Heat engine with corrugated shape memory drive belt

An endless drive belt made of shape memory material is entrained about spd pulleys, one of which projects into a thermal heating region within which the drive belt undergoes contraction to form corrugations therein through which variable spaced contact is established with said one of the pulleys to induce rotation thereof and movement of the belt. The belt expands as it moves out of the thermal heating region causing the corrugations to flatten out as the belt approaches the other pulley.

BACKGROUND OF THE INVENTION 
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. 
SUMMARY OF THE INVENTION 
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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
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.