Title of Invention	A BELT-TYPE CONTINUOUSLY VARIABLE TRANSMISSION HAVING A RESIN BLOCK BELT FOR A MOTORCYCLE
Abstract	A belt-type continuously variable transmission includes a primary sheave, a secondary sheave, a resin block belt, and a transmission case. The resin block belt is wound around the primary sheave and the secondary sheave. The transmission case defines the section of a belt chamber accommodating the primary sheave, the secondary sheave, and the resin block belt. The transmission case includes an exhaust passage, intake passages, and a sound absorbing member. The sound absorbing member is attached to the inner wall of the exhaust passage in such a position as to collide with sound wave traveling through the exhaust passage. The sound absorbing member has a sound absorbing surface crossing an extending direction of the exhaust passage.

Title of Invention

A BELT-TYPE CONTINUOUSLY VARIABLE TRANSMISSION HAVING A RESIN BLOCK BELT FOR A MOTORCYCLE

Abstract

A belt-type continuously variable transmission includes a primary sheave, a secondary sheave, a resin block belt, and a transmission case. The resin block belt is wound around the primary sheave and the secondary sheave. The transmission case defines the section of a belt chamber accommodating the primary sheave, the secondary sheave, and the resin block belt. The transmission case includes an exhaust passage, intake passages, and a sound absorbing member. The sound absorbing member is attached to the inner wall of the exhaust passage in such a position as to collide with sound wave traveling through the exhaust passage. The sound absorbing member has a sound absorbing surface crossing an extending direction of the exhaust passage.

Full Text	BELT-TYPE CONTINUOUSLY VARIABLE TRANSMISSION HAVING RESIN BLOCK BELT AND MOTORCYCLE INCLUDING BELT-TYPE CONTINUOUSLY VARIABLE TRANSMISSION This application claims priority from Japanese Patent Application No. 2007-016491 filed on January 26, 2007. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a belt-type continuously variable transmission having a resin block belt, and a motorcycle including this belt-type continuously variable transmission. 2. Description of the Related Art For example, JP-A-2002-147582 discloses a motorcycle which includes a belt-type continuously variable transmission having a resin block belt, and others. The resin block belt has higher durability than that of a related rubber belt, and therefore a belt-type continuously variable transmission which uses the resin block belt has higher durability as well. The resin block belt is formed by combining a plurality of resin blocks having higher hardness than that of rubber. Thus, the sound generated by collision between the resin block belt and a primary sheave or a secondary sheave is larger than the sound generated by collision between the rubber belt and 1 the primary or secondary sheave in related art. Thus, noise generated from a belt-type continuously variable transmission using the resin block belt is larger than noise generated from a related-art belt-type continuously variable transmission using the rubber belt. For reducing the noise generated by the resin block belt, such a structure is considered which includes a sound absorbing material disposed inside and outside a transmission case as in the structure of the belt-type continuously variable transmission shown in JP-A-2002-147582, for example. However, even when the sound absorbing material is provided inside and outside the transmission case, it is difficult to sufficiently prevent escape of noise generated by the resin block belt to the outside. SUMMARY OF THE INVENTION The invention has been developed to solve the problems described above. It is an object of the invention to provide a technology which sufficiently prevents escape of noise generated by a resin block belt to the outside. A belt-type continuously variable transmission according to a first aspect of the invention includes a primary sheave, a secondary sheave, a resin block belt, and a transmission case. The resin block belt is wound around the primary sheave and the secondary sheave. The transmission 2 case defines the section of a belt chamber accommodating the primary sheave, the secondary sheave, and the resin block belt. The transmission case includes an air passage connecting the inside and the outside of the belt chamber, and a sound absorbing member. The sound absorbing member is attached to the inner wall of the air passage. The sound absorbing member is disposed in such a position as to collide with sound wave traveling from the inside of the belt chamber toward the outside. A belt-type continuously variable transmission according to a second aspect of the invention includes a primary sheave, a secondary sheave, and a resin block belt, and a transmission case. The resin block belt is wound around the primary sheave and the secondary sheave. The transmission case defines the section of a belt chamber accommodating the primary sheave, the secondary sheave, and the resin block belt. The transmission case includes an air passage communicating with the belt chamber, and a sound absorbing member. The sound absorbing member is attached to the inner wall of the air passage. The sound absorbing member has a sound absorbing surface crossing the extending direction of a portion of the air passage close to the belt chamber and away from the sound absorbing member. The technology provided according to the invention can sufficiently prevent escape of noise generated by a resin block 3 belt to the outside. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a right side view of a motorcycle according an embodiment of the invention; Fig. 2 is a right side view of a central portion of the motorcycle according to the embodiment of the invention; Fig. 3 is a cross-sectional view of an engine unit; Fig. 4 (a) is a cross-sectional view of a resin block belt, and Fig. 4(b) is a side view of the resin block belt; Fig. 5 is a right side view of a second case block; Fig. 6 is a right side view of the second case block to which a clutch cover is attached; Fig. 7 is a right side view of the second case block to which the clutch cover and an inside case are attached; Fig. 8 is a perspective view of the second case block to which the clutch cover, the inside case, and an outside case are attached as viewed from below inclined to the front; Fig. 9 is a right side view of the second case block to which the clutch cover, the inside case, and the outside case are attached; Fig. 10 is a cross-sectional view taken along a line X-X in Fig. 9; Fig. 11 is a cross-sectional view taken along a line XI-XI in Fig. 10; 4 Figs 12(a) and 12(b) are development elevations showing two divided portions of an air chamber; Fig. 13 is a cross-sectional view taken along a line XIII-XIII in Fig, 12; Fig. 14 schematically illustrates a position of a sound absorbing member according to a modified example 1; Fig. 15 schematically illustrates positions of the sound absorbing members according to a modified example 2; Fig. 16 schematically illustrates a position of the sound absorbing member according to a modified example 3; and Fig. 17 schematically illustrates positions of the sound absorbing members according to a modified example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors found that the main component of noise generated from a belt-type continuously variable transmission having a resin block belt is a pitch noise produced by sequential shifts of plural resin blocks. In addition, they found that the pitch noise is so-called high-frequency sound. Furthermore, they directed their attention to the fact that high-frequency sound generally has such characteristics as high rectilinear propagation and low penetrability. Based on these findings, the inventors have developed the invention described herein. When an air passage communicating with a belt chamber 5 extends in a straight direction, the high-frequency sound having high rectilinear propagation escapes chiefly through the air passage to the outside. Considering this fact, a sound absorbing material is attached to the inner wall of the air passage connecting the inside and the outside of the belt chamber in such a position that sound wave traveling through the air passage can collide with the sound absorbing material according to this embodiment. This arrangement of the sound absorbing material effectively prevents escape of the high-frequency sound generated by the resin block belt from the belt chamber. According to this embodiment, at least a bended portion is formed on the air passage for effectively preventing the escape of the high-frequency sound. More specifically, a plurality of bended portions are formed on an exhaust passage, and the sound absorbing materials are provided on the bended- portions . Additional sound absorbing materials may be affixed to the inside and outside of a transmission case for further reducing escape of noise to the outside. However, since the noise generated by the resin block belt can be effectively prevented by disposing the sound absorbing material within the air passage in such a position that the main flow of air traveling through the air passage collides with the sound absorbing material as discussed above due to the 6 characteristics of high-frequency sound as high rectilinear propagation and comparatively low penetrability through an object, relatively high sound prevention effect can be obtained even when the sound absorbing materials are not affixed to the inside and outside of the transmission case. That is, the sound from the belt chamber can be effectively prevented and the size reduction of the belt-type continuously variable transmission can be achieved by attaching the sound absorbing material to the inside wall of the air passage such that the main flow of air passing through the air passage collides with the sound material and by eliminating the sound absorbing materials affixed to the inside and outside of the transmission case. Moreover, the cooling effect inside the transmission case can be enhanced by eliminating the sound absorbing materials affixed to the area having thermal insulation effect and the inside and outside of the transmission case. As a result, the life of the belt-type continuously variable transmission can be prolonged. A motorcycle 1 according to this embodiment is hereinafter described in detail with reference to Figs. 1 through 13. In this embodiment, the off-road-type motorcycle 1 shown in Fig. 1 is discussed as an example of a straddle-type vehicle according to the invention. However, the straddle-type vehicle of the invention is not limited to this type, but may be a motorcycle of types other than the off-road 7 type. More specifically, examples of the straddle-type vehicle according to the invention include motorcycle type, motor-scooter type, so-called moped type, and other types of motorcycle. The invention is also applicable to a straddle-type vehicle other than a motorcycle. For example, the straddle-type vehicle according to the invention may be an all terrain vehicle (ATV). «General Structure of Motorcycle 1» Fig. 1 is a side view of the motorcycle 1 according to this embodiment. Initially, the general structure of the motorcycle 1 is explained with reference to Fig. 1. In the following description, the front-rear and left-right directions refer to the front-rear and left-right directions as viewed from a rider sitting on a seat 3. The motorcycle 1 has a body frame 2, a body cover 14, and the seat 3.. The body cover 14 is attached in such a manner as to cover a part of the body frame 2. The seat 3 is attached to the body cover 14. The body frame 2 has a steering head pipe 4, a down tube 5, and a main pipe 6. The down tube 5 is extended downward from the steering head pipe 4, bended at an intermediate portion, and further extended substantially in the horizontal direction from the intermediate portion. The main pipe 6 positioned above the down tube 5 extends toward the rear from the steering head pipe 4. 8 A pivot shaft 10 is attached to the lower end of the main pipe 6. A rear arm 9 extending toward the rear is attached to the pivot shaft 10 such that the rear arm 9 can swing. A rear wheel 13 is rotatably attached to the rear end of the rear arm 9. The lower end of the steering head pipe 4 is connected with a front fork 11. A front wheel 12 is rotatably attached to the lower end of the front fork 11. As illustrated in Fig. 2, a pair of seat rails 7 extending toward the rear are provided at an intermediate portion of the main pipe 6 . A back stay 8 is connected with a position slightly shifted toward the rear from the centers of the respective seat rails 7. The back stay 8 extends diagonally downward toward the front from the connecting portion with the seat rails 7. The distal end of the back stay 8 is connected with the lower end of the main pipe 6. As illustrated in Figs. 1 and 2, an engine unit.15 is disposed between the down tube 5 and the main pipe 6 and attached to both. As illustrated in Fig. 3, the engine unit 15 is formed by combining an engine 16, a belt-type continuously variable transmission 17, and other components into one piece. The driving force generated by the engine unit 15 is transmitted to the rear wheel 13 via not-shown power transmitting means such as chain belt. In the following description, the belt-type continuously variable transmission 17 is abbreviated as CVT 17. 9 «Structure of Engine Unit 15» Fig. 3 shows the cross section of the engine unit 15. As illustrated in Fig. 3, the engine unit 15 has the engine 16, the CVT 17, a centrifugal clutch 18, and a speed reduction mechanism 19. While the engine 16 is a four-stroke single-cylinder engine in this example, the engine 16 may be a two-stroke engine or multi-stroke engine, for example. The engine 16 has a crank case 80, a cylinder 21, and a cylinder head 22. The cylinder 21 is attached to the crank case 80. The cylinder head 22 is attached to the distal end of the cylinder 21. A piston 25 is inserted into the cylinder 21 such that the piston 25 can slide therein. One end of a connecting rod 26 is connected with the piston 25. The other end of the connecting rod 26 is connected with a crank pin 28. The crank pin 28 is inserted into through holes formed on a left crank arm 27a and a right crank arm 27b, and fixed to the through holes. The cylinder head 22 has a concave 22a communicating with the inside space of the cylinder 21, and intake port and exhaust port (not shown) communicating with the concave 22a. The concave 22a constitutes a part of a combustion chamber. An ignition plug 29 is attached to the cylinder head 22 such that the ignition area of the ignition plug 29 can be exposed to the outside. 10 As illustrated in Figs. 1 and 2, an intake pipe 40 is connected with the intake port. As illustrated in Fig. 2, the intake pipe 40 extends toward the rear from the cylinder head 22. An air chamber 43 is connected with the rear end of the intake pipe 40. The air chamber 43 has an intake hole 43a. Outside air is taken through the intake hole 43a into the air chamber 43. The outside air taken into the air chamber is supplied to the combustion chamber via the intake pipe 40 and the intake port. As illustrated in Figs. 1 and 2, an exhaust pipe 41 is connected with the exhaust port. As illustrated in Fig. 2, the exhaust pipe 41 is connected with the front region of the cylinder head 22. The exhaust pipe 41 extends toward the front from the cylinder head 22, crosses over the down tube 5, extends downward before the engine unit 15, and then extends below the engine unit 15 toward the rear. A muffler 42 is connected with, the rear end of the exhaust pipe 41. As illustrated in Fig. 3, a cam chain chamber 31 connecting the interior of the crank case 80 and the interior of the cylinder head 22 is provided in the left part inside the cylinder 21. A timing chain 32 is accommodated in the cam chain chamber 31. The timing chain 32 is wound around a crank shaft 23 and a cam shaft 33. Thus, the cam shaft 33 rotates in accordance with the rotation of the crank shaft 23. The rotation of the cam shaft 33 opens and closes not-shown intake 11 valve and exhaust valve. The crank case 90 has a first case block 81 disposed on the left side, a second case block 82 disposed on the right side, and a clutch cover 83. The first case block 81 and the second case block 82 face each other in the vehicle width direction. A concave 82a extending to the left is formed in the rear half of the second case block 82. The clutch cover 83 closes the concave 82a. A space defined by the concave 82a and the clutch cover 83 constitutes a clutch chamber containing the centrifugal clutch 18. The crank shaft 23 is accommodated in the crank case 80. The crank shaft 23 horizontally extends in the vehicle width direction. The crank shaft 23 is supported by the first case block 81 via a bearing 24a. The crank shaft 23 is also supported by the second case block 82 via a bearing 24b. A dynamo case 35 Is attached to the left side of the front- half of the first case block 81. A dynamo chamber is defined by the dynamo case 35 and the first case block 81. A dynamo 34 is accommodated in the dynamo chamber. The dynamo 34 is attached to the crank shaft 23 within the dynamo chamber. The dynamo 34 has a stator 34a and a rotor 34b. The rotor 34b is fixed to a sleeve 39 rotating with the crank shaft 23. The stator 34a is fixed to the dynamo case 35. This structure allows the rotor 34b to rotate relative to the stator 34a in accordance with the rotation of the crank shaft 23 for power 12 generation. A transmission case 61 containing the CVT 17 is attached to the right side of the second case block 82 . The transmission case 61 defines the section of a belt chamber 38 accommodating the CVT 17. The transmission case 61 has an inside case 62 made of resin and disposed on the right side of the second case block 82, and an outside case 63 positioned on the right side of the inside case 62. The CVT 17 has a primary sheave 51 and a secondary sheave 52. The primary sheave 51 is attached to the crank shaft 23. More specifically, the right end of the crank shaft 23 penetrates through the second case block 82 and the inside case 62, and reaches the belt chamber 38. The primary sheave 51 is attached to the right end of the crank shaft 23. In the following description, the right portion of the crank shaft 23 is also referred to as a "primary sheave shaft 23a". More accurately, the primary sheave shaft 23a is constituted by the portion of the crank shaft 23 positioned on the right side of the bearing 24b. More specifically, the primary sheave 51 has a primary fixed sheave member 51a and a primary movable sheave member 51b. The primary fixed sheave member 51a is fixed to the right end of the primary sheave shaft 23a . The primary movable sheave member 51b positioned on the left side of the primary fixed sheave member 51a is attached to the primary sheave shaft 23a. 13 The primary movable sheave member 51b can shift relative to the primary sheave shaft 23a in its axial direction. The left side surface of the primary fixed sheave member 51a has a tapered shape expanding to the right. The right side surface of the primary movable sheave member 51b has a tapered shape expanding to the left. These left side surface of the primary fixed sheave member 51a and right side surface of the primary movable sheave member 51b form a substantially V-shaped belt groove 51c which has a width increasing toward the outside in the radial direction. A plurality of fan vanes 60 are provided on the right side surface of the primary fixed sheave member 51a. A cam surface 56 is disposed on the left side surface of the primary movable sheave member 51b. A cam plate 57 is located on the left side of the primary movable sheave member 51b in such a. position as to be opposed to the cam surface 56. The cam plate 57 is fixed to the primary sheave shaft 23a. The cam plate 57 engages with the primary movable sheave member 51b. This engagement prevents rotation of the primary movable sheave member 51b relative to the primary sheave shaft 23a. Roller weights 58 movable in the radially inside-outside direction are disposed between the cam surface 56 and the cam plate 57. The secondary sheave 52 is positioned behind the primary sheave 51. The secondary sheave 52 is attached to a secondary 14 sheave shaft 53. The secondary sheave 52 has a secondary fixed sheave member 52a and a secondary movable sheave member 52b. The secondary fixed sheave member 52a is fixed to the secondary sheave shaft 53. The secondary movable sheave member 52b positioned on the right side of the secondary fixed sheave member 52a is attached to the secondary sheave shaft 53. The secondary movable sheave member 52b can shift in the axial direction of the secondary sheave shaft 53. The right side surface of the secondary fixed sheave member 52a has a tapered shape expanding to the left. The left side surface of the secondary movable sheave member 52b has a tapered shape expanding to the right. These right side surface of the secondary fixed sheave member 52a and left side surface of the secondary movable sheave member 52b form a substantially V-shaped belt groove 52c having a width increasing toward the outside in the radial direction. A compression coil spring 59 is provided on the right side of the secondary movable sheave member 52b. The secondary movable sheave member 52b is urged to the left by the compression coil spring 59. Thus, the secondary movable sheave member 52b is urged toward the secondary fixed sheave member 52a by the compressing coil spring 59. A resin block belt 55 is wound around the belt groove 51c of the primary sheave 51 and the belt groove 52c of the secondary sheave 52. The resin block belt 55 is a so-called 15 resin block belt having a substantially V-shaped cross section. More specifically, the resin block belt 55 has a plurality of resin blocks 55a as illustrated in Fig. 4 (a) . The plural resin blocks 55a are arranged in a ring-band shape, and are connected with one another by a pair of flexible connecting members 55b. More specifically, each of the resin blocks 55a has a pair of concaves 55c opposed to each other. The plural resin blocks 55a are connected with one another by fitting the connecting members 55b into the concaves 55c. As illustrated in Fig. 3, the secondary sheave shaft 53 penetrates through the inside case 62 and the clutch cover 83 and reaches a clutch chamber. The centrifugal clutch 18 is attached to the secondary sheave shaft 53 in the clutch chamber. The centrifugal clutch 18 may be a wet-type multi-disc clutch as illustrated in Fig. 3, for example. The centrifugal clutch 18 engages with the speed reduction mechanism 19. The rotation of the secondary sheave shaft 53 is transmitted to the speed reduction mechanism 19 via the centrifugal clutch 18. Then, the torque thus generated is transmitted from an output shaft (not shown) of the speed reduction mechanism 19 to the rear wheel 13 shown in Fig. 1 via the power transmitting means (not shown). «Air Intake and Exhaust to and from Belt Chamber 38» The air intake and exhaust to and from the belt chamber 38 are now explained in detail with reference to Fig. 5 and 16 other figures. Fig. 5 is a right side view of the second case block 82. Fig. 6 is a right side view of the second case block 82 to which the clutch cover 83 is attached. Fig. 7 is a right side view of the second case block 82 to which the clutch cover 83 and the inside case 62 are attached. Fig. 8 is a perspective view of the second case block 82 to which the clutch cover 83, and the inside and outside cases 62 and 63 are attached as viewed from below inclined to the front. Fig. 9 is a right side view of the second case block 82 to which the clutch cover 83 and the inside and outside cases 62 and 63 are attached. Fig. 10 is a cross-sectional view taken along a line X-X in Fig. 9. Fig. 11 is a cross-sectional view taken along a line XI-XI in Fig. 10. Fig. 10 shows only the second case block 82, the clutch cover 83, and the transmission case 61 for simplifying the explanation. -Detailed Structures of Second Case Block 82, Transmission Case 61 and Others- As illustrated in Fig. 5, an opening 82e through which the primary sheave shaft 23a is inserted is formed in the front half of the second case block 82. A concave 82a containing the clutch chamber is formed in the rear half of the second case block 82. As illustrated in Figs. 3 and 6, the concave 82a is closed by the clutch cover 83. An opening 83a through which the secondary sheave shaft 53 is inserted is formed at the center of the clutch cover 83. 17 A plurality of linear convexes (ribs) 82b are formed below the concave 82a. The plural convexes 82b are arranged in a line substantially in the horizontal direction. More accurately, the plural linear convexes 82b are positioned in a line in a direction slightly diagonally upward toward the rear. The respective linear convexes 82b extend in the up-down direction, and project further to the right from the right side surface of the second case block 82. That is, the respective linear convexes 82b project toward the inside case 62 from the right side surface of the second case block 82. As illustrated in Fig. 11, the plural linear convexes 82b contact the inside case 62. This structure allows the inside case 62 having relatively low strength to be appropriately supported. As can be seen from the cross section shown in Fig. 11, a concaved portion having an arch shape is formed between each of the contact portions of the inside case 62 contacting the linear convexes 82b. An expanding portion 82c is formed immediately below the plural linear convexes 82b of the second case block 82. The expanding portion 82c extends to a position on the right side of the right end of the linear convexes 82b. In other words, the expanding portion 82c expands to the outside of the right end of the linear convexes 82b. The expanding portion 82c extends in a wider range than the area where the plural linear convexes 82b are formed in the front-rear direction. 18 As illustrated in Figs. 3 and 7, the inside case 62 is disposed on the right side of the second case block 82. The inside case 62 covers substantially the entire part of the right region of the second case block 82 except for the openings 82e and 83a, the expanding portion 82c, and the lower region of the area where the plural linear convexes 82b are formed. As illustrated in Fig. 10, a space is produced between the inside case 62 and the second case block 82. A plurality of communication openings 62a through which this space communicates with the belt chamber 38 are formed in the upper region of the inside case 62 (see Fig. 3 as well) . This structure allows the belt chamber 38 to communicate with the outside air via the communication openings 62a and the space between the inside case 62 and the second case block 82. According to this embodiment, the space between the inside case 62 and the second case block 82 constitutes an exhaust passage 65. As illustrated in Fig. 10, the exhaust passage 65 is bended to the right by the expanding portion 82c to form a labyrinth structure. That is, the exhaust passage 65 has a plurality of bended portions 65b. While the exhaust passage 65 has the plural bended portions 65b in this embodiment, the exhaust passage 65 may have one or plural curved portions. Alternatively, the exhaust passage 65 may have one or plural curved portions as well as one or plural bended portions. As illustrated in Fig. 10, the outside case 63 is 19 positioned on the right side of the inside case 62. The belt chamber 38 is defined by the outside case 63 and the inside case 62. An extension 63a extending downward to a position lower than the lower end of the inside case 62 is provided on the lower rear portion of the outside case 63. The extension 63a and the second case block 82 are positioned away from each other. The extension 63a extends to a position opposed to the expanding portion 82c in the up-down direction. In other words, the extension 63a has a portion opposed to the linear convexes 82b in the vehicle width direction and a portion opposed to the expanding portion 82c provided below the linear convexes 82b. The exhaust passage 65 is bended downward by the extension 63a at a position downstream from the bended portion 65b. Thus, the exhaust passage 65 has a bended portion 65c positioned.downstream from the bended portion. 65b. The bended portion 65c may be a curved portion. A sound absorbing member 36 is attached to the inside surface (left surface) of the extension 63a. That is, the sound absorbing member 36 is attached to the left side surface of the extension 63a. The sound absorbing member 36 has a sound absorbing surface 36a crossing the projecting direction of the linear convexes 82b. More specifically, the sound absorbing member 36 as a face material is disposed in such a position as to cross the projection direction of the linear convexes 20 82b. The angle formed by the sound absorbing face 36a and the projecting direction of the linear convexes 82b may be a right angle. Alternatively, the angle formed by the sound absorbing surface 36a and the projecting direction of the linear convexes 82b may be an acute angle or an obtuse angle. For obtaining high sound absorbing efficiency, it is preferable that the sound absorbing member 36 has a number of spaces inside its body. For example, the sound absorbing member 36 may be made of foamed material, glass wool, or steel wool. Examples of the foamed material include foamed resin such as foamed urethane, foamed rubber, and other materials. As illustrated in Figs. 8 and 9, an expanding portion 63b is formed before the extension 63a of the outside case 63. The expanding portion 63b is expanded to a position lower than the upper end of the expanding portion 82c in the up-down direction. The expanding portion 63b covers the .space between the extension 63a and the second case block 82 in the front view. As illustrated in Fig. 3, an intake opening 78 is formed on the upper surface of the outside case 63. An intake duct 71 is connected with the intake opening 78 (see Figs. 1, 2 and 8 as well) . As illustrated in Figs. 1 and 2, the intake duct 71 extends upward from the transmission case 61, and then extends in the horizontal direction toward the rear from the intermediate portion of the intake duct 71. An air chamber 21 94 is connected with the rear side end of the intake duct 71. The air chamber 94 has a function of purifying the outside air introduced thereto. More specifically, the air chamber 94 has a function of removing dust contained in the outside air thus taken. Figs. 12(a) and 12 (b) are development elevations showing two divided parts of the air chamber 94. Fig. 13 is a cross-sectional view of the air chamber 94. As illustrated in Figs. 12, the air chamber 94 has a first casing 95 and a second casing 96 combined in such a manner as to be opposed to each other. As illustrated in Fig. 12(b), walls 95b and 95c are provided inside the first casing 95. These walls 95b and 95c define a first intake passage 98 extending in a zigzag line. As illustrated in Fig. 12(a), walls 96a, 96b and 96c are provided inside the second casing 96. The wall 96a divides the interior of the second casing 96 into two areas. The second casing 96 has an intake opening 94a open to an upper inside area 100 within the second casing 96. The inside area 100 communicates with a base end 98a of the first intake passage 98 of the first casing 95 (see Fig. 12(b)). The walls 96b and 96c are provided in the lower inside area of the second casing 96. These walls 96b and 96c define a second intake passage 99 extending in a zigzag line within the lower inside area of the second casing 96. As illustrated 22 in Fig. 13, the second intake passage 99 and the first intake passage 98 face each other with an air cleaner 97 interposed therebetween. The wall 96b has a shape corresponding to that of the wall 95b. The wall 96c has a shape corresponding to the shape of the wall 95c. Thus, the first intake passage 98 and the second intake passage 99 have mirror images of each other. -Intake and Exhaust Operations to and from Belt Chamber 38- As discussed above, the plural vanes 60 are provided on the left side surface of the primary fixed sheave member 51a disposed within the belt chamber 38 (see Fig. 3) . The plural vanes 60 rotate with the rotation of the primary sheave shaft 23a. That is, the plural vanes 60 rotate with the rotation of the crank shaft 23. As a result, absorbing force toward the belt chamber 38 is generated, and the outside air taken from the air chamber 94 is taken into the belt chamber .38. by the rotation of the plural vanes 60. More specifically, the outside air is initially taken from the intake opening 94a into the air chamber 94. The outside air taken from the intake opening 94a is introduced to the base end 98a of the first intake passage 98 via the inside area 100 (see Figs. 12 and Fig. 13). The air introduced to the base end 98a flows from the base end 98a to a distal end 98b, and a part of this air passes through the air cleaner 97 and flows into the second intake passage 99. The air having 23 flowed into the second intake passage 99 is supplied to the intake duct 71 via an opening 101 formed at the distal end of the second intake passage 99 (see Figs. 1 and 2). The air supplied to the intake duct 71 is supplied to the front half of the belt chamber 38 (see chiefly Figs. 3 and 10) . That is, the air supplied to the intake duct 71 is further supplied to the area where the primary sheave 51 is disposed. The CVT 17 is cooled by the outside air thus taken. The air supplied to the belt chamber 38 flows within the belt chamber 38, passes through the exhaust passage 65 formed between the inside case 62 and the second case block 82, and then is discharged through the communication openings 62a. The discharge air initially advances downward in the exhaust passage 65 (see Fig. 10). Then, the flow direction of the discharge air is changed by the bended portion 65b. That is, the air flowing downward is changed to the air flowing to the right by collision with a wall 82f. Then, the discharge air collides with the sound absorbing surface 36a of the sound absorbing member 36 at the bended portion 65c, where the flow direction is further changed to the downward direction. Thereafter, the air is discharged through an exhaust opening 65a. As discussed above, the sound absorbing member 36 is attached to the inner wall of the discharge passage 65 in such a position as to collide with the air passing through the 24 discharge passage 65. More specifically, the sound absorbing member 36 is attached to the inside wall of the extension 63a constituting the bended portion 65c. The sound absorbing member 36 has the sound absorbing surface 36a. The sound absorbing surface 36a crosses the extending direction of a portion of the exhaust passage 65 close to the belt chamber 38 and away from the sound absorbing member 36. In other words, the sound absorbing surface 36a is not disposed in parallel with the extending direction of the portion of the exhaust passage 65 close to the belt chamber 38 and away from the sound absorbing member 36. More specifically, the sound absorbing surface 36a may be disposed orthogonal to the extending direction of the portion of the exhaust passage 65 close to the belt chamber 38 and away from the sound absorbing member 36. Alternatively, the angle formed by the sound- absorbing surface 36a and the extending direction of the portion of the exhaust passage 65 close to the belt chamber 38 and away from the sound absorbing member 36 may be an acute angle or an obtuse angle. According to this embodiment, the area of the exhaust passage 65 close to the belt chamber 38 and away from the sound absorbing member 36 is specifically the area between the bended portion 65b and the bended portion 65c. The plural linear convexes 82b extend along the extending direction of the exhaust passage 65. 25 «Operation and Advantage» As discussed above, the sound absorbing member 36 has the sound absorbing surface 36a inclined at an angle to the projecting direction of the linear convexes 82b. In other words, as illustrated in Fig. 10, the sound absorbing member 36 has the sound absorbing surface 36a which crosses an extending direction Al of the portion of the exhaust passage 65 close to the belt chamber 38 upstream from the sound absorbing member 36, i.e. the area disposed between the bended portion 65b and the bended portion 65c. The sound member 36 is located in such a position as to collide with the sound wave traveling from the inside of the belt chamber 38 toward the outside. Concerning the relationship between the flow of exhaust air and the sound absorbing member 36, the sound absorbing member 36 is disposed in such a position as to collide with the air flowing through the exhaust passage 65. Thus, the sound absorbing member 36 effectively absorbs high-frequency sound having high rectilinear propagation generated by the resin block belt 55. As a result, escape of the high-frequency sound generated by the resin block belt 55 from the exhaust passage 65 can be effectively prevented. Moreover, the high-frequency sound having low penetrability through an object does not easily penetrate through the outside case 63 or other components to escape therefrom. Thus, escape of noise generated by the resin block belt 55 to the outside 26 can be effectively prevented. These advantages can be obtained as long as the sound absorbing member 36 is disposed in such a position as to collide with the sound wave traveling from the inside of the belt chamber 38 toward the outside. Thus, it is not necessarily required that the sound absorbing surface 36a is disposed orthogonal to the traveling direction of the sound wave traveling from the inside of the belt chamber 38 toward the outside. More specifically, it is not necessarily required that the sound absorbing surface 36a is disposed orthogonal to the extending direction of the portion of the exhaust passage 65 close to the belt chamber 38 and away from the sound absorbing member 36. For example, even when the angle formed by the sound absorbing surface 36a and the traveling direction of the sound traveling from the inside of the belt chamber 38 toward the outside is an acute angle or an obtuse angle, the above advantages can be offered. In other words, even when the angle formed by the sound absorbing surface 36a and the extending direction of the portion of the exhaust passage 65 close to the belt chamber 38 and away from the sound absorbing member 36 is an acute angle or an obtuse angle, the above advantages can be offered. For reducing the escape of noise generated by the resin block belt 55 to the outside more effectively, it is preferable that the sound absorbing member is provided on the inside or 27 outside Of the outside case 63. In this case, escape of the high-frequency sound penetrating through the outside case 63 can be more securely prevented, However; as discussed above, the high-frequency sound has low penetrability through an object. Thus, the escape of the sound generated by the resin block belt 55 to the outside can be effectively prevented even when the sound absorbing member is not disposed on the inside or outside of the outside case 63. Thus, the escape of the sound generated by the resin block belt 55 to the outside can be effectively prevented without requiring the sound absorbing member on the inside or outside of the outside case 63 and therefore without increasing the size of the CVT 17 and further the size of the engine unit 15. Moreover, since the necessity for providing the sound absorbing member having thermal insulation on the inside or outside of the outside case 63 is eliminated, relatively high heat release efficiency through the outside case 63 can be achieved. As a result, the cooling efficiency of the CVT 17 can be improved. It is preferable that the sound absorbing member 36 is disposed on the exhaust side as in this embodiment, since high-frequency sound does not easily escape from the intake side where the air filter 79 having the sound absorbing capability as well is generally disposed. In addition, this structure is preferable since noise in the belt chamber 38 28 escaping to the outside from the exhaust passage for discharging the air is relatively larger than noise in the belt chamber 38 escaping from the intake passage. The sound absorbing member 36 may be disposed at a position other than the extension 63a. It is preferable that the sound absorbing member 36 is provided on the inner wall of the exhaust passage 65 at the outside corner of the portion where flow of the air to be discharged changes such as the bended portion 65b and the bended portion 65c. For example, the sound absorbing member 36 may be located on the wall 82f of the second case block 82. Also, the sound absorbing member 36 may be provided on both of the inner walls of the wall 82f and the extension 63a. In this case, further higher noise proof effect can be obtained. According to this embodiment, the exhaust passage 65 has a labyrinth structure in addition to the equipment of the sound absorbing member 36. More specifically, the exhaust passage 65 has the plural bended portions 65b and 65c. Thus, high-frequency sound having entered the exhaust passage 65 collides with the wall at the positions of the plural bended portions 65b and 65c, and thereby decreases. More specifically, the high-frequency sound having entered the exhaust passage 65 collides with the wall 82f of the second case block 82 and decreases. Thus, escape of sound generated by the resin block belt 55 to the outside can be reduced further 29 effectively. This noise reduction effect can be obtained by the collision between the high-frequency sound having entered the exhaust passage 65 and the wall of the components of the CVT 17. Thus, the noise reduction effect Can be similarly obtained even when curved portions are provided instead of the bended portions 65b and 65c as in this embodiment. For acquiring further high noise reduction effect, it is particularly preferable that the number of the bended portions or curved portions to be formed is plural. It is also preferable that each of the intake passages 98 and 99 covered by the air cleaner having sound absorbing capability has a labyrinth structure as in this embodiment. This structure further effectively prevents escape of high-frequency sound from the intake passages 98 and 99. As illustrated in Fig. 11, the inside case 62 made of resin and having relatively low hardness is supported by the linear convexes 82b in this embodiment. This structure improves the durability of the inside case 62. As a method for enhancing the durability of the inside case 62, it is also considered to form a linear convex extending in the front-rear direction along the contour of the inside case 62, for example. In this case, a slit needs to be formed on the linear convex so as to secure the space of the exhaust passage 65. In this structure, however, it is difficult to secure a sufficiently wide space of the exhaust passage 65. When the width of the 30 slit is enlarged to secure a sufficient space of the exhaust passage 65, the durability of the linear convex lowers. As a result, the durability of the inside case 62 lowers accordingly. However, in the structure having the linear convexes 82b which extend substantially in parallel with the extending direction of the exhaust passage 65 as in this embodiment, the durability of the inside case 62 increases while securing a relatively large space of the exhaust passage 65. According to this embodiment, each portion between the contacting portions of the inside case 62 contacting the linear convexes 82b is concaved in an arched shape. Thus, a further wide space of the exhaust passage 65 can be secured. The structure having the linear convexes 82b which extend along the flow of exhaust air as in this embodiment offers rectification effect, of exhaust air. This effect reduces the noise of exhaust air. For further enhancing the rectification effect of exhaust air, it is preferable that the arrangement pitch of the linear convexes 82b is decreased. On the other hand, for enlarging the opening area of the exhaust passage 65, it is preferable that the pitch of the linear convexes 82b is increased. For widening the opening area of the exhaust passage 65, only the single linear convex 82b may be formed. According to this embodiment, the communication openings 62a through which the exhaust passage 65 and the belt chamber 31 38 communicate with each other are open in the upper region of the belt chamber 38 as illustrated in Figs. 7, 9 and 10. Thus, even when water or mud enters the exhaust passage 65 through the exhaust opening 65a, the water or mud does not easily enter the belt chamber 38 . In addition, since the lower portion of the exhaust opening 65a is covered by the extending portion (lower extending portion) 82c, enter of splashed water or mud through the exhaust opening 65a into the exhaust passage 65 can be effectively reduced. Moreover, since the exhaust opening 65a is covered by the extending portion 63b and the expanding portion 82d (front expanding portion) in the front view, enter of water or mud splashed by the front wheel 12 through the exhaust opening 65a into the exhaust passage 65 can be particularly effectively prevented. The center of the secondary sheave 52 is positioned above the center of the primary sheave 51 from a lateral view. Thus, the exhaust opening 65a is located at a relatively high position from the ground level. Accordingly, enter of the splashed water or mud into the exhaust passage 65 through the exhaust opening 65a can be effectively prevented. (Modified Examples 1 through 4) In the above embodiment, the structure having the sound absorbing member 36 attached to the extension 63a has been discussed as an example. However, the attachment position of the sound absorbing member 36 is not particularly limited as 32 long as the sound absorbing member 36 is disposed in such a position as to collide with sound wave traveling from the belt chamber 38 to the outside. For example, as illustrated in Fig. 14, the sound absorbing member 36 may be attached to the belt chamber 38 side surface of a projecting portion 37 provided inside the exhaust passage 65 having the plural bended portions. As illustrated in Fig. 15, the sound absorbing member 36 may be provided on each belt chamber 38 side surface of the plural projecting portions 37 disposed in staggered arrangement within the exhaust passage 65 extending straight, for example. In this case, it is preferable that the plural sound absorbing members 36 are so disposed as to cover the flow path of the exhaust passage 65 as viewed from an extending direction A2 of a portion of the exhaust passage 65 close to the belt chamber 38 and away from the region where the projecting portions 37 are formed. According to this modified example, the extending direction A2 of the portion of the exhaust passage 65 close to the belt chamber 38 and away from the region where the projecting portions 37 are formed coincides with the extending direction of the exhaust passage 65. As illustrated in Fig. 16, the sound absorbing member 36 may be attached to each inner wall of plural curved portions provided on the exhaust passage 65 having the plural curved 33 portions and extending in a zigzag line, for example. In this case, it is preferable that the sound absorbing member 36 has a sound absorbing surface 36b extending substantially in the vertical direction with respect to the extending direction of the portion of the exhaust passage 65 close to the belt chamber 38 and away from the region where the sound absorbing member 36 is provided as shown in Fig. 16. In this case, high-frequency sound having high rectilinear propagation can be effectively absorbed by the absorbing surface 36b. As illustrated in Fig. 17, the sound absorbing member 36 may be provided on each of plural bended portions formed on the exhaust passage 65, for example. The plural sound absorbing members 36 thus attached can effectively absorb sound high-frequency sound. The invention is applicable to a belt-type continuously variable transmission and a motorcycle. 34 WE CLAIM: 1. A belt-type continuously variable transmission comprising: a primary sheave; a secondary sheave; a resin block belt wound around the primary sheave and the secondary sheave; and a transmission case which defines the section of a belt chamber accommodating the primary sheave, the secondary sheave, and the resin block belt, wherein the transmission case includes: an air passage connecting the inside and the outside of the belt chamber; and a sound absorbing member attached to the inner wall of the air passage in such a position as to collide with sound wave traveling from the inside of the belt chamber toward the outside. 2. A belt-type continuously variable transmission comprising: a primary sheave; a secondary sheave; a resin block belt wound around the primary sheave and the secondary sheave; and a transmission case which defines the section of a belt 35 chamber accommodating the primary sheave, the secondary sheave, and the resin block belt, wherein: the transmission case includes: an air passage communicating with the belt chamber; and a sound absorbing member attached to the inner wall of the air passage; and the sound absorbing member has a sound absorbing surface crossing an extending direction of a portion of the air passage close to the belt chamber and away from the sound absorbing member. 3. The belt-type continuously variable transmission as claimed in claim 1 or 2, wherein the air passage is an exhaust passage. 4. The belt-type continuously variable transmission as claimed in claim 3, wherein the transmission case further includes: an intake passage communicating with the belt chamber; and an air filter disposed in the intake passage to transmit air passing through the intake passage. 36 5. The belt-type continuously variable transmission as claimed in claim 1 or 2, wherein the air passage has at least a bended portion or curved portion. 6. The belt-type continuously variable transmission as claimed in claim 5, wherein the sound absorbing member is disposed on the inner wall of the bended portion or the curved portion. 7. The belt-type continuously variable transmission as claimed in claim 1 or 2, further comprising: an engine; and a crank case accommodating the engine, wherein: the transmission case is attached to the side surface of the crank case in such a position as to define the section of the air passage between the transmission case and the crank case; and the transmission case has a communication opening through which the belt chamber and the air passage can communicate with each other. 8. The belt-type continuously variable transmission as claimed in claim 7, wherein: the transmission case further includes: 37 an outside case; and an inside case disposed at a position shifted toward the crank case from the outside case such that the section of the belt chamber is defined by the inside case and the outside case and such that the section of the air passage is defined by the inside case and the crank case; and one or plural linear convexes extending in the extending direction of the air passage and projecting toward the inside case are provided on the crank case within the air passage. 9. The belt-type continuously variable transmission as claimed in claim 8, wherein the one or plural linear convexes contact the inside case. 10. The belt-type continuously variable transmission as claimed in claim 7, wherein the transmission case has a. lower expanding portion disposed below the opening of the air passage and expanding to a position outside the air passage in the front view. 11. The belt-type continuously variable transmission as claimed in claim 7, wherein: the air passage is positioned behind the center of the primary sheave; and the crank case has a front expanding portion which is 38 disposed before the air passage, expands to a position below the opening of the air passage, and expands to a position outside the air passage in the front view. 39 12. A motorcycle including the belt-type continuously variable transmission as claimed in claim 1 or 2. 13. The motorcycle as claimed in claim 12, wherein the center of the secondary sheave is positioned above the center of the primary sheave. A belt-type continuously variable transmission includes a primary sheave, a secondary sheave, a resin block belt, and a transmission case. The resin block belt is wound around the primary sheave and the secondary sheave. The transmission case defines the section of a belt chamber accommodating the primary sheave, the secondary sheave, and the resin block belt. The transmission case includes an exhaust passage, intake passages, and a sound absorbing member. The sound absorbing member is attached to the inner wall of the exhaust passage in such a position as to collide with sound wave traveling through the exhaust passage. The sound absorbing member has a sound absorbing surface crossing an extending direction of the exhaust passage.

Full Text

BELT-TYPE CONTINUOUSLY VARIABLE TRANSMISSION HAVING RESIN
BLOCK BELT AND MOTORCYCLE INCLUDING BELT-TYPE CONTINUOUSLY
VARIABLE TRANSMISSION
This application claims priority from Japanese Patent
Application No. 2007-016491 filed on January 26, 2007.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a belt-type
continuously variable transmission having a resin block belt,
and a motorcycle including this belt-type continuously
variable transmission.
2. Description of the Related Art
For example, JP-A-2002-147582 discloses a motorcycle
which includes a belt-type continuously variable transmission
having a resin block belt, and others. The resin block belt
has higher durability than that of a related rubber belt, and
therefore a belt-type continuously variable transmission
which uses the resin block belt has higher durability as well.
The resin block belt is formed by combining a plurality
of resin blocks having higher hardness than that of rubber.
Thus, the sound generated by collision between the resin block
belt and a primary sheave or a secondary sheave is larger than
the sound generated by collision between the rubber belt and
1

the primary or secondary sheave in related art. Thus, noise
generated from a belt-type continuously variable transmission
using the resin block belt is larger than noise generated from
a related-art belt-type continuously variable transmission
using the rubber belt.
For reducing the noise generated by the resin block belt,
such a structure is considered which includes a sound absorbing
material disposed inside and outside a transmission case as
in the structure of the belt-type continuously variable
transmission shown in JP-A-2002-147582, for example. However,
even when the sound absorbing material is provided inside and
outside the transmission case, it is difficult to sufficiently
prevent escape of noise generated by the resin block belt to
the outside.
SUMMARY OF THE INVENTION
The invention has been developed to solve the problems
described above. It is an object of the invention to provide
a technology which sufficiently prevents escape of noise
generated by a resin block belt to the outside.
A belt-type continuously variable transmission
according to a first aspect of the invention includes a primary
sheave, a secondary sheave, a resin block belt, and a
transmission case. The resin block belt is wound around the
primary sheave and the secondary sheave. The transmission
2

case defines the section of a belt chamber accommodating the
primary sheave, the secondary sheave, and the resin block belt.
The transmission case includes an air passage connecting the
inside and the outside of the belt chamber, and a sound
absorbing member. The sound absorbing member is attached to
the inner wall of the air passage. The sound absorbing member
is disposed in such a position as to collide with sound wave
traveling from the inside of the belt chamber toward the
outside.
A belt-type continuously variable transmission
according to a second aspect of the invention includes a primary
sheave, a secondary sheave, and a resin block belt, and a
transmission case. The resin block belt is wound around the
primary sheave and the secondary sheave. The transmission
case defines the section of a belt chamber accommodating the
primary sheave, the secondary sheave, and the resin block belt.
The transmission case includes an air passage communicating
with the belt chamber, and a sound absorbing member. The sound
absorbing member is attached to the inner wall of the air
passage. The sound absorbing member has a sound absorbing
surface crossing the extending direction of a portion of the
air passage close to the belt chamber and away from the sound
absorbing member.
The technology provided according to the invention can
sufficiently prevent escape of noise generated by a resin block
3

belt to the outside.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a right side view of a motorcycle according
an embodiment of the invention;
Fig. 2 is a right side view of a central portion of the
motorcycle according to the embodiment of the invention;
Fig. 3 is a cross-sectional view of an engine unit;
Fig. 4 (a) is a cross-sectional view of a resin block belt,
and Fig. 4(b) is a side view of the resin block belt;
Fig. 5 is a right side view of a second case block;
Fig. 6 is a right side view of the second case block to
which a clutch cover is attached;
Fig. 7 is a right side view of the second case block to
which the clutch cover and an inside case are attached;
Fig. 8 is a perspective view of the second case block
to which the clutch cover, the inside case, and an outside case
are attached as viewed from below inclined to the front;
Fig. 9 is a right side view of the second case block to
which the clutch cover, the inside case, and the outside case
are attached;
Fig. 10 is a cross-sectional view taken along a line X-X
in Fig. 9;
Fig. 11 is a cross-sectional view taken along a line XI-XI
in Fig. 10;
4

Figs 12(a) and 12(b) are development elevations showing
two divided portions of an air chamber;
Fig. 13 is a cross-sectional view taken along a line
XIII-XIII in Fig, 12;
Fig. 14 schematically illustrates a position of a sound
absorbing member according to a modified example 1;
Fig. 15 schematically illustrates positions of the sound
absorbing members according to a modified example 2;
Fig. 16 schematically illustrates a position of the sound
absorbing member according to a modified example 3; and
Fig. 17 schematically illustrates positions of the sound
absorbing members according to a modified example 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present inventors found that the main component of
noise generated from a belt-type continuously variable
transmission having a resin block belt is a pitch noise produced
by sequential shifts of plural resin blocks. In addition, they
found that the pitch noise is so-called high-frequency sound.
Furthermore, they directed their attention to the fact that
high-frequency sound generally has such characteristics as
high rectilinear propagation and low penetrability. Based on
these findings, the inventors have developed the invention
described herein.
When an air passage communicating with a belt chamber
5

extends in a straight direction, the high-frequency sound
having high rectilinear propagation escapes chiefly through
the air passage to the outside. Considering this fact, a sound
absorbing material is attached to the inner wall of the air
passage connecting the inside and the outside of the belt
chamber in such a position that sound wave traveling through
the air passage can collide with the sound absorbing material
according to this embodiment. This arrangement of the sound
absorbing material effectively prevents escape of the
high-frequency sound generated by the resin block belt from
the belt chamber.
According to this embodiment, at least a bended portion
is formed on the air passage for effectively preventing the
escape of the high-frequency sound. More specifically, a
plurality of bended portions are formed on an exhaust passage,
and the sound absorbing materials are provided on the bended-
portions .
Additional sound absorbing materials may be affixed to
the inside and outside of a transmission case for further
reducing escape of noise to the outside. However, since the
noise generated by the resin block belt can be effectively
prevented by disposing the sound absorbing material within the
air passage in such a position that the main flow of air
traveling through the air passage collides with the sound
absorbing material as discussed above due to the
6

characteristics of high-frequency sound as high rectilinear
propagation and comparatively low penetrability through an
object, relatively high sound prevention effect can be obtained
even when the sound absorbing materials are not affixed to the
inside and outside of the transmission case. That is, the sound
from the belt chamber can be effectively prevented and the size
reduction of the belt-type continuously variable transmission
can be achieved by attaching the sound absorbing material to
the inside wall of the air passage such that the main flow of
air passing through the air passage collides with the sound
material and by eliminating the sound absorbing materials
affixed to the inside and outside of the transmission case.
Moreover, the cooling effect inside the transmission case can
be enhanced by eliminating the sound absorbing materials
affixed to the area having thermal insulation effect and the
inside and outside of the transmission case. As a result, the
life of the belt-type continuously variable transmission can
be prolonged.
A motorcycle 1 according to this embodiment is
hereinafter described in detail with reference to Figs. 1
through 13. In this embodiment, the off-road-type motorcycle
1 shown in Fig. 1 is discussed as an example of a straddle-type
vehicle according to the invention. However, the
straddle-type vehicle of the invention is not limited to this
type, but may be a motorcycle of types other than the off-road
7

type. More specifically, examples of the straddle-type
vehicle according to the invention include motorcycle type,
motor-scooter type, so-called moped type, and other types of
motorcycle. The invention is also applicable to a
straddle-type vehicle other than a motorcycle. For example,
the straddle-type vehicle according to the invention may be
an all terrain vehicle (ATV).
«General Structure of Motorcycle 1»
Fig. 1 is a side view of the motorcycle 1 according to
this embodiment. Initially, the general structure of the
motorcycle 1 is explained with reference to Fig. 1. In the
following description, the front-rear and left-right
directions refer to the front-rear and left-right directions
as viewed from a rider sitting on a seat 3.
The motorcycle 1 has a body frame 2, a body cover 14,
and the seat 3.. The body cover 14 is attached in such a manner
as to cover a part of the body frame 2. The seat 3 is attached
to the body cover 14.
The body frame 2 has a steering head pipe 4, a down tube
5, and a main pipe 6. The down tube 5 is extended downward
from the steering head pipe 4, bended at an intermediate portion,
and further extended substantially in the horizontal direction
from the intermediate portion. The main pipe 6 positioned
above the down tube 5 extends toward the rear from the steering
head pipe 4.
8

A pivot shaft 10 is attached to the lower end of the main
pipe 6. A rear arm 9 extending toward the rear is attached
to the pivot shaft 10 such that the rear arm 9 can swing. A
rear wheel 13 is rotatably attached to the rear end of the rear
arm 9. The lower end of the steering head pipe 4 is connected
with a front fork 11. A front wheel 12 is rotatably attached
to the lower end of the front fork 11.
As illustrated in Fig. 2, a pair of seat rails 7 extending
toward the rear are provided at an intermediate portion of the
main pipe 6 . A back stay 8 is connected with a position slightly
shifted toward the rear from the centers of the respective seat
rails 7. The back stay 8 extends diagonally downward toward
the front from the connecting portion with the seat rails 7.
The distal end of the back stay 8 is connected with the lower
end of the main pipe 6.
As illustrated in Figs. 1 and 2, an engine unit.15 is
disposed between the down tube 5 and the main pipe 6 and attached
to both. As illustrated in Fig. 3, the engine unit 15 is formed
by combining an engine 16, a belt-type continuously variable
transmission 17, and other components into one piece. The
driving force generated by the engine unit 15 is transmitted
to the rear wheel 13 via not-shown power transmitting means
such as chain belt. In the following description, the
belt-type continuously variable transmission 17 is
abbreviated as CVT 17.
9

«Structure of Engine Unit 15»
Fig. 3 shows the cross section of the engine unit 15.
As illustrated in Fig. 3, the engine unit 15 has the engine
16, the CVT 17, a centrifugal clutch 18, and a speed reduction
mechanism 19. While the engine 16 is a four-stroke
single-cylinder engine in this example, the engine 16 may be
a two-stroke engine or multi-stroke engine, for example.
The engine 16 has a crank case 80, a cylinder 21, and
a cylinder head 22. The cylinder 21 is attached to the crank
case 80. The cylinder head 22 is attached to the distal end
of the cylinder 21.
A piston 25 is inserted into the cylinder 21 such that
the piston 25 can slide therein. One end of a connecting rod
26 is connected with the piston 25. The other end of the
connecting rod 26 is connected with a crank pin 28. The crank
pin 28 is inserted into through holes formed on a left crank
arm 27a and a right crank arm 27b, and fixed to the through
holes.
The cylinder head 22 has a concave 22a communicating with
the inside space of the cylinder 21, and intake port and exhaust
port (not shown) communicating with the concave 22a. The
concave 22a constitutes a part of a combustion chamber. An
ignition plug 29 is attached to the cylinder head 22 such that
the ignition area of the ignition plug 29 can be exposed to
the outside.
10

As illustrated in Figs. 1 and 2, an intake pipe 40 is
connected with the intake port. As illustrated in Fig. 2, the
intake pipe 40 extends toward the rear from the cylinder head
22. An air chamber 43 is connected with the rear end of the
intake pipe 40. The air chamber 43 has an intake hole 43a.
Outside air is taken through the intake hole 43a into the air
chamber 43. The outside air taken into the air chamber is
supplied to the combustion chamber via the intake pipe 40 and
the intake port.
As illustrated in Figs. 1 and 2, an exhaust pipe 41 is
connected with the exhaust port. As illustrated in Fig. 2,
the exhaust pipe 41 is connected with the front region of the
cylinder head 22. The exhaust pipe 41 extends toward the front
from the cylinder head 22, crosses over the down tube 5, extends
downward before the engine unit 15, and then extends below the
engine unit 15 toward the rear. A muffler 42 is connected with,
the rear end of the exhaust pipe 41.
As illustrated in Fig. 3, a cam chain chamber 31
connecting the interior of the crank case 80 and the interior
of the cylinder head 22 is provided in the left part inside
the cylinder 21. A timing chain 32 is accommodated in the cam
chain chamber 31. The timing chain 32 is wound around a crank
shaft 23 and a cam shaft 33. Thus, the cam shaft 33 rotates
in accordance with the rotation of the crank shaft 23. The
rotation of the cam shaft 33 opens and closes not-shown intake
11

valve and exhaust valve.
The crank case 90 has a first case block 81 disposed on
the left side, a second case block 82 disposed on the right
side, and a clutch cover 83. The first case block 81 and the
second case block 82 face each other in the vehicle width
direction. A concave 82a extending to the left is formed in
the rear half of the second case block 82. The clutch cover
83 closes the concave 82a. A space defined by the concave 82a
and the clutch cover 83 constitutes a clutch chamber containing
the centrifugal clutch 18.
The crank shaft 23 is accommodated in the crank case 80.
The crank shaft 23 horizontally extends in the vehicle width
direction. The crank shaft 23 is supported by the first case
block 81 via a bearing 24a. The crank shaft 23 is also supported
by the second case block 82 via a bearing 24b.
A dynamo case 35 Is attached to the left side of the front-
half of the first case block 81. A dynamo chamber is defined
by the dynamo case 35 and the first case block 81. A dynamo
34 is accommodated in the dynamo chamber. The dynamo 34 is
attached to the crank shaft 23 within the dynamo chamber. The
dynamo 34 has a stator 34a and a rotor 34b. The rotor 34b is
fixed to a sleeve 39 rotating with the crank shaft 23. The
stator 34a is fixed to the dynamo case 35. This structure
allows the rotor 34b to rotate relative to the stator 34a in
accordance with the rotation of the crank shaft 23 for power
12

generation.
A transmission case 61 containing the CVT 17 is attached
to the right side of the second case block 82 . The transmission
case 61 defines the section of a belt chamber 38 accommodating
the CVT 17. The transmission case 61 has an inside case 62
made of resin and disposed on the right side of the second case
block 82, and an outside case 63 positioned on the right side
of the inside case 62.
The CVT 17 has a primary sheave 51 and a secondary sheave
52. The primary sheave 51 is attached to the crank shaft 23.
More specifically, the right end of the crank shaft 23
penetrates through the second case block 82 and the inside case
62, and reaches the belt chamber 38. The primary sheave 51
is attached to the right end of the crank shaft 23. In the
following description, the right portion of the crank shaft
23 is also referred to as a "primary sheave shaft 23a". More
accurately, the primary sheave shaft 23a is constituted by the
portion of the crank shaft 23 positioned on the right side of
the bearing 24b.
More specifically, the primary sheave 51 has a primary
fixed sheave member 51a and a primary movable sheave member
51b. The primary fixed sheave member 51a is fixed to the right
end of the primary sheave shaft 23a . The primary movable sheave
member 51b positioned on the left side of the primary fixed
sheave member 51a is attached to the primary sheave shaft 23a.
13

The primary movable sheave member 51b can shift relative to
the primary sheave shaft 23a in its axial direction.
The left side surface of the primary fixed sheave member
51a has a tapered shape expanding to the right. The right side
surface of the primary movable sheave member 51b has a tapered
shape expanding to the left. These left side surface of the
primary fixed sheave member 51a and right side surface of the
primary movable sheave member 51b form a substantially V-shaped
belt groove 51c which has a width increasing toward the outside
in the radial direction. A plurality of fan vanes 60 are
provided on the right side surface of the primary fixed sheave
member 51a.
A cam surface 56 is disposed on the left side surface
of the primary movable sheave member 51b. A cam plate 57 is
located on the left side of the primary movable sheave member
51b in such a. position as to be opposed to the cam surface 56.
The cam plate 57 is fixed to the primary sheave shaft 23a. The
cam plate 57 engages with the primary movable sheave member
51b. This engagement prevents rotation of the primary movable
sheave member 51b relative to the primary sheave shaft 23a.
Roller weights 58 movable in the radially inside-outside
direction are disposed between the cam surface 56 and the cam
plate 57.
The secondary sheave 52 is positioned behind the primary
sheave 51. The secondary sheave 52 is attached to a secondary
14

sheave shaft 53. The secondary sheave 52 has a secondary fixed
sheave member 52a and a secondary movable sheave member 52b.
The secondary fixed sheave member 52a is fixed to the secondary
sheave shaft 53. The secondary movable sheave member 52b
positioned on the right side of the secondary fixed sheave
member 52a is attached to the secondary sheave shaft 53. The
secondary movable sheave member 52b can shift in the axial
direction of the secondary sheave shaft 53.
The right side surface of the secondary fixed sheave
member 52a has a tapered shape expanding to the left. The left
side surface of the secondary movable sheave member 52b has
a tapered shape expanding to the right. These right side
surface of the secondary fixed sheave member 52a and left side
surface of the secondary movable sheave member 52b form a
substantially V-shaped belt groove 52c having a width
increasing toward the outside in the radial direction.
A compression coil spring 59 is provided on the right
side of the secondary movable sheave member 52b. The secondary
movable sheave member 52b is urged to the left by the
compression coil spring 59. Thus, the secondary movable
sheave member 52b is urged toward the secondary fixed sheave
member 52a by the compressing coil spring 59.
A resin block belt 55 is wound around the belt groove
51c of the primary sheave 51 and the belt groove 52c of the
secondary sheave 52. The resin block belt 55 is a so-called
15

resin block belt having a substantially V-shaped cross section.
More specifically, the resin block belt 55 has a plurality of
resin blocks 55a as illustrated in Fig. 4 (a) . The plural resin
blocks 55a are arranged in a ring-band shape, and are connected
with one another by a pair of flexible connecting members 55b.
More specifically, each of the resin blocks 55a has a pair of
concaves 55c opposed to each other. The plural resin blocks
55a are connected with one another by fitting the connecting
members 55b into the concaves 55c.
As illustrated in Fig. 3, the secondary sheave shaft 53
penetrates through the inside case 62 and the clutch cover 83
and reaches a clutch chamber. The centrifugal clutch 18 is
attached to the secondary sheave shaft 53 in the clutch chamber.
The centrifugal clutch 18 may be a wet-type multi-disc clutch
as illustrated in Fig. 3, for example.
The centrifugal clutch 18 engages with the speed
reduction mechanism 19. The rotation of the secondary sheave
shaft 53 is transmitted to the speed reduction mechanism 19
via the centrifugal clutch 18. Then, the torque thus generated
is transmitted from an output shaft (not shown) of the speed
reduction mechanism 19 to the rear wheel 13 shown in Fig. 1
via the power transmitting means (not shown).
«Air Intake and Exhaust to and from Belt Chamber 38»
The air intake and exhaust to and from the belt chamber
38 are now explained in detail with reference to Fig. 5 and
16

other figures. Fig. 5 is a right side view of the second case
block 82. Fig. 6 is a right side view of the second case block
82 to which the clutch cover 83 is attached. Fig. 7 is a right
side view of the second case block 82 to which the clutch cover
83 and the inside case 62 are attached. Fig. 8 is a perspective
view of the second case block 82 to which the clutch cover 83,
and the inside and outside cases 62 and 63 are attached as viewed
from below inclined to the front. Fig. 9 is a right side view
of the second case block 82 to which the clutch cover 83 and
the inside and outside cases 62 and 63 are attached. Fig. 10
is a cross-sectional view taken along a line X-X in Fig. 9.
Fig. 11 is a cross-sectional view taken along a line XI-XI in
Fig. 10. Fig. 10 shows only the second case block 82, the clutch
cover 83, and the transmission case 61 for simplifying the
explanation.
-Detailed Structures of Second Case Block 82, Transmission Case
61 and Others-
As illustrated in Fig. 5, an opening 82e through which
the primary sheave shaft 23a is inserted is formed in the front
half of the second case block 82. A concave 82a containing
the clutch chamber is formed in the rear half of the second
case block 82. As illustrated in Figs. 3 and 6, the concave
82a is closed by the clutch cover 83. An opening 83a through
which the secondary sheave shaft 53 is inserted is formed at
the center of the clutch cover 83.
17

A plurality of linear convexes (ribs) 82b are formed
below the concave 82a. The plural convexes 82b are arranged
in a line substantially in the horizontal direction. More
accurately, the plural linear convexes 82b are positioned in
a line in a direction slightly diagonally upward toward the
rear. The respective linear convexes 82b extend in the up-down
direction, and project further to the right from the right side
surface of the second case block 82. That is, the respective
linear convexes 82b project toward the inside case 62 from the
right side surface of the second case block 82. As illustrated
in Fig. 11, the plural linear convexes 82b contact the inside
case 62. This structure allows the inside case 62 having
relatively low strength to be appropriately supported.
As can be seen from the cross section shown in Fig. 11,
a concaved portion having an arch shape is formed between each
of the contact portions of the inside case 62 contacting the
linear convexes 82b.
An expanding portion 82c is formed immediately below the
plural linear convexes 82b of the second case block 82. The
expanding portion 82c extends to a position on the right side
of the right end of the linear convexes 82b. In other words,
the expanding portion 82c expands to the outside of the right
end of the linear convexes 82b. The expanding portion 82c
extends in a wider range than the area where the plural linear
convexes 82b are formed in the front-rear direction.
18

As illustrated in Figs. 3 and 7, the inside case 62 is
disposed on the right side of the second case block 82. The
inside case 62 covers substantially the entire part of the right
region of the second case block 82 except for the openings 82e
and 83a, the expanding portion 82c, and the lower region of
the area where the plural linear convexes 82b are formed. As
illustrated in Fig. 10, a space is produced between the inside
case 62 and the second case block 82. A plurality of
communication openings 62a through which this space
communicates with the belt chamber 38 are formed in the upper
region of the inside case 62 (see Fig. 3 as well) . This
structure allows the belt chamber 38 to communicate with the
outside air via the communication openings 62a and the space
between the inside case 62 and the second case block 82.
According to this embodiment, the space between the inside case
62 and the second case block 82 constitutes an exhaust passage
65. As illustrated in Fig. 10, the exhaust passage 65 is bended
to the right by the expanding portion 82c to form a labyrinth
structure. That is, the exhaust passage 65 has a plurality
of bended portions 65b. While the exhaust passage 65 has the
plural bended portions 65b in this embodiment, the exhaust
passage 65 may have one or plural curved portions.
Alternatively, the exhaust passage 65 may have one or plural
curved portions as well as one or plural bended portions.
As illustrated in Fig. 10, the outside case 63 is
19

positioned on the right side of the inside case 62. The belt
chamber 38 is defined by the outside case 63 and the inside
case 62.
An extension 63a extending downward to a position lower
than the lower end of the inside case 62 is provided on the
lower rear portion of the outside case 63. The extension 63a
and the second case block 82 are positioned away from each other.
The extension 63a extends to a position opposed to the expanding
portion 82c in the up-down direction. In other words, the
extension 63a has a portion opposed to the linear convexes 82b
in the vehicle width direction and a portion opposed to the
expanding portion 82c provided below the linear convexes 82b.
The exhaust passage 65 is bended downward by the
extension 63a at a position downstream from the bended portion
65b. Thus, the exhaust passage 65 has a bended portion 65c
positioned.downstream from the bended portion. 65b. The bended
portion 65c may be a curved portion.
A sound absorbing member 36 is attached to the inside
surface (left surface) of the extension 63a. That is, the sound
absorbing member 36 is attached to the left side surface of
the extension 63a. The sound absorbing member 36 has a sound
absorbing surface 36a crossing the projecting direction of the
linear convexes 82b. More specifically, the sound absorbing
member 36 as a face material is disposed in such a position
as to cross the projection direction of the linear convexes
20

82b. The angle formed by the sound absorbing face 36a and the
projecting direction of the linear convexes 82b may be a right
angle. Alternatively, the angle formed by the sound absorbing
surface 36a and the projecting direction of the linear convexes
82b may be an acute angle or an obtuse angle.
For obtaining high sound absorbing efficiency, it is
preferable that the sound absorbing member 36 has a number of
spaces inside its body. For example, the sound absorbing
member 36 may be made of foamed material, glass wool, or steel
wool. Examples of the foamed material include foamed resin
such as foamed urethane, foamed rubber, and other materials.
As illustrated in Figs. 8 and 9, an expanding portion
63b is formed before the extension 63a of the outside case 63.
The expanding portion 63b is expanded to a position lower than
the upper end of the expanding portion 82c in the up-down
direction. The expanding portion 63b covers the .space between
the extension 63a and the second case block 82 in the front
view.
As illustrated in Fig. 3, an intake opening 78 is formed
on the upper surface of the outside case 63. An intake duct
71 is connected with the intake opening 78 (see Figs. 1, 2 and
8 as well) . As illustrated in Figs. 1 and 2, the intake duct
71 extends upward from the transmission case 61, and then
extends in the horizontal direction toward the rear from the
intermediate portion of the intake duct 71. An air chamber
21

94 is connected with the rear side end of the intake duct 71.
The air chamber 94 has a function of purifying the outside air
introduced thereto. More specifically, the air chamber 94 has
a function of removing dust contained in the outside air thus
taken.
Figs. 12(a) and 12 (b) are development elevations showing
two divided parts of the air chamber 94. Fig. 13 is a
cross-sectional view of the air chamber 94. As illustrated
in Figs. 12, the air chamber 94 has a first casing 95 and a
second casing 96 combined in such a manner as to be opposed
to each other.
As illustrated in Fig. 12(b), walls 95b and 95c are
provided inside the first casing 95. These walls 95b and 95c
define a first intake passage 98 extending in a zigzag line.
As illustrated in Fig. 12(a), walls 96a, 96b and 96c are
provided inside the second casing 96. The wall 96a divides
the interior of the second casing 96 into two areas. The second
casing 96 has an intake opening 94a open to an upper inside
area 100 within the second casing 96. The inside area 100
communicates with a base end 98a of the first intake passage
98 of the first casing 95 (see Fig. 12(b)).
The walls 96b and 96c are provided in the lower inside
area of the second casing 96. These walls 96b and 96c define
a second intake passage 99 extending in a zigzag line within
the lower inside area of the second casing 96. As illustrated
22

in Fig. 13, the second intake passage 99 and the first intake
passage 98 face each other with an air cleaner 97 interposed
therebetween.
The wall 96b has a shape corresponding to that of the
wall 95b. The wall 96c has a shape corresponding to the shape
of the wall 95c. Thus, the first intake passage 98 and the
second intake passage 99 have mirror images of each other.
-Intake and Exhaust Operations to and from Belt Chamber 38-
As discussed above, the plural vanes 60 are provided on
the left side surface of the primary fixed sheave member 51a
disposed within the belt chamber 38 (see Fig. 3) . The plural
vanes 60 rotate with the rotation of the primary sheave shaft
23a. That is, the plural vanes 60 rotate with the rotation
of the crank shaft 23. As a result, absorbing force toward
the belt chamber 38 is generated, and the outside air taken
from the air chamber 94 is taken into the belt chamber .38. by
the rotation of the plural vanes 60.
More specifically, the outside air is initially taken
from the intake opening 94a into the air chamber 94. The
outside air taken from the intake opening 94a is introduced
to the base end 98a of the first intake passage 98 via the inside
area 100 (see Figs. 12 and Fig. 13). The air introduced to
the base end 98a flows from the base end 98a to a distal end
98b, and a part of this air passes through the air cleaner 97
and flows into the second intake passage 99. The air having
23

flowed into the second intake passage 99 is supplied to the
intake duct 71 via an opening 101 formed at the distal end of
the second intake passage 99 (see Figs. 1 and 2).
The air supplied to the intake duct 71 is supplied to
the front half of the belt chamber 38 (see chiefly Figs. 3 and
10) . That is, the air supplied to the intake duct 71 is further
supplied to the area where the primary sheave 51 is disposed.
The CVT 17 is cooled by the outside air thus taken. The air
supplied to the belt chamber 38 flows within the belt chamber
38, passes through the exhaust passage 65 formed between the
inside case 62 and the second case block 82, and then is
discharged through the communication openings 62a.
The discharge air initially advances downward in the
exhaust passage 65 (see Fig. 10). Then, the flow direction
of the discharge air is changed by the bended portion 65b. That
is, the air flowing downward is changed to the air flowing to
the right by collision with a wall 82f. Then, the discharge
air collides with the sound absorbing surface 36a of the sound
absorbing member 36 at the bended portion 65c, where the flow
direction is further changed to the downward direction.
Thereafter, the air is discharged through an exhaust opening
65a.
As discussed above, the sound absorbing member 36 is
attached to the inner wall of the discharge passage 65 in such
a position as to collide with the air passing through the
24

discharge passage 65. More specifically, the sound absorbing
member 36 is attached to the inside wall of the extension 63a
constituting the bended portion 65c.
The sound absorbing member 36 has the sound absorbing
surface 36a. The sound absorbing surface 36a crosses the
extending direction of a portion of the exhaust passage 65 close
to the belt chamber 38 and away from the sound absorbing member
36. In other words, the sound absorbing surface 36a is not
disposed in parallel with the extending direction of the
portion of the exhaust passage 65 close to the belt chamber
38 and away from the sound absorbing member 36. More
specifically, the sound absorbing surface 36a may be disposed
orthogonal to the extending direction of the portion of the
exhaust passage 65 close to the belt chamber 38 and away from
the sound absorbing member 36. Alternatively, the angle
formed by the sound- absorbing surface 36a and the extending
direction of the portion of the exhaust passage 65 close to
the belt chamber 38 and away from the sound absorbing member
36 may be an acute angle or an obtuse angle. According to this
embodiment, the area of the exhaust passage 65 close to the
belt chamber 38 and away from the sound absorbing member 36
is specifically the area between the bended portion 65b and
the bended portion 65c.
The plural linear convexes 82b extend along the extending
direction of the exhaust passage 65.
25

«Operation and Advantage»
As discussed above, the sound absorbing member 36 has
the sound absorbing surface 36a inclined at an angle to the
projecting direction of the linear convexes 82b. In other
words, as illustrated in Fig. 10, the sound absorbing member
36 has the sound absorbing surface 36a which crosses an
extending direction Al of the portion of the exhaust passage
65 close to the belt chamber 38 upstream from the sound
absorbing member 36, i.e. the area disposed between the bended
portion 65b and the bended portion 65c. The sound member 36
is located in such a position as to collide with the sound wave
traveling from the inside of the belt chamber 38 toward the
outside. Concerning the relationship between the flow of
exhaust air and the sound absorbing member 36, the sound
absorbing member 36 is disposed in such a position as to collide
with the air flowing through the exhaust passage 65.
Thus, the sound absorbing member 36 effectively absorbs
high-frequency sound having high rectilinear propagation
generated by the resin block belt 55. As a result, escape of
the high-frequency sound generated by the resin block belt 55
from the exhaust passage 65 can be effectively prevented.
Moreover, the high-frequency sound having low penetrability
through an object does not easily penetrate through the outside
case 63 or other components to escape therefrom. Thus, escape
of noise generated by the resin block belt 55 to the outside
26

can be effectively prevented.
These advantages can be obtained as long as the sound
absorbing member 36 is disposed in such a position as to collide
with the sound wave traveling from the inside of the belt
chamber 38 toward the outside. Thus, it is not necessarily
required that the sound absorbing surface 36a is disposed
orthogonal to the traveling direction of the sound wave
traveling from the inside of the belt chamber 38 toward the
outside. More specifically, it is not necessarily required
that the sound absorbing surface 36a is disposed orthogonal
to the extending direction of the portion of the exhaust passage
65 close to the belt chamber 38 and away from the sound absorbing
member 36. For example, even when the angle formed by the sound
absorbing surface 36a and the traveling direction of the sound
traveling from the inside of the belt chamber 38 toward the
outside is an acute angle or an obtuse angle, the above
advantages can be offered. In other words, even when the angle
formed by the sound absorbing surface 36a and the extending
direction of the portion of the exhaust passage 65 close to
the belt chamber 38 and away from the sound absorbing member
36 is an acute angle or an obtuse angle, the above advantages
can be offered.
For reducing the escape of noise generated by the resin
block belt 55 to the outside more effectively, it is preferable
that the sound absorbing member is provided on the inside or
27

outside Of the outside case 63. In this case, escape of the
high-frequency sound penetrating through the outside case 63
can be more securely prevented, However; as discussed above,
the high-frequency sound has low penetrability through an
object. Thus, the escape of the sound generated by the resin
block belt 55 to the outside can be effectively prevented even
when the sound absorbing member is not disposed on the inside
or outside of the outside case 63. Thus, the escape of the
sound generated by the resin block belt 55 to the outside can
be effectively prevented without requiring the sound absorbing
member on the inside or outside of the outside case 63 and
therefore without increasing the size of the CVT 17 and further
the size of the engine unit 15.
Moreover, since the necessity for providing the sound
absorbing member having thermal insulation on the inside or
outside of the outside case 63 is eliminated, relatively high
heat release efficiency through the outside case 63 can be
achieved. As a result, the cooling efficiency of the CVT 17
can be improved.
It is preferable that the sound absorbing member 36 is
disposed on the exhaust side as in this embodiment, since
high-frequency sound does not easily escape from the intake
side where the air filter 79 having the sound absorbing
capability as well is generally disposed. In addition, this
structure is preferable since noise in the belt chamber 38
28

escaping to the outside from the exhaust passage for
discharging the air is relatively larger than noise in the belt
chamber 38 escaping from the intake passage.
The sound absorbing member 36 may be disposed at a
position other than the extension 63a. It is preferable that
the sound absorbing member 36 is provided on the inner wall
of the exhaust passage 65 at the outside corner of the portion
where flow of the air to be discharged changes such as the bended
portion 65b and the bended portion 65c. For example, the sound
absorbing member 36 may be located on the wall 82f of the second
case block 82. Also, the sound absorbing member 36 may be
provided on both of the inner walls of the wall 82f and the
extension 63a. In this case, further higher noise proof effect
can be obtained.
According to this embodiment, the exhaust passage 65 has
a labyrinth structure in addition to the equipment of the sound
absorbing member 36. More specifically, the exhaust passage
65 has the plural bended portions 65b and 65c. Thus,
high-frequency sound having entered the exhaust passage 65
collides with the wall at the positions of the plural bended
portions 65b and 65c, and thereby decreases. More
specifically, the high-frequency sound having entered the
exhaust passage 65 collides with the wall 82f of the second
case block 82 and decreases. Thus, escape of sound generated
by the resin block belt 55 to the outside can be reduced further
29

effectively. This noise reduction effect can be obtained by
the collision between the high-frequency sound having entered
the exhaust passage 65 and the wall of the components of the
CVT 17. Thus, the noise reduction effect Can be similarly
obtained even when curved portions are provided instead of the
bended portions 65b and 65c as in this embodiment. For
acquiring further high noise reduction effect, it is
particularly preferable that the number of the bended portions
or curved portions to be formed is plural.
It is also preferable that each of the intake passages
98 and 99 covered by the air cleaner having sound absorbing
capability has a labyrinth structure as in this embodiment.
This structure further effectively prevents escape of
high-frequency sound from the intake passages 98 and 99.
As illustrated in Fig. 11, the inside case 62 made of
resin and having relatively low hardness is supported by the
linear convexes 82b in this embodiment. This structure
improves the durability of the inside case 62. As a method
for enhancing the durability of the inside case 62, it is also
considered to form a linear convex extending in the front-rear
direction along the contour of the inside case 62, for example.
In this case, a slit needs to be formed on the linear convex
so as to secure the space of the exhaust passage 65. In this
structure, however, it is difficult to secure a sufficiently
wide space of the exhaust passage 65. When the width of the
30

slit is enlarged to secure a sufficient space of the exhaust
passage 65, the durability of the linear convex lowers. As
a result, the durability of the inside case 62 lowers
accordingly. However, in the structure having the linear
convexes 82b which extend substantially in parallel with the
extending direction of the exhaust passage 65 as in this
embodiment, the durability of the inside case 62 increases
while securing a relatively large space of the exhaust passage
65.
According to this embodiment, each portion between the
contacting portions of the inside case 62 contacting the linear
convexes 82b is concaved in an arched shape. Thus, a further
wide space of the exhaust passage 65 can be secured.
The structure having the linear convexes 82b which extend
along the flow of exhaust air as in this embodiment offers
rectification effect, of exhaust air. This effect reduces the
noise of exhaust air. For further enhancing the rectification
effect of exhaust air, it is preferable that the arrangement
pitch of the linear convexes 82b is decreased. On the other
hand, for enlarging the opening area of the exhaust passage
65, it is preferable that the pitch of the linear convexes 82b
is increased. For widening the opening area of the exhaust
passage 65, only the single linear convex 82b may be formed.
According to this embodiment, the communication openings
62a through which the exhaust passage 65 and the belt chamber
31

38 communicate with each other are open in the upper region
of the belt chamber 38 as illustrated in Figs. 7, 9 and 10.
Thus, even when water or mud enters the exhaust passage 65
through the exhaust opening 65a, the water or mud does not
easily enter the belt chamber 38 . In addition, since the lower
portion of the exhaust opening 65a is covered by the extending
portion (lower extending portion) 82c, enter of splashed water
or mud through the exhaust opening 65a into the exhaust passage
65 can be effectively reduced. Moreover, since the exhaust
opening 65a is covered by the extending portion 63b and the
expanding portion 82d (front expanding portion) in the front
view, enter of water or mud splashed by the front wheel 12
through the exhaust opening 65a into the exhaust passage 65
can be particularly effectively prevented.
The center of the secondary sheave 52 is positioned above
the center of the primary sheave 51 from a lateral view. Thus,
the exhaust opening 65a is located at a relatively high position
from the ground level. Accordingly, enter of the splashed
water or mud into the exhaust passage 65 through the exhaust
opening 65a can be effectively prevented.
(Modified Examples 1 through 4)
In the above embodiment, the structure having the sound
absorbing member 36 attached to the extension 63a has been
discussed as an example. However, the attachment position of
the sound absorbing member 36 is not particularly limited as
32

long as the sound absorbing member 36 is disposed in such a
position as to collide with sound wave traveling from the belt
chamber 38 to the outside.
For example, as illustrated in Fig. 14, the sound
absorbing member 36 may be attached to the belt chamber 38 side
surface of a projecting portion 37 provided inside the exhaust
passage 65 having the plural bended portions.
As illustrated in Fig. 15, the sound absorbing member
36 may be provided on each belt chamber 38 side surface of the
plural projecting portions 37 disposed in staggered
arrangement within the exhaust passage 65 extending straight,
for example. In this case, it is preferable that the plural
sound absorbing members 36 are so disposed as to cover the flow
path of the exhaust passage 65 as viewed from an extending
direction A2 of a portion of the exhaust passage 65 close to
the belt chamber 38 and away from the region where the
projecting portions 37 are formed. According to this modified
example, the extending direction A2 of the portion of the
exhaust passage 65 close to the belt chamber 38 and away from
the region where the projecting portions 37 are formed
coincides with the extending direction of the exhaust passage
65.
As illustrated in Fig. 16, the sound absorbing member
36 may be attached to each inner wall of plural curved portions
provided on the exhaust passage 65 having the plural curved
33

portions and extending in a zigzag line, for example. In this
case, it is preferable that the sound absorbing member 36 has
a sound absorbing surface 36b extending substantially in the
vertical direction with respect to the extending direction of
the portion of the exhaust passage 65 close to the belt chamber
38 and away from the region where the sound absorbing member
36 is provided as shown in Fig. 16. In this case,
high-frequency sound having high rectilinear propagation can
be effectively absorbed by the absorbing surface 36b.
As illustrated in Fig. 17, the sound absorbing member
36 may be provided on each of plural bended portions formed
on the exhaust passage 65, for example. The plural sound
absorbing members 36 thus attached can effectively absorb sound
high-frequency sound.
The invention is applicable to a belt-type continuously
variable transmission and a motorcycle.
34

WE CLAIM:
1. A belt-type continuously variable transmission
comprising:
a primary sheave;
a secondary sheave;
a resin block belt wound around the primary sheave and
the secondary sheave; and
a transmission case which defines the section of a belt
chamber accommodating the primary sheave, the secondary sheave,
and the resin block belt,
wherein the transmission case includes:
an air passage connecting the inside and the
outside of the belt chamber; and
a sound absorbing member attached to the inner wall
of the air passage in such a position as to collide with sound
wave traveling from the inside of the belt chamber toward the
outside.
2. A belt-type continuously variable transmission
comprising:
a primary sheave;
a secondary sheave;
a resin block belt wound around the primary sheave and
the secondary sheave; and
a transmission case which defines the section of a belt
35

chamber accommodating the primary sheave, the secondary sheave,
and the resin block belt,
wherein:
the transmission case includes:
an air passage communicating with the belt
chamber; and
a sound absorbing member attached to the
inner wall of the air passage; and
the sound absorbing member has a sound absorbing
surface crossing an extending direction of a portion of the
air passage close to the belt chamber and away from the sound
absorbing member.
3. The belt-type continuously variable transmission
as claimed in claim 1 or 2, wherein the air passage is an exhaust
passage.
4. The belt-type continuously variable transmission
as claimed in claim 3, wherein the transmission case further
includes:
an intake passage communicating with the belt chamber;
and
an air filter disposed in the intake passage to transmit
air passing through the intake passage.
36

5. The belt-type continuously variable transmission
as claimed in claim 1 or 2, wherein the air passage has at least
a bended portion or curved portion.
6. The belt-type continuously variable transmission
as claimed in claim 5, wherein the sound absorbing member is
disposed on the inner wall of the bended portion or the curved
portion.
7. The belt-type continuously variable transmission
as claimed in claim 1 or 2, further comprising:
an engine; and
a crank case accommodating the engine,
wherein:
the transmission case is attached to the side
surface of the crank case in such a position as to define the
section of the air passage between the transmission case and
the crank case; and
the transmission case has a communication opening
through which the belt chamber and the air passage can
communicate with each other.
8. The belt-type continuously variable transmission
as claimed in claim 7, wherein:
the transmission case further includes:
37

an outside case; and
an inside case disposed at a position shifted
toward the crank case from the outside case such that the
section of the belt chamber is defined by the inside case and
the outside case and such that the section of the air passage
is defined by the inside case and the crank case; and
one or plural linear convexes extending in the extending
direction of the air passage and projecting toward the inside
case are provided on the crank case within the air passage.
9. The belt-type continuously variable transmission
as claimed in claim 8, wherein the one or plural linear convexes
contact the inside case.
10. The belt-type continuously variable transmission
as claimed in claim 7, wherein the transmission case has a. lower
expanding portion disposed below the opening of the air passage
and expanding to a position outside the air passage in the front
view.
11. The belt-type continuously variable transmission
as claimed in claim 7, wherein:
the air passage is positioned behind the center of the
primary sheave; and
the crank case has a front expanding portion which is
38

disposed before the air passage, expands to a position below
the opening of the air passage, and expands to a position
outside the air passage in the front view.
39
12. A motorcycle including the belt-type continuously
variable transmission as claimed in claim 1 or 2.
13. The motorcycle as claimed in claim 12, wherein the
center of the secondary sheave is positioned above the center
of the primary sheave.

A belt-type continuously variable transmission includes
a primary sheave, a secondary sheave, a resin block belt, and
a transmission case. The resin block belt is wound around the
primary sheave and the secondary sheave. The transmission
case defines the section of a belt chamber accommodating the
primary sheave, the secondary sheave, and the resin block belt.
The transmission case includes an exhaust passage, intake
passages, and a sound absorbing member. The sound absorbing
member is attached to the inner wall of the exhaust passage
in such a position as to collide with sound wave traveling
through the exhaust passage. The sound absorbing member has
a sound absorbing surface crossing an extending direction of
the exhaust passage.

Documents:

01743-kol-2007-abstract.pdf

01743-kol-2007-claims.pdf

01743-kol-2007-correspondence others.pdf

01743-kol-2007-description complete.pdf

01743-kol-2007-drawings.pdf

01743-kol-2007-form 1.pdf

01743-kol-2007-form 2.pdf

01743-kol-2007-form 3.pdf

01743-kol-2007-form 5.pdf

01743-kol-2007-gpa.pdf

1743-KOL-2007-(16-02-2012)-ABSTRACT.pdf

1743-KOL-2007-(16-02-2012)-AMANDED CLAIMS.pdf

1743-KOL-2007-(16-02-2012)-DESCRIPTION (COMPLETE).pdf

1743-KOL-2007-(16-02-2012)-DRAWINGS.pdf

1743-KOL-2007-(16-02-2012)-EXAMINATION REPORT REPLY RECEIVED.pdf

1743-KOL-2007-(16-02-2012)-FORM-1.pdf

1743-KOL-2007-(16-02-2012)-FORM-2.pdf

1743-KOL-2007-(16-02-2012)-FORM-3.pdf

1743-KOL-2007-(16-02-2012)-OTHERS.pdf

1743-KOL-2007-(16-02-2012)-PCT SEARCH REPORT.pdf

1743-KOL-2007-(16-02-2012)-PETITION UNDER RULE 137.pdf

1743-KOL-2007-AMANDED CLAIMS.pdf

1743-KOL-2007-CORRESPONDENCE 1.1.pdf

1743-KOL-2007-CORRESPONDENCE OTHERS 1.1.pdf

1743-KOL-2007-CORRESPONDENCE.pdf

1743-KOL-2007-FORM 13.pdf

1743-KOL-2007-OTHERS 1.1.pdf

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Patent Number

255404

Indian Patent Application Number

1743/KOL/2007

PG Journal Number

08/2013

Publication Date

22-Feb-2013

Grant Date

18-Feb-2013

Date of Filing

27-Dec-2007

Name of Patentee

YAMAHA HATSUDOKI KABUSHIKI KAISHA

Applicant Address

2500 SHINGAI, IWATA-SHI, SHIZUOKA-KEN

Inventors:

#	Inventor's Name	Inventor's Address
1	YOUSUKE ISHIDA	C/O. YAMAHA HATSUDOKI KABUSHIKI KAISHA 2500 SHINGAI, IWATA-SHI, SHIZUOKA 4388501

PCT International Classification Number

F16H7/02; B23P17/04; B62K11/04

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2007-016491	2007-01-26	Japan