The present invention relates to tracked vehicles for agricultural vehicles and the like, more particularly a pneumatic drive tire and wheel for such tracked vehicles.
The use of pneumatic tires on agricultural vehicles dominates the agricultural industry as it is known today.
Nevertheless, there is an increasing use of track vehicles for agricultural use. These track vehicles use an endless belt, preferably made of elastomeric material reinforced by cords of steel. The belt has a ground engaging tread surface similar to that found on a tire. The primary benefit to a track system is clearly the increase flotation tracks have over tires. Tracks can bridge a longer surface area, helping to keep the vehicle afloat. In many agricultural applications the use of tracked vehicles is becoming ever increasingly more popular.
In a prior art patent, U.S. Pat. No. 5,279,378 to Charles E. Grawey, et al. a frictionally driven belted work vehicle is disclosed. In that application Grawey discloses the use of a metal-coated wheel assembly having a pair of rigid wheels with a rubber coating as a drive wheel. Also a cushion wheel can be used as a drive wheel and in an alternative embodiment a bias belted pneumatic tire is used in pairs to provide a drive wheel for the belted vehicle. In that application, Grawey et al. advises that the metal or cushioned wheels are preferred over the pneumatic wheels for a variety of reasons. Grawey notes that panagraphing and relative motion between the drive wheel and the belt can not be tolerated and still provide reasonable wear. He further notes that other than the well-known panagraphing which all bias tires experience, bias tires when under load also exhibit a tracing out of the footprint for one revolution thereof which is shorter by approximately 2 or 3% than the circumference around such tires outer periphery when unloaded. Such circumferential changing phenomena causes relative motion between the belt interior surface and the drive wheel tread portions. Such motion results in wear of the leading edge of the tread lugs and, thus, reduces the tractive length of their drive portions. The practical effect of such wearing substantially reduces the wiping action of the tread lugs upon the surface of the belt which in turn reduces the friction coupling between the drive wheel structure and the belt when they are operated in mud or other adverse friction coefficient reducing requirements. Such relative bias wheel to belt movement carrying frictional engagement results in wear of the belt and the tire. The inventor then goes on to note that the lack of relative movement between the track or belt and a cushioned or rigid wheel structure greatly reduces these wear problems.
While the rigid wheels and semi-cushioned or cushioned wheels dramatically reduce the wear problems it is well-known that the vehicle suspension system must be greatly enhanced in order to provide any ride comfort. This dramatically increases the cost of the vehicle and overall the cost of operating a track vehicle system.
It is an object to the present invention to provide a pneumatic wheel that does not exhibit unusual mud packing characteristics.
It is a further object of the invention that the pneumatic wheel can be used which can accommodate debris and wet soil conditions while still maintain frictional engagement with the belt itself so that forward or reverse propulsion of the vehicle is not dramatically reduced due to a wet or muddy soil condition.
It is a further object of the invention to provide a pneumatic tire in the drive wheel position that has improved traction characteristics in the tread area to minimize any slippage.
The present invention relates to a pneumatic drive tire (10) for track vehicles. The tire (10) has a carcass reinforcing structure (30) having two or more bias angled plies (32, 34). The cords of the first ply (32) are oppositely oriented relative to the cords of the second ply (34). Preferably the tire (10) has no belts or breakers and preferably has an aspect ratio of 100%. The tire (10) has tread (12) with voids that extend across the entire tread creating soil discharge channels (70). Preferably the tire tread (12) has a central area (66) exhibiting high contact area and axially outer areas (60, 62) having a lower contact area. The tread lugs (40) also have a radius portion (48) designed to limit the tire sidewalls (16) from contacting the track (2).
Each tire (10) has a pair of annular beads (24), a carcass reinforcing structure (30) extending radially outward from bead (24) to bead (24), an elastomeric sidewall (16) extending radially outward from each bead (24) adjacent the carcass reinforcing structure (30) to a radially outer tread (12). The tread (12) is characterized by an inner tread surface (14), a plurality of lugs (40) extending radially outward from the inner tread (14) a distance (h). The lugs (40) are divided into a first row and a second row. The first row extends from the sidewall (16) toward the center plane of the tread. The second row extends from the opposite sidewall toward the center plane of the tread (12). The lugs (40) from the first row are circumferentially offset and similar in shape but oppositely oriented relative to the lugs (40) of the second row. Each lug (40) has an enlarged axially inner end (46). A shallow circumferentially continuous central rib (50) extends radially outward from the inner tread (14) a distance of less than half (h). A combination of lugs (40), inner tread (14) and a shallow central continuous rib (50) are spaced to create voids of continuous soil discharge channels (70) extending across the tread (12) from sidewall (16) to opposite sidewall (16).
The tread (12) is divided into three parts (60, 62, 66). A first axially outer portion (60) being ⅙ of the tread width. A second axially outer portion (62) being ⅙ of the tread width and a central portion (66) of ⅔ of the tread width. Each portion (60, 62, 66) has a net contact area measured around the circumference of the tire (10). The contact area of the first tire portion (60) and the second portion (62) is less than 60% of the gross circumferential area of the respective portion. The central portion (66) has a net contact area about 60%. In the preferred embodiment the outer portions (60, 62) had a net contact area 52% while the net contact area of the central portion was approximately 60%.
In a preferred embodiment tire (10) each lug (40) has an axially outer surface (42) tangent to a sidewall (16) extending generally radially outwardly therefrom, the radially outer surface (44) of circumferentially adjacent lugs (40) are spaced by the soil discharge channel (70) preferably the radially outer surface (44) joins the axially outer surface (42) at a radius portion (48). The radius portion (48) is less than the radius of the central guide of the track thereby minimizing the contact of the axially outer portion (42) of the lug (40) and sidewall (16) with the track (2).
In the preferred embodiment tire (10) the lugs (40) extend radially from the central rib (50) a distance of less than half of an inch (2 cm), the central rib (50) extends outwardly less than a quarter of an inch (1 cm), the total distance (h) being less than 0.75 inches (3 cm). The lugs (40) each have a centerline (41) as measured between the leading edges (43) and the trailing edges (45) of the respective lug. The centerline (41) being about 90xc2x0 relative of the circumferential direction.