THERMOELECTRODYNAMIC PRIME MOVERS Joseph R. Harkness, Milwaukee, Wis., assignor to Briggs & Station Corporation, Milwaukee, Wis., a corporation of Delaware
Filed Apr. 7, 1960, Ser. No. 20,662
14 Claims. (Ci. 310—4)
This invention relates to thermoelectrodynamic prime movers and refers more particularly to devices of the type comprising a thermocouple or thermopile, and an electric motor connected with such a thermoelectric current generating device for energization thereby.
Recent progress in the development of thermocouples and thermopiles has offered the possibility of using such ■a device as a component of a prime mover comprising a heat source, a thermocouple or thermopile exposed to heat from the source and to cooling air, and an electric motor connected with the thermocouple for energization by current which the thermocouple generates as a result of the temperature difference across it. Such a machine is extremely quiet in operation and requires almost no maintenance, but to be suitable for powering portable equipment, and even for many stationary applications, it must be reasonably inexpensive, light, compact and efficient.
In general it is the object of the present invention to provide a thermoelectrodynamic prime mover having to a marked degree the attributes of low cost, lightness, compactness and efficiency, and which is therefore particularly well suited for use in applications where small internal combustion engines have heretofore been employed.
More specifically, it is an object of this invention to provide a thermoelectrodynamic prime mover of the character described wherein the components of the machine are associated with one another in an arrangement which affords great compactness, particularly by reason of the provision of an annular thermocouple, a motor energized by the thermocouple and disposed coaxially with the thermocouple, and a fan for cooling the cold junction of the thermocouple which is coaxially driven by the motor.
Other objects of this invention relate to the problems posed by the characteristic low voltage output of thermocouples and thermopiles. Although the current generated by a thermocouple is substantially in proportion to its size and is therefore limited only by practical considerations, the voltage of the output is very low, even when individual thermocouples are connected in series in a thermopile, unless the thermopile comprises an inordinately large number of thermocouples. It has been thought heretofore that practical utilization of the output of thermocouples required the provision of an inverter or the like for stepping up voltage, but any device for voltage step-up increases the size, weight and complexity of the prime mover without actually improving its overall efficiency. However, if the low voltage D.C. output of a thermocouple or thermopile is to be delivered directly to a motor, the conductors for transmitting electrical energy from the thermocouple to the motor must have very low losses and the motor must be of a type that can operate efficiently with low voltage, high current energization.
With the foregoing considerations in mind, it is another object of this invention to provide a thermoelectrodynamic prime mover which requires no inverter or other voltage step-up means, and wherein the arrangement of the thermocouple or thermopile and the motor energized by it is so compact as to permit very short conductors to be used for connecting the current source with the motor, thus minimizing electrical transmission losses.
In this same connection it is also an object of this invention to provide a thermoelectrodynamic prime mover which advantageously incorporates a known motor that is suitable for energization from a low voltage high cur5 rent D.C. source.
While motors ^are known that are suitable for energization by the low voltage high current output of a thermocouple or thermopile, such motors are neither inexpensive nor compact, and therefore they would not be suit10 able for a portable or mobile thermoelectrodynamic prime mover.
It is therefore another object of this invention to provide a novel motor adapted to be energized by low voltage direct current and which is compact, low in cost, simple 15 in construction 'and efficient in operation.
In connection with the last stated object, it is a further object of this invention to provide a low voltage D.C. motor that is very well adapted, by reason of the shape and arrangement of its parts, to comprise an ele20 ment of a relatively compact and inexpensive thermoelectrodynamic prime mover.
With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement 25 of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiments of the hereindisclosed invention may be made as come within the scope of the claims. 30 The accompanying drawings illustrate several complete examples of physical embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:
35 FIGURE 1 is a vertical sectional view of a thermoelectrodynamic prime mover embodying principles of this invention, taken on the axis of the machine;
FIGURE 2 is a fragmentary vertical sectional view of a modified form of the prime mover of this invention,
40 incorporating a somewhat different type of electric motor; FIGURE 3 is a vertical sectional view of a thermoelectrodynamic prime mover incorporating another suitable type of motor; FIGURE 4 is a horizontal sectional view taken on the
45 plane of the line 4—4 in FIGURE 3;
FIGURE 5 is a top view on a reduced scale of a type of thermopile suitable for use in the prime mover shown in FIGURE 3; and
FIGURE 6 is a vertical sectional view of a modified
50 embodiment of the motor shown in FIGURES 3 and 4. Referring now to the accompanying drawings, in which like numerals designate like parts throughout the several views, the numeral 5 designates generally a thermoelectrodynamic prime mover embodying the principles of this
55 invention and which comprises, in general, a substantially annular thermopile 6, the axis of which is upright, a coaxial heat source 7 which cooperates with the thermopile, a low voltage motor 8 coaxially mounted beneath the thermopile, and a fan 9 coaxially mounted on the shaft
60 10 of the motor, between the motor and the thermopile. The annular thermopile 6 comprises an inner ring 48 of one kind of metal, a plurality of spoke-like elements 49 of a semi-conductor material such as lead telluride or bismuth telluride, and an outer metal ring 50. The radi
65 ally extending spoke-like elements abut the inner ring at their inner ends, to provide a hot junction 11, and abut the outer ring at their outer ends to provide a cold junction 12, and the E.M.F. produced by the thermopile is dependent upon the difference in temperature between the two junctions. The inner and outer rings may be considered the terminals of the thermocouples comprising