Exhaust muffler layout structure in motorcycle

Abstract

 In a motorcycle, to firmly support an exhaust muffler (17) onto a power unit (P) while dispersing the weight of the power unit and the exhaust muffler (17) to both the left and right sides of a rear wheel (6r).
In the motorcycle in which both end portions of a horizontal pivot shaft (24) for turnably supporting a hanger arm (26) formed on a casing (10) of the power unit (P) are connected to a vehicle body frame (1), the exhaust muffler (17) disposed on the side opposite to an engine (E) with the rear wheel (6r) therebetween is connected to an exhaust pipe (16) extended from the engine (E) and bypassing the rear wheel (6r), and the exhaust muffler (17) is supported on an end portion of the hanger arm (26) on the side of the exhaust muffler (17) through a muffler stay (30).

Description

Specification

[0001] The present invention relates to a motorcycle in which a power unit including an engine and a transmission connecting a rear wheel to an output shaft is disposed on one of the left and right sides of the rear wheel, and both end portions of a horizontal pivot shaft for turnably supporting a hanger arm formed on a casing of the power unit are connected to a vehicle body frame, and particularly to a structure of laying out an exhaust muffler for the engine onto the power unit.

[0002] The motorcycle as above-mentioned has already been known, as for example disclosed in Japanese Patent Laid-open No. Hei 11-2125. Conventionally, in such a motorcycle, the exhaust muffler for the engine is disposed on one of the left and right sides of a rear wheel together with the power unit, and is mounted to an appropriate portion of the power unit.

[0003] In the exhaust muffler layout structure in the motorcycle according to the prior art, the adjacent arrangement of the power unit and the exhaust muffler permits the exhaust muffler to be firmly supported on the power unit. On the other hand, however, the weight of the power unit inclusive of the exhaust muffler is concentrated on one of the left and right sides of the rear wheel, and it is not easy to set the length of an exhaust pipe connecting between the engine and the exhaust muffler to be sufficiently large.

[0004] The present invention has been made in consideration of the above circumstances. Accordingly, it is an object of the present invention to provide an exhaust muffler layout structure in a motorcycle by which it is possible to firmly support the exhaust muffler on the power unit while enabling dispersion of the weight of the power unit and the exhaust muffler to both left and right sides of the rear wheel and, simultaneously, it is possible to set the length of the exhaust pipe to be sufficiently large.

[0005] In order to attain the above object, the present invention is firstly characterized in that, in a motorcycle including a power unit comprised of an engine and a transmission connecting a rear wheel to an output shaft, the power unit being disposed on one of the left and right sides of the rear wheel, and a horizontal pivot shaft for turnably supporting a hanger arm formed on a casing of the power unit, both end portions of the pivot shaft being connected to a vehicle body frame, an exhaust muffler disposed on the side opposite to the engine with the rear wheel therebetween is connected to the downstream end of an exhaust pipe extended from the engine and bypassing the rear wheel, and the exhaust muffler is supported on an end portion of the hanger arm on the exhaust muffler side.

[0006] Incidentally, the above-mentioned casing corresponds to a crankcase 10 in an embodiment of the present invention which will be described later, and the above-mentioned connection portions correspond to connection bosses 31.

[0007] According to the first characteristic feature, the power unit and the exhaust muffler are disposed separately on both left and right sides of the rear wheel, resulting in that the weight balance on the left and right sides of the vehicle body can be contrived to the utmost.

[0008] In addition, since the downstream end of the exhaust pipe extended from the engine of the power unit and bypassin a front portion of the rear wheel is connected to the exhaust muffler, the exhaust pipe can easily be made to have a sufficiently large length, thereby contributing to enhancement of the output performance, particularly in low- and medium-speed ranges, of the engine.

[0009] Moreover, since a tip end portion of the muffler stay for supporting the exhaust muffler is fastened to an end portion of the hanger arm on the exhaust muffler side, a comparatively short muffler stay can be used notwithstanding the exhaust muffler is disposed remote from the power unit, and, therefore, rigidity in supporting the exhaust muffler can be enhanced.

[0010] In addition, the present invention is secondly characterized in that, in addition to the first characteristic feature, the base end of the muffler stay is attached to the exhaust muffler, an upper-lower pair of connection portions are formed at the tip end of the muffler stay, and the connection portions are fastened to the hanger arm through fastening members in the state of being disposed respectively on the upper and lower sides of the pivot shaft.

[0011] According to the second characteristic feature, it is possible to disperse the weight of the exhaust muffler exerted on the hanger arm to the surroundings of the pivot shaft, to thereby alleviate the concentration of the weight on the hanger arm, and to contrive enhancement of the durability thereof.

[0012] Furthermore, the invention is thirdly characterized in that, in addition to the first or second characteristic feature, tapped holes having axes parallel to the pivot shaft are cut in an end face of the hanger arm on the exhaust muffler side, and bolts as the fastening members passed through the connection portions from an outer lateral side of the vehicle body are screwed tightly into the tapped holes, whereby the connection portions are fastened to the hanger arm.

[0013] According to the third characteristic feature, the screwing and tightening of the bolts can be easily performed without being interfered by other component parts, and it is possible to contrive enhancement of the assembleability of the muffler stay onto the hanger arm. Besides, a bearing hole in the hanger arm supported by the pivot shaft and prepared holes of the tapped holes can be formed at a stroke by multi-spindle machining, and the tapped holes can be laid out close to the pivot shaft, whereby a compact hanger arm can be contrived.

[0014] A mode for carrying out the present invention will be described below based on one embodiment of the present invention shown in the accompanying drawings.

Fig. 1 is a side view of a motorcycle comprising an exhaust muffler layout structure according to the present invention.

Fig. 2 is an enlarged side view of an essential part of FIG. 1.

Fig. 3 is a view taken along arrow 3-3 of FIG. 2.

Fig. 4 is a sectional view taken along line 4-4 of FIG. 2.

[0015] First, in FIG. 1, a vehicle body frame 1 of the motorcycle S is comprised of a front frame 1f which extends downwards from a head pipe 1h for steerably supporting a front fork 2 and supports a step floor 3, and a rear frame 1r which extends skewly upwards from the rear end of the front frame 1f and supports a luggage box 4, a rider's seat 5 and a fuel tank 7. A front wheel 6f is shaft-supported at the lower end of the front fork 2, a power unit P for supporting a rear wheel 6r and for driving the rear wheel 6r is vertically oscillatably suspended on the rear frame 1r, and a rear cushion 8 is mounted between the rear frame 1r and the power unit P. In addition, a stand 9 for self-standing of the vehicle body is mounted to the front frame 1f. Thus, the motorcycle S is constituted to be of the motor scooter type.

[0016] As shown in FIGS. 2 and 3, the power unit P has a structure in which a transmission mechanism is contained in a crankcase 10 of an engine E together with a crankshaft, and the power unit P is disposed on one of the left and right sides, in the example shown, on the right side, of the rear wheel 6r. The rear wheel 6r is mounted to an output shaft 12 of the transmission mechanism, which projects from a side wall of a rear portion of the crankcase 10.

[0017] A carburetor 15 is connected, via an intake pipe 14, to an upper surface of a cylinder head 13 inclined toward the front side of the vehicle body, of the engine E, and an exhaust pipe 16 is connected to a lower surface of the cylinder head 13. The exhaust pipe 16 is so curved as to bypass a front portion of the rear wheel 6r with a large radius of curvature, and an exhaust muffler 17 disposed on the side opposite to the power unit P with the rear wheel 6r therebetween is connected to the downstream end of the exhaust pipe 16.

[0018] Next, a suspension system for the power unit P will be described, referring to FIGS. 2 to 4.

[0019] As clearly shown in FIGS. 3 and 4, a left-right pair of brackets 21, 21 are welded to the tip ends of support arms 20, 20 fixed to left and right side surfaces of a rear end portion of the front frame 1f, and a suspension link 22 is oscillatably connected to the brackets 21, 21 through a horizontal first pivot shaft 23. The suspension link 22 comprises a single front arm 22a and a left-right pair of rear arms 22b, 22b, and the front arm 22a is inserted into, and borne on, a rear end portion of the front frame 1f through a cushion rubber 25.

[0020] On the other hand, the crankcase 10 of the engine E is integrally provided with a hanger arm 26. The hanger arm 26 is comprised of an arm portion 26a projecting skewly from a front surface of the crankcase 10 toward the front side of the rear wheel 6r and toward the rotational center plane O of the rear wheel 6r, and a bearing boss 26a disposed horizontally so as to extend in the left-right direction from the front end of the arm portion 26a and to cross the rotational center plane (in other words, the vertical center plane of the vehicle body) on the front side of the rear wheel 6r, and a lightening hole 28 is bored in the range from the bearing boss 26a to the arm portion 26a.

[0021] Rubber bushes 27, 27 are pressed respectively into both end portions of a bearing hole in the bearing boss 26a. The bearing boss 26a is disposed between rear end portions of both the left and right rear arms 22b, 22b of the suspension link 22, and both ends of a horizontal second pivot shaft 24 for turnably bearing the bearing boss 26a through the left and right rubber bushes 27, 27 are connected to both the rear arms 22b, 22b. Therefore, the power unit P is vertically oscillatable around the second pivot shaft 24, and oscillational impact forces exerted on the suspension link 22 from the power unit P are absorbed by the cushion rubber 25.

[0022] The above-mentioned exhaust muffler 17 is supported by utilizing the suspension system for the power unit P, as follows.

[0023] The base end of a muffler stay 30 is welded to an upper surface of the exhaust muffler 17. A tip end portion of the muffler stay 30 is branched into upper and lower prong portions 30a, 30a, and a pair of connection bosses 31, 31 having axes parallel to the second pivot shaft 24 are attached to the tip ends of the prong portions 30a, 30a. On the other hand, muffler mount portions 32, 32 (see FIG. 2, particularly) bulging to the upper and lower sides with the second pivot shaft 24 therebetween are formed at an end portion of the bearing boss 26a of the hanger arm 26 on the side of the exhaust muffler 17. Therefore, an end face of the bearing boss 26a on the side of the exhaust muffler 17 is broader than an end face on the side of the power unit P by the amount of the muffler mount portions 32, 32. A pair of tapped holes 33, 33 disposed on the upper and lower sides with the second pivot shaft 24 therebetween and having axes parallel to the second pivot shaft 24 are cut in the end faces of the muffler mount portions 32, 32. Bolts 34, 34 passed through a pair of connection bosses 31, 31 of the muffler stay 30 from an outer lateral side of the vehicle body are screwed tightly into the pair of tapped holes 33, 33 in the muffler mount portions 32, 32, whereby the connection bosses 31, 31 are fastened to the end face of the bearing boss 26a.

[0024] Next, the functions of this embodiment will be described.

[0025] When the rear wheel 6r rises and falls in the manner of following up to the ruggedness of the road during running of the motorcycle S, the power unit P which supports the rear wheel 6r and integrally comprises the hanger arm 26 and the exhaust muffler 17 which is supported on the hanger arm 26 through the muffler stay 30 are vertically oscillated as one body around the second pivot shaft 24, and the vertical oscillation can be damped by the rear cushion 8.

[0026] Meanwhile, since the power unit P and the exhaust muffler 17 are disposed separately on the left and right sides of the rear wheel 6r, the weight balance on the left and right sides of the vehicle body can be contrived to the utmost. In addition, notwithstanding the power unit P is disposed on one side of the rear wheel 6r, the layout in which the hanger arm 26 for supporting the heavy component parts such as the rear wheel 6r, the power unit P, the exhaust muffler 17, etc. is so disposed as to cross the rotational center plane O of the rear wheel 6r makes it possible to obviate, to the utmost, a partial load on the suspension system including the hanger arm 26 and the second pivot shaft 24. By these, it is possible to contrive enhancement of the riding feeling on the motorcycle S.

[0027] Besides, since the downstream end of the exhaust pipe 16 extending from the engine E of the power unit P and bypassing the front portion of the rear wheel 6r is connected to the exhaust muffler 17, the exhaust pipe 16 can easily be provided with a sufficiently large length, thereby contributing to enhancement of the output performance, particularly in low- and medium-speed ranges, of the engine E.

[0028] Moreover, notwithstanding the exhaust muffler 17 is disposed remote from the power unit P, the arrangement in which the tip end portion of the muffler stay 30 for supporting the exhaust muffler 17 is fastened to the end portion of the bearing boss 26a of the hanger arm 26 on the side of the exhaust muffler 17 makes it possible to use a comparatively short muffler stay 30, to thereby enhance rigidity in supporting the exhaust muffler 17, and to ensure stable supporting thereof.

[0029] Particularly, since the connection bosses 31, 31 of the prong portions 30a, 30a of the muffler stay 30 are fastened to the pair of muffler mount portions 32, 32 of the bearing boss 26a of the hanger arm 26 in the state of being disposed on the upper and lower sides with the second pivot shaft 24 therebetween, it is possible to disperse the load of the exhaust muffler 17 on the hanger arm 26 to the surroundings of the second pivot shaft 24, to thereby alleviate the concentration of load on the hanger arm 26, and to contrive enhancement of the durability of the hanger arm 26.

[0030] In addition, at the time of assembling the muffler stay 30 onto the hanger arm 26, the bolts 34, 34 passed through the connection bosses 31, 31 from an outer lateral side of the vehicle body are screwed tightly into the tapped holes 33, 33 opening to the end faces of the muffler mount portions 32, 32 of the bearing boss 26a of the hanger arm 26. Therefore, the screwing and tightening of the bolts 34, 34 can be easily performed without being interfered by other component parts, and the assembleability of the muffler stay 30 onto the hanger arm 26 is extremely good.

[0031] Furthermore, since the pair of tapped holes 33, 33 are cut in the end faces of the pair of muffler mount portions 32, 32 of the bearing boss 26a in parallel to the second pivot shaft 24, the bearing hole in the bearing boss 26a and the prepared holes of the tapped holes 33, 33 can be formed at a stroke by multi-spindle machining, and, in addition, it is possible to lay out the tapped holes 33, 33 close to the second pivot shaft 24, thereby making the bearing boss 26a compact.

[0032] The present invention is not limited to the above-described embodiment, and various design modifications are possible without departing from the gist of the invention. For example, both end portions of.the muffler stay can be bolted to the exhaust muffler and the hanger arm. Besides, in contrary to the above-described embodiment, the muffler stay may be formed as one body with the hanger arm, and the tip end thereof the muffler stay may be bolted to the exhaust muffler.

[0033] The invention can be summarized as follows:

[0034] In a motorcycle, to firmly support an exhaust muffler onto a power unit while dispersing the weight of the power unit and the exhaust muffler to both the left and right sides of a rear wheel.

[0035] In the motorcycle in which both end portions of a horizontal pivot shaft 24 for turnably supporting a hanger arm 26 formed on a casing 10 of the power unit P are connected to a vehicle body frame 1, the exhaust muffler 17 disposed on the side opposite to to an engine E with the rear wheel 6r therebetween is connected to an exhaust pipe 16 extended from the engine E and bypassing the rear wheel 6r, and the exhaust muffler 17 is supported on an end portion of the hanger arm 26 on the side of the exhaust muffler 17 through a muffler stay 30.

Claims

1. An exhaust muffler layout structure in a motorcycle comprising a power unit (P) comprised of an engine (E) and a transmission (T) connecting a rear wheel (6r) to an output. shaft (12), said power unit being disposed on one of the left and right sides of said rear wheel (6r), and a horizontal pivot shaft (24) for turnably supporting a hanger arm (26) formed on a casing (10) of said power unit (P), both end portions of said pivot shaft (24) being connected to a vehicle body frame (1), wherein
   an exhaust muffler (17) disposed on the side opposite to said engine (E) with said rear wheel (6r) therebetween is connected to the downstream end of an exhaust pipe (16) extended from said engine (E) and bypassing said rear wheel (6r), and said exhaust muffler (17) is supported on an end portion of said hanger arm (26) on the side of said exhaust muffler (17) through a muffler stay (30).

2. An exhaust muffler layout structure in a motorcycle as set forth in claim 1, wherein
   the base end of said muffler (30) is attached to said exhaust muffler (17), an upper-lower pair of connection portions (31) are formed at the tip end of said muffler stay (30), and said connection portions (31) are fastened to said hanger arm (26) through fastening members (34) in the state of being disposed respectively on the upper and lower sides of said pivot shaft (24).

3. An exhaust muffler layout structure in a motorcycle as set forth in claim 1 or 2, wherein
   tapped holes (33) having axes parallel to said pivot shaft (24) are cut in an end face of said hanger arm (26) on the side of said exhaust muffler (17), and bolts (34) as said fastening members passed through said connection portions (31) from an outer lateral side of the vehicle body are screwed tightly into said tapped holes (33), whereby said connection portions (31) are fastened to said hanger arm (26).

Drawing