Abstract:
In some implementations, a flexible track for a tracked vehicle comprises a flexible belt with an inner surface and a ground-engaging surface, the ground-engaging surface comprising outwardly projecting lugs spaced apart along the track, wherein at least one of the lugs comprises a vertical section having a curved leading edge. In some implementations, the flexible track comprises a flexible belt with an inner belt surface, an opposite outer belt surface and at least one track bar attached to the outer surface and extending approximately perpendicular to a direction of the track&#39;s travel, the track bar having an outer surface with multiple projecting lugs and an inner surface with at least one holding element, and wherein when the track bar is tightened against the outer belt surface, the holding element engages the outer belt surface, thereby reducing slipping between the flexible belt and the track bar.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/407,850, filed Oct. 28, 2010, which is hereby incorporated by reference. 
    
    
     FIELD 
     The present application relates to endless track-driven vehicles, and in particular to improved tracks for such vehicles. 
     BACKGROUND 
     Endless track-driven vehicles are commonly used off-road in difficult terrain and under difficult terrain conditions, such as in mud, snow, sand, and tundra. For example, tracked vehicles are used in snow country for grooming ski slopes and snow mobile trails, for transporting skiers to back-country slopes, for ski resort maintenance work, and for snow and mountain rescue. They are also used in various types of terrain for utility company maintenance work, and for oil exploration and oil pipeline maintenance in arctic tundra. 
     Tracked vehicles are generally of two types. Many are two-tracked in which a pair of endless drive track units, one on each of the opposite sides of the vehicle, support and drive the vehicle. Others are four-tracked, in which four separately driven and independently suspended drive track units, two in front and two in the rear, support and drive the vehicle. 
     Four-tracked vehicles have certain advantages over two-tracked vehicles under extreme conditions such as on steep slopes and in very rough terrain because of the flexible independent suspensions of the track drive units and the constant power available to all of the track drive units, even while turning. Unlike a two-tracked vehicle which relies on the differential speed of the two tracks for turning, a four-tracked vehicle steers much like a wheeled vehicle. Its endless drive track units can be physically turned for steering. 
     In any tracked vehicle, the tracks play an important role in the vehicle&#39;s overall performance. It would be advantageous to extend the useful life or to increase the durability of conventional tracks, and also to improve their performance, particularly in snow. 
     SUMMARY 
     Described below are implementations of flexible track for a tracked vehicle that improve upon conventional tracks. 
     According to one implementation, a flexible track comprises a flexible belt with an inner surface and a ground-engaging surface, the ground-engaging surface comprising outwardly projecting lugs spaced apart along the track, wherein at least one of the lugs comprises a vertical section having a curved leading edge. It has been discovered that the curved leading edge tends not to retain snow and/or ice, thus keeping these track surfaces free, which lowers the weight of the track, reduces possible interference between the track and the chassis due to a build-up of snow and/or ice and keeps the lugs in a condition ready to provide satisfactory traction. 
     Similar to the curved leading edge, at least one of the lugs can comprise a curved trailing edge opposite the curved leading edge. 
     The flexible track&#39;s outwardly projecting lugs can be spaced apart in the longitudinal direction of the ground-engaging surface. The lugs can be spaced apart in a lateral direction of the ground-engaging surface. 
     The flexible track&#39;s ground-engaging surface can comprise outer surfaces of multiple track belts. For example, the ground-engaging surface can comprise four spaced apart track belts interconnected by laterally extending tread strips. As another example, the flexible track can be configured as a single track belt. 
     The curved leading edge of the at least one lug can be defined by a spline curve. In some implementations, at least an outer extent of the at least one of the lugs has a curved side surface about an entire periphery. 
     In some implementations, at least one of the lugs comprises a distal end surface. For example, the at least one lug may comprise at least a side surface and an end surface, and wherein the side surface and the end surface are curved surfaces. 
     In some implementations, the lugs comprise bi-directional V-shaped lugs. In some implementations, at least one of the lugs may be in a series of generally alternating V-shaped lugs extending in a lateral direction. At least two of the alternating V-shaped lugs may be joined together. 
     In another implementation, a flexible track for a tracked vehicle comprises a flexible belt with an inner belt surface, an opposite outer belt surface and at least one track bar attached to the outer surface and extending approximately perpendicular to a direction of the track&#39;s travel, the track bar having an outer surface with multiple projecting lugs and an inner surface with at least one holding element, and wherein when the track bar is tightened against the outer belt surface, the holding element engages the outer belt surface, thereby reducing slipping between the flexible belt and the track bar. By reducing the slipping between the track bar and the flexible belt, traction is improved and wear on the belt is reduced. 
     The flexible belt can be configured in multiple belt sections, and wherein the attachments of the track bar to the multiple belts can thus assist in maintaining the multiple belt sections in desired positions relative to each other. 
     The track bar can have a two-piece construction, and the outer surface with the multiple projecting lugs can be formed of a resilient material, and the inner surface can be formed of a metal or other similar material. 
     In some implementations, the holding element comprises at least one raised rib. In some implementations, there is at least one rib positioned on each side of a central axis of the track bar. In some implementations, there is at least one pair of ribs positioned on either side of a central axis of the track bar. In some implementations, the rib or ribs has a generally triangular cross-section. 
     The rib and inner surface of the track bar can be made of a metal, and the flexible belt can be made of a resilient material so that when the track bar is installed on the flexible belt, the track bar&#39;s deformation of the resilient material serves to keep the track bar in place. 
     These and other implementations are described below. The foregoing features and advantages will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is side elevation view of a single track unit having an endless drive track with the new tread features. 
         FIG. 2  is a perspective view of a section of a track unit showing the traction bars that contact the surface over which the vehicle is driven. 
         FIG. 3  is a perspective view of the section of a track unit of  FIG. 2  viewed from the opposite side and showing the inner surface. 
         FIG. 4  is an exploded perspective view of the section of a track unit of  FIGS. 2 and 3 ; 
         FIG. 5  is a perspective view of a drive saddle. 
         FIG. 6  is a perspective view of the traction bar showing a row of lugs extending in the lateral direction along the tread strip. 
         FIG. 7A  is an elevation view of an end of the tread strip showing the lugs in elevation. 
         FIG. 7B  is an elevation view of a section of a one-piece track unit. 
         FIG. 8  is a perspective view of the traction bar extending from the end view of  FIG. 7A  and showing an inner surface of the traction bar configured for mounting to the track. 
         FIG. 9  is a section view in elevation showing the traction bar attached to the track. 
         FIG. 10  is a side view showing a left portion of the traction bar in elevation as viewed in the direction of the arrow in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a side elevation view of a single track unit  10  for use on a multi-track vehicle, such as the four-track all terrain vehicle shown in the assignee&#39;s U.S. Pat. No. 6,983,812, which is incorporated herein by reference. The track unit  10  comprises a horizontal carrier beam  24  extending in a longitudinal direction and connected to a vehicle chassis through a drive axle and other supporting members (not shown). Multiple guide wheel assemblies  30 , such as the six such assemblies in the illustrated implementation, and a drive wheel assembly  32 , support an endless drive track  34  to be driven in either direction about a generally triangular configuration as shown. The endless drive track  34  is configured in the form of a belt assembly made of resilient material with attached lugs, as will be described below in greater detail. 
       FIG. 2  is a perspective view of a section of track  100  from the track unit  10 . The direction of track travel, which is parallel to the longitudinal axis, is indicated at T. As can be seen in the figure, one or more continuous belts  106  configured in parallel can comprise the endless drive track  34 . In the illustrated example, there are four such belts  106  that are spaced apart from each other in the lateral direction. In the illustrated example, the outermost belts are slightly narrower than the inner belts. 
     Extending laterally across and interconnected with the belts  106  are tread strips  102 . In the  FIG. 2  implementation, the tread strips  102  overlie and are supported by traction bars  104 . Referring to  FIG. 3 , which is a perspective view of the tread section  100  from the opposite side, the traction bars  104  are preferably made of a metal or other comparatively high strength material and form a support over which the tread strips  102 , which are made of rubber or other similar material, are applied. For example, the treads strips  102  can be extruded or molded over the traction bars  104 . In one implementation, the track section is about 38 inches wide in the lateral direction. 
       FIG. 4  is an exploded perspective view of the track section  100  showing how the various components are assembled together. Each of the traction bars  104  (for clarity, only one is shown in  FIG. 4 ) is secured to the belts  106  with fasteners  112 , such as threaded bolts. Optionally, as described in more detail below, backer plates  110  and bushings  114  may be provided to prevent the comparatively resilient material of the belts  106  from tearing. 
     At the lateral center of the track section  100 , there is drive saddle  130  secured to each traction bar  104  with bolts or other fasteners. As best shown in  FIG. 3 , the drive saddle  130  defines a guide wheel path  132  along which the guide wheels  30  travel as the endless drive track  34  circulates. On either side of the guide wheel path  132 , there are drive teeth receiving spaces  134  defined for receiving the teeth of the drive wheel assembly  32 . The drive saddle is preferably made of a durable and strong material, such as a metal.  FIG. 5  is a perspective view that shows the drive saddle  130  in greater detail. 
       FIG. 6  is a perspective view of the tread strip  102 . The tread strip  102  comprises a series of lugs  120 , which are raised projections extending away from a base level  122  of the rubber-covered track bar  104 . Each of the lugs  120  has at least one side surface, such as a curved side surface, and more specifically, a surface having a curved profile or edge  124  when viewed as a vertical section. Stated differently, each lug has at least a portion having a curved leading or trailing edge as seen in a vertical section of the lug, such as at the right and left sides of the lugs shown in  FIG. 7A . 
     In the illustrated implementation, the lugs  120  have end surfaces  126  defined at their distal ends. In the illustrated implementation, the end surface  126  is generally parallel to adjacent sections of the belts  106  (when the track is stretched flat). 
     In the illustrated implementation, the lugs  120  are configured as V-shaped lugs arranged in a generally alternating pattern in the lateral direction, with breaks between most of the V-shaped lugs, as best shown in  FIG. 2 . More specifically, there are seven discrete V-shaped lugs  120  projecting from each tread strip  102 , including: (1) outermost single V-shaped lugs pointing in a first direction, (2) intermediate single V-shaped lugs spaced inwardly from the outermost V-shaped lugs and pointed in a second direction opposite the first direction, (3) joined V-shaped lugs positioned inwardly of the intermediate single V-shaped lugs and (4) a center V-shaped lug pointed in the first direction. The center V-shaped lug can have ends that extend laterally as shown. The illustrated implementation is exemplary only, and the lugs may be provided in a number greater or lesser than seven, and in configurations having other than V-shaped. As can be seen, the tread strip  102  is highly balanced, as there are lugs “pointed” in each of the two possible directions of track travel (i.e., for forward travel and for reverse travel), and thus the pattern of lugs is also described as “bi-directional.” 
       FIG. 7A  is an enlarged end view in elevation of the tread strip  102  and traction bar  104 .  FIG. 8  is a corresponding perspective view extending from the  FIG. 7A  end view. As shown at the left sides of  FIGS. 7A and 8 , the side surfaces of the lugs  120 , such as is shown for the exemplary side surfaces S 1 , S 2 , S 3  and S 4 , are curved. As can be seen in the end view of  FIG. 7A , the curved side surface profiles, e.g., S 1 , S 2 , S 3  and S 4 , are distinct from their corresponding straight tangent lines T 1 , T 2 , T 3  and T 4 . These curved side surface profiles are also referred to as the leading and trailing edges of the lugs when viewed in a vertical section such as  FIG. 7A . It has been discovered that curved side surfaces such as those shown in the figures tend to release snow and ice, whereas conventional straight surfaces tend to retain snow and ice, which is a disadvantage. In the illustrated implementations, the side surfaces that are curved when viewed in elevation have profiles defined by a spline curve. 
     In the illustrated implementation, the side surfaces have a concave curvature. A concave curvature produces a “scooping” effect as the lugs circulate, and improves traction. It would also be possible to achieve at least some of the snow and ice shedding benefits with a convex curvature, or mixed convex and concave curvatures. In the illustrated implementation of  FIG. 7 , an average curvature for the exemplary side surfaces S 1 , S 2 , S 3  and S 4  can be expressed as second order polynomial equation:
 
 y= 0.0009 x   2 +0.0061 x+ 0.0003
 
where x is the height of the tread measured from the base level of the lug. In general, an effective range of curvatures is y=0.0009x 2 +0.0061x+0.0003, ±25%.
 
     It should be noted that the surface S 5 , which is generally straight in  FIG. 7A , could be curved, but even as a straight surface, it does not overly detract from satisfactory snow and ice shedding because it is located near the end of the tread strip  102  and is not located close to other surfaces tending to define a closed area. Although omitted from the drawings for clarity in showing the curvature of the side surfaces (see  FIG. 7A ), these side surfaces are typically radiused in areas adjacent the tread strip  102  so as to smoothly blend the protruding lugs and the base tread strip  102  together. 
     In the description above, the track unit  10  has a multi-piece configuration comprising belt(s)  106 , tread bars  104  and tread strips  102 . The curved side surfaces can also be implemented for a so-called “one piece” track unit, a section  100 ′ of which is shown in  FIG. 7B . In the section  100 ′, generally triangular drive lugs  150  are formed as one-piece with and extend from an inner side of a belt  156 . Traction lugs  158  each having at least one curved side surface are formed as one piece with and extend from an outer side of the belt  156 . Additional details on the construction of belts and track units is given in U.S. Pat. No. 6,007,166, which is hereby incorporated by reference. 
       FIG. 8  shows the inner side of the track bar  104  in more detail. In the illustrated implementations, the track bar is shown with optional ribs  140  that permit the track bar  104  to be secured in place with greater assurance than conventional track bars. The ribs  140  extend in a generally lateral direction and are designed to at least bear against and preferably deform the adjacent resilient material of the belts  106  when assembled. 
       FIG. 9  is an elevation view from one end of  FIG. 3  along one of the tread strips  102 . As assembled, the fastener or bolt  112  extends through the backer plate  110 , the bushing  114  (which is within an opening through the belt  106 ) and is threadedly engaged with the track bar  104  on the opposite side of the belt  106 . As a result, the ribs  140  and similar ribs  144  on the backer plate  110  each engage an adjacent surface of the belt  106  when the bolt  112  is tightened, tending to retain the track bar  104  in its position approximately perpendicular to the belt  106  and the direction of travel. The bushing  114  is sized to permit sufficient compression of the belt  106  for satisfactory grip, and to serve as a stop to prevent further tightening that might damage the belt given the range of movement that must be accommodated as the belt  106  and the attached tread strips  102  circulate. In the illustrated implementation, the belt  106  has a thickness of about 0.50 in, and the bushing is sized with a height of about 0.40 in, thus allowing the bolt  112  to be tightened against the track bar  104  until the belt  106  is compressed by about 0.10 in. In other embodiments, it is sufficient to compress the belt  106  by about 0.050 in. With the increased holding power of the ribs  140  and/or the ribs  144  against the belt  106 , the track bar  104  is less likely to become loosened under torsional loads such as during extreme turning maneuvers. 
     In  FIG. 9 , the ribs  140  and the ribs  144  each have a triangular profile and are generally continuous along the length of the tread strip  102  and backer plate  110 , respectively. The ribs are one form of holding element, which also comprises recesses and protrusions relative to the surrounding surfaces of all forms, including ribs, dimples, bumps, etc. The cross section of the recesses and protrusions may be any appropriate cross section, including rounded and/or angular cross-sections. The recesses and protrusions may be continuous, such as the ribs  140  and  144 , or they may configured as a line of discrete elements. 
     In  FIG. 9 , there are two pair of the ribs  140 , and two pair of the ribs  144  on either side. Although not required, providing a second rib spaced apart from a first rib allows the belt material to be compressed longitudinally to some degree for enhanced gripping. 
       FIG. 10  is a side view of a left portion of the tread strip  102  and the track bar  104  in elevation. As can be seen in the figure, intersecting surfaces are smoothly joined together, and in the case of surfaces that are normal relative to each other or nearly so, have radiused junctions, such as the radiused junctions  107  labeled for the two leftmost lugs. 
     In view of the many possible embodiments to which the disclosed principles may be applied, it should be recognized that the illustrated embodiments are only preferred examples and should not be taken as limiting in scope. Rather, the scope of protection is defined by the following claims. We therefore claim all that comes within the scope and spirit of these claims.