intermediate shaft90, at its shaft part on the left side, is supported on the left case half13athrough a bearing95and a bearing housing96connected to the left case half13a. Of the intermediate shaft90, a shaft end part protruding rightward from the bearing94is accompanied by a driven gear93through the input cam member101, and a shaft end part protruding leftward from the bearing94is integrally provided with a drive gear97.

The torque damper100of a cam type includes the input cam member101as an input member, which is rotatably supported on the intermediate shaft90and by which the torque of the output shaft72is inputted. An output cam member102as an output member is engaged with the input cam member101. The torque from the input cam member101is transmitted to the intermediate shaft90by the output cam member102. A damper spring103as an urging member for urging the output cam member102in the axial direction brings the latter into contact with the input cam member101. The damper spring103, which is composed of a coil spring, is disposed between a spring retainer95a, which serves also as a stationary member of the bearing95, and the output cam member102.

The input cam member101is rotatably supported on the intermediate shaft90, so that the driven gear93is also rotatably supported on the intermediate shaft90. The input cam part101apossessed by the input cam member101and the output cam part102apossessed by the output cam member102are brought into mutual contact in the axial direction and in the circumferential direction by the urging force of the damper spring103, and are relatively slidable in the circumferential direction. The torque damper100rotates the input cam member101and the output cam member102as one body when a torque of not more than the above-mentioned second set torque acts between both the cam members101,102. When an excess torque of more than the second set torque acts at the time of deceleration of the motorcycle V (seeFIG. 1) or the internal combustion engine E or in similar situations, for example, at the time of engine brake of the motorcycle V, sliding in the rotating direction occurs between the input cam member101and the output cam member102. Therefore, the input cam member101and the output cam member102are rotated relative to each other while the output cam member102is being driven by the input cam member101to move in the axial direction against the urging force of the damper spring103, whereby the excess torque is absorbed.

The above-mentioned second transmission mechanism is composed of the drive gear97composed of a bevel gear, and a driven gear98composed of a bevel gear which is meshed with the drive gear97and which is formed as one body with the power take-off shaft91.

The power take-off shaft91is disposed in the gear cover17connected to the left case half13a, and is rotatably supported through a pair of bearings99a,99b. In addition, the gear cover17is provided with a rotating position sensor19for detecting the rotating position of the driven gear98. The vehicle velocity is detected based on a detection signal generated by the sensor19.

Referring toFIGS. 2 and 3, most part of the left case half13aand the left cover14and the gear cover17(hereinafter the whole body of “the left case half13a, the left cover14and the gear cover17” will be referred to as “the side part cover,” if necessary) constituting a side wall of the power unit P in the vehicle width direction (which is also the axial direction of the crankshaft33) is covered with an armor cover C1on the outside of the power unit P from the left side, which is a predetermined direction. Most part of the right case half13band the right cover16constituting another side wall of the power unit P in the vehicle width direction is covered with an armor cover C2from the right side, which is the outside of the power unit P. Both the armor covers C1, C2, which are formed from a synthetic resin, are sound insulation covers as cover members that enhance the appearance quality of the power unit P and reduce the radiant sound generated by the power unit P.

The armor cover C1reduces the radiant sound generated by the side part cover, mainly the radiant sound generated by the left cover14. Incidentally, in the following description, “the radiant sound” means the radiant sound generated by the side part cover, unless otherwise specified.

The armor cover C1is fixed to mounting seats112provided in the left case half13a, the left cover14and the gear cover17(inFIG. 3, the mounting seat112provided in the left case half13ais shown) by bolts110at a plurality of, specifically three, mounting parts111. The armor cover C1covers substantially the whole body of the left cover14, exclusive of a lower edge part of the left cover14, and the whole body of the gear cover17, from the left side. The armor cover C1is mounted to the mounting seats112through a vibration isolating material113(seeFIG. 3(b)) composed of an elastic material having rubber-like elasticity, at the mounting parts111. Therefore, the vibration of the armor cover C1is reduced by the vibration isolating material113, so that the noise generated by the armor cover C1is reduced.

A space S is formed between the side part cover and the armor cover C1, which are so disposed as to form a spacing in the left-right direction. The armor cover C1has a cover part Ca, which covers the side part cover from the left side. An outer peripheral part Cb is bent from the cover part Ca toward the right side opposite to the left side, so as to approach the power unit P, and thereafter extends rightward substantially in parallel. The outer peripheral part Cb covers at least a part of the side part cover from an orthogonal direction (hereinafter referred to as “the orthogonal direction”) orthogonal to the axial direction. Therefore, the armor cover C1covers the side part cover to surround the side part cover from the left side and from the orthogonal direction, so that the radiant sound reducing effect of the armor cover C1is enhanced.

For reducing the radiant sound, the armor cover C1is provided with a sound absorbing material115which is composed of a foamed material (for example, polyurethane foam) and is disposed along an inner surface Ci fronting on the space S. The sound absorbing material115is attached over the whole area of the inner surface Ci of the cover part C1, and is adhered to the inner surface Ci with an adhesive or the like. Furthermore, the sound absorbing material115is also disposed between the outer peripheral part Cb and the left cover14in the orthogonal direction in the state of making contact with the left cover14, and is disposed also between a resonator120which will be described later and the armor cover C1. Incidentally, while the sound absorbing material115is disposed in contact with the resonator120in this embodiment, the sound absorbing material115may be so disposed as to form a gap between itself and the resonator120and to be out of contact with the resonator120.

Therefore, the resonator120is disposed in the space S while being located between the sound absorbing material115and the side part cover and being out of contact with the armor cover C1. In the space S, the resonator120, which is capable of resonating at a specified frequency of the radiant sound, is disposed between the sound absorbing material115and the side part cover.

Referring toFIG. 4, the resonator120as a member separate from the power unit P and the armor cover C1includes an inside volume part124, which has a synthetic resin-made first case121and a synthetic resin-made second case122coupled gas-tightly to each other at a connecting part123by welding and which forms a resonance chamber125. A straight tube-like neck part126forms an aperture part127for communication between the resonance chamber125and the space S. Mounting parts128,129are connected to the left cover14and the gear cover17. Most part of the resonator120, inclusive of the whole body of the neck part126, is disposed in the space S. Substantially the whole part of the resonator120is covered with the armor cover C1from the left side (seeFIG. 2).

The inside volume of the resonance chamber125and the passage area and length of the aperture part127(namely, the inside volume of the aperture part127) are so set as to reduce the radiant sound at the specified frequency, in order to particularly enhance the reducing effect on the noise among the radiant sounds. In this embodiment, the oscillation source of the radiant sound at the specified frequency is the transmission60. Therefore, the vibration of the transmission60vibrates at the specified frequency the side part cover inclusive of the left cover14, to which the bearing66as a support member for supporting the transmission60is attached, whereby the radiant sound at the specified frequency is generated.

The aperture part127is a column-shaped passage having an axis parallel to the vertical direction, and has a passage section of the same shape in the axial direction. The aperture part127is opened in the space S in a direction along the armor cover C1and in a sense A1(in this embodiment, a sense in the vertical direction) toward the inner side in the space S in relation to the position of the aperture part127. The sense A1toward the inner side is that sense of the direction A (in this embodiment, coincident with the vertical direction) parallel to the aperture part127(or the axis of the aperture part127) in which the distance from the aperture end127aon the space S side of the aperture part127to an edge part Cb1of the outer peripheral part Cb of the armor cover C1increases. Therefore, in relation to the aperture part127, a wider space S in the direction A is present in the sense A1than in the sense (in this embodiment, the downward sense in the vertical direction) opposite to the sense A1.

In addition, the aperture part127of the neck part126is located on the front side relative to the seat9(seeFIG. 1). While the sense A1in which the aperture part127is opened is the upward sense parallel to the vertical direction (in other words, straight above) in this embodiment, the sense may be an upward sense inclusive of skew upward senses in addition to the straight-above sense.

The mounting parts128,129are composed of main body parts128a,129aformed integrally with the inside volume part124. Collars128b,129b, which are metallic reinforcing members, are fixed by being press fit onto the main body parts128a,128b. The pair of mounting parts128,129are respectively connected by bolts132as connecting means inserted in the collars128b,129b, in the condition where the collars128b,129bare in contact with boss-shaped mount seats130,131provided in the left cover14and the gear cover17. Therefore, the resonator120is mounted directly to the side part cover, without any vibration isolating material therebetween. It is therefore mounted in contact with the side part cover. Accordingly, the vibration of the left cover14and the gear cover17is transmitted directly to the resonator120via the collars128b,129b.

The resonator120is attached to those parts of the mounting parts128,129, which are in the vicinity of the bearing66, or that part of the left cover14, which is in the vicinity of the mounting part14bfitted with the bearing66. Therefore, the vibration of the side part cover, particularly the vibration of the left cover14fitted with the bearing66, is transmitted to the resonator120and the resonator120itself is vibrated together with the side part cover inclusive of the left cover14. The vicinity is such a portion that the distance between the bearing66and that part of the collar128bof the mounting part128, which is in contact with the left cover14as viewed from the left side, is not more than ½ times the maximum width d (seeFIG. 2) in the orthogonal direction of the range surrounded by the bearing66as viewed from the left side.

In addition, the inside volume part124is provided with a drain hole124a(seeFIG. 2) for draining water upon penetration of water via the aperture part127. By changing the size of the drain hole124a, the resonance frequency of the resonator120can be controlled.

Now, the operation and effects of this embodiment configured as above will be described below.

In the sound insulation structure including the armor cover C1for covering the power unit P generating the radiant sound from the side part cover composed of the left case half13a, the left cover14and the gear cover17from the left side as the predetermined direction so as to reduce the radiant sound and for enhancing the appearance quality of the power unit P, and the resonator120capable of resonating at a specified frequency of the radiant sound, the resonator120is disposed in the space S formed between the side part cover as a side wall of the power unit P and the armor cover C1in the state of being out of contact with the armor cover C1and is attached to the side wall cover in contact with the latter, whereby the radiant sound generated from the side part cover in the space S between the power unit P and the armor cover C1is reduced by the resonator120disposed in the space S. In this case, the resonator120and the armor cover C1are not in contact with each other. Therefore, the vibration of the armor cover C1is prevented from suppressing the vibration of the resonator120itself, which is in a resonating state, so as to hinder the resonance of the resonator120. Moreover, since the resonator120is attached directly to the side part cover, the resonator120itself is also directly oscillated at the specified frequency, the resonance at the specified frequency is promoted by the vibration of the resonator120itself. As a result, the noise reducing effect of the resonator120is enhanced, and the nose reducing effect of the sound insulation structure is enhanced.

The armor cover C1includes the cover part covering the side part cover from the left side, and the outer peripheral part Cb bent toward the side (right side) opposite to the left side so as to approach the side part cover. The outer peripheral part Cb covers the side part cover from the above-mentioned orthogonal direction. The sound absorbing material115is disposed in the space S along the inner surface Ci of the armor cover C1and between the armor cover C1and the resonator120. According to this structure, the armor cover C1covers the side part cover also from the orthogonal direction with the outer peripheral part Cb, in addition to the covering with the cover part Ca, so that the noise reducing effect of the armor cover C1is enhanced. In addition, by utilizing the fact that the resonator120and the armor cover C1are not in contact with each other, the sound absorbing material115can be disposed in the space S over a wide range along the inner surface of the armor cover C1, without being blocked by the resonator120.

As a result, in addition to the noise reducing effect of the resonator120on the radiant sound at the specified frequency, the noise of the whole radiant sounds inclusive of the radiant sound at the specified frequency can be reduced by the sound absorbing material115disposed along the inner surface Ci of the armor cover C1, so that the noise reducing effect is enhanced.

The resonator120is mounted in the vicinity of the bearing66for rotatably bearing the transmission60, which is the oscillation source of the radiant sound at the specified frequency. The aperture part127of the neck part126of the resonator120is opened in the space S in a direction along the inner surface Ci of the armor cover C1and in the sense toward the inner side in the space S in relation to the position of the aperture part127, whereby the resonance at the resonator120is made to occur more easily. In addition, since the neck part126is opened to the direction along the armor cover C1, sounds are propagated along the armor cover C1or the sound absorbing material115. Therefore, it is possible to effectively reduce by the resonator120the radiant sound at the specified frequency, among the radiant sounds on which the noise reducing effect of the armor cover C1or the sound absorbing material115is slight. Furthermore, since the resonator120is mounted in the vicinity of the bearing66supporting the transmission60serving as an oscillation source, the resonator120itself is effectively oscillated at the specified frequency, so that the resonance at the specified frequency is more promoted.

Consequently, the noise reducing effect of the resonator120is enhanced, and the noise reducing effect of the sound insulation structure is enhanced.

The power unit P is disposed below the rider' seat9in the motorcycle V, the aperture part127of the resonator120is located on the front side relative to the seat9, and the aperture part127is opened in an upward direction. Therefore, the radiant sound coming from the side part cover toward the rider(s) on the motorcycle V is effectively reduced by the resonator120. Hence, the noise reducing effect for the rider(s) is enhanced.

Now, a mode obtained by partly modifying the above-described embodiment will be described below, the description being centered on the modified part.

The cover member may include only the crankcase13of the internal combustion engine E or the side part cover or include both the crankcase13and the side part cover, and may cover the engine main body other than the crankcase13, for example, the cylinder blocks10and the cylinder heads11from the outside.

The noise source device, which generates the radiant sound, may be a unit or apparatus other than the power unit P.

The power unit P for driving the object of driving may not necessarily be a unit obtained by integrating the internal combustion engine E and the mission unit as in the above-described embodiment, and may be composed of only the internal combustion engine or the mission unit, or may be composed of an engine other than the internal combustion engine.

The internal combustion engine may be a multi-cylinder internal combustion engine other than the V-type 2-cylinder internal combustion engine, or may be a single-cylinder internal combustion engine. Furthermore, the transmission may be a hydrostatic continuously variable transmission other than the swash plate type, or a continuously variable transmission other than the hydraulic type, or a transmission other than the continuously variable transmission.