Heat Supply For Thermal Battery and Thermal Battery Having the Heat Supply

Abstract

A thermal battery including: a casing; a battery cell disposed in the casing; a heat generating pyrotechnic material, separate from the battery cell, at least partially surrounding the battery cell; and insulation disposed between the heat generating pyrotechnic material and the casing, wherein the heat generating pyrotechnic material is disposed in a flattened tube having a flat cross-section where at least two sides are substantially parallel, the flattened tube being spirally wound to form a shape corresponding to a complimentary shape of at least a portion of the battery cell.

Claims

1. A thermal battery comprising: a casing; a battery cell disposed in the casing; a heat generating pyrotechnic material, separate from the battery cell, at least partially surrounding the battery cell; and insulation disposed between the heat generating pyrotechnic material and the casing; wherein the heat generating pyrotechnic material is disposed in a flattened tube having a flat cross-section where at least two sides are substantially parallel, the flattened tube being spirally wound to form a shape corresponding to a complimentary shape of at least a portion of the battery cell.

2. The thermal battery of claim 1, wherein the shape is one or more of a cylindrical shape and a flat shape.

3. The thermal battery of claim 1, further comprising a piezoelectric generator disposed in a portion of the casing.

4. A heat supply for encasing at least a portion of a thermal battery cell, the heat supply comprising: a flattened tube having a flat cross section in which at least two sides are substantially parallel; and a heat generating pyrotechnic material disposed in an interior of the flattened tube; wherein the flattened tube being spirally wound to form a shape corresponding to a complimentary shape of at least a portion of the battery cell.

5. The heat supply of claim 4, wherein the shape is one or more of a cylindrical shape and a flat shape.

6. A method for fabricating a heat supply for encasing at least a portion of a thermal battery, the method comprising: filling a tube with a heat generating pyrotechnic material; flattening a cross section of the tube such that at least two sides are substantially parallel; and spirally winding the flattened tube to form a shape corresponding to a complimentary shape of at least a portion of the battery cell.

7. The method of claim 6, wherein the flattened tube is spirally wound in one or more of a cylindrical shape and a flat shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] These and other features, aspects, and advantages of the apparatus of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

[0025] FIGS. 1a-1d illustrate a process of fabricating heating fuse strips for use a hybrid power source.

[0026] FIG. 2 illustrates an embodiment of a hybrid power source.

[0027] FIG. 3 illustrates a diagram of the safety and firing event detection electronics and logic circuitry for integration into the hybrid power source of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] FIGS. 1a-1d illustrate a process for fabricating a heat supply, such as a heat generating fuse strip for use in a thermal battery where the heat generating fuse strip occupies a relatively small volume in an interior of the thermal battery. A thermal battery that may make use of such heat supply is illustrated in FIG. 2 and referred to generally by reference numeral 100. The thermal battery shown in FIG. 2 is a hybrid thermal battery similar to that disclosed in U.S. patent application Ser. No. 15/060,818, corresponding to U.S. Patent Application Publication No. 2017-0040619, filed on Mar. 4, 2016, the contents of which is incorporated herein by reference. However, the heat supply disclosed herein has application in other power sources and in thermal batteries that do not include the hybrid functionality discussed in U.S. Patent Application Publication No. 2017-0040619.

[0029] The thermal battery 100 includes a casing 102, a battery core (cell) 104 and one or more layers of thermal insulation 106, 108 disposed between the battery core 104 and the casing 102. A piezoelectric stack 110 may be provided as an inertial starter disposed in the casing for at least activating the thermal battery upon the casing experiencing a predetermined acceleration event. The thermal battery further having a heat supply 112, such as a heat generating pyrotechnic material, which is separate from the battery core 104, at least partially surrounding the battery core 104.

[0030] As discussed in U.S. Patent Application Publication No. 2017-0040619, providing a slow burning and heat generating heat supply, 112 that is wrapped around the thermal battery core that is initiated upon battery activation to keep the core above its operational temperature for an extended period of time, such as 200-300 seconds.

[0031] Such heat supply 112 can be a heat strip (alternatively referred to as a fuse strip) as shown in FIGS. 1c and 1d. A process for fabricating heat strips is shown in FIGS. 1a-1d. As shown in FIG. 1a, pyrotechnic material 114 is first compacted in an interior of a tube 116, which can be a thin wall aluminum tube. As shown in FIG. 1b, the tube 116 is flattened into a flattened tube 116a by any known process for flattening tubes, such as pressing or rolling, while maintaining the pyrotechnic material in the interior. The flattened tube 116a is then formed into spiral shapes, such as a cylindrical spiral shape 118 shown in FIG. 1c and/or a flat spiral shape 120 as shown in FIG. 1d, to cover around and/or top and bottom surfaces, respectively, of the battery core 104, as shown schematically in FIG. 2. Such forming methods for spirally winding tubes is well known in the art.

[0032] The flattened tube 116a being any tube that is processed to have a flat cross-section where at least two sides are substantially parallel, for example, as is shown in FIG. 1b. Also, the flattening of the tube can be performed either prior to or subsequent to the flattening, although the former is preferred.

[0033] Although shown completely surrounding the battery core 104 in FIG. 2, the heat supply 112 may be configured to partially surround such battery core 104. Furthermore, although shown to be disposed between heat insulation layers 106, 108, the heat supply 112 may be provided directly against the battery core 104 or in any configuration where heat from the heat supply 112 is transferred to the battery core 104 to increase rise and/or run time of the same.

[0034] The pyrotechnic material 114 can be a pyrotechnic compound that would burn slowly and reliably in a relatively thin layer in the thin walled flattened tubing 116a. In the thermal battery design shown in FIG. 2, the thickness of the flattened fuse strip can be about 1.1 mm. In such exemplary size, with a wall thickness of around 0.15-0.2 mm, leaves a pyrotechnic material 114 thickness of 0.7-0.8 mm, and a width of slightly less than 2 mm. It is, however, noted that by providing the heating fuse strip around the battery core, the required volume of the battery core is expected to be slightly reduced since regular core volumes are routinely oversized to provide the required heat mass to achieve as long a run time as possible.

[0035] If the thermal battery is a hybrid thermal battery, as is disclosed in U.S. Patent Application Publication No. 2017-0040619, the piezoelectric element 110 can make electrical power available to the fuze electronics within a predetermined time period, such as 8 msec with a standard deviation of 1 msec to 6.4 msec and standard deviation of 1.3 msec at 3 Volts and 5 mA power. Since the thermal battery can be activated within 45-50 msec, therefore the piezoelectric element 110 needs to provide power for around 40 msec, i.e., equivalent of around 600 micro-Joules.

[0036] The required piezoelectric volume that is required to provide 600 micro-J of electrical energy with a very conservative assumed mechanical to electrical energy efficiency of 40 percent and an added 10 percent margin was determined to be about 16 mm.sup.3. The required piezoelectric (stack) element volume was determined through detailed modeling and testing of actual piezoelectric elements in shock loading simulator. A diagram of a safety and firing event detection electronics and logic circuitry is shown in FIG. 3. The piezoelectric element can be integrated into the power source as shown in FIG. 2 in a recess provided at the center of the battery bottom cap without requiring any reduction in the battery core volume.

[0037] While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.