Abstract:
A cooling system is provided for enclosed volumes having payloads of electronic or other equipment that are susceptible to failures when overheated. One particularly useful application of the present invention is in a cooling system for a turreted gimbaled system (i.e. a gimbal) that includes electronic and optical equipment typically used for surveillance, but many other applications will become apparent to those skilled in the art after being taught by the present disclosure. According to one aspect of the invention, a cooling system includes a pair of reciprocal openings between a gimbal sphere and yoke allowing for passage of air therethrough and a pair of fans for circulating the air between the sphere and yoke, thereby expanding the surface area available for heated air from the interior to conduct into the exterior air. In another example, a heat exchanger is provided in the yoke to allow further cooling of the circulated air. In another example, a heat pipe is provided in the yoke to allow heat to be transferred to the heat exchanger.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to cooling systems, and in particular to a system for cooling enclosed volumes containing payloads such as electronics and sensor equipment. 
   BACKGROUND OF THE INVENTION 
   It is well known that heat can be a problem, and that overheating can lead to failures of components such as electronics. This is particularly true with enclosed, largely airtight payloads filled with electronics and other gear. 
   As shown in  FIG. 1 , enclosed volume  100  is bounded by a shell that has an exterior skin  108  and interior skin  106 . Within the enclosed volume is a hot spot  102  and interior air  104 . Conventional cooling techniques typically rely on air transfer (e.g. fans) to cool down hot spots. But air is a poor transfer medium, and such cooling techniques are sometimes insufficient. Meanwhile, if the enclosed volume  100  is in an environment (e.g. airborne at high altitudes) where the exterior air  110  is much colder than the interior air, the much colder exterior air  110  could be used to cool down the hot spot. This however, requires an efficient means of transferring heat from hot spot  102  to interior air  104  to interior skin  106  to exterior skin  108  to exterior air  110 . 
   One particular problem in this transfer is that interior air  104  is a poor heat conductor. Rather than directing heat from hot spot  102  efficiently to the interior skin  106 , where it can be then transferred to exterior air  110 , heat tends to disperse throughout all available interior air  104 . Not only does this lead to unreliable cooling of the hot spot, but the interior air  104  also heats up, further leading to its inability to provide cooling to the hot spot  102  and other components in the interior of the enclosed volume. 
   Accordingly, it would be desirable if there was a system for more reliably cooling the interior of an enclosed volume, including the cooling of hot spots in the volume such as electronics equipment. 
   SUMMARY OF THE INVENTION 
   The present invention relates to cooling systems, and more particularly relates to cooling systems for enclosed volumes having payloads of electronic or other equipment that are susceptible to failures when overheated. One particularly useful application of the present invention is in a cooling system for a turreted gimbaled system (i.e. a gimbal) that includes electronic and optical equipment typically used for surveillance, but many other applications will become apparent to those skilled in the art after being taught by the present disclosure. According to one aspect of the invention, a cooling system includes a pair of reciprocal openings between a gimbal sphere and yoke allowing for passage of air therethrough and a pair of fans for circulating the air between the sphere and yoke, thereby expanding the surface area available for heated air from the interior to conduct into the exterior air. In another example, a heat exchanger is provided in the yoke to allow further cooling of the circulated air. In another example, a heat pipe is provided in the yoke to allow heat to be transferred to the heat exchanger. According to another aspect of the invention, focused cooling is provided for a hot spot in an enclosed volume. According to one example, the focused cooling is provided by mounting a fan on or near the hot spot and directing a stream of air to the interior skin of the enclosed volume. A heat sink may be provided on the skin in the direction of the focused exhaust and/or a heat sink is provided between the hot spot and the fan. According to another example, a fan is provided along with a heat sink on the interior skin of the enclosed volume, and exhaust is directed toward the hot spot, which may further include its own heat sink. According to a further example, a heat pipe is provided between the hot spot and a fan, whose exhaust is directed toward the interior skin. The above aspects of the invention may be provided in combination or separately. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, wherein: 
       FIG. 1  illustrates problems in conventional enclosed volume cooling systems; 
       FIG. 2  illustrates conventional cooling techniques in an example application of a gimbal; 
       FIG. 3A  illustrates a first example implementation in a gimbal of a cooling system according to a first aspect of the invention; 
       FIG. 3B  illustrates a second example implementation in a gimbal of a cooling system according to a first aspect of the invention; 
       FIG. 3C  illustrates a third example implementation in a gimbal of a cooling system according to a first aspect of the invention; 
       FIG. 4  illustrates a second aspect of a cooling system according to the invention; 
       FIG. 5  illustrates an alternative of the second aspect of a cooling system according to the invention; 
       FIG. 6  illustrates a first example of combining the aspects of the cooling system according to the invention; and 
       FIG. 7  illustrates a second example of combining the aspects of the cooling system according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not necessarily be limited to other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration. 
     FIG. 2  illustrates conventional approaches to cooling systems for an example enclosed volume being a gimbal, identified in general by the reference numeral  200 , such as a gimbal as described in more detail in U.S. Pat. No. 6,454,229, commonly owned by the present assignee, the contents of which are incorporated herein by reference. 
   Generally, gimbal  200  compensates for movement by a vehicle (not shown) to which the gimbal  200  is mounted, such as, for example, any land, sea, or air type of a vehicle. The gimbal  200  maintains alignment of a sensor (or sensors) that it carries with an object of interest while the vehicle moves. This is accomplished by proportionately controlling the various axes so as to move the sensors in response to detected movement that is experienced by the vehicle. 
   The gimbal  200  may be of any desired size. It includes a gimbal sphere  212  which has a shell  270  that encloses an interior volume  272 . The sphere  212  is supported by an outer axis support structure  214 , which is sometimes referred to as a “yoke”. In one example, the interior volume  272  is approximately 0.2 (cubic meters), and shell  270  is comprised of carbon fiber/epoxy or aluminum or similar material and is approximately 2 mm thick. It should be noted that shell  270  may not be completely opaque and surrounding interior volume  272 , such as when the sphere  212  further includes a window through which optical sensors and the like receive optical images, in which case a window may be integrally formed in shell  270 . Yoke  214  is comprised of 3 mm thick aluminum, for example. 
   Dotted lines  242  indicate the available volume for payloads within the sphere  212 . This available volume can include a vibration clearance around the payload to prevent any part of the payload from contacting the inside of the sphere  212 . Generally, the volume within lines  242  below the shaft  248  will include sensors such as cameras and the like, while the volume above the shaft  248  within lines  242  will include gyroscopes and electronics packages to control motors (not shown) that will provide adjustments of the payload, and thus the alignment of the sensors with respect to an object of interest. 
   The entire volume within sphere  212  is fairly airtight and is dry and desiccated. Meanwhile, certain components in the payload within sphere  212  are capable of generating significant heat, such as electronic components. Conventionally, fans (not shown) are provided within the sphere  212  and circulate air within the sphere  212 . However, as the payload becomes more packed with electronic components, the conventional approach becomes less sufficient. 
   One aspect of the present invention provides a means of cooling the interior of sphere  212 , including but not limited to hot spots (e.g. certain components) in the payload. It should be noted that although the present invention finds useful application in enclosed volumes such as gimbal  200 , the present invention is not limited to this particular application. Furthermore, although fairly distinct aspects of the invention will be described in more detail below, these aspects can be practiced either separately or in combination together, whether for the illustrative gimbal application or other enclosed volume applications. 
   In general, a first aspect of the invention provides a means for effectively expanding the surface area of the shell of the enclosed volume, thus providing a means for reducing the temperature of the air within the enclosed volume by allowing for greater heat transfer from the interior to the exterior air through the surface area. 
   As shown in  FIG. 3A , in a first embodiment according to the first aspect of the invention, “pull” fan  390  and “push” fan  392  are provided in yoke  214 , in addition to reciprocating holes  380  and  382  that are provided in both the shell  270  and the yoke  214 . These additional features permit the flow of air between the interior volume  272  of the sphere  212  and the interior volume  384  of the yoke  214 . As shown in  FIG. 3A , in this example, air from the interior volume  272  of sphere  212  is drawn through reciprocal first holes  380  in the yoke  214  and in the shell of sphere  212  and into the interior volume  384   a  of yoke  214  by fan  390 . Fan  392  causes air to be further circulated into interior volume  384   b  of yoke  214 . The exhausted air then flows into second reciprocating holes  382 , and thus back into interior volume  272  of sphere  212 . As further shown in  FIG. 3A , the flow of air between the interior volumes  272  and  384  of the sphere  212  and yoke  214 , respectively, allows air to circulate over hot spots in the payload areas outlined by dotted lines  242  in both the upper and lower portions of sphere  212 . 
   As set forth above, yoke  214  includes first hole  380  and second hole  382  that align with similar holes  380  and  382  in shell  270 . In one example, first hole  380  is about 1.7 inches in diameter, while second hole  382  is about 1.9 inches in diameter. In this example, where fan  390  is a “pull” fan, and fan  392  is a “push” fan, air is drawn through first hole  380  into the interior volume  384   a  by fan  390 . In one example, interior volume  384   a  is a channel formed in yoke  214  having a circumference of about 4 sq. in. and about 12 in. long. Similarly, fan  392  exhausts air into interior volume  384   b  which, for example, is a channel formed in yoke  214  also having a cross sectional area of about 4 sq. in. and about 12 in. long. In one example of the invention, fans  390  and  392  are small tubeaxial or vaneaxial fans used commonly in the aerospace and commercial industries. Although fans  390  and  392  are shown as being placed at the top (i.e. the portion of the gimbal that is adjacent the vehicle to which the gimbal is mounted) of the yoke  214  opposite the channels  384   a  and  384   b  from the holes  380  and  382 , respectively, (i.e. the “top” is the portion of the gimbal that is adjacent the vehicle to which the gimbal is mounted) the fan placement is not limited to this example, and the particular fan placement can be made based on the air flow properties for an individual application. Generally, the placement of fans  390  and  392  is chosen so as to maximize the heat transfer resulting from circulating air into the yoke  214  and thus into the exterior air. 
   Referring now to  FIG. 3B , in a second embodiment according to the first aspect of the invention, heat exchange area  302  is further provided in the top of yoke  214 . As shown in  FIG. 3B , in this example, fan  390  further draws warm air from yoke interior volume  384   a  into exchanger area  302 . Air circulates within exchange area  302  by action of fan  390  and “push” fan  392 , allowing heat to be transferred through the shell of the top of the yoke  214  and into the exterior air. Fan  392  causes cooled air from exchanger  302  to be exhausted into interior volume  384   b  of yoke  214 . The exhausted air then flows into second reciprocating holes  382 , and thus back into interior volume  272  of sphere  212 . 
   In one example of the invention, exchanger  302  is, in combination with the arrangement of fans  390  and  392 , a hollow area formed within the top of yoke  214  and has a volume of approximately 200 in. 3  The volume of the heat exchanger  302  can further include fins or other features (not shown) to allow for improved conduction of heat to the shell of the yoke  214  and thus to the exterior air. Whether or not exchanger  302  includes these features, the volume of exchanger  302  increases the surface area that the circulating air comes into contact with. Increasing the surface area improves the heat transfer from the internal air to the external air. The surface area inside the heat exchanger volume  302  can be a 50% or larger percentage increase of the total internal surface area without the cooling system in this embodiment according to the first aspect of the present invention. 
   Referring now to  FIG. 3C , in a third embodiment according to the first aspect of the invention, yoke  214  includes one or more heat pipe structures to help move heat up from the yoke/sphere holes  380  to the heat exchanger  302 , which improves overall heat transfer and/or reduces the yoke cross-section. More particularly, as shown in  FIG. 3C , yoke  214  includes heat pipe  304  and heat sink  306  which is adjacent to yoke/sphere holes  380 . The hot air drawn into yoke interior  384   a  through holes  380  impinges onto the heat sink  306  coupled to heat pipe  304 , and the heat pipe  304  transfers heat to heat exchanger  302 . Heat pipes are well known structures, such as those provided by Thermacore, Inc. of Lancaster, Pa., and so further details thereof will not be presented here so as not to obscure the present invention. Instead, publications and texts describing the construction and operation of heat pipes, such as R. DeHoff and K. Grubb, “Heat Pipe Application Guidelines,” which can be downloaded from http://www.theremacore.com/pdfs/hpapp.pdf, are incorporated herein by reference. It should be noted that the number and placement of heat pipe structures can be optimized for a particular application, and so the invention is not limited to this described example. 
   Another aspect of the cooling system of the present invention will now be described in more detail in conjunction with the following figures. 
   As shown in  FIG. 4 , enclosed volume  400  (which can be, for example, a gimbal sphere such as sphere  212  described above) includes a hot spot  402  (which can be, for example, an electronic component in the payload portion of the gimbal sphere). Coupled to or mounted on or adjacent to hot spot  402  is a heat sink  412 . Still further coupled to or mounted on or adjacent to the heat sink  412  is a fan  414 . It should be noted that, alternatively, heat sink  412  need not be included. Fan  414  is, for example, a small tubeaxial or vaneaxial fan used commonly in the aerospace and commercial industries. Fan  414  has exhaust  416  directed to the interior skin  406  of shell of enclosed volume  400 , such as, for example, shell  270 . Although not necessary for the present invention, it is preferred that in the path of exhaust  416  on interior skin  406  there is mounted another heat sink  418 . This allows heat from exhaust air  416  to be better conducted onto the shell and into the exterior air  410  due to the better heat transfer possible with the increase in surface area provided by the shell mounted heat sink  418 . 
   An alternative arrangement in keeping with this other aspect of the invention is illustrated in  FIG. 5 . As shown in  FIG. 5 , enclosed volume  500  (which can be, for example, a gimbal sphere such as sphere  212  described above) includes a hot spot  502  (which can be, for example, an electronic component in the payload portion of the gimbal sphere). Coupled to or mounted on or adjacent to hot spot  502  is a heat sink  512 . It should be noted that, alternatively, heat sink  512  need not be included. As in the arrangement of  FIG. 4 , on interior skin  506  there is mounted another heat sink  518 . Differently from the previous arrangement, however, coupled to or mounted on or adjacent to the heat sink  518  is a fan  514 . Fan  514  is, for example, a small tubeaxial or vaneaxial fan used commonly in the aerospace and commercial industries. In this alternate arrangement, fan  514  has exhaust  516  directed toward the hot spot  502 . 
   Other additional or alternative features in accordance with this other aspect of the invention are illustrated in  FIG. 5 . As shown in  FIG. 5 , heat sink  518  is integrally formed with the shell of enclosed volume  500 . Still further, this structure can include grooves  520 , or other heat transfer features such as pins, heat sinks, etc. It should be noted that the illustration of these grooves is not necessarily to scale. Rather, in one example implementation, they have a width of about 0.06 in. and a depth of about 0.20 in. The combination of the integral formation of heat sink  518  in the shell of enclosed volume  500 , with the provision of grooves  520  allows for further cooling from exterior air  510  to hot spot  502  because of the increased heat transfer due to the increased surface area provided by the grooves  520 . 
   As set forth more fully above, the two aspects of the present invention may be practiced separately or in combination with each other. Certain embodiments of a cooling system according to the invention will now be described in more detail in connection with some possible combinations. 
     FIG. 6  illustrates a first embodiment of the combined aspects of the invention. In this embodiment, heat is exhausted from a hot spot to more directly facilitate transferring heat into the yoke. 
   More particularly, as shown in  FIG. 6 , enclosed volume  600  (which can be, for example, a gimbal sphere such as sphere  212  described above) includes a hot spot  602  (which can be, for example, an electronic component in the payload portion of the gimbal sphere). Coupled to or mounted on or adjacent to hot spot  602  is a heat sink  612 . Still further coupled to or mounted on or adjacent to the heat sink  612  is a fan  614 . It should be noted that, alternatively, heat sink  612  need not be included. Fan  614  is, for example, a small tubeaxial or vaneaxial fan used commonly in the aerospace and commercial industries. Fan  614  has exhaust  616  directed to the hole  680   a  in the shell of enclosed volume  600 , such as, for example, shell  270 . Reciprocal hole  680   b , which can be, for example a hole in the shell of yoke  214  described above, allows exhaust air  616  to flow into the interior volume  784  of the yoke. 
     FIG. 7  illustrates a second embodiment of the combined aspects of the invention. This embodiment accounts for the possibility that some or all hot spots in an enclosed volume might not be conveniently located near a yoke/sphere hole (or sphere heat sink). 
   More particularly, as shown in  FIG. 7 , enclosed volume  700  (which can be, for example, a gimbal sphere such as sphere  212  described above) includes one or more hot spots  702   a  and  702   b  (which can be, for example, an electronic component in the payload portion of the gimbal sphere). Coupled to or mounted on or adjacent to hot spots  702   a  and  702   b  is a heat pipe  716 . Heat pipe  716  is a conduit that has openings near or over hot spots  702   a  and  702   b  so as to gather heat emanating from these spots. Heat pipe  716  further includes an opening near hole  780   a  in the shell of enclosed volume  700 , such as, for example, shell  270 . Reciprocal hole  780   b , which can be, for example a hole in the shell of yoke  214  described above, allows heat carried by heat pipe  716  to flow into the interior volume  784  of the yoke. In one example of the invention, heat pipe  716  is comprised of structures such as those provided by Thermacore, Inc. of Lancaster, Pa., though various other suppliers and structures are well known in the art. 
   It should be noted that instead of directing heat to a yoke/sphere hole, heat pipe  716  may direct heat to a heat sink, pins or other heat transfer structures formed on the interior of shell  270 , for example. It should be further noted that heat pipe  716  may include opening  706  as shown in  FIG. 7  so as to receive hot air from the interior of the enclosed volume. 
   Although the present invention has been particularly described with reference to the preferred embodiments thereof, it should be readily apparent to those of ordinary skill in the art that changes and modifications in the form and details may be made without departing from the spirit and scope of the invention. It is intended that the appended claims encompass such changes and modifications.