Heating Device

The present invention is a heating device incorporated in an article of clothing or a shoe, notably a ski boot.

We already know of heating devices incorporated in articles of clothing such as gloves or in other clothing or in shoes, notably ski boots. These devices generally comprise an electrical heating resistance connected to a battery or a cell through a switch which can be shut off manually or automatically under the control of a system of temperature regulation including a temperature sensor. Such an electrical resistance heating device has the drawback that the cells used to supply the electricity for the heating resistance are used up very quickly, since the resistance must be used frequently in order to to maintain a desired comfortable temperatures.

The present invention aims to overcome the drawback by using a heating device of particularly simple conception, and by ensuring the maintenance of a comfortable temperature for a long period of time at the cost of a low consumption of electrical energy.

To this end, this heating device, incorporated in an article of clothing or a shoe, notably a ski boot, including an electrical heating resistance connected, through a switch, to a source of electrical current, this heating resistance being placed near a section of the body to be heated, has a sealed enclosure in contact with the section of the body to be heated, this enclosure containing a salt which changes between liquid and solid phase and has a latent fusion heat of a temperature close to the normal temperature of the section of the body, from 30 to 40.degree. C., and in which the heating resistance is in a relation of heat exchange with the salt contained in the sealed enclosure such that the electrical current of the heating resistance, in a short period of time, causes the salt contained in the sealed enclosure to enter a liquid state, after which this salt, in returning to the solid state, progressively gives off heat over a long period of time, thereby maintaining a substantially constant comfortable temperature.

In order that the invention may be more clearly understood, reference will now be made to the attached drawings in which several embodiments of the invention are shown for purposes of illustration, and in which:

FIG. 1 is a vertical and longitudinal schematic section of a ski boot equipped with a heating device according to the invention.

FIG. 2 is a diagram which illustrates the operation of the heating device according to the invention.

FIG. 3 is a vertical and cross-wise sectional view of a second embodiment of the heating device according to the invention.

FIG. 1 represents a ski boot 1 in the interior of which incorporates a heating device according to the invention. This heating device includes a sealed enclosure 2 which is placed on the insole of the shoe, inside the normally used inner casing. This sealed enclosure 2 can be constituted by two elements, namely a plate with a rigid base 3, and a wall 4 of flexible material applied against the area to be heated and having good heat conductivity. The sealed enclosure 2 contains a certain quantity of salt 5 which changes between liquid and solid phase and has a latent fusion heat and this salt is chosen so that this change of phase takes place at a temperature near the normal temperature of the area to be heated, i.e., from 30 to 40.degree. C.

Additionally, the sealed enclosure 2 contains an electrical heating resistance 6 which is connected, by electrical conductors, to a current source 7, such as a cell or a battery, through a switch 8.

By way of example, the heating device according to the invention could use, as a phase-changing salt with latent fusion heat, disodium hydrogen phosphate (Na.sub.2 HPO.sub.4. 12H.sub.2 O), which has a fusion temperature of 33.5.degree. C. The sealed enclosure 2 could contain for example 25 grams of this salt. The resistance 6 could have a value of 2.6 ohms, the heated surface area being 3000 mm.sup.2, while the heating surface of the electrical conductor is 1100 mm.sup.2. The supply of electrical current can come from two accumulators of the Ni-Cd type with an electrical potential of 2.4 V and a capacity of 1.2 AH. The base plate 3 of the sealed enclosure 2 is made of a sheet of polyvinyl-polyethylene chloride with a thickness of 500 micrometers having average heat conductivity and good mechanical resistance. The upper wall 4 is made of a film of polyamide-polyethylene with a thickness of 50 micrometers having a very good heat conductivity.

To use the heating device when the need arises, the skier closes the switch 8 which has the effect of triggering the supply of electrical current of the heating resistance 6 incorporated inside the sealed enclosure 2. The heat given off by the resistance 6 causes a progressive rise in the temperature in the interior of the sealed enclosure 2, a temperature whose variation is indicated by the full-line curve, as shown in FIG. 2, starting from the ambiant temperature which is presumed to be 20.degree. C. The electrical resistance 6 furnishes by Joule's Effect the amount of heat necessary to cause the salt 5 to pass from solid phase to liquid phase. In the particular case considered by way of example, in which the sealed enclosure contains 25 grams of disodium hydrogen phosphate, it is determined that at the end of 30 minutes the salt has passed entirely into the liquid phase, and at this moment, the heating is turned off by opening the switch 8. The heating period, i.e., the period during which electricity flows through the electrical resistance 6, is indicated by Zone A in FIG. 2. At the end of this period, the temperature attained equals about 40.degree. C. After the heating is cut off, the salt 5 returns progressively to the solid state, releasing its heat for about one hour. As seen in FIG. 2, the temperature falls very slowly throughout this one-hour period, remaining close to the comfort temperature of 35.degree..

By way of comparison, the temperature variation curve has been shown as a function of time when only the resistance heat (direct heating) is used (broken lines on FIG. 2). After 30 minutes of heating, the temperature attained is 80.degree., the inertia of the resistance provides about another 20 minutes of heat and the temperature falls back to 30.degree. at the end of this period. The effect of the heating is thus shorter and more violent than in the case when one uses the salt 5 with latent fusion heat.

Another advantage obtained by means of the heating device according to the invention is that, if the temperature at which the phase change occurs is exactly the same as the normal temperature of the foot, an adjustment of the latter temperature is produced automatically. In effect, if the foot is too hot, the salt absorbs the excess calories by passing to the liquid state while on the other hand if the foot becomes too cold, the salt returns to the solid state by releasing calories.

To avoid the salt 5 in liquid phase spilling under the toes, its displacement can be limited by incorporating it in a gel incorporated in the interior of the sealed pouch 2 to act as a sponge.

While the preceding indicated that the heating device 2,6 is placed under the toes of the foot, it is evident that it could be placed anywhere in the shoe and that it could in particular be formed as a complete insole placed in an inner shell which will assure that the impression of the plantar support of the skier will be made during the solidification of the mixture in the enclosure 2.

In the embodiment shown in FIG. 3 the sealed enclosure 2 is the upper part 9 of the insole 10 which contacts the foot, while the lower part 11 of this insole, to which the upper sealed enclosure 5 is attached, is made of a heat insulating material.

The heating device according to the invention can be incorporated in any article of clothing, notably in a glove, a helmet and any other wearables.

It is possible to include a temperature display and a temperature gauge which would permit the automatic triggering of the electrical heating resistance when the temperature of the body area to be heated falls below a predetermined level.