JP2011188654A - Sma heat engine and sma type power generating device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new SMA (shape memory alloy) power generating device which obtains high output in low load strain and has a mechanism in which an SMA element can be uniformly heated and cooled, and to provide an SMA type power generating device in which a large number of the SMA power generating engines are combined with one another to be operated by low quality heat energy. <P>SOLUTION: In the SMA heat engine, a spiral spring 200 shaped with shape memory alloy plate is housed in a cylindrical container 100 which is rotatably installed, a pair of spiral spring type actuators A1, A2 is provided which rotates the cylindrical container 100 by the winding/unwinding force obtained by heating-cooling of the spiral spring 200, the respective actuators A1, A2 are connected by a belt 400 so as to be windable and unwindable, an induction coil 600 is disposed between the actuators A1-A2, a permanent magnet 700 is mounted on a belt part 401 inserted into the induction coil 600, and electromotive current feeding circuits 610, 620 are connected to the induction coil 600. The SMA type power generating device is made of a plurality of the SMA heat engines. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a so-called SMA heat engine using a shape memory alloy and an SMA power generator using the so-called SMA heat engine.

In order to overcome problems such as global environmental problems and resource depletion, it is necessary to construct a rational energy utilization system. Therefore, the construction of a recovery system for unused energy discharged from factories is desired.
Fig. 1 shows the exhaust rate by temperature of factory waste heat. Exhaust heat above 200 ° C can recover 50 to 90% of energy with heat exchangers and thermoelectric elements.
However, about 80% of exhaust heat is occupied by low-grade heat energy below 200 ° C. Exergy efficiency at 100 ° C is as low as about 10%, and low-grade thermal energy recovery uses a liquid phase change such as Rankine cycle, which increases the heat transfer area or auxiliary power such as pump power. It has a big problem in energy cost. In order to use thermoelectric elements, a temperature difference of 250 ° C or more is required.

For these reasons, low grade thermal energy is currently used as a heat source for heat pumps or hot water supply.
However, since heat supply is difficult to transport over long distances, it is limited to the case where the heat source and the heat demand area are adjacent to each other, and only a part of the exhaust heat is effectively utilized. Therefore, if low-grade thermal energy can be converted into mechanical and electrical energy, energy transport will be easier and more effective use of exhaust heat will be possible.

From this point of view, there is a need to develop a system that converts low-grade thermal energy below 200 ° C into mechanical and electrical energy. So far, low-level thermal power generation systems have been developed that use low-grade thermal energy to evaporate low-boiling ammonia and drive the turbine to generate electricity. However, because the equipment is large and installation costs are high, it is only used in some large factory facilities such as industrial complexes. For these reasons, an engine using a shape memory alloy (hereinafter referred to as SMA) has been studied as a low-cost low-grade thermal energy recovery system.

<About shape memory alloy (SMA) engine>
Shape memory alloy (SMA) is a functional material that recovers its shape when it is heated above its transformation temperature even when it is deformed, and generates a large recovery force when recovering its shape. SMA is applied not only to consumer products but also to fields requiring high reliability such as nuclear power plants, bullet trains, and medical / biomaterials. The working temperature range of Ti-Ni shape memory alloys currently in practical use is near room temperature to 80 ° C, and generates a large recovery force just by heating to the so-called hot water temperature. For these reasons, SMA heat engines using Ti-Ni alloys have attracted attention as a system that "converts low-grade thermal energy into mechanical and electrical energy". There are four types of SMA heat engines studied so far: crank type, pulley type, swash plate type, and reciprocating type.

<Operation principle of SMA heat engine>
The basic operating principles of the four SMA heat engines are almost the same.
Figure 2 shows the SMA stress-strain relationship.
The SMA heat engine basically has a structure in which two SMA elements are arranged in an antagonistic manner, and operates as an engine by performing a deformation-recovery cycle by performing a heating-cooling cycle.
Since the alloy is soft martensite phase at low temperatures, the tensile stress required for deformation at point A is small. When one SMA element is strained and heated, it transforms to the austenite phase, which is a high-temperature phase, and recovers its shape. At this time, a stress difference with respect to the amount of strain is generated, which can be used as a restoring force. The other SMA element being cooled is deformed by the generated recovery force. If the shape is restored to point b and then heating and cooling are switched, the same process as above is performed. By repeating the heating-cooling cycle, the SMA heat engine operates continuously. Here, the region surrounded by c-A-a-b-c is the work available per unit volume of the alloy in the SMA heat engine.

<Features of SMA heat engine>
Table 1 shows the characteristics of each SMA heat engine. Both are mechanisms that convert thermal energy into mechanical energy such as rotational and reciprocating motions. In addition, the energy conversion efficiency of SMA is as large as 1-2% for load strain of 3-7%. The output per unit mass and strain of each system is about 0.04 to 0.07 W / g /%. Furthermore, the SMA heat engine does not require a complicated mechanism and can be manufactured at low cost.

<Problems of SMA heat engine>
The SMA heat engines listed above have a problem in durability, and the SMA element breaks in a cycle of 10 ³ to 10 ⁴ times. Therefore, the SMA heat engine does not have an industrial practical level of durability and has not yet been put into practical use as it is in the research stage. There are two possible causes for low durability.
(1) In order to increase the engine output, it is necessary to increase the load strain (Fig. 2, E ₂ ). However fatigue life of the SMA is about 10 ⁴ times the load strain of 1%, also an increase of the load strain causes a reduction in the fatigue life of the SMA element.
(2) The pulley type and the reciprocating type have a temperature distribution in the SMA element due to the mechanism. Therefore, the temperature change and shape change of the SMA element become non-uniform, and an overload tends to occur in a part of the element, which causes a decrease in fatigue life.
In order to solve these problems, it is necessary to develop a new SMA heat engine with a mechanism that can obtain high output with low load strain and can uniformly heat and cool the SMA element.
New SMA heat engine proposed by the present invention overcomes this problem, the goal is to have practical durability and is 10 ⁶ times or more cycle life. If this heat engine can be put into practical use, an exhaust heat recovery mechanism type SMA power generator that recovers by converting low-grade heat energy that has been treated as waste heat into mechanical and electrical energy will be constructed.

The features of the SMA heat engine of the exhaust heat recovery mechanism type and the SMA power generation device of the present invention satisfying the above-mentioned problems are as follows (1) to (2) as in the embodiment shown in FIGS. It is as follows.
(1) A spiral spring 200 molded with a shape memory alloy plate is housed in a cylindrical container 100 rotatably mounted on a fixed central shaft 101 so as to be rewound and unwound. 200B is fixedly mounted on the fixed central shaft 101 located in the center of the cylindrical container 100, and the outer spring end 200T of the spring spring 200 is fixedly mounted on the inner peripheral wall 102 of the cylindrical container 100. A pair of spring-type actuators A1, A2 are provided, and a cooling / heating medium supply / discharge device 300 for alternately supplying / discharging the cooling medium and the heating medium is provided in the cylindrical container 100 of each actuator A1, A2, and each actuator A1, The outer peripheral portion of the outer peripheral chamber 110 of the cylindrical container 100 of A2 is connected by a belt 400 so as to be rewound and rewound, and a dielectric coil 600 is disposed around a predetermined section 501 of the belt passage 500 between the actuators A1 and A2. Permanent magnets on the belt 401 inserted through the dielectric coil 600 700 and fixedly mounted, SMA heat engine, characterized in that connecting the electromotive current transmission circuit 610 and 620 to the induction coil 600.
(2) An SMA power generator in which a plurality of the SMA heat engines are arranged in parallel.

The present invention is an SMA type power generator using a spring spring type actuator as described above, and has the excellent effect of solving all the above problems as described below.
(1) The fatigue life when bending strain is applied to SMA is 10 ⁵ times or more with a bending strain amplitude of 1%, which is more advantageous than tensile deformation. Therefore, the shape of the SMA element is changed to a spring spring shape, and only deformation in the bending direction is given. The operating distance can be increased by increasing the number of turns, and high output (work load) can be realized with low load strain.
(2) Since the long SMA element is housed in the spring shape, heating and cooling can be performed uniformly.
<Expected effect>
In the SMA type power generator shown in the following example, if it becomes an SMA heat engine having a cycle life of 10 ⁶ times or more (8 hours / day × 200 days = about 3 × 10 ⁶ cycles), practical durability will be obtained. It will be a heat engine. If an SMA heat engine can be put into practical use, it is possible to convert low-grade energy below 200 ° C discharged from heat engines such as factories into mechanical and electrical energy. By converting to mechanical and electrical energy, energy transportation to the demand area becomes easy, and effective use of energy that has been used only for hot water supply near the heat source can be expected. In addition, the effect of reducing CO ₂ , one of the causes of global warming, is great.

BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the invention will be described in detail by the following examples (specific examples).

<Proposal of a long-life SMA heat engine>
The SMA heat engine in the SMA power generator of the present invention that has solved the problems (1) and (2) uses the principle of the spring-spring actuators A1 and A2 shown in FIG.
In FIG. 3, the spring spring type actuators A1 and A2 accommodate a winding spring 200 molded with a shape memory alloy plate in a cylindrical container 100 rotatably mounted on a fixed central shaft 101 so as to be rewound and unwound. An inner winding end portion 200B of the mainspring spring 200 is fixedly attached to the fixed central shaft 101 located in the central portion of the cylindrical container 100, and an outer winding end portion 200T of the mainspring spring 200 is fixed to the inner peripheral wall 102 of the cylindrical container 100. It is a spring type that is fixedly attached to the part.
In other words, the spring spring type actuators A1 and A2 include the spring spring 200 having the inner winding end portion 200B fixedly connected to the fixed central shaft 101 of the cylindrical container 100 and the outer winding end portion 200T connected to the inner peripheral wall 102 portion of the cylindrical container 100. Because it is fixedly connected to. At a temperature lower than the transformation temperature, the spring force of the mainspring 200 is small, and the mainspring 200 can be wound by rotating the cylindrical container 100. When the temperature is higher than the reverse transformation temperature, the shape of the mainspring spring 200 is recovered, and the cylindrical container 100 is rotated reversely by the rewind recovery force. The spring-spring type actuator A using this mechanism can obtain a high output with a low load strain, and can directly supply / discharge a cooling medium directly into / from the cylindrical container 100 or cool / heat into the cylindrical container 100. The spring spring 200 can be heated and cooled uniformly uniformly by supplying and discharging the medium alternately. Therefore, the mainspring 200 has a long life, and is a heat engine that is more durable than the conventional heat engine mechanism.

<SMA heat engine using spring-spring actuator>
The SMA heat engine using the spring spring type actuator is a new mechanism shown in FIG.
As shown in FIG. 4, the SMA heat engine of the new mechanism connects a pair of spring-spring type actuators A1 and A2 with a flexible belt 400, and a dielectric coil around a predetermined section of the belt path of the actuators A1 and A2. 600, a permanent magnet 700 is fixedly attached to the belt portion 401 inserted through the dielectric coil 600, and electromotive force transmission circuits 610 and 620 are connected to the dielectric coil 600, so that a spring spring type actuator can be used with thermal energy. The A1 and A2 springs 200, 200 are expanded and contracted and the belt winding / rewinding by the expansion / contraction force is alternately operated to convert it into mechanical energy. The mechanical energy is converted into the belt 401, the permanent magnet 700, and the dielectric coil 600. Is converted to electrical energy by the electromotive force transmission circuit 610, 620 and recovered.
That is, the SMA heat engine has a cooling / heating medium mainly composed of a cooling medium supply pipe 301, a heating medium supply pipe 302, and a discharge pipe 303 for alternately supplying / discharging the cooling medium and the heating medium to / from the cylindrical container 100. When one actuator A1 is heated by the supply / discharge device 300 and the other actuator A2 is cooled, the belt 400 is moved to one side due to the shrinkage tightening due to the shape recovery of the spring spring 200 of the one A1 and the rewinding reaction force of the spring spring 200 of the other A2. Wind up the A1 spring 200 side. Next, when the heated one A1 spring 200 is cooled and the other A2 spring 200 is heated, the belt 400 is wound on the other A2 spring 200 side. By repeating this heating-cooling cycle, the thermal energy is converted into mechanical energy called reciprocating motion of the belt 400. The mechanical energy is induced by the linear reciprocation of the permanent magnet 700 by the belt 400 located between the springs 200, and an induction current is induced in the dielectric coil 600 to generate power.

<SMA power generator of the present invention using the SMA heat engine>
The schematic diagram of the SMA power generator of the present invention that uses the SMA heat engine to recover exhaust heat is shown in FIG. The system is a tandem power generator in which a plurality of the SMA heat engines shown in FIG. 4 are arranged in parallel to integrate the electromotive force transmission circuit 610 and the cooling / heating medium supply / discharge device 300.
The cooling / heating medium supply / discharge device 300 is an exhaust heat recovery mechanism type cooling / heating medium supply / discharge device, and is installed in the cylindrical container 100 or the cylindrical container 100 in the spring spring type actuators A1, A2 of each SMA heat engine. The cooling medium supply pipe 301, the heating medium supply pipe 302, and the discharge pipe 303, which alternately supply and discharge the cooling medium and the heating medium, are connected and integrated to have a control function for switching between these cooling and heat supply / discharge. Configured.
If the operation of the switching valve 300V of the cooling medium supply pipe 301 and the heating medium supply pipe 302 is mechanically performed in conjunction with the switching operation of each SMA heat engine as in the example shown in FIG. 6, no external power is required. .

FIG. 6 shows a schematic diagram of the switching mechanism of the cold / heat supply / discharge device for each pair of spring spring type actuators A1, A2. In this switching mechanism, a pair of switching valves 300V are provided with limit bars L1 and L2, and the limit bars L1 and L2 are connected by a link arm R so that they can be interlocked. The permanent magnet 700 is adjacent to the reciprocating operation path of the permanent magnet 700 so as to be operable. As a result, the permanent magnet 700 on the belt 400 kicks the limit bar L1 at the forward operation limit position to switch the switching valve 300V on the spring-spring type actuator A1 side from cold water supply to hot water supply, and in parallel with this, the limit bar L2 Switches the switching valve 300V on the spring-spring type actuator A2 side from the hot water supply to the cold water supply in conjunction with the limit bar L1 via the link arm R. Further, the permanent magnet 700 kicks the limit bar L2 at the return operation limit position to switch the switching valve 300V on the spring-spring type actuator A2 side from cold water supply to hot water supply, and in parallel, the limit bar L1 passes through the link arm R. In conjunction with the limit bar L2, the switching valve 300V on the spring-spring type actuator A1 side is switched from hot water supply to cold water supply. The above procedure is alternately performed to automatically supply and discharge the refrigerant and the heat medium to the spring-spring actuators A1 and A2, thereby performing the continuous power generation operation.

<Output of exhaust heat recovery mechanism>
As an example, we estimate the output of a spring-spring actuator using a 10 g SMA material with a cross-sectional area of 1 mm ² and a length of 1500 mm, and a container with an outer diameter of 100 mm and a central axis diameter of 16 mm. When the SMA element is wound in the shape of a spring in this container, the number of turns is 5, and the maximum bending strain is about 1%.
From the stress-strain curve of a commonly used Ti-Ni shape memory alloy, the stress at points A and c in Fig. 2 is 100 MPa, the stress at point a is 200 MPa, and the stress at point b is 600 MPa. suppose, also the strain E ₁ at the point b to 0.2%.
The amount of strain that can be used is 0.8%, which is the difference between E ₂ and E ₁ , which is the maximum bending strain.
1500 (mm) x 0.8 (%) x 10 ^-2 = 12 (mm) = 0.012 (m)
It is.
Since the cross-sectional area is 1 mm ^2, so that if the 100 MPa 100 N force is acting.
From this, the available energy c → A → a → b in Fig. 2 is approximated by approximating its area to a trapezoid.
0.012 (m) × ((600 (N) -100 (N)) + (200 (N) -100 (N)) × 2 ^-1 = 3.6 (N ・ m) = 3.6 (J)
Is calculated.
If two spring-type actuators are used and tension is performed in 1 second and compression is performed in 1 second, that is, 1 cycle is performed in 2 seconds, the work rate is
3.6 (J) × 2 ÷ 2 (s) = 3.6 (J / s) = 3.6 (W)
It is estimated.
The output of one SMA heat engine that consists of a pair of spring-spring actuators is estimated. The conversion efficiency from kinetic energy to electrical energy is 60% when a small dielectric coil and permanent magnet are used. The power generation of one SMA heat engine is estimated to be 2.16W, which is 60% of the output 3.6W. In this case, the output per unit element mass and strain is 0.102 W / g /%, which is a highly efficient mechanism compared to the other SMA heat engines shown in Table 1.
The output and size of an SMA power generator (waste heat recovery mechanism type) in which 25 sets of SMA heat engines (50 mainspring screw type actuators) are arranged in parallel are estimated. The output of the SMA power generator is about 50W, which can generate enough power to illuminate a small streetlight. In addition, since no complicated mechanism is required, the overall size of the device is about 80 cm long x 50 cm wide x 30 cm high, and can be manufactured at low cost.

Since the SMA power generator of the present invention exhibits excellent effects as described above, waste heat energy that has been used only for hot water supply in the vicinity of the heat source can be effectively used for electric energy. Also it contributes greatly like to global environmental improvement and maintenance industries greater reduction effect of CO ₂ which is one of the causes of global warming.

It is the graph which showed the discharge ratio according to temperature of factory waste heat. Left (a) When cooling, the deformation force of SMA is small because it is below the transformation temperature. Right (b) During heating, the shape of SMA recovers above the transformation temperature. It is the graph which showed the stress-strain relationship of SMA. It is explanatory drawing of the principle of a mainspring spring type SMA actuator. It is explanatory drawing which shows typically the basic principle structure of the SMA heat engine using a spring spring type | mold actuator. It is explanatory drawing of the SMA type electric power generating apparatus which uses an SMA heat engine and collect | recovers exhaust heat. It is a schematic explanatory drawing of the switching mechanism in the cold / heat supply / discharge device in FIG.

101 Fixed center axis
100 cylindrical container
200 Spring mainspring
200B Inner winding end
200T outer winding end
102 Inner peripheral walls A1, A2 Spring-spring type actuator
110 Outer chamber
300 Cooling / heating medium supply / discharge device
400 belts
500 belt path
501 Predetermined section
600 dielectric coil
700 permanent magnet
610, 620 electromotive force transmission circuit

Claims (2)

A spiral spring 200 molded with a shape memory alloy plate is accommodated in a cylindrical container 100 rotatably mounted on a fixed central shaft 101 so as to be rewound and unwound, and an inner winding end 200B of the spiral spring 200 is accommodated in the cylindrical container 100. A spring-spring type actuator that is fixedly mounted on the fixed central shaft 101 located in the center of the cylindrical container 100, and the outer winding end 200T of the spring 200 is fixedly mounted on the inner peripheral wall 102 of the cylindrical container 100. A1 and A2 are provided, and a cooling / heating medium supply / discharge device 300 for alternately supplying and discharging the cooling medium and the heating medium is provided in the cylindrical container 100 of each actuator A1 and A2, and the cylindrical shape of each actuator A1 and A2 is provided. The outer peripheral portion of the outer peripheral chamber 110 of the container 100 is connected by a belt 400 so as to be rewound and rewound, and a dielectric coil 600 is disposed around a predetermined section 501 of the belt passage 500 between the actuators A1-A2. The permanent magnet 700 is fixed to the belt part 401 through which the An SMA heat engine characterized in that it is fixedly mounted and electromotive force transmission circuits 610 and 620 are connected to the dielectric coil 600. An MSA power generator in which a plurality of the SMA heat engines are arranged.

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