Patent Publication Number: US-2003221890-A1

Title: Three-wheeled vehicle with a continuously variable transmission

Description:
[0001] This application claims priority to U.S. Provisional Patent Application Nos. 60/358,400 and 60/358,398, both filed Feb. 22, 2002. These applications are hereby incorporated by reference herein.  
     [0002] This application is related to U.S. Ser. No. 09/944,159, filed Sep. 4, 2001, and the contents of which are incorporated by reference herein. This application is also related but does not claim priority to the following U.S. provisional applications that were filed on Feb. 22, 2002: No. 60/358,362; No. 60/358,394; No. 60/358,390; No. 60/358,395; No. 60/358,436; No. 60/358,397; and No. 60/358,439 and any non-provisional patent applications claiming priority to the same. This application is also related but does not claim priority to U.S. provisional application No. 60/358,737 filed on Feb. 25, 2002, and U.S. provisional application No. 60/418,355, which was filed on Oct. 16, 2002 and any non-provisional patent applications claiming priority to the same. The entirety of the subject matter of these applications is incorporated by reference herein.  
     [0003] This application is also related to but does not claim priority to U.S. Design Application 29/155,964 filed on Feb. 22, 2002, and U.S. Design Application 29/156,028 filed on Feb. 23, 2002. This application is also related to but does not claim priority to U.S. patent application Ser. No. 10/346,188 and U.S. patent application Ser. No. 10/346,189 which were filed on Jan. 17, 2003. The entirety of the subject matter of these applications is incorporated by reference herein. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0004] 1. Field of the Invention  
       [0005] This invention relates to vehicles, particularly vehicles designed for road use. Specifically, this invention is directed to three-wheeled vehicles driven by a power unit. In particular, this invention relates to a transmission system for such a vehicle.  
       [0006] 2. Background of the Invention  
       [0007] Known three-wheeled vehicles are typically designed as all terrain vehicles or as snowmobiles that have been modified to include wheels. Three-wheeled all terrain vehicles are traditionally designed with one wheel in front and two wheels in the rear, while snowmobiles have been adapted to run on wheels with a pair of front wheels and a single rear wheel. In the past, these vehicles have suffered from instability and/or poor performance and handling characteristics. As a result, these vehicles are not suitable for road use.  
       [0008] For example, U.S. Pat. No. 4,787,470 discloses a three-wheel vehicle with two front wheels and a sole rear wheel having a body formed by an all terrain vehicle (ATV) frame carrying two front fenders and one rear fender and a saddle type seat. An engine is supported on the frame but is exposed to the exterior of the vehicle body, as is common for motorcycles. In such a vehicle, the center of gravity of the rider and the vehicle are quite a distance above the ground.  
       [0009] U.S. Pat. No. 4,662,468 also discloses a three-wheel vehicle with two front wheels and a sole rear wheel. The three-wheel vehicle of the &#39;468 patent uses a conventional snowmobile chassis, which has been modified to include two driving wheels at its front portion.  
       [0010] U.S. Pat. No. 5,564,517 discloses a snowmobile conversion frame kit which includes a frame having two wheels with a steering assembly in the front and a rear wheel with a swing arm in the rear. The kit shown and described in the &#39;517 patent is designed to be secured to a conventional snowmobile chassis. The conventional snowmobile chassis offers less rigidity and structural strength than are required for ATVs.  
       [0011] As these and other prior art three wheeled vehicles are not designed for high performance road use, the powerplant in place in these vehicles has not been adapted for a three-wheeled high performance road vehicle.  
       [0012] The demands of high performance road vehicles include rapid acceleration, a wide range of gears, and reliable and smooth shifting between gears. The powerplant must be sufficient to drive the vehicle at high speeds for extended periods of time. Such a powerplant must be connected to a reliable, flexible transmission to efficiently change gears during operation.  
       [0013] Conventional engines have a narrow rpm (revolutions per minute) range in which horsepower (hp) and torque are at their maximum efficiency. Vehicles have multiple gears to take advantage of the most desirable rpm range depending on the desired speed of the vehicle. Shifting between gears allows the engine to stay below the maximum rpm limit and near the rpm band of best performance at different speeds. The transmission allows the gear ratio between the engine and the driven wheel(s) to change as the vehicle speeds up and slows down. For peak performance, and especially to accommodate the performance demands during road use, a vehicle should have a transmission that allows the engine to run at its single best performance rpm value. Conventional transmissions do not provide maximum flexibility that would be desired in a high performance vehicle.  
       [0014] Accordingly, there is a need for a three-wheeled vehicle, especially suitable for road use, that has a transmission that can accommodate high performance.  
       SUMMARY OF THE INVENTION  
       [0015] An aspect of this invention is to provide a three-wheeled straddle type vehicle having two wheels in the front of the vehicle and one wheel in the rear of the vehicle.  
       [0016] Another aspect of this invention provides a three-wheeled straddle type vehicle designed for road use. Off-road use is also contemplated, but it is not the primary focus of the design.  
       [0017] An additional aspect of this invention is to provide a three-wheeled straddle type vehicle having a high performance transmission associated with the drive system of the vehicle.  
       [0018] The vehicle in accordance with this invention is a three-wheeled straddle type vehicle that is designed with sufficient structural rigidity that it may operate as a high performance road vehicle. The vehicle may include an engine with an output power of 80-135 or more horsepower. A continuously variable transmission (CVT) is provided in connection with the engine to transmit engine power to the drive assembly of the three-wheeled vehicle.  
       [0019] A CVT is considered to be superior to a traditional geared transmission because, unlike a traditional gearbox that provides four or five separate gears, a CVT provides an infinite number of different “gears.” As a result, CVTs are much more efficient at transmitting torque from the engine to the output shaft of the transmission.  
       [0020] A CVT operates in general with a V-shaped drive belt that is supported by a drive pulley having a tapered belt engaging surface. In operation, the torque from the engine is transferred from the drive pulley to a driven element. When the engine is operating at low speed, the belt engages the tapered surface and slides radially along the drive pulley to effect a change in “gears.”  
       [0021] In a three-wheeled vehicle according to the invention, the driver may need to shift his or her weight when turning to facilitate turning, especially at high speeds. Unlike motorcycles, where the entire vehicle leans in a turn, the driver on a three-wheeled vehicle often will need to shift his or her weight on the vehicle to lean into the turn. This can complicate foot shifting. Use of a CVT eliminates this complication.  
       [0022] The three-wheeled vehicle in accordance with this invention comprises a frame, an engine mounted to the frame, a pair of front wheels supported by the frame and a single rear wheel supported by the frame. The rear wheel is operatively connected to the engine such that the engine drives the rear wheel. Alternatively, the vehicle could be designed for front wheel drive. Tires are mounted on each of the wheels, and the tires are suitable for road use. A straddle-type seat is supported by the frame and is disposed between the front wheels and the rear wheel. A CVT is operatively connected to the engine.  
       [0023] Other objects, aspects and features of the invention will be apparent in view of the following description and drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0024] Referring to the drawings that form a part of the original disclosure:  
     [0025]FIG. 1 is a front view of the three-wheeled straddle-type vehicle in accordance with a preferred embodiment of the invention;  
     [0026]FIG. 2 is a right side view of the three-wheeled vehicle of FIG. 1;  
     [0027]FIG. 3 is a top view of the three-wheeled vehicle of FIG. 1;  
     [0028]FIG. 4 is a front left perspective view of the frame assembly for the three-wheeled vehicle in accordance with the preferred embodiment of this invention;  
     [0029]FIG. 5 is left side view of the frame assembly of the three-wheeled vehicle, illustrated in FIG. 4, showing the rear wheel and rear swing arm assembly attached thereto;  
     [0030]FIG. 6 is a partial view of the connection between the transmission and the rear swing arm assembly of FIG. 5;  
     [0031]FIG. 7 is a schematic illustration of the connection between the engine and the transmission;  
     [0032]FIG. 7A is a schematic illustration of an alternative drive belt connection;  
     [0033]FIG. 7B is a schematic illustration of another alternative transmission shaft connection;  
     [0034]FIG. 8 is an exploded, perspective illustration of the CVT of the engine of the present invention;  
     [0035]FIG. 9 is a cross-sectional side view illustration of the drive pulley of the CVT in a state where the engine is operating at low speed;  
     [0036]FIG. 10 is a cross-sectional side view illustration of the driven pulley of the CVT in a state where the engine is operating at low speed;  
     [0037]FIG. 11 is a cross-sectional side view illustration of the drive pulley of the CVT in a state where the engine is operating at high speed;  
     [0038]FIG. 12 is a cross-sectional side view illustration of the driven pulley of the CVT in a state where the engine is operating at high speed;  
     [0039]FIG. 13 is an enlarged cross-sectional view of a portion of the drive pulley of the CVT in a state where the engine is operating at low speed;  
     [0040]FIG. 14 is a cross-sectional side view illustration of the slide sleeve from the drive pulley of the CVT of the present invention;  
     [0041]FIG. 15 is a top view of the slide sleeve from the drive pulley of the CVT of the present invention;  
     [0042]FIG. 16 is a perspective, side-view of the slide sleeve of the drive pulley of the CVT of the present invention;  
     [0043]FIG. 17 is a perspective illustration of the guide member element of the driven pulley of the CVT of the present invention;  
     [0044]FIG. 18 is a perspective illustration of the connector of the driven pulley of the CVT of the present invention;  
     [0045]FIG. 19 is a perspective illustration of the inner half of the driven pulley of the CVT of the present invention;  
     [0046]FIG. 20 is a rear view illustration of the inner half of the driven pulley of the CVT of the present invention;  
     [0047]FIG. 21 is an enlarged, top view illustration of an alternate embodiment of one of the centrifugal weights pivotally attached to the outer half of the driven half of the CVT of the present invention; and  
     [0048]FIG. 22 is a cross-sectional side view illustration of an alternative driven pulley for the CVT of the present invention, showing the construction for a pneumatically-operated driven pulley. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION  
     [0049] A three-wheel straddle type vehicle  10  in accordance with the present invention is generally illustrated in FIGS.  1 - 3 . The vehicle  10  is designed with a straddle-type seat assembly  90  that preferably accommodates two adult-sized riders, a driver and a passenger. While the vehicle  10  is not designed to accommodate more than two adult-sized riders, the present invention contemplates that the design of vehicle  10  may be changed easily to accommodate more than two adult-sized riders.  
     [0050] It should be noted that the conventions “left,” “right,” “front,” “rear,” “up,” and “down” are defined according to the normal, forward travel direction of the vehicle  10 . As a result, the “left” side of the vehicle  10  corresponds to the left side of a rider seated in a forward-facing position on the vehicle  10 .  
     [0051] The vehicle  10  is designed along a longitudinal axis and includes a left front wheel  11 , a right front wheel  12  and a rear wheel  13 . The front wheels  11  and  12  are equally offset from the longitudinal axis, and the rear wheel is aligned with the longitudinal axis. The left and right front wheels  11  and  12  have tires  111  and  121  secured thereto, respectively. The rear wheel  13  has tire  131  secured thereto. The rear wheel  13  may include multiple rims, with each rim accommodating a tire. In the case of a multi-rim arrangement, the rims would be rigidly connected to form a single wheel. For purposes of simplicity, when the rear tire is referred to in this application, it will be understood that the rear tire may include multiple tire components mounted on individual rims but acting as a single wheel.  
     [0052] The tires  111 ,  121 ,  131  have a friction coefficient in accordance with the tire manufacturer&#39;s specifications. Preferably, each of the wheels  11 ,  12  and  13  is sized to accommodate a 15-inch automobile tire. The present invention, however, is not limited to equal sized wheels; rather, it is contemplated that the front wheels  11  and  12  may be smaller in size to accommodate a 13-inch automobile tires. Furthermore, other wheel sizes are considered to be well within the scope of the present invention.  
     [0053] The front wheels  11  and  12  are supported by a front suspension assembly  20 . The rear wheel  13  is supported by a rear suspension assembly  30 . The front suspension assembly  20  and the rear suspension assembly  30  are secured to a vehicle frame assembly  40 , illustrated in FIG. 4. The front suspension assembly  20  includes a pair of suspension support arms (A-arms)  21  and a shock absorber  22  extending from each side of the frame assembly  40  to support each front wheel  11  and  12 . The rear suspension assembly  30  includes a rear swing arm assembly  301  that is attached to the frame assembly  40  by an axle  302 , that extends through the frame assembly  40 , as seen in FIGS. 5 and 6.  
     [0054] As shown in FIG. 4, the frame assembly  40  of the vehicle  10  includes left and right laterally-spaced rear suspension plates  41  and  42 . The rear suspension plates  41  and  42  generally form vertically and longitudinally extending reinforced plates. The suspension plates  41  and  42  are preferably made of a strong light material such as cast aluminum. Left and right laterally extending swing arm pivot bores  411  (only one being shown) are centrally disposed on each suspension plate  41  and  42  to accommodate pivotal mounting of the rear suspension swing arm assembly  301 .  
     [0055] As shown in FIG. 5, the rear swing arm assembly  301  includes a rear swing arm  303  that is pivotally supported by the axle  302 , which is retained in pivot bore  411 . The swing arm  303  is formed in a generally U-shape with a pair of parallel arm portions, that extend rearwardly from the axle  302  to the rear tire  13 . The rear swing arm  303  is suspended from the frame assembly  40  by a linkage system  304  and is biased by a shock absorber  305 . By this arrangement, the rear wheel  13  has a controlled range of pivotal movement about a lateral axis with respect to the frame assembly  40 .  
     [0056] Referring back to FIG. 4 and the frame assembly  40 , laterally-spaced left and right spars  43  and  44  extend upwardly and forwardly from upper forward portions of the left and right rear suspension plates  41  and  42 , respectively. As illustrated in FIG. 2, the outer side of the frame spar  44  is visible from the right side of the vehicle  10 . Preferably, the frame assembly  40  is a tubular frame, with at least some of the frame elements being formed of tubular members. The tubular members can have any cross section, including but not limited to square, rectangular, circular, oval and channel shaped. As such, tubular members contemplated by this invention include both closed and open cross sections, which may be made by casting, forging, stamping, or extrusion. The advantage of tubular members is that such elements are very strong, yet lightweight.  
     [0057] An engine  50  is secured to the vehicle frame assembly  40  adjacent to an engine cradle assembly  45 , as described with reference to FIG. 5. The engine  50  may be secured directly to the frame assembly  40  at several points of attachment. Alternatively, the engine  50  may be secured to the frame assembly  40  using a suitable mounting assembly, not shown. The engine  50  can be a structural element of the frame assembly  40  adding rigidity. Alternatively, the engine  50  may be merely supported by the frame assembly  40 .  
     [0058] As FIGS. 4 and 5 illustrate, the engine  50  is supported just behind the front suspension assembly  20  immediately above the lowest part of the frame assembly  40 . This positioning provides a low center of gravity, which is useful in ensuring good handling and stability of the vehicle  10 . Because of the rigidity and improved structural strength of the frame assembly  40 , the engine  50  can generate 80-135 horsepower or more without sacrificing stability and/or maneuverability of the vehicle  10 . The frame assembly  40  provides sufficient structural rigidity to withstand the forces created during high performance operation of the vehicle  10 .  
     [0059] The engine  50  includes an internal combustion engine and is preferably a four--stroke engine. In particular, the engine  50  may be a 1000 cc V-twin (V2) four-stroke engine manufactured by ROTAX®. The vehicle  10  in accordance with the present invention, however, is not limited to a 1000 cc engine. It is also contemplated that a 600 cc engine may be used. Furthermore, other engine displacement sizes are considered to be well within the scope of the present invention. Moreover, while a four-stroke engine is contemplated for use on the vehicle  10 , a two-stroke engine also may be employed. Alternatively, the engine  50  may be an electric motor.  
     [0060] The engine  50  is preferably connected to a CVT, which is discussed in detail below. Alternatively, the three-wheeled vehicle  10  may utilize a manual speed transmission with a clutch in a manner similar to those available on typical motorcycles.  
     [0061] A fender assembly  60  is associated with each of the front wheels  11  and  12 . As shown FIGS. 1 and 2, each fender assembly  60  includes a cover assembly  61  that covers the top rear portion of the tires  111  and  121 . The fender assembly  60  prevents dirt, water and road debris from being kicked up onto the rider, while the rider operates the vehicle  10 . Each fender assembly  60  is linked to the front suspension assembly  20  and a steering assembly  70  such that the cover assemblies  61  move with the wheels  11  and  12  during steering of vehicle. This arrangement ensures that the tires  111  and  121  will not kick up dirt, water and road debris at the operator as the vehicle  10  turns. Each fender assembly  60  preferably includes a turn signal  62  located on the top surface of each cover assembly  61 , as shown in FIGS.  1 - 3 .  
     [0062] The steering of the front wheels  11  and  12  is accomplished through the use of the steering assembly  70 . The steering assembly  70  includes handlebars  71  and steering linkages (not shown) connected to the wheels  11  and  12  for purposes of turning the wheels  11  and  12  in response to movement of the handlebars  71 . The steering assembly  70  of the vehicle  10  is preferably provided with a progressive steering system (not shown). The progressive steering system allows the handlebars  71  to be turned to their maximum position (up to about 50 degrees of arc), while the wheels  11  and  12  turn to an increasingly greater extent. The linkage between the handle bars  71  and the steering linkages that makes progressive steering possible are designed so that small variations in the handlebars  71  when the vehicle  10  is traveling straight will not turn the wheels  11 ,  12  to any significant degree. In other words, when the vehicle  10  is traveling forward, especially at high speed, there should be a good amount of play in the handlebars  71  so that small movements made by the driver do not result in a sudden (or unexpected) turning of the vehicle  10 . On the other hand, when the handlebars  71  are turned to a more significant displacement, the degree of play preferably should decrease as the angular displacement of the handlebars  71  increases. The closer the handlebars  71  are turned to their most rotated position, the less play there should be in the linkage between the handlebars  71  and the wheels  11 ,  12  of the vehicle  10 .  
     [0063] The front of the vehicle  10  includes a fairing assembly  80 , which encloses the engine  50  to protect it and to provide an external shell that can be decorated so that the vehicle  10  is aesthetically pleasing. The fairing assembly  80  is preferably made from fiberglass having a gel coat, although other materials including plastic are considered to fall within the scope of the invention. The fairing assembly  80  includes an upper portion  81 , a hood  82  removably secured to the upper portion  81  and a bottom pan  83 . The fairing assembly  80  is secured to the vehicle frame assembly  40  by a plurality of fairing anchors. At least two fairing anchors  84  and  85  are illustrated.  
     [0064] The hood  82  includes at least one air intake opening  821  to provide a supply of air to an air box (not shown) for supplying air to the air intake of the engine  50  and/or to an oil cooler (not shown). As previously mentioned, the hood  82  is removable to permit access to an interior storage compartment located in the front portion of the vehicle  10 . The storage compartment offers the driver a place to store personal belongings when the vehicle  10  is parked in a public location. The hood  82  may be locked. The storage compartment is removable to permit access to the engine  50 . The upper portion  81  of the fairing assembly  80  further includes a cluster of headlamps  811 . A windshield  812  may be connected to the steering assembly  70 , as shown in FIG. 1.  
     [0065] The bottom pan  83  of the fairing assembly  80  may also include one or more fog lamps  831 . The bottom pan  83  has a pair of lateral extensions protruding outwardly, which form radiator covers  832 . The radiator covers  832  surround and protect a pair of laterally spaced radiator assemblies, which together form a radiator for the engine  50 . The radiator covers  832  also function to provide a windbreak for the feet and lower legs of the driver. The radiators permit liquid cooling of the engine  50 . The liquid coolant is cooled by air, as is known in the art, and may additionally aided by an automatic fan installed ahead of (or behind) the radiator when the vehicle  10  is idling for an extended period of time.  
     [0066] The vehicle  10  includes a cushioned rider seat assembly  90  that is mounted to the frame assembly  40  between the front wheels  11  and  12  and the rear wheel  13 , as shown in FIGS.  1 - 3 . The seat assembly  90  is connected to an upper support assembly  48  and a seat support assembly  49  of the vehicle frame assembly  40 , as shown in FIG. 4. The seat assembly  90  is positioned so that a weight of the rider thereon will be disposed generally above the rear suspension links of the frame assembly  40 . Consequently, the weight of the rider will be transferred through the seat assembly  90  and frame assembly  40  to the rear suspension link  494 , and from the rear suspension link  494  to the rear suspension assembly  30 , and to the front suspension sub-frame  46  and front suspension assembly  20  through the front supports  482  and  483  at least to some degree.  
     [0067] Referring back to the rear suspension assembly  30  and swing arm assembly  301 , FIGS.  5 - 7  illustrate how the power from the engine  50  is transmitted to the rear wheel  13  of the vehicle  10 . The engine  50  has an output shaft  501  that is connected to a CVT  1000 . The CVT  1000  described herein is intended to be exemplary of one possible CVT suitable for use in this three-wheeled vehicle. Any other known CVT (a CVT to be developed) also can be used with this vehicle, if desired.  
     [0068] Preferably, the CVT  1000  operates at the highest rpm (revolutions per minute) transmitted from the engine  50 . As can be understood from the description below, there is a direct relation between the engine rpm and the operation of the CVT  1000  due to the mechanical connection. Thus, the CVT  1000  is controlled by the engine rather than the operator. It is also possible to add an electronic control to the CVT  1000  that would modify the direct mechanical relationship.  
     [0069] The CVT  1000  includes a drive pulley  502  connected to a driven pulley  503  by a belt  504 . Driven pulley  503  is connected to a transmission shaft  505  having a small sprocket  506  in a gear box  507 . (The gear box  507  is used if the engine employed cannot provide the appropriate range of rpm to directly connect the CVT  1000  driven pulley  503  with the final drive.) Small sprocket  506  is in turn connected to a large sprocket  508  by a chain  509 , which can be adjusted by a chain tensioner  510 . The large sprocket  508  is mounted to the transmission drive shaft  52  having at least a drive shaft sprocket  53 . The drive shaft sprocket  53  is attached to a concentric sprocket  306  by a drive chain  54 . The concentric sprocket  306  is supported about the swing arm axle  302  and includes a first sprocket connected to the output drive shaft  52  of the transmission  1000  and a second sprocket attached to the axle  132  of rear wheel  13  by a chain  307 . By this arrangement, rotation of the transmission output drive shaft  52  causes the sprocket  53  to rotate and move the chain  54 . Chain  54  moves concentric sprocket  306 , which in turn moves the chain  307  and turns the rear wheel axle  132 .  
     [0070] As seen in FIG. 5, the CVT  1000  is disposed on one side of the vehicle, offset from the longitudinal centerline. As can be appreciated from FIG. 7, the drive pulley  502  and driven pulley  503  are mounted at a fixed distance from each other.  
     [0071]FIG. 7A shows an alternative construction of the engine  50  and a gear box  507   a . In this embodiment, the gear box  507   a  is enclosed within the engine  50  housing. The output drive shaft  52   a  extends directly from the gear box  507   a  from within the engine  50  to the concentric sprocket  306 , which in this case is also supported within the housing of the engine  50 . The rear swing arm  42  is mounted for pivotal movement about the axis of the output drive shaft  52   a  on the other side of the gear box  507   a  on the side of the housing of the engine  50 . It is also possible to mount the swing arm  42  on either side of the housing of the engine  50  with the gear box  507   a  positioned laterally between the arms of the swing arm assembly  42 . The concentric sprocket  306  is then connected to a driven sprocket  132   a  of the rear axle  132  to drive the rear wheel  13  by a chain  307 .  
     [0072]FIG. 7B shows another variation of the engine  50  and gear assembly  507   b . In this embodiment, the gear box  507   b  is enclosed within the engine  50  housing. The output drive shaft  52   b  extends from the gear box  507   b  and the engine  50  to the driven axle  132  of wheel  13 . An articulating connection  55 , of any known type, may be provided in the output shaft  52   b  to allow for movement between the rear axle  132  and the engine  50 . The output drive shaft  52   b  drives the rear axle  132  through a conventional geared arrangement. Thus, the concentric sprocket  306  and drive chain  307  of the other embodiments are not necessary. The dotted output shaft  52   bb  shows an alternative placement of the output shaft  52   bb  extending directly from the gear box  507   b.    
     [0073] In still another alternative embodiment, which is not illustrated, it is possible that the transmission shaft  505  may be used as the transmission output drive shaft  52 . In other words, it is contemplated that the gear box  507  may be eliminated altogether so that the transmission shaft  505  contains the drive shaft sprocket  53 .  
     [0074] The CVT  1000  is shown in detail FIGS.  8 - 22 . The CVT  1000 , which as noted above, includes the drive pulley  502  and the driven pulley  503 , both of which have inner and outer halves. The inner half of the drive pulley is designated  1234 . The outer half of the drive pulley is designated  1326 . The driven pulley inner half is designated  1328  while the outer half is designated  1330 .  
     [0075] Since the drive pulley  502  is connected to the output shaft  501  as illustrated in FIG. 7, torque is transmitted from the output shaft  501  to the drive pulley  502 . A belt  504  connects the drive pulley  502  to the driven pulley  503 , permitting the torque to be transmitted to the driven pulley  503 . The belt  504  is a thick rubber belt having tapered sides. The belt  504  transmits a pulling force to the driven pulley  503 . Alternatively, the belt  504  may be formed of metal, in which case the belt  504  may either transmit a pushing force or a pulling force to the driven pulley  503 .  
     [0076]FIGS. 9 and 10 illustrate the positions of the drive pulley  502 , the driven pulley  503 , and the belt  504  when the engine  50  is operating at a low engine speed. FIGS. 11 and 12 illustrate the respective positions of the drive pulley  502 , driven pulley  503  and belt  504  when the engine  50  is operating at high engine speeds. Any intermediate positions between these extremes would indicate that the engine  50  is operating at an intermediate speed.  
     [0077] The CVT  1000  operates in the following manner. The drive pulley inner half  1234  is provided with a belt engagement surface  1334 . The drive pulley outer half  1326  is provided with a belt engagement surface  1336 . Similarly, the driven pulley inner half  1328  includes a belt engagement surface  1338 . Finally, the driven pulley outer half  1330  includes a belt engagement surface  1340 . The belt  504  extends between the drive pulley  502  and the driven pulley  503  and, during operation, predominantly engages the belt engagement surfaces  1334 ,  1336  and  1338 ,  1340 , respectively. The belt  504  transfers the torque of the engine  50  from the drive pulley  502  to the driven pulley  503 .  
     [0078] The drive pulley inner half  1234  includes the starter gear  1232 , which is connected thereto via one or more screws  1236 . The drive pulley inner half  1234  is connected to the output shaft  501 . The drive pulley outer half  1326  is biased by a drive pulley spring  1342  away from the drive pulley inner half  1234  when the engine  50  operates at low speeds.  
     [0079] The drive pulley outer half  1326  is provided with a number of centrifugal weights  1344  that are mounted to pivot axes  1346  disposed about the periphery of the rear surface of the drive pulley outer plate member  1348  that forms the belt engagement surface  1336 . The outward surfaces  1350  of the centrifugal weights rest against rollers  1352  on the drive pulley roller member  1354 .  
     [0080] The drive pulley spring  1342  exerts sufficient force on the drive pulley outer half  1326  to force the outer half  1326  away from the inner half  1234 . In particular, the drive pulley spring  1342  exerts its force on the outer plate member  1348 . The centrifugal weights  1344  on the outer plate member  1348 , in turn, contact the roller member  1354 . Due to the force exerted by the drive spring  1342 , the centrifugal weights  1344  are in constant engagement with the rollers  1352 . The force of the drive spring  1342  biases the outer half  1326  of the drive pulley  502  away from the inner half  1234 , as shown in cross-section in FIG. 9.  
     [0081] At low engine speeds, the inner half  1234  and the outer half  1326  of the drive pulley  502  are positioned as illustrated in FIG. 9. However, at high speeds, the halves  1234 ,  1326  take the positions shown in FIG. 11. The centrifugal weights  1344  are instrumental in making this transitional change. In particular, as the rotation speed of the drive pulley  502  increases, the centrifugal force on the centrifugal weights  1344  becomes sufficiently high that the centrifugal weights  1344  begin to swing outwardly in the direction of arrow  1356 . The greater the rotational speed, the greater the outward swing of the weights  1344  until the weights  1344  reach their maximum outward swing and the rollers  1352  rest against the stops  1358  on the centrifugal weights  1344 . The maximum swing position is illustrated in FIG. 11.  
     [0082] As the centrifugal weights  1344  swing outwardly, their outer surfaces  1350  press against the rollers  1352 . This causes the drive pulley outer plate member  1348  and the roller member  1354  to separate from one another, collapsing the drive spring  1342 . As a result, the belt engagement surface  1334 ,  1336  move toward one another. Since the belt  504  is angled to ride on the belt engagement surfaces  1334 ,  1336 , and since it is effectively incompressible (albeit elastic), the belt  504  travels outwardly from the inner position shown in FIG. 9 to the outer position illustrated in FIG. 11.  
     [0083] Since the tension on the drive belt  504  must remain constant regardless of the position of the belt  504  in the CVT  1000 , the driven pulley  503  acts in a manner opposite to that of the drive pulley  502 . In particular, the driven pulley  503  includes a driven spring  1360  that forces the inner half of the driven pulley  1328  toward the outer half of the driven pulley  1330  in the rest (or low speed) condition. Therefore, when the engine  50  operates at a low speed, the inner and outer halves  1328 ,  1330  of the driven pulley  503  are at their closest point to one another, as illustrated in FIG. 10.  
     [0084] When the engine  50  is operating at high speed, however, the tension on the belt  504 , which must remain constant to avoid breakage of the belt  504 , causes the inner and outer halves of the driven pulley  503  to separate. Accordingly, the belt  504  travels from its highest point as shown in FIG. 10 to its lowest point, as illustrated in FIG. 12.  
     [0085] The CVT  1000  disclosed herein is designed so that, if desired, it is possible to equip the three-wheeled vehicle  10  with a brake assembly that may be engaged while the engine  50  is operating. The CVT  1000  is also designed so that, if desired, the three-wheeled vehicle  10  may be towed or pushed so that the transmission can be used to start the engine  50 . In both cases, the direction of the transmitted torque is changed from a positive direction (where the engine  50  drives the vehicle) to a negative direction (where the wheels  11 ,  12  drive the engine  50  or the engine  50  brakes the vehicle). The latter condition (i.e., the negative direction) will be referred to as a “reverse torque transmission” mode or an “RTT” mode in the description that follows.  
     [0086] Of course, it is also possible to use a CVT with the three wheeled vehicle disclosed herein that does not run in a reverse mode. In fact, it is contemplated that the CVT  1000  will not need to operate in an RTT mode of operation, because the engine  50  will be a unidirectional four-stroke engine. Where as RTT mode of operation is not used, the CVT  1000  will be connected to the rear tire  13  via a gearbox (not shown) that will provide a reverse gear. Such gearboxes are known in the art and, as a result, a detailed description is not provided herein.  
     [0087] Prior art CVTs with an RTT are known. These prior art CVTs, however, rely on conventional CVT design parameters. One example of such a CVT is made by Polaris®, a snowmobile manufacturer located in the United States. Polaris&#39;s snowmobile incorporates a CVT based on a poly-V-section belt/drive pulley combined with a conventional freewheel and clutch unit. The poly-V-section belt and pulley engage one another when the belt is in the low speed position on the drive pulley (analogous to the position illustrated in FIG. 11). This design, however, has at least one significant drawback. The elastic belt become significantly worn when it engages the pulley section and thus tends to fray, thereby greatly reducing its useful life.  
     [0088] To overcome difficulties such as these, to provide the ability to brake the three-wheeled vehicle  10  when the engine  50  is operating, and to provide an RTT, a mechanism to permit free wheel operation was developed for the CVT  1000  of the present invention. In particular, the CVT  1000  of the present invention incorporates a slide sleeve  1364  on the drive pulley  502 . The slide sleeve  1364  cooperates with one or more spring loaded pins  1366  to affect its operation. An enlarged view of the slide sleeve  1364  construction is provided in FIG. 13.  
     [0089] The slide sleeve  1364  has two modes of operation. The first is the non-engaged mode where the slide sleeve  1364  permits the inner and outer halves  1234 ,  1326  of the drive pulley  502  to rotate without imparting any torque to the belt  504 . This operational position is illustrated in FIG. 10. The second operational mode permits the CVT  1000  to act as an RTT to impart torque from the wheel  13  of the three-wheeled vehicle  10  to the engine  50 .  
     [0090] To permit free rotation of the slide sleeve  1364 , the sleeve  1364  is journaled by two antifriction bearings  1368 ,  1370  on shaft  1374 . In operation, when the engine  50  is operating at low speeds, the belt  504  engages the slide sleeve  1364 . At low operational speeds of the engine  50 , the inner and outer halves  1234 ,  1326  of the drive pulley  502  do not clamp the belt  504  between them. In fact, as illustrated in FIGS. 9 and 13, while the belt  504  is shown as abutting the belt engagement surface  1336 , there is a gap  1372  at least between the belt and the inner half  1234  of the drive pulley  502 . Preferably, a gap also exists between the belt  504  and the belt engagement surface  1336 . Accordingly, the slide sleeve  1364  is permitted to float on the underlying shaft  1374  while the inner and outer halves  1234 ,  1326  of the drive pulley  502  rotate. More accurately, the shaft  1374  rotates beneath the slide sleeve  1364 . As a result, the slide sleeve  1364  and belt  504  are stationary during low speed operation of the engine  50 , especially during idle speed.  
     [0091] When the rotational speed of the engine  50  exceeds a predetermined threshold, the centrifugal weights  1344  begin their outward swing, causing the outer half  1326  of the drive pulley  502  to move toward the inner half  1234 , clamping the belt  504  between them. Once this occurs, torque from the engine  50  is transmitted to the driven pulley  503 , where it is transmitted to the wheels  11 ,  12 .  
     [0092] The slide sleeve  1364  permits the construction of a brake assembly  1362 , which may be engaged while the engine  50  is operating. Without the slide sleeve  1364 , torque from the engine  50  always would be transferred to the CVT  1000 . As a result, even if the engine  50  were operating at low speeds, the wheels  11 ,  12  would be encouraged to move and the vehicle  10  would have a tendency to creep forward. With the slide sleeve  1364 , however, the belt  504  does not transfer torque to the driven pulley  503 , which means that the vehicle  10  does not have a tendency to creep forward. As a result, the brake assembly  1362  maybe engaged even while the engine  50  is operating without fear of damage to the brake assembly  1362 .  
     [0093] So that the slide sleeve  1364  also permits the CVT  1000  to operate as an RTT, at least one pin  1366 , but preferably two or more pins  1366 , biased outwardly with a spring  1376 , projects from the shaft  501 . Preferably, the pin  1366  is hexagonally shaped but, as would be understood by those skilled in the art, the pin  1366  could take any suitable shape. In particular the pin  1366  could be replaced by a ball bearing disposed at the top of the spring  1376  so that it engages the inside of the slide sleeve  1364 .  
     [0094] Various views of the slide sleeve  1364  are provided in FIGS.  14 - 16 . These views highlight the construction of the inner surface  1378  of the slide sleeve  1364 , which includes at least one helically-shaped groove  1380 . As illustrated in FIG. 15, three helically shaped grooves  1380  are preferably provided. One pin  1366  preferably engages each groove  1380 .  
     [0095] The grooves are shaped to be shallow  1382  in one direction and steep  1384  in another. The shallow sides  1382  permit the pins  1366  to slide over them when the engine  50  operates in the forward direction (positive torque). In other words, the shallow sides  1382  of the grooves do not engage the pins  1366 . Moreover, the shallow sides  1382  are shallow enough that the pins  1366  generate little noise as they move over the grooves  1380  during forward operation of the engine  50 .  
     [0096] The steep portions  1384  of the grooves  1380  permit the slide sleeve  1364  to operate as an RTT. In particular, if the vehicle  10  is pushed forward so that the torque from the wheels  11 ,  12  is applied to the slide sleeve  1364 , the pins  1366  will engage the groove  1380 , hold the slide sleeve  1364  stationary with respect to the shaft  1374 , and, thereby, transfer the torque from the wheels  11 ,  12  to the engine  50 . The shallower guide paths can result in less noise from the pins moving over the guide paths. The number and width of the guide paths can be varied as desired.  
     [0097] In addition, on one side, the slide sleeve  1364  includes an annular, flange-shaped end  1386  with an external radius larger than that of the remaining portion of the slide sleeve  1364 . This annular flange  1386  serves as catch flank for the elastic belt  504  so as to press it against the outer part  1326  of the drive pulley  502  during the RTT-mode, which is illustrated in FIG. 13. The axial pressing effect is achieved by co-action with the spiral grooves  1380  and the pins  1366 . The flange  1386  preferably has a minimum height so as to not ride under the belt  504 . In addition, the flange  1386  preferably has a maximum height so as to not overly reduce the effective belt engagement surface  1334  of the drive pulley inner half  1234 .  
     [0098] As illustrated in FIGS. 9 and 13, the belt engagement surface  1334  of the drive pulley inner half  1234  includes a recess  1335  that accommodates the flange  1386 . As such, there is a smooth transition as the belt  504  moves outwardly within the drive pulley  502  from the slide sleeve  1364 .  
     [0099] The drive spring  1342  serves one additional function with respect to the slide sleeve  1364 . On one hand, it serves to enable the starting position of the drive pulley  502  when the engine  50  stands still as illustrated in FIG. 9. On the other hand, it functions to return the catch flank  1386  of the slide sleeve  1364  into its starting position during normal operation. This prevents the flange  1386  from catching the belt  504  as it moves down the drive pulley  502  when the engine speed decreases.  
     [0100] If the engine  50  is started by thrust and the belt  504  is pressed by the flange  1386  against the outer pulley part  1326  of the drive pulley  502 , a connection is made between the pulley halves  1234 ,  1326  and the elastic belt  504  via the flank sides of the belt  504 . The minimum coupling speed can be designed into the CVT  1000  so that the belt  504  must move at a sufficient speed before the RTT mode will engage. Once engaged, as the speed of the belt  504  (or number of revolutions of the drive pulley  502 ) increases, the centrifugal weights  1344  will move outwardly. This will cause the drive pulley outer plate member  1348  to move inwardly, clamping the belt  504  between the belt engaging surfaces  1334 ,  1336 .  
     [0101] During normal operation (e.g., non-RTT operation), it is preferred to maintain as constant a tension in the elastic belt  504  as possible, because a constant tension will ensure satisfactory torque transmission from the drive pulley  502  to the driven pulley  503 . The driven pulley  503  assures that the tension on the belt  504  remains constant. The inner half  1328  of the driven pulley  504  is instrumental here.  
     [0102] The inner half  1328  of the driven pulley  503  includes a guide member  1388 . The guide member  1388  is illustrated in greater detail in FIG. 17. The guide member  1388  engages with a toothed wheel  1390 , which is fixedly connected to the driven-side axle  505 . The guide member  1388  and the inner half  1328  of the driven pulley  503  are mutually engaged via projections  1394 . As illustrated in FIG. 17, three two-sided projections  1394  are preferred for guide member  1388 . However, as would be understood by those skilled in the art, any number of projections  1394  may be employed. The projections  1394  enable the guide member  1388  and the inner half  1328  of the driven pulley  503  to slide into each other and to slide apart from one another during operation.  
     [0103] Each of the projections  1394  include a normal operation ramp  1396  and an RTT operation ramp  1398 , which are engaged alternatively depending on the operation of the CVT  1000 . The shapes of the ramps  1396 ,  1398  are designed for each of the two operation types. In particular, the normal operation ramps  1396  are given a steep slope. The RTT ramps  1398 , however, are not given as steep a slope as the normal operation ramps  1396 . The outer ends (the flank region) of the projections  1394  are designed to be flat, which helps to maintain the tension in the belt  504  approximately constant, e.g., when the vehicle is pushed or towed to start the engine  50  (RTT mode of operation). The flat portions  1400  of the RTT ramps  1398  increase the force applied by the inner half  1328  to the outer half  1330 , thereby compensating for the lack of force (or reduced force) applied by the expanded driven spring  1360  and the inactive centrifugal weights  1344 . The flat portion  1400  of the projections  1394  preferably are provided with approximately a  150  inclination.  
     [0104] During RTT operation of the CVT  1000 , the RTT ramps engage corresponding surfaces on the interior of the inner half of the driven pulley  503 , which are illustrated in FIG. 20. The gearing characteristics of the guide member  1388  may be determined by the shape and slope of the corresponding ramps  1396 ,  1398 .  
     [0105] The guide member  1388  preferably is made of a synthetic material. Besides providing a light-weight construction, a synthetic material also offers a great acoustic advantage since the noise development at the onset of driving, when the two ramps collide, is greatly reduced as compared to other materials. Preferably, the guide member  1388  is made from fiberglass. For example, it is contemplated that the guide member  1388  may be constructed from a carbon fiber material. Of course, as would be appreciated by those skilled in the art, other materials may be selected therefore without deviating from the scope of the present invention.  
     [0106] The outer half  1330  of the driven pulley  503  is operationally coupled to the inner half  1328  through a connector  1402 , which is illustrated in greater detail in FIG. 18. The connector, which is preferably made of a material that is at least 2% Teflon® (polytetrafluoroethylene), includes ribbed sections  1404  connected by non-ribbed sections  1406 . The ribbed sections  1406  engage similarly-shaped indentations  1408  on the hub  1410  of the inner half  1328  of the driven pulley  503 , as shown in FIG. 19. While not shown, the ribbed sections  1404  also engage similar indentations on the outer half  1330  of the driven pulley  503 .  
     [0107] The outer and inner halves  1330 ,  1328  of the driven pulley  503  are journaled on the pulley shaft  505  by both slide bearings  1403  and ball bearings  1405 . Thus, they are not rigidly coupled to the shaft  505 . The transmission of torque from the pulley shaft  505  to the driven pulley  503  is accomplished solely by the guide member  1388  and its associated ramps  1396 ,  1398 . In contrast to CVT constructions known in the prior art, where the outer half of the driven pulley is rigidly fixed to the driven pulley shaft, the outer half  1330  and the pulley shaft  505  in the CVT  1000  of the present invention are decoupled. The decoupling of these two elements eliminates or at least greatly reduces torsional vibrations which are otherwise caused by the inertia of the outer half of the driven pulley. Furthermore, the connector  1402  prevents relative movement between the inner and outer halves  1328 ,  1330  of the driven pulley  503 , which reduces considerably slip and friction between the belt  504  and the pulley halves  1328 ,  1330 .  
     [0108] As illustrated in FIG. 20, the inner surface of the inner half  1328  of the driven pulley  503  includes radial ribs  1410  and circumferential ribs  1412 . These ribs  1410 ,  1412  increase to structural strength of the half  1328  to prevent micro-cracks from forming during operation.  
     [0109]FIG. 21 illustrates on alternative embodiment of the centrifugal weights  1344 . In FIG. 21, a centrifugal weight  1414  is illustrated. The centrifugal weight  1414  includes a hole  1416  at one end that may be pivotally connected to the drive pulley outer plate  1336 . The centrifugal weight  1414  is essentially the same as the centrifugal weight  1344 , except that the centrifugal weight  1414  includes a plurality of indentations  1418  along its outer surface  1420 , inward from the stop  1422 . The indentations  1418  are designed to delay the advancement of the centrifugal weights  1414  as they pivot outwardly against the rollers  1352 . When provided with the indentations  1418 , the centrifugal weights  1414  behave such that the operator feels like the vehicle  10  is changing gears.  
     [0110] Specifically, the wave-type geometry on the outer surfaces  1420  of the centrifugal weights  1414  defines the indentations  1418 . The rollers  1352  will come to rest in one of the wave indentations  1418  only within a certain range of engine speeds. Only when a certain engine speed limit is exceeded will the rollers  1352  advance to the next indentation  1418 , thus, progressing in a step-wise fashion to simulate changes from a lower gear to a higher one.  
     [0111] Alternatively, while specific outer surfaces  1350 ,  1420  are illustrated for the centrifugal weights  1344 ,  1414 , there are many alternative shapes that may be applied. It is expected that different shapes will influence the operation of the CVT  1000  to change the operational characteristics of the vehicle  10 . Specifically, the geometry of the outer surface  1350 ,  1420  conceivably could offer more/less aggressive operational characteristics for the vehicle  10 . In addition, the centrifugal weights  1344 ,  1414  do not all need to be the same shape. It is envisioned that weights  1344 ,  1414  of differing shapes could be positioned about the periphery of the drive gear  501  to alter or control the operational characteristics of the vehicle  10 .  
     [0112]FIG. 22 illustrates an alternative embodiment of a driven pulley, which is a pneumatically-actuated driven pulley  1424 . In the pneumatic driven pulley  1424 , movement between the inner half  1426  and the outer half  1428  of the pulley  1424  is actuated pneumatically, preferably with vacuum pressure from the crankcase of the engine  50 . In this embodiment, guide member  1388  may be eliminated altogether. Alternatively, guide member  1388  may be provided, so that the driven pulley  1424  may continue to operate even upon loss of pneumatic control.  
     [0113] So that the pneumatically driven pulley  1424  may operate, a number of seals  1430 ,  1432 ,  1434 ,  1436 ,  1438 ,  1440  are provided between the inner half  1426  and the outer half  1428 . The application of vacuum to the inner chamber  1442  via the vacuum connector  1446  draws the two halves  1426 ,  1428  together to provide a tight clamping force on the belt  504  positioned therebetween. The vacuum can be supplied by a pneumatic coupling (not shown) mounted to the CVT cover  528  that allows vacuum to be selectively supplied from the engine  50  (or other vacuum source, such as a vacuum pump) to chamber  1442  via connector  1446 .  
     [0114] It is expected that this type of driven pulley  1424  should be especially effective for providing engine braking to the three-wheeled vehicle  10 . In particular, upon deceleration of the engine  50 , the throttle will be closed, resulting in a high vacuum in the engine  50 , which will provide a strong clamping force between the two halves  1426 ,  1428 . As a result, the belt  504  will be clamped more tightly between the pulley halves  1426 ,  1428  as compared with other driven gears for CVTs. This means that engine braking may be applied effectively from the engine  50  to the vehicle  10 . Alternatively, a pressure chamber could be positioned on the opposite side of pulley half  1426  such that a pressure source (rather than a vacuum source) could be used to clamp the pulley halves  1426 ,  1428  together. Furthermore, it is contemplated that a vacuum valve may be provided to control vacuum pressure. If provided, it is contemplated that the vacuum valve could be a solenoid whose operation is controlled by the electronic control unit (or “ECU”) of the engine  50 . Moreover, the pneumatic arrangement may be replaced by any fluid pressure system, including hydraulics.  
     [0115] As noted above, it is preferred that the three-wheeled vehicle  10  of this invention be provided with a CVT to eliminate the problem of shifting gears with the driver&#39;s foot as in conventional geared systems. The addition of the CVT allows the driver to lean into turns and lift his or her foot off the foot peg during leaning. If a CVT is used, left side shifting control would not be required. In that case, the handle bar  71  would carry different controls. The vehicle  10  would preferably be provided with additional bonus braking controls on the left handle bar  72 . The right handle bar  73  would carry the front wheel brake  74 , as is customary, and the left handle bar  72  would carry front and rear braking control  75 , as seen in FIG. 3.  
     [0116] As noted above, however, use of a CVT is not required, and the three-wheeled vehicle  10  can also be used with an engine  50  connected to standard gearing. In that configuration, the arrangement of the foot pedals and handle bars normally associated with a motorcycle and an all terrain vehicle (ATV) would be used. In particular, the gearing would be positioned on the left of the driver, with the gear shifter being the left foot pedal. The right handle bar would carry the front wheel brake, and the right foot peg would control the braking of the front and rear wheel. This arrangement has the advantage of easy and familiar use by drivers accustomed to driving ATVs and motorcycles. Standard gearing may also be preferred for racing vehicles for more precise shifting control.  
     [0117] Other conventional components of a drive system and a road vehicle are provided as seen in the figures but need not be described in detail as one of ordinary skill in the art would readily recognize the remaining components.  
     [0118] All of the above noted dimensions are provided for purposes of description and are in no way intended to be limiting. The various parameters could of course be varied and remain within the scope of the invention. Further, the size of the various components that may appear in the drawings can vary from the size shown.  
     [0119] The embodiments described herein are intended to be illustrative of this invention. As will be recognized by those of ordinary skill in the art, various modifications, combination of features, equivalent arrangements and changes can be made and would remain within the scope of the invention defined in the appended claims.