SUMMARY OF THE INVENTION
The present invention pertains to a sole component for footwear incorporating a sealed, fluid containing chamber and resilient material to harness the benefits of both a pneumatic system and a mechanical system, i.e., provide a large deflection at high impact, controlled stiffness response, a smooth transition to maximum deflection and stability. The sole component of the present invention is specifically designed to optimally combine pneumatic and mechanical structures and properties. The sealed, fluid containing chamber can be made by sealing an appropriately shaped void in the resilient material, or forming a bladder of resilient barrier material.
Recognizing that resilient material, such as a foamed elastomer, and air systems each posses advantageous properties, the present invention focuses the design of cushioning systems combining the desirable properties of both types, while reducing the effect of their undesirable properties.
Foamed elastomers as a sole cushioning material possesses a very desirable material property: progressively increasing stiffness. When foamed elastomers are compressed the compression is smooth as its resistance to compression is linear or progressive. That is, as the compression load increases, foamed elastomers become or feel increasingly stiff. The high stiffness allows the foamed elastomers to provide a significant contribution to a cushioning system. The undesirable properties of foamed elastomers include limitations on deflection by foam density, quick compression set, and limited design options.
Gas filled chambers or bladders also possess very desirable properties such as high deflection at impact and a smooth transition to bottom-out. The soft feel of a gas filled bladder upon loading is the effect of high deflection, which demonstrates the high energy capacity of a pneumatic unit. Some difficulties of designing gas filled bladder systems include instability and the need to control the geometry of the bladder. Pressurized bladders by their very nature tend to take on a shape as close to a ball, or another round cross-section, as possible. Constraining this tendency can require complex manufacturing methods and added elements to the sole unit.
In the past these two types of structures were used together but were not specifically designed to work together to exhibit the best properties of each system while eliminating or minimizing the drawbacks.
This is now possible due to the specially designed single chamber, pear-shaped, or taper-shaped bladder that can be used in a variety of locations and configurations in a midsole. The tapered shape has at least one planar major surface and a contoured surface, which is contoured from side to side and front to back. This contoured surface, when used with a resilient material, such as a foamed elastomer, provides a smooth stiffness transition from the resilient material to the bladder and vice-versa. The single chamber tapered bladder can be used in a variety of locations and configurations in a midsole to provide desired response characteristics. Only one bladder shape is required to be stocked which will significantly reduce manufacturing costs.
The present invention provides the best of pneumatic and mechanical cushioning properties without high pressurization of the air bladder. The air bladder used in the present invention is simply sealed with air at ambient pressure or at a slightly elevated pressure, within 5 psi (gauge) of ambient, and does not require nitrogen or specialized gases. Since the bladder is pressurized to a very low pressure if at all, the air bladder of the present invention also does not require a special barrier material. Any available barrier material can be used to make the bladder, including recycled materials which presents another substantial cost advantage over conventional pressurized bladders. Against the prevailing norm of pressurization, the cushioning system of the present invention is engineered to provide sufficient cushioning with an air bladder sealed at ambient pressure.
The single chamber air bladder of the present invention can be formed by blow-molding or vacuum forming with the bladder sealed from ambient air at ambient pressure or at slightly elevated pressure. Because high pressurization is not required, the additional manufacturing steps of pressurizing and sealing a pressurized chamber are not required. Minimizing complexity in this way will also be less expensive resulting in a very cost-effective system that provides all of the benefits of more expensive specially designed pneumatic systems.
When a cushioning system is loaded, the desired response is one of large deflection at initial load or strike to absorb the shock of the greatest force, and a progressively increasing stiffness response to provide stability through the load. The overall stiffness is controlled primarily by the density or hardness of the resilient material--the foam density or hardness when a foamed elastomer is used. Because of the smoothly contoured transition areas of the foam material and air bladder interface, foam densities are even and high concentrations are eliminated. The gentle slopes and contours of the tapered air bladder provide gradual transitions between the foam material and air bladder responses. Thus, because of the shape of the air bladder, the response to a load can be controlled by its placement. Placing the tapered, for example, pear-shaped air bladder at ambient or very low pressure under the area of greatest force of the wearer's foot affords greater deflection capacity than current systems, which employ high pressurization. This is due to the relatively large volume of the tapered air bladder, in combination with the lack of internal connections or structure within the interior area of the bladder, allowing for a relatively large deflection upon load. For example, when the pear shape is used, the larger, more bulbous end of the pear shaped bladder will deflect more than the narrower end. With this parameter in mind, rotation and movement of the air bladder can provide very different cushioning characteristics, which can mimic the effect of more complex and expensive foam structures within a midsole. In this way the air bladder and foam material work in concert to provide the desired response.
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