Abstract:
The present invention generally provides a wheel replacing traction assembly which uses, for propulsion, a longitudinally extending endless track disposed around and cooperating with a sprocket wheel, idler and/or road wheels and a supporting frame. The endless track generally comprises an inner wheel-engaging surface and an outer ground-engaging surface, the latter being provided with traction lugs. The outer surface further comprises at least one laterally extending portion which also extends along the circumference of the track; the traction lugs located on this laterally extending portion being generally higher than the traction lugs located on the remainder of the outer surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application claims the benefits of priority of commonly assigned Canadian Patent Application No. 2,619,542, entitled “Traction Assembly with Endless Track Having Variable Ground-Contacting Area” and filed at the Canadian Intellectual Property Office on Feb. 6, 2008. 
     FIELD OF THE INVENTION 
     The present invention generally relates to traction assemblies used as wheel replacements for wheeled vehicles. More particularly, the present invention relates to traction assemblies used as wheel replacements for the wheels that steer vehicles and to the endless tracks mounted thereon. 
     BACKGROUND OF THE INVENTION 
     Nowadays, there are an ever-increasing number of people who enjoy riding all-terrain vehicles and other similar off-road vehicles. In order to further adapt these vehicles to the increasing variety of terrains and surfaces onto which they are ridden, companies have started to offer traction assemblies which can be used to replace the wheels on these vehicles. 
     Generally, a traction assembly comprises a supporting frame, a sprocket wheel, idler and/or road wheels and an endless elastomeric track disposed therearound and cooperating therewith. By using an endless track instead of a regular tire, a traction assembly generally provides increased floatation and better traction to the vehicle since the ground contacting area, also referred to as the contact patch, of the endless track is generally significantly larger than the contact patch of a regular tire. 
     In short, the larger ground-contacting area of the endless track effectively spreads the weight of the vehicle over a larger area (i.e. increased floatation) and provides additional ground-engaging surface to the vehicle (i.e. increased traction). 
     Though the larger contact patch of the endless track of the traction assembly is generally a significant advantage when the vehicle is ridden over soft surfaces such as snow, mud or sand, the larger contact patch can become a hindrance when the vehicle is ridden over harder surfaces such as concrete, asphalt or pavement. Indeed, the larger contact patch generally implies more friction between the track and the ground, making the vehicle more difficult to steer and manoeuvre. 
     Therefore, there is a need for an improved traction assembly which generally mitigates the aforementioned shortcomings. 
     OBJECTS OF THE INVENTION 
     Accordingly, one of the main objectives of the present invention is to provide a traction assembly having an endless track which defines a generally small contact patch when ridden over hard surfaces but a large contact patch when ridden over soft surfaces. 
     Another object of the present invention is to provide a traction assembly having an endless track which outer ground-engaging surface comprises at least two laterally extending portions, one of which being provided with traction lugs which are higher than the traction lugs provided on the other portion or portions. 
     Other and further objects and advantages of the present invention will be obvious upon an understanding of the illustrative embodiments about to be described or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice. 
     SUMMARY OF THE INVENTION 
     The aforesaid and other objectives of the present invention are realized by generally providing a traction assembly comprising a novel endless track which provides a large contact patch when ridden over soft surfaces (e.g. snow, mud, sand and the like) but a small contact patch when ridden over hard surfaces (e.g. pavement, concrete and the like). 
     The traction assembly of the present invention generally comprises a sprocket wheel which is adapted to be mounted to the vehicle, preferably on the wheel hub thereof. The traction assembly also generally comprises a support structure which preferably, but not necessarily, supports idlers wheels and/or road wheels. The traction assembly also comprises a longitudinally extending endless elastomeric track disposed around and cooperating with the sprocket wheel, the support structure and, if any, the idler and/or road wheels. 
     The endless track comprises an inner wheel-engaging surface and an outer ground-engaging surface. The outer ground-engaging surface, which is provided with a plurality of traction lugs, further defines at least two laterally extending portions extending along the circumference of the track. In accordance with the present invention, one of the laterally extending portions is provided with traction lugs, or portions thereof, which are generally higher than the traction lugs, or portions thereof, located on the other laterally extending portion or portions. 
     Consequently, when a vehicle equipped with the traction assembly of the present invention is ridden over a hard surface such as, but not limited to, concrete or pavement, only the higher traction lugs of the endless track will effectively engage the ground. Conversely, when the same vehicle is ridden over a soft surface such as, but not limited to, snow, mud or sand, all the traction lugs of the track will generally engage the ground since the higher traction lugs will at least partially penetrate into the soft surface, thereby allowing the smaller traction lugs to also engage the ground. 
     Since the contact patch of the endless track of the traction assembly is generally defined by the area effectively in contact with the ground at a given time, the contact patch defined by the higher traction lugs will be smaller than the contact patch defined by all the traction lugs. 
     Preferably, the laterally extending portion which is provided with higher traction lugs is positioned on the outer ground-engaging surface so that the contact patch defined by the higher traction lugs effectively in contact with the ground roughly approximates the contact patch of a regular tire. 
     Preferably, the laterally extending portion which is provided with higher traction lugs is positioned on the outer ground-engaging surface so that the contact patch defined by the higher traction lugs is generally intersected by the steering axis of the suspension and steering system to which the traction assembly is mounted. 
     Consequently, by providing an endless track which has a smaller contact patch when used on hard surfaces, the traction assembly of the present invention is generally easier to steer and manoeuvre. 
     The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawings in which: 
         FIG. 1  is a side view of an exemplary traction assembly, in accordance with the present invention, as installed on an ATV. 
         FIG. 2  is a front partial cross-sectional view of the traction assembly of  FIG. 1 , showing an embodiment of the endless track. 
         FIGS. 3A and 3B  are enlarged views of the lower run of the endless track shown in  FIG. 2 . 
         FIG. 4  is a front partial cross-sectional view of the traction assembly of  FIG. 1 , showing another embodiment of the endless track. 
         FIG. 5  is an enlarged view of the lower run of the endless track shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A novel traction assembly will be described hereinafter. Although the invention is described in terms of specific illustrative embodiments, it is to be understood that the embodiments described herein are by way of example only and that the scope of the invention is not intended to be limited thereby. 
     Referring first to  FIG. 1 , a traction assembly  100 , in accordance with the present invention, generally comprises a sprocket wheel  110  adapted to be fixedly mounted to the wheel hub or axle which is generally operationally connected to the suspension and/or steering system  20  of a vehicle (not shown). The traction assembly  100  also comprises a supporting frame structure  120  to which idler wheels  130  and road wheels  140  are preferably pivotally mounted. The idler wheels  130  are preferably respectively mounted at the fore and at the aft of the supporting frame  120  while the road wheels  140  are generally mounted along the frame  120 , between the front and rear idler wheels  130 . Finally, disposed around the sprocket wheel  110 , the idler wheels  130 , the road wheels  140  and the supporting frame  120  is a longitudinally extending endless track  150  made preferably of reinforced elastomeric material. Though not shown, the endless track  150  is preferably provided with at least one row of longitudinally aligned holes adapted to be engaged by the sprocket wheel  110 . Other configurations are however possible; the present invention is not so limited. 
     Referring now to  FIG. 2 , the endless track  150  generally defines an inner wheel-engaging surface  160  and an outer ground-engaging surface  170 . The inner wheel-engaging surface  160  is preferably provided with guide lugs  161  and  163  which are adapted to guide the endless track  150  and to prevent lateral movement thereof. Other configurations are also possible; the present invention is not so limited. 
     The ground-engaging surface  170  is provided with a plurality of generally laterally extending tractions lugs  171  and  172  which are disposed along the circumference of the track  150 . 
     In accordance with the present invention and as best shown in  FIG. 3A , the outer surface  170  comprises at least a first laterally extending portion or region  175  and a second laterally extending portion or region  176 . The traction lugs  171 , or portions thereof, located on the first laterally extending portion  175  are higher by a distance  173  than the traction lugs  172 , or portions thereof, located on the remainder of the outer surface  170 , hence, on the second laterally extending portion  176 . 
     By providing the endless track  150  with traction lugs  171  and  172  having different heights, the track  150  generally defines two ground-contacting areas or contact patches. Indeed, when the vehicle is ridden over hard surfaces such as, but not limited to, concrete and pavement, only the higher traction lugs  171  will effectively contact the ground  30  as shown in  FIGS. 3A and 3B . However, when the vehicle is ridden over soft surfaces such as, but not limited to, snow, mud and sand, both traction lugs  171  and  172  will effectively contact the ground since the higher traction lugs  171  will at least partially penetrate into the soft surface, thereby allowing traction lugs  172  to also contact the ground. 
     Accordingly, when the vehicle is ridden over hard surfaces, the ground-contacting area of the track  150  is the area generally defined by the length  177  shown in  FIG. 1  and by the width  178  shown in  FIG. 3B  whereas when the vehicle is ridden over soft surfaces, the ground-contacting area of the track  150  is the area generally defined by the length  177  shown in  FIG. 1  and by the width  179  shown in  FIG. 3B . Since the width  178  is smaller than the width  179 , the ground-contacting area of the track  150  defined by the length  177  and by the width  178  is correspondingly smaller. 
     Accordingly, depending on the type of surface over which the vehicle is ridden, the endless track  150  of the traction assembly  100  will have different ground-contacting areas; smaller when the surface is hard, larger when the surface is soft. By having a smaller ground-contacting area when the vehicle is ridden over hard surfaces, the endless track  150  will generate less friction and the traction assembly  100  will be easier to steer and manoeuvre. However, by having a larger ground-contacting area when the vehicle is ridden over soft surfaces, the endless track  150  will still generate increased floatation and traction, as in prior art traction assemblies. 
     Preferably, the distance  173  between the tractions lugs  171  and  172  is chosen so that despite the normal wear of the higher traction lugs  171  over the lifespan of the endless track  150 , the distance  173  will remain significant enough to provide two different contact patches. 
     Preferably, but not necessarily, as shown in  FIGS. 1 ,  3 A and  3 B, the position of the first laterally extending portion  175  along the width of the endless track  150  is chosen so that the ground-contacting area defined by the length  177  and by the width  178  is intersected by the steering axis  21  of the suspension and steering system  20  of the vehicle onto which the traction assembly  100  is mounted. When the first laterally extending portion  175  is so positioned, the ground-contacting area defined by the length  177  and by the width  178  will generally roughly approximate the ground-contacting area of the tire replaced by the traction assembly  100 . 
     In the preferred embodiment shown in  FIGS. 2 ,  3 A and  3 B, the first laterally extending portion  175  is preferably positioned to be essentially adjacent to the lateral side of the endless track  150  which is nearer the vehicle when the traction assembly  100  is mounted thereto. However, as the skilled addressee would understand and as shown in  FIGS. 4 and 5 , depending on the exact constructions of the traction assembly  100 , of the endless track  150  and of the vehicle, the first laterally extending portion  175  could be positioned elsewhere along the width of the endless track  150 . In that case, the first laterally extending portion  175  would generally be interposed between a second laterally extending portion  176   a  and a third laterally extending portion  176   b  comprising respectively traction lugs  172   a  and  172   b . Understandably, in accordance with the present invention, the traction lugs  171  of the first laterally extending portion  175  would be higher than the traction lugs  172   a  and  172   b  of the second and third laterally extending portions  176   a  and  176   b . However, the traction lugs  172   a  and  172   b  need not to be at the same height. 
     Additionally, though the endless track  150  shown herein comprises only one laterally extending portion having higher traction lugs, the present invention is not so limited and the endless track  150  could possibly comprise more than one such laterally extending portion. 
     While illustrative and presently preferred embodiments of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.