Patent Publication Number: US-2007102215-A1

Title: Induction System for a Four Cycle Engine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is related to and claims priority to U.S. Provisional Patent Application Ser. No. 60/402,709, which was filed on Aug. 13, 2002. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a four-cycle engine that is intended for use in a vehicle, such as for example a snowmobile or a three-wheeled vehicle. More particularly, the present invention relates to a four-cycle engine having an improved induction system that complies with the strict emission control regulations currently developed in the United States without having a negative effect on the balance of the vehicle. The engines disclosed herein are described in connection with a snowmobile. The present invention, however, is not intended to be so limited; rather, it is contemplated that the engines described herein may be used in motorcycles, all-terrain vehicles, and various watercraft.  
      2. Description of Related Art  
      Snowmobiles are used for cross-country travel, during which it is frequently necessary to negotiate steep ascending and descending gradients, which requires powerful engines. Snowmobiles are used for both leisure-time pursuits as well as in a work environment. With this in mind, various demands are placed on the engine characteristics with respect to engine speed and torque. Known snowmobiles include a frame. Two steerable spring-mounted skis are installed on the front of the frame. A track driven by the engine is located on the lower rearward end of the frame. The track serves to propel the snowmobile over snow or ice covered ground. The engine and the track are usually connected by way of a continuously variable transmission (CVT), and a positive connection between the engine and the CVT. The positive connection is typically a centrifugal clutch that is integrated into the CVT.  
      At present, two-cycle engines are typically used to drive snowmobiles because these engines are capable of delivering a relatively large power output for a small installed size and low weight. Two-cycle engines, however, emit a considerable quantity of unburned hydrocarbons and other pollutants into the environment in the form of exhaust gas. The hydrocarbons and other pollutants are formed within the engine cylinders during the combustion process when the cylinder is inadequately flushed, and as a result of the lubricating oil that is added to the fuel.  
      Considerable structural and design modifications must be incorporated into the two-cycle engine to comply with current and ever more rigorous emission control regulations, which results in higher production costs. These modifications may include fuel injection and the use of catalysts. Furthermore, costly design features must be incorporated when the engines are used in snowmobiles to ensure that noise emissions are comparable to those of four-cycle engines.  
      One known snowmobile having a four-cycle engine is manufactured by Redline. The engine is a single overhead cam (SOHC), V-twin internal combustion engine that develops approximately 90 kW of power. The engine was originally designed for use in a motorcycle. These snowmobiles, which are up-market vehicles that are marketed under the brand name “954 Revolution,” are sport machines having a tubular frame. As such, these vehicles are only suitable for small-scale production. Due to predetermined minimum track width, the CVT is always remote from the longitudinal axis of the snowmobile. This arrangement is problematic especially for V-twin designs. If the center of gravity of the engine and the center of gravity of the CVT are on the same side of the vehicle, this would have a negative impact on the balance of the snowmobile and handling is made more difficult.  
      If the center of gravity of the engine (without auxiliary units) is arranged on the longitudinal axis of the snowmobile or on the opposite side of the vehicle relative to the center of gravity of the CVT, such an arrangement would require a relatively long drive shaft between the engine and the CVT. This arrangement, however, would generate undesirable oscillations within the drive train, which could result in a reduction of the service life or the destruction of the drive train. Furthermore, an engine in a snowmobile should be located to the rear as far as possible in order to locate its center of gravity as close possible to the track, which enhances the snowmobile handling and improves driving dynamics. This arrangement is not possible in the Redline design because the engine would collide with the steering rod.  
      Maximumsled also produces a snowmobile under the brand name “Venom” that is also based on a motorcycle engine. This snowmobile suffers from many of the same problems discussed above.  
      Large-scale production snowmobiles are typically manufactured from a sheet metal profile frame that is preferably of aluminum. A snowmobile of this kind is sold, for example, by Yamaha under the brand name “RX-1” and “RX-1 ER.” This snowmobile is powered by a four-cycle, four-cylinder, in-line, carburetor-type motorcycle engine that is installed transversely to the longitudinal axis of the vehicle. The engine has a dry-sump lubrication system, and develops approximately 107 kW of power. This engine has a relatively high nominal engine speed. As a result, additional reduction gearing has to be installed between the crankshaft and the drive pulley of the CVT. This engine has numerous drawbacks including a greater installed length and a greater weight. Furthermore, the exhaust runs beneath the tank and beneath the seat to the rear of the snowmobile. This produces a significant buildup of heat beneath the tank and the seat.  
      Published U.S. patent application Ser. No. 09/925,522 to Yatagai et al. discloses a snowmobile four-cycle engine arrangement. Yatagai discloses a four-cycle engine arranged in an engine compartment formed in the front body of a snowmobile. The crankshaft of the engine is laid substantially parallel to the body width of the snowmobile. The engine has a cylinder case inclined in a forward direction. The engine has a dry sump oil supplying system and an oil tank separate from the engine. This engine arrangement has several drawbacks. First, the cylinders are inclined in the forward direction. The turbocharger and oil tank are located in front of the engine. With this arrangement, the center of gravity of the engine is positioned relatively far away from a center point of the vehicle and the track. This adversely impacts the handling and maneuverability of the snowmobile. Second, the snowmobile is typically operated in severe working conditions (temperature changes between +15° C. to −40° C., ice formation, etc.). The water pump and alternator are belt driven. The belt is prone to failure.  
     OBJECTS OF THE INVENTION  
      It is an object of the present invention to provide a four cycle engine for use in a vehicle.  
      It is another object of the present invention to provide a four cycle engine having a low center of gravity for improved vehicle handling and maneuvering.  
      It is another object of the present invention to provide a four cycle engine overcoming the drawbacks of the prior art.  
      It is another object of the present invention to provide a four cycle engine having a single cylinder.  
      It is another object of the present invention to provide a four cycle engine having a pair of cylinder arranged in a V-shaped orientation.  
      It is another object of the present invention to provide a four cycle engine having a small installed size and low weight with a high a level of performance relative to the volumetric displacement of the engine.  
      It is another object of the present invention to locate and orient the four cycle engine in accordance with the present invention in a vehicle such that vehicle has a relatively low center of gravity.  
      It is another object of the present invention to provide a four cycle engine that has a longitudinal axis that is transverse to the longitudinal axis of the vehicle, wherein the center of gravity of the four cycle engine is located as close to the longitudinal axis of the vehicle as possible.  
      It is another object of the present invention to provide a four cycle engine having specific components that are located on opposing sides of the longitudinal axis of the vehicle to balance the engine with respect to the vehicle and locate the center of gravity of the engine as close to the longitudinal axis of the vehicle as possible.  
      It is another object of the present invention to arrange the induction system and the exhaust system on opposite sides of the engine, such that the combustion air is not heated to improve cylinder charging.  
      It is another object of the present invention to provide an engine that enhances the manner in which a snowmobile handles, whereby the resulting center of gravity that is determined by the vehicle frame and the engine is located as close as possible to the center of the vehicle in order to reduce the inertia of the snowmobile about its vertical axis.  
      It is another object of the present invention to provide an engine for use in a snowmobile having engine components and auxiliary units arranged as close as possible to the track of the snowmobile.  
      It is another object of the present invention to provide an engine having the cylinders rotated as far as possible to the rear, whereby the rear cylinder crankcase is located to one side of the steering rod.  
     SUMMARY OF THE INVENTION  
      To overcome the deficiencies of the prior art and achieve the above described objectives, applicants have developed a four cycle engine for use in a vehicle. The four cycle engine includes a crankcase having a crankshaft extending therethrough. The crankshaft has a crankshaft axis that is transverse to the longitudinal axis of the vehicle. The engine further includes at least one cylinder unit connected to the crankcase. Each cylinder unit includes a cylinder and a cylinder head. It is contemplated that a single cylinder unit may provided. It is also contemplated that two or more cylinder units may be provided. In such a configuration, the cylinder units are arranged at an angle with respect to each other. The engine in accordance with the present invention further includes a continuously variable transmission (CVT) connected to the crankcase on one side of the longitudinal axis of the vehicle. The CVT is driven by the crankshaft. An air box is also provided that is located on the same side of the longitudinal axis as the CVT. The engine further includes an intake manifold operatively connected to the air box for connecting the air box to each cylinder unit and a throttle assembly operatively connected to the air box and the intake manifold.  
      When two or more cylinder units are present, the cylinder units are arranged at an angle with respect to each other, wherein a space is formed between the cylinder units. With such an arrangement, the intake manifold is located in the space.  
      When a pair of cylinder units are provided, the intake manifold may have a generally Y-shaped manifold having a connector leg connected to the throttle assembly and a pair of branches. One branch is operatively connected to one of the cylinder units and another branch is connected to another of the cylinder units. The connector leg is generally parallel to the axis of the crankshaft. The intake manifold may further include a baffle assembly, which directs gas flow within the intake manifold. The baffle assembly divides each of the branches into two separate flow paths of approximately equal size.  
      When additional intake capacity is desired, a surge tank located within the space between the cylinder units may be provided. The surge tank is operatively coupled to the throttle assembly and the intake manifold. In such an arrangement, the intake manifold includes rising manifold branches connected at one end to the surge tank and the cylinder units at another end.  
      When the engine is a naturally aspirated engine, the air box also includes at least two chambers. A first chamber is connected through at least one opening to the atmosphere. A second chamber is connected to the throttle assembly. The first and second chambers are also operatively connected to each other.  
      In accordance with the present invention, the engine may further include a charger assembly for compressing gas before it is supplied to the at least one cylinder unit. The charger assembly is located on a side opposite the CVT. This arrangement balances the weight of the CVT. When a charger is provided, the air box includes at least two chambers. A first chamber is connected through at least one opening to the atmosphere and is operatively connected to the charger. The second chamber is operatively connected to the charger and the throttle assembly. The center of gravity of the charger assembly is located on the rear side of the engine. The charger may be either a supercharger, which is driven by the crankshaft of the engine and attached to the crankcase, or a turbocharger, which is driven by exhaust gases.  
      It is preferable that the engine in accordance with the present invention include fuel injection. At least one injection nozzle is associated with each cylinder unit. It is preferable that a pair of injection nozzles are associated with each cylinder unit. A first injection nozzle is operatively connected to the intake manifold adjacent the cylinder head unit. A second injection nozzle is operatively connected to the intake manifold upstream of and spaced apart from the first injection nozzle. The first injection nozzle operates under all engine loads. The second injection nozzle operates only during predetermined engine loads (e.g., full open throttle).  
      The present invention is also directed to a vehicle containing a four cycle engine. The combination of the vehicle and the engine produces a vehicle having improved handling and maneuverability and lower emissions when compared to prior art vehicles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the following description and claims, the references to front and rear relate to the direction of travel of the vehicle. The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein:  
       FIG. 1  is a top view of a four-cycle engine according to an embodiment of the present invention with an air box and the throttle assembly being omitted, wherein the four-cycle engine is illustrated within a snowmobile;  
       FIG. 2  is an end view of an output side of the engine of  FIG. 1 ;  
       FIG. 3  is an end view of the output side shown in  FIG. 2 , wherein the continuously variable transmission (CVT) and the air box are omitted;  
       FIG. 4  is an end view of the engine of  FIG. 1  opposite the output side, as shown in  FIG. 2 ;  
       FIG. 5  is a perspective view from the right rear side of the engine of  FIG. 1 ;  
       FIG. 6  is a front view of the engine, in partial cross section;  
       FIG. 7  is an end view of the engine shown in  FIG. 4  having a secondary housing omitted;  
       FIG. 8  is an end view of the engine illustrated in  FIG. 4  having the water pump housing omitted;  
       FIG. 9  is a top view of a single-cylinder engine in partial cross-section according to another embodiment of the present invention;  
       FIG. 10  is an end view of the engine of  FIG. 9 ;  
       FIG. 11  is an end view of the engine illustrated in  FIG. 3  having the oil tank and throttle assembly omitted, wherein chamber  24  and the oil filter  41  are shown in partial cross section;  
       FIG. 12  is a cross sectional view of the engine of  FIG. 1  through the crankcase, transverse to the crankshaft;  
       FIG. 13  is a cross sectional view of the lubricating-oil tank of the engine illustrated in  FIG. 1 ;  
       FIG. 14  is a schematic view of the oil pickup assembly;  
       FIG. 15  is a cross sectional view of the oil pick up assembly of  FIG. 14  along the main axis of the oil pickup assembly located within the engine of  FIG. 1 ;  
       FIG. 16  is a cross sectional view of a non-return valve within the crankcase of the engine illustrated in  FIG. 1 ;  
       FIG. 17  is a top view of a turbocharged version of the engine illustrated in  FIG. 1  illustrating the induction and exhaust systems;  
       FIG. 18  is an end view of the supercharged version of engine of  FIG. 1  illustrating a centrifugal blower;  
       FIG. 19  is the end view shown in  FIG. 18  illustrating the induction system ducts;  
       FIG. 20  is a partial cross sectional view of the air box according to the present invention;  
       FIG. 21  is a cross sectional view of the air box along section lines XXI-XXI in  FIG. 20 ;  
       FIG. 22  is bottom schematic view of a Y-manifold used in the engine of  FIG. 1  according to the present invention;  
       FIG. 23  is an end schematic view of the Y-manifold of  FIG. 22 ;  
       FIG. 24  is a partial cross sectional view of one of the secondary branches of the Y-manifold of  FIG. 22 ; and  
       FIG. 25  is a partial end view of a variation of the engine of  FIG. 1  having increased capacity. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      A four-cycle engine having one or more cylinders  4  will now be described in greater detail. A two cylinder engine  1  in accordance with the present invention is illustrated in  FIG. 1 . A single cylinder engine  100  in accordance with the present invention is illustrated in  FIG. 9 . As shown in  FIG. 1 , the engine  1  is mounted to a chassis of a snowmobile  90 . The engine  100  may be similarly mounted in the chassis of the snowmobile  90 . The present invention is not limited to four-cycle engines used in snowmobiles; rather, it is intended that the engines  1  and  100  disclosed herein and any variations thereof may be used in multiple vehicles including but not limited to three-wheeled vehicles, ATVs, motorcycles, and watercraft.  
      The four-cycle engine  1  having a pair of cylinders  4 A and  4 B will now be described in greater detail. Although a pair of cylinders  4 A and  4 B are disclosed, the present invention is not limited to a pair of cylinders; rather, it is contemplated that a single cylinder  4  may be provided, as described below in connection with  FIGS. 9 and 10 . It is further contemplated that more than two cylinders maybe provided (e.g. V-four cylinder engine). As shown in  FIGS. 2 and 3 , the engine  1  includes a crankcase  2  having a crankshaft  3  rotatably supported therein. The engine  1  further includes a pair of cylinders  4 A and  4 B that are arranged in a V configuration, as shown in  FIGS. 3, 4 ,  5  and  8 . The angle between the cylinders  4 A and  4 B is approximately 80°. Angles greater than 80° and less than 80° are considered to be well within the scope of the present invention. In order to locate the center of gravity of the engine  1  as close as possible to the middle of the snowmobile  90  or the track  96  and the same time to provide space for the steering rod  51 , the cylinder axis  70  of the front cylinder  4 B should be closer to the longitudinal axis  9  of the snowmobile  90  and the cylinder axis  70  of the rear cylinder  4 A, so that the center of gravity of the engine  1  is moved as close as possible towards the longitudinal axis of the snowmobile  90 .  
      Each of the cylinders  4 A and  4 B includes at least one inlet valve and at least one exhaust valve, which are located within the cylinder heads  8 A and  8 B, respectively. A pair of inlet valves and a pair of exhaust valves associated with each cylinder  4 A and  4 B is preferred.  
      The crankcase  2  includes a drive-side or output side section  34  and a second side section  33 , as shown in  FIG. 4 . The sections  33  and  34  together form a crankshaft chamber  5  that encloses the crankshaft  3 . The crankshaft  3  extends from opposite ends of the crankshaft chamber  5 . Each of the cylinders  4 A and  4 B includes a piston  6  movably mounted therein. The piston  6  is operatively connected to the crankshaft  3  by a connecting rod  7 , as shown in  FIG. 12 . The reciprocating movement of the pistons  6  is converted into a rotary movement at the crankshaft  3 .  
      The intake and exhaust valves of each cylinder are actuated by a single overhead camshaft (SOHC) (not shown) located within the cylinder heads  8 A and  8 B. The cams on the camshaft may directly operate the valves or indirectly operate the valves through rocker arms. The camshaft is operatively connected to the crankshaft  3  by way of a chain-drive system. The present invention, however, is not limited to the use of a single camshaft and rocker arms to operate the valves. It is, of course, understood that any other type of valve operating system such as DOHC and/or a camshaft driven by way of a notched belt could be used, without departing from the underlying concept of the present invention.  
      The arrangement of the engine  1  will now be described. As shown in  FIG. 1 , the four-cycle engine  1  may be installed in a snowmobile adjacent to a steering rod  51 . The engine  1  is arranged such that the axis  10  of the crankshaft  3  is transverse to the longitudinal axis  9  of the snowmobile. The rear cylinder  4 A is located adjacent the steering rod  51 . The cylinder axis of the front cylinder  4 B is located closer to the longitudinal axis  9  of the snowmobile than the cylinder axis of the rear cylinder  4 A.  
      A CVT  11  is supported on the engine  1 , as shown in  FIG. 2 , on one side of the longitudinal axis  9 . The CVT  11  is driven by the crankshaft  3 . A plurality of auxiliary units, shown in  FIGS. 1 and 4  and described below, are supported on an opposite side of the engine  1  on an opposite side of the longitudinal axis  9 . Relative to the CVT  11 , the auxiliary units are located on the opposite side of the longitudinal axis  9  of the snowmobile  90 . As shown in  FIGS. 8, 17  and  18 , the auxiliary units include but are not limited to an alternator or generator  12 , a starter motor  13 , a water pump  14 , at least two oil pumps including a suction pump  15  and a force pump  16 , and an optional charger. The charger may either be a mechanical supercharger  17  or a turbocharger  22 . The alternator  12 , the starter motor  13  and the optional supercharger  17  or turbocharger  22  are arranged with their centers of gravity on the same side of the axis  10  of the crankshaft  3  on the rear engine side. The auxiliary units (except the turbocharger  22 ) are driven by a common drive unit operatively connected to the crankshaft  3 . It is preferable that the common drive unit is a toothed wheel gearing  18 , as shown in  FIG. 7 . The use of common drive unit produces a particularly compact construction for the engine  1 . It is advantageous to have the starter motor  13  arranged to the rear of the axis  10  of the crankshaft  3 , which locates the resultant center of gravity of the engine even further towards the rear of the snowmobile. The CVT  11  and the auxiliary units will now be described in greater detail.  
      The toothed-wheel gearing  18  is accommodated in a secondary housing  20  that is located on the end of the second section  33  of the crankcase  2  to protect the gearing  18  from the external environment. As illustrated in  FIGS. 4-6 , the secondary housing  20  protects the toothed-wheel gearing  18  from environmental influences. The water pump  14  and the generator  12  are mounted on the exterior of the secondary housing  20 . Their respective drive shafts pass through the secondary housing  20  and mesh with the toothed-wheel gearing  18 . The suction pump  15  and the force pump  16  are located within the secondary housing  20 . All of these components are located on a side of the engine opposite the CVT  11 .  
      The generator  12  is preferably connected to the toothed-wheel gearing  18  through a dynamic damper to damp out excessive oscillations associated with the great inertial moment of the generator  12 . The generator  12  is driven by a gear wheel  18 A of the toothed-wheel gearing  18  that is arranged on the crankshaft  3  in the secondary housing  20 , as shown in  FIG. 7 . The drives for the water pump  14  and for the starter motor  13  also mesh with the same gear wheel  18 A. The starter motor  13  is coupled to the driving gear wheel  18 A and thus to the crankshaft  10  through a plurality of intermediate gear wheels in order to arrive at the required transmission ratio. The starter motor  13  is connected through a slip clutch  21  to the crankshaft to compensate for torque peaks. The suction pump  15  and the force pump  16 , are driven through the driving gear wheel  18 B of the toothed-wheel gearing  18 .  
      The water pump  14  delivers engine coolant through the coolant channels  81  within the engine  1 , shown in  FIGS. 7 and 8 . The water pump  14  includes a spiral housing  82 , shown in  FIG. 8  and an outer housing  83 , shown in  FIG. 4 . The housing  83  forms connecting pieces for coolant feed and return lines and incorporates a thermostat  84 , which is shown in  FIG. 4 . The thermostat  84  controls the flow of coolant.  
      A heat exchanger (not shown) is preferably arranged between the engine  1  and the track  96  in such a manner that when the snowmobile  90  is operated, snow or ice crystals are continuously thrown against the heat exchanger when the snowmobile track  96  is moving. This provides a simple yet highly effective means for cooling the engine without the need for any costly components.  
      As shown in  FIG. 2 , the CVT  11  comprises, amongst other things, a drive pulley  91  and driven pulley  92 . The drive pulley  91  is secured to the crankshaft  3 . The driven pulley  92  is secured to one end of an output shaft  94  that is supported by the chassis  90  of the vehicle. The drive pulley  91  and driven pulley  92  are operatively connected by a belt  93 . The transmission ratio between drive pulley  91  and driven pulley  92  is variable as a function of the load on the engine and engine speed. A reduction gear assembly  95  is connected to an opposite end of the output shaft  94 , as shown in  FIG. 1 . The reduction gearing  95  drives the track  96  of the snowmobile.  
      A supercharger or turbocharger can be used to compress the intake air and increase the cylinder charge. As shown in  FIGS. 18 and 19 , the supercharger  17  is preferably a centrifugal blower. The supercharger  17  is driven by the crankshaft  3  through the gearing  18 . The supercharger  17  is located on a side of the engine  1  that is opposite the CVT  11 . The supercharger  17  is located adjacent the rear cylinder  4 A. The axis  72  of the supercharger  17  is located parallel to and behind the axis  10  of the crankshaft  3 . Since the supercharger  17  is relatively heavy, it advantageously serves as a counterweight to the CVT. This arrangement improves both the handling and balance of the snowmobile  90 . This location of the supercharger  17  requires relatively short ducts for connection to the induction system.  
      Alternatively, a turbocharger  22  can be provided to improve the power output of the engine  1  instead of the mechanically driven supercharger described above. The turbocharger  22  is connected to the exhaust system. Like the supercharger  17 , the turbocharger  22  is mounted on the opposite side of the longitudinal axis  9  of the snowmobile  90  relative to the CVT  11 . With this arrangement, the axis  72  of the turbocharger impeller is behind the axis  10  of the crankshaft  3 , adjacent to the cylinder  4 A. The turbocharger  22  acts as a counterweight to the CVT  11 .  
      The induction system for the engine  1  will now be described. To configure the exchange of gases for the V-twin four cycle engine  1  in as simple a manner as possible, the inlet ports into the cylinder heads  8 A and  8 B are arranged on opposing sides of the cylinder heads  8 A and  8 B such that the inlet ports on cylinder head  8 A face the inlet ports on cylinder head  8 B, as shown in  FIG. 8 . The exhaust manifolds associated with each cylinder  4 A and  4 B are arranged on the opposing sides of the cylinders such that the exhaust ports on cylinder head  8 A face away from the exhaust ports on cylinder head  8 B.  
      Air and blow-by gas is drawn in through an air box or plenum  52 , which is advantageously arranged on the same side of the engine  1  as the CVT  11 , as shown in  FIGS. 2, 5  and  6 . The air box  52  is illustrated in greater detail in  FIGS. 20 and 21 . The air box  52  serves to equalize pressure waves and attenuate sound waves. A throttle assembly  55  is installed in a recess  53  that is formed in the air box  52 , as shown in  FIG. 20 . The throttle assembly  55  is operatively connected to an intake manifold  54 . The air and unburned gas mixture is supplied to the cylinder heads  8 A and  8 B and subsequently to the cylinders  4 A and  4 B by way of the intake manifold  54 . To protect the throttle assembly  55  against dirt, the recess  53  in the air box  52  is covered from above by a removable cover  56 , shown in  FIG. 21 .  
      As discussed above, the snowmobile  90  is typically operated in severe working conditions (e.g., as low as −40° C.). Under such conditions, icing around the throttle assembly  55  can occur, which could have an adverse impact on engine performance. Furthermore, at full loads, the velocity of air around the throttle assembly can also increase ice build up. In accordance with the present invention, a portion of the engine coolant is directed through a portion of the throttle assembly  55 . The coolant is fed through an inlet opening  551  through a passageway (not shown) to an outlet opening  552 , as shown in  FIG. 20 . Although the passageway typically only extends through a small portion of the throttle assembly  55 , the heat transfer properties of the material forming the throttle assembly are sufficient such that the coolant warms substantially the entire throttle assembly to prevent ice formation.  
      The air box  52  is arranged above the CVT  11  and incorporates at least two separate chambers  57  and  58 . The first chamber  57  of the air box  52  communicates with the atmosphere through openings  59  formed therein through which air is drawn into the induction system.  
      In the event that the engine  1  is a naturally aspirating engine (i.e., no turbocharger or supercharger), the first chamber  57  is connected to the chamber  58  through venturi tubes  60 , which attenuate induction noise. Air is first drawn into the first chamber  57  and then through the venturi tubes  60  into the second chamber  58 . The air is then routed through the throttle assembly  55  into the intake manifold  54  to the cylinder heads  8 A and  8 B into the cylinders  4 A and  4 B.  
      In the event that the engine  1  is a charged engine (i.e., turbocharged or supercharged), air is drawn into the first chamber  57  through the openings  59 . There are no venturi tubes  60  in the air box  52 . Unlike the naturally aspirating engine, the two chambers  57  and  58  are no longer connected directly to each other. The turbocharger or supercharger draws air from the first chamber  57  by way of a suction line  110 , as shown in  FIGS. 17 and 19 . The charger then compresses the air and returns the air to the second chamber  58  through a pressure line  111 , as shown in  FIGS. 17 and 19 . The second chamber  58  acts as an equalizer tank. The pressure in the chamber  58  is higher than the pressure in the chamber  57  and corresponds to the charge pressure. The compressed air then passes through the second chamber  58  into the throttle assembly  55  to the intake manifold  54  where it is delivered to the cylinders  4 A and  4 B. The same air box  52  can be used in either the aspirated version of the engine or the charged version of the engine with only minor modification.  
      It is preferable that the suction line  110  is routed around the rear cylinder  4 A and the cylinder head  8 A. It is preferable that the pressure line  111  is routed around the front cylinder  4 B and the cylinder head  8 B of the engine. The suction line  110  and the pressure line  111  are preferably formed as flexible hoses and/or rigid pipes. The present invention, however, is not limited to the use of hoses and/or pipes; rather, it is contemplated that the lines  110  and  111  may be at least partially integrated into the crankcase  2  or air box  52 . A charge-air cooler or intercooler  62  may be integrated into the pressure line  111  to cool the charge air. The cooler  62  has a relatively low weight and is preferably located in front of the axis  10  without adversely impacting the center of gravity. Furthermore, this location aids in cooling the air because it is exposed to wind during operation of the vehicle.  
      In the turbocharged version of the engine  1 , the suction line  10  is connected to deflector housing  73 , which redirects the air flow into the turbocharger  22  through an angle of 90°, so that the compressor impeller is acted upon by the air flow in an axial direction. There is limited space within the vehicle between the engine and the frame, the use of the deflector housing reduces the overall length of the tubocharger. As shown in  FIG. 17 , the turbocharger  22  is on a side of the engine  1  opposite the CVT  11  and the airbox  52 . The axis  72  of the turbocharger  22  is oriented so as to be essentially parallel to and behind the axis  10  of the crankshaft  3 .  
      In the event that additional capacity is required in the induction system, a surge tank  63  may be located in the space between the cylinders  4 A and  4 B, as shown in  FIG. 25 . Locating the surge tank  63  between the space formed by the angled cylinders  4 A and  4 B provides for additional capacity without increasing the space required for the engine. One side of the surge tanks  63  is connected to the throttle assembly  55 . The top side of the surge tank  63  opens into rising manifolds  54 A and  54 B. Manifold  54 A is operatively connected to the cylinder head  8 A. Manifold  54 B is operatively connected to the cylinder head  8 B.  
      In order to ensure that the cylinders  4 A and  4 B of the V-twin engine  1  are equally supplied with a homogenous mixture of air and fuel gas and that the cylinders are equally charged, the intake manifold  54  is preferably configured as a Y-shaped manifold  64 , as shown in  FIGS. 8, 11 ,  17  and  22 - 24 . The air flows into the main branch  65  of the Y-manifold  64  from the air box  52  and is divided equally between two secondary branches  66 . One branch  66  is operatively connected to the cylinder  4 A through the cylinder head  8 A. Another branch  66  is operatively connected to the cylinder  4 B through the cylinder head  8 B. The main branch  65  of the Y-shaped manifold  64  is essentially parallel to the axis  10  of the crankshaft  3 .  
      The Y-shaped manifold  64  has excellent flow characteristics and generates little air turbulence within the manifold  64 . This is especially important when each cylinder has two or more inlet valves. The Y-shaped manifold  64  offers significant benefits over conventional curved intake manifolds. Intake manifolds that follow a curved path to the cylinder heads will often admit unequal quantities of the homogenous mixture into the cylinder. This uneven admission is caused by the centrifugal forces that are generated in the intake flow within the intake duct of the manifold. As such, the valve that is associated with the inner area of the manifold always receives less gas than the valve that is associated with the outside curved area of the manifold, which results in downgraded cylinder charging. This has a negative effect on exhaust gas values and the power output achieved by the engine.  
      Little, if any, interference is created within the Y-manifold  64 . To ensure an even distribution of the air to each of the inlet ports of the two cylinders  4 A and  4 B, at least one baffle  67  is provided within the interior of the Y-manifold, as shown in  FIGS. 22-24 . As shown in  FIG. 24 , the baffles  67  are oriented in the direction of flow and divide the flow cross section of the main branch  65  and of at least the two secondary branches  66  into flow cross sections that are of approximately equal size such that equal volumes of the air are delivered to each inlet valve for each cylinder. The baffles  67  are in the form of dividers  68  that are formed in the Y-manifold and are oriented parallel to the axis  70 , shown in  FIGS. 4 and 6 , of each cylinder  4 A or  4 B in the area  69  where the Y-manifold  64  opens out into the cylinder heads  8 A and  8 B of the engine  1 .  
      As shown in  FIG. 11 , the engine  1  includes exhaust pipes  71  that extend from the outlet ports in the cylinder heads  8 A and  8 B. In accordance with the present invention, the exhaust pipes  71  may be connected directly to a muffler  19 , as shown in  FIG. 1 . In the event that the engine  1  includes a turbocharger  22 , the exhaust pipes  71  are connected to the turbocharger  22 , as shown in  FIG. 17 . In this way, the exhaust gases are utilized to drive the turbine of the turbocharger  22  before being directed to the muffler  19 . The muffler  19  is positioned on a side of the engine  1  opposite the output side (i.e. on a side opposite the CVT  11  and the oil tank  23 ). The exhaust gases generated by the engine  1  are routed from the muffler  19  in a downwardly towards the underside of the snowmobile and against the snow-covered surface of the ground. This greatly reduces exhaust noises.  
      The engine  1  is preferably equipped with a fuel-injection system to deliver fuel to the air as it is being fed into the cylinders  4 A and  4 B. The fuel-injection system preferably includes at least one injection nozzle  120 ,  121  associated with each cylinder  4 A and  4 B. The supercharged version of the engine preferably includes a pair of nozzles  120  and  121  for each cylinder  4 A and  4 B. One injection nozzle  120  supplies the engine  1  with its basic fuel supply. The other injection nozzle  121  ensures that a sufficient supply of fuel is available when the engine  1  is operating in the upper area of the engine load range. The operation of the injection nozzles is controlled by a control unit (not shown). Each injection nozzle  120  is preferably located in an area where the intake manifold  54  connects to the cylinder head  8 A or  8 B. Each injection nozzle  121  is preferably arranged upstream and spaced apart from the injection nozzle  120 . The engines described in accordance with the present invention, however, are not limited to the use of a fuel-injection system; rather, it is contemplated that a conventional carburetor may be used instead of a fuel-injection system. In such a case, the carburetor would replace the throttle assembly  55 . While the two nozzle arrangement is preferred for the supercharged version of the engine  1 , one nozzle for each cylinder can be used. Furthermore, multiple nozzles maybe used for other versions of the engine.  
      The lubrication system for the engine  1  will now be described in greater detail. The engine  1  is lubricated by a dry-sump lubrication system, in which the lubricating oil is held in two areas until required for further use. The first area is a chamber  24  formed in the crankcase  2 . The second area is an oil tank  23  that is located between the crankcase  2  and the CVT  11 , as shown in  FIGS. 1-3 . Both the tank  23  and the chamber  24  are near the engine  1  so that long connection conduits for transporting the lubricating oil are avoided. The oil tank  23  is connected to the chamber  24  through a common opening  25 . The chamber  24  and oil tank  23  are in fluid communication at all times. The oil tank  23  is preferably formed from a plastic material. The oil tank  23  is releasably secured to the output side of the crankcase  2 . As shown in  FIG. 3 , the crankshaft  3  passes through an opening formed in the oil tank  23 . As shown in  FIGS. 2 and 3 , the oil tank  23  includes a filler neck  36  and a lubricating oil dipstick  37 . This arrangement of the oil tank  23  does not adversely effect the position of the center of gravity of the engine because of the relative low weight of the oil tank  23  and the low weight of the lubricant that it contains.  
      The chamber  24  is formed in a lower portion of the crankcase  2  essentially beneath the axis  10  of the crankshaft  3 . Because a volume of the lubricating oil is in part stored in the chamber  24  in the crankcase  2 , the size of the external lubricating-oil tank  23  can be reduced to save space. The chamber  24  can accommodate a predetermined volume of the total volume of lubricating oil required for the engine. The chamber  24  should accommodate at least 30% of the total volume of lubricating oil. It is preferable that the chamber  24  accommodates at least 50% of the total volume of lubricating oil. In the embodiment shown in the figures, the volume makes up approximately 55% of the total volume. The chamber  24  in accordance with the present invention is not limited to these prescribed volumes; rather, it contemplated that chambers holding volumes of less than 30% or greater than 50% are considered to be well within the scope of the present invention.  
      The integration of the chamber  24  into the crankcase  2  is also useful during engine start-up. During a cold start, the lubricating oil is brought to operating temperature more quickly by the radiated or waste heat generated by the engine  1 . Thus wear on the engine is greatly reduced.  
      During engine operation, some lubricating oil collects in the crankcase chamber  5 . As seen in  FIG. 12 , a skimmer bar  101  located in the chamber  5  collects and directs the lubricating oil towards an outlet area in the bottom side of the crankshaft chamber  5 . A non-return valve  26  is arranged in the outlet area at the bottom of the crankshaft chamber  5  and is held positively between the crankcase halves  33  and  34 , as shown in  FIG. 16 . The non-return valve  26  is intended to prevent large quantities of lubricating oil flowing back into the crankcase chamber  5  as a result of the suction force generated during upward movement of the piston  6 . The non-return valve  26  is preferably a reed valve. The lubricating oil is pumped out of the crankshaft chamber  5  by the pressure pulses that are generated within the crankshaft chamber  5  by the pistons  6 . After passing through the valve  26 , the oil passes through a strainer  27  and collects in a collection space  28  that is within the crankcase  2 . The lubricating oil is returned to the tank  23  by the suction pump  15  by way of the connecting channel  29 .  
      Some blow-by gas enters into the crankshaft chamber  5  from the combustion chamber. The blow-by gas in the crankcase chamber  5  helps remove the lubricant from the crankshaft chamber  5 . The blow-by gas exits the crankcase chamber  5  through the non-return valve  26  with the lubricating oil. The blow-by gas passes through an oil separator that separates the lubricating oil from the blow-by gas. The oil separator is located on a sprocket of the camshaft (i.e., the separator is integrated into the camshaft drive system) and is described in detail in co-pending U.S. patent application Ser. No. 09/944,144, filed on Sep. 4, 2001 entitled “Blow-By Gas Separator And Decompressor for an Internal Combustion Engine,” which is incorporated specifically herein by reference. The clean blow-by gas is returned to the air box  52 .  
      The suction pump  15  is preferably an eccentric rotor (trochoidal) pump that is arranged on one end face of the crankcase  2  and driven by the toothed-wheel gearing  18 . The present invention, however, is not limited to an eccentric rotor pump; rather, other pumping assemblies are considered to be well within the scope of the present invention. As shown in  FIG. 13 , the connecting channel  29  opens out into the oil tank  23  through a riser line  35 . The riser line  35  prevents the lubricating oil from flowing back out of the oil tank  23 . In the event that the non-return valve  26  does not form a tight seal, the riser line  35  prevents the lubricating oil from flowing into the crankshaft chamber  5  when the engine  1  is not running, and thereby flooding the crankcase chamber  5 . As shown in  FIG. 13 , the riser line  35  is formed by a baffle  38  in the lubricating-oil tank  23 .  
      Various portions of the engine  1  are linked to the lubrication system. A timing-chain passageway  30  associated with the rear cylinder  4 A, shown in  FIG. 11 , opens into the collection space  28 . A timing chain passageway  32  associated with the front cylinder  4 B, shown in  FIG. 8 , opens into the secondary housing  20 . The secondary housing  20  is connected to the collection space  28 . Lubricating oil flowing from the valve gear through the timing chain passageways  30  and  32  can thus collect in the aforementioned collection space  28  at the bottom of the crankcase  2 . As shown in  FIG. 12 , the collection space  28  is separated from the first volume of lubricating oil within the chamber  24 . It is preferable that the engine  1  includes more than one strainer  27 . One strainer is located within each crankcase half  33  and  34  in such a way that the lubricating oil flowing from the timing chain passageways  30  and  32  passes through the strainer before it flows into the collection area  28 . This ensures that all the lubricating oil is filtered and no coarse impurities can enter the suction pump  15 .  
      The oil tank  23  includes a vent port  102 , which vents the tank  23  into the timing chain shaft  32  of the cylinder  4 B. In principle, of course, the other timing chain shaft  30  could also be used for this purpose. On its way to the collection area  28 , the lubricating oil that flows back from the timing chain shaft  32  passes through the driving gear for the auxiliary units to help lubricate the toothed-wheel gearing  18 .  
      The engine  1  includes various lubrication points located throughout the engine  1 , which are supplied with lubricant by the force pump  16  mounted on an end of the crankcase  2  within the secondary housing  20 . The force pump  16  is preferably an eccentric rotor (trochoidal) pump driven by the toothed-wheel gearing  18 . The present invention, however, is not limited to an eccentric rotor pump; rather, other pumping assemblies are considered to be well within the scope of the present invention. The force pump  16  draws the lubricating oil from the chamber  24  through an oil pickup assembly  39 , and routes the oil to various lubrication points within the engine (e.g., the crankshaft and connecting-rod bearings, the valve gear, etc.) by way of a lubricating oil cooler  40  and a lubricating oil filter  41 , shown in  FIGS. 4 and 11 . The oil cooler  40  is preferably a plate-type heat exchanger that is releasably secured to the crankcase  2 . Preferably, the engine coolant is routed to the cooler  40  through passageways  47 A to cool the lubricating oil and the lubricating oil is routed through the passageways  47 B, shown in  FIG. 6 . The present invention, however, is not limited to a plate-type heat exchanger; rather, other heat exchangers and other cooling assemblies are considered to be well within the scope of the present invention. It is also contemplated that relative wind could also be used for cooling. For engine versions with low power output, the oil cooler may also be eliminated and the passageways  47 A and  47 B are closed by a cover (not shown) that is attached to the crankcase.  
      In order to simplify the oil filter changes that are performed during routine maintenance operations, an oil filter  41  that cleans the oil circulating in the lubrication system is mounted on the engine with its oil filter axis directed in an upward direction. The lubricating oil filter  41  has an oil filter axis  48  that is essentially parallel to the cylinder axis  70  of the cylinder  4 B. The lubricating oil filter  41  is located within a housing  49 , which is arranged between the front cylinder  4 B and the oil tank  23 , ahead of the axis  10 . The oil filter  41  can be replaced by loosening the cover screw  106 , after which the oil filter  41 , the filter cover  50  and the cover screw  106  can be removed from the housing  49  as a single unit.  
      The oil pickup assembly  39  is shown in detail in  FIGS. 14 and 15  is operatively connected to the suction side of the force pump  16 , as shown in  FIG. 7 . The oil pickup assembly  39  is preferably formed from a plastic material. The oil pickup assembly  39  has a suction end  42  that includes a strainer  43  for trapping coarse impurities. The suction end  42  is submerged in the chamber  24 , as shown in  FIG. 15 . An opposite end  44  of the oil pickup assembly  39  opens into a riser channel  45  that is formed in section  33  of the crankcase  2 . The riser channel  45  extends into the suction side of the force pump  16 , as shown in  FIG. 7 . The force pump  16  thus draws in lubricating oil through the strainer  43  of the oil pickup  39  and the riser channel  45 .  
      The lower end of the riser channel  45  is closed off by a drain plug  46 . It is possible to drain the lubrication system by removing a single drain plug. As discussed above, the lubricating-oil tank  23  is connected to the chamber  24  through the opening  25 . Oil from the tank  23 , chamber  24  may be drained by removing the oil drain plug  46 . Oil from the collection space  28  is drained through a connecting channel  103  that is opened when the drain plug  46  is removed, as shown in  FIG. 15 .  
      A single cylinder four-cycle engine  100  in accordance with the present invention will now be described in connection with  FIGS. 9 and 10 . The engine  100  shares many of the same components with V-twin four-cycle engine  1 , described above. A discussion of these shared components has been omitted from the description of the engine  100 . The single-cylinder engine  100  is constructed by omitting the cylinder  4 B and cylinder head  8 B, which are located in front of the axis  10  of the crankshaft in the V-twin engine  1 . The opening in the crankcase  2  left by omitting the cylinder  4 B and cylinder head  8 B is closed by a cover  75 . As shown in  FIG. 9 , a balance shaft  76  is arranged in the crankcase  2  in area of the omitted cylinder  4 B and cylinder head  8 B to balance any first order inertial forces. The balance shaft  76  is driven by the crankshaft  3  through a toothed-wheel gearing  77 . The balance shaft  76  rotates in a direction opposite to the rotation direction of the crankshaft  3 . The balance shaft  76  also drives the pump shaft  78  of the coolant pump  14 . It is contemplated that the balance shaft  76  may be omitted, which may increase engine vibration.  
      It is desirable to move the center of gravity of the engine  100  as far to the rear as possible. In order to locate the center of gravity of the engine  100  as close as possible to the track  96 , the cylinder  4 B that is located in front of the crankshaft axis in engine  1  is omitted. To move the center of gravity of the engine  100  still further to the rear, the cylinder axis  70  can be rotated by more than 30° to the rear, relative to a vertical axis, and the cylinder  4  is arranged adjacent to it and alongside the steering rod  51 . In the embodiment shown in  FIG. 10 , the angle α between the axis  70  of the cylinder  4  and the vertical axis is approximately 37°. The steering rod  51  extends to one side of and adjacent to the cylinder  4  and cylinder head  8 . The angle β between the steering rod  51  and the vertical axis is approximately 34°. The present invention, however, is not limited to the angles; rather, other angles, both larger and smaller, are contemplated to be within the scope of the present invention. In general, it should be noted that the angle α between the axis of the cylinder  4  and a vertical axis is greater than the angle β between the steering rod  51  and the vertical axis.  
      While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments and elements, but, to the contrary, is intended to cover various modifications, combinations of features, equivalent arrangements, and equivalent elements included within the spirit and scope of the appended claims. Furthermore, the dimensions of features of various components that may appear on the drawings are not meant to be limiting, and the size of the components therein can vary from the size that may be portrayed in the figures herein. It is contemplated that the lubrication system can also be used to cool the pistons  6  when the engine  1  is running and lubricate them at the same time. This can be accomplished by providing at least one lubricating oil nozzle (not shown) in the crankcase  2 . The nozzles direct a stream of lubricant directly onto the inner surface of the piston for both cooling and lubrication. Thus, it is intended that the present invention covers the modifications and variations of the invention, provided they come within the scope of the appended claims and their equivalents.