Abstract:
A snowmobile drive train employing a drive belt and an endless track is provided. The snowmobile comprises an engine including an output shaft, with a support member located adjacent to the engine. A drive pulley and a driven pulley are mounted on the support member so that the drive belt can be removed from the snowmobile by passing the drive belt over the pulleys. An isolation member couples the engine output shaft to the driven pulley, and the support member maintains the drive and driven pulleys in a constant positional relationship relative to each other. The support member also includes reduction gears for driving the endless track.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to snowmobiles. More particularly, the invention concerns a snowmobile with an improved drive train.  
         BACKGROUND OF THE INVENTION  
         [0002]    A drive train is the transmission system that connects a vehicle&#39;s engine output shaft to the vehicle drive axle or axles. For example, automobile drive trains may include a transmission, drive shaft, and drive axles. Snowmobile drive trains generally include a variable ratio belt drive system having a driving pulley that is directly coupled to the engine output shaft. The driving pulley usually includes a centrifugal clutch through which the drive ratio of the belt drive varies as a function of engine speed and torque. The drive belt connects the drive pulley to a driven pulley that is coupled to a jack shaft which in turn drives a chain and sprocket reduction drive. The reduction drive is coupled to an axle that drives sprocket wheels, which turn an endless track. This arrangement suffers a number of drawbacks, one of which is that the engine heat, vibrations and movements are directly translated to the driving pulley.  
           [0003]    Snowmobile engines are generally attached to the frame by rubber isolation mounts, to minimize vibration transmitted to the operator. However, the rubber mounts allow the engine to vibrate and move, which also allows the drive pulley to move. The efficiency of the belt drive system is decreased by any variation in the relative position and/or alignment of the two pulleys. The forces present in the drive belt during operation create a force that tends to pull both pulleys together. Therefore, with the engine mounted on flexible rubber supports, the position and alignment of the drive pulley relative to the driven pulley varies constantly during snowmobile operations, decreasing drive train efficiency.  
           [0004]    Moreover, the misalignment between the two pulleys causes heat to build up in the drive belt, decreasing the operating life of the drive belt. And, because the pulleys are generally made of aluminum, which has a high thermal conductivity, heat from the engine output shaft is transferred to the drive pulley, which heats the drive belt even more, further decreasing operating life. For these reasons, most snowmobiles are equipped with a spare drive belt, like a spare tire, for replacing drive belts that have failed due to excessive heat.  
           [0005]    Efforts to minimize engine movement by removing the isolators and directly attaching the engine to the frame have generally been unsuccessful because the engine vibration is transmitted to the frame, detrimentally affecting operator comfort, and increasing fatigue failure of snowmobile components attached to the frame.  
           [0006]    Another shortcoming of conventional snowmobile drive trains is the jack shaft and drive chain. The driven pulley is connected to a jack shaft that runs across the engine bay to chain-driven reduction gears. Endless track sprockets are connected to the reduction gears through another shaft. The extra rotational mass and weight of these components, combined with the relative movement between the two pulleys, results in a drive train efficiency of about 50%. This means that only about half of the engine&#39;s power is transmitted to the endless track for propelling the snowmobile. Moreover, the extra weight of the jack shaft and related components increases the overall snowmobile weight, further decreasing efficiency and performance.  
           [0007]    Therefore, there exists a need for a snowmobile drive train that maintains a constant alignment between the two pulleys and reduces the weight and complexity of the drive train system, increasing efficiency.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention alleviates to a great extent the disadvantages of conventional snowmobile drive trains by providing a drive train system that maintains the drive and driven pulleys in a fixed relationship relative to each other, while allowing the drive belt to be easily removed from the pulleys.  
           [0009]    In a preferred embodiment, a support member is located adjacent to the snowmobile engine. The drive pulley and driven pulley are rotatably mounted to the support member, with the drive belt looped around the pulleys, the pulleys mounted on the support member so that the drive belt can be removed from the snowmobile by passing the drive belt over the pulleys. The support member maintains the two pulleys in a precise alignment, greatly extending the operating life of the drive belt and simultaneously increasing drive train efficiency.  
           [0010]    An isolation member couples the drive pulley to the engine output shaft, thereby permitting the engine to move relative to the support member, so that operator comfort is maintained.  
           [0011]    According to one aspect of the present invention, the support member may include two gears for coupling the driven pulley to the endless track. The gears decrease the weight and complexity of the drive train, while increasing efficiency.  
           [0012]    According to another aspect of the present invention, the support member is constructed to absorb heat generated by the engine, thereby minimizing heat transfer to the pulleys. By decreasing engine heat transfer to the pulleys, the operating life of the drive belt is substantially increased.  
           [0013]    In yet another aspect of the present invention, a housing is structured to encompass the pulleys and drive belt, increasing ascetics of the snowmobile, and protecting the pulleys and drive belt from the environment.  
           [0014]    These and other features and advantages of the present invention will be appreciated from review of the following detailed description of the invention, along with the accompanying figures in which like reference numerals refer to like parts throughout. It should be understood that the description and examples, while indicating preferred embodiments of the present invention, are not intended to limit the scope of the invention, and various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a perspective view of a snowmobile incorporating a drive train constructed according to one embodiment of the present invention;  
         [0016]    [0016]FIG. 2 is a perspective view of a drive train support member constructed according to a preferred embodiment of the present invention;  
         [0017]    [0017]FIG. 3 is a side view of the drive train support member illustrated in FIG. 2;  
         [0018]    [0018]FIG. 4 is a partial sectional view taken along cutting plane  4 — 4  of FIG. 3;  
         [0019]    [0019]FIG. 5 is a partial sectional view taken along cutting plane  5 — 5  of FIG. 3; and  
         [0020]    [0020]FIG. 6 is an exploded view of the isolation member illustrated in FIG. 2.  
         [0021]    It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    In the following paragraphs, the present invention will be described in detail by way of example with reference to the attached drawings. Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention. As used herein, “the present invention” refers to any one of the embodiments of the invention described herein. Reference to various features of the “present invention” in this document does not mean that the claimed embodiments must include all the referenced features.  
         [0023]    The present invention contemplates a snowmobile drive train that isolates the drive train pulleys from engine heat and vibration and mounts the pulleys rigidly, thereby maintaining precise pulley alignment. In addition, the present invention eliminates the jack shaft and chain drive found on conventional snowmobiles, and instead mounts two gears in a support member. This decreases drive train weight and allows the engine to be mounted lower in the frame, thereby lowering the center of gravity, which improves the snowmobile handling and stability characteristics.  
         [0024]    Referring to FIG. 1, a snowmobile  10  incorporating a drive train assembly  12  constructed according to the present invention is illustrated. The snowmobile  10  comprises a seat  30  for the operator and a handlebar assembly  25  that steers the skis  20 , which are connected to the snowmobile  10  through the front suspension assembly  22 . An engine  32  drives the endless track  15  through the drive train assembly  12 , the endless track  15  positioned around a rear suspension assembly  18 . The rear suspension assembly  18  and other features of the snowmobile  10  are further described in U.S. patent application, Ser. No. 09/502,280, entitled “SNOWMOBILE SUSPENSION”, filed Feb. 10, 2000, which is incorporated herein by reference in its entirety.  
         [0025]    Referring to FIGS. 2 and 3, a drive train casing or support member  40  is illustrated. The support member  40  comprises a rigid member that is preferably cast aluminum. Other embodiments can be made of other materials such as steel or composite materials such as Kevlar or carbon fiber. The support member  40  is bolted or otherwise attached to the frame  35 . The support member  40  is located adjacent to the engine  32  and is connected to the engine  32  by the isolator assembly  70 . Located outboard of the support member  40  is a drive pulley  45  and a driven pulley  50 . In a preferred embodiment, both pulleys  45  and  50  are centrifugal clutches arranged to form a constantly variable transmission. However, unlike conventional snowmobile drive train arrangements, the pulleys  45  and  50  of the present invention are rigidly mounted on the support member  40  so that relative movement between the pulleys  45  and  50  is eliminated.  
         [0026]    Referring to FIGS.  2 - 3 , another aspect of the present invention is illustrated. The engine water pump  60  is also mounted on the support member  40 . The water pump  60  is mounted on the inboard side of the support member  40  with a water pump pulley  65  located on the outboard side of the support member pulley  40 . A water pump belt  67  connects the water pump pulley  65  to the drive pulley axle  47 . Therefore, when the drive pulley axle  47  rotates, the water pump pulley  65  rotates which drives the water pump  60 , circulating water through the engine  32  cooling system. By mounting the water pump  60  to the support member  40 , the water pump  60  is isolated from the harsh engine  32  vibrations, which can cause fatigue failures of metal components, such as the water pump  60 .  
         [0027]    Referring to FIGS. 4 and 5, two cross-sectional views of the drive train assembly  12  are illustrated. The drive pulley  45  and the driven pulley  50  are rotatably mounted in the support member  40  by pulley bearings  49 . In a preferred embodiment, the pulley bearings  49  are tapered roller bearings, but other types of bearing arrangements such as needle bearings, ball bearings, journal bearings or other suitable bearing arrangements are contemplated. Because the drive and driven pulleys  45  and  50  are securely but rotatably mounted in the support member, the pulleys are free to rotate. However, they are not free to move closer together or in other directions. This ensures that a drive belt  55  that is positioned between the pulleys  45  and  50  operates at maximum efficiency. Relative movement between the drive pulley  45  and driven pulley  50  causes the edges of the drive belt  55  to slip or otherwise not engage correctly with the pulleys  45  and  50 , thereby causing heat buildup in the drive belt  55  and decrease efficiency in the drive train.  
         [0028]    Another feature of the present invention incorporated within the drive train assembly  12  is that even though the drive pulley  45  and driven pulley  50  are rigidly mounted, removal of the drive belt  55  can still be easily accomplished by simply looping the drive belt  55  over the pulleys  45  and  50 . Easy replacement of the drive belt  55  is important because when a drive belt  55  fails, the snowmobile is inoperable, leaving the operator possibly stranded in winter conditions. The operator must be able to easily install another drive belt  55  without the use of tools. The drive train assembly  12  constructed according to the present invention allows an operator to easily install a drive belt  55  over the drive and driven pulleys  45  and  50 .  
         [0029]    A snowmobile  10  constructed according to the present invention attaches the engine  32  to the frame  35  by isolation mounts. The engine isolation mounts are generally comprised of a rubber and are structured to absorb relative movement. The isolation mounts absorb the engine  32  vibration minimizing transfer of the engine  32  vibration to the operator. In a conventional snowmobile drive train arrangement, the engine output shaft  34  is directly connected to the drive pulley  45 . When the snowmobile accelerates or decelerates, the engine moves on the isolation mounts and generates relative movement between the drive pulley  45  and the driven pulley  50 .  
         [0030]    In the present invention, an isolation member or isolator assembly  70  is positioned between the engine output shaft  34  and the drive pulley  45  to absorb engine  32  vibration. Illustrated in FIGS. 2, 5 and  6 , the isolator assembly  70  includes an engine hub  72  connected to the engine output shaft  34 . A drive pulley hub  74  is connected to the drive pulley axle  47 . The engine hub  72  and drive pulley hub  74  contain projections  76  that engage an isolator  78 . The isolator  78  includes isolator projections  82  that engage the projections  76  on both the engine hub  72  and the drive pulley hub  74 . In a preferred embodiment, the isolator is made from a durable rubber, but other types of materials such as urethanes, polyurethanes, polymers, elastomers and other suitable materials are contemplated. In a preferred embodiment, the isolator  78  is oil-resistant and remains flexible at the low temperatures encountered during winter conditions.  
         [0031]    One advantage of the present invention is that the isolator assembly  70  greatly reduces the amount of heat transferred from the engine output shaft  34  to the drive pulley  45 . The rubber or other suitable type of material of the isolator  78  acts to insulate the drive pulley  45  from engine heat. In addition, in one embodiment, the support member  40  is cast from aluminum and absorbs heat transferred from the engine  32  to the support member  40 . In this manner, heat transferred to the drive pulley  45  is greatly reduced, which greatly increases the life of the drive belt  55  because the drive belt is not subjected to engine temperatures and temperature cycling.  
         [0032]    Referring to FIGS. 4 and 5, the drive pulley  45  and driven pulley  50  are rotatably mounted in the support member  40  by respective pairs of inboard pulley bearings  48  and outboard pulley bearings  49 . The bearing sets  48  and  49  are located about the drive pulley axle  47  and the driven pulley axle  52 , and resist the bending forces that are transmitted from the drive pulley  45  and the driven pulley  50  to their respective axles  47  and  52 .  
         [0033]    Specifically, the drive belt  55  pulls the drive pulley  45  and driven pulley  50  together during snowmobile  10  accelerations and decelerations. The force exerted by the drive belt  55  is resisted by the inboard and outboard pulley bearings  48  and  49 . Therefore, the arrangement, as illustrated in FIG. 4, permits the drive pulley  45  and driven pulley  50  to be securely mounted in the support member  40 , yet also permits the drive belt  55  to be easily removed without removing any additional components from the drive train assembly  12 .  
         [0034]    Referring to FIGS.  2 - 4 , another aspect of the present invention is illustrated. A pulley gear  85  and a sprocket gear  90  are rotatably mounted within the support member  40 . The pulley gear  85  is connected to the driven pulley  50  through the driven pulley axle  52 . The pulley gear  85  engages the sprocket gear  90 . The sprocket gear  90  attaches to at least one sprocket  80  through sprocket axle  75 . The sprocket axle  75  is rotatably mounted in the support member  40  by an inboard sprocket bearing  77  and an outboard sprocket bearing  79 . In a manner similar to the pulley bearings  48  and  49 , discussed above, the sprocket bearings  77  and  79  resist the bending forces transmitted to the sprocket axle  75  from the sprocket  80 .  
         [0035]    In a preferred embodiment, the sprocket axle  75  includes three or more sprockets  80  that drive the endless track  15 . Other arrangements of sprockets or other devices to drive the endless track  15  can be employed. Preferably, the pulley gear  85  and sprocket gear  90  are sealed within the support member  40 , keeping dust, dirt, snow, water and other elements from entering the gear cavity  87 . A gear ratio between the pulley gear  85  and sprocket gear  90  can range from between 1.5:1 up to 2:1. This ratio is necessary to reduce the rotational velocity of the driven pulley  50  to a rotational velocity suitable for the sprocket axle  75  that drives the endless track  15 .  
         [0036]    In one embodiment, the pulley gear  85  has  17  teeth and the sprocket gear  90  has  28  teeth, resulting in a gear ratio of about 1.6:1. Other ratios designed for different engine horsepower and torque characteristics can be employed. For example, an engine having low horsepower and torque would employ a gear ratio of about 1.5:1, and an engine having more horsepower and torque would employ a gear ratio of about 2:1. It is appreciated that the gear ratios can be changed to suit specific requirements, such as hill climbing, racing, and other activities requiring specific gear ratios. By including the pulley gear  85  and sprocket gear  90  within the support member  40 , the jack shaft and chain drive arrangement of conventional snowmobiles is eliminated. Because the jack shaft and chain drive are eliminated, the engine  32  can be rotated 180 degrees, so that the output shaft  34  is on the right side of the engine  32 , and the engine exhaust manifold (not illustrated) facing toward the rear of the snowmobile  10 . With the engine exhaust manifold facing rearward, an engine exhaust (not shown) can be positioned under the seat  30 .  
         [0037]    The elimination of the jack shaft and chain drive decreases the number of parts in the drive train assembly  12  and increases the efficiency of the drive train assembly  12 . Also, elimination of the jack shaft and chain drive allows the engine  32  to be mounted lower in the frame  35  increasing the snowmobile  10  stability. One advantage of the present invention is that the support member  40  has been designed to position the engine  32  as low as possible by optimizing the location of the pulley gear  85  and sprocket gear  90 .  
         [0038]    Many variations of the above-described snowmobile drive train are possible. One skilled in the art will appreciate that the present invention can be practiced by other than the preferred embodiments, which are presented in this description for purposes of illustration and not of limitation, as the present invention is limited only by the claims that follow. It is noted that various equivalents for the particular embodiments discussed in this description may practice the invention as well.