Abstract: A positive temperature coefficient heater for enhancing the response time of thermal actuators is disclosed. The PTC heater is formed of a generally low resistance material that has an anomaly temperature above which the resistance of the heater increases dramatically. The anomaly temperature is chosen to substantially match the phase change temperature of a thermally expansive medium useful to power the actuator. The heater is self-regulating and provides a maximum surface area for heating the medium rapidly with a minimum of thermal mass and energy use. Preferably, the heater is formed of doped BaTiO.sub.3 in the general shape of an elongated annular cylinder.

Abstract: An electro-thermal fluid displacement actuator includes a fixed volume boiler chamber and a variable volume actuation chamber formed by a ported partition being received in the main body of the actuator between a positive temperature coefficient heat source for the contained fluid and an elastomeric diaphragm. Upon energization of the heat source, a portion of the contained fluid vaporizes to increase the pressure in the boiler chamber resulting in displacement of some of the remainingfluid through the partition ports and into contact with the diaphragm to drive the same and the piston assembly mounted thereon through the predetermined stroke thereof. The displaced fluid contacting the diaphragm has a lower temperature than the fluid adjacent the heater because of its passage through the ported partition to a position remote from such heater, such reduction in fluid temperature resulting in a lower permeation rate for the fluid through the elastomer and consequently increasing the life of the actuator.

Abstract: A partitioning sleeve is positioned in the main body of a thermal actuator to form a separate internal liquid reservoir from which fluid may be supplied to the actuator heater. The heater is part of a heater sub-assembly that is sealed in an opening formed in the main body of the actuator so that the coil-type electric resistance heater is accurately positioned for submersion in liquid in the variable volume chamber formed in the main body of the actuator. Moreover, the recycling or cool down time for the thermal actuator is reduced by thermal transfer between an appreciable contacting surface area of an extensible diaphragm that partly forms the actuator chamber and a guide cap that also supports and guides the diaphragm during its extension to enlarge the variable volume chamber.

Abstract: A partitioning sleeve is positioned in the main body of a thermal actuator to form a separate internal liquid reservoir from which fluid may be supplied to the actuator heater. The heater is part of a heater sub-assembly that is sealed in an opening formed in the main body of the actuator so that the coil-type electric resistance heater is accurately positioned for submersion in liquid in the variable volume chamber formed in the main body of the actuator. Moreover, the recycling or cool down time for the thermal actuator is reduced by thermal transfer between an appreciable contacting surface area of an extensible diaphragm that partly forms the actuator chamber and a guide cap that also supports and guides the diaphragm during its extension to enlarge the variable volume chamber.