Thermal actuator

Claim 2

A thermal actuatOr comprising a casing having an opening at one end thereof, a movable member having a force applying surface and a force receiving surface supported within said casing and adapted to be moved from a first retracted position to a second actuated position, means coupled to said movable member for maintaining said member in said first retracted position and effecting return thereto subsequent to actuation, a container supported within said casing and spaced from said one end thereof, said container having an opening at one end adapted to accommodate a portion of said movable member including the force receiving surface thereof, means disposed within said opening in said container for sealingly mounting said portion of said movable member with respect to the interior of said container, a thermally expansible, force-transmitting medium disposed within the interior of said container, said medium being adapted to apply a preselected force to the force receiving surface of said movable member so as to effect movement of said movable member toward its actuated position in response to a predetermined elevated temperature of said medium and associated expansion thereof, and heating means mounted in thermal communication with said medium, said heating means including a self-regulating heating element adapted to generate heat in response to electrical energization thereof and having a steeply-sloped positive temperature coefficient of resistance at temperatures above an anomaly temperature so as to generate heat at a substantially constant temperature in order to maintain said predetermined elevated temperature of said medium responsive to continuous electrical energization.

Claim 3

A thermal actuator in accordance with claim 1 wherein said movable member comprises a piston assembly adapted for reciprocal movement, said force receiving surface being disposed in communication with the interior of said container in force-receiving relationship with said medium.

Claim 4

A thermal actuator in accordance with claim 2 wherein said piston assembly includes a piston head adapted to be slidingly received within said opening at said one end of said container, said piston head defining said force receiving surface at an exposed end thereof and including a piston rod extending from said piston head defining an opposite end of said piston assembly and defining said force applying surface at its exposed end, said piston rod being adapted to be slidingly received within the opening at said one end of said casing.

Claim 5

A thermal actuator in accordance with claim 3 wherein said piston head and piston rod are generally cylindrical and an integral circumferential shoulder member extends from said piston rod including a depending portion surrounding a portion of said container including the end thereof which receives said piston head.

Claim 6

A thermal actuator in accordance with claim 4 wherein said piston rod includes an integral flange projecting outwardly from said depending portion, said flange bearing against the interior of said casing to aid in maintaining the path of movement of said piston.

Claim 7

A thermal actuator in accordance with claim 5 wherein said means for maintaining said piston in said first retracted position and effecting return thereof to said first retracted position subsequent to actuation comprises a spring extending between said flange and an opposing inner surface of said casing, said spring being disposed intermediate said depending shoulder portion and said casing.

Claim 8

A thermal actuator in accordance with claim 3 wherein said container comprises a generally cup-shaped member having an open-ended generally elongated, thin neck defining a bore terminating in said opening at said one end of said container, said bore being in registration with said opening in said casing for receiving said piston head, and a reciprocating elastomeric seal disposed within said bore adjacent said force receiving surface of said piston head to substantially prevent undesired leakAge of said medium from said container.

Claim 9

A thermal actuator in accordance with claim 7 wherein said reciprocating elastomeric seal includes a flexible O-ring.

Claim 10

A thermal actuator in accordance with claim 8 wherein said piston head is slidingly mounted within said bore and includes a projecting member extending outwardly therefrom into said bore toward the interior of said container, said projecting member being spaced from the wall of said bore, and said O-ring is disposed intermediate said projecting member and the wall of said bore in surrounding relationship with a portion of said projecting member.

Claim 11

A thermal actuator in accordance with claim 7 wherein said piston head is of a substantially smaller diameter than said bore, a force-transmitting floating head piston is disposed within said bore intermediate the force receiving surface of said piston head and said medium, and said reciprocating elastomeric seal is disposed within said bore adjacent said floating head piston for supportingly maintaining said floating head piston centered within said bore and preventing said medium from passing said floating head piston.

Claim 12

A thermal actuator in accordance with claim 10 wherein said floating head piston includes a portion having a diameter which is less than that of said bore so as to define a space between said portion and said bore and said reciprocating elastomeric seal comprises an O-ring disposed within said space, thereby providing a seal between said medium and said piston head.

Claim 13

A thermal actuator in accordance with claim 11 wherein said self-regulating heating element includes a ceramic wafer comprising semiconducting barium titanate disposed adjacent to the external wall of said container and in heat transfer relationship with said medium.

Claim 14

A thermal actuator in accordance with claim 12 wherein said ceramic wafer comprises Ba0.997La0.003Tio3.

Claim 15

A thermal actuator in accordance with claim 11 wherein said self-regulating heating element comprises a positive temperature coefficient thermistor and is adapted to maintain a constant elevated temperature in response to continued electrical energization thereof.

Claim 16

A thermal actuator in accordance with claim 12 wherein a heat radiating element of a thermally conductive material is disposed in thermal communication with said self-regulating heating element and with said medium for transmitting heat through said medium at an accelerated rate.

Claim 17

A thermal actuator in accordance with claim 7 wherein said container includes a base in opposition with said bore, said base being peripherally defined by a circumferential arcuate edge, said base being spaced from said casing, and a plurality of support members secured within said casing rockably support said container at said arcuate edge.

Claim 18

A thermal actuator in accordance with claim 7 wherein a calibration means including a vent passage is defined in the wall of said bore longitudinally spaced from the path of travel of said elastomeric seal and separated from said medium by said seal, said vent passage being adapted to pass surplus quantities of said medium therethrough when said medium is subjected to additional heating substantially beyond the temperature capacity of said heating element effecting expansion thereof and consequent piston head movement beyond said actuated position whereby said vent passage drains excess quantities of said medium so that subsequent heating applied by said heating element cannot cause sufficient expansion of the remaining medium to effect movement of said piston head beyond said actuated position.

Claim 19

A thermal actuator comprising a casing having an opening at one end and being substantially closed at an opposite end, a generally cup-shaped chamber supported within said casing, said chamber having a base arranged adjacent the closed end of said casing and having an oppositely disposed elongated neck portion defining an open-ended bore in axial reGistry with said opening in said casing and spaced therefrom, a thermally expandable medium carried within and substantially filling the interior of said chamber, said medium being adapted to expand in volume in response to an elevation of the temperature thereof to a preselected level, a self-regulating heat generating element disposed in thermal communication with said medium and spaced therefrom by the wall of said chamber, said heating element being adapted to generate heat at a substantially constant temperature substantially equal to said preselected level in response to electrical energization thereof and having a positive temperature coefficient of resistance so as to substantially maintain said preselected level responsive to continuous electrical energization thereof, a piston assembly including a piston head received within said bore and having an external face at one end oriented toward the interior of said chamber, a floating head piston slidingly mounted within said bore intermediate the external face of said piston head and the interior of said chamber for transmitting force applied thereto by expansion of said medium to effect movement of said piston head in said bore, and a piston rod projecting outwardly from an opposite end of said piston head toward said opening in said casing and adapted to undergo movement between first and second positions in response to expansion of said medium, and means coupled to said piston assembly for maintaining said piston rod in said first position prior to expansion of said medium and for effecting return of said piston rod to said first position upon contraction of said medium.

Claim 20

A thermal actuator comprising a casing having an opening at one end and being substantially closed at an opposite end, a generally cup-shaped chamber supported within said casing, said chamber having a base arranged adjacent the closed end of said casing and having an oppositely disposed elongated neck portion defining an open-ended bore in axial reGistry with said opening in said casing and spaced therefrom, a thermally expandable medium carried within and substantially filling the interior of said chamber, said medium being adapted to expand in volume in response to an elevation of the temperature thereof to a preselected level, a self-regulating heat generating element disposed in thermal communication with said medium and spaced therefrom by the wall of said chamber, said heating element being adapted to generate heat at a substantially constant temperature substantially equal to said preselected level in response to electrical energization thereof and having a positive temperature coefficient of resistance so as to substantially maintain said preselected level responsive to continuous electrical energization thereof, a piston assembly including a piston head received within said bore and having an external face at one end oriented toward the interior of said chamber, a floating head piston slidingly mounted within said bore intermediate the external face of said piston head and the interior of said chamber for transmitting force applied thereto by expansion of said medium to effect movement of said piston head in said bore, and a piston rod projecting outwardly from an opposite end of said piston head toward said opening in said casing and adapted to undergo movement between first and second positions in response to expansion of said medium, and means coupled to said piston assembly for maintaining said piston rod in said first position prior to expansion of said medium and for effecting return of said piston rod to said first position upon contraction of said medium.

Claim 21

A thermal actuator in accordance with claim 18 wherein said medium substantially completely fills the interior of said chamber, said floating head piston is supported within said bore and a movable elastomeric seal is disposed within said bore intermediate a portion of said floating head piston and said medium to maintain said floating head piston concentric with respect to said bore and preclude leakage of said medium from said container during movement of said piston assembly.

Claim 22

A thermal actuator in accordance with claim 18 wherein said self-regulating heating element is mounted exteriorly of said chamber and within said casing.

Claim 23

A thermal actuator in accordance with claim 20 wherein said self-regulating heating element comprises a positive temperature coefficient of resistance thermistor formed of semiconducting barium titanate.