Abstract:
An improved component layout in a snowmobile includes a muffler is disposed on the front side of an engine, and a lower portion of a steering shaft extends between the muffler and the engine. The engine is disposed rearwardly of the lower portion of the steering shaft. In other words, the steering shaft lower portion is disposed on the front side of the engine, whereby the engine is easily relocated rearwards with respect to the vehicle body so as to concentrate the center of mass at a central location of the vehicle body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2004-069190, filed on Mar. 11, 2004. The subject matter of this priority documents is incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a snowmobile used for traveling on a snow field and having an engine as a drive source.  
         [0004]     2. Description of the Background Art  
         [0005]     Snowmobiles have been used for many years, and the basic operation thereof is well known. However, a variety of proposals have been made as to an improved layout of components, such as the arrangement of an air cleaner and a muffler around the engine. Examples of such proposals are provided in Japanese Patent Laid-open No. 2002-364468, and in Japanese Patent Laid-open No. Hei 7-228288.  
         [0006]     In general terms, it is desirable to provide an arrangement of components in which the center of gravity of the snowmobile is in the center of the vehicle body, and is generally low with respect to overall vehicle height. A snowmobile is disclosed in Japanese Patent Laid-open No. 2002-364468 (see especially  FIG. 3  thereof), the snowmobile having an engine, a steering post, and a steering handle bar. In this disclosure, the engine is disposed on the front side of the steering post  26 . However, in order to relocate the engine, which is a heavy component, to a more rearward position within the vehicle in consideration of the need to regulate the position of the center of gravity, the presence of the steering post hampers the engine from being displaced rearwards. Therefore, the layout disclosed in Japanese Patent Laid-open No. 2002-364468 is inconvenient because it is difficult to regulate the position of the center of gravity of the vehicle.  
         [0007]     An alternative snowmobile component layout is described in Japanese Patent Laid-open No. Hei 7-228288. In this layout, a generator, a recoil starter and a muffler are disposed on a lateral side (the right side) of the engine (see especially paragraph No. 19 thereof).  
         [0008]     In recent years, for the purposes of reducing undesired emissions and enhancing the silencing performance and the like, the muffler has been increased in size and weight. When the muffler 21 of Japanese Patent Laid-open No. Hei 7-228288 is increased in size and weight, it becomes difficult to maintain the left-right weight balance, which may adversely affect the turning performance of the snowmobile.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the present invention to provide a snowmobile in which an engine can be relocated towards the rear of the vehicle, and which provides excellent turning performance.  
         [0010]     According to a first aspect of the invention, a snowmobile is provided which comprises a left-right pair of skis, an engine, and a track belt all disposed on a vehicle body in this order from the front side toward the rear side of the snowmobile. The track belt is driven by the power of the engine to thereby cause the snowmobile to travel, and the skis are steered by operation of a steering handle. The snowmobile further comprises a muffler, provided in an exhaust system of the engine and disposed forwardly of the engine. In addition, a steering shaft, which transmits a steering force from the steering handle to the skis, extends between the muffler and the engine.  
         [0011]     According to a second aspect of the invention, the engine includes a plurality of cylinders, and the exhaust system further includes an exhaust pipe manifold portion for bringing together a plurality of exhaust pipes. The steering shaft passes between adjacent exhaust pipes at a location adjacent to, or upstream from, the manifold portion.  
         [0012]     According to a third aspect of the invention, the steering shaft includes a universal joint interposed in the course of the steering shaft, and a lower portion of the steering shaft is disposed close to the engine.  
         [0013]     According to a fourth aspect of the invention, an angle of inclination of an upper portion of the steering shaft is adjustable.  
         [0014]     According to a fifth aspect of the invention, a snowmobile is provided which comprises a left-right pair of skis, an engine, and a track belt all disposed on a vehicle body in this order from the front side toward the rear side of the snowmobile. The track belt is driven by the power of the engine to thereby cause the snowmobile to travel, and the skis are steered by operation of a steering handle. The snowmobile further comprises a muffler, provided in an exhaust system of the engine, and disposed forwardly of the engine between left and right front suspensions for suspending the left and right skis. A connection portion of the muffler, for connection with each of exhaust pipes, is provided on the front side or the rear side of the muffler.  
         [0015]     According to a sixth aspect of the invention, the exhaust pipes and an exhaust pipe manifold portion extend on the upper side of the muffler. In addition, a downstream-side exhaust pipe on the downstream side of the exhaust pipe manifold portion is bent back in a U shape and is connected to a front portion of the muffler.  
         [0016]     According to a seventh aspect of the invention, a snowmobile is provided which comprises a left-right pair of skis, an engine, and a track belt all disposed on a vehicle body in this order from the front side toward the rear side of the snowmobile. The track belt is driven by the power of the engine to thereby cause the snowmobile to travel, and the skis are steered by operation of a steering handle. The snowmobile further comprises a muffler, provided in an exhaust system of the engine, and disposed forwardly of the engine between left and right front suspensions for suspending the left and right skis. A connection portion of the muffler, for connection with each of exhaust pipes, is provided on a lateral side of the muffler.  
         [0017]     According to an eighth aspect of the invention, the muffler is generally flat so as to be small in height and broad in the width direction.  
         [0018]     According to the first aspect of the invention, the muffler is disposed on the front side of the engine. As a result, the muffler can be disposed at, or in the vicinity of, the center of the vehicle width. In this arrangement, the left-right weight balance of the snowmobile is easily equalized, and turning performance of the snowmobile is enhanced. In addition, since the engine is disposed on the rear side of the steering shaft, the engine can be easily displaced rearwards.  
         [0019]     It is possible to provide both a structure in which the steering shaft extends on the front side of the muffler, and a structure in which the steering shaft extends between the muffler and the engine. If the steering shaft is arranged so as to extend on the front side of the muffler, a longer steering shaft is required. On the other hand, if the steering shaft extends between the muffler and the engine, the steering shaft can be made shorter in length. Therefore, according to the first aspect of the invention, a shortening of the steering shaft is easily achieved.  
         [0020]     According to the second aspect of the invention, the steering shaft extends between the exhaust pipes at a location forwardly of a connection of the exhaust pipes with the manifold, and at a location in which the exhaust pipes are adjacent to each other. As a result, the dead space inevitably generated between the adjacent exhaust pipes is changed to a useful space.  
         [0021]     According to the third aspect of the invention, a universal joint is interposed in the course of the steering shaft. Further, the lower portion of the steering shaft is disposed close to the engine. Because the steering shaft lower portion is disposed close to the engine, the muffler can also be disposed close to the engine in conjunction therewith. As a result, concentration of mass in the vehicle body longitudinal (front-rear) direction is achieved.  
         [0022]     According to the fourth aspect of the invention, the angle of inclination of an upper portion of the steering shaft is adjustable, so that the height and angle of the steering handle can be changed in conformity with the rider&#39;s physique or preference. This feature provides an enhanced convenience in use of the snowmobile.  
         [0023]     According to the fifth aspect of the invention, the muffler is disposed between the left and right front suspensions. In this way, the heavy muffler body is disposed close to the longitudinal centerline of the vehicle body. As a result, the turning performance is further enhanced, a slim vehicle body is adopted, and the vehicle body is reduced in size.  
         [0024]     In addition, since the connection portion between the muffler and each of exhaust pipes is provided on the front side or the rear side of the muffler, the longitudinal axis of the muffler is set parallel to the longitudinal axis of the vehicle body, the vehicle width is reduced without being affected by the width of the muffler, and slimming of the vehicle body is promoted.  
         [0025]     According to the sixth aspect of the invention, the exhaust pipes and an exhaust pipe manifold portion pass on the upper side of the muffler. In other words, the muffler is disposed below the exhaust pipes. In recent years, mufflers are comparatively large in size and heavy. Since the muffler, being a heavy body, is laid out at a low position, lowering of the center of gravity of the vehicle body is promoted.  
         [0026]     According to the seventh aspect of the invention, the muffler is disposed between the left and right front suspensions. Thus, the heavy muffler body is disposed close to the center of the vehicle body. As a result, the turning performance of the snowmobile is enhanced, a slim vehicle body is adopted, and the vehicle body is reduced in size.  
         [0027]     It can be noted that when the connection portion between the muffler and each of exhaust pipes is provided on the front side of the muffler, the exhaust pipes must pass on the upper or lower side of the muffler, leading to the tendency that a front portion of the vehicle body is large in height. From this point of view, according to the seventh aspect of the invention, the connection portion between the muffler and each of the exhaust pipes is provided on a lateral side of the muffler. As a result, the exhaust pipes are absent from the upper side of the muffler or the like, and the height of the front portion of the vehicle body is made small.  
         [0028]     According to the eighth aspect of the invention, a muffler is provided having a generally flat shape so as to be small in height and broad sideways. With a relatively short muffler, it is possible to lower the center of gravity of the muffler, and to further lower the center of gravity of the vehicle body.  
         [0029]     Modes for carrying out the present invention are explained below by reference to an embodiment of the present invention shown in the attached drawings. The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent form the detailed description of the embodiment of the invention presented below in conjunction with the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0030]      FIG. 1  is an overall side view of a snowmobile according to the present invention showing the shape and location of the muffler with respect to the engine and steering shaft.  
         [0031]      FIG. 2  is a partial side view of a front portion of the snowmobile according to the present invention showing the frame structures surrounding the engine.  
         [0032]      FIG. 3  is a plan view of the front portion of the snowmobile according to the present invention with the vehicle body cover omitted, showing alignment of the muffler and other exhaust system components with the vehicle longitudinal center line.  
         [0033]      FIG. 4  is a perspective view of a muffler adopted in the present invention, with a muffler housing partly broken away to revel inner structure.  
         [0034]      FIG. 5  is a front view of the snowmobile according to the present invention with the vehicle body cover omitted, showing the connection of the enhanced frame structure to the snowmobile suspension.  
         [0035]      FIG. 6  is a sectional view along line  6 - 6  of  FIG. 2  showing the crossbar which joins the opposed side frames, and showing the steering bar mounted to the cross bar.  
         [0036]      FIG. 7  is a view along arrow  7  of  FIG. 2  showing the engine mounting hangers arranged on the front and rear, left and right sides of the frame.  
         [0037]      FIG. 8  is a sectional view of a fuel tank according to the present invention showing the fuel tank top surface at the front portion thereof raised upward relative to the top surface at a rear portion of the fuel tank, and showing the fuel pump provided in the raised top surface portion for feeding pressurized fuel to the engine.  
         [0038]      FIG. 9  is a view similar to  FIG. 2  of another embodiment of a snowmobile according to the present invention, with a modification in the steering handle.  
         [0039]      FIG. 10  is a view similar to  FIG. 2  of still another embodiment of a snowmobile according to the present invention, with a different modification in the steering handle.  
         [0040]      FIG. 11  is a plan view of a central portion of the snowmobile, showing a modification in the layout of the muffler.  
         [0041]      FIG. 12  is a figure corresponding to a side view of  FIG. 11 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]     The best mode for carrying out the present invention will be described below, based on the accompanying drawings. In the drawings and the figures, L is a subscript indicating the left as viewed from the driver, and R is a subscript indicating the right as viewed from the driver.  
         [0043]      FIG. 1  is an overall side view of a snowmobile according to the present invention. The snowmobile  10  is a snow vehicle which comprises a left-right pair of skis  12 L,  12 R ( 12 R is behind  12 L, here and hereinafter), an engine  13  and a track belt  14  in this order from the front side toward the rear side of a vehicle body  11 . The snowmobile  10  can travel by driving the track belt  14  by the power of the engine  13 . The skis  12 L,  12 R are steered by operating a steering handle  15 . The configuration of a steering system will be described in detail referring to another figure.  
         [0044]     As seen in  FIG. 1 , a rider M is shown in a seated position on a seat  24  of the snowmobile  10 . Also shown are a vehicle body cover  16 , an air cleaner  17 , an oil tank  18 , an exhaust pipe  19 , a catalytic converter  21 , a muffler  22 , a tail pipe  23 , and a fuel tank  25 .  
         [0045]     First, an intake and exhaust system will be described. Air taken in through the air cleaner  17  is fed into a combustion chamber of the engine  13 . An exhaust gas generated upon combustion is discharged into the atmosphere through the exhaust pipe  19 , the catalytic converter  21 , the muffler  22 , and the tail pipe  23 . The tail pipe  23  extends rearward from the muffler  22 , then bends so as to extend transverse to the longitudinal direction of the snowmobile, and then bends again to extend downward, whereby the exhaust gas is blown toward the snow surface.  
         [0046]     Next, a drive system will be described. The engine  13  is mounted on a vehicle body frame through engine hangers  26 L,  26 R,  27 L,  27 R (details of the layout of them will be described later), and a drive pulley  31  is mounted to a crankshaft  28  of the engine  13 .  
         [0047]     A continuously variable transmission (CVT) belt  33  is wrapped around both the drive pulley  31  and a driven pulley  32  disposed under the air cleaner  17 , whereby a belt-type non-stage transmission  30  is constituted. A cross shaft  34  supports the driven pulley  32  and extends in the transverse direction of the vehicle. A first sprocket  35  is attached to the tip end of the cross shaft  34 , and a chain  38  is wrapped around both the first sprocket  35  and a second sprocket  37  annexed to a drive wheel  36 .  
         [0048]     The power of the engine  13  is transmitted sequentially through the drive pulley  31 , the CVT belt  33 , the driven pulley  32 , the cross shaft  34 , the sprocket  35 , the chain  38 , and the sprocket  37 , whereby the drive wheel  36  can be rotated to drive the snowmobile  10  in the forward and reverse directions.  
         [0049]     A drive wheel  36  is disposed at a front portion of the track belt  14 , a driven wheel is disposed at a rear portion of the track belt  14 , and a plurality of rotary wheels are disposed at a intermediate lower portion of the track belt  14 . An idler  42  is disposed at an upper portion of the track belt  14 . The track belt  14  is wrapped around the drive wheel  36 , the driven wheel  39 , the plurality of rotary wheels  41  disposed at an intermediate lower portion, and the idler  42 . Projections  43  are provided on the outside surface of the track belt  14 , and are driven into the snow surface, to provide traction for traveling. Vertical movements, generated at the time of riding over rugged snow surfaces and the like, are absorbed by rear shock absorbers  44 ,  45 .  
         [0050]      FIG. 2  is a side view of a front portion of the snowmobile according to the present invention, in which the steering handle  15  and the skis  12 L,  12 R are connected by use of a steering shaft  50  (described below) and links. Also shown in  FIG. 2  is an air cleaner  17 , a throttle valve  46  provided on the downstream side of the air cleaner  17 , and an injector  47  provided on the downstream side relative to the throttle valve  46 .  
         [0051]     The steering shaft  50  is composed of a steering shaft upper portion  52 , a steering shaft lower portion  54 , and a universal joint  53 . The steering shaft upper portion  52  is provided with a steering handle holder  51  at the top end thereof, and is inclined forwardly downwards. The universal joint  53  is attached to the lower end of the steering shaft upper portion  52 , and the steering shaft lower portion  54  extends substantially vertically downwards from the universal joint  53 .  
         [0052]     A lever  55  is provided at the lower end of the steering shaft lower portion  54 . A drive member  56  extends in the vehicle width direction (transverse to the longitudinal direction) and is connected to the lever  55 . Levers  57  are attached respectively to the left and right ends of the drive member  56 , and vertically directed spindles  58 L,  58 R are rotated about roughly vertical axes by the levers  57 , whereby the skis  12 L,  12 R can be steered.  
         [0053]     The spindles  58 L,  58 R are rotatably contained in front leg portions  59 L,  59 R, and are vertically movably supported by lower arms  80 L,  80 R, upper arms  90 L,  90 R and front suspensions  64 L,  64 R which are vertically movably mounted to the vehicle body frame.  
         [0054]     In addition, a characteristic feature lies in that the muffler  22  is disposed on the front side (the left side as seen in the figure) or forwardly of the engine  13 , and the steering shaft lower portion  54  of the steering shaft  50  passes between the muffler  22  and the engine  13 . The engine  13  is disposed on the rear side or rearwardly of the steering shaft lower portion  54 . Namely, the steering shaft lower portion  54  is disposed on the front side of the engine  13 , so that the engine  13  can be easily relocated rearwards.  
         [0055]     It is possible to provide both a structure in which the steering shaft  50  is passed on the front side of the muffler  22 , and a structure in which the steering shaft  50  is passed between the muffler  22  and the engine  13 . If the steering shaft is arranged so as to pass on the front side of the muffler  22 , a longer steering shaft  50  is required. On the other hand, if the steering shaft  50  passes between the muffler  22  and the engine  13 , the steering shaft  50  can be made shorter in length. Therefore, on this basis, in the present invention the steering shaft lower portion  54  is arranged to pass between the muffler  22  and the engine  13  so that a shortening of the steering shaft  50  is easily achieved.  
         [0056]     In addition, another characteristic feature of the invention resides in that the universal joint  53  is interposed at an intermediate portion of the steering shaft  50 , and the steering shaft lower portion  54  is set close to the engine  13 . When the steering shaft lower portion  54  can be set close to the engine  13 , the muffler  22  can also be set close to the engine  13  in conjunction with this. As a result, mass is concentrated in the vehicle body longitudinal direction.  
         [0057]     The vehicle body frame  76  comprises intermediate frames  78 L,  78 R, a rear frame  77 , and a front frame  79 . The intermediate frames  78 L,  78 R are formed in U shape in side view, and are connected to front portions of the rear frame  77 . The rear frame  77  has a roughly U shaped section opened to the lower side so as to be situated astride the top surface and the left and right side surfaces of the track belt  14 . The front frame  79  is connected to front portions of the intermediate frames  78 L,  78 R. The vehicle body frame is characterized in that a reinforcement as described below is applied to the intermediate frames  78 L,  78 R.  
         [0058]     The intermediate frames  78 L,  78 R are made to be U-shaped in side view, and each are provided with a cutout portion  81  for permitting the crankshaft  28  or the like to be passed therethrough. Since the intermediate frames  78 L,  78 R are U-shaped frames, it is desirable to apply appropriate reinforcement to the frames. In view of this, an L-shaped reinforcement member  82  and an I-shaped reinforcement member  83  are annexed to each of the intermediate frames  78 L,  78 R along the cutout portion  81 , to thereby reinforce the cutout portion  81 .  
         [0059]     Further, an upper portion of the front frame  79  and a front upper portion of the rear frame  77  are connected by side frames  84 L,  84 R so as to cross the cutout portion  81 . Specifically, the front suspensions  64 L,  64 R are mounted to the front frame  79 , and the tip ends of the side frames  84 L,  84 R are connected in the vicinity of a suspension receiving portion  85 , provided for mounting the front suspensions  64 L,  64 R to the vehicle body frame. The rear shock absorber  44  is mounted to the rear frame  77 , and the rear ends of the side frames  84 L,  84 R are connected to rear frame  77  in the vicinity of a shock absorber receiving portion  86 , provided for mounting the shock absorber  44  to the rear frame  77 . By this configuration, the front frame  79  and the rear frame  77  are firmly connected to each other.  
         [0060]     Returning to  FIG. 1 , the engine  13  is disposed so as to be inclined toward the rear of the vehicle. Specifically, the engine head portion  13   a  and the cylinder  13   b  are inclined rearward relative to the vertical axis by an angle θ. Thus, the center of gravity of the engine is lowered, and the center of gravity of the snowmobile is set to be close to the center of the vehicle body. Since the center of gravity is set to be close to the center of the vehicle body, it is possible to keep the vehicle body stable, particularly during high-speed operation and operation on a largely rugged snow surface. As a result, a more pleasant operating experience is achieved.  
         [0061]      FIG. 3  is a plan view of a front portion of the snowmobile according to the present invention, illustrated with the vehicle body cover omitted. The engine  13 , shown in this embodiment as a series 4-cylinder engine, is disposed so that the crankshaft extends in the vehicle width direction and that the plural exhaust ports  61  are directed toward the front side.  
         [0062]     The plural exhaust pipes  19  extend respectively from the exhaust ports  61 , and are united into a single pipe at an exhaust pipe manifold portion  62 . A single manifolded exhaust pipe  63  extends forward from an outlet of the exhaust pipe manifold portion  62 , is then bent back in a U shape, and is connected to a front portion of the muffler  22 . The left and right front suspensions  64 L,  64 R are disposed respectively on the left side and the right side of the muffler  22 .  
         [0063]     As is clear from the figure, the muffler  22  is disposed so that the longitudinal axis of the muffler  22  is parallel to the longitudinal axis  65  of the vehicle body (an axis aligned with the vehicle centerline extending from front to rear of the vehicle). Thus, the length of the muffler  22  does affect the overall vehicle body width. The muffler  22  is disposed between the left and right front suspensions  64 L,  64 R, which allows adoption of a slim vehicle body and a reduction in the vehicle body size.  
         [0064]     In addition, since the muffler  22  is disposed on the front side of the engine  13 , the muffler  22  can be laid out on the longitudinal axis  65  or in the vicinity of the longitudinal axis  65 . As a result, the vehicle is easily balanced in the left-right direction, and steering performance is enhanced.  
         [0065]     Furthermore, the steering shaft  50  passes between adjacent exhaust pipes  19 ,  19 . As a result, a dead space  66 , which is customarily generated between the adjacent exhaust pipes  19 ,  19 , is now used as an effective space.  
         [0066]      FIG. 4  is a perspective view of the muffler adopted in the present invention. The muffler  22  is a silencing box having a structure in which a porous plate  68  and a partition wall  69  are interposed in the inside of an elliptic tube  67  having an elongate section. The front and rear openings of the elliptic tube  67  are closed with front and rear lids  72 ,  73 . The partition wall  69  is provided with a pass through pipe  71 . An exhaust gas inlet pipe  74  is provided so as to extend through the front lid  72 , the partition wall  69  and the porous plate  68 . An exhaust gas outlet pipe  75  is provided so as to pass through the partition wall  69 , the porous plate  68  and the rear lid  73 .  
         [0067]     An exhaust gas flows through the exhaust gas inlet pipe  74  into a first chamber C 1 , flows from the first chamber C 1  through the porous plate  68  into a second chamber C 2 , flows from the second chamber C 2  through the passing pipe  71  into a third chamber C 3 , and flows from the third chamber C 3  through the exhaust gas outlet pipe  75  into the tail pipe  23 .  
         [0068]     The muffler  22  is formed to be short in height and broad sideways. This form makes it possible lower the center of gravity of the muffler  22 . By laying out the muffler  22  of the low center-of-gravity type as shown in  FIG. 2  and in  FIG. 5 , described later, it is possible to further lower the center of gravity of the vehicle body.  
         [0069]      FIG. 5  is a front view of the snowmobile according to the present invention in which the vehicle body cover is omitted. The lower arms  80 L,  80 R extend to the left and right sides from the front frame  79 , upper arms  90 L,  90 R are extended to the left and right sides from the front frame  79 , and the front leg portions  59 L,  59 R are connected to the tip ends of the arms  80 L,  80 R,  90 L,  90 R. In addition, the lower ends of the front suspensions  64 L,  64 R are connected to the tip ends of the lower arms  80 L,  80 R, whereby a suspension mechanism for the skis  12 L,  12 R is constituted.  
         [0070]     The left and right J-shaped frames  84 L,  84 R are present behind (as viewed in this figure) portions for supporting the left and right front suspensions  64 L,  64 R, and front and rear two cross pipes  87 ,  88  are bridgingly disposed between the J-shaped frames  84 L,  84 R, to form a structure for enhancing the rigidity in the vehicle body sectional direction.  
         [0071]      FIG. 6  is a sectional view along line  6 - 6  of  FIG. 2 , in which the left and right J-shaped frames  84 L,  84 R coupled by the cross pipe  88  are composed of extruded members being substantially rectangular-shaped in section. Two ribs  89 ,  89  are bridgingly provided in the inside of the extruded member, in addition to the substantially rectangular-shaped section, whereby it is possible to drastically enhance the flexural rigidity and deflectional rigidity. Since extrusion permits free selection of the sectional shape, a substantially rectangular-shaped section with a single bridging rib and a substantially rectangular-shaped section with more than two bridging ribs can be obtained by decreasing or increasing the number of the ribs  89 .  
         [0072]     In addition, the cross pipe  88  is provided with a bracket  91 , a bearing block  92  is attached to the bracket  91 , and the steering shaft upper portion  52  is rotatably supported on the bearing block  92 . Although the cross pipe  88  is provided for the purpose of holding the left and right side frames  84 L,  84 R from moving in the transverse direction, the cross pipe also movably supports the steering shaft upper portion  52 . Thus the cross pipe  88  provides dual functions in the structure of the snowmobile.  
         [0073]      FIG. 7  is a view along arrow  7  of  FIG. 2 , showing that the left intermediate frame  78 L is provided with the engine hangers  26 L,  27 L. In addition, the right intermediate frame  78 R is provided with the engine hangers  26 R,  27 R. The engine  13  is supported on the vehicle body frame  76  through the four engine hangers  26 L,  26 R,  27 L,  27 R arranged on the front and rear sides and the left and right sides thereof.  
         [0074]      FIG. 8  is a sectional view of the fuel tank according to the present invention, in which a radiator  93  is formed as one body with the rear frame  77 . The radiator  93  is provided with heat-radiating fins  94  oriented so that the snow raked up by the track belt  14  will make contact with the heat-radiating fins  94 . The radiator  93  may naturally be so shaped as to extend over the entire part of the lower surface of the rear frame  77 , to provide a large heat-radiating area.  
         [0075]     In addition, it is shown that the generally box-shaped fuel tank  25  is disposed on an upper surface of the rear frame  77 , and the seat  24  is disposed on the upper side of the fuel tank  25 . The seat  24  is formed to be thicker at the portion on which the hip point Mh of the rider M rests, and to be thinner at the portion which is clamped by both knees Ms of the rider M and on which no load is substantially exerted.  
         [0076]     On the other hand, while the fuel tank  25  is fitted with the fuel tank supply pipe  96 , a fuel tank supply cap  97  and the fuel pump  98 , it is desirable to provide the fuel tank supply pipe  96  at a position as high as possible. Additionally, the fuel pump  98  is inserted into the fuel tank  25  from the upper side so that the fuel pump  98  can be inspected immediately upon opening the seat  24 .  
         [0077]     The engine according to the present invention is a fuel injection type engine, and, for this purpose, it is essential for the fuel pump  98  to be a high-pressure pump and be a large-sized pump. In order to contain the large-sized pump, it is necessary for the fuel tank  25  to have a predetermined height (depth).  
         [0078]     In order to provide the predetermined height, a ceiling plate  99  of the fuel tank  25  is not level. Specifically, the portion of the ceiling plate  99  ranging from an intermediate position to a front portion of the fuel tank is slanted upwards toward the front of the fuel tank so as to provide a raised portion  101 . As a result, the fuel tank supply pipe  96  can be mounted at a higher position of the fuel tank. Similarly, the fuel pump  98  is attached to the higher portion so that the height of the fuel pump  98  can be accommodated.  
         [0079]     Correspondingly to this, the height of the fuel tank  25  at a rear half portion is set to be small so as to allow for the thickness of the seat  24 , whereby the seating comfort is enhanced. As is clear from the figure, in the present invention, the overall height of both the seat  24  and the fuel tank  25  are harmonized, whereby it is possible to secure the required thickness of the seat  24  and the required height of the fuel tank  25 , while maintaining a substantially constant overall height from the top surface of the seat  24  to the bottom surface of the fuel tank  25 .  
         [0080]     Now, another embodiment of the present invention will be described below, based on the drawings.  FIG. 9  is a view similar to  FIG. 2  showing another embodiment of the present invention with a modification in the steering handle, in which the same portions as in  FIG. 2  are denoted by the same symbols as used above, detailed description thereof is omitted, and modified portions will be described principally.  
         [0081]     An arcuate plate  102  is attached to the cross pipe  88 , an arcuate hole  103  is bored in the arcuate plate  102 , and the bearing block  92  is fastened to the arcuate hole  103  by a bolt  104 . An arcuate plate  105  attached to the lower cross pipe  87  and the bearing block  92  are attached in the same manner. Incidentally, the arcuate plates  102  and  105  may be rectangular plates inasmuch as the arcuate hole  103  can be securely bored therein.  
         [0082]     By the action of the arcuate hole  103 , the steering handle  15  indicated by solid lines can be raised or lowered to the position indicated by imaginary lines, whereby the inclination angle of upper portion  52  of the steering shaft  50  can be selectively regulated. With the bolt  104  fixed in situ, the position of the steering handle  15  is determined. Namely, the height and angle of the steering handle  15  can be changed in conformity with the rider&#39;s physique or preference, whereby the convenience in use of the snowmobile is enhanced accordingly.  
         [0083]      FIG. 10  is a is a view similar to  FIG. 2  showing another embodiment of the present invention with a different modification in the steering handle, in which the same portions as in  FIG. 2  are denoted by the same symbols as used above, detailed description thereof is omitted, and modified portions will be described principally.  
         [0084]     In  FIG. 10 , it is shown that, by adopting a steering shaft  106  which passes through the oil tank  18 , the universal joint  53  shown in  FIG. 2  can be omitted. Specifically, the unitary, unsegmented steering shaft  106  passes on the front side of the engine  13  and on the rear side of the muffler  22 , whereby it is possible reduce the number of component parts of the steering system.  
         [0085]      FIG. 11  is a plan view of the mid portion of the snowmobile  10 , showing a modification in the layout of the muffler, in which the muffler  22  is so laid out that its longitudinal axis extends in the vehicle width direction. A curved exhaust pipe  108  extends from the left end (as viewed from the rider) of an exhaust manifold  107  annexed to the engine  13 . The curved exhaust pipe  108  is connected to the left side surface of the muffler  22 , and the tail pipe  23  is extended from the right side surface of the muffler  22 . The other component elements are denoted by the same symbols as used in  FIG. 3 , and detailed description thereof is omitted.  
         [0086]      FIG. 12  is a figure corresponding to a side view of  FIG. 11 , and shows that the muffler  22  is extended in the depth direction of the drawing. The curved exhaust pipe  108  is compact, and, returning to  FIG. 11 , the curved exhaust pipe  108  and the tail pipe  23  can be laid out substantially symmetrically on the left and right sides of the muffler  22 , so that the left-right weight balance property is easily enhanced. In addition, since the exhaust pipes are not present on the upper side of the muffler  22 , it is possible to reduce the height of the front portion of the vehicle body. The other component elements are denoted by the same symbols as used in  FIG. 2 , and detailed description thereof is omitted.  
         [0087]     The present invention is preferable for application to snowmobiles designed to travel on a snow surface or a snow field.  
         [0088]     While a working example of the present invention has been described above, the present invention is not limited to the working example described above, but various design alterations may be carried out without departing from the spirit or scope of the present invention as set forth in the claims.