Patent Publication Number: US-2009237887-A1

Title: Electronic device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of prior Japanese Patent Application No. 2008-34394, filed on Feb. 15, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments of the present invention relate to an electronic device in which a device generating heat in the operation state is accommodated in a chassis. 
     BACKGROUND 
     In an electronic device installed outdoors, electronic parts are generally accommodated in a chassis in order to protect the electronic device from, for example, rainwater and dust. However, in the outdoor electronic device, the temperature in the chassis is easily increased by heat generated from the electronic parts and direct exposure to sunlight, for example. The likelihood of an increase in temperature in an outdoor electronic device is greater than the likelihood of an increase in temperature of an indoor device. The increase in temperatures may result in damage to the outdoor electronic device. Therefore, a radiation mechanism with high cooling effect such as a cooling fin is usually provided in the chassis of an outdoor electronic device. Heat generated from the electronic parts is absorbed by a heat pipe or the like to be transmitted to the radiation mechanism, whereby the inside of the chassis is cooled. 
     Additionally, it is assumed that the outdoor electronic device is used under high temperature. On the other hand, it is also assumed that the electronic device is used under low temperature such as below freezing, for example. In fact, the electronic device used outdoors may be required to normally operate under the environment of about −40° C. However, the usual electronic part requires temperature of about 0° C. to normally operate. Heat obtained by self-heating is drawn away by the radiation mechanism with high cooling effect, and therefore, a sufficient temperature may not be obtained when the environmental temperature is lower, whereby an operation failure of the electronic device may occur during operation, or the electronic parts of the electronic device may be damaged by malfunction. Especially, when the electronic device is turned on, the temperature in the chassis is reduced to the same level as the environmental temperature; therefore, there is a problem that the electronic part cannot be started. 
     In view of the above problem, an apparatus for automatically opening and closing a ventilating hole is described in Japanese Patent Laid-Open Publication No. 11-307970 (hereinafter, patent document 1). In this related apparatus, a ventilating hole for allowing external air in a chassis to cool the inside of the chassis is provided, and it is opened and closed by using bimetal deformed in accordance with change of heat, for example. According to the related apparatus, the ventilating hole is closed in a low temperature state, and therefore, the inside of the chassis may be cooled by opening the ventilating hole only at high temperature, and, at the same time, it is possible to alleviate a problem of rainwater entering the chassis through the ventilating hole. 
     However, the inside of the chassis at high temperature may not be satisfactorily cooled only by opening and closing the ventilating hole in accordance with the environment temperature, and the temperature in the chassis at low temperature may not be increased to a specified temperature at which the electronic part can normally operate. Therefore, it is considered preferable that a heat pipe, a heater, and the like are used together in the apparatus described in the patent document 1, the heat generated from the electronic part at high temperature is absorbed by the heat pipe to be efficiently dissipated, and the electronic part at low temperature is heated by the heater. 
     However, even if the electronic part at low temperature is heated by the heater, the heat itself applied to the electronic part is dissipated outside the chassis through the heat pipe, and therefore, there is a problem that it takes time to satisfactorily increase the temperature of the electronic part, or the electric power consumed by the heater is increased to increase the operational cost. 
     SUMMARY 
     At least in part due to the above issues of related technologies, embodiments discussed herein provide an electronic device which may efficiently regulate the temperature in the chassis while reducing the electric power consumption. 
     An example of an embodiment provides an electronic device. The electronic device includes a circuit board on which a device generating heat in an operation state is mounted; a chassis to accommodate the circuit board and including a holding part; and at least one temperature-responsive arrangement to extend and contract in accordance with temperature so as to dispose the device apart from the holding part at a first temperature less than a threshold temperature, and to dispose the device in contact with the holding part at a second temperature exceeding the threshold temperature. 
     An example of an embodiment provides an electronic device. The electronic device includes a circuit board on which a device generating heat in an operation state is mounted; a chassis to accommodate the circuit board and including a holding part; and a displacement machine to substantially, thermally couple/decouple the holding part and the device according to ambient temperature. 
     An example of an embodiment provides an electronic device. The electronic device includes a circuit board on which a device generating heat in an operation state is mounted; a chassis to accommodate the circuit board and including a holding part; and a displacement machine to selectively change a heat transfer mode of the device from a conductive mode to a convective mode based on a temperature within the chassis. 
     According to an aspect of the embodiments, an electronic device disclosed includes a chassis which accommodates a circuit board on which a device generating heat in an operation state is mounted, has a holding part coming in contact with the device to absorb heat from the device, and radiates the heat from the device, and a temperature-responsive arrangement which extends and contracts in accordance with temperature so that while the device is spaced from the holding part at a temperature not more than a given temperature, the device is in contact with the holding part at a temperature exceeding the given temperature. 
     Additional objects and advantages of the embodiments will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the embodiments. The object and advantages of the embodiments will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing summary description and the following detailed description are explanatory as to some embodiments of the present invention, and not restrictive of the present invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       Embodiments are illustrated by way of example and not limited by the following figures. 
         FIG. 1  is an outline diagram of a communication device; 
         FIG. 2  is a transmission diagram illustrating an inside of a box; 
         FIG. 3  is a view illustrating a first support part and a second support part; 
         FIG. 4  is a view illustrating extension and contraction of the first and second support parts due to temperature change; 
         FIG. 5  is a cross-sectional view of the box according to a high temperature condition; 
         FIG. 6  is a cross-sectional view of the box according to a low temperature condition; 
         FIG. 7  is a transmission diagram illustrating the inside of the box in the low temperature condition; 
         FIGS. 8A and 8B  are views illustrating a first support part and a second support part in a second embodiment; 
         FIG. 9  is a view illustrating a first support part in a third embodiment; and 
         FIG. 10  is a cross-sectional view of the box in the third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLES OF EMBODIMENTS 
     In the figures, dimensions and/or proportions may be exaggerated for clarity of illustration. It will also be understood that when an element is referred to as being “connected to” another element, it may be directly connected or indirectly connected, i.e., intervening elements may also be present. Further, it will be understood that when an element is referred to as being “between” two elements, it may be the only element layer between the two elements, or one or more intervening elements may also be present. Like reference numerals refer to like elements throughout. 
     Hereinafter, examples of embodiments of the disclosed electronic device is described with reference to the drawings. 
     FIRST EMBODIMENT 
       FIG. 1  is an outline diagram of a communication device  1  which is a specific first embodiment of the disclosed electronic device. 
     The communication device  1  is installed outdoors. The communication device  1  may include an enclosure such as a box  20 , for example. A circuit board and the like and a cooling fin  10  for dissipating heat in the box  20  by coming in contact with the box  20  may be accommodated in the box  20 . 
     The box  20  includes various devices for executing a function as the communication device  1 . In the communication device  1 , the temperature in the box  20  may be increased by heat generated from the device during its operation and direct exposure to sunlight. Therefore, when the temperature in the box  20  is high, heat generated in the device is transmitted to the cooling fin  10 , and the inside of the box  20  should be cooled. On the other hand, when the temperature in the box  20  is low, the temperature in the box  20  should be rapidly increased to a given temperature at which the device may operate normally operate. 
       FIG. 2  is a diagram illustrating the inside of the box  20 . The box  20  includes an upper lid part  21  and a bottom part  22 . A plurality of second support parts  52  extending and contracting in a substantially vertical direction in accordance with temperature may be fixed to the bottom part  22 . A circuit board  30  on which a plurality of devices  31  are mounted may be supported from a lower side by the second support parts  52 . The device  31  corresponds to an example of a device of the disclosed electronic device, and the circuit board  30  corresponds to an example of a circuit board of the disclosed electronic device. 
     Meanwhile, a plurality of first support parts  51  extending and contracting in a parallel, but opposite direction to the second support part  52  in accordance with temperature may be fixed to the upper lid part  21  and press the circuit board  30  from the upper side. Namely, the circuit board  30  is supported from the top and bottom sides by being sandwiched between the first support part  51  and the second support part  52 , and the first support part  51  and the second support part  52  extend and contract in opposite directions to each other in accordance with temperature, whereby the circuit board  30  is moved in the upward and downward directions. The first support part  51  and the second support part  52  correspond to an example of a temperature-responsive arrangement, or in other words a temperature change element, of the disclosed electronic device. Accordingly, the first support part  51  and the second support part  52  are examples of displacement machines for moving the circuit board  30  and components arranged thereon. 
     In the temperature change element of this embodiment, at least one of the first support part  51  and the second support part  52 , which support the circuit board  30  from the top and bottom sides so as to sandwich the circuit board  30  therebetween, extends and contracts in accordance with temperature. Therefore, the circuit board  30  may be moved by a simple mechanism without using electric power. 
     Further, in the temperature change element, a pair of the first and second support parts  51  and  52  extend and contract in opposite directions to each other in accordance with temperature. Therefore, a variation in an extension and contraction characteristic of the temperature change element may be absorbed, whereby the circuit board  30  may be stably moved in accordance with temperature. 
     A holding part  40  which is provided so that a part of the box  20  protrudes and is in contact with the device  31  may be fixed onto the upper surface of the upper lid part  21 . The holding part  40  corresponds to an example of a holding part in the basic configuration of the above electronic device. 
       FIG. 2  illustrates a state that the temperature in the box  20  is higher than a specified and/or threshold temperature. In  FIG. 2 , the circuit board  30  is moved to a position at which the device  31  is in contact with the holding part  40 , and the heat generated in the device  31  is transmitted to the cooling fin  10  (see  FIG. 1 ) by the holding part  40 , whereby the inside of the box  20  is cooled. 
     Although a heater  70  (see  FIG. 5 ) for heating the device  31  at low temperature and other elements are disposed in the box  20 , the illustration of the heater  70 , for example, is omitted in  FIG. 2  for the sake of clarity. 
       FIG. 3  depicts an example of a first support part  51 . It is noted that the second support part  52  has a similar structure.  FIG. 4  is a view illustrating the extension and contraction of the first and second support parts  51  and  52  due to temperature change. 
     Referring to  FIG. 3 , in the first support part  51 , a plurality of coil springs  63  that extend and contract in accordance with temperature are accommodated in two boxes  61  and  62 , nested inside one another, so as to be stacked in a vertical direction, for example. The coils springs  63  include a bimetal that extends and contracts in accordance with temperature. The coil spring  63  corresponds to an example of a bimetal component in the embodiment of the disclosed electronic device, and at the same time, corresponds to an example of a plurality of coil springs in the embodiment of the disclosed electronic device. 
     In the bimetal component, two kinds of metal plates having a coefficient of thermal extension different from each other are bonded to each other. For example, the characteristics of the two kinds of metal plates respectively extend with the increase in temperature, and the metal plate having a relatively higher coefficient of thermal extension more significantly extends, whereby the entire bimetal component is warped. An inexpensive bimetal component that curves according to temperature may be used as the temperature change element, whereby the circuit board may be moved while reducing the manufacturing cost as compared with related technologies. In addition, the plurality of coil springs may be stacked in extension and contraction directions, whereby the amount of extension and contraction of the temperature change element may be increased, and the circuit board may be reliably moved. 
     As illustrated in  FIG. 3 , the coil springs  63  extending and contracting in opposite directions to each other in accordance with a temperature change are accommodated in the first support part  51  and the second support part  52 . In the present embodiment, the coil springs, which extend in the up and down directions as illustrated from (B) to (A) in  FIG. 4  when temperature is decreased, are accommodated in the first support part  51  for supporting the circuit board  30  from the upper side on which the holding part  40  is provided. Meanwhile, the coil springs, which contract in the up and down directions as illustrated from (B) to (A) in  FIG. 4  when temperature is decreased, are accommodated in the second support part  52  for supporting the circuit board  30  from below. 
     The circuit board  30  is supported by the first support part  51  and the second support part  52 . Each of the first support part  51  and the second support part  52  include the bimetal which is a metal material, whereby the electric potential at required positions between the box  20  and the circuit board  30  is standardized to be able to improve the resistance against emission/immunity. The first support part  51  and the second support part  52  include the coil springs  63 , whereby vibration applied to the box  20  is decreased, and the resistance against the vibration may be improved. 
       FIG. 5  is a cross-sectional view corresponding to the box  20  being cut in the vertical direction (e.g., up and down directions) in high temperature conditions.  FIG. 6  is a cross-sectional view corresponding to the box  20  being cut in the up and down directions in low temperature conditions. 
     The heater  70  for heating the device  31  at low temperature is attached to the side of the device  31  of the circuit board  30 , and heat dissipation rubber  80  for transmitting heat to the holding part  40  is applied onto the upper surface of the device  31 . 
     As illustrated in  FIG. 5 , in the state that the temperature in the box  20  is higher than a specified and/or threshold temperature, the first support part  51  pressing the circuit board  30  from above contracts, and the second support part  52  pressing the circuit board  30  from below extends, whereby the circuit board  30  is moved upward. As a result, the device  31  is pressed against the holding part  40  through the heat dissipation rubber  80 , and the heat generated in the device  31  is absorbed by the holding part  40  to be dissipated from the cooling fin  10  illustrated in  FIG. 1 . The extension and contraction amount of the first support part  51  and the second support part  52  is changed in accordance with temperature. For example, if the temperature is higher, the heat dissipation rubber  80  applied to the device  31  is more strongly pressed against the holding part  40  to increase the degree of adhesion and the contact pressure, whereby a heat radiation rate may be regulated in response to temperature. The first support part  51  and the second support part  52  include a plurality of the coil springs  63  stacked in the up and down directions to increase the movement amount of the circuit board  30 . The first support part  51  and the second support part  52  extend and contract in opposite directions to each other in accordance with temperature, and the first support part  51  and the second support part  52  are provided at a plurality of positions to absorb the difference in characteristics of the bimetal included in the coil spring  63  to provide stable support for the circuit board  30 . 
     When the temperature in the box  20  is lower than the specified and/or threshold temperature, as illustrated in  FIG. 6 , the first support part  51  pressing the circuit board  30  from above extends, and the second support part  52  pressing the circuit board  30  from below contracts, whereby the circuit board  30  is moved downward, and the device  31  is separated from the holding part  40 . As a result, an air layer is provided between the device  31  and the holding part  40 , and the heat dissipation by the holding part  40  is reduced. 
       FIG. 7  is a transmission diagram illustrating the inside of the box  20  in low temperature conditions. 
     As illustrated in  FIG. 7 , in the state that the temperature in the box  20  is less than a specified and/or threshold temperature, the circuit board  30  is moved downward to a position below the position of the circuit board  30  in the high temperature state illustrated in  FIG. 2 . Accordingly, in the state that the temperature is less than the specified and/or threshold temperature, the device  31  is spaced from the holding part  40 . When heat is generated from the heater  70  illustrated in  FIG. 6 , the device  31  is heated without the heat being drawn away by the holding part  40 , and therefore, the temperature in the box  20  may be increased without requiring as much electric power consumption as is consumed according to related technologies. 
     As the bimetal of the coil spring  63  illustrated in  FIG. 4 , inver (an alloy of nickel and iron) may be applied as a metal material having a relatively low coefficient of thermal expansion, and an alloy of nickel, stainless steel, copper, and so on may be used as a metal material having a relatively high coefficient of thermal expansion. 
     For example, the bimetal with a length of about 100 mm is formed in a shape of a coil with a radius of about 8 mm, whereby a warpage of about 0.14 mm is generated per one coil due to a temperature change of about 70° C. between −30° C. and 40° C. As a result, the contraction of about 0.26 mm is obtained in the diameter of the one coil. 
     The four above-mentioned coils are stacked to thereby generate a fluctuation of about 1 mm on the whole, and further, the coils having these characteristics are curved in opposite directions to each other to be respectively disposed on the front and rear surface sides of the circuit board  30 , whereby the circuit board  30  may be moved upwards and downwards. 
     As described above, according to the present embodiment, in the state that the temperature in the box  20  is larger than a specified and/or threshold temperature, heat generated during the operation and heat due to direct exposure to sunlight are dissipated by the device  31  being in contact with the holding part  40 , whereby it is possible to reduce the likelihood of damage to or breakage of the device  31  due to high temperature. When the temperature in the box  20  is not more than the specified and/or threshold temperature, the device  31  is displaced from the holding part  40  to thereby reduce the heat dissipation by the holding part  40 , and the device  31  may be efficiently heated by the heater  70 , whereby the likelihood of operation failure and malfunction under a low temperature environment may be reduced. 
     Namely, while a heat conductivity of air is about 0.0241 [W/m·K], the heat conductivity of iron is 83.5 [W/m·K], and the heat conductivity of aluminum alloy is 100 to 250 [W/m·K]; thus, thermal resistance of air is considerably larger than metal widely used as a heat sink. 
     At this time, according to the present embodiment, when the temperature in the box  20  exceeds a specified and/or threshold temperature, the device  31  is in contact with the holding part  40 , whereby the heat generated in the device  31  is absorbed by the holding part  40  to be dissipated outside the box  20 . Meanwhile, when the temperature in the box  20  is less than the specified and/or threshold temperature, the circuit board  30  is moved, whereby the device  31  is spaced apart from the holding part  40 . Therefore, an air layer with large thermal resistance is sandwiched between the device  31  and the holding part  40  at low temperature, whereby it is possible to reduce a problem that heat generated in the device  31  and heat applied to the device  31  by the heater  70  are dissipated outside the box  20 . Accordingly, the temperature in the box  20  may be efficiently regulated. 
     SECOND EMBODIMENT 
     A second embodiment of the disclosed electronic device will be described. The same components as those in the first embodiment are assigned the same reference numerals and description of the same components are omitted for the sake of brevity. Differences between the first embodiment and the second embodiment will be described below. 
       FIGS. 8A and 8B  are views illustrating a first support part  51 _ 2  and a second support part  52 _ 2  according to the second embodiment. 
     As illustrated in  FIG. 8A , the first support part  51 _ 2  in which a first spring  63 _ 2  made of a shape memory alloy is accommodated is provided instead of the first support part  51  in which the coil springs  63  made of bimetal illustrated in  FIG. 3  are accommodated. The shape memory alloy is highly deformed at a specified and/or threshold temperature. The first spring  63 _ 2  has a characteristic that the elastic force and the spring modulus become smaller with increasing temperature. The first spring  63 _ 2  corresponds to an example of a shape memory alloy in the embodiment of the disclosed electronic device. 
     As described above, the shape memory alloy deformed by the temperature change is used as the temperature change element. Accordingly, a circuit board may be moved by a simple mechanism without using electric power. In addition, the spring of the shape memory alloy has a characteristic that the spring modulus varies in accordance with temperature. Thus, the spring of the shape memory alloy is used as the temperature change element, whereby the circuit board may be significantly moved. 
     As illustrated in  FIG. 8B , the second support part  52 _ 2  for supporting the circuit board  30  from the lower side includes a second spring  63 _ 3 . The second spring  63 _ 3  may be formed of stainless steel and have a spring modulus that changes less, according to the temperature change, than the first spring  63 _ 2 . The second spring  63 _ 3  is accommodated in the second support part  52 _ 2 . The second spring  63 _ 3  corresponds to an example of an elastic member in the embodiment of the disclosed electronic device. 
     As described above, in the pair of the support parts  51 _ 2  and  52 _ 2 , the first support part  51 _ 2  is the temperature change element extending and contracting in accordance with temperature, and the second support part  52 _ 2  is an elastic member absorbing the extension and contraction of the temperature change element, whereby the circuit board  30  may be reliably moved in accordance with temperature. 
     When the temperature in the box  20  illustrated in  FIG. 2  increases, the spring modulus of the first spring  63 _ 2  supporting the circuit board  30  from above reduces. As a result, the force with which the first spring  63 _ 2  presses the circuit board  30  downward becomes smaller than the force with which the second spring  63 _ 3  presses the circuit board  30  upward, whereby the first support part  51 _ 2  contracts, and the second support part  52 _ 2  extends. At this time, the circuit board  30  is moved upward, whereby the device  31  is pressed against the holding part  40 . The heat of the device  31  is absorbed by the holding part  40  to be dissipated from the cooling fin  10  illustrated in  FIG. 1 . 
     Meanwhile, when the temperature in the box  20  decreases, the spring modulus of the first spring  63 _ 2  increases, the first support part  51 _ 2  extends, and the second support part  52 _ 2  contracts, whereby the circuit board  30  is pressed downward. As a result, the circuit board  30  is spaced apart from the holding part  40 , and the heat dissipation of the device  31  is reduced. 
     The first support part  51 _ 2  and the second support part  52 _ 2  in the second embodiment illustrated in  FIGS. 8A and 8B  may provide a larger amount of movement based on temperature than the first support part  51  and the second support part  52  using the coil springs  63  formed of bimetal of  FIG. 3 . Therefore, the distance between the circuit board  30  and the holding part  40  may be significantly increased at low temperature, whereby the heat dissipation of the device  31  may be reliably reduced. 
     THIRD EMBODIMENT 
     A third embodiment of the disclosed electronic device will be described. The same components as those in the first and second embodiments are assigned the same reference numerals and description thereof is omitted for the sake of brevity. Differences from the second embodiment will be described below. 
       FIG. 9  is a view illustrating a first support part  51 _ 3  in the present embodiment. 
     As with the first support part  51 _ 2  of the second embodiment illustrated in  FIG. 8A , the first spring  63 _ 2  formed of a shape memory alloy is accommodated in the first support part  51 _ 3  in the present embodiment. Further, a stopper  90  for limiting the extension and contraction amount of the first support part  51 _ 3  is inserted into the center of the first spring  63 _ 2 . The stopper  90  may include a material with small compression. For example, the stopper  90  may include metal, plastic, glass, and other materials. The stopper  90  corresponds to an example of a stopper in the embodiment of the disclosed electronic device. 
     The stopper  90  limits the extension and contraction amount of the temperature change element. The stopper  90  may be used to prevent the circuit board  30  from colliding with the box  20 . 
     When the temperature in the box  20  illustrated in  FIG. 2  increases, the spring modulus of the first spring  63 _ 2  accommodated in the first support part  51 _ 3  reduces, and the first support part  51 _ 3  is contracted by the bias force of the second spring  63 _ 2  accommodated in the second support part  52 _ 2  illustrated in  FIG. 8B , whereby the circuit board  30  is moved upward. At this time, since the contraction amount of the first support part  51 _ 3  is limited by the stopper  90 , the movement amount of the circuit board  30  in the upward direction is also limited, whereby it is possible to avoid the problem that the device  31  is too strongly pressed against the holding part  40 , which may result in damage to the device  31 . 
     FOURTH EMBODIMENT 
     A fourth embodiment of the disclosed electronic device will be described. Since the fourth embodiment has substantially the same constitution as the first embodiment, only differences from the first embodiment will be described. 
       FIG. 10  is a cross-sectional view corresponding to the box  20  illustrated in  FIG. 2  being cut in the vertical direction. 
     Also in the present embodiment, as with the first embodiment illustrated in  FIG. 5 , the circuit board  30 , the first support part  51 , the second support part  52 , the holding part  40 , the device  31 , the heater  70 , and the like are accommodated in the box  20 . Further, a stopper  91  extending downward is attached to the upper lid part  21  of the box  20 . 
     When the temperature in the box  20  increases, the first support part  51  contracts, and the second support part  52  extends, whereby the circuit board  30  is moved in the upward direction, and the device  31  is pressed against the holding part  40 . At this time, since the movement of the circuit board  30  is limited by the stopper  91 , the device  31  may be prevented from being pressed too hard against the holding part  40  and being damaged. 
     According to the above, the stopper  91  is attached not to the inside of the first support part  51 , but to the box  20 , whereby the device  31  may be reliably prevented from being damaged. 
     As described above, according to the electronic devices of the first to fourth embodiments, the temperature in the chassis may be efficiently regulated without while reducing the electric power consumption. 
     In the first to fourth embodiments, a displacement machine is provided (e.g., the supporting members) that includes an engine for converting thermal energy into mechanical force or motion. Examples of the engines in the first to fourth embodiment include a shape memory alloy spring and a bimetal coil spring. 
     In the first to fourth embodiments, although a communication device is illustrated as an example of the disclosed electronic device, this electronic device may be other devices such as a server device to be installed outdoors, for example. In addition, in the first to fourth embodiments, although the bar-like stopper with small extension and contraction is provided in the center of the spring or in the chassis, a spring for limiting the extension and contraction amount of a support member may be used as the stopper, for example. Further, in the first to fourth embodiments, although an example in which the coil spring is formed of bimetal is described, the bimetal component may be formed in a leaf spring shape, and deflection may be utilized, for example. Still further, in the first to fourth embodiments, although an example in which the cooling fin is provided in the chassis is described, a heat pipe as a radiation mechanism may be provided in the chassis, or water cooling may be used instead of air cooling, for example. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.