Abstract:
An exhaust control apparatus for a motorcycle includes an exhaust collection pipe, which collects and combines exhaust gas from a plurality of exhaust pipes, and an exhaust valve. The exhaust valve is operatively attached to the collection pipe and controls flow of exhaust gas within the collection pipe. A pivot shaft of the exhaust valve is situated at an angle and is displaced from the centers of the exhaust pipes, such that the shaft is not aligned with the centers of the exhaust pipes. This arrangement of the pivot shaft provides a smooth, non-turbulent flow of exhaust gas, and reduces impedance to the flow of exhaust gas. The exhaust control apparatus may be mounted to reside within a recess formed in a motorcycle body frame, to reduce vehicle width.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present invention claims priority under 35 USC 119 based on Japanese Patent Application No. 2003-339789, filed Sep. 30, 2003.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to vehicle exhaust systems. More particularly, the present invention relates to an exhaust control apparatus for use on a motorcycle, in which the apparatus is operable to ensure a smooth flow of an exhaust gas.  
         [0004]     2. Description of the Background Art  
         [0005]     Exhaust systems are conventionally used with virtually all types of vehicles, to dampen and muffle sound made by the engine. A number of flow control valves are known for controlling exhaust flow through an exhaust pipe.  
         [0006]     One example of a known motorcycle exhaust control apparatus which mounts a valve in an exhaust passage of an engine exhaust system, and uses the valve to control a flow rate of exhaust gas in the exhaust passage, is disclosed in Japanese Unexamined Patent Publication Hei7 (1995)-145732. The motorcycle exhaust control apparatus described in this reference is somewhat effective, provided that the valve is mounted on the exhaust pipe which constitutes an exhaust passage, and the valve can be opened or closed.  FIG. 18  of the accompanying drawings is a reproduction of FIG. 2 in Japanese Unexamined Patent Publication Hei7 (1995)-145732, wherein the reference numbers from the original publication are maintained.  
         [0007]     As shown in  FIG. 18 , the motorcycle exhaust control apparatus described in Japanese Unexamined Patent Publication Hei7 (1995)-145732 includes an exhaust valve  20 , which allows a shaft  22  to penetrate a cylindrical surface of an exhaust pipe  21 . The exhaust valve  20  includes a throttle plate  23  attached to the shaft  22  for controlling an exhaust flow rate. The shaft  22  penetrates the approximate center of the pipe  21 , extending along a line corresponding to the diameter of the pipe  21 .  
         [0008]     However, in the motorcycle exhaust control apparatus described in Japanese Unexamined Patent Publication Hei7 (1995)-145732, since the shaft  22 , extends across the pipe  21  at the approximate center of the pipe  21 , exhaust gas which flows through the approximate center of the pipe  21  is forced to flow in a roundabout route around the shaft  22 . Hence, a turbulent flow is generated inside of the pipe  21 , with the result that that the exhaust efficiency is lowered.  
         [0009]     Therefore, a need still exists for an exhaust control apparatus for a motorcycle which can ensure a smooth flow of an exhaust gas when an exhaust valve  20  is arranged in an exhaust passage including an exhaust pipe.  
       SUMMARY OF THE INVENTION  
       [0010]     It is an object of the present invention to provide a motorcycle exhaust control apparatus which can enhance the exhaust efficiency and can enhance the performance of exhaust control by ensuring a smooth flow of an exhaust gas which flows along the centerline of the exhaust pipe by improved arrangement of an exhaust valve within an exhaust pipe.  
         [0011]     The first aspect of the invention is directed to a motorcycle exhaust control apparatus which includes a collection pipe which collects a plurality of exhaust pipes and an exhaust valve which controls a flow rate of an exhaust gas to the collection pipe, wherein the improvement is characterized in that a shaft of the exhaust valve is arranged at a position away from the centers of the plurality of exhaust pipes. It is possible to ensure a smooth flow of the exhaust gas and to enhance the discharge efficiency of the exhaust gas by arranging the exhaust valve such that the interruption of the flow of the exhaust gas by the exhaust valve is reduced.  
         [0012]     Accordingly, the exhaust valve, which controls a flow rate of the exhaust gas, is provided within the collection pipe, and the shaft of the exhaust valve is arranged at a position away from the centers of the plurality of exhaust pipes. By providing the exhaust valve within the collection pipe and by arranging the shaft of the exhaust valve at a position away from the centers of the plurality of exhaust pipes, the smooth flow of the exhaust gas is ensured and the exhaust efficiency is enhanced.  
         [0013]     Further, the a second aspect of the invention is characterized in that when the plurality of exhaust pipes are formed of two pipes, the shaft of the exhaust valve is inclined within a range of 35 to 55 degrees with respect to a straight line which connects the centers of two exhaust pipes. By imparting the inclination to the shaft of the exhaust valve within a range of 35 to 55 degrees to the straight line which connects the centers of two exhaust pipes, a desired height of the motorcycle above the ground is ensured, and the position of the exhaust control apparatus relative to the motorcycle body is accommodated, even at a maximum a bank angle.  
         [0014]     According to the first aspect of the invention, the exhaust valve, which controls a flow rate of the exhaust gas, is provided within the collection pipe, and the shaft of the exhaust valve is arranged at a position away from the centers of the plurality of exhaust pipes. Therefore, it is possible to ensure the smooth flow of the exhaust gas and to enhance the exhaust efficiency. As a result, it is possible to obtain the advantageous effect that the ability of the exhaust control apparatus to control the exhaust gas is enhanced.  
         [0015]     According to a second aspect of the invention, when the plurality of exhaust pipes are formed of two pipes, the shaft of the exhaust valve is inclined within a range of 35 to 55 degrees with respect to a straight line which connects the centers of two exhaust pipes. Therefore, it is possible to ensure desired a height of the motorcycle above the ground and easily accommodate the exhaust control apparatus upon the motorcycle within a bank angle. As a result, it is possible to obtain increased freedom in placement of the exhaust control apparatus in the overall design of the motorcycle.  
         [0016]     For a more complete understanding of the present invention, the reader is referred to the detailed description section below, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a left-side perspective view of a motorcycle having an exhaust control apparatus according to a selected illustrative embodiment of the present invention mounted thereon.  
         [0018]      FIG. 2  is a right-side perspective view of the motorcycle of  FIG. 1 .  
         [0019]      FIG. 3  is a side cross-sectional view of the motorcycle of  FIG. 1 .  
         [0020]      FIG. 4  is a perspective view of a vehicle body frame of the motorcycle of  FIG. 1 .  
         [0021]      FIG. 5  is a left side view of an engine, a power transmission mechanism and a seat mounted within the vehicle body frame of  FIG. 4 .  
         [0022]      FIG. 6  is a side view of the rear portion of the motorcycle of  FIG. 1  showing an exhaust control apparatus according to the present invention mounted to the exhaust system.  
         [0023]      FIG. 7  is an exploded perspective view of the exhaust system of  FIG. 6 , including the exhaust control apparatus according to the present invention mounted thereon.  
         [0024]      FIG. 8  is a detail perspective view of an exhaust control apparatus of the motorcycle of  FIG. 1 .  
         [0025]      FIG. 9  is a layout view of the arrangement relationship between an exhaust pipe and an exhaust valve of the exhaust control apparatus of the motorcycle of  FIG. 1 , showing the angle of the valve rod relative to a line connecting the centers of the individual exhaust pipes.  
         [0026]      FIG. 10  is a front partial cross-sectional view of the exhaust valve of the exhaust control apparatus of the motorcycle of  FIG. 1 .  
         [0027]      FIG. 11  is a plan view of an exhaust valve of an exhaust control apparatus of the motorcycle of  FIG. 1 .  
         [0028]      FIG. 12  is a side view of an exhaust valve of an exhaust control apparatus of the motorcycle of  FIG. 1 .  
         [0029]      FIG. 13  is an explanatory view for explaining the manner of operation of the exhaust control apparatus of the motorcycle of  FIG. 1  in which  FIG. 13   a  shows the operational wires acting to place the valve in an open state, and  FIG. 13    b  shows the operational wires acting to place the valve in a closed state.  
         [0030]      FIG. 14  is a perspective view of the exhaust control apparatus of the motorcycle of  FIG. 1  as viewed from an upper rear position, illustrating the servomotor acting through operational wires to actuate the valve within the exhaust control apparatus.  
         [0031]      FIG. 15  is a perspective view showing a rear side of the exhaust control apparatus of the motorcycle of  FIG. 1 .  
         [0032]      FIG. 16  is a plan view showing the arrangement relationship of a swing arm and an exhaust valve of the exhaust control apparatus of the motorcycle of  FIG. 1  showing the exhaust valve positioned within a recessed portion of the swing arm.  
         [0033]      FIG. 17  is an explanatory view for explaining a mounting angle of the exhaust valve of the exhaust control apparatus of the motorcycle of  FIG. 1  wherein the maximum allowable bank angle θ 1  is illustrated.  
         [0034]      FIG. 18  is a reproduction of a prior art exhaust valve, included for purposes of explanation. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     A selected illustrative embodiment of the present invention, installed on a vehicle, will now be described in conjunction with attached drawings.  FIG. 1  is a left-side perspective view of a motorcycle  10  which employs an exhaust control apparatus according to a selected illustrative embodiment of the present invention, wherein the motorcycle  10  is a scooter-type vehicle having a low-floor-type floor  25 .  
         [0036]     A vehicle body cover  20  which covers the whole vehicle body frame of the motorcycle  10  includes a front cowl  21  which covers a front portion of the vehicle body frame described later and an upper portion of a front wheel. An upper cover  22  covers an upper opening formed in the front cowl  21 , an inner cover  23  covers a rear portion of the front cowl  21 , and a center cover  24  extends rearwardly from a rear end of the inner cover  23  and covers the longitudinal center of the vehicle body frame. The low-floor-type floor  25  extends outwardly from an outer periphery of a lower end of the center cover  24  and allows the placing of a driver&#39;s feet thereon. A floor skirt  26  extends downwardly from an outer periphery of the low-floor-type floor  25 , and rear side covers  27 ,  27  (the rear side cover  27  at a the right side not shown in the drawing) extend rearwardly from the center cover  24  and cover the rear side portion of the vehicle body frame. Rear cover  28  extends rearwardly from the rear end of the rear side covers  27 ,  27  and covers the rear side portion of the vehicle body frame. Here, the rear side covers  27 ,  27  and the rear cover  28  constitute a seat cowl  29 .  
         [0037]     The front cowl  21  includes a transparent wind screen  95  on an upper portion thereof. The inner cover  23  includes a leg shield  91  for covering a front portion of a driver&#39;s legs. Further, the motorcycle  10  includes a handle  203  at a front portion of the body and also includes a seat  208  and a step holder  300  on a rear portion of the body.  
         [0038]     The handle  203  is a product of a type similar to a so-called chopper type handle in which grips  203   a,    203   a  are arranged at a relatively high position and are retracted in the rearward direction. The handle  203  is covered with a handle cover  101 . The handle cover  101  is formed of a lower handle cover  102  which covers left and right lower portions of the handle  203  and an upper handle cover  103  which covers an upper portion of the handle  203 .  
         [0039]     The seat  208  is of a double seat type which is formed of a front seat portion  208   a  on which a driver sits and a rear seat portion  208   b  on which an occupant sits. The step holder  300  is arranged close to the rear portion of the center cover  24  and is provided for mounting a pillion step (an occupant step)  310  thereon such that the pillion step  310  can be stored in or exposed from the step holder  300 . Here, the pillion step  310  is served for allowing an occupant to put his/her foot thereon.  
         [0040]     In the drawing, reference numeral  261  indicates a head lamp, reference numeral  262  indicates a blinker, reference numerals  263 ,  263  indicate mirrors, reference numeral  264  indicates a front fender, and reference numeral  265  indicates a lock for seat lock. Further, reference numeral  266  indicates a rear spoiler, reference numeral  267  indicates a tail lamp, reference numeral  268  indicates a rear fender, reference numeral  269  indicates a sub stand, reference numeral  320  indicates a main stand, reference numeral  330  indicates a lid for oil supply, and reference numeral  360  indicates a side lid for inspection. Here, reference numerals  271 ,  272  are master cylinders and generate a fluid pressure for braking with the manipulation of brake levers  273 ,  274 .  
         [0041]      FIG. 2  is a right-side perspective view of the motorcycle of  FIG. 1 . The drawing shows that a meter panel  92  is provided above the front cowl  21  and, at the same time, behind a wind screen  95 . As clearly understood from the explanation made heretofore, the wind screen  95 , the leg shield  91  and the meter panel  92  are provided at the front portion of the body. Further, this drawing also shows that the step holder  300 , which includes the pillion step  310 , is also arranged at the right side of the motorcycle  10 . Reference numeral  34  indicates an exhaust muffler.  
         [0042]      FIG. 3  is a side cross-sectional view of the motorcycle of  FIGS. 1-2 . The motorcycle  10  is a scooter-type vehicle and includes, as the main components thereof, a vehicle body frame  110 , a front fork  201  which is mounted on the head pipe  111  of the vehicle body frame  110  in such a manner that the front fork  201  can swing in the left-and-right direction, a front wheel  202  which is mounted on the front fork  201 , and the above-mentioned handle  203  which is connected to the front fork  201 . It further includes an engine  211  which is mounted on the rear portion of the vehicle body frame  110 , a power transmission mechanism  212  which is swingable in the upward-and-downward direction about the crankshaft of the engine  211 , and a rear wheel  205  which is mounted on a rear portion of the power transmission mechanism  212 . A rear shock absorber unit  206  suspends a rear end portion of the power transmission mechanism  212  on the vehicle body frame  110 , an accommodation box  207  is mounted on the rear upper portion of the vehicle body frame  110 , and the above-mentioned seat  208  is arranged on the accommodation box  207  in such a manner that the seat  208  can be opened or closed.  
         [0043]     The front fork  201  is a U-shaped fork arranged below the head pipe  111 . An upper portion of the front fork  201  and the head pipe  111  are covered by the front cowl  21 .  
         [0044]     The engine  211  is a water-cooled two-cylinder engine which is substantially horizontally arranged, wherein the engine  211  has two left and right cylinder heads  215  which are slightly inclined in the frontward and upward direction. The power transmission mechanism  212  is a belt converter variable-speed drive mechanism equipped with a centrifugal clutch and transmits the power of the engine  211  to the back wheel  205 .  
         [0045]     The accommodation box  207  is a long and narrow box that extends in the fore-and-aft direction of the body such that the accommodation box  207  can accommodate two helmets Hf, Hr in front and rear portions thereof. That is, the accommodation box  207  is formed of a lower box  207   a,  and an upper box  207   b  which is overlaps a rear upper portion of the lower box  207   a.    
         [0046]     In the drawing, reference numeral  93  indicates a front lower cover, reference numeral  94  indicates an under cover, reference numeral  191  indicates an air cleaner, and reference numeral  221  indicates a radiator. Also in the drawing, reference numeral  230  indicates a fuel tank, reference numeral  234  indicates a refueling opening, reference numeral  282  indicates a connecting tube, reference numeral  283  indicates an air chamber, reference numeral  284  indicates a throttle valve, reference numeral  285  indicates an inlet pipe and reference numeral  286  indicates a battery.  
         [0047]      FIG. 4  is a perspective view of the vehicle body frame  110  of the motorcycle  10 . The vehicle body frame  110  is a double cradle-type integrated frame which joins by welding a front frame  112 , which is contiguously formed with the head pipe  111 , and a pair of left and right seat rails (rear frames)  115 ,  115  which are extended rearwardly from a rear portion of the front frame  112 . The head pipe  111  includes a bracket  111   a  for cowl securement purposes.  
         [0048]     The front frame  112  is configured as follows. A pair of left and right upper frames  113 ,  113  extend downwardly and rearwardly from the head pipe  111 . A pair of left and right down tubes  114 ,  114  extend downwardly from the head pipe  111  below the pair of upper frames  113 ,  113 . The lower ends of the pair of down tubes  114 ,  114  extend rearwardly and are connected to lower ends of the pair of upper frames  113 ,  113  and, thereafter, extend in the rearward and upward direction. The front frame  112  is constructed so as to define a space portion Sp 1 . Space portion Sp 1  has an approximately triangular shape as viewed from the side and is surrounded by the pair of upper frames  113 ,  113  and the pair of down tubes  114 ,  114 .  
         [0049]     A first cross member  121  is positioned between a front end of the left rear frame  115  and a front end of the right rear frame  115 . First cross member  121  is a gate type as viewed from the front. A second cross member  122  is positioned between a lower end of the left upper frame  113  and a lower end of the right upper frame  113 . Further, a first engine bracket  123  is connected to the second cross member  122  at the center position thereof in the vehicle width direction.  
         [0050]     A third cross member  124  is positioned between a rear end portion of a horizontal portion of the left down tube  114  and a rear end portion of the horizontal portion of the right down tube  114 . A second engine bracket  125  is joined to the third cross member  124  at a center position thereof in the vehicle width direction. Further, left and right third brackets for engine  126 ,  126  are joined to rear ends of the left and right down tubes  114 ,  114 .  
         [0051]     A pair of left and right rear frames  115 ,  115  have first ends thereof connected to longitudinal mid portions of the pair of left and right upper frames  113 ,  113 , and have second ends thereof extended rearwardly The pair of left and right rear frames  115 ,  115  have vertically-elongated cross sectional shapes. Here, “vertically-elongated cross-sectional shape” means a cross-sectional shape having a vertical size set larger than a lateral size. To be more specific, the rear frames  115 ,  115  are formed of a quadrangular pipe having vertically-elongated rectangular cross section.  
         [0052]     In the drawing, reference numeral  131   a  indicates a U-shaped stay, reference numeral  131   b  indicates a seat hinge support portion, and reference numeral  131   c  indicates an extending member. In addition, reference numeral  141  indicates a floor support stay, reference numeral  143  indicates an under frame, reference numeral  144  indicates a pin with a head, and reference numeral  142  indicates a stay. Reference numerals  143   a,    143   a  indicate left and right side members, reference numeral  143   b  indicates a center cross member, reference numeral  143   c  indicates a rear cross member, and reference numerals  145  to  147  indicate brackets. Reference numeral  148  indicates a hook, reference numeral  151  indicates a front cross member, reference numerals  152 ,  153  indicate reinforcement members, reference numeral  226  indicates an ignition coil for engine and reference numeral  227  indicates a bolt.  
         [0053]      FIG. 5  is a left side view of the engine, the power transmission mechanism and the seat of the motorcycle  10 . This figure shows that the engine  211  and the power transmission mechanism  212  are arranged behind the front frame  112  and below a pair of rear frames  115 ,  115 . The engine  211  is mounted in the vicinity of the connection portion of the front frame  112  and the left and right rear frames  115 ,  115  (only left rear frame  115  shown in the drawing).  
         [0054]     To be more specific, behind the front frame  112 , a space portion Sp 2  is formed having an approximately triangular shape as viewed from the side and is surrounded by the pair of upper frames  113 ,  113 , the pair of down tubes  114 ,  114  and the pair of rear frames  115 ,  115 . A cylinder head  215  and a head cover  216  of the engine  211  are arranged in the space portion Sp 2 . A front lower portion of the engine  211  is mounted on the first engine bracket  123 , a rear lower portion of the engine  211  is mounted on the second engine bracket  125  and a rear upper portion of the engine  211  is mounted on the third engine brackets  126 ,  126 . Here, front and middle rear cross members  131 ,  132  are arranged above the engine  211 .  
         [0055]     Further, this drawing shows a rear end portion of the power transmission mechanism  212  suspended on left and right shock absorber brackets  134 ,  134  by way of left and right rear shock absorber units  206 ,  206 , and the front rear cross member  131  also serves as a member for supporting a seat hinge  208   c  of the open-and-close type seat  208 .  
         [0056]     That is, the vehicle body frame  110  of the scooter-type vehicle has the following construction: the pair of left and right rear frames  115 ,  115  (one rear frame  115  not shown in the drawing) extend rearwardly from the rear section of the front frame  112  which is contiguously formed with the head pipe  111  and seat  208 ; the rear shock absorber units  206 ,  206  (one rear shock absorber unit  206  not shown in the drawing) are supported on the rear frames  115 ; the engine  211  is arranged behind the front frame  112  and below the pair of rear frames  115 ,  115 ; and the cross members  131  to  133  (see  FIG. 4  with respect to symbol  133 ) are replaceably positioned between the pair of left and right rear frames  115 ,  115  about the engine  211 .  
         [0057]     The exhaust control apparatus  11  of the motorcycle is explained in detail hereinafter.  FIG. 6  is a side view of the exhaust control apparatus  11  according to the selected illustrative embodiment of the present invention, shown installed on the motorcycle  10 . The exhaust control apparatus  11  is provided for controlling the flow of an exhaust gas therethrough. The exhaust control apparatus  11  includes an exhaust valve  12  which is attached to an exhaust pipe  39 . The exhaust control apparatus  11  also includes two control cables  13 ,  14  which operate the exhaust valve  12 . The exhaust control apparatus  11  also includes a servo motor  15  which drives these control cables  13 ,  14  and an electronic control unit (ECU)  16  which controls the flow rate of the exhaust gas by controlling operation of the servo motor  15 . Generally, an ECU is an electric control apparatus which uses a computer to control vehicle components such as the engine, the automatic transmission, and the antilock brake system, and the like.  
         [0058]     A rear shock absorber arm  17  is positioned in the vicinity of the exhaust valve  12 , and is integrally attached to the previously-mentioned power transmission mechanism  212 . The rear shock absorber arm  17  is provided for supporting the right rear shock absorber unit  206  and, at the same time, for rotatably supporting the rear wheel  205 . The rear shock absorber arm  17  includes a shock absorber support portion  213  which supports the rear shock absorber unit  206 , a rear wheel support portion  214  which supports the rear wheel  205 , and a recessed portion  18  which is recessed toward the center of the vehicle body. A swing arm (a rear fork)  19  which rotatably supports the rear wheel  205  includes the power transmission mechanism  212  and the rear shock absorber arm  17 .  
         [0059]      FIG. 7  is an exploded perspective view of the exhaust system  30  of the motorcycle  10 , including the exhaust control apparatus  11  of the present invention. The exhaust system  30  includes a first takedown pipe  31  and a second takedown pipe  32  which extend from the engine  211  (see  FIG. 6 ). The exhaust system  30  also includes an exhaust collection pipe  33  which merges exhaust from these first and second pipes  31 ,  32  together. The exhaust system  30  also includes the control apparatus  11  hereof, as noted. The exhaust system  30  further includes a muffler  34  which is connected to the exhaust collection pipe  33 , a muffler protector  35  which covers the muffler  34 , a muffler guard  36  which protects the muffler  34 , and a band  38  which fixes the muffler  34  to the exhaust collection pipe  33  by way of a gasket  37 .  
         [0060]     Generally, although the exhaust pipe means exhaust pipes which are connected to respective cylinders of the engine, in this specification, the exhaust pipe  39  means a pipe assembly which includes the first and second takedown pipes  31 ,  32  and the exhaust collection pipe  33 .  
         [0061]     The exhaust collection pipe  33  is formed of a first connection portion  41  to which the first takedown pipe  31  is connected, a second connection portion  42  to which the second takedown pipe  32  is connected, a valve mounting portion  43  which mounts the exhaust valve  12  thereon, and a connection portion  44  to which a muffler  34  is connected.  
         [0062]     The muffler  34  includes a muffler body  45 , a tail pipe assembly  46  which is mounted on the muffler body  45  and a tail cover  47  which covers the tail pipe assembly  46 . The muffler protector  35  is made up of a protector body portion  48  which covers the side surface of the muffler body  45  and a cover portion  49  which is integrally extended from the protector body portion  48  to the front of the body and covers the exhaust valve  12 .  
         [0063]     In the drawing, reference numeral  51  indicates bolts which fix a protector body portion  48  to the muffler body  45  by way of elastic bushings  56 , reference numeral  52  indicates a bolt which fixes the cover portion  49  to a mounting portion  58  of the exhaust valve  12  by way of an elastic bushing  57 , and reference numeral  53  indicates a bolt which fixes the muffler guard  36  to the muffler body  45 . Reference numeral  54  indicates a bolt which fixes the tail pipe assembly  46  to the muffler body  45  and reference numeral  55  indicates bolts which fix the tail cover  47  to the muffler body  45  by way of the tail pipe assembly  46 .  
         [0064]     The exhaust control apparatus  11  is constructed as follows. That is, in the motorcycle  10  (see  FIG. 2 ) in which the engine  211  (see  FIG. 6 ) is mounted on the vehicle body frame  110  (see  FIG. 4 ), the exhaust pipe  39  is connected to the engine  211 , the muffler  34  is mounted on the exhaust pipe  39 , and the exhaust valve  12  controlling the flow rate of the exhaust gas is provided on the exhaust pipe  39 , the muffler protector  35  is mounted on the muffler  34 , the cover portion  49  is integrally extended from the muffler protector  35 , and the exhaust valve  12  is covered with the cover portion  49 .  
         [0065]     The manufacturing cost of the motorcycle can be suppressed, for example, when the exhaust valve is covered with a cover or the like, particularly if the exhaust valve can be covered without increasing the number of parts by making use of existing parts. Accordingly, by integrally extending the cover portion  49  from the muffler protector  35  and by covering the exhaust valve  12  with the cover portion  49 , the number of parts is reduced compared to a case in which the exhaust valve is covered with separate members. As a result, the manufacturing cost of motorcycle  10  is reduced.  
         [0066]     Further, by integrally extending the cover portion  49  from the muffler protector  35  and by covering the exhaust valve  12  with the cover portion  49 , the design and the merchantability of the motorcycle  10  can be enhanced.  
         [0067]     Further, by employing the mounting portion  58 , which serves to mount the cover portion  49  to the exhaust valve  12 , vibration of both the cover portion  49  and the exhaust valve  12  are stopped.  
         [0068]      FIG. 8  is a perspective view of the exhaust control apparatus of the motorcycle according to the present invention. Here, the exhaust control apparatus  11  includes an exhaust collection pipe  33  which collects a plurality of exhaust pipes, for example, first and second pipes  31 ,  32 . The exhaust control apparatus  11  also includes an exhaust valve  12  which is mounted on the exhaust collection pipe  33  and controls a flow rate of an exhaust gas within the exhaust collection pipe  33 . The exhaust control apparatus  11  includes a valve rod  62  (see  FIG. 9 ) which forms a shaft of the exhaust valve  12  and is arranged at a position away from the centers of the plurality of exhaust pipes. In the illustrated case, valve rod  62  is arranged at a position away from the centers of both the first and second pipes  31 ,  32 . In  FIG. 9 , C 1 , C 2  indicate respective centers of the first and the second pipes and L 1  indicates a straight line which connects the centers C 1 , C 2 .  
         [0069]     For example, in arranging the exhaust valve which controls the flow rate of the exhaust gas in the exhaust passage including the exhaust pipe, it is desirable to arrange the exhaust valve such that the interruption of the flow of the exhaust gas by the exhaust valve can be reduced with the result that a smooth flow of the exhaust gas can be ensured, and the discharge efficiency is enhanced.  
         [0070]      FIG. 9  shows the arrangement relationship of the exhaust pipe and the exhaust valve of the exhaust control apparatus of the motorcycle according to the present invention. The exhaust control apparatus  11  ensures a smooth flow of the exhaust gas and the exhaust efficiency is improved by providing the exhaust valve  12 , which controls the flow rate of the exhaust gas, within the exhaust collection pipe  33 , and by arranging the valve rod (shaft)  62  of the exhaust valve  12  at a position away from the centers C 1 , C 2  of the plurality of exhaust pipes (first and second pipes)  31 ,  32 . As a result, the ability to control the exhaust gas using the exhaust control apparatus is enhanced. In  FIG. 9 , reference numeral  61  indicates a valve of the exhaust valve  12  which is mounted on the valve rod (shaft)  62 .  
         [0071]     The exhaust control apparatus  11  should be understood such that when the number the plurality of exhaust pipes is set to two, the valve rod (shaft)  62  of the exhaust valve  12  can be inclined or tilted within a range of E 1  to E 2  (35 to 55 degrees) with respect to the straight line L 1  which connects the centers of two exhaust pipes (first pipe and second pipe)  31 ,  32 .  
         [0072]     That is, the exhaust control apparatus  11  is formed such that when the number of the plurality of exhaust pipes is set to two, the valve rod (shaft)  62  of the exhaust valve  12  is inclined within a range of E 1  to E 2  (35 to 55 degrees) with respect to a straight line which connects the respective centers of the first exhaust pipe  31  and the second exhaust pipe  32 . Hence, it is possible to ensure a desired height of the motorcycle  10  (see  FIG. 1 ) above a ground and to accommodate the exhaust control apparatus  11  within a bank angle. As a result, it is possible to obtain increased freedom in placement of the exhaust control apparatus in the overall design of the motorcycle.  
         [0073]     The detailed shape of the exhaust valve  12  is explained hereinafter in conjunction with  FIG. 10  to  FIG. 13 .  
         [0074]      FIG. 10  is a front cross-sectional view of the exhaust valve of the exhaust control apparatus of the motorcycle according to the present invention, wherein the exhaust valve  12  includes a valve  61  (see  FIG. 9 ) which changes the flow rate of the exhaust gas in the exhaust pipe  39  (the exhaust collection pipe  33 ) and a valve rod  62  to which the valve  61  is mounted. The exhaust valve  12  includes a pulley  63  which rotates the valve rod  62 , a casing  66  which houses the pulley  63 , and a lid  67  (see  FIG. 8 ) having the previously-mentioned mounting portion  58  which covers the casing  66 . The exhaust valve  12  also includes a torsion spring  68  which is arranged in a biased manner between the casing  66  and the pulley  63 , and a nut  69  which threadedly engaged with a male screw portion  59  formed in one end  62   a  of the valve rod  62 .  
         [0075]     In  FIG. 10 , reference numeral  62   b  indicates the second end of the valve rod  62 , reference numeral  74  indicates a stay which is served for mounting the case  66 , reference numeral  75  indicates bolts which fixes the valve  61  (see  FIG. 8 ) to the valve rod  62  by way of washers  75   a  and reference numeral  77  is a locking member which locks one end of the torsion spring  68 .  
         [0076]      FIG. 11  is a plan view of the exhaust valve of the exhaust control apparatus  11 . Within casing  66 , a pulley  63  is provided with a first connection portion  81  into which a cable end  79 , which is fixed to a distal end of an inner cable  13   a  of an control cable  13 , is fitted. The pully  63  is provided with a second connection portion  82  into which a cable end  89 , which is fixed to the distal end of an inner cable  14   a  of an control cable  14 , is fitted. Further, the control cables  13 ,  14  are engaged with an control cable holder and the control cable holder is fixed to the casing. Here, reference numerals  13   b,    14   b  respectively indicate outer tubes of the control cables  13 ,  14 .  
         [0077]      FIG. 12  is a side view of the exhaust valve of the exhaust control apparatus of the motorcycle according to the present invention. With respect to the exhaust valve  12 , another end  62   b  of the valve rod  62  is inserted into the valve mounting portion  43  of the exhaust connection pipe  33 . The casing  66  is mounted on one end  62   a  of the valve rod  62 . The pulley  63  (see  FIG. 11 ) is mounted in the casing  66 . The control cables  13 ,  14  are connected to the pulley  63 . By driving the operational wires  13 ,  14  using the servomotor  15  (see  FIG. 6 ), the valve rod  62  is rotated and hence, the valve  61  (see  FIG. 8 ), which is mounted on the valve rod  62 , can be opened and closed.  
         [0078]     Next, the manner of operation of the exhaust valve  12  of the exhaust control apparatus  11  is explained.  
         [0079]      FIG. 13 ( a ) and  FIG. 13 ( b ) are operation explanatory views of the exhaust control apparatus of the motorcycle according to the present invention.  FIG. 13 ( a ) shows the exhaust valve  12  wherein the valve  61  is positioned in an open state. In  FIG. 13 ( b ), the servomotor  15  (see  FIG. 6 ) is driven so as to loosen the control cable  13  as indicated by an arrow a 1 , the control cable  14  is pulled as indicated by an arrow a 2 , and the pulley  63  is rotated as indicated by an arrow a 3  thus setting the exhaust valve  12  in a closed state.  
         [0080]      FIG. 14  is a perspective view as viewed from a position behind and above the exhaust control apparatus of the motorcycle according to the present invention. The servomotor  15  includes a motor body  181 , a motor-side pulley  182  which is connected to the motor body  181  by way of a gear train (not shown in the drawing), a motor casing  183  which covers the gear train, and a motor cover  184  which covers the motor casing  183 . Here, reference numeral  185  indicates a front end portion of the servomotor  15 , reference numeral  186  indicates a rear end portion of the servomotor, reference numeral  187  indicates a motor bracket which is provided for mounting the servo motor  15  on the left seat rail  115 .  
         [0081]      FIG. 15  is a perspective view which shows a rear side face of the exhaust control apparatus of the motorcycle according to the present invention. As shown in  FIG. 15 , in the motorcycle  10  (see  FIG. 2 ) in which the engine  211  (see  FIG. 6 ) is mounted on the vehicle body frame  110  (see  FIG. 4 ), the exhaust pipe  39  is connected to the engine  211  and the muffler  34  (see  FIG. 7 ) is mounted on the exhaust pipe  39 . The exhaust valve  12 , which controls the flow rate of the exhaust gas, is provided in the vicinity of the connection portion  44  between the exhaust pipe  39  and the muffler  34  as well as on the exhaust pipe  39  side.  
         [0082]     Often a plurality of types of motorcycles which belong to the same motorcycle line are provided by mounting different mufflers on one type of motorcycle to cope with tastes of users. In this example, it is advantageous to exchange only the muffler, rather than both the muffler and the exhaust control apparatus, both in terms of improving the ease of the exchanging operation and of lowering of the cost of the exchanging operation. Accordingly, by positioning the exhaust valve  12 , which controls the flow rate of the exhaust gas, in the vicinity of a connection portion  44  between the exhaust pipe  39  and the muffler  34  (see  FIG. 6 ) and on the exhaust-pipe- 39  side, it is possible to exchange the muffler  34  without influencing the exhaust valve  12 . As a result, the ease of replacing the muffler is enhanced and the cost of the muffler  34  which is replaced is reduced.  
         [0083]      FIG. 16  is a plan view showing the arrangement relationship of the swing arm and the exhaust valve  12  of the exhaust control apparatus  11  of the motorcycle according to the present invention. As shown in the drawing, the swing arm  19  is mounted on the vehicle body frame  110  in such a manner that the swing arm  19  can swing in the upward and downward direction. The engine  211  is mounted on the vehicle body frame  110 , the exhaust pipe  39  is connected to the engine  211 , and the muffler  34  is mounted on the exhaust pipe  39 . The exhaust valve  12 , which controls the flow rate of the exhaust gas, is provided on the exhaust pipe  39  side of muffler  34 . A recessed portion  18 , which extends toward the vehicle body center, is formed on a lateral face of the swing arm  19  side. The exhaust valve  12  is positioned in the vicinity of the recessed portion  18  so as to face the recessed portion  18 .  
         [0084]     It is desirable from a viewpoint of efficient utilization of a layout space to position the exhaust valve  12  on the exhaust pipe without widening the vehicle width. That is, by forming the recessed portion  18  in the swing arm  19  and making the exhaust valve  12  face the recessed portion  18 , the exhaust valve  12  can positioned adjacent to the body center side. Hence, the exhaust valve  12  of the exhaust control apparatus  11  (see  FIG. 6 ) can be arranged on the exhaust pipe  39  without widening the vehicle width.  
         [0085]     Further, by also making the control cables  13 ,  14  which operate the exhaust valve  12  face the recessed portion  18  side, the control cables  13 ,  14  can be pulled out from the exhaust valve  12  while preventing the control cables  13 ,  14  from projecting to the outside beyond the vehicle width.  
         [0086]      FIG. 17  is an explanatory operational view for showing a mounting angle of the exhaust valve of the exhaust control apparatus of the motorcycle according to the present invention. When mounting the exhaust valve  12  on the exhaust pipe  39 , whether a height of the motorcycle above a ground is sufficiently ensured or not and whether the control cables can be easily pulled out or not are matters to be taken into consideration. Here, assuming an angle by which the motorcycle body can be fully inclined in the vehicle width direction as a maximum allowable bank angle θ1, the valve rod (shaft)  62  of the exhaust valve  12  is arranged so as to be approximately parallel to the ground surface C when the body is inclined at the maximum allowable bank angle θ1.  
         [0087]     By arranging the valve rod (shaft)  62  of the exhaust valve  12  approximately parallel to the ground surface C when the body is inclined at the maximum allowable bank angle θ1, it is possible to suppress the projection of the exhaust valve  12  and to arrange the exhaust valve  12  within the maximum allowable bank angle and, at the same time, the control cables  13 ,  14  (the control cable  14  at a depth side not shown in the drawing) can be easily pulled out from the exhaust valve.  
         [0088]     Here, as shown in  FIG. 7 , although the exhaust pipe  39  includes two pipes  31 ,  32  and the exhaust collection pipe  33 , the present invention is not limited to such a construction and the exhaust pipe  39  may be formed of only one pipe or the exhaust pipe  39  may be formed such that two pipes are connected to a first exhaust collection pipe and two other pipes are connected to a second exhaust collection pipe and a connection pipe which connects these first and second collection pipes is provided.  
         [0089]     That is, in the exhaust pipe, the number of the pipes which extend from the cylinders of the engine is arbitrary and, further, the connection of the pipes is also arbitrary provided that the exhaust valve which controls the flow rate of the exhaust gas is formed in the vicinity of the connection portion between the exhaust pipe and the muffler, and on the exhaust pipe side.  
         [0090]     Here, as shown in  FIG. 1 , although the invention has been described by adopting the motorcycle  10  as the vehicle, the vehicle is not limited to a two-wheel vehicle and the vehicle may be a four-wheel vehicle or a tricycle.  
         [0091]     The exhaust control apparatus for a motorcycle according to the present invention is preferably adopted by the motorcycle which mounts a multi-cylinder engine thereon.  
         [0092]     Although the present invention has been described herein with respect to an illustrative embodiment, the foregoing description is intended to be illustrative, and not restrictive. Those skilled in the art will realize that many modifications of the embodiment could be made which would be operable. All such modifications which are within the scope of the claims are intended to be within the scope and spirit of the present invention.