Frame construction for a vehicle

A frame assembly is described including a tunnel, an engine cradle disposed forward of the tunnel and connected thereto, and a sub-frame disposed forward of the engine cradle and connected thereto. A forward support assembly extends upwardly from the subframe. An upper column extends upwardly from the engine cradle to connect with the forward support assembly. A rear brace assembly extends upwardly from the tunnel to connect with the forward support assembly and the upper column. In one embodiment, the frame assembly further includes an engine disposed in the engine cradle. An endless track is operatively connected to the engine and disposed beneath the tunnel for propulsion. A pair of skis is operatively connected to a steering device for steering. In another embodiment, the frame assembly further includes an engine disposed in the engine cradle. A rear wheel is operatively connected to the engine and disposed beneath the tunnel for propulsion, and two front wheels are operatively connected to a steering device for steering.

1. FIELD OF THE INVENTION

The present invention relates to the construction of vehicles such as snowmobiles, all terrain vehicles (“ATVs”), and other similar vehicles. More specifically, the present invention concerns the construction of a frame and related structural elements that enhance the ruggedness and ability of such vehicles to operate across a wide variety of different terrains and under a wide variety of conditions. In addition, the present invention concerns the design and construction of a frame for snowmobiles, ATVs, and related vehicles that facilitate the construction of such vehicles with an improved rider positioning.

2. DESCRIPTION OF RELATED ART AND GENERAL BACKGROUND

Snowmobiles, ATVs, and related vehicles (hereinafter, “recreational vehicles,” although the appellation should not be construed to be limited only to the vehicles or type of vehicles described herein) often function under similar operating conditions. Despite this, snowmobiles, ATVs, and other recreational vehicles often do not share a common design approach or a commonality of components. This is due, in large part, to the different stresses and strains (mainly at the extremes) that the different vehicles experience during routine operation.

Specifically, snowmobiles are designed with frame assemblies and suspensions that easily absorb the shock of obstacles encountered on groomed trails and in deep snow. They are also designed to handle the forces generated when the snowmobile is driven aggressively (e.g., under racing conditions). In addition, their frame assemblies are designed to provide optimum steering and performance in snow, whether on groomed snowmobile trails (packed snow) or in ungroomed, off-trail areas (powder or natural snow).

ATVs, on the other hand, are designed with suspensions and frame assemblies that are expected to absorb the type of momentarily intense forces associated with more rugged terrain, specifically of the type encountered in forests and woodland environments. In addition, an ATV frame is designed to withstand forces associated with significant torsional stresses that are typical when an ATV straddles large objects or when the wheels are disposed at different elevations because of the extreme terrain in which the ATV often operates.

It should be kept in mind that the design parameters of the frame assemblies for these two vehicles are also different. In a snowmobile, the frame at the rear of the vehicle is only about 15 inches wide. This is sufficient to cover the endless track that propels the vehicle and to provide a seating area for the driver. The narrow width, however, imposes certain design restrictions on the vehicle. ATVs, on the other hand, are designed with a significantly wider base, which is typically 50 inches or more. This width also imposes certain design restrictions on the ATV.

Snowmobiles and ATVs are also'designed with different centers of gravity. In the typical snowmobile, the center of gravity is very low. This assists the snowmobile rider when he or she is on a slope or in a turn because the snowmobile will naturally resist the tendency to lean or tip. ATVs, on the other hand, like off-road trucks and the like, are expected to traverse taller objects. Accordingly, their frames are designed so that the engine and seating area is further from the ground than a snowmobile. Thus, ATVs have higher centers of gravity.

Naturally, since both vehicles are designed with off-road use in mind, there are similarities between the two. Both are provided with rugged frames. Moreover, both are provided with strong suspensions. Despite this, there have been few vehicles designed that capitalize on these similarities.

Recognizing this basic similarity between the two vehicles, some after-market designers have developed kits that permit snowmobiles to be converted to ATVs and vice-versa. However, such kits are limited in their effectiveness because the two vehicles are so completely different from one another in their basic designs. The resulting, converted vehicles suffer from drawbacks that are associated with the purpose for which the primary vehicle was designed. For example, a snowmobile converted to an ATV is not expected to be able to traverse the same type of terrain as a pure ATV. Similarly, an ATV that has been converted to a snowmobile is not expected to be able to traverse the same terrain that a pure snowmobile can.

Partly due to the consumer's use of snowmobiles in the winter and ATVs in the summer, the evolution of both snowmobiles and ATVs has converged in recent years. Also, in recent years, designers have begun to apply the same basic design concepts to both vehicle types. What has resulted is a recognition that vehicles may be designed that incorporate many of the same structural elements and follow very similar design approaches.

The basis for the present invention stems from this basic recognition.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a frame assembly with a tunnel, an engine cradle disposed forward of the tunnel and connected thereto, and a sub-frame disposed forward of the engine cradle and connected thereto. The frame assembly further includes a forward support assembly extending upwardly from the subframe, an upper column extending upwardly from the engine cradle to connect with the forward support assembly, and a rear brace assembly extending upwardly from the tunnel to connect with the forward support assembly and the upper column.

It is another object of the present invention to provide a frame assembly wherein the forward support assembly, the upper column, and the rear brace assembly connect at an apex above the upper column.

Another object of the present invention is to provide a frame assembly where the forward support assembly and the rear brace assembly form a pyramidal construction.

A further object of the present invention is to provide a frame assembly further including a steering bracket connected at the apex for supporting a steering shaft at its upper end. In an alternate embodiment, the steering bracket may include a plurality of pairs of holes for positioning of the steering shaft in a plurality of positions.

One other object of the present invention is to provide a frame assembly that also includes an engine disposed in the engine cradle and an endless track operatively connected to the engine and disposed beneath the tunnel for propulsion. In this embodiment, a pair of skis are operatively connected to a steering device for steering.

Still another object of the present invention is to provide a frame assembly with an engine disposed in the engine cradle and a rear wheel operatively connected to the engine and disposed beneath the tunnel for propulsion. In this embodiment, two front wheels operatively connected to a steering device for steering.

It is yet another object of the present invention to provide a frame assembly for a vehicle that includes a tunnel and an engine cradle adapted to receive an engine therein. A rear brace assembly is attached to the tunnel at a point between its front and rear ends and extends upwardly therefrom. A forward support assembly is attached to the rear brace assembly and extends forwardly and downwardly therefrom. In a further variation of this frame assembly, the rear brace assembly comprises a left and a right leg and the forward support assembly comprises a left and a right leg. The left and right legs of the rear brace assembly and the forward support assembly connect to one another at an apex to form a pyramidal structure above the tunnel and engine cradle.

Still other objects of the present invention will be made apparent by the discussion that follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before delving into the specific details of the present invention, it should be noted that the conventions “left,” “right,” “front,” and “rear” are defined according to the normal, forward travel direction of the vehicle being discussed. As a result, the “left” side of a snowmobile is the same as the left side of the rider seated in a forward-facing position on the vehicle (or travelling in a forward direction on the vehicle).

FIG. 1illustrates a rider operator10sitting on a prior art snowmobile12. Rider10is positioned on seat14, with his weight distributed over endless track16. Motor18(shown in general detail) is located over skis20. As with any snowmobile, endless track16is operatively connected to motor (or engine)18to propel snowmobile12over the snow. Motor or engine18typically is a two-stroke internal combustion engine. Alternatively, a 4-stroke internal combustion engine may be substituted therefor. In addition, any suitable engine may be substituted therefor.

FIG. 2provides a side view of a snowmobile22constructed according to the teachings of the present invention. Here, rider/operator24is shown in a more forward, motor cross racing-like position, which is one of the aspects of the present invention. In this position, the weight of operator24is forward of the position of rider10in the prior art example.

The positioning of rider24closer to motor36offers several advantages that are not achieved by the prior art. For example, since rider24is positioned closer to the engine36, the center of gravity of rider24is closer to the center of gravity of the vehicle, which is often at the drive axle of the vehicle or near thereto. In other words, rider24has his weight distributed more evenly over the center of gravity of the vehicle. As a result, when the vehicle traverses rough terrain, rider24is better positioned so that he does not experience the same impact from an obstacle as rider10on snowmobile12. The improved rider positioning illustrated inFIG. 2also improves the rider's ability to handle the vehicle.

FIG. 2illustrates the basic elements of snowmobile22. Snowmobile22includes an endless track26at its rear for propulsion. A rear suspension28connects endless track26to the vehicle frame. Snowmobile22also includes a front suspension30. Skis32, which are operatively connected to handlebars34, are suspended from the front suspension30for steering the vehicle. A motor or engine (preferably, an internal combustion engine)36is located at the front of snowmobile22, above skis32. Operator24is seated on a seat38, which is positioned above the endless track26.

Three positional points of particular relevance to the present invention are also shown inFIG. 2. Specifically, seat position40, foot position42, and hand position44of operator24are shown. In the modified seating position of operator24, which is made possible by the teachings of the present invention, hand position44is forward of foot position42, which is forward of seat position40. The three positions define three angles, a, b, and c between them that help to define the seating position of operator24, which permits rider24to be closer to center of gravity45of the vehicle. Moreover, hand position44is forward of center of gravity45of snowmobile22.

FIG. 3provides an overlay between prior art snowmobile12and snowmobile22constructed according to the teachings of the present invention. Rider10(of prior art snowmobile12) is shown in solid lines while operator24(of snowmobile22) is shown in dotted lines for comparison. The comparative body positions of rider10and operator24are shown. As is apparent, the present invention permits the construction of a snowmobile22where the rider24is in a more forward position. Moreover seat position40, foot position42, and hand position44differ considerably from seat position46, foot position48, and hand position50in the prior art snowmobile12. In this position, the center of gravity of operator24is closer to center of gravity45of snowmobile22than in the prior art example.

As a basis for comparison with the figures that provide the details of the present invention,FIG. 4provides an exploded view of a frame assembly52for a snowmobile constructed according to the teachings of the prior art. Frame assembly52includes, as its major components, a tunnel54and an engine cradle56. As illustrated, engine cradle56is positioned in front of tunnel54. Engine cradle56receives motor18.

As shown inFIG. 4, tunnel54is basically an inverted U-shaped structure with a top plate58integrally formed with left and right side plates60,62, respectively. Top plate58provides the surface onto with seat14is mounted, as would be known to those skilled in the art. Foot boards64(of which only the left foot board is visible inFIG. 4) are integrally formed with the side plates60,62and extend outwardly, perpendicular to the plane of side plates60,62. Foot boards64provide a location on which rider10may place his feet during operation of snowmobile12. While top plate58, side plates60,62, and foot boards64are preferably formed from aluminum, any suitable alternative material may be used, as would be recognized by those skilled in the art. Moreover, while top plate58, side plates60,62and footboards64are shown as an integral structure, an integral construction is not required. Instead, top plate58, side plates60,62, and foot boards64may be separately manufactured and connected to one another by any suitable means known in the art.

FIG. 4also shows that engine cradle56is connected to tunnel54by any suitable means known to those skilled in the art. For example, engine cradle56may be welded or bolted to tunnel54. Engine cradle includes a bottom plate66and left and right side walls68,70, which are provided with left and right openings72,74, respectively. Left opening72is provided so that the shafts for the transmission (typically a continuously variable transmission or CVT) may extend outwardly from left wall68. The shafts that connect the engine18to the transmission pass through left opening72. A gearbox (not shown) typically is provided on the right side of snowmobile10. The shafts that connect engine18to the gearbox pass through right opening74. Left and right openings72,74also allow heat from engine18to be radiated from engine cradle56, which assists in cooling engine18.

AsFIG. 4illustrates, left side wall68is provided with a beam76that is removably connected thereto. Beam76may be removed during servicing, for example, to facilitate access to the engine components and peripheral elements disposed within left opening72.

FIG. 4also illustrates the placement of a handlebar support element78, which connects to the rear of engine cradle56. Handlebar support element78is generally an inverted U-shaped structure that extends upwardly from the combined engine cradle56and tunnel54. A bracket80is positioned at the midpoint of handlebar support element78and provides structural support for handlebars82, which is used to steer snowmobile12.

To provide an improved driver positioning, as described above, the inventors of the present invention appreciated the advantages of moving handlebars82forward of the position shown inFIG. 1. To do this, however, required a novel approach to the construction of frame assembly52of snowmobile12. The redesign resulted in the present invention, which is described in detail below.

As illustrated inFIG. 5, snowmobile22incorporates a completely redesigned frame assembly84. Frame assembly84includes, among other elements, tunnel86, engine cradle88, and over-arching frame elements90. As with snowmobile12, snowmobile22includes a seat94on which rider24sits while operating snowmobile22. Tunnel86is connected to a rear suspension96that contains a number of wheels98disposed on a slide frame100around which an endless track102rotates to propel snowmobile22across the snow.

Endless track102is connected to engine104(preferably a two or four stroke internal combustion engine) positioned within engine cradle88. Endless track102is connected to engine104through a transmission106, which is preferably a continuously variable transmission (or “CVT”), as is known in the art.

Two skis108are provided at the front of snowmobile22for steering. Skis108are connected to engine cradle88through a front suspension110. Front suspension110connects to skis108through a pivot joint112on the top of skis108. Skis108are operatively connected to a steering shaft114that extends over engine104. Steering shaft114is connected, in turn, to handlebars116, which are used by operator24to steer snowmobile22.

FIG. 6illustrates the individual elements of rear frame assembly84in greater detail. Rear frame assembly84includes an upper column118, which is an inverted U-shaped structural element. If necessary, upper column118may be reinforced with a cross-member120, but this is not needed to practice the present invention. A left brace122and a right brace124are connected to a bracket126above upper column118. A bushing or bearing (or other similar element)128is attached to bracket126and accepts steering shaft114therethrough. It also secures steering shaft114to rear frame assembly84. Left and right braces122,124include left and right brackets130,132at their lower portions. Left and right brackets130,132secure left and right braces122,124to tunnel86of snowmobile22.

It should be noted that, while the construction of frame assembly84is illustrated involves the use of tubular members, frame assembly84may also be constructed according to a monocoque or pseudo-monocoque technique. A monocoque construction is one where a single sheet of material is attached to an underlying frame (such as with the construction of an aircraft). The skin applied to the frame adds rigidity to the underlying frame structure. In a similar manner, a pseudo-monocoque technique provides a rigid structure by providing a frame constructed from a single sheet of material.

Instead of constructing frame assembly84from a number of tubular members, frame assembly84may be constructed from a single sheet of material (such as aluminum) that has been pressed or molded into the appropriate shape using a pseudo-monocoque manufacturing technique. As would be understood by those skilled in the art, this would result in a construction that has a high strength with a low weight.

FIG. 7illustrates a forward support assembly134(also called front triangle134), which connects to bracket126and extends forwardly of bracket126. Forward support assembly134includes a bracket136at its rear end that connects to bracket126of frame assembly84(preferably bolted). Forward support assembly134also has left and right braces138,140that extend forwardly and downwardly from bracket136and are connected thereto preferably by welding. Left and right braces138,140are connected at their forward ends by a cross-member142, which includes a plurality of holes144therein to lighten the weight thereof. Left and right connecting brackets145,146are connected to cross-member142. The left and right connecting brackets145,146connect, in turn, to front suspension110.

FIGS. 8,9, and10illustrate upper column118in greater detail. As described above, upper column118is essentially an inverted U-shaped member that is preferably tubular in shape to facilitate its construction. Upper column118preferably is bent into the appropriate shape from a straight tube with the dimensions shown. As would be understood by those skilled in the art, however, upper column118need not be made as a tubular member.

Upper column118has left and right legs148,150that extend downwardly from an apex152. A bracket154is disposed at apex152for connection to bracket126of frame assembly84. Preferably, bracket154is welded at the apex of upper column118(however any other suitable attachment means is possible). Left leg148includes a bracket156at its lower-most portion that connects left leg148to engine cradle88. Similarly, right leg150includes a bracket158at its lower-most portion to connect right leg150to engine cradle88. Preferably, brackets156,158are welded to upper column118. Left and right legs148,150preferably attach to engine cradle88via bolts or other suitable fasteners.

FIGS. 11 and 12illustrate tunnel86in greater detail. Tunnel86includes a top plate160with left and right downwardly extending side plates162,164. A left foot rest166extends outwardly from the bottom of left side plate162. Similarly, a right foot rest168extends outwardly from the bottom portion of right side plate164. Left and right foot rests166,168provide a location along tunnel86onto which rider24may place his or her feet while operating snowmobile22.

Left side plate162extends forwardly beyond the front portion170of tunnel86to form a left engine cradle wall172. Similarly, right side plate164extends forwardly of front end170of tunnel86to form right engine cradle wall174. At the lower edge of left and right engine cradle walls172,174, there are laterally extending portions176,178, which serve to strengthen left and right engine cradle walls172,174. Removable elements180extend between left foot rest166and left laterally extending portion176. Removable portions180may or may not be removed between left foot rest166and left laterally extending portion176.FIG. 11shows removable portions180removed, whileFIG. 12shows removable portions180not removed. It should be noted that the same removable portions180may or may not extend between right foot rest168and right laterally extending portion178.

Left engine cradle wall172preferably includes an opening182therethrough. Opening182permits the shafts from transmission106to pass therethrough. Unlike left engine cradle wall172, right engine cradle wall174does not include such an opening. Instead, right engine cradle wall174is essentially solid. Due to its construction, right engine cradle wall174reflects radiant heat from engine104back to engine104to assist in minimizing heat dissipation from engine104. Left and right openings184,186are provided through left and right engine cradle walls172,174so that a drive shaft188may pass therethrough. Drive shaft186connects to endless track102for propulsion of snowmobile22. Opening182may include a member189about its periphery, also as illustrated inFIGS. 11 and 12, that provides clearance for the engine. Left engine cradle wall172also includes an opening192above opening184through which a shaft passes for part of transmission106.

FIGS. 13 and 14illustrate a combination of a variation of frame assembly190connected to tunnel86. Frame assembly190includes upper column118as illustrated inFIGS. 8-10. However, frame assembly190differs somewhat from frame assembly84. For example, left and right braces194,196are shaped so that they extend outwardly from the positions defined by left and right braces122,124. As illustrated, left and right braces194,196include elbows198,200. A cross-brace202optionally may be placed between left and right braces194,196to add structural rigidity to frame assembly190. As with frame assembly84, a bracket126is provided at apex204where left and right braces194,196meet one another. Forward support assembly134is the same as depicted inFIG. 7. A front engine cradle wall206is also shown inFIG. 13.

FIGS. 15-17illustrate various aspects of front suspension110and associated structures. While the figures illustrate the embodiment preferably used in combination with snowmobile22, it should be recognized that front suspension110may also be used in combination with a wheeled vehicle, as will be discussed in connection withFIGS. 23-27.

Front suspension110includes left and right ski legs208,210. Left and right ski legs208,210are preferably made from aluminum and are preferably formed as extrusions. While an aluminum extrusion is preferred for left and right ski legs208,210, those skilled in the art would appreciate that ski legs could be made from any suitable material and in any acceptable manner that would provide similar strength and low weight characteristics. Left and right ski legs208,210include holes212,214through which a fastener (not shown) is disposed to pivotally connect skis32to snowmobile22, as shown inFIG. 2.

Left and right ski legs208,210are movably connected to left and right support arms216,218. Left and right suspension arms216,218include lower left and right suspension support arms220,222and upper left and right suspension support arms224,226.

As shown inFIGS. 15 and 17, lower left suspension support arm220connects to left ski leg at lower left attachment point228preferably through a ball joint (not shown) so that left ski leg208may pivot and rotate with respect to lower left suspension support arm220. Similarly, lower right suspension support arm222connects to right ski leg210at lower right attachment point230, preferably through a ball joint. Upper left suspension support arm224preferably attaches to left ski leg208at upper left attachment point232, preferably through a ball joint or other suitable means. In addition, upper right suspension support arm226connects to right ski leg210at upper right attachment point234through a ball joint or other suitable means.

Lower left suspension support arm220includes front and rear members236,238, which meet at apex240where they connect with left lower eyelet242. Front member236includes a joint244at an inner end, and rear member238includes a joint246also at an inner end. Similarly, lower right suspension support arm222includes front and rear members248,250, which meet at apex252where they connect with right lower eyelet254. Front member248includes a joint256at an inner end and rear member250includes a joint258also at an inner end.

Upper left suspension support arm224includes front and rear members260,262, which meet at apex264where they connect with upper left eyelet266. Front member260includes a joint268at an inner end, and rear member262includes a joint270also at an inner end. Similarly, upper right suspension support arm226includes front and rear members272,274, which meet at apex276where they connect with upper right eyelet278. Front member272includes a joint280at an inner end and rear member274includes a joint282also at an inner end.

At a point inward from apex240, lower left suspension support arm220includes a left bracket284that is connected to and extends partially along front and rear members236,238. Similarly, lower right suspension support arm222includes a right bracket286that is connected to and extends partially along front and rear members248,250. Slidably attached to rear member238of lower left suspension arm220is a left pivot block288. A right pivot block290is slidably attached to rear member250of lower right suspension support arm222. A stabilizer bar292is connected between left and right pivot blocks288,290. Stabilizer bar292is adapted to slide and pivot by way of left and right pivot blocks288,290. These blocks288,290slide relative to left and right lower suspension support arms220,222. Left and right bushings296,298are provided to allow some rotation of the components of front suspension110. Left and right ski legs208,210rotatably connect to front suspension110for facilitating movement of skis32.

FIG. 16illustrates sub-frame294, which is essentially a unitary, V-shaped structure. Sub-frame294, which forms a part of front suspension110, includes a central channel300flanked on either side by left and right upwardly extending panels302,304. Left upwardly extending panel302includes a left lower panel306connected to left transition structure308and left triangular panel310. Similarly, right upwardly extending panel304includes a right lower panel312connected to right transition structure314and right triangular panel316. While sub-frame294preferably is a unitary structure (an integrally-formed structure), sub-frame294need not be constructed in this manner. As would be understood by those skilled in the art, sub-frame294may be assembled from a number of separate elements that are connected together by any suitable means such as by welding or by fasteners.

As illustrated inFIG. 17, sub-frame294is an integral part of front suspension110and connects to left support arm216and right support arm218through a number of brackets318connected at various locations on sub-frame294.

FIG. 18is a side view of one embodiment of the completed frame assembly84of the present invention. As shown, over-arching frame elements90are connected between tunnel86and sub-frame294to establish an apex320to which steering shaft114is connected.

FIG. 19is a perspective illustration of the embodiment of the present invention shown inFIGS. 13 and 14to assist in understanding the scope and content of the present invention. As illustrated, drive shaft322extends through left opening182in left engine cradle wall172. A portion of gearbox324is also visible. In addition, left shock absorber326, which is connected between cross-member142and left support arm216, is illustrated. Right shock absorber, which extends between cross-member142and right support arm218is visible inFIG. 20. Furthermore, left forward foot wall330is shown at the forward end of left foot rest166. A similar forward foot wall may be provided on the right side of snowmobile22(but is not illustrated herein).

FIGS. 20 and 21illustrate further details of the present invention by showing the various elements from slightly different perspective views.FIG. 22illustrates the modified version of the elements of the present invention shown inFIGS. 6 and 7. Here, left and right braces122,124are illustrated instead of left and right braces194,196. As discussed previously, left and right braces122,124differ from left and right braces194,196in that they are not bent but, instead, are straight elements of overarching frame90. The same left and right braces122,124are shown inFIG. 18. As would be understood by those skilled in the art, the two different embodiments of these braces are interchangeable. In addition, their shape may be altered depending on the requirements of the particular vehicle design, as would be understood by those skilled in the art.

Left and right braces194,196are bent to accommodate an airbox (not shown) between them. Left and right braces122,124are not bent because they do not need to accommodate an airbox.

FIG. 20also illustrates steering gear box115at the bottom end of steering shaft114that translates the movement of handlebars116into a steering motion of skis32.

FIGS. 23-27illustrate alternate embodiments of the present invention that are designed for a wheeled vehicle332, rather than a snowmobile22. For the most part, the elements designed for wheeled vehicle332are the same as those for snowmobile22, except for those elements required to attach wheels334to wheeled vehicle332.

In the preferred embodiment of wheeled vehicle332, the vehicle includes two front wheels334and a single rear wheel336. As would be understood by those skilled in the art, however, wheeled vehicle332may be constructed with two rear wheels rather than one. If so, wheeled vehicle332would be a four-wheeled vehicle rather than the three-wheeled vehicle shown.

Wheeled vehicle332includes a seat338disposed over tunnel86in the same manner as snowmobile22. The vehicle includes engine104at its forward end, encased by fairings340. Fairings340protect engine104and provide wheeled vehicle332with an aesthetically pleasing appearance. Engine104is connected to CVT106, which translates the power from engine104into motive power for wheeled vehicle332.

As shown inFIG. 23, CVT106is connected by suitable means to drive shaft342, which is connected to rear wheel336by a drive chain344. A sprocket346is connected to drive shaft342. A similar sprocket348is provided on the shaft connected to rear wheel336. Drive chain344is an endless chain that connects sprockets346,348to one another. To stop wheeled vehicle332during operation, disc brakes350are connected to front wheels334. Disc brakes350clamp onto discs352to slow or stop wheeled vehicle332in a manner known to those skilled in the art.

A rear suspension354is provided under tunnel86. Rear suspension354absorbs shocks associated with the terrain over which wheeled vehicle332travels. Rear suspension354replaces rear suspension28on snowmobile22.

FIG. 24illustrates an alternate embodiment of wheeled vehicle356. Wheeled vehicle356differs in its construction at the rear. Specifically, rear end358is shorter than that shown for wheeled vehicle332. In addition, wheeled vehicle356includes a four stroke engine, rather than the two stroke engine104illustrated for wheeled vehicle332. Also, wheeled vehicle356includes a manual speed transmission360(with a clutch) rather than continuously variable transmission106, as illustrated with other embodiments of the present invention. Both constructions of the wheeled vehicle, as well as many other variations, are contemplated within the scope of the present invention. In addition, as discussed above, the present invention may be used with a two or four stroke engine (or any other type of engine that provides the motive power for the vehicle).

FIG. 25illustrates in greater detail the embodiment of the present invention shown inFIG. 24.

FIGS. 26-27illustrate the basic frame assembly contemplated for wheeled vehicles332,356. For either vehicle, the construction of frame assembly191is similar to that previously described. This embodiment differs in that left and right wheel knuckles366,368are provided so that wheels334may be attached thereto. In most other respects, the construction of frame assembly191is the same as that previously described.

The variable geometry of steering shaft364will now be described in connection withFIGS. 28-34.

As illustrated inFIG. 28, left brace122and right brace124extend upwardly from tunnel370to apex372where they connect to variable geometry steering bracket374. Upper column118extends from left engine cradle wall376and right engine cradle wall174and also connects to variable geometry steering bracket374. Forward support assembly134extends from sub-frame294to variable geometry steering bracket374.

Variable geometry steering bracket374is essentially a U-shaped element with a rear end376and a forward end378. At rear end376, a first cross-member380extends between left and right legs382,384of variable geometry steering bracket374to define a closed structure. A second cross member386extends between left and right legs382,384forward of first cross member380and defines a U-shaped opening387toward forward end378of variable geometry steering bracket374. A first pair of holes388and a second pair of holes390are disposed through left and right legs382,382of variable geometry steering bracket374and provide separate attachment points for steering shaft364.FIG. 29illustrates the same structures in side view andFIG. 30illustrates the same structures in top view.

This embodiment of the frame assembly of the present invention differs from the previous embodiments in a few respects. First, left engine cradle wall393includes a C-shaped opening392instead of opening182. C-shaped opening392facilitates maintenance of an engine (not shown) in engine cradle394. Second, an elongated radiator396is integrated into tunnel370. Radiator396includes an inlet398and an outlet400that are connected to the cooling system of the engine to assist in reducing the temperature of the coolant therein. To facilitate dissipation of heat, radiator396includes fins402on its underside.

FIG. 31provides another side view of the frame assembly of the present invention and illustrates the two positions of steering shaft364made possible by the construction of variable geometry steering bracket374. To accommodate the variable geometry of steering shaft362and handlebars116, steering shaft364includes a bend402at its lower end. Steering shaft364passes through a bearing or bushing (not shown) at its upper end that is connected to variable geometry steering bracket374at either of first or second pairs of holes388,390. By selecting either first or second pairs of holes388,390, first and second handlebar positions404,406are selectable. As would be recognized by those skilled in the art, however, variable geometry steering bracket374may be provided with greater that two pairs of holes388,390to further increase the variability handlebars116. Also, variable geometry steering bracket374may be provided with a construction that permits infinite variation of the position of handlebars, as would be understood by those skilled in the art, should such a construction be desired.

FIGS. 32-34provide additional views of the variable positioning of the handlebars116to facilitate an understanding of the scope of the present invention.

Frame assembly84,190,191of the present invention uniquely distributes the weight loaded onto the vehicle, whether it is snowmobile22or one of wheeled vehicles332,356. Each of the main components of the frame assembly84,190,191forms a triangular or pyramidal configuration. All of the bars of the frame assembly84,190,191work only in tension and compression, without bending. Therefore, each bar of frame assembly84,190,191intersects at a common point, the bracket126(in the non-variable steering geometry) or variable geometry steering bracket374. With this pyramidal shape, the present invention creates a very stable geometry.

Specifically, the structure of frame assembly84,190,191enhances the torsional and structural rigidity of the frame of the vehicle. This improves handling. Usually, with a snowmobile, there is only a small torsional moment because the width of the snowmobile is only about 15 inches. An ATV, on the other hand, has a width of about 50 inches and, as a result, experiences a significant torsional moment. Therefore, to construct a frame assembly that is useable in either a snowmobile or an ATV, the frame must be able to withstand the torsional forces associated with an ATV.

Not only does frame assembly84,190,191reduce torsional bending, it also reduces the bending moment from front to rear. The increased rigidity in both directions further improves handling.

In addition, the creation of frame assembly84,190,191has at least one further advantage in that the frame can be made lighter and stronger than prior art frame assemblies (such as frame assembly52, which is illustrated inFIG. 4). In the conventional snowmobile, frame assembly52included a tunnel54and an engine cradle56that were riveted together. Because frame assembly84,190,191adds strength and rigidity to the overall construction and absorbs and redistributes many of the forces encountered by the frame of the vehicle, the panels that make up the tunnel86and the engine cradle88need not be as strong or as thick as was required for the construction of frame assembly52.

In the front of the vehicle, left and right shock absorbers326,328are connected to forward support assembly134so that the forces experienced by left and right shock absorbers326,328are transmitted to frame assembly84,190,191. In the rear of the vehicle, the left and right braces122,124are orientated with respect to the rear suspension. Upper column118is positioned close to the center of gravity of the vehicle's sprung weight. The sprung weight equals all of the weight loaded onto the vehicle's entire suspension. The positioning of these elements such that they transmit forces encountered at the front, middle and rear of the vehicle to an apex creates a very stable vehicle that is capable of withstanding virtually any forces that the vehicle may encounter during operation without sacrificing vehicle performance.

FIG. 35illustrates the degree to which the rigidity of a frame constructed according to the teachings of the present invention is improved. The highest line on the graph shows that for a 100 kg load, the vertical displacement of the frame of the present invention is only −2 mm. However, in the prior art Bombardier ZX™ model snowmobile, a load of only 50 kg produced a vertical displacement of −6 mm. In addition, a load of about 30 kg on the frame for the prior art Arctic Cat® snowmobile produced a vertical displacement of −6 mm. In other words, the structural rigidity of the frame assembly of the present invention is greatly improved.

While the invention has been described by way of example embodiments, it is understood that the words which have been used herein are words of description, rather than words of limitation. Changes may be made, within the purview of the appended claims without departing from the scope and the spirit of the invention in its broader aspects. Although the invention has been described herein with reference to particular structures, materials, and embodiments, it is understood that the invention is not limited to the particulars disclosed.