Induction system for a four cycle engine

A four cycle engine having at least one cylinder unit is disclosed. The engine includes a continuously variable transmission (CVT) connected to the engine on one side of the engine. An air box is also provided that is located on the same side of the engine 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 air box and the intake manifold. 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.

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.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A four-cycle engine having one or more cylinders4will now be described in greater detail. A two cylinder engine1in accordance with the present invention is illustrated inFIG. 1. A single cylinder engine100in accordance with the present invention is illustrated inFIG. 9. As shown inFIG. 1, the engine1is mounted to a chassis of a snowmobile90. The engine100may be similarly mounted in the chassis of the snowmobile90. The present invention is not limited to four-cycle engines used in snowmobiles; rather, it is intended that the engines1and100disclosed 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 engine1having a pair of cylinders4A and4B will now be described in greater detail. Although a pair of cylinders4A and4B are disclosed, the present invention is not limited to a pair of cylinders; rather, it is contemplated that a single cylinder4may be provided, as described below in connection withFIGS. 9 and 10. It is further contemplated that more than two cylinders maybe provided (e.g. V-four cylinder engine). As shown inFIGS. 2 and 3, the engine1includes a crankcase2having a crankshaft3rotatably supported therein. The engine1further includes a pair of cylinders4A and4B that are arranged in a V configuration, as shown inFIGS. 3,4,5and8. The angle between the cylinders4A and4B 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 engine1as close as possible to the middle of the snowmobile90or the track96and the same time to provide space for the steering rod51, the cylinder axis70of the front cylinder4B should be closer to the longitudinal axis9of the snowmobile90and the cylinder axis70of the rear cylinder4A, so that the center of gravity of the engine1is moved as close as possible towards the longitudinal axis of the snowmobile90.

Each of the cylinders4A and4B includes at least one inlet valve and at least one exhaust valve, which are located within the cylinder heads8A and8B, respectively. A pair of inlet valves and a pair of exhaust valves associated with each cylinder4A and4B is preferred.

The crankcase2includes a drive-side or output side section34and a second side section33, as shown inFIG. 4. The sections33and34together form a crankshaft chamber5that encloses the crankshaft3. The crankshaft3extends from opposite ends of the crankshaft chamber5. Each of the cylinders4A and4B includes a piston6movably mounted therein. The piston6is operatively connected to the crankshaft3by a connecting rod7, as shown inFIG. 12. The reciprocating movement of the pistons6is converted into a rotary movement at the crankshaft3.

The intake and exhaust valves of each cylinder are actuated by a single overhead camshaft (SOHC) (not shown) located within the cylinder heads8A and8B. 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 crankshaft3by 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 engine1will now be described. As shown inFIG. 1, the four-cycle engine1may be installed in a snowmobile adjacent to a steering rod51. The engine1is arranged such that the axis10of the crankshaft3is transverse to the longitudinal axis9of the snowmobile. The rear cylinder4A is located adjacent the steering rod51. The cylinder axis of the front cylinder4B is located closer to the longitudinal axis9of the snowmobile than the cylinder axis of the rear cylinder4A.

A CVT11is supported on the engine1, as shown inFIG. 2, on one side of the longitudinal axis9. The CVT11is driven by the crankshaft3. A plurality of auxiliary units, shown inFIGS. 1 and 4and described below, are supported on an opposite side of the engine1on an opposite side of the longitudinal axis9. Relative to the CVT11, the auxiliary units are located on the opposite side of the longitudinal axis9of the snowmobile90. As shown inFIGS. 8,17and18, the auxiliary units include but are not limited to an alternator or generator12, a starter motor13, a water pump14, at least two oil pumps including a suction pump15and a force pump16, and an optional charger. The charger may either be a mechanical supercharger17or a turbocharger22. The alternator12, the starter motor13and the optional supercharger17or turbocharger22are arranged with their centers of gravity on the same side of the axis10of the crankshaft3on the rear engine side. The auxiliary units (except the turbocharger22) are driven by a common drive unit operatively connected to the crankshaft3. It is preferable that the common drive unit is a toothed wheel gearing18, as shown inFIG. 7. The use of common drive unit produces a particularly compact construction for the engine1. It is advantageous to have the starter motor13arranged to the rear of the axis10of the crankshaft3, which locates the resultant center of gravity of the engine even further towards the rear of the snowmobile. The CVT11and the auxiliary units will now be described in greater detail.

The toothed-wheel gearing18is accommodated in a secondary housing20that is located on the end of the second section33of the crankcase2to protect the gearing18from the external environment. As illustrated inFIGS. 4–6, the secondary housing20protects the toothed-wheel gearing18from environmental influences. The water pump14and the generator12are mounted on the exterior of the secondary housing20. Their respective drive shafts pass through the secondary housing20and mesh with the toothed-wheel gearing18. The suction pump15and the force pump16are located within the secondary housing20. All of these components are located on a side of the engine opposite the CVT11.

The generator12is preferably connected to the toothed-wheel gearing18through a dynamic damper to damp out excessive oscillations associated with the great inertial moment of the generator12. The generator12is driven by a gear wheel18A of the toothed-wheel gearing18that is arranged on the crankshaft3in the secondary housing20, as shown inFIG. 7. The drives for the water pump14and for the starter motor13also mesh with the same gear wheel18A. The starter motor13is coupled to the driving gear wheel18A and thus to the crankshaft10through a plurality of intermediate gear wheels in order to arrive at the required transmission ratio. The starter motor13is connected through a slip clutch21to the crankshaft to compensate for torque peaks. The suction pump15and the force pump16, are driven through the driving gear wheel18B of the toothed-wheel gearing18.

The water pump14delivers engine coolant through the coolant channels81within the engine1, shown inFIGS. 7 and 8. The water pump14includes a spiral housing82, shown inFIG. 8and an outer housing83, shown inFIG. 4. The housing83forms connecting pieces for coolant feed and return lines and incorporates a thermostat84, which is shown inFIG. 4. The thermostat84controls the flow of coolant.

A heat exchanger (not shown) is preferably arranged between the engine1and the track96in such a manner that when the snowmobile90is operated, snow or ice crystals are continuously thrown against the heat exchanger when the snowmobile track96is moving. This provides a simple yet highly effective means for cooling the engine without the need for any costly components.

As shown inFIG. 2, the CVT11comprises, amongst other things, a drive pulley91and driven pulley92. The drive pulley91is secured to the crankshaft3. The driven pulley92is secured to one end of an output shaft94that is supported by the chassis90of the vehicle. The drive pulley91and driven pulley92are operatively connected by a belt93. The transmission ratio between drive pulley91and driven pulley92is variable as a function of the load on the engine and engine speed. A reduction gear assembly95is connected to an opposite end of the output shaft94, as shown inFIG. 1. The reduction gearing95drives the track96of the snowmobile.

A supercharger or turbocharger can be used to compress the intake air and increase the cylinder charge. As shown inFIGS. 18 and 19, the supercharger17is preferably a centrifugal blower. The supercharger17is driven by the crankshaft3through the gearing18. The supercharger17is located on a side of the engine1that is opposite the CVT11. The supercharger17is located adjacent the rear cylinder4A. The axis72of the supercharger17is located parallel to and behind the axis.10of the crankshaft3. Since the supercharger17is relatively heavy, it advantageously serves as a counterweight to the CVT. This arrangement improves both the handling and balance of the snowmobile90. This location of the supercharger17requires relatively short ducts for connection to the induction system.

Alternatively, a turbocharger22can be provided to improve the power output of the engine1instead of the mechanically driven supercharger described above. The turbocharger22is connected to the exhaust system. Like the supercharger17, the turbocharger22is mounted on the opposite side of the longitudinal axis9of the snowmobile90relative to the CVT11. With this arrangement, the axis72of the turbocharger impeller is behind the axis10of the crankshaft3, adjacent to the cylinder4A. The turbocharger22acts as a counterweight to the CVT11.

The induction system for the engine1will now be described. To configure the exchange of gases for the V-twin four cycle engine1in as simple a manner as possible, the inlet ports into the cylinder heads8A and8B are arranged on opposing sides of the cylinder heads8A and8B such that the inlet ports on cylinder head8A face the inlet ports on cylinder head8B, as shown inFIG. 8. The exhaust manifolds associated with each cylinder4A and4B are arranged on the opposing sides of the cylinders such that the exhaust ports on cylinder head8A face away from the exhaust ports on cylinder head8B.

Air and blow-by gas is drawn in through an air box or plenum52, which is advantageously arranged on the same side of the engine1as the CVT11, as shown inFIGS. 2,5and6. The air box52is illustrated in greater detail inFIGS. 20 and 21. The air box52serves to equalize pressure waves and attenuate sound waves. A throttle assembly55is installed in a recess53that is formed in the air box52, as shown inFIG. 20. The throttle assembly55is operatively connected to an intake manifold54. The air and unburned gas mixture is supplied to the cylinder heads8A and8B and subsequently to the cylinders4A and4B by way of the intake manifold54. To protect the throttle assembly55against dirt, the recess53in the air box52is covered from above by a removable cover56, shown inFIG. 21.

As discussed above, the snowmobile90is typically operated in severe working conditions (e.g., as low as −40° C.). Under such conditions, icing around the throttle assembly55can 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 assembly55. The coolant is fed through an inlet opening551through a passageway (not shown) to an outlet opening552, as shown inFIG. 20. Although the passageway typically only extends through a small portion of the throttle assembly55, 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 box52is arranged above the CVT11and incorporates at least two separate chambers57and58. The first chamber57of the air box52communicates with the atmosphere through openings59formed therein through which air is drawn into the induction system.

In the event that the engine1is a naturally aspirating engine (i.e., no turbocharger or supercharger), the first chamber57is connected to the chamber58through venturi tubes60, which attenuate induction noise. Air is first drawn into the first chamber57and then through the venturi tubes60into the second chamber58. The air is then routed through the throttle assembly55into the intake manifold54to the cylinder heads8A and8B into the cylinders4A and4B.

In the event that the engine1is a charged engine (i.e., turbocharged or supercharged), air is drawn into the first chamber57through the openings59. There are no venturi tubes60in the air box52. Unlike the naturally aspirating engine, the two chambers57and58are no longer connected directly to each other. The turbocharger or supercharger draws air from the first chamber57by way of a suction line110, as shown inFIGS. 17 and 19. The charger then compresses the air and returns the air to the second chamber58through a pressure line111, as shown inFIGS. 17 and 19. The second chamber58acts as an equalizer tank. The pressure in the chamber58is higher than the pressure in the chamber57and corresponds to the charge pressure. The compressed air then passes through the second chamber58into the throttle assembly55to the intake manifold54where it is delivered to the cylinders4A and4B. The same air box52can 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 line110is routed around the rear cylinder4A and the cylinder head8A. It is preferable that the pressure line111is routed around the front cylinder4B and the cylinder head8B of the engine. The suction line110and the pressure line111are 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 lines110and111may be at least partially integrated into the crankcase2or air box52. A charge-air cooler or intercooler62may be integrated into the pressure line111to cool the charge air. The cooler62has a relatively low weight and is preferably located in front of the axis10without 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 engine1, the suction line110is connected to deflector housing73, which redirects the air flow into the turbocharger22through 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 inFIG. 17, the turbocharger22is on a side of the engine1opposite the CVT11and the airbox52. The axis72of the turbocharger22is oriented so as to be essentially parallel to and behind the axis10of the crankshaft3.

In the event that additional capacity is required in the induction system, a surge tank63may be located in the space between the cylinders4A and4B, as shown inFIG. 25. Locating the surge tank63between the space formed by the angled cylinders4A and4B provides for additional capacity without increasing the space required for the engine. One side of the surge tanks63is connected to the throttle assembly55. The top side of the surge tank63opens into rising manifolds54A and54B. Manifold54A is operatively connected to the cylinder head8A. Manifold54B is operatively connected to the cylinder head8B.

In order to ensure that the cylinders4A and4B of the V-twin engine1are equally supplied with a homogenous mixture of air and fuel gas and that the cylinders are equally charged, the intake manifold54is preferably configured as a Y-shaped manifold64, as shown inFIGS. 8,11,17and22–24. The air flows into the main branch65of the Y-manifold64from the air box52and is divided equally between two secondary branches66. One branch66is operatively connected to the cylinder4A through the cylinder head8A. Another branch66is operatively connected to the cylinder4B through the cylinder head8B. The main branch65of the Y-shaped manifold64is essentially parallel to the axis10of the crankshaft3.

The Y-shaped manifold64has excellent flow characteristics and generates little air turbulence within the manifold64. This is especially important when each cylinder has two or more inlet valves. The Y-shaped manifold64offers 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-manifold64. To ensure an even distribution of the air to each of the inlet ports of the two cylinders4A and4B, at least one baffle67is provided within the interior of the Y-manifold, as shown inFIGS. 22–24. As shown inFIG. 24, the baffles67are oriented in the direction of flow and divide the flow cross section of the main branch65and of at least the two secondary branches66into 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 baffles67are in the form of dividers68that are formed in the Y-manifold and are oriented parallel to the axis70, shown inFIGS. 4 and 6, of each cylinder4A or4B in the area69where the Y-manifold64opens out into the cylinder heads8A and8B of the engine1.

As shown inFIG. 11, the engine1includes exhaust pipes71that extend from the outlet ports in the cylinder heads8A and8B. In accordance with the present invention, the exhaust pipes71may be connected directly to a muffler19, as shown inFIG. 1. In the event that the engine1includes a turbocharger22, the exhaust pipes71are connected to the turbocharger22, as shown inFIG. 17. In this way, the exhaust gases are utilized to drive the turbine of the turbocharger22before being directed to the muffler19. The muffler19is positioned on a side of the engine1opposite the output side (i.e. on a side opposite the CVT11and the oil tank23). The exhaust gases generated by the engine1are routed from the muffler19in a downwardly towards the underside of the snowmobile and against the snow-covered surface of the ground. This greatly reduces exhaust noises.

The engine1is preferably equipped with a fuel-injection system to deliver fuel to the air as it is being fed into the cylinders4A and4B. The fuel-injection system preferably includes at least one injection nozzle120,121associated with each cylinder4A and4B. The supercharged version of the engine preferably includes a pair of nozzles120and121for each cylinder4A and4B. One injection nozzle120supplies the engine1with its basic fuel supply. The other injection nozzle121ensures that a sufficient supply of fuel is available when the engine1is 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 nozzle120is preferably located in an area where the intake manifold54connects to the cylinder head8A or8B. Each injection nozzle121is preferably arranged upstream and spaced apart from the injection nozzle120. 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 assembly55. While the two nozzle arrangement is preferred for the supercharged version of the engine1, one nozzle for each cylinder can be used. Furthermore, multiple nozzles maybe used for other versions of the engine.

The lubrication system for the engine1will now be described in greater detail. The engine1is 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 chamber24formed in the crankcase2. The second area is an oil tank23that is located between the crankcase2and the CVT11, as shown inFIGS. 1–3. Both the tank23and the chamber24are near the engine1so that long connection conduits for transporting the lubricating oil are avoided. The oil tank23is connected to the chamber24through a common opening25. The chamber24and oil tank23are in fluid communication at all times. The oil tank23is preferably formed from a plastic material. The oil tank23is releasably secured to the output side of the crankcase2. As shown inFIG. 3, the crankshaft3passes through an opening formed in the oil tank23. As shown inFIGS. 2 and 3, the oil tank23includes a filler neck36and a lubricating oil dipstick37. This arrangement of the oil tank23does not adversely effect the position of the center of gravity of the engine because of the relative low weight of the oil tank23and the low weight of the lubricant that it contains.

The chamber24is formed in a lower portion of the crankcase2essentially beneath the axis10of the crankshaft3. Because a volume of the lubricating oil is in part stored in the chamber24in the crankcase2, the size of the external lubricating-oil tank23can be reduced to save space. The chamber24can accommodate a predetermined volume of the total volume of lubricating oil required for the engine. The chamber24should accommodate at least 30% of the total volume of lubricating oil. It is preferable that the chamber24accommodates 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 chamber24in 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 chamber24into the crankcase2is 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 engine1. Thus wear on the engine is greatly reduced.

During engine operation, some lubricating oil collects in the crankcase chamber5. As seen inFIG. 12, a skimmer bar101located in the chamber5collects and directs the lubricating oil towards an outlet area in the bottom side of the crankshaft chamber5. A non-return valve26is arranged in the outlet area at the bottom of the crankshaft chamber5and is held positively between the crankcase halves33and34, as shown inFIG. 16. The non-return valve26is intended to prevent large quantities of lubricating oil flowing back into the crankcase chamber5as a result of the suction force generated during upward movement of the piston6. The non-return valve26is preferably a reed valve. The lubricating oil is pumped out of the crankshaft chamber5by the pressure pulses that are generated within the crankshaft chamber5by the pistons6. After passing through the valve26, the oil passes through a strainer27and collects in a collection space28that is within the crankcase2. The lubricating oil is returned to the tank23by the suction pump15by way of the connecting channel29.

Some blow-by gas enters into the crankshaft chamber5from the combustion chamber. The blow-by gas in the crankcase chamber5helps remove the lubricant from the crankshaft chamber5. The blow-by gas exits the crankcase chamber5through the non-return valve26with 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 box52.

The suction pump15is preferably an eccentric rotor (trochoidal) pump that is arranged on one end face of the crankcase2and driven by the toothed-wheel gearing18. 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 inFIG. 13, the connecting channel29opens out into the oil tank23through a riser line35. The riser line35prevents the lubricating oil from flowing back out of the oil tank23. In the event that the non-return valve26does not form a tight seal, the riser line35prevents the lubricating oil from flowing into the crankshaft chamber5when the engine1is not running, and thereby flooding the crankcase chamber5. As shown inFIG. 13, the riser line35is formed by a baffle38in the lubricating-oil tank23.

Various portions of the engine1are linked to the lubrication system. A timing-chain passageway30associated with the rear cylinder4A, shown inFIG. 11, opens into the collection space28. A timing chain passageway32associated with the front cylinder4B, shown inFIG. 8, opens into the secondary housing20. The secondary housing20is connected to the collection space28. Lubricating oil flowing from the valve gear through the timing chain passageways30and32can thus collect in the aforementioned collection space28at the bottom of the crankcase2. As shown inFIG. 12, the collection space28is separated from the first volume of lubricating oil within the chamber24. It is preferable that the engine1includes more than one strainer27. One strainer is located within each crankcase half33and34in such a way that the lubricating oil flowing from the timing chain passageways30and32passes through the strainer before it flows into the collection area28. This ensures that all the lubricating oil is filtered and no coarse impurities can enter the suction pump15.

The oil tank23includes a vent port102, which vents the tank23into the timing chain shaft32of the cylinder4B. In principle, of course, the other timing chain shaft30could also be used for this purpose. On its way to the collection area28, the lubricating oil that flows back from the timing chain shaft32passes through the driving gear for the auxiliary units to help lubricate the toothed-wheel gearing18.

The engine1includes various lubrication points located throughout the engine1, which are supplied with lubricant by the force pump16mounted on an end of the crankcase2within the secondary housing20. The force pump16is preferably an eccentric rotor (trochoidal) pump driven by the toothed-wheel gearing18. 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 pump16draws the lubricating oil from the chamber24through an oil pickup assembly39, 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 cooler40and a lubricating oil filter41, shown inFIGS. 4 and 11. The oil cooler40is preferably a plate-type heat exchanger that is releasably secured to the crankcase2. Preferably, the engine coolant is routed to the cooler40through passageways47A to cool the lubricating oil and the lubricating oil is routed through the passageways47B, shown inFIG. 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 passageways47A and47B 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 filter41that 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 filter41has an oil filter axis48that is essentially parallel to the cylinder axis70of the cylinder4B. The lubricating oil filter41is located within a housing49, which is arranged between the front cylinder4B and the oil tank23, ahead of the axis10. The oil filter41can be replaced by loosening the cover screw106, after which the oil filter41, the filter cover50and the cover screw106can be removed from the housing49as a single unit.

The oil pickup assembly39is shown in detail inFIGS. 14 and 15is operatively connected to the suction side of the force pump16, as shown inFIG. 7. The oil pickup assembly39is preferably formed from a plastic material. The oil pickup assembly39has a suction end42that includes a strainer43for trapping coarse impurities. The suction end42is submerged in the chamber24, as shown inFIG. 15. An opposite end44of the oil pickup assembly39opens into a riser channel45that is formed in section33of the crankcase2. The riser channel45extends into the suction side of the force pump16, as shown inFIG. 7. The force pump16thus draws in lubricating oil through the strainer43of the oil pickup39and the riser channel45.

The lower end of the riser channel45is closed off by a drain plug46. It is possible to drain the lubrication system by removing a single drain plug. As discussed above, the lubricating-oil tank23is connected to the chamber24through the opening25. Oil from the tank23, chamber24may be drained by removing the oil drain plug46. Oil from the collection space28is drained through a connecting channel103that is opened when the drain plug46is removed, as shown inFIG. 15.

A single cylinder four-cycle engine100in accordance with the present invention will now be described in connection withFIGS. 9 and 10. The engine100shares many of the same components with V-twin four-cycle engine1, described above. A discussion of these shared components has been omitted from the description of the engine100. The single-cylinder engine100is constructed by omitting the cylinder4B and cylinder head8B, which are located in front of the axis10of the crankshaft in the V-twin engine1. The opening in the crankcase2left by omitting the cylinder4B and cylinder head8B is closed by a cover75. As shown inFIG. 9, a balance shaft76is arranged in the crankcase2in area of the omitted cylinder4B and cylinder head8B to balance any first order inertial forces. The balance shaft76is driven by the crankshaft3through a toothed-wheel gearing77. The balance shaft76rotates in a direction opposite to the rotation direction of the crankshaft3. The balance shaft76also drives the pump shaft78of the coolant pump14. It is contemplated that the balance shaft76may be omitted, which may increase engine vibration.

It is desirable to move the center of gravity of the engine100as far to the rear as possible. In order to locate the center of gravity of the engine100as close as possible to the track96, the cylinder4B that is located in front of the crankshaft axis in engine1is omitted. To move the center of gravity of the engine100still further to the rear, the cylinder axis70can be rotated by more than 30° to the rear, relative to a vertical axis, and the cylinder4is arranged adjacent to it and alongside the steering rod51. In the embodiment shown inFIG. 10, the angle α between the axis70of the cylinder4and the vertical axis is approximately 37°. The steering rod51extends to one side of and adjacent to the cylinder4and cylinder head8. The angle β between the steering rod51and 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 cylinder4and a vertical axis is greater than the angle β between the steering rod51and 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 pistons6when the engine1is running and lubricate them at the same time. This can be accomplished by providing at least one lubricating oil nozzle (not shown) in the crankcase2. 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.