Cross-Reference to Related Applications

This application claims the benefit of US Provisional Application Serial No. 61/748,527, filed January 3, 2013 and US Provisional Application Serial No. 61/871,607, filed August 29, 2013, both of which are incorporated by reference.

Technical Field

The present invention relates to apparatus for regulating the interior temperature of footwear and, more particularly, to apparatus comprising the combination of phase change material (PCM) with a human locomotion-based thermal energy-generating apparatus to regulate and control the internal temperature of footwear.

Background of the Invention

High-power harvesting of mechanical energy from human locomotion is a well- known concept, but has not been widely commercialized to date due to the lack of viable energy harvesting technologies. One of the potentially important applications of high- power harvesting of mechanical energy from human locomotion is associated with the ability to regulate the interior temperature of a person's footwear - in both cold and hot climates.

In cases where the ambient temperature is low, thermally-insulated boots are typically worn. In the most straightforward case, the source of heat in these boots is the foot itself. More recently, additional heat sources that generate thermal energy within the boot have been utilized. There are a number of popular products that are currently available to provide heat for outdoor footwear, including electrical heaters powered by batteries and specially-designed footwear inserts that chemically generate heat (i.e., an exothermic reaction upon activation of the insert). However, both of these types of devices have several drawbacks. These include the need to replace or recharge batteries for the electrical heaters, as well as the disposal and replacement of the exothermic elements once the chemical reaction has been exhausted.

Regardless of the drawbacks of these devices, however, this need to prevent the footwear temperature from dropping too low in cold weather constitutes only part of the footwear temperature regulation problem. Equally common and problematic is the issue of footwear overheating, that is, where the temperature inside the footwear increases to an uncomfortable level. This overheating problem exists not only in hot weather, but in cold weather as well. The latter case may be due to the fact that the amount of thermal insulation utilized in outdoor boots to prevent the foot from freezing at low ambient temperatures often causes boot overheating at more moderate temperatures (e.g., just above the freezing point).

The overheating problem is particularly exuberated in cases where well insulated outdoor boots are used with the heaters that do not automatically adjust the heat generation level as a function of footwear temperature. In particular, footwear inserts that chemically generate heat are often prone to this problem.

More generally, for many types of footwear heaters the level of heat generation is naturally determined not by the temperature inside the footwear but by some other external or internal factors, often leading to either insufficient heating or overheating. Thus, for the chemically powered heaters the main factor determining the rate of heat generation is the intensity of the exothermic chemical reaction, which, in turn, depends on the availability of the reagents and the time elapsed form the reaction activation. In the cases where the heater is powered by energy harvesting from human locomotion a similar problem might exist, where the rate of heat generation is mostly determined by such factors as the person's weight and walking speed.

There are two main approaches to solving this problem. One is to provide some means of dynamically adjusting the heat generation rate. Thus, in the case of electrically powered heaters this can be achieved by regulating the electrical current supplied to the heater as a function of the footwear temperature. Similarly, for the heater powered by energy harvesting from human locomotion the amount of the harvested power (and, thus, the heat generation) can be increased or decreased depending on the footwear temperature.

The second approach is to allow unrestricted heat generation by the heater.

However, instead of releasing the generated heat directly into footwear, the idea is to redirect most of the heat to some storage means adapted to absorb, store and release the heat as needed, depending on the footwear temperature. The unrestricted heat generation is particularly beneficial in the case where the heater is powered by energy harvesting from human locomotion, as it allows one to produce and store the maximum possible amount of heat without risking either insufficient heating or overheating. To date, no type of device that is capable of providing the benefit of unrestricted heat generation coupled with the effective temperature regulation of footwear (including the prevention of overheating as part of regulation) is available.

Summary of the Invention

The limitations of the prior art as described above are addressed by the present invention, which relates to an apparatus for regulating the internal temperature of footwear and, more particularly, to a footwear temperature regulation apparatus based on a combination of a human locomotion-powered heater (for heat generation) and phase change materials (for heat storage and controlled release). The use of human locomotion to generate heat eliminates the need to recharge and/or replace traditional footwear heating products. The use of phase change materials (PCMs) provides the ability to harvest a maximum amount of available power whenever possible (such as during a fast walk). At the same time, the utilization of PCM allows precise control of the temperature within the footwear itself, by absorbing most of the heat generated by the heater (and, therefore, preventing overheating) and then releasing this heat when the footwear temperature drops below a predetermined level.

Since the inventive human locomotion-powered heater in combination with PCM is able to generate heat at a maximum power level whenever possible, the total amount of generated and stored heat is maximized, providing the ability to support footwear temperature above some preset comfortable level for substantial period of time even when no heat is generated, such as in cases where the user is at rest.

In accordance with one embodiment of the present invention, multiple components of PCM may be utilized, each having a different transition temperature between its solid phase and liquid phase (and perhaps of differing volumes), allowing for finer regulation of the temperature control.

The heat generation via human locomotion may comprise simply the heat given off by the foot itself, or take the form of an arrangement that harvests mechanical energy from human locomotion and converts the mechanical energy into thermal energy.

In accordance with one embodiment of the present invention, an apparatus for regulating footwear temperature comprises a heat generator for converting human locomotion into thermal energy and a heat storage and release module disposed adjacent to the heat generator, the heat storage and release module including at least one phase change material exhibiting a predetermined phase transition temperature, the heat storage and release module for storing generated heat produced by the heat generator and releasing stored heat upon a decrease in an ambient temperature of the footwear below the predetermined phase transition temperature so as to regulate the temperature of footwear.

Other and further embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.

Brief Description of the Drawings

Referring to the drawings, where like numerals represent like parts in several views:

FIG. 1 is an isometric view of an exemplary human locomotion-based footwear temperature regulation apparatus formed in accordance with an embodiment of the present invention;

FIG. 2 is an exploded view of the apparatus of FIG. 1, illustrating both the heat generator arrangement as well as the heat storage and release module, the latter in the form of a slab of phase changing material;

FIG. 3 shows an alternative configuration of the embodiment of FIG. 1, in this case where the heat generator is embedded with the phase changing material forming the heat storage and release module;

FIG. 4 is an exploded view of an alternative embodiment of the present invention, in this case utilizing an electromagnetic heat generator (also powered by human locomotion) in combination with a heat storage and release module;

FIG. 5 illustrates a different configuration of the embodiment of FIG. 4, in this case with the electromagnetic heat generator embedded within the phase changing material used to form the heat storage and release module;

FIG. 6 contains a graph illustrating the heat regulation properties of the present invention when measured during a two hour period of walking;

FIG. 7 contains a graph illustrating the latent heat properties of the temperature regulator of the present invention, providing additional heat once the heat generator becomes inactive; FIG. 8 illustrates yet another embodiment of the present invention, in this case utilizing multiple types of phase changing material within the heat storage and release module, each type of phase changing material exhibiting a different phase transition temperature;

FIG. 9 shows an alternative configuration of the embodiment of FIG. 8;

FIG. 10 is an exploded view of a configuration similar to that of FIG. 9; and FIG. 11 is a graph illustrating the temperature regulation properties of one exemplary embodiment of the present invention.

Detailed Description

FIG. 1 is an isometric view of one exemplary embodiment of the present invention for capturing mechanical energy from human locomotion and converting it into thermal energy, incorporating the use of phase change material (PCM) to absorb, store and release (as needed) the generated thermal energy and thus regulate the temperature of the footwear itself. As shown, apparatus 10 includes a human locomotion-powered heat generator 12 and an associated heat storage and release module 14, where these elements are configured to fit within a conventional footwear outsole 100. FIG. 2 is an exploded view of apparatus 10, clearly showing the various elements forming heat generator 12, as well as the relative placements of heat generator 12 and heat storage and release module 14 within outsole 100. The terms "insole", "midsole" and "outsole" as used throughout the specification are intended to be non-limiting descriptions of various type of inserts that may be disposed within footwear and used to provide temperature regulation in accordance with the present invention.

In this particular embodiment, heat generator 12 comprises a pair of flexible chambers 20 and 22, with a length of energy-generating tubing 24 coupled between the chambers. Flexible chamber 20 is defined in this embodiment as a "heel" chamber and flexible chamber 22 is defined in this embodiment as a "toe" chamber, as evidenced by their placement with respect to outsole 100. A liquid of a selected viscosity is disposed within this combination of elements and travels back and forth within tubing 24 as a mechanical force is alternately applied to heel chamber 20 and toe chamber 22 (that is, during human locomotion). The liquid is not particularly illustrated in FIGs. I and 2 for the sake of clarity. As described in detail in our co-pending application Serial No. 14/146,034, filed of even date herewith, the flow of fluid within heat generator 12 causes viscous energy dissipation and results in heating both the fluid and the material forming tubing 24, generating heat within the footwear. The particular serpentine shape of tubing 24 is this configuration allows for the coverage of a relatively large surface area of an insole in the region between flexible heel chamber 20 and flexible toe chamber 22. In one exemplary embodiment, about 25 ml of a viscous fluid with a freezing point less than -30°C and a boiling point greater than +150°C was able to generate between 1 and 5 W of thermal energy (heat), as a function of the walking speed of the user.

While this configuration is useful in keeping the internal temperature of footwear from dropping too low in cold weather, the continued locomotion-based generation of heat during an extended time period of walking or running may result in increasing the interior temperature of the footwear to an uncomfortable level; that is, overheating the footwear.

In accordance with the present invention, therefore, phase change material (PCM) is utilized as a heat storage and release module, and combined with the apparatus described thus far to allow harvesting of human locomotion energy at full power without risking either insufficient heating or overheating, thus creating a footwear temperature regulator. In particular, a footwear temperature regulator as formed in accordance with the present invention functions as heat storage and release module 14, preventing the overheating of the footwear by absorbing and storing the thermal energy generated by the heater without allowing the interior footwear temperature to rise above the melting point of the particular PCM. Conventional PCMs include, but are not limited to, octadecane, hexadecane, saturated hydrocarbons, paraffin waxes and hydrated salts. The selected material, as well as its particular chemistry, will determine the specific temperature at which it will change phase from a solid to a liquid. For example, a PCM having a phase change temperature of about 26°C-28°C (i.e., just above room temperature) may be used as heat storage and release module 14 in the present invention. In this case, heat storage and release module 14 will begin to melt as the interior temperature of the footwear rises above room temperature, absorbing heat and preventing overheating of the footwear. If and when the interior footwear temperature begins to fal I again (e.g., the ambient temperature drops, the user stops walking, etc.), the PCM will begin to solidify and release heat, preventing the interior footwear temperature from dropping too low. Thus, it can be seen that a heat generated combined with a heat storage and release module allows for the interior temperature of the footwear to be well regulated.

While the embodiment as shown in FIGs. 1 and 2 utilizes a separate layer 14 of PCM to form the heat storage and release module, it is also possible to embed heat generator 12 within a phase change material (such as a paraffin wax, for example), thus forming a heat storage and release module that essentially encapsulates the heat generated. FIG. 3 illustrates this latter configuration as a footwear insole 28, with heat generator 12 embedded within a heat storage and release module 30 formed of a body of PCM.

Although not shown, this combination may then be enclosed within a standard shoe insole and inserted in the footwear.

FIG. 4 is an exploded view of an alternative embodiment of the present invention, in this case utilizing a different type of heat generator. In particular, instead of depending upon the dissipation of viscous energy as in the arrangement described above, the embodiment of FIG. 4 utilizes an electromagnetic arrangement to generate resistive heat via eddy currents formed within segments of conductive material as magnetic material disposed along a flexible chain moves back and forth relative to the conductive segments.

In particular, a heat generator 40 is shown as comprising a pair of flexible chambers 42 and 44, each containing a volume of an inert dielectric liquid. Chambers 42 and 44 are shown as connected to an energy-generating tube 46. During a heel strike, chamber 42 will be compressed, causing a portion of the inert fluid in chamber 42 to be displaced and enter tube 46. This flow of fluid causes sliding motion of an energy- generating chain (not shown) from heel chamber 42 towards toe chamber 44. During toe- off, the pressure on flexible toe chamber 44 forces the flow of the fluid in the opposite direction, reversing the direction of movement of the energy-generating chain within energy-generating tube 46 back toward heel chamber 42.

Energy-generating tube 46 itself is shown as comprising a set of substantially rigid energy-producing modules 48, separated by flexible tube segments 50. Each energy- producing module 48 includes a segment of electrically conductive material (not shown) that is embedded in the rigid material forming module 48. A chain that moves back and forth within tube 46 (as a result of the fluid flow within the tube) contains separate sections of magnetic material. Therefore, as the sections of magnetic material slide along within the sections of conductive segments, electrical eddy currents are generated within each segment. The mechanism of electrical current generation in the conductive material is based on Faraday's law of electromagnetic induction and is well known to those skilled in the art. The generated eddy currents cause resistive heating of the conductive segments within each module 48 and, as a result, cause an increase in the temperature of heat generator 40. Depending on the pace of human locomotion, about 3 W of heat can be generated with this arrangement. A complete description of the details of this type of human locomotion- based thermal energy generation is found in our co-pending application cited above.

As with the embodiment described above in FIGs. 1 and 2, heat generator 40 is disposed over a layer of PCM forming heat storage and release module 14, where the combination is then disposed within conventional outsole 100. Temperature regulation is achieved in the same manner as previously described, with the phase change materia) forming storage and release module 14 absorbing the generated heat via liquefaction (created by heat generator 40 and/or from the body heat of the individual), and then releasing this absorbed heat when the temperature falls and the phase change material begins to solidify.

FIG. 5 is an alternative configuration of the embodiment of FIG. 4, in this case where electromagnetic heat generator 40 is embedded within a phase change material SO forming storage and release module 14. This encapsulation of heat generator 40 within phase change material 50 creates an arrangement similar to that shown in FIG. 3, where again this configuration may be disposed within an insole to maintain the phase change material in place.

FIG. 6 contains a number of plots illustrating the results of utilizing a heat storage and release module in conjunction with a human locomotion-powered heat generator to regulate the interior temperature of footwear. The data for these plots were collected over a two hour time span, associated with an individual walking at a pace of about 2 mph in an ambient temperature of 0°C.

Plot A of FIG. 6 contains a plot of the increase in temperature as a function of time for a standard footwear insert (i.e., a regular non-heating footwear insert normally supplied with outdoor boots and used for the comfort of the wearer). In plot A, the temperature increases relatively quickly (i.e., over a period of about 20 minutes) and then remains at a constant value of about 25°C.

Plot B of FIG. 6 is associated with the use of a human locomotion-based heater, such as shown in FIGs. 1 -5, under the same conditions as used for the data collection of plot A. As shown, the temperature increased over a time period of about forty minutes to a level higher than the standard footwear insert (about an additional 8°C of heating provided via human locomotion). Under certain conditions, this unregulated heating may not be appropriate and the use of a heat storage and release module in accordance with the present invention improves the usefulness of the apparatus.

Plot C of FIG. 6 is associated with an apparatus formed in accordance with the present invention, utilizing both a human locomotion-powered heat generator and a heat storage and release module (in the form of one or more sections of phase change material). As shown, the incorporation of the PCM slows down the rate of temperature increase. In this particular experimental arrangement, the PCM had a transition temperature slightly above room temperature (i.e., in the range of 26°C - 28°C), where the utilization of the PCM is shown to control the interior temperature of the footwear to remain at this preferable level.

As discussed above, one advantage of incorporating a heat storage and release module in a human locomotion-powered heat generator is the ability of the module to absorb and store the generated thermal energy when it is not required, and then release this energy when the footwear temperature starts to drop. That is, as the temperature within the footwear goes above the phase transition temperature, the PCM will change phase from solid to liquid (i.e., melt) and absorb and store the generated thermal energy, thus preventing an undesirable increase in temperature. As the ambient temperature drops, the PCM will begin to solidify and release the stored heat to the footwear. The presence of the PCM, therefore, provides a dual function of energy storage and release, as well as regulation of the temperature within the footwear.

FIG. 7 is a plot of the interior footwear temperature as a function of time during "cool down"; in the case, for a period at time beyond the completion of the two hour walk used to collect the data shown in FIG. 6. The X-coordinate along the bottom of the plot is of elapsed time since the beginning of the two-hour walk, while the X-coordinate along the top of the plot is "cool down" minutes only. Plot I is associated with a standard footwear insert (such as that used to generate plot A of FIG. 6), while plot II is associated with the use of a footwear temperature regulator formed in accordance with the present invention (such as that used to generate plot C of FIG. 6)

It is evident from the data shown in FIG. 7 that the inclusion of PCM as a heat storage and release module extends the time period during which the user will remain comfortable, with the interior temperature dropping only about 4°C over a time period of 80 minutes. In contrast, footwear containing only a standard footwear insert dissipates energy at a faster rate (e.g., dropping 6°C in only 40 minutes, and thereafter dropping to a much lower temperature (e.g., about 16°C) than the 'regulated' temperature achieved by utilizing a heat storage and release module in accordance with the present invention.

While the embodiments described above illustrate the use of a heat storage and release module containing PCM of a uniform quality (mat is, with a uniform phase change temperature), other embodiments of the present invention may utilize a plurality of PCM components to form the heat storage and release module, where each component exhibits a different temperature at which phase change occurs (and, therefore, a different temperature at which energy wil l be released or stored).

FIG. 8 illustrates an alternative embodiment of the present invention, where an exemplary footwear temperature regulator 80 is shown as including a viscous dissipation energy-based heater component 82 (similar to the arrangement shown in FIG.l) and a heat storage and release module 84 that comprises a main component 86 filled with a first phase change material 88 and a pair of auxiliary components 90 and 92 filled with a second phase change material 94. The first phase change material 88 is selected to have a phase change temperature slightly above room temperature (e.g., 26°C - 28°C). Thus, first phase change material 88 will transition between the solid and liquid states at this elevated temperature and absorb heat when the interior footwear temperature goes too high (i.e., above room temperature). First phase change material will release the stored heat energy when the ambient temperature in the interior of the footwear drops and material 88 begins to solidify.

In accordance with this embodiment of the present invention, second phase change material 94 is selected to have a lower phase change temperature. For example, material 94 may be formed to exhibit a phase transition temperature in the range of about 16-18°C. In this case, second phase change material 94 will naturally melt when the footwear is not in use (e.g., when outdoor boots are removed and stored overnight at room temperature). In this liquid state, phase change material 94 will naturally absorb a certain amount of thermal energy from the environment.

Under the circumstances where the footwear temperature has dropped well below the melting temperature of first phase change material 88 (that is, approaching the transition temperature of second material 94), second phase change material 94 will begin to solidify and release heat, thus preventing a further drop in the interior temperature of the footwear. While this particular embodiment utilizes only two phase change materials, it is to be understood that the scope of the present invention is not so limited, and any desired number of different phase change materials may be used, each configured to exhibit a different, selected phase transition temperature. Moreover, while the

configuration of FIG. 8 illustrates the use of a multi-component heat storage and release module with a human locomotion-based heat generator, it should be clear to those skilled in the art that other types of heat generators (such as prior art heat generators or body heat) may also advantageously be improved by using multiple phase change materials as an energy storage and release module.

FIG. 9 illustrates an alternative multi-PCM footwear temperature regulator 96 formed in accordance with the present invention, where FIG. 10 is an exploded view of an arrangement similar to regulator 96. In this case, the heat is generated by generator 82 in the same manner as described above. The heat storage and release module takes the form of multiple sections and layers of ethylene vinyl acetate (EVA) foam that have been impregnated with a selected phase changing material. As best seen in FIG. 10, a first heat storage component 98 comprises a pair of foam sections 98-1 and 98-2 that are disposed midsole and adjacent to the tubing forming heat generator 82. Foam sections 98-1 and 98- 2 are impregnated with a PCM having a relatively low transition temperature. A second heat storage component 99 comprises a separate piece of EVA foam, impregnated with a PCM having a higher transition temperature than foam sections 98-1 and 98-2. A layer 97 of thermoplastic polyurethane is used as a barrier between the two different PCMs, with the combination of layers fit within outsole 100, in the same manner as described above.

FIG. 1 1 is a graph containing a set of plots that illustrates the ability of the temperature regulator apparatus of the present invention to prevent footwear overheating. The data for these plots were collected over a one hour time space, associated with an individual walking at a pace of about 2 mph in an ambient temperature of 21°C.

For comparison, plot "a" is a graph of temperature as a function of time for footwear having a standard insert (such as a regular non-heating footwear insert normally supplied with outdoor boots and used for comfort of the wearer). In this case, the generated body heat is found to increase the interior temperature of the footwear to about 35°C, which many users might find uncomfortable. Plots "b" and "c" are associated with heat-generating inserts, where the data for plot "b" is associated with a conventional battery-powered heater and the data for plot "c" is associated with a human locomotion- based heat generator as described above. As shown, over an extended period of time, the interior temperature of the footwear for either of these embodiments may go well above room temperature, causing severe overheating. Plot "d" in FIG. 11 illustrates the regulation property of the apparatus of the present invention, where the inclusion of one or more types of phase change material with a heat generator allows for the generated heat to be stored and released as needed. In this case, the temperature of the footwear interior never rises above about 30°C, and never falls below about 20°C.

Although only several preferred embodiments of the present invention has been described in detail here, those of ordinary skill in the art should understand that they could make various changes, substitutions and alterations herein without departing from the scope of the invention. In particular, only one exemplary embodiment of the expanding assembly of chain elements is discussed in detail here. However, those of ordinary skill in the art should understand that other embodiments of expanding assemblies of elements based on elastic polymeric materials, mechanical springs, etc. can be advantageously utilized without departing from the scope of the current invention.