Heat Engine With Corrugated Shape Memory Drive Belt

This invention relates generally to the conversion of heat energy into mechanical energy using shape memory alloys, such as NITINOL as disclosed for example in U.S. Pat. Nos. 4,010,612 and 4,030,298 to Sandoval, and in my prior pending U.S. Pat. Application No. 07/539,942, pending filed Jun. 18, 1990.

The properties of shape memory alloys, especially Nitinol, have been extensively studied and applied to the construction of heat engines including those employing endless drive belts made of the shape memory alloy entrained about pulleys, the belt material being heated and cooled locally at different points in the apparatus so that the changes in shape of the belt material when heated cause the pulleys to rotate.

In the heat engine of this invention, a thin sheet of Nitinol material formed into an endless drive belt has corrugations in discontinuous contact at spaced locations with a pulley type roller disposed within a thermal heating region such as a heated body of liquid in which a portion of the belt is immersed. The portion of the belt as it enters the heating region contracts to induce rotation as a result of unbalanced forces transmitted at the spaced points of contact on one of the pulleys. The other pulley is located at a lower temperature region within which the belt expands to engage such other pulley along a flattened portion of the drive belt.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing wherein:

FIG. 1 is a side elevation view of the heat engine of this invention with parts broken away and shown in section.

FIG. 2 is a partial section view of the heat engine taken along section line 2--2 in FIG. 1.

FIG. 3 is an enlarged partial section view of the heat engine taken along section line 3--3 in FIG. 2.

The heat engine of this invention, generally referred to by reference numeral 10, comprises a pair of drive roller pulleys 12 and 14 mounted in spaced relation to each other on a frame 16 as shown in FIG. 1. An endless drive belt 18 made of thin Nitinol sheet material is entrained about the pulleys. A portion of the drive belt entrained about pulley 14 is undulated or formed with corrugations 20 having variable spacing between contact points or pitch P (the distance between two adjacent contact points) and a sheet material thickness t as denoted in FIG. 3. The portion of the drive belt 18 having the corrugations 20 is in one state while exposed to a source of heat energy through a body of heated liquid 22 as shown in FIGS. 1 and 2. On the other hand, the flattened portion of drive belt 18 entrained about pulley 12 is in its other state while exposed to a colder region than the heating region of the heated liquid body 22. The dimensions of the corrugated portion of the drive belt will be "remembered" by the flattened portion as it transforms from one state to the other during operation of the heat engine.

The pulleys 12 and 14 carried by the support frame 16 are rotatably mounted about axes, which are adjustably spaced from each other according to the embodiment shown in FIG. 2. The pulley 14 includes a shaft 24 rotatably supported in bearing 26 affixed to the frame by an adjustably positioned plate 28 of a suitable adjustment device to establish the desired belt tension. The shaft 24 is connected to a pulley wheel having an annular drum portion 30 recessed radially inwardly of outer flange portions 32 between which the drive belt is received as shown in FIGS. 1 and 3. The pulley 12 may be of similar construction as that of pulley 14 and is journaled for rotation about an axis spaced from the axis of pulley shaft 24. Mechanical energy is extracted from the engine 10 through either of the pulley shafts.

As shown in FIG. 2, the Nitinol drive belt 18 receives heat through the body of liquid 22 from a heating power source 34 electrically connected to a heating element 36 within the body of liquid 22. The engine 10 is oriented by attachment of its frame 16 to the liquid container 38 within which the liquid body is retained to establish a thermal heating region.

The portion of the Nitinol drive belt exposed to the thermal heating region heats up and assumes its austenitic, contracted state characterized by the undulations or corrugations 20. The Nitinol drive belt moving upwardly as shown or away from the liquid body 22 loses heat primarily through radiation to colder surroundings so as to cool down within the thermally colder region within which the pulley 12 is located. The tension in the drive belt and engagement with pulley 12 within the colder region transforms the shape memory material to its martensitic expanded state in which the belt is substantially flattened for continuous contact engagement with the pulley 12 as shown in FIG. 1.

The pitch spacing P of the corrugations 20 on the Nitinol belt 18 in its contracted austenitic varies during movement through the thermal heating region during which the corrugations are in spaced contact with pulley drum 30 as shown in FIG. 3. The reformation of the corrugations 20 sustains rotation of the pulley 14 and movement of the drive belt in one direction under unbalanced contact forces resulting from exposure to the heat supplied to the body of liquid 22.

As the Nitinol belt moves the corrugations 20 are formed therein as the belt enters the thermal heating region and heats up through absorption of heat undergoing transformation to the austenitic state. In so doing, the corrugations 20 exiting the thermal heating region enter the colder region and are cooled down as the belt enters the martenistic state in which the Nitinol material is soft and pliable. In this latter state, the corrugations 20 flatten out as the belt approaches the pulley 12 as seen in FIG. 1.

According to one operating embodiment, a drive belt 18 having a thickness (t) of 3 mil extends between pulleys 12 and 14 having their axes spaced from each other by 16 inches, The pulleys 12 and 14 have diameters of 4 inches and 2 1/4 inches, respectively, and the colder region for pulley 12 is ambient air at approximately 20.degree. C. while the thermal heating region is at a temperature of 85.degree. C. to 100.degree. C. within the heated water as the liquid body 22.

Numerous other modifications and variations of the present invention are possible in light of the foregoing teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.