Abstract:
A snowmobile is provided including an internal combustion engine, an induction system communicating with the engine, and a body defining an engine compartment in which the engine is at least in part contained. The body of the snowmobile includes at least two openings which communicate with the induction system, and a door movably positioned at at least one of the openings. The door is adapted to selectively open and close the opening to regulate a flow of induction air through the opening.

Description:
PRIORITY INFORMATION 
     This application is based on and claims priority to Japanese Patent Application No. 11-042313, filed Feb. 19, 1999. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an induction system for an internal combustion engine and more particularly to an induction system for the powering internal combustion engine of a snowmobile. 
     2. Description of the Related Art 
     It is the normal practice to position a powering internal combustion engine of a snowmobile within an engine compartment. This is done at least in part to protect the engine from the surrounding environment. Air is generally drawn from the engine compartment into the induction system of the engine. 
     When the snowmobile is operated, the temperature of the air drawn from inside the engine compartment is generally warmer than that of the outside air because of the heat generated by the engine. If the temperature of the induction air is too high, engine performance is compromised. 
     It is, therefore, a principal object of the present invention to provide an induction system for the internal combustion engine of a snowmobile wherein induction air is normally supplied to the induction system from outside of the engine compartment. 
     However, because the induction air is drawn from the outside rather than from the protected confines of the engine compartment, in certain operating conditions it may be more likely that snow and other foreign materials will enter the induction system along with the induction air, thereby degrading engine performance or harming the engine. Thus, in certain limited conditions, such as when the snowmobile is operated in deep snow, it may be more desirable to induct air from inside the engine compartment. 
     It is therefore a further object of the present invention to provide an induction system for the internal combustion engine of a snowmobile wherein the induction air can selectively be drawn from either outside or inside of the engine compartment. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention involves a snowmobile comprising an internal combustion engine and an induction system communicating with the engine. A body of the snowmobile defines an engine compartment in which the engine is located, at least in part. The body also includes first and second opening that communicate with the induction system. A door is movably positioned at the first opening to selectively regulate a flow of induction air through the first opening 
     In one embodiment of the invention, the first opening is an air inlet opening that admits air from outside the engine compartment. The inlet opening preferably is formed on a raised portion of the body, which is located in front of a seat of the snowmobile. 
     One or more sub-openings may also be provided for admitting induction air into the intake passage from inside or outside of the engine compartment. A sub-door is provided at each sub-opening and is movable with respect to the sub-opening to open and close the sub-opening. The sub-doors are arranged to be opened to admit induction air into the intake passage when the air inlet doors are closed. 
     For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been and will be described. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a snowmobile having an induction system in accordance with a preferred embodiment of the present invention. 
     FIG. 2 is a top plan view of the snowmobile of FIG. 1, with certain elements of the induction system shown in phantom. 
     FIG. 3 is a front elevational view of the snowmobile of FIG.  1 . 
     FIG. 4 is a side elevational view of the powering internal combustion engine of the snowmobile of FIG.  1  and an attached air box, with a portion of the air box broken away. 
     FIG. 5 is a side elevational view of the snowmobile of FIG. 1 with a portion of the upper engine shroud removed. 
     FIG. 6 is a top plan view of a center portion of the snowmobile of FIG. 1, with certain elements of the induction system shown in phantom. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference initially to FIGS. 1-3, a snowmobile constructed in accordance with an embodiment of the present invention is identified generally by the reference numeral  10 . The snowmobile  10  includes a body assembly  12  made up of a number of parts which may be formed from suitable materials. The body assembly  12  includes an upper engine shroud  14  and a lower tray  16 , which together define an engine compartment  18 . The engine compartment  18  houses an internal combustion engine  20  for powering the snowmobile  10 . 
     The body assembly  12  further includes a rear portion  22  that accommodates a seat  24  adapted to seat one or more riders in a straddle fashion. A handlebar assembly  26  is positioned in front of the seat  24  for operation by the rider. 
     The upper engine shroud  14  includes a raised portion  28  located in front of the handlebar assembly  26 . The raised portion  28  carries a windshield  29  for affording protection to the rider from wind, snow, branches and other objects when operating the snowmobile  10 . 
     A pair of front skis  30  are supported at a forward portion of the body  12  by means of a front suspension system  32 . The handlebar assembly  26  is linked to the front skis  30  in a suitable manner such that movement of the handlebar  26  results in a corresponding steering movement of the front skies  30 , as is well known in the art. 
     A carriage assembly  34  is supported at the rear portion of the body  12  below the seat  24  by a rear suspension system  36 . The carriage assembly  34  includes a pair of guide rails  38  that carry a plurality of idler rollers  40 , including a main rear idler roller  42 . 
     The guide rails  38  and idler rollers  40 ,  42  cooperate to form a path around which a drive track  44  is trained. The drive track  44  is driven by an output shaft (not shown) of the engine  20  through a suitable variable belt-type transmission (not shown), as is well known in the art. 
     With reference now to FIGS. 1 and 4, the engine  20  is comprised of a cylinder block  60  which extends generally transversely across the engine compartment  18  and is supported in the engine compartment  18  on suitable engine mounts (not shown). In the illustrated embodiment, the engine  20  is of the three cylinder inline variety and operates on a two cycle crankcase compression principal. However, the invention is not to be limited to any specific type of engine, and an engine having greater or fewer cylinders and/or operating on a four cycle or rotary cycle can be used. 
     The cylinder block  60  has three transversely aligned cylinder bores formed therein. The cylinder bores are closed by a cylinder head assembly  62  mounted to an upper end of the cylinder block  60 . 
     Air is delivered to the engine  20  by an induction system which is identified generally by the reference numeral  80 . The induction system  80  includes an air box  82 . In the illustrated embodiment, the air box  82  is shaped to fit below the raised portion  28  of the upper engine shroud  14  immediately in front of the handlebar assembly  26 . 
     A filter element  90  is provided at a suitable location in the induction air path for preventing foreign materials such as snow and ice from entering the engine  12  through the induction system  80 . In the embodiment illustrated in FIG. 4, the filter element  90  is provided at the top or inlet of the air box  82 . In addition or in the alternative, the induction system  80  may be configured to eliminate the need for a filter element, such as by forcing the induction air to follow a circuitous path through the induction system  80  in order to separate out any snow, water or other debris that may be present in the induction air. 
     In the embodiment illustrated in FIG. 4, the air box  82  is divided into three chambers. Induction air flows through the filter element  90  and then expands into a first expansion chamber  96 . From the first expansion chamber  96 , the induction air flows through a first connection passage  98  and into a second expansion chamber  100 . The induction air flows through the relatively small diameter connection passage  98  and expands upon entering the second expansion chamber  100 . From the second expansion chamber  100  the induction air flows through a second connection passage  102  and into a third expansion chamber  104 , where it expands again. This successive expansion of the induction air results in silencing of the air flow. 
     The air box  82  delivers air to a fuel supply unit  84 , which may include a carburetor for forming a fuel/air charge. The fuel also can be injected into the induction system or into the engine  12  by one or more fuel injectors. The carburetor delivers the fuel/air charge to an intake port of the engine  20  through a short connecting manifold. A reed type check valve is provided in the intake port to permit flow into the crankcase of the engine  12  and to prevent flow in the opposite direction. 
     The air/fuel charge is admitted to the crankcase chamber of the cylinder block  60  of the engine  12  and transferred through scavenge ports to the combustion chamber where it is fired by a suitable ignition system. The charge is exhausted from the combustion chamber through exhaust ports formed on the front side of the cylinder block  60  in the illustrated embodiment and delivered to an exhaust system, indicated generally by the reference numeral  110 . The exhaust product is then discharged to the atmosphere through an exhaust pipe  112 . 
     In accordance with the present invention, and as illustrated in FIGS. 1-3, air inlet openings  120  are provided in the body  12  of the snowmobile  10  for admitting air into the induction system  80  of the engine  12 . Preferably, the air inlet openings  120  are provided in the raised portion  28  of the upper engine shroud  14  and face forwardly in the normal direction of travel of the snowmobile  10 . However, the air inlet openings  120  may be provided at other locations in the body  12  of the snowmobile e.g., on the rear side of the windshield  29 , and need not necessarily face in a forward direction. For instance, in the illustrated embodiment, at least one air inlet opening  120  is provided on either side of the windshield  29  (i.e., on the front side of the windshield  29 ). The openings can also face rearward, upward, downward, outward to the sides, or any combination thereof. 
     An air intake passage  122  is provided between the air inlet openings  120  and the air box  82 . In the illustrated embodiment, the air intake passage  122  generally fills the space above the air box  82  and below the raised portion  28  of the upper engine shroud  14 . Upon entering through the air inlet openings  120 , air from the atmosphere flows through the air intake passage  122  and into the air box  80 . Because the induction air is not circulated in the engine compartment  18  before entering the induction system  80 , the temperature of the induction air is not significantly increased by engine heat, and engine performance is therefore not degraded. 
     With reference now to FIG. 5, an air inlet door  140  is provided at each air inlet opening  120 . In the illustrated embodiment, the air inlet doors  140  are pivotally attached to the upper engine shroud  14  and pivot with respect to the upper engine shroud  14  to open and close the air inlet openings  120 . The flow of induction air through the air inlet openings  120  is thereby regulated. Although the illustrated embodiment employs doors that pivot about an axis positioned at one edge of the opening, the doors can move relative to the opening in any of a wide variety of known ways. For example, the air inlet doors  140  may open and close the air inlet openings  120  by sliding toward and away from the air inlet openings  120 , or by rotating about a central axis of the air inlet doors  140  similar to a butterfly valve. In the illustrated embodiment, a spring  142  (see FIG. 6) is provided between each air inlet door  140  and an adjacent location on the engine shroud  14  in the to bias the air inlet doors  140  in a normally open position. 
     A sub-opening  160  may also be provided for admitting air into the air intake passage  122 . In the illustrated embodiment, the sub-opening  160  is provided in a lower wall surface of the air intake passage  122  between the two air inlet openings  120 , as shown in FIGS. 5 and 6. The sub-opening  160  is located in the lower surface of the air intake passage  122  behind the air inlet openings  120  and in front of the air box  82 . 
     As illustrated in FIG. 5, a sub-door  164  preferably is provided at the sub-opening  160 ; however, certain aspects of the present invention can be practiced without the use of the sub-door. In the illustrated embodiment, the sub-door is pivotally attached to the lower wall surface of the intake passage  122  for opening and closing the sub-opening  160 . When open, the sub-opening  160  allows air from the engine compartment  18  to flow into the intake passage  122  and into the induction system  80  of the engine  20 . A spring  166  is provided between the sub-door  164  and an adjacent location on the wall surface of the intake passage  122  or the engine shroud  14  to bias the sub-door  164  in a normally closed position. As with the air inlet doors  140 , the sub-door  164  also can be configured to move relative to the sub-opening  164  in any of a wide variety of ways, including, but not limited to, those recited above. 
     Either alternatively or in addition to the sub-opening  160  located in the lower wall surface of the intake passage  122 , a second sub-opening  170  may be provided in an upper wall surface of the intake passage  122 , as illustrated in FIG.  6 . The second sub-opening  170  is preferably located behind the windshield  29  of the snowmobile  10  and in front of the handlebar assembly  26 . In the illustrated embodiment, a second sub-door  172  is pivotally attached to the upper engine shroud  14  to open and close the second sub-opening  170  in a manner similar to that of the other sub-door  164  and sub-opening  160 . The second sub-door  172  is similarly biased in a normally closed position. However, when the second sub-door  172  is open, outside air (i.e., air from outside the engine compartment  18 ) is allowed to flow into the intake passage  122  and into the induction system  80  of the engine  20 . Again, as with the air inlet doors  140  and the sub-door  164 , the second sub-door  172  also can be configured to move relative to the second sub-opening  170  in any of a wide variety of ways, including, but not limited to, those recited above. 
     In a preferred embodiment of the invention, a handle operator  180  is provided for selectively opening and closing the air inlet doors  140 , and possibly for opening and closing the other doors, as will described below. In the embodiment illustrated in FIG. 6, the handle operator  180  extends from the raised portion  28  of the upper engine shroud  14  between the windshield  29  and handlebar assembly  26 . However, the handle operator  180  may be positioned at any location within reach of a rider while positioned on the snowmobile  10 . 
     The handle operator  180  operates an actuator mechanism which, in turn, actuates the air inlet doors  140  to open and close the air inlet openings  120 . In the embodiment shown in FIG. 6, the actuator mechanism is a wire and pulley system. However, it is to be understood that other types of actuators, which could include mechanical linkages and/or electrical actuators connected to the operator by fly-by-wires, may also be used. 
     In the illustrated embodiment, the actuator mechanism includes control wires  196  which link the handle operator  180  to the air inlet doors  140 . The control wires  196  extend from the handle operator  180  around pulley pins  184  and are attached to the air inlet doors  140 . A control wire  198  is also provided for linking the handle operator  180  to the sub-door  164  for opening and closing the sub-opening  160  in the lower wall surface of the intake passage  122 . The control wire  198  extends from the handle operator  180  around a pulley pin (not shown) and is attached to the sub-door  164 . Similarly, if a second sub-opening is provided in the upper wall surface of the intake passage  122 , another control wire would be provided between the handle operator  180  and the second sub-door  172 . 
     When the handle operator  180  is turned, the control wires  196  pull on the air inlet doors  140  to overcome the force of the springs  142 . The air inlet doors  140  are thereby pivoted from their normally open positions to close the air inlet openings  120 . Outside air is thus prevented from entering the intake passage  122  through the air inlet openings  120 . In like manner, the turning of the handle operator  180  also causes the control wire  198  to pull on the sub-door  164 . The sub-door  164  is thereby pivoted from its normally closed position to open the sub-opening  160 . Air from the engine compartment  122  is thus allowed to enter the intake passage  122  through the sub-opening  160 . Thus, the sub-door  164  is opened as the air inlet openings  140  are closed. 
     During normal operation of the snowmobile  10 , the air inlet doors  140  remain opened to allow outside air to enter the intake passage  122  and induction system  80  directly through the air inlet openings  120 . Because the induction air is not circulated in the engine compartment  18  before entering the induction system  80 , the temperature of the induction air is not significantly increased by engine heat, and engine performance is therefore not degraded. 
     However, when deep snow or other adverse environmental conditions are encountered, the operator of the snowmobile  10  can turn the handle operator  180  to close the air inlet doors  140  and thereby prevent snow and water from entering the induction system  80  through the air inlet openings  120 . As a result, clogging of the filter element  90  and/or water damage to the engine  20  is prevented. As the air inlet doors  140  are closed, the sub-door  164  is opened to allow air into the induction system  80  from the protected engine compartment  18 . The opening of the sub-door  164  preferably occurs simultaneously with the closing of the air inlet doors  140 . 
     In certain conditions (e.g., when the outside air temperature is relatively low), it may be desirable to admit a mixture of outside air and air from the engine compartment  18  into the intake passage  122  to optimize engine performance. In such conditions, the handle operator  180  may be turned only slightly to partially close the air inlet doors  140 , and partially open the sub-door  164 . 
     If a second sub-opening  170  is provided in the upper wall surface of the intake passage  122  in addition to, or instead of, the sub-opening  160 , the second sub-door  172  is similarly opened as the air inlet doors  140  are closed. As a result, outside air enters the intake passage  122  and induction system  80  directly. However, because the second subopening  170  is located immediately behind the windshield  29 , it is generally protected from snow and other foreign materials that might otherwise enter the sub-opening  170  and clog the filter element  90  or damage the engine  20 . In addition, one advantage of the location of the second sub-opening  170  is that outside air can be admitted to the intake passage  122  directly even when the air inlet openings  120  are closed because of adverse conditions. As a result, engine performance is not degraded even when the air inlet doors  140  are closed. 
     It should be readily apparent from the foregoing that the described embodiment provides an effective induction system for the engine of a snowmobile wherein the operator of the snowmobile can selectively open and close air inlet openings formed in the body of the snowmobile to allow or prevent outdoor air from entering the induction system directly. Of course, the foregoing description is that of a preferred embodiment of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.