Heat-actuated release mechanism

A release mechanism passively releases a mechanical coupling as a result of a temperature rise. The release mechanism includes a breakable element, such as a shape memory alloy (SMA) element, that is configured to break when the element is heated to a predetermined temperature. The breakage of the breakable element releases a mechanical coupling, such as a coupling holding a lid onto a container. The release mechanism may be part of a handle or other device to close the container. The release mechanism may have a mechanical load on it prior to release, a load that in part passes through the breakable element. Most of the load may pass through one or more other members of the release mechanism, providing the force for separation after the release mechanism is triggered. The release mechanism may be used to provide a passive way of releasing a mechanical coupling in response to heating.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is in the field of mechanical release mechanisms.

2. Description of the Related Art

Many situations require activation of a mechanism in response to heating, or in response to a condition that accompanies heating. Examples include pressure release for an overheating boiler, a fire in a storage area for munitions, or a fire or other pressure-increasing event within a storage container. Active actuation systems, for example with a powered actuator coupled to a temperature or heat sensor, have been tried in the past to detect and react to such events, but there are shortcomings in such approaches.

SUMMARY OF THE INVENTION

According to an aspect of the invention, a release mechanism includes: a first member; a second member; and a separable element mechanically coupled to the first member and the second member; wherein, the separable element separates when heated to a predetermined temperature, releasing the first member from the second member, and separating the first member from the second member.

According to another aspect of the invention, a containment system includes: a container; a lid on the container; and one or more release mechanisms that couple the lid to the container; wherein the one or more release mechanisms release when heated to a predetermined temperature.

According to yet another aspect of the invention, a method of releasing a mechanical coupling includes: providing a first member of the coupling; providing a second member of the coupling; and separating a separable element of the coupling when heated to a predetermined temperature, thereby releasing and separating the first member from the second member.

According to still another aspect of the invention, a release mechanism includes a separable plastic element that separates when heated, releasing the mechanism.

According to a further aspect of the invention, a release mechanism includes a breakable shape memory alloy element.

DETAILED DESCRIPTION

A release mechanism passively releases a mechanical coupling as a result of a temperature rise, and the mechanical coupling includes a tendon (first part) and a tendon retainer (second part). The release mechanism includes a breakable element, such as a shape memory alloy (SMA) element, that is configured to break when the element is heated to a predetermined temperature. The breakage of the breakable element releases a mechanical coupling, such as a coupling holding a lid onto a container. The release mechanism may be part of a handle or other device to close the container. The release mechanism may have a mechanical load on it prior to release, a load that in part passes through the breakable element. Most of the load may pass through one or more other members of the release mechanism, providing the force for separation after the release mechanism is triggered. The release mechanism may be used to provide a passive way of releasing a mechanical coupling in response to some sort of heating.

FIG. 1shows part of a containment system8that includes a release mechanism10that is part of a handle12for closing a lid14of a container16, and for mechanically securing the lid14to the container16. The handle12, which may be part of the container16and/or the lid14, is used to secure the lid14by pivoting relative to the lid14and the container16. The container16may be a rectangular box, or more generally a container of any suitable shape. Multiple of the handles12may be located around a perimeter of the container16, to secure the lid14to the container16at multiple locations.

A grip portion18of the handle12is coupled to the release mechanism10with a pin20, which allows the release mechanism10to pivot relative to the grip portion18. The grip portion18is in turn pivotally coupled to the container16, allowing the grip portion18to pivot about a pivot axis22in the container16.

The release mechanism10includes a stud30that has a threaded shaft32, with a half-barrel nut36threaded onto it. The half-barrel nut36engages a corresponding curved recess38in the lid14. When the handle12is engaged by rotating the grip portion18into a recess39in the container16, the nut36is pulled down against the top of the lid14. This pulls the lid14tight against the container16, with a force running through the handle12while the handle12is engaged.

The container16may enclose any of a variety of items. In one embodiment, the container16encloses rocket motors, or devices containing rocket motors. One issue with storing rocket motors is providing protection against explosion, should the fuel in any of the rocket motors begin to burn. If the container16remains closed then pressure can build up, possibly triggering an explosion. The risk of a catastrophic outcome is greatly reduced if the pressure build-up can be relieved, for example by allowing the lid14to at least partially separate from the container16. Therefore the release mechanism10is configured to separate the handle's mechanical connection when sufficient heat is applied to the release mechanism10. Whether the rocket motors burn in a slow cook or fast cook process, heat is generated which heats the container16and the handle12. This heating can be used as a passive trigger to release the lid14from the container through the release mechanism10. The release mechanism10advantageously does not require any active sensors or power to trigger the release of the lid14from the container16.

Referring now in addition toFIG. 2, the release mechanism10includes a tendon40that is connected to the handle grip portion18(FIG. 1). The tendon40has a hole44that receives the pin20(FIG. 1) coupling together the tendon40and the grip portion18. The pin connection20allows for pivoting between the tendon40and the grip portion18.

When the release mechanism10is intact (prior to release), the tendon40is between an inner member50and a tendon retainer52. The inner member50is a continuous monolithic piece that includes the stud30that receives the half-barrel nut36(FIG. 1). As an alternative, the inner member50may be in multiple pieces. The member50has a recess58on its inner surface60. The recess58receives a portion64of the tendon40, the same portion of the tendon40that has the pin-receiving hole44. The tendon retainer52, on the opposite side of the tendon40, includes a protrusion68that engages a corresponding recess70in the tendon40. The engagement of the tendon40by the tendon retainer52prevents the tendon40from sliding out of engagement within the release mechanism10. The engagement also helps transmit loads within the release mechanism10.

The tendon retainer52is able to pivot relative to the inner member50at a joint76between the two. The joint76allows the tendon retainer52to rotate relative to the inner member50when the release mechanism is released, to allow the tendon40to escape from between the inner member50and the tendon retainer52. When the mechanism10is released, the inner member50and the tendon retainer52remain coupled to the lid14(FIG. 1), and the tendon40remains with the container16(FIG. 1). As explained in greater detail later, the release of the mechanism10allows the lid14to at least locally separate from the container16. This may allow release of pressure that may have built up within the container16, and may aid in preventing further pressure build up in the container16.

The release mechanism10also includes a separable element80that breaks or otherwise separates when heated, in order to release the engagement of the parts of the mechanism10. The separable element80in the illustrated embodiment is a shape memory alloy element that is configured to break when heated. The element80has a pair of indentations or notches82(FIG. 1) that reduce the width of the element80at a given separation location84(FIG. 1). The reduction in width produces a weak point in the element80, where the element80would preferentially break. The notches82are shown as semi-circles, but alternatively may be any of a variety of other shapes. Other types of preferential weakening are also possible, including scoring, thinning, and local changes in material composition and/or other characteristics.

The separable element80is secured at opposite ends by a pair of clamps86and88. The upper clamp86secures the upper end of the element80to the tendon retainer52. The lower clamp88secures the lower end of the element80to a hinged load reduction latch90. The clamps86and88may be metal blocks that are screwed or bolted (or otherwise fastened) onto the tendon retainer52and the load reduction latch90, respectively. The separable element80may be folded over or otherwise engaged with the clamps86and88, to locally increase the strength of the separable element80in the vicinity of the clamps86and88, to avoid having the separable element80be locally weakened in the vicinity of the clamps86and88.

The latch90aids in retaining the mechanism10together, prior to release by separation (severing) of the separable element80. The latch90is coupled to the inner member50by a pin94, at a lower end96of the inner member50. This allows the latch90to rotate relative to the inner member50, about the pin94. Prior to release of the mechanism10, the latch90fits around a lower end98of the tendon retainer52. This keeps the tendon retainer lower end98held against the inner member lower end96. The tendon retainer lower end98has a roller100, which presses against the latch90prior to release of the mechanism10. The roller100aids in allowing movement between the tendon retainer52and the latch90, when the mechanism10is released. As an alternative, the roller100may be omitted if desired.

The mechanism10is loaded when the handle12(FIG. 1) is closed, providing a force to hold the lid14(FIG. 1) against the top of the container16(FIG. 1). The load also provides a mechanical force to separate the lid14from the container16when the mechanism10is released. There is a load path passing through the mechanism10, through the tendon retainer52. The path through the tendon retainer52also puts a tension load on the separable element80. It is desirable to provide enough load on the separable element80so that the separable element80is in tension, but to avoid overloading the separable element80in tension, since overloading could cause undesired separation, which would result in release of the mechanism10. Therefore some of the load (e.g., less than half of the load) on the mechanism10may be directed through the separable element80. The release mechanism10has a separable element tensioner104that is used to control the tension in the separable element80. The tensioner104is a set screw that engages a threaded hole in the latch90, to allow a tip of the set screw to press against an end surface of the tendon retainer52. Turing the set screw positions the latch90relative to the tendon retainer52, adjusting the tension in the separable element80.

The separable element80may be made of any of a variety of materials that exhibit shape memory properties, such as shape memory alloys. Shape memory alloys undergo a temperature related phase change that is characterized by the memory of a mechanical configuration imposed on the material at an annealing temperature. When the shape memory alloy is below some lower temperature, the alloy possesses a particular crystal structure whereby it may be deformed into an arbitrary shape with relative ease. Upon heating the alloy above a higher temperature, the alloy undergoes a change in crystal structure and the shape memory effect is manifested by a resumption of the originally imparted shape, representing the onset of a restoring stress. Further details regarding the behavior of shape memory materials may be found in co-owned U.S. Patent Pub. 2010/0139264, which is incorporated herein by reference in its entirety. Examples of suitable shape memory alloys include nickel-titanium alloys (e.g., Nitinol), titanium-nickel alloys, copper-zinc-aluminum alloys, copper aluminum nickel alloys, nickel titanium hafnium alloys, and other shape memory alloys.

The separable element80may be imparted with a “remembered” set shape that is far different from the shape it later has when installed in the release mechanism10. In installing the element80in the release mechanism10, the element80may be element stretched or strained from its original shape. When the separable element80is heated, such as from slow or fast combustion of external environmental elements, the separable element80undergoes a force as it tries to contract or otherwise return to its remembered set shape. This puts a stress on the separable element80. With the indentations or notches82, this stress causes the separable element80to break at the weakened location84. The dimensions and other characteristics of the separable element80, and of its indentions or notches82, and its weakened location84, may be selected to achieve breakage of the element80(and release of the mechanism10) when heating occurs that is associated with a desired release of the mechanism10. For example, combustion of the item or items in the vicinity of the container16will be expected to cause a certain amount of heating, and the element80may be configured to release the mechanism10when an amount of heating occurs that is associated with a need to provide some pressure release by loosening the lid14.

The separable element80alternatively may include another sort of material, a material that separates by a different mechanism. For example the separable element80may be a plastic material that melts or weakens when heated. This melting or weakening results in breaking or otherwise separating of parts of the plastic element, releasing the mechanism10. A plastic material for the separable element80may be selected to achieve release of the mechanism at a desired heating.

The other parts of the mechanism (and the container16and the lid14) may be made of any of a variety of suitable materials. Suitable stainless steel is an example of a suitable material.

FIG. 3-5illustrate release of the mechanism10.FIG. 3shows the separable element80being heated, as shown at120. The heating may be by any of a variety of mechanisms, such as by conduction through the mechanism10, or by radiation or convention from the container16(FIG. 1) or the surrounding environment.

FIG. 4shows the mechanism10immediately following separation of the element80. The latch90and the tendon retainer52separate from one another, each rotating relative to the inner member50. The roller100on the tendon retainer52helps prevent binding between the tendon retainer52and the latch90.

The rotation continues until the tendon retainer52becomes fully disengaged from the tendon40, as illustrated inFIG. 5. The inner member50, the tendon retainer52, and the latch50are all pulled upward, along with the lid14(FIG. 1). These parts of the mechanism10become separated from the tendon40, which remains coupled to the container16(FIG. 1). The separation of the parts of the mechanism10allows the lid14to become mechanically decoupled from the container16, at least locally where the handle12(FIG. 1) provide part of that coupling.

The release mechanism10described above is only one possible application.FIG. 6schematically shows a generalized system200in which a release mechanism210couples together a pair of members212and214. The mechanism210may have some of the same characteristics as the mechanism10(FIG. 1) described above. For instance the mechanism210may have a separable element that is similar in configuration and function to the separable element80(FIG. 2). However, other parts of the mechanism210may have a different configuration as to how the mechanism210is held together prior to release, and to how the parts of the mechanism210release from one another after separation of the separable element.

The members212and214may be any sort of parts or devices that change position and/or function (or other characteristics) when the release mechanism210is released. To give one example, one or both members212and214may be parts of a boiler or other device that would benefit from release or pressure (or other change in operation) when overheating. In such a situation the release of the mechanism210may trigger opening of a relief mechanism, such as a venting door, to relieve pressure within the boiler or other device.

In another example, release the mechanism210may cause closing of one or more fire doors that may be, or may be coupled to, the members212and214. Heating from a fire may release the mechanism210, resulting directly or indirectly in closing the fire doors.

The mechanisms10and210have the advantage of being passive devices actuated by heat. No power is required for operation of the release mechanisms, nor is there any need for a temperature or other sensor.