Patent Grant
7174936
The present disclosure relates generally to work machine tires, and more specifically to non-pneumatic work machine tires.
Because work machines often operate in harsh environments and are continuously cycling through no load and relatively heavy loads, work machine tires must be durable and not susceptible to flats. In fact, it has been found that although conventional pneumatic tires provide a smooth ride, pneumatic tires often are less durable than solid tires. However solid tires are known to provide a less than smooth ride.
In order to provide sufficient durability, work machine tires can be non-pneumatic, and thus, are comprised of solid or semi-solid products. Although the non-pneumatic work machine tires are more durable than pneumatic tires, the non-pneumatic tires are often too stiff to provide a smooth ride and lack the contact area with the ground to provide relatively good traction. In order to improve the ride of the work machine, some non-pneumatic tires include a radial band of unpressurized cavities, or recesses. The radial band lessens the stiffness and increases the deformation of the tire so it will ride better than a solid tire. Such a tire is sold by MITL under a trademark that suggests flexibility, but it still provides a stiff ride more similar to a solid tire than a pneumatic tire.
In another example, the non-pneumatic tire described in U.S. Pat. No. 5,042,544, issued to Dehasse, on Aug. 27, 1991, defined a radial band of recesses that enable the tire to deform due to a load and provides an area of contact with the road that is supposedly similar to that provided by a pneumatic tire. Further, in order to better control the deformability of the tire and to limit the collapse of the recesses, the recesses of the Dehasse non-pneumatic tire are taught as being intrinsically dissymmetrical to any radial direction and overlap one another. Although the Dehasse non-pneumatic tire uses recesses in order to control the tire performance and road handling, the Dehasse tire is intended to have a weight and bulk similar to that of pneumatic tires. Thus, the Dehasse tire would not possess the durability required for high load, low speed work machine applications.
Work machine tires are also subjected to tangential forces, such as braking and traction forces, and widely varying radial forces associated with payload. A single radial band of cavities, especially those that are angled, would exhibit unequal clockwise and counterclockwise torsional stiffness. In addition, they would have the tendency to rotate the outer portion of the tire relative to the hub as radial load is varied. This torsional stiffness bias could result in undesirable and unpredictable work machine motion.
The present disclosure is directed at overcoming one or more of the problems set forth above.
In one aspect, a work machine tire includes an annular body of elastomeric material. A radial middle region of the elastomeric material defines a plurality of unpressurized cavities distributed in a pattern that includes a first radial band of cavities and a second radial band of cavities. Each cavity of the first radial band of cavities is oriented at a positive angle with respect to a radius therethrough, and each cavity of the second radial band of cavities is oriented at a negative angle with respect to a radius therethrough. In one aspect, a material volume of the radial middle region is more than one and a half times greater than a combined void volume of the plurality of unpressurized cavities. In another aspect, each of the cavities is defined by first and second arches connected by first and second deflectable wall portions.
a is a cross-sectioned view of a radial outer or tread region of the work machine tire of
b is an isometric view of a radial middle region of the work machine tire of
a is a cross-sectioned view of a radial outer or tread region of the work machine tire of
a is a cross-sectioned view of a radial outer or tread region of the work machine tire of
a is a diagrammatic representation of a portion of the work machine tire of
a is a cross sectional view of a radial outer or tread region of the work machine tire of
Referring to
The radial outer region 13 and the radial inner region 14 are preferably, but not necessarily cavity-free, and the radial middle region 12 defines a plurality of unpressurized cavities 15 that are distributed in a pattern that includes a first radial band of cavities 16 and a second radial band of cavities 17. The bands may or may not overlap, depending upon the desired properties of the particular application. As illustrated, the cavities 15 are evenly spaced throughout each radial band 16 and 17. Each cavity within the first radial band of cavities 16 is oriented at a positive angle with respect to a radius therethrough, and each cavity within the second radial band of cavities 17 is oriented at a negative angle with respect to a radius therethrough. The first and second radial bands of cavities 16 and 17 are oriented at opposing angles in order to cancel or reduce any torsional stiffness bias created by each radial band of cavities 16 and 17. Without the first radial band of cavities 16 canceling the torsional stiffness bias of the second radial band of cavities 17, and vice versa, a tangential force acting in a forward direction on the work machine tire 10, when compared with the reverse direction, might cause a significantly different degree of rotation of an outer portion of the work machine tire 10 to rotate with respect to an inner portion. This could result in unpredictable work machine motion during acceleration, stopping, pulling, pushing, digging, or any other work cycle that could produce a tangential force on the tire. In the illustrated preferred embodiment, the positive angle is 63° and the negative angle is 52° with respect to a radial line through the center of the cavity. However, those skilled in the art appreciate that the positive and negative angles can vary, and are determined based on various factors, including but not limited to, the size and shape of cavities within the first radial band and the second radial band. Moreover, although the positive angle of the first radial band 16 is preferably different than the negative angle of the second radial band 17, those skilled in the art will appreciate that the positive angle and the negative angle could be the same. However, to do so, the shape and/or size and/or number of the cavities within the first radial band may need to be different than the shape and/or size and/or number of cavities in the second radial band in order to generate similar performance. When scaling, the number of cavities is preferably proportional to the diameter of the tire.
The work machine tire 10 includes less than fifty unpressurized cavities 15. In the illustrated preferred embodiment of
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Referring to Table I, there is shown data summarizing the geometry for the six embodiments of the work machine tire 10, 110, 210, 310, 410 and 510. Each work machine tire 10, 110, 210, 310, 410 and 510 are 31 inch diameter tires made for a skid steer loader.
However, in order to provide a desired stiffness and rubber strain, while also being able to support sufficient tread depth, the number and size of the cavities vary among the illustrated embodiments. Whereas, the work machine tire 410 of the fifth embodiment may require the thinnest tread, it may have the stiffness closest to that of a pneumatic tire. For embodiments 1, 2, 3 and 6 that all have twenty cavities per row, increasing the material volume to combined void volume ratios increases the radial stiffness and also enables that design to carry a greater tread depth. Decreasing the numbers of apertures to eighteen cavities per row, such as shown in the fourth embodiment, or increasing the number of cavities to twenty-four cavities per row, such as in the fifth embodiment, changes the material to void ratio, stiffness of the tire, elastomer strain, and tread depth. These embodiments have larger material to void ratios, but their longer cavities, radial placement, and angular orientations combine to provide less radial stiffness. Though, it should be noted that they have not been optimized for maximum tread lug depth.
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During normal operation of the skid steer loader, the work machine tire 10 will be subjected to a predictable range of radial loads. Under this range of radial loads, the material around the plurality of cavities 15 absorbs the radial load primarily by bending rather than by pure compression or stretching, thereby maintaining a relatively low maximum strain on the material. The deflection of the work machine tire 10 by bending the material that defines cavities 15 will cause a larger contact area with the ground, which provides increased traction. Due to the bending around the cavities 15 during normal operation of the work machine, the work machine tire 10 will have a stiffness more comparable to that of a pneumatic tire than a solid tire, and thus, provide the work machine operator with a relatively smooth ride. As illustrated in
However, during operation of the skid steer loader, the greater the radial load, the greater the material strain. Although the work machine tire 10 preferably includes the deflection rate of 0.3 inches per 1000 pounds up to 4000 pounds, the work machine tire 10 includes a progressive spring rate that provides protection for the work machine tire 10 and the skid steer loader. Thus, the work machine tire 10 may become stiffer at higher radial loads. Because the work machine tire 10 is stiffer at higher radial loads, the cavities 15 can remain open under the higher radial loads. However, at a point of overload, illustrated in the preferred embodiment as 6000 pounds, the cavities 15 will collapse, and the rubber-to-rubber contact will absorb the overload. The collapse will limit the strain that can be placed on the material.
During operation of the skid steer loader, there are certain situations, such as stopping the forward movement of the skid steer loader, that may create tangential forces on the work machine tire 10. These tangential forces could also occur in a typical work cycle due to traction forces from digging, pushing, pulling, etc. The material surrounding the cavities 15 oriented at opposing angles can bend to absorb the tangential force. Although each radial band of cavities 16 and 17 will have a torsional stiffness bias in the direction of their respective angles, the second radial band of cavities 17 at the negative angle can cancel the torsional stiffness bias of the first radial band of cavities 16 at the positive angle, and vice versa. Thus, the torque will not move an outer portion of the tire 10 in relation to an inner portion of the tire 10 different amounts depending on whether the tangential force from the torque is in a forward direction or a reverse direction. The opposing angles of the cavities 15 provide a balanced clockwise and counterclockwise torsional stiffness for the work machine tire.
In order to achieve a desired ride while maintaining durability under radial loads and a maximum tread depth of a work machine tire, the material volume to combined void volume can be altered. In choosing a preferred embodiment other considerations were made, including an assessment of how similar the ride would be to a pneumatic tire, whether there was adequate lateral stability (i.e. no worse than a pneumatic tire), and whether the flotation and traction approximated a pneumatic tire. Other considerations included maximizing torsional stiffness, minimizing elastomer strain and finally, maximizing the radial load at which the cavities would collapse. Although all work machine tires contemplated by the present disclosure have a material volume to void volume ratio more than one and a half, in the preferred embodiment for the work machine tire 10 for a skid steer loader, the material volume is about twice the combined void volume.
As shown in Table I, the material volume to combined void volume can be altered by altering the size, angle and number of the cavities 15. For instance, the work machine tires 10, 110, 210 of the first, second and third embodiments have different material volume to combined void volume, ratios because the size, rather than the number, of the cavities 15, 115, 215 differs among the work machine tires 10, 110 and 210. Although a relatively low stiffness is desirable, the decrease in stiffness and strain is limited by the normal operating radial loads and the desired tread depth. The greater the normal operating load, the greater material volume to combined void volume may be required. The decrease in stiffness is also limited by the desired depth of the tread. Although maximum depth of tread is desired for traction and wear, the deeper the tread, the greater the radial area between the outer band of cavities and the outer diameter of the tire is required. Thus, in order for the tire to include a relatively deep tread, the cavities might need to be either reduced in size or made more compact to one another. In the preferred embodiment, the depth 22 of the tread 21 is 1.74 inches. Overall, it is generally a goal to maximize tread depth while maintaining a relatively low stiffness and material strain.
Further, those skilled in the art will appreciate that the present disclosure contemplates various methods for limiting the torsional stiffness bias through the opposing radial bands of cavities. In the preferred embodiment, the radial bands of cavities 16 and 17 are at different opposing angles, 63° positive angle and 52° negative angle with respect to a radial line through the center of the cavity, but each cavity within the plurality 15 has a uniform shape and size, which may include a taper. Each cavity 15 has straight segments or deflectable wall portions 15a separated by curved segments or arches 15b that have a width of approximately 0.9 inch. The total cavity length is about 2.3 inches. However, the present disclosure contemplates the torsional stiffness bias being cancelled by altering the angles, size, number and shape of the cavities 15. For instance, the torsional stiffness bias could also be cancelled by radial bands having the same positive and negative angles, but different sizes and/or shapes. There are various patterns that will provide a balanced clockwise and counterclockwise torsional stiffness for the work machine tire. Reducing torsional stiffness bias can prevent or reduce uncontrolled forward/reverse motion of the work machine during a change of a vertical load. In addition this same factor can serve to prevent or reduce uncontrolled vertical motion from a forward or reverse torque. There is also a desire to provide equal displacements in response to forward and reverse torques. Finally, there is a desire to balance strain in the material around the cavities during forward/reverse drive torque applications.
The present disclosure is advantageous because it provides a durable work machine tire that provides a relatively smooth ride for a work machine operator, the work machine and the load. Because the material volume of the radial middle region 12 is, at least, one and a half times greater than the combined void volume of the plurality of cavities 15, the work machine tire can provide the durability required of a work machine tire in harsh environments and under relatively substantial loads. However, because the work machine tire 10 defines the plurality of cavities 15, the rubber can mostly bend, rather than purely compress or stretch, under the loads. Thus, the work machine tire 10 can also provide more deflection, creating a softer ride, at lower rubber strains. Moreover, the radial bands of cavities 16 and 17 being oriented at positive and negative angles relative to a respective radius therethrough can cancel the torsional stiffness bias of one another. Thus, the material surrounding the cavities 15 can absorb the tangential forces acting on the tire 10 while limiting the rotation of the outer portion of the tire relative to the inner portion during periods of acceleration, deceleration, and torques due to normal work cycles.
The present disclosure is also advantageous because the work machine tire 10 and work machine is protected from overload. Because the work machine tire 10 include the progressive deflection rate, the increased stiffness at higher radial loads allows the cavities 15 to remain open at the higher radial loads. However, when the tire is subjected to an overload situation, the work machine tire 10 will limit the material strain by collapsing the cavities 15. The rubber-to-rubber contact can absorb the overload but the tire then performs more like a solid tire.
Moreover, the present disclosure is advantageous because the dimensions of the radial middle region can be adjusted to fit the desired operating goals of each specific work machine tire. The compromise between tread depth and strain and stiffness can be adjusted by adjusting the material volume to combined void volume ratio. Further, the angles, size, number and shapes of the cavities can be adjusted in order to sufficiently cancel the torsional stiffness bias of the radial band of cavities and produce other known performance characteristics.
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspect, objects, and advantages of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
This application is a continuation-in-part of patent application Ser. No. 29/196,261, filed on Dec. 22, 2003 now U.S. Pat. No. D, 507,522.
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| Number | Date | Country | |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 29196261 | Dec 2003 | US |
| Child | 10864898 | US |
