Memory alloy heat engine and method of operation

A method of converting thermal energy from a heat source into mechanical work by means of a memory alloy which when heated undergoes a phase transformation causing contraction thereof, and when cooled the alloy undergoes another phase transformation while undergoing elongation, including the steps of cyclically moving the alloy serially through a heat sink, along a first path extending from the heat sink to a heat source, through the heat source, and thereafter along a second path back to the heat sink in counter-flow heat exchange relationship with the alloy moving in the first path, heating the alloy in the heat source, cooling the alloy in the heat sink, transferring thermal energy from the heated alloy in the second path to the cooled alloy in the first path, permitting the alloy in the second path to elongate when it undergoes phase transformation as it is cooled, and causing the alloy in the first path to apply a force through a distance as it contracts during its phase transformation as it is heated to perform mechanical work.

A method of operating a heat engine which converts thermal energy from a heat source into mechanical energy with an alloy having a shape memory effect wherein the alloy assumes a trained configuration when at a first temperature and the alloy assumes a memory configuration when at a second temperature above said first temperature, including cyclically performing the steps of heating the alloy in the heat source to said second temperature, moving the heated alloy along a first path through a heat regeneration zone toward the heat sink, cooling the alloy in the heat sink to said first temperature, moving the cooled alloy along a second path through said zone in heat exchange relationship with the alloy moving along the first path whereby heat energy is transferred from the heated alloy to the cooled alloy in said zone, and applying movement of the alloy from its trained configuration to its memory configuration as it is heated to act as a force through a distance to produce mechanical work.

A method for starting operation of a heat engine employing a shape memory alloy formed in an endless loop one end of which is reeved in non-slip engagement about a first pulley and the second end of which is reeved in non-slip engagement about a second pulley having a diameter greater than the diameter of the first pulley, the method of starting operation comprising the steps of applying heat to a portion of the wire reeved about the first pulley, extracting heat from a portion of the wire reeved about the second pulley, applying a torque to the pulleys so that they conjointly turn at equal angular rates and in the same rotational direction for moving the loop through at least one complete cycle around the pulleys, progressively applying tension in the loop as the loop continues to cycle about the pulleys, and removing the applied torque when the torque generated by the engine is sufficient to rotate the pulleys.

A method for starting a heat engine employing a shape memory alloy which is formed in a loop one end of which is reeved in non-slip engagement about a first pulley and the opposite end of which is reeved in non-slip engagement about a second pulley having a diameter greater than the diameter of the first pulley, including the steps of heating a reach of the loop which extends from the first pulley and causing the alloy of the heated reach to contract towards its memory shape, cooling the opposite reach of the loop which extends from the second pulley and causing the alloy of the cooled reach to elongate towards its trained shape, moving the pulleys apart a distance which applies predetermined tensions in the reaches of the loop, conjointly rotating the pulleys in the same rotational direction for cyclically moving the loop about the pulleys, and varying the angular phase relationship between the pulleys to maintain said predetermined tensions until a steady state operation is reached.

A method of operating a heat engine employing a shape memory alloy which is formed in a loop one end of which is reeved in non-slip engagement about a first pulley and the opposite end of which is reeved in non-slip engagement about a second and in which a reach of the loop extending from the first pulley is heated to cause such reach to contract toward its memory shape and the opposite reach of the loop extending from the second pulley is cooled to cause such portion to elongate toward its trained shape, with the differential in tension between the contracting and elongating reaches of the loop applied as a resultant force acting through a distance against a load to produce mechanical power, including the steps of constraining the pulleys to conjointly rotate at a given angular phase relationship which maintains the elongating and contracting reaches of the loop at respective predetermined tensions, and varying the angular phase relationship between the pulleys for maintaining the predetermined tensions in the loop during changes in said load, or during changes in the temperatures of the loop portions being heated or cooled, or during changes in the rate of rotation of the pulleys.

A heat engine for converting thermal energy into mechanical work including the combination of a working element composed of a shape memory alloy which assumes a trained shape when cooled below its transition temperature and which assumes a memory shape when heated above its transition temperature, heat source means for heating the element above its transition temperature, heat sink means for cooling the element below its transition temperature, transport means for cyclically moving the element through the heat source, along a first path toward the heat sink, through the heat sink and along a second path back to the heat source, and means for transferring heat energy from portions of the element moving along the first path to portions of the element moving along the second path whereby the element portions in the first path are cooled and elongate under a given tension toward their trained shape and the element portions moving along the second path contract under a second tension greater than the given tension as they are heated.