US3546996A - Release latch actuated by temperature excursion - Google Patents

Description

United States Patent [72] inventors Ramon J. Grijalva Sepulveda;

George F. Queener, Sherman Qalts, Calif. [21] AppLNo. 814,967

[22] Filed April 10, i969 15 [45] Patented Dec. 15, 1970 [73] Assignec the United States of America as represented by the United States Atomic Energy Commission. by mesne assignments {54] RELEASE LATCH ACTUATED BY TEMPERATURE EXCURSION 9 Claims, 7 Drawing Figs.

[52] US. Cl. 85/1, 85/9, 85/8.8, 85/61, i 16/] 14, 176/38 [51] lnt.Cl F16b3l/00 [50] Field of Search 85/6 I (inquired):

[56] References Cited UNITED STATES PATENTS 3,408,890 ll/l968 BoChman.Jr. 3,449,996 6/1969 Takahashi.

Primary Examiner-Edward C. Allen Attorney-Roland A. Anderson ABSTRACT: Latch mechanism including colinear elements constructed of materials having dissimilar temperature coefficients of elongation arranged to allow differential elongation which effects arming of the device during a temperature excursion exceeding a predetermined limit; and then to contract differentially to apply a strain sufficient to rupture a retainer element on reversal of the temperature excursion. The latch device may be utilized as a severable link or retainer in a failsafe mechanism to prevent further operation of a device subjected to an excessive temperature excursion.

PATENTED DEC] SL976 3; 546; 996

' SHEET 1 OF 2 IN VENTORS RAMONJ GR/JAL VA BY GEORGE FOUEENER ATTORNEY PATENTEU um 5:970 354G996 66 INVENTORS RAMON J. GRIJALVA BY GEORGE E QUEENER flaw; 4- W ATTORNEY RELEASE LATCH ACTUATEDBY TEMPERATURE EXCURSION BACKGROUND OF THE INVENTION i This invention was made in the course of, or under, Contract No. At(ll-l)-GEN-8 with the-United States Atomic Energy Commission.

Field of the Invention Latch or retainer link mechanisms which are actuated by an excessive increase in temperature havev been'used in the past for a variety of purposes. Such a mechanism, for example, has been used to actuate fire doors, sprinkler systems, and also 'to inactivate a variety of other systems. These mechanisms are generally characterized in that they are actuated when the temperature excursion exceeds a predetermined limit and while the'temperature'is still at the excursion level. There are certain situations, however, where actuation'of the latch while still at an excessive elevated or possibly excessively depressed temperature level would create an even more hazardous condition. Accordingly,- there is a need for a! latch or link device which senses or is set or armed whenthe temperature of a system increasesor decreases excessively but remains intact until a normal temperature is reestablished and is then actuated to prevent any further activity in the system. Such situations might arise, for example, when a coolant freezes in a heat exchange system possibly rupturing elements thereof or when overheating occurs so that containment materials, or other components such as core or control-elements in a nuclear reactor may bev damaged so that restarting of. the mechanism may be hazardous. In many instances external accessory apparatus and/or electrical circuitry is neededto actuate the mechanism. One example of such a severable fastener is disclosed in U.S. Pat. No. 3,277,766, issued '.Oct. 11, l966, to Francis B. Burkdoll for an Explosively Releasable Bolt. A need exists for a self-contained} compact releasable mechanism of uncomplicated design and of dependable reliability. 1 J

SUMMARY OF THE invaurion The present invention relates, generally, to latch or bolttype mechanisms which are actuated subsequent to occurrence of a temperature excursion and, more particularly, to'a self-contained latch or retainer mechanism includingan element such as a bolt 01 pin especially arranged'and adapted to be armed and then severed to inactivate an accessory mechanism by actuating or inactivating an element, essential to the operation thereof, by an excursion in temperature to exceed a preselected normal limit and then followed by return to a normal temperature.

In the latch mechanism of the invention, two elements constructed of materials having dissimilar coefficients of thennal expansion are arranged in colinear relation, e.g., such as a tube and rod arranged concentrically,. to serve as'the self-contained actuators. At a first retainer end of said colinear elements an arrangement is provided which retains the ends thereof in fixed relation. This first arrangement generally includes linkage means for incorporating thelatch as a tension member in a band or other linkage retaining,"a ctuating or inactivating said essential element of the mechanism with which the device is employed. The linkage means include separable elements retained by a severable member to which the first end of said colinear elements are coupled so as to apply a shear or a tensile stress so that the resulting strain breaks the severable member releasing the link. At the the second or arming end of said colinear elementsjan arrangement is provided which effectively allows free differential expansionof'.

' mal strain therebetween which is transferred to said severable member by said first end arrangement. On return to a normal 7 or other appropriate temperature level, the severable member the colinear elements until a predetermined temperature level limit of a normal operating range is attained or exceeded but which then firmly locks the second ends of 'the colinear eleruptures and the linkage separates toinactivate the accessory mechanism.

Accordingly, it is an object of the invention to provide a release latch linkage mechanism which is armed on undergoing an excessive temperature excursion but which is actuated for release on reestablishment of 'the temperature to a preselected level.

Another object of the invention is to provide a latch linkage mechanism utilizing colinear elements having dissimilar coefficients of thermal expansion to sense occurrence of an excessive temperature excursion and thence forth to actuate a severable'link element releasing the latch linkage on reattainment of a normal temperature level.

Other objects and features of advantage will be apparent in the following description taken in conjunction with the accompanying drawing, of which:

BRIEF DESCRIPTION OF THEDRAWINGS FIG. I is a longitudinal cross-sectional view 'of a first embodiment of the latch mechanism of the invention which is armed by an excessive increase in temperature; I

FIG. 2 is a view of the arming end portion of the device shown in FIG. 1 on attainment of a predetermined excessive temperature level whereat arming is effected, and whenceforth the link is severed on a reduction in temperature;

FIG. 3 is a longitudinal cross-sectional side view of a second embodiment of the latch mechanism of the invention;

FIG. 4 is a plan view of the release linkage means of the device illustrated in FIG. 3 and FIG. 5 .is a similar view shown in released position;

FIG. 6 is a partially cross-sectional viewof a modified release linkage means end arrangement which may be employed with either of the colinear actuating-element arrangements of FIGS. 1 and 3; and

FIG. 7 is a view partially in cross section of an arming end portion which may be substituted for any of those in the foregoing embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In brief, the differential temperatureactuating latch of this invention includes essentially paired colinear elements, particular'ly, a generally concentric rod or'drawbar and sleeve actuating unit having, at one end, i.e., the arming end, a means for restricting the thermal expansion of said rod relative to said tube in a desired direction once a predetermined temperature has been attained and, at a second end, i.e., the retainer end, a severable fastening member fixing the relative positions of said rod and said sleeve on attainment of a second predetermined temperature. Said severable-fastening member may be either a notched tension or shear pin member which is incorporated as a part of a severable fastening linkage of the character described more fully hereinafter.

More particularly, a preferred embodiment of the invention 10, illustrated in FIG. I, is provided as a release latch having an actuating unit including a sleeve 12 of ajfirst material encompassing a generally cylindrical elongated'drawbar member 13 of a second material in loose fitting concentric relation. As

described hereinafter, the materials of saidsleeve and drawbar members must have dissimilar coefficient of thermal expansion such that as heat is applied to raise-the temperature of said device said drawbar member 13"will expand, i.e., elongate, at a rate greater than that of said sleeve 12. For example, a difference in the thermal expansion coefficient of the sleeve and rod of at least about 7 X l0 in/in/T F. has been found satisfactory. Determination of said differential rate of expansion and, therefore, the selection of materials from data supplied for customary material from data supplied for customary materials of construction will depend upon the temperature difference at which said device is utilized and the tensile strain necessary to cause rupture of the severable fastening member.

he drawbar member 13 includes at the first retainer end an irged head portion 14 provided with a threaded terminal :ptacle and, at the second end, with an enlarged guide por- 15. An elongated generally uniform reduced-diameter ral portion 16 is provided between the head 14 and guide ion 15. The lowermost second end of member 13 terites in a somewhat constricted threaded portion 17. ve 12, at a first retainer end, has an outwardly flanged lip vhich engages a severable joint portion 19 of a link, e.g., iner band, of the accessory system into which "the latch hanism is incorporated. More specifically, said retainer l includes a first elongated portion of which a perforated 21 extends over the upper end of sleeve flange 18 together a spacer 22 at the level of said flange 18 and with a perted lower slotted lip portion 23 bearing against the lower of flange 18. A perforated end portion 24 of a second porof said retainer band is disposed to overlap elongated por- 21 so that a severable threaded bolt means 26 may be .ed through the aligned perforations in said band ends 21 24 of said retainer band joint to engage threaded receptaend 14 of drawbar 13. Thereby said link ends 21 and 24 firmly secured together. It will be observed that the going arrangement also secures the receptacle end of "bar 14 in fixed relation to the retainer end of sleeve 12. 'lected prestressing of the severable bolt 26 is provided by lating the tightening torque of bolt 26. The accessory link- : nds 21 and 24 may be, for example, terminal portions of 'idual band tension members incorporated as a severable in a control valve, switch or other mechanism (not m) which controls the operating level of an accessory ce with which the latch device is used. The link might also circular band (not shown) with the ends 21 and 24, prod thereon. The latter arrangement may be used, e.g., to in essentialoperating elements .of a cylindrical device in 'ating condition until an excessive temperature excursion '8. One particular application to which such a circular 1 link is adapted is for retaining neutronic reflector or ld segments (not shown) in position about a compact car reactor core such as those of the so called SNAP reac- Heat may be supplied by convective and radiative arements or by conduction to the latch. One particularly efve method would be to bypass a portion of heat exchange ia, e.g., that which is discharged from the reactor core ugh a conduit (not shown) wound or otherwisedisposed ontact with sleeve 12, e.g., as by being passed longitully in close proximity to or in contact with sleeve 12. reby, the latch mechanism would be subjected to any exive temperature excursion occurring in the reactor core as as to a subsequent temperature decrease brought about ther means such as the usual fail-safe scram mechanisms 1e reactor. Upon cooling, the bolt 26 is severed releasing oint members to loosen the link and allowing the reflector rents to separate from the reactor core thereby eliminatany further possibility of producing a nuclear reaction ein. The link could similarly be used to retain poison rods ide a nuclear reactor core to be inserted on rupture of the order to develop the tensile stress by appropriate move- .t of drawbar 13 and sleeve 12 needed to sever bolt 26, an :cially constructed arming means is provided proximate second end of said sleeve. in the embodiment of FIG. 1,

arming means comprises a ring retainer collar 30 icated of the same material as said sleeve and attached to second end of sleeve 12. Retainer collar 30'has an inner pheral groove 32, having the upper side thereof aligned l the lowermost end surface 33 of said sleeve 12. A -aded collar 34 engages the lower threaded portion 17 of drawbar member 13 and is disposed in sliding relation to ring retainer means 30. Said adjustable collar means is icated of the same material as said drawbar 13 and is aded to set the desired arming temperature. A snap ring 36 is 'osed within groove 32 bearing inwardly against the pheral surface 38 of said adjustable collar 34, in loose fit tion. For obtaining desired flexibility the ring 36 is made with enlarged inner and outer peripheral portions joined by a 1 preselected temperature level to arm the device by preventing retraction of drawbar 13 on any subsequent decrease in the temperature below the excursion level.

With the foregoing arrangement as the ambient temperature increases, said actuating drawbar member 13 expands, i.e., elongates at a rate greater than that of said sleeve and is allowed to respond thereto freely as long as the selected temperature is not exceeded. During said free response, said adjustable collar means 34 moves in essentially unhindered sliding relation within the ring retainer means 30. However, when the temperature excursion exceeds the preselected level the notched shoulder 40 aligns with said groove 32, so that said snap ring 36 is partially released from groove 32 to fit against the end 33 of sleeve 12 and to bear against surface 43 defining a longitudinal stop of shoulder notch 40, as shown in H6. 2, when the temperature again decreases. Generally with snap ring 36 released as described, actuating drawbar 13 is free to expand as long as the temperature level is above the selected arming temperature. However, as the ambient temperature decreases,said drawbar member contracts at a rate greater than that of said sleeve. When the snap ring 36 engages shoulder surface 43, contraction of drawbar 13 is restrained and member 13 together with bolt 26 are placed under tension.

For the purposes of the invention, bolt means 26 is provided with a circumferential groove or notch 44 to provide for reliable severance at a consistent tensile stress level and location. The design of bolt 26to'obtain such a consistent severance characteristic is critical to the operation of the latch mechanism. The bolt must be fabricated of a material which will rupture reproducibly at an appropriate tensile force level generated as described. The material should generally have a relatively low ductility otherwise the bolt would stretch but not break. All of the materials must have physical properties which do not undergo significant change with operation at elevated or reduced temperatures as the case may be. Further, said notch must be closely dimensioned as proper severance depends upon the contour and diameter of said notch. It is to be noted that if the notch radius of curvature isless than 0.005 inch, the surface finish thereof is critical to performance since at that dimension the surface crystal lattices therein become a large percentage of the surface as is well known in physical testing of notched tensile specimen. The groove may be of a depth in the range of about 5 to 15 percent of the diameter of the bolt to afford proper severance without unduly weakening the member and the bolt may also be prestressed to at least partially adjust the severance temperature level. Accordingly, a radius of curvature above 0.005 inch is preferred. The sleeve 12 may be made of a hard strong material such as molybdenum or tungsten which has a low coefficient of expansion and the drawbar member of a material such as 316 stainless steel, aluminum alloy or the like which have a relatively higher coefficient of expansion. On the other hand by constructing the drawbar of a material with a relatively low coefficient of expansion, such as, molybdenum, and the sleeve of a material with a relatively high coefficient of expansion, the latch will be armed by a selected decrease in temperature and severed'on a subsequent increase in temperature.

A second embodiment 50 of the latch mechanism of the invention, illustrated in FIGS. 3, 4 and 5, includes a drawbar actuating member having a modified construction and fabricated of a material having a relatively high coefficient of expansion. The drawbar has a central uniform diameter portion 52 and an enlarged generally cylindrical head 53 at the second arming end. Portion 52 of the drawbar is disposed contion to the lowermost'end surface 55 of. sleeve 54. A terminal conical tip 58 is provided on said drawbar to facilitate assembly.

To provide for selection and adjustment of the arming temperature level an adjustable stop collar 59 is secured as by means of an interior threaded portion which engages the lower arming end of sleeve 54. A lock nut 61 and washer 62 are employed to retain collar 59 in a selected fixed position. Collar 59 further includes an internal cylindrical stop 63 disposed in the space between end surface 55 of sleeve 54 and shoulder 57 of drawbar head 53. A terminal secondend tubular portion 64 of collar 59 extends beyond said drawbarhead 53.

Engagement means is provided in the second end of collar 59'to limit the withdrawal of drawbar head'53 following an excessive temperature excursion so as to, develop the necessary strain force. More particularly, the engagement means may take the form of an assembly including an externally threaded tubular retainer 66 provided with inwardly tapering radially spaced longitudinal grooves 67, e.g., four at 90 spacing. Jaw

stops, or latches 68 are seated in the forward end of grooves 67. To actuate the latches 68, a spring having a cylindrical rearward portion 71 is disposed with tab portions 72 extending along the grooves 67 with the forward end portions seated behind and attached to jaw or latches 68 pressing axially inward. The assembly is screwed into place within the second end portion 64 of collar 59 and is locked in place by means of a skirt nut 74.

As said, drawbar member expands, i.e., elongates relative to said sleeve 54 responsive to an increasing excursion in temperature, the trailing edge of said drawbar head 53 moving as the temperature increases and finally, at a preselected temperature travels past jaw or latches 68 releasing said jaws to lock unto said drawbar at an anterior'position adjacent head surface 57. Whenthe ambient temperature again decreases said drawbar contracts at a rate greater than that of said sleeve, so that the jaws 68 are wedged securely between shoulder surface 57 of drawbar head 53 and the end surface 76 of stop 63 of collar 59, thereby limiting the contraction of said drawbar somewhat in the manner shown in FIG. 2 and developing a tensile strain in the drawbar. V

For utilizing the stress generated in the drawbar an enlarged eyebolt portion 77 having a transverse perforation 78 is provided at the upper end of the drawbar. Moreover, paired split block portions 79 having a longitudinal bore are mounted, as by means of machine screws 81, on the upper retainer end of sleeve'54. Said bore includes a radial groove 83 into which a flanged rim 84 of sleeve 54 fits closely providing a secure grip therebetween. Blocks 79 are slotted at opposing sides to receive wing plate members 86 pivotally mounted as by means of machine screws 81. Threaded sockets 87, 88 are provided inmembers 84 and 86, respectively, in alignment with perforation 78, of eyebolt portion 77 of drawbar 51. A severable ceramic pin 91, e.g., steatite, porcelain, etc., threaded at both ends is then seated in .the aligned sockets 87,88 to pass through eyebolt perforation 78. Retainers 92a, 92b, secured by machine screws 93 may be used to secure the ends of pin 91 in said sockets. Pin 91 includes a circumferential groove 94 disposed centrally within the perforation 78 of drawbar eyebolt 77 to provide proper severance on application of a preselected bending strain.

.For the purpose of joining the latch mechanism in a hoop or band-type linkage of the character described, tabs 96, 97 are provided on the outside surfaces of wing plate members 84 and 86. Strap ends 98, 99 which may be terminal portions of a hoop (not shown) whichretains essential element of the accessory mechanism in place or may be portions ofa strap linkage, by which a control valve, switch or the like is actuated, may then be attached to said tabs 96, 97, respectively.

Accordingly, as the temperature changes to' exceed a selected arming temperature limit, the shoulder surface 57 (FIG. 3) of drawbar head 53 passes beyond jaws 68 as the drawbar 51 differentially elongates and the jaws 68 snap into place as described above. Thereafter, as the temperature excursion reverses, a progressively increasing tensile strain is developed in the drawbar and is applied by eyebolt 77 to the severable element 91 as a bending strain so that at a preselected reduced temperature level the element 91 severs at groove 94 and the wing plates 84 and 86 swing outwardly releasing the accessory linkage as shown in FIG. 5, thereby inactivating the accessory mechanism. lt will be appreciated that if the materials of the drawbar and sleeve 54 have inverted magnitude coefficients of expansion and the arming-arrangement is rearranged to respond at a decreased temperature level, in a manner similar to the embodiment described above, latch mechanism may then be used where an excessively decreased temperature excursion may occur.

A third linkage retainer arrangement which can be used with a drawbar and sleeve actuator provided with either of the arming structures described above is shown in FIG. 6 of the drawing. More particularly a sleeve 101 and drawbar 102 are arranged concentrically. The upper end 103 of sleeve 101 is adapted to provide such retainer arrangement by means of a cap member 104 fitted thereto instead of the flanged construction described above. An adjustable severable stud bolt. member 106 is secured by a threaded end 107 in a threaded receptacle 108 at the upper end 109 of drawbar 102; The I lower side 111, of a flanged portion 112, of stud 106 is seated firmly against the upper end of drawbar 102, while the upper side 113 is seated against a bushing 114 nested within cap 104. The terminal portion of stud 106 extends through the bushing 114 and axial bore of cap 104. Exterior to cap 104, mounting retainer tab pairs 116, 117, are arranged with angularly disposed perforated plate portions 118, 119, respectively, encompassing the extended terminals portion of stud 106 and separated therefrom by means of insulator bushings (not shown) if desired. A nut 123 and washer 124 engage the exterior threaded end 126 of stud 106 to secure retainer tabs 116, 117 against cap 104. By applying a torque wrench (not shown) to nut 123 while retaining stud 106 held in fixed position as by means of a screwdriver (not shown) fitted into slot 127 in the end 126 of stud 106, an adjustable or standard tension can be applied thereto. The terminal end of stud 106 is provided with a circumferential groove 128, e.g., adjacent the juncture of plate portions 118, 119 of retainer tabs 116, to provide for reliable severance as above.

A third arming arrangement which can be utilized with a drawbar-sleeve actuator provided with any of the retainer structures described above is shown in FIG. 7. More specifically, a drawbar constructed of material having a relatively high coefficient of expansion and having an elongated, uniform diameter, cylindrical rod portion'llSl is employed. A sleeve 152 constructed of material having a relatively low thermal coefficient of expansion is disposed concentrically about rod 151 leaving the lower end portion of rod 151 projecting beyond the lower end 153 thereof. A collar member 156 is secured to the lower end of sleeve 152 with a portion thereof projecting beyond the lower end 153 of sleeve 152 and encompassing the lower projecting end of rod 151. To eachside of a slot disposed along the median plane bisecting the lower end of collar 156 pairs of tabs 157 are provided for mounting of cams 158 and 159 in diametric opposition across the lower end of rod 151. The cams 158, 159 are perforated to receive pins 161 which pass'through aligned perforations in collar tabs 157 so that curved shoe portions 162, 163, of cams 158, 159, respectively, can pivot to bear against opposing sides of rod 151. Springs 166, 167, are arranged with a coiled portion disposed about each pin 161 with one end bearing against the upper portion of collar 156 and with the other end bearing against a lower projecting portion 168. 169 of cams 158, 159, respectively, to resiliently urge said cam shoes 162. 163, against said rod. The cam shoes may be provided with serrations tilted downwardly to allow free motion of the rod 151 therebetween during a rise in temperature but to securely clamp and retain the rod in fixed relation on reversal of the temperature excursion. The cams may therefore be seen to operate somewhat in the manner of a ratchet. Using such an arrangement with operating parameters and materials of construction corresponding to the specific example given below. reliable severance can be obtained with as little as a 200 F. excursion in temperature.

For determining dimensional clearances to select the arming and severance temperatures as well as other characteristics of the materials and elements the following is noted. Drawbar elements and fixtures associated therewith may be made of a material C as 3 l6 stainless steel and similar refractory corrosion resistant alloys while the sleeves may be made of molybdenum or other refractory metal alloy having a lower coefficient of expansion. The difference in thermal coefficients of expansion for 3 l 6 stainless steel and molybdenum is 7 X lin/in/ F. The severable bolt 26 or stud 106 may be made of a hard, short-elongation spring steel or similar material having a low degree of ductility. A precipitation-hardening, nickel-base, high-temperature alloy (Rene 41) having the percentage by weight composition C 0.6l.2 percent; Si 0.50 percent max.; Mm 0.50 percent max.; Fe 5.0 percent max; Cr l8-20 percent; 8 0.01 percent max; Co l0 l 2 percent max; Mo 9l0.5 percent; Ti 3.00-3.30 percent; Al l.5-l.8 percent and the balance Ni is especially suitable.

The dimensions of the notches or grooves employed in the severable members are somewhat critical in determining reliable and reproducible severance. In accordance with R. .l. Ruark in Formulas for Stress and Strain and Timosehenko and Lessills Applied Elasticity whenever the notch radius is less than 0.005 inch, especially as the notch diameter increases, causes wide variations in the rupture stress value. The dimensionless ratio R/D (ratio of radius to diameter of the notch) can be shown to have an optimum value which is of the order of 0.055 but may vary from about 0.050 to 0.060 without seriously affecting results.

The primary equation governing the operation of the foregoing drawbar and sleeve arrangements is as follows:

wherefor each a=c0efficient of linear expansion in in./in./ F. L=length in inches P=force induced in rod or tube, pounds A=cross-sectional area of members, square inch E =modulus of elasticity AT=Diiferentia1 temperature, F.

The foregoing equation, for the embodiments of FIG. I, 2, 3, 6 and 7, takes the following form on expansion and omitting plastic yielding and creep:

( )n0n- )'ruaa-l- (LAT)BOLT= Q B AEROD AETUBE A notxr The net deflection (D) available is given by the formula:

It will be noted that the foregoing deflection can be verified or determined experimentally by measurement of the deflection at successively increased temperature levels. Excellent correlation has been found in practice.

The force output can also be measured by utilizing a tensile testing device and allowing the temperature to drop from a high level approximating the predetermined excess temperature limit to ambient temperature. The basic equation then takes the form:

Three relationships that can be used to determine operating characteristics can be found from the foregoing, i.e.. force vs. deflection, force vs. temperature, and deflection vs. temperatur es. A similar procedure can be used for the embodiment of FLO. 3 noting that no term is necessary for pin 91 to the term for bolts 26 or 106 as shown in the equations above.

When an initial takeup pressure is applied to the severable bolt the equation above takes the following final form:

( )ROD )TUBE+( )BOLT 3 P11 fl )aoo (AE)TUBE (AE)BOLT where e initial takeup force since rupture of the bolt is desired E in the above equation for the bolt is replaced by E,, the second modulus obtained by computing the ratio of stress to strain throughout a full stress-strain curve at an elevated temperature. However, rupture data can also be obtained by tensile testing at an appropriate temperature and equated to the force generated principally by the rod and tube astuatas as. shown above.

EXAMPLE Dimensions of the components of a typical device and typical operating conditions of the embodiments T. 3. The inherent force output 103 lbs. per 0.001

inch deflection nominally.

In practice deviation above and below these values will be caused by changes in tolerances.

While there has been described in the foregoing what may be considered to be preferred embodiments of the invention, modifications may be made therein without departing from teachings of the invention and it is intended to cover all such as fall within the scope of the appended claims.

We claim:

1. A latch mechanism for use in a severable linkage including separable link elements utilized to support and retain an essential operating component of a mechanism subject to temperature excursions comprising:

a. an elongated tubular sleeve member constructed of a first material having a first thermal coefficient of expansion;

b. an elongated generally cylindrical drawbar member constructed of a second material having a second thermal coefficient of expansion substantially differing from said first coefficient of expansion and arranged within said sleeve;

c. a severable retainer means associated with a first end of said sleeve and drawbar members including a severable member securing said ends of the sleeve and drawbar members in fixed relation and adapted to simultaneously retain the separable link elements of said severable linkage in position; and

d. an arming means associated with the second end of said drawbar and sleeve members and arranged to allow free thermal diflerential expansive movement in one direction between said sleeve and drawbar members on occurrence of a thermal excursion beyond a preselected temperature limit to arm the device so as to retain the second end of said members in fixed unidirectional movement restricting relation on reversal of the temperature excursion, thereby generating a strain between said members which is transmitted to rupture said severable member so as to release said linkage.

2. Apparatus as defined in claim 1 wherein said first material has a coefficient of thermal expansion differing from that of said second material by at least about 7 X 10- in/in/ F.

3. Apparatus as defined in claim 1 wherein said tubular sleeve is equipped at said first end to provide a load bearing surface, wherein said retainer means includes perforated link end portions disposed in overlapping relation over said load bearing sleeve surface and wherein said severable element is a bolt means engaging said first end of said drawbar member and extending through the perforation of said link end portions with an upper end portion positioning said link ends securely against said load bearing sleeve surface, said bolt means including a circumferential groove in the region between said drawbar and the upper end portion thereof.

4. Apparatus as defined in claim 1 wherein said first retainer means includes a pair of split block members engaging said 7 first end of said sleeve member, wing plate members having matching socket portions and also provided with means for attachment of said separable link elements and pivotally mounted on opposite sides of said first end of said sleeve member, wherein an enlarged transversely perforated eyebolt portion of said drawbar is positioned between said wing plate members, and wherein a brittle rod extends through the perforation of said eyebolt to be secured in said sockets of said wing plates, said brittle rod being provided with a circumferential groove between said sockets to provide reliable severance thereof upon application of said strain thereby releasing said pivoted split block members simultaneously releasing said separable link elements.

5. Apparatus as defined in claim 3 wherein said arming means includes an adjustable collar disposed on the second end of said drawbar, said collar having an enlarged cylindrical portion terminating in an inwardly extending shoulder stop surface, wherein said arming means includes a collar affixed to the second end of said sleeve member and including a portion defining an internal circumferential groove which projects beyond the second end of said sleeve, and wherein said arming means includes a snap ring disposed in said circumferential groove and adapted to slide along the cylindrical portion of the drawbar collar during said thermal differential expansive movement and, at attainment of said preselected temperature limit, to snap partially from said groove to provide a side por tion bearing against said adjustable shoulder stop, thereby unidrectionally restricting movement of said second ends of said sleeve and drawbar members on reversal of the temperature excursion to generate said strain which ruptures the severable element.

6. Apparatus as defined in claim 4 wherein said arming means includes an adjustable collar disposed on the second end of said drawbar, said collar having an enlarged cylindrical portion terminating in an inwardly extending shoulder stop surface, wherein said arming means includes a collar affixed to the second end of said sleeve member and including a portion defining an internal circumferential groove which projects beyond the second end of said sleeve, and wherein said arming means includes a snap ring disposed in said circumferential groove and adapted to slide along the cylindrical portion of the drawbar collar during said thermal differential expansive movement and, at attainment of said preselected temperature limit, to snap partially from said groove to provide a side portion bearing against said adjustable shoulder stop, thereby unidirectionally restricting movement of said second ends of said sleeve and drawbar members on reversal of the tempera ture excursion to generate said strain which ruptures the severable elements.

7. Apparatus as defined in claim 3 wherein said arming means includes a collar adjustably disposed on the second end of said sleeve, said collar including an inwardly projecting shoulder stop, wherein said drawbar includes a uniformdiameter portion with an enlarged cylindrical head portion defining a shoulder stop therebetween, and wherein spring loaded jaw stops are mounted within said collar to slide along the cylindrical head portion of said drawbar during said temperature excursion and to drop into position between said cylindrical stop portion of said collar and the shoulder of said drawbar head portion into position for unidirectionally restricting movement therebetween for generating said strain between the drawbar and sleeve members on reversal of said temperature excursion.

8. Apparatus as defined in claim 4 wherein said arming means includes a collar adjustably disposed on the second end of said sleeve, said collar including an inwardly projecting shoulder stop, wherein said drawbar includes a uniformdiameter portion with an enlarged cylindrical head portion defining a shoulder stop therebetween, and wherein spring loaded jaw stops are mounted within said collar to slide along the cylindrical head portion of said drawbar during said temperature excursion and to drop into position between said cylindrical stop portion of said collar and the shoulder of said drawbar head portion into position for unidirectionally restricting movement therebetween for generating said strain between the drawbar and sleeve members on reversal of said temperature excursion.

9. Apparatus as defined in claim 3 wherein said drawbar includes a uniform-diameter second arming head portion projecting beyond the second end of said sleeve member, wherein a collar having a portion defining diametrically-opposed longitudinal slots is secured with the slotted portion extending beyond the s second end of said sleeve member, and wherein spring loaded cam members are pivotally mounted in said slots with a shoe portion in contact with said arming head portion of said drawbar so as to slide unidirectionally therealong during said temperature excursion and restricting movement therebetween on reversal of the temperature excursion for generating said strain which severs said severable member.

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