Breather structure of internal combustion engine for vehicles

Abstract: The invention provides a breather structure of an internal combustion engine for vehicles which is of a simple construction having a short breather passage and capable of preventing entry of dust into, and attachment of dust on, the breather. In the breather structure of an internal combustion engine for vehicles, an outer cover (48) is installed through a sound absorbing material (49) for noise suppression on the outside of a body cover (46) which covers a power unit including at least one of the internal combustion engine and a power transmission device. An outlet of the breather (81) provided in the power unit is open at the sound absorbing material (49).

Description: This invention relates to a breather structure of an internal combustion engine for vehicles according to the preamble part of claim 1. A breather structure of the generic kind is known from document EP 1 138 591 A2 which forms prior art according to Art. 54 (3) EPC with regard to the present application. Further prior art is discussed in the following: As a breather structure of a crankcase or a transmission case of an internal combustion engine, there has been an example disclosed in for example Japanese Patent Laid-Open No. Sho 61-160665, which will be explained with reference to Fig. 11 showing a major portion thereof. The example relates to a unit-swing internal combustion engine, in which a transmission case 02 is located at the rear of a belt-drive case 01. In the upper part of the transmission case 02 is formed a breather chamber 03. A breather pipe 05 is longitudinally and horizontally inserted in a through hole in a partition wall 03a of the breather chamber 03 through a grommet 04. The breather pipe 05 whose one end is inserted in the breather chamber 03 is bent downward in the belt-drive case 01, extending vertically through the lower wall of the belt-drive case 01 via a grommet 06 and opening at its lower end out to the atmosphere. There also has been such an example that the breather cube is extended directly outside from the transmission case with the forward end of the tube inserted into an air cleaner box to release the air. The example described above, however, has such a drawback that since the open end of the breather pipe 05 is open to the atmosphere at the lower part of the vehicle, there is a fear of entrance of dusts and attachment of dust at the outlet depending on layout, impairing appearance. Furthermore, the breather pipe 05, having its open end on the underside of the vehicle, increases in length. In the latter example, when the air cleaner box is mounted on the vehicle body frame, the belt-drive case is likely to oscillate. Therefore, it becomes necessary to increase the length of the breather tube to absorb oscillation or to provide a special cleaner box for the belt-drive case. In view of the above-described drawback associated with the prior art, it is an object of this invention to provide a breather structure of simple construction of an internal combustion engine for vehicles which can prevent the entry of dusts into, and attachment of dusts on, a breather by using a short breather passage. To attain the above-described object, the breather structure of an internal combustion engine for vehicles according to this invention has an outer cover which is mounted, through a sound absorbing material for noise suppression, on the outside of a body cover covering a power unit including at least one of the internal combustion engine and the power transmission device. In the breather structure, the breather outlet provided in the power unit opens in the sound absorbing material. Since the breather outlet opens in the sound absorbing material interposed between the body cover covering the power unit and the outer cover located on the outside thereof, entry of dusts at the breather outlet and attachment of the dusts on the outlet can be prevented. Therefore no adverse effect will be given to the appearance. Because it is sufficient only to direct the breather outlet toward the sound absorbing material, the breather of a simple structure having a high degree of freedom of layout can be designed as short as possible. The breather structure of a preferred embodiment of this invention is a breather structure of an internal combustion engine for vehicles, which is mounted in the transmission case located on the driven pulley side of a belt-drive vehicle. In this breather structure, a breather pipe extends nearly upward from the breather chamber of the transmission case and then is bent, extending horizontally for a specific length as far as the pipe outlet. The upstream side of the breather pipe extends nearly upward from the transmission case. Therefore, the oil liquid that has entered the breather pipe easily returns to the transmission case, and the breather pipe is bent after extending nearly upward, then extending horizontally for a specific length as far as the pipe outlet. Thus there takes place gas-liquid separation in the horizontal portion, thereby enhancing a breather performance. Furthermore, since the breather pipe has a horizontal portion of a specific length, the oil will not be forced out by up-down oscillation of the transmission case mounted on the driven pulley side of the belt-drive vehicle. The unit-swing internal combustion engine is also provided with a transmission case on the driven pulley side of i belt-drive vehicle. A further preferred embodiment of the present invention is characterized in that, in the breather structure of the internal combustion engine for vehicles stated in claim 2, the pipe outlet of the breather pipe opens in the sound absorbing material for noise suppression interposed between the inside surface of the outer cover and the body cover. Since the outlet of the breather is open in the sound absorbing material interposed between the inside surface of the outer cover and the body cover, it is possible to prevent dusts from entering at, or holding on, the breather outlet. Therefore the appearance of the breather will never be adversely affected by the dusts. It is sufficient only to direct the breather outlet to the sound absorbing material, the breather of a simple structure having a high degree of freedom of layout can be designed as short as possible. A still further preferred embodiment of the present invention also provides a breather structure of an internal combustion engine for vehicles. In the advantageous breather structure of the transmission case mounted on the driven pulley side of the belt-drive vehicle, the belt-drive chamber is provided with an air-cooled structure. The sound absorbing material for noise suppression is interposed between the inside surface of the outer cover and the body cover. And the outlet of the breather extended from the transmission case is located at the cooled air outlet of the belt-drive chamber, being open in the sound absorbing material. Since the breather outlet opens in the sound absorbing material, dusts can be prevented from entering, and holding on, the breather outlet. Furthermore, oil content discharged out of the outlet of the breather extended from the transmission case is adsorbed by the sound absorbing material; however, because the breather outlet is located at the cooled air outlet of the belt-drive chamber, the sound absorbing material that has adsorbed the oil content is dried with cooled air which is warm air, and therefore can keep its adsorbing performance for a prolonged period of time. Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings, in which: Fig. 1 is a left side view of a motorcycle mounted with a power transmission device equipped with a belt-drive transmission according to this invention; Fig. 2 is a sectional view taken along line II-II of Fig. 1; Fig. 3 is a view of a cover unit taken along the arrow III in Fig. 2; Fig. 4 is an enlarged view of a major portion of Fig. 2; Fig. 5 is a left side view of a transmission cover attached to a left case; Fig. 6 is a sectional view taken along line VI-VI of Fig. 5 with the cover unit also installed; Fig. 7 is a left side view of an inner cover; Fig. 8 is a left side view of a sound absorbing material before installation; Fig. 9 is a left side view of an outer rear cover; Fig. 10 is a left side view of an outer front cover; and Fig. 11 is a side view of a conventional belt-drive case. The first embodiment of this invention will be explained with reference to Figs. 1 to 10. Fig. 1 is a left side view of a motorcycle mounted with a power transmission system provided with a belt-drive transmission device of this invention, in which a steering shaft 3 is rotatably supported on a head pipe 2 of a motorcycle 1; a handlebar 4 is fixedly attached on the upper part of the steering shaft 3; and a front fork 5 supporting a front wheel 5 is fixedly attached at the lower part of the steering shaft 3. Furthermore, the vehicle body frame is provided with a pair of right and left main pipes 7, 7 extending to the rear and obliquely downward from the upper part of the head pipe 2, a pair of right and left support pipes 8, 8 connected to the main pipes 7, 7 extending nearly horizontally to the rear from the lower part of the head pipe 2, a pair of right and left down pipes 9, 9 connected to the support pipes 8, 8, and further a pair of right and left seat rails 10, 10. The down pipes 9, 9 comprise front portions 9a, 9a spreading to either side and then extending to the rear obliquely downward at a sharp angle than the main pipes 7, 7, central portions 9b, 9b bent to the rear under the down pipes 9, 9 and then extending nearly horizontally, and rear portions 9c, 9c bent and extending obliquely upward to the rear after the central portions 9b, 9b. The seat rails 10, 10 are connected a little behind the center of the main pipes 7, 7, extending rearward nearly obliquely upward to the rear of the vehicle body. The down pipes 9, 9 are connected at the rear end of the rearward portions 9c, 9c to about the central portion of the seat rails 10, 10, thereby supporting the seat rails 10,10 from below. In the internal combustion engine 11, a cylinder block 13, a cylinder head 14, and a cylinder head cover 15 are assembled in order of mention to a crankcase 12 which is located to the rear of the rear portions 9c, 9c of the down pipes 9, 9, and are disposed projecting, in a forward upward inclined position, forward of the rear portions 9c, 9c of the down pipes 9, 9. The crankcase 12 is supported on a pair of right and left support brackets 9d, 9d and 9e, 9e mounted at the upper and lower parts of the rear portions 9c, 9c of the down pipes 9, 9. In the front of the internal combustion engine 11 is mounted a fuel tank 16 which is surrounded by the right and left main pipes 7, 7 and the right and left down pipes 9, 9. On the left side of the vehicle body, as described later, the power transmission device 17 disposed slightly obliquely downward to the rear from the left of the crankcase 12 is rotatably supported at the front part, in the crankcase 12, on the axis of the crankshaft 22 as an axis of rotation. The rear end portion of the power transmission device 17 is supported through shock absorbers 18 on the rear end portion of the left seat rails 10, 10, so that the power transmission device 17 is vertically swingable in relation to the internal combustion engine 11. At the rear of the power transmission device 17 a rear wheel 19 is axially supported. Now, referring to Fig. 2 to Fig. 4, an explanation will be made with a particular emphasis on the internal combustion engine 11 and the power transmission device 17. As shown in Fig. 2, the internal combustion engine 11 is a four-cycle two-cylinder internal combustion engine, in which the crankcase 12 is split to right and left crankcases 12L and 12R. Reciprocating motion of pistons 20, 20 slidably inserted in the cylinders 13a, 13a of the cylinder block 13 is transmitted to the crankshaft 22 rotatably supported laterally in the crankcase 12 through connecting rods 21, 21, to thereby rotate the crankshaft 22. On the right end portion of the crankshaft 22 is fixedly attached a rotor of an alternator 23, the right of which is covered with an alternator cover 24 connected to the right crankcase 12R. On the left end portion of the crankshaft 22 is mounted a driving pulley 50 of a later-described V-belt transmission T which is a component element of the power transmission device 17. Referring to Fig. 3, a valve mechanism is mounted in the cylinder head 14. An intake camshaft 25 and an exhaust camshaft 26 rotatably supported in the cylinder head 14 are driven to rotate at a reduction ratio of 1/2 of the crankshaft 22 by a timing chain 29 mounted on a driven sprocket secured on the right end portion of the camshafts 25 and 26 (shown is only a driven sprocket 27 of the intake camshaft 25) and a driving sprocket 28 secured on the right end portion of the crankshaft 22, thereby opening two intake valves 30, 30 and two exhaust valves 31, 31 mounted in the cylinders 13a, 13a. Fuel injected from a fuel injection valve 32 into the intake passage is drawn together with the air into a combustion chamber 33 through intake valves 30, 30. After firing for combustion by a spark plug 34, burned gases are discharged into the exhaust passage via exhaust valves 31, 31. Next, mainly the power transmission device 17 will be explained. The alternator cover 24 connected to the right crankcase 12R is provided with a bearing hole which is a through hole formed on the centerline of the axis of the crankshaft 22. The right end portion of a support shaft 36 rotatably supported on a needle bearing 35 mounted in the bearing hole is fitted in a fitting hole provided at the base end portion 37a of the right case 37 which partly covers the right crankcase 12R. Then the right case 37 is fixedly mounted on the support shaft 36. The right case 37 has a joining section 37b which is routed around from the base end portion 37a to the inside of the vehicle body along the rear surface of the right crankcase 12R. The joining section 37b is joined by four bolts 39 to a joining section 38b of the left case 38 which is a component member of the transmission case C which is a component element of the power transmission device 17. The right case 37 is thus joined into one body with the left case 38. Furthermore, the front end of the right fork portion 42 is bolted to the rear end of the right case 37. And the right end of the rear axle 40 is supported on a ball bearing 41 mounted in the rear end of the right fork portion 42. On the other hand, an annular support member 43 is connected by bolting on the periphery of the crankshaft 22 on the left side of the left crankcase 12L where the crankshaft 22 is mounted through. The left case 38 is rotatably supported in relation to the crankcase 12 by fitting the base end portion 38a of the left case 38 on the outer periphery of the support member 43 through a ball bearing 44. The left case 38 has the joining section 38b previously stated which is arranged around the inside of the vehicle body from the base end portion 38a along the rear surface of the left crankcase 12L, and further extending to the rear to support the middle portion of the rear axle 40 by a ball bearing 45 at the rear part. Therefore, the right case 37 and the right fork portion 42 which constitute the right rear fork section and the left case 38 which constitutes the left rear fork section integrally form the rear fork of the motorcycle 1, thus being vertically rockably supported with respect to the internal combustion engine 11 on the centerline of the axis of the crankshaft 22. Furthermore, the left case 38 is open to the left; and the open portion is covered a cover unit U. That is, the cover unit U is of a double structure including an inner cover 46 which is the body cover covering the open portion of the left case 38 and connected to a joint surface thereof, and an outer front cover 47 and an outer rear cover 48 covering the inner cover 46 on the left with a space provided therebetween. Particularly between the inner cover 46 and the outer rear cover 48 covering the rear half part thereof is interposed the sound absorbing material 49 for noise suppression. In the belt-drive chamber C formed by the left case 38 and the inner cover 46 are housed a V-belt transmission T, a centrifugal clutch L, and a reduction device R which are component elements of the power transmission device 17 for transmitting the power of the crankshaft 22 to the rear wheel 19. The transmission T is provided with the driving pulley 50, the driven pulley 51, and a V-belt 52 installed on these pulleys 50 and 51. The driving pulley 50 mounted on the left end portion of the crankshaft 22 in the front of the belt-drive chamber C has a stationary pulley piece 50a on the drive side which is secured in the directions of axis and rotation in relation to the crankshaft 22 as the driving shaft, and has a conical surface in contact with the V-belt 52; a movable pulley piece 50b on the drive side which is positioned to the right of the stationary pulley piece 50a on the drive side, connected axially movable in relation to the crankshaft 22 and unmovable in the direction of rotation, and having a conical surface in contact with the V-belt 52; a ramp plate 50c fixed in the axial direction and in the direction of rotation in relation to the crankshaft 22; and a plurality of weight rollers 50d disposed between the movable pulley piece 50b on the drive side and the ramp plate 50c. On the other hand, the driven pulley 51 is disposed at the rear of the belt-drive chamber C, and mounted on the left end portion of the driven shaft 53 mounted in the lateral direction of the motorcycle 1. The driven shaft 53 is rotatably supported at the right end portion at the rear part of the left case 38, and at the intermediate portion in a later-described transmission cover 70, and furthermore at the left end portion in the inner periphery of a later-described inner sleeve 57a via ball bearings 54, 55 and 56. The ball bearing 54 is a support portion for supporting the driven shaft 53 in the left case 38, while the ball bearing 55 is a support portion for supporting the driven shaft 53 in the transmission cover 70. Furthermore, referring to Fig. 4, the driven pulley 51 has a driven-side stationary pulley piece 57 rotatably axially secured with respect to the driven shaft 53, a driven-side movable pulley piece 58 which is axially movable with respect to the driven-side stationary pulley piece 57 and slightly axially movable within a range of formation of a later-described cam groove 64, and a spring 59 consisting of a cylindrical compression coil spring pressing by its pressure the driven-side movable pulley piece 58 toward the driven-side stationary pulley piece 57. The driven-side stationary pulley piece 57 includes an inner sleeve 57a disposed radially outward on the same axis as the driven shaft 53, and a conical plate 57b secured integrally with the right end portion of the inner sleeve 57a and having a conical surface in contact with the V-belt 52. The left end portion of the inner sleeve 57a is a rotatably supported on the driven shaft 53 through the needle bearing 60 mounted on the inner periphery, and a journal portion 57a 1 which is the outer periphery of the left end portion of the inner sleeve 57a and positioned radially outward of the driven shaft 53 is inserted in a ball bearing 62 mounted on the inner periphery of the bearing bore 46 formed in the inner cover 46, being rotatably supported in the inner cover 46. Therefore, the ball bearing 62 functions as a support portion of the driven-side stationary pulley piece 57 in the inner cover 46. The driven-side movable pulley piece 58 includes an outer sleeve 58a which is mounted on the same axis as the driven shaft 53 and is slidable in the directions of axis and rotation of the driven shaft 53 on the outer periphery of the inner sleeve 57a, and a conical plate 58b which is integrally fixed at the right end portion of the outer sleeve 58a, is located on the left of the conical plate 57b of the driven-side stationary pulley piece 57, and has a conical surface in contact with the V-belt 52. The outer sleeve 58a is provided with a cam groove 64 in which a pin 63 fixed in the inner sleeve 57a is fitted to thereby enable relative movement in the axial direction of the driven-side movable pulley piece 58 in relation to the driven-side stationary pulley piece 57, and has an inclined portion which allows movement in the directions of axis and rotation when a speed difference between the driven-side stationary pulley piece 57 and the driven-side movable pulley piece 58 exceeds a specific value. The driven-side stationary pulley piece 57 and the driven-side movable pulley piece 58 are normally designed to be rotatable as one body. The transmission T is of the constitution stated above, and therefore when the internal combustion engine 11 is running at a low speed, the drive-side movable pulley piece 50b of the driving pulley 50 is off the drive-side stationary pulley piece 50a. In this case, the wrapping radius of the V-belt 52 becomes small; in the driven pulley 51, the driven-side movable pulley piece 58 being pressed by the spring 59 approaches the driven-side stationary pulley piece 57, thereby increasing the wrapping radius of the V-belt 52 and therefore enabling to transmit the power of the crankshaft 22 to the output shaft at a great transmission gear ratio. In the driving pulley 50, when the speed of rotation is increased, a plurality of weight rollers 50d are moved radially outward by a centrifugal force to push the drive-side movable pulley piece 50b close to the drive-side stationary pulley piece 50a. Therefore, the wrapping radius of the V-belt 52 increases to move the driven-side movable pulley piece 58 of the driven pulley 51 against the spring force of the spring 59 away from the driven-side stationary pulley piece 57, thus decreasing the wrapping radius of the V-belt 52 to decrease the transmission gear ratio. Next, in the driven shaft 53, on the right of the driven-side stationary pulley piece 57 is disposed the centrifugal clutch L as a starting clutch between the driven-side stationary pulley piece 57 and the transmission cover 70 which forms the transmission case M holding a later-described reduction device R. The centrifugal clutch L has a cup-shaped outer clutch 65 which, fixed on the driven shaft 53, rotates as one unit with he driven shaft 53, and a drive plate 66 which is secured on the right end portion of the inner sleeve 57a inside of the outer clutch 65. Then, when the inner sleeve 57a rotates at a higher speed than the specific speed, a plurality of clutch shoes 67 rockably supported by the drive plate 66 is swung radially outward by a centrifugal force against the spring force of the clutch spring 68, so that a friction member 69 used on the outer peripheral surface of each clutch shoe 67 contacts the inner peripheral surface of the outer clutch 65, thus connecting the centrifugal clutch L to transmit the rotation of the driven pulley 51 to the driven shaft 53. Furthermore, the driven shaft 53 is connected with the rear axle 40 through a series of gears constituting the reduction device R. That is, at the rear of the belt-drive chamber C is further provided the transmission case M located between the rear part of the left case 38 and the centrifugal clutch L and formed by the transmission cover 70. The reduction device R housed in the transmission case M is provided with a small-diameter first pinion located on the right end portion of the driven shaft 53 which is mounted through the transmission cover 70, a large-diameter first reduction gear 73 and a small-diameter second pinion 74 mounted on an intermediate shaft 71 which is rotatably supported at both ends on needle bearings 76 and 77 in the left case 37 and the transmission cover 70, and a large-diameter second reduction gear 75 mounted on the rear axle 40 rotatably supported on the ball bearings 45 and 78 in the left case 38 and the transmission cover 70. The first pinion 72 is in mesh with the first reduction gear 73, and the second pinion 74 is in mesh with the second reduction gear 75, whereby the rotation of the driven shaft 53 is transmitted to the rear axle 40 after speed reduction in two speeds. Because of the above-described constitution of the power transmission device 17, the power of the crankshaft 22 is inputted into the driving pulley 50 of the transmission T. Then after being automatically changed to a transmission gear ratio by the transmission T according to the speed of the internal combustion engine 11, the power of the crankshaft 22 is transmitted to the driven pulley 51, and further to the driven shaft 53 through the centrifugal clutch L. Subsequently the rotation of the driven shaft 53 is transmitted to the rear axle 40 after speed reduction through the reduction device R in the transmission case M. In the transmission case M is reserved the lubricating oil, in which a series of gears constituting the reduction device R are partly immersed for lubrication. Therefore, a breather mechanism is provided to connect the interior of the transmission case M to the outside air in order to prevent a pressure rise in the transmission case M when the lubricating oil temperature rises during operation of the power transmission device 17. As shown in Figs. 5 and 6, a breather chamber B is defined by a partition wall in a space located above the transmission case M. In the rear upper part of the breather chamber B, a connecting pipe 80 is fitted in through the peripheral wall of the transmission cover 70, protruding obliquely upward toward the rear. The connecting pipe 80 communicates the inside and outside of the transmission case M with the lower end of the connecting pipe 80 located in the breather chamber B and the upper end disposed outside of the transmission case M. In a part of the connecting pipe 80 protruding out upward one end of the breather pipe 81 is pressed for connection. The breather pipe 81 shown in Fig. 6 is an L-bent pipe, with the end of a short straight portion 81a pressed for connection in the connecting pipe 80, while a long straight portion 81c extended horizontally for a specific length through a bent portion 81b. The long straight portion 81c is routed along the inside surface of the rear peripheral wall of the left case 38, and the left case 38 has a guide groove 38p formed to guide the breather pipe 81 which is extended from the connecting pipe 80. The long straight portion 81c of the breather pipe 81 extending horizontally to the right protrudes further to the left beyond the joint face of the left case 38 as shown in Fig. 6, being inserted into the round hole 46p of the inner cover 46. The round hole 46p of the inner cover 46 faces the sound absorbing material for noise suppression 49 interposed between the inside cover 46 and the outer rear cover 48; the end opening of the breather pipe 81 which is inserted in the round hole 46p being located in the sound absorbing material 49. That is, the breather pipe 81 extended obliquely upward in connection with the connecting pipe 80, which communicates with the breather chamber B, is bent squarely along the guide groove 38p, extending horizontal to the left for a specific length. Inserted in the round hole 46p of the inner cover 46 is the left end portion, with the outlet in the end portion located in the sound absorbing material installed in the inside surface of the outer rear cover 48. The sound absorbing material 49 has a round hole 49c in a part where the outlet in the end portion of the breather pipe 81 is located, so that a rib protruding out of the inner surface of the outer rear cover 48 will not close the outlet. Since the guide groove 38p serves as a stopper, the breather pipe 81 will not drop off; and when the breather pipe 81 is installed, one end of the breather pipe 81 is connected to the transmission cover 70 through the connecting pipe 80 and fitted for supporting in the guide groove 38p. Therefore, the breather pipe 81 can reliably and easily be installed. At the outlet of the breather pipe 81 is disposed the sound absorbing material 49 installed on the inside of the outer rear cover 48; therefore it is possible to prevent entry of dusts at the outlet of the breather pipe 81 and attachment of dusts at the outlet, whereby the appearance of the breather pipe 81 will not be adversely affected by the dusts. The upstream side of the breather pipe 81 is extended nearly upward from the upper breather chamber B of the transmission case M. Therefore oil liquid content that has entered the breather pipe 81 can easily flow back into the transmission case M; and the breather pipe 81, together with the transmission case M, rocks up and down to allow easy return of the oil liquid content into the transmission case M. Furthermore, the breather pipe 81, after extending nearly upward, is bent to form a long horizontal portion 81c for a specific length, going to the pipe outlet. Therefore there takes place air-liquid separation in the long horizontal portion 81c, thereby improving the breather performance. The long horizontal portion 81c of the breather pipe 81 extends to the pipe outlet. Therefore the oil will never be forced out by the up-down oscillation of the breather pipe 81. The sound absorbing material 49, which adsorbs the oil content, is dried by the air-cooling structure in the belt-drive chamber C. Hereinafter the air-cooling structure together with the cover unit U connected to the left case 38 will be explained. The cover unit U is of a double structure including the inner cover 46, the outer front cover 47, and the outer rear cover 48; and the sound absorbing material 49 is interposed between the cover 46 and the outer rear cover 48. The inner cover 46, as shown in Fig. 7, covers the left open space of the left case 38 in which the transmission T is housed. The rear half part bulges leftward into a cup shape as if to cover the driven pulley 51. At the center of the bulged portion 46a is mounted the bearing portion 46b by which the left end portion of the inner sleeve 57a is rotatably supported. The rib 46c of the bulged portion 46a which is further curved to the rear inner surface protrudes to form an air discharge passage 85 between the rib 46c and the rear peripheral wall, guiding the air downward from above along the rear peripheral wall of the air discharge passage 85 to thereby discharge the air out at the air outlet 86 formed in the rear lower part. The left case 38 jointed to the inner cover 46 is also provided with a rib 38q which is formed correspondingly to the rib 51c (shown in Fig. 3); both ribs together forming the air discharge passage 85 and the air discharge port 86. In the upper part of the air discharge passage 85 is formed a round hole 46p in which the end portion of the breather pipe 81 is inserted. In the front part of the inner cover 46 is formed an air inlet 46d. At about the center of the bearing portion 46b are formed mounting bosses 46e for mounting the external rear cover 48 in four places: two at upper and lower places on the front side and another two at upper and lower places on the rear side. And furthermore at six places of about the front peripheral edge of the inner cover 46 are provided mounting bosses 46f for mounting the outer front cover 47. On the inner cover 46 are also formed mounting bosses 46g at five places for mounting the left case 38. On the left case 38 are also formed mounting bosses 38g for mounting the inner cover 46 or the inner cover 46 and the outer front cover 47 together (shown in Fig. 3). On the other hand, the outer rear cover 48 covering the rear half of the inner cover 46 has a bulged portion 48a at the central part as shown in Fig. 9 and a guide portion 48b formed in the forward extended portion to thereby prevent the entrance of foreign substances and guide the flow of the air. Mounting bosses 48c are provided in four places of the outer rear cover 48: two at upper and lower places on the front side and another two at upper and lower places on the rear side. On the back side of the outer rear cover 48, the sound absorbing material 49 is lined as shown in Fig. 8. The sound absorbing material 49 is formed flat in shape, and has, at the center, an approximately Y-shaped slit 49a. Furthermore round holes 49b are formed in positions corresponding to the mounting bosses 48c provided in four places. In the vicinity of the right lower part of the round hole 49b formed in the right upper part in Fig. 8, there is formed a round hole 49c in which the outlet in the end portion of the breather pipe is located. The sound absorbing material 49 is lined, being deformed into a cup shape along the inner surface by spreading the slit 49a in the bulged portion 48a of the outer rear cover 48. The outer rear cover 48 lined with the sound absorbing material 49 is installed on the rear half of the inner cover 46 mounted on the left case 17, and tightened by screws into one body with mutually corresponding four mounting bosses 46f and 48c matched each other. The outer front cover 47 to be installed at the front half of the inner cover 46 is slightly bulged leftward into an approximately dish-like shape as shown in Fig. 10, and has a lower peripheral wall 47c through the front peripheral wall 47b which is curved from the upper peripheral wall 47a, then being open at the rear peripheral edge. In the peripheral wall 47a, 47b and 47c are provided with mounting bosses 47d in six places, and several ribs 47e are parallelly formed obliquely on the inner surface of the front half of the outer front cover 47. Next, as shown Fig. 2, an air-cleaning element 90 is in contact with the end face of the several ribs 47e, and an element holding cover 91 presses to support the air-cleaning element 90 against the ribs 47e. After the outer rear cover 48 is mounted on the rear half of the inner cover 46, the outer front cover 47 is attached by screws with the mounting bosses 46f and 47d matched at six mutually corresponding places, overlapped on the front end portion of the outer rear cover 48 and partly on the front half of the inner cover 46. The inner cover 46, the outer front cover 47 and the outer rear cover 48 form a double structure with the sound absorbing material 49 and the air-cleaning element 90 interposed therebetween. Thus the cover unit U is integrally installed. As shown in Fig. 2, there is formed an outside air inlet opening 92 which is open to the rear between the rear peripheral edge open to the outer front cover 47 and the outer rear cover 48. And the element holding cover 91 attached to support the air-cleaning element 90 to the front half of the outer front cover 47 is fitted in the air inlet 46d of the inner cover 46. With the reduction device R, the transmission cove 70, the driven shaft 53, the centrifugal clutch L, and the driven pulley 51 installed to the left case 38 (shown in Fig. 3), the inner cover 46, the outer rear cover 48 and the outer front cover 47 are installed in order of mention to thereby attach the cover unit U. Thus the sound absorbing material of the cover unit U forms a sound insulation construction for lessening noise resulting from vibrations of the transmission T and the reduction device R housed in the belt-drive chamber C. When the transmission cover 70 is installed to the left case 38, a breather pipe 81 is pre-installed to the connecting pipe 80 inserted in the transmission cover 70, then the transmission cover 70 is installed while fitting the breather pipe 81 in the guide groove 38p of the left case 38. Thereafter when the cover unit U is installed, the end portion of the breather pipe 81 which protrudes a little out of the joint surface of the left case 38 is inserted into the round hole 46p of the inner cover 46. Subsequently the end opening of the breather pipe 81 is placed at the sound absorbing material 49 inside of the outer rear cover 48. With the cover unit U thus installed to the left case 38, the air inlet 46d provided in the front part of the inner cover 46, and the air-cleaning element 90, are located oppositely to the left end of the crankshaft 22. A cooling fin 50a' (shown in Fig. 2) installed on the back of the stationary pulley half 50a of the driving pulley 50 mounted on the left end of the crankshaft 22 rotates to function as a blower. Therefore, with the rotation of the cooling fin 50a', the outside air is drawn in at the air inlet 92 in the rear edge of the outer front cover 47. The air thus drawn in is guided forward by means of the guide portion 48b formed in the front part of the outer rear cover 48, and into the belt-drive case C after cleaning by the air-cleaning element 90. The air introduced into the belt-drive case C flows through the air discharge passage 85 in the rear part of the belt-drive case C after cooling the V-belt 52 and the component elements of the power transmission device 17 of the transmission T, being discharged out at the air outlet 86. In the above-described air-cooling structure, the sound absorbing material 49 is exposed, at the upstream of the air discharge passage 85, to warm air used for cooling the transmission T. Oil content is adsorbed by the sound absorbing material 49 located at the outlet of the breather pipe 81. The sound absorbing material 49 is dried by the warm air from the air-cooling structure. Thus the adsorbing performance of the sound absorbing material 49 can be kept for a prolonged period of time. In summary it is an object to provide a breather structure of an internal combustion engine for vehicles which is of a simple construction having a short breather passage and capable of preventing entry of dust into, and attachment of dust on, the breather. In the breather structure of an internal combustion engine for vehicles, an outer cover 48 is installed through a sound absorbing material 49 for noise suppression on the outside of a body cover 46 which covers a power unit including at least one of the internal combustion engine and a power transmission device. An outlet of the breather 81 provided in the power unit is open at the sound absorbing material 49.

Claims: A breather structure of an internal combustion engine (11) for vehicles, wherein an outer cover (48) is mounted, through a sound absorbing material (49) for noise suppression, on the outer side of a body cover (46) which covers a power unit including at least one of an internal combustion engine (11) and a power transmission device (17), characterized in that the outlet of said breather (81) provided in said power unit opens in said sound absorbing material (49). A breather structure according to claim 1, characterized in that , in said breather structure (81), which is provided to connect the interior of a transmission case (M) mounted on the driven pulley side of a belt-drive vehicle to the outside air, a breather pipe (81) is bent backward after extending nearly upwardly from a breather chamber (B) of said transmission case (M), then extends horizontally for a specific length to a pipe outlet. A breather structure according to claim 2, wherein said pipe outlet of said breather pipe (81) opens in said sound absorbing material (49) for sound suppression interposed between the inside surface of said outer cover (48) and said body cover (46). A breather structure according to one of the preceding claims, characterized in that , in said breather structure of a transmission case (M) mounted on the driven pulley side of a belt-drive vehicle, a belt-drive chamber (C) is provided with an air-cooled structure; a sound absorbing material (49) for sound suppression is interposed between the inside surface of an outer cover (48) and a body cover (46); and the outlet of a breather (81) extended from said transmission case (M) is formed at a cooled air outlet port (86) of said belt-drive chamber (C), facing said sound absorbing material (49).

Inventors: KUGA SHINJI, MAEDA TETSUAKI, KUGA, SHINJI, MAEDA, TETSUAKI
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 2001
Main classification: F01M13
IPC codes: F01M13