Abstract:
A snowmobile, having an arrangement of components in which the layout of various accessory devices is improved for an internal combustion engine mounted thereon. A dry sump oil tank, a water pump and a starter motor are disposed in a concentrated space at a forward-facing portion of an internal combustion engine, which is mounted on a snowmobile at a position close to the front side of a body of the snowmobile. A steering shaft is arranged close to the front portion of the internal combustion engine, and is accommodated by modifying the shape of closely adjacent parts. Accordingly, the limited available space in a snowmobile is effectively used, and a rider riding in back of the engine can easily and closely approach the engine. The limited space inside the snowmobile cover is used effectively, by efficiently arranging selected accessory devices for an internal combustion engine mounted on the snowmobile.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2004-069608, filed on Mar. 11, 2004. The subject matter of the referenced priority document is incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a snowmobile, and more particularly to an arrangement of components within a snowmobile, in which the layout of selected accessory devices for an internal combustion engine mounted on the snowmobile is improved.  
         [0004]     2. Description of the Background Art  
         [0005]     There are some examples of known snowmobiles in which the snowmobile has an internal combustion engine with compactly arranged accessory devices, to accommodate limited available interior space in the snowmobile body. These arrangement considerations are especially relevant in a small-sized snowmobile. An example of a small snowmobile having such a structure is disclosed in Japanese Laid-Open Patent No. 2002-266653 (pp. 4-5,  FIG. 2 ), in which an internal combustion engine is installed within a limited space in the vehicle body to ensure an advantage in the mounting space. The snowmobile disclosed in Japanese Laid-Open Patent No. 2002-266653 has a shaft layout structure such that a crankshaft, as well as a traveling power output shaft and a pump drive shaft (auxiliary device shaft), are arranged parallel with one another in the vehicular transverse direction. As such, the shafts form a triangular shape when viewed from the side of the vehicle body. To achieve this configuration, the pump drive shaft is disposed below the power output shaft, and the crankshaft is disposed at an intermediate position between the power output shaft and the pump drive shaft, and on a rear side of the engine. According to this shaft layout structure, accessory devices to be arranged around the internal combustion engine are arranged compactly on both front and rear sides of the engine.  
         [0006]     According to a snowmobile  060  of the invention disclosed in Japanese Laid-Open Patent No. 2002-266653, which is illustrated in  FIGS. 13 and 14  of the present drawings for comparative purposes, there is used a power output shaft  02 . The power output shaft  02  is connected through the engagement of gears to a crankshaft  01  of an internal combustion engine  0 E mounted on the snowmobile  060 , and rotation of the power output shaft  02  is transmitted to an endless track belt  065  through a V belt type automatic transmission  066 , whereby the snowmobile is driven for travel.  
         [0007]     In the internal combustion engine  0 E mounted on the snowmobile  060  of this prior art reference, the crankshaft  01 , the power output shaft  02  for driving the snowmobile  060 , and a pump drive shaft  03  as an auxiliary device shaft, are arranged so as to be parallel with one another in the transverse direction of the snowmobile  060  and so as to mutually form a triangle when viewed from the side of the vehicle body.  
         [0008]     More particularly, a pump drive shaft  03 , for activating a cooling pump and an oil pump, is disposed below the power output shaft  02 . The crankshaft  01  is disposed at an intermediate position between and behind the power output shaft  02  and the pump drive shaft  03 . As a result, various accessory devices to be arranged around the engine  0 E are disposed compactly, especially on both front and rear sides of the engine  0 E.  
         [0009]     The compact layout structure of various accessory devices around the engine  0 E in the invention disclosed in Japanese Laid-Open Patent No. 2002-266653 leads to a reduction in size of the internal combustion engine  0 E. Such a small-sized internal combustion engine  0 E in the small-sized snowmobile  060  not only facilitates the installation thereof, but also provides an advantageous structure in point of space.  
         [0010]     Thus, Japanese Laid-Open Patent No. 2002-266653 provides an improved structure for effective use of such an extremely limited body space as in the small-sized snowmobile, as compared to older art which preceded publication of this reference. However, the provision of a further improved structure for effective use of body space in the snowmobile, and for facilitating installation of an internal combustion engine onto the snowmobile body is needed. Particularly, an improved structure is needed for a small-sized snowmobile for effective use of mounting space for an internal combustion engine, and various accessory devices associated with the engine, which occupy a large relative importance related to the available space.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention is concerned with an improved structure of a snowmobile which will solve the above-mentioned problems and effectively use the limited available space in the snowmobile. The present invention takes into consideration the layout arrangement of accessory devices with respect to an internal combustion engine mounted on the snowmobile. According to the present invention a snowmobile is provided which includes an internal combustion engine mounted on a front side of a body of the snowmobile. The snowmobile also includes a seat provided behind the internal combustion engine and a crankshaft of the internal combustion engine. The rotation of the crankshaft is transmitted to an endless track belt through a transmission mechanism, whereby the endless track belt is driven to propel the snowmobile. The improvement in the arrangement of the engine and the auxiliary components is characterized in that accessory devices are disposed in a concentrated manner in a front portion of the internal combustion engine.  
         [0012]     The present invention is also characterized in that the accessory devices disposed in a concentrated manner in a front portion of the internal combustion engine are a water pump, a dry sump oil tank, and a starter motor.  
         [0013]     The present invention is further characterized in that the water pump and the starter motor, both disposed in the front portion of the internal combustion engine, are received respectively within cutout spaces defined within the dry sump oil tank.  
         [0014]     According to a first aspect of the invention, a snowmobile includes an internal combustion engine mounted on a front side of a body of the snowmobile, a seat provided behind the internal combustion engine, and a crankshaft of the internal combustion engine. In the snowmobile, the rotation of the crankshaft is transmitted to an endless track belt through a transmission mechanism. Accessory devices are disposed in a concentrated manner in a front portion of the internal combustion engine. Thus, since accessory devices are closely clustered together at the front portion of the engine, and are not disposed in the rear portion of the engine, i.e., on the seat side of the internal combustion engine, it becomes possible for the rider to closely approach and easily access the engine. Further, a limited mounting space in the body of the snowmobile is effectively used.  
         [0015]     Moreover, since accessory devices are concentrated in the front portion of the internal combustion engine, the engine itself is small-sized and made compact. It becomes easy to ensure an effective space around the engine, so that the mounting of the internal combustion engine onto the vehicle body becomes easier and the engine mounting work efficiency is improved, whereby it is possible to reduce the cost.  
         [0016]     According to a second aspect of the invention, in combination with the first aspect, the accessory devices concentrated in the front portion of the internal combustion engine include a water pump, a dry sump oil tank, and a starter motor. Consequently, it is possible to provide an orderly arrangement of the auxiliary components of the engine, and an effective space around the engine is easily ensured. Moreover, since the engine can be constructed in a small and compact form, the mounting of the engine to the vehicle body is more easily accomplished, and the engine mounting work efficiency is improved, whereby the cost can be reduced.  
         [0017]     Further, according to a third aspect of the invention, in combination with the second aspect of the invention, the water pump and the starter motor, both disposed in the front portion of the internal combustion engine, are received respectively within cutout spaces formed by the dry sump oil tank. Consequently, so-called “dead space” around the engine diminishes to attain effective use of space, and the surroundings of the engine are compactly ordered, whereby it becomes easier to ensure an effective space. In addition, since the engine can be made compact, mounting of the engine onto the vehicle body can be done easily with a space margin and the engine mounting work efficiency is improved, whereby it is possible to attain the reduction of cost.  
         [0018]     Selected examples of 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 DRAWINGS  
       [0019]      FIG. 1  is a side plan view of a snowmobile according to an illustrative embodiment of the present invention, with an exterior cover, etc. removed for showing a main structural portion and internal combustion engine thereof;  
         [0020]      FIG. 2  is a top plan view of a mid portion of the snowmobile of  FIG. 1  according to the present invention, with an exterior cover, etc. removed for showing a main structural portion thereof and showing the relative locations of the intake pipes and exhaust pipes of the engine;  
         [0021]      FIG. 3  is an enlarged side detail view of the internal combustion engine of the snowmobile of  FIG. 1 , showing the engine mounting portion;  
         [0022]      FIG. 4  is a longitudinal sectional view of the internal combustion engine of  FIG. 3 , taken along a vertical plane and showing the location of the oil pumps and oil cooling and filtering unit, as well as a portion of the oil flow passages;  
         [0023]      FIG. 5  is a partial sectional view of an automatic transmission in a drive mechanism for the snowmobile of  FIG. 1  showing the V belt type pulleys on one end, and the starter motor on the opposed end;  
         [0024]      FIG. 6  is a front plan view of the internal combustion engine of  FIG. 3 , (ie, as viewed from the advancing direction), showing the oil tank in which a lower right portion of the tank is provided with a cutout in which the cooling pump resides, and in which a upper left portion of the tank is provided with a cutout in which the starter motor resides;  
         [0025]      FIG. 7  is a side plan view of the engine of  FIG. 3 , showing oil tank mounted on a front side of the engine with the steering shaft extending therethrough, and showing a portion of the lubrication pathways through the engine;  
         [0026]      FIG. 8  is a top plan view of a portion of the internal combustion engine of  FIG. 3  showing lubricating oil supply paths formed therein in the vicinity of the cam shafts;  
         [0027]      FIG. 9  is an enlarged sectional view of a lower end portion of the engine of  FIG. 3 , showing lubricating oil supply paths associated with the oil feed pump and oil scavenging pump;  
         [0028]      FIG. 10  is a schematic diagram of the lubricating oil supply system in the internal combustion engine of  FIG. 3 , showing oil being transferred by the feed pump from the dry sump oil tank to the oil gallery and valve operating system, and accumulated oil transferred by the scavenger pump from the oil sump in the bottom of the crankcase back to the dry sump oil tank;  
         [0029]      FIG. 11  is a diagram of cooling water supply paths in the internal combustion engine of  FIG. 1 ;  
         [0030]      FIG. 12  is a partial sectional view of the main cooling water supply structure in the internal combustion engine of  FIG. 3  showing the concave portion in the oil tank shaped to accommodate the steering shaft;  
         [0031]      FIG. 13  is a perspective view of a prior art internal combustion engine showing the conventional internal combustion isolated from a snowmobile and the triangular arrangement of the power output shaft, the crankshaft, and the pump drive shaft; and  
         [0032]      FIG. 14  is a side plan view of a prior art snowmobile on which the internal combustion engine shown in  FIG. 13  is mounted. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     In an internal combustion engine mounted on a snowmobile, a number of accessory devices such as a dry sump oil tank, a water pump and a starter motor are disposed in a concentrated area at a front portion of the engine which faces the front side of the vehicle. An embodiment of the present invention will be described herein, with reference to FIGS.  1  to  12 .  
         [0034]      FIG. 1  is a side plan view of a snowmobile  60  incorporating an engine and accessory component arrangement according to an embodiment of the invention, and  FIG. 2  is a top plan view of the snowmobile  60  of  FIG. 1 . As can be seen from  FIGS. 1-2 , an internal combustion engine E is mounted on a body of the snowmobile  60  at a position close to the front of the body. Left and right front suspensions  61   a ,  61   b  are disposed in the front portion of the vehicle body and a steering ski  62   a  and  62   b  is connected to each of the front suspensions  61   a  and  61   b , respectively.  
         [0035]     The steering skis  62   a  and  62   b  are connected to a handlebar  63   b , located in the approximate center of the vehicle body, through a steering shaft  63   a  and members of a steering system  63  such as pivot arms and link rods. The members of the steering system  63  are disposed so as to pass through the front portion of the internal combustion engine E. A seat  64  is disposed on the vehicle body at a position behind the handlebar  63   b.    
         [0036]     Further provided is a V belt type automatic transmission  66  having a driving pulley  66 A and a driven pulley  66 B. The driving pulley  66 A and the driven pulley  66 B constitute a drive section for transmitting a drive force of the internal combustion engine, mounted at a position close to the front side of the vehicle body, to an endless track belt  65 . In accordance with a transmission method to be described later, a rotational drive force, shifted by the automatic transmission  66 , is transmitted to a driving wheel  67 . The driving wheel  67  transmits the drive force to the endless track belt  65 , whereby the endless track belt  65  is driven to propel the snowmobile  60 . A radiator  68  is disposed under the seat  64 .  
         [0037]     Intake pipes E 21  and exhaust pipes E 11  of the engine E are shown  FIGS. 1, 2 , and  3 . The intake pipes E 21  extend toward the back of the vehicle body from the rear portion of the engine E and are then bent upward, with an air cleaner E 22  being disposed on the upwardly bent portion. As can be seen from  FIG. 2 , four exhaust pipes E 11  are combined into two sets, each consisting of two pipes, from the front portion of the engine E toward the front side of the vehicle body. The two sets of pipes are then are gathered into one pipe, then the pipe is bent in U shape on the front side of the vehicle body, and again extends backward of the vehicle body to form a backward bent portion. A muffler E 12  is disposed on the backward bent portion.  
         [0038]     In  FIG. 3 , an enlarged view of a portion of the snowmobile body is shown, in an area thereof where the internal combustion engine E is mounted. Part of the vehicle body frame is also shown. The V belt type automatic transmission  66  is included as a part of the drive section, and a part of the steering system  63  such as the steering shaft  63   a , is also shown in the same figure. The internal combustion engine E is mounted on the vehicle body so that a cylinder portion E 0  thereof is somewhat inclined backward (see  FIG. 1 ). In the same figure, at the left side of the figure, a front portion E 1  of the engine E faces the front side of the body of the snowmobile  60 . The front portion E 1  of the engine E constitutes an exhaust side, and therefore the exhaust pipes E 11  extend from the front portion E 1 .  
         [0039]     The internal combustion engine E, whose principal portion is shown in a longitudinal section view of  FIG. 4 , has a body structure including a crank case  20 , a cylinder block  30 , a cylinder head  40 , and a cylinder head cover  50 . Within the crank case  20 , a crankshaft  1  is rotatably supported through bearings. The large end portions  1   c  of connecting rods  1   b  are respectively pivotally supported by four crank pins  1   a  of the crankshaft  1 , and pistons If are respectively secured to small end portions  1   d  of the connecting rods  1   b  through pistons  1   e . As is seen from this description, the internal combustion engine E in this embodiment is an in-line four-cylinder four-cycle engine.  
         [0040]     The crankshaft  1  is supported by five journal portions  1   g  of the crank case  20  and is further supported at a position close to a right end  1   h  by a ball bearing  1   i , taking into account the presence of the V belt type automatic transmission  66 . The driving pulley  66 A of the V belt type automatic transmission  66  is mounted on a right extending shaft portion  1   j  of the crankshaft  1  extending outside the shaft bearing portion constituted by the ball bearing  1   i.    
         [0041]     More specifically, the V belt type automatic transmission  66  transmits the shifted rotational drive force to the driving wheel  67 , for propulsion to enable travel of the vehicle. The V belt type transmission is constructed such that, as shown in  FIGS. 1 and 3 , a rotational drive force of the driving pulley  66 A is transmitted, at a desired reduction gear (transmission gear) ratio, to the driven pulley  66 B side through a V belt  66 C. It is then transmitted from the driven pulley  66 B to a sprocket (not shown) coaxial with the driving wheel  67  through a sprocket (not shown) coaxial with the pulley  66 B. The transmission of the drive force between both sprockets is performed through a chain (not shown) or the like which is stretched between the two.  
         [0042]     The rotational drive force is thus transmitted to the sprocket coaxial with the driving pulley  67 . The rotational drive force causes the driving wheel  67  to rotate, whereby the endless track belt  65  is rotated along a slide rail  65   a  while being guided by the slide rail.  
         [0043]     The V belt type automatic transmission  66  will now be described with reference to  FIG. 5 . When the engine E is rotating at a low speed or is OFF, the driving pulley  66 A is held under the action of a spring (not shown) disposed on the driven pulley  66 B side. The action of the spring is such that a V groove  66   a  thereof becomes wider, that is, a substantial effective diameter of the pulley  66 A becomes smaller, and a V groove  66   b  of the driven pulley  66 B becomes narrower, that is, a substantial effective diameter of the pulley  66 B becomes larger.  
         [0044]     A movable pulley piece  66 A 2  of the driving pulley  66 A is provided with a weight member not shown in  FIG. 5 . The weight member functions to change the reduction gear (transmission gear) ratio in the V belt type automatic transmission  66 . The weight member moves radially of the pulley piece  66 A 2  under the action of a centrifugal force proportional to the rotation of the engine E (crankshaft  1 ), so that the pulley piece  66 A 2  moves in a direction in which the width of the V groove  66   a  is changed. In this way, the reduction gear ratio is changed and a shift is made automatically in a continuously variable manner.  
         [0045]     According to this structure, when the engine E, and specifically when the crankshaft  1 , rotates at a high speed, the weight member (not shown) moves radially outwards of the movable pulley piece  66 A 2  against the spring force (the spring of the driven pulley  66 B). The movable pulley piece  66 A 2  is moved in a direction in which the width of the V groove  66   a  of the driving pulley  66 A is narrowed. Consequently, the position of contact of the V belt  66 C with the V groove  66   a  on which it is entrained is shifted radially outwards, and thus a substantial effective diameter of the driving pulley  66 A is made large.  
         [0046]     On the other hand, in the driven pulley  66 B, as the position of contact of the V belt  66 C on the driving pulley  66 A side shifts radially outwards, a pulley piece  66 B  1  is moved against the spring force (not shown) conversely in a direction in which the width of the V groove  66   b  becomes larger, whereby a substantially effective diameter of the driven pulley  66 B is made small and so is the reduction gear ratio. The endless track belt  65  is driven at this reduction gear ratio and the snowmobile  60  runs at a high speed.  
         [0047]     When the engine E, specifically crankshaft  1 , rotates at a low speed, the weight member is positioned radially inside of the movable pulley piece  66 A 2 . The movable pulley piece  66 A 2  is moved in a direction in which the V groove  66   a  is widened, so that a substantially effective diameter of the driving pulley  66 A is made small. On the other hand, in the driven pulley, the V groove  66   b  is conversely narrowed, a substantial effective diameter of the driven pulley  66 B is made large and so is the reduction gear ratio. The endless track belt  65  is driven at this reduction gear ratio and the snowmobile  60  runs at a low speed. Such a V belt type automatic transmission  66  itself is already known.  
         [0048]     Referring again to  FIG. 4 , as can be seen from the same figure, a sprocket  1   k  of a small diameter is disposed at a position adjacent to the support portion of ball bearing  1   i  close to the right end  1   h  of the crankshaft  1 . A chain Pwc is stretched between the sprocket  1   k  and a sprocket Pwb. The sprocket Pwb is mounted on a pump shaft Pwa of a water pump Pw which will be described later (see  FIGS. 3 and 12 ). The water pump Pw is activated with the chain Pwc, in interlock with rotation of the crankshaft  1 .  
         [0049]     On the other hand, a rotor  2   a  of a generator  2  is mounted near a left end  1   m  of the crankshaft  1 . A bolt B is implanted into the left end  1   m  of the shaft  1  to form an extending shaft portion  1   n . An oil pump shaft  1   q  is coaxial with the extending shaft portion  1   n . The oil pump shaft  1   q  is connected to the extending shaft portion In and is thereby connected with the end portion  1   m  through a joint  1   p . Two oil pumps, the oil feed pump Pf and the oil scavenger pump Ps, are mounted side by side on the oil pump shaft  1   q.    
         [0050]     One oil pump Pf is a feed pump for the supply of lubricating oil, while the other oil pump Ps is a scavenging pump for return of oil staying in a bottom  21  of the crank case  20  to a dry sump oil tank. A description will be given later of the supply and delivery of lubricating oil by both pumps Pf and Ps, and therefore an explanation thereof will be deferred.  
         [0051]     A timing sprocket  1   r  of a small diameter is mounted on the crankshaft  1  at a position close to the left end  1   m  of the crankshaft. The timing sprocket  1   r  is for actuating two cam shafts  4   a  and  4   b  in a valve operating system  4 . A cam chain  4   e  is stretched between sprockets  4   c ,  4   d  mounted on the cam shafts  4   a ,  4   b , and the timing sprocket  1   r . The rotation of the crankshaft  1  is transmitted to the two cam shafts  4   a  and  4   b  by the timing sprocket  1   r  at ½ the number of revolutions.  
         [0052]     A flywheel gear  1   s  is of a relatively large diameter and is mounted on the crankshaft  1  through a one-way clutch it at a position adjacent to the timing sprocket  1   r . The flywheel gear is, which is for a starter motor  5  (see  FIG. 5 ), is interconnected to another gear  5   a  through the engagement of intermediate gears  5   b  and  5   c . The gear  5   a  is integral with a motor shaft  5 A of the starter motor  5  (see  FIG. 5 ).  
         [0053]     The cylinder block  30  is connected to an upper portion of the crank case  20 . Four side by side cylinder bores  31  are formed through the cylinder block  30 . Pistons  1   f  are adapted to slide respectively through the interiors of the four cylinder bores  31 . The cylinder head  40  is connected to an upper portion of the cylinder block  30 .  
         [0054]     In the cylinder head  40 , four combustion chambers  42  are formed of four concave portions  41  and of the upper portions of the four cylinder bores  31 . In each combustion chamber  42  there are provided intake and exhaust ports  43 ,  44 , intake and exhaust valves  45 ,  46  for opening and closing the intake and exhaust ports  43 ,  44 , and a spark plug  47 .  
         [0055]     Intake and exhaust passages  48 ,  49  are formed within the cylinder head  40 . Intake and exhaust passages  48 ,  49  communicate with the intake and exhaust ports  43 ,  44  which are provided in the combustion chambers  42 . In an upper portion of the cylinder head  40 , there are provided a valve operating mechanism for actuating the intake and exhaust valves  45 ,  46 . The valve operating mechanism includes, for example, cams  4   f ,  4   g  and cam shafts (two)  4   a ,  4   b , a drive mechanism for the valve operating mechanism, and tappets  4   h . Further, a cylinder head cover  50  is attached to the upper portion of the cylinder head  40 .  
         [0056]     As shown in  FIGS. 3 and 7 , the dry sump oil tank is disposed in the front portion E 1  of the internal combustion engine E at a position corresponding to wall portions of the crank case  20  and the cylinder block  30  in the engine E. In other words, the dry sump oil tank is disposed in the front portion E 1  of the wall portions of the engine E, substantially orthogonal to the vehicle advancing direction. The dry sump oil tank has a length corresponding to approximately the entire width of the front portion E 1 . As shown in  FIG. 6 , in a front view of the tank  3  as seen from the front portion E 1  of the engine E, a lower right portion of the tank  3  has a first recess formed therein, which is cut out in a rectangular shape to form a space E 1   a  in the engine front portion E 1 . In addition, a upper left portion of the tank has a second recess formed therein, which is cut out in a rectangular shape to form a space E 1   b  in the engine front portion E 1 .  
         [0057]     The cooling pump Pw is positioned in the space E 1   a  formed by the lower right cutout portion of the dry sump oil tank. The pump Pw is received within the space E 1   a  and thereby is mounted in the front portion E 1  of the engine E in such a manner that a cooling water intake suction port PwA 1  thereof is located at a lower position and a discharge port PwB thereof is located at an upper position.  
         [0058]     The starter motor  5  is positioned within the space E 1   b  formed by the upper left cutout portion. The starter motor  5  is received within the space E 1   b  and thereby is mounted in the engine front portion E 1  in such a manner that the motor shaft  5 A of the starter motor  5  projects leftwards in the figure, i.e., in a transversely outward direction of the engine E.  
         [0059]     A concave groove  3   b  is formed in a nearly transversely central portion  3   a  of the tank  3 , as seen in the front view of the dry sump oil tank shown in  FIG. 6 . The concave groove  3   b  has a generally arcuate section. The concave groove  3   b  is used to receive the steering shaft  63   a  therein (see  FIG. 7 ) so that the steering shaft  63   a  passes vertically through the tank  3  and is connected to the steering handlebar  63   b  of the snowmobile  60 . The concave groove  3   b  has a steering post  3 A which faces somewhat obliquely in the vertical direction to match the extending direction of the steering shaft  63   a.    
         [0060]     As can be seen from the above description and from  FIG. 6 , in the front portion E 1  of the engine E, the water pump Pw and the starter motor  5  are disposed in a well-balanced state at respective right and left positions. As such, the water pump Pw and the starter motor  5  sandwich the concave groove  3   b  therebetween, which extends vertically through the tank  3  at the tank central portion  3   a  for the steering post  3 A. It should be emphasized that a characteristic structure of the invention is that the dry sump oil tank, the water pump Pw, and starter motor  5  are disposed so as to be concentrated within a small space in the front portion E 1  of the engine E. With this arrangement, the rider who rides next to a rear portion E 2  of the engine E can closely approach and easily access the engine.  
         [0061]     An oil cooler  11  and an oil filter  12  are disposed in a side portion of the engine E (the left side face in  FIG. 4 ), parallel to the vehicle advancing direction of the engine E, as shown in  FIGS. 4, 7  and  11 . The oil cooler  11  and an oil filter  12  are disposed in the portion corresponding to the wall portions of cylinder block  30  and the cylinder head  40 , and at positions approximately above the oil pumps Pf, Ps and the generator  2  on the left end  1   m  of the crankshaft  1 . The oil cooler  11  and the oil filter  12  are integral with each other as an oil processing unit  10 . In its mounted state, a lower structural portion of the oil processing unit  10  is attached to an upper portion of a crank case cover  23 , whereby the above layout is effected.  
         [0062]     The oil cooler  11  is integrally formed as the lower structural portion in the mounted state of the oil processing unit  10 . For example, the oil cooler  11  comprises the lower structural portion of oil processing unit  10  mounted to the upper portion of the crank case cover  23 . The oil cooler  11  has a cylindrical heat exchanger portion (not clearly shown), and a cooling water inlet pipe  11   a  and discharge pipe  11   b  for the heat exchanger are provided (see  FIG. 11 ). Oil filter  12  comprises an upper structural portion of the oil processing unit  10 .  
         [0063]     A description will now be given of the lubricating oil supply structure in connection with the internal combustion engine E according to this embodiment. The lubricating oil supply structure adopts a so-called dry sump method. The structure of the lubricating oil supply path is shown fragmentarily in plural drawings and is difficult to understand. In the following description, therefore, reference is made to  FIG. 10  which is a schematic diagram showing a lubricating oil supply system used in this embodiment.  
         [0064]     As already described and as shown in  FIGS. 4 and 9 , at the left end  1   m  of the crankshaft  1 , the feed pump Pf and the scavenging pump Ps are mounted side by side on the pump shaft  1   q . The shaft  1   q  is adapted to rotate coaxially and interlockingly with the crankshaft  1 .  
         [0065]     As shown in  FIG. 7 , a suction port PfA of the feed pump Pf is in communication through a lubricating oil suction path F 1  with an opening  3   c  formed in a lower portion of the dry sump oil tank. Further, a discharge port PfB of the feed pump Pf is in communication through a lubricating oil supply path F 2  with the oil processing unit  10  which is an integral structure of the oil cooler  11  and the oil filter  12 . The lubricating oil supply path F 2  provides a communication between the oil cooler  11  as the lower structural portion of the oil processing unit  10  and the discharge port PfB of the feed pump Pf. When the feed pump Pf is activated, lubricating oil present within the dry sump oil tank is fed to the oil processing unit  10 .  
         [0066]     A branch oil path F 01  (see  FIG. 10 ) is provided in the lubricating oil supply path F 2  and a relief valve V 1  (see  FIGS. 1 and 7 ) is disposed in the branch oil path F 01 . The relief valve V 1  functions to regulate the lubricating oil supply pressure in the lubricating oil supply path F 2 . Oil flowing out from the relief valve V 1  passes through a branch oil path F 02  (see  FIG. 10 ) and is again returned to the lubricating oil suction oil path F 1 .  
         [0067]     As can be seen by reference to  FIGS. 4, 7 ,  8  and  9 , the lubricating oil is fed to the oil processing unit  10 , cooled by the oil cooler  11  within the oil processing unit  10 , and filtered by the oil filter  12 . The lubricating oil is then fed from a lubricating oil outlet of the oil processing unit  10  to the oil gallery F 5  and valve operating system  4  through branch supply paths. The branch supply paths include lubricating oil supply paths F 3  and F 4  (see  FIG. 7 ) for the supply of lubricating oil to the oil gallery F 5 , and lubricating oil supply paths F 10  and F 11  (see  FIG. 4 ) for the supply of lubricating oil to the valve operating system  4 .  
         [0068]     A check valve V 2  is disposed in the lubricating oil supply paths F 3  and F 4 , which are branch supply paths to the oil gallery F 5  communicating with the lubricating oil outlet of the oil processing unit  10  (see  FIG. 9 ). The check valve V 2  is disposed by utilizing a connection  24  between the crank case  20  and the case cover  23 .  
         [0069]     As shown in  FIG. 4 , the oil gallery F 5  extends below and in parallel with the crankshaft  1  so that the length of the extension corresponds to approximately the overall length of the crankshaft  1 . Plural lubricating oil supply paths F 6  and F 7  communicate with the journal portions  1   g  of the crankshaft  1  and with the crank pin portions  1   a  to which the connecting rods are connected, injection ports F 8  for inner walls of the cylinder bores  31 , and a lubricating oil supply path F 9  communicating with the ball bearing  1   i  positioned close to the right end of the crankshaft  1 . The plural lubricating oil paths F 6  and F 7  are also in communication with the oil gallery F 5 .  
         [0070]     Lubricating oil supply paths F 10  and F 11  communicate with the cam shafts  4   a  and  4   b  in the valve operating system  4  and are formed as in  FIG. 4 . As shown in the same figure, the lubricating oil supply path F 10  communicates with the lubricating oil outlet of the oil processing unit  10  and extends horizontally past the connection  24  between the crank case  20  and the crank case cover  23 . The lubricating oil supply path F 11  is bent at approximately right angles from the supply path F 10 , and extends upward along openings  30 A and  40 A. Openings  30 A and  40 A are formed respectively in the cylinder block  30  and the cylinder head  40  at the upper portion of the crank case  20  to allow for the cam chain  4   e . The lubricating oil supply paths F 10  and F 11  communicate through a branch supply path F 12  with lubricating oil supply paths F 13  and F 14  formed within the cam shafts  4   a  and  4   b . Plural apertures F 15  and F 16 , which are open to cam surfaces, are formed respectively in the lubricating oil supply paths F 13  and F 14  (see  FIG. 8 ).  
         [0071]     A suction port PsA (see  FIG. 4 ) of the scavenging pump Ps, juxtaposed to the feed pump Pf, is connected to an oil path S 1  which is for the suction of the oil (to be described later) accumulated in the bottom  21  of the crank case  20 . In  FIG. 4 , the bottom oil suction oil path S 1  extends from the pump suction port PsA to an oil sump portion  22 . The oil sump portion  22  is positioned nearly centrally of the bottom  21  of the crank case  20 . An opening S 0  for the suction of oil remaining in the oil sump portion  22  is formed in an extending end of the suction oil path S 1 . The extending end of opening S 0  faces the oil sump portion  22 .  
         [0072]     The bottom oil suction oil path S 1  extends from the oil sump portion  22  substantially horizontally along the bottom  21  of the crank case  20 , and below and in parallel with the crankshaft  1  and the oil gallery F 5 . The bottom oil suction path S 1  then is brought into communication with the suction port PsA of the scavenging pump Ps.  
         [0073]     As shown in  FIG. 7 , a discharge port PsB of the scavenging pump Ps communicates through with an upper opening  3   d  of the dry sump oil tank through a bottom oil return oil path S 2 , the oil path S 2  extending substantially obliquely upwards toward an upper portion of the oil tank  3  from the pump discharge port PsB. Thus, with the bottom oil recovering oil paths S 1  and S 2  communicating with the scavenging pump Ps, the oil staying in the crank case bottom  21  is returned to the dry sump oil tank upon operation of the scavenging pump Ps.  
         [0074]     A description will now be given of the supply of lubricating oil in the internal combustion engine E with reference to  FIGS. 4, 7 ,  8  and  9 . In the following description, as in the above description, reference is made to  FIG. 10  which is a schematic diagram of the lubricating oil supply system.  
         [0075]     Upon start-up of the internal combustion engine E and with rotation of the crankshaft  1 , the feed pump Pf and the scavenging pump Ps are each activated. When the feed pump Pf is activated, as shown in  FIG. 7 , the lubricating oil present within the dry sump oil tank is sucked into the pump Pf from the pump suction port PfA through the lubricating oil suction oil path F 1 . The pump pressure of the lubricating oil is increased within the pump Pf and then the pressurized lubricating oil is discharged from the discharge port PfB of the pump Pf.  
         [0076]     The pressurized lubricating oil is then fed from the lubricating oil feed path F 2  to the oil processing unit  10 , which is an integral structure comprising both the oil cooler  11  and the oil filter  12 . The feed pressure in the lubricating oil feed path F 2  is regulated by the relief valve V 1  disposed in the branch oil path F 01  (see  FIG. 10 ) and the lubricating oil flowing out under the pressure regulating action of the valve V 1  passes through the branch oil path F 02  (see  FIG. 10 ) and is again returned to the lubricating oil suction oil path F 1 .  
         [0077]     The lubricating oil which has entered the oil processing unit  10  circulates through the oil processing unit  10  while being cooled by the heat exchanger portion of the oil cooler  11  and filtered by the oil filter  12 . The lubricating oil thus cooled and filtered within the oil processing unit  10  is then fed to the oil gallery F 5  and the cam shafts  4   a ,  4   b  in the valve operating system  4  through the branch lubricating oil supply paths F 3 , F 4  and F 10 , F 11  (see  FIG. 4 ).  
         [0078]     The lubricating oil, which has been fed under pressure to the branch lubricating oil supply path F 3  communicating with the oil gallery F 5 , pushes open the check valve V 2  (see  FIG. 9 ), then flows through the lubricating oil supply path F 4  and is fed to the oil gallery F 5 . The lubricating oil thus fed to the oil gallery F 5  flows through the oil gallery F 5  which extends below and along the crankshaft  1 .  
         [0079]     The lubricating oil thus flowing through the oil gallery F 5  then passes through the branch lubricating oil supply paths F 6  and F 7 , and is fed to the journal portions  1   g  of the crankshaft  1  and the crank pin portions  1   a  to which the connecting rods  1   b  are connected. The lubricating oil is also fed to the inner wall portions of the cylinder bores  31  from the lubricating oil injection port F 8 , and is further fed through the branch lubricating oil supply path F 9  to the ball bearing  1   i  positioned close to the right end of the crankshaft  1  (see  FIG. 4 ).  
         [0080]     On the other hand, the lubricating oil, which has been fed under pressure to the branch lubricating oil supply paths F 10  and F 11  communicating with the cam shafts  4   a  and  4   b  in the valve operating system  4 , first flows through the lubricating oil supply path F 10  which extends horizontally through the connection  24  between the crank case  20  and the case cover  23 , then turns at approximately right angles and flows into the lubricating oil supply path F 11 . The oil supply path F 11  extends upward inside and along the wall portions of the openings  30 A,  40 A in the cylinder block  30  and the cylinder head  40  and also along a water jacket  32  of the cylinder block  30  (see  FIG. 4 ).  
         [0081]     The lubricating oil which has flowed through the lubricating oil supply path F 11  is divided by, and within, the lubricating oil supply path F 12  which branches in two at an upper portion of the supply path F 11 . The lubricating oil then flows through the lubricating oil supply paths F 13  and F 14 , formed as hollow bores  4   i  and  4   j  within the two cam shafts  4   a  and  4   b , i.e., the intake-side cam shaft  4   a  and the exhaust-side cam shaft  4   b . The lubricating oil then flows out from plural cam surfaces through the apertures F 15  and F 16  which are open to the cam surfaces, and is used for lubricating and cooling the cam surfaces of the cams  4   f ,  4   g  and the tappets  4   h  (see  FIGS. 4 and 8 ). The return oil which has been used for lubrication, though not clearly shown, is allowed to flow to the oil sump portion  22  of the bottom  21  of the crank case  20  through a return oil path or the like which extends through the cylinder block  30 .  
         [0082]     Though not clearly shown and explanations are omitted, lubricating oil is fed to drive shafts of accessory devices through other branch lubricating oil supply paths. The lubricating oil which has been used for lubricating various portions of the engine E then flows down dropwise through the interior of the engine E and is allowed to flow to the oil sump portion  22  of the bottom  21  of the crank case  20  through a lubricating oil return oil path though not clearly shown (see  FIG. 4 ).  
         [0083]     The lubricating oil, which has been used for lubricating the above various portions of the internal combustion engine E, and then has flowed down and or dripped into the oil sump portion  22  of the bottom  21  of the crank case  20  or has flowed into the oil sump portion  22  through a return oil path (not shown), is sucked in from the pump suction port PsA through the bottom oil suction oil path S 1  by means of the scavenging pump Ps which is driven along with the feed pump Pf. The bottom oil, whose pressure has been raised within the pump Ps, is returned and recovered from the upper opening  3   d  of the dry sump oil tank into the tank  3  through the bottom oil return oil path S 2  (see  FIGS. 4 and 7 ), then is again fed to the various portions of the engine E through the foregoing lubricating oil supply paths.  
         [0084]     A description will now be provided for the cooling structure in the internal combustion engine E.  
         [0085]     As shown in  FIG. 6  and as described earlier, the water pump Pw is disposed in the cutout space Ela of the dry sump oil tank in the front portion E 1  of the internal combustion engine E. The water pump Pw is adapted to be rotated in synchronism with rotation of the crankshaft  1  through the chain Pwc. The chain Pwc is stretched between the sprocket  1   k , (see  FIGS. 3 and 4 ) positioned close to the right end  1   h , and the sprocket Pwb, mounted on the water pump shaft Pwa (see  FIGS. 3 and 12 ).  
         [0086]     As can be seen by reference to  FIGS. 6 and 12 , there is formed a cooling water return path W 1  which provides communication between the cooling water suction port PwA 1  of the water pump Pw and a cooling water outlet of the radiator  68  (see  FIG. 1 ) disposed below the seat  64  of the snowmobile  60  not shown in  FIGS. 6 and 12 . Also provided is a cooling water supply path W 2 . The cooling water supply path W 2  provides communication between the cooling water discharge port PwB of the water pump Pw and the cooling water inlet port E 01  for the interior of the central part of the front portion E 1  of the internal combustion engine E. Further provided is a cooling water supply path W 3 . The cooling water supply path W 3  includes the water jacket  32  for conducting the cooling water introduced from the cooling water inlet port E 01  to around the cylinder bores  31  in the engine E. (see  FIG. 11 ).  
         [0087]     Additionally, there is provided a cooling water path W 4 , with a thermostat and a reservoir tank (neither shown) interposed therein, for communication between an outlet of the cooling water supply path W 3 , i.e., a cooling water discharge port E 02  from the engine E, and a cooling water inlet of the radiator  68 . Also provided is a cooling water bypath W 10 . The cooling water by path W 10  branches from the thermostat to bypass the cooling water when the cooling water temperature is low, such as during warming up (see  FIGS. 6 and 11 ). The cooling water bypath W 10  is in communication with a suction port PwA 2  (see  FIG. 6 ) of the water pump Pw.  
         [0088]     The cooling water inlet port E 01  for the interior of the engine E is positioned nearly centrally in the vertical direction of the cylinder block  30 . The cooling water discharge port E 02  for the discharge of cooling water from the interior of the engine E is located at an upper position in the vertical direction of the cylinder block  30 . Thus, the cooling water inlet port E 01  and the cooling water discharge port E 02  are disposed in a generally vertically aligned (up and down) positional relation in the cylinder block  30  (see  FIG. 6 ).  
         [0089]     A cooling water supply path W 20  is formed in the vicinity of the connection between the cooling water supply path W 2  and the cooling water inlet port E 01  (see  FIGS. 6 and 11 ). The cooling water supply path W 20  is connected to the cooling water inlet pipe  11   a  of the oil cooler  11 . A cooling water path W 21  (see  FIG. 11 ) is connected to the cooling water discharge pipe  11   b  of the oil cooler  11 . Though not shown, the cooling water path W 21  is in communication with the cooling water path W 4 , which provides communication between the cooling water discharge port E 02  and the cooling water inlet of the radiator  68 .  
         [0090]     Therefore, the water pump Pw rotates in interlock with rotation of the crankshaft  1  upon start-up of the internal combustion engine E to suck in cooling water from the suction port PwA 1  after being cooled by the radiator  68 . The pump pressure of the cooling water thus sucked into the pump Pw is increased within the same pump and is discharged from the discharge port PwB of the pump. The cooling water then passes through the cooling water supply path W 2 , further through the cooling water inlet port E 01  for the interior of the central part of the front portion E 1  of the internal combustion engine E (see  FIG. 6 ), and flows into the cooling water supply path W 3  including the water jacket  32 , etc. in the engine E (see  FIG. 11 ).  
         [0091]     The cooling water thus flowing into the cooling water supply path W 3  in the engine E is introduced into the water jacket  32  around the cylinder bores  31 . The water jacket constitutes a main portion of the cooling water path W 3 . The cooling water then passes through the jacket  32  and further through the cooling water supply paths formed within the cylinder head  40  (not shown) and absorbs heat. The thus-warmed cooling water is allowed to flow out to the exterior the engine E from the outlet of the cooling water path W 3  in the engine, that is, from the cooling water discharge port E 02  which is for the discharge of cooling water from the interior of the engine E. The water then flows through the cooling water path W 4 , which is a connection path to the radiator  68  communicating with the discharge port E 02  (see  FIG. 11 ), and is introduced from the upper portion of the radiator  68  into the radiator through the inlet of the radiator.  
         [0092]     After being introduced into the radiator  68 , the warmed cooling water circulates through the radiator while being deprived of heat and is cooled thereby. The cooling water thus cooled is again sucked into the suction port PwA 1  of the water pump Pw through the cooling water return path W 1  (see  FIG. 6 ) and is circulated for cooling various portions of the engine E through the cooling water supply paths.  
         [0093]     According to this embodiment constructed as above there are attained the following unique functions and effects.  
         [0094]     Since accessory devices, such as the dry sump oil tank, the water pump Pw and the starter motor  5 , as well as the steering shaft, are disposed closely clustered together in the front portion E 1  of the engine E, that is, since the accessory devices and the steering shaft  63   a  are not disposed on the rider&#39;s side of the engine E, the rider can easily and closely approach the engine E.  
         [0095]     The steering post  3 A, including the concave groove  3   b  which receives the steering shaft  63   a , is provided at approximately the central portion  3   a  of the dry sump oil tank. The dry sump oil tank is disposed in the front portion E 1  of the internal combustion engine E. The right and left cutout spaces E 1   a , E 1   b  are formed within the dry sump oil tank in a sandwiching relation to the steering post  3 A. Further, the water pump Pw and the starter motor  5  are received within the cutout spaces E 1   a  and E 1   b , respectively. Therefore, the engine E is well-balanced in its weight on the right and left sides. Additionally, the oil tank  3 , the water pump Pw and the starter motor  5  are arranged compactly without waste in point of space. Thus, the amount of so-called dead space is decreased, and it is possible to not only compactly configure the surroundings of the engine E, but also ensure an effective space around the engine.  
         [0096]     Since the surroundings of the internal combustion engine E can be made compact, there arises a space margin between the engine E and the snowmobile  60  which is useful in mounting the engine E onto the snowmobile  60 . Specifically, as a result of obtaining a space margin, it becomes easier to install the engine E, the engine mounting work efficiency is improved, and costs are reduced.  
         [0097]     The structure of the snowmobile described herein, including the internal combustion engine having the characteristic layout structure of accessory devices as described in the present invention, is also applicable to other vehicles within the scope including a common technical matter, e.g., a technical subject such that an advantage in point of space is to be ensured in engine installation.  
         [0098]     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 present invention as set forth in the claims.