Electronic Card Mount and Heat Transfer Assembly for Underwater Vehicles

This invention relates generally to mounting devices for electronic circuit boards or cards, and more particularly to an improved card mount and thermal transfer assembly.

Because of the density of electronic circuitry and the amount of electrical power handled on some electronic circuit cards, a considerable amount of heat is generated that must be carried away from the card to prevent thermal damage to electronic components. In some well ventilated applications this can be accomplished by simple convection air currents. In some, the addition of blowers can be used to augment the natural air flow.

Other applications that require less readily ventilated packaging of circuit cards, such as in an aircraft or spacecraft, have used mechanical refrigeration systems, one example of which is provided by U.S. Pat. No. 3,776,305 to C. E. Simmons.

The removal of heat from electronic circuit cards by thermal transfer to heat sink means such as a mounting frame has been utilized in the apparatus disclosed in U.S. Pat. No. 3,550,681 to P. G. Stier, et al. In that apparatus a T-shaped bar is adapted to be held in heat transfer contact with a frame by frame mounted spring clips and has a lost motion connection with one edge of a circuit card that permits heat transfer from the card and limited positioning thereof for effecting mating with a connector.

While the foregoing expedients have been satisfactory for some applications they are not suitable for certain other special situations, particularly in the case of mounting of electronic circuit cards in small, high powered underwater devices such as towed sonar instruments or apparatus. Those apparatus are necessarily characterized by severe space, weight, and power limitations in that the size and weight of the vehicle are important factors in determining the speeds and depths of tow, and also whether the apparatus can be easily handled and steamed from a tow craft. In addition, the use of refrigeration systems, coolant circulating pumps, and the like, are prone to produce acoustic and electronic signatures that are detrimental to the operation of sonar systems. Another factor is that of accessibility of the cards for inspection or replacement, in view of the usually tubular configuration of the apparatus hull or housing, a portion of which must be removed for access to the cards.

With the foregoing in mind, it is a principal object of this invention to provide an improved circuit card mounting and thermal transfer device.

Another object is the provision of a novel electronic circuit card mounting and heat removal device particularly suited to use in an underwater vehicle having a generally tubular hull or housing.

Still another object is the provision, in an underwater instrument, of an electronic card mounting and thermal transfer device of the foregoing character that provides more complete and effective transfer of excess heat from a plurality of cards to an adjacent wall, and which provides for ease in access to the cards for inspection or servicing without disturbing the mounting of the cards unless actual removal or replacement is required.

Yet another object is the provision of a card mount that effects the conduction of heat to the pressure hull of an underwater vehicle via a flow path having a relatively direct route and ample cross-sectional area.

As another object the invention aims to provide, in an underwater vehicle having a pressure hull, a circuit card supporting structure that provides automatic coupling and uncoupling of a thermal flow path to a tubular pressure hull section upon assembly and disassembly of that hull section relative to the remainder of the pressure hull.

Other objects and many of the attendant advantages will be readily appreciated as the subject invention becomes better understood by reference to the following detailed description, when considered in conjunction with the accompanying drawings.

FIG. 1 is a perspective view of an underwater sonar apparatus including an electronic card mounting and thermal transfer device embodying the invention, a cover portion of the pressure hull being separated from the apparatus to reveal electronic cards and their support means;

FIG. 2 is an enlarged transverse sectional view of the apparatus of FIG. 1 with the cover portion in place;

FIG. 3 is a fragmentary sectional view taken substantially along line 3--3 of FIG. 2; and

FIG. 4 is a fragmentary sectional view taken substantially along line 4--4 of FIG. 2.

The exemplary preferred embodiment of the invention is illustrated and described as used in a sonar system wherein an instrumentation vehicle is towed underwater from a towing craft. Referring first to FIG. 1, a portion of the sonar instrumentation vehicle is indicated generally at 10 and comprises a tubular pressure hull having a main hull section 12a and a separable cover section 12b. These hull sections are preferably formed of a rigid, corrosion resisting material such as marine aluminum, and at least the cover section 12b must have good thermal conductivity. The main hull section 12a is supported by a pylon or strut 14 from a stabilizer section (not shown) and houses components such as transducers that are not part of the invention per se but are served by a plurality of electronic circuit cards 16 carried in a card mount and heat transfer assembly, generally indicated at 18 and mounted on a bulkhead 20 so as to cooperate with and be housed by the pressure hull cover section 12b, when in place. Referring additionally now to FIGS. 2-4, the assembly 18 comprises a pair of rectangular, laterally spaced, parallel, card mounting plates 22, 24 that are edge mounted on the bulkhead 20 as by screws 26. These platesare formed of aluminum or other rigid material having good thermal conductivity. The outer surfaces of the plates 22, 24 are provided with a plurality of parallel, electronic card edge receiving grooves 28, 30, respectively. The cards 16, which are of the type comprising a layer of cladding of a thermally conductive metal such as copper or aluminum, each have one edge disposed in a respective groove 28, 30 and clamped securely therein against the wall of the groove as by a suitable clamp 32. The clamps 32 may conveniently be any of several commercially available types such as can be actuated to clamp or release the circuit cards, for example by a wedging action. The particular clamp construction is not important to the invention so long as it secures the edge portions of the cards 16 in good heat transferring relation to the card mounting plates 22, 24.

The lower ends of the cards 16 are adapted to be received in electrical terminal connectors or sockets 36 mounted on angular brackets 38, 40 that are secured to the outer faces of the plates 22, 24, respectively, by screws 42. Suitable wire conductor leads 44 extend to each of the sockets 36.

During operation of the sonar, the circuit cards 16 tend to generate heat that is transferred to the mounting plates 22, 24 and must continually be carried away in order to prevent damaging temperature build-up in the circuit cards and damage to the electronic components thereon. The present invention provides for substantially direct, large cross-sectional flow paths for conduction of thermal energy from the plates 22, 24, through the wall of hull cover section 12b to the relatively cool ambient water medium in which the vehicle 10 operates, while still permitting ease of removal of the hull cover section for inspection and removal of the cards 16. To this end, a plurality of thermally conductive slip plates 50, 52, 54, and 56 are provided in the space between the card mounting plates 22, 24. These slip plates have the major areas of their outwardly facing surfaces held in contact with the inwardly facting surfaces of the card mounting plates 22, 24. This is accomplished by compression springs 60 disposed in facing cavities in the slip plates 50, 52 and compression springs 62 disposed in facing cavities in the slip plates 54, 56. The springs 60, 62 serve to resiliently bias the slip plates outwardly into the mentioned contact with the plates 22, 24 while permitting limited sliding movement of the slip plates for a reason which will become apparent as this specification procedes.

The slip plates 50 and 54, which are in an edge-to-edge relation in a common plane, are biased outwardly away from one another by compression springs 64, while the slip plates 52 and 56, in a similar relation, are biased outwardly away from one another by springs 66.

The inner surface of the tubular housing cover section 12b is provided with thermally conductive slip plate seat members 70, 72 that are conveniently secured as by screws 74. When the cover section 12b is in place as shown in FIGS. 2 and 4, the upper edge surfaces of the slip plates 50 and 52 are resiliently biased by springs 64, 66 into thermally conductive contact with the seat member 70. Similarly, the lower edge surfaces of the slip plates 54 and 56 are resiliently biased into thermally conductive contact with the seat member 72. Such contact of the slip plates 50, 52, 54 and 56 with the seat members 70, 72 complete heat flow paths from the cards 16 through the mounting plates 22, 24, the slip plates, the seat members, and the wall of the hull section 12b to the ambient water medium.

The card mounting plates 22, 24 are provided with through bolts 80 to prevent spreading of those plates under the influence of the springs 60, 62. The bolts are provided with spacers 82 to further assure that the plates 22, 24 are held in a parallel relation. The slip plates 50, 52, 54, and 56 are provided with enlarged openings 84, through which the bolts 80 and spacers 82 extend, and are thereby permitted only the limited movement mentioned earlier.

It will be appreciated that the hull cover section 12b can be easily removed from its covering relation to the cards 16 and the assembly 18, to reveal the cards and their electrical components and connections, without disturbing the cards or their mountings. It will also be appreciated that when the cover section 12b is replaced, that the seat members 70, 72 will slide smoothly over the edges of the slip plates and re-establish the heat flow paths without requiring any further connections or operations. The inwardly facing surfaces of the seat members 70, 72 are advantageously curved concentrically with the hull section, and the outer edge surfaces of the slip plates 50, 52, 54, and 56 are provided with a complementary curvature, thereby assuring good thermal contact even though small angular misalignments occur between the various parts.

It will be understood that a variety of mechanical equivalents may be resorted to. For example, the seat members 70, 72 may be made integral with the hull section wall, or may be omitted entirely, allowing the slip plates to contact the hull section wall directly. Also, other forms of springs may be used; for example leaf springs can replace the springs 60, 62, and 64.

Obviously, other embodiments and modifications of the subject invention will readily come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing description and the drawing. It is, therefore, to be understood that this invention is not to be limited thereto and that said modifications and embodiments are intended to be included within the scope of the appended claims.